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Host Effects Of Nano-crystalline Zeolite In The Macromolecular Metal-Complexes

Posted on:2003-01-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:H X YangFull Text:PDF
GTID:1101360092996852Subject:Industrial Catalysis
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This dissertation includes two parts: the first part discusses the synthesis of nano-zeolite Y and the proposal of a new 'layer-by-layer' zeolite crystallization mechanism; the second part invoves the preparation and charaterization of metal complex/faujasite nano-materials.1. Synthesis of nano-zeolite Y and the proposal of a new 'layer-by-layer' zeolite crystallization mechanismThe synthesis of nano-meter zeolites has recently received much attention owing to their utility in the fundamental studies of zeolite crystal growth, in the preparation of ultra-thin zeolite films and nano-composites, and as a support for catalytic and photochemical reactions. The synthesis approach of nanosized faujasite reported in literature show disadvantages when using high shear agitation (not less than 3000rpm) or thermal shattering techniques, aging at very low temperature and adding organic compounds to the reaction mixture. In this paper, our attention paid on the development of a new nanosized faujasite synthesis approach, study of physical-chemical properties of nanosized faujasite, as well as the study of zeolite crystallization mechanisms.(1) Well-crystallized nanometer-sized zeolite Y of particle size less than 70nm (denoted as nano-Y) have been successfully synthesized for the first time by a two-step-process in an organic free system, without using any unusual techniques. Several types of zeolite Y of different particle sizes with similar Si/Al ratio have also been synthesized by adjusting the temperature and water content.(2) XRD. FTIR. TG-DTA, DRS, NMR and BET characterizations of these macrocrystalline and nanocrystalline materials all show that their physicochemical properties change systematically with crystal size: as the particle size decreases, the XRD lines of the samples bordene; the bands around 700cm-1 and 1000 cm-1 of FTIR patterns shift to the lower frequencies;the specified surface area and mesoporosity of the samples increase; DRS adsorption thresholds shift towards the longer wavelengths (attributed to the change of the particle size but also the degree of aggregation). (3) Based on our HRTEM, XRD, FTIR experimental studies and a systematical analysis, we proposed a new 'layer-by-layer' mechanism for zeolite crystallization in the present system: the aluminosilicate precursor gel contained small amorphous particles of about 40 run that agglomerated during the beginning of the crystallization to form a layered structure along <733>, the layered structure then further crystallized to the cubic structure of zeolite Y.2. Nano-host effect on the preparation and physicochemical properties of the complex/faujasite nano-compositesMetal complexes immobilized into molecular sieves have gained great interest and become a hot point in the field of catalytic materials due to their mild reaction conditions, high catalytic activity and selectivity, easy separation, recovery, shape selectivity and unique site isolation. However the immobilized metal complexes partly clog the channel of zeolite, which makes the diffusion of ligands, reactants and product difficult. The diffusion problem causes a low complex loading content and heterogeneity of the immobilized metal complexes in the zeolite crystal. Activities of these materials are also not satisfactory due to the diffusion problems, especially when the amount of complex loaded in the zeolites increases.Large surface area and short diffusion pathways of nano-sized zeolites could possible be one solution to this question, which has not been remarked on in the literature until now. The special properties of nano-zeolite, such as possession of a highly catalytic center, high surface-atom ratio, large surface area, high surface energy and better retro-wear may also give this material some new application.In this paper we report the synthesis of a series of complex/nano-faujasite materials by a template synthesis method and a zeolite synthesis method. The guest/host nano-materials are further studied by various p...
Keywords/Search Tags:Nano-zeolite, Synthesis, Crystallization mechanism, Metal complex, Immobilization, Oxidation reaction
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