Study On Modification Of Double Metal Cyanide And Its Catalytic Performance On Styrene

Epoxy styrene?also known as styrene oxide?is an important intermediate in synthesis of perfume and pharmaceutical,and is usually used as the epoxy resin thinner and ultraviolet absorber.Therefore,there is important significance and application prospects of styrene epoxidation.Usually,epoxy styrene was prepared by the halohydrin method,but this method would cause serious environmental pollution.Hence,it was necessary to study the environmentally friendly and efficient catalyst for styrene epoxidation to reduce pollution and energy consumption.Double metal cyanide?DMC?is the cyano-bridged multi-metal complex,which has the advantages of changeable valence of two transition metals,the adjustable active site and functional group of DMC,easy handling and high recovery,so it is known as a promising heterogeneous catalyst in traditional catalysis.Because of unique and excellent catalytic characteristics of DMC,DMC was used to catalyze the epoxidation of styrene in this laboratory.Based on the previous research,coordination modification of alkyl amide organic compounds and plasma irradiation modification,chemical coating modification were used to modify DMC in this paper,so as to further improve the catalytic performance of DMC on styrene epoxidation reaction.1.The FeCo DMC was modified using an alkyl amide organic compound as a ligand,and then utilized in the styrene epoxidation reaction.The structure,composition and valence of the catalyst were investigated by some characterizations,such as Scanning electron microscopy?SEM?,Transmission electron microscopy?TEM?,X-ray diffraction?XRD?,Fourier infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?,NH₃-programmed desorption curves?NH₃-TPD?,etc.By the modification of alkyl amide ligands,the content of Fe³⁺in FeCo DMC has been increased,the active crystal plane has been exposed,and the acidity of Lewis has been enhanced,which is conducive to the catalytic reaction.Compared with the original FeCo DMC,the catalytic activities of the catalysts binding with ligand on styrene epoxidation have been improved.Thereinto,FeCo DMC/DMF?N,N-dimethylformamide?has the highest catalytic activity,that is,its conversion rate of styrene reaches 96%,and its selectivity to epoxy styrene is 62%.2.The CoCo DMC,CoFe DMC and FeCo DMC were irradiated with Ar and O₂plasma,respectively,and the modified catalyst was applied to catalyze the epoxidation of styrene.A series of characterization methods?SEM,TEM,XRD,FT-IR,TG and XPS,etc.?were utilized to characterize the catalysts before and after modification.The experimental results indicate that the plasma technology has different effects for various catalysts.Compared with the original CoFe DMC,the content of water molecules in the CoFe DMC-O₂ crystal is decreased,more active metal sites are exposed and the transition metal are also oxidized,thereby the catalytic activity of CoFe DMC modified by O₂ plasma irradiation is improved,the conversion rate of styrene can be increased by 30%.While for FeCo DMC,the results indicate that the crystal structure of FeCo DMC modified by the plasma irradiation is etched,hence some catalytic active sites are buried and then the catalytic performance of the modified FeCo DMC is reduced.3.CoFe DMC was chemically modified with precious metals?Au and Pt?,chitosan carbon dots,polydopamine and poly?m-phenylenediamine?,respectively,several composite materials were synthesized and applied on styrene epoxidation.The catalysts were analyzed by characterization methods such as SEM,TEM,XRD,FT-IR,TG and XPS.The experimental results show that the modification of precious metals and organic polymers can effectively improve the catalytic performance of CoFe DMC.Because poly?m-phenylenediamine??PmPD?can adjust the metal valence state,CoFe DMC@PmPD has the best catalytic performance.