CO₂ Chemisorption Behavior of Coordination‐Derived Phenolate Sorbents

Abstract

CO2 chemisorption via C−O bond formation is an efficient methodology in carbon capture especially using phenolate‐based ionic liquids (ILs) as the sorbents to afford carbonate products. However, most of the current IL systems involve alkylphosphonium cations, leading to side reactions via the ylide intermediate pathway. It is important to figure out the CO2 chemisorption behavior of phenolate‐derived sorbents using inactive and easily accessible cation counterparts without active protons. Herein, phenolate‐based systems were constructed via coordination between alkali metal cations with crown ethers to avoid the participation of active protons in CO2 chemisorption. Reaction pathway study revealed that CO2 uptake could be achieved by O−C bond formation to afford carbonate. CO2 uptake capacity and reaction enthalpy were significantly influenced by the coordination effect, alkali metal types, and alkyl groups on the benzene ring.

CO2 Chemisorption Behavior in Conjugated Carbanion-Derived Ionic Liquids via Carboxylic Acid Formation

“…Ionic liquids (ILs) represent one of the most attractive and extensively studied systems in carbon capture, which possess the inherent advantages of low vapor pressure, high thermal stability, and large tunability. − Particularly, the nonvolatility of ILs allows the captured CO 2 to be easily released from the saturated solvents, resulting in lower energy consumption and environmental concerns than the traditional amine scrubbing method . After the initial achievements in ILs (e.g., imidazolium or phosphonium cations coupled with BF 4 – , PF 6 – , or NTf 2 – anions) for CO 2 physisorption, task-specific ILs (TSILs) were developed for CO 2 chemisorption, which delivered much higher CO 2 uptake capacity and enhanced interaction strength. ,− State-of-the-art TSILs in CO 2 chemisorption can be divided into two categories, including amino group-functionalized ILs (AILs) − and superbase-derived TSILs (STSILs). − Generally, CO 2 was absorbed via the N–C or O–C bond formation, leading to the production of carbamate or carbonate through the nucleophilic attack of the amino groups (for AILs) or basic nitrogen- or oxygen-based anions (for STSILs) on the carbon atom of CO 2 .…”

Dihydroxybenzene‐derived ILs as Halide‐Free, Single‐component Organocatalysts for CO2 Insertion Reactions

“…In particular, it is difficult to asses independently the role of the anion, requiring alternative liquid sorbents composed of phenolate and alkali metal cations coordinated by crown ethers. [9]…”

“…Phenolate‐based organocatalysts are suitable for capture, storage and chemical conversion of CO 2 . ILs containing phenolate moieties are active towards CO 2 chemisorption, thanks to their low volatility, good thermal stability, high CO 2 capacity and selectivity, and fast carbon capture kinetics, leading to a direct and reversible interaction with CO 2 [5–9] . Moreover, simple polyhydroxybenzene derivatives have been employed as organocatalyst for CO 2 insertion in epoxides.…”

Computational Insights into Malononitrile-Based Carbanions for CO2 Capture

“…However, they suffer from low capture ratio (MEA:CO 2 = 2:1), solvent degradation and loss, and high regeneration temperature . As such, advanced liquid sorbents based on ionic liquids have been developed employing anionic N and O sites to chemisorb CO 2 at close to an equimolar ratio. − …”