Glycerol Hydrogenolysis To 1,3-Propanediol Over Bifunctional Catalysts Of Platinum Loaded On Solid Acid

Produced by transesterification of oil with methanol or ethanol,biodiesel is one kind of green and renewable energy,which can partly replace petroleum products.However,glycerol,the main by-product of biodiesel,had earned a serious surplus,and the price of glycerol also kept falling.Therefore,it is highly motivtated to transform low-cost glycerol into high value-added chemicals,which can both be helpful in utilizing glycerol,promoting the biodiesel industry,and save abundant fossil resources.At present,1,3-propanediol（1,3-PDO）,a popular chemical in the market,is the most valuable product in glycerol catalytic process.It can be used as the raw material of polyether and polyester,as well as in the food,cosmetics and pharmaceutical industries,and it can also be used in the synthes is process of antibacterial agents,plasticizers,preservatives and emulsifiers.However,the chemical reactivity of 1°OH and 2°OH in glycerol differs very little,and the steric hindrance makes the activity of2°OH worse.It is thermodynamically unfavorable for the glycerol hydrogenolys is to 1,3-PDO.So catalysts are essential and important for this process.Among all the catalysts systems,Pt-W and Ir-Re systems were the most prevalent catalysts for glycerol hydrogenolysis to 1,3-PDO.However,the Re O_x additive in Ir-Re catalyst system is unstable in water.Therefore,Pt-W system had been studied extensively.In fact,it was not unified on the state and function of W,and the source of acid in Pt-W system was a little confused either.Based on Pt-W catalyst system,WO₃-Al₂O₃-SiO₂ composite and W,Aldoped SBA-15 molecular sieve were prepared as support,which improved the dispersion of W,Al.After Pt was loaded,these above prepared catalysts were used in glycerol hydrogenolys is to 1,3-PDO reaction and better results were caught.Considering that W in the two systems mentioned above was partially reduced and the W species had oxygen vacancies,we prepared WO₃ with oxygen vacancy to load Pt for the target reaction.Concluded from the characterization results and experiments behavior of the as-prepared catalysts,the state of W,the source and role of acid sites in Pt-W catalysts were explained.Based on these results,Al-SBA-15-SO₃H solid acid was prepared and used to load Pt for the same hydrogenolysis process,which was also effective and this result expedited the catatlysts system for the glycerol hydrofgenolysis to1,3-PDO reaction.These research were conducive to biodiesel industry development,meeting the requirement of green chemistry.It was also meaningful for vicinal diol selective reduction and polyhydroxyl reagents deoxygenation-hydrogenation.The main research contents and conclusions are as follows:1.Platinum supported on WO₃-doped aluminosilicate catalyst system:A homogeneous stable WO₃-Al₂O₃-SiO₂ support was prepared by sol-gel process,and then the reaction of glycerol hydrogenolysis to1,3-PDO was carried out after Pt loading.The powder XRD,FT-IR and XPS experiments were hired to characterize the support and it showed that the WO₃-Al₂O₃-SiO₂ complex was formed.The W,Al,and Siwere uniformly dispersed in the as-prepared complex.NH₃-TPD experiment illustrated that the acid sites in this kind of material was mainly medium-strong acid,and the ac id amount was affected by W/Alratio:the acid amount of the above material gave the maximum when the mass ratio of WO₃ to Al₂O₃ was 2:1.It was found that 2Pt/WAlSiwith the mass ratio of WO₃ to Al₂O₃ at 2 contributed to a high selectivity to 1,3-PDO close to 56%at 48%glycerol conversion with a TOF of 101.73g_glycerol/(g_Pt﹒h),and the space time yield for 1,3-PDO in an optimized reaction condition could reach 18.34 g_1,3-PDO/(g_Pt·h).A plaus ible mechanism of glycerol hydrogenolysis over the 2Pt/2WAlSiwas proposed from the characterization and reaction results.The hydrogen bonds played a key role in bridging the primary hydroxyl of glycerol with the surface OH groups derived from Si-OH or Al-OH in the support.The Br（?）nsted acid sites were responsible for dehydration and the loaded platinum as the active centre for the hydrogenation of the intermediate to1,3-PDO.2.Platinum supported on W