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 O-2 is carried out on Ag-decorated facet-dominated TiO2. The {001}-dominated TiO2 shows a durable CH3OH yield of 4.8mmolg(-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 center dot CH3 and center dot 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(center dot)-> Ti-OO-Ti and Ti-(OO)-> Ti-O-center dot pairs), thus achieving high selectivity and yield for CH4 photooxidation into CH3OH. The photocatalytic conversion of CH4 into CH3OH with high activity and selectivity must avoid product overoxidation. Here, authors minimize overoxidation by using a (001)-dominated TiO2 nanosheet to circumvent CH4 overoxidation intermediates plus reaction pathways that occur on (101) facets.

Automated summary

In this study, the photocatalytic conversion of CH4 into CH3OH on Ag-decorated facet-dominated TiO2 with high yield and selectivity is achieved, showing a key role of oxygen vacancies generation on {001} in avoiding overoxidation. The research comprehensively clarifies the underlying mechanism and presents distinct reaction pathways on {001} compared to {101} TiO2, leading to enhanced selectivity and yield.