A three-dimensional CFD-microkinetic modeling approach for mechanistic elucidation and performance prediction of Cu-Zeolite SCR catalysts

A high-fidelity three-dimensional computational fluid dynamics (CFD) model was developed to simulate the selective catalytic reduction (SCR) of NOx over copper-exchanged zeolite catalysts. The model integrates detailed surface microkinetics, intraparticle diffusion, and conjugate heat transfer within a representative monolith channel geometry. Two kinetic frameworks were implemented and validated: a single-site mechanism (where all active sites are assumed identical, with Langmuir-Hinshelwood-type surface reaction steps) with five reactions, and a dual-site mechanism with nine reactions accounting for site heterogeneity.The model successfully predicts NH₃ and NOx conversion across a 300–400 °C temperature range, showing excellent agreement with experimental data. Key mechanistic insights reveal that the standard SCR reaction is kinetically front-loaded, with NO consumed within the first 25% of the catalyst length. Axial and radial stratification of temperature and species concentrations highlights the coupling between exothermic reactions, adsorption thermodynamics, and heat losses. Microkinetic analysis demonstrates that the dual-site model more realistically captures the catalyst’s operational behavior, where competition between sites with different adsorption enthalpies leads to an attenuated global temperature response, explaining the broader operational window of industrial catalysts. This work provides a validated computational framework that transcends performance prediction, offering a quantitative tool for deconvoluting complex transport-kinetic interactions and guiding the rational design of next-generation SCR catalysts with enhanced efficiency, selectivity, and durability under transient exhaust conditions.