Synthesis, Characterization And Catalytic Propertise Of Pt-A Supported Microporus/mesoporous Core-shell Molecular Sieves

The synthesis of micro-mesoporous molecular sieve greatly promotes its wide application in the important areas of petrochemicals, fine chemicals and bio-chemical. Owing to the reason that the smaller aperture of the micropore in mesoporous or the mesoporous in micropore has hindered a number of molecular diffusion and material flow, the applications of the micro-mesoporous material is much more restricted in the specific catalytic. The successful preperation of the core-shell zeolite with unique structure not only compensates for the drawback of micro-mesoporous composite molecules, but also expands the applications range of molecular sieve. The novel molecular sieve has promising application in catalysis industry due to the advantages of its unique dual pore structure, regular pore size with gradient distribution and the adjustable acidity properties. The core-shell material with core-shell structure is able to provide different type of catalytic active center, and itself can also be used as the carrier of a number of noble metal catalyst. The supported noble metal catalyst is very important in the process of hydrodesulfurization and dearomatization, and has a higher hydrogenation catalytic activity compared with the conventional catalyst of CoMo, NiMo, and so on. Therefore, the noble metal materials has drawn much attention of the researchers at home and abroad. Especially, the material using the core-shell structured core-shell zeolite as the carrier has important research value. However, the research in this area has been rarely reported. Therefore, in the paper, based on the research background above, we have studied from the following aspects:(1) In an extremely diluted alcohol water system, the NaA@Mesosilica Core-Shell Zeolites with traditional NaA zeolite and Mesoporous SiO2as nuclear phase and shell, respectively, was synthetized by the nano self-loading method (2) Pt-A@Mesosilica Core-Shell Zeolites with Pt-A zeolite and Mesoporous SiO2as nuclear phase and shell, respectively, was synthetized by the same method.(3) The prepared Pt-A@Mesosilica core-Shell Zeolites was demonstrated to be used as catalysts for hydrogenation of benzene to cyclohexane, and the catalytic properties was investigated. The sample of NaA@Mesosilicaand Pt-A@Mesosilica was characterized via X-ray diffraction, N2absorption-desorption, transmission electron microscopy (TEM), scanning electronic microscopy (SEM) etc.The conclusions are as follows:1. Pt-A molecular sieve with Pt encapsulated in NaA zeolite pores was synthesized by the dynamic hydrothermal crystallization method. The scanning electron microscopy (SEM) characterization show that the addtion of Pt not only affects the morphology of the NaA zeolite, but also changes the crystal forms from the original smooth surface cube to the rough rule polymorphs. The involvement of Pt promotes the nanocrystallization of NaA zeolite nano, and the particle size becomes from1μm to about200nm.2. In an extremely diluted alcohol water system, the obvious core-shell structured NaA@Mesosilica Core-Shell Zeolites with traditional NaA zeolite and Mesoporous SiO2as nuclear phase and shell, respectively, was synthetized by the nano self-loading method. The analysis results of XRD show that with the increase of silicon content, the shell growing on the surface of nuclear phase NaA zeolite gradually becomes thick. The results of SEM characterization indicate that the morphology of the synthetized sample is similar to that of the nuclear phase NaA zeolite, which implies the structure of the core phase has not been destroyed in the process of the shell growing. The TEM images reveal that the synthetic samples with an obvious core-shell structure grows uniformly along the surface of the nuclear phase. When the value of (TEOS)/m(NaA) is1.2, the thickness of the shell is about30nm. When high high magnified, the Mesoporous shell of SiO2grows vertically along the surface of the nuclear phase.3. The Obvious core-shell structured Pt-A@Mesosilica core-shell Zeolites with Pt-A zeolite and Mesoporous SiO2as nuclear phase and shell, respectively, is synthetized by the same method. The results of the wide-angle XRD characterization show that the thickness of the mesoporous shell is adjusted by the addtion of TEOS, while the low-angle XRD characterization indicate the mesoporous shell adjusted by weak alkali is more regular than that of by strong alkali. The N2adsorption-desorption isotherm belongs to the typical type IV, and has a significant hysteresis loop, which demonstrates the synthetic shell has the mesoporous structure with the pore size distributed about2nm. The reault agrees well with the reault of the low-angle XRD; the TEM characterization reveals the prepared core-shell zeolite Pt-A@Mesosilica has the obvious core-shell structure and the thickness of the shell is about80nm.4. Research found that the synthetized Pt-A@Mesosilica have no catalytic effect in the process of hydrogenation of Benzene to cyclohexane. However, the addtion of aluminum source changes the acidity and total acid content of the mesoporous shell, making it has catalytic effect on the process of hydrogenation of Benzene to cyclohexane. When the value of n(SiO2)/n(Al2O3) is2, the conversion of Benzene turnning into cyclohexane is16.6%.