Detailed surface reaction mechanism in a three-way catalyst

Monolithic three-way catalysts are applied to reduce the emission of combus tion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parameters ( in the simplest case, e.g., length, cell densities or metal coverage of the catalyst). Numerical simulation can be used as an effective tool for the i nvestigation of the catalytic properties of a catalytic converter and for t he prediction of the performance of the catalyst. To attain this goal, a tw o-dimensional flow-field description is coupled with a detailed surface rea ction model (gas-phase reactions can be neglected in three-way catalysts). This surface reaction mechanism (with C3H6 taken as representative of unbur nt hydrocarbons) was developed using sub-mechanisms recently developed for hydrogen, carbon monoxide and methane oxidation, literature values for C3H6 oxidation, and estimates for the remaining unknown reactions. Results of t he simulation of a monolithic single channel are used to validate the surfa ce reaction mechanism. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic c onditions, the oxidation of propene and carbon monoxide and the reduction o f NO on a typical Pt/Rh coated three-way catalyst were simulated as a funct ion of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupl ing between chemical reactions and transport processes within the monolithi c channel.