Combined effects Na and SO2 in flue gas on Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO by NH3 simulated by Na2SO4 doping

Abstract A series of Mn-Ce/TiO 2 catalysts were synthesized through an impregnation method and used for low temperature selective catalytic reduction (SCR) of NOx with ammonia (NH 3 ). Na 2 SO 4 was added into the catalyst to simulate the combined effects of alkali metal and SO 2 in the flue gas. Experimental results showed that Na 2 SO 4 had strong and fluctuant influence on the activity of Mn-Ce/TiO 2 , because the effect of Na 2 SO 4 included pore occlusion and sulfation effect simultaneously. When Na 2 SO 4 loading content increased from 0 to 1 wt.%, the SCR activities of Na 2 SO 4 -doped catalysts decreased greatly. With further increasing amount of Na 2 SO 4 , however, the catalytic activity increased gradually. XRD results showed that Na 2 SO 4 doping could induce the crystallization of MnOx phases, which were also confirmed by TEM and SEM results. BET results showed that the surface areas decreased and a new bimodal mesoporous structure formed gradually with the increasing amount of Na 2 SO 4 . XPS results indicated that part of Ce 4+ and Mn 3+ were transferred to Ce 3+ and Mn 4+ due to the sulfation after Na 2 SO 4 deposition on the surface of the catalysts. When the doped amounts of Na 2 SO 4 increased, NH 3 -TPD results showed that the Lewis acid sites decreased and the Bronsted acid sites of Mn-Ce/TiO 2 increased quickly, which could be considered as another reason for the observed changes in the catalytic activity. The decreased Mn and Ce atomic concentration, the changes of their oxidative states, and the variation in acidic properties on the surface of Na 2 SO 4 -doped catalysts could be the reasons for the fluctuant changes of the catalytic activity.