CO2 capture by 1-ethyl-3-methylimidazolium acetate: Solubility at low pressure and quantification of chemisorption and physisorption

Reactive capture and electrochemical conversion of CO2 with ionic liquids and deep eutectic solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture and conversion (RCC) of CO2 due to their wide electrochemical stability window, low volatility, and high CO2 solubility. There is environmental and economic interest in the direct utilization of the captured CO2 using electrified and modular processes that forgo the thermal- or pressure-swing regeneration steps to concentrate CO2, eliminating the need to compress, transport, or store the gas. The conventional electrochemical conversion of CO2 with aqueous electrolytes presents limited CO2 solubility and high energy requirement to achieve industrially relevant products. Additionally, aqueous systems have competitive hydrogen evolution. In the past decade, there has been significant progress toward the design of ILs and DESs, and their composites to separate CO2 from dilute streams. In parallel, but not necessarily in synergy, there have been studies focused on a few select ILs and DESs for electrochemical reduction of CO2, often diluting them with aqueous or non-aqueous solvents. The resulting electrode-electrolyte interfaces present a complex speciation for RCC. In this review, we describe how the ILs and DESs are tuned for RCC and specifically address the CO2 chemisorption and electroreduction mechanisms. Critical bulk and interfacial properties of ILs and DESs are discussed in the context of RCC, and the potential of these electrolytes are presented through a techno-economic evaluation.

CO2 conversion to formamide using a fluoride catalyst and metallic silicon as a reducing agent

Metallic silicon could be an inexpensive, alternative reducing agent for CO₂ functionalization compared to conventionally used hydrogen or hydrosilanes. Here, metallic silicon recovered from solar panel production is used as a reducing agent for formamide synthesis. Various amines are converted to their corresponding amides with CO₂ and H₂O via an Si-H intermediate species in the presence of a catalytic amount of tetrabutylammonium fluoride. The reaction system exhibits a wide substrate scope for formamide synthesis. Spectroscopic analysis, including in situ Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N₂ adsorption/desorption analyses, and isotopic experiments reveal that the fluoride catalyst effectively oxidizes Si atoms on both surface and interior of the powdered silicon particles. The solid recovered after catalysis contained mesopores with a high surface area. This unique behavior of the fluoride catalyst in the presence of metallic silicon may be extendable to other reductive reactions, including those with complex substrates. Therefore, this study presents a potential strategy for the efficient utilization of abundant resources.

Reviewing and screening ionic liquids and deep eutectic solvents for effective CO2 capture

CO₂ capture is essential for both mitigating CO₂ emissions and purifying/conditioning gases for fuel and chemical production. To further improve the process performance with low environmental impacts, different strategies have been proposed, where developing liquid green absorbent for capturing CO₂ is one of the effective options. Ionic liquids (IL)/deep eutectic solvents (DES) have recently emerged as green absorbents with unique properties, especially DESs also benefit from facile synthesis, low toxicity, and high biodegradability. To promote their development, this work summarized the recent research progress on ILs/DESs developed for CO₂ capture from the aspects of those physical- and chemical-based, and COSMO-RS was combined to predict the properties that are unavailable from published articles in order to evaluate their performance based on the key properties for different IL/DES-based technologies. Finally, top 10 ILs/DESs were listed based on the corresponding criteria. The shared information will provide insight into screening and further developing IL/DES-based technologies for CO₂ capture.