One-pot Synthesis Of Hollownest-structured Zeolites And The Catalytic Application In Epoxidation Of Alkenes

The catalytic epoxidation of alkenes is an important reaction in the manufacturing of fine chemicals and pharmaceuticals,since epoxides are key building blocks in the organic synthesis.As one of the most important members of zeolite family,Ti-containing zeolites have shown scientific and technological interests due to the excellent property in the environmentally-benign selective epoxidation of alkenes to epoxides.Among various titanosilicate zeolites,Ti-MWW zeolite has displayed superior catalytic performance in the selective epoxidation of linear or other small alkenes.However,for conventional direct synthesis and post structural rearrangement methods,long crystallization time of 7 days and relatively complex synthesis process are unavoidable.In this work,a novel Ti-containing zeolite with micro-meso-macro hierarchical structure has been constructed.After simple acid washing,this zeolite shows high catalytic activity in the epoxidation of both small linear alkenes and bulky cycloalkenes.Firstly,through one-step hydrothermal rota-crystallization mode,Ti-containing hollownest-structured zeolite(Ti-HSZ)is successfully constructed without using any solid or supramolecular as template.Thus-synthesized Ti-HSZ precursor contains a microcavity with large external surface area,and its shell composed of randomly intergrown MWW nanosheet crystals owns hierarchical pore distribution.Due to the unique physical and chemical properties of Ti-HSZ,through simple acid-washing,the majority of piperidine molecules can be removed from the precursor,and the resultant Ti-HSZ catalyst shows an excellent catalytic activity and stability in the epoxidation of allyl chloride and bulky cycloalkenes.Secondly,seeding method is applied in the synthesis of Ti-HSZ.By adjusting the seed amount,rotating rate and synthesis time,we determine the scope of synthetic conditions in seeding method rapid synthesis of Ti-HSZ.When the adding amount of seed is 3 wt%,Ti-HSZ precursor can be obtained within 48 h under rotating rate of 56 rpm.Tirdly,B-HSZ and Al-HSZ can also be successfully synthesized by using the hydrothermal rota-crystallization mode.It is found that samples with different morphologies can be synthesized under different reaction conditions.