Browse Publications Technical Papers 2019-01-0024
2019-01-15

Kinetics Modeling of Ammonia-SCR and Experimental Studies over Monolith Cu-ZSM-5 Catalyst 2019-01-0024

Ammonia-selective catalytic reduction (SCR) systems have been introduced commercially in diesel vehicles, however catalyst systems with higher conversion efficiency and better control characteristics are required to know actual driving emissions and emissions in random test cycles. Computational fluid dynamics (CFD) is effective when applied to SCR catalyst development, and many models have been proposed, but these models need experimental verification and are limited in the situations they apply to. Further, there are a few models taking account of the copper redox cycle, and this causes a low validity of SCR reaction calculations in the transient conditions of engine operation. Model development considering the redox reactions in a zeolite catalyst, Cu-ZSM-5, is an object of the research here, and the effects of exhaust gas composition on the SCR reaction and ammonia oxidation at high temperatures are investigated. The simulations are compared with the experimental results of a surrogate gas, a mixture of nitrogen mono-oxide (NO), oxygen (O2), water vapor (H2O), and nitrogen (N2), and the accuracy of the developed model is validated. To investigate the effect of oxygen concentration on standard SCR and ammonia oxidation, the experiments are conducted with the following surrogate gas conditions: 3-12% or 3-10% of O2, 300 ppm of NO, and/or 300 ppm of NH3 with the balanced N2. The results suggest that the oxygen has a 1.0 reaction order to the standard SCR and 1.0 to NH3 oxidation. A transient operation experiment was conducted with the Cu-ZSM-5 catalyst. The catalyst was exposed to surrogate gas of 300 ppm of NO, and 300 ppm of NH3 after saturation adsorption with ammonia, where the re-oxidizing of copper does not occur. The results clearly show that the Cu+ does not contribute to the standard SCR reaction. The ammonia SCR model was much improved with taking into account of the effects of oxygen and Cu state on the reactions.

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