Abstract
AbstractA MgAl hydrotalcite‐like material intercalated with hexaniobate has been prepared by the anion exchange method from the corresponding nitrate precursor; the sample and the oxides obtained upon its calcination were characterized by element chemical analysis, powder X‐ray diffraction, thermal analyses (thermogravimetric and differential), nitrogen adsorption‐desorption isotherms at –196 °C, transmission electron microscopy, and FT‐IR and UV/Vis spectroscopy. The results show the formation of a microporous hydrotalcite‐type solid with a gallery height of 7.2 Å where the H3Nb6O195– anions are oriented with their C3 axes perpendicular to the layers. This material preserves its layered structure upon calcination up to 400 °C; calcination above this temperature causes decomposition of the hexaniobate and the layered structure collapses, giving rise to amorphous mesoporous solids (Nb‐Mg‐Al‐O) with a large specific surface area (157 m2 g–1). At 800 °C crystallization of Mg4Nb2O9 takes place. FT‐IR studies on the acid‐basic properties carried out by pyridine and 2‐propanol adsorption, showed that all solids obtained through hydrotalcite calcination present Lewis‐type acid and Brönsted‐type basic sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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