CFD simulations, experimental validation and parametric studies for the catalytic reduction of NO by hydrogen in a fixed bed reactor

Abstract

A 3D reactor model was developed for the reduction of NO by hydrogen over a Pd(1 wt%)/Al₂O₃ catalyst. The reactor model built in COMSOL Multiphysics CFD software is based on momentum conservation equations corrected by the Brinkman equation for the catalytic bed zone and on mass balance equations which consist of diffusion–convection equations along and across the reactor. The kinetic model used in the proposed 3D reactor model is an adaptation of a previously reported reaction mechanism, and validated according to our experimental observations which showed that reduction of NO by H₂ on the Pd(1 wt%)/Al₂O₃ catalyst leads to the formation of N₂ and N₂O only, without formation of ammonia. The results of numerical simulations performed with the proposed mathematical model are in good agreement with the experimental results obtained in the temperature range of 50–350 °C, proving the validity of the employed kinetic model. Moreover, simulation results evidenced that already at 100 °C or above, total NO conversion, with corresponding maximum N₂ yield around 85% could be attained with half of the catalytic bed length employed in the experimental tests. The developed reactor model was further used to carry out parametric studies involving the reaction temperature (T), GHSV, NO concentration in the feed (Cⁱⁿ_NO), or the reactants ratio (NO/H₂), in order to investigate their influence upon the catalytic performance of the reactor. These studies emphasize the possibility of using less catalyst volumes without affecting the catalytic performances, and showed that total NO conversion can be achieved in the temperature range of 100–150 °C irrespective of the employed GHSVs, the concentration of NO in the feed or the reactants ratio. Experimental runs performed with half of the catalyst volume confirmed the conclusions obtained by simulations. The 3D reactor model has important application potential for the reactor and associated control system design.