Microkinetic modelling for selective catalytic reduction (SCR) of NO_x by propane in a silver-based automotive catalytic converter

摘要

A numerical simulation is designed in order to better understand the selective catalytic reduction of NO, by propane (C3H8-SCR) in the presence of hydrogen. The simulation was designed for a single channel of a monolith typical for automotive catalytic converters, coated with a silver alumina catalyst (Ag/Al2O3). The complicated physical and chemical processes occurring during the reactions are solved by computational fluid dynamics (CFD) coupled with a surface-reaction mechanism. This mechanism is developed based on detailed microkinetic analysis. The elementary-step-like surface reaction mechanism (consisting of 94 reactions, 24 gas-phase species and 24 adsorbed surface species) is applied to investigate the effect on the conversion of NO_x to N2 of chemical kinetic steps, such as intermediate species. Results from the modelling emphatically agree with the experimental data. The modelling can predict the NO_x conversion at various operating conditions. Furthermore, the modelling can also provide information that is difficult to measure, for example predicts the channel wall temperature and surface coverage of surface species.