Nanoparticulate Pt-catalyzed hydrogenation of Yb films: Towards hydrides with higher hydrogen compositions

[Display omitted] •Moderate condition synthesis of β-YbH3−δ was achieved by nanoparticulate Pt-catalyzed hydrogenation.•Hydrogenation using the Pt nanoparticle catalyst capping method demonstrated room-temperature synthesis of α-YbH2±δ.•Thermodynamic kinetics in syntheses of β-YbH3−δ and α-YbH2±δ were analyzed. It is more difficult to synthesize β-phase ytterbium trihydride (β-YbH3−δ) under moderate conditions than other rare-earth metal trihydrides because it requires a valence change from a fully occupied 4f shell (4f14) in Yb2+ to an unclosed shell (4f13) in Yb3+. We synthesized β-YbH3−δ at ambient pressure through hydrogenation of a Yb film capped with platinum (Pt) nanoparticle (NP) catalysts. In addition, Pt NP capping enabled us to synthesize α-phase Yb dihydride (α-YbH2±δ) at room temperature. The difficulty of trihydrogenating Yb to β-YbH3−δ is explained by kinetic analyses based on temperature and time dependences of molar fractions of α-YbH2±δ and β-YbH3−δ. Pt NP capping can be used to synthesize other hydrogen-rich rare-earth metal hydrides under ambient pressure and lower temperatures.