title: The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts.
abstract: Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1-7.3 wt %). Collectively, this series of catalysts provides a range of metal particle sizes (1.2-8.5 nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)(111) and (111)(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1 wt % loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.
authors.affiliation: Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom.
authors.forename: Timothy
authors.initials: T
authors.lastname: Lear
authors.forename: Robert
authors.initials: R
authors.lastname: Marshall
authors.forename: J Antonio
authors.initials: JA
authors.lastname: Lopez-Sanchez
authors.forename: S David
authors.initials: SD
authors.lastname: Jackson
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Klapötke
authors.forename: Marcus
authors.initials: M
authors.lastname: Bäumer
authors.forename: Günther
authors.initials: G
authors.lastname: Rupprechter
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Freund
authors.forename: David
authors.initials: D
authors.lastname: Lennon