EFFECTS OF ZINC ADDITION TO SILICA-SUPPORTED COPPER-CATALYSTS FOR THEHYDROGENOLYSIS OF ESTERS

When using silica supported copper-zinc oxide catalysts in the hydroge nolysis of methyl acetate, a profound effect of zinc on the activity a nd selectivity of the catalysts has been observed. The activity and se lectivity improve with increasing zinc content. The increase in activi ty is likely to be an effect that originates either from finely disper sed copper particles in close contact with the zinc oxide phase or fro m the promotion of copper metal crystallites by zinc oxide particles. A decrease in ethane formation with higher zinc content is attributed to the elimination of dehydrating surface sites. This lowering of etha ne selectivity goes hand in hand with a higher production of diethyl e ther, which is explained in terms of a less severe dehydration on acid and basic surface sites. Catalysts supported on aerosil are more sele ctive than catalysts supported on sol-gel silica, probably because of differences in the contents of impurities and surface density of hydro xyl groups. In addition to this, a hysteresis has been observed in the conversion as a function of the reaction temperature. The effects hav e been studied in relation to the role of adsorbed hydrogen and the na ture of the adsorbed phase. The increase in the hysteresis with higher zinc content provides indirect evidence for the participation of the zinc oxide component in the activation of the reactants.