C: Chemical and Catalytic Reactivity at InterfacesOctober 5, 2023

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al₂O₃ Surfaces: DFT and AIMD Studies
揭示受 Al₂O₃ 表面影响的 Pd 簇的静态和动态结构：DFT 和 AIMD 研究
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Kazumasa Murata
Kazumasa Murata
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
More by Kazumasa Murata
Akira Oda
Akira Oda
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan
More by Akira Oda
https://orcid.org/0000-0002-0217-4202
Atsushi Satsuma
Atsushi Satsuma
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan
More by Atsushi Satsuma
https://orcid.org/0000-0001-6946-7678
Kyoichi Sawabe*
Kyoichi Sawabe
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan
*Email: sawabe@chembio.nagoya-u.ac.jp
More by Kyoichi Sawabe
https://orcid.org/0000-0001-6228-1395

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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2023, 127, 41, 20267–20275

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https://doi.org/10.1021/acs.jpcc.3c02483

Published October 5, 2023

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Abstract 抽象

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Metal nanoparticles (MNPs) supported on oxides are used in various catalytic reactions, such as petrochemical processes and exhaust gas purification. Metal–support interactions (MSIs) between MNPs and oxides affect the morphology and thermal stability of the MNPs, which are known to be related to the catalytic activity of the MNPs. However, the effect of MSIs is still a matter of debate. We conducted density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) to investigate the geometric structure and migration behavior of Pd clusters on various Al₂O₃ surfaces. The MSIs of the Pd clusters with different Al₂O₃ surfaces resulted in different morphologies of the clusters. The shape of Pd clusters on α-Al₂O₃(0001) were deformed to oblate and on γ-Al₂O₃(110) to prolate. On the other hand, the shape of Pd clusters on γ-Al₂O₃(100) did not change from that in a vacuum. The migration rate of Pd clusters was also affected by the MSI, which was higher on γ-Al₂O₃(110) than on α-Al₂O₃(0001) and γ-Al₂O₃(100). To evaluate the interactions between Pd clusters and Al₂O₃ surfaces, we calculated the interaction energies for Pd clusters with various sizes on Al₂O₃ surfaces. The interaction energy of Pd/Al₂O₃ systems depended on the coordination number (CN, number of bonds per Pd atom) of Pd–Al and Pd–O. Despite the smaller atomic density of Al and O of the γ-Al₂O₃(110) surface than that of α-Al₂O₃(0001) and γ-Al₂O₃(100) surfaces, the number of bonds formed between Pd clusters and γ-Al₂O₃(110) was greater than that of α-Al₂O₃(0001) and γ-Al₂O₃(100). According to AIMD simulations and perpendicular displacements of Al and O atoms bound to the Pd cluster on the Al₂O₃ surface from the bare Al₂O₃ surface, coordinatively unsaturated Al³⁺ sites on γ-Al₂O₃(110) were more flexible than those on α-Al₂O₃(0001) and γ-Al₂O₃(100). The flexibility of γ-Al₂O₃(110) facilitated the formation of bonds with the Pd cluster, resulting in stronger MSIs. When the coordinatively unsaturated Al³⁺ sites were hydrated, the MSIs were found to be weakened.
负载在氧化物上的金属纳米颗粒（MNP）用于各种催化反应，例如石化过程和废气净化。MNPs 和氧化物之间的金属-载体相互作用（MSI）影响 MNPs 的形貌和热稳定性，已知这与 MNPs 的催化活性有关。然而，MSI 的效果仍然是一个有争议的问题。我们通过密度泛函理论（DFT）计算和从头分子动力学（AIMD）研究了 Pd 簇在各种 Al₂O₃ 表面上的几何结构和迁移行为。具有不同 Al₂O₃ 表面的 Pd 簇的 MSIs 导致了簇的不同形貌。α-Al₂O₃（0001）上的 Pd 簇形状变形为扁圆形，γ-Al₂O₃（110）上的 Pd 簇形状变形为扁圆形。另一方面，γ-Al₂O₃（100）上的 Pd 簇形状与真空中的 Pd 簇形状没有变化。Pd 簇的迁移速率也受到 MSI 的影响，MSI 在γ-Al₂O₃（110）上高于α-Al₂O₃（0001）和γ-Al₂O₃（100）。为了评估 Pd 簇与 Al₂O₃ 表面之间的相互作用，我们计算了 Al₂O₃ 表面上各种尺寸的 Pd 簇的相互作用能。Pd/Al₂O₃ 体系的相互作用能取决于 Pd-Al 和 Pd-O 的配位数（CN，每个 Pd 原子的键数）。尽管γ-Al₂O₃（110）表面的 Al 和 O 原子密度小于α-Al₂O₃（0001）和γ-Al₂O₃（100）表面，但 Pd 簇与γ-Al₂O₃（110）之间形成的键数大于α-Al₂O₃（0001）和γ-Al₂O₃（100）。根据 AIMD 模拟和 Al2_O3 表面与 Al₂O 3 表面 Pd 簇结合的 Al 和 O 原子从裸露的 Al₂O₃ 表面的垂直位移，γ-Al₂O₃（110）上的配位不饱和 Al³⁺ 位点比α-Al₂O₃（0001）和γ-Al₂O₃（100）上的位点更灵活。γ-Al₂O₃（110）的柔韧性促进了与 Pd 簇的键形成，从而产生了更强的 MSI。当配位不饱和的 Al³⁺ 位点水合时，发现 MSIs 被削弱。

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Subjects

1. Introduction 1. 简介

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The morphology of metal nanoparticles (MNPs) is closely related to their catalytic activity; therefore, their control is significant. The relation between the morphology of MNPs and the catalytic activity has been reported for various catalytic reactions. (1) In general, small-sized MNPs have been supported on oxide and carbon supports with a large surface area in order to efficiently utilize the active metal species. The metal–support interactions (MSIs), which are induced at the interface between the MNPs and the support, affect not only the stability of the small MNPs but also the geometric structure of the MNPs. (2) Even for small MNPs or metal clusters, the number of unsaturated coordination sites on the surface varies depending on their morphology. In addition, the electronic structure of the MNPs is significantly affected by their morphology. (3) Thus, understanding MSIs that control the size and morphology of MNPs on the supports leads to catalytic design.
金属纳米颗粒（MNPs）的形貌与其催化活性密切相关;因此，他们的控制很重要。MNPs 的形貌与催化活性之间的关系已被报道用于各种催化反应。（1）一般来说，为了有效利用活性金属物质，小型 MNPs 被支撑在具有大表面积的氧化物和碳载体上。在 MNPs 和载体之间的界面处诱导的金属-载体相互作用（MSIs）不仅影响小 MNPs 的稳定性，还影响 MNPs 的几何结构。（2）即使对于小 MNPs 或金属团簇，表面不饱和配位位点的数量也因形貌而异。此外，MNP 的电子结构受其形貌的显着影响。（3）因此，了解控制载体上 MNP 尺寸和形态的 MSI 可以进行催化设计。

γ-Al₂O₃ is a nonreducible oxide and commonly used as the support due to its high surface area. The surface of γ-Al₂O₃ has coordinatively unsaturated Al³⁺ sites derived from structural defects and shows unique acid–base properties. (4−6) It has been reported that the coordinatively unsaturated Al³⁺ sites, such as pentacoordinated Al³⁺ (Al_V) sites on the γ-Al₂O₃(100) surface, are strongly anchoring metal species, and the difference in the strength of MSIs affects the morphology of MNPs. (7−15) At low Pt loadings, isolated Pt atoms were present on the γ-Al₂O₃(100) surface, and at high Pt loading, raft-like Pt particles were formed. On the other hand, three-dimensional Pt particles were formed on the α-Al₂O₃ surface without Al_V sites. (11) In addition, the structural disorder of a Pt crystal was induced by strong MSIs in Pt/γ-Al₂O₃, and amorphous Pt particles were generated on γ-Al₂O₃. (16,17) Pt nanoparticles were unevenly distributed at defect sites such as edges, steps, or kinks in γ-Al₂O₃. (18) Moreover, Pt particles on γ-Al₂O₃ were deformed for three-dimensional to a raft-like structure during H₂ reduction at high temperature. (19) Hydroxyl groups formed by the hydration of Al₂O₃ surfaces also contributed to the stabilization of metal species. (20−22)
γ-Al₂O₃ 是一种不可还原的氧化物，由于其高表面积，通常用作载体。γ-Al₂O₃ 的表面具有源自结构缺陷的配位不饱和 Al³⁺ 位点，并表现出独特的酸碱特性。（4−6）据报道，配位不饱和的 Al³⁺ 位点，如γ-Al₂O₃（100）表面的五配位 Al³⁺ （Al_V）位点，是强锚定金属物质，MSI 的强度差异影响 MNP 的形貌。（7−15）在低 Pt 负载下，γ-Al₂O₃ 上存在孤立的 Pt 原子（100）表面，在高 Pt 负载下，形成筏状 Pt 颗粒。另一方面，在没有 Al_V 位点的α-Al₂O₃ 表面上形成了三维 Pt 颗粒。（11）此外，Pt/γ-Al₂O₃ 中的强 MSI 诱导了 Pt 晶体的结构紊乱，并在γ-Al₂O₃ 上生成了无定形的 Pt 颗粒。（16,17）铂纳米颗粒在γ-Al₂O₃ 的边缘、台阶或扭结等缺陷部位分布不均匀。（18）此外，在高温下 _H2 还原过程中，γ-Al₂O₃ 上的 Pt 颗粒被三维变形为筏状结构。（19）由 Al₂O₃ 表面水合形成的羟基也有助于金属物质的稳定。（20−22）

In the case of Pd supported on Al₂O₃, the morphology of the Pd particles and their surface structure were changed by the crystalline phase of Al₂O₃ used as supports. Spherical Pd particles were formed on θ-Al₂O₃ and α-Al₂O₃, and they showed a high activity in complete methane oxidation and hydrogenation of unsaturated aldehyde. (23,24) On the other hand, amorphous-like Pd particles with a high fraction of corner sites preferentially were formed on γ-Al₂O₃, and they were active in the oxidation of carbon monoxide. (25) In addition, the interaction between Pd and Al₂O₃ stabilized the active Pd phase in catalysts. (26−28) It is inferred that the different Pd–Al₂O₃ interactions affected the geometric structure and stability of the Pd particles. However, only a few theoretical reports deal with the geometric structures and the stabilization mechanism of Pd particles on different Al₂O₃ surfaces, and the details are not well understood. (29,30)
在 Al₂O₃ 负载的 Pd 的情况下，Pd 颗粒的形貌及其表面结构因用作载体的 Al₂O₃ 的晶相而改变。在 _θ-Al2O3 和α-Al2O3 上形成球形 Pd 颗粒，在甲烷完全氧化和不饱和醛加氢中表现出较高的活性。（23,24）另一方面，在γ-Al₂O₃ 上优先形成具有高比例角位点的无定形状钯颗粒，它们在一氧化碳的氧化中具有活性。（25）此外，Pd 与 _Al2O3 之间的相互作用稳定了催化剂中的活性 Pd 相。（26−28）推断不同的 Pd-Al₂O₃ 相互作用影响了 Pd 颗粒的几何结构和稳定性。然而，只有少数理论报告涉及 Pd 颗粒在不同 Al₂O₃ 表面上的几何结构和稳定机理，细节尚不清楚。（29,30）

DFT calculations have been used to understand the interactions between metals and Al₂O₃. DFT studies show that isolated metal species on the Al₂O₃ surface were stabilized by coordinatively unsaturated Al³⁺ sites or terminal hydroxyl groups formed by hydration. (12,20−22) An optimized structure for metal clusters on Al₂O₃ has been proposed based on screening adsorption sites for metal clusters. (18,29−32) However, as the size of metal clusters increases, metal clusters interact with multiple adsorption sites on the Al₂O₃. Therefore, it is difficult to determine the thermodynamically stable adsorption sites and orientations for the metal clusters on Al₂O₃. In the case of Pd/γ-Al₂O₃, the adsorption structures of Pd clusters consisting of 1–5 atoms and Pd(111) monolayers on nonhydrated γ-Al₂O₃(100) and hydrated γ-Al₂O₃(110) were investigated. (30) In addition, the morphology of Pd particles was estimated from the adhesion of the Pd(111) monolayer on the Al₂O₃ surface using the Young–Dupré model. However, the Young–Dupré model can only reproduce the morphology of MNPs on the oxide on a macroscopic scale. It was reported that the structure of Pd₁₃ clusters optimized in a vacuum was used to perform the geometry optimization of Pd₁₃ clusters on γ-Al₂O₃. (29) However, these are the optimized structures at 0 K. In real catalysis systems, Pd clusters deform due to the finite temperature. To understand the relation between the morphology of metal clusters and the Al₂O₃ surfaces, ab initio molecular dynamics (AIMD) is needed to reveal the MSIs at the atomic scale.
DFT 计算已用于了解金属与 Al₂O₃ 之间的相互作用。DFT 研究表明，Al₂O₃ 表面上分离的金属物质被配位不饱和的 Al³⁺ 位点或水合形成的末端羟基稳定。（12,20−22）基于金属团簇的筛选吸附位点，提出了一种在 Al₂O₃ 上金属团簇的优化结构。（18,29−32）然而，随着金属团簇尺寸的增加，金属团簇与 _Al2O₃ 上的多个吸附位点相互作用。因此，很难确定 Al₂O₃ 上金属团簇的热力学稳定吸附位点和取向。在 Pd/γ-Al₂O₃ 中，研究了由 1-5 个原子和 Pd（111）单层组成的 Pd 簇在非水合γ-Al₂O₃（100）和水合γ-Al₂O₃（110）上的吸附结构。（30）此外，使用 Young-Dupré模型从 Pd（111）单层在 Al₂O₃ 表面的粘附度中估计了 Pd 颗粒的形貌。然而，Young-Dupré 模型只能在宏观尺度上再现氧化物上 MNP 的形态。据报道，利用在真空中优化的 Pd₁₃ 簇结构在γ-Al₂O₃ 上对 Pd₁₃ 簇进行几何优化。（29）然而，这些是 0 K 下的优化结构。在实际催化系统中，Pd 簇由于有限的温度而变形。为了了解金属团簇形貌与 Al₂O₃ 表面之间的关系，需要从头开始分子动力学（AIMD）来揭示原子尺度的 MSI。

In this study, we investigate the static and dynamic structures of Pd clusters on various Al₂O₃ surfaces by a theoretical approach combining DFT calculations and AIMD simulations. During AIMD annealing, Pd clusters migrate on the Al₂O₃ surfaces with a structural change. By optimizing their structures obtained by AIMD annealing, the morphology of Pd particles on Al₂O₃ can be proposed with minimal artificial effects. Based on a systematic study of the MSIs for Pd clusters with different sizes on Al₂O₃, we elucidate the MSIs that depend on the Al₂O₃ surfaces. The objective of this work is to enhance our understanding of the influence of exposed atomic sites of Al₂O₃ on the morphology of Pd nanoparticles, which offers significant insights into the strategic development of active metal nanoparticles.
本研究采用 DFT 计算和 AIMD 模拟相结合的理论方法，研究了各种 Al₂O₃ 表面上 Pd 簇的静态和动态结构。在 AIMD 退火过程中，Pd 簇在 Al₂O₃ 表面上迁移并发生结构变化。通过优化 AIMD 退火获得的结构，可以提出 Pd 颗粒在 Al₂O₃ 上的形貌，而人工效应最小。基于对 Al₂O₃ 上不同尺寸的 Pd 簇的 MSI 的系统研究，我们阐明了依赖于 Al₂O₃ 表面的 MSI。这项工作的目的是加强我们对 Al₂O₃ 暴露原子位点对 Pd 纳米颗粒形态影响的理解，这为活性金属纳米颗粒的战略发展提供了重要的见解。

2. Computational Methods 2. 计算方法

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Density functional theory (DFT) calculations were performed using the Vienna ab initio simulation package (VASP) code. (33−35) The electron–ion interaction with the frozen-core approximation was described using the projector-augmented wave (PAW) method. (36) Wave functions for valence electrons were represented using a periodic-wave basis set with a cutoff energy of 420 eV. The RPBE functional with the D3(BJ) dispersion correction of Grimme was adopted. (37,38) Structural optimization was performed until the energy and force converged within criteria of 1.0 × 10^–5 eV and 0.02 eV/Å, respectively. The vacuum spacing for the isolated Pd_n clusters (n = 1–4, 6, 9, and 13) was set to 13 × 14 × 15 Å³. All calculations for Al₂O₃ surfaces were performed on slab models with eight atomic layers. The dehydrated α-Al₂O₃(0001) (39) and dehydrated γ-Al₂O₃(100), dehydrated/hydroxylated γ-Al₂O₃(110) (40) were modeled with 3 × 3 supercells (14.3 × 12.4 Å²) and 2 × 2 supercells (11.1 × 16.7 Å²), 2 × 2 supercells (16.7 × 16.1 Å²), respectively. In the case of Pd₁₃/γ-Al₂O₃(100), 3 × 2 supercells of dehydrated γ-Al₂O₃(100) (16.6 × 16.7 Å) were used to avoid the artificial lateral interaction. Based on the previous thermodynamic analysis, the hydroxyl coverage of hydroxylated γ-Al₂O₃(110) at 773 K in a vacuum was 5.9 OH nm^–2. (40) The vacuum spacing of the Al₂O₃ slab and Pd_n cluster (n = 1–4, 6, 9, and 13) on the Al₂O₃ slab was set to 14 Å. In the structure optimization of Pd_n/Al₂O₃ (n = 1–4, 6, 9, and 13), an ab initio molecular dynamics (AIMD) annealing procedure described below was employed to reduce artifacts manually placing Pd_n/Al₂O₃ (n = 1–4, 6, 9, and 13). (41) AIMD simulations in the NVT ensemble implemented in VASP were performed by applying the PBE exchange-correlation functional coupled with the D3(BJ) dispersion correction method. The Nosé mass control was set to a value of SMASS = 0. The temperature in the simulation was controlled with a Nosé–Hoover thermostat. First, the temperature was raised to 773 K from 0 K within 2 ps with a time step of 1.0 fs and then held at 773 K for up to 8 ps. Upon simulated annealing, the temperature and potential energy do not exhibit any overshoot (Figure S1). However, this annealing process results in the Pd atoms gaining sufficient energy to significantly alter their structure, and they also undergo bond breaking at the interface with Al and O atoms during the annealing (Movies S1–S3). The Pd clusters migrate on the Al₂O₃ surface, and their adsorbed positions shift from one symmetrically unique site to another within the surface unit. Regardless of the Al₂O₃ surface used, the Pd clusters did not remain in their initial arbitrary positions. The changes in the structure and position of the Pd clusters before and after simulated annealing suggest that AIMD annealing eliminates the artificial placement of Pd clusters on the Al₂O₃ surface. After holding for 3 ps, the system was expected to reach equilibrium based on the variation of the average atomic distances (vide infra). To verify that the temperature distribution is monomodal in equilibrium, the histogram distributions of the temperature by holding from 3 to 8 ps are plotted (Figure S2). All temperature distributions are centered around T = 773 K. In equilibrium, the variance of temperature fluctuations in a canonical ensemble is represented by the equation (42)
使用维也纳从头开始模拟包（VASP）代码进行密度泛函理论（DFT）计算。（33−35）使用投影仪增强波（PAW）方法描述了电子-离子与冻结核心近似的相互作用。（36）价电子的波函数使用截止能量为 420 eV 的周期波基集表示。采用 RPBE 函数与 Grimme 的 D3（BJ）色散校正。（37,38）进行结构优化，直到能量和力分别收敛在 1.0 × 10^–5 eV 和 0.02 eV/Å 的标准范围内。将分离的 Pd_n 簇（n = 1–4、6、9 和 13）的真空间距设置为 13 × 14 × 15 Å³。Al₂O₃ 表面的所有计算都是在具有 8 个原子层的板坯模型上进行的。分别用 3 个×3 个超级细胞（14.3 × 12.4 Å²）和 2 个×2 超级细胞（11.1 × 16.7 Å 2）、2 × 2 个超级细胞（16.7 × 16.1 Å 2）、2 2 个超级细胞（16.7 16.1 Å²）对脱水γ α-Al₂O₃（100）、脱水/羟基化γ-Al₂O₃（100）进行建模。在 Pd₁₃/γ-Al₂O₃（100）的情况下，使用了 3 个×2 个脱水γ-Al₂O₃（100）（16.6 × 16.7 Å）的超级细胞来避免人工横向相互作用。根据之前的热力学分析，羟基化γ-Al₂O₃（110）在真空中 773 K 的羟基覆盖率为 5.9 OH ^nm-2。（40）Al₂O₃ 板和 Pd_n 簇（n = 1-4、6、9 和 13）在 Al₂O₃ 板上的真空间距设置为 14 Å。在 Pd_n/Al₂O₃（n = 1–4、6、9 和 13）的结构优化中，采用了下述从头开始分子动力学（AIMD）退火程序来减少手动放置 Pd_n/Al₂O₃（n = 1–4、6、9 和 13）的伪影。（41）采用 PBE 交换相关泛函耦合 D3（BJ）色散校正方法，对 VASP 中实现的 NVT 集合进行 AIMD 模拟。将 Nosé 质量控制设置为 SMASS = 0 的值。模拟中的温度由 Nosé-Hoover 恒温器控制。首先，在 2 ps 内将温度从 0 K 提高到 773 K，时间步长为 1.0 fs，然后保持在 773 K，持续 8 ps。在模拟退火时，温度和势能没有表现出任何过冲（图 S1）。然而，这种退火过程导致 Pd 原子获得足够的能量来显着改变其结构，并且在退火过程中它们也会在与 Al 和 O 原子的界面处发生键断裂（电影 S1-S3）。Pd 簇在 Al₂O₃ 表面上迁移，它们的吸附位置从表面单元内的一个对称独特的位点移动到另一个位点。无论使用何种 Al₂O₃ 表面，Pd 簇都不会保持在其初始任意位置。模拟退火前后 Pd 簇结构和位置的变化表明，AIMD 退火消除了 Pd 簇在 Al₂O₃ 表面的人工放置。在保持 3 ps 后，系统有望根据平均原子距离的变化达到平衡（ 见下图 ）。为了验证温度分布在平衡状态下是单峰的，绘制了保持 3 至 8 ps 的温度直方图分布（图 S2）。所有温度分布都以 T = 773 K 为中心。在平衡状态下，规范集合中温度波动的方差由方程（42）表示

