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