Nickel Catalysts Liberate Lots Of H₂

Newly minted nickel catalysts help the promising hydrogen-fuel-storage compound ammonia borane (H₃NBH₃, or AB) release almost all of its hydrogen atoms in a relatively short time (J. Am. Chem. Soc. 2007, 129, 1844). R. Tom Baker and his colleagues at Los Alamos National Laboratory prepared nickel complexes containing N-heterocyclic carbene ligands and tried them on AB, finding that more than 2.5 equivalents of H₂ evolved at 60 °C. Stripped of most of its hydrogen atoms, AB forms a cross-linked borazine ring structure. One catalyst (shown) was particularly active, completing the H₂ release in 150 minutes. Scientists are studying numerous methods (such as heating) and catalysts (such as acids or precious metals iridium and palladium) for dehydrogenating AB. The authors note this is the first example of a first-row transition-metal catalyst used on AB. The Los Alamos researchers say a large amount of H₂ evolution from AB is necessary to reach government goals for a practical hydrogen storage system (9% hydrogen by weight for the overall system by 2015).