Bimetallic RuCo and RuCu catalysts supported on γ-Al2O3. A comparative study of their activity in hydrolysis of ammonia-borane

Bimetallic-based RuCo and RuCu catalysts, supported on gamma-Al2O3 (1.5 wt% Ru as theoretical value), were synthesized by polyol method. Ru, Co, and Cu acetylacetonates were used as precursors and ethylene glycol as reducing agent. The as-synthesized catalysts were characterized by SEM, TEM, XRD and XPS, and tested in ammonia-borane (NH3BH3) hydrolytic dehydrogenation at variable amount of catalyst (10-30 wt%), concentration of NH3BH3 (1.0-0.65 M), and temperatures (50-65 degrees C). The reactions were monitored by volumetric (inverted burette) and spectroscopic methods (B-11 and B-11{H-1} NMR). It was found that the best bimetallic catalysts are those having a molar ratio Ru:Co and Ru:Cu of 1:1 such as RuCo > RuCu similar to Ru. They, i.e. RuCo and RuCu, consist of nanosized spherical particles of Ru Co(OH)(2) and Ru Cu, respectively. Kinetic investigation highlights similar rate laws with activation energies of 47 kJ mol(-1) and 52 kJ mol(-1), respectively, and, for both, reaction orders of 1 versus both the NH3BH3 and the catalytic free sites concentrations. B-11 and B-11{H-1} NMR investigation confirmed (i) a more effective NH3BH3 hydrolytic dehydrogenation in the presence of RuCo catalyst even though a loss of activity after the first run was observed for both catalysts, and (ii) a rapid NH3BH3 hydrolysis with initial formation of B(OH)(4)(-), which besides favors equilibriums of formation of polyborates. These results are reported and the reaction mechanism discussed herein. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.