Preparation Of Hierarchical TS-2 And Its Catalytic Performance For Cyclododecene Epoxidation

Epoxides are widely used as intermediates in petrochemical industry.In recent years,epoxidation of cycloolefins and its catalysts have attracted much attention.Titanium silicalite molecular sieve TS-2 is a typical MEL-type zeolite.It is attractive to the researchers both at home and abroad due to its excellent catalytic performance which is similar to TS-1 in olefin oxidation,ketone oximation,hydroxylation of benzene with phenol,etc.TS-2 has stronger hydrophobicity than TS-1.It can facilitate the desorption of epoxy compound and improve the reaction selectivity and stability.In this paper,microporous TS-2 molecular sieve was synthesized by seed method.Different hierarchical TS-2 with enhanced diffusion performance by post-treatment and soft template method were also synthesized,and their catalytic performances in the cyclododecene epoxidation were evaluated.Firstly,the microporous TS-2 was synthesized by seeding method in order to reduce the size of the molecular sieve and to explore the guiding effect of seed and template on the structure of molecular sieve.The results show that the seeds initiate the dissolution-recrystallization process and effectively promotes the formation of a large number of crystal nuclei in the precursor body in the early stage of crystallization.TS-2 zeolite with small particle size forms due to the interaction between the crystal nuclei and the template in the crystallization process.The microporous structure of TS-2 synthesized by traditional hydrothermal method restricts the entry of large olefin molecules to the pores,leading to low reaction conversion and selectivity.The synthesis of hierarchical TS-2 by post-treatment and soft template was further studied,and its catalytic performance in cyclododecene epoxidation was investigated.The results show that due to its developed hierarchical pores,TS-2 post-treated by the different ammonium sources as templates reduces the diffusion resistance of cyclododecene molecules,improves the diffusion efficiency of products in the pores,and increases the cyclododecene epoxidation conversion from 1.33% to 13.15% and the selectivity from52.72% to 69.04%.In addition,the hierarchical porous S-2 using the long carbon chain trimethylammonium bromide as template can further improve the epoxy compound selectivity to 89.89% while maintaining a high cyclododecene conversion of 12.11%.