Simultaneous removal of SO2 and NOx from flue gas using a CuO/Al2O3 catalyst sorbent: II. Promotion of SCR activity by SO2 at high temperatures

Promoting effect of SO2 on selective catalytic reduction (SCR) of NO by NH3 over a CuO/Al2O3 catalyst sorbent has been investigated. Transient experiment, X-ray photoelectron spectroscopy (XPS), in situ DRIFT, NH3-TPD, and temperature-programmed reduction (TPR) were used to evaluate the promoting mechanism. The results show that the presence of SO2 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/Al2O3 catalyst sorbent. Sulfation of CuO/Al2O3 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 H2 suggest that sulfation of the catalyst sorbent weakens the catalystʹs oxidation ability and inhibits NH3 oxidation to NO in the process of SCR, which may be another main promoting effect of SO2 on SCR.