Solvent‐ and Catalyst‐Free Carbon Dioxide Capture and Reduction to Formate with Borohydride Ionic Liquid

Abstract

The metal- and solvent-free capture and reduction of large amounts of CO₂ to formate under ambient conditions is achieved by combining a pyrrolidinium-based ionic liquid with a borohydride anion. This material demonstrates one of the highest CO₂ capacities at room temperature and 1 bar with up to 1 g <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow></mml:mrow> <mml:mrow><mml:mi>CO</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> g^-1 _IL . CO₂ gas reacts with the BH₄ ^- anion to give triformatoborohydride, [HB(OCHO)₃ ]^- . The reaction occurs without loss in capacity at low CO₂ concentration (6 vol % diluted with N₂ ). The thermodynamics and kinetics of the reaction were monitored by using a magnetic suspended balance. In addition, more than 1 mol <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow></mml:mrow> <mml:mrow><mml:mi>CO</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> mol^-1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow></mml:mrow> <mml:mrow><mml:mrow><mml:mo>[</mml:mo> <mml:mi>EMPY</mml:mi> <mml:mo>]</mml:mo></mml:mrow> <mml:mrow><mml:mo>[</mml:mo> <mml:mi>BH</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mn>4</mml:mn></mml:msub> <mml:mo>]</mml:mo></mml:mrow> </mml:mrow> </mml:msub> </mml:math> is captured and reduced if air is used as a CO₂ source. The product can be then treated with HCl to give formic acid and the corresponding ionic liquid chloride, which can be recycled. This ionic liquid borohydride demonstrates great potential as a CO₂ absorber and reducer to produce alternative fuels.