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

Caprolactam is an important raw material for many industrial chemicals,and plays an important role in national life.At present,there are a series of environmental and economic problems in the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam with oleum as a catalyst,such as equipment corrosion,environmental pollution,and a large amount of ammonium sulphate as by-product,etc.Therefore,the development of an environmentally-friendly solid acid catalyst is one of the focuses of Beckmann rearrangement study of cyclohexanone oxime.Metal-organic frameworks,a new class of crystalline porous materials feature with ultra-high specific surface area,large window size,regular pore structure,and tailorable functionalities,have received considerable attention in the field of catalysis research.In this thesis,MIL-101?Cr?was selected as the matrix for acid-base bifunctional modification to prepare four kinds of acid-base bifunctional metal organic framework materials.The prepared bifunctional materials were used for catalyzing the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam,aiming to solve the problem of deactivation of single sulfonic acid-functionalized MIL-101?Cr?through the synergistic effect of acid-base sites.The morphology,structure,thermal stability,and acid-base properties of the catalysts were measured and analyzed by systematic characterization.At the same time,their catalytic performance and reusability in the liquid-phase Beckmann rearrangement reaction were investigated.Firstly,an acid-base bifunctional metal organic framework material AMSA/MIL-101-NO₂was prepared by first grafting nitro group and aminomethanesulfonic acid on organic ligand and metal center of MIL-101?Cr?,respectively,the synthesized AMSA/MIL-101-NO₂,was then reduced to AMSA/MIL-101-NH₂ through stannous chloride.The characterization results of FT-IR,XRD,N₂ physical adsorption,SEM,TGA,elemental analysis,XPS showed that the amino groups and sulfonic acid groups were successfully grafted and the physicochemical structure characteristics of MIL-101?Cr?were retained.The catalytic performance for Beckmann rearrangement of cyclohexanone oxime in benzonitrile was poor because of the less amount of sulfonic acid groups grafted by the post-grafting method and prone to fall off.However,due to the presence of amino groups,the catalyst can be reused 4 times without significant deactivation.Then,the bifunctional metal organic framework material MIL-101/NH₂/SO₃H can be prepared by first hydrothermal synthesis the MIL-101?Cr?matrix with terephthalic acid as a ligand,and then gradually grafting the amino groups and sulfonic acid groups on the metal sites and benzene ring,respectively,with the help of BOC protection and deprotection process.The bifunctional catalyst was characterized by FT-IR,XRD,N₂ physical adsorption,SEM,TGA,elemental analysis,XPS,pyridine infrared,etc.The results showed that the amino and sulfonic acid groups were successfully introduced,and the typical framework features of MIL-101?Cr?were retained.However,due to the strong oxidizing and corrosive properties of chlorosulfonic acid,the amino group linked to chromium was oxidized and the framework structure was destroyed to a certain extent,so that the amount of effective-SO₃H groups in the synthesized catalyst is less,thereby making the catalytic effect general.Compared with the post-grafting single sulfonic acid-functionalized MIL-101/SO₃H,MIL-101/NH₂/SO₃H can realize the coordination of the reaction catalyzed by sulfonic acid group and the separation promoted by amino group in liquid-phase Beckmann rearrangement of cyclohexanone oxime,and the catalyst has better reusability.In addition,two acid-base bifunctional metal organic framework materials MIL-101-SO₃H/NH₂ were synthesized by first synthesized the MIL-101-SO₃Na in one step under different chromium sources and mineralizers,and then grafting amino groups on the metal sites,with the help of BOC protection and deprotection process.A series characterization results showed that the MIL-101?Cr?type acid-base bifunctional metal organic framework materials can be successfully synthesized with two different mineralizers,and the framework structure of the materials remains intact during the functionalization process.MIL-101-SO₃H/NH₂ synthesized with sodium acetate as a mineralizer has lower specific surface area and less amount of grafted sulfonic acid groups,because acetate contains the same carboxyl group as the ligand,it will compete with the ligand for coordination.Therefore,the catalytic effect is not as good as the catalyst synthesized when concentrated hydrochloric acid was used as a mineralizer.Compared with the in-situ single sulfonic acid-functionalized MIL-101-SO₃H,the two kinds of bifunctional catalysts can achieve the synergistic effect of acid-base sites and have preferable reusability.Finally,the process of preparing MIL-101-SO₃H/NH₂ with concentrated hydrochloric acid as the mineralizer was optimized.Proton exchange was carried out between a saturated sodium chloride solution and one-step hydrothermal synthesized MIL-101-SO₃Na to make the possible-SO₃H completely converted to-SO₃Na,and then the amino groups was grafted through the protection and deprotection process of BOC.The improved acid-base bifunctional MIL-101-SO₃H/NH₂ metal organic framework material was successfully synthesized.A series of characterizations results showed that although the crystallinity was lower than that of the unmodified sample,and the specific surface area and pore volume were further reduced after grafting the amino protecting group,but the crystal structure of the synthesized acid-base bifunctional material remained intact,and the acidic and basic functional groups was well isolated.The amount of sulfonic group increased after proton exchange.When the improved MIL-101-SO₃H/NH₂ was used for catalyzing the liquid-phase Beckmann rearrangement reaction,the conversion of cyclohexanone oxime and the selectivity of caprolactam was 20.87%and 69.73%,respectively.Compared with the unimproved sample,its catalytic performance and reusability were improved.