Studies On The Structure And Catalytic Performance Of Pt/WO₃/ZrO₂ Catalysts For Selective Hydrogenation Of Glycerol

The cost of biodiesel application can be reduced by converting by-product of biodiesel, i.e. glycerol to other high value down-stream chemical products, so that researches and development of catalysts for catalytic hydrogenation of glycerol to C3 alcohols have both theoretical and practical significances. In this dissertation, the relation among the composition, structure and catalytic performance of Pt/WO3/ZrO2, Pt/NbOx-WO3/ZrO2 and Pt/ReOx-WO3/ZrO2 catalysts have been systematically and deeply studied by using microreactor tests combined with various physical and chemical techniques such as scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), BET surface area measurements (BET), Laser Raman spectra (LRS), CO chemisorption, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD),1H magic angle spinning nuclear magnetic resonance (1H MAS NMR), Py-IR pyridine adsorption Fourier-transform infrared (Py-IR) and diffuse reflectance Fourier-transform infrared spectroscopy of NH3 (NH3-DRIFTs). The results obtatined in this work have provided important reference informations for development of catalysts with excellent catalytic properties for glycerol hydrogenation to C3 alcohols. The experimental results have shown that:1.The WO3 component in Pt/WO3/ZrO2 catalyst (2.0 wt.% Pt) can remarkably improve the both glycerol conversion and 1,3-propanediol (1,3-PDO) selectivity, which may be related to the formation of HxWO3 Br(?)nsted (B) acid by reaction of hydrogen spilt-over from Pt with WO3. When WO3 loading was below its dispersion capacity (3.3 W/nm2 ZrO2), although the Pt dispersion decreased with increasing WO3 loading, the increase of acidic sites on the catalyst surface resulted in the increases of glycerol conversion and 1,3-PDO selectivity. When WO3 loading was higher than its dispersion capacity, WO3 crystallites formed and Pt dispersion decreased furtherly, leading to the decrease of glycerol conversion with 1,3-PDO selectivity almost unchanged. The optimum WO3 loading in the Pt/WO3/ZrO2 catalyst is around the WO3 dispersion capacity on the ZrO2 support, i.e.3.3 W/nm2 ZrO2.2. Adding NbOx with appropriate amount into Pt/WO3/ZrO2 catalyst (2.0 wt.%Pt, 4.5 wt.% WO3) increased the both glycerol conversion and 1,3-PDO selectivity. With increasing NbOx loading, the amount of B acidic sites on the Pt/NbOx-WO3/ZrO2 catalysts increased, resulting in the increases of glycerol conversion and 1,3-PDO selectivity. When the Nb loading exceeded 1.5 wt.%, the WO3 species gradually aggregated to form WO3 crystallites and the Pt dispersion decreased obviously, leading to the remarkable decreases of glycerol conversion and 1,3-PDO selectivity on the Pt/NbOx-WO3/ZrO2 catalysts. The optimum Nb loading in the Pt/NbOx-WO3/ZrO2 catalyst is around 1.5 wt.%.3. Adding ReOx with appropriate amount into Pt/WO3/ZrO2 catalyst (2.0 wt.%Pt, 5.0 wt.%WO3) can futher improve the catalytic properties for glycerol hydrogenation. With increasing ReOx loading, not only the amount of weak acidic sites on the Pt/WO3/ZrO2 catalyst increased, but also the Pt dispersion increased remarkably, resulting in the increase of glycerol conversion to about 100% with total C3 alcohols selectivities almost unchanged (>95%). When Re loading was higher than 0.8 wt.%, the exceeded ReOx caused the decrease of Pt active surface, leading to the decrease of glycerol conversion. The optimum Re loading in Pt/ReOx-WO3/ZrO2 catalyst is around 0.8 wt.%.