TEMPERATURE-PROGRAMMED DESORPTION STUDY ON SUPPORTED COPPER-CONTAINING METHANOL SYNTHESIS CATALYSTS

Cu/ZnO/Al2O3, Cu/ZnO/SiO2 and Cu/ZnO/activated carbon impregnation cat alysts were studied by temperature-programmed desorption (TPD) after m ethanol synthesis from CO/H-2 (1:2) and CO/H-2/CO2 (30:61:9). Carbon m onoxide desorption in the temperature range 575-620 K was attributed t o the decomposition of previously formed formate on ZnO. The amount of formate was less after reaction in CO/H-2/CO2 than in CO/H-2, due to the lower number of adsorption sites (surface oxygen vacancies) on ZnO in CO/H-2/CO2. Carbon dioxide desorption was found after reaction in CO/H-2 in the range 500-570 K and was attributed to decomposition of f ormate on copper. Most catalysts were much more active in CO/H-2/CO2, but the amount of formate detected was usually much smaller. The decom position temperature of the formate was some 40-90 K lower than of the formate formed in CO/H-2, indicating a more reactive species. Evidenc e was found for the formation of formate from CO/H-2 on ZnO and Al2O3 supports. The absence of formate formation on SiO2 and activated carbo n supports could be an explanation for the very low activity of silica - and carbon-supported copper in CO/H-2