Tertiary Amine-Ethylene Glycol Based Tandem CO2 Capture and Hydrogenation to Methanol: Direct Utilization of Post-Combustion CO2

Glycerol-Derived Water-Lean Amines for Post-Combustion CO2 Capture: The Improvement in Capacity and Viscosity

Water-lean absorbents are regarded as a new generation of post-combustion CO2 capture technology that could significantly relieve those drawbacks posed by traditional aqueous alkanolamines. However, the exponential increase in viscosity during CO2 absorption remains an urgent issue that needs to be resolved before their practical deployment. In this work, novel water-lean amines based on biomass glycerol have been devised as single-component CO2 absorbents with low viscosity (79~110 cP at 25 ∘ C ${{\rm{{^\circ}C}}}$ , 29~39 cP at 40 ∘ C ${{\rm{{^\circ}C}}}$ ) under high capacity (12~18 wt % at 25 ∘ C ${{\rm{{^\circ}C}}}$ , 10~17 wt % at 40 ∘ C ${{\rm{{^\circ}C}}}$ ). The captured CO2 could be smoothly released by thermal desorption. Results from preliminary stability test and 10 absorption-desorption cycles showed that such non-aqueous absorbents had significant structural toughness as well as reusability. Spectroscopic measurements including 13C NMR and in situ FTIR were performed to gain mechanistic insights by monitoring the entire CO2 absorption and desorption process, while DSC, VLE and DFT calculations provided rational interpretation for reaction kinetics and thermodynamics. The synergistic promotion of glycerol ether group on both CO2 chemical and physical absorption was also verified under high pressure conditions.

Homogeneous catalytic hydrogenation of CO2 - amino acid-based capture and utilization

In this review, we provide an overview of research efforts to integrate carbon dioxide capture specifically using amino acid-based sorbents with its thermocatalytic hydrogenation promoted by homogeneous metal complexes. Carbon capture and utilization (CCU) is a promising strategy for the production of fuels, chemicals and materials using CO2 scrubbed from point sources and the atmosphere as a C1 feedstock while mitigating CO2 emissions. Compared to established (alkanol)amines, amino acids offer some advantages as CO2 capture agents due to their lower volatility, higher oxygen stability and lower regeneration energies. We report how the structural diversity of amino acids and the possibility of combining them with cations in salts and ionic liquids have been exploited in the design of absorbers for improved absorption kinetics and capacity. Furthermore, we discuss selected examples from the literature illustrating the use of 1°/2° (poly)amines, since the 1°/2° amino groups are mainly responsible for CO2 chemisorption in amino acid-based capture media, the nature of the corresponding adducts, and the most promising catalysts capable of converting the latter to formate and methanol while regenerating the scrubber. General trends regarding the influence of catalyst structure and reaction parameters on the efficiency, productivity, and selectivity of such processes will be highlighted. We will detail how this knowledge has informed the design of novel processes in which CO2 is chemisorbed by amino acid-based solvents and hydrogenated in situ to formate and methanol, or alternatively used as a fuel to implement a "hydrogen battery" where, after metal-catalyzed H2 release from formate, CO2 is retained by the amino acid-based solvent in the "spent battery" which can then be recharged by hydrogenation of the retained CO2 promoted by the same catalyst. The topic is still in its infancy, and several issues have emerged that will be critically discussed in the final section of this review. These issues need to be addressed in order to improve performance and provide a playground for researchers whose interest we hope to have aroused with this review.

Amino Acid-Based Ionic Liquids-Aided CO2 Hydrogenation to Methanol

This study explored the use of amino acid-based ionic liquids to facilitate the conversion of carbon dioxide (CO2) into methanol through catalytic hydrogenation. Combining tetrabutylammonium L-argininate (TBA⋅Arg) with the ruthenium Ru-MACHO-BH complex allowed achieving significant yields of methanol under optimized conditions, with a turnover number (TON) up to 700. By systematically varying key reaction parameters, we demonstrated that the TBA⋅Arg ionic liquid promotes the efficient hydrogenation pathway leading to methanol formation, thus offering a sustainable approach to CO2 valorization. These findings underscore the potential of amino acid-based ionic liquids in catalyzing the transformation of CO2 into valuable chemicals, contributing to carbon mitigation efforts.

