Influence of morphology of hollow silica–alumina composite spheres on their activity for hydrolytic dehydrogenation of ammonia borane

Abstract

Hollow silica-alumina composite spheres were prepared by a polystyrene (PS) template method using various amounts of PS suspension. Homogeneous hollow spheres prepared using 40 g were found to be with a diameter of about 300 nm in scanning electron microscopy, and transmission electron microscopy demonstrated their hollow sphere morphology. From the nitrogen adsorption isotherm results, the homogeneous hollow spheres prepared using 40 g of the PS suspension were found to be an ordered pore structure. The activities of the hollow spheres prepared using various amounts of the PS suspension for hydrolytic dehydrogenation of ammonia borane were compared. The results showed that 10, 7, and 6 mL of hydrogen were evolved from the aqueous ammonia borane solution in about 40 min in the presence of the hollow spheres prepared using 40, 80, and 120 g of PS suspension, respectively. The homogeneous hollow spheres with an ordered pore structure showed the highest activity among all the hollow spheres. The amount of acid sites and the coordination number of aluminum active species were characterized using neutralization titration and solid-state 27 Al magic angle spinning nuclear magnetic resonance spectroscopy. The homogeneous hollow spheres with an ordered pore structure had high amount of acid sites and 4-coordinated aluminum species. The relative proportion of 4-coordinated aluminum species was related to the dispersion of aluminum species. These results indicate that the homogeneous hollow spheres with an ordered pore structure showed the high activity because of high amount of acid sites induced by the highly dispersed aluminum species.

Fabrication of copper supported porous silica–alumina hollow spheres for catalytic decomposition of nitrous oxide

“…Forty grams of spherical polystyrene template particle suspension in ethanol prepared according to ref. 24–29 and 42 was mixed with 0–160 mL of deionized water, 28 wt% aqueous ammonia solution (Kanto Chem. Co., %), and 4 mL of 0.07 mol L −1 aqueous solution of decyltrimethylammonium bromide (DeTAB), dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB, Kanto Chem.…”

“…[18][19][20][21][22][23] Our research group has elucidated specific Brønsted acidity of silica-alumina hollow sphere particles probably derived from integrated acid sites in interparticle spaces formed by fine primary particles in the hollow sphere shells. [24][25][26][27] The acidity further increased with the hollow spheres with well-ordered interparticle spaces in the shells obtained by using surfactant micelles, and the hollow spheres effectively promoted hydrolytic hydrogen generation from ammonia borane probably due to the increase of the integrated sites in the interparticle spaces. 28,29 To identify the effect of the integrated sites of another cation, we investigated copper supported silica-alumina hollow sphere particles with well-ordered mesoporous interparticle spaces for decomposition of nitrous oxide.…”

Hollow Silica Particles: Recent Progress and Future Perspectives

“…During carbonization at 400 • C, vaporized carbon made from the sucrose formed the inner layer of the shell, whereas the silica formed the outer layer of the shell. Similarly, hybrid HSPs with composite shells made of silica and alumina were created by co-deposition of alumina and silica precursors on preformed polystyrene particles [57]. Recently, hybrid HSPs with a two-layered shell (inner layer silica and outer layer polymer or carbon) have been reported [58].…”

Function of Shirasu-based materials for acid-promoted hydrolysis of ammonia borane

“…By employing proper catalysts, AB can release hydrogen in a sustained manner at room temperature. The hydrolysis reaction can promote at appreciable rate in the presence of a suitable acid such as aluminosilicates at ambient temperature [16][17][18][19][20][21][22][23][24]. The main components of Shirasu based materials are silica and alumina, and thus the Shirasu based materials are expected to promote the hydrolysis reaction.…”