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

The dynamics of the selective catalytic reduction (SCR) reaction over a commercial V 2 O 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 2 O 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.

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