Chemical kinetic mechanism for selective catalytic reduction of nitrogen oxides†

A generic chemical kinetic mechanism for nitric oxide reduction by ammonia is developed exploiting similarities in redox cycles exhibited by different catalysts. The mechanism comprises 28 reactions, the rate constants of which were estimated through analysis of the individual sub-processes and identifying the overall rate with the rate of the limiting step. The chemical kinetics so developed was used to simulate operation of several catalysts in a plug flow reactor. These simulations show that, after taking into account differences in feed gas composition, active site concentration and residence time, varying only one kinetic parameter, namely activation energy for the low-temperature catalytic site oxidation allows one to reconcile the observed differences between copper and iron exchanged zeolites and cerium dioxide with tungsta on titania. Prediction of the NO conversion by vanadia at high temperatures required changes of two kinetic parameters.