Redox Properties Of Manganese Oxides And Their Application In Epoxidation Of Vegetable Oil

Traditional phthalate plasticizers are normally poisonous and could increase the risk of cancer.European Union had already carried out the safety inspection and set some safety standards for traditional plasticizers at the end of 20th century.The plasticizer storm in Taiwan drew people's attention on the safety of traditional phthalate plasticizers once again.It's urgent for the plasticizer industry to seek for substitution for phthalate plasticizers.Epoxidized soybean oil has attached much attention because of renewable raw material and non-toxic environmental protection.However,the traditional epoxidation processes of soybean oil with a great deal of percarboxylic acid wastewater generated have an adverse effect on the environment,and it does not meet the requirement of green chemistry.Thus,it is far-reaching significant for the epoxidation of soybean oil to explore a new green catalytic system.In this paper,molybdenum-doped manganese oxide octahedral molecular sieves with varied Mo/Mn molar ratios were prepared by a simple reflux method.Lots of techniques such as X-ray diffraction?XRD?,transmission electron microscopy?TEM?,hydrogen temperature-programmed reduction?H₂-TPR?,thermal Gravity Analysis?TGA?and diffuse reflectance infrared fourier transform?DRIFT?spectroscopy of adsorbed pyridine were employed to indentify the features of prepared catalysts.The characterization results indicate that Mo dopants were successfully incorporated into the crystal structure of manganese oxide.When molybdenum-doped manganese oxide octahedral molecular sieves with varied Mo/Mn molar ratios were used as catalysts,the oxidation of cyclohexene was served as probe reaction and the catalytic activity of catalysts was evaluated.By comparison,1%Mo-OMS-2 catalyst exhibited the highest yield of 32.4%for the allylic oxidation,with no selectivity towards the epoxidation of cyclohexene.Epoxy products were generated only in the reaction with 10%Mo-OMS-2 as catalyst attribute to its stronger redox properties than the others.Thereby,those results provide ideas for this series of catalysts in the epoxidation of soybean oil.Based on the above results,the molybdenum-doped manganese oxide octahedral molecular sieves with varied Mo/Mn molar ratios were also applied in the epoxidation of soybean oil.The catalytic activity of these catalysts were investigated.Among them,10%Mo-OMS-2 catalyst exhibited a better catalytic performance,which was consistent with the results of the oxidation of cyclohexene.Then,we chose 10%Mo-OMS-2 catalyst as the research object,the effects of the types and concentration of oxidants,reaction time,charging order and the solvents on the epoxidation of soybean oil were discussed in detail.Meanwhile,the catalytic performance of the catalytic system soybean oil/TBHP/catalyst was compared to the traditional catalytic system soybean oil/H₂O₂/HCOOH/catalyst.The results indicated that,under solvent-free condition,the epoxy value reached 1.687%at 65?for 2h with 65%TBHP as oxidant and 10%Mo-OMS-2 as catalyst,when 6.0g?43.28mmol?TBHP was dropped into the mixture in positive dropping order.Besides,the addition of Mo-doped manganese oxide octahedral molecular sieves suppressed the epoxidation reaction of the soybean oil/H₂O₂/HCOOH/catalyst system,while promoted the epoxidation reaction of the soybean oil/TBHP/catalyst system.