汽相转化法制备纳米晶组成的块状ZSM-5多孔沸石

在ZSM-5沸石前驱体中加入羧甲基纤维素钠并制得干胶, 然后通过蒸汽相转化制得了大块状ZSM-5沸石。由于羧甲基纤维素钠与硅铝物种之间的相互作用干扰了沸石晶体的正常生长, 这种干扰所产生的“键阻断”作用导致合成的大块状ZSM-5沸石由100~150 nm的初级ZSM-5沸石晶体组成, 在这些初级粒子之间存在2~20 nm的二次介孔结构。异丙苯催化裂化结果表明, 由于纳米沸石具有较高的外表面积和较大的介孔孔容, 比参比催化剂表现出更高的异丙苯转化率。

Synthesis of Monolith Hierachical ZSM-5 Zeolite Composed of Nanocrystals by Vapor-phase Transformation Method

A monolith ZSM-5 composed of nano-sized MFI crystals was prepared from a dry gel by a vapor-phase transformation method, in which the dry gel was obtained from a mixture of sodium carboxymethylcellulose and a precursor yielding ZSM-5 zeolite crystals. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N₂ adsorption-desorption, in-situ IR spectra of pyridine and FT-IR. Organic Si- or/and Al-species replace the classic inorganic Si- or/and Al-species to take part in the construction of MFI zeolite frameworks. And the long chain organic groups, which connect with the Si- and Al-species, disturb the normal growth of the zeolites crystals in the manner of the so called “bond block”. The evenly nano-sized zeolite crystals with the sizes of 100-150 nm are therefore formed and then subsequently self-assembly form a monolith ZSM-5. A mesoporous system which centers around 2-20 nm is therefore introduced into the as-synthesized hierachical zeolites samples. As compared with the references catalysts, the monolith ZSM-5 zeolite composed of nano-sized crystals displays an enhanced conversion of isopropylbenzene because of the dramatically increased external surface areas and mesopores volume as tested by the catalytic cracking of isopropylbenzene.