EFFECT OF ALKALI-METAL PROMOTER ON SILICA-SUPPORTED COPPER-CATALYSTS IN BENZYL ALCOHOL OXIDATION

The effect of alkali metals, such as Na, added to silica-supported cop per (Cu/SiO2) catalysts has been studied in the gas-phase catalytic ox idation of benzyl alcohol. The main products were benzaldehyde as a pa rtial oxidation product and carbon dioxide as a complete oxidation pro duct. The silica-supported copper catalysts were prepared using both i on-exchange and impregnation methods. The catalyst prepared by the imp regnation method (Cu-imp/SiO2) had a higher oxidation activity than (C u-ex/SiO2) prepared by the ion-exchange method. The effects of reactio n temperature and the amount of supported Cu on the oxidation activity were investigated using the catalysts both with and without added Na. The addition of alkali metal to the silica-supported copper catalysts prepared by both methods was found to promote the oxidation activity, particularly the partial oxidation activity. The coordination and red ox properties of the Cu/SiO2 catalysts, with and without alkali metal, were investigated using diffuse reflectance (DR) spectroscopy and tem perature-programmed reduction (TPR) measurements. It is suggested, bas ed on the DR spectra, that the alkali-metal added to the Cu/SiO2 catal ysts decreases the electronegativity of the supported Cu species; this decrease makes dissociative oxygen adsorption easier. The other role of the added alkali metal was thought to be to remove the oxidic Cu sp ecies which do not have catalytic activity for the partial oxidation.