Catalytic Hydrogenation of CO2 by Direct Air Capture to Valuable C1 Products Using Homogenous Catalysts

Growing atmospheric CO2 concentrations are a global concern and a primary factor contributing to global warming. Development of integrated CO2 capture and conversion protocols is necessary to mitigate this alarming challenge. Though CO2 hydrogenation to produce formic acid and methanol has seen many strides in the past decades, most studies utilize pure CO2 for this transformation. The CO2 concentration in the atmosphere stands at 400 ppm and reports that utilize direct air capture as the strategy to capture CO2 and utilize it for production of formic acid and methanol have only been reported in the past few years. This perspective summarizes such reports with a focus on the CO2-capturing additive, reaction solvent, and the molecular catalyst used to affect the transformation.

Using Support Effects to Increase the Productivity of Immobilized Ruthenium Hydride Catalysts for the Hydrogenation of CO2

Interfaces between catalytically active metal surfaces/sites and metal oxides (such as those formed by metal oxides covering metal nanoparticles by strong metal-support interactions) allow both the metal and metal oxide to react with substrates simultaneously and are important for the activity of many heterogeneously catalyzed reactions. However, similar interactions for well-defined immobilized catalysts have not been investigated, despite their potential for increasing catalytic activity. We test the reactivity of a ruthenium hydride [H2Ru(PPh3)2(Ph2P)2NC3H6Si(OEt)3 (1)] in the amine-promoted hydrogenation of CO2 as both a homogeneous catalyst and anchored on SiO2, Al2O3, ZnO, and SBA-15. Anchoring 1 on the surfaces resulted in varying degrees of surface collapse (formation of H-Ru-O linkages to the surface), with ZnO and confinement in SBA-15 pores giving the least surface collapse. Immobilization of 1 on ZnO gave a 6-fold improvement of the catalytic rate over the corresponding homogeneous catalyst. This increase in the catalytic productivity was only possible when the complex was in close contact with ZnO and is most likely due to a combination of increased catalytic activity and slower deactivation. These results demonstrate the ability of surface effects to vastly improve the productivity of even mediocre catalysts upon surface immobilization.

Nanoparticle-enabled integration of air capture and conversion of CO2

Integrating air capture and conversion of CO2 is key to realizing energy sustainability. However, current integration approaches require high temperature and pressure, making them energy intensive. Here, we demonstrate a nanoparticle (NP) catalysis approach for the hydrogenation of alkyl carbonate, an intermediate obtained from the CO2 capture process, to formate, achieving one-pot air capture and conversion of CO2 under ambient conditions. The capture is realized in an ethylene glycol (EG) solution of KOH (EG-KOH) at room temperature, where CO2 is selectively converted into HO-CH2CH2-O-COOK (∼100% conversion). This carbonate is then hydrogenated using ammonia borane (under ambient pressure and at 50 °C) to formate (HCOOK) (>90% yield) in the presence of a stable Pd NP catalyst with EG being regenerated. Atomistic simulations suggest that the CO2 absorption process in the EG-KOH solution is energetically stable, and the catalyst surface provides the reaction site to break the C-O bond in the -O-COOK structure, enabling the hydrogenation of the alkyl carbonate to formate and the regeneration of EG. Our study provides a promising NP-catalysis approach for air capture and conversion of CO2 into value-added chemicals/fuels under ambient conditions.

Addition of Imidazolium-Based Ionic Liquid to Improve Methanol Production in Polyamine-Assisted CO2 Capture and Conversion Systems Using Pincer Catalysts

Ionic liquids have been studied as CO2 capture agents. However, they are rarely used in combined CO2 capture and conversion processes. Utilizing imidazolium-based ionic liquids, the conversion of CO2 to methanol was greatly improved in polyamine assisted systems catalyzed by homogeneous pincer catalysts with Ru and Mn metal centers. Among the ionic liquids tested, [BMIM]OAc was found to perform the best under the given reaction conditions. Among the polyamine tested, pentaethylenehexamine (PEHA) led to the highest conversion rates. Ru-Macho and Ru-Macho-BH were the most active catalysts. Direct air capture utilizing PEHA as the capture material was also demonstrated and produced an 86 % conversion of the captured CO2 to methanol in the presence of [BMIM]OAc.

