Synthesis And Catalytic Performance Of Metal Organic Frameworks For Liquid-phase Beckmann Rearrangement Of Cyclohexanone Oxime

Metal organic frameworks(MOFs)is a new type of adsorbent and catalytic materials with excellent physical and chemical properties.Most of the current studies apply it to the adsorption process,and only a small amount of MOFs are applied to several kinds of fixed catalytic reactions.The Beckmann rearrangement of cyclohexanone oxime is a typical acid-catalyzed reaction.The traditional oleum catalytic process has the problems of ammonium sulfate as by-product,corrosion of equipment and environmental pollution.In this thesis,four kinds of MOFs as solid acid catalysts were prepared,which were applied to the liquid Beckmann rearrangement of cyclohexone oxime for the first time,and the catalytic action of acid sites on different framework for the reaction was discussed.The effect of the acid amount,acid strength and acid type were also examined.Firstly,MIL-101(Cr)metal organic framework material was prepared by hydrothermal synthesis method with different mineralizers.The characterization results of N2 physisorption,XRD,FT-IR and thermogravimetric analysis showed that the metal organic framework structure was successfully constructed.The pyridine adsorption infrared characterization of the MIL-101(Cr)framework was performed to the investigation of acid type.In the liquid phase Beckmann rearrangement reaction,MIL-101(Cr)showed both low conversion of cyclohexanone oxime and selectivity of caprolactam.The main reason is that only the Lewis acid sites formed by Cr metal unsaturated coordination in its framework can not effectively catalyze the formation of caprolactam..At the same time,the presence of hydroxyl groups at the end of the backbone leads to partial hydrolysis of cyclohexanone oxime to cyclohexanone.Then,the metal node Cr was changed to Al,the MIL-53(Al)metal organic framework material was prepared by a hydrothermal synthesis method with different solvents.A series of characterization showed that the metal organic framework structure was successfully constructed.NH3-TPD,pyridine adsorption infrared and vacuum infrared were also performed to investigate the frameword acidity,acid strength and hydroxyl distribution for MIL-53(Al).In the liquid Beckmann rearrangement process,MIL-5 3(Al)exhibits slightly higher caprolactam selectivity due to the presence of both B acid and L acid sites,but the coversion of cyclohexanone oxime is very low due to the small amount of acid.In addition,three sulfonated MIL-101(Cr)-SO3H metal organic frameworks were synthesized by in-situ sulfonic functionalization under different chromium sources and mineralizers as well as single or dual ligands.The characterization results showed that the obtained samples all have the typical framework of MIL-101(Cr)material,howerver,introduced sulfonic acid component led to the decrease of surface area and pore volume,and resulted in some possible framework defects.MIL-101(Cr)-S2 synthesized from chromium nitrate nonahydrate as the chromium source and hydrofluoric acid as the mineralizer has the worst caprolactam selectivity,resulted from the instability of the sulfonic acid group easy falling off from the framework,and the existing R-SO3-R structure in the skeleton was another reason.MIL-101(Cr)-S1 synthesized from chromium oxide as the chromium source and hydrochloric acid as the mineralizer exhibits the best catalytic performance due to the most sulfonic acid content and the conversion of cyclohexanone oxime can reach 20%with caprolactam selectivity 71.5%.The catalyst MIL-101(Cr)-S3 synthesized by double ligands exhibited caprolactam selectivity 49%because of the limited amount of sulfonic acid ligands added.At the same time,the effects of reaction time,temperature and solvent on the Beckmann rearangement of cyclohexanone oxime catalyzed by MIL-101(Cr)-SO3H were investigated.Benzonitrile with the most suitable polarity and basicity can make the rearrangement reaction proceed effectively.Finally,MIL-101(Cr)prepared under different mineralizers was functionalized by sulfonic acid through post-grafting method.The skeleton structure of MIL-101(Cr)-NaOAc synthesized with sodium acetate as mineralizer was obviously destroyed during the post treatment process.The partial peak of XRD disappeared and the specific surface area of BET decreased significantly.However,the MIL-101(Cr)-HF synthesized with HF as mineralizer can endure acid post-treatment,because F element has a stabilizing effect on the skeleton and the synthesize process was in lower pH environment.From the point of catalytic performance,the post-treatment S/MIL-101(Cr)-NaOAc exhibited higher caprolactam selectivity because of more sulfonic acid groups grafted on its framework defect sites.The total amount of sufonic acid groups introduced in the post-treatment is limited,the obtained catalyst acid content is similar to that of the MIL-101(Cr)-S3 catalyst synthesized by the two ligand in the in situ method.The conversion rate of oxime and the selectivity of caprolactam are similar as well.