Photocatalytic Conversion of Methane: Recent Advancements and Prospects

Abstract

Abundant and affordable methane is not only a high‐quality fossil fuel, it is also a raw material for the synthesis of value‐added chemicals. Solar‐energy‐driven conversion of methane offers a promising approach to directly transform methane to valuable energy sources under mild conditions, but remains a great challenge at present. In this Review, recent advances in the photocatalytic conversion of methane are systematically summarized. Insights into the construction of effective semiconductor‐based photocatalysts from the perspective of light‐absorption units and active centers are highlighted and discussed in detail. The performance of various photocatalysts in the conversion of methane is presented, with the photooxidation classified according to the oxidant systems. Lastly, challenges and future perspectives in the photocatalytic oxidation of methane are described.

Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ+

“…Thus, CB and valence band (VB) positions of the Cu 0.029 -def-WO 3 vs. NHE (pH = 0) are established as −0.10 and 2.78 V, respectively 57 , 58 . Therefore, the potentials of VB and CB positions are sufficient to drive O 2 reduction (−0.05 V vs. NHE) and H 2 O oxidation (2.38 V vs. NHE) to generate reactive species, such as ·OOH and ·OH radicals, respectively 59 , 60 .…”

Synergistic effects of Fe-substitutional-doping and a surface close-contact Fe2O3/CeO2 heterojunction in Fe/CeO2 for enhanced CH4 photocatalytic conversion

“…S17 †) of the reaction system without using H 2 O 2 strongly conrmed this fact again, as the oxidation potential of Fe 2 O 3 (1.74 V) is not high enough to oxidize H 2 O to produce $OH (the oxidation potential of H 2 O/$OH is 2.38 eV). 21,49,50 Therefore, the holes-rich CeO 2 is the active species during CH 4 conversion.…”

Retrofitting Zr-Oxo Nodes of UiO-66 by Ru Single Atoms to Boost Methane Hydroxylation with Nearly Total Selectivity

“…Moreover, the high reactivity of oxygenated products can lead to the side reaction of overoxidation to CO 2 , both of which make the direct selective oxidation of methane (DSOM) to liquid oxygenates extremely challenging. 4 Until now, it has been considered as the "holy grail of catalysis" in chemical reactions to achieve total selectivity in the DSOM process with highly efficient catalysts under mild conditions. 5,6 In general, there is a trade-off effect between methane activation and oxygenate selectivity on supported transitionmetal catalysts for the DSOM reaction, which can be caused by harsh reaction conditions, 7 strong adsorption of oxygenates on the active sites, 8 or the use of excessive oxidant.…”

“…Methane, the main component of natural gas, shale gas, and combustible ice, has attracted considerable attention worldwide not only in terms of reducing greenhouse gas emissions to protect the environment but also as an energy resource oriented toward high value-added products. − However, the conversion rates are often limited due to the nonpolarity and high symmetry of CH 4 . Moreover, the high reactivity of oxygenated products can lead to the side reaction of over-oxidation to CO 2 , both of which make the direct selective oxidation of methane (DSOM) to liquid oxygenates extremely challenging . Until now, it has been considered as the “holy grail of catalysis” in chemical reactions to achieve total selectivity in the DSOM process with highly efficient catalysts under mild conditions. , …”