Ammonia cracking by microwave plasma under reduced pressure

The cracking of pure ammonia by microwave discharges under reduced pressure (typically 50-500 mbar) is studied as a hydrogen formation process. The lowest energy cost associated with the production of 1 kg of hydrogen is 33 kWh (i.e. 13 % energy efficiency for a dissociation ratio of 28 %). With the same process, NH3 can be fully dissociated at a greater energy expense (50 kWh/kgH2). The plasmas produced have electron densities of no more than 5 x 1011 cm- 3 at electron temperatures close to 0.5 eV. We show that the molecule is dissociated thermally and by electron collisions. Some of the waste heat lost in this process can be recovered in post- discharge by activating surface reactions. With flowrates exceeding 10 L per minute, it is plausible that the process could be even more efficient by reducing the gradients that are responsible for the loss of energy efficiency.