Ruthenium Nanoparticles on Water-Stable Supported Ionic Liquid Phases as Catalytic Systems for Aqueous Phase CO$_2$ Hydrogenation

The first example of a hydrothermally stable Supported Ionic Liquid Phase (SILP) material was designed and used successfully as a support for ruthenium nanoparticles (Ru NPs) in catalytic hydrogenation of CO$_2$ to formic acid in water/amine media. Imidazolium-based ionic liquids (ILs) were grafted on activated carbon (AC) through the formation of robust carbon–carbon bonds via diazotization, followed by deposition of Ru NPs using an organometallic approach. Compared to reference materials, the presence of the IL on the solid material led not only to improved catalyst performance of the nanoparticles but also to higher formic acid concentrations in the reaction mixture due to additional thermodynamic stabilization of the product. The Ru@SILPAC catalysts showed high activity (turnover frequencies (TOFs) exceeding 3000 h$^{–1}$), productivity (turnover numbers (TONs) up to 15,000 in a single batch), and stability (10 recycling with no apparent loss of activity). These results define a new benchmark for NP-based catalysts in CO2 hydrogenation to formic acid and suggest promising potential for the application of such NP@SILP materials in aqueous phase hydrogenation reactions in general.