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

Abstract

The poor low-temperature (200–300 °C) activity and N₂ 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/γ-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/γ-Al₂O₃, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/γ-Al₂O₃ exhibited the highest activity/selectivity (i.e., about 90% at 200 °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.