The Catalytic Performance Of Supported Nitro-substituted Metalloporphyrins In Cyclohexane Oxidation

The inert cyclohexane reacts with the oxidant to formation the desirable chemical products have always been a very important process. Due to cyclohexane belongs to be a saturated hydrocarbon, and the C-H is very stable, so it is necessary to take this reaction under relatively harsh conditions: such as high temperature, high pressure. Metalloporphyrins as a biomimetic catalyst, which simulates the cytochrome P-450 enzyme, have many advantages of efficiency and specificity, and which is used in cyclohexane oxidation and has been attracting more attention since it was synthesized in 1979. However, the metalloporphyrins are easier to aggregate or decompose, and it is difficult to recovery and reuse in cyclohexane oxidation. immobilization of the metalloporphyrins on some inorganic stable supports has become the most effective way to overcome the above drawbacks and retain the catalytic properties of porphyrin catalysts. Therefore, looking for a better catalytic performance of metalloporphyrins and a stable inorganic carrier are becoming a very meaningful work. Generally speaking, there are some ways to modify the metalloporphyrin catalysts: the different types of substituents, different central metal atoms and different supports.Studies show that it is good for the reaction of cyclohexane oxidation when the strong electron-withdrawing groups as a substituent. Thus, in this paper, the strong electron withdrawing groups of –Cl,-Br and –NO2 were chosen and synthesized Mn-T(p-Cl)PP, Mn-D(p-Cl)D(p-Br)PP, Mn-T(p-Br)P, Mn-TNPP, Co-TNPP and Ni-TNPP 6 kinds of metalloporphyrins catalysts. Meanwhile, the better catalytic performances of Mn-TNPP and Co-TNPP were chosen to supported on five different kinds of supports(ZnO, BM, Zr(OH)2, ZrO2, Kaolin) and the supported metalloporphyrins have been successfully prepared. The better catalytic performances of Co-TNPP/ZnO and Mn-TNPP/ZnO also were characterized by FT-IR, UV–vis, XRD, ICP and TGA/DTG. The result shows that metalloporphyrin could form new bond of Zn O-M-TNPP with ZnO, which make it is possible for the active ingredient to be dispersed well and stable onto support. The catalyst could be reused 5 times for the cyclohexane oxidation, and the average cyclohexane conversion and the average selectivity of KA oil are higher than 7% and 83%, respectively. Which presents high commercial value and application prospect.To find the reasons that why the catalytic performances are difference of metalloporphyrins in cyclohexane oxidation, the energies of different metal ions and different substituents to metalloporphyrins also have been calculated by the Dmol3 module of the MS in this paper. After calculated the orbits energies of the HOMO and LUMO, the result shows that electron-withdrawing groups could reduce the LUMO energy, the stronger of the electron-withdrawing abilities, the easier declined of the orbit energy. For the metalloporphyrins of different metal ions, the Mn porphyrins has a better ability to activate molecular oxygen, while the intermediates of Co porphyrins has a better ability to activate cyclohexane. Compared with the process of activate the oxygen, the process that the metalloporphyrin intermediate activate cyclohexane are more important in the reaction of cyclohexane oxidation when the metal porphyrins as the catalyst.