Magnetically separable rhodium nanoparticles as catalysts for releasing hydrogen from the hydrolysis of ammonia borane.

Magnetically separable catalysts attract considerable attention in catalysis due to their facile separation from the reaction medium. This propensity is crucial for efficient multiple use of precious noble metal nanoparticles in catalysis. In fact, the isolation of catalysts from the reaction medium by filtration and washing results usually in the loss of huge amount of activity in the subsequent run of catalysis. Although many transition metal nanoparticle catalysts have been reported for the H2 generation from the hydrolysis of ammonia borane, there is no study reporting the magnetically separable rhodium based catalysts for the hydrolytic dehydrogenation of ammonia borane. Here, we report the preparation of rhodium(0) nanoparticles supported on the surface of Fe3O4 and CoFe2O4 magnetic nanopowders as the first example of magnetically separable rhodium nanocatalysts. The resulting magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles are highly active, long-lived and reusable catalysts in H2 generation from the hydrolysis of ammonia borane providing a turnover frequency value of 273 and 720  min−1, respectively, at 25.0 ± 0.1 °C. These magnetically separable catalysts show high reusability and long-term stability in the hydrolysis reaction. They retain their complete initial activity even after the 5th use releasing exactly 3.0 equivalent H2 gas per mole of ammonia borane. The long-term stability tests show that Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles provide a total turnover number of 125,000 and 245,000, respectively, in releasing H2 from the hydrolysis of ammonia borane at room temperature. The long term stability and reusability of magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles make them attractive catalysts for hydrogen generation in fuel cell applications.