Efficient and selective photocatalytic CH₄ conversion to CH₃OH with O₂ by controlling overoxidation on TiO₂

The conversion of photocatalytic methane into methanol in high yield with selectivity remains a huge challenge due to unavoidable overoxidation. Here, the photocatalytic oxidation of CH₄ into CH₃OH by O₂ is carried out on Ag-decorated facet-dominated TiO₂. The {001}-dominated TiO₂ shows a durable CH₃OH yield of 4.8 mmol g^-1 h^-1 and a selectivity of approximately 80%, which represent much higher values than those reported in recent studies and are better than those obtained for {101}-dominated TiO₂. Operando Fourier transform infrared spectroscopy, electron spin resonance, and nuclear magnetic resonance techniques are used to comprehensively clarify the underlying mechanism. The straightforward generation of oxygen vacancies on {001} by photoinduced holes plays a key role in avoiding the formation of •CH₃ and •OH, which are the main factors leading to overoxidation and are generally formed on the {101} facet. The generation of oxygen vacancies on {001} results in distinct intermediates and reaction pathways (oxygen vacancy → Ti-O₂^• → Ti-OO-Ti and Ti-(OO) → Ti-O^• pairs), thus achieving high selectivity and yield for CH₄ photooxidation into CH₃OH.