中空ZSM-5分子筛微球及其吸附与催化性能

doi:10.15541/jim20150611

摘要/Abstract

摘要：

首先利用聚乙二醇作为软模板合成出具有一定介孔结构的ZSM-5分子筛微球, 再通过快速可控碱刻蚀的方法, 成功制备出尺寸均一的中空分子筛微球。利用X射线衍射(XRD)、氮气吸附等温线分析(N₂ isotherm)、扫描和透射电子显微镜(SEM, TEM)对所制备的中空分子筛微球进行了表征, 并研究了中空分子筛微球对有机物废水的吸附性能和对大分子的催化裂解性能。结果表明, 刻蚀后分子筛结晶度略有下降, 但是介孔度和孔体积明显提升。中空分子筛微球外径在600 nm, 壳层厚度在100 nm左右。此外, 该中空结构不仅对苯等有机分子具有吸附富集作用, 其饱和吸附量几乎达到了常规分子筛微球的3倍, 并且六次循环使用后的吸附容量依然保持基本不变, 显示出较高的吸附容量和循环使用稳定性。在异丙苯和三异丙苯裂解反应中中空分子筛微球也显示出较高的催化活性。

关键词: 中空分子筛微球, 碱刻蚀, 吸附, 苯废水, 催化裂解

Abstract:

A new kind of uniform hollow zeolite spheres were successfully synthesized by non-hard template synthetic method, which involves two key steps: firstly, the conventional hydrothermal synthesis process of zeolite spheres by using polyethylene glycol (PEG) as soft template, and then, the rapid post-alkaline-etching (PAE) technique. Structural features were characterized by XRD, N₂ isotherm, SEM, and TEM. The performance in the organic-waste-water treatment and catalytic cracking of bulky molecules were also measured. It was found that crystallinity of the product underwent a reducing tendency after alkaline etching treatment, but the mesoporosity and pore volume were promoted. The diameter and shell thickness of hollow zeolite spheres were about 600 nm and 100 nm, respectively. Moreover, such hollow structure demonstrates remarkably a threefold capability increase in adsorption of benzene molecules in methanol solution if compared with conventional zeolite spheres. Such capability can be basically kept after repeating 6 times, indicating high capability and stability in adsorption. Enhanced catalytic activities were also approved in cracking of isopropyl benzene and triisopropyl benzene.

Key words: hollow zeolite sphere, alkaline etching, adsorption, benzene, waste water, catalytic cracking

中图分类号:

TQ174

孙莉莉, 闫凯, 罗稳, 周健. 中空ZSM-5分子筛微球及其吸附与催化性能[J]. 无机材料学报, 2016, 31(8): 834-840.

SUN Li-Li, YAN Kai, LUO Wen, ZHOU Jian. Hollow ZSM-5 Zeolite Microspheres with Improved Adsorption and
Catalytic Properties[J]. Journal of Inorganic Materials, 2016, 31(8): 834-840.

图/表 11

图1 沸石分子筛微球(ZS)与中空沸石分子筛微球(HZS)的XRD图谱

Fig. 1 XRD patterns of zeolite spheres (ZS) and hollow zeolite spheres (HZS)

图2 沸石分子筛微球(ZS)与中空沸石分子筛微球(HZS)的N2吸附-脱附等温线与孔径分布(插图)图

Fig. 2 N2 isotherms and pore size distributions (inset) of zeolite spheres (ZS) and hollow zeolite spheres (HZS)

图3 沸石分子筛微球(a, b)与中空沸石分子筛微球(c~f)的扫描电镜照片

Fig. 3 SEM images of zeolite spheres (a, b) and hollow zeolite spheres (c-f)

表1 两种分子筛微球的组成、结构和性能比较

Table1 Textural and structural properties of zeolite spheres(ZS) and hollow zeolite spheres(HZS)

Sample	Al content^a/%	S_BET^b/ (m²·g^-1)	S_meso^c/ (m²·g^-1)	V_pore^d/ (cm³·g^-1)	V_meso^c/ (cm³·g^-1)
ZS	1.74	347	152	0.21	0.09
HZS	2.01	335	167	0.37	0.29

图4 沸石分子筛微球(a, b)与中空沸石分子筛微球(c, d)的TEM照片

Fig. 4 TEM images of zeolite spheres (ZS) and hollow zeolite spheres (HZS)

图5 沸石分子筛微球与中空沸石分子筛微球吸附苯/甲醇溶液的吸附动力学曲线

Fig. 5 Adsorption dynamic curves of benzene by zeolite spheres (ZS) and hollow zeolite spheres (HZS) in methanol solution

图6 沸石分子筛微球与中空沸石分子筛微球的吸附等温线

Fig. 6 Adsorption isotherms of benzene by zeolite spheres (ZS) and hollow zeolite spheres (HZS). Ce is the equilibrium concentration in the benzene/methanol solution and Qe is the amount of benzene adsorbed at equilibrium concentration

图7 沸石分子筛微球与中空沸石分子筛微球的吸附稳定性

Fig. 7 Adsorption stability testing results of zeolite spheres (ZS) and hollow zeolite spheres (HZS). Relative adsorption amount is the ratio of adsorption amount in the single cycle to the adsorption amount in the first cycle

图8 中空沸石分子筛微球在循环使用后的TEM照片及电子衍射斑点

Fig. 8 TEM images and electron diffraction patterns (insert) of hollow zeolite spheres (HZS) after cycle use

表2 两种分子筛微球的催化裂解性能比较

Table2 Catalytic properties of zeolite spheres (ZS) and hollow zeolite spheres (HZS) in cracking reaction

Reaction	Conversion in cumene cracking /%		Conversion in triisopropylbenzene cracking /%
Catalyst	ZS	HZS	ZS	HZS
573 K	55.1	66.9	12.6	34.8
623 K	72.6	80.2	27.6	50.0
673 K	82.7	90.0	39.9	61.1
723 K	88.8	94.3	51.0	72.5
773 K	92.2	97.3	61.0	78.4

表3 两种分子筛微球在三异丙苯裂解反应中产物选择性

Table3 Selectivity of products by zeolite spheres (ZS) and hollow zeolite spheres (HZS) in cracking reaction of TIPB

Reaction	Selectivity of benzene: isopropylbenzene: diisopropylbenzene
Catalyst	ZS	HZS
300	11: 20: 69	13: 23: 64
350	15: 18: 67	16: 22: 62
400	19: 19: 62	19: 24: 57
450	22: 25: 55	25: 26: 49
500	28: 30: 42	28: 33: 39

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