Optimized Synthesis and Characterization of Highly Ordered Mesoporous Al-SBA-15 with High Hydrothermal Stability†

doi:10.7503/cjcu20150543

Abstract

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

CLC Number:

O613
O643

TrendMD:

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^†[J]. Chem. J. Chinese Universities, 2015, 36(12): 2355.

Figures/Tables 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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