ACTIVITY-ENHANCED COPPER-ZINC BASED CATALYSTS FOR THE HYDROGENOLYSIS OF ESTERS

For silica-supported copper-zinc catalysts, a fivefold enhancement of the activity in the hydrogenolysis of methyl acetate has been obtained by high-temperature reductions in the range between 550 K and 700 K. Furthermore, simultaneously, the selectivity was significantly improve d. At equal conversion of methyl acetate, catalysts reduced at high te mperature make less side products than catalysts reduced at low temper ature. The selectivities to methane and ethane as a function of the re duction temperature indicate that these side products are formed on co pper metal sites. The formation of ethene most likely proceeds by dehy dration of ethanol on acid sites. The presence of copper crystallites in the range of 3-5 nm and the absence of crystalline zinc oxide were established by X-ray diffraction. The activity increase is ascribed to the formation of additional highly active copper sites in interaction with the zinc-containing phase. Fourier-transform infrared spectrosco py of adsorbed carbon monoxide confirmed that metallic copper is more important in the activity than oxidized copper. Reduction at 750 K res ults in brass formation and catalyst deactivation by evaporation of zi nc. The enhanced catalyst activity can be preserved by passivation and is therefore relevant to practical applications. After passivation an d prolonged exposure to air the original high activity can be restored by low-temperature reduction.