Effects of the Fe/Ce ratio on the activity of CuO/CeO2-Fe2O3 catalysts for NO reduction by CO

Copper catalysts on Fe-loaded ceria were studied for NO reduction by CO. Catalysts with different Fe/Ce molar ratios (Cu/C1Fx) were synthesized by a wet impregnation method. Catalysts were characterized by XRD, BET, Raman, EPR, H-2-TPR and in situ DRIFTS. CuO was highly dispersed on the support surface to form active species. Ceria modification by incorporation of a lower amount of Fe3+ was beneficial for NO conversion and N-2 selectivity as compared with pure ceria and iron-rich ones, which resulted from the strong interaction between ceria and iron. Cu/C1F1 showed better catalytic performance at 100-200 degrees C, whereas Cu/C1F0.5 gave higher N-2 selectivity than the other samples. In situ DRIFTS suggested that iron-rich catalysts ensured inhibition of NO reduction by increasing the partial pressure of NO. Two mechanisms could explain formation of the NCO intermediate and N2O intermediate over ceria-rich catalysts. With an increase in the Fe/Ce molar ratio and temperature, a mechanism in which N2O is the intermediate dominates the reaction, whereas a process in which NCO species are produced as intermediates results in their gradual disappearance.