σ^{2} = \frac{2 {⟨ T ⟩}^{2}}{3 N}

where T, σ, and N denote temperature, the standard deviation, and the number of free atoms, respectively. This equation yields the following standard deviations at 773 K: 53.5 for Pd₁₃/α-Al₂O₃(0001), 53.5 for Pd₁₃/γ-Al₂O₃(100), and 54.7 for Pd₁₃/γ-Al₂O₃(110). These values are comparable to the standard deviations of the temperatures derived from the 5 ps molecular dynamics (MD) simulation conducted at 773 K, which are 52.6 for Pd₁₃/α-Al₂O₃(0001), 51.7 for Pd₁₃/γ-Al₂O₃(100), and 51.3 for Pd₁₃/γ-Al₂O₃(110). The structure optimization of Pd_n/Al₂O₃ (n = 1–4, 6, 9, and 13) was performed, starting from the initial structure obtained through AIMD annealing. The top four atomic layers of the Al₂O₃ slab and Pd_n cluster (n = 1–4, 6, 9, and 13) were allowed to relax, and the rest of the bottom atoms were fixed. For the sampling of the reciprocal space, Monkhorst–Pack k-point sets of (2 × 2 × 1) and (4 × 3 × 1), (2 × 3 × 1) were sampled for dehydrated α-Al₂O₃(0001) and dehydrated γ-Al₂O₃(100), dehydrated/hydroxylated γ-Al₂O₃(110), respectively. Structure models are illustrated using the open visualization tool (OVITO) package. (43) The threshold values for the Pd–Pd and Pd–Al bonds are 3.30 Å, and those for the Pd–O and Al–O bonds are 2.44 Å, respectively. The number of bonds and coordination numbers were calculated for adjacent atoms at distances below the threshold values. It should be noted that our Al₂O₃ surface model for DFT-AIMD calculations may not correspond to the true state of the Al₂O₃ surface under experimental conditions.
其中 T、σ 和 N 分别表示温度、标准差和自由原子数。该方程在 773 K 时产生以下标准差：Pd₁₃/α-Al₂O₃（0001）为 53.5，Pd₁₃/γ-Al₂O₃（100）为 53.5，Pd₁₃/γ-Al₂O₃（110）为 54.7。这些值与在 773 K 下进行的 5 ps 分子动力学（MD）模拟得出的温度标准差相当，Pd₁₃/α-Al₂O₃（0001）为 52.6，Pd₁₃/γ-Al₂O₃（100）为 51.7，Pd₁₃/γ-Al₂O₃（110）为 51.3。从 AIMD 退火获得的初始结构开始，对 Pd_n/Al₂O₃（n = 1–4、6、9 和 13）进行结构优化。让 Al₂O₃ 板和 Pd_n 簇的顶部四个原子层（n = 1–4、6、9 和 13）松弛，其余底部原子固定。对于倒数空间的采样，分别对脱水α-Al₂O₃（0001）和脱γ水/羟基化γ-Al 2 O 3（110）和脱水/羟基化 _-Al₂O₃（110）的（2 × 2 × 1）和（4 × 3 × ××1）的 Monkhorst-Pack k 点集进行采样。结构模型使用开放可视化工具（OVITO）包进行说明。（43）Pd-Pd 和 Pd-Al 键的阈值分别为 3.30 Å，Pd-O 和 Al-O 键的阈值分别为 2.44 Å。计算距离低于阈值的相邻原子的键数和配位数。需要注意的是，我们用于 DFT-AIMD 计算的 Al₂O₃ 表面模型可能与实验条件下 Al₂O₃ 表面的真实状态不符。

3. Results and Discussion

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3.1. Al₂O₃ Surface Models

Initial structures of dehydrated α-Al₂O₃(0001), γ-Al₂O₃(100), and γ-Al₂O₃(110) surfaces for DFT calculations and AIMD simulations were based on a previous report. (40) Previous studies have shown that the (110) surfaces are predominantly present on γ-Al₂O₃ (about 70% of all surfaces), followed by (100) surfaces (about 20%). (44,45) In the bulk of α-Al₂O₃, Al is present only at octahedral sites, whereas Al is present at octahedral (75%) and tetrahedral (25%) sites in the bulk of γ-Al₂O₃. In this study, Al₂O₃ surface models were obtained by AIMD simulation using the initial structures described above at 773 K (Movies S4–S6), followed by structural optimization at 0 K. The α-Al₂O₃(0001), γ-Al₂O₃(100), and γ-Al₂O₃(110) surface models are shown in Figure 1. The α-Al₂O₃(0001) surface had one coordinately unsaturated tricoordinated Al atom (Al_III) per unit cell, generated from the octahedral site in bulk. The γ-Al₂O₃(100) surface had four Al_V sites per unit cell, generated from octahedral sites in bulk. The α-Al₂O₃(0001) and γ-Al₂O₃(100) surface models were consistent with previously reported surface structures. (40) The γ-Al₂O₃(110) surface model was more complex than γ-Al₂O₃(110) surface model without AIMD simulations (shown in Figure S3) due to the surface reconstruction during AIMD annealing at 773 K. The periodicity of (2 × 2) supercells for γ-Al₂O₃(110) surface was reduced to (2 × 1) supercells after the procedure of the AIMD annealing and structural optimization. The γ-Al₂O₃(110) surface displayed an uneven structure with six tetracoordinated Al³⁺ (Al_IV) sites, a hexacoordinated Al³⁺ (Al_VI) site, an Al_V site, and two Al_III sites per surface unit cell. Such coordinatively unsaturated Al³⁺ sites function as Lewis acid sites. (4,5,22) Table 1 shows the density of the O and Al atoms on the topmost layers of Al₂O₃ (see Figure 1). The atom density of O on the Al₂O₃ surface increased in the order γ-Al₂O₃(110) < γ-Al₂O₃(100) < α-Al₂O₃(0001). In contrast, the atom density of Al was larger in the order α-Al₂O₃(0001) < γ-Al₂O₃(110) < γ-Al₂O₃(100). Despite the same crystalline phase, the O and Al atom density of the γ-Al₂O₃(110) surface was smaller than that of γ-Al₂O₃(100).

Figure 1. Top and side views of (a, b) α-Al₂O₃(0001), (c, d) γ-Al₂O₃(100), and (e, f) γ-Al₂O₃(110) surface. Only the topmost layers of the periodic slab are represented using color balls. A dashed line indicates the unit cell; the O and Al atoms are shown as red and brown balls.

Table 1. Density of the O and Al Atoms on the Topmost Layers of Al₂O₃

model	density of O atom (nm^–2)	density of Al atom (nm^–2)
α-Al₂O₃(0001)	15.2	5.1
γ-Al₂O₃(100)	13.0	10.8
γ-Al₂O₃(110)	10.4	7.5

3.2. Static Structure of Pd Clusters on Al₂O₃

For structural optimization of Pd_n clusters (n = 1–4, 6, 9, 13) on the Al₂O₃ surfaces, AIMD simulations were employed to reduce artifacts manually placing Pd_n clusters on the Al₂O₃. (41) AIMD simulations showed that the Pd clusters on the Al₂O₃ surfaces migrate to stable adsorption sites with structural changes. At least three structures of Pd_n/Al₂O₃ with low energy in AIMD annealing held at 773 K for 4 ps were sampled as initial structures for the structural optimization at 0 K (Figure S4), (46) which resulted in different optimized structures. Among them, the optimized geometry with the lowest energy was adopted as the most stable structure. Figure 2 and Tables S1–S4 show the optimized structures of the Pd_n clusters on the Al₂O₃ surface and those in a vacuum. The adsorption sites and geometric structure of the Pd_n clusters (n = 1–4) on γ-Al₂O₃(100) in this work agreed with previous reports by Valero et al. (Table S2). (30) At cluster sizes of n ≥ 4, three-dimensional Pd_n clusters were formed on γ-Al₂O₃(100). The point group can classify the shape of clusters with high symmetry. However, such a classification cannot be applied to clusters having no symmetry. Here, we adopt the molecular shape classification used in rotational spectra of polyatomic molecules. The diagonalized matrix of moments of inertia was used to classify the morphology of clusters. Three elements of the diagonal component are called the principal axes of inertia, which are generally assigned to I_A, I_B, and I_C in descending order. Comparing the values of I_A, I_B, and I_C leads to the systematic classification of molecular shapes. Thus, the shape of Pd₁₃ clusters was quantitatively evaluated by the moment of inertia (Table 2). (47) Because the moment of inertia of a Pd₁₃ cluster in a vacuum was I_A < I_B < I_C, the Pd₁₃ cluster displayed an asymmetric geometry. (46,48) A Pd₁₃ cluster on γ-Al₂O₃(100) also showed an asymmetric geometry and consisted of three layers (Figures 2c,d). On the other hand, because the moment of inertia of a Pd₁₃ cluster on α-Al₂O₃(0001) was I_A ≈ I_B < I_C, the morphology of the Pd₁₃ cluster was oblate, and its polar axis was perpendicular to the surface (Figures 2a,b). In contrast, the moment of inertia of a Pd₁₃ cluster on γ-Al₂O₃(110) was I_A < I_B ≈ I_C. Thus, the morphology of the Pd₁₃ cluster on γ-Al₂O₃(110) was prolate and consisted of two layers, and its polar axis was parallel to the surface (Figures 2e,f).

Figure 2. Top and side views of (a, b) Pd₁₃/α-Al₂O₃(0001), (c, d) Pd₁₃/γ-Al₂O₃(100), and (e, f) Pd₁₃/γ-Al₂O₃(110). O, Al, and Pd atoms are shown as red, brown, and navy-blue balls.

Table 2. Moment of Inertia of Pd₁₃ Clusters in a Vacuum and on Al₂O₃ Surfaces

	moment of inertia
model	I_A (amu Å²)	I_B (amu Å²)	I_C (amu Å²)	I_A/I_A	I_B/I_A	I_C/I_A		morphology
Pd₁₃ cluster	5202	6536	8175	1.0	1.3	1.6	I_A < I_B < I_C	asymmetric top molecule
Pd₁₃/α-Al₂O₃(0001)	5695	6215	8255	1.0	1.1	1.4	I_A ≈ I_B < I_C	oblate
Pd₁₃/γ-Al₂O₃(100)	5220	6662	8514	1.0	1.3	1.6	I_A < I_B < I_C	asymmetric top molecule
Pd₁₃/γ-Al₂O₃(110)	4656	8348	10485	1.0	1.8	2.3	I_A < I_B ≈ I_C	prolate

3.3. Interactions between Pd Clusters and Al₂O₃ Surfaces

The static geometry of the Pd clusters in the Pd/Al₂O₃ systems was strongly affected by the Pd–Al₂O₃ interactions originating from the surface structures. The Pd–Al₂O₃ interactions can be discussed based on the binding energy per Pd atom (E_b) and the interaction energy per Pd atom (E_i) shown in the following equations: (29,32)

E_{b} ({for isolated Pd}_{n} cluster) = \frac{1}{n} (E_{{Pd}_{n} cluster} - n E_{Pd atom})

E_{b} ({for Pd}_{n} / {Al}_{2} O_{3}) = \frac{1}{n} (E_{{Pd}_{n} / {Al}_{2} O_{3}} - n E_{Pd atom} - E_{{Al}_{2} O_{3}})

E_{i} = \frac{1}{n} (E_{{Pd}_{n} / {Al}_{2} O_{3}} - E_{{Pd}_{n} cluster} - E_{{Al}_{2} O_{3}})

where E_{Pd_n/Al₂O₃}, E_Pd atom, E_Al₂O₃, and E_{Pd_n cluster} are the total energies of Pd_n/Al₂O₃, Pd atom, Al₂O₃, and Pd_n clusters, respectively. Thus, the larger the negative values of these energetic parameters, the more stable the Pd clusters are on the Al₂O₃ surfaces. Figure 3a shows a plot of the binding energies, E_b, against the number of constituent atoms of Pd clusters on Al₂O₃. E_b of any Pd_n clusters on the Al₂O₃ surfaces was more negative than those of the isolated Pd_n clusters, indicating that the Pd clusters are stabilized by Al₂O₃ supports. As the size of the Pd clusters increased, E_b generally decreased. This means that the formation of larger Pd clusters is energetically more stable. When the size of the Pd clusters was small (n ≤ 4), E_b changed significantly with increasing the size of Pd clusters to strongly reflect the interactions of Pd with the local structure of the Al₂O₃. The E_b value of Pd₁/γ-Al₂O₃(100) was more negative than those of Pd₂/γ-Al₂O₃(100) and Pd₃/γ-Al₂O₃(100). In the case of Pd_n/γ-Al₂O₃(110), E_b had a local minimum when n = 2. These results are similar to the previous report for Pt/Al₂O₃, suggesting that the Pd clusters consisting of a few atoms were energetically stabilized on γ-Al₂O₃. (12) In the size region of n ≥ 4, E_b of Pd_n/Al₂O₃ decreased gradually with increasing the size. As the size increased, E_b was more strongly affected by the surface structures of Al₂O₃ than by the cluster size. Comparing E_b of the Pd₁₃ clusters on the different Al₂O₃ surfaces, they were in the order γ-Al₂O₃(110) < α-Al₂O₃(0001) < γ-Al₂O₃(100). This means that the Pd₁₃ cluster was most stabilized on γ-Al₂O₃(110). The interactions between Pd clusters and Al₂O₃ surfaces reflected the broad region of the surface corresponding to the entire unit cell, rather than the local sites on Al₂O₃ surfaces. The interaction energy E_i for the Pd/Al₂O₃ systems contains the deformation of Pd clusters and Al₂O₃ surfaces by the adsorption of Pd clusters on the Al₂O₃ surfaces. Figure 3b shows a plot of the E_i of Pd_n/Al₂O₃ versus Pd cluster size. In the size region of n ≤ 4, E_i increased rapidly as the size increased. In sizes of n > 4, all E_i values were slightly changed with respect to the cluster size, whereas the differences in E_i for the Al₂O₃ surfaces were varied. E_i of Pd/Al₂O₃ was in the order γ-Al₂O₃(110) < α-Al₂O₃(0001) < γ-Al₂O₃(100). Thus, the interactions between the Pd clusters and Al₂O₃ were stronger for Pd/γ-Al₂O₃(110) than those for Pd/γ-Al₂O₃(100) and Pd/α-Al₂O₃(0001). Furthermore, it is suggested that the suppression of the Pd₁₃ shape on γ-Al₂O₃(110) comes from the increase in the interactions between Pd atoms and the Al₂O₃ surface. Such suppression on the other Al₂O₃ surfaces was less than that on the γ-Al₂O₃(110) surface.

Figure 3. Binding and interaction energies for isolated Pd_n clusters and Pd_n clusters (n = 1–4, 6, 9, and 13) supported on various Al₂O₃ surfaces as a function of the number of Pd atoms per Pd cluster.

3.4. Relation between Pd–Al₂O₃ Interactions and Surface Structure of Al₂O₃

To understand the relation between Pd–Al₂O₃ interactions and the surface structure of Al₂O₃, the interaction energies, E_i, were plotted against the CN (coordination number of bonds per Pd atom) of Pd–O and Pd–Al (Figure 4). E_i generally decreased as the coordination numbers, CN, of Pd–O and Pd–Al decreased. When the CN of Pd–O was less than 0.5 and the CN of Pd–Al was less than 1, E_i was linearly proportional to CN regardless of the Al₂O₃ surfaces. When CN was greater than the above values, the linear proportionality to CN was lost. The surface-to-surface variation increased because the contact area between Al₂O₃ and small clusters was restricted. Furthermore, because almost all of the atoms composing the small clusters were bound to the surface atoms, the interfacial interaction of the small clusters is strongly influenced by the local structure of the surface. As the cluster size increased, the Pd atoms on the interface could not be freely arranged due to the influence of other Pd atoms. As a result, CN decreased and the Pd–Al₂O₃ interactions are approximately determined by the number of Al and O atoms of Al₂O₃ bound to the Pd clusters. As in Table S5, CNs of Pd–O and Pd–Al at the same size of the Pd cluster were the largest for Pd₁₃/γ-Al₂O₃(110), followed by Pd₁₃/α-Al₂O₃(0001). That is to say, Pd/γ-Al₂O₃(110) could form more bonds between Pd clusters and Al₂O₃, and the strong Pd–Al₂O₃ interactions were induced. Here, one might infer that the Pd–Al₂O₃ interactions depend on the Al and O atom density of the top surface of Al₂O₃, which is directly involved in the bonding with Pd. However, the E_i values of Pd/γ-Al₂O₃(110) were smaller than those of Pd/α-Al₂O₃(0001) and Pd/γ-Al₂O₃(100) even though the atom density of Al and O in γ-Al₂O₃(110) was not so large (Table 1). The reason the interactions cannot be explained in terms of the atomic density was involved with the surface flexibility. During the AIMD annealing (Movies S4–S6), the Al_III sites and adjacent O atoms in γ-Al₂O₃(110) were flexibly oscillating. The γ-Al₂O₃(110) surface showed that the Al_III sites in γ-Al₂O₃(110) did not bond with the O atoms in the direction perpendicular to the surface. The α-Al₂O₃(0001) with Al_III sites was also a flexible structure. On the other hand, the flexibility of the γ-Al₂O₃(100) surface was less because the Al_V sites on the γ-Al₂O₃(100) surface were bound to O atoms not only in the direction parallel but also in the direction perpendicular to the surface. Furthermore, to evaluate the flexibility of the Al₂O₃ surface, the displacement of atoms on the surface due to the adsorption of Pd clusters on Al₂O₃ was investigated (Table 3). In Table 3, the z-axis was the direction perpendicular to the surface, and only the coordinates of Al and O atoms bonded to Pd were used for the statistics. The absolute value of the average z-coordinates of the displacement was largest in the Pd₁₃/γ-Al₂O₃(110). The z-coordinates of the Al_III sites in close proximity to the Pd₁₃ cluster on the Pd₁₃/γ-Al₂O₃(110) system were significantly changed upward. On the other hand, the z-coordinates of O atoms on Pd₁₃/γ-Al₂O₃(110) were changed downward. Thus, the γ-Al₂O₃(110) surface was flexible to the adsorption of the Pd cluster. In contrast, for Pd₁₃/α-Al₂O₃(0001), the average z-coordinates of displacement of the Al and O atoms were almost zero. However, they did not mean no change of the z-coordinates of Al atoms on the Pd₁₃/α-Al₂O₃(0001). According to the maximum and minimum displacement, the z-coordinates of Al atoms in α-Al₂O₃(0001) fluctuated up (+0.45 Å) and down (−0.54 Å) due to the adsorption of the Pd₁₃ cluster, resulting in an average displacement of zero. Although the α-Al₂O₃(0001) surface had Al_III sites, the absolute value of the maximum displacement for α-Al₂O₃(0001) was less than that for γ-Al₂O₃(110). Therefore, the α-Al₂O₃(0001) surface was less flexible than the γ-Al₂O₃(110) surface. The absolute values of average displacement of O and Al atoms on Pd₁₃/γ-Al₂O₃(100) was the smallest, and the surface structure of γ-Al₂O₃(100) was stiff. The above results indicate that the Pd–Al₂O₃ interactions are influenced by not only the atomic density but also the surface flexibility of Al₂O₃. The increase in the interaction between Pd and Al₂O₃ surface induced by the surface flexibility also led to the shape suppression of the Pd₁₃ cluster on γ-Al₂O₃(110). On the other hand, such suppression on the γ-Al₂O₃(100) was less than that on the other Al₂O₃ surfaces.

Figure 4. Interaction energies for Pd_n clusters (n = 1–4, 6, 9, and 13) supported on various Al₂O₃ surfaces as a function of the coordination number of (a) Pd–O and (b) Pd–Al.

Table 3. Average, Minimum, and Maximum z-Coordinate Values of the Displacement of Al and O Atoms Bonded to Pd in the Pd₁₃-Supported Al₂O₃ Surface from the Bare Al₂O₃ Surface

	Al atom (Å)			O atom (Å)
model	av	min	max	av	min	max
Pd₁₃/α-Al₂O₃(0001)	0.05	–0.54	0.45	0.01	–0.09	0.06
Pd₁₃/γ-Al₂O₃(100)	0.05	0.00	0.12	–0.05	–0.14	0.05
Pd₁₃/γ-Al₂O₃(110)	0.21	–0.16	0.72	–0.11	–0.36	0.05

In practical terms, coordinatively unsaturated Al³⁺ sites on the Al₂O₃ surface are hydrated, forming partially terminal/bridging hydroxyl groups. (49−52) The structures of metal clusters and isolated metal atoms on hydrated Al₂O₃ surfaces were investigated in previous studies. For example, for the γ-Al₂O₃(100), Rh_n clusters (n ≤ 5) interacted more strongly on the nonhydrated surface than on the hydrated surface. (31) Also, on hydrated γ-Al₂O₃(110), Rh_n clusters bonded strongly to hydroxyl groups. Pt₁₃ and Pd₁₃ clusters interacted more strongly with the nonhydrated γ-Al₂O₃(100) surface than with the hydrated γ-Al₂O₃(110) surface. (29) The morphology of Pt₂₂ changed from a biplanar shape on pristine γ-Al₂O₃(110) to three-dimensional, if hydroxyl coverage on γ-Al₂O₃(110) is greater than 8.9 OH nm^–2. (53) Immobilization of Ag species by terminal hydroxyl groups on the Al₂O₃ surface was reported. (20) Isolated Ag⁺ ions were reversibly dispersed by exchange with protons of terminal hydroxyl groups adjacent to strong Lewis acid sites (coordinatively unsaturated Al³⁺ sites) on Al₂O₃. (21) With the transfer of terminal hydroxyl groups and protons on the Al₂O₃ surfaces onto Pt clusters, the interaction between Pt and Al₂O₃ becomes stronger. (32) In this study, the effect of hydration of Al₂O₃ on the supported Pd clusters was also investigated. The hydration of γ-Al₂O₃(110) at 773 K is 5.9 OH nm^–2, which was used as a model. (40) Table S6 shows the Pd clusters on the hydrated γ-Al₂O₃(110) surface obtained by AIMD simulations and structural optimization. During the AIMD annealing at 773 K, the movement of hydroxyl groups on the hydrated Al₂O₃ surface occurred, but no proton was transferred from the terminal hydroxyl groups onto the Pd cluster. The E_i values of Pd_n/hydrated γ-Al₂O₃(110) (n = 1, 4, 13) were larger than those of Pd_n/dehydrated γ-Al₂O₃(110) (Figure S5). This result was consistent with previous report that the adsorption of Pd clusters (n = 1–5) on the hydrated γ-Al₂O₃(110) surface is weaker than on the nonhydrated γ-Al₂O₃(110) surface. (30) The coordinatively unsaturated Al³⁺ sites on the Al₂O₃ surface were hydrated, resulting in weakening of Pd–Al₂O₃ interactions. Although Al₂O₃ surfaces are very complex in practice, it was unveiled that Al₂O₃ surfaces with coordinatively unsaturated Al³⁺ sites have stronger interactions with Pd.

