One “cowboy” derived from a triphenyl phosphino complex (the Lewis Base) with its feet firmly on the ground (a silica support) has teamed up with an initially free-floating tri phenyl borano cowboy (the Lewis Acid); together they form a Frustrated Lewis Pair that has captured a CO2 molecule. The entire complex is effectively bound to the support.
In this elegant study, the Erasmus team demonstrates that anchoring of properly functionalized Lewis acids and bases onto silica supports is feasible. The interaction between the grounded Lewis acid and a dissolved Lewis base as partner in frustration indeed produces associated heterogeneously supported Frustrated Lewis Pairs. The approach also works with the base grounded and the acid in solution. Moreover, the team demonstrated convincingly that these novel systems successfully capture CO2 at low temperature (-65 °C) and release it again at room temperature so that they are interesting candidates for carbon capture and storage (CCS).
Perhaps even more exciting is that these anchored complexes successfully convert CO2 to formic acid, HCOOH. One of the easiest ways to reduce CO2 is to incorporate a hydride (H–) to the carbonyl carbon, H–···CO2, and a proton to one of the carbonyl oxygens, H+···OCO, to ultimately produce formic acid, HCOOH. The proton and the hydride are generated by heterolytic dissociation of H2 on the Frustrated Lewis Pair, which already happens at room temperature. Exposing this modified pair to CO2 at slightly higher temperatures (60°C) leads to formic acid, HCOOH, and eliminates the need for low temperatures to capture the CO2.
The story was well received by the journal Inorganic Chemistry who published it on the web just before the Christmas Holidays started. We congratulate Dr Lisette Erasmus with this nice project and wish her many more successes in the future.
Cite this article
K. Mentoor, L. Twigge, J.W. Niemantsverdriet, J.C. Swarts, E. Erasmus*, “Silica Nanopowder-Supported Frustrated Lewis Pairs for CO2 Capture and Conversion to Formic Acid”, Inorganic Chemistry 60 (2021) 55-69 (published December 22, 2020)