Dehydrogenation of Ammonia Borane with transition metal-doped Co-B alloy catalysts

The catalytic performance of transition metal-doped Co-B ternary alloys were tested for H-2 generation by hydrolysis of Ammonia Borane (AB). Chemical reduction method was used to dope Co-B catalyst with various transition metals, namely Cu, Cr, Mo, and W, using their corresponding metal salts. All transition metals induce significant promoting effects on the Co-B catalyst by increasing the H-2 generation rate by about 3-6 times as compared to the undoped catalyst. The effect of metal dopant concentration on overall catalyst structure, surface morphology, and catalytic efficiency were examined by varying the metal/(Co + metal) molar ratio. Characterizations such as XPS, XRD, SEM, BET surface area measurement, and particle size analysis were carried out to understand the promoting role of each dopant metal during AB hydrolysis. Dopant transition-metals, in either oxidized or/and metallic state, act as an atomic barrier to avoid Co-B particle agglomeration thus preserving the effective surface area. In addition, the oxidized species such as Cr3+, Mo4+, and W4+, act as Lewis acid sites to enhance the absorption of OH- group to further assist the hydrolysis reaction over alloy catalysts. The promoting nature of transition metal dopants in Co-B alloy powders is demonstrated by the evaluated low activation energy of the rate limiting step and high H-2 generation rate (2460 ml H-2 min(-1) (g of catalyst)(-1) for Co-Mo-B) in the hydrolysis of AB. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.