Influence of catalyst pretreatment on catalytic properties and performances of Ru-Re/SiO2 in glycerol hydrogenolysis to propanediols

摘要

Bimetallic Ru-Re/SiO2 and monometallic Ru/SiO2 catalysts were prepared by impregnation method and their catalytic performances were evaluated in the hydrogenolysis of glycerol to propanediols (1,2-propanediol and 1,3-propanediol) with a batch type reactor (autoclave) under the reaction conditions of 160 °C, 8.0 MPa and 8 h. Ru-Re/SiO2 showed much higher activity in the hydrogenolysis of glycerol than Ru/SiO2, and the pretreatment conditions of the catalyst precursors had great influence on the catalytic performance of both Ru-Re/SiO2 and Ru/SiO2 catalysts. The physicochemical properties of Ru-Re/SiO2 and Ru/SiO2, such as specific surface areas, crystal phases, morphologies/microstructures, surface element states, reduction behaviors and dispersion of Ru metal, were characterized by N2 adsorption/ desorption, XRD, Raman, TEM-EDX, XPS, H2-TPR and CO chemisorption. The results of XRD, TEM-EDX and CO chemisorption characterizations showed that Re component had an effect on promoting the dispersion of Ru species on the surface of SiO2, and the measurements of H2-TPR revealed that the co-existence of Re and Ru components on SiO2 changed the respective reduction behavior of Re or Ru alone. High pre-reduction temperatures would decrease the activities of Ru-Re/SiO2 and Ru/SiO2 catalysts, compared with the corresponding calcined catalysts (without pre-reduction), which actually went through an in-situ reduction during the reaction. XPS analysis indicated that Ru species was in Ru~0 metal state, while Re species was mostly in Re oxide state in the spent Ru-Re/SiO2 sample. Re component was probably in rhenium oxide state rather than Re~0 metal state to take part in the reaction via interaction with Ru~0 metal.