Preparation Of Phosphonic Molybdic Acid And Transition-metal Ions Modified Imine-based Covalent Organic Framework Materials And Olefin Epoxidation Performance

Covalent organic frameworks(COFs)as one of the emerging catalytic materials,are porous crystalline covalently bonded organic framework materials composed with H,B,C,N and O elements.These materials are characterized by extremely low density,large specific surface area,ordered pores,and good thermal and hydrothermal stability.In addition,good chemical and physical stability,synthetic diversity and controllability of pore size make it performence great potential for catalytic reactions.Polyoxometalates(POMs)have a good catalytic effect on the epoxidation of various olefins.Due to the difficulties of traditional homogeneous catalysts,such as difficulty in recovery and easy deactivation,researchers have fixed homogeneous catalysts to on porous materials such as molecular sieves,the use of covalent organic frameworks as carriers will be a new challenge.In this thesis,we prepared imine-based COFs(COF-300,COF-LZU1,and CIN-1)via a reaction kettle.PMA and iron ions were immobilized onto the COF supports for Fe/PMA@COFs.A series of characterization methods verified that PMA and Fe ions were uniformly dispersed on the surface/cavities of COFs.A relatively strong interaction was achieved between the dual-site units and COF frameworks.The experimental results show that the Fe/PMA@CIN-1 composite can act as an efficient heterogeneous catalyst for the epoxidation of cyclooctene.The intramolecular charge transfer between COFs and the dual-site units(Fe ions and PMA)and the spatial configuration and nitrogen content of COFs have played critical roles in dispersing and stabilizing the activity species,which are closely connected with the activity and stability of the catalysts.This experiment features notable application prospect for the covalent organic skeleton as catalyst carriers.In this paper,COF-300,COF-LZU1 and CIN-1 were used as carriers functionalized by Co-substituted phosphomolybdate compound.This type of catalyst catalyzes the epoxidation of styrene to produce styrene oxide with oxygen as the oxygen source,the conversion rate is up to 99%,the selectivity is more than 86%,and the preparation method is simple,the short reaction time,high selectivity,environmental protection and energy saving,etc.,has broad application prospects in the field of catalysis.