Kinetic Analysis of the Inhibition of CH4 Oxidation by H2O on PdO/Al2O3 and CeO2/PdO/Al2O3 Catalysts

Abstract

Addition of CeO2 to a PdO/Al2O3 catalyst, assessed for the oxidation of CH4 in the presence of 5% H2O at various temperatures, reduces the inhibition effects of H2O. A simplified kinetic analysis that assumes Langmuir adsorption of H2O on the catalyst active sites is used to model both the dynamic response and the steady-state CH4 conversion following H2O addition to the feed gas and to quantify the effect of CeO2 addition. The analysis shows that less H2O is adsorbed on the 2.9Ce/6.5Pd/Al2O3 than the 6.5Pd/Al2O3 catalyst and that the rate of H2O desorption is higher on the Ce-promoted catalyst. Both factors result in reduced inhibition of CH4 conversion by H2O on the 2.9Ce/6.5Pd/Al2O3 catalyst compared to the 6.5Pd/Al2O3 catalyst. The apparent activation energy for CH4 oxidation over the 2.9Ce/6.5Pd/Al2O3 catalyst (61 ± 11 kJ mol–1) is shown to be statistically the same over the 6.5Pd/Al2O3 (56 ± 9 kJ mol–1). Catalyst characterization data show minimal changes in catalyst properties after reaction, and r...