Influence of aluminum precursors on structure and acidic properties of hollow silica-alumina composite spheres, and their activity for hydrolytic dehydrogenation of ammonia borane

In this study, we investigated the influence of aluminum precursors on structure and acidic properties of hollow silica-alumina composite spheres, as well as their activity for hydrolytic dehydrogenation of ammonia borane. Hollow silica-alumina composite spheres were prepared via the sol-gel method using polystyrene particles as templates. Activities of the hollow spheres prepared using various aluminum precursors for hydrolytic dehydrogenation of ammonia borane were compared. The molar ratios of evolved hydrogen to ammonia borane introduced were 1.0, 2.8, 1.5, and 3.0 in the presence of the hollow spheres prepared using aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, and aluminum-tri-sec-butoxide, respectively. Hollow spheres prepared using aluminum precursors with branched alkyl groups exhibit more hydrogen evolution than those prepared using aluminum precursors with normal alkyl groups. From the result of solid-state 27Al nuclear magnetic resonance spectra and temperature-programmed desorption of ammonia, 4-coordinated aluminum species are related to Brønsted acid sites, and highly dispersed aluminum species increase the number of Brønsted acid sites.