Reaction kinetics of the CO2 reforming of methane

The kinetics of the CO2 reforming of methane was investigated in the temperature range 700-850 degrees C at normal pressure with a 1:1 mixture of CH4 and CO2 on Ir/Al2O3 catalysts. The feed composition was kept constant to avoid a change in mechanism associated with composition changes. Various rate models were fitted to the experimental data by numerically integrating the rate equations. All rate models included the reverse water gas shift reaction as the most important side reaction at these reaction conditions. The best agreement was obtained with a rate model based on the stepwise mechanism, where in the rate-determining step methane is decomposed to hydrogen and active carbon followed by the direct and fast conversion of this active carbon with CO2 to 2 CO. This model is also the first and only one containing a complete subset of reactions necessary to describe the network of reactions known to occur at these reaction conditions. Comparable fit quality was obtained with a simple first order model and with a model based on a Langmuir-Hinshelwood rate expression, where the latter provided physically meaningless parameters. Values of the reaction parameters are given for the 5 best rate models studied.