Preparation And Application Of Zeolite Molecular Sieve Bulk Material, Film And Its Magnetic Functionalization

Zeolites, as a kind of microporous materials, have been widely used in catalysis, adsorption, separation, photoelectrical materials, functional materials, drug delivery and release, host-guest materials, etc. for their rich pore structures, order channel regularity and high hydrothermal stability. Moreover, zeolite materials have brought huge economic benefits for our society. In1756, zeolite has been discovered in nature. Under a condition of high temperature calcination, some natural materials can bubble and swell, even boil. Therefore, this kind of minerals is named as zeolite (zeolite origin from Greek, meaning "boiling" and "rock"). In a long term of practical activities, people further realize its microporosity and properties such as adsorption, ion exchange etc. In1940s, scientist simulated the forming conditions of natural zeolites and thus synthesized the first batch of zeolite with low Si/Al ratio in a hydrothermal condition. In1960s, zeolite Y was successfully synthesized and showed an excellent catalysis performance in an alkane inversion reaction. The discovery of zeolite Y greatly promoted the development of zeolite with medium Si. In1970s, ZSM-5with high Si was invented by Mobile Company, which induced a revolution of oil industry. Zeolites with high silicon percentage possessed a high thermal stability and acidity, which endows it with an important practical application value. In1980s, a new type of zeolite, phosphorus and aluminum molecular sieve AlPO4-n (n is the series number), was synthesized. It is an important milestone in the development history of porous materials. Until now,204unique zeolite framework types have been identified, which establishs a scientific foundation for the great development of molecular science and industry. As the development of science, zeolite materials with a single pore size and component can not meet the requirement of practical applications. The small-pore zeolites are not suitable for the catalysis and adsorption process of compounds with large molecular sizes or biological large molecules. The large molecule can not enter into the micro channel of zeolite and come out from it. If the meso-or macroporosity is introduced into the zeolite materials to form a hierarchical structure, the diffusion efficiency of guest species will be improved.Conventional zeolites are produced in the form of powder. In order to elevate the efficiency of zeolite, it is usually molded to meet the requirement of practical applications. For example, in the petroleum cracking process, the catalysts are usually composed of zeolite and silica-aluminum-matrix, similar to the structure of concrete. According to the different application requirements, zeolites can be molded into different structures. In a special structured reactor, zeolites can be synthesized into monolithic materials. In a separation field, zeolite can be shaped into membrane to increase the separation efficiency. In order to expand the application field, zeolite can be combined with different guest species to form hybrid materials that show the characterized properties in the field of photo, electricity and magnetism. The inexhaustible synthetic options for zeolite can make the imagination exert to design and obtain some hybrid materials with novel structures.In chapter2, we designed and prepared a ZSM-5monolith with hierarchical structure. The catalytic performance of ZSM-5monolith in methanol to propylene was investigated. A silica sol was used as source to prepare a viscous zeolite precursor. Due to the hydroscopicity of polyurethane (PU) foam, the precursor can be infused into its macropores. After the viscous precursor was solidified, the steam assisted crystallization (SAC) technique was used to transform the amorphous precursor into the ZSM-5crystals. A ZSM-5monolith with a structured shape was obtained. The monolithic zeolite materials possess a high crystallinity, high surface area and hierarchical pore structure. After the remove of the sacrificed PU foam skeleton through the calcination, the interconnecting macropores (～33μm) are left in the ZSM-5monolith. In the original macropores of PU foam, the intergrown zeolite nanocrystals (～500nm) aggregate to give another level of macroporosity with wide pore size distribution (200nm～1700nm). Besides the intrinsic microporosity of zeolite ZSM-5, the third porosity stems from the intracrystalline mesopores (～50nm) in each ZSM-5crystal. The intracrystalline mesopores are generated and encapsulated without adding any porogen. They are connected through the micropores of zeolite. The control experiment shows that the formation of these intracrystalline mesopores is related to the used silica source but not to the PU foam. When the TEOS is used as the silica source, no intracrystalline mesopore is formed under the same condition. While the silica sol is used, due to the existence of dispersed silica nanoparticles, the amorphous aluminosilicate nanoparticles can be formed during the aging of zeolite precursor. During the solidified process, these nanoparticles cross link with each other and leave substantial voids between them. In a fast crystallization during the SAC process, the voids are transformed and preserved in the zeolite crystals. In a SAC process, aluminosilicate species can