Study on chemisorption of H2, O2, CO and C2H4 on Pt-Ag/SiO2 catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO2 Catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H-2, O-2, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H-2 and O-2 adsorption that the addition of Ag to Pt/SiO2 leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO2 catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO2. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemsorption of C2H4 on Pt-Ag/SiO2. The differential heat vs. uptake plots for C2H4 adsorption on the oxygen-preadsorbed Pt/SiO2 and Pt-Ag/SiO2 catalysts suggest that the incorporation of Ag to Pt/SiO2 could decrease the ability for the oxidation of C2H4.