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3. Methanol oxidation on a copper catalyst investigated using in situ X-ray photoelectron spectroscopy

Author

Bluhm, Hendrik, Havecker, Michael, Knop-Gericke, Axel, Salmeron, Miquel, Kleimenov Evgueni, Frank Ogletree, D, Schlogl, Detre, and Bukhtiyarov, Valerii I.

Subjects
Photoelectron spectroscopy -- Usage, Copper -- Chemical properties, Methanol -- Chemical properties, Oxidation-reduction reaction -- Analysis, Chemicals, plastics and rubber industries
Abstract

An investigation on the surface and near-surface regions of an active catalyst and the adjacent gas-phase reactants is presented under reaction conditions using in situ X-ray photoelectron spectroscopy (XPS). The study concluded that the active catalyst surface is metallic copper that contains a subsurface oxygen species.

Published
2004

4. Tuning the acid/base properties of nanocarbons by functionalization via amination

Author

Arrigo, Rosa, Havecker, Michael, Wrabetz, Sabine, Blume, Raoul, Lerch, Martin, McGregor, James, Parrott, Edward P.J., Zeitler, J. Axel, Gladden, Lynn F., Knop-Gericke, Axel, Schlogl, Robert, and Dang Sheng Su

Subjects
Carbon compounds -- Chemical properties, Carbon compounds -- Electric properties, Chemistry
Abstract

The coexistence of acidic and basic O and N sites were functionalized via amination to characterize the samples of vapor grown carbon nanofibers (VGCNFs) modified by treatment of the oxidized CNFs with N[H.sub.3]. The results revealed the potential application of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.

Published
2010

5. 1s2p Resonant inelastic X-ray scattering of iron oxides

Author

de Groot, Frank M. F., Glatzel, Pieter, Bergmann, Ume, van Aken, Peter A., Barrea, Raul A., Klemme, Stephan, Havecker, Michael, Knop-Gericke, Axel, Heijboer, Willem M., and Weckhuysen, Bert M.

Subjects
Iron oxides -- Structure, Iron oxides -- Properties, Iron oxides -- Spectra, Surface chemistry -- Analysis, X-ray spectroscopy -- Analysis, Chemicals, plastics and rubber industries
Abstract

1s2p Resonant inelastic X-ray scattering (RIXS) spectroscopy is measured for a series of iron oxides, including octahedral and tetrahedral Fe(super II) and Fe (super III) systems, crystal-field multiplet simulations are used to analyze their spectral shapes. The full power and possibilities of 1s2p RIXS needs an overall resolution of 0.3 eV and this yields a technique with more detailed information than K-edge and L-edge X-ray absorption combined, obtained in a single experiment.

Published
2005

6. Pt-Co/SiO2 bimetallic planar model catalysts for selective hydrogenation of crotonaldehyde

Author

Borgna, Armando, Anderson, Bruce G., Saib, Abdool M., Bluhm, Hendrick, Havecker, Michael, Knop-Gericke, Axel, Kuiper, A. E. T., Ton, Tamminga, Yde, and Niemantsverdriet, J. W., Hans

Subjects
Metal catalysts -- Spectra, Backscattering -- Analysis, Hydrogenation -- Analysis, Chemicals, plastics and rubber industries
Abstract

Spin-coating technique was used to prepare surface science models of silica-supported Pt-Co bimetallic catalysts with various Pt/Co ratios. Platinum and cobalt loadings on a series of silica-supported model catalysts were quantified by Rutherford backscattering spectrometry.

Published
2004

7. In situ X-ray absorption of Co/Mn/TiO2 catalysts for Fisher-Tropsch synthesis

Author

Morales, Fernando, Groot, Frank M.F. de, Glatzel, Pieter, Kleimenov, Evgueni, Bluhm, Hendrik, Havecker, Michael, Knop-Gericke, Axel, and Weckhuysen, Bert M.

Subjects
Titanium dioxide -- Research, Manganese -- Research, Cobalt -- Research, Chemicals, plastics and rubber industries
Abstract

The reduction behavior of Co/TiO2 and Co/Mn/TiO2 catalysts for Fisher-Tropsch synthesis is investigated. Catalytic tests in the Fisher-Tropsch synthesis reaction at the pressure of 1 bar indicate that the selectivity of these catalysts might be related to the extent of Co reduced after the activation treatment.

Published
2004

8. In-Situ soft X-ray absorption of over-exchanged Fe/ZSM5

Author

Heijboer, Willem M, Battiston, Andrea A., Knop-Gericke, Axel, Havecker, Michael, Mayer, Ralf, Bluhm, Hendrik, Schlogl,Robert, Weckhuysen, Bert M., Koninhsberger, Diek C., and Groot, Frank M.F. de

Subjects
X-ray spectroscopy -- Analysis, Spectrum analysis -- Analysis, Iron compounds -- Spectra, Chemicals, plastics and rubber industries
Abstract

In-situ soft X-ray absorption spectroscopy (XAS) is applied to study the iron redox behavior in over-exchanged Fe/ZSM5. The tool claims to provide new information on the geometry and valence of the Fe sites and yields an accurate method to determine the average iron valence during oxidation/reduction cycles.

