Synthesis Of Micro-mesoporous Zeolite And Its Catalytic Performance In Aromatic Hydrogenation

A serial of novel micro-mesoporous material was prepared and investigated.Palladium-platinum on these materials was prepared by ion exchange method, and itwas applied on the aromatics saturation reactions in the absence and presence ofDMDBT.In chapter2, a serial of mesoporous materials with different Si/Al have beenprepared with assembling from zeolite Y seed. It is demonstrated that Si/Al ratioshave great influence on the structure and hydrothermal stability. With higher Si/Alratios, the sample is similar to the material Al-MSU-SFAU, which has highly orderedhexagonal mesoporous structure but very poor hydrothermal stability; with lowerSi/Al ratios, the material has micropores and mesopores, but it is proved that thestructure was same to the mechanical mixture; only with suitable Si/Al ratios, thesample has the well-ordered hexagonal mesostructure and good hydrothermal stability.Due to the suitable Si/Al ratios, the crystalline in the mesopore wall grew up duringthe hydrothermal treatment and improved the degree of mesopore walls, and thenimprove the hydrothermal stability of mesoporour structure.In chapter3, a micro/meso porous composite zeolite by combining the Al-MSUmethod and secondary crystallization was prepared, which improves the stability ofthe structure greatly. Characterization results prove that the composite shows betteracidity and higher surface area than Al-MSU-SFAU. After aging in water at120oC for72h, the material remains the mesopore structure, which displays its highhydrothermal stability.When the composite is used as the support of the Pd-Pt catalyst for thehydrogenation of naphthalene, the conversion of naphthalene can achieve100%afterreaction for180min, which shows a high activity. For the hydrogenation ofnaphthalene in the presence of4,6-dimethyldibenzothiophene, the conversion ofnaphthalene can reach100%after200min, which exhibits a high sulfur tolerance. Forthe hydrogenation of pyrene, the conversion achieves80%after350min, whichdisplays a high activity for bulky aromatic compound conversion.When compared to other catalysts, though the acidity of the composite is farlower than the zeolite Y, the catalyst still shows a higher activity than the catalyst using the zeolite Y as the support because of the unique pore structure of thecomposite. The catalyst also shows a higher activity than the catalyst using theAl-MSU-SFAUas the support for the naphthalene hydrogenation, due to the suitableacidity of the composite. Even though the catalyst has the similar activity and sulfurtolerance for the naphthalene hydrogenation to the catalyst using the USY as thesupport, the higher activity revealed in pyrene hydrogenation can still display itspotential for application in the polycyclic aromatics hydrogenation.Through investigating the effect of Y seed aging time on structure, a synthesismechanism was proposed. The small particles in the seeds suspension assembled tothe mesoporous wall in the templates solution, which improves maximumly thecrystalline structure of mesoporous wall; while the larger particles in seed suspensionsdispersed outside of the mesopores during the hydrothermal synthesis process. Thehydrothermal treatment promotes these particles gathering and growing up.In chapter4, the hierarchical zeolite Y was synthesized successfully at lowtemperature with a novel surfactant, multi-head group quaternary ammonium, astemplate, which can be prepared from a simple process. Characterization results showthe material possesses a hierarchical pore system of connected mesopores andmicropores. From XRD patterns, the material has a perfect crystalline structure,corresponding to zeolite Y; from the N2adsorption-desorption isothermal, the materialhas high surface areas at around446cm2/g, the pore size distribution curve displaysthe pore structure is consist of mesopores (averaged at2.8nm and5.6nm) andmicropores (at around0.5nm); while from the SEM images, they clearly show theuniform particles and rough surface, and in high magnification directly visualize thepresence of hierarchical mesopores.The conditions of synthesis were also investigated. Comparing the samplesprepared at different temperatures, the right sample can be gotten at60oC. At lowertemperature, such as room temperature, the sample also has the hierarchical structurewith mesopores (averaged at around2.8nm,6.6nm) and micropores (at0.5nm and1.8nm). However, the sample has low surface area only around370cm2/g, and fromthe SEM images, the surface of particle is also smoother than that gotten at60oC.This is because at low temperature the speed of zeolite Y seeds or fragmentsaggregating to the zeolite Y is much slower. While at higher temperature120oC, thesample shows the zeoliet P structure instead of zeolite Y and almost no pore system. Itis maybe at high synthesis temperature, the surfactant decomposed firstly at high temperature instead of working as the template. Comparing the samples prepared withthe different amounts of surfactants, it is also clearly that the right sample was gotwith suitable amount. Less amount surfactants couldn’t work as the templateefficiently, while more surfactants wrap the seeds and limit their growth.