Unravelling the structure sensitivity of CuO/SiO2 catalysts in the NO + CO reaction

Abstract

CuO/SiO₂ catalysts with a vast difference in copper dispersion were prepared by impregnation (denoted as CuSi-IM) and ammonia-evaporation (denoted as CuSi-AE) methods and tested for NO reduction by CO. Despite the inferior dispersion of copper species in the CuSi-IM catalysts, they exhibited significantly higher NO conversion efficiency, with more than one order of activity enhancement achieved in comparison with the CuSi-AE samples. Ex situ XRD, in situ DRIFTS, and CO-TPR characterization were carried out to study the nature of active copper species and their evolution under reaction conditions. A clear dispersion-dependent reduction behavior (for CuSi-AE, step-wise reduction; for CuSi-IM, one step reduction) under a CO atmosphere was observed, and the generation of Cu⁰ preferentially occurred at lower temperatures for the CuSi-IM samples, which accounted for the better performance in the NO + CO reaction. Lastly, NO-TPD and TPSR experiments were performed and the essential role of Cu⁰ in promoting NO dissociation was proposed. The results of the present study would deepen our understanding on the reaction behaviors of copper catalysts in the NO + CO reaction.