Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

A 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 H 3 Nb 6 O 19 5– anions are oriented with their C 3 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 m 2  g –1 ). At 800 °C crystallization of Mg 4 Nb 2 O 9 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)