Nanocrystalline alumina was synthesized by using the sol−gel method with aluminum sec-butoxide as the precursor. FTIR, TG, XRD, and crystalline structure refinement were used to analyze the phase transformations and their crystalline structures. When samples were annealed at 200 °C, they had two nanocrystalline phases γ-boehmite and γ*-boehmite, which had the same crystalline structure but different lattice parameters and defect numbers in the structure. After sample annealing above 400 °C, the γ-boehmite and γ*-boehmite phases were transformed into nanocrystalline γ-Al2O3 and θ-Al2O3. The γ-alumina crystalline structure contained hydroxyls that brought about cationic defects in aluminum sites, mainly in those of octahedral symmetry. In the 27Al NMR spectra of the samples calcined at 400, 600, and 800 °C, a chemical shift around 33 ppm was observed, which occurred between that of aluminum in oxygen octahedra and aluminum in oxygen tetrahedra. Its origin can be explained by assuming the existence the substitution of some lattice oxygen ions in the octahedral symmetry by hydroxyl groups.

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A series of MgAl hydrotalcites (HTs) were synthesized by a sol-gel procedure with ethanol, 2-propanol, and 1-butanol as solvents. Particular attention was paid to controlling hydrolysis reactions by means of using a substoichiometric H 2 O/Al molar ratio equal to 1. The sol-gel HTs were characterized by means of thermogravimetry, mass spectrometry (MS) of the decomposition products, X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), electron microscopy, and N 2 adsorption-desorption. Decomposition products of sol-gel HTs were identified by MS and included, among others, C x H y fragments from alkoxy groups, which were partially withdrawn between 250 and 450 °C. Alkoxy groups, from the alcohols employed as solvents, are probably intercalated within the HT layers, as indicated by XRD and DRIFT analyses. C x H y groups in these alkoxy groups were detected by DRIFT at ∼2945 and ∼2831 cm -1 in dried HTs, even after annealing at 500 °C. The HTs obtained by the sol-gel procedure described in this work showed nanocapsular morphology. Transmission electron microscopy and Rietveld refinement techniques evidenced the curvature of the HT layers. In comparison with coprecipitated MgAl-CO 3 HT particles (>10 µm), sol-gel HTs showed very small particle aggregates (ca. 300∼350 nm). Calcined HTs presented specific surface area and pore volume values between 254∼332 m 2 /g and 0.81∼1.39 cm 3 /g, respectively, depending on the alcohol used in the sol-gel procedure.