CO 2 . The key issues are selectivity to methane, carbon lay-down, and the high temperatures needed to drive the reaction forward, and they are being addressed at present. Also, a range of catalysts is being evaluated. Many of these are based on copper, but iron, nickel, platinum, and molyb- denum carbide catalysts are also under investigation. In light of the challenges to develop a commercialised RWGS process, other methods for activation of CO 2 to CO such as electrochemistry or photo-chemistry are interesting. The George Olah methanol plant in Iceland, commissioned in 2011, follows the second method. The production unit captures CO 2 from flue gas released by an adjacent geo - thermal power plant, which is purified to make it suitable for downstream methanol synthesis. Following adequate compression, synthesis gas containing green hydrogen generated by electrolysis of water and CO 2 is catalytically reacted to form methanol. Direct CO 2 hydrogenation to produce methanol is licensed by several leading companies. Recently, China made great progress in employing copper-based and oxide catalyst systems. Also, a novel technique for converting CO 2 to methanol was recently created at TU Wien (Vienna). Liquid methanol is formed from CO 2 with the aid of a unique cata- lyst material consisting of sulphur and molybdenum. The new technology has already been patented, and now it must be ramped up to industrial size in collaboration with business partners. Increasingly abundant low-cost renewable electricity
enabled electrochemical processes to compete with tra- ditional thermocatalysis methods. The George Olah plant mentioned above couples the hydrogen through electrolysis with thermocatalysis to produce methanol. The availability of electrolysis at the scale needed to supply hydrogen to methanol plants is a key challenge, and significant efforts are being made to scale up electrolysers. Also, the high- temperature electrolysis to produce CO and syngas using solid oxide electrolyser cell (SOEC) systems could be advantageous if coupled with thermochemical processes to reduce heating cycles. However, SOECs cannot reduce CO 2 directly to other hydrocarbons and oxygenates, unlike low-temperature electrolysis. Methanol synthesis from CO 2 over heterogeneous cata- lysts suffers from several shortcomings, such as harsh operating conditions like high pressure and temperature. Also, CO 2 thermocatalytic hydrogenation is limited by thermodynamics, and continuous separation of methanol from CO 2 and by-products is necessary for the recirculating process. Several alternatives for CO 2 reduction to methanol have emerged in recent years involving homogeneous, enzymatic catalysis, photocatalysis, and electrocatalysis. Advantages of these emerging processes include tem- perature lower than in heterogeneous catalysis, alternative sources of energy (light or electricity) use, and potentially higher methanol selectivity. In some alternatives, water is used for CO 2 reduction instead of costly green hydrogen.
PTQ Q1 2023
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