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

Abstract

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.