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.