Modeling of transport and chemistry in channel flows of automotive catalytic converters

A novel comprehensive numerical study is presented for a better understanding of mass transfer in channel flows with catalytically active walls at moderate temperatures and surface reaction rates. Altogether, 18 different numerical models are compared, which represent mass transfer in single channels of a honeycomb-type automotive catalytic converter operated under direct oxidation conditions. Three different channel geometries have been investigated: circular cross-section, square cross-section, and square cross-section with rounded corners (fillets). 1D plug-flow, 2D boundary-layer and Navier–Stokes, and 3D Navier–Stokes equations are applied to model the reactor geometry. The diffusion limitation within the porous washcoat has been modeled by a simplified zero-dimensional effectiveness factor model as well as multidimensional reaction–diffusion models. Furthermore, simulations are also carried out for cases with instantaneous diffusion within the washcoat. All numerical models account for the coupled interactions of mass-transfer and heterogeneous chemistry within the channels. The chemical conversion of the pollutants on the platinum catalyst is described by an elementary-step-like heterogeneous reaction mechanism consisting of 74 reactions among 11 gas-phase species and 22 adsorbed surface species. The results of numerical simulations are compared with experimental data.