Optimization of ruthenium based catalysts for the aqueous phase hydrogenation of furfural to furfuryl alcohol

The catalytic performance of a series of 4 wt.% Ru-based catalysts in the aqueous-phase hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) has been studied in a batch reactor under very mild conditions of 20 degrees C and 10 bar hydrogen. The effects induced by different commercial supports (SiO2, TiO2, Al2O3, activated carbon and high surface area graphite) and two lab synthesized graphenic materials (with and without N-doping); as well as the influence of the catalyst preparation using three metal precursors (RuCl3, RuNO(NO3)(3) and Ru-3(CO)(12)) have been assessed. Materials were characterized by mean of nitrogen physisorption (BET), transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The different supports significantly modify the catalytic behavior, with the catalysts prepared using graphenic materials found to produce the highest conversion of FAL and the maximum of selectivity to FOL. On these latter supports, the highest FAL yield was achieved by using triruthenium dodecacarbonyl as ruthenium precursor. Ruthenium supported on reduced graphene oxide (rGO) shows 93.3% conversion with 98% selectivity towards FOL. This catalyst was found to exhibit excellent stability, and was reused at least 4 times without loss of activity or selectivity. Characterization data suggest that the catalytic differences can be attributed to the particle size of Ru nanocrystals as well as to their interaction with the surface of graphenic materials. Furthermore, the catalytic results are influenced by the type of metal precursor and the reduction temperature, these facts suggesting that the genesis of the Ru nanoparticles can also play a key role controlling the catalytic activities obtained with these catalysts in the hydrogenation of FAL into FOL.