Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol by using Ultrasmall Rh Nanoparticles Embedded on Diamine-Functionalized KIT-6

A Rh/ED-KIT-6 catalyst comprised of Rh nanoparticles embedded on mesoporous silica (KIT-6) functionalized with N1-[3-(trimethoxysilyl) propyl] ethane-1,2-diamine was synthesized by Rh3+ adsorption and chemical reduction in the liquid phase. The structure of ED-KIT-6 and textural properties of the pristine and supported Rh catalysts, as well as particle size and chemical state of the Rh species were examined by various analytical methods. The homogeneous dispersion of ultrasmall Rh nanoparticles, approximately 1.2 nm in size, stabilized by the grafted diamine (ED) species was confirmed. Rh/ED-KIT-6 was applied to the transfer hydrogenation of furfural (FFR) to furfuryl alcohol (FAL) by using formic acid (FA) as the hydrogen source. The effect of the solvent and reaction parameters, such as temperature, reaction time, and FA/FFR ratio, were investigated. The Rh-embedded catalyst exhibited a significantly high turnover frequency (TOF approximate to 204 h(-1)) to that of Ru, Pd, or Ni-based catalysts on KIT-6. A plausible reaction mechanism was proposed after examining an independent FA decomposition reaction over the same Rh-ED-KIT-6 catalyst. The heterogeneity of the catalyst was verified by a hot filtration experiment. The Rh/ED-KIT-6 could be reused for up to three cycles without any decrease in catalytic activity and selectivity, but the slow oxidation of Rh species was detected.