Simultaneous removal of SO 2 and NO x from flue gas using a CuO/Al 2O 3 catalyst sorbent : II. Promotion of SCR activity by SO 2 at high temperatures

Abstract

Promoting effect of SO 2 on selective catalytic reduction (SCR) of NO by NH 3 over a CuO/Al 2O 3 catalyst sorbent has been investigated. Transient experiment, X-ray photoelectron spectroscopy (XPS), in situ DRIFT, NH 3-TPD, and temperature-programmed reduction (TPR) were used to evaluate the promoting mechanism. The results show that the presence of SO 2 in the reaction stream can significantly promote catalytic activity of NO reduction at temperatures above 300 °C due to the formation of sulfate species on the catalyst surface. Sulfate species affect SCR activity by changing the acidity and redox property of the catalyst sorbent. In situ DRIFT shows that only ammonia coordinated on Lewis acid sites is found on the CuO/Al 2O 3 catalyst sorbent. Sulfation of CuO/Al 2O 3 catalyst sorbent greatly increases the concentration and strength of Lewis acid sites and the concentration of Brønsted acid sites. However, the ammonia bound to Brønsted acid sites does not play an important role in the SCR reaction in the catalyst system. Moreover, there is a close relationship between the SCR activity and ammonia oxidation activity. Ammonia oxidation experiments and TPR in H 2 suggest that sulfation of the catalyst sorbent weakens the catalyst's oxidation ability and inhibits NH 3 oxidation to NO in the process of SCR, which may be another main promoting effect of SO 2 on SCR.