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

Nano-clusters of noble metals Ru, Rh, Pd, Pt and An have been supported on gamma-Al2O3, C and SiO2, of which the catalytic activities have been investigated for hydrolysis of NH3BH3. 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 An catalysts are less active. Support effect has been studied by testing the hydrogen generation reaction in the presence of Pt supported on gamma-Al2O3, VULCANO carbon and SiO2, and it is found that Pt on gamma-Al2O3, which has the smallest particle size, is the most active. Concentration dependence of the hydrogen generation from aqueous NH3BH3 solutions has been investigated in the presence of Pt-gamma-Al2O3 by keeping the amount of Pt/gamma-Al2O3 catalyst unchanged, which exhibits that the hydrogen release versus time (ml H-2 min(-1)) does not significantly change with increasing the NH3BH3 concentration, indicating that the hydrogen release rate is not dependent on the NH3BH3 concentration and the high activity of the Pt catalyst can be kept at high NH3BH3 concentrations. Activation energies have been measured to be 23, 21 and 21 kJ mol(-1) for Ru/gamma-Al2O3, Rbl-y-A]203 and Pt/gamma-Al2O3 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. (C) 2007 Elsevier B.V. All rights reserved.