Oxygen Vacancy Distribution as a Structural Switch for Oxygen Cycling: A Local Oxygen Chemical Potential Descriptor for Methane Oxidative Coupling on SrTiO3

Oxygen species evolution is central to the catalytic performance of oxidative coupling of methane (OCM), yet understanding and controlling this evolution remains a major challenge. SrTiO3 is a promising OCM catalyst due to its high C2 selectivity and stability but suffers from low activity. Here, DFT calculations combined with kMC simulations were employed to investigate facet-dependent oxygen species cycling on SrTiO3. Our findings reveal that SrTiO3(100)-Ti is the most favorable facet, sustaining a regenerable oxygen cycle (“O2− → OV → O22− → Ti-OH → O2−”). The local oxygen chemical potential (μO) is further identified as a thermodynamic descriptor linking oxygen stability with CH4* activation ability, following the order OV > O22− > Ti-OH > O2−. Furthermore, the spatial distribution of OV acts as a structural switch, directing two competing Mars–van Krevelen (MvK) cycles. kMC simulations reveal that the peroxide-mediated pathway dominates under operando conditions, whereas the overall activity is limited by the low activity of O2− and the accumulation of inert OlatH that further poisons active sites. Notably, B-site La doping effectively overcomes this bottleneck by activating OlatH and increasing the μO of O2− from –9.12 eV to –6.57 eV, which enhances the CH4(g) turnover frequency from 4.79 × 10−1 to 2.40 s−1 at 1073.15 K. These results establish μO and oxygen vacancy distribution as general design principles for perovskite oxide catalysts, offering a promising strategy to enhance OCM activity.