Ammonia is produced globally on the 140-megatonne scale per year and has recently been the subject of a revived interest as a clean energy vector (it is easy to store/transport, has good specific energy and releases nitrogen and water on combustion/use in a fuel cell). The activity of ammonia decomposition catalysts reflects that of ammonia synthesis, where ruthenium is state-of-the-art (but expensive) and iron is also active. This study uses neutron diffraction and gravimetric analysis simultaneously (see Figure 1) to show that the iron catalyst is either iron or Fe<sub>4</sub>N under ammonia decomposition conditions. The large incoherent neutron scattering cross-section of hydrogen is used to elucidate the gas composition under non-flowing conditions. This enables the rate-limiting steps of the ammonia decomposition, iron nitriding and iron denitriding reactions to be correlated. This has implications for how to maximise the catalytic activity of iron for ammonia decomposition.

Simultaneous in-situ neutron diffraction and thermogravimetric analaysis of iron catalysts under ammonia decomposition conditions

254th National Meeting (2017)

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