Published
2003

9. Treading in the Limited Stability Regime of Lanthanum Strontium Ferrite - Reduction, Phase Change and Exsolution

Author

Gotsch, Thomas, Kopfle, Norbert, Schlicker, Lukas, Carbonio, Emilia A., Havecker, Michael, Knop, Axel, Schloegl, Robert, Bekheet, Maged F., Gurlo, Aleksander, Doran, Andrew, Bernardi, Johannes, Klotzer, Bernhard, and Penner, Simon

Abstract

We present an in situ investigation of the iron exsolution from lanthanum strontium ferrite perovskites. Using in situ X-ray diffraction experiments at the synchrotron, the exact onset of exsolution was determined by a change in the lattice parameter before any iron reflexes become visible. For an initially orthorhombic thin film, on the other hand, a phase transition to a fluorite/rock-salt structure is observed to occur during the exsolution. Also, a difference in the iron oxidation states between bulk and surface is found since photoelectron spectroscopy and X-ray absorption spectroscopy both indicate the existence of the Fe(III)/Fe(II) couple in oxidation/reduction cycles, whereas magnetic measurements would suggest Fe(IV)/Fe(III).

Published
2019

10. Dynamic electronic structure of a Au/TiO2 catalyst under reaction conditions

Author

Willneff, Elizabeth A., Braun, Simon, Rosenthal, Dirk, Bluhm, Hendrik, Havecker, Michael, Kleimenov, Evgenyi, Knop-Gericke, Axel, Schlogl, Robert, and Schroeder, Sven L.M.

Subjects
Electron configuration -- Research, Titanium dioxide -- Atomic properties, Photoelectron spectroscopy -- Usage, Chemistry
Abstract

The electronic structure of a practical Au/TiO2 catalyst is probed in situ by synchrotron X-ray photoelectron spectroscopy (XPS). The results have highlighted the dynamic nature of supported Au and the importance of in situ studies for the determination of gas/surface mechanisms.

Published
2006

11. In situ XPS study of Pd(111) oxidation. Part 1: 2D oxide formation in 10 3 mbar O2

Author

Zemlyanov, Dmitry, Aszalos-Kiss, Balazs, Kleimenov, Evgueni, Teschner, Detre, Zafeiratos, Spiros, Havecker, Michael, Knop-Gericke, Axel, Schlogl, Robert, Gabasch, Harald, Unterberger, Werner, Hayek, Konrad, Klotzer, Bernhard, Zemlyanov, Dmitry, Aszalos-Kiss, Balazs, Kleimenov, Evgueni, Teschner, Detre, Zafeiratos, Spiros, Havecker, Michael, Knop-Gericke, Axel, Schlogl, Robert, Gabasch, Harald, Unterberger, Werner, Hayek, Konrad, and Klotzer, Bernhard

Abstract

The oxidation of the Pd(111) surface was studied by in situ XPS during heating and cooling in 3 · 10 3 mbar O2. A number of adsorbed/dissolved oxygen species were identified by in situ XPS, such as the two dimensional surface oxide (Pd5O4), the supersaturated Oads layer, dissolved oxygen and the ð ffiffiffiffiffi p67 ffiffiffiffiffi p67ÞR12.2 surface structure. Exposure of the Pd(111) single crystal to 3 · 10 3 mbar O2 at 425 K led to formation of the 2D oxide phase, which was in equilibrium with a supersaturated Oads layer. The supersaturated Oads layer was characterized by the O 1s core level peak at 530.37 eV. The 2D oxide, Pd5O4, was characterized by two O 1s components at 528.92 eV and 529.52 eV and by two oxygen-induced Pd 3d5/2 components at 335.5 eV and 336.24 eV. During heating in 3 · 10 3 mbar O2 the supersaturated Oads layer disappeared whereas the fraction of the surface covered with the 2D oxide grew. The surface was completely covered with the 2D oxide between 600 K and 655 K. Depth profiling by photon energy variation confirmed the surface nature of the 2D oxide. The 2D oxide decomposed completely above 717 K. Diffusion of oxygen in the palladium bulk occurred at these temperatures. A substantial oxygen signal assigned to the dissolved species was detected even at 923 K. The dissolved oxygen was characterised by the O 1s core level peak at 528.98 eV. The ‘‘bulk’’ nature of the dissolved oxygen species was verified by depth profiling. During cooling in 3 · 10 3 mbar O2, the oxidised Pd2+ species appeared at 788 K whereas the 2D oxide decomposed at 717 K during heating. The surface oxidised states exhibited an inverse hysteresis. The oxidised palladium state observed during cooling was assigned to a new oxide phase, probably the ð ffiffiffiffiffi p67 ffiffiffiffiffi p67ÞR12.2 structure.

Published
2006

12. Aerosol-Derived Bimetallic Alloy Powders: Bridging the Gap

Author

Halevi, Barr, primary, Peterson, Eric J., additional, DeLaRiva, Andrew, additional, Jeroro, Ese, additional, Lebarbier, Vanessa M., additional, Wang, Yong, additional, Vohs, John M., additional, Kiefer, Boris, additional, Kunkes, Edward, additional, Havecker, Michael, additional, Behrens, Malte, additional, Schlögl, Robert, additional, and Datye, Abhaya K., additional

Published
2010
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