Kinetic study of the ethene oxidation by oxygen in the presence of carbon dioxide and steam over Pt/Rh/CeO2/g-Al2O3

The oxidation of ethene by oxygen in the presence of steam and carbon dioxide over a commercially available Pt/Rh/CeO2/¿-Al2O3 three-way automotive catalyst was studied. Experiments were carried out in a fixed-bed micro reactor under intrinsic conditions, i.e. in the absence of external and internal mass and heat transport limitations. A kinetic model based on elementary reaction steps was developed for the following range of experimental conditions: a total pressure of 110 kPa, temperatures between 463 and 483 K, ethene inlet partial pressures between 0.04 and 0.14 kPa, oxygen inlet partial pressures between 0.25 and 1.10 kPa and steam and carbon dioxide inlet partial pressures equal to 10 kPa. For these conditions, only the total oxidation of ethene to carbon dioxide and steam was observed. The reaction rate was found to decrease with increasing ethene partial pressure and decreasing oxygen partial pressure. Both carbon dioxide ans steam were found to inhibit the reaction rate. The activity of CeO2 can be neglected at the investigated conditions. The kinetic model comprises the following elementary steps: irreversible adsorption of oxygen and reversible adsorption of ethene on the noble metal surface, followed by a surface reaction between adsorbed ethene and oxygen. The values of the kinetic parameters, i.e. preexponential factors and activation energies, were estimated by non-linear regression of the ethene conversion and found to be physically meaningful.