FritzHaber Institut der MaxPlanck Gesellschaft Faradayweg 46 14195 Berlin Germany 65th International Symposium on Molecular Spectroscopy Vibrational Spectroscopy of Binary Metal Oxide Clusters ID: 1031923
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1. Ling JiangDepartment of Molecular PhysicsFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4-6, 14195 Berlin, Germany65th International Symposium on Molecular SpectroscopyVibrational Spectroscopy of Binary Metal Oxide ClustersIR Spectroscopy + Theory[(CeO2)(V2O4)]+Gas-phase model systemVanadium oxideSupported catalyst
2. Motivation: Supported Vanadium Oxide CatalystsLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 23) It is difficult to calculate cerium 4f electrons in the bulk. Can we use gas-phase IR spectroscopy to understand the supportactive site interactions?Enhanced reactivity is due to the ability of CeO2 to stabilize the reduced Ce3+.2) Reactivity of VOx depends on support material: CeO2 > TiO2 > SiO21) Vanadium oxide catalyst is very important in industry.
3. Gas-phase Model: Binary Ce-V, Ti-V, Si-V Oxide ClustersLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 31) Test system for benchmarking theory: [(CeO2)(VO2)]+: fully oxidized [(CeO2)(V2O4)]+: one unpaired electron (). [(Ce2O3)(VO2)]+: two unpaired electrons ( ). 2) To compare the reducibility of Ce4+, Ti4+, and Si4+: [(MO2)(V2O4)]+ ()M = Ce, Ti, SiCe:4f13d14s2(Ce4+)V:3d34s2 (V5+) Ti:3d24s2(Ti4+) Si:3d24s2(Si4+)
4. cluster source region dual laser vaporization electron ionization ion sprayhigh vacuum10-8 mbarD. J. Goebbert, G. Meijer, K. R. Asmis, AIP Conf. Proc. 1104, 22 (2008).Exp. Setup: Infrared Photodissociation SