Al2O3-SiO2 xerogels with various chemical compositions have been prepared by coprecipitation and their porous properties investigated by nitrogen gas adsorption, transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR). The precipitates were formed by adding conc. aqueous ammonia to an ethanol solution of Al(NO3)3 · 9H2O and Si(OC2H5)4 (TEOS). The syntheses were performed both with and without added H2O(H2O/TEOS≥18/1). The xerogels were dried and calcined at 300°C for 4 h. The porous properties [specific surface area (S(A)), pore volume (V(p)) and pore size (r(p))] varied with their chemical composition, especially the SiO2 rich xerogels. The experimental S(A) values ranged from ca. 10 to 560 m2g-1, the V(p) values from 0.02 to 1.55 ml g-1 and the r(p) values from 2 to 34 nm. The addition of H2O during the preparation markedly influenced the porous properties of the xerogels with SiO2 rich composition. The structure and microtexture of the xerogels are discussed on the basis of the NMR, SAXS and TEM data.
ASJC Scopus subject areas
- Materials Chemistry