Cobalt Oxide Model Catalysis Across the Materials and Pressure Gap (COMCAT)
Zusammenfassung der Projektergebnisse
The D-A-CH project “COMCAT: Cobalt oxide model catalysts across the materials and pressure gap” aimed at gaining a fundamental understanding of the catalytic activity of cobalt oxide at the atomic scale using a model catalysis approach with complementary surface science methods. A variety of cobalt oxide substrates were used: as model catalysts we employed epitaxial films of CoO(111), CoO(100) and Co3O4 (111) grown on Ir(100), to make contact to catalytic applications also commercial Co3O4 powder catalysts were used. Most intensively the properties of Co3O4 were studied. Concerning the adsorption and oxidation of CO in ultra-high vacuum we could identify two configurations in which CO is weakly bound to the Co2+ sites of the Co-terminated Co3O4 (111) surface from which it desorbs unreacted. Conversely a carbonate species adsorbed on sites related to defects proved to be much stronger bound and remained on the surface up to temperatures around 470 K. These results were obtained combining infrared absorption spectroscopy, temperature programmed desorption and high-resolution (synchrotron) x-ray photoelectron spectroscopy. Oxidation studies revealed that a small fraction of the carbonate species, i.e. CO at defect sites, react to CO 2. Repeated CO oxidation cycles led to a decrease of the lattice oxygen content and a coherent switching of Co3O4 (111) grains towards well-ordered CoO(111) as evidenced by scanning tunnelling microscopy and low-energy electron diffraction. Crossing the materials and pressure gap the structural changes during CO oxidation were confirmed at near-ambient pressures. Further, Co3O4 powder catalysts in a mixture of nearambient pressure H2, CO and O2 showed preferential CO oxidation (PROX) at temperatures between 370 and 500 K whereas higher temperatures lead to increased H2O and CH4 production. Operando near-ambient-pressure x-ray photoelectron spectroscopy and infrared spectroscopy revealed that the reduction of Co3O4 to CoO is responsible for the declining selectivity of the PROX reaction whereas in the PROX regime the catalyst remained fully oxidized always indicated a fast re-oxidation process. The studies were complemented by investigating the adsorption of CO, H2O and CO2 on all three model catalyst surfaces indicating low binding energy adsorbate states of CO and CO 2 and a strong structural dependence of the adsorption of H2O caused by the varying presence of surface Co2+ at the different systems. Subsequently the model catalysts were modified by adsorbing metallic Co and Pt in ultra-high vacuum. Here it was identified that the metals on Co3O4(111) provide strong adsorption sites for CO. For temperatures below 500K Co stays in the presence of CO disperse on the surface and only sinters and eventually diffuse into the Co3O4 support. On Pt modified Co3O4(111) a spill-over effect and the importance of metal-oxide interface states for the oxidation of CO could be identified by infra-red spectroscopy. Complementary investigations of a special metal-metal-oxide hybrid phase of CoO2 on Ir(100) also showed the importance of metal adsorption sites for the lowtemperature oxidation of CO.
Projektbezogene Publikationen (Auswahl)
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Adsorption and Activation of CO on Co3O4(111) Thin Films. Journal of Physical Chemistry C 2015, 119, 16688–16699
Ferstl, P.; Mehl, S.; Arman, M. A.; Schuler, M.; Toghan, A.; Laszlo, B.; Lykhach, Y.; Brummel, O.; Lundgren, E.; Knudsen, J.; Hammer, L.; Schneider, M. A.; Libuda, J.
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Different synthesis protocols for Co3O4-CeO2 catalysts. Part 1: Influence on the morphology on the nanoscale. Chemistry – A European Journal 2015, 21, 885–892
Yang, J.; Lukashuk, L.; Akbarzadeh, J.; Stöger-Pollach, M.; Peterlik, H.; Föttinger, K.; Rupprechter, G.; Schubert, U.
