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Oscillations and bistability in heterogeneous catalytic reactions are well known. Oxidation of CO by O 2 on a Pt surface is the renowned example in this category. Extensive literature is available for the NO-CO reaction specially related to oscillation and bistability at low pressure conditions on the Pt catalyst surface. Detailed reaction mechanisms have been proposed for the NO-CO reaction on Pt(100), which shows bifurcations, kinetic oscillations, and multiple steady states under ultra high vacuum (10 -6 -10 -7 bar) conditions due to complex surface dynamics (Fink et al., 1992;Makeeva and Kevrekidis, 2004). It was found that oscillations are observed when C NO /C CO is greater than one and in the temperature range of 100-250ºCDue to the importance of the NO-CO reaction in current catalytic converters, reduction of NO by CO on Pt group catalysts is important to study. Various reaction mechanisms have been proposed for the NO-CO reaction on Pt(100), which shows bifurcations, kinetic oscillations and multiple steady states under ultra high vacuum (UHV) conditions due to complex surface dynamics. Some experiments on supported Pt group catalysts reported in literature show oscillations and bistability under atmospheric conditions as well. Industrially relevant conditions require the modelling and detailed analysis of the system at atmospheric pressure. We have proposed a reaction mechanism for the NO-CO system on Pt group catalysts and coupled it with an isothermal PSR model to obtain solutions at atmospheric conditions with the continuation software CONTENT 1.5, at different operating conditions. Simulation results suggest that Pt(111) shows bifurcations at certain operating conditions while Ir(111) shows stable solutions at all the operating conditions studied here.En raison de l'importance de la réaction entre NO et CO dans les convertisseurs catalytiques habituels, il est important d'étudier la réduction de NO par le CO sur des catalyseurs du groupe Pt. Divers mécanismes de réaction ont été proposés pour la réaction de NO-CO sur Pt(100), qui montre des bifurcations, des oscillations cinétiques et de multiples états permanents dans des conditions de vide extrême en raison de la dynamique de surface complexe. Certaines expériences dans la littérature scientifi que sur des catalyseurs de groupe Pt supportés montrent en outre des oscillations et une bi-stabilité dans des conditions atmosphériques. Des conditions industrielles pertinentes requièrent la modélisation et l'analyse détaillée du système à la pression atmosphérique. On a proposé un mécanisme de réaction pour le système de NO-CO sur des catalyseurs de groupe Pt et on l'a couplé avec un modèle PSR isotherme afi n d'obtenir des solutions dans des conditions atmosphériques avec le logiciel de continuation CONTENT 1.5, dans différentes conditions opératoires. Les résultats des simulations suggèrent que Pt(111) montre des bifurcations à certaines conditions opératoires, tandis que l'Ir(111) montre des solutions stables à toutes les conditions opératoires étudié...

Catalytic reduction using CO has significant potential for the control of NOx using Pt group catalysts as CO is already present in the exhausts and Pt group catalysts have high durability in the presence of SO2 and H2O. Different reaction mechanisms are given in the literature for this reaction based on NO dissociation, -NCO formation and so on, but the exact reaction mechanism capable of capturing experimentally observed features is as yet unavailable. To determine the kinetics and reaction mechanism, we propose here an elementary reaction mechanism based on NO dissociation applicable to Pt group catalysts and simulated with CHEMKIN 4.0.2 using single and multiple PSR (Perfectly Stirred Reactor) model. The activation energies of the elementary steps are found from the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. Excellent agreement between literature experiments and our simulation results are observed for the NO-CO reaction on Pt and Rh catalysts and for the NO-CO-O2 reaction on Ir catalyst. The effect of temperature on the NO reduction activity is captured well by the model. Additionally the simulations can also point towards importance of particular reactions, selectivity to N2, effects of surface coverage, effects of residence time and catalytic surface area on NO reduction.