Bus Eveline, van Bokhoven Jeroen A
Institute for Chemical Engineering and Bioengineering, ETH Zurich, 8093, Zurich, Switzerland.
Phys Chem Chem Phys. 2007 Jun 14;9(22):2894-902. doi: 10.1039/b701402c. Epub 2007 Apr 10.
Alloyed catalysts receive considerable attention, because of their unique catalytic properties; they often show higher selectivity, activity, and stability compared to the pure metal particles. To provide insights in the origins of these features, we report the structure and the interaction of hydrogen with each of the metals in an intimately mixed platinum-gold catalyst and compare these characteristics to those in the single metal particles. X-Ray absorption spectroscopy (XAS) and electron microscopy analysis showed that the structure of the mixed particle differed from the single metal particles. The interaction of platinum with hydrogen is stronger than the H-Au interaction and the adsorption sites were different. EXAFS analysis showed that the structure of the platinum clusters changes with increasing hydrogen coverage, observed as a relaxation of the contracted Pt-Pt distance and an increase in the Pt-Pt coordination number. No such changes were observed for gold clusters. Well-mixed PtAu-alloy clusters, with a bulk Au-to-Pt ratio of two, supported on SiO(2), adsorb hydrogen on both platinum and gold atoms, which indicates that gold cannot be regarded as an inert metal. The heat of adsorption on the platinum ensembles does not decrease upon alloying; the weakening of the overall hydrogen adsorption strength when alloying platinum with gold is an ensemble-size effect.
合金催化剂因其独特的催化性能而备受关注；与纯金属颗粒相比，它们通常表现出更高的选择性、活性和稳定性。为了深入了解这些特性的起源，我们报告了紧密混合的铂-金催化剂中每种金属与氢的结构和相互作用，并将这些特性与单金属颗粒中的特性进行比较。X射线吸收光谱（XAS）和电子显微镜分析表明，混合颗粒的结构与单金属颗粒不同。铂与氢的相互作用比氢-金相互作用更强，且吸附位点不同。扩展X射线吸收精细结构（EXAFS）分析表明，铂簇的结构随着氢覆盖率的增加而变化，表现为收缩的铂-铂距离的松弛和铂-铂配位数的增加。金簇未观察到此类变化。负载在SiO(2)上的体相金与铂比例为2的充分混合的铂金合金簇在铂和金原子上均吸附氢，这表明金不能被视为惰性金属。合金化后，铂簇上的吸附热并未降低；铂与金合金化时整体氢吸附强度的减弱是一种簇尺寸效应。
