Recent Advances in Photocatalytic Oxidation of Methane to Methanol

Abstract

Methane is one of the promising alternatives to non-renewable petroleum resources since it can be transformed into added-value hydrocarbon feedstocks through suitable reactions. The conversion of methane to methanol with a higher chemical value has recently attracted much attention. The selective oxidation of methane to methanol is often considered a “holy grail” reaction in catalysis. However, methanol production through the thermal catalytic process is thermodynamically and economically unfavorable due to its high energy consumption, low catalyst stability, and complex reactor maintenance. Photocatalytic technology offers great potential to carry out unfavorable reactions under mild conditions. Many in-depth studies have been carried out on the photocatalytic conversion of methane to methanol. This review will comprehensively provide recent progress in the photocatalytic oxidation of methane to methanol based on materials and engineering perspectives. Several aspects are considered, such as the type of semiconductor-based photocatalyst (tungsten, titania, zinc, etc.), structure modification of photocatalyst (doping, heterojunction, surface modification, crystal facet re-arrangement, and electron scavenger), factors affecting the reaction process (physiochemical characteristic of photocatalyst, operational condition, and reactor configuration), and briefly proposed reaction mechanism. Analysis of existing challenges and recommendations for the future development of photocatalytic technology for methane to methanol conversion is also highlighted.

Photocatalytic conversion of carbon dioxide, methane, and air for green fuels synthesis

“…CH 4 is one of the prospective substitutes for non-renewable petroleum resources since it can be converted to other added value-chemicals, such as syngas for NH 3 production and CH 3 OH. 48 Currently, CH 3 OH is produced using a thermal catalytic process in which syngas is produced (H 2 and CO) from steam reforming of CH 4 at high process conditions (very high temperature and pressure), and then hydrogenated to produce CH 3 OH. Photocatalytic partial oxidation of CH 4 is an alternative way of producing CH 3 OH at ambient temperatures and potentially using solar light; reducing the energy requirements means reducing the greenhouse gas emissions released to the atmosphere.…”

“…74–76 A few review papers have been recently published on photo-partial oxidation of CH 4 , and we invite the reader to consult them for a deeper knowledge of the topic. 48,77,78 CH 4 + ˙OH → ˙CH 3 + H 2 O…”

Methane conversion and hydrogen production over TiO2/WO3/Pt heterojunction photocatalysts

“…25 In particular, heterojunction systems have been attempted as an effective strategy for enhancing the overall photocatalytic efficiency of TiO 2 -based photocatalysts. 26 For heterojunctions, the incorporation of alternative semiconductors such as WO 3 may synergistically improve the photocatalytic efficiency of TiO 2 under visible light irradiation, resulting from optical and electronic property modification. 27,28 Additionally, the use of various co-catalysts is proven to be an effective approach to augment charge carrier separation.…”

Partial Methane Oxidation to Methanol on Ru‐Porphyrins – on the Role of Non‐Innocent Ligands and Spin Crossover

“…They demonstrated that the reaction is catalyzed by a [Cu−O−Cu] 2+ motif formed via a hypothesized proton‐assisted diffusion of hydrated Cu ions in the cages of SSZ‐13 zeolites [4] . Recently, photocatalytic oxidation of methane to methanol has been intensively discussed based on materials and engineering perspectives [24] . However, so far it has not been possible to develop a catalyst that would give satisfactory reaction results.…”

“…[4] Recently, photocatalytic oxidation of methane to methanol has been intensively discussed based on materials and engineering perspectives. [24] However, so far it has not been possible to develop a catalyst that would give satisfactory reaction results. As it has been shown in the literature, reasonable methanol yields with high selectivity have still not been achieved.…”