Acetylene and carbon monoxide oxidation over a Pt/Rh/CeO 2/ γ-Al 2O 3 automotive exhaust gas catalyst: kinetic modelling of transient experiments

Abstract

The transient kinetics of acetylene (C 2H 2) conversion by oxygen over a commercial Pt/Rh/CeO 2/ γ-Al 2O 3 three-way catalyst have been modelled. Experiments to validate the model were carried out in a fixed-bed reactor with two separate inlets, enabling alternate feeding of acetylene and oxygen. Frequencies of feed composition cycling up to 1/6 Hz were applied. The experimental conditions resemble the cold-start period of an Otto engine. Two types of adsorbed acetylene species seem to exist. A selective catalyst deactivation for oxygen adsorption, due to deposition of carbonaceous deposits, was found. Ceria proved to have a significant influence on the acetylene oxidation. A kinetic model was developed for the conversion of acetylene to carbon monoxide, based on elementary reaction steps. This model was combined with the published kinetics for transient carbon monoxide oxidation to carbon dioxide over the same catalyst (Nibbelke, R. H., Chapman, M. A. J., Hoebink, J. H. B. J., & Marin, G. B. (1997). Kinetic study of the CO oxidation over Pt/V-Al 2O 3 and Pt/Rh/ CeO 2/ γ−Al 2O 3 in the presence of H 2O and CO 2. Journal of Catalysis, 171, 358–373.), in order to describe the total oxidation of acetylene quantitatively. The combined model is able to describe the results of the transient experiments on simultaneous acetylene and carbon monoxide oxidation. During a transient, both acetylene and carbon monoxide react mainly in a front moving through the reactor, carbon monoxide hardly influencing the acetylene oxidation.