The Synthesis And Catalytic Performance Of Mesoporous Heteroatom Molecular Sieve Based On Photoinduced Self-assembly Method

Mesoporous heteroatom molecular sieves have ordered mesoporous pores,adjustable pore size,large specific surface area,and unsaturated four-coordinate framework metal,which has a wide range of applications in the field of heterogeneous catalysis.However,at present,the preparation of the catalyst is still limited to the traditional hydrothermal synthesis method,which is cumbersome to operate,time-consuming and energy-consuming,and environmentally unfriendly,and the valence state of the framework metal cannot be precisely controlled.To this end,this paper proposes to adopt a new light-induced self-assembly method and a light-induced p H-regulation method,using conventional P123 as a template,and using ultraviolet light to induce photolysis of a photo-initiator to generate strong acid species,which catalyze the simultaneous hydrolysis and polymerization of silicon and metal sources.Synthesis of mesoporous heteroatom molecular sieve.The paper synthesized the mesoporous heteroatom molecular sieve catalysts containing titanium and zirconium.Fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction analysis（XRD）,ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis）,N₂ adsorption and desorption,transmission electron microscopy（TEM）,X-ray electron spectroscopy（XPS）and other means to characterize its pore structure and metal valence.The characterization results show that the synthesized three metal-doped mesoporous heteroatom molecular sieves all have an ordered mesoporous structure,and the metal ions mainly exist in the molecular sieve framework in the form of four coordination.In this paper,cyclohexane oxidation reaction and cyclohexanone ketal reaction were used as probe reactions to explore the catalytic performance of the synthesized mesoporous heteroatom molecular sieve.The specific research content of the paper is as follows.（1）A series of mesoporous titanium silicon molecular sieves（PSMTS）with different silicon to titanium ratios were prepared by the light-induced self-assembly method.Various characterization methods were used to thoroughly study the optimal synthesis conditions,including the effects of light time,light intensity,and photoacid generator content on the mesoporous structure and Ti coordination environment,and the catalytic oxidation of cyclohexane was evaluated performance.The results show that the optimal synthesis conditions of the mesoporous titanium silicalite（PSMTS）are:15 min of light,18 m W/cm² of light intensity and 3 wt%of photoacid generator.When the Si/Ti molar ratio is 40,the synthesized mesoporous titanium silicon molecular sieve PSMTS（40）has ordered mesoporous channels.Metal Ti is doped in the framework in a four-coordinate state,and no free Ti species outside the framework are found.At the same time,PSMTS（40）showed the best catalytic performance（the conversion rate of cyclohexane was 52%,and the selectivity to cyclohexanone and cyclohexanol was about 99%）.However,when the Ti content continues to increase,relatively disordered mesoporous channels and free Ti species outside the framework are generated in the synthesized mesoporous titanium silicate molecular sieve,and the catalytic performance is correspondingly reduced.（2）In order to increase the content of Ti in the framework and improve the photo-induced self-assembly method,the mesoporous titanium silicalite catalyst（PIMTS）was prepared by the photo-induced p H adjustment method.Compared with the Ti-SBA-15 molecular sieve catalyst synthesized by the traditional hydrothermal crystallization method,the series of characterization results prove that the mesoporous order of PIMTS is slightly inferior,but it has a large amount of four-coordinated framework titanium（Ti content as high as 2.92%）.Using cyclohexane oxidation reaction as a probe reaction,the results show that PIMTS has better catalytic performance.When the cyclohexane conversion rate is49.9%,the maximum TOF of KA oil can reach 393 min^-1.（3）Try to synthesize a zirconium-containing mesoporous zirconium silicate molecular sieve by light-induced self-assembly method,and use cyclohexanone ketal reaction as a probe reaction to explore its catalytic performance.The paper explored the best conditions for the synthesis of zirconium silicate molecular sieve.The results showed that the light time was 15 min,the light intensity was 60%,P123was 0.2 g,PDMOS（polymethoxysilane）was 1.0 g,and PAG was 0.04 g.The mesoporous molecular sieve has the best catalytic effect.In the catalytic reaction of cyclohexanone ketal,the yield of cyclohexanone ketal reached 58.9%,and the conversion rate of cyclohexanone reached 95%.In this paper,the mesoporous heteroatom molecular sieve was synthesized innovatively by light-induced self-assembly method and light-induced p H-regulation method.This method is convenient.The material synthesis can be completed within a few minutes,and the content of the framework metal can be precisely controlled.What’s more valuable is that the preparation method does not add any organic solvents,does not produce any three wastes,and is very environmentally friendly.The research in this thesis provides a new idea for the functionalization of mesoporous molecular sieves and a new method for the synthesis of mesoporous heteroatom molecular sieves.