Theoretical and experimental studies of Ag-Pt interactions for supported Ag-Pt bimetallic catalysts

The electronic structure and chemical properties of catalysts prepared by the electroless deposition (ED) of Ag onto Pt/SiO2 were studied using a combination of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. XPS studies revealed a negative shift (up to -0.75 eV) in the Ag 3d binding energy (BE) relative to bulk Ag. Both the magnitude and direction of the shift are consistent with DFT calculations of model Ag/Pt(111) surfaces. DFT calculations have also been employed to study the adsorption of two probe molecules, carbon monoxide and 1-epoxy-3-butene (EpB), on the model surfaces. Combined with previously published reports, the results presented here suggest that (1) the AgPt/SiO2 catalysts that are most active for hydrogenation of the EpB olefin function consist of an adlayer of Ag on Pt rather than a surface or bulk alloy and that (2) the higher activity and selectivity of ED-prepared Ag-Pt/SiO2 catalysts for C=C hydrogenation of EpB to 1-epoxybutane are consistent with computed electronic (ligand) and bifunctional effects. (C) 2009 Elsevier B.V. All rights reserved.