Characterization of silicon-aluminum-zirconium oxide obtained by the sol-gel process

Abstract

A new silicon-aluminum-zirconium ternary oxide (SiO2/Al2O3/ZrO2) was prepared by the sol-gel method followed by one-step washing with absolute ethanol or two-step washing with absolute ethanol followed by ultra-pure water. Both ternary oxides presented high surface area (over 340 m2 g-1). The binding energy values for Zr3d and Al2p levels showed the insertion of Zr and Al atoms in silica matrix, confirming the dispersion surface of these elements as shown by scanning electron microscope (SEM) and energy dispersive X-ray fluorescence spectroscopy (EDXRF) data. A weight loss around 40 wt.% was found for both samples submitted to thermogravimetric analysis (TGA). Crystallographic data showed the presence of monoclinic and tetragonal ZrO2 phases in different proportions according to the calcination temperature. Regarding the acid-base properties, temperature-programmed desorption of CO2 (CO2-TPD) profiles suggested that washing with water reduced the overall basicity of the samples and removed the strongest basic sites. However, according to temperature-programmed desorption of NH3 (NH3-TPD) profiles, washing significantly increased the amount of weak acid sites, in agreement with pyridine adsorption data. Bronsted acid sites (BAS) are ever dominant but washing with ethanol followed by water reduced the number of Lewis acid sites (LAS).