Metal Organic Frameworks and their Derivatives as Catalysts of Magnesium Hydrogenation

This article presents results of the 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 was 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-synthesized MOFs and their CoNi@C derivatives in the hydrogenation of Mg during high-energy reactive ball milling in hydrogen (HRBM) has been studied. These catalysts were shown to increase the rate of hydrogenation of Mg during HRBM in about 9 times as compared to the non-catalysed magnesium. The kinetic improvements are superior to the earlier observed ones 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 of magnesium hydrogenation were incomplete. It was found that the use of the as-synthesized MOFs as additives to Mg during HRBM results in the slow hydrogenation of the pristine magnesium at the room temperature during pauses between the first milling sessions, and 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.