Hydrosilylation Catalyst Pt/PAA@MIL-125 Preparation And Use In Highly Selective Synthesis Of γ-(2,3-epoxypropoxy) Trimethoxysilane

Hydrosilylation is widely used in industrial production of silicone products,with economical,green and efficient advantages.γ-(2,3-epoxypropoxy)trimethoxysilane is an important silicone product that can be synthesized by hydrosilylation and used in the preparation of polysulfide adhesives and sealants,epoxy resins,filled or reinforced thermosetting resins,fiberglass adhesives and thermoplastic resins for filling inorganic or reinforced glass.However,in industrial production,homogeneous platinum-based catalysts(such as Speier catalysts)are often used to face problems such as difficult to recycle,experience,low selectivity,and instability in the air,which are not conform with the development route of green economic chemistry.Therefore,the research and development of new heterogeneous catalysts to achieve efficient and green hydrosilylation is an urgent research task.Metal-organic frameworks(MOFs)is self-assembled by metal ions/oxygen clusters coordinated with organic ligands are widely used in heterogeneous catalytic reaction systems because of their highly ordered pore structure,large specific surface area,rich tunable sites and functionalized modifications.The research show that the selectivity of the catalytic reaction can be improved by controlling the factors such as metal nodes,organic linkers and pore environment by taking advantage of the versatility of MOFs heterogeneous catalysts.In this study,a MOF-supported catalyst with mesoporous structure—Pt/PAA@MIL-125 was synthesized,which aimed to solve the problems of difficult recovery and low selectivity of homogeneous platinum-based catalysts in the hydrosilylation.As an excellent metal-organic framework material,MIL-125(Ti)has a large specific surface area and good hydrothermal stability.The metal node Ti in its skeleton has empty 3d orbitals,giving it unique capabilities,making it a promising candidate for heterocatalytic materials.However,the microporous structure of MIL-125(Ti)will reduce the contact between the reaction substrate and the active center,which in turn will affect the catalytic conversion performance.To solve this problem,we introduced PAA,a flexible chain-like anionic surfactant.PAA contains a large number of carboxyl groups,and by introducing PAA in the synthesis process of MIL-125(Ti),it can compete with the original ligand terephthalic acid,which can not only produce a mesoporous structure for improving the mass transfer efficiency of the catalyst,but also regulate the electron valence state of the active center of the supported metal,so as to improve the catalytic reaction performance of the catalyst and obtain a high-yield γ-(2,3-epoxypropoxy)trimethoxysilane product.The main work contents are as follows:(1)PAA was added in situ by hydrothermal synthesis,and the catalyst carrier PAA@MIL-125 was synthesized in one-pot.The catalyst Pt/PAA@MIL-125 was obtained by impregnation method to support Pt nanoparticles.A variety of test methods such as XRD,XPS,SEM,TEM and nitrogen adsorption-desorption were used to analyze the phase and structure of the catalyst,and it was found that the introduction of PAA would have a significant impact on the pore structure of the catalyst and improve the dispersion of Pt nanoparticles in the catalyst.At the same time,the XPS characterization results showed that the valence state of Pt nanoparticles was between zero valence and divalent,indicating that the catalyst support had the effect of valence regulation on Pt nanoparticles,which could significantly improve the catalytic performance of the reaction.(2)The catalyst prepared above was used to catalyze the synthesis of γ-(2,3-epoxypropoxy)trimethoxysilane.The experimental results show that when the reactant ratio is AGE:TMOS = 1:1.27 in toluene solution,the catalyst Pt/PAA-2@MIL-125 can achieve the complete conversion of allyl glycidyl ether,and the yield of the product is as high as 97%.Compared with commercial catalyst Pt/C,Pt/PAA-2@MIL-125 exhibits excellent catalytic performance and recyclability.In addition,compared with the reported homogeneous or heterogeneous catalysts,the catalytic performance of Pt/PAA-2@MIL-125 catalyst is in the forefront.In amplification experiments,it was further confirmed that the catalyst has high industrial application potential.