Metal–organic frameworks and their derivatives as catalysts of magnesium hydrogenation

Abstract This article presents the results of an experimental study on the preparation and characterisation of metal–organic frameworks (MOFs) formed by coordination polymers of Ni(II) and Co(II) itaconates (Ni–IA and Co–IA), as well as the products of thermolysis of their mixtures. It is found that the thermolysis results in the formation of heterometallic CoNi nanoparticles enveloped in a porous carbonaceous matrix (CoNi@C core-shell structures). The catalytic effect of the as-synthesised MOFs and their CoNi@C derivatives on the hydrogenation of Mg during high-energy reactive ball milling (HRBM) in hydrogen has been studied. These catalysts were shown to increase the rate of hydrogenation of Mg during HRBM by about ninefold as compared with non-catalysed magnesium. The kinetic improvements are superior to those observed earlier for other catalysts, including Pd-doped UiO-66 MOF and Ni nanoparticles deposited onto graphene-like materials. At the same time, the achieved reacted fractions when using MOFs and their derivatives as catalysts for magnesium hydrogenation were incomplete. It was found that the use of the as-synthesised MOFs as additives to Mg during HRBM results in the slow hydrogenation of pristine magnesium at room temperature during pauses between the first milling sessions. Almost full conversion of Mg into MgH₂ was achieved when the milling vial was kept during these pauses until pressure stabilisation. Based on this observation, it was assumed that the intermediate products of MOF decomposition are more active catalysts of magnesium hydrogenation than the CoNi@C core–shell structures formed as the final MOF decomposition product.