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Low temperature hydrogen production from ammonia

Dr Laura Torente (Cambridge)

Hydrogen is commonly presented as a fossil fuel alternative in what is called the hydrogen economy. Despite the vast potential of the use of hydrogen as an energy vector, its widespread implementation is currently limited by the lack of a feasible hydrogen storage capacity and the safety issues associated with its storage and transportation [1, 2]. Within this context, ammonia is presented as an attractive carbon-free energy vector molecule with a hydrogen content of 17.3 wt.%. Its feasibility as energy vector relies on releasing hydrogen via its decomposition at similar temperature than those of the PEM fuel cell (150-180oC).

Ruthenium-based catalysts currently present the highest catalytic activity of ammonia decomposition due to its optimum N adatom binding energy that allows a compromise between activity and desorption of nitrogen (limiting step at low temperatures). Addition of electron donating promoters such as cesium, does not only increase the activity, but it also allows the decomposition of ammonia at considerable lower temperatures due to the electronic modification of the ruthenium active sites [3]. A similar electronic effect can be achieved by increasing the conductivity of the carbon nanotubes (CNT) support [4]. Interestingly, a synergy effect of both modifications can be achieved for the low temperature decomposition of ammonia of ruthenium-based catalysts, with activities below 200oC [5].

In this presentation, we will show our latest results regarding the development of highly active ammonia decomposition catalysts including the effect of metal particle size, properties of the support and addition of promoters, including bi-metallic systems for the development of non-noble metal catalysts [6]  for the low temperature decomposition of ammonia for on-demand hydrogen production.

References

  1. Suh, M.P., et al., Hydrogen Storage in Metal-Organic Frameworks. Chemical Reviews, 2012. 112(2): p. 782-835.
  2. Schlapbach, L. and A. Zuttel, Hydrogen-storage materials for mobile applications. Nature, 2001. 414(6861): p. 353-358.
  3. Hill, A.K. and L. Torrente-Murciano, In-situ H-2 production via low temperature decomposition of ammonia: Insights into the role of cesium as a promoter. International Journal of Hydrogen Energy, 2014. 39(15): p. 7646-7654.
  4. Bell, T.E., et al., Modification of Ammonia Decomposition Activity of Ruthenium Nanoparticles by N-Doping of CNT Supports. Topics in Catalysis, 2017. 60(15-16): p. 1251-1259.
  5. Hill, A.K. and L. Torrente-Murciano, Low temperature H2 production from ammonia using ruthenium-based catalysts: Synergetic effect of promoter and support. Applied Catalysis B: Environmental, 2015. 172–173(0): p. 129-135.
  6. Torrente-Murciano, L., A.K. Hill, and T.E. Bell, Ammonia decomposition over cobalt/carbon catalysts-Effect of carbon support and electron donating promoter on activity. Catalysis Today, 2017. 286: p. 131-140.