Simulating the Effects of Poisoning on the Rate of the Oxidation of Ammonia over a V<sub>2</sub>O<sub>5</sub>/TiO<sub>2</sub> Monolithic Diesel SCR Catalyst Using a Multichannel Model

Abstract

The background to this study is the need to find out if some reactions of O 2 oxidation of ammonia oxidation are important in the Selective Catalytic Reduction (SCR) of NO by NH 3 . The objective of the study was to shed light on the influence of poisoning on these reactions over a diesel SCR catalyst by compounds in the exhaust gases. The method used was to experimentally determine the amounts of products formed at several temperatures and compared them to simulated values. About 700 ppm NH 3 was oxidized by 2% O 2 in helium yielding N 2 , N 2 O, and NO at increasing temperatures. Comparisons are given for a 4.56% vanadia on titania fresh catalyst and the ones used for 890 and 2299 h. The kinetics was simulated using a multichannel model of the monolithic catalyst. The experimental values of the products were nicely fitted by the kinetic model where all three ammonia oxidation reaction rates were of the first order in the concentration of ammonia. The fit was somewhat better for the non-isothermal case than the isothermal one. The deactivation reduces the activation energies for the formation of all products. Effects of flow and concentration maldistribution are shown to be present but are quite small. The temperature increase is 1.30 K for the most active catalyst at the highest temperature (733 K). The use of the multichannel model shows that quite considerable deviations in inlet ammonia concentrations are obtained over the catalyst cross section. This means that the catalyst is not used to its full potential.