NO/NO2/N2O-NH3 SCR reactions over a commercial Fe-zeolite catalyst for diesel exhaust aftertreatment: Intrinsic kinetics and monolith converter modelling

We present a systematic kinetic investigation of the full NO/NO2/N2O-NH3 SCR reacting system performed over a commercial Fe-promoted zeolite catalyst in the form of powder in a representative temperature range (150-550 degrees C) at high space velocities. The well-known reactions of the NO/NO2-NH3 SCR system, namely NH3 adsorption, NH3 and NO oxidation, standard-, fast- and NO2-SCR reactions, ammonium nitrate formation, and N2O formation are considered. In addition, dedicated runs with N2O added to the feed stream showed that two more reactions, namely N2O reduction by NO (N2O + NO --> N-2 + NO2) and N2O reduction by NH3 (2NH(3) + 3 N2O --> 4 N-2 + 3H(2)O) become significant at T > 330 degrees C and need to be considered for kinetic modelling. The kinetic runs were fitted by multiresponse nonlinear regression to obtain estimates of the intrinsic rate parameters. Such parameters, as well as the relevant geometrical and morphological catalyst properties, were then successfully used to simulate on a purely predictive basis additional transient SCR runs performed over core honeycomb samples of the same Fe-zeolite catalyst, revealing modest effects of mass transfer limitations. In comparison with other published SCR kinetic models, the model herein developed accounts also for the N2O reactivity with NO and NH3, which is shown to be an important feature in order to accurately reproduce high-T operation of SCR converters based on Fe-zeolite catalysts. (C) 2011 Elsevier B.V. All rights reserved.