Study On The Microstructure And Properties Of Chitosan/Montmorillonite Supported Palladium Heterogenous Catalyst

In this study, natural cationic polymer, chitosan(CS), has been used for the intercalants of Na-type montmorillonite(Na-MMT). The chitosan chains intercalated between the montmorillonite layers to form a polymer-modified montmorillonite by ion exchange. The composites have a larger surface area than Na-MMT. Then, loading transition metal palladium(Pd) is immobilized on the CS/MMT composite forming heterogeneous catalysts, and a comprehensive assessment for microscopic structure and catalytic properties of heterogeneous catalysts has been done. Experiments mainly consist of three parts. Firstly, we prepared CS-base/MMT/Pd catalyst porous microspheres by freeze-drying method. Its morphology was observed by SEM, the results showed that the prepared microspheres have a high internal porosity and containing a thin crust of surface. It was found that montmorillonite dispersed well in the chitosan matrix, having a good interfacial adhesion between the chitosan and montmorillonite. According to the ICP-AES results, every microsphere catalyst contained Pd element 5x10-5mmol. XRD measurement was used to determine the layer spacing changes of MMT, according to Bragg equation, the calculated pure MMT layer spacing is 1.26 nm and the interlayer spacing of CS/MMT/Pd microsphere is 1.77 nm. This increase in the layer spacing indicats that the chitosan chains has been inserted into the montmorillonite lamellae, forming a good intercalated structure. The thermal stability of the catalyst has been characterized by TG. Compared with pure CS/Pd, the thermal stability of CS/MMT/Pd microsphere catalysts significantly increased. The catalytic performance and reusability of catalysts has been assessed by application in typical Heck coupling reaction. The yield was up to 95% and the number of re-use was up to 8 times. Secondly, on the basis of preliminary experiments, on CS/MMT/Pd heterogeneous catalyst has been further optimized. We used common drying method to prepare the CS/MMT/Pd catalyst microspheres and use the same characterization methods with the first part of the experiment to analyze the new CS/MMT/Pd catalyst microspheres. Its catalytic activity and reusability have been studied by application in Sonogashira reactions. Under the optimal reaction conditions: dimethyl sulfoxide as solvent, potassium acetate(base), ethylene glycol(aids), 110 ℃, 6h, the reaction yield is very good(90%) and can be reused for 10 times. Obviously, the common drying CS/MMT/Pd catalyst microspheres have a better overall performance than freeze-dried microspheres. Thirdly, the previous two parts of the experiment as the basis for the next step, we used MMT-based matrix and CS as modifier to prepare MMT / CS nanocomposites by solution ion exchange method. Using XRD, BET, TG, HR-TEM, XPS and other means characterized these kind of MMT/CS/Pd heterogeneous catalyst materials. Heck reaction has been used to explore the catalytic activity and usability of MMT/CS/Pd heterogeneous catalyst. The results show that compared with the previous two forms(with CS-based matrix CS/MMT/Pd freeze-drying and general dry microspheres) heterogeneous catalyst, have a greater surface area, narrow pore size distribution, a micro mesoporous structure, better catalytic activity, thermal stability and recyclability(32 times).The attempts of this study especially for the MMT/CS/Pd catalysts with super sability has great significance in the development of the green catalytic systems.