Inelastic neutron scattering studies of the interaction of hydrogen with palladium black

Abstract Incoherent inelastic neutron scattering has been used to investigate the interaction of hydrogen with palladium black (a high-surface-area Pd powder). Vibrational spectra of chemisorbed hydrogen have been measured in the energy range 30–230 meV at 80 and 295 K. The dominant surface adsorption site of hydrogen has been identified by comparison of the vibrational frequencies and intensities provided by the scattering data with normal coordinate calculations for model structures of different geometries, force constants and bond lengths. The “best fit” to the data is obtained for surface adsorption sites of threefold symmetry. A vibrational feature observed at 58 meV, which is inconsistent with either surface or bulk PdH species, is assigned to hydrogen occupying subsurface sites of bulk-like octahedral symmetry.