3.5. Dynamic Structure of Pd Clusters on Al₂O₃

Understanding the dynamics of Pd clusters on Al₂O₃ surfaces is important to gain more insight into the stability of Pd clusters and the interactions between Pd and Al₂O₃. AIMD simulations were performed in which the Pd₁₃/Al₂O₃ systems were held at 773 K for 8 ps (Movies S7–S9 and Figure S6) after a temperature increase from 0 to 773 K during 2 ps. Figure 5 shows the average distances d_adj between only adjacent Pd atoms and d_all between all Pd atoms. For 0–3 ps, d_all of Pd₁₃/Al₂O₃ decreased significantly with time; after 3 ps, the d_all remained almost constant, suggesting that the Pd₁₃ clusters on Al₂O₃ were almost in equilibrium. On the other hand, d_adj showed little change with respect to time. Therefore, the Pd clusters underwent structural changes while keeping the distance between adjacent Pd atoms constant. Figure 6 shows the variation of the x-, y-, and z-coordinates of the centroid of the Pd₁₃ clusters. The Pd₁₃ cluster on γ-Al₂O₃(100) migrated while stretching perpendicular to the Al₂O₃ surface (Figures 6b and S3b and Movie S8). On the other hand, the Pd₁₃ cluster on γ-Al₂O₃(110) was anchored on the surface while maintaining the prolate shape (Figures 6c and S3c and Movie S9). Moreover, the migration rates of the Pd₁₃ clusters on the Al₂O₃ surfaces were calculated by dividing the variation of the centroid of the Pd₁₃ cluster by time (Table 4). The migration rate of the Pd₁₃ cluster on γ-Al₂O₃(110) was 0.31 Å/ps, which was smaller than those of the Pd₁₃ clusters on γ-Al₂O₃(100) and α-Al₂O₃(0001). The γ-Al₂O₃(110) surface suppressed the migration of the Pd₁₃ cluster more in comparison with the γ-Al₂O₃(100) and α-Al₂O₃(0001) surface. This indicated that a barrier for the migration of the Pd₁₃ cluster on γ-Al₂O₃(110) was higher than that on γ-Al₂O₃(100) and α-Al₂O₃(0001). During the thermal deformation of the Pd₁₃ cluster, the γ-Al₂O₃(110) surface could keep the Pd–Al and Pd–O bonds without migration of the Pd₁₃ cluster because the Al₂O₃ surface deforms flexibly in response to the deformation. In contrast, the deformation of the Pd₁₃ cluster on the γ-Al₂O₃(100) surface was accompanied by the breakage of the Pd–Al or Pd–O bonds as the surface structure was stiff. As a result, the entire Pd cluster had to move across the Al₂O₃ surface to form new bonds with other surface atoms to stabilize the Pd cluster. The migration rate of the Pd₁₃ cluster was also suppressed on α-Al₂O₃(0001) compared to γ-Al₂O₃(100). Therefore, we showed that the design of the Al₂O₃ surface can control the shape and dispersion of Pd clusters on Al₂O₃. Because the AIMD simulation time for calculating the migration rate is very short (5 ps), one should be aware that the simulation does not provide a complete sampling of the diffusion path on the surface. Thus, the migration rate may not correspond to the real values. However, the above results, which indicate the dependence of the diffusion of Pd NPs on the Al₂O₃ surfaces, are supported by the movies and the calculated migration rates.

Figure 5. Variation of the d_all and d_adj of (a) Pd₁₃/α-Al₂O₃(0001), (b) Pd₁₃/γ-Al₂O₃(100), and (c) Pd₁₃/γ-Al₂O₃(110) for the MD cycle.

Figure 6. Variation of the average position of Pd₁₃ clusters in (a) Pd₁₃/α-Al₂O₃(0001), (b) Pd₁₃/γ-Al₂O₃(100), and (c) Pd₁₃/γ-Al₂O₃(110) in the x-, y-, and z-axis direction for MD cycle (center). Top and side views of Pd₁₃/Al₂O₃ at 3 and 8 ps (left and right). O, Al, and Pd atoms are shown as red, brown, and navy-blue balls.

Table 4. Average Distance between Adjacent Pd Atoms d_adj, Average Distance between All Pd Atoms d_all, and Migration Rate of Pd₁₃ Cluster for Pd₁₃/α-Al₂O₃(0001), Pd₁₃/γ-Al₂O₃(100), and Pd₁₃/γ-Al₂O₃(110)

model	d_adj (Å)	d_all (Å)	migration rate of Pd particle (Å/ps)
Pd₁₃/α-Al₂O₃(0001)	2.77 ± 0.03	4.12 ± 0.10	0.66
Pd₁₃/γ-Al₂O₃(100)	2.77 ± 0.04	4.24 ± 0.17	1.34
Pd₁₃/γ-Al₂O₃(110)	2.77 ± 0.03	4.00 ± 0.06	0.31

4. Conclusions

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The geometric structure and dynamics of Pd clusters on various Al₂O₃ surfaces were investigated by DFT calculations combined with AIMD simulations. The structure of a Pd₁₃ cluster with low symmetry on the γ-Al₂O₃(100) was similar to that of a Pd₁₃ cluster in a vacuum. On the other hand, Pd₁₃ clusters on α-Al₂O₃(0001) and γ-Al₂O₃(110) were oblate and prolate, respectively. These Pd clusters deformed to bond more with the Al₂O₃ surface. Comparing the reconstruction of the Al₂O₃ surface when Pd clusters were adsorbed, the γ-Al₂O₃(110) surface showed a greater displacement of the Al and O atoms than did the other surfaces. The γ-Al₂O₃(110) surface with coordinatively unsaturated 3-coordinated Al³⁺ sites was found to be more flexible than the other surfaces. From the point of view of dynamics, Pd₁₃ clusters on γ-Al₂O₃(100) diffused during AIMD annealing at 773 K, stretching and shrinking perpendicularly to the Al₂O₃ surface. In contrast, Pd₁₃ clusters on γ-Al₂O₃(110) were anchored on Al₂O₃ while maintaining a prolate shape. Focusing on Al₂O₃, the γ-Al₂O₃(110) surface deformed flexibly as the Pd₁₃ cluster deformed, so that surface Al and O atoms moved closer to the Pd cluster to form more bonds. Because the γ-Al₂O₃(100) surface was stiff, the deforming of the Pd cluster led to the migration of the entire Pd cluster across the Al₂O₃ surface to maintain the number of Pd–Al and Pd–O bonds per Pd atom. The interactions between Pd and Al₂O₃ were discussed in terms of binding energy E_b and interaction energy E_i per Pd atom. In the case of Pd₁₃ on Al₂O₃, both E_b and E_i were stronger in the order γ-Al₂O₃(100) < α-Al₂O₃(0001) < γ-Al₂O₃(110). The interactions between Pd clusters and Al₂O₃ were larger as the number of Al and O atoms bonded to the Pd cluster increased at the interface. However, the Al and O atom density of the γ-Al₂O₃(110) surface was smaller than that of α-Al₂O₃(0001) and γ-Al₂O₃(100). The γ-Al₂O₃(110) surface bonded more with Pd clusters due to the structural flexibility of the 3-coordinated Al³⁺ sites and the adjacent O atoms, causing stronger Pd–Al₂O₃ interactions. Hydration of the Al₂O₃ surface weakened the Pd–Al₂O₃ interaction because hydroxyl adsorbates covered the coordinatively unsaturated Al³⁺ sites.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.3c02483.

Figure S1: transition of the temperature and the potential energy of Pd₁₃ cluster on Al₂O₃ surfaces for MD cycle; Figure S2: histograms of the temperature distribution for 5 ps after 3 ps of holding at 773 K; Figure S3: initial structure of γ-Al₂O₃(110) surface before AIMD simulation; Figure S4: sampled initial structures for the structural optimization; Table S1: molecular structures of Pd clusters supported on α-Al₂O₃(0001); Table S2: molecular structures of Pd clusters supported on γ-Al₂O₃(100); Table S3: molecular structures of Pd clusters supported on γ-Al₂O₃(110); Table S4: molecular structures of Pd clusters in a vacuum; Table S5: coordination number, average interatomic distance_, binding energies, and interaction energies, for Pd clusters supported on Al₂O₃; Table S6: molecular structures of Pd clusters supported on hydrated γ-Al₂O₃(110); Figure S5: binding energies for Pd cluster supported on dehydrated and hydrated γ-Al₂O₃(110) surface as a function of the number of Pd atoms per Pd cluster; Figure S6: snapshots of MD simulations at 773 K for Pd₁₃/Al₂O₃ (PDF)
Movie S1a: top view of Pd₁₃/α-Al₂O₃(0001) (MP4)
Movie S1b: side view of Pd₁₃/α-Al₂O₃(0001) (MP4)
Movie S2a: top view of Pd₁₃/γ-Al₂O₃(100) (MP4)
Movie S2b: side view of Pd₁₃/γ-Al₂O₃(100) (MP4)
Movie S3a: top view of Pd₁₃/γ-Al₂O₃(110) (MP4)
Movie S3b: side view of Pd₁₃/γ-Al₂O₃(110) (MP4)
Movie S4a: top view of α-Al₂O₃(0001) (MP4)
Movie S4b: side view of α-Al₂O₃(0001) (MP4)
Movie S5a: top view of γ-Al₂O₃(100) (MP4)
Movie S5b: side view of γ-Al₂O₃(100) (MP4)
Movie S6a: top view of γ-Al₂O₃(110) (MP4)
Movie S6b: side view of γ-Al₂O₃(110) (MP4)
Movie S7a: top view of Pd₁₃/α-Al₂O₃(0001) (MP4)
Movie S7b: side view of Pd₁₃/α-Al₂O₃(0001) (MP4)
Movie S8a: top view of Pd₁₃/γ-Al₂O₃(100) (MP4)
Movie S8b: side view of Pd₁₃/γ-Al₂O₃(100) (MP4)
Movie S9a: top view of Pd₁₃/γ-Al₂O₃(110) (MP4)
Movie S9b: side view of Pd₁₃/γ-Al₂O₃(110) (MP4)

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al₂O₃ Surfaces: DFT and AIMD Studies

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Supporting information

Unveiling Static and Dynamic Structures of Pd Clusters

Influenced by Al

Surfaces: DFT and AIMD Studies

Kazumasa Murata

†

, Akira Oda

†

, ‡

, Atsushi Satsuma

†

, ‡

, Kyoichi Sawabe*

†

, ‡

†

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

‡

Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-

8520, Japan

Corresponding Author

* E-mail:

sawabe@chembio.nagoya-u.ac.jp

Figure S1.

Transition of the temperature and potential energy of Pd

cluster on Al

surfaces during the simulated annealing

and holding by AIMD. (a) Pd



-Al

(0001), (b) Pd



-Al

(100), and (c) Pd



-Al

(110).

(

)

(

)

(

)

Figure S2.

Histograms of the temperature distribution for 5 ps after 3 ps of holding at 773K. (a) Pd



-Al

(0001), (b)



-Al

(100), and (c) Pd



-Al

(110).

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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Corresponding Author
- Kyoichi Sawabe - Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan; Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan; https://orcid.org/0000-0001-6228-1395; Email: sawabe@chembio.nagoya-u.ac.jp
Authors
- Kazumasa Murata - Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
- Akira Oda - Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan; Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan; https://orcid.org/0000-0002-0217-4202
- Atsushi Satsuma - Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan; Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan; https://orcid.org/0000-0001-6946-7678
Notes
The authors declare no competing financial interest.

Acknowledgments

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This work was partly supported by the JSPS KAKENHI Grant-in-Aids for Scientific Research (B) (Grant No. 18H01787) and JSPS Fellows (Grant No. 19J15440) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. A portion of this work was performed under the management of the Elements Strategy Initiative for Catalysts & Batteries (ESICB, JPMXP0112101003), which is also supported by MEXT. We used the supercomputer of ACCMS, Kyoto University.

Abbreviations

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MNPs	metal nanoparticles
MSIs	metal–support interactions
DFT	density functional theory
AIMD	ab initio molecular dynamics
CN	coordination number.

