Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

Abstract

Vanadia−silica mixed oxides were prepared via the sol−gel method involving acid catalysis together with prehydrolysis in order to achieve matching of the reactivities of vanadium(V) oxide triisopropoxide and tetraethoxysilicon(IV) precursors. Gelation was forced by the addition of basic solution. The as-received gels were supercritically dried by semicontinuous extraction with supercritical CO2 at 313 K (low-temperature aerogels). The effects of composition, aging, and calcination temperature on the chemical, structural, and textural properties of the solids were investigated. The oxides were characterized by N2 physisorption, XRD, vibrational spectroscopy, thermal analysis, UV−vis, and 51V NMR. The low-temperature vanadia−silica aerogels were mesoporous and highly disperse. The increasing V content from 5 to 20 wt % nominal V2O5 caused a gradual decline in V dispersion. For 30 wt % “V2O5” the continuous formation of V−O−V connectivity resulted in crystallization of V2O5. The effect of aging in basic medium confined to the textural properties, significantly increasing BET surface area and especially pore volume. The prepared aerogels revealed a marked lack of stability against both apolar solvents in the presence of peroxides and polar solvents. The marked thermal stability in air at ≤873 K, however, combined with mesoporosity and high V dispersion, render these solids promising catalysts for gas-phase reactions.

Preparation and Catalytic Performance of Al2O3, TiO2 and SiO2 Supported Vanadium Based-Catalysts for C–H Activation

“…The VO x /SiO 2 catalysts prepared by grafting and impregnation with different loadings display the characteristic bands of silica at 450, 804, 1,080, 1,624 and 3,424 cm -1 . The band at 804 cm -1 is characteristic for a symmetric m(Si-O-Si) stretching vibration, and the band at 1,080-1,220 cm -1 [36] is characteristic for an asymmetric m(Si-O-Si) stretching vibration. The silica impregnated catalysts with high V loadings exhibit a very weak band at 955 cm -1 , which indicates an asymmetric stretching mode of Si-O-V [37].…”

Characteristics of organic–inorganic hybrid coating films synthesized from colloidal silica-silane sol

“…Using sol-gel process, it is possible to synthesize the organic-inorganic hybrid materials in thin film coatings [9][10][11]. Sol solutions containing the desired alkoxide are prepared with a solvent and water.…”

NMR characterization of the role of silane precursors on the catalytic activity of sol–gel encapsulated lipase

“…The most efficient systems (EN1-TEOS and EN1-MTMS) appeared to be worthy of further study, owing to their potential application as biocatalysts. In addition, further characterization of the gel structural properties is warranted, given the difficulty in correlating these properties with the enzymatic activity [5][6][7].…”