Micro-kinetic simulations of the catalytic decomposition of hydrazine on the Cu(111) surface

Hydrazine (N₂H₄) is produced at industrial scale from the partial oxidation of ammonia or urea. The hydrogen content (12.5 wt%) and price of hydrazine make it a good source of hydrogen fuel, which is also easily transportable in the hydrate form, thus enabling the production of H₂in situ. N₂H₄ is currently used as a monopropellant thruster to control and adjust the orbits and altitudes of spacecrafts and satellites; with similar procedures applicable in new carbon-free technologies for power generators, e.g. proton-exchange membrane fuel cells. The N₂H₄ decomposition is usually catalysed by the expensive Ir/Al₂O₃ material, but a more affordable catalyst is needed to scale-up the process whilst retaining reaction control. Using a complementary range of computational tools, including newly developed micro-kinetic simulations, we have derived and analysed the N₂H₄ decomposition mechanism on the Cu(111) surface, where the energetic terms of all states have been corrected by entropic terms. The simulated temperature-programmed reactions have shown how the pre-adsorbed N₂H₄ coverage and heating rate affect the evolution of products, including NH₃, N₂ and H₂. The batch reactor simulations have revealed that for the scenario of an ideal Cu terrace, a slow but constant production of H₂ occurs, 5.4% at a temperature of 350 K, while the discharged NH₃ can be recycled into N₂H₄. These results show that Cu(111) is not suitable for hydrogen production from hydrazine. However, real catalysts are multi-faceted and present defects, where previous work has shown a more favourable N₂H₄ decomposition mechanism, and, perhaps, the decomposition of NH₃ improves the production of hydrogen. As such, further investigation is needed to develop a general picture.