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 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.

Bismuth Vacancy-Induced Efficient CO2 Photoreduction in BiOCl Directly from Natural Air: A Progressive Step toward Photosynthesis in Nature

“…BiOCl has an open-layered, PbFCl-type tetragonal structure with an indirect transition. In BiOCl, the [Cl–Bi–O–Bi–Cl] layers are stacked through nonbonding interactions, and double layers consisting of the Cl – /[Bi 2 O 2 ] 2+ pair are alternately arranged . This layered structure possessing a strong inherent electrostatic field provides copious space to polarize atoms and atomic orbitals, which contributes to the induced dipole moment to separate electrons and holes .…”

Partial oxidation of methane to methanol on boron nitride at near critical acetonitrile

“…Oxidation of methane to methanol using O 2 and H 2 is known to produce methanol in water 6 – 10 . Even though the direct partial oxidation of methane is thermodynamically feasible, the overoxidation of subsequent products such as methanol, formaldehyde and formic acid to CO 2 have less activation barrier than activation of methane 11 – 13 .…”

Synergy of Single Atoms Pd and Oxygen Vacancies on In2O3 for Highly Selective C1 Oxygenates Production from Methane under Visible Light

“…Photocatalysis offers an appealing alternative to drive many tough redox reactions under mild conditions including CO 2 conversion [18,19], N 2 reduction [20] and selective CH 4 oxidation [8]. Recently, various value-added chemicals such as methanol [1,[21][22][23], formaldehyde [24,25], ethanol [26,27], ethane and ethylene [28][29][30][31][32][33] were produced by photocatalysis. For example, we found that up to 90 % selectivity with a yield of 3.5 µmol•h − 1 methanol could be achieved over the optimized FeO x /TiO 2 photocatalyst under ambient condition using H 2 O 2 as an oxidant [22].…”