only crystallize in a short range. The voids can be preserved in a single zeolite crystal and transformed into mesopores. This kind of ZSM-5monolith possesses a high macroporosity (75.2%) and mechanical stability (100kPa). The ZSM-5monolith as a catalyst for methanol to propylene (MTP) conversion shows excellent catalytic performance with high methanol conversion (above95%) and propylene selectivity (above40%) using a higher velocity (3.6h-1). The selectivity over grounded and sieved catalyst is below40%. It is important that the reaction can reach a steady state in a short time (5h) over the ZSM-5monolith. However, on the traditional catalyst it needs a long activated time to reach the steady state. It suggests that the transfer and diffusion of species are improved.In chapter3, a functional MFI type zeolite membrane was prepared. MFI type zeolite membrane possesses a channel system similar to the molecule size and can endure the corrosion of high temperature, chemistry and biology. Therefore, the separation in a molecular level can be performed to realize the integration of catalysis and separation. The MFI zeolite membrane can be widely used in environment protection, petroleum industry, biological industry, et al. A secondary growth approach was used to synthesize the Silicalite-1membrane on a porous Al2O3substrate. First of all, we introduce the iron oxide nanoparticle into the confined space of commercially porous silica gel to obtain SiO2-Fe3O4composites. After a short hydrothermal treatment, SiO2-Fe3O4composites can be transformed into the hybrid of nano zeolite crystals and iron oxide nanoparticles which are used as the seeds for the preparation of membrane. Through a manual rubbing method, the zeolite seeds can be deposited on the porous Al2O3substrate. After a secondary growth, a continuous oriented Silicalite-1membrane with the modification of iron oxide nanoparticle was obtained. The thickness of membrane can be7μm. Iron oxide nanoparticles are well dispersed through the membrane. The permeation for N2is4.0×10-8mol/(m2s Pa). The permeation for He is9.5×10-8mol/(m2s Pa).In chapter4, we try to endow a function to the zeolite, especially the magnetic function. The zeolite with a magnetic function not only can give the intrinsic functionalities of zeolites (ion exchange, adsorption and catalysis) but also can make use of the unique magnetic responsivity. The magnetic zeolite can be quickly separated from the medium in an external magnetic field, increasing its application efficiency. In the same way, we firstly introduced the magnetic nanoparticle into the confined space of commercially porous silica gel to obtain SiO2-Fe3O4composites with magnetic responsiveness. Through a simplified hydrothermal process, nanorod-assembled ZSM-5microspheres are obtained. The Fe3O4nanoparticles are well dispersed between the spaces of nanorods. The obtained magnetic ZSM-5microspheres possess a uniform size (6-9μm), ultrafine uniform Fe3O4nanoparticles (～10nm), high surface area (340m2/g) and large magnetization (～8.6emu/g). The growth of such unique microspheres undergoes a nanoparticle-assisted recrystallization process from surface to core. In a hydrothermal treatment, the incomplete dissolution of the Fe3O4@SiO2composite at a low alkalinity prevents escape of the Fe3O4nanoparticles from the silica gel. A high hydrothermal temperature leads to a fast crystallization of ZSM-5nanocrystals. The aggregation of zeolite nanocrystals is faster than the growth of zeolite. During the growth of zeolite, the Fe3O4nanoparticles can not be involved in the growth of zeolite crystal due to the large particle size (～10nm) but obstruct the growth of zeolite crystals to form the aggregates of nanorod polycrystals. To minimize the surface energy, the recrystallization begins from the surface to form polycrystals and replicates to the core. The polycrystals assemble to the spherical hybrids. The zeolite microspheres not only possess a characteristic of magnetic responsiveness, but also can be regarded as a kind of zeolite supported catalysts. We investigated its catalytic performance in the Fischer-Tropsch synthesis. The catalyst has a long life (～110h) and good selectivities. The selectivity of C5-C12can reach44.6%. But the selectivity of C13-C20is3.2%. No C20+hydrocarbons are detected. The zeolite acid sites suppress the formation of the long chain alkane.In chapter5, we expand the synthesis of magnetic zeolite to obtain the hybrids with different morphology and structure. Cobalt ferrite with spinel structure not only can endow a magnetic function to the zeolite materials, but also has a potential application in catalysis, machine, electricity and biology. Meanwhile, cobalt ferrite can keep the structure stability in the hydrothermal process. Likewise, we firstly introduced the CoFe2O4nanoparticle into the confined space of commercially porous silica gel to obtain SiO2-CoFe2O4composites. After a hydrothermal process, the CoFe2O4-ZSM-5composites with a magnetic function are obtained. The composites possess high surface area (320m2/g) and large magnetization (～4.7emu/g). It is noticeable that the CoFe2O4nanoparticles do not impact the growth of zeolite crystals. The zeolite particles are the single crystals. The smaller CoFe2O4nanoparticles (<5nm) can be encapsulated in the zeolite single crystals. The big particles are located on the surface of zeolite crystals.