Unravelling the structure sensitivity of CuO/SiO2 catalysts in NO + CO reaction
CuO/SiO2 catalysts with 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 CuSi-IM catalysts, they exhibited significantly higher NO conversion efficiency, with more than one order of activity enhancement achieved in comparison with CuSi-AE samples. Ex situ XRD, in situ DRIFTS, and CO-TPR characterizations 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 CO atmosphere was observed, and the generation of Cu0 preferentially occurred at lower temperatures for CuSi-IM samples, which accounted for the better performance in NO+CO reaction. Lastly, NO-TPD and TPSR experiments were operated and the essential role of Cu0 in promoting NO dissociation was proposed. The results of present study would deepen our understanding on the reaction behaviors of copper catalysts in NO + CO reaction.