Key factors controlling the catalytic activity of supported noble metal catalysts in oxidizing atmosphere

摘要

Key factors controlling the catalytic activity of supported noble metal catalysts in oxidizing atmosphere was studied. In the propane combustion over supported platinum catalysts, the catalytic activity was enhanced with the electrophilic property of the support materials and the additives. Pt L_(III)-edge XANES spectra of oxidized catalysts showed that the oxidation of platinum was depressed by the electrophilic property of the support materials and the additives. Thus, it is shown that the high performance of platinum with electrophilic supports or additives is due to higher oxidation-resistance provided by the electrophilic supports or additives, since metallic platinum is more active than platinum oxide. The support and the additive effect is attributed to the stabilization of oxo-anion of noble metal like PtO_(#alpha#)~(#delta#-) by the electrophobic supports and additives, since the more electrophobic oxide gives the larger Gibbs free energy change for the formation of binary oxide containing noble metal. This study proposes that the electrophilic/electrophobic property of the support materials and the additives are determinant factors for design of the active noble metal catalysts in the oxidizing atmosphere.