Formation and Acid–Base Surface Properties of Highly Dispersed η-Al2O3 Nanopowders

Resumo

Highly dispersed η-Al₂O₃-based nanopowders have been prepared via glycine–nitrate combustion followed by heat treatment in air. The resultant materials have been characterized by X-ray diffraction, Fourier transform IR spectroscopy, scanning electron microscopy, simultaneous thermal analysis, and other techniques. We have optimized the glycine-to-nitrate ratio (G/N = 0.2) and found heat treatment conditions for combustion products (isothermal holding at a temperature of 700°C for 6 h) that allow one to obtain single- phase nanocrystalline η-Al₂O₃ powders with an average particle size of 5 ± 1 nm and specific surface area of 54 ± 5 m²/g. The acid–base surface properties of the η-Al₂O₃ nanopowder have been analyzed using pyridine sorption–desorption processes as an example. The specific concentrations of weak, intermediate, and strong Lewis acid centers on the surface of the η-Al₂O₃ nanocrystals have been shown to markedly exceed those on the surface of commercially available γ-Al₂O₃ (A-64). The synthesized nanopowders can thus be used as effective supports of acid catalysts.