3D pore-scale model for prediction of diffusion-limited conversion of gas components in soot-loaded catalytic filters

The influence of soot deposits on the conversion of gaseous pollutants in catalytic particulate filters used for exhaust gas aftertreatment is investigated within a single pore, as well as in 3D reconstructed sections of the filter wall with complex geometry obtained from X-ray tomography (XRT) scans. Two cordierite filters, differing in the distribution of Pd/Al 2 O 3 catalyst within the wall pores, are examined. The developed model newly considers resistance of the soot deposits in the 3D wall structure for diffusion of gas species to the coated catalyst. Following virtual deposition of soot layers inside the wall pores, simulations of fluid flow, diffusion, and catalytic reactions are performed. CO oxidation is studied at varying soot layer thicknesses and superficial gas velocities. Soot deposits hinder direct contact between the gas flow and the catalyst. At lower flow rates, complete CO conversion is achieved even in the presence of soot. However, at higher space velocities, transport limitations become evident, leading to a slip of up to several tens of ppm CO that persists above the CO light-off temperature. The residual CO concentration increases with gas velocity, soot layer thickness, and pore diameter. Compressibility of the deposited layer results in milder increase of transport limitation. The performance of a real wall structure cannot be approximated using mean pore diameter obtained from standard characterization methods. The predicted trends are consistent with experimental observations. • Deposited soot affects the conversion of gaseous pollutants in catalytic filters. • Simulations are performed in a single pore and in a 3D-reconstructed filter wall. • At lower flow rates, complete conversion is achieved even in the presence of soot. • Reactant slip increases with both gas velocity and soot layer thickness. • The predicted trends are consistent with experimental observations.