AN EXAFS STUDY OF CU/ZNO AND CU/ZNO-AL2O3 METHANOL SYNTHESIS CATALYSTS

Cu K-absorption edge and EXAFS measurements on binary Cu/ZnO and ternary Cu/ZnO-Al2O3 catalysts of varying compositions on reduction with hydrogen at 523 K, show the presence of Cu microclusters and a species of Cu1+ dissolved in ZnO apart from metallic Cu and Cu2O. The proportions of different phases critically depend on the heating rate especially for catalysts of higher Cu content. Accordingly, hydrogen reduction with a heating rate of 10 K/min predominantly yields the metal species (>50%), while a slower heating rate of 0.8 K/min enhances the proportion of the Cu1+ species (approximately 60%). Reduced Cu/ZrnO-Al2O3 catalysts show the presence of metallic Cu (upto 20%) mostly in the form of microclusters and Cu1+ in ZnO as the major phase (approximately 60%). The addition of alumina to the Cu/ZnO catalyst seems to favour the formation of Cu1+/ZnO species.