Reactivity of V{sub 2}O{sub 5} catalysts for the selective catalytic reduction of NO by NH{sub 3}: Influence of vanadia loading, H{sub 2}O, and SO{sub 2}

A systematic investigation of the selective catalytic reduction (SCR) of NO by NH{sub 3} over V{sub 2}O{sub 5}/TiO{sub 2} catalysts of variable vanadia loading has been carried out at 623 K. Kinetic studies were conducted both in the presence and in the absence of H{sub 2}O and SO{sub 2}. The structure of the various catalysts, as well as adsorbed species present on their surface, was characterized by in situ Raman and infrared spectroscopies. Under dry and SO{sub 2}-free conditions, the turnover frequency of the SCR reaction was found to go through a maximum with vanadia surface coverage at approximately half a monolayer. The observed decrease in the SCR turnover frequency at vanadia surface coverages exceeding half a monolayer can be attributed to the loss of strong acid sites which are associated with the TiO{sub 2} support. Addition of H{sub 2}O to the reacting gas mixture results in a decrease in the SCR turnover frequency of approximately 40-50%, which is independent of the vanadia surface coverage. In situ Raman results suggest that such a decrease can be attributed to the competitive adsorption of H{sub 2}O on the active vanadia sites. The presence of SO{sub 2} in the gas phase during themore » SCR reaction results in a significant increase of the turnover frequency at low vanadia surface coverages, while is has no effect at vanadia surface coverages above half a monolayer. Raman and infrared results suggest that the effect of SO{sub 2} can be attributed to the formation of surface sulfate species, which are only present on the titania surface below half a monolayer coverage due to repulsive interactions between the surface vanadia and sulfate species. 32 refs., 5 figs., 2 tabs.« less