Integrated Carbon Dioxide Capture and Conversion to Methanol Utilizing Tertiary Amines over a Heterogenous Cu/ZnO/Al2O3 Catalyst

Increasing carbon dioxide emissions has sparked a growing interest in capturing these emissions at the source of their release. For such processes, amines can be used as carbon dioxide capture agents. Herein, CO2 was captured under ambient conditions using solutions of amines and polyamines in ethylene glycol. The captured solutions were then successfully hydrogenated to methanol under hydrogen pressure with a heterogeneous Cu/ZnO/Al2O3 industrial catalyst. An extensive amine scope found that tetramethyl-1,6-hexanediamine, with two tertiary amine sites, provided the highest methanol productivity. This reaction was then optimized to achieve up to 89% methanol yield under relatively mild conditions of 250 °C and 80 bar H2 pressure. The catalyst was shown to be recyclable over five reaction cycles.

Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy

The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO2 emissions. Outpacing the natural carbon cycle, atmospheric CO2 levels increased by 50 % since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chemical recycling of CO2 to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO2 , CO and their derivatives as potential low-temperature alternatives to the commercial processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the critical assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.

Homogeneous Carbon Capture and Catalytic Hydrogenation: Toward a Chemical Hydrogen Battery System

Recent developments of CO₂ capture and subsequent catalytic hydrogenation to C1 products are discussed and evaluated in this Perspective. Such processes can become a crucial part of a more sustainable energy economy in the future. The individual steps of this catalytic carbon capture and usage (CCU) approach also provide the basis for chemical hydrogen batteries. Here, specifically the reversible CO₂/formic acid (or bicarbonate/formate salts) system is presented, and the utilized catalysts are discussed.

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

As the world pledges to significantly cut carbon emissions, the demand for sustainable and clean energy has now become more important than ever. This includes both production and storage of energy carriers, a majority of which involve catalytic reactions. This article reviews recent developments of homogeneous catalysts in emerging applications of sustainable energy. The most important focus has been on hydrogen storage as several efficient homogeneous catalysts have been reported recently for (de)hydrogenative transformations promising to the hydrogen economy. Another direction that has been extensively covered in this review is that of the methanol economy. Homogeneous catalysts investigated for the production of methanol from CO2, CO, and HCOOH have been discussed in detail. Moreover, catalytic processes for the production of conventional fuels (higher alkanes such as diesel, wax) from biomass or lower alkanes have also been discussed. A section has also been dedicated to the production of ethylene glycol from CO and H2 using homogeneous catalysts. Well-defined transition metal complexes, in particular, pincer complexes, have been discussed in more detail due to their high activity and well-studied mechanisms.

Integrated Capture and Conversion of CO2 to Methane Using a Water-lean, Post-Combustion CO2 Capture Solvent

Integrated carbon capture and conversion of CO₂ into materials (IC³ M) is an attractive solution to meet global energy demand, reduce our dependence on fossil fuels, and lower CO₂ emissions. Herein, using a water-lean post-combustion capture solvent, [N-(2-ethoxyethyl)-3-morpholinopropan-1-amine] (2-EEMPA), >90 % conversion of captured CO₂ to hydrocarbons, mostly methane, is achieved in the presence of a heterogenous Ru catalyst under relatively mild reaction conditions (170 °C and <15 bar H₂ pressure). The catalytic performance was better in 2-EEMPA than in aqueous 5 m monoethanol amine (MEA). Operando nuclear magnetic resonance (NMR) study showed in situ formation of N-formamide intermediate, which underwent further hydrogenation to form methane and other higher hydrocarbons. Technoeconomic analyses (TEA) showed that the proposed integrated process can potentially improve the thermal efficiency by 5 % and reduce the total capital investment and minimum synthetic natural gas (SNG) selling price by 32 % and 12 %, respectively, compared to the conventional Sabatier process, highlighting the energetic and economic benefits of integrated capture and conversion. Methane derived from CO₂ and renewable H₂ sources is an attractive fuel, and it has great potential as a renewable hydrogen carrier as an environmentally responsible carbon capture and utilization approach.

An amino acid based system for CO2 capture and catalytic utilization to produce formates

Herein, we report a novel amino acid based reaction system for CO2 capture and utilization (CCU) to produce formates in the presence of the naturally occurring amino acid l-lysine. Utilizing a specific ruthenium-based catalyst system, hydrogenation of absorbed carbon dioxide occurs with high activity and excellent productivity. Noteworthy, following the CCU concept, CO2 can be captured from ambient air in the form of carbamates and converted directly to formates in one-pot (TON > 50 000). This protocol opens new potential for transforming captured CO2 from ambient air to C1-related products.