Inhibition of carbon monoxide on methanol oxidation over γ-alumina supported Ag, Pd and Ag-Pd catalysts

The activities of CH₃OH and CO oxidative reactions over the γ-alumina supported Ag, Pd and Ag-Pd catalysts were measured with the MR-GC method. The CO-temperature-programmed desorption (CO-TPD) and in situ IR techniques were used to characterize the CO adsorption behavior on the surface of the catalysts. The oxidative activity for CO to CO₂ increased in the following sequence: 5% Ag/γ-Al₂O₃ < 0.1% Pd/γ-Al₂O₃ < 5% Ag-0.1% Pd/γ-Al₂O₃. An inhibition action of CO to CH₃OH oxidation, that is dependent of the active components of the catalysts, was observed when CO was present in the methanol-fed stream. The results of IR and CO-TPD showed that the poor oxidative activity of CO over Ag catalyst was due to its low adsorption capacity on this catalyst. The very strong adsorption ability of CO on the Pd catalyst was responsible for the strong inhibition of CO to CH₃OH oxidation activity. The plausible mechanisms of CO strong inhibition behavior on methanol oxidation over the different catalysts are discussed in detail from the viewpoints of both electronic and geometric effects.