References

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Wan, Chuan; Hu, Mary Y.; Jaegers, Nicholas R.; Shi, Dachuan; Wang, Huamin; Gao, Feng; Qin, Zhaohai; Wang, Yong; Hu, Jian Zhi
Journal of Physical Chemistry C (2016), 120 (40), 23093-23103CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
The metal-support interaction in γ-Al2O3 supported WOX catalysts is investigated by a combination of high field quant. single pulse (SP) 27Al MAS NMR spectroscopy, 2D MQMAS, 1H-27Al CP/MAS, and electronic structure calcns. NMR allows the observation of at least seven different Al sites, including a pentahedral Al site (AlP), three different tetrahedral Al sites (AlT), and three octahedral Al sites (AlO). It is found that the AlP site d. decreases monotonically with an increased WOX loading, the AlO site d. increases concurrently, and the d. of AlT sites remains const. This suggests that the AlP sites are the preferred surface anchoring positions for the WOX species. Importantly, the AlP site isotropic chem. shift obsd. for the unsupported γ-Al2O3 at about 38 ppm migrates to the octahedral region with a new isotropic chem. shift value appearing near 7 ppm when the AlP site is anchored by WOX species. D. functional theory (DFT) computational modeling of the NMR parameters on proposed WOX/γ-Al2O3 cluster models is carried out to accurately interpret the dramatic chem. shift changes from which the detailed anchoring mechanisms are obtained. It is found that tungsten dimers and monomers are the preferred supported surface species on γ-Al2O3, wherein one monomeric and several dimeric structures are identified as the most likely surface anchoring structures.
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Kwak, J. H.; Hu, J. Z.; Kim, D. H.; Szanyi, J.; Peden, C. H. F. Penta-Coordinated Al³⁺ Ions as Preferential Nucleation Sites for BaO on Al₂O₃: An Ultra-High-Magnetic Field ²⁷Al MAS NMR Study. J. Catal. 2007, 251, 189– 194, DOI: 10.1016/j.jcat.2007.06.029
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Penta-coordinated Al3+ ions as preferential nucleation sites for BaO on γ-Al2O3: an ultra-high-magnetic field 27Al MAS NMR study
Kwak, Ja Hun; Hu, Jian Zhi; Kim, Do Heui; Szanyi, Janos; Peden, Charles H. F.
Journal of Catalysis (2007), 251 (1), 189-194CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Ltd.)
We report the first observation of preferential anchoring of an impregnated catalytic phase onto penta-coordinated Al3+ sites on the surface of γ-Al2O3. The interaction of barium oxide with a γ-alumina support was investigated by high resoln. solid state 27Al magic angle spinning NMR at an ultra-high magnetic field of 21.1 T and at sample spinning rates of up to 23 kHz. Under these exptl. conditions, a peak in the NMR spectrum at ∼23 ppm with relatively low intensity, assigned to 5-coordinated Al3+ ions, is clearly distinguished from the two other peaks representing Al3+ ions in tetra-, and octahedral coordination. Spin-lattice 27Al relaxation time measurements clearly show that these penta-coordinated Al3+ sites are located on the surface of the γ-alumina support. BaO deposition onto this γ-alumina sample resulted in the loss of intensity of the 23 ppm peak. The intensity loss obsd. was linearly proportional to the amt. of BaO deposited. The results of this study strongly suggest that, at least for BaO, these penta-coordinated Al3+ ions are the nucleation sites.
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Kwak, J. H.; Hu, J.; Mei, D.; Yi, C.-W.; Kim, D. H.; Peden, C. H. F.; Allard, L. F.; Szanyi, J. Coordinatively Unsaturated Al³⁺ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al₂O₃. Science 2009, 325, 1670– 1673, DOI: 10.1126/science.1176745
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Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al2O3
Kwak, Ja Hun; Hu, Jianzhi; Mei, Donghai; Yi, Cheol-Woo; Kim, Do Heui; Peden, Charles H. F.; Allard, Lawrence F.; Szanyi, Janos
Science (Washington, DC, United States) (2009), 325 (5948), 1670-1673CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a crit. role in detg. particle morphol. and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning NMR spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with d. functional theory calcns. to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a γ-Al2O3 catalyst support material. The results obtained show that coordinatively unsatd. pentacoordinate Al3+ (Al3+penta) centers present on the (100) facets of the γ-Al2O3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al3+penta = 1), whereas two-dimensional Pt rafts form at higher coverages.
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Mei, D.; Kwak, J. H.; Hu, J.; Cho, S. J.; Szanyi, J.; Allard, L. F.; Peden, C. H. F. Unique Role of Anchoring Penta-Coordinated Al³⁺ Sites in the Sintering of γ-Al₂O₃-Supported Pt Catalysts. J. Phys. Chem. Lett. 2010, 1, 2688– 2691, DOI: 10.1021/jz101073p
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Unique Role of Anchoring Penta-Coordinated Al3+ Sites in the Sintering of γ-Al2O3-Supported Pt Catalysts
Mei, Donghai; Kwak, Ja Hun; Hu, Jianzhi; Cho, Sung June; Szanyi, Janos; Allard, Lawrence F.; Peden, Charles H. F.
Journal of Physical Chemistry Letters (2010), 1 (18), 2688-2691CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
γ-Al2O3-supported Pt group catalysts are widely used in many industrially important catalytic processes. However, γ-Al2O3-supported Pt catalysts are prone to deactivation via metal sintering at high temps., in oxidative reaction environments, or both. Using a combination of exptl. HRTEM and EXAFS measurements and theor. DFT calcns., we find that pentacoordinated Al3+ sites (Alp) on the γ-Al2O3(100) surface can inhibit Pt sintering both thermodynamically and kinetically because of their strong interactions with at. Pt or Pt oxide species. The present work suggests a promising approach for stabilizing the size and morphol. of supported catalytically active phases.
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Zhang, Z.; Zhu, Y.; Asakura, H.; Zhang, B.; Zhang, J.; Zhou, M.; Han, Y.; Tanaka, T.; Wang, A.; Zhang, T.; Yan, N. Thermally Stable Single Atom Pt/m-Al₂O₃ for Selective Hydrogenation and CO Oxidation. Nat. Commun. 2017, 8, 16100, DOI: 10.1038/ncomms16100
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Thermally stable single atom Pt/m-Al2O3 for selective hydrogenation and CO oxidation
Zhang, Zailei; Zhu, Yihan; Asakura, Hiroyuki; Zhang, Bin; Zhang, Jiaguang; Zhou, Maoxiang; Han, Yu; Tanaka, Tsunehiro; Wang, Aiqin; Zhang, Tao; Yan, Ning
Nature Communications (2017), 8 (), 16100CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsatd. pentahedral Al3+ centers. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atm. at 200 aluminum oxideC for 24 h. Compared to com. Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550°C for 48 h, although agglomeration of Pt single-atoms into clusters is obsd. after reaction. In CO oxidn., the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 aluminum oxideC over a one-month period.
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Hackett, S. F. J.; Brydson, R. M.; Gass, M. H.; Harvey, I.; Newman, A. D.; Wilson, K.; Lee, A. F. High-Activity, Single-Site Mesoporous Pd/Al₂O₃ Catalysts for Selective Aerobic Oxidation of Allylic Alcohols. Angew. Chemie - Int. Ed. 2007, 46, 8593– 8596, DOI: 10.1002/anie.200702534
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High-activity, single-site mesoporous Pd/Al2O3 catalysts for selective aerobic oxidation of allylic alcohols
Hackett, Simon F. J.; Brydson, Rik M.; Gass, Mhairi H.; Harvey, Ian; Newman, Andrew D.; Wilson, Karen; Lee, Adam F.
Angewandte Chemie, International Edition (2007), 46 (45), 8593-8596CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Pd does it alone: Tailored heterogeneous catalysts offer exciting, alternative, clean technologies for regioselective mol. transformations. A mesoporous alumina support stabilizes atomically dispersed PdII surface sites, thereby dramatically enhancing catalytic performance in the aerobic selective oxidn. of alcs.
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Tang, N.; Cong, Y.; Shang, Q.; Wu, C.; Xu, G.; Wang, X. Coordinatively Unsaturated Al³⁺ Sites Anchored Subnanometric Ruthenium Catalyst for Hydrogenation of Aromatics. ACS Catal. 2017, 7, 5987, DOI: 10.1021/acscatal.7b01816
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Coordinatively Unsaturated Al3+ Sites Anchored Subnanometric Ruthenium Catalyst for Hydrogenation of Aromatics
Tang, Nanfang; Cong, Yu; Shang, Qinghao; Wu, Chuntian; Xu, Guoliang; Wang, Xiaodong
ACS Catalysis (2017), 7 (9), 5987-5991CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Single metal atoms and metal clusters have attracted much attention because of their high dispersity, special electronic structures, and uniformity of active sites as heterogeneous catalysts, but it is still challenging to generate stable single atoms and clusters with high metal loadings. Supports play a crucial role in detg. particle morphol. and maintaining dispersion. Herein we synthesize an amorphous alumina with 29% coordinatively unsatd. pentacoordinate Al3+ (Al3+penta) sites, which can anchor atomically dispersed Ru species with 1 wt. % loading. Strong interactions between Ru and Al3+penta centers were detected, resulting in distinct Ru geometric and electronic features. When used in benzene hydrogenation reaction, fairly high specific activity (TOF = 5180 h-1) were obtained. The high catalytic performance is considered closely correlated with the high utilization of special Ru active sites.
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Li, L.; Wang, L. L.; Johnson, D. D.; Zhang, Z.; Sanchez, S. I.; Kang, J. H.; Nuzzo, R. G.; Wang, Q.; Frenkel, A. I.; Li, J. Noncrystalline-to-Crystalline Transformations in Pt Nanoparticles. J. Am. Chem. Soc. 2013, 135, 13062– 13072, DOI: 10.1021/ja405497p
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Noncrystalline-to-Crystalline Transformations in Pt Nanoparticles
Li, Long; Wang, Lin-Lin; Johnson, Duane D.; Zhang, Zhongfan; Sanchez, Sergio I.; Kang, Joo H.; Nuzzo, Ralph G.; Wang, Qi; Frenkel, Anatoly I.; Li, Jie; Ciston, James; Stach, Eric A.; Yang, Judith C.
Journal of the American Chemical Society (2013), 135 (35), 13062-13072CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
We show that the noncryst.-to-cryst. transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncryst. phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resoln. transmission electron microscopy show a noncryst.-to-cryst. transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist. The NP size at which this transition occurs is strongly dependent on both the adsorbate and the support, and this effect is general for late 5d transition metals. All results are reconciled via a statistical description of particle-support-adsorbate interactions.
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Murata, K.; Onoda, J.; Yamamoto, Y.; Oda, A.; Ohyama, J.; Satsuma, A. Enhancement of Toluene Hydrogenation Activity of Supported Pt Nanoparticles with Increasing the Crystallinity of Pt. Appl. Catal. A, Gen. 2022, 629, 118425, DOI: 10.1016/j.apcata.2021.118425
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Enhancement of toluene hydrogenation activity of supported Pt nanoparticles with increasing the crystallinity of Pt
Murata, Kazumasa; Onoda, Junya; Yamamoto, Yuta; Oda, Akira; Ohyama, Junya; Satsuma, Atsushi
Applied Catalysis, A: General (2022), 629 (), 118425CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)
The activity of Pt/Al2O3 in the hydrogenation of toluene (TOL) was found to monotonically increase in line with an increase in the Pt particle size from 1.0 to 2.5 nm, but was const. for a size above 2.5 nm. Comparing different cryst. phases of Al2O3, the activity of Pt/θ-Al2O3 was found to be around 1.5 times higher than that of Pt/γ-Al2O3 for the same Pt particle size. Scanning transmission electron microscopy showed the presence of amorphous Pt nanoparticles (NPs) with a size of < 2.0 nm and Pt nanocrystals (NCs) with a size of ≥ 2.0 nm on Al2O3. Furthermore, the fraction of amorphous Pt NPs in Pt/γ-Al2O3 was higher than that in Pt/θ-Al2O3. Pt NCs were shown to be more active than the amorphous Pt NPs in the hydrogenation of TOL owing to them having an abundance of Pt plane.
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Batista, A. T. F.; Baaziz, W.; Taleb, A.; Chaniot, J.; Moreaud, M.; Aguilar-tapia, A.; Proux, O.; Hazemann, J.; Diehl, F.; Gay, A. Atomic Scale Insight into the Formation, Size, and Location of Platinum Nanoparticles Supported on γ-Alumina. ACS Catal. 2020, 10, 4193– 4204, DOI: 10.1021/acscatal.0c00042
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Atomic Scale Insight into the Formation, Size, and Location of Platinum Nanoparticles Supported on γ-Alumina
Batista, Ana T. F.; Baaziz, Walid; Taleb, Anne-Lise; Chaniot, Johan; Moreaud, Maxime; Legens, Christele; Aguilar-Tapia, Antonio; Proux, Olivier; Hazemann, Jean-Louis; Diehl, Fabrice; Chizallet, Celine; Gay, Anne-Sophie; Ersen, Ovidiu; Raybaud, Pascal
ACS Catalysis (2020), 10 (7), 4193-4204CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
A clear description of the morphol. and location, with respect to the support, of metallic subnanometric particles remains a current strenuous exptl. challenge in numerous catalytic applications such as naphtha reforming and biomass conversion. High-resoln. HAADF-STEM coupled with in situ and tomog. analyses have been undertaken on a platinum (Pt) active phase supported on chlorinated alumina (γ-Al2O3) with 0.3 and 1 wt % Pt loadings, highlighting the formation of flat nanoparticles (NPs) of 0.9 nm diam. and Pt single atoms (SAs) in the reduced state. While SAs and weakly cohesive clusters are predominantly obsd. in the oxide state, with a coordination sphere of Pt composed of O and Cl as revealed by EXAFS, the ratio between SAs and Pt NPs in the reduced state is found to be about 2.8. This ratio is the same for the two metal loadings: both the total nos. of NPs and SAs increase at a higher metal loading. Electron tomog. reveals that the vast majority of NPs are located on the edges or defects (steps, kinks) of the γ-alumina support crystallites. DFT calcns. further highlight the optimized structures of NPs located at the γ-Al2O3 (110)-(100) edge and near-edge with a stability competing with NPs located either on the (110) or on the (100) γ-Al2O3 facet. A math. anal. of the segmented vols. shows that the av. geodesic distances between NPs is linked to Pt loading: 9 nm for 1 wt % Pt and 16 nm for 0.3 wt % Pt. Evaluation of support tortuosity descriptors using the nanoparticle positions confirms a uniform distribution on the support. A square network geometric model compatible with the geodesic distances between NPs reveals that one to five NPs can be present at the same time on each alumina crystallite depending on Pt loading.
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Vaarkamp, M.; Miller, J. T.; Modica, F. S.; Koningsberger, D. C. On the Relation between Particle Morphology, Structure of the Metal-Support Interface, and Catalytic Properties of Pt/γ-Al₂O₃. J. Catal. 1996, 163, 294– 305, DOI: 10.1006/jcat.1996.0330
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On the relation between particle morphology, structure of the metal-support interface, and catalytic properties of Pt/γ-Al2O3
Vaarkamp, Marius; Miller, Jeffrey T.; Modica, Frank S.; Koningsberger, Diek, C.
Journal of Catalysis (1996), 163 (2), 294-305CODEN: JCTLA5; ISSN:0021-9517. (Academic)
The relation between catalytic activity, electronic properties, morphol., and structure of the metal support interface was studied for Pt/γ-Al2O3 after low (300°C, LTR) and high temp. redn. (450°C, HTR). EXAFS revealed that after LTR the platinum particles were three-dimensional, contained 11 Pt atoms on av., and were at a distance of 2.7 Å from the support oxygen. During HTR, the morphol. of the platinum particles changed from three-dimensional to rafts with a structure similar to Pt(100), as indicated by a decrease in the Pt-Pt coordination no. and the absence of the third coordination shell in the EXAFS spectrum. After HTR the Pt-O distance was shortened to 2.2 Å due to the desorption of hydrogen from the metal-support interface. The shortening of the Pt-O distance upon HTR treatment agrees with previous studies on zeolite supported platinum. However, zeolite supported platinum particles retained their three-dimensional structure upon HTR. The changes in the structure of the catalyst affected the catalytic, chemisorption, and electronic properties. After HTR the selectivity for hydrogenolysis of both neopentane and methylcyclopentane to methane decreased. At the same time the specific activity for neopentane isomerization and methylcyclopentane ring opening increased. The hydrogen chemisorption capacity after HTR was lower than after LTR. HTR shifted the sym. linear CO IR absorption from 2063 to 2066 cm-1. Comparison of the PtLIII and LII X-ray absorption edge intensities after LTR and HTR revealed that the no. of holes in the d-band of the platinum atoms increased by 9.5% during HTR. It was suggested that the decrease in hydrogen chemisorption capacity, hydrogenolysis selectivity, and no. of holes in the d-band are related to the change in the structure of the metal-support interface. The increase in specific activity for isomerization of neopentane and the shift in the CO IR absorption band with a raise in redn. temp. agreed with reported results for single crystals and was attributed to the higher concn. of atoms with Pt(100) symmetry in the catalyst after HTR.
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Wang, F.; Ma, J.; Xin, S.; Wang, Q.; Xu, J.; Zhang, C.; He, H.; Cheng Zeng, X. Resolving the Puzzle of Single-Atom Silver Dispersion on Nanosized γ-Al₂O₃ Surface for High Catalytic Performance. Nat. Commun. 2020, 11, 529, DOI: 10.1038/s41467-019-13937-1
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Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance
Wang, Fei; Ma, Jinzhu; Xin, Shaohui; Wang, Qiang; Xu, Jun; Zhang, Changbin; He, Hong; Xiao, Cheng Zeng
Nature Communications (2020), 11 (1), 529CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
Ag/γ-Al2O3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphol. and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al2O3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al2O3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al2O3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al2O3. D.-functional-theory calcns. confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al2O3, but not on microsized γ-Al2O3. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts.
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Kubota, H.; Mine, S.; Toyao, T.; Maeno, Z.; Shimizu, K. Redox-Driven Reversible Structural Evolution of Isolated Silver Atoms Anchored to Specific Sites on γ-Al₂O₃. ACS Catal. 2022, 12, 544– 599, DOI: 10.1021/acscatal.1c04924
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Redox-Driven Reversible Structural Evolution of Isolated Silver Atoms Anchored to Specific Sites on γ-Al2O3
Kubota, Hiroe; Mine, Shinya; Toyao, Takashi; Maeno, Zen; Shimizu, Ken-ichi
ACS Catalysis (2022), 12 (1), 544-559CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Reversible structural transformation between at. Ag(I) and large Ag metal nanoparticles (NPs) on γ-Al2O3-supported Ag (Ag/Al2O3) catalysts for H2-assisted NOx selective catalytic redn. by NH3 was monitored by in situ X-ray absorption spectroscopy, UV-visible spectroscopy, IR spectroscopy, and ex situ microscopy. Fresh Ag/Al2O3 was deactivated by H2 redn. at 800°C owing to sintering of the at. Ag(I) species to form large (10-52 nm) Ag metal NPs. Reoxidn. of the sintered catalyst using NO + O2 at 400°C resulted in the redispersion of Ag metal NPs to the at. Ag(I) species, leading to the recovery of the catalytic activity. Sintering and dispersion occurred reversibly for 10 repetitive treatments of H2↔NO + O2 at 600°C. The structure of the anchoring site and the mechanism of oxidative dispersion were elucidated by kinetic studies, in situ spectroscopy, 27Al NMR spectroscopy, and d. functional theory calcns. The isolated Ag(I) cation was exchanged with H+ of the HO-μ1-AlVI site adjacent to the strong Lewis acid sites (unsatd. AlIV3+) on γ-Al2O3, and, consequently, the anchored Ag(I) species reduced the Lewis acid strength of the adjacent AlIV3+ sites. During sintering under H2, the isolated AgO-μ1-AlVI species aggregated to form Ag metal NPs, regenerating the HO-μ1-AlVI sites on the support. During oxidative dispersion under the NO + O2 flow, the Ag metal NPs were oxidized to furnish mobile AgNO3 species that moved across the support surface and reacted with the anchoring site, HO-μ1-AlVI, to yield the original AgO-μ1-AlVI species and HNO3; the latter reacts with the γ-Al2O3 surface to yield the nitrate species. This study provides mol. level insights into the deactivation/reactivation of supported metal catalysts under reductive/oxidative conditions.
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Valero, M. C.; Raybaud, P.; Sautet, P. Influence of the Hydroxylation of γ-Al₂O₃ Surfaces on the Stability and Diffusion of Single Pd Atoms: A DFT Study. J. Phys. Chem. B 2006, 110, 1759– 1767, DOI: 10.1021/jp0554240
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Influence of the Hydroxylation of γ-Al2O3 Surfaces on the Stability and Diffusion of Single Pd Atoms: A DFT Study
Valero, Manuel Corral; Raybaud, Pascal; Sautet, Philippe
Journal of Physical Chemistry B (2006), 110 (4), 1759-1767CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
Using recent well-defined models of γ-Al2O3 surfaces, the authors study the interaction of single Pd atoms with γ-Al2O3 surfaces corresponding to realistic pretreatment conditions by d. functional theory periodic calcns. For relevant hydroxylation states of the surface, the authors det. potential energy surfaces (PES) that depict the relation between structure and interaction at the metal-oxide interface. This approach enables the detn. of the low-energy diffusion paths of the adsorbed Pd species. The authors applied classical transition-state theory to derive the temp.-dependent hopping rate of Pd on γ-Al2O3 surfaces. The authors' work provides new insight into the chemisorption and diffusion process of single Pd atoms on alumina and show that the binding energy and hopping rate of Pd atoms decrease as the surface OH coverage increases. These results offer new highlights on Pd cluster formation at the initial nucleation steps on γ-Al2O3 surfaces.
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Murata, K.; Mahara, Y.; Ohyama, J.; Yamamoto, Y.; Arai, S.; Satsuma, A. The Metal-Support Interaction Concerning the Particle Size Effect of Pd/Al₂O₃ on Methane Combustion. Angew. Chemie Int. Ed. 2017, 56, 15993– 15997, DOI: 10.1002/anie.201709124
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The Metal-Support Interaction Concerning the Particle Size Effect of Pd/Al2O3 on Methane Combustion
Murata, Kazumasa; Mahara, Yuji; Ohyama, Junya; Yamamoto, Yuta; Arai, Shigeo; Satsuma, Atsushi
Angewandte Chemie, International Edition (2017), 56 (50), 15993-15997CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The particle size effect of Pd nanoparticles supported on alumina with various cryst. phases on methane combustion was investigated. Pd/θ-, α-Al2O3 with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al2O3 increased with the particle size. Based on a structural anal. of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration-cor. scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina cryst. phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal-support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al2O3 for methane combustion.
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Murata, K.; Shiotani, T.; Ohyama, J.; Satsuma, A. Selective Hydrogenation of C═C Bond in Cinnamaldehyde on Pd Step Sites of Pd/Al₂O₃. Chem. Lett. 2021, 50, 599– 602, DOI: 10.1246/cl.200856
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Selective Hydrogenation of C=C bond in Cinnamaldehyde on Pd Step Sites of Pd/Al2O3
Murata, Kazumasa; Shiotani, Takumi; Ohyama, Junya; Satsuma, Atsushi
Chemistry Letters (2021), 50 (4), 599-602CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
We found a pos. correlation between C=C selective hydrogenation activity of cinnamaldehyde (CAL) and the fraction of the Pd step site on Pd nanoparticles. Owing to a high fraction of step sites, Pd/θ-Al2O3 catalysts with Pd particle size of 5-10 nm were highly active for the C=C selective hydrogenation of CAL.
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Murata, K.; Eleeda, E.; Ohyama, J.; Yamamoto, Y.; Arai, S.; Satsuma, A. Identification of Active Sites in CO Oxidation over a Pd/Al₂O₃ Catalyst. Phys. Chem. Chem. Phys. 2019, 21, 18128– 18137, DOI: 10.1039/C9CP03943K
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Identification of active sites in CO oxidation over a Pd/Al2O3 catalyst
Murata, Kazumasa; Eleeda, Eleen; Ohyama, Junya; Yamamoto, Yuta; Arai, Shigeo; Satsuma, Atsushi
Physical Chemistry Chemical Physics (2019), 21 (33), 18128-18137CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
The active sites of Pd/Al2O3 catalysts for CO oxidns. were identified by investigating the dependence of CO oxidn. activities on the surface structure and morphol. of Pd nanoparticles. The max. catalytic activity was obtained for Pd particles approx. 2 nm in particle size. We performed structural analyses on the Pd surface through IR (IR) spectroscopy of the adsorbed CO mols. A pos. correlation was obtained between catalytic activity and the fraction of linear CO adsorbed on Pd corner sites and Pd(111) facets, indicating that these sites are highly active for CO oxidn. X-ray absorption fine structure (XAFS) and spherical aberration-cor. scanning transmission electron microscopy (Cs-STEM) measurements demonstrated that Pd nanoparticles less than 2 nm in particle size with amorphous-like structures and Pd particles with large, well-ordered structures favor the formation of a high fraction of corner sites and Pd(111) facets, resp.
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Duan, H.; You, R.; Xu, S.; Li, Z.; Qian, K.; Cao, T.; Huang, W.; Bao, X. Penta-Coordinated Al³⁺ Stabilized Active Pd Structures on Al₂O₃ Coated Palladium Catalysts for Methane Combustion. Angew. Chemie Int. Ed. 2019, 58, 12043– 12048, DOI: 10.1002/anie.201904883
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Pentacoordinated Al3+-Stabilized Active Pd Structures on Al2O3-Coated Palladium Catalysts for Methane Combustion
Duan, Huimei; You, Rui; Xu, Shutao; Li, Zhaorui; Qian, Kun; Cao, Tian; Huang, Weixin; Bao, Xinhe
Angewandte Chemie, International Edition (2019), 58 (35), 12043-12048CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO2 catalysts with porous Al2O3 overlayers coated by at. layer deposition (ALD). 27Al magic angle spinning NMR anal. showed that Al2O3 overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al3+ sites capable of strongly interacting with adjacent surface PdOx phases on supported Pd particles. Consequently, Al2O3-decorated Pd/SiO2 catalysts exhibit active and stable PdOx and Pd-PdOx structures to efficiently catalyze methane combustion between 200 and 850°. These results reveal the unique structural characteristics of Al2O3 overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.
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Yang, X.; Li, Q.; Lu, E.; Wang, Z.; Gong, X.; Yu, Z.; Guo, Y.; Wang, L.; Guo, Y.; Zhan, W.; Zhang, J.; Dai, S. Taming the Stability of Pd Active Phases through a Compartmentalizing Strategy toward Nanostructured Catalyst Supports. Nat. Commun. 2019, 10, 1611, DOI: 10.1038/s41467-019-09662-4
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Taming the stability of Pd active phases through a compartmentalizing strategy toward nanostructured catalyst supports
