TRANSIENT AND ISOTOPIC STUDIES OF THE OXYGEN-TRANSPORT AND EXCHANGE DURING OXIDATIVE COUPLING OF METHANE ON SR PROMOTED LA2O3

Isotopic transient techniques were applied to study oxidative coupling of methane over lanthanum oxide and strontium promoted La2O3 catalysts. Results of the O-18(2)/O-16(2) isotopic exchange experiments indicate that Sr promotion increases oxygen uptake from the lattice of the catalyst. Oxygen self diffusion coefficients, which were determined for the series of lanthana catalysts, reach a maximum for the 1% Sr/La2O3. Steps of O-18(2) in the presence of a steady flow of methane over Sr/La2O3 catalysts, indicate that surface and bulk oxygen appear in the reaction products before gas-phase O-18(2). Steps of CO2 over catalysts in which lattice oxygen has been exchanged with O-18(2), show that gas/solid exchange involves over 50% of the lattice oxygen. Under reaction conditions, methane pulses with no gas-phase oxygen yield negligible amounts of products which indicates that methane interacts with lattice oxygen only in the presence of the gas-phase oxygen.