Preparation And Characterization Of Highly Dispersed Nickel Molecular Sieves Catalysts

MCM-41is a type of mesoporous molecular sieve with uniformlyhexagonal pore structure， large specific surface area and excellentadsorption property.It is an important method to introducing heteroatominto molecular sieves for modification of the characters. On one hand, theintroduced heteroatoms may lead to the charge disequilibrium ofmolecular sieves bringing more acid sites. On the other hand, heteroatomwith inherent characteristics makes the molecular sieves asmulti-functional catalysts. Generally speaking, the active sites of catalystare noble metallic element. In order to take advantage of these active sites,those are dispered on the surface of carriers with large specific surfacearea. High-temperature calcination and reduction are essential in thetraditional preparation method of metal catalyst, which can make themetal components transfer and assemble reducing the dispersion andhaving bad effects on the catalyst.In this thesis, a series of Ni-MCM-41mesoporous molecular sieveswere synthesized through a facile hydro-thermal method basing onS+I-I+I-synthetic mechanism, in which NH3was used as coordination agent coordinating with Ni2+to form [Ni(NH3)6]2+avoiding theprecipitation of Ni2+. The structure of samples, the coordination status ofNi and the stability of molecular sieves were characterized with acollection of testing measures. The results turned out that the Ni contentis up to16.3wt%highly dispersed in the silica framework and the typicalhexagonal pore structure was still existed. Further more, in this thesis,highly dispersed metal catalysts were obtained using Ni-MCM-41asprecursor, taking advantages of the strong interaction between Ni and Siin the framework. The main research results are as following:1. Mesoporous molecular sieves with high Ni content Ni-MCM-41were successfully synthesized and the characterization results confirmthat the Ni content is up to16.3wt%, pore diameters are about2.77-3.16nm, pore volume are1.05-1.22cm3g-1and specific surface areas are580-800m2g-1. At the same time, the typical hexagonal pore structurewas still existed.2. Highly dispersed metal catalysts were obtained by reduction usingNi-MCM-41as precursors. The characterization results confirm that theNi particles under20nm were highly dispersed on the surfaces ofmesoporous molecular sieves, and the typical hexagonal pore structurewas still existed.3. In this thesis, the catalytical performance of Ni-MCM-41hasbeen investigated through hydrocracking of coker wax oil. The results reveal that these sort of catalysts showed high conversions (70.0~83.0%)and selectivity of low boiling point hydrocarbons (78.0~81.3%), these areexcellent catalysts for hydrogenation.