Research On Catalytic Oxidation Of Cyclohexanol To Cyclohexanone Over Keggin Heteropolyacid Compounds

Catalytic dehydrogenation of cyclohexanol to cyclohexanone is of great importance in the manufacture of nylon,because the cyclohexanone is the precursor of two major raw materialsin nylon-6 and nylon-66 producing polyamide fiber.Also,cyclohexanone can be widely used in fiber,synthetic rubber,industrial coating,medicine,pesticides,organic solvent and organic synthesis industry.The preferred industrial route involves the direct oxidation of liquid cyclohexane,using inorganic oxidant of chromium???and manganese???type inorganic oxidants.these preparation process have the disadvantage of complex technology,low product yield and environmental unfriendlly oxidant and so on.In recent years,looking for an efficient and environmental benig catalysts and clean oxidation in liquid phase using H₂O₂ to produce cyclohexanone directly from cyclohexanol has been received considerable attention in both academia and industry.Heteropoly compound have drawn wide attention because of high Br?nsted acidity and redox properties.As a kind of low cost,high benefit and environmental friendly catalyst,their thermal and chemical stability as well as redox and acidic properties could be controlled at the atomic/molecular level by changing addenda atoms without affecting the primary structure.Because transition metal-substituted Keggin HPAs catalysts possess superior performance in the catalytic oxidation reaction,it has great significance to study the catalytic oxidation of cyclohexanol to cyclohexanone in the presence of transition metal mono-substituted Keggin HPAs catalysts.In this article,different transition metal mono-substituted Keggin type heteropoly acid salts were synthesized,characterized and applied to oxidation reaction of cyclohexanol.The main contents are as follows:1. Synthesis and characterization of Na₅PW₁₁Fe O₃₉Transition metal Fe mono-substituted Keggin type heteropoly acid sodium salt were synthesized,and characterized by Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?.It turned out that substituted heteropoly acid sodium salt still has Keggin structure after iron atoms into heteropoly acid salt Keggin structure.2.Catalytic oxidation of cyclohexanol by Keggin-type Ni mono-substituted cesium phosphotungstateSynthesis of the transition metal Ni mono-substituted Keggin-type catalyst Cs PW₁₁Ni O₃₉by degradation method,and characterize by Fourier transform infrared spectroscopy,X-ray diffraction and scanning electron microscope.The results indicate that the synthetic compounds is the target product Cs PW₁₁Ni O₃₉,which possess the structure of Keggin-type anion.Catalytic performance of Cs PW₁₁Ni O₃₉ was studied by oxidation reaction of cyclohexanol.And the optimum technological conditions of the reaction was obtained that the quantity of Cs PW₁₁Ni O₃₉ was 0.2 mmol,cyclohexanol was 0.05 mol,hydrogen peroxide was0.2 mol,acetonitrile was 0.2 mol at 85?for 2.5 h.3.Keggin-type tin mono-substituted heteropolyacid salt catalyst in the synthesis of cyclohexanoneUsing sodium tungstate,cobalt acetate and stannic chloride as raw materials,Sn substituted heteropoly acid potassium salt K₇M^?W₁₁Sn^?O₃₉OH?M=Co,Fe,Ni,Zn,Mn?and quaternary ammonium salt were synthesized by the acidification method,and characterized by Fourier transform infrared?FTIR?,X-ray diffraction?XRD?and Inductively Coupled Plasma-Atomic Emission Spectrometry?ICP-AES?.Its catalytic activity was measured in the oxidation of cyclohexanol to cyclohexanonewith mass fraction 30%aqueous hydrogen peroxide as an oxidant.The conversion of cyclohexanol and the selectivity of cyclohexanone were found to be as high as 95.68%and 96.75%under the optimum conditions which the quantity of catalyst?C₄H₉?₄NHx Co^?W₁₁Sn^?was 0.25mmol,cyclohexanol was 0.05 mol,hydrogen peroxide was 0.2 mol,acetonitrile was 0.2 mol at 85?for 2 h,and a possible reaction mechanism of the oxidation of cyclohexanol was concluded that transition metal Sn was act as catalytic active center.