CONTROLLED-ENVIRONMENT XRD STUDY OF CU/ZNO RELATED TO ACTIVITY IN METHANOL DECOMPOSITION

Cu/ZnO catalysts of different compositions and pretreated under different conditions were studied for methanol decomposition. The structural evolution of the catalyst precursors during pretreatment was monitored by controlled-environment X-ray diffraction (XRD). The catalyst activity is affected by the calcination temperature. High-temperature calcination causes a decrease in the activity. The onset temperature for a significant reduction of the catalyst activity depends on the composition and decreases with increasing Cu composition. XRD studies showed that the catalyst precursors decompose to CuO and ZnO during calcination in air. The onset temperature for the formation of crystalline CuO phase also depends on the composition and decreases with increasing Cu composition. The formation of crystalline CuO species in calcination leads to a metallic Cu phase of low dispersion after subsequent hydrogen reduction. It is believed that Cu is the active species. Thus, the catalyst activity can be related to a phase transition during the pretreatment. The catalyst composition determines the maximum calcination temperature, above which a significant loss in activity in methanol decomposition occurs.