Direct CO₂ Capture and Reduction to High‐End Chemicals with Tetraalkylammonium Borohydrides

Abstract

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO2, even at low CO2 concentrations, and reduce it to formate under ambient conditions. These materials show CO2 absorption capacities up to 30 mmolCO2 g−1 at room temperature and 1 bar CO2. Every BH4− anion can react with three CO2 molecules to form triformatoborohydride ([HB(OCHO)3]−). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO2 capture and reduction from air was achieved with tetraethyl, ‐propyl, and ‐butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO2 diffusivity (crystallinity and free‐volume), activation energy (charge‐transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N‐formylation of an amine.

[AsCCAs]-Coordinated Rhenium Hydrides and Their Reactivities Toward Unsaturated Hydrocarbons, Heterocumulenes, and CO2

“…This stereochemical similarity was then exploited by reacting 14 with NaBEt 3 H (1.1 equiv) in order to recycle the cis -configured hydride cis - 10 in yields of 93%. The resulting synthetic cycle (see Scheme ), however, is not (yet) suited for establishing a catalytic process due to the incompatibility of the employed reagents: borohydrides are known to rapidly react with CO 2 to afford formates as well, i.e., a less reactive (and less expensive) hydride source needs to be found in future studies.…”

Direct air capture: process technology, techno-economic and socio-political challenges

“…341 Inspired by the high reactivity of hydrides with CO 2 under mild conditions, ILs with BH 4 À ions have also been studied for capture and conversion of CO 2 directly from air. 342,343 Competition between hydrolysis of the BH 4 À and CO 2 reduction is observed, with significant conversion to products taking a number of days. Recovery of the IL is possible by introducing hydrochloric acid to form formic acid.…”

Novel Fluid Ionic Liquid Composites with Self-Assembled Porosity and Chemical Sites for Facilitating CO2 Separation

“…This characteristic was quite encouraging due to the greater demand for low concentration/partial pressures of CO 2 capture and separation in industries. 29,30 Besides, it could be deduced that CO 2 absorption of the fluid porous IL composites is a chemisorption process and the strong chemical interactions between [N 2222 ][Gly], [HDBU][Im] and CO 2 are dominated.…”