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

Abstract

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 CH 4 into CH 3 OH by O 2 is carried out on Ag-decorated facet-dominated TiO 2. The {001}-dominated TiO 2 shows a durable CH 3 OH 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 TiO 2. 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 •CH 3 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–O 2• → Ti–OO–Ti and Ti–(OO) → Ti–O• pairs), thus achieving high selectivity and yield for CH 4 photooxidation into CH 3 OH.