Oxygen Defect Engineering of SrTiO ₃ Catalysts for Oxidative Coupling of Methane

Herein, SrTiO3 modified with SrCO3 and SrTiO3 modified with SrCO3 and CeO2 are synthesized via a hydrothermal method and studied as the catalysts for the oxidative coupling of methane (OCM) reaction. The oxygen defect density of SrTiO3 is enhanced by loading of finely sized SrCO3 particles and further by an additional loading of CeO2. The enhanced oxygen defect density weakens the stability of surface lattice oxygen in SrTiO3, which results in the abundant creation of oxygen defects and consequently electrophilic oxygen species during the OCM reaction, enhancing both CH4 conversion and C2+ selectivity. The optimal 5%CeO2/15%SrCO3/SrTiO3 catalyst with the largest oxygen defect density attains a CH4 conversion of 20% and a C2+ selectivity of 70% in the OCM reaction at 740 °C. Characterized by an online synchrotron vacuum ultraviolet photoionization mass spectrometry, more gaseous methyl radicals are generated during the OCM reaction over the catalysts with larger oxygen defect densities and, meanwhile, they exhibit higher selectivity toward gas-phase coupling to C2 products, consistent with the apparent catalytic performance. These results deepen our fundamental understanding of perovskite catalysts for the OCM reaction.