An attempt at modelling the activity of Pt-Rh/Al2O3 three-way catalysts in the CO plus NO reaction

This study deals with the kinetic behaviour of a Pt-Rh/Al2O3 three-way catalyst (TWC) in the CO + NO reaction close to the actual conditions. Practically, it consists in validating a previous rate equation, established at 300 degreesC from a selected mechanism [P. Granger. J.J. Lecomte. L. Leclercq, G. Leclercq, J. Catal. 175 (1998) 194], in a wider range of temperature particularly near 100% NO conversion. Preliminary calculations using a non linear least square method lead to an estimation of pre-exponential factors (for k, the rate constant of the rate limiting step and for lambda (CO) and lambda (NO), the adsorption equilibrium constants of CO and NO). the activation energy for the dissociation of adsorbed NO molecules. and the enthalpies of CO and NO adsorption (DeltaH(ads.CO) and DeltaH(ads.NO)) Thr temperature-programmed conversion and selectivity curves obtained in differential conditions using a recycle fixed bed flow reactor have been modelled using these adjusted parameters. Based on CO chemisorption observations it was found that a better fit is obtained by accounting for the coverage dependency of DeltaH(ads.co) and DeltaH(ads.NO). Finally, we have attempted to quantify such effects. (C) 2001 Elsevier science B.V. All rights reserved.