Preparation Of Magnetic Nano Solid Acid For Catalytic Epoxidation Of Olefins

Liquid acids, known as one of the most important catalysts, have acquired a crucial place in industrial processes such as oil refining and production of pharmaceutical chemicals. However, the utilization of these catalysts suffers from a lot of disadvantages such as the difficulty in separation and recovery of catalysts from the product, severe equipment corrosion and the large discharge of hazardous waste. It has been an inevitable trend that liquid acids are replaced by eco-friendly and renewable solid acids in the background of advocating harmonious progress of resources, economy, environment, and society. In recent years, magnetic nano solid acids have attracted more and more attention owing to their high catalytic efficiency, good stability and reusability. In this dissertation, the strategy of fractional steps, which combines the traditional liquid-phase synthesis method and surface modification technology, has been developed for the preparation of nearly monodisperse γ-Fe2O3@C@MoO3core/shell magnetic nano solid acid. The catalytic performance of them in the epoxidation of olefins with tert-butyl hydroperoxide (tBuOOH) as an oxidant was studied and then the epoxidation of cyclooctene was carried out as model reaction to examine the effect of reaction temperature and reaction time on the result of experiment. Meanwhile, the reusability of the catalyst was also investigated. Based on the experiment datas and relevant literatures, we proposed a new reaction mechanism. The concerns of the dissertation include following several aspects:1. The γ-Fe2O>3magnetic nanoparticles (MNPs), with an average diameter of about300run, were firstly obtained by solvothermal reaction, and then coated with a thin layer of carbon by using glucose as the carbon source via a hydrothermal route. After that, the obtained material was modified with PDDA to improve the adsorption efficiency of magnetic microspheres for the precursor, followed by hydrothermal treatment using a mixed solution of ethylene glycol and deionized water as a solvent, to ultimately provide the multifunctional hybrid materials. The results of characterization by several techniques such as SEM, TEM, XRD, XPS etc, confirm that a nearly monodisperse superparamagnetic γy-Fe2O3@C@MoO3nanocomposites with core-shell structure was observed; 2. The catalytic performance of them has been demonstrated in heterogeneously catalyzed oxidation of ole fins using tert-butyl hydroperoxide (tBuOOH) as oxidant and carbon tetrachloride (CCI4) as solvent. The experiment results show that, high conversion in cyclooctene (97%), selectivity in cyclooctene oxide (nearly100%) and TOF (66.7h"1) were achieved at80℃for6hours with relatively low catalyst dosage(0.5wt%), conversion of styrene reached98.4%with reaction time increased to12hours in the same reaction condition. The epoxidation of cyclooctene was carried out as model reaction to evaluate the effect of reaction temperature, reaction time and the reusability of the catalyst. Subsequent recycle test prove that the hybrid catalyst could be easily separated by an external magnet and reused up to9times with no significant loss of activity and selectivity;3. The reaction mechanism over MoO3has been proposed based on experiment datas and relevant literatures. It is suggested that the formation of the transition state, a Mo-alkyl peroxide and olefin complex, offers a convenient and readily accessible means for efficient transfer of the charge and oxygen atom in the epoxidation by converting intermolecular process directly into an intramolecular process.