Synthesis And Properties Of Bi-phases Zeolite Composites

The narrow porous structure and single acidity of zeolites lead to their poor performances on reactions that macromolecular participates in. The porous structure of Mesoporous material is bigger than zeolite. However, the thermal stability and hydrothermal stability of mesoporous material are weak that hampers the practical applications in industry. Zeolite composites with hierarchically porous structure and tunable acidity can be synthesized with a silicon-aluminium source rule, and the zeolite phases in the zeolite composites still retain its highly thermal stability and hydrothermal stability. Consequently, synthesis of zeolite composites has become hot.A series of zeolite composites with hierarchically porous structure and tunable acidity were prepared by using Y or Beta zeolite as the silicon-aluminium resources of the other zeolite. The structural, crystalline, and textural properties of the as-synthesized materials, as well as the reference Y and Beta zeolite samples, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) analyses, Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption-desorption techniques. The acid properties of surface were determined by in-situ FT-IR of adsorbed pyridine. Hierarchy factor is an appropriate tool to classify hierarchically structured materials. The hierarchical pores of the as-synthesized zeolite composite samples were therefore investigated during catalytic cracking of isopropylbenzene. The results show that the catalytic activity of isopropylbenzene cracking over the catalysts shows a linear dependence with their hierarchy factor (HF). The tunable acidities were tested by methanol dehydration to DME, and the dehydration activity of methanol over the catalysts shows a linear decrease with the increased ratio concentration of Lewis/Bronsted ratio, while the selectivity of DME shows a linear increase with the enhanced Lewis/Bronsted ratio.Zeolite composite ZSM-5/BEA was synthesized with a silicon-aluminium source rule by using the solid/liquid mixture of the pre-synthesized Beta zeolite as the silicon-aluminium resources of the post-synthesized zeolite ZSM-5. The as-synthesized samples were characterized by XRD, SEM and FT-IR. The acid properties of surface were determined by in-situ FT-IR of adsorbed pyridine. It is unexpected that ZSM-5 crystals have not overgrown on the external surface of Beta zeolite crystals, but are embedded in the polycrystalline Beta zeolite shell. The property of Beta zeolite crystals with aluminum-poor interior and aluminum-rich outer rim results in silicon extraction favorably in the aluminum-poor bulk rather than the aluminum-rich external surface. Subsequently, alkaline treatment of Beta zeolite crystals during the second-step synthesis leads to a preferential dissolution of the aluminum-poor center and the formation of hollow Beta zeolite crystals. ZSM-5 zeolite crystals are therefore embedded and grown within the hollow Beta zeolite. The catalytic activities of Co-HBeta, Co-HZSM-5 and Co-HZSM-5/BEA are investigated during the reaction of methane catalytic reduction NO in the presence of O2. When the temperature is higher than 400℃, the Co-HZSM-5/BEA shows much higher conversion of NO and CH4 than both of the Co-HBeta and the Co-HZSM-5.