Changes in bimetallic silver – platinum catalysts during activation and oxidation of methanol and propene

Abstract

A series of bimetallic silver-platinum catalysts based on pure-silica mesostructured cellular foam (MCF) with various Ag/Pt atomic ratios were prepared, tested in methanol oxidation and propene oxidation and characterized by UV–vis spectroscopy, X-Ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS) and Transmission Electron Microscopy (TEM). Bimetallic catalysts were not more active than monometallic ones in propene oxidation but their selectivity to acrolein was significantly higher, especially over 4AgPt/M activated in inert gas. This catalyst showed also high activity and selectivity to methyl formate in methanol oxidation. Upon activation of the catalysts in different environments and oxidation reactions, the reduction of silver oxide and segregation of bimetallic nanoparticles took place. This effect was the highest upon activation in hydrogen flow and was responsible for exposition of metallic platinum leading to high conversion of substrates (methanol or propene) and their total oxidation. Segregation of bimetallic species and increasing dispersion after activation and exposition of the activated samples to the reagents (propene, methanol, oxygen) were consequences of the mobility of silver species and their susceptibility to change the oxidation state.