Synthesis and characterization of mesoporous VOx/MgO aerogels with high surface area

Homogeneously mixed mesoporous VOx/MgO aerogels with vanadium concentrations ranging up to 26 wt.% with the surface area as high as 1200 m2/g were synthesized by hydrolysis of a mixture of vanadium and magnesium alkoxides followed by gelation and high-temperature supercritical drying. Dehydration conditions were optimized to obtain nanocrystalline VOx/MgO oxides with the surface area exceeding 450 m2/g after calcination at 550 °C. The synthesized aerogels were extensively characterized by physicochemical methods (XRD, NMR, HRTEM, EDX). According to the EDX data, vanadium atoms were very uniformly distributed in the MgO structure of the mixed oxide aerogels. No magnesium vanadate phases were observed by XRD in the samples with the vanadium concentrations 26% or lower. As the vanadium concentration increased, vanadium ions were introduced into the MgO nanocrystals changing their symmetry from the initial cubic (Fm3 m) to orthorhombic (Cmca). Simulation of the XRD patterns of as-prepared aerogels suggests that the Mg(OH)2 phase in these samples is substantially distorted due to the presence of methoxide groups between the layers.

Mixed VOx/MgO aerogels with vanadium concentrations ranging from 5 to 26 wt.% feature crystallite sizes about 5 nm, homogeneous vanadium distribution, surface areas of 1200 m2/g after supercritical drying and more than 450 m2/g after calcination at 550 °C.Figure optionsDownload as PowerPoint slideHighlights
► Mixed VOx/MgO hydroxide aerogels with 1200 m2/g surface area are prepared.
► Structure of as-prepared aerogels is shown to have turbostratic disordering.
► Calcination conditions were optimized yielding oxides with 450 m2/g surface area.
► Vanadium atoms are uniformly distributed in the structure of mixed aerogels.