Yang Xinwei; Li Qing; Wang Zhiqiang; Gong Xueqing; Guo Yun; Wang Li; Guo Yanglong; Zhan Wangcheng; Lu Erjun; Yu Zhiyang; Zhang Jinshui; Dai Sheng; Dai Sheng
Nature communications (2019), 10 (1), 1611 ISSN:.
The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions is ubiquitous in many industrial catalytic processes and still a big challenge in implementing nanostructured metal catalyst systems. Herein, we demonstrate a strategy for designing robust nanocatalysts through a sintering-resistant support via compartmentalization. Ultrafine palladium active phases can be highly dispersed and thermally stabilized by nanosheet-assembled γ-Al2O3 (NA-Al2O3) architectures. The NA-Al2O3 architectures with unique flowerlike morphologies not only efficiently suppress the lamellar aggregation and irreversible phase transformation of γ-Al2O3 nanosheets at elevated temperatures to avoid the sintering and encapsulation of metal phases, but also exhibit significant structural advantages for heterogeneous reactions, such as fast mass transport and easy access to active sites. This is a facile stabilization strategy that can be further extended to improve the thermal stability of other Al2O3-supported nanocatalysts for industrial catalytic applications, in particular for those involving high-temperature reactions.
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Murata, K.; Shiotani, T.; Ohyama, J.; Wakabayashi, R.; Maruoka, H.; Kimura, T.; Satsuma, A. Relationship between Penta-Coordinated Al³⁺ Sites in the Al₂O₃ Supports and CH₄ Combustion Activity of Pd/Al₂O₃ Catalysts. Catal. Sci. Technol. 2021, 11, 2374– 2378, DOI: 10.1039/D1CY00098E
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Relationship between penta-coordinated Al3+ sites in the Al2O3 supports and CH4 combustion activity of Pd/Al2O3 catalysts
Murata, Kazumasa; Shiotani, Takumi; Ohyama, Junya; Wakabayashi, Ryutaro; Maruoka, Hirokazu; Kimura, Tatsuo; Satsuma, Atsushi
Catalysis Science & Technology (2021), 11 (7), 2374-2378CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
Pd/Al2O3 catalysts were prepd. using various Al2O3 supports with different structural features such as cryst. phase and crystallinity related to Al3+ coordination, revealing a significant insight into the methane (CH4) combustion activity of Pd nanoparticles with the fraction of penta-coordinated Al3+ sites in the Al2O3 supports.
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Hu, C. H.; Chizallet, C.; Mager-Maury, C.; Corral-Valero, M.; Sautet, P.; Toulhoat, H.; Raybaud, P. Modulation of Catalyst Particle Structure upon Support Hydroxylation: Ab Initio Insights into Pd₁₃ and Pt₁₃/γ-Al₂O₃. J. Catal. 2010, 274, 99– 110, DOI: 10.1016/j.jcat.2010.06.009
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Modulation of catalyst particle structure upon support hydroxylation: Ab initio insights into Pd13 and Pt13/γ-Al2O3
Hu, Chao Hao; Chizallet, Celine; Mager-Maury, Christophe; Corral-Valero, Manuel; Sautet, Philippe; Toulhoat, Herve; Raybaud, Pascal
Journal of Catalysis (2010), 274 (1), 99-110CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
An at. picture of highly dispersed palladium and platinum catalysts supported on gamma-alumina is provided. Understanding the structure-reactivity relationship in the field of catalysis by metals requires the rationalization of the role of the metal-support interaction on the morphol. and electronic properties of nanometer size metallic particles. Thus, the interaction energies and the structures of Pd13 and Pt13 clusters deposited on two relevant gamma-alumina surfaces are systematically investigated by d. functional theory calcns. The hydroxylation of the support weakens the metal adhesion and influences the cluster morphologies. Flat lying bi-planar clusters with strong interaction energies are stabilized on the dehydrated (1 0 0) surface, whereas clusters with a three-dimensional morphol. are favored by the hydroxyl groups of the (1 1 0) surface. A consistent comparison of Pt and Pd is achieved. The shortest metal-oxygen (M-O) bond distances calcd. by DFT agree well with EXAFS M-O distances. Moreover, the presence of metal-aluminum bond distances close to 2.61-2.64 Å may explain exptl. features. The present work also provides structural and electronic clues for the understanding of the reactivity of highly dispersed Pd and Pt catalysts.
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Valero, M. C.; Raybaud, P.; Sautet, P. Nucleation of Pd_n (N = 1–5) Clusters and Wetting of Pd Particles on γ-Al₂O₃ Surfaces: A Density Functional Theory Study. Phys. Rev. B 2007, 75, 1– 12, DOI: 10.1103/PhysRevB.75.045427
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Shi, X. R.; Sholl, D. S. Nucleation of Rh_n (n = 1–5) Clusters on γ-Al₂O₃ Surfaces: A Density Functional Theory Study. J. Phys. Chem. C 2012, 116, 10623– 10631, DOI: 10.1021/jp301114n
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Nucleation of Rhn (n = 1-5) Clusters on γ-Al2O3 Surfaces: A Density Functional Theory Study
Shi, Xue-Rong; Sholl, David S.
Journal of Physical Chemistry C (2012), 116 (19), 10623-10631CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
The interaction of Rhn (n = 1-5) clusters with nonhydrated γ-Al2O3(100), hydrated γ-Al2O3(100), and hydrated γ-Al2O3(110) surfaces was studied using d. functional theory methods. On these surfaces, Rh3 prefers a triangular geometry, while Rh4 and Rh5 adopt 3-dimensional structures. On the (100) surfaces, Rhn binds considerably more strongly on the nonhydrated surface than on the hydrated surface. On the hydrated (110) surface, Rhn binds to surface hydroxyl groups, which is consistent with exptl. observations. Characterizing the structure of Rhn clusters makes it possible to identify the crit. cluster size for nucleation on each surface.
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Mager-Maury, C.; Chizallet, C.; Sautet, P.; Raybaud, P. Platinum Nanoclusters Stabilized on γ-Alumina by Chlorine Used As a Capping Surface Ligand: A Density Functional Theory Study. ACS Catal. 2012, 2, 1346– 1357, DOI: 10.1021/cs300178y
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Platinum Nanoclusters Stabilized on γ-Alumina by Chlorine Used As a Capping Surface Ligand: A Density Functional Theory Study
Mager-Maury, C.; Chizallet, C.; Sautet, P.; Raybaud, P.
ACS Catalysis (2012), 2 (7), 1346-1357CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Controlling the size of metallic nanoclusters supported on an oxide support such as γ-alumina represents a challenging but important task in the case of noble metals such as platinum. By using d. functional theory (DFT), we investigate the thermodn., structural and electronic properties of small nanometer-sized Ptn clusters (n ≤ 13) interacting with four relevant γ-alumina surfaces exhibiting various hydroxylation and chlorination states. The presence of chlorine on the (110) surface of γ-alumina implies a thermodn. stabilization of small platinum clusters. This stabilization originates from the simultaneous migrations of chlorine atoms and protons from the support toward the Pt clusters. The migration of H and Cl from the support induces a stronger interaction of the Ptn cluster with the available AlIII site, assocd. with strong H-Ptn-Cl interaction. In particular, this trend leads to a local energy min., as a function of cluster size, for the Pt3 cluster. This at.-scale stabilization of subnanometer clusters is thus proposed to be at the origin of the formation of highly dispersed platinum particles and to prevent their sintering into supranano ones. A detailed energetic and electronic anal. is provided to rationalize this effect of chlorine. A rational interpretation of exptl. data is finally given.
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Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15– 50, DOI: 10.1016/0927-0256(96)00008-0
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Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
Kresse, G.; Furthmuller, J.
Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)
The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
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Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169– 11186, DOI: 10.1103/PhysRevB.54.11169
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Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
Kresse, G.; Furthmueller, J.
Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
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Kresse, G.; Hafner, J. Ab. Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, 558– 561, DOI: 10.1103/PhysRevB.47.558
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Ab initio molecular dynamics of liquid metals
Kresse, G.; Hafner, J.
Physical Review B: Condensed Matter and Materials Physics (1993), 47 (1), 558-61CODEN: PRBMDO; ISSN:0163-1829.
The authors present ab initio quantum-mech. mol.-dynamics calcns. based on the calcn. of the electronic ground state and of the Hellmann-Feynman forces in the local-d. approxn. at each mol.-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using sub-space alignment. This approach avoids the instabilities inherent in quantum-mech. mol.-dynamics calcns. for metals based on the use of a factitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows one to perform simulations over several picoseconds.
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Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.17953
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Projector augmented-wave method
Blochl
Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
There is no expanded citation for this reference.
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Hammer, B.; Hansen, L. B.; Nørskov, J. K. Improved Adsorption Energetics within Density-Functional Theory Using Revised Perdew-Burke-Ernzerhof Functionals. Phys. Rev. B - Condens. Matter Mater. Phys. 1999, 59, 7413– 7421, DOI: 10.1103/PhysRevB.59.7413
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Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals
Hammer, B.; Hansen, L. B.; Norskov, J. K.
Physical Review B: Condensed Matter and Materials Physics (1999), 59 (11), 7413-7421CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
A simple formulation of a generalized gradient approxn. for the exchange and correlation energy of electrons has been proposed by J. Perdew et al. (1996). Subsequently, Y. Zhang and W. Wang (1998) have shown that a slight revision of the Perdew-Burke-Ernzerhof (PBE) functional systematically improves the atomization energies for a large database of small mols. In the present work, we show that the Zhang and Yang functional (revPBE) also improves the chemisorption energetics of atoms and mols. on transition-metal surfaces. Our test systems comprise at. and mol. adsorption of oxygen, CO, and NO on Ni(100), Ni(111), Rh(100), Pd(100), and Pd(111) surfaces. As the revPBE functional may locally violate the Lieb-Oxford criterion, we further develop an alternative revision of the PBE functional, RPBE, which gives the same improvement of the chemisorption energies as the revPBE functional at the same time as it fulfills the Lieb-Oxford criterion locally.
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Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132, 154104, DOI: 10.1063/1.3382344
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A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu
Grimme, Stefan; Antony, Jens; Ehrlich, Stephan; Krieg, Helge
Journal of Chemical Physics (2010), 132 (15), 154104/1-154104/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
The method of dispersion correction as an add-on to std. Kohn-Sham d. functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coeffs. and cutoff radii that are both computed from first principles. The coeffs. for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos. (CN). They are used to interpolate between dispersion coeffs. of atoms in different chem. environments. The method only requires adjustment of two global parameters for each d. functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of at. forces. Three-body nonadditivity terms are considered. The method has been assessed on std. benchmark sets for inter- and intramol. noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean abs. deviations for the S22 benchmark set of noncovalent interactions for 11 std. d. functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs. also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. (c) 2010 American Institute of Physics.
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Eng, P. J.; Trainor, T. P.; Brown, G. E., Jr.; Waychunas, G. A.; Newville, M.; Sutton, S. R.; Rivers, M. L. Structure of the Hydrated α-Al₂O₃(0001) Surface. Science 2000, 288, 1029– 1033, DOI: 10.1126/science.288.5468.1029
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Structure of the hydrated α-Al2O3 (0001) surface
Eng, Peter J.; Trainor, Thomas P.; Brown, Gordon E., Jr.; Waychunas, Glenn A.; Newville, Matthew; Sutton, Stephen R.; Rivers, Mark L.
Science (Washington, D. C.) (2000), 288 (5468), 1029-1033CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
The phys. and chem. properties of the hydrated α-Al2O3 (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-contg. oxides. The structure of this surface was detd. in the presence of water vapor at 300 K by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between α-Al2O3 and γ-Al(OH)3, a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean α-Al2O3 (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces.
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Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H. Use of DFT to Achieve a Rational Understanding of Acid-Basic Properties of γ-Alumina Surfaces. J. Catal. 2004, 226, 54– 68, DOI: 10.1016/j.jcat.2004.04.020
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Use of DFT to achieve a rational understanding of acid-basic properties of γ-alumina surfaces
Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H.
Journal of Catalysis (2004), 226 (1), 54-68CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
In a recent priority communication [M. Digne et al., J. Catal. 211 (2002) 1], we proposed the first ab initio constructed models of γ-alumina surfaces. Using the same d.-functional approach, we investigate in further detail the acid-basic properties of the three relevant γ-alumina (100), (110), and (111) surfaces, taking into account the temp.-dependent hydroxyl surface coverages. The simulations, compared fruitfully with many available exptl. data, enable us to solve the challenging assignment of the OH-stretching frequencies, as obtained from IR spectroscopy. The precise nature of the acid surface sites (concns. and strengths) is also detd. The acid strengths are quantified by simulating the adsorption of relevant probe mols. such as CO and pyridine in correlation with surface electronic properties. These results seriously challenge the historical model of a defective spinel for γ-alumina and establish the basis for a more rigorous description of the acid-basic properties of γ-alumina.
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Sawabe, K.; Satsuma, A. Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al₂O₃-Supported Silver Nanoparticles: Size, Shape, and Support Effects. ACS Omega 2022, 7, 4405– 4412, DOI: 10.1021/acsomega.1c06208
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Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al2O3-Supported Silver Nanoparticles: Size, Shape, and Support Effects
Sawabe, Kyoichi; Satsuma, Atsushi
ACS Omega (2022), 7 (5), 4405-4412CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
Nanoparticles (NPs) supported on metal oxides exhibit high catalytic activities for various reactions. The shape and oxidn. state of such NPs, which are related to the catalytic activity, are often detd. by the support. Herein, we conducted a d. functional theory study on isolated silver (Ag) NPs and two types of Ag-NPs supported on gamma-aluminum oxide (γ-Al2O3). First, carbon monoxide (CO) adsorption on the isolated Ag NPs was investigated for decahedra (D5h), icosahedra (Ih), and cuboctahedra (Oh) of various sizes. Ih and Oh NPs showed moderate size dependence, whereas D5h NPs showed high size dependence when the height was below 1.4 nm. The enhancement of CO adsorption on D5h NPs was attributed to the presence of superat. states. Next, we performed geometrical optimization of Ag54/γ-Al2O3(110) with a decahedral shape. Two types of structures were obtained: amorphous Ag54(A) and locally fivefold sym. Ag54(B) structures. Both NPs on γ-Al2O3(110) were found to be pos. charged, but electron transfer to the support occurred only from the Ag atoms at the two bottom layers, and the upper part of NPs was relatively neutral. The enhancement of CO adsorption on Ag54(B) disappeared due to loss of the high symmetry. In turn, the moderate size dependence of neutral isolated NPs can be applied.
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Frenkel, D.; Smit, B. Understanding Molecular Simulation: From Algorithms to Applications; Academic press: 2002, p 141
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Stukowski, A. Visualization and Analysis of Atomistic Simulation Data with OVITO-the Open Visualization Tool. Model. Simul. Mater. Sci. Eng. 2010, 18, 015012, DOI: 10.1088/0965-0393/18/1/015012
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Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H. Hydroxyl Groups on γ-Alumina Surfaces: A DFT Study. J. Catal. 2002, 211, 1– 5, DOI: 10.1006/jcat.2002.3741
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Hydroxyl Groups on γ-Alumina Surfaces: A DFT Study
Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H.
Journal of Catalysis (2002), 211 (1), 1-5CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
Despite numerous exptl. studies devoted to the acid-base properties of γ-alumina, the precise nature of surface acid sites remains unsolved. Using d. functional (DFT) calcns., we propose realistic models of γ-alumina (110) and (100) surfaces accounting for hydroxylation/dehydroxylation processes induced by temp. effects. The vibrational anal., based on DFT calcns., leads to an accurate assignment of the OH stretching frequencies obsd. by IR spectroscopy. The extension to chlorinated surfaces, which brings new insights into the understanding of the role of dopes, is also addressed.
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Nortier, P.; Fourre, P.; Saad, A.B. M.; Saur, O.; Lavalley, J.C. Effects of Crystallinity and Morphology on the Surface Properties of Alumina. Appl. Catal. 1990, 61, 141– 160, DOI: 10.1016/S0166-9834(00)82140-5
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Effects of crystallinity and morphology on the surface properties of alumina
Nortier, P.; Fourre, P.; Saad, A. B. Mohammed; Saur, O.; Lavalley, J. C.
Applied Catalysis (1990), 61 (1), 141-60CODEN: APCADI; ISSN:0166-9834.
Five samples of Al2O3, (1 amorphous and 4 γ-Al2O3's prepd. from different boehmites) were compared by using phys. methods (x-ray diffraction, transmission electron microscopy, 27Al NMR and Fourier transform IR spectrometry) and the butene isomerization test. All the γ-Al2O3 samples preferentially present the (110) face, whereas the ratio of the (001) and (111) faces depends on the precursor. Isomerization tests and IR expts. with different probe mols. show very similar acidities for the crystd. samples, which is discussed taking various models into account. The lower Lewis acidity of the amorphous sample is related to the smaller no. of AlIV sites shown by NMR expts. The crystallinity effect is also indicated by an IR study of the OH groups, with the amorphous sample showing a specific band at 3787 cm-1.
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Wang, L. L.; Johnson, D. D. Density Functional Study of Structural Trends for Late-Transition-Metal 13-Atom Clusters. Phys. Rev. B 2007, 75, 1– 10, DOI: 10.1103/PhysRevB.75.235405
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Atkins, P.; de Paula, J. Atkins’ Physical Chemistry, 8th ed.; Oxford University Press: 2006; pp 441– 442.
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Zhang, W.; Xiao, L.; Hirata, Y.; Pawluk, T.; Wang, L. The Simple Cubic Structure of Ir Clusters and the Element Effect on Cluster Structures. Chem. Phys. Lett. 2004, 383, 67– 71, DOI: 10.1016/j.cplett.2003.11.005
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The simple cubic structure of Ir clusters and the element effect on cluster structures
Zhang, Wenqin; Xiao, Li; Hirata, Yasuhiro; Pawluk, Tiffany; Wang, Lichang
Chemical Physics Letters (2004), 383 (1,2), 67-71CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
The simple cubic was found to be the most stable structure for Ir clusters in the subnanometer range from our d. functional theory calcns. We further examd. various structures of group 8-10 precious metal clusters. The tendency to form the simple cubic structure becomes stronger from right to left across a period and from top to bottom in the group, while the trend is opposite for the formation of icosahedrons or cubo-octahedrons.
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Hendriksen, B. A.; Pearce, D. R.; Rudham, R. Heats of Adsorption of Water on α- and γ-Alumina. J. Catal. 1972, 24, 82– 87, DOI: 10.1016/0021-9517(72)90010-3
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Heats of adsorption of water on α- and γ-alumina
Hendriksen, B. A.; Pearce, D. R.; Rudham, R.
Journal of Catalysis (1972), 24 (1), 82-7CODEN: JCTLA5; ISSN:0021-9517.
Heats of immersion of α- and γ-alumina in water were detd. for samples outgassed at temps. up to 600°. The results are combined with values of the residual surface-water content, detd. by D exchange, to give heats of adsorption of water as a function of uptake. The results are discussed and compared with similar data obtained or calcd. from the published literature.
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Thissen, P.; Grundmeier, G.; Wippermann, S.; Schmidt, W. G. Water Adsorption on the α-Al₂O₃ (0001) Surface. Phys. Rev. B - Condens. Matter Mater. Phys. 2009, 80, 1– 6, DOI: 10.1103/PhysRevB.80.245403
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Pigeon, T.; Chizallet, C.; Raybaud, P. Revisiting γ-Alumina Surface Models through the Topotactic Transformation of Boehmite Surfaces. J. Catal. 2022, 405, 140– 151, DOI: 10.1016/j.jcat.2021.11.011
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Revisiting γ-alumina surface models through the topotactic transformation of boehmite surfaces
Pigeon, Thomas; Chizallet, Celine; Raybaud, Pascal
Journal of Catalysis (2022), 405 (), 140-151CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
The rational understanding of γ-alumina (γ-Al2O3) supported catalysts requires an ever more improved at. scale detn. of the support's surface properties. By using d. functional theory (DFT) calcns., we show how the structural and energetic surface properties of alumina crystallites intrinsically depend on its synthesis pathway. Considering the case study of the topotactic transformation of boehmite (γ-AlOOH) into γ-Al2O3 taking place during calcination, we propose a methodol. to mimic this pathway by reconstructing relevant slabs of boehmite into γ-alumina slabs following 3 steps: dehydration, contraction/translation and Al migration into spinel or non-spinel sites. On the one hand, we confirm the reliability of some earlier 100, 110 and 111 surface structures detd. by std. bulk cleavage approach. Moreover, we find new γ-alumina surfaces harboring Bronsted acid sites (BAS) and Lewis acid sites (LAS) with specific local structures. More strikingly, we find that the basal (110)b surface of alumina inherited from the (0 1 0) basal surface of boehmite, exhibits a larger no. of isolated μ2-OH groups than the lateral( 110)l surface. For the lateral (110)l (resp. 111) orientation, four (resp. three) thermodynamically competing surfaces are identified, including models earlier proposed. These results are induced by finite size and morphol. effects during the topotactic transformation of boehmite crystallites. Thanks to a thorough comparative anal. of morphol. and nature of BAS and LAS as a function of thermal treatment and water pressure for each surface, we identify coherent chem. families of surfaces across the main crystallog. orientations. These features open the door to a better differentiation of the reactivity of the basal alumina surfaces from the lateral ones.
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Ranea, V. A.; Schneider, W. F.; Carmichael, I. DFT Characterization of Coverage Dependent Molecular Water Adsorption Modes on α-Al₂O₃(0001). Surf. Sci. 2008, 602, 268– 275, DOI: 10.1016/j.susc.2007.10.029
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52
DFT characterization of coverage dependent molecular water adsorption modes on α-Al2O3(0 0 0 1)
Ranea, Victor A.; Schneider, William F.; Carmichael, Ian
Surface Science (2008), 602 (1), 268-275CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
Ab initio d. functional theory was used to investigate the stable and metastable states of adsorbed mol. water on the α-Al2O3(0 0 0 1) surface as a function of coverage. The atoms of the dry surface undergo pronounced inward relaxations with respect to their bulk positions. At low coverages (Θ ≤ 0.5) water adsorbs nearly parallel to the surface plane, with an O atom atop a surface Al. The adsorption is mainly due to the donation from water lone pairs into vacant p orbital of surface Al, drawing the surface Al outward. With increasing coverage, water adsorption atop Al competes with an alternative configuration with water bound through H to surface oxygen. These two competing modes generate a variety of distinct but nearly isoenergetic adsorption modes that terminate in a hexagonal, ice-like layer at a coverage of two water mols. per surface Al. The binding energy per water mol. is maximized in the two limits of coverage, but deviates from this extreme only slightly at intermediate coverages. At no coverage is the water binding great enough to overcome the energetic preference for water to dissociatively adsorb.
53
Erfani, G. S.; Hong, S.; Rahman, T. S. Effects of γ-Al₂O₃ Support on the Morphology and Electronic Structure of Pt Nanoparticles. J. Phys. Chem. C 2019, 123, 16893– 16901, DOI: 10.1021/acs.jpcc.9b04770
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53
Effects of γ-Al2O3 Support on the Morphology and Electronic Structure of Pt Nanoparticles
Erfani, Ghazal S.; Hong, Sampyo; Rahman, Talat S.
Journal of Physical Chemistry C (2019), 123 (27), 16893-16901CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
We have studied the effects of γ-Al2O3(110) support on the morphol. and electronic structure of clean and H-covered Pt nanoparticles (NPs) contg. 22 and 44 atoms (Pt22 and Pt44) using d. functional theory (DFT)-based calcns. We find that the morphol. of Pt22 changes from three-dimensional (3D), when free-standing, to a biplanar shape on pristine γ-Al2O3(110) and back to 3D, if hydroxyl coverage on γ-Al2O3(110) is greater than 0.325 ML. Morphol. change of Pt NPs is governed by cohesive Pt-Pt interaction at high hydroxyl coverage and by adhesive Pt-support interaction at low hydroxyl coverage. However, such morphol. change does not occur for Pt44, indicating that such transition only happens for smaller Pt NPs. Not surprisingly, the electronic structure of the Pt NPs is sensitive to both the presence of the support and to the extent to which it is hydroxylated. A competing effect also comes from adsorbed hydrogen atoms on the surface of Pt NPs. However, with increasing temp. the effect of adsorbed hydrogen weakens but that of the support becomes stronger, resulting in a correlation between the shift of the unoccupied d-band and the extent of the metal-support interaction. These results provide insight into the dependence of the catalytic properties of Pt NPs on several competing extrinsic factors-the hydroxylation level of the γ-Al2O3 support, H adsorbate coverage on Pt NPs, and ambient temp.

