Catalytic effects of magnesium-transition metal (Fe and Ni) hydrides on oxygen and nitrogen reduction: A case study of explosive characteristics and their environmental contaminants

The catalytic effects of magnesium-transition metal (Mg–TM) hydrides on O₂ and N₂ reduction were examined. The results indicated that magnesium hydrides (MHs) combustion process primarily occurred in three stages: dehydrogenation, active Mg combustion, and residual Mg combustion. After the dehydrogenation stage, the active Mg particles and released H atoms became more likely to be oxidised and nitrified in MgFeH than in MgH₂. Moreover, a large quantity of NH₃ was observed after the combustion of MgFeH. Fe has a rich electronic structure and an active surface position, which enables it to activate N₂ and thus facilitate the catalytic reduction of N₂. Due to the lower temperature and pressure requirements of the initial reaction in the MgFeH combustion or explosion process, compared to those of the Haber-Bosch process, the combustion and explosion of MgFeH can result in the release of significant amounts of NH₃. However, the addition of Ni can prevent the activation of O₂ and N₂, thereby inhibiting their reduction. This means that Ni not only inhibits N₂ reduction but also enhances the dehydrogenation capacity of MHs. Therefore, to develop and design hydrogen storage materials for MHs, Ni is a safer and more environmentally friendly catalyst than Fe.