Insights into the active sites of copper species in CuO/SiO2 catalysts for NH3-SCR: Quantitative analysis and mechanism study

Cu-based catalysts are attractive for selective catalytic reduction of NO with NH3 (NH3-SCR). However, the inherent contribution from different copper species is still elusive. Herein, by adopting a novel solvent-free preparation, CuO/SiO2 catalysts with controlled copper species (highly dispersed CuO, clustered CuO and bulk CuO) were constructed for investigation. Evidence for the presence of distinct copper species was provided by diverse characterizations like XRD, N2 sorption, TEM and XPS. Quantitative analysis based on the number of active sites disclosed the reaction rates for different copper species actually followed the order of highly dispersed CuO (0.19–0.3 min−1) > bulk CuO (0.14 min−1) > clustered CuO (0.03 min−1). Regarding the crucial information of activity contribution and reaction mechanism, results from NO/NH3-TPD, kinetics measurement and in situ DRIFTS conveyed that despite with the unique feature of more NO2 generation, the presence of clustered CuO induced the formation of stable NOx species and aggravation of NH3 oxidation, delivering a detrimental effect on NO conversion. As a contrast, the formation of highly dispersed CuO was advantageous to enhance NH3 adsorption and NOx activation via weakly bonded NOx species, which accelerated the reaction via both L-H and E-R pathways.