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Study On Preparation And Catalytic Performances Of Novel Nano-Porous Clay-Based Composite Materials

Posted on:2004-12-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:C H ZhouFull Text:PDF
GTID:1101360092498096Subject:Industrial Catalysis
Abstract/Summary:PDF Full Text Request
Porous clay-based composites, analogues to ordered porous molecular sieves, have demonstrated excellent prospects of application in the fields of the chemical production, electronics, medicals and environmental protection so the scientific research and development of these composites have attracted extensively attention in recent several decades worldwide and is always one of scientific frontiers in clay minerals, chemistry and material sciences. Using naturally abundant clay minerals as starting layered host, porous clay-based composites (denoted pillared layered clays) can be synthesized by interlayer intercalation of a variety of cross-linking agent or metal oxide sol particles, for example bulky polyoxocation aluminum Keggion ions [Al13O4 (OH) 24]7+ and titania oxide sol particles. Previous study reveals that pillared clays prepared by the intercalation of traditional cross-linking agent or oxide sol particle suffer from some defects such as non-uniform pore diameter, non-controllable pillar structure and low thermal stability. So to explore new preparation methodology has become a critical and hot topic among scientists and technicians in this field. It was noted recently that the disclosure of novel porous materials such as M41S, HMS and SBA-15, which possess frameworks with ordered and tunable pore diameters within the mesoporous range (~2-50nm), and great achievements on their preparation, structure and synthetic mechanism provide a large quantity of valuable information for the controllable assemble and design for ordered porous materials.On the basis of previous theory and technology on pillared clays and related porous materials scored by scientists and researchers, in the present dissertation a series of nanoporous clay-based composites such as silica, silica/alumina, silica/titania clay-based composites were prepared through new preparation approaches, which include combination of several techniques such as ion-exchange, intercalation and template assembly. The structure and surface properties of synthetic clay-based composite materials were characterized by using modern physical and chemical techniques such asX-ray diffraction (XRD), transmitting electronic microscopy (TEM), scanning electronic microscopy, Fourier transformation infra-red spectra (FTIR), thermal analysis (TG), nitrogen adsorption-desorption isotherms, pyridine-adsorption infra-red spectra, temperature programmed ammonia desorption techniques. The catalytic performances over the synthetic clay-based materials were evaluated by probe acid-catalyzed alkylation and catalytic partial oxidative hydroxylation. Several conclusions can be drawn as follows.Using natural clay minerals, montmorillonites (Mont), as layer host, the purified Mont is modified by cetyltrimethylammonium bromide (CTAB) through ion-exchange reaction. So the basal spacing of organoclay was expanded to 2.08 nm. The basal spacing was further expanded to 4.79 nm by the intercalation of dodecylamine (DDA). Mixtures of the organoclay, DDA and tetraethylorthosilicate (TEOS) at organoclay/amine/TEOS molar ratio of 1:20:150 were allowed to react for 6~8 h. Then the resulting intercalates were centrifuged, dried in air and finally calcined at 540℃ for more than 4 hours to remove the organic templates. After that the novel silica-montmorilllonite composites was successfully yielded. The results of characterization reveal that the silica-clay composites possess a nanopore (average pore size is 2.17 nm), super-gallery height of 2.75 nm, a large BET specific surface area of 821.6 m2/g and a high thermal stability up to 800℃.It is found that the pore size and gallery height can be adjusted through changing the chain length of the quaternary-ammonium salt and neutral amine used. The increment of pore size is directly proportional to the increment of chain length of the neutral amine used. The possible mechanism of pore formation include the intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensati...
Keywords/Search Tags:Clay, Montmorillonite, Nano-composites, Solid acid catalysts, Alkylation, Catalytic partial oxidation, p-tert-butyl catechol, Self-assembly
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