Production of HCOOH/NEt₃ Adducts by CO₂/H₂ Incorporation into Neat NEt₃

Abstract

Research efforts are currently devoted to hydrogen storage in CO 2 as formic acid derivatives, a thirty-year old idea [1] not yet implemented. A chemical loop is conceivable based on a formate intermediate which can be produced in a pure and storable form under moderately high CO 2 and H 2 pressures and which can release gases at atmospheric pressure on demand when in contact with an appropriate catalyst. The catalytic decomposition of HCOOH itself has received renewed attention.[2] Remarkably, M. Beller and co-workers have demonstrated that HCOOH/NEt 3 adducts can also be catalytically decomposed at 40 8C to H 2 free of CO, albeit diluted by CO 2 .[3] However, a procedure for the production of either HCOOH or HCOOH/NEt 3 adducts from CO 2 and H 2 is still lacking. The formation of HCOOH by CO 2 hydrogenation is hampered by unfavorable thermodynamics (DG o 298 = + 33 kJ mol À1

A Process for the Synthesis of Formic Acid by CO2 Hydrogenation: Thermodynamic Aspects and the Role of CO

“…Addition of small amounts of water or alcohols, as reported by Jessop, Noyori et al.,7 did not lead to significant improvement. Furthermore, the protocol of Fachinetti et al.,3k in which small amounts of formic acid salts were added as initiator in the NEt 3 system, was not successful in the case of NHex 3 as the sole solvent.…”

“…Many trialkylamines form formic acid rich liquid salts, which are not miscible with the free amine 3k. In these salts, only one equivalent of formic acid is deprotonated, whereas the excess (with respect to the amine) is presumably coordinated through hydrogen bonding.…”

Interconversion between Formic Acid and H2/CO2 using Rhodium and Ruthenium Catalysts for CO2 Fixation and H2 Storage

“…known, the hydrogenation of CO 2 and the decomposition of formic acid are, except for a few studies, [26][27][28][29] usually reported independently.…”

Direct synthesis of formic acid from carbon dioxide by hydrogenation in acidic media

“…In contrast to the direct reaction of H 2 with CO 2 , the hydrogenation of carbonate and bicarbonate are well-established reactions282930 that have been achieved in a wide variety of organic solvents, ionic liquids, water and supercritical CO 2 (ref. 20).…”