and Alincorporated SBA-15 catalyst system:The W and Aldoped SBA-15 with uniform distribution of Br（?）nsted and Lewis acid sites was synthes ized by hydrothermal method.The hydrogenolys is of glycerol to 1,3-PDO was carried out after loading Pt on the above mentioned SBA-15.A combination of the characterization techniques including XRD,UV-Vis DRS and Raman spectra showed the tungsten and aluminium were incorporated into SBA-15 framework homogeneously.Concluded from XPS,NH₃-TPD and Py-IR measurements,there were three kinds of Br（?）nsted acid sites in Pt/（W+Al）-SBA-15 catalysts.WO_x captured electrons from H,which resulted into H⁺and gave rise to Br（?）nsted acidity,the other one of the Br（?）nsted acid site arose in situ on Pt/（W+Al）-SBA-15 samples by spillover H atoms during glycerol hydrogenolysis,and the third kind of Br（?）nsted acid sites could be ascribed to the protons due to the presence of Alin the SBA-15 framework.It was found that 2Pt/20（W+Al）-SBA-15contributed to a high selectivity to 1,3-PDO close to 50%at 66%glycerol conversion.The glycerol hydrogenolys is towards 1,3-PDO over Pt/（W+Al）-SBA-15 proceeds through a dehydration-hydrogenation process,and the enhanced 1,3-PDO selectivity greatly benefited from the synergism effect between Lewis and Br（?）nsted acid sites,which were tightly related to the incorporation of W and Alspecies on the modified SBA-15.3.Platinum supported on oxygen defect type WO₃ catalyst system:The oxygen defect rich WO₃（D-WO₃）was prepared by one-step hydrothermal-reduction method.The as prepared WO₃ was used to support Pt for glycerol hydrogenolysis to 1,3-PDO.By hiring ESR,UV-Vis DRS and XPS tests,the as prepared WO₃ was proved to possess oxygen defects,and the oxygen defects sites could be adjusted by calcining the D-WO₃in air.Concluded from the XPS,NH₃-TPD and Py-IR measurements,there were Br（?）nsted acid sites and Lewis acid sites in the D-WO₃.Which was same to Pt/（W+Al）-SBA-15 catalysts,there were also three kinds of Br（?）nsted acid sites in Pt/D-WO₃:WO_x captured electrons from H,which resulted in H⁺and gave rise to Br（?）nsted acidity,the other one of the Br（?）nsted acid site arose in situ during glyceol hydrogenolys is on Pt/D-WO₃ samples by spillover H atoms,and the third kind of Br（?）nsted acid sites coulded be ascribed to the hydroxyl located on the surface of the D-WO₃.Moreover,the number of acid sites in D-WO₃was positively correlated with the number of defect sites,that was,the more defect sites,the stronger for the acidity of D-WO₃.The glycerol hydrogenolys is also showed a positive correlation with acid sites amount,that is,defect site:the more acid sites amount,the higher conversion for glycerol and the selectivity for 1,3-PDO.Among which,the Lewis acid sites played the role of anchoring 1°OH in glycerol,and the Br（?）nsted acid sites played the role of dehydration.The enhanced catalytic performance greatly benefited from the synergism effect between Lewis and Br（?）nsted acid sites.4.Platinum loaded on Aland-SO₃H modified SBA-15 catalyst system:The Aland-SO₃H incorporated SBA-15 with uniform distribution of Br（?）nsted and Lewis acid sites was synthesized by hydrothermal method.The hydrogenolys is of glycerol to 1,3-PDO was carried out after loading Pt on the above mentioned SBA-15.A combination of the characterization techniques of XRD and FT-IR showed that the aluminium and-SO₃H were incorporated into SBA-15framework homogeneously.Seen from the test results of NH₃-TPD and Py-IR experiments,there were three kinds of Br（?）nsted acid sites in Pt/Al-SBA-15-SO₃H catalysts.The first kind of Br（?）nsted acid site SBA-15 skeleton which was used to balance the negative charge of[AlO₄]^-tetrahedron,and the third one was ascribed to the hydroxyl group of Al₂O₃ dispersed on the SBA-15 surface.The glycerol hydrogenolysis towards 1,3-PDO over Pt/Al-SBA-15-SO₃H proceeded through a dehydration-hydrogenation process,and the enhanced 1,3-PDO selectivity greatly benefited from the synergism effect between Lewis and Br（?）nsted acid sites,which were tightly related to the incorporation of Aland-SO₃H species on the modified SBA-15.This kind of catalyst didn’t contain W species,so it was helpful to enrich the catalyst system for glycerol hydrogenolys is to 1,3-PDO.