Ruthenium nanoparticles supported on nanotubes/nanowires: highly active and long lived nanocatalysts in hydrolytic dehydrogenation of ammonia borane /

Ammonia borane (NH3BH3, AB) is one of the most promising solid hydrogen storage materials due to its high hydrogen storage capacity (19.6% wt.), non-toxicity and high stability under ambient conditions. Ammonia borane can release hydrogen upon hydrolysis in the presence of suitable catalysts even at room temperature. Although a large variety of catalysts have been tested in hydrogen generation from the hydrolysis of ammonia borane, the development of efficient, long-lived, reusable catalysts is still an important issue. This dissertation reports the preparation, characterization and catalytic use of highly active, reusable and long-lived ruthenium catalysts for the hydrolysis of ammonia borane. Ruthenium(0) nanoparticles supported on multiwalled carbon nanotubes (Ru0/MWCNT) were prepared for the hydrolysis of AB and characterized by advanced analytical techniques including ICP-OES, XRD, TEM, SEM, EDX, and XPS. The results reveal that ruthenium(0) nanoparticles of size in the range 1.4−3.0 nm are well-dispersed on multiwalled carbon nanotubes. Ru0/MWCNT were found to be highly active catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value of 329 min−1 at 25.0 ± 0.1 ᵒC. vi For comparison, ruhenium(0) nanoparticles were also formed on an inorganic nanowire, xonotlite (Ca6(Si6O17)(OH)2). Ruhenium(0) nanoparticles supported on xonotlite (Ru0/X-NW) were prepared by the ion exchange of Ru3+ ions with Ca2+ cations in the lattice of xonotlite nanowire followed by their reduction with sodium borohydride in aqueous solution at room temperature. Ru0/X-NW was also characterized by the same analytical methods. Ru0/X-NW are found to be a long lived catalyst with a TTO value of 134,100 in hydrolysis of ammonia borane 25.0 ± 0.1ᵒC. The comparisons in terms of activity, life-time and reusability were also extended to the ruthenium(0) nanoparticles supported on hydroxyapatite (HAp) and silica coated cobalt ferrite (CoFe2O4) supported ruthenium catalysts. Ru0/HAp and Ru0/SiO2- CoFe2O4 catalysts were found to be highly active in hydrolysis of AB with a TOF value of 137 min-1 and 172.5 min-1, respectively. Ru0/HAp provides a TTO value of 87,000 in hydrolysis of ammonia borane at 25.0 ± 0.1ᵒC. Ru0/SiO2- CoFe2O4 catalyst was found to be highly reusable catalyst in hydrolysis of AB retaining 94% of its initial catalytic activity even after tenth use.