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A one-dimensional model of a NOx trap system was developed to describe NOx storage during the lean operation, and NOx release and subsequent reduction during the rich regeneration process. The development of a NOx trap model potentially enables the optimisation of catalyst volume, precious metal loading, substrate type and regeneration strategy for these complex systems. To develop a fundamental description of catalytic activity, experiments were conducted to investigate the key processes involved in isolation (as far as possible), using a Pt/Rh/BaO/Al2O3 model catalyst. A description of the storage capacity as a function of temperature was determined using NOx breakthrough curves and the storage portion of more dynamic lean-rich cycling experiments. NOx breakthrough curves were also used for determination of rate of NOx storage. Kinetics for NOx reduction, as well as CO and HC oxidation, were determined using steady state reactor experiments.

A one-dimensional numerical model for a Cu-zeolite SCR catalyst has been developed. The model is based on kinetics developed from laboratory microreactor data for the various NH₃-NOX reactions, as well as for NH₃ oxidation. The kinetic scheme used is discussed and evidence for it presented. The model is capable of predicting the conversion of NO and NO₂, NH₃ slip and the formation of N₂O, as well as effects associated with NH₃ storage and desorption. To obtain a good prediction of catalyst temperature during cold start tests, it was found necessary to include storage and desorption of H₂O in the model; storage of H₂O is associated with a sizable exotherm and the subsequent desorption of this water produces a correspondingly large endotherm.

The relationship between H2S emissions from three-way catalysts and the storage of sulphur on the catalyst surface has been investigated. Thermodynamic data predict that sulphur storage primarily will occur on Al2O3 and CeO2 under lean and stoichiometric conditions, at up to 500°C. Rich transients could then induce the decomposition of the Ce-S-O and Al-S-O compounds, releasing sulphur into the gas phase. Experimental studies have supported this model. A mechanism has been proposed for the subsequent formation of H2S. The mechanism by which catalyst poisons attenuate H2S emissions from engine-aged catalysts also has been studied. The effect has been shown to be related to decreased storage of sulphur, caused by stable catalyst-poison species at the catalyst surface.