Study On Heterogeneous Catalyst For Alkene Epoxidation By Molecular Oxygen

Many researchers used alkyl hydroperoxide, hydrogenperoxide and molecular oxygen (oxygen or air) as oxidant for alkene epoxidation. Alkyl hydroperoxide is a good oxidant for alkene epoxidation, but it is expensive. Molecular oxygen is the most ideal oxidant between the three, because it is cheap and green. Hydrogenperoxide is also a cheap and environment-friendly oxidant, but it is expensive and hard for storage compared with molecular oxygen. Hydroperoxide will bring co-product-water when using it as oxidant, but not for molecular oxygen under the condition of no sacrificial reductant. Therefor, epoxidation of styrene, cyclohexene, propene and butene with molecular oxygen (oxygen or air) over heterogeneous catalyst was investigated in this paper. Alkene epoxidations under various catalytic system over different catalyst synthesized in the paper based on different alkenes were researched. Concretely, the following content were researched in this paper:(1) Co/TS-1 synthesized by impregnating method was applied in styrene epoxidation. Styrene epoxidation by oxygen using N, N-dimethylformamide (DMF) as solvent was carried out under the condition of 100℃and atmospheric pressure. In the experiment, oxgen was added into the system by bubbling. The effects of cobalt amount in the catalyst, calcination temperature of the catalyst, supports of the catalyst, reaction temperature and flow rate of oxygen on the catalytic results were investigated.94.5% styrene conversion with 74.3% epoxide selectivity was obtained under the optimal conditions. The stability of the catalyst was tested. The catalyst was used consecutively for 5 times without significant styrene conversion and epoxide selectivity change. In addition, the mechanism of the catalytic reaction was explored and the reaction follows the free-radical mechanism.(2) Two different metal Schiff-base composite catalysts with montmorillonite as support (Co-mont (Lx) and Mn-mont(Lx)) were synthesized successfully and applied into the epoxidation of cyclohexene under Mukaiyama catalytic system. The catalytic system was carried out under mild conditions (35℃and atmospheric pressure) using air as oxidant and aldehyde as sacrificial reductant. The effect of metal loading, kinds of Schiff-base and reaction conditions (temperature, air flow rate, kinds of solvent, the ratio of aldehyde and alkene, and catalyst amount) on the catalytic results were investigated.95.1% cyclohexene conversion with 87.0% epoxide selectivity was obtained under the optimal condition. In addition, the mechanism of the catalytic reaction was explored and the reaction also follows the free-radical mechanism.(3) Liquid phase epoxidation of propene and butene catalyzed by TS-1 and Au/TiO2 under CO/O2/H2O/CH3OH system was investigated in the thesis. Carbon oxide was firstly used as sacrificial reductant for the epoxidation of propene and butene. When using a mixture of methanol and water (methanol≥80%) as solvent in the reaction, the epoxide selectivity reached more than 90%. TS-1, Au/TiO2 and carbon oxide are all necessary for producing epoxide, no epoxide formed without any one of them. To investigate the catalytic mechanism carefully by isotope labeling experiment, we found out that the oxygen atom in the epoxide was all from molecular oxygen but not water. By thermodynamics analysis, the molecular oxygen (O2) needs to be activated in an asymmetric fashion in the catalytic process.