Room temperature hydrogen generation from aqueous ammonia-borane using noble metal nano-clusters as highly active catalysts

Abstract Nano-clusters of noble metals Ru, Rh, Pd, Pt and Au have been supported on γ-Al 2 O 3 , C and SiO 2 , of which the catalytic activities have been investigated for hydrolysis of NH 3 BH 3 . Among these catalysts, the Ru, Rh and Pt catalysts exhibit high activities to generate stoichiometric amount of hydrogen with fast kinetics, whereas the Pd and Au catalysts are less active. Support effect has been studied by testing the hydrogen generation reaction in the presence of Pt supported on γ-Al 2 O 3 , VULCAN ® carbon and SiO 2 , and it is found that Pt on γ-Al 2 O 3 , which has the smallest particle size, is the most active. Concentration dependence of the hydrogen generation from aqueous NH 3 BH 3 solutions has been investigated in the presence of Pt/γ-Al 2 O 3 by keeping the amount of Pt/γ-Al 2 O 3 catalyst unchanged, which exhibits that the hydrogen release versus time (ml H 2 min −1 ) does not significantly change with increasing the NH 3 BH 3 concentration, indicating that the hydrogen release rate is not dependent on the NH 3 BH 3 concentration and the high activity of the Pt catalyst can be kept at high NH 3 BH 3 concentrations. Activation energies have been measured to be 23, 21 and 21 kJ mol −1 for Ru/γ-Al 2 O 3 , Rh/γ-Al 2 O 3 and Pt/γ-Al 2 O 3 catalysts, respectively, which may correspond to the step of B–N bond breaking on the metal surfaces. The particle sizes, surface morphology and surface areas of the catalysts have been obtained by TEM and BET experiments.