Catalytic Hydrogenation of CO2 to Formate Using Ruthenium Nanoparticles Immobilized on Supported Ionic Liquid Phases.

Abstract

Ruthenium nanoparticles (NPs) immobilized on imidazolium-based supported ionic liquid phases (Ru@SILP) act as effective heterogeneous catalysts for the hydrogenation of carbon dioxide (CO2 ) to formate in a mixture of water and triethylamine (NEt3 ). The structure of the imidazolium-based molecular modifiers is varied systematically regarding side chain functionality (neutral, basic, and acidic) and anion to assess the influence of the IL-type environment on the NPs synthesis and catalytic properties. The resulting Ru@SILP materials contain well-dispersed Ru NPs with diameters in the range 0.8-2.9nm that are found 2 to 10 times more active for CO2 hydrogenation than a reference Ru@SiO2 catalyst under identical conditions. Introduction of sulfonic acid groups in the IL modifiers results in a greatly increased turnover number (TON) and turnover frequency (TOF) at reduced metal loadings. As a result, excellent productivity with TONs up to 16100 at an initial TOF of 1430 h-1 can be achieved with the Ru@SILP(SO3 H-OAc) catalyst. H/D exchange and other control experiments suggest an accelerated desorption of the formate species from the Ru NPs promoted by the presence of ammonium sulfonate species on Ru@SILP(SO3 H-X) materials, resulting in enhanced catalyst activity and productivity.