THE SYNERGY BETWEEN CU AND ZNO IN METHANOL SYNTHESIS CATALYSTS

The hydrogenation of CO2 over physically-mixed Cu/SiO2 and ZnO/SiO2 wa s carried out to clarify the synergetic effect between Cu and ZnO in C u/ZnO methanol synthesis catalysts. The activity of the physical mixtu res significantly increased with increasing reduction temperature in t he range of 573-723 K. TEM-EDX results definitely showed that ZnOx moi eties migrated from ZnO/SiO2 particles onto the surface of Cu particle s when the physical mixtures were reduced at high temperatures above 5 73 K. Upon the migration of the ZnOx species, the oxygen coverage on t he surface of Cu, measured after the hydrogenation of CO2, increased w ith the reduction temperature. The results clearly showed that the syn ergetic effect of ZnO in the physical mixtures can be ascribed to the creation of active sites such as Cu+ which the ZnOx moieties stabilize on the Cu surface. Further, XRD results showed that the migrated ZnOx species partly dissolved into the Cu particles to form a Cu-Zn alloy.