Kinetics of Selective Catalytic Reduction of Nitric Oxide by Ammonia over Vanadia/Titania

A kinetic model based on a previously proposed reaction scheme was used to describe reaction kinetics measurements for the selective catalytic reduction of nitric oxide by ammonia over a 6 wt% vanadia/titania catalyst in the presence of oxygen (2 mol%) at nitric oxide and ammonia concentrations from 100 to 500 ppm and at temperatures of 523 and 573 K. This reaction scheme involves adsorption of ammonia on Brønsted acid sites (V5+–OH), followed by activation of ammonia via reaction with redox sites (V=O). This activated form of ammonia reacts with gaseous or weakly adsorbed NO, producing N2and H2O, and leading to partial reduction of the catalyst. The V4+–OH species formed by the selective catalytic reduction (SCR) reaction combine to form water, and the catalytic cycle is completed by reaction of the reduced sites with O2. Water adsorbs competitively with ammonia on acid sites. This reaction scheme can be used to describe the kinetics of the SCR reaction under laboratory as well as under industrially relevant reaction conditions.