Catalytic effect of monoclinic WO3, hexagonal WO3 and H0.23WO3 on the hydrogen sorption properties of Mg

The H sorption properties of mixtures Mg + WO3 (having various structures) and Mg + H0.23WO3 are reported. First, the higher conversion of Mg into MgH2 during reactive mechanical grinding (under 1.1 MPa of H2) for higher WO3 content is due to the improvement of the milling efficiency. Then, it is shown that the hydrogen absorption properties are almost independent of the crystal structure of the catalyst and that only the particles' size and the specific surface play a major role. Finally, for the desorption process, it appears that the chemical composition and structure of the catalyst, together with the particle size and specific surface have an effect.