Recent efforts in heterogeneous catalysis research have emphasized the goal of more efficient utilization of the precious metal components of supported catalysts. When supported metals exist at or near atomic dispersion, the support surface largely controls the properties of the highly dispersed metal species: the local chemical bonding environment critically influences the electronic structure, and therefore catalytic activity, of metal sites. This presentation will examine the local environments of highly dispersed metals, and discuss how this influences outcomes that are relevant to their use as catalysts.<br/>The framework structures of zeolites afford unique bonding environments for supported metals. The first portion of this presentation discusses zeolites as supports for catalysts containing chromium or platinum – two industrially applied catalyst metals whose intra-zeolite chemistries are not fully resolved in the literature. Primary insights are drawn from the combined use of probe molecular FTIR spectroscopy and X-ray absorption spectroscopy to understand (1) the use of supported chromium cations for the direct and carbon dioxide-assisted dehydrogenation of ethane, and (2) the nature of the structure, bonding, and local environment of cationic platinum species in zeolites, which are key intermediates in the oxidative re-dispersion of platinum clusters within zeolite pores.<br/>The second portion of the presentation will describe studies toward understanding the chemical environments of isolated cations supported by bulk oxides. X-ray absorption spectroscopy – especially extended X-ray absorption fine structure spectra interpreted through calculations using density functional theory – reveals that the local coordination environment of atomically dispersed platinum on magnesium oxide can be controlled by treatment conditions after the initial deposition of metal cations using a simple wet chemical approach. This local environment is shown to critically influence catalytic activity of isolated platinum centers, using carbon monoxide oxidation as a probe reaction.

Understanding the local environments of supported atomically dispersed metal cations: Impacts on catalyst function

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