Microkinetic modeling of steady-state NO/H2/O2 on Pt/BaO/Al2O3 NOx storage and reduction monolith catalysts

Abstract

A steady-state microkinetic model for NO reduction by H2 and NH3 in O2 on alumina supported Pt/BaO monolith catalysts is developed based on the measurements from a parallel experimental study (R. Clayton, M.P. Harold, V. Balakotaiah, Selective catalytic reduction of NO by H2 in O2 on Pt/BaO/Al2O3, Appl. Catal. B: Environ. 81 (3–4) (2008) 161–18). The microkinetic model describes pertinent Pt-catalyzed regeneration chemistry during NOx storage and reduction with H2. Kinetic parameters not available from the literatures are estimated to capture the experimental trends and to meet thermodynamic constraints. The kinetic model is incorporated into a short monolith reactor model to simulate the steady-state NH3/O2, NH3/NO and NO/NH3/H2 reaction systems. The predicted conversion and product distribution are in excellent qualitative and good quantitative agreement with the experimental data. Among other features, the model predicts for the three reaction systems the non-linear light-off, and the product selectivity dependencies on temperature and feed composition. The model predicted trends in the species surface coverages with operating conditions help to elucidate the selectivity trends. A sensitivity analysis of the rate constants identified the critical steps in the reaction network. The effects of external mass transfer on the conversions and product distributions are assessed and discussed.