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 terna ry Cu/ZnO-Al2O3 catalysts of varying compositions on reduction with hy drogen at 523 K, show the presence of Cu microclusters and a species o f Cu1+ dissolved in ZnO apart from metallic Cu and Cu2O. The proportio ns of different phases critically depend on the heating rate especiall y 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 proport ion of the Cu1+ species (approximately 60%). Reduced Cu/ZrnO-Al2O3 cat alysts 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.