Novel sol-gel-derived Ag/SiO2-Al2O3 catalysts for highly selective oxidation of methanol to formaldehyde

Novel Ag/SiO2-Al2O3 catalysts with low silver content prepared by the sol-gel method exhibit excellent catalytic properties in the catalytic oxidation of methanol to formaldehyde. The silver content was as low as 2% and the yield of formaldehyde was achieved as 90.3%, which is 16% higher than that of pumice-supported silver and even 5-6% higher than that of a commercial electrolytic silver catalyst. XRD, XPS and SEM results reveal that all silver was present as Ag+ before catalytic reaction and was partially reduced to the metallic state after the reaction. It was also found that silver was aggregated on the surface after its reduction.