Catalytic Hydrolysis of Ammonia Borane Using Co-B Nanoparticles Embedded In Mesoporous Silica Particles: a Very Efficient Catalyst for Hydrogen Production
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Ammonia Borane (AB), with high hydrogen storage capacity (19.5 wt.%), is predicted to be possibly a future fuel for providing pure H2 to fuel cell at room temperature for on-board and portable applications. However, a heterogeneous catalyst plays a vital role for first initiating and then controlling H2 production during hydrolysis reactions. Thus, the present work is focused to develop nano-catalyst to be used for dehydrogenation reactions of AB. Firstly, mesoporous silica nanoparticles (~ 100 nm) with pore size of ~ 3 nm were synthesis by hydrolysis and condensation of alkoxy silane using CTAB surfactant as a template. Later, cobalt salt was embedded inside the pores of the mesoporous silica by chemical impregnation method followed by reduction using NaBH4 to form Co-B nanoparticles. It was observed that Co-B nanoparticles act as highly active catalytic centers to produce significantly higher rate (about 6 times) of H2 by hydrolysis of AB than the same amount of the corresponding Co-B powders (produced by similar chemical reduction method but without mesoporous silica support). Almost complete conversion (95%) of AB was obtained during hydrolysis, as confirmed by 11B NMR, by using nano-catalyst at room temperature. The nano-catalyst were characterized by TEM, SEM, AFM, XPS, EDS, XRD and BET surface area measurement to understand the enhanced activity of the catalyst. Availability of a large number of under-coordinated Co active atoms owing to the size and shape of nanoparticles, better dispersion & polycrystalline nature of nanoparticles, and optimum interaction with reactant provided by electron enrichment on Co sites from B, are the main features acquired by the Co-B nanoparticles that exhibit high catalytic efficiency. The efficient nature of Co-B nanoparticles is well supported by the very low activation energy and high H2 generation rate obtained from the hydrolysis of AB.