Design and Understanding of Adaptive Hydrogenation Catalysts Triggered by the H 2 /CO 2 -Formic Acid Equilibrium

An adaptive catalytic system for selective hydrogenation was developed exploiting the H + CO HCOOH equilibrium for reversible, rapid, and robust on/off switch of the ketone hydrogenation activity of ruthenium nanoparticles (Ru NPs). The catalyst design was based on mechanistic studies and DFT calculations demonstrating that adsorption of formic acid to Ru NPs on silica results in surface formate species that prevent C═O hydrogenation. Ru NPs were immobilized on readily accessible silica supports modified with guanidinium-based ionic liquid phases (Ru@SILP ) to generate in situ sufficient amounts of HCOOH when CO was introduced into the H feed gas for switching off ketone hydrogenation while maintaining the activity for hydrogenation of olefinic and aromatic C═C bonds. Upon shutting down the CO supply, the C═O hydrogenation activity was restored in real time due to the rapid decarboxylation of the surface formate species without the need for any changes in the reaction conditions. Thus, the newly developed Ru@SILP catalysts allow controlled and alternating production of either saturated alcohols or ketones from unsaturated substrates depending on the use of H or H /CO as feed gas. The major prerequisite for design of adaptive catalytic systems based on CO as trigger is the ability to shift the H + CO HCOOH equilibrium sufficiently to exploit competing adsorption of surface formate and targeted functional groups. Thus, the concept can be expected to be more generally applicable beyond ruthenium as the active metal, paving the way for next-generation adaptive catalytic systems in hydrogenation reactions more broadly.