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

Abstract

Hydrazine (NH) 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 Hin situ. NH 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 NH decomposition is usually catalysed by the expensive Ir/AlO 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 NH 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 NH coverage and heating rate affect the evolution of products, including NH, N and H. The batch reactor simulations have revealed that for the scenario of an ideal Cu terrace, a slow but constant production of H occurs, 5.4% at a temperature of 350 K, while the discharged NH can be recycled into NH. 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 NH decomposition mechanism, and, perhaps, the decomposition of NH improves the production of hydrogen. As such, further investigation is needed to develop a general picture.

Kinetic and mechanistic analysis of NH3decomposition on Ru(0001), Ru(111) and Ir(111) surfaces

“…[61][62][63] Although the TST has weaknesses, it is widely used to provide useful information on the design of catalysts. 64,65 Some of the TST weaknesses are that it assumes (i) no quantum tunnelling, (ii) the intermediates are long-lived to follow the Boltzmann distribution of energy, and (iii) all the species reaching the transition state evolve only to products. In the used model, the lateral adsorbate-adsorbate interactions are assumed to be negligible, i.e.…”

Stability and mobility of supported Nin (n = 1–10) clusters on ZrO2(111) and YSZ(111) surfaces: a density functional theory study

“…We have used kinetic Monte Carlo simulations in order to understand how time (t) and Ni coverage (q) inuence the coalescence of Ni clusters on top of the YSZ(111) surface. To achieve our kinetic Monte Carlo study, we have used the same equations as the ones described in the ESI of the investigation by Tafreshi et al 56 Additionally, quantum-mechanical tunnelling 57 has been taken into account. Coverage has been dened in eqn (4):…”

Hydrogen Generation from Additive-Free Formic Acid Decomposition Under Mild Conditions by Pd/C: Experimental and DFT Studies

“…Metal hydrides such those of Mg-Al-Fe has been reported to achieve a maximum rate of 499.5 ml min −1 g −1 of hydrogen at 25 °C for Mg 60 -Al 30 -Fe 10 (wt%) in 0.6 mol l −1 NaCl solution [15]. One of the most promising solutions consists on the utilization of hydrous hydrazine as reagent [16]. It presents the unique advantage that N 2 is the only by-product for the complete decomposition [17].…”