In-situ synthesized hollow spheres of silica-ruthenium-nickel composite catalyst for hydrolytic dehydrogenation of ammonia borane
The present study investigated fabrication of hollow spheres of silica-ruthenium-nickel composite catalyst for hydrolitic dehydrogenation of ammonia borane. The hollow spheres was obtained by originally developed in-situ synthesized method. In this method, the hollow spheres was formed by treating in aqueous solution including sodium borohydride and ammonia borane from the spherical silica-nickel-ruthenium composite particles prepared by sol-gel method. In this process, formation of hollow voids, activation of active ruthenium and nickel species, hydrolysis of ammonia borane for hydrogen evolution were parallely occurred. Compared with the catalytic activity of the hollow spheres with various ruthenium/(ruthenium+nickel) ratios and total amount of metals, the hollow spheres with ruthenium/(ruthenium+nickel) ratio = 0.5 and total amount of metals = 8.0 mol% shows highest activity for the hydrogen evolution with its comparative turnover frequency (33.6 mol-H2 min-1 [mol-(Ru+Ni)]-1) of previously reported catalyst. The hollow spheres included spherical particles with the diameter of hollow void = ca. 250 nm, and their specific surface area was about ten times as high as the spherical particles precursor, indicating that the obtained hollow spheres consists of porous structure.The highly active hollow spheres showed cycle ability for the hydrogen evolution and its activity did not significantly decrease with increasing cycle number.