Effect of cavities and cracks on diffusivity in coated catalyst layer

[Display omitted] •Cracks and cavities enhance transport of reactants within catalytic coating.•Coating of commercial LNT monolith was scanned in 3D by X-ray microtomography.•Cracks and cavities represented about 20% of the coated layer volume.•Effective diffusivity was 1.7 times higher in comparison with compact coating.•Multi-scale simulations predicted improved light-off characteristics. In this paper we apply novel experimental and computational methods that investigate the contribution of cracks and cavities to diffusion in catalytic coating (washcoat). A sample of commercial catalytic monolith for automotive exhaust gas aftertreatment is scanned by X-ray microtomography (μCT) to obtain realistic 3D images of the coated layer. In the tested sample the cracks and cavities represent about 20% of the coated layer volume. A 3D diffusion is then simulated within sections of the virtually reconstructed porous structure. Benchmark simulations performed for the coating without any cracks or cavities (i.e. containing only standard meso- and macro-pores) indicate that the overall effective diffusivity is approx. 1.7 times lower in absence of these structural defects and the difference increases with temperature. The effect of cracks and cavities is further tested in combined reaction and transport simulation and corresponding effectiveness factors are evaluated. Finally, spatially averaged reaction rates are employed in multi-scale simulations of light-off curves that reveal the impact of the structural defects in the catalytic coating on overall performance of the monolith reactor.