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Thermal evolution of cobalt deposits on Co3O4(111): atomically dispersed cobalt, two-dimensional CoO islands, and metallic Co nanoparticles. Physical Chemistry Chemical Physics 2015, 17, 23538–23546
Mehl, S.; Ferstl, P.; Schuler, M.; Toghan, A.; Brummel, O.; Hammer, L.; Schneider, M. A.; Libuda, J.
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CO Adsorption on Reconstructed Ir(100) Surfaces from UHV to mbar Pressure: a LEED, TPD and PM-IRAS Study. Journal of Physical Chemistry C 2016,120, 10838–10848
Anic, K.; Bukhtiyarov, A. V.; Li, H.; Rameshan, C.; Rupprechter, G.
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Ionic-Liquid- Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C(1)C(2)Im][OTf] Monitored by In Situ IR Spectroscopy. Langmuir 2016, 32, 8613–8622
Mehl, S.; Bauer, T.; Brummel, O.; Pohako-Esko, K.; Schulz, P.; Wasserscheid, P.; Libuda, J.
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Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and CeO2-Co3O4 catalysts. Journal of Catalysis 2016, 344, 1–15
Lukashuk, L.; Föttinger, K.; Kolar, E.; Rameshan, C.; Teschner, D.; Hävecker, M.; Knop-Gericke, A.; Yigit, N.; Li, H.; McDermott, E.; Stöger–Pollach, M.; Rupprechter, G.
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Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains. Phys. Rev. Lett. 2016, 117, 046101
Ferstl, P.; Hammer, L.; Sobel, C.; Gubo, M.; Heinz, K.; Schneider, M. A.; Mittendorfer, F.; Redinger, J.
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Structure and Ordering of Oxygen on Unreconstructed Ir(100). Phys. Rev. B 2016, 93, 235406
Ferstl, P.; Schmitt, T.; Schneider, M. A.; Hammer, L.; Michl, A.; Müller, S.
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Structure-Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic Acid on Co3O4(111), CoO(100), and CoO(111). Chemistry-a European Journal 2016, 22, 5384–5396
Xu, T.; Schwarz, M.; Werner, K.; Mohr, S.; Amende, M.; Libuda, J.
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The surface structure matters: thermal stability of phthalic acid anchored to atomically-defined cobalt oxide films. Physical Chemistry Chemical Physics 2016, 18, 10419–10427
Xu, T.; Schwarz, M.; Werner, K.; Mohr, S.; Amende, M.; Libuda, J.
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Anchoring of a Carboxyl-Functionalized Norbornadiene Derivative to an Atomically Defined Cobalt Oxide Surface. Journal of Physical Chemistry C 2017, 121, 11508–11518
Schwarz, M.; Mohr, S.; Xu, T.; Döpper, T.; Weiß, C.; Civale, K.; Hirsch, A.; Görling, A.; Libuda, J.
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Gluing Ionic Liquids to Oxide Surfaces: Chemical Anchoring of Functionalized Ionic Liquids by Vapor Deposition onto Cobalt(II) Oxide. Angewandte Chemie-International Edition 2017, 56, 9072–9076
Xu, T.; Waehler, T.; Vecchietti, J.; Bonivardi, A.; Bauer, T.; Schwegler, J.; Schulz, P. S.; Wasserscheid, P.; Libuda, J.
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Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability. ChemPhysChem 2017
Xu, T.; Waehler, T.; Vecchietti, J.; Bonivardi, A.; Bauer, T.; Schwegler, J.; Schulz, P. S.; Wasserscheid, P.; Libuda, J.
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Monatomic Co, CoO2 and CoO3 nanowires on Ir(100) and Pt(100) surfaces: Formation, structure, and energetics. Phys. Rev. B 2017, 96, 085407
Ferstl, P.; Mittendorfer, F.; Redinger, J.; Schneider, M. A.; Hammer, L.
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Synthesis and Properties of monolayer protected Cox(SC2H4Ph)m nanoclusters. Journal of Physical Chemistry C 2017, 121, 10948–10956
S. Pollitt, E. Pittenauer, C. Rameshan, T. Schinger, G. Allmaier, N. Barrabes, G. Rupprechter
