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Growth and reconstruction of Rh particles deposited onto different Al2O3 substrates were studied. Three single crystalline α-alumina substrates, having (0 0 0 1), (1 1¯ 0 2) and (1 1 2¯ 0) surface orientations, and polycrystalline γ-alumina were positioned simultaneously on the same sample holder. Consequently, all performed procedures (Rh deposition, sample annealing, CO and O2 adsorption) were completely identical.The sample conditions were checked after every particular procedure by means of electron spectroscopy, especially AES and EPES. Morphology parameters (Rh particle size and density) of Rh deposit were measured ex situ using transmission electron microscopy of the sample carbon replica. The difference among the electron spectra obtained on the identically treated samples is discussed to study the influence of the substrate orientation on the properties of Rh/Al2O3 model catalysts. [Copyright &y& Elsevier]

Abstract: Vibrational spectroscopy of adsorbed CO is commonly used for the characterization of oxide-supported metal catalysts, in spite of persisting ambiguities concerning the band assignment. Here, we present reference data on well-defined Pt/CeO2(111)/Cu(111) model catalysts aiming at clear identification of the related features. Growth and morphology of the Pt particles are investigated by scanning tunneling microscopy (STM), the adsorption properties are probed by temperature programmed desorption (TPD), and the electronic structure has previously been studied by photoelectron spectroscopy (PES) and resonant photoelectron spectroscopy (RPES). Combining molecular beam (MB) methods and infrared reflection absorption spectroscopy (IRAS), we correlate this information to the interaction with CO. Two types of defect adsorption sites are identified on the ceria support (2097cm−1, 2120cm−1), which are assigned to structural defects and reduced Ce3+ centers. The relative abundance of these sites changes upon thermal treatment. On the Pt nanoparticles, CO first adsorbs on-top at step and edge sites (2066cm−1), before adsorption on the (111) facets occurs in bridging (1875cm−1) and on-top (2080–2097cm−1) geometry. For the first time, we identify vibrational CO features, which arise from electronic metal-support interactions and from oxygen reverse spillover. On reduced CeO2− x (111), a red-shifted band at 2053cm−1 appears, which is attributed to increased π-backbonding from Pt to CO, as a result of a change in electronic metal-oxide interaction. Thermal treatment also activates oxygen reverse spillover from the support to the Pt nanoparticle, which gives rise to a blue-shifted feature in the CO spectrum (2090–2105cm−1) due to coadsorbed oxygen next to CO sites. [Copyright &y& Elsevier]

Abstract: We have investigated the structure and growth of Pd and BaO containing nanoparticles sequentially co-deposited on an ordered Al2O3/NiAl(110) by scanning tunneling microscopy (STM), and their interaction with CO and NO2 by infrared reflection absorption spectroscopy (IRAS). Ba deposition and subsequent oxidation result in Ba x Al2 y O x +3 y nanoparticles being formed which are characterized by high particle densities and nucleation both on regular terraces and at oxide defects. In contrast, Pd interaction with the model support is weaker and preferential nucleation occurs mainly at rotational domain boundaries and to a lesser extent at anti-phase domain boundaries. For subsequent co-deposition of Pd on preformed Ba x Al2 y O x +3 y /Al2O3/NiAl(110), Pd nucleates at the Ba x Al2 y O x +3 y nanoparticles and covers them. The reverse deposition sequence, i.e. subsequent Ba co-deposition and oxidation on preformed Pd/Al2O3/NiAl(110), leads to formation of small isolated Ba x Al2 y O x +3 y nanoparticles without contact to Pd, together with large Pd crystallites modified by Ba x Al2 y O x +3 y . The present results provide control over the degree of interaction between metal nanoparticles and oxide nanoparticles on a well-defined model catalyst and thus allow us to study effects related effects on the reactivity and catalytic behavior. [Copyright &y& Elsevier]