Modeling catalytic reduction of NO by ammonia over V2O5

Preservation of the natural environment and therefore elimination of pollutants has become a major concern in the present world, NOx is efficiently removed from the gas exhausts produced by fixed plants by the selective catalytic reduction processes where NOx is reduced by ammonia. Despite the wide use of this process, many aspects concerning the reaction mechanism are still poorly understood. The reaction is very exothermic but requires a catalyst. Here we report the present status of the proposed mechanisms for the selective catalytic reduction of NO by ammonia on V2O5/titania catalyst. The discussion is centered on the last decade and focuses on new theoretical findings in the field. We provide ab initio calculations based on cluster and periodic models to analyze the adsorption of the reactants in reduced, oxidized and stoichiometric surfaces, assuming dry and wet conditions, to evaluate the intermediates proposed in the literature. Several conditions are settled to propose an active catalyst. Coadsorption is investigated and in dry conditions quasi spontaneous reaction is obtained on an oxidized catalyst when the model includes NO and NE3 and is allowed easy hydration-dehydration processes. We conclude that adsorption of reactants takes place on reactive O sites provided by the catalyst, V2O5 dispersed on TiO2-anatase phase. Dispersion is essential to generate reactive O atoms necessary for a good catalytic activity. Finally, we propose a new pathway to proceed in oxidizing conditions. Results are compared to recent theoretical calculations and to experimental data. (C) 2004 Elsevier B.V. All rights reserved.