Hysteresis during CO-oxidation activity measurements on carbon-supported copper/chromium catalysts†

Carbon-supported catalysts containing Cu and Cr are active in oxidation and reduction reactions. In CO oxidation experiments, an activity hysteresis has been observed for the Cu/Cr-carbon catalyst during temperature cycling. From results of CO oxidation experiments and Temperature-Programmed Reduction (TPR) in CO of fresh, pre-reduced and pre-oxidized samples, it is concluded that an oxidation–reduction cycle of the active phase is the reason for this hysteresis phenomenon. Furthermore, TPR(CO) reveals the presence of highly active oxygen species on a Cu/Cr catalyst, which might be the reactive intermediate in CO oxidation. It is also shown that the active phase catalytically oxidizes the carbon support, resulting in a high TPR(CO) background.