Preparation Of Catalysts Based On Metalloporphyrins And Their Catalytic Performance On Epoxidation

Epoxidized vegetable oil is an important environment-friendly plasticizer, which has high thermal stability, water resistance and oil resistance and can be used in poly vinyl chloride (PVC). Especially in recent years, more and more rules ban the products containing the phthalic acid ester which are harmful to our health. Epoxidized vegetable oil obtained from vegetable oil has great practical value and wide applications in the future only which can be used for the food-packaging bags because it is safety and innocuity. In this paper, metalloporphyrins were used as catalysts for synthesis of the epoxidized vegetable oil and other epoxidized compounds.The catalytic properties of metalloporphyrins with various metals (Mn, Fe, Co, Ni and Zn) and different electron-donating substituents in phenyl rings with hydrogen peroxide (H2O2,30wt.%) as oxidant have been studied in oxidation of unsaturated fatty acid methyl esters (FAMEs) under mild conditions. These materials were analyzed by UV-vis, FTIR and thermal analysis. The catalytic activities of metalloporphyrins in the oxidation of FAMEs not only changed with the variety of metal ions in metalloporphyrins but also changed with variety of substituents on the porphyrin rings in the same pattern of metalloporphyrins. Co-catalyst effects of inorganic salts had a crucial role in the catalytic performance. Furthermore, different electron-donating substituents in phenyl rings led to better catalytic performance and worse thermal degradation temperature.Tetraphenylporphyrin manganese (Ⅲ) chloride (Mn(TPP)C1) was grafted on the hexagonal mesoporous silica (HMS) modified by Cu and Zn oxides as heterogeneous catalysts. The catalytic performance of these novel materials was investigated by carrying out the oxidation of fatty acid methyl esters (FAMEs) at room temperature. The formation of epoxides:Mn(TPP)Cl/Zn-HMS>Mn(TPP)C1/Cu-HMS>Mn(TPP)C1/HMS)>Mn(TPP)C1. A slight blue shift was observed when compared with the spectra of free Mn(TPP)Cl. This indicated that the nature of Zn influenced the redox properties of the Mn complexes, which was consistent with the result for phenyl rings of metalloporphyrins with electron-withdrawing groups. Mn(TPP)C1/Zn-HMS had a better hydrophobic nature which could slow water coordination to the metal center and a fewer existence of silanol groups (=Si-OH) on the catalyst surface than Mn(TPP)C1/Cu-HMS. So, Mn(TPP)C1/Cu-HMS exhibited a lower selectivity because silanol groups (=Si-OH) may accelerate the ring opening of the epoxides. The formation of epoxides:Mn-NH-HMS> Mn-NH-HY> Mn-NH-Hβ. Mn(TCPP)Cl was grafted through amide bond on silica zeolite Y (HY), zeolite beta (Hβ) and hexagonal mesoporous silica (HMS). The effect of support structure on catalytic performance was also discussed. These silica supported catalysts especially Mn-NH-HMS were shown to be used for epoxidation of cyclohexene, cyclooctene, methyl oleate and soybean oil. Interestingly, cyclooctene could be easily epoxidized. NaIO4was the best choice among three different kinds of oxidants TBHP, NaIO4and H2O2. A good shape selectivity was observed when imidazole was used as organic promotor and acetonitrile was used as solvent. The energy barriers about epoxidation of alkenes by NaIO4and H2O2were also computationally calculated to explain the different catalytic efficiency. Energy barrier existed at the formation of intermediate for both reactions. The activity performance for different oxidant NaIO4or H2O2were consistent with the results being the formation of the intermediate. More energy was needed for H2O2compared with NaIO4, which was consistent with the experimental results.