Preparation of nano-scale nickel-tungsten catalysts by pH value control and application in hydrogenolysis of cellulose to polyols

The Ni-W/SBA-15 catalysts prepared by incipient-wetness impregnation method and controlled by the pH value were developed. Potassium hydroxide and citric acid regarded as the pH value regulators were added to the solution before impregnation to provide an acidic or basic condition at different pH values (0.83, 1.00, 3.09, 5.00, 7.03, 8.97 and 11.0). The 74.5% yield of total low carbon (C_{2, 3}) polyols including ethylene glycol (EG), 1, 2-propylene glycol (1, 2-PG) and glycerol (Gly) was obtained over 10%Ni-20%W/SBA-15 catalyst prepared at pH value of 1.00 and 518 K under H₂ pressure of 5.0 MPa. Furthermore, the physical properties of this series of nickel-tungsten catalysts were characterized by BET and SEM. The results demonstrated that the catalysts showed excellent thermal stability and the surface area was mainly in range of 330-450 m²/g. The particles had a good dispersion on the surface of SBA-15 but some aggregations were existed which could be characterized by TEM and SEM-EDX. However, the reduction of metallic oxides especially for NiO was obviously influenced by pH value control and some metallic species characterized by XRD. According to XRD results, the impregnation pH value influenced the reduction of NiO and the phase states of nickel and tungsten species.