干凝胶法合成复合孔分子筛的研究

Synthesis of Mesoporous MFI Zeolite by Dry-gel Conversion

以含有模板剂的介孔氧化硅原粉(HMS)作为原料,通过浸渍法引入微孔沸石合成导向剂,再利用有机模板剂作为介孔产生的模板,通过干凝胶转换方法将介孔材料孔壁晶化得到微孔-介孔复合孔分子筛.采用X射线衍射(XRD)、红外光谱(IR)法对样品的结晶度进行了表征,采用氮气吸附等温线测定了样品比表面积和孔分布.结果表明:全硅HMS介孔分子筛在180℃经过6 h水蒸汽加热转化后,无定形介孔氧化硅转化为微孔沸石,结晶度达到80%,比表面和孔体积分别为595 m2.g-1和0.65cm3.g-1.而含铝HMS介孔分子筛,因铝的引入阻碍了沸石的转化.当HMS分子筛Si/Al比达到25时,在180℃经过6 h水蒸汽加热,所得样品(MZ25-6)孔壁仍为无定型结构.

Mesoporous zeolite was prepared through impregnating the structure directing agent （tetra-n-propylammonium hydroxide） into the as-synthesized mesoporous silica （HMS） followed by dry-gel conversion to transform amorphous silica to zeolite crystal. The resulting sample was characterized by X-ray diffraction, IR spectroscopy, N2 adsorption to evaluate the textural properties of mesoporous zeolite. The results show that mesoporous zeolite with high surface area （595 m^2g-1） and pore volume （0.65 cm^3g^-1） were obtained when heated at 180 ℃ for 6 h from all silica HMS. When the aluminum was introduced into HMS, the Al component hindered this conversion and lowered the zeolite crystallization. Therefore no ZSM-5 phase was observed in the sample of MZ25-6, obtained from A1HMS （Si/Al=25） when heated at 180 ℃ for 6 h.