“蒸汽相转化”法制备纳米多级Beta沸石催化材料

doi:10.15541/jim20170141

摘要/Abstract

摘要：

由于多级孔沸石具有实际及潜在的应用价值, 合成具有微孔-介孔孔道体系的多孔沸石引起了广泛关注。本研究在不添加二次模板剂的基础上, 采用“蒸汽相转化”法制备了多级孔Beta沸石催化材料, 对影响多级孔Beta沸石形成因素, 如凝胶碱度、模板剂用量、硅铝比、蒸汽压力和晶化时间等进行了讨论。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅立叶变换红外(FT-IR)光谱、拉曼(Raman)光谱、N₂吸附-脱附以及NH₃-TPD等表征手段对制备材料的结构性能进行了表征。在借助红外光谱、拉曼光谱及扫描电镜等表征手段的基础上, 对多级孔Beta沸石的形成机制进行了探索。结果表明: 通过“蒸汽相转化”法所制备的Beta沸石为纳米多晶聚集体, 这些多晶聚集体由粒径为10~40 nm的初级晶粒构成, 在初级纳米粒子之间形成了2~30 nm的介孔结构; 干胶制备过程中生成的初级和次级结构单元有利于快速形成大量的Beta沸石核, 较高的成核速率有利于Beta沸石纳米晶粒形成, 这些纳米晶粒相互聚集最终形成纳米多晶Beta沸石聚集体。

关键词: 多级孔, Beta沸石, “蒸汽相转化”法

Abstract:

Synthesis of hierarchical zeolite with complex micropore-mesopore structures has attracted great attention because of their practical or potential applications. In present study, hierarchical Beta zeolite was synthesized by the “steam-assisted conversion (SAC)” method without secondary template. Factors affecting formation of the hierarchical Beta, such as the added amount of organic template, alkalinity and silica to alumina ratio of the gel precursors yielding the hierarchical Beta zeolite, vapor pressure and crystallization time during the “steam-assisted conversion (SAC)” process, were investigated. The structural, crystalline and textural properties of the as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscope, Raman spectrum, N₂ adsorption-desorption, and NH₃-TPD. The formation mechanism of the hierarchical Beta was explored on the base of the results detected by FT-IR, Raman spectrum, and SEM. Results showed that the as-synthesized Beta zeolite was composed of primary nano-sized crystals with a diameter of 10-40 nm, and a mesoporous structure ranging from 2 to 30 nm was therefore introduced. A tremendous amount of primary and/or subprime building units, which were bred during preparation of dry gel, induced a burst in nucleation rate. Nano-sized zeolite crystals were, therefore, created that subsequently formed polycrystalline Beta zeolite material by aggregating the nanocrsytals with each other.

Key words: hierarchical pore, Beta zeolite, “steam-assisted conversion” method

中图分类号:

TQ426

孙晓勃, 杜艳泽, 秦波, 孔庆岚, 吴亮, 郑家军, 潘梦, 李瑞丰. “蒸汽相转化”法制备纳米多级Beta沸石催化材料[J]. 无机材料学报, 2018, 33(1): 27-34.

SUN Xiao-Bo, DU Yan-Ze, QIN Bo, KONG Qing-Lan, WU Liang, ZHENG Jia-Jun, PAN Meng, LI Rui-Feng. Hierarchical Beta Zeolite Prepared by Steam-assisted Conversion Method[J]. Journal of Inorganic Materials, 2018, 33(1): 27-34.

图/表 8

图1 多级Beta沸石的XRD图谱

Fig. 1 XRD patterns of the as-synthesized Beta zeolite^(a) With different TEAOH/SiO2 ratios in the precursors gel 1-5 of 0.10, 0.08, 0.06, 0.04, 0.02, respectively; (b) With different Na2O/SiO2 ratios in the precursors gel 1-5 of 0.24, 0.18, 0.12, 0.08, 0.06, respectively; (c) With different H2O/dry gel ratios during the “steam-assisted conversion” process 1-7 of 0.50, 0.40, 0.30, 0.25, 0.20, 0.10, 0.02, respectively; (d) With different steaming-treated time 1-5 for 72 h, 60 h, 48 h, 36 h, 24 h, respectively; (e) With different SiO2/Al2O3 ratios in the precursors gel 1-5 at 100, 80, 60, 40, 20, respectively

图2 合成的Beta沸石样品的N2吸附-脱附曲线(a)和DFT孔径分布曲线(b)

Fig. 2 N2 adsorption-desorption isotherms (a) and DFT pore size distributions curves (b) of Beta zeolite samples

表1 多级Beta沸石的结构参数

Table 1 Structure parameters of hierarchical Beta zeolite

Sample	S_BET/(m²•g^-1)	S_MIC/(m²•g^-1)	S_EXT/(m²•g^-1)	V_MIC/(cm³•g^-1)	V_MESO/(cm³•g^-1)	Size of primary crystalline grain/nm
Beta-40-48-s	754	600	154	0.24	0.13	30^a
Beta-60-48-s	728	581	147	0.23	0.17	35^a
Beta-80-48-s	702	569	133	0.23	0.21	39^a
Beta-100-48-s	692	535	157	0.21	0.15	44^a
Beta-40-96-h	672	621	51	0.25	0.07	1500^b

图3 Beta-40-48-s沸石的SEM (a, b)和TEM (c)照片

Fig. 3 SEM (a, b) and TEM (c) images of Beta zeolite Beta-40-48-s

图4 干胶及合成的Beta沸石的红外光谱图

Fig. 4 FT-IR spectra of dry gel and the hierarchical Beta zeolite samples

图5 样品的SEM照片(a~h)和拉曼光谱(i)

Fig. 5 SEM images (a-h) and Raman spectrum (i) of Beta-40^(a) Beta-40-48-h; (b, c) Beta-40-96-h; (d) Beta-40-0-s; (e) Beta-40-12-s; (f) Beta-40-24-s; (g) Beta-40-36-s; (h) Beta-40-48-s; (i): Raman spectrum of Beta-40-0-s

图6 多级孔Beta沸石形成机制示意图

Fig. 6 Schematic representation of the process of hierarchical Beta composed of nanocrystals

图7 多级Beta沸石的NH3-TPD图谱

Fig. 7 NH3-TPD spectra of hierarchical Beta zeolite^(a) Beta-40-48-s; (b) Beta-60-48-s; (c): Beta-80-48-s; (d) Beta-100- 48-s

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