Preparation And Performances Of Pt-based Catalysts For Glycerol Hydrogenolysis To 1,3-propanediol

The continuous development of biodiesel has resulted in a large excess of glycerol.Therefore,it is important to transform the cheap glycerol into high value-added chemical products.Among the derivatives of glycerol,1,3-propanediol has a wide application and high market value.So,Glycerol as a by-product of the biodiesel can be converted to 1,3-propanediol in the presence of hydrogen,which could be of a great significance to increase economic benefits of biodiesel industry.In this dissertation,WOx-promoted Pt/SiO2,Al2O3-doped Pt-WOx/SiO2 and SAPO-34 supported Pt-WOx catalysts were prepared by sequential impregnation,whose physicochemical properties,such as structure,morphology,surface acidity and chemical state were characterized,The relationships between the physicochemical properties of the catalysts and their catalytic performances were investigated in order to discover the reaction mechanism of glycerol on the catalysts,and provide the basis for the industrial production of glycerol hydrogenolysis to 1,3-propanediol.1.Glycerol hydrogenolysis to 1,3-Propanediol over WOx-promoted Pt/SiO2 CatalystsPt-WOx catalysts were loaded on different supports(ZrO2,Al2O3,SiO2),the WOx concentrations and their calcinations temperature were investigated.The resulting catalysts were characterized by low temperature nitrogen adsorption(BJH),X-ray diffraction(XRD),Raman spectrum(Raman),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM)and X-ray photoelectron spectroscopy(XPS),etc.The experiment results show that the Pt based catalysts supported on ZrO2 and Al2O3 perform strong cleavage activity of C-O bond and have a high conversion of glycerol and a low slectivity to 1,3-propanediol.The catalysts supported on SiO2 exhibit weak breaking activity of C-O bond and have a low conversion of glycerol and a high selectivity to propanediol(almost 1,2-propanediol).The incorporation of WOx in Pt/SiO2 can not only promote the reduction of Pt,but also promote the dispersion of Pt on the surface of the support and reduce the size of Pt particles.The doping of WOx mainly increases the amount of weak and moderate acidic sites on the catalysts,which facilitates the formation of 1,3-propanediol.In addition,the doping of WOx can not only improve the hydrogenolysis activity of the glycerol and the selectivity of 1,3-propanediol,but also inhibit the hydrogenolysis activity of 1,3-propanediol.The highly dispersed WOx on Pt-WOx/SiO2 increases the hydrogenolysis activity and the selectivity of 1.3-propanediol.The crystalline WO3 leads to further hydrogenolysis of propanediol to n-propanol.When the mass fraction of Pt is 2%,WOx is 10%and the calcination temperature of the precursor of WOx is 823 K,the conversion of glycerol and selectivity of 1,3-propanediol on the Pt-WOx/SiO2 catalyst is up to 26.0%and 21.3%,respectively.2.Glycerol hydrogenolysis to 1,3-Propanediol over Al2O3-doped Pt-WOx/SiO2 catalystsPt-WOx/SiO2 promoted by Al2O3 were prepared by incipient wetness impregnation and characterized by BJH,XRD,Raman,TEM,HRTEM,XPS,etc.The effects of the calcination temperature of the precursor of Al2O3 and the content of Al2O3 on the physicochemical properties and the hydrogenolysis activity of glycerol and the selectivity of 1,3-propanediol on the Pt-WOx/SiO2 catalysts were investigated.The results show that doping of Al2O3 to SiO2 can increase the population of weak and moderate acidic sites,and improve the strength of the surface acid,which promote the dehydration-hydrogenation performances of the bifunctional catalyst Pt-WOx/SiO2-Al2O3 and facilitate the hydrogenolysis of glycerol and selectivity of 1,3-propanediol.What's more,the addition of Al2O3 can promote the dispersion of WOx and increase the number of oxygen defect sites of WOx on the surface of support,reducing the particle size of the active metal Pt and increase the dispersion of the active components,and then promote the glycerol hydrogenolysis to 1,3-propanediol.When the content of Al2O3 is 5%and the calcination temperature is 823 K,Pt-WOx/SiO2-5%Al2O3(1073K)exhibits the highest activity.The conversion of glycerol and the selectivity of 1,3-propanediol is 46.1%and 26.9%,respectively.3.Glycerol hydrogenolysis to 1,3-propanediol over Pt-WOx/SAPO-34Pt/SAPO-34 modified with VIB oxides(Cr2O3,M0O3,WOx)were prepared by stepwise incipient wetness impregnation.The effects of different promoters and the different contents of WOx on the physicochemical properties of Pt/SAPO-34 and the hydrogenolysis activity of glycerol were investigated.The optimized catalyst was used to study the different temperatures,the residence time and the pressure of H2 on hydrogenolysis activity of glycerol and selectivity of 1,3-propanediol.The results show that among the VIB oxides,only the WOx has the positive effect on the hydrogenolysis activity of glycerol.The doped WOx on the catalyst show a strong interaction with the carrier,which have a high dispersion degree and lead to the more surface acidic sites.The higher the dispersion of Pt particles is,the better the performances of glycerol hydrogenolysis of the catalysts are.When the mass fraction of WOx was 20%(Pt-20%WOx/SAPO-34),the conversion of glycerol and the selectivity to 1,3-propanediol were optimal,which is 48.0%and 18.8%,respectively.The high reaction temperature promote glycerol conversion,but results in a decrease in 1,3-propanedil due to a over hydrogenolysis of 1,3-propanediol to n-propanol.High hydrogen pressure favors the formation of 1,3-propanediol,and longer reaction time leads to partial deactivation of the catalyst.Through the detail study on Pt-based catalysts catalytic glycerol hydrogenolysis to 1,3-propanediol,we found that Pt-WOx catalysts supported on SiO2 have a higher hydrogenolysis activity of glycerol and selectivity of 1,3-propanediol than those on ZrO2 and Al2O3.WOx improves the number of the surface acidity,promotes the dispersion of Pt and facilitates the reduction of Pt precursor,which increase the conversion of glycerol and selectivity of 1,3-propanediol;Doping of Al2O3 to Pt-WOx/SiO2 promotes the dispersion of WOx and increases the number of oxygen vacancies in the WOx,then reduce the size of Pt particle,which improve the hydrogenolysis activity of glycerol and selectivity of 1,3-propanediol;Among the VIB oxides,only WOx exhibits a positive effect on the hydrogenolysis of glycerol,simultaneously,the high dispersion degree of WOx promote the selective hydrogenolysis of glycerol to 1,3-propanediol.In this dissertation,Pt-WOx/SiO2 promoted by Al2O3 exhibits the best performances on glycerol hydrogenolysis to 1,3-propanediol.