Relationship between structure and sorption kinetic behaviour for ternary CeMX compounds

The crystal structure and the hydrogenation behaviour of more than 10 ternary compounds based on cerium (i.e. CeMX with M=Mn, Ni, Cu and X=Al, Ga, In, Si, Ge, Sn) is presented. Most of the structures can be described as a stacking of [Ce6] trigonal prisms occupied by a M or a X atom. All these compounds form stable hydrides and the kinetic behaviour can be linked to the H insertion sites and to the structural changes upon hydrogenation. If no structural change is observed during the formation of the hydride and if H atoms occupy [Ce3M] tetrahedral sites, the reaction with hydrogen is fast. But if a structural change occurs during hydrogenation, then, the reaction takes place slowly. Particular behaviour is reported when H atoms occupy (i) [Ce4] tetrahedral sites (slow kinetics without structural change) and (ii) [Ce3Ni2] or [Ce3Si2] bipyramidal sites (high kinetics without a structural change).