The synthesis of CuyMnzAl1−zOx mixed oxide as a low-temperature NH3-SCR catalyst with enhanced catalytic performance

Abstract

A new type of low-temperature selective catalytic reduction (SCR) catalyst, Cu_yMn_zAl_1−zO_x, derived from layered double hydroxides is presented in this contribution. By tuning the Cu/Mn/Al ratio, the optimal catalyst Cu₂Mn_0.5Al_0.5O_x resulted in a NO_x conversion of 91.2% at 150 °C, which is much higher than that of all other control catalysts, Cu₂AlO_x (71.1%), Cu–Mn/γ-Al₂O₃ (65.23%), and Mn/γ-Al₂O₃ (59.32%). All samples were characterized in detail using various physico-chemical techniques including XRD, BET, FTIR, TEM, H₂-TPR, NH₃-TPD, and XPS analyses, and the results revealed that the superior catalytic performance of the Cu₂Mn_0.5Al_0.5O_x catalyst can be attributed to its high specific surface area, high reducibility of MnO₂ and CuO species, abundance of surface acid sites, and the good dispersion of MnO₂ and CuO species. FTIR analyses of pyridine adsorbed samples revealed that the catalytic activity is proportional to the amount of Lewis acid sites. Cu₂Mn_0.5Al_0.5O_x also showed much higher resistance to 100 ppm SO₂ and 5% H₂O than the control catalysts. The poisoning mechanism and the regenerability of the Cu₂Mn_0.5Al_0.5O_x catalyst was also investigated. In all, compared with the control catalysts of Cu₂AlO_x, Cu–Mn/γ-Al₂O₃, and Mn/γ-Al₂O₃, the newly designed Cu₂Mn_0.5Al_0.5O_x catalyst is not only more active at low temperatures (100–250 °C), but is also relatively more robust in the presence of SO₂ and H₂O.