Unveiling the dynamic structure evolution of In2O3(110) in the direct oxidation of methane to methanol

Abstract

Direct oxidation of methane (CH₄) to methanol (CH₃OH) (DMTM) is appealing for the value-added utilization of natural gas, yet challenged by poor reactivity and selectivity, which urges to develop efficient catalysts and accurately unveil reaction mechanisms. Here, we focus on the In₂O₃-catalyzed DMTM process via the first principle calculations and energetic span model (ESM). Considering the facile storage and release of lattice oxygen on In₂O₃, the stoichiometric (S-110), reduced (R-110), and reoxidized (O₂-R-110) surface states were all investigated under the same footing. As the dynamic surface transformation of S-110→R-110→O₂-R-110, the corresponding CH₄ activation mechanisms present synchronous changes of polarization activation→σ* activation→σ activation, which was identified by the electron transfer patterns between the adsorbates and catalytic sites. Furthermore, the optimal site for non-stoichiometric DMTM emerges on S-110, and the binding ability of dual H atoms was searched to be valid for describing the involved reaction barriers and the turnover frequency. Based on deciphering the complete DMTM pathway, the Mars-van Krevelen+Eley-Rideal route is favorable in kinetics determined by ESM analysis, accompanied by low overoxidation tendency. This work provides insights for further optimization and design of DMTM catalysts from the surface geometry evolution.