高水热稳定有序介孔Al-SBA-15材料的优化合成及表征

doi:10.7503/cjcu20150543

摘要/Abstract

摘要：

借助无机铝盐自水解所产生的弱酸性环境, 通过改变水热处理温度及无机铝盐的引入种类和引入量来调控合成体系中Al—OH及材料孔壁中Si—OH的相对含量, 在不引入矿物质强酸的条件下, 一步合成了具有高Al引入量且孔壁硅、铝物种达到原子水平均匀分散的Al-SBA-15介孔材料. 表征结果表明, 当以硝酸铝为铝源, 水热处理温度和投料硅铝比分别为140 ℃和10时, 所得样品具有高度有序的二维六方介孔结构及较高的水热稳定性, 在经800 ℃高温水蒸气处理2 h后, 其介孔比表面积和孔体积仅分别降低了18.82%和16.67%. 此外, 骨架Al的引入使所得样品同时具有B酸和L酸中心, 且具有相对较强的酸性, 在异丙苯催化裂化反应中表现出明显活性.

关键词: 介孔材料, Al-SBA-15, 水热稳定性, 水热嫁接

Abstract:

Highly ordered mesoporous Al-SBA-15 materials with high aluminum content and high hydrothermal stability were synthesized by one-step hydrothermal grafting approach under the weak acid medium produced only by the hydrolysis of inorganic aluminum salt. By selectively introducing inorganic aluminum salt in the synthesis system, and further optimizing hydrothermal treatment temperature and the introduced amount of inorganic aluminum salt, the hydrolysis of Al ion and the condensation of silicon hydroxyl(Si—OH) species within the mesoporous walls could be efficiently controlled to adjust the relative amount of Al—OH and Si—OH groups and their interaction. As a result, the ordered mesostructure of Al—SBA—15 could be assembled at the mesoscale and the coordination status/the acidic sites could be controlled at the atomic scale. The characteristic results by means of XRD, N₂ adsorption, TEM, EDX, SEM, FTIR and NMR techniques showed that when aluminium nitrate was used as the aluminum precursor, and hydrothermal treatment temperature and initial molar ratio of silicate to aluminium were adjusted as 140 ℃ and 10, respectively, the synthesized sample exhibited highly ordered hexagonal mesostructure and extremely high hydrothermal stability. The highly ordered mesostructure can be maintained even after steam treatment at 800 ℃ for 2 h with only 18.82% and 16.67% decreases in the Brunauer-Emmett-Teller surface area and total pore volume, respectively. Moreover, the hydrothermal grafting process at 140 ℃ was advantageous for the homogeneous incorporation of Al into the silica mesoporous framework to form the Si—OH—Al bond, leading to the production of Brönsted and Lewis acid sites with relatively strong acidity on the mesoporous walls.

Key words: Mesoporous material, Al-SBA-15, Hydrothermal stability, Hydrothermal grafting approach

中图分类号:

O613
O643

TrendMD:

徐倩, 董朝阳, 石国亮, 潘大海, 于峰, 陈树伟, 李瑞丰. 高水热稳定有序介孔Al-SBA-15材料的优化合成及表征. 高等学校化学学报, 2015, 36(12): 2355.

XU Qian, DONG Zhaoyang, SHI Guoliang, PAN Dahai, YU Feng, CHEN Shuwei, LI Ruifeng. Optimized Synthesis and Characterization of Highly Ordered Mesoporous Al-SBA-15 with High Hydrothermal Stability^†. Chem. J. Chinese Universities, 2015, 36(12): 2355.

图/表 13

Table 1 Physicochemical properties of calcined S(n)-10-T prepared at different hydrothermal treatment temperatures*

Sample	a₀/nm	S_BET/(m²·g^-1)	V_p/(cm³·g^-1)	D_p/nm
S(n)-10-100	12.7	623	0.72	6.4
S(n)-10-120	12.4	559	1.21	11.6
S(n)-10-140	12.3	473	1.26	12.0
S(n)-10-160	12.1	298	1.14	17.1
S(n)-10-180	12.0	287	1.06	16.9

Fig.1 XRD patterns of calcined S(n)-10-100(a), S(n)-10-120(b), S(n)-10-140(c), S(n)-10-160(d) and S(n)-10-180(e)

Fig.2 29Si MAS NMR spectra of as-synthesized S(n)-10-100(a), S(n)-10-140(b) and S(n)-10-160(c)

Fig.3 N2 adsorption/desorption isotherms(A) and the corresponding pore size distribution curves(B) of calcined S(n)-10-100(a), S(n)-10-120(b), S(n)-10-140(c), S(n)-10-160(d), S(n)-10-180(e)

Fig.4 TEM images along [100](A) and [110](B) directions and EDX spectrum(C) of calcined S(n)-10-140

Fig.5 Effect of hydrothermal treatment temperature on the molar ratio of Si/Al

Fig.6 27Al MAS NMR spectra of calcined S(n)-10-120(a), S(n)-10-140(b) and S(n)-10-160(c)

Fig.7 SEM images of calcined S(n)-10-120(A), S(n)-10-140(B) and S(n)-10-160(C)

Fig.8 XRD patterns of calcined S(n)-5-140(a), S(n)-10-140(b), S(n)-15-140(c) and S(n)-∞-140(d) prepared with different Si/Al molar ratios

Table 2 Physicochemical properties of calcined S(n)-N-140 prepared with different Si/Al molar ratios*

Sample	a₀/nm	S_BET/(m²·g^-1)	V_p/(cm³·g^-1)	D_p/nm
S(n)-5-140	13.4	398	0.97	11.1
S(n)-10-140	12.3	473	1.26	12.0
S(n)-15-140	12.3	438	1.13	12.7

Fig.9 XRD patterns of calcined S(n)-10-140(a), S(h)-10-140(b) and S(s)-10-140(c)

Fig.10 XRD pattern(A) and N2 adsorption-desorption isotherm(B) of calcined S(n)-10-140 steamed at 800 ℃ for 2 h Inset in (B) is the corresponding pore size distribution curve.

Fig.11 Pyridine-FTIR spectra of calcined S(n)-10-140

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