Fabrication And Application Of Zeolitic Microcapsular Reactor

In recent years, the synthesis and applications of microcapsule reactor have attracted much attention in fields of physics, chemistry, material science, biology and so on. With regular microporous structure, adjustable surface properties, great surface area, nano-zeolite has a wide range of applications in shape-selecting catalysis, adsorption separation and many other fields. The zeolitic microcapsule reactor (ZMR) could keep the advantages of both nano-zeolite and microcapsule rector at the same time with the special micro-environment and the protective effect of zeolitic shell. In detail, the zeolite shell could contain the following characteristics:(1) the selectivity for the reactant/product/intermediate-complex, which then changes the equilibrium of the reaction and enhances the final selectivity of the desired product;(2) the screening effect of the molecules, which protects the activity of the active species inside the ZMR from poisoning and leaching outside;(3) the isolation effect of the multi-step reactions, which divides the reaction system into different regions and avoids the interaction of different reactants as well as catalysts;(4) the synergistic effect of various catalysts, which makes the multi-functional catalyst become possible. Correspondingly, it should have great development potential in various domains like the controllable drug release, the chemical and biological catalyst.However, there are still challenges in the urgent research of ZMR. Firstly, the present fabrication methods are expensive; secondly, it is difficult to control the morphology of ZMR precisely; thirdly, its formation mechanism is still not clear in the previous report, and finally, there are only a few practical applications of ZMR and rare reports about the deep functionalization of ZMR. These problems would limit the further modification and application of ZMR. Therefore, the research dealing with synthesis and growth mechanism of ZMR as well as designing other functional microcapsule has been expected to promote the development of such nano-materials.This dissertation focuses on the fabrication, application and functionalization of ZMR. A new method was originally developed and the formed hollow microcapsule was well characterized. New growth mechanisms were proposed on the basis of systematic study about their fabrication. Afterwards, the catalytic species were encapsulated into the ZMR (such as Pt@S1), and then applied in series of practical catalytic reactions. Finally, the ZMR was further modified with various functional methods. Besides, due to the facilities of the process, novel product structures and excellent performance of ZMR, the special material proposed in this work will open opportunities for the synthesizing and designing of functional microcapsules. The details of each chapter are listed below.In Chapter2, hollow silicalite-1microcapsules (HSMs) were fabricated through the mesoporous silica spheres template approach by hydrothermal method in a simple system containing only sodium hydroxide. The mechanism for this process was investigated. The formed microcapsule was well characterized. During the synthesis, the dissolution rate of mesoporous silica spheres was hastened with the increasing of the alkalinity in solution. When the rates of zeolite inter-growth and template dissolution were matched with each other, the perfect ZMR could be successfully obtained.In Chapter3, the detailed formation process of ZMR was investigated in the hydrothermal system. The effects of the starting gel composition together with the hydrothermal synthesis conditions such as alkalinity, tetra-propylammonium cation (TPA+) content, and temperature on the features of microcapsules were comprehensively discussed, and a related mechanism was presented. It is found that the matching of core dissolution rate (Red) and silicalite-1shell inter-growth rate (Rsi) is crucial for the formation of perfect ZMR. The excellent ZMR with dense inter-grown shell structure as well as perfect hollow center can be fabricated by controlling the relative rates of the dissolution of silica template core and the formation of zeolitic shell.In Chapter4, zeolitic microcapsule with active Pt nanoparticles encapsulated (Pt@S1) was fabricated firstly and then successfully explored in the controllable multistep reactions. So far, the most effective approaches for hydrazone preparation is based on the condensation of the N-H group in phenylhydrazine and the carbonyl group in ketone, and the ketone is industrially prepared by the selective oxidation of alcohol. If these two operations could be integrated into one reactor, i. e., synthesizing hydrazone directly from alcohol, the eco-efficiency and the value of the fabrication process would be significantly enhanced. However, the problem for achieving such goal relies on the fact that the platinum, known as a good catalyst for alcohol oxidation, would loss its activity by the strong interaction with N atoms in phenylhydrazine. Comparison between the commercial Pt/SiO2, the broken Pt@S1and the intact Pt@S1indicates that it is the microcapsule that ensures the successful tandem reaction. The zeolitic shell could not only protect the active site from poisoning by the molecular of big size but also enable the good reusability of Pt@S1. Besides, the catalyst could be easily dispersed and recollected, presenting variety functions in the catalytic domain.In Chapter5, the platinum-encapsulated ZMR catalyst is successfully employed in the dynamic kinetic resolution of amine and this kind of catalyst could avoid the disadvantages of the interaction between the metal and the enzyme. It is found that the existence of the silicalite-1shell not only effectively prevents the deactivation of both enzyme and Pt by isolating them in different regions of reaction system, but also significantly reduces the formation of by-products on the Pt nanoparticles within the confined space of ZMR. Such features of zeolitic shell should further promote the designing of various catalysts for multi-step reaction network.In Chapter6, the deep functionalization of ZMR was studied. This chapter and the following chapter are both extension works. In this chapter, the preparation process of the functionalized ZMR was discussed. At the external shell, the ZMR was successfully modified with mesoporous materials. While inside the ZMR, the mesoporous carbon network could also be successfully formed through the injection of sugar into the template. Each functionalized ZMR was well characterized.In Chapter7, the extend research for the ZMR was discussed. The synthesis method and the mechanism proposed before were explored to other kind of ZMR containing Al and Ti species. Because of their different catalytic activities and chemical properties, different types of ZMR can be adapted to meet various needs of different catalytic reaction. They will probably find wide applications in the construction of catalysis, photonic or electronic materials.