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

Abstract

• Moderate condition synthesis of β-YbH 3− δ was achieved by nanoparticulate Pt-catalyzed hydrogenation. • Hydrogenation using the Pt nanoparticle catalyst capping method demonstrated room-temperature synthesis of α-YbH 2± δ . • Thermodynamic kinetics in syntheses of β-YbH 3− δ and α-YbH 2± δ were analyzed. It is more difficult to synthesize β-phase ytterbium trihydride (β-YbH 3− δ ) under moderate conditions than other rare-earth metal trihydrides because it requires a valence change from a fully occupied 4 f shell ( 4 f 14 ) in Yb 2+ to an unclosed shell ( 4 f 13 ) in Yb 3+ . We synthesized β-YbH 3− 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-YbH 2± δ ) at room temperature. The difficulty of trihydrogenating Yb to β-YbH 3− δ is explained by kinetic analyses based on temperature and time dependences of molar fractions of α-YbH 2± δ and β-YbH 3− δ . Pt NP capping can be used to synthesize other hydrogen-rich rare-earth metal hydrides under ambient pressure and lower temperatures.