Synthesis And Properties Of Catalysts For Epoxidation Of Dichloropropanol Based On Mesoporous Alumina

Mesoporous materials are widely used in the industrial field due to their excellent chemical,mechanical and thermal properties.Since the synthesis of silicon-based mesoporous materials,aluminum has been reported to be added to the mesoporous silica skeleton.Subsequently,mesoporous alumina has been successfully synthesized and studied intensively.As a non-silicon-based mesoporous material,mesoporous alumina opens up a new application field for mesoporous materials,showing the application prospects of silicon-based mesoporous materials.Mesoporous alumina has a high specific surface area,a wide range of pore diameters,and an acid-base position on the surface.It is often used as a catalyst or catalyst carrier in various large-scale processes,and its catalytic performance is very high.It depends to a large extent on its specific surface area,pore volume,pore size,and crystallographic structural characteristics,which can be adjusted by changing the preparation conditions.Mesoporous alumina has many crystal phases.In the transition phase of various aluminas,mesoporous?-alumina has a relatively high specific surface area,loose and porous structure,and more active sites,which can have a better effect on the catalytic molecules on the surface.Therefore,it is the most widely used in catalytic applications.In this paper,firstly,mesoporous alumina was prepared by using the self-synthesized organosiloxanes KH560-540 and KH560-660 as template.The effects of the molar ratio of water and aluminum isopropoxide,hydrolysis temperature,hydrolysis time,pH,and amount of templating agent on the pore structure of the synthesized sample were investigated by nitrogen adsorption desorption test and X-ray diffraction,and we obtained the optimum conditions for the synthesis of mesoporous alumina under acidic conditions and alkaline conditions;Scanning electron microscopy and projection electron microscopy were used to observe the final synthesized samples to understand their morphology and internal structure;The coordination state of aluminum in the samples before and after calcination was analyzed by NMR,therefore,we infer the role of the template in the synthesis process,and then the synthesis mechanism of mesoporous alumina was obtained.Then we used the prepared mesoporous alumina as a catalyst to catalyze the cyclization of dichloropropanol to epichlorohydrin.Finally,the synthesized mesoporous alumina was used as the catalyst carrier,and the modified mesoporous alumina was prepared by in-situ synthesis and impregnation respectively.It was also used to catalyze the reaction of dichloropropanol cyclization to epichlorohydrin,and their catalytic properties were compared.The self-made mesoporous alumina has a large pore volume,pore size and specific surface area relative to industrial alumina,so it has certain advantages in catalysis and as a catalyst carrier;In the catalytic reaction,we use a gas-solid heterogeneous reaction system,and solid catalysts,compared with the traditional reaction system and use liquid catalysts,the reaction process is short,the by-products are few,no waste liquid,the catalyst is easy to separate,the operating conditions easy to control,and easy for continuous production,so it has broad application prospects.Through researched,we have reached the following conclusions:Preparation of mesoporous alumina using kh560-540 as template under acidic conditions,The optimal synthesis conditions are:the molar ratio of water and aluminum isopropoxide is 200:1,the hydrolysis temperature is 70°C,the hydrolysis time is 2 h,pH=6,adding amounts of KH560-540 is 0.4 ml.Under the optimal synthesis conditions,the synthesized mesoporous alumina has a specific surface area of 401 m²g^-1,a pore volume of 0.89 cm³g^-1 and a pore diameter of 8.1 nm.The morphology of the sample is an irregular sheet-like stacked structure,and the inside of the sample is a rod-like and flaky-like stent structure.Preparation of mesoporous alumina using kh560-540 as template under alkaline conditions,The optimal synthesis conditions are:the molar ratio of water and aluminum isopropoxide is 200:1,the hydrolysis temperature is 80°C,the hydrolysis time is 1 h,pH=8,adding amounts of KH560-540 is 0.4 ml.Under the optimal synthesis conditions,the synthesized mesoporous alumina has a specific surface area of 444 m²g^-1,a pore volume of 1.26 cm³g^-1 and a pore diameter of 9.4 nm.The morphology of the sample is small blocky and spherical,and the inside of the sample is a short rod-like and flaky hybrid scaffold structure.Preparation of mesoporous alumina using kh560-660 as template under acidic conditions,The optimal synthesis conditions are:the molar ratio of water and aluminum isopropoxide is 200:1,the hydrolysis temperature is 80°C,the hydrolysis time is 1 h,pH=6,adding amounts of KH560-540 is 0.6 ml.Under the optimal synthesis conditions,the synthesized mesoporous alumina has a specific surface area of 334 m²g^-1,a pore volume of 0.47 cm³g^-1 and a pore diameter of 6.4 nm.The morphology of the sample was packed in a massive structure with some nanoparticles attached to the surface.The inside of the sample is elongated and has a worm-like pore structure.Preparation of mesoporous alumina using kh560-660 as template under alkaline conditions,The optimal synthesis conditions are:the molar ratio of water and aluminum isopropoxide is 300:1,the hydrolysis temperature is 80°C,the hydrolysis time is 2 h,pH=8,adding amounts of KH560-540 is 0.4 ml.Under the optimal synthesis conditions,the synthesized mesoporous alumina has a specific surface area of 337 m²g^-1,a pore volume of 0.59 cm³g^-1 and a pore diameter of 7.2 nm.The morphology of the sample is similar to a small spherical shape of about 2?m,and the inside of the sample is a short rod-like structure with a worm-like pore structure.?5?By comparing the catalytic properties of mesoporous alumina synthesized under different conditions,we obtained that the mesoporous alumina synthesized by KH560-540 as a template under alkaline conditions has better catalytic performance.By comparing the catalytic properties of mesoporous alumina modified by in-situ synthesis,we obtained that mesoporous alumina modified with barium nitrate and magnesium chloride have better catalytic performance.By comparing the catalytic properties of mesoporous alumina modified by impregnation method,we obtained that mesoporous alumina modified with barium nitrate and magnesium chloride have better catalytic performance.We tested the catalytic stability and found that the modified mesoporous alumina has better catalytic stability than the mesoporous alumina before modification,and it is better to modify it by in-situ synthesis than by impregnation.Finally,it is concluded that the mesoporous alumina modified by barium nitrate as the precursor prepared by in-situ synthesis has relatively good catalytic stability.