Effects of K<sub>2</sub>O and SO<sub>2</sub> on the selective catalytic reduction of NO by NH<sub>3</sub> over CuO/Al<sub>2</sub>O<sub>3</sub> catalyst

Abstract

CuO/Al 2 O 3 catalyst containing 2 wt% CuO was prepared by pore volume impregnation of γ-Al 2 O 3 with an aqueous solution of Cu(NO 3 ) 2 and then calcination. K 2 O was loaded onto the catalyst with an aqueous solution of KNO 3 as the precursor. The catalysts were sulphated before being subjected to an activity test. Activity test was performed at 400 o C to investigate the effect of K 2 O and SO 2 on the selective catalytic reduction of NO by NH 3 over CuO/Al 2 O 3 catalyst. The catalyst samples were characterized by ICP-MS, XRD, IS-FTIR, NH 3 -TPD and H 2 -TPR to elucidate the possible poisoning reason. Results indicate that in the absence of SO 2 , K 2 O promotes conversion of CuSO 4 to water-insoluble copper, possibly due to reduction of CuSO 4 to Cu 3 N by NH 3 . This reaction consumes the NH 3 for SCR reaction and weakens acidity of the catalyst, which are responsible for the reduced SCR activity by K 2 O. In the presence of SO 2 , conversion of CuSO 4 to water-insoluble copper is inhibited, and the net influence of SO 2 on the SCR activity is determined by the promotion of SO 4 2− on the acidity of the catalyst, the competitive adsorption between SO 2 and NH 3 , and the weakened acidity of the catalyst caused by K 2 O. SO 2 reduces the SCR activity of the catalyst without K 2 O, has no influence at K/Cu ratio of 0.13, and promotes the SCR reaction at K/Cu ratios of higher than 0.13.