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The Synthesis, Characterizations and Properties of Novel Micro/mesoporous and Bi-micro/mesoporous Composite Molecular Sieves

Author: LiXuGuang
Tutor: HuangZuo
School: Fudan University
Course: Materials Physics and Chemistry
Keywords: Alkali / acid system synthesis The attached crystal growth method Ternary complex molecular sieve Y-Beta/MCM-41 Binary complex molecular sieves Beta/MCM-41 Catalytic properties
CLC: TB33
Type: Master's thesis
Year: 2009
Downloads: 506
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Abstract


With dual-pore structure of microporous - mesoporous composite molecular sieve high hydrothermal stability due to a combination of strong acidic microporous zeolites and mesoporous molecular sieve aperture and adjustable, with potential applications, making it In recent years the field of materials science research hot spots. For a deeper understanding of microporous and mesoporous molecular sieve composite mechanism, the paper is relatively simple system synthesis of microporous - binary complex mesoporous molecular sieve Beta/MCM-41 in the synthesis process, each phase growth and the evolution of its composite mechanism and from the perspective of thermodynamics and interaction. Further, for the preparation of the out configured with different pore structure and acidity distribution more optimized composite materials, this thesis breakthrough micropores have been reported - Mesoporous binary composite zeolite areas developed a new double microporous - mesoporous ternary composite molecular sieves. However, the complexity of the synthesis system diversification led to the synthesis system, making it more challenging topics. In this thesis systematically studied synthesis method of the material in acid, alkali system and synthesis of the law, to characterize its structure and performance, improve the scientific understanding of the ternary complex molecular sieve synthesis, provides for the development of the oil fields for the selection of new catalytic material. The paper has important theoretical and practical significance. This thesis is divided into three main parts: the first part of tetraethyl ammonium hydroxide and cetyltrimethylammonium bromide as the micropore phase and mesoporous phase template, using the two-step crystallization method prepared by four different zeolites containing microporous and mesoporous dual-mode the pore structure Beta/MCM-41 composite molecular sieve. X-ray diffraction (XRD), N2 adsorption - desorption their structure characterized by pyridine adsorption infrared spectroscopy (Py-IR), and n-heptane cracking probe reaction test, the amount of acid and catalytic properties. The experimental results show that the increase of the silica to alumina ratio of the feed, the the composite zeolite intermediary hole relative order gradually increased, the degree of crystallinity of the microporous phase gradually decreases, the amount of acid is reduced, the conversion rate of n-heptane cracking decreased. Illustrate the properties of the materials can be modulated with the silicoaluminophosphate ratio variation, to meet the needs of different catalytic reactions. From the basic point of study evolution Beta/MCM-41 composite molecular sieve in the crystallization process, the microporous phase Beta and mesoporous phase growth of MCM-41, and found that the increase of crystallization time, the morphology and composition of the composite molecular sieve experienced Beta particles adhering sheet on MCM-41, directed by the sheet assembled into MCM-41 inter-layer packet Beta particles sandwiches like to Beta particles package of MCM-41 skeleton wreck sandwiches like the last Mesoporous phase MCM-41 into the annular pure beta phase. And from the perspective of thermodynamics and interaction of its formation the composite mechanism was discussed. The second part of this thesis, first proposed the synthesis of multi-level pore structure of dual pore - the new ideas of the ternary complex mesoporous molecular materials. The design uses overgrowth method, alkaline hydrothermal conditions, Y and Beta Zeolite crystals as precursors, binary mixtures of cationic (CTAB) - non-ionic (OP-10) surfactant as a template, by assembling Directions S S0 I - synthesized Y-Beta/MCM-41 double microporous - ternary complex mesoporous molecular sieve. More systematic study of the impact of a variety of factors to Y-Beta/MCM-41 synthesis made to optimize the synthesis conditions: CTAB / SiO 2 = 0.15 CTAB/OP-10 = 6: 1, pH = 11.1, feeding Si / Al = 25 the W Y Beta / W SiO2 (g / g) = 0.534, the W Y / W Beta (g / g) = 1:1, the crystallization temperature of 100 ° C, the crystallization time of 2 days. The composite zeolite obtained completely different mechanical mixture, its catalytic cracking activity of α-methyl naphthalene is a mechanical mixture of the two times. The ternary composite zeolite the micropores in phase between the ratio between the proportion of any adjustable and a pore-phase and mesoporous phase in alkaline systems, the microporous phase alumina ratio is adjustable within a certain range. And microporous phase desilication in alkaline medium prepared the lower alumina ratio ternary complex molecular sieve. Third part in order to broaden the composite molecular sieve composite molecular sieve microporous alumina ratio of the zeolite synthesis High-SiO2/Al2O3 this paper to overcome the assembly of cationic surfactants in acidic system difficulties of mesoporous MCM-41, for the first time in acidic system, overgrowth method, Y and Beta Zeolite crystals as precursors cation - non-ionic binary mixed surfactant as a template, the through the assembly route S XI < / sup>, using the acid dealumination of the zeolite, synthetic high silicon aluminum the ratio Y-Beta/MCM-41 composite molecular sieve. More systematic study of the influence of various factors on synthesis, optimized synthesis conditions: of CTAB / SiO 2 = 0.28, CTAB/OP-10 = 7:1 system at pH = 1.8, W Y Beta / W SiO2 (g / g) = 0.794, W Y / W Beta (g / g): 2:1, the crystallization temperature of 100 ℃, crystallization time of 2 days. Control of the synthesis conditions, can effectively regulate the ratio between microporous phase and mesoporous phase composite molecular sieve, the ratio between the two microporous phase and silica-alumina ratio. The acidic system synthesis Y-Beta/MCM-41 conversion rate of the catalytic reaction of α-methyl naphthalene is 1.55 times of the mechanical mixture. The material also has good water and heat stability (600 ° C, 100% steam for 6 h). By alkali, acid system synthesis Y-Beta/MCM-41 composite molecular sieve contrast, found that in many ways the two can complement each other, and can choose a variety of new catalytic materials for practical applications.

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