Coexistence of Cu+ and Cu2+ in star-shaped CeO2/CuxO catalyst for preferential CO oxidation

Star-shaped CeO2/CuxO catalysts very effective towards the CO-PROX reaction were synthesized by the impregnation method and characterized via FESEM, XRD, N-2 physisorption, H-2-TPR, XPS and in-situ DRIFTS. The importance of this work lies in the fact that the Cu oxidation state in the CeO2/CuxO catalysts was correlated with their activity and the former was influenced by the calcination temperature applied. In particular, CeO2/CuxO calcined at 300 and 350 degrees C consist of Cu+ and Cu2+ and their catalytic activity is higher than that of CeO2/CuxO calcined at 400 degrees C for which copper is in the Cu2+ state, as well as that of CeO2/CuxO calcined at 250 degrees C for which copper is in the Cu+ state. The star -shaped CeO2/CuxO catalysts calcined at 300 and 350 degrees C due to the presence of sufficient surface Cu+ and Cu2+ concentrations result in an enhanced CO-PROX performance. The slight deactivation observed after 30 h on reaction stream at T = 115 degrees C can result from the small progressive reduction of Cu+ and formation of carbonate and bicarbonate species on the catalyses surface.