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.