Selective aqueous-phase hydrogenation of D-fructose into D-mannitol using a highly efficient and reusable Cu-Ni/SiO2 catalyst

D-fructose hydrogenation in aqueous phase, at 373 K and 40 bar, was performed using monometallic and bimetallic Cu-Ni/SiO2 catalysts prepared by precipitation-deposition at controlled pH, without any type of co-catalysts and/or additives in solution. The precursors and catalysts were characterized by X-ray diffraction (XRD), N2 physisorption at 77 K, temperature programmed reduction (TPR), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS) analysis, temperature programmed desorption of H2 (H2-TPD) and X-ray photoelectron spectroscopy (XPS). The characterization of the mono and bimetallic samples showed that metal phase is composed of nanoparticles highly dispersed on SiO2 surface. It was also found evidence that a Cu-Ni like-alloy forms in the bimetallic sample. Precisely, the best catalytic performance was obtained with the bimetallic catalyst. This was attributed to a synergistic effect between Cu and Ni, favored by the intimate contact between both elements, which was reached from the Cu-Ni coprecipitation at controlled pH over SiO2. In a three cycles experiment performed with CuNi/SiO2, partial catalyst deactivation was observed. The original activity could be recovered by ex-situ reduction under H2 flow. By temperature programmed oxidation (TPO), it was found that this deactivation is due to surface carbon species strongly chemisorbed on the metallic phase.