Kinetic features of the size effect in methane oxidation over Pt/γ-Al 2 O 3 catalysts

The correlation between the kinetic parameters of methane oxidation and the size of supported platinum nanoparticles was studied. The reaction order with respect to methane appeared to differ from unity while that for water was significantly negative. An impact of carbon dioxide was not found and the order with respect to oxygen was suggested to be equal to zero at an excess of oxygen in the mixture. The numerically optimized kinetic equations were proposed for each catalyst based on the results of fifty experiments. According to the most realistic models, competitive adsorption of methane and water affected considerably the reaction over the catalysts with the highly dispersed platinum particles (1.3 nm in size). In the case of the catalysts with the large platinum particles (10–16 nm in size), the competitive methane adsorption did not influence the process. The apparent activation energies for the process ranged between 65 and 90 kJ/mol and depended slightly on the average size of the supported platinum nanoparticles.