Effect of SO2 on the Low-Temperature Selective Catalytic Reduction of Nitric Oxide with Ammonia over TiO2, ZrO2, and Al2O3

Abstract

The selective catalytic reduction (SCR) of NO to N 2 by NH 3 over TiO 2 , ZrO 2 , and Al 2 O 3 was studied at 90°C using a feed stream that was simulated to represent the effluent from a coal combustion boiler. The effects of SO 2 on the reduction of NO were studied. It is interesting that the SCR reaction was interrupted when SO 2 was absent from the feed gas. This indicated that SO 2 participated in the reduction process of NO at low temperature. A mechanism for this low-temperature SCR process was proposed, which was based on the reaction results and studies of NO, NH 3 , and SO 2 temperature-programmed desorption (TPD) profiles under different experimental conditions. Among the three catalysts, ZrO 2 and TiO 2 had higher activities than Al 2 O 3 . The selectity to N 2 over the different catalysts changed in the sequence of ZrO 2 >TiO 2 >Al 2 O 3 . The activities of these three catalysts decayed with reaction time as a result of the accumulation of ammonium sulfate and nitrate salts plugged in the pores of the catalysts. However, the deactivated catalysts could be easily regenerated by washing with water.