Transient kinetic study of the reaction of CH4 and C2H6 with the lattice oxygen of Li+-doped TiO2 catalyst

Abstract

A transient kinetic study of the reaction of CH4/He and C2H6/He with the lattice oxygen of Li+-doped TiO2 catalyst was performed. The results obtained indicate that lattice oxygen species must be considered as oxidation sites for both CH4 and C2H6 molecules leading mainly to the formation of gas-phase CO2. It was also found that more than one kind of carbon species accumulate on the catalyst surface in large quantities, following reaction with C2H6/He mixture in the range 700-845°C, a result opposite to that found with the CH4/He mixture. The amount of these carbon species removed by reaction with gas-phase oxygen (O2 titration) was found to strongly depend on the temperature of titration. A kinetic model, based on a sequence of elementary steps is proposed to interpret the transient oxygen titration results. An activation energy of 15.3 kcal · mol-1 for the reaction of carbon species with gas-phase oxygen is estimated. Activation energies of 34 and 28 kcal · mol-1 for CH4 and C2H5 reactions with lattice oxygen, respectively, are calculated from initial rates. © 1993 Academic Press, Inc.