Ammonia Storage in Metal Ammines


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Ammonia has attracted interest as a promising alternative fuel for internal combustion engines due to the fact that ammonia does not release carbon dioxide during combustion.[1] Storing ammonia in the form of metal ammines is the most notable way to overcome the challenges that are related to the use of NH3 in liquid form, namely the toxicity and corrosive nature of ammonia.[2] Ammine complexes of light transition metal halides (such as Co, Ni) are very promising candidates because they exhibit high ammonia contents and they are relatively stable at room temperature.

The CoX2 system is an interesting candidate, especially cobalt chloride, as it possesses a NH3 capacity of 44 wt. % and desorption is completed by 330 °C. We are currently investigating the chemical and structural properties of the Co halides during ammonia-uptake at ambient conditions and ammonia-release (upon heating). The ammoniated metal halides were studied by powder X-ray diffraction, FTIR and Raman spectroscopy. The crystal structure of hexammine has been determined and the products of the first and second decomposition steps were confirmed as diamine and monoamine. The thermal properties of the hexammine cobalt halides were studied by TPD (TG-DTA-MS) measurements. These measurements were intended to investigate their deammoniation properties and the products of decomposition. In addition, the cycling behaviour and the stability of the ammonited cobalt chloride in air were also investigated.

[1] Steele, R. B. Chemtech 1999, (August), 28.
[2] C. H. Christensen, R. Z. Sørensen, T. Johannessen, U. J. Quaade, K. Honkala, T. D. Elmøe, R. Køhler, J. K. Nørskov, J. Mater. Chem., 2005, 15, 4106–4108.