B–N Polymer Embedded Iron(0) Nanoparticles as Highly Active and Long Lived Catalyst in the Dehydrogenation of Ammonia Borane

Abstract

B-N polymer embedded iron(0) nanoparticles (NPs) were in-situ generated from the reduction of iron(III) acetylacetonate during the dehydrogenation of ammonia borane (AB) in THF solution at 40.0 +/- 0.5 degrees C. The iron(0) NPs could be isolated as powder from the reaction solution by centrifugation and characterized by UV-Vis, TEM, and XRD. They are redispersible in polar solvent such as THF and yet highly active catalysts in the dehydrogenation of AB providing a TOF value of 202 h(-1) at 40.0 +/- 0.5 degrees C. The catalytic activity of iron(0) NPs compare well with those of the known homogenous and heterogeneous precious metal catalysts reported so far. They are also long-life catalysts in the dehydrogenation of AB providing 1410 turnovers over 18 h at 40.0 +/- 0.5 degrees C. The poisoning experiments using carbon disulfide show that the dehydrogenation of AB catalyzed by iron(0) NPs is a heterogeneous catalysis. The catalytic dehydrogenation of AB in the presence of iron(0) NPs was followed by measuring the volume of hydrogen generated and by 11B-NMR spectroscopy. Our report also includes the results of a detailed kinetic study on the catalytic dehydrogenation of AB depending on the catalyst concentration, substrate concentration, and temperature. The dehydrogenation of AB produces sparingly soluble B-N polymers which provide just enough stability to the iron(0) NPs. The co-precipitation of some iron(0) NPs with the sparingly soluble polymers causes a slight decrease in the catalytic activity toward the end of dehydrogenation. However, iron(0) NPs embedded in B-N polymers appear to be an efficient catalyst in hydrogen generation from ammonia borane at moderate temperature.