Insights into the structure-activity relationship in aqueous-phase hydrogenation of levulinic acid to 1,4-pentanediol over bimetallic Ru-Re/C catalysts

Hydrogenation of biomass-derived levulinic acid (LA) to 1,4-pentanediol (PDO) is a sustainable route to replace petroleum-derived polyols. Although the combination of ruthenium (Ru), a hydrogenating metal, and rhenium (Re), an oxophilic promoter, results in high activity for PDO production, the synergistic effect between Ru and Re and the effect of carbon support are not well understood. In this study, the factors determining the catalytic activity and selectivity of carbon-supported RuRe for PDO production were investigated. Bimetallic RuRe nanoparticles with various atomic ratios and monometallic Ru and Re were supported on various carbon materials with different surface properties such as activated carbon (AC) carbon black (CB), mesoporous carbon (CMK-3), carbon nanofiber (CNF) and their reaction kinetics were compared. The structural and physicochemical properties of the catalysts were characterized using X-ray diffraction, temperature-programmed reduction, N-2-physisorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic activity and PDO selectivity were correlated with the metal particle size, pore structure, and surface oxygen functionalities, in which the smaller RuRe nanoparticles with a Re-enriched surface supported on carbon with a larger pore size exhibited a higher PDO production rate. Among the catalysts, RuRe supported on CB exhibited the highest PDO selectivity (similar to 75 %) at 130 degrees C and 50 bar-H-2. The impact of the Re promoter in the RuRe/C catalyst on the LA hydrogenation mechanism was also investigated for the first time using in situ FT-IR spectroscopy.