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Abstract
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Figure 1
Figure 1. Top and side views of (a, b) α-Al₂O₃(0001), (c, d) γ-Al₂O₃(100), and (e, f) γ-Al₂O₃(110) surface. Only the topmost layers of the periodic slab are represented using color balls. A dashed line indicates the unit cell; the O and Al atoms are shown as red and brown balls.
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Figure 2
Figure 2. Top and side views of (a, b) Pd₁₃/α-Al₂O₃(0001), (c, d) Pd₁₃/γ-Al₂O₃(100), and (e, f) Pd₁₃/γ-Al₂O₃(110). O, Al, and Pd atoms are shown as red, brown, and navy-blue balls.
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Figure 3
Figure 3. Binding and interaction energies for isolated Pd_n clusters and Pd_n clusters (n = 1–4, 6, 9, and 13) supported on various Al₂O₃ surfaces as a function of the number of Pd atoms per Pd cluster.
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Figure 4
Figure 4. Interaction energies for Pd_n clusters (n = 1–4, 6, 9, and 13) supported on various Al₂O₃ surfaces as a function of the coordination number of (a) Pd–O and (b) Pd–Al.
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Figure 5
Figure 5. Variation of the d_all and d_adj of (a) Pd₁₃/α-Al₂O₃(0001), (b) Pd₁₃/γ-Al₂O₃(100), and (c) Pd₁₃/γ-Al₂O₃(110) for the MD cycle.
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Figure 6
Figure 6. Variation of the average position of Pd₁₃ clusters in (a) Pd₁₃/α-Al₂O₃(0001), (b) Pd₁₃/γ-Al₂O₃(100), and (c) Pd₁₃/γ-Al₂O₃(110) in the x-, y-, and z-axis direction for MD cycle (center). Top and side views of Pd₁₃/Al₂O₃ at 3 and 8 ps (left and right). O, Al, and Pd atoms are shown as red, brown, and navy-blue balls.
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References
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  Wischert, R.; Laurent, P.; Copéret, C.; Delbecq, F.; Sautet, P. γ-Alumina: The Essential and Unexpected Role of Water for the Structure, Stability, and Reactivity of “Defect” Sites. J. Am. Chem. Soc. 2012, 134, 14430– 14449, DOI: 10.1021/ja3042383
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  γ-Alumina: The Essential and Unexpected Role of Water for the Structure, Stability, and Reactivity of Defect Sites
  Wischert, Raphael; Laurent, Pierre; Coperet, Christophe; Delbecq, Francoise; Sautet, Philippe
  Journal of the American Chemical Society (2012), 134 (35), 14430-14449CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Combining expts. and DFT calcns., we show that tricoordinate AlIII Lewis acid sites, which are present as metastable species exclusively on the major (110) termination of γ- and δ-Al2O3 particles, correspond to the defect sites, which are held responsible for the unique properties of activated (thermally pretreated) alumina. These defects are, in fact, largely responsible for the adsorption of N2 and the splitting of CH4 and H2. In contrast, five-coordinate Al surface sites of the minor (100) termination cannot account for the obsd. reactivity. The AlIII sites, which are formed upon partial dehydroxylation of the surface (the optimal pretreatment temp. being 700 °C for all probes), can coordinate N2 selectively. In combination with specific O atoms, they form extremely reactive Al,O Lewis acid-base pairs that trigger the low-temp. heterolytic splitting of CH4 and H2 to yield Al-CH3 and Al-H species, resp. H2 is found overall more reactive than CH4 because of its higher acidity, hence it also reacts on four-coordinate sites of the (110) termination. Water has the dual role of stabilizing the (110) termination and modifying (often increasing) both the Lewis acidity of the aluminum and the basicity of nearby oxygens, hence the high reactivity of partially dehydroxylated alumina surfaces. In addn., we demonstrate that the presence of water enhances the acidity of certain four-coordinate Al atoms, which leads to strong coordination of the CO mol. with a spectroscopic signature similar to that on AlIII sites, thus showing the limits of this widely used probe for the acidity of oxides. Overall, the dual role of water translates into optimal water coverage, and this probably explains why in many catalyst prepns., optimal pretreatment temps. are typically obsd. in the activation step of alumina.
5. 5
  Wischert, R.; Copéret, C.; Delbecq, F.; Sautet, P. Optimal Water Coverage on Alumina: A Key to Generate Lewis Acid-Base Pairs That Are Reactive towards the C-H Bond Activation of Methane. Angew. Chemie - Int. Ed. 2011, 50, 3202– 3205, DOI: 10.1002/anie.201006794
  5
  Optimal Water Coverage on Alumina: A Key to Generate Lewis Acid-Base Pairs that are Reactive Towards the C-H Bond Activation of Methane
  Wischert, Raphael; Coperet, Christophe; Delbecq, Francoise; Sautet, Philippe
  Angewandte Chemie, International Edition (2011), 50 (14), 3202-3205, S3202/1-S3202/9CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Combined exptl. and DFT studies reveal that the reactivity of γ-alumina and probably of many other oxides towards CH4 and other mols. with polarizable bonds results from a combined action of (metal,O) Lewis acid-base pairs.
6. 6
  Zhao, Z.; Xiao, D.; Chen, K.; Wang, R.; Liang, L.; Liu, Z.; Hung, I.; Gan, Z.; Hou, G. Nature of Five-Coordinated Al in Γ-Al₂O₃ Revealed by Ultra-High-Field Solid-State NMR. ACS Cent. Sci. 2022, 8, 795– 803, DOI: 10.1021/acscentsci.1c01497
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  Nature of Five-Coordinated Al in γ-Al2O3 Revealed by Ultra-High-Field Solid-State NMR
  Zhao, Zhenchao; Xiao, Dong; Chen, Kuizhi; Wang, Rui; Liang, Lixin; Liu, Zhengmao; Hung, Ivan; Gan, Zhehong; Hou, Guangjin
  ACS Central Science (2022), 8 (6), 795-803CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
  Five-coordinated Als (Al(V)) on the surface of aluminas play important roles when they are used as catalysts or catalyst supports. However, the comprehensive characterization and understanding of the intrinsic structural properties of the Al(V) remain a challenge, due to the very small amt. in commonly used aluminas. Herein, the surface structures of γ-Al2O3 and Al(V)-rich Al2O3 nanosheets (Al2O3-NS) have been investigated and compared in detail by multinuclear high-field solid-state NMR. Thanks to the high resoln. and sensitivity of ultra-high-field (up to 35.2 T) NMR, the arrangements of surface Als were clearly demonstrated, which are substantially different from the bulk phase in γ-Al2O3 due to the structure reconstruction. It reveals for the first time that most of the commonly obsd. Al(V)s tend to exist as aggregated states on the surface of γ-Al2O3, like those in amorphous Al2O3-NS liable to structure reconstruction. Our new insights into surface Al(V) species may help in understanding the structure-function relationship of alumina.
7. 7
  Ayoola, H. O.; Bonifacio, C. S.; Zhu, Q.; Li, C. H.; House, S. D.; Kas, J. J.; Jinschek, J.; Rehr, J. J.; Saidi, W. A.; Yang, J. C. Probing the Local Bonding at the Pt/γ-Al₂O₃ Interface. J. Phys. Chem. C 2020, 124, 9876– 9885, DOI: 10.1021/acs.jpcc.9b12029
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  Probing the Local Bonding at the Pt/γ-Al2O3 Interface
  Ayoola, Henry O.; Bonifacio, Cecile S.; Zhu, Qing; Li, Cheng-Han; House, Stephen D.; Kas, Joshua J.; Jinschek, Joerg; Rehr, John J.; Saidi, Wissam A.; Yang, Judith C.
  Journal of Physical Chemistry C (2020), 124 (18), 9876-9885CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Metal-support interactions significantly affect the performance of heterogeneous catalysts, of which Pt supported on γ-Al2O3 is one of the most widely used. Characterizing the bonding of Pt on the γ-Al2O3 surface is key to fully understanding the catalyst-support interaction. Herein aberration-cor. and monochromated scanning transmission electron microscopy-based electron energy-loss spectroscopy (STEM-EELS) were employed on a model Pt/γ-Al2O3(111) catalyst to locally investigate the bonding between Pt and the γ-Al2O3 support. Differences in the aluminum L2,3-edge and oxygen K-edge EELS near-edge fine structure between spectra acquired at the Pt/γ-Al2O3(111) interface and the bulk γ-Al2O3 served as signatures of the interfacial bonding environment. Fine structure in the interface-localized Al-L2,3 edge suggested a larger fraction of tetrahedrally coordinated Al atoms at the Pt/γ-Al2O3(111) interface, which was confirmed by DFT simulations. The interface-localized O-K edge EELS revealed a prepeak assocd. with several types of oxygen bonding. To det. the specific interfacial O bonding, O-K edge EELS spectra were simulated from an array of Pt/γ-Al2O3(111) bonding configuration models. The simulated EELS from the interfacial bonding models revealed an O bonding motif consistent with the exptl. O-K edge EELS fine structure.
8. 8
  Dessal, C.; Sangnier, A.; Chizallet, C.; Dujardin, C.; Morfin, F.; Rousset, J. L.; Aouine, M.; Bugnet, M.; Afanasiev, P.; Piccolo, L. Atmosphere-Dependent Stability and Mobility of Catalytic Pt Single Atoms and Clusters on γ-Al₂O₃. Nanoscale 2019, 11, 6897– 6904, DOI: 10.1039/C9NR01641D
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  Atmosphere-dependent stability and mobility of catalytic Pt single atoms and clusters on γ-Al2O3
  Dessal, Caroline; Sangnier, Alexis; Chizallet, Celine; Dujardin, Christophe; Morfin, Franck; Rousset, Jean-Luc; Aouine, Mimoun; Bugnet, Matthieu; Afanasiev, Pavel; Piccolo, Laurent
  Nanoscale (2019), 11 (14), 6897-6904CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
  Atomically dispersed metals promise the ultimate catalytic efficiency, but their stabilization onto suitable supports remains challenging owing to their aggregation tendency. Focusing on the industrially-relevant Pt/γ-Al2O3 catalyst, in situ X-ray absorption spectroscopy and environmental scanning transmission electron microscopy allow us to monitor the stabilization of Pt single atoms under O2 atmosphere, as well as their aggregation into mobile reduced subnanometric clusters under H2. D. functional theory calcns. reveal that oxygen from the gas phase directly contributes to metal-support adhesion, maximal for single Pt atoms, whereas hydrogen only adsorbs on Pt, and thereby leads to Pt clustering. Finally, Pt cluster mobility is shown to be activated at low temp. and high H2 pressure. Our results highlight the crucial importance of the reactive atm. on the stability of single-atom vs. cluster catalysts.
9. 9
  Wan, C.; Hu, M. Y.; Jaegers, N. R.; Shi, D.; Wang, H.; Gao, F.; Qin, Z.; Wang, Y.; Hu, J. Z. Investigating the Surface Structure of γ-Al₂O₃ Supported WO_X Catalysts by High Field ²⁷Al MAS NMR and Electronic Structure Calculations. J. Phys. Chem. C 2016, 120, 23093– 23103, DOI: 10.1021/acs.jpcc.6b09060
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  Investigating the Surface Structure of γ-Al2O3 Supported WOX Catalysts by High Field 27Al MAS NMR and Electronic Structure Calculations
  Wan, Chuan; Hu, Mary Y.; Jaegers, Nicholas R.; Shi, Dachuan; Wang, Huamin; Gao, Feng; Qin, Zhaohai; Wang, Yong; Hu, Jian Zhi
  Journal of Physical Chemistry C (2016), 120 (40), 23093-23103CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  The metal-support interaction in γ-Al2O3 supported WOX catalysts is investigated by a combination of high field quant. single pulse (SP) 27Al MAS NMR spectroscopy, 2D MQMAS, 1H-27Al CP/MAS, and electronic structure calcns. NMR allows the observation of at least seven different Al sites, including a pentahedral Al site (AlP), three different tetrahedral Al sites (AlT), and three octahedral Al sites (AlO). It is found that the AlP site d. decreases monotonically with an increased WOX loading, the AlO site d. increases concurrently, and the d. of AlT sites remains const. This suggests that the AlP sites are the preferred surface anchoring positions for the WOX species. Importantly, the AlP site isotropic chem. shift obsd. for the unsupported γ-Al2O3 at about 38 ppm migrates to the octahedral region with a new isotropic chem. shift value appearing near 7 ppm when the AlP site is anchored by WOX species. D. functional theory (DFT) computational modeling of the NMR parameters on proposed WOX/γ-Al2O3 cluster models is carried out to accurately interpret the dramatic chem. shift changes from which the detailed anchoring mechanisms are obtained. It is found that tungsten dimers and monomers are the preferred supported surface species on γ-Al2O3, wherein one monomeric and several dimeric structures are identified as the most likely surface anchoring structures.
10. 10
  Kwak, J. H.; Hu, J. Z.; Kim, D. H.; Szanyi, J.; Peden, C. H. F. Penta-Coordinated Al³⁺ Ions as Preferential Nucleation Sites for BaO on Al₂O₃: An Ultra-High-Magnetic Field ²⁷Al MAS NMR Study. J. Catal. 2007, 251, 189– 194, DOI: 10.1016/j.jcat.2007.06.029
  10
  Penta-coordinated Al3+ ions as preferential nucleation sites for BaO on γ-Al2O3: an ultra-high-magnetic field 27Al MAS NMR study
  Kwak, Ja Hun; Hu, Jian Zhi; Kim, Do Heui; Szanyi, Janos; Peden, Charles H. F.
  Journal of Catalysis (2007), 251 (1), 189-194CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Ltd.)
  We report the first observation of preferential anchoring of an impregnated catalytic phase onto penta-coordinated Al3+ sites on the surface of γ-Al2O3. The interaction of barium oxide with a γ-alumina support was investigated by high resoln. solid state 27Al magic angle spinning NMR at an ultra-high magnetic field of 21.1 T and at sample spinning rates of up to 23 kHz. Under these exptl. conditions, a peak in the NMR spectrum at ∼23 ppm with relatively low intensity, assigned to 5-coordinated Al3+ ions, is clearly distinguished from the two other peaks representing Al3+ ions in tetra-, and octahedral coordination. Spin-lattice 27Al relaxation time measurements clearly show that these penta-coordinated Al3+ sites are located on the surface of the γ-alumina support. BaO deposition onto this γ-alumina sample resulted in the loss of intensity of the 23 ppm peak. The intensity loss obsd. was linearly proportional to the amt. of BaO deposited. The results of this study strongly suggest that, at least for BaO, these penta-coordinated Al3+ ions are the nucleation sites.
11. 11
  Kwak, J. H.; Hu, J.; Mei, D.; Yi, C.-W.; Kim, D. H.; Peden, C. H. F.; Allard, L. F.; Szanyi, J. Coordinatively Unsaturated Al³⁺ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al₂O₃. Science 2009, 325, 1670– 1673, DOI: 10.1126/science.1176745
  11
  Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al2O3
  Kwak, Ja Hun; Hu, Jianzhi; Mei, Donghai; Yi, Cheol-Woo; Kim, Do Heui; Peden, Charles H. F.; Allard, Lawrence F.; Szanyi, Janos
  Science (Washington, DC, United States) (2009), 325 (5948), 1670-1673CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a crit. role in detg. particle morphol. and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning NMR spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with d. functional theory calcns. to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a γ-Al2O3 catalyst support material. The results obtained show that coordinatively unsatd. pentacoordinate Al3+ (Al3+penta) centers present on the (100) facets of the γ-Al2O3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al3+penta = 1), whereas two-dimensional Pt rafts form at higher coverages.
12. 12
  Mei, D.; Kwak, J. H.; Hu, J.; Cho, S. J.; Szanyi, J.; Allard, L. F.; Peden, C. H. F. Unique Role of Anchoring Penta-Coordinated Al³⁺ Sites in the Sintering of γ-Al₂O₃-Supported Pt Catalysts. J. Phys. Chem. Lett. 2010, 1, 2688– 2691, DOI: 10.1021/jz101073p
  12
  Unique Role of Anchoring Penta-Coordinated Al3+ Sites in the Sintering of γ-Al2O3-Supported Pt Catalysts
  Mei, Donghai; Kwak, Ja Hun; Hu, Jianzhi; Cho, Sung June; Szanyi, Janos; Allard, Lawrence F.; Peden, Charles H. F.
  Journal of Physical Chemistry Letters (2010), 1 (18), 2688-2691CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  γ-Al2O3-supported Pt group catalysts are widely used in many industrially important catalytic processes. However, γ-Al2O3-supported Pt catalysts are prone to deactivation via metal sintering at high temps., in oxidative reaction environments, or both. Using a combination of exptl. HRTEM and EXAFS measurements and theor. DFT calcns., we find that pentacoordinated Al3+ sites (Alp) on the γ-Al2O3(100) surface can inhibit Pt sintering both thermodynamically and kinetically because of their strong interactions with at. Pt or Pt oxide species. The present work suggests a promising approach for stabilizing the size and morphol. of supported catalytically active phases.
13. 13
  Zhang, Z.; Zhu, Y.; Asakura, H.; Zhang, B.; Zhang, J.; Zhou, M.; Han, Y.; Tanaka, T.; Wang, A.; Zhang, T.; Yan, N. Thermally Stable Single Atom Pt/m-Al₂O₃ for Selective Hydrogenation and CO Oxidation. Nat. Commun. 2017, 8, 16100, DOI: 10.1038/ncomms16100
  13
  Thermally stable single atom Pt/m-Al2O3 for selective hydrogenation and CO oxidation
  Zhang, Zailei; Zhu, Yihan; Asakura, Hiroyuki; Zhang, Bin; Zhang, Jiaguang; Zhou, Maoxiang; Han, Yu; Tanaka, Tsunehiro; Wang, Aiqin; Zhang, Tao; Yan, Ning
  Nature Communications (2017), 8 (), 16100CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsatd. pentahedral Al3+ centers. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atm. at 200 aluminum oxideC for 24 h. Compared to com. Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550°C for 48 h, although agglomeration of Pt single-atoms into clusters is obsd. after reaction. In CO oxidn., the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 aluminum oxideC over a one-month period.
14. 14
  Hackett, S. F. J.; Brydson, R. M.; Gass, M. H.; Harvey, I.; Newman, A. D.; Wilson, K.; Lee, A. F. High-Activity, Single-Site Mesoporous Pd/Al₂O₃ Catalysts for Selective Aerobic Oxidation of Allylic Alcohols. Angew. Chemie - Int. Ed. 2007, 46, 8593– 8596, DOI: 10.1002/anie.200702534
  14
  High-activity, single-site mesoporous Pd/Al2O3 catalysts for selective aerobic oxidation of allylic alcohols
  Hackett, Simon F. J.; Brydson, Rik M.; Gass, Mhairi H.; Harvey, Ian; Newman, Andrew D.; Wilson, Karen; Lee, Adam F.
  Angewandte Chemie, International Edition (2007), 46 (45), 8593-8596CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Pd does it alone: Tailored heterogeneous catalysts offer exciting, alternative, clean technologies for regioselective mol. transformations. A mesoporous alumina support stabilizes atomically dispersed PdII surface sites, thereby dramatically enhancing catalytic performance in the aerobic selective oxidn. of alcs.
15. 15
  Tang, N.; Cong, Y.; Shang, Q.; Wu, C.; Xu, G.; Wang, X. Coordinatively Unsaturated Al³⁺ Sites Anchored Subnanometric Ruthenium Catalyst for Hydrogenation of Aromatics. ACS Catal. 2017, 7, 5987, DOI: 10.1021/acscatal.7b01816
  15
  Coordinatively Unsaturated Al3+ Sites Anchored Subnanometric Ruthenium Catalyst for Hydrogenation of Aromatics
  Tang, Nanfang; Cong, Yu; Shang, Qinghao; Wu, Chuntian; Xu, Guoliang; Wang, Xiaodong
  ACS Catalysis (2017), 7 (9), 5987-5991CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Single metal atoms and metal clusters have attracted much attention because of their high dispersity, special electronic structures, and uniformity of active sites as heterogeneous catalysts, but it is still challenging to generate stable single atoms and clusters with high metal loadings. Supports play a crucial role in detg. particle morphol. and maintaining dispersion. Herein we synthesize an amorphous alumina with 29% coordinatively unsatd. pentacoordinate Al3+ (Al3+penta) sites, which can anchor atomically dispersed Ru species with 1 wt. % loading. Strong interactions between Ru and Al3+penta centers were detected, resulting in distinct Ru geometric and electronic features. When used in benzene hydrogenation reaction, fairly high specific activity (TOF = 5180 h-1) were obtained. The high catalytic performance is considered closely correlated with the high utilization of special Ru active sites.
16. 16
  Li, L.; Wang, L. L.; Johnson, D. D.; Zhang, Z.; Sanchez, S. I.; Kang, J. H.; Nuzzo, R. G.; Wang, Q.; Frenkel, A. I.; Li, J. Noncrystalline-to-Crystalline Transformations in Pt Nanoparticles. J. Am. Chem. Soc. 2013, 135, 13062– 13072, DOI: 10.1021/ja405497p
  16
  Noncrystalline-to-Crystalline Transformations in Pt Nanoparticles
  Li, Long; Wang, Lin-Lin; Johnson, Duane D.; Zhang, Zhongfan; Sanchez, Sergio I.; Kang, Joo H.; Nuzzo, Ralph G.; Wang, Qi; Frenkel, Anatoly I.; Li, Jie; Ciston, James; Stach, Eric A.; Yang, Judith C.
  Journal of the American Chemical Society (2013), 135 (35), 13062-13072CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  We show that the noncryst.-to-cryst. transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncryst. phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resoln. transmission electron microscopy show a noncryst.-to-cryst. transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist. The NP size at which this transition occurs is strongly dependent on both the adsorbate and the support, and this effect is general for late 5d transition metals. All results are reconciled via a statistical description of particle-support-adsorbate interactions.
17. 17
  Murata, K.; Onoda, J.; Yamamoto, Y.; Oda, A.; Ohyama, J.; Satsuma, A. Enhancement of Toluene Hydrogenation Activity of Supported Pt Nanoparticles with Increasing the Crystallinity of Pt. Appl. Catal. A, Gen. 2022, 629, 118425, DOI: 10.1016/j.apcata.2021.118425
  17
  Enhancement of toluene hydrogenation activity of supported Pt nanoparticles with increasing the crystallinity of Pt
  Murata, Kazumasa; Onoda, Junya; Yamamoto, Yuta; Oda, Akira; Ohyama, Junya; Satsuma, Atsushi
  Applied Catalysis, A: General (2022), 629 (), 118425CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)
  The activity of Pt/Al2O3 in the hydrogenation of toluene (TOL) was found to monotonically increase in line with an increase in the Pt particle size from 1.0 to 2.5 nm, but was const. for a size above 2.5 nm. Comparing different cryst. phases of Al2O3, the activity of Pt/θ-Al2O3 was found to be around 1.5 times higher than that of Pt/γ-Al2O3 for the same Pt particle size. Scanning transmission electron microscopy showed the presence of amorphous Pt nanoparticles (NPs) with a size of < 2.0 nm and Pt nanocrystals (NCs) with a size of ≥ 2.0 nm on Al2O3. Furthermore, the fraction of amorphous Pt NPs in Pt/γ-Al2O3 was higher than that in Pt/θ-Al2O3. Pt NCs were shown to be more active than the amorphous Pt NPs in the hydrogenation of TOL owing to them having an abundance of Pt plane.
18. 18
  Batista, A. T. F.; Baaziz, W.; Taleb, A.; Chaniot, J.; Moreaud, M.; Aguilar-tapia, A.; Proux, O.; Hazemann, J.; Diehl, F.; Gay, A. Atomic Scale Insight into the Formation, Size, and Location of Platinum Nanoparticles Supported on γ-Alumina. ACS Catal. 2020, 10, 4193– 4204, DOI: 10.1021/acscatal.0c00042
  18
  Atomic Scale Insight into the Formation, Size, and Location of Platinum Nanoparticles Supported on γ-Alumina
  Batista, Ana T. F.; Baaziz, Walid; Taleb, Anne-Lise; Chaniot, Johan; Moreaud, Maxime; Legens, Christele; Aguilar-Tapia, Antonio; Proux, Olivier; Hazemann, Jean-Louis; Diehl, Fabrice; Chizallet, Celine; Gay, Anne-Sophie; Ersen, Ovidiu; Raybaud, Pascal
  ACS Catalysis (2020), 10 (7), 4193-4204CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  A clear description of the morphol. and location, with respect to the support, of metallic subnanometric particles remains a current strenuous exptl. challenge in numerous catalytic applications such as naphtha reforming and biomass conversion. High-resoln. HAADF-STEM coupled with in situ and tomog. analyses have been undertaken on a platinum (Pt) active phase supported on chlorinated alumina (γ-Al2O3) with 0.3 and 1 wt % Pt loadings, highlighting the formation of flat nanoparticles (NPs) of 0.9 nm diam. and Pt single atoms (SAs) in the reduced state. While SAs and weakly cohesive clusters are predominantly obsd. in the oxide state, with a coordination sphere of Pt composed of O and Cl as revealed by EXAFS, the ratio between SAs and Pt NPs in the reduced state is found to be about 2.8. This ratio is the same for the two metal loadings: both the total nos. of NPs and SAs increase at a higher metal loading. Electron tomog. reveals that the vast majority of NPs are located on the edges or defects (steps, kinks) of the γ-alumina support crystallites. DFT calcns. further highlight the optimized structures of NPs located at the γ-Al2O3 (110)-(100) edge and near-edge with a stability competing with NPs located either on the (110) or on the (100) γ-Al2O3 facet. A math. anal. of the segmented vols. shows that the av. geodesic distances between NPs is linked to Pt loading: 9 nm for 1 wt % Pt and 16 nm for 0.3 wt % Pt. Evaluation of support tortuosity descriptors using the nanoparticle positions confirms a uniform distribution on the support. A square network geometric model compatible with the geodesic distances between NPs reveals that one to five NPs can be present at the same time on each alumina crystallite depending on Pt loading.
19. 19
  Vaarkamp, M.; Miller, J. T.; Modica, F. S.; Koningsberger, D. C. On the Relation between Particle Morphology, Structure of the Metal-Support Interface, and Catalytic Properties of Pt/γ-Al₂O₃. J. Catal. 1996, 163, 294– 305, DOI: 10.1006/jcat.1996.0330
  19
  On the relation between particle morphology, structure of the metal-support interface, and catalytic properties of Pt/γ-Al2O3
  Vaarkamp, Marius; Miller, Jeffrey T.; Modica, Frank S.; Koningsberger, Diek, C.
  Journal of Catalysis (1996), 163 (2), 294-305CODEN: JCTLA5; ISSN:0021-9517. (Academic)
  The relation between catalytic activity, electronic properties, morphol., and structure of the metal support interface was studied for Pt/γ-Al2O3 after low (300°C, LTR) and high temp. redn. (450°C, HTR). EXAFS revealed that after LTR the platinum particles were three-dimensional, contained 11 Pt atoms on av., and were at a distance of 2.7 Å from the support oxygen. During HTR, the morphol. of the platinum particles changed from three-dimensional to rafts with a structure similar to Pt(100), as indicated by a decrease in the Pt-Pt coordination no. and the absence of the third coordination shell in the EXAFS spectrum. After HTR the Pt-O distance was shortened to 2.2 Å due to the desorption of hydrogen from the metal-support interface. The shortening of the Pt-O distance upon HTR treatment agrees with previous studies on zeolite supported platinum. However, zeolite supported platinum particles retained their three-dimensional structure upon HTR. The changes in the structure of the catalyst affected the catalytic, chemisorption, and electronic properties. After HTR the selectivity for hydrogenolysis of both neopentane and methylcyclopentane to methane decreased. At the same time the specific activity for neopentane isomerization and methylcyclopentane ring opening increased. The hydrogen chemisorption capacity after HTR was lower than after LTR. HTR shifted the sym. linear CO IR absorption from 2063 to 2066 cm-1. Comparison of the PtLIII and LII X-ray absorption edge intensities after LTR and HTR revealed that the no. of holes in the d-band of the platinum atoms increased by 9.5% during HTR. It was suggested that the decrease in hydrogen chemisorption capacity, hydrogenolysis selectivity, and no. of holes in the d-band are related to the change in the structure of the metal-support interface. The increase in specific activity for isomerization of neopentane and the shift in the CO IR absorption band with a raise in redn. temp. agreed with reported results for single crystals and was attributed to the higher concn. of atoms with Pt(100) symmetry in the catalyst after HTR.
20. 20
  Wang, F.; Ma, J.; Xin, S.; Wang, Q.; Xu, J.; Zhang, C.; He, H.; Cheng Zeng, X. Resolving the Puzzle of Single-Atom Silver Dispersion on Nanosized γ-Al₂O₃ Surface for High Catalytic Performance. Nat. Commun. 2020, 11, 529, DOI: 10.1038/s41467-019-13937-1
  20
  Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance
  Wang, Fei; Ma, Jinzhu; Xin, Shaohui; Wang, Qiang; Xu, Jun; Zhang, Changbin; He, Hong; Xiao, Cheng Zeng
  Nature Communications (2020), 11 (1), 529CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
  Ag/γ-Al2O3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphol. and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al2O3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al2O3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al2O3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al2O3. D.-functional-theory calcns. confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al2O3, but not on microsized γ-Al2O3. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts.
21. 21
  Kubota, H.; Mine, S.; Toyao, T.; Maeno, Z.; Shimizu, K. Redox-Driven Reversible Structural Evolution of Isolated Silver Atoms Anchored to Specific Sites on γ-Al₂O₃. ACS Catal. 2022, 12, 544– 599, DOI: 10.1021/acscatal.1c04924
  21
  Redox-Driven Reversible Structural Evolution of Isolated Silver Atoms Anchored to Specific Sites on γ-Al2O3
  Kubota, Hiroe; Mine, Shinya; Toyao, Takashi; Maeno, Zen; Shimizu, Ken-ichi
  ACS Catalysis (2022), 12 (1), 544-559CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Reversible structural transformation between at. Ag(I) and large Ag metal nanoparticles (NPs) on γ-Al2O3-supported Ag (Ag/Al2O3) catalysts for H2-assisted NOx selective catalytic redn. by NH3 was monitored by in situ X-ray absorption spectroscopy, UV-visible spectroscopy, IR spectroscopy, and ex situ microscopy. Fresh Ag/Al2O3 was deactivated by H2 redn. at 800°C owing to sintering of the at. Ag(I) species to form large (10-52 nm) Ag metal NPs. Reoxidn. of the sintered catalyst using NO + O2 at 400°C resulted in the redispersion of Ag metal NPs to the at. Ag(I) species, leading to the recovery of the catalytic activity. Sintering and dispersion occurred reversibly for 10 repetitive treatments of H2↔NO + O2 at 600°C. The structure of the anchoring site and the mechanism of oxidative dispersion were elucidated by kinetic studies, in situ spectroscopy, 27Al NMR spectroscopy, and d. functional theory calcns. The isolated Ag(I) cation was exchanged with H+ of the HO-μ1-AlVI site adjacent to the strong Lewis acid sites (unsatd. AlIV3+) on γ-Al2O3, and, consequently, the anchored Ag(I) species reduced the Lewis acid strength of the adjacent AlIV3+ sites. During sintering under H2, the isolated AgO-μ1-AlVI species aggregated to form Ag metal NPs, regenerating the HO-μ1-AlVI sites on the support. During oxidative dispersion under the NO + O2 flow, the Ag metal NPs were oxidized to furnish mobile AgNO3 species that moved across the support surface and reacted with the anchoring site, HO-μ1-AlVI, to yield the original AgO-μ1-AlVI species and HNO3; the latter reacts with the γ-Al2O3 surface to yield the nitrate species. This study provides mol. level insights into the deactivation/reactivation of supported metal catalysts under reductive/oxidative conditions.
22. 22
  Valero, M. C.; Raybaud, P.; Sautet, P. Influence of the Hydroxylation of γ-Al₂O₃ Surfaces on the Stability and Diffusion of Single Pd Atoms: A DFT Study. J. Phys. Chem. B 2006, 110, 1759– 1767, DOI: 10.1021/jp0554240
  22
  Influence of the Hydroxylation of γ-Al2O3 Surfaces on the Stability and Diffusion of Single Pd Atoms: A DFT Study
  Valero, Manuel Corral; Raybaud, Pascal; Sautet, Philippe
  Journal of Physical Chemistry B (2006), 110 (4), 1759-1767CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
  Using recent well-defined models of γ-Al2O3 surfaces, the authors study the interaction of single Pd atoms with γ-Al2O3 surfaces corresponding to realistic pretreatment conditions by d. functional theory periodic calcns. For relevant hydroxylation states of the surface, the authors det. potential energy surfaces (PES) that depict the relation between structure and interaction at the metal-oxide interface. This approach enables the detn. of the low-energy diffusion paths of the adsorbed Pd species. The authors applied classical transition-state theory to derive the temp.-dependent hopping rate of Pd on γ-Al2O3 surfaces. The authors' work provides new insight into the chemisorption and diffusion process of single Pd atoms on alumina and show that the binding energy and hopping rate of Pd atoms decrease as the surface OH coverage increases. These results offer new highlights on Pd cluster formation at the initial nucleation steps on γ-Al2O3 surfaces.
23. 23
  Murata, K.; Mahara, Y.; Ohyama, J.; Yamamoto, Y.; Arai, S.; Satsuma, A. The Metal-Support Interaction Concerning the Particle Size Effect of Pd/Al₂O₃ on Methane Combustion. Angew. Chemie Int. Ed. 2017, 56, 15993– 15997, DOI: 10.1002/anie.201709124
  23
  The Metal-Support Interaction Concerning the Particle Size Effect of Pd/Al2O3 on Methane Combustion
  Murata, Kazumasa; Mahara, Yuji; Ohyama, Junya; Yamamoto, Yuta; Arai, Shigeo; Satsuma, Atsushi
