Modelling of an SCR catalytic converter for diesel exhaust after treatment: Dynamic effects at low temperature

As part of a fundamental and applied work on the development of an unsteady mathematical model of the NH₃-selective catalytic reduction (SCR) process for design and control of integrated after-treatment systems of heavy-duty engines, we present herein a transient kinetic analysis of the standard SCR NO + NH₃ system which provides new insight in the catalytic kinetics and mechanism prevailing at low temperatures. Based on kinetic runs performed over a commercial powdered V₂O₅–WO₃–TiO₂ catalyst in the 175–450 °C T-range feeding NH₃ and NO (1000 ppm) in the presence of H₂O (1–10%, v/v) and O₂ (2–6%, v/v), an original dual-site modified redox rate law is derived which effectively accounts for NH₃ inhibition effects observed during transient reactive experiments at T < 250 °C. We also demonstrate that implementation of the novel modified redox kinetics into a fully predictive 1D + 1D model of SCR monolith reactors can significantly improve simulations of SCR transient runs at different scales, including engine test bench experiments over full-scale SCR honeycomb catalysts.