A Steady-State Tracing Kinetic Analysis of Oxidative Coupling of Methane over Li+-Doped TiO2: Mechanistic Aspects of the Carbon and Oxygen Reaction Pathways to Form CO2

Abstract

A steady-state tracing kinetic study of the oxidative coupling of methane reaction at 800°C over Li+-doped TiO2 catalyst was performed. In particular, the carbon and oxygen reaction pathways which lead to the formation of CO2 have been probed using 13CH4 and 18O2 isotope gases under reaction conditions. The results obtained indicate that there is practically no reversibly adsorbed CH4 on the catalyst surface, while there is a very small reservoir of carbon-containing intermediate species which eventually lead to CO2 (0.1 μmol/g). A large reservoir of oxygen species, participating in the formation of CO2 (at least 12.0 μmol/g), was detected, while subsurface lattice oxygen species also participate in the oxygen reaction pathway to form CO2. In addition, large amounts of inactive carbonaceous species (17.0 μmol/g) accumulate on the catalyst surface after 1 h on stream. These species do not participate in the reaction route to form CO2 (spectator species).