Facile synthesis by polyol method of a ruthenium catalyst supported on γ-Al2O3 for hydrolytic dehydrogenation of ammonia borane

Ruthenium (1.5 wt% Ru) supported on gamma-Al2O3 was synthesized in the presence of ethylene glycol using ruthenium acetylacetonate as precursor. The catalyst was characterized by inductively coupled plasma (ICP) emission spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that it consisted of Ru-0 and RuO2 as spherical nanoparticles, with an average size of 4.2 nm, and aggregates deposited at the surface of the support. The catalyst was tested in hydrolysis of ammonia borane, NH3BH3. Experiments with variable amounts of catalyst (10-30 wt%), concentrations of the substrate (1.0-0.65 M), and temperatures (50-66 degrees C) were performed. The reaction was followed by volumetric (inverted burette) and spectroscopic (B-11 and B-11{H-1} NMR) methods. A kinetic study was developed (apparent activation energy of 67 kJ mol(-1); reaction orders vs. the concentration of NH3BH3 and ruthenium active sites of 0.4 and 1.0, respectively). Hydrogen generation rates up to 76.4 mL(H-2) min(-1) or 158.5 L(H-2) min(-1) g(-1) (for the highest catalyst loading) were measured, which classify our catalyst among the most reactive ones. The NMR study showed a rapid NH3BH3 hydrolysis also at room temperature with initial formation of B(OH)(4)(-), which besides would favor following equilibriums of formation of polyborates. Finally, after deactivation of the catalyst in the first run, the hydrolysis mechanism resulted substantially unmodified. These results are reported and discussed herein. (C) 2011 Elsevier B.V. All rights reserved.