Progress in One-Step Conversion of Methane to Ethanol: Recent Techniques, Molecular Insights, Market and Future Perspective

Methane, which is a greenhouse gas, is released into the atmosphere through anthropogenic activities. An increase in the methane content in the atmosphere is 25 times more harmful than carbon dioxide; hence, utilizing and converting it into liquid fuels (or ethanol) could be a viable option. Industrially, methane is oxidized into syngas, followed by Fischer–Tropsch synthesis, producing liquid hydrocarbons. The process requires harsh conditions (i.e., 700–800 °C and 20–30 bar) to activate the methane C–H bond and thus become energy intensive. Recently, newer techniques have demonstrated methane C–H bond activation followed by its conversion into ethanol near ambient conditions, owing to lesser energy requirements and reduced process cost. This review assembles recent developments in one-step methane-to-ethanol (MTE) conversions comprising thermocatalytic, photocatalytic, piezocatalytic, electrocatalytic, and nonthermal plasma (NTP) routes. Thermocatalytic processes provided the highest ethanol yield from methane, while piezocatalytic, photocatalytic, and electrocatalytic processes appeared economically attractive for large-scale employment because of ambient operating conditions. The NTP without a catalyst enabled better ethanol selectivity but with higher coke formation. The insights into each technique are critically discussed in light of experimental findings. The molecular studies helped to further elucidate the MTE conversion mechanism. Further, the fate of new techniques for the ethanol market (considering ethanol demand in transportation and chemical manufacturing) is presented. This review is crucial for researchers investigating MTE conversions (with optimized operating conditions) for increased ethanol production.