Catalytic NO reduction with ammonia at low temperatures on V2O5/AC catalysts: effect of metal oxides addition and SO2

The catalytic behavior of the: V-M/AC (M = W, Mo, Zr, and Sn) catalysts wer e studied for the NO reduction with ammonia at low temperatures, especially in the presence of SO2. The presence of the metal oxides does not increase the V2O5/AC activity but decreases it. Except V-Mo/AC, the other catalysts are promoted by SO2 at 250 degreesC, especially for V-Sn/AC. However, the promoting effect of SO2 is gradually depressed by catalyst deactivation. Ch anges in catalyst preparation method can improve the catalyst stability in short-term but cannot completely prevent the catalyst from a long-term deac tivation. Mechanisms of the promoting effect and the deactivation of V-Sn/A C catalyst by SO2 were studied using Fourier transform infrared spectroscop y (FT-IR) spectra and measurement of catalyst surface area and pore volume. The results showed that both the SO2 promotion and deactivation are associ ated with the formation of sulfate species on the catalyst surface. In the initial period of the selective catalytic reduction (SCR) reaction in the p resence of SO2, the formed sulfate species provide new acid sites to enhanc e ammonia adsorption and thus the catalytic activity. However, as the SCR r eaction proceeds, excess amount of sulfate species and then ammonium-sulfat e salts are formed which is stabilized by the presence of tin oxide, result ing in gradual plugging of the pore structures and the catalyst deactivatio n. (C) 2001 Elsevier Science B.V. All rights reserved.