Preparation And Catalytic Oxidation Performance Of Metal-Salen Composite Catalyst Based On Natural Polymer Chitosan

In recent years,with the deepening of chemical research and the deterioration of environmental pollution,the research on catalysts has not only applied a certain active component to directly catalyze chemical reactions,but also pursued a non-toxic,harmless and efficient a pollution-free“environmentally friendly catalyst”.The direct application of the traditional homogeneous catalyst in the chemical reaction not only limits the selectivity of the reaction,but also brings a series of,for example,poor thermal stability,serious environmental pollution,toxic,low reaction efficiency,and difficulty in recycling and reuse problem.To improve this situation,scientists have studied the immobilization of homogeneous active ingredients to form heterogeneous composite catalysts.The most important point of heterogeneity is to select a carrier with excellent characteristics suitable for its immobilization,which not only improves the catalytic efficiency of the catalytic material to a certain extent,but also can improve those problems,and it is an effective method for realizing its application.In this paper,we use a natural polymer chitosan which has much amino groups on the surface with salicylaldehyde to form a Schiff base functionalized chitosan composite?called CS-Schiff?,and acetate coordination to form a metal-Salen modification namely CS-Salen-M type composite catalyst.The details are as follows:1.Using natural polymer chitosan as a carrier,after dissolving in an acidic environment,adding salicylaldehyde dropwise,adjust the pH of the solution to about 7 to form a CS-Schiff composite,and then use the CS-Schiff as a ligand to add Mn?OAc?₂·4H₂O.After coordination,a Mn-Salen modified chitosan composite named CS-Salen-Mn was formed.The composition and structure of the catalyst were analyzed by means of characterization techniques such as by fourier transform infrared spectroscopy?FT-IR?,UV-visible diffuse reflectance spectroscopy?UV-Vis?,thermogravimetric analysis?TGA?,wide-angle X-ray powder diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?and scanning electrons?SEM?.The styrene epoxidation reaction was used as the probe reaction,dichloromethane was used as the solvent,H₂O₂ was used as the oxidant,and 4-phenylpyridine oxynitride?PPNO?was used as the promoter.The catalytic properties of the CS-Salen-Mn composite catalyst were investigated by parameters such as different catalyst comparison,the amount of catalyst,the amount of PPNO and the reaction time were changed.Finally,the number of cycles of CS-Salen-Mn composite catalyst was investigated.The result of this action showed that the yield of ethylene oxide was 88.5%,the selectivity was 100%,and it was recycled at least four times.2.The Schiff base functionalized chitosan composites CS-Schiff was used as a ligand,and Cu?OAc?₂·H₂O was added to form a CS-Salen-Cu composite catalyst.Analysising the catalyst by means of fourier transform infrared spectroscopy?FT-IR?,UV-visible diffuse reflectance spectroscopy?UV-Vis?,thermogravimetric analysis?TGA?,wide-angle X-ray powder diffraction?XRD?and scanning electron microscopy?SEM?Segment structure and surface morphology.The catalytic activity of the prepared composite catalyst was investigated by using methyl phenyl sulfide oxidation reaction as probe reaction and H₂O₂ as oxidant with the blank test,changing the catalyst dosage,oxidant dosage,solvent type and reaction temperature.Finally,the recycling of CS-Salen-Cu composite catalyst was studied.The result showed that the yield of single product methyl phenyl sulfoxide could reach 57%,and it could be recycled for three times.