A comparative kinetic study on the oxidative coupling of methane over LSCF perovskite-type catalyst

A gas-phase heterogeneous kinetics is described over perovskite with formula La0.6Sr0.4Co0.8Fe0.2O3-delta (LSCF) for the oxidative coupling of methane under differential conversion conditions in a microcatalytic fixed-bed reactor. The ethane (C2H6) and carbon oxides (COx) formation and methane conversion rates were obtained as a function of methane and oxygen partial pressure under experimental conditions of: 0.20 < P-CH4 < 0.82 atm, 0.04 <0.15 atm, and 1073 < T < 1173 K. The different kinetic models were examined and two Eley-Ricleal mechanisms (a and b) were successfully performed to fit the experimental data into the theoretical relations from which two mechanisms having a first step of reversible adsorption of molecular oxygen on the catalyst surface with a subsequent reaction of methane molecule with the adsorbed oxygen were selected for data analysis. The parity graph of the ethane formation rate and the F-test statistical analysis were indicated mechanism a involving the formation of CH3O2 (methylperoxy) intermediate species can be suggested as the favorable (main) model for the analysis of kinetic parameters of OCM reaction over LSCF perovskite catalyst. Furthermore, the kinetic rate constants and activation energies were estimated for the selected models. Eventually the best model was introduced in course of conceptual and statistical analysis. (C) 2008 Elsevier B.V. All rights reserved.