Catalytic Ammonia Decomposition in Green Energy Supply

Rising population has led to higher energy consumption of fossil fuel and thus trigger severe environmental crisis like global warming, sea level rise, acid rains etc. To address the ongoing environmental problem, extreme effort has been placed on the development of green energy source. Hydrogen, amongst all the others, has shown to be a promising candidate.

Not only due to its high energy by mass, but also as the only product of combustion is water. However, commercializing hydrogen still faces some challenges. As hydrogen is the smallest molecule, it is extremely hard to store, not to mention its transportation.

This leads to one essential bottleneck within the hydrogen economy, hydrogen storage and transportation.

Ammonia (NH3) is considered as an effective solution to tackle down the above question. On one hand, ammonia contains relatively high hydrogen content. On the other hand, ammonia itself has a standard process for synthesis and storage.

Ammonia synthesis is achieved through a sophisticated technique called the Haber-Bosch process, where nitrogen and hydrogen react to give ammonia. The produced ammonia can then be pressurized and safely stored as liquid form under mild condition at a relative low cost. This leaves the decomposition of ammonia back to nitrogen and hydrogen being the last puzzle for the hydrogen system via ammonia.

Hence, development of effective catalyst for ammonia decomposition has become an essential task with high priority. In this project, effective ammonia decomposition is studied over a metal embedded on nitrogen doped carbon material. Evidence has shown that nitrogen doping on a layered carbon material can promote the catalytic activity of ammonia decomposition.

However, the underlying mechanism is still unknown. It has been suggested by one previous paper published in our group that, during ammonia decomposition, the nitrogen from the N-Graphene might help to break the N-H bond in ammonia, via a H-N-M-N-H like Lewis pair transition state. Furthermore, nitrogen exists in different forms on the carbon layer, namely pyrrolic, pyridinic, quaternary and terminal.

Each of them has different chemical properties which would have different impact on the overall reaction kinetics. Thus, further investigation would be carried out on the function of nitrogen environments towards the overall catalysis. The fundamental study would provide mechanistic understanding for future novel catalyst design.

The project would be carried out with a combination of catalyst activity testing and essential in-situ and ex-situ characterisations. Catalyst will be tested in a quartz tube which is held in the vertical fixed-bed flow reactor. Ammonia is flown through the set-up with ammonia decomposition taking place in the reaction while the residue gas is analysed with an in-situ Gas chromatography.

The conversion rate is calculated based on the intensity of the peaks of nitrogen, hydrogen and unreacted ammonia. As for characterisation, ex-situ BET, XRD, TEM TPD and TGA are used to understand the structure and chemical property of the catalyst. XPS will be carried out the reveal the nitrogen content and environment, in-situ IR will be performed to understand the bond formation and breakage during the reaction.

Together with further computational calculation, a fundamental mechanism can be proposed for the reaction over this catalyst. My project would collaborate with Oxford Green Innotech (OXGRIN), a spin-out company from the University of Oxford, which is aiming for building a world-class One-Stop Catalyst Platform that comprises research, manufacture and integration with end user applications. This project falls within the EPSRC Energy and decarbonisation research area.