This work reports the influence of the water/titanium alkoxide ratio during the preparation of titania-nickel composite particles on their morphology and catalytic activity toward the hydrolysis of ammonia borane. The titania-nickel composite particle catalysts were fabricated by using a sol-gel method, followed by an activation process in aqueous solution containing sodium borohydride and ammonia borane. From the scanning electron microscopy images and pore-size distributions calculated from nitrogen sorption data, the particle dispersion was significantly enhanced at ratios above 6000, and increased with increasing water/titanium alkoxide ratio. Stoichiometric amounts of hydrogen were evolved in the presence of all of the prepared titania-nickel composite particle catalysts. The particle dispersion influenced the hydrogen evolution rate from aqueous ammonia borane solution, and the samples with the most highly dispersed particles showed the highest hydrogen evolution rate. The most active catalyst showed an apparent activation energy comparable to that of other reported catalysts and high cycle ability for the hydrolysis of ammonia borane.
Keywords: ammonia borane; composite particles; hydrogen evolution; titania–nickel; water/titanium alkoxide ratio.