Promoted partial oxidation activity of supported Ag catalysts in the gas-phase catalytic oxidation of benzyl alcohol

The gas-phase catalytic oxidation of benzyl alcohol was carried out using Ag catalysts impregnated on a SiO2 or CaO support, as well as a potassium-added counterpart (K/Ag/SiO2), to clarify the surface state of the Ag species active in the oxidation reaction, the effect of the basic support and the added alkali metal. Benzaldehyde was obtained as the main oxidation product. The effects of the calcination temperature of the Ag/SiO2 catalyst and the reaction temperature on oxidation activity were investigated. The benzaldehyde yield markedly increased between 553 and 593 K. Increasing the calcination temperature from 773 to 1173 K also caused a significant increase in partial oxidation activity. Both a CaO support for the Ag species and potassium added to the Ag/SiO2 catalyst promoted partial oxidation at a comparatively low reaction temperature. X-ray diffraction and extended X-ray absorption fine structure demonstrated that a high calcination temperature, a basic support, and addition of an alkali metal led to a more ready reduction of the supported Ag to metallic Ag. Oxidized surface Ag species on the metallic Ag were inferred to be the active Ag components for the partial oxidation of benzyl alcohol based on the amount of O2 uptake and the diffuse reflectance spectra of the supported Ag catalysts.