Transient kinetics of ethylene and carbon monoxide oxidation for automotive exhaust gas catalysis: experiments and modelling

The transient oxidn. of ethylene by oxygen over a com. available Pt/Rh/CeO2/g-Al2O3 three-way exhaust gas catalyst is described. Expts. were carried out in a fixed-bed micro-reactor with two sep. inlets, enabling alternate feeding of ethylene and oxygen. The exptl. conditions were chosen so as to obtain intrinsic kinetics, i.e., in the absence of external and internal mass and heat transport limitations. Also, these conditions resemble the cold-start period of an Otto engine in a car. For these conditions, only total oxidn. of ethylene to carbon dioxide and steam was obsd. From the shape of the CO2 peaks, two types of adsorbed ethylene species seem to exist. The presence of ceria in the catalyst did not influence the ethylene oxidn. significantly at the investigated conditions. A kinetic model, based on elementary reaction steps, is presented, which can be combined with the model for transient carbon monoxide oxidn. on the same catalyst