Abstract: Bimodal porous alumina-silica composite oxides were prepared via the sol-gel method using nonionic surfactant C16EO10 as the structure-directing agent. Tetramethoxysilane and aluminum nitrate were used as the silicon and aluminum precursors, respectively. Scanning electron microscopy and N2 adsorption/desorption measurements indicated that the composite oxides possess interconnected macropores and texture mesopores. The micrometer-range interconnected macropores were obtained by freezing the transitional structure of spinodal phase separation in the sol-gel process. The evolution of nanometer-range mesopores in the gel skeletons can possibly be attributed to the supramolecular templating by the nonionic surfactant. Energy dispersive spectroscopy proved that a large part of initially added aluminium was incorporated in the gel network. The Hammett indicator method and infrared spectra showed that the alumina-silica composite oxides were mild strong solid acids, and the amount of acid with acid strength H0 of -5.6 to -3.0 was 0.35 mmol/g. Moreover, these oxides contained abundant Lewis acid sites and less Bronsted acid sites.

Key words: alumina, silica, composite oxide, sol-gel, phase separation, template, mesopore, macropore