Catalytic NO reduction with ammonia at low temperatures on V_2O_5/AC catalysts: effect of metal oxides addition and SO_2

摘要

The catalytic behavior of the V -MI AC (M = W., Mo, Zr, and Sn) catalysts were studied for the NO reduction with ammonia at low temperatures, especially in the presence of SO_2. The presence of the metal oxides does not increase the V205/AC activity but decreases it. Except V-Mo/AC, the other catalysts are promoted by SO_2 at 250°C, especially for V-Sn/AC. However, the promoting effect of SO_2 is gradually depressed by catalyst deactivation. Changes in catalyst preparation method can improve the catalyst stability in short-term but cannot completely prevent the catalyst from a long-term deactivation. Mechanisms of the promoting effect and the deactivation of V -Sn/ AC catalyst by SO_2 were studied using Fourier transform infrared spectroscopy (FT -IR) spectra and measurement of catalyst surface area and pore volume. The results showed that both the SO_2 promotion and deactivation are associated with the formation of sulfate species on the catalyst surface. In the initial period of the selective catalytic reduction (SCR) reaction in the presence of SO_2, the formed sulfate species provide new acid sites to enhance ammonia adsorption and thus the catalytic activity. However, as the SCR reaction proceeds, excess amount of sulfate species and then ammonium-sulfate salts are formed which is stabilized by the presence of tin oxide, resulting in gradual plugging of the pore structures and the catalyst deactivation.