Getting insight into the effect of CuO on red mud for the selective catalytic reduction of NO by NH3

A series of copper-modified red mud catalysts (CuO/PRM) with different copper oxide contents were synthesized by wet impregnation method and investigated for selective catalytic reduction of NO by NH3 (NH3-SCR). The catalytic results demonstrated that the red mud catalyst with 7 wt% CuO content exhibited the excellent catalytic performance as well as resistance to water and sulfur poisoning. The red mud support and copper-containing catalysts were characterized by XRF, XRD, N2 adsorption-desorption, HRTEM, EDS mapping, XPS, H2-TPR, NH3-TPD and in situ DRIFT. The obtained results revealed that well dispersed copper oxide originating from 1 to 7 wt% CuO contents was more facile for the redox equilibrium of Cu2+ + Fe2+ ↔ Cu+ + Fe3+ shifting to right to form Cu+ and surface oxygen species than crystalline CuO generating from high CuO loading (9 wt% CuO), which was beneficial to the enhancement of reducibility and the formation of Lewis acid sites on the catalyst surface. All these factors made significant contributions to the improvement of NH3-SCR activities for CuO/PRM catalysts. Moreover, in situ DRIFT analysis combined with DFT calculated results confirmed that the finely dispersed copper species not only enhanced the NH3 activation but also promoted the NOx desorption, which synergistically facilitated the NH3-SCR process via the Eley-Rideal mechanism.