H. Zhang, Y.A. Alhamed, L. Petrov, Y. Kojima
King Abdulaziz University, SA
ammonia, cobalt, catalyst, decomposition, hydrogen, generation
Liquid ammonia has both high energy density and high hydrogen storage capacity which makes it suitable for on-board generation of COx free hydrogen by catalytic ammonia decomposition (AD). Cheap catalysts based on cobalt were considered in this study to investigate the effect of support on its performance. Cobalt (5% loading) supported on carbon nanotubes (CNTs) and three different types of active carbons (AC) were prepared and tested for AD. For the AC supported catalysts, the cobalt particle size (determined from CO adsorption measurements) decreased with increasing surface area and ammonia conversion increased with decreasing particle size due the increase in the number of active centers (higher dispersion). CNTs supported cobalt, although it has a larger size of cobalt particles than the most active AC supported catalyst, it exhibited a much higher activity. This higher activity could be attributed to the different structure and electronic properties of the CNTs support. It is established in literature that for Ru based catalysts, N2 desorption is the controlling step. The stronger interaction between cobalt and the CNTs surface and its electron donation ability seems to facilitate a much easier N2 desorption and thus a higher activity.