Heterogeneous Catalysis and Metal/Metal-Oxide Interfaces.

摘要

Unlike supported particles of larger size or extended solid surfaces, size-selected small metal clusters (in particular gold) adsorbed at specific sites of a support material (e.g. oxygen vacancies in the case of a MgO(100) surface) exhibit unique properties that originate from the highly reduced dimensions of the individual metal aggregates. Our first-principles electronic structure and MD simulations, in conjunction with experiments, show that these properties underlie the remarkable newly found catalytic activity of small gold clusters, and they include: (1) structural dynamical fluxionality that exhibits itself through the propensity of small clusters to transform in the course of chemical reactions between various energetically accessible structural isomers, thus enhancing the rates for overcoming reaction barriers. (2) quantum size effects that are reflected in size-dependent characteristics of the electronic energy-level spectra of small gold clusters, as well as in charging of the clusters by the support. (3) impurity-doping effects that allow modification and control of the electronic structure and consequent chemical reactivity of small supported clusters.