Oxidation of supported rhodium clusters by support hydroxy groups.
Oxidation of supported rhodium clusters by support hydroxy groups.
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DOI：
10.1002/anie.200390357
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发表时间：
2003-03
影响因子：
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通讯作者：
G. Vayssilov;B. Gates;N. Rösch
中科院分区：
文献类型：
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作者：
G. Vayssilov;B. Gates;N. Rösch
多孔氧化物和沸石载体上的金属簇或颗粒是重要的工业催化剂，载体的作用通常超出了金属稳定分散的单纯平台的范围。[1-3]金属-载体相互作用涉及载体配体，推测为表面氧或OH基团。金属的键合、反应性和催化性能如何取决于这些配体基本上尚未解决。此外，负载型金属催化剂通常会促进“溢出”，即吸附物（通常是 H2）与金属发生反应，产生迁移到载体上的物质。氢分子在金属上解离，部分 H2 最终在载体上形成 OH 基团。溢出效应已被证明，[4]但其化学性质尚不明确；它必须涉及氧化还原过程，因为 H2 转化为与金属和 OH 基团中的质子结合的氢化物。为了帮助阐明金属-载体相互作用和溢出效应，我们对沸石桥接 OH 基团与负载团簇 Rh6 的相互作用进行了计算建模，并将理论结果与实验结果进行了比较。选择该模型系统是因为它与 EXAFS 衍生的沸石支持的 Rh6 团簇的结构参数密切对应 [5]。 [6]我们的计算表明，六核簇与载体上的 OH 基团相互作用，导致与载体紧密接触的 Rh 原子被氧化；每个 OH 基团释放的能量估计约为 120 kJmolÀ1。结果证明了氢气溢出的氧化还原特征，其中包括负载金属氧化态的变化。
Metal clusters or particles on porous-oxide and zeolite supports are important industrial catalysts, with the role of the support often going beyond that of a mere platform for the stable dispersion of the metal.[1–3] The metal–support interaction involves support ligands, inferred to be surface oxygen or OH groups. How the bonding, reactivity, and catalytic properties of the metal depend on these ligands is essentially unresolved. Furthermore, supported metal catalysts often facilitate “spillover”, whereby an adsorbate, typically H2, reacts with the metal to give species that migrate onto the support. Molecular hydrogen dissociates on metals, and some of the H2 ultimately forms OH groups on the support. Spillover has been demonstrated,[4] but its chemistry is ill defined; it must involve redox processes, since H2 is converted into a hydride bound to the metal and the protons in OH groups.To help clarify metal–support interactions and spillover effects, we modeled computationally the interaction of the bridging OH groups of zeolites with a supported cluster, Rh6, and compared the theoretical results with the experimental results. The model system was selected because of its close correspondence [5] to the EXAFS-derived structure parameters for zeolite-supported Rh6 clusters.[6] Our calculations show that the interaction of the hexanuclear cluster with OH groups from the support leads to the oxidation of Rh atoms that are in close contact with the support; the energy released per OH group is estimated to be about 120 kJmolÀ1. The results demonstrate the redox character of hydrogen spillover, which includes changes in the oxidation state of the supported metal.