Synthesis of High-Surface-Area Alumina Aerogels without the Use of Alkoxide Precursors

Abstract

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl 3 •6H 2 O or Al(NO 3) 3 •9H 2 O, followed by drying with supercritical CO 2. This technique affords low-density (60-130 kg/m 3), high surface area (600-700 m 2 /g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, highresolution transmission electron microscopy, powder X-ray diffraction, solid state NMR, acoustic measurements and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl 3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2-5 nm in diameter and of varying lengths, while the aerogels prepared from hydrated Al(NO 3) 3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5-15 nm range. The difference in microstructure resulted in each type of aerogel displaying distinct physical and mechanical properties. In particular, the alumina aerogels with the weblike microstructure were far more mechanically robust than those with the colloidal network, based on acoustic measurements. Both types of alumina aerogels can be transformed to γ-Al 2 O 3 through calcination at 800 o C without a significant loss in surface area or monolithicity.

Structure of Low-Density Nanoporous Dielectrics Revealed by Low-Vacuum Electron Microscopy and Small-Angle X-ray Scattering

“…Table I gives a brief description of these AGs, while additional details of AG synthesis and their basic properties can be found elsewhere. [11][12][13] Figures 1(a-c) show typical LVSEM images of a crosssection of the α-AlOOH AG, which has a string-of-pearls morphology. 14 Such cross sections were prepared by fracturing AG monoliths.…”

Preparation and characterization of monolithic Al₂O₃–SiO₂ aerogel

“…It is difficult to control the hydrolysis and condensation process of aluminum alkoxides during the preparation of the mixed sol. 10) Therefore, it would be desirable to adopt hydrated aluminum salts as the precursor. As described in the previous research, Itoh H, et al 11) added propylene oxide to mixed solution of hydrated aluminum salts and prepared transparent alumina gels.…”

“…As described in the previous research, Itoh H, et al 11) added propylene oxide to mixed solution of hydrated aluminum salts and prepared transparent alumina gels. T. F. Baumann, et al 10) prepared alumina aerogel with high surface area and low density through the solgel process using hydrated aluminum salts as the precursor.…”

Effect of γ-alumina as active matrix added to HZSM-5 catalyst on the aromatization of methanol

“…Although the functions of calumina in methanol reaction have been reported in several previous studies, their emphasis was simply focused on the crucial role of c-alumina in the dehydration reaction of methanol into dimethyl ether (DME) [25][26][27][28][29][30][31][32]. According to above studies, the reaction of methanol could be promoted by c-alumina, it was an intuitive guess that c-alumina could facilitate the formation of aromatics from methanol.…”