Influence of cobalt on performance of Cu–CeO2 catalysts for preferential oxidation of CO

Abstract

Copper and cobalt oxides supported on CeO2 were investigated for preferential oxidation of carbon monoxide (CO-PROX) in the presence of excess hydrogen and CO2. (CuO)1−x(Co3O4)x/3−(CeO2)2.5 (x = 0, 0.25, 0.50, 0.75, 0.85 and 1) catalysts were prepared by coprecipitation method. These mixed oxide catalysts were characterized by several physicochemical techniques, such as BET surface area (SBET), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). XRD studies show the peaks related to CuO and Co3O4 phases in copper and cobalt containing CeO2 catalysts. The average particle size of the CeO2 crystallites is in the range of 8–10 nm as evaluated from HRTEM studies. XPS studies demonstrate that Cu, Co and Ce in (CuO)1−x(Co3O4)x/3−(CeO2)2.5 catalysts are presented in +2 and +1, +3 and +2 and +4 and +3 oxidation states, respectively. The catalyst with x = 0.75 shows better activity and selectivity towards CO-PROX. Though the catalyst with only copper (CuO–CeO2, x = 0) shows good activity but reverse water gas shift (RWGS) reaction is noticed at high temperature. On the other hand, RWGS reaction is suppressed on the cobalt containing CuO–CeO2 catalyst. Cobalt on CeO2 with x = 1 shows hardly any activity for PROX reaction at low temperatures. No methanation activity is observed on CuO–CeO2 or Co3O4–CeO2 catalysts. In contrast, combination of copper and cobalt on CeO2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.