Dalton Transactions FRONTIER Cite this: Dalton Trans., 2020, 49, 17140 Received 23rd October 2020, Accepted 3rd November 2020 DOI: 10.1039/d0dt03667f rsc.li/dalton Integrated CO 2 capture and one-pot production of methanol Mrinmay Mandal The capture, storage, and utilization (CSU) of CO 2 to produce methanol which can be used as a fuel, fuel additive, and precursor in organic synthesis is an area of fascinating research. This directly influences the reduction of the CO 2 concentration by capturing CO 2 from industrial and automobile emissions. The development of integrated CO 2 capture and conversion to a fuel and fuel additive has garnered consider- able attention as it eliminates costly processes to produce pure CO 2 . This contribution presents a summary of integrated CO 2 capture and conversion to methanol (MeOH) using amine-assisted and alkali hydroxide-assisted one-pot systems. The superiority of the alkali hydroxide-based system to the amine- based system for the conversion to MeOH is systematically presented. The world is suffering from an energy crisis and resource shortage owing to industrialization and population explosion. Fossil fuels, such as natural gas, coal, and oil, are the major energy resources available presently. The combustion of all these resources emits greenhouse gases, which are a global health threat for humanity. 1 The burning of fossil fuels involves an inefficient conversion of chemical energy into elec- tric energy. Besides, it can cause extensive environmental pol- lution. 2 Moreover, as the global energy resources are limited, a void between the existing energy resources and the increasing demand for energy is emerging. These have attracted increas- ing attention toward the development of an alternative and renewable energy technology. The capture, storage, and utiliz- ation (CSU) of CO 2 to produce MeOH has led to a decrease in the CO 2 concentration in the atmosphere and global warming. 3,4 MeOH, an attractive C1 feedstock, can be used as a fuel for internal combustion engines and direct methanol fuel cells (DMFC). The CO 2 emitted by the burning of fuels can be captured and recycled back as a fuel. Hence, an overall carbon-neutral cycle is established. 5 MeOH is also used as a fuel additive, a precursor for organic synthesis, and most importantly a medium for H 2 storage (12.6 wt% of H 2 ). 4,6 In an integrated CO 2 capture and utilization system (CUS), the captured CO 2 is directly converted into MeOH or other value-added chemicals. 7–15 This system is of particular interest because energy-consuming intermediate steps are avoided to produce pure CO 2 . Herein, we will highlight the recent devel- opment of the integrated capture of CO 2 and one-pot pro- duction of MeOH. Writing in the Journal of the American Chemical Society, 12 G. K. Surya Prakash and colleagues have reported the integrated capture of CO 2 and hydrogenation to MeOH using amine-based systems (Fig. 1A). Under the optimized conditions and with the proper selec- tion of amines, catalyst (C-1, Fig. 2), and organic solvents, MeOH was produced in 95% yield. Moreover, direct air capture of CO 2 was performed and it was hydrogenated to MeOH in 89% yield. The formation of associated CO/CH 4 side products was not observed during the reactions. The production of a trace amount of MeOH (5% yield) or no yield of MeOH was observed when C-7 (Mn-catalyst) or C-8 (Fe-catalyst) was used as the catalyst (Fig. 2). It is worth mentioning that low vapor pressure amines were found to be the best to avoid atmos- pheric amine contamination. Although the catalysts and amines were recycled success- fully up to four times without losing activity for the production of MeOH, the use of amine-based systems has several disad- vantages such as volatility, degradation under experimental conditions, and toxicity of the amines. 16 Hence, the practical implementation of direct air capture (DAC) on a large scale for CO 2 hydrogenation to MeOH remained a challenge. Very recently, G. K. Surya Prakash and his research group, for the first time, came up with an idea to replace the amine- based system with an alkali hydroxide-based system for inte- grated CO 2 capture from air to produce MeOH (Fig. 1B). 17 The advantages of the alkali hydroxide-based system include (1) high stability and efficiency of CO 2 capture under reaction con- ditions; (2) low toxicity and volatility; (3) ready availability of a large number of hydroxide bases; (4) high capability of DAC of CO 2 ; and (5) formation of an ester intermediate which can be easily hydrogenated to MeOH in comparison with the forma- mide intermediate when amine-based systems are used. 18 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA. E-mail: mrinmay.mom@gmail.com, mrinmay.mandal@chbe.gatech.edu; Tel: +1 4703384453 17140 | Dalton Trans. , 2020, 49, 17140–17142 This journal is © The Royal Society of Chemistry 2020 Published on 03 November 2020. Downloaded by Georgia Institute of Technology on 12/15/2020 4:40:54 PM. View Article Online View Journal | View Issue