A kinetic study of methane and carbon dioxide interconversion over 0.5%Pt/SrTiO3 catalysts

The kinetics of interconversion of methane with carbon dioxide was studied over a 0.5%PUSrTiO3 solid catalyst in the temperature range 813893 K and partial pressure range 0.083 < P-CH4, P-CO2 < 0.667. The fitting of the experimental data for the rate of methane conversion, RCH4' using the empirical equation R-CH4 = k(1) (P-CH4)(m) (P-CO2)(n) Showed that both reaction orders n and m are steady and obtain values equal to m approximate to 1 and n approximate to 0. The results are explained using Langmuir-Hinshelwood kinetics with the reactants adsorbed on distinct and discreet active sites of the solids, namely the methane is weakly adsorbed on the metallic phase and the carbon dioxide is strongly adsorbed on the oxidic phase of the catalyst. The apparent activation energy for the reforming of methane was estimated to be similar to 123 kJ mol(-1). The rate of conversion of the carbon dioxide, R-CO2, was also fitted using a similar empirical equation R-CO2 = k(2)(P-CH4)(m) (P-CO2)(n). The results indicate that there is a positive but variable dependence on both reaction orders which increases in the temperature range 813-893 K from m approximate to 0.0 to m approximate to 0.30 and from n approximate to 0.3 to n approximate to 0.6. This variation is attributed to the variable participation of the rate of the reverse water gas shift reaction, R-rwgs, to the overall rate R-CO2 of CO2 conversion. The dependence of R-rwgs, on the partial pressure of CO2 appears similar to that of R-CH4 on the same reactant but shows strong inhibition by the reaction products. The results are discussed using Langmuir-Hinshelwood kinetics with the reactants and products adsorbed competitively on similar active sites of the catalyst. (C) 2007 Elsevier B.V. All rights reserved.