Nano-Scale Environmental Effects In the Reactivity of Platinum Clusters

Recent advances in techniques for synthesizing supported, size-defined metal clusters have brought single-site, size-defined nano-catalysts closer to reality. The effect of size and interaction with the chemical environment will however need to be thoroughly understood before this type of novel catalyst can be successfully deployed. The ability of theory to investigate the properties of objects in this size regime makes it a powerful tool for nano-catalysis research. The versatility of platinum catalysts in many important environmental and energy applications, and the high cost of the platinum metal makes Pt a prime candidate for going “nano.” Therefore, we have performed density functional theory calculations to examine the oxidation of a series of small isolated Pt clusters (Pt_x, x=1-5,10), and compare the reactivity of the reduced and oxidized clusters by examining their response toward two model oxidation reactions, CO and NO oxidation. Strongly size-dependent and non-bulk-like behaviors are revealed. We also examine the effect of support on the clusters by comparing the molecular and electronic structures and the oxidation of several isolated Pt_x clusters vs. their MgO(100)-supported counterparts. The results provide insight into the coupling among reactivity, particle size, chemical environment, and support, and complement experiments in exploring the chemistry of supported metal clusters.