Studies On The Promotional Effects Of Niobium Components In The Supported Pt/NbO_x-WO₃/ZrO₂ Catalysts For Selective Hydrogenation Of Glycerol

The promotional effect of niobium components in the supported Pt/NbOx-WO3/ZrO2 catalysts for selective hydrogenation of glycerol have been studied by using X-ray powder diffraction(XRD),BET surface area measurements,laser Raman spectroscopy(LRS),CO chemisorption,hydrogen temperature-programmed reduction(H2-TPR),NH3 temperature-programmed desorption(NH3-TPD)and NH3-infrared spectroscopy(NH3-DRIFTS)combined with micro-reactor tests of selective hydrogenation of glycerol.The effects of catalyst composition and structure on the surface properties and catalytic properties of Pt/NbOx-WO3/ZrO2 catalysts were investigated.The main research results are as follows.(1)With increasing niobium loading,glycerol conversion and 1,3-Propanediol(1,3-PDO)selectivity on the Pt/NbOx-WO3/ZrO2 catalysts first increase,while niobium content is higher than 1.5 wt%,glycerol conversion and 1,3-PDO selectivity gradually decrease.The optimum loading of niobium WO3 on the Pt/NbOx-WO3/ZrO2 catalyst is determined to be ca.1.5 wt%.(2)With increasing niobium loading,Pt dispersion of Pt/NbOx-WO3/ZrO2 catalyst decreases while the amount of Bronsted(B)acidic center increases.The higher amount of B acidic center on the catalyst results in the higher glycerol conversion and 1,3-PDO selectivity.(3)When the niobium loading exceeds 1.5 wt%,the WO3 species gradually aggregates to form WO3 crystallites and the Pt dispersion decreases obviously,which leads to remarkable decreases of glycerol conversion and 1,3-Propanediol(1,3-PDO)selectivity on the Pt/NbOx-WO3/ZrO2 catalysts.