Preparation and characterization of spherical mesoporous ZrO₂-Al₂O₃ composites with high thermal stability

Abstract

Spherical mesoporous ZrO₂-Al₂O₃ composites containing different zirconia content have been synthesized by an oil-column sol-gel method. A mixed alumina-zirconia hydrosol and hexamethylenetetramine solution were mixed together and added dropwise into a hot oil column. Due to the surface tension, spherical gel particles were formed in the oil column. The spherical gel particles were then aged and washed by deionized water and dried at 120 °C for 12 h and then calcined at 600 °C for 8 h, 960 °C for 8 h or 1200 °C for 12 h. X-ray diffraction and nitrogen adsorption-desorption measurements indicated that the presence of zirconia prevents the sintering of alumina and the obtained ZrO₂-Al₂O₃ composites have much larger surface areas than pure alumina. Temperature-programmed desorption of ammonia results illustrated that the addition of zirconia leads to an increase in the number of strong acid sites and the total number of acid sites compared with pure alumina. Thus, the spherical mesoporous ZrO₂-Al₂O₃ composites prepared in this way were shown to be suitable for high temperature catalytic processes as a catalyst support.