  Angewandte Chemie, International Edition (2017), 56 (50), 15993-15997CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The particle size effect of Pd nanoparticles supported on alumina with various cryst. phases on methane combustion was investigated. Pd/θ-, α-Al2O3 with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al2O3 increased with the particle size. Based on a structural anal. of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration-cor. scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina cryst. phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal-support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al2O3 for methane combustion.
24. 24
  Murata, K.; Shiotani, T.; Ohyama, J.; Satsuma, A. Selective Hydrogenation of C═C Bond in Cinnamaldehyde on Pd Step Sites of Pd/Al₂O₃. Chem. Lett. 2021, 50, 599– 602, DOI: 10.1246/cl.200856
  24
  Selective Hydrogenation of C=C bond in Cinnamaldehyde on Pd Step Sites of Pd/Al2O3
  Murata, Kazumasa; Shiotani, Takumi; Ohyama, Junya; Satsuma, Atsushi
  Chemistry Letters (2021), 50 (4), 599-602CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
  We found a pos. correlation between C=C selective hydrogenation activity of cinnamaldehyde (CAL) and the fraction of the Pd step site on Pd nanoparticles. Owing to a high fraction of step sites, Pd/θ-Al2O3 catalysts with Pd particle size of 5-10 nm were highly active for the C=C selective hydrogenation of CAL.
25. 25
  Murata, K.; Eleeda, E.; Ohyama, J.; Yamamoto, Y.; Arai, S.; Satsuma, A. Identification of Active Sites in CO Oxidation over a Pd/Al₂O₃ Catalyst. Phys. Chem. Chem. Phys. 2019, 21, 18128– 18137, DOI: 10.1039/C9CP03943K
  25
  Identification of active sites in CO oxidation over a Pd/Al2O3 catalyst
  Murata, Kazumasa; Eleeda, Eleen; Ohyama, Junya; Yamamoto, Yuta; Arai, Shigeo; Satsuma, Atsushi
  Physical Chemistry Chemical Physics (2019), 21 (33), 18128-18137CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  The active sites of Pd/Al2O3 catalysts for CO oxidns. were identified by investigating the dependence of CO oxidn. activities on the surface structure and morphol. of Pd nanoparticles. The max. catalytic activity was obtained for Pd particles approx. 2 nm in particle size. We performed structural analyses on the Pd surface through IR (IR) spectroscopy of the adsorbed CO mols. A pos. correlation was obtained between catalytic activity and the fraction of linear CO adsorbed on Pd corner sites and Pd(111) facets, indicating that these sites are highly active for CO oxidn. X-ray absorption fine structure (XAFS) and spherical aberration-cor. scanning transmission electron microscopy (Cs-STEM) measurements demonstrated that Pd nanoparticles less than 2 nm in particle size with amorphous-like structures and Pd particles with large, well-ordered structures favor the formation of a high fraction of corner sites and Pd(111) facets, resp.
26. 26
  Duan, H.; You, R.; Xu, S.; Li, Z.; Qian, K.; Cao, T.; Huang, W.; Bao, X. Penta-Coordinated Al³⁺ Stabilized Active Pd Structures on Al₂O₃ Coated Palladium Catalysts for Methane Combustion. Angew. Chemie Int. Ed. 2019, 58, 12043– 12048, DOI: 10.1002/anie.201904883
  26
  Pentacoordinated Al3+-Stabilized Active Pd Structures on Al2O3-Coated Palladium Catalysts for Methane Combustion
  Duan, Huimei; You, Rui; Xu, Shutao; Li, Zhaorui; Qian, Kun; Cao, Tian; Huang, Weixin; Bao, Xinhe
  Angewandte Chemie, International Edition (2019), 58 (35), 12043-12048CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO2 catalysts with porous Al2O3 overlayers coated by at. layer deposition (ALD). 27Al magic angle spinning NMR anal. showed that Al2O3 overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al3+ sites capable of strongly interacting with adjacent surface PdOx phases on supported Pd particles. Consequently, Al2O3-decorated Pd/SiO2 catalysts exhibit active and stable PdOx and Pd-PdOx structures to efficiently catalyze methane combustion between 200 and 850°. These results reveal the unique structural characteristics of Al2O3 overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.
27. 27
  Yang, X.; Li, Q.; Lu, E.; Wang, Z.; Gong, X.; Yu, Z.; Guo, Y.; Wang, L.; Guo, Y.; Zhan, W.; Zhang, J.; Dai, S. Taming the Stability of Pd Active Phases through a Compartmentalizing Strategy toward Nanostructured Catalyst Supports. Nat. Commun. 2019, 10, 1611, DOI: 10.1038/s41467-019-09662-4
  27
  Taming the stability of Pd active phases through a compartmentalizing strategy toward nanostructured catalyst supports
  Yang Xinwei; Li Qing; Wang Zhiqiang; Gong Xueqing; Guo Yun; Wang Li; Guo Yanglong; Zhan Wangcheng; Lu Erjun; Yu Zhiyang; Zhang Jinshui; Dai Sheng; Dai Sheng
  Nature communications (2019), 10 (1), 1611 ISSN:.
  The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions is ubiquitous in many industrial catalytic processes and still a big challenge in implementing nanostructured metal catalyst systems. Herein, we demonstrate a strategy for designing robust nanocatalysts through a sintering-resistant support via compartmentalization. Ultrafine palladium active phases can be highly dispersed and thermally stabilized by nanosheet-assembled γ-Al2O3 (NA-Al2O3) architectures. The NA-Al2O3 architectures with unique flowerlike morphologies not only efficiently suppress the lamellar aggregation and irreversible phase transformation of γ-Al2O3 nanosheets at elevated temperatures to avoid the sintering and encapsulation of metal phases, but also exhibit significant structural advantages for heterogeneous reactions, such as fast mass transport and easy access to active sites. This is a facile stabilization strategy that can be further extended to improve the thermal stability of other Al2O3-supported nanocatalysts for industrial catalytic applications, in particular for those involving high-temperature reactions.
28. 28
  Murata, K.; Shiotani, T.; Ohyama, J.; Wakabayashi, R.; Maruoka, H.; Kimura, T.; Satsuma, A. Relationship between Penta-Coordinated Al³⁺ Sites in the Al₂O₃ Supports and CH₄ Combustion Activity of Pd/Al₂O₃ Catalysts. Catal. Sci. Technol. 2021, 11, 2374– 2378, DOI: 10.1039/D1CY00098E
  28
  Relationship between penta-coordinated Al3+ sites in the Al2O3 supports and CH4 combustion activity of Pd/Al2O3 catalysts
  Murata, Kazumasa; Shiotani, Takumi; Ohyama, Junya; Wakabayashi, Ryutaro; Maruoka, Hirokazu; Kimura, Tatsuo; Satsuma, Atsushi
  Catalysis Science & Technology (2021), 11 (7), 2374-2378CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  Pd/Al2O3 catalysts were prepd. using various Al2O3 supports with different structural features such as cryst. phase and crystallinity related to Al3+ coordination, revealing a significant insight into the methane (CH4) combustion activity of Pd nanoparticles with the fraction of penta-coordinated Al3+ sites in the Al2O3 supports.
29. 29
  Hu, C. H.; Chizallet, C.; Mager-Maury, C.; Corral-Valero, M.; Sautet, P.; Toulhoat, H.; Raybaud, P. Modulation of Catalyst Particle Structure upon Support Hydroxylation: Ab Initio Insights into Pd₁₃ and Pt₁₃/γ-Al₂O₃. J. Catal. 2010, 274, 99– 110, DOI: 10.1016/j.jcat.2010.06.009
  29
  Modulation of catalyst particle structure upon support hydroxylation: Ab initio insights into Pd13 and Pt13/γ-Al2O3
  Hu, Chao Hao; Chizallet, Celine; Mager-Maury, Christophe; Corral-Valero, Manuel; Sautet, Philippe; Toulhoat, Herve; Raybaud, Pascal
  Journal of Catalysis (2010), 274 (1), 99-110CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
  An at. picture of highly dispersed palladium and platinum catalysts supported on gamma-alumina is provided. Understanding the structure-reactivity relationship in the field of catalysis by metals requires the rationalization of the role of the metal-support interaction on the morphol. and electronic properties of nanometer size metallic particles. Thus, the interaction energies and the structures of Pd13 and Pt13 clusters deposited on two relevant gamma-alumina surfaces are systematically investigated by d. functional theory calcns. The hydroxylation of the support weakens the metal adhesion and influences the cluster morphologies. Flat lying bi-planar clusters with strong interaction energies are stabilized on the dehydrated (1 0 0) surface, whereas clusters with a three-dimensional morphol. are favored by the hydroxyl groups of the (1 1 0) surface. A consistent comparison of Pt and Pd is achieved. The shortest metal-oxygen (M-O) bond distances calcd. by DFT agree well with EXAFS M-O distances. Moreover, the presence of metal-aluminum bond distances close to 2.61-2.64 Å may explain exptl. features. The present work also provides structural and electronic clues for the understanding of the reactivity of highly dispersed Pd and Pt catalysts.
30. 30
  Valero, M. C.; Raybaud, P.; Sautet, P. Nucleation of Pd_n (N = 1–5) Clusters and Wetting of Pd Particles on γ-Al₂O₃ Surfaces: A Density Functional Theory Study. Phys. Rev. B 2007, 75, 1– 12, DOI: 10.1103/PhysRevB.75.045427
  There is no corresponding record for this reference.
31. 31
  Shi, X. R.; Sholl, D. S. Nucleation of Rh_n (n = 1–5) Clusters on γ-Al₂O₃ Surfaces: A Density Functional Theory Study. J. Phys. Chem. C 2012, 116, 10623– 10631, DOI: 10.1021/jp301114n
  31
  Nucleation of Rhn (n = 1-5) Clusters on γ-Al2O3 Surfaces: A Density Functional Theory Study
  Shi, Xue-Rong; Sholl, David S.
  Journal of Physical Chemistry C (2012), 116 (19), 10623-10631CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  The interaction of Rhn (n = 1-5) clusters with nonhydrated γ-Al2O3(100), hydrated γ-Al2O3(100), and hydrated γ-Al2O3(110) surfaces was studied using d. functional theory methods. On these surfaces, Rh3 prefers a triangular geometry, while Rh4 and Rh5 adopt 3-dimensional structures. On the (100) surfaces, Rhn binds considerably more strongly on the nonhydrated surface than on the hydrated surface. On the hydrated (110) surface, Rhn binds to surface hydroxyl groups, which is consistent with exptl. observations. Characterizing the structure of Rhn clusters makes it possible to identify the crit. cluster size for nucleation on each surface.
32. 32
  Mager-Maury, C.; Chizallet, C.; Sautet, P.; Raybaud, P. Platinum Nanoclusters Stabilized on γ-Alumina by Chlorine Used As a Capping Surface Ligand: A Density Functional Theory Study. ACS Catal. 2012, 2, 1346– 1357, DOI: 10.1021/cs300178y
  32
  Platinum Nanoclusters Stabilized on γ-Alumina by Chlorine Used As a Capping Surface Ligand: A Density Functional Theory Study
  Mager-Maury, C.; Chizallet, C.; Sautet, P.; Raybaud, P.
  ACS Catalysis (2012), 2 (7), 1346-1357CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Controlling the size of metallic nanoclusters supported on an oxide support such as γ-alumina represents a challenging but important task in the case of noble metals such as platinum. By using d. functional theory (DFT), we investigate the thermodn., structural and electronic properties of small nanometer-sized Ptn clusters (n ≤ 13) interacting with four relevant γ-alumina surfaces exhibiting various hydroxylation and chlorination states. The presence of chlorine on the (110) surface of γ-alumina implies a thermodn. stabilization of small platinum clusters. This stabilization originates from the simultaneous migrations of chlorine atoms and protons from the support toward the Pt clusters. The migration of H and Cl from the support induces a stronger interaction of the Ptn cluster with the available AlIII site, assocd. with strong H-Ptn-Cl interaction. In particular, this trend leads to a local energy min., as a function of cluster size, for the Pt3 cluster. This at.-scale stabilization of subnanometer clusters is thus proposed to be at the origin of the formation of highly dispersed platinum particles and to prevent their sintering into supranano ones. A detailed energetic and electronic anal. is provided to rationalize this effect of chlorine. A rational interpretation of exptl. data is finally given.
33. 33
  Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15– 50, DOI: 10.1016/0927-0256(96)00008-0
  33
  Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
  Kresse, G.; Furthmuller, J.
  Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)
  The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
34. 34
  Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169– 11186, DOI: 10.1103/PhysRevB.54.11169
  34
  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
  Kresse, G.; Furthmueller, J.
  Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
35. 35
  Kresse, G.; Hafner, J. Ab. Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, 558– 561, DOI: 10.1103/PhysRevB.47.558
  35
  Ab initio molecular dynamics of liquid metals
  Kresse, G.; Hafner, J.
  Physical Review B: Condensed Matter and Materials Physics (1993), 47 (1), 558-61CODEN: PRBMDO; ISSN:0163-1829.
  The authors present ab initio quantum-mech. mol.-dynamics calcns. based on the calcn. of the electronic ground state and of the Hellmann-Feynman forces in the local-d. approxn. at each mol.-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using sub-space alignment. This approach avoids the instabilities inherent in quantum-mech. mol.-dynamics calcns. for metals based on the use of a factitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows one to perform simulations over several picoseconds.
36. 36
  Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.17953
  36
  Projector augmented-wave method
  Blochl
  Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
  There is no expanded citation for this reference.
37. 37
  Hammer, B.; Hansen, L. B.; Nørskov, J. K. Improved Adsorption Energetics within Density-Functional Theory Using Revised Perdew-Burke-Ernzerhof Functionals. Phys. Rev. B - Condens. Matter Mater. Phys. 1999, 59, 7413– 7421, DOI: 10.1103/PhysRevB.59.7413
  37
  Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals
  Hammer, B.; Hansen, L. B.; Norskov, J. K.
  Physical Review B: Condensed Matter and Materials Physics (1999), 59 (11), 7413-7421CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  A simple formulation of a generalized gradient approxn. for the exchange and correlation energy of electrons has been proposed by J. Perdew et al. (1996). Subsequently, Y. Zhang and W. Wang (1998) have shown that a slight revision of the Perdew-Burke-Ernzerhof (PBE) functional systematically improves the atomization energies for a large database of small mols. In the present work, we show that the Zhang and Yang functional (revPBE) also improves the chemisorption energetics of atoms and mols. on transition-metal surfaces. Our test systems comprise at. and mol. adsorption of oxygen, CO, and NO on Ni(100), Ni(111), Rh(100), Pd(100), and Pd(111) surfaces. As the revPBE functional may locally violate the Lieb-Oxford criterion, we further develop an alternative revision of the PBE functional, RPBE, which gives the same improvement of the chemisorption energies as the revPBE functional at the same time as it fulfills the Lieb-Oxford criterion locally.
38. 38
  Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132, 154104, DOI: 10.1063/1.3382344
  38
  A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu
  Grimme, Stefan; Antony, Jens; Ehrlich, Stephan; Krieg, Helge
  Journal of Chemical Physics (2010), 132 (15), 154104/1-154104/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  The method of dispersion correction as an add-on to std. Kohn-Sham d. functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coeffs. and cutoff radii that are both computed from first principles. The coeffs. for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos. (CN). They are used to interpolate between dispersion coeffs. of atoms in different chem. environments. The method only requires adjustment of two global parameters for each d. functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of at. forces. Three-body nonadditivity terms are considered. The method has been assessed on std. benchmark sets for inter- and intramol. noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean abs. deviations for the S22 benchmark set of noncovalent interactions for 11 std. d. functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs. also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. (c) 2010 American Institute of Physics.
39. 39
  Eng, P. J.; Trainor, T. P.; Brown, G. E., Jr.; Waychunas, G. A.; Newville, M.; Sutton, S. R.; Rivers, M. L. Structure of the Hydrated α-Al₂O₃(0001) Surface. Science 2000, 288, 1029– 1033, DOI: 10.1126/science.288.5468.1029
  39
  Structure of the hydrated α-Al2O3 (0001) surface
  Eng, Peter J.; Trainor, Thomas P.; Brown, Gordon E., Jr.; Waychunas, Glenn A.; Newville, Matthew; Sutton, Stephen R.; Rivers, Mark L.
  Science (Washington, D. C.) (2000), 288 (5468), 1029-1033CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  The phys. and chem. properties of the hydrated α-Al2O3 (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-contg. oxides. The structure of this surface was detd. in the presence of water vapor at 300 K by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between α-Al2O3 and γ-Al(OH)3, a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean α-Al2O3 (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces.
40. 40
  Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H. Use of DFT to Achieve a Rational Understanding of Acid-Basic Properties of γ-Alumina Surfaces. J. Catal. 2004, 226, 54– 68, DOI: 10.1016/j.jcat.2004.04.020
  40
  Use of DFT to achieve a rational understanding of acid-basic properties of γ-alumina surfaces
  Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H.
  Journal of Catalysis (2004), 226 (1), 54-68CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
  In a recent priority communication [M. Digne et al., J. Catal. 211 (2002) 1], we proposed the first ab initio constructed models of γ-alumina surfaces. Using the same d.-functional approach, we investigate in further detail the acid-basic properties of the three relevant γ-alumina (100), (110), and (111) surfaces, taking into account the temp.-dependent hydroxyl surface coverages. The simulations, compared fruitfully with many available exptl. data, enable us to solve the challenging assignment of the OH-stretching frequencies, as obtained from IR spectroscopy. The precise nature of the acid surface sites (concns. and strengths) is also detd. The acid strengths are quantified by simulating the adsorption of relevant probe mols. such as CO and pyridine in correlation with surface electronic properties. These results seriously challenge the historical model of a defective spinel for γ-alumina and establish the basis for a more rigorous description of the acid-basic properties of γ-alumina.
41. 41
  Sawabe, K.; Satsuma, A. Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al₂O₃-Supported Silver Nanoparticles: Size, Shape, and Support Effects. ACS Omega 2022, 7, 4405– 4412, DOI: 10.1021/acsomega.1c06208
  41
  Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al2O3-Supported Silver Nanoparticles: Size, Shape, and Support Effects
  Sawabe, Kyoichi; Satsuma, Atsushi
  ACS Omega (2022), 7 (5), 4405-4412CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
  Nanoparticles (NPs) supported on metal oxides exhibit high catalytic activities for various reactions. The shape and oxidn. state of such NPs, which are related to the catalytic activity, are often detd. by the support. Herein, we conducted a d. functional theory study on isolated silver (Ag) NPs and two types of Ag-NPs supported on gamma-aluminum oxide (γ-Al2O3). First, carbon monoxide (CO) adsorption on the isolated Ag NPs was investigated for decahedra (D5h), icosahedra (Ih), and cuboctahedra (Oh) of various sizes. Ih and Oh NPs showed moderate size dependence, whereas D5h NPs showed high size dependence when the height was below 1.4 nm. The enhancement of CO adsorption on D5h NPs was attributed to the presence of superat. states. Next, we performed geometrical optimization of Ag54/γ-Al2O3(110) with a decahedral shape. Two types of structures were obtained: amorphous Ag54(A) and locally fivefold sym. Ag54(B) structures. Both NPs on γ-Al2O3(110) were found to be pos. charged, but electron transfer to the support occurred only from the Ag atoms at the two bottom layers, and the upper part of NPs was relatively neutral. The enhancement of CO adsorption on Ag54(B) disappeared due to loss of the high symmetry. In turn, the moderate size dependence of neutral isolated NPs can be applied.
42. 42
  Frenkel, D.; Smit, B. Understanding Molecular Simulation: From Algorithms to Applications; Academic press: 2002, p 141
  There is no corresponding record for this reference.
43. 43
  Stukowski, A. Visualization and Analysis of Atomistic Simulation Data with OVITO-the Open Visualization Tool. Model. Simul. Mater. Sci. Eng. 2010, 18, 015012, DOI: 10.1088/0965-0393/18/1/015012
  There is no corresponding record for this reference.
44. 44
  Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H. Hydroxyl Groups on γ-Alumina Surfaces: A DFT Study. J. Catal. 2002, 211, 1– 5, DOI: 10.1006/jcat.2002.3741
  44
  Hydroxyl Groups on γ-Alumina Surfaces: A DFT Study
  Digne, M.; Sautet, P.; Raybaud, P.; Euzen, P.; Toulhoat, H.
  Journal of Catalysis (2002), 211 (1), 1-5CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
  Despite numerous exptl. studies devoted to the acid-base properties of γ-alumina, the precise nature of surface acid sites remains unsolved. Using d. functional (DFT) calcns., we propose realistic models of γ-alumina (110) and (100) surfaces accounting for hydroxylation/dehydroxylation processes induced by temp. effects. The vibrational anal., based on DFT calcns., leads to an accurate assignment of the OH stretching frequencies obsd. by IR spectroscopy. The extension to chlorinated surfaces, which brings new insights into the understanding of the role of dopes, is also addressed.
45. 45
  Nortier, P.; Fourre, P.; Saad, A.B. M.; Saur, O.; Lavalley, J.C. Effects of Crystallinity and Morphology on the Surface Properties of Alumina. Appl. Catal. 1990, 61, 141– 160, DOI: 10.1016/S0166-9834(00)82140-5
  45
  Effects of crystallinity and morphology on the surface properties of alumina
  Nortier, P.; Fourre, P.; Saad, A. B. Mohammed; Saur, O.; Lavalley, J. C.
  Applied Catalysis (1990), 61 (1), 141-60CODEN: APCADI; ISSN:0166-9834.
  Five samples of Al2O3, (1 amorphous and 4 γ-Al2O3's prepd. from different boehmites) were compared by using phys. methods (x-ray diffraction, transmission electron microscopy, 27Al NMR and Fourier transform IR spectrometry) and the butene isomerization test. All the γ-Al2O3 samples preferentially present the (110) face, whereas the ratio of the (001) and (111) faces depends on the precursor. Isomerization tests and IR expts. with different probe mols. show very similar acidities for the crystd. samples, which is discussed taking various models into account. The lower Lewis acidity of the amorphous sample is related to the smaller no. of AlIV sites shown by NMR expts. The crystallinity effect is also indicated by an IR study of the OH groups, with the amorphous sample showing a specific band at 3787 cm-1.
46. 46
  Wang, L. L.; Johnson, D. D. Density Functional Study of Structural Trends for Late-Transition-Metal 13-Atom Clusters. Phys. Rev. B 2007, 75, 1– 10, DOI: 10.1103/PhysRevB.75.235405
  There is no corresponding record for this reference.
47. 47
  Atkins, P.; de Paula, J. Atkins’ Physical Chemistry, 8th ed.; Oxford University Press: 2006; pp 441– 442.
  There is no corresponding record for this reference.
48. 48
  Zhang, W.; Xiao, L.; Hirata, Y.; Pawluk, T.; Wang, L. The Simple Cubic Structure of Ir Clusters and the Element Effect on Cluster Structures. Chem. Phys. Lett. 2004, 383, 67– 71, DOI: 10.1016/j.cplett.2003.11.005
  48
  The simple cubic structure of Ir clusters and the element effect on cluster structures
  Zhang, Wenqin; Xiao, Li; Hirata, Yasuhiro; Pawluk, Tiffany; Wang, Lichang
  Chemical Physics Letters (2004), 383 (1,2), 67-71CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
  The simple cubic was found to be the most stable structure for Ir clusters in the subnanometer range from our d. functional theory calcns. We further examd. various structures of group 8-10 precious metal clusters. The tendency to form the simple cubic structure becomes stronger from right to left across a period and from top to bottom in the group, while the trend is opposite for the formation of icosahedrons or cubo-octahedrons.
49. 49
  Hendriksen, B. A.; Pearce, D. R.; Rudham, R. Heats of Adsorption of Water on α- and γ-Alumina. J. Catal. 1972, 24, 82– 87, DOI: 10.1016/0021-9517(72)90010-3
  49
  Heats of adsorption of water on α- and γ-alumina
  Hendriksen, B. A.; Pearce, D. R.; Rudham, R.
  Journal of Catalysis (1972), 24 (1), 82-7CODEN: JCTLA5; ISSN:0021-9517.
  Heats of immersion of α- and γ-alumina in water were detd. for samples outgassed at temps. up to 600°. The results are combined with values of the residual surface-water content, detd. by D exchange, to give heats of adsorption of water as a function of uptake. The results are discussed and compared with similar data obtained or calcd. from the published literature.
50. 50
  Thissen, P.; Grundmeier, G.; Wippermann, S.; Schmidt, W. G. Water Adsorption on the α-Al₂O₃ (0001) Surface. Phys. Rev. B - Condens. Matter Mater. Phys. 2009, 80, 1– 6, DOI: 10.1103/PhysRevB.80.245403
  There is no corresponding record for this reference.
51. 51
  Pigeon, T.; Chizallet, C.; Raybaud, P. Revisiting γ-Alumina Surface Models through the Topotactic Transformation of Boehmite Surfaces. J. Catal. 2022, 405, 140– 151, DOI: 10.1016/j.jcat.2021.11.011
  51
  Revisiting γ-alumina surface models through the topotactic transformation of boehmite surfaces
  Pigeon, Thomas; Chizallet, Celine; Raybaud, Pascal
  Journal of Catalysis (2022), 405 (), 140-151CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
  The rational understanding of γ-alumina (γ-Al2O3) supported catalysts requires an ever more improved at. scale detn. of the support's surface properties. By using d. functional theory (DFT) calcns., we show how the structural and energetic surface properties of alumina crystallites intrinsically depend on its synthesis pathway. Considering the case study of the topotactic transformation of boehmite (γ-AlOOH) into γ-Al2O3 taking place during calcination, we propose a methodol. to mimic this pathway by reconstructing relevant slabs of boehmite into γ-alumina slabs following 3 steps: dehydration, contraction/translation and Al migration into spinel or non-spinel sites. On the one hand, we confirm the reliability of some earlier 100, 110 and 111 surface structures detd. by std. bulk cleavage approach. Moreover, we find new γ-alumina surfaces harboring Bronsted acid sites (BAS) and Lewis acid sites (LAS) with specific local structures. More strikingly, we find that the basal (110)b surface of alumina inherited from the (0 1 0) basal surface of boehmite, exhibits a larger no. of isolated μ2-OH groups than the lateral( 110)l surface. For the lateral (110)l (resp. 111) orientation, four (resp. three) thermodynamically competing surfaces are identified, including models earlier proposed. These results are induced by finite size and morphol. effects during the topotactic transformation of boehmite crystallites. Thanks to a thorough comparative anal. of morphol. and nature of BAS and LAS as a function of thermal treatment and water pressure for each surface, we identify coherent chem. families of surfaces across the main crystallog. orientations. These features open the door to a better differentiation of the reactivity of the basal alumina surfaces from the lateral ones.
52. 52
  Ranea, V. A.; Schneider, W. F.; Carmichael, I. DFT Characterization of Coverage Dependent Molecular Water Adsorption Modes on α-Al₂O₃(0001). Surf. Sci. 2008, 602, 268– 275, DOI: 10.1016/j.susc.2007.10.029
  52
  DFT characterization of coverage dependent molecular water adsorption modes on α-Al2O3(0 0 0 1)
  Ranea, Victor A.; Schneider, William F.; Carmichael, Ian
  Surface Science (2008), 602 (1), 268-275CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
  Ab initio d. functional theory was used to investigate the stable and metastable states of adsorbed mol. water on the α-Al2O3(0 0 0 1) surface as a function of coverage. The atoms of the dry surface undergo pronounced inward relaxations with respect to their bulk positions. At low coverages (Θ ≤ 0.5) water adsorbs nearly parallel to the surface plane, with an O atom atop a surface Al. The adsorption is mainly due to the donation from water lone pairs into vacant p orbital of surface Al, drawing the surface Al outward. With increasing coverage, water adsorption atop Al competes with an alternative configuration with water bound through H to surface oxygen. These two competing modes generate a variety of distinct but nearly isoenergetic adsorption modes that terminate in a hexagonal, ice-like layer at a coverage of two water mols. per surface Al. The binding energy per water mol. is maximized in the two limits of coverage, but deviates from this extreme only slightly at intermediate coverages. At no coverage is the water binding great enough to overcome the energetic preference for water to dissociatively adsorb.
53. 53
  Erfani, G. S.; Hong, S.; Rahman, T. S. Effects of γ-Al₂O₃ Support on the Morphology and Electronic Structure of Pt Nanoparticles. J. Phys. Chem. C 2019, 123, 16893– 16901, DOI: 10.1021/acs.jpcc.9b04770
  53
  Effects of γ-Al2O3 Support on the Morphology and Electronic Structure of Pt Nanoparticles
  Erfani, Ghazal S.; Hong, Sampyo; Rahman, Talat S.
  Journal of Physical Chemistry C (2019), 123 (27), 16893-16901CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  We have studied the effects of γ-Al2O3(110) support on the morphol. and electronic structure of clean and H-covered Pt nanoparticles (NPs) contg. 22 and 44 atoms (Pt22 and Pt44) using d. functional theory (DFT)-based calcns. We find that the morphol. of Pt22 changes from three-dimensional (3D), when free-standing, to a biplanar shape on pristine γ-Al2O3(110) and back to 3D, if hydroxyl coverage on γ-Al2O3(110) is greater than 0.325 ML. Morphol. change of Pt NPs is governed by cohesive Pt-Pt interaction at high hydroxyl coverage and by adhesive Pt-support interaction at low hydroxyl coverage. However, such morphol. change does not occur for Pt44, indicating that such transition only happens for smaller Pt NPs. Not surprisingly, the electronic structure of the Pt NPs is sensitive to both the presence of the support and to the extent to which it is hydroxylated. A competing effect also comes from adsorbed hydrogen atoms on the surface of Pt NPs. However, with increasing temp. the effect of adsorbed hydrogen weakens but that of the support becomes stronger, resulting in a correlation between the shift of the unoccupied d-band and the extent of the metal-support interaction. These results provide insight into the dependence of the catalytic properties of Pt NPs on several competing extrinsic factors-the hydroxylation level of the γ-Al2O3 support, H adsorbate coverage on Pt NPs, and ambient temp.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.3c02483.
- Figure S1: transition of the temperature and the potential energy of Pd₁₃ cluster on Al₂O₃ surfaces for MD cycle; Figure S2: histograms of the temperature distribution for 5 ps after 3 ps of holding at 773 K; Figure S3: initial structure of γ-Al₂O₃(110) surface before AIMD simulation; Figure S4: sampled initial structures for the structural optimization; Table S1: molecular structures of Pd clusters supported on α-Al₂O₃(0001); Table S2: molecular structures of Pd clusters supported on γ-Al₂O₃(100); Table S3: molecular structures of Pd clusters supported on γ-Al₂O₃(110); Table S4: molecular structures of Pd clusters in a vacuum; Table S5: coordination number, average interatomic distance_, binding energies, and interaction energies, for Pd clusters supported on Al₂O₃; Table S6: molecular structures of Pd clusters supported on hydrated γ-Al₂O₃(110); Figure S5: binding energies for Pd cluster supported on dehydrated and hydrated γ-Al₂O₃(110) surface as a function of the number of Pd atoms per Pd cluster; Figure S6: snapshots of MD simulations at 773 K for Pd₁₃/Al₂O₃ (PDF)
- Movie S1a: top view of Pd₁₃/α-Al₂O₃(0001) (MP4)
- Movie S1b: side view of Pd₁₃/α-Al₂O₃(0001) (MP4)
- Movie S2a: top view of Pd₁₃/γ-Al₂O₃(100) (MP4)
- Movie S2b: side view of Pd₁₃/γ-Al₂O₃(100) (MP4)
- Movie S3a: top view of Pd₁₃/γ-Al₂O₃(110) (MP4)
- Movie S3b: side view of Pd₁₃/γ-Al₂O₃(110) (MP4)
- Movie S4a: top view of α-Al₂O₃(0001) (MP4)
- Movie S4b: side view of α-Al₂O₃(0001) (MP4)
- Movie S5a: top view of γ-Al₂O₃(100) (MP4)
- Movie S5b: side view of γ-Al₂O₃(100) (MP4)
- Movie S6a: top view of γ-Al₂O₃(110) (MP4)
- Movie S6b: side view of γ-Al₂O₃(110) (MP4)
- Movie S7a: top view of Pd₁₃/α-Al₂O₃(0001) (MP4)
- Movie S7b: side view of Pd₁₃/α-Al₂O₃(0001) (MP4)
- Movie S8a: top view of Pd₁₃/γ-Al₂O₃(100) (MP4)
- Movie S8b: side view of Pd₁₃/γ-Al₂O₃(100) (MP4)
- Movie S9a: top view of Pd₁₃/γ-Al₂O₃(110) (MP4)
- Movie S9b: side view of Pd₁₃/γ-Al₂O₃(110) (MP4)
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Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al2O3 Surfaces: DFT and AIMD Studies揭示受 Al2O3 表面影响的 Pd 簇的静态和动态结构：DFT 和 AIMD 研究Click to copy article link点击复制文章链接Article link copied!

