汽相转化法制备纳米晶组成的块状ZSM-5多孔沸石

doi:10.15541/jim20150171

摘要/Abstract

摘要：

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。

关键词: ZSM-5, 汽相转化法, 纳米沸石, 多级孔, 键阻断

Abstract:

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.

Key words: ZSM-5, vapor-phase transformation, nano-zeolite, hierachical pores, bond block

中图分类号:

TQ426

郑家军, 张鸿雁, 潘梦, 李彪, 张球, 孔庆岚, 刘芝平, 李瑞丰. 汽相转化法制备纳米晶组成的块状ZSM-5多孔沸石[J]. 无机材料学报, 2015, 30(11): 1161-1166.

ZHENG Jia-Jun, ZHANG Hong-Yan, PAN Meng, LI Biao, ZHANG Qiu, KONG Qing-Lan, LIU Zhi-Ping, LI Rui-Feng. Synthesis of Monolith Hierachical ZSM-5 Zeolite Composed of Nanocrystals by Vapor-phase Transformation Method[J]. Journal of Inorganic Materials, 2015, 30(11): 1161-1166.

图/表 8

图1 合成样品的XRD图谱

Fig. 1 XRD patterns of the samples (1) ZSM-5(A); (2) ZSM-5(B); (3) ZSM-5(C)

图2 样品的FT-IR图谱

Fig. 2 FT-IR spectra of sample of ZSM-5 zeolite (A): (1) ZSM-5(A); (2) ZSM-5(B); (3) ZSM-5(C); (B): (a) CMC-Na; (b) the precursor gel with CMC-Na; (c) ZSM-5 contained CMC-Na; (d) ZSM-5 has been removed the concealed CMC-Na

图3 合成样品的扫描电镜照片

Fig. 3 SEM images of sample ZSM-5 zeolite (1) and (2): ZSM-5(A); (3) ZSM-5(B); (4): ZSM-5(C)

示意图1 羧甲基纤维素钠对纳米沸石组成的大块状ZSM-5形成的影响

Scheme 1 Schematic representation of the process which CMC-Na affects the formation of monolith ZSM-5 consists of nanocrystals

图4 样品的N2吸附-脱附等温线及孔径分布图

Fig. 4 N2 adsorption-desorption isotherm and pore size distribution curve (inset) of the samples (1) ZSM-5(A); (2) ZSM-5(B); (3) ZSM-5(C)

表1 样品的物理结构性质

Table 1 Physical structural properties of the samples

Samples	S_BET /(m²·g^-1)	S_mic /(m²·g^-1)	S_ext /(m²·g^-1)	S_meso /(m²·g^-1)	V_mic /(cm³·g^-1)	V_meso /(cm³·g^-1)	Acidity (Py)*/ (μmol·g)^-1		B/L (Py)	Total acidity /(μmol·g^-1)
Samples	S_BET /(m²·g^-1)	S_mic /(m²·g^-1)	S_ext /(m²·g^-1)	S_meso /(m²·g^-1)	V_mic /(cm³·g^-1)	V_meso /(cm³·g^-1)	Brönsted	Lewis	B/L (Py)	Total acidity /(μmol·g^-1)
ZSM-5(A)	467	362	105	25	0.13	0.10	191	280	0.7	471
ZSM-5(B)	423	396	27	15	0.15	0.03	279	173	1.6	452
ZSM-5(C)	443	438	5	9	0.16	0.02	240	163	1.5	403

图5 200℃时的吡啶红外图谱

Fig. 5 Infrared spectra of pyridine absorbed at 200℃ (1) ZSM-5(A); (2) ZSM-5(B); (3) ZSM-5(C)

图6 300℃下催化剂的异丙苯裂解性能

Fig. 6 Cracking of isopropyl benzene at 300℃ (1) ZSM-5(A); (2) ZSM-5(B); (3) ZSM-5(C)

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