Preparation Of Copper-and Cobalt-Based Bimetallic Catalyst And Its Application On Styrene Epoxidation

Styrene oxide is an important chemical raw material,mainly used in the production of spices and medicines,usually prepared by selective oxidation of styrene.So far,a large number of heterogeneous catalytic systems for the epoxidation of styrene have been studied,and noble metals are always used as active catalyst,which can obviously promote the epoxidation of styrene.However,the limited resources and high cost of noble metals hinder their practical application.Hence,exploring highly active and low-cost catalysts for styrene epoxidation is of great significance,but it is still challenging to simultaneously achieve efficient styrene conversion and excellent styrene oxide selectivity.Inexpensive and resource-abundant copper-based and cobalt-based catalysts have good epoxidation activity and can serve as effective substitutes for noble metals.Compared with their monometallic counterparts,bimetallic catalysts which were composed of two metal elements are expected to achieve higher catalytic activity,selectivity,and cycling stability for styrene epoxidation,because of the synergistic effect between the two metals.In this paper,three different types of copper-cobalt bimetallic catalysts were prepared and used for styrene epoxidation.The details are as follows:1.Firstly,Cu/Co-Co Prussian blue analogues（Cu/Co-Co PBA）bimetallic catalysts were successfully synthesized,and a series of Cu/Co-Co PBA derivatives were prepared by the pyrolysis process of Cu/Co-Co PBA and were applied in the epoxidation of styrene.The results indicate that the Cu/Co-Co PBAs-250 obtained by pyrolysis at 250°C shows excellent catalytic performance for the epoxidation of styrene.Through a series of physical and chemical tests,it was found that the Cu/Co-Co PBAs-250 derivatives have higher catalytic performance because a large number of cyano vacancies were generated by pyrolysis at 250°C,which have more pore structures and larger surface areas,exposing more metal active sites.Meanwhile,the crystal structure of the metal-organic framework did not collapse during the whole pyrolysis process,still retaining the confinement effect of CN^-on metal cations.In addition,the partial conversion of Cu²⁺to Cu⁺in the Cu/Co-Co PBA-250 during pyrolysis may be an important reason for its excellent selectivity.This work provides new insights and ideas for pioneering the design of bimetallic catalysts derived from PBA-based catalysts.2.Secondly,the sheets porous graphitic carbon nitride（S-g-C₃N₄）and Co-Cu bimetallic doped sheets porous graphitic carbon nitride（S-Cu/Co-g-C₃N₄-1:1）were synthesized in one step by using a folding fan-shaped aluminum foil as a template.Compared with the bulk graphitic carbon nitride（B-g-C₃N₄）synthesized by the traditional method,the sheets porous graphitic carbon nitride synthesized by this method has a larger specific surface area,more pore structure,so it has a higher catalytic activity in the styrene epoxidation reaction.S-Cu/Co-g-C₃N₄-1:1 was used for the epoxidation of styrene and achieved excellent catalytic results,the styrene conversion was 89%and the styrene oxide selectivity was 85%.And through a series of test characterization,it could be seen that the doped copper and cobalt coordinate with N in g-C₃N₄,which hinders the ordered growth of graphitic carbon nitride sheets and forms more pore structures.The structure increases more catalysis active sites and hinders the re-aggregation of nanosheets in the catalytic process,which is beneficial to the mass transfer in the catalytic process.Due to the synergistic effect between Cu and Co,the band structure of the material is changed,which facilitates the electron transfer during the catalytic process.Therefore,S-Cu/Co-g-C₃N₄-1:1 has higher catalytic activity and selectivity compared with its monometallic counterpart.The S-Cu/Co-g-C₃N₄-1:1 can still maintain good catalytic activity after five consecutive cycles.This study provides a new idea for the synthesis of sheets porous graphitic carbon nitride and the development of highly active,stable and low-cost styrene epoxidation catalysts.3.Lastly,hypercrosslinked organic polymers（HCPs）containing functional monomers were successfully synthesized,and then copper-cobalt layered double hydroxide（Cu Co LDH）was grown in situ on HCPs to synthesize bimetallic composites（HCPs@Cu Co LDH）with heterostructures,which were used for styrene epoxidation.It is demonstrated that the composite（HCPs-4-CN-py@Cu Co LDH）synthesized by in situ growth of copper-cobalt metal double hydroxides on hypercrosslinked polymers synthesized with 4-cyanopyridine as functional monomer exhibited excellent catalytic activity,the styrene conversion was 85%and the styrene oxide selectivity was 85%,which was higher than its corresponding single-metal composites.Moreover,the nitrogen-containing functional monomers of the hypercrosslinked polymer substrates have a great influence on the selectivity of styrene oxide.The essential reason is that the structural properties of nitrogen atoms in the monomers are different.And the monomers contain the nitrogen atoms of C≡N structures,which is beneficial to the selectivity of styrene oxidation.To the best of our knowledge,this is the first study of in situ growth of Cu Co LDH on hypercrosslinked polymers to prepare composites for styrene epoxidation.This work also provides a research idea for the development of new high-performance composites.