Abstract
The kinetic parameters of the lean oxidation of CH 4 over alumina and ceria-alumina supported platinum catalysts in the presence of H 2S and SO 2 were derived in a stagnation point flow reactor at atmospheric pressure and at temperatures up to 1150 K . A novel methodology similar to that of plug-flow reactors was devised to calculate the best-fit values for frequency factors and activation energies for the proposed heterogeneous gas–solid reactions of oxidation. Doping the N 2-diluted CH 4/air reactant flow with H 2S or SO 2 concentrations between 30 and 100 ppm had a significant promotional effect on the methane combustion rate. Al 2O 3 and CeO 2/Al 2O 3 were shown to be inert with respect to the oxidation of CH 4 to CO 2, and also in the oxidation of SO 2 to SO 3 in air. Pt catalysed the oxidation of CH 4, SO 2 and that of H 2S. A temperature window of conversion of SO 2 to SO 3 on the Pt-supported catalysts was found experimentally, and could be of practical use in combustion exhaust clean-up techniques. The repeated use of the foil resulted in a slight ageing effect for Pt/Al 2O 3. The presence of ceria in the washcoat helped prevent the loss of activity in CH 4 oxidation by mitigating the extent of sintering of the Pt particles upon ageing. One-step and two-step chemical reaction mechanisms are proposed for the CH 4 and the SO 2 lean oxidations, respectively.
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