Synthesis, Characterization And Catalytic Performance Of Composite Molecular Sieve

Composite molecular sieve is a new type of inorganic porous material. This kind of new molecular sieve possesses both mesopore structure and micropore structure. Due to its unique mesoporous channel and high acidity and high hydrothermal stability of microporous material, the composite molecular sieve has widely application prospects in some fields such as petrochemical industry, adsorption separation, macromolecule shape selective catalysis, and so on.First of all, the synthesis of the mesoporous molecular sieve was carried out successfully by hydrothermal and microwave radiation method using kaolin as raw material, respectively. The effects of the different silicon sources, the amount of kaolin, the amount of template and different synthesis methods on the textural properties of the as synthesized samples was investigated to obtain the optimal synthesis condition. The resultant materials were characterized by X-ray diffraction (XRD) and N2 adsorption-desorption technique. The results show that the long-range and well-ordered mesoporous molecular sieves were successfully synthesized under the experimental condition, and have an average pore size of ca.275nm. The one-dimensional mesoporous structure still maintained even after calcination at 900℃for 3h and hydrothermally treatment at 100℃for 6d, indicating that the mesoporous molecular sieve synthesized via using kaolin as a precursor possesses highly thermal and hydrothermal stabilities.Secondly, composite molecular sieve Y/MCM-41 was successfully prepared by using a two-step crystallization method. The effects of different orders of raw materials, crystallization temperature and crystallization time on the synthesized products were investigated. The composite materials were characterized by XRD, FT-IR, SEM, TEM and N2 adsorption-adsorption technique. The XRD results reveal that Y/MCM-41 possesses both characteristic peak of Y and characteristic peak of MCM-41. The morphology and crystalline phase of Y/MCM-41 are different from that of Y and MCM-41. The N2 adsorption-desorption isotherm of Y/MCM-41 exhibited only a typical IV type isotherm. The optimal synthesis conditions for hydrothermal method:n(CTAB)/n(SiO2)=0.16, the first step:crystallization time is 12h and crystallization temperature is 100℃; the second step:crystallization time is 2d and crystallization temperature is 120℃. The thermal and hydrothermal stabilities results show that the mesoporous framework still retains after the composite molecular sieve was calcined at 800℃for 3 h or hydro thermally treated at 100℃for 10 d.Thirdly, adopting the optimal synthesis condition obtained hydrothermal method, the synthesis of composite molecular sieve Y/MCM-41 was carried out via microwave radiation method. The results indicate that the crystallinity of the obtained sample increased first and then decreased with an increase of microwave power. The favourite power is 220W. By comparing with the mesoporous molecular sieve obtained by hydrothermal method, the hydrothermal stability of the samples syntheszed via microwave radiation method was a little poor.Finally, the performance of the catalysts was investigated by the alkylation reaction of phenol and tert-butyl alcohol. The results show that the catalytic activity is higher than that of MCM-41 and Y/MCM-41 is a good catalyst for the alkylation reaction of phenol and tert-butyl alcohol. Furthermore, for Y/MCM-41, the conversion of phenol increased as reaction temperature increased, and the conversion of phenol decreased as WHSV increased. The reaction time had little effect on the catalytic activity.