Experimental and modelling aspects in microstructured reactors applied to environmental catalysis

Shallow microchannels (Ø = 460 μm, length = 9.5 mm, and depth 75 μm) were successfully coated with an Ag/Al2O3 catalyst by washcoating. The coated microchannels were characterized and tested for the selective catalytic reduction (SCR) of NOx, using a simulated diesel engine exhaust in the temperature range of 150–550 °C at atmospheric pressure. Hexadecane, which is regarded as a high-quality diesel fuel, was used as reducing agent. The prediction of flow characteristics inside the microchannels was done by a two-dimensional finite element model and computational fluid dynamics (CFD) simulations. Theoretical calculations of the microchannels were done to describe the concentration profiles in the radial direction. The dynamic model consisting of a system of partial differential equations was discretized using a finite difference formulation with respect to the spatial coordinate. The resulting ordinary differential equations were solved with backward difference method to guarantee stability and convergence. The concentration profiles of the reactants (C16H34, NO) and products (CO2, N2) of the HC-SCR system were calculated. The outcome indicates that a rigorous model for microchannels coated with a catalyst layer of variable thickness can be obtained to evaluate the reactive flow inside the channels.