Transient response method applied to the kinetic analysis of the DeNO x–SCR reaction

Abstract

The dynamics of the selective catalytic reduction (SCR) reaction over a commercial V 2O 5–WO 3/TiO 2 catalyst is investigated by concentration programmed surface reaction (CPSR), i.e. a modified transient response method based on linear temporal evolution of the reactant feed concentrations. The adsorption–desorption of the reactants NH 3 and NO and their surface reaction are addressed independently. The data confirm that over the investigated catalyst NH 3 is stored on the catalyst surface, and that the reaction occurs between adsorbed NH 3 and gaseous or weakly adsorbed NO. H 2O significantly inhibits the SCR reaction, but this effect is not due to competition with NH 3 for the adsorption on the surface acid sites at any surface coverage. A slight inhibiting effect of adsorbed NH 3 on the SCR reaction is also evident. The whole set of data is quantitatively described according to a dynamic kinetic model which superimposes the surface reaction of NO reduction to the NH 3 adsorption–desorption processes, and accounts for NH 3 oxidation at high temperatures. It is also shown that the transient SCR–DeNO x data, as well as the related kinetic analysis, approach steady-state data in the limit of slow variations.