The Study On The Heterogeneous Photocatalytic Selective Oxidation Cleavage Reation Of Vicinal Diol

Due to the limited reserves of fossil energy and the serious pollution to the environment during the utilization,developing the green and sustainable new energy has aroused the great attentions of scientist.Biomass is the most abundant renewable carbon resource,and has great development potential for the sustainable production of chemicals in the future.Considering that biomass raw materials are mostly composed of monosaccharide and aromatic ring linked with specific C-O and C-C bonds,the design and development of the catalytic system for C-C bond activation and precise cleavage is helpful for the selective transformation of biomass feedstock;the common thermal reactions for the oxidative C-C bond cleavage reaction needed the high reaction temperature and relatively high pressure,while the photocatalytic technology exhibits the advantages of mild conditions and high selectivity.Therefore,the research on the oxidative C-C bonds cleavage of vicinal diols by heterogeneous photocatalysis has important scientific significance and application value..In this thesis,heterogeneous photocatalytic systems including the solid VOx/Zn O,VOx and flower-like Bi2O2CO3 have been designed and developed for seletive oxidative C-C bond cleavage of vicinal diols,and the efficient and highly selectivive preparations of aromatic aldehydes were achieved under mild conditions.Otherwise,the physical characterization and analysis of photocatalysts was also used to explore the reaction mechanism of photocatalytic oxidation.At first,the VOx/Zn O,VOx/γ-Al2O3,VOx/Ni O,VOx/Ti O2 and VOx photocatalysts were prepared by precipitation method and solvothermal method,respectively,and then were used for the photocatalytic aerobic oxidative cleavage of hydrobenzoin.As a result,it is found that the used heterogeneous vanadium oxide-based photocatalysts could regulate the product distributions of vicinal diol oxidative cleavage reactions.During the selective aerobic oxidative cleavage of hydrobenzoin,the selectivity of the product benzaldehyde can reach 91% at the complete conversion of hydrobenzoin when VOx/Zn O was employed as the catalyst and reation was performed under suitable conditions.However,when VOx/Ti O2 or VOx is used as the catalyst,the selectivity of main productbenzoic acid is 100% and the conversion rate of hydrobenzoin reaches 99% in the dichloromethane solvent.Next,the photocatalysts were characterized by XRD,PL,XPS,EPR,EIS,BET,SEM,UV-vis DRS and NH₃-TPD techniques,and the results showed that VOx/Zn O and VOx give larger photocurrent density and smaller impedance,indicating that the catalyst has a higher separation efficiency of electrons and holes that elevates the number of photogenerated carriers;moreover,VOx/Zn O also contains a larger absorption wavelength and a lower band gap energy,which assisted the photocatalytic selective oxidative cleavage processes to be easier to proceed.In addition the Lewis acid sites on the catalyst surface could also accelerate the aerobic oxidative cleavage reaction.The recycling of catalyst further confirmed that the activity,crystal form and specific surface area of VOx/Zn O and VOx remained almost unchanged after being resued for more than five times that indicates that the photocatalysts keep very stable in the catalytic oxidation reactions under the visible light irradiations..In the following,Bi₂O₂CO₃ photocatalysts with various morphologies were synthesized in water solvent,and the promotion effect on selective aerobic oxidative cleavage of vicinal diols was investigated under the light irradiation.The results showed that the surface morphology of photocatalysts is closely related to the catalytic activity.Among them,the flower-like Bi2O2CO3 shows the good activity in the selective oxidative cleavage reaction;when Xe lamp was employed as light source for the catalytic reaction,the conversion of raw material 1-phenyl-ethane-1,2-diol was 95%,and the selectivity of the product benzaldehyde could reach 99% in reaction.After the optimized experiments,it is concluded that the chosen reaction solvent was the n-butanol and tetramethylammonium bromide（TMAB）,and the suitable oxygen pressure and the reaction time are 0.3 MPa and 12 h,respectively.Otherwise,the Bi2O2CO3 catalysts were tested by XRD,EPR,SEM,TEM,UV-Vis,XPS,PL and EIS.It is found that flower-like Bi2O2CO3 had relatively large specific surface area,small impedance,very large photocurrent density and the low fluorescence emission peak intensity,which improve the effective separation efficiency of electron and holes,and increase the adsorption capacity of the vicinal diol owing to the exsistance of the special numerous oxygen vacancies.These characters efficiently accelarated the selective aerobic oxidative C-C bond cleavage reaction.