Treatment induced remarkable enhancement of low-temperature activity and selectivity of copper-based catalysts for NO reduction

The poor low-temperature (200-300 degrees C) activity and N-2 selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offers a simple but very promising strategy to achieve this goal by CO pre-treatment of the binary CuM/gamma-Al2O3 (M = V, Mn, Fe, Co, Ni, Zn) catalysts to tailor the surface active sites. The results demonstrate that CO pre-treatment significantly enhanced the low temperature NO conversion and N2 selectivity of CuM/gamma-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/gamma-A(l)2O(3) exhibited the highest activity/ selectivity (i.e., about 90% at 200 degrees C) and excellent stability. The activity improvement resulted from the following: 1) the obtainment of oxygen vacancies and more Cu+ species with the suitable ratio of dispersed Cu2+/Cu+, 2) the decrease of apparent activation energy for NO conversion and 3) the more favourable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transform infrared (FTIR) spectroscopy results.