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Abstract 抽象

1. Introduction 1. 简介

2. Computational Methods 2. 计算方法

3. Results and Discussion

3.1. Al2O3 Surface Models

Figure 1

3.2. Static Structure of Pd Clusters on Al2O3

Figure 2

3.3. Interactions between Pd Clusters and Al2O3 Surfaces

Figure 3

3.4. Relation between Pd–Al2O3 Interactions and Surface Structure of Al2O3

Figure 4

3.5. Dynamic Structure of Pd Clusters on Al2O3

Figure 5

Figure 6

4. Conclusions

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Abstract

Figure 1

Figure 2

Figure 3

Figure 4

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Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al₂O₃ Surfaces: DFT and AIMD Studies
揭示受 Al₂O₃ 表面影响的 Pd 簇的静态和动态结构：DFT 和 AIMD 研究
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3.1. Al₂O₃ Surface Models

3.2. Static Structure of Pd Clusters on Al₂O₃

3.3. Interactions between Pd Clusters and Al₂O₃ Surfaces

3.4. Relation between Pd–Al₂O₃ Interactions and Surface Structure of Al₂O₃

3.5. Dynamic Structure of Pd Clusters on Al₂O₃

Methane Combustion over Pd/Al₂O₃ Catalysts in the Presence of Water: Effects of Pd Particle Size and Alumina Crystalline Phase

Nature of Five-Coordinated Al in γ-Al₂O₃ Revealed by Ultra-High-Field Solid-State NMR

Methane Combustion over Pd/Al₂O₃ Catalysts in the Presence of Water: Effects of Pd Particle Size and Alumina Crystalline Phase

Nature of Five-Coordinated Al in γ-Al₂O₃ Revealed by Ultra-High-Field Solid-State NMR