Modified aging process for silica aerogel

He, Fang; Zhao, Hailei; Qu, Xuanhui; Zhang, Cuijuan; Qiu, Weihua

doi:10.1016/j.jmatprotec.2008.04.009

Cited by 79 publications

(42 citation statements)

References 15 publications

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“…When silica-gel was reinforced by TEOS solution, silica with large mesopores was prepared. For example, BJH surface area, pore volume and pore diameter (PD) for 100SiO 2 Although the Ostwald ripening effect to strengthen a gel surface is often described [12][13][14][15][16][17][18][19], our results suggest that the thorough removal of water in the inside of the gel and the gel skeletal reinforcement are essential for making large mesopores. Figure 4 shows the conceptual scheme of the gel skeletal reinforcement.…”

Section: Catalytic Cracking Reactionmentioning

confidence: 71%

“…[12][13][14][15][16][17]. In the preparation of these materials, supercritical or subcritical conditions [12][13][14][15][16] and alkoxysilylation [14,15] or methylsilylation [17][18][19] are used to inhibit the extensive shrinkage of large pores at the removal process of entrapped solvent from the wet gel. In particular, alkoxysilylation and methylsilylation are promising methods because they can produce aerogels at ambient pressure by inhibiting rapid hydrolysis and the successive condensation which leads to pore shrinkage.…”

Section: Introductionmentioning

confidence: 99%

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Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

Ishihara¹,

Hashimoto²,

Nasu³

2012

Catalysts

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Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm 3 /g. The results from N 2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt%) and prepared silica-aluminas with large mesopore (58 wt%) and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed.

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Section: Catalytic Cracking Reactionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

Ishihara¹,

Hashimoto²,

Nasu³

2012

Catalysts

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“…For example, three values of ref.SA, which is prepared by a conventional method using water glass and aluminum sulfate, were 537 m 2 /g, 0.86 cm 3 /g, and 6.2 nm (PD), respectively. Although the Ostwald ripening effect to strengthen a gel surface is often described [16][17][18][19], our results suggest that the thorough removal of water in the inside of the gel and the gel skeletal reinforcement are essential for making large mesopore. Figure 4 shows the schematic mechanism of the gel skeletal reinforcement.…”

Section: Catalytic Property Of Amorphous Silica-aluminamentioning

confidence: 74%

“…[16,17]. In preparing these materials, supercritical or subcritical conditions [16,17] and alkoxysilylation [16] or methylsilylation [18,19] are used to inhibit the extensive shrinkage of large pores at removal process of entrapped solvent from the wet gel. However, most of these reports are related to the preparation of bulk materials and there is very few report where the prepared extremely large mesopore has been utilized for various catalyses or supports for catalysts.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Amorphous Silica-Alumina Using the Sol–Gel Method and its Reactivity for a Matrix in Catalytic Cracking

Ishihara

2012

Catal Surv Asia

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Amorphous silica-aluminas were prepared by the sol-gel method using organic templates such as carboxylic acid and the gel skeletal reinforcement method. Their reactivities as a matrix for the catalytic cracking were investigated. Malic acid (MA) was used as a catalyst for the sol-gel method, an organic template and a reagent for the dispersion of Al. When the ratio of MA/TEOS (tetraethoxysilane) increased from 0.22 to 1.22, surface area, pore volume and pore diameter increased and the mesopore was formed at 1.22. Their average BET pore diameters for 0.22 and 1.22 of MA/TEOS were 2.0 to 5.1 nm, respectively. Although conversions of n-dodecane were around 20% or less with single amorphous silica-aluminas, both single beta-zeolite and the mixed catalysts of zeolite and amorphous silica-aluminas showed much higher activity. Further, the mixed catalyst using silica-alumina with mesopore (MAT(MA122-5)) exhibited the higher ratio of multi-branched paraffin to single branched paraffin in the gasoline franction of products (C5-C11) than the mixed catalysts using silica-alumina with only micropore and silica with mesopore or single zeolite. In the gel skeletal reinforcement method, tetraethoxy orthosilicate (TEOS) was used as not only a precursor of silica but also an agent which reinforces the skeleton of silica-gel to prepare an aerogel and extremely large mesopores were formed for resultant silicas and silica-aluminas. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume reached 30 nm and 3.1 cm 3 /g, respectively, in the N 2 adsorption measurement by the BJH method, indicating that most of pores for this silica consisted of mesopores. In catalytic clacking reaction of n-dodecane, the mixed catalyst prepared by beta-zeolite and silica-alumina with large mesopore exhibited not only the comparable activity to that for single zeolite but also the unique selectivity where large amounts of branched products were formed. When the catalyst beds of silica-alumina and zeolite were separated, the reference silica-alumina (ref.SA) ? zeolite system exhibited the higher activity and the product selectivity close to those for MAT(ref.SA). It is likely that the primary cracking of n-dodecane on silica-alumina would occur to produce the primary cracked product which effectively reacted with zeolite and inhibited the coke formation by overcracking.

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“…In summary, most of these studies indicate that long aging times and several solvent exchanges before drying are typically employed during the synthesis of silica aerogels. The effect of both aging and drying processes on the final physico-chemical properties of silica aerogels was investigated for SCD TEOS based silica aerogels [55,57] and for APD water-glass based silica aerogels [52,58,59].…”

Section: Introductionmentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

141

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Silica aerogels' unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO 2 . Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.

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Modified aging process for silica aerogel

Cited by 79 publications

References 15 publications

Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

Preparation of Amorphous Silica-Alumina Using the Sol–Gel Method and its Reactivity for a Matrix in Catalytic Cracking

Effect of aging on silica aerogel properties

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