Nanoceria supported rhodium(0) nanoparticles as catalyst for hydrogen generation from methanolysis of ammonia borane

This work reports the preparation and catalytic use of nanoceria supported rhodium(0) nanoparticles, Rh(0)/nanoCeO(2), as catalyst for hydrogen generation from the methanolysis of ammonia borane. Rh(0)/nanoCeO(2) was in situ formed from the reduction of rhodium(II) octanoate on the surface of nanoceria during the catalytic methanolysis of ammonia borane at room temperature. The results of analysis using PXRD, TEM, STEM-EDS, XPS, SEM, SEM-EDX, N-2 adsorption-desorption and ICP-OES reveal that rhodium(0) nanoparticles were well dispersed on the surface of nanoceria with an average size of 3.9 +/- 0.6 nm. Rh(0)/nanoCeO(2) shows high catalytic activity in the methanolysis of ammonia borane with a turnover frequency of 144 min(-1). Note that hydrogen generation from the methanolysis of ammonia borane catalyzed by Rh(0)/nanoCeO(2) is slightly less than 3.0 equivalent, due to the reduction of Ce4+ ions to Ce3+ ions on the surface of nanoceria during the methanolysis of ammonia borane. The reduction of Ce4+ ions leading to the formation of Ce3+ defects on the surface of nanoceria under the catalytic reaction conditions could be investigated by high resolution Ce 3d XPS analysis. Additionally, the formation kinetic of rhodium(0) nanoparticles could be studied by using the hydrogen generation from the methanolysis of ammonia borane as reporter reaction; thus, the rate constants for the slow nucleation, k(1) and autocatalytic surface growth of rhodium(0) nanoparticles, k(2) were determined. Our report also includes the results of kinetic study of the catalytic methanolysis of ammonia borane depending on rhodium concentration and temperature.