Kinetic analysis of selective catalytic NOx reduction (SCR) in a catalytic filter

A multifunctional reactor allows substitution of two or more process units with a single reactor, where all the operations of interest are executed simultaneously. For example, when ceramic filter materials, used in flue gas cleaning, are doped with compounds of transition metals, high efficiencies in particulate separation and catalytic activity for the removal of NOx, CO and CHx are obtained. The present study addresses a kinetic analysis of NOx reduction occurring in the catalytic filter material, including experimental data reported in the literature. A numerical model, based on available knowledge of SCR kinetics, is developed, validated with catalytic filter data and with honeycomb profiles, and finally used for case studies regarding design variables (GHSV, inlet concentration). The results indicate that NOx conversion typically required is possible on time scales of gas flow through a catalytic filter medium in the temperature range 250–350 °C, with strong temperature effects due to the competition of the desired SCR reaction and NH3 oxidation with O2. Application of the model and parameter values derived from the catalytic filter analysis to a SCR honeycomb situation constitutes a sort of indirect validation.