Abstract
The influence of the catalytic activity of metal oxide nanoparticles on the hydrogen sorption properties of nanocrystalline MgH 2 prepared by mechanical (ball) milling was investigated. The simple geometrical model nano-sized particles distributed on the surface of a micro-sized particle is presented. Some trends relating different geometrical features and densities for both powders are shown. With this model, the weight quantities of some metal oxide nanopowders were calculated, and their hydrogen absorption and desorption catalytic activities were compared. The commercial MgH 2 powder was mixed with the nanoparticles of different metal oxides (Cr 2O 3, TiO 2, Fe 3O 4, Fe 2O 3, In 2O 3, ZnO) and subsequently ball milled for 20 h in an inert atmosphere. The hydrogen absorption and desorption kinetics were evaluated using a volumetric Sievert's apparatus and characterized at 325 °C or 300 °C under 1 bar and 10 bar of hydrogen pressure during desorption and absorption, respectively. In both the absorption and desorption reactions, the superior catalytic effect of Cr 2O 3 and TiO 2 was observed. The catalytic effect of the investigated metal oxides is also expressed in the lowering of the activation energy of the dehydriding reaction. The decomposition enthalpies seem not to be affected by the introduction of nano-sized metal oxides.
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