Study On Preparation Of Monolithic Hierarchical Porous Titanosilicate Materials And Corresponding Catalytic Oxidation Performances

Microporous titanosilicates,such as TS-1,are recognized as green selective oxidation catalysts,and have been extensively studied in alkene epoxidation,cyclohexanone ammoxidation,phenol hydroxylation,etc.,because of their unique structural characteristics and excellent catalytic performance.However,the narrow pores of the conventional zeolite are too small to allow bulky molecules access to the interior active sites,which restrict its application in the catalytic oxidation of bulky molecular.To overcome this limitation,a hot topic in recent research studies is to construct hierarchically porous zeolites with meso-and macro-porosity,where the macropore system can enhance mass transport,and the mesopores in the skeleton can increase the specific surface area greatly and improve the accessibility of active sites.In this paper,we have designed a simple method which combines the characteristics of macro-sized materials with nano-materials to prepare hierarchical porous titanosilicate materials,which effectively solves the problems of small pore size,large internal diffusion resistance,easy aggregation and difficult to recycle,while applying it to bulky olefins epoxidation reaction.The specific contents are as follows:（1）A monolithic amorphous titanosilicate material（HPM-Ti Si）with a three-dimensional continuous macroporous structure constructed by microporous ultra-thin nano-film was prepared by using macro-sized monolithic epoxy macroporous polymer as a template and TPAOH as a structure director.The physical properties and pore structure properties of the materials were characterized by SEM,TEM,BET,FT-IR,UV-Vis and other characterization methods.The results show that the HPM-Ti Si has 3D continuous pass-through macroporous structure;its pore wall is constructed by continuous titanosilicate nano-film and the thickness is about 20 nm.The specific surface area and porosity are 323 m²/g,83.4%,respectively.HPM-Ti Si also showed excellent catalytic performance in epoxidation of olefin.By using H₂O₂and TBHP as oxidants,the conversion rate and TOF value of the macro-sized HPM-Ti Si in the catalytic oxidation of 1-octene are significantly improved compared with the traditional TS-1 particles,with high reusability and high recovery.And the stability of Ti species in the skeleton of HPM-Ti Si is much higher.（2）A monolithic titanosilicate material（MNCMM-Ti Si）constructed of microporous-mesoporous ultra-thin nano-film was prepared by using the pillared epoxy resin macroporous polymer as monolithic macroporous template and cetyltrimethylammonium bromide（CTAB）as mesoporous porogen through the titanosilicate species assembled with CTAB micelles growing into nanofilm on the surface of the polymer skeleton by hydrogen bonding and electrostatic interaction.The characterization results show that the thickness of the macropores of MNCMM-Ti Si nanofilms is about 20 nm,and there are plenty of disordered micropores（0.57 nm）and short-range ordered mesopores（3.53 nm）on the macropore walls.The specific surface area is 504 m²/g,and the porosity is as high as 92.8%.Using bulky olefins（cyclohexene,cis-cyclooctene）as probes,the catalytic activities of TS-1 molecular sieve,mesoporous Ti-MCM-41 and macro-sized MNCMM-Ti Si in the oxidation of bulky olefins were evaluated.The results showed that with TBHP as the oxidant,the conversion of MNCMM-Ti Si and TOF in the reaction of catalyzed cyclohexene and cis-cyclooctene were 22.7%,39.9 h^-1;33.0%,24.9 h^-1,respectively.Compared with TS-1 as a catalyst,the conversion rate in this reaction when using MNCMM-Ti Si as a catalyst was increased by 2.3 times and 2.7 times,respectively,while the TOF value also increased by 8.5times and 4.9 times.In addition,repeatability experiments indicated that Ti species have strong stability in MNCMM-Ti Si and exhibit excellent catalytic activity in the bulky molecular olefin epoxidation reaction.