Hydrothermal Synthesis Of Single-crystalline/Hierarchical TS-1 Nano-zeolite For Hydroxylation Of Benzene

TS-1 zeolite has an MFI-type topological structure,three-dimensional ten-membered ring cross pores,good thermal/hydrothermal stability and excellent shape selectivity.It is widely used in petrochemical,fine chemical synthesis and other fields.The introduction of titanium atoms in the zeolite framework makes it have excellent catalytic performance in a series of catalytic oxidation reactions involving hydrogen peroxide.At the same time,its by-product is usually only water,which is an environmentally friendly process,which makes TS-1 molecular sieve in the field of chemical catalysis It plays an extremely important role and has good application prospects.In recent years,it has been reported in the literature that most of the synthesized TS-1 zeolite has a polycrystalline structure.The larger particle size and single microporous pore structure affect the mass transfer rate of the reactants,which largely limits the catalyst’s performance.Industrial applications.At present,the main production process for producing phenol and benzenediol in industry is relatively complicated,and its disadvantages of high energy consumption and low yield cannot be avoided.Using TS-1 zeolite as a catalyst,benzene and hydrogen peroxide as raw materials,only one step reaction is required to obtain phenol.If the catalytic performance of the catalyst can be further improved,the method will have a good application prospect in the industrial production of phenol and diphenol.This article is aimed at the problem that TS-1 zeolite cannot quickly contact reactive sites due to the large particle size and single pore structure.Using a novel synthesis strategy of MFI zeolite,adding different amino acids to the concentrated gel system,and obtaining single-crystal nano-TS-1 zeolite and multi-porous TS-1 zeolite through two-step crystallization.The addition of different amino acids and amino acids was studied.The influence of the amount and water content on the hydrothermal synthesis of zeolite is aimed at improving the catalytic performance and stability of zeolite.And zeolites are used in the hydroxylation of benzene,the main research contents and conclusions are as follows:（1）In the concentrated gel system,five kinds of amino acids are used as additives to synthesize TS-1 zeolite hydrothermally through a two-step crystallization method.The five amino acids have different physical and chemical properties.Except for the amino group,each amino acid contains different groups,and the p H value of the solution is also different.By studying the influence of different amino acids on the gel,observe the influence of different amino acids on the final morphology and particle size of the zeolite.The synthesized zeolite was applied to the benzene hydroxylation reaction,using hydrogen peroxide as the oxidant and deionized water as the solvent to study the catalytic performance of the zeolite synthesized by different amino acids.Five kinds of amino acids can synthesize single crystal TS-1 nano zeolite.The zeolite synthesized with lysine as an additive has high crystallinity,and most of the titanium atoms exist in the form of four-coordination,which has the best catalytic performance in the hydroxylation of benzene..（2）Using cheap and easily available L-lysine as a crystallization additive,a two-step synthesis method is used to synthesize a single crystal nano-TS-1 zeolite.The synthesized zeolite has a particle size of less than 100 nm.By adjusting the amount of L-lysine added,single crystal TS-1 zeolites with different particle sizes can be obtained.The content of L-lysine in the gel system can also affect the rate of hydrolysis of phthalate esters,thereby affecting the content of titanium in the zeolite framework.The zeolites synthesized with different amounts of L-lysine was used as a catalyst,benzene was used as the reactant,hydrogen peroxide was used as the oxidant,and deionized water was used as the solvent to study the catalytic performance of the zeolite.The optimal L-lysine/Si O₂molar ratio for the synthesis of single-crystal TS-1 nano-zeolite is 0.2.Under this condition,the synthesized TS-1 zeolite has relatively good crystallinity and has the largest specific surface area.Compared with the original zeolite,the catalytic performance of the single-crystal TS-1nano-zeolite has been improved,the conversion rate of benzene can reach 50.2%,the yield of phenol can reach 30.8%,and the catalytic performance is not significantly reduced after repeated use for three times.（3）Add excess L-lysine to the initial gel system to synthesize a hierarchical pore TS-1zeolite.Adjusting the water content in the gel system can change the particle size and pore structure of the zeolite.At the same time,the change of water content causes the p H of the gel system to change,thereby affecting the titanium content in the zeolite framework.Using hydrogen peroxide as the oxidant and deionized water as the solvent,benzene was hydroxylated on the hierarchical TS-1 to study the catalytic performance of the hierarchical TS-1 zeolite.The results show that when the H₂O/Si O₂molar ratio is 27,the zeolite has a larger specific surface area and a larger pore volume.The catalytic performance of the hierarchical TS-1 zeolite in the benzene hydroxylation reaction has been improved,the yield of phenol can reach 26.5%,and the selectivity of phenol has also been improved.