Ge, Mn-doped CeO2–WO3 catalysts for NH3–SCR of NOx: Effects of SO2 and H2 regeneration

Abstract

The addition of Ge and Mn to CeO2–WO3 catalysts for NH3–SCR of NOx was investigated. The effect of calcination temperature and the influence of SO2 on SCR activity were studied, and heat treatment with H2 was used to regenerate sulfated catalysts. The results showed that doping with Ge and Mn enhanced the SCR activity of Ce3W2Ox (molar ratio of Ce:W=3:2) at 100–250°C. More than 95% NOx conversions were obtained between 200 and 470°C over (Ce3W2)0.9Ge0.1Ox-500 (molar ratio of (Ce+W):Ge=9:1, calcined at 500°C) catalyst. The characterization results indicated that the formation of amorphous phase and high atomic ratio of W/Ce on the surface might contribute to the high activity over (Ce3W2)0.9Ge0.1Ox-500. The NOx conversions decreased over Ce3W2Ox series catalysts calcined at 700°C, however, the activities of (Ce3W2)0.9Ge0.1Ox calcined at 700°C were higher than those of the others, suggesting the addition of Ge weakened the effect of high calcination temperature. The deactivation of (Ce3W2)0.9Ge0.1Ox-500 by SO2 was much slower than that of Ce3W2Ox-500. The sulfated (Ce3W2)0.9Ge0.1Ox-500 catalysts could be easily regenerated by heat treating with H2 at 300°C since the sulfates species were unstable over these catalysts. H2 regeneration is an effective way to recycle GeO2–CeO2–WO3 catalyst.