Activity Enhancement of W–CeZr Oxide Catalysts by SO2 Treatment in NH3-SCR

Abstract

The impact of sulphur and hydrothermal aging on W–CeZr and CeZr catalysts was investigated. Sulphur treatments for W–CeZr and CeZr were done in the absence and presence of water (S- and S + H2O-treatments, respectively) for 5 h at 400 °C. Similarly, hydrothermal aging (H2O-treatment) for W–CeZr and CeZr catalysts was done in a gas phase. The W and S contents were analyzed using XRF. The studied catalysts were characterized by BET, BJH, DRIFTS, XPS and NH3 desorption methods. In addition, the activity of the catalysts was tested in NH3-SCR reaction. The NOx conversion over the fresh W–CeZr catalyst was 85 % at 350 °C whereas the fresh CeZr was not active in NOx reduction. In the case of W–CeZr and CeZr catalysts, S + H2O and S-treatments increased the NOx conversion up to 92–98 % at the temperature range of 350–400 °C. The increased portion of chemisorbed oxygen due to S- and S + H2O-treatments enhances the NOx reduction reactions. The water treatment had no effect on the NH3-SCR activity which indicates that the S-compounds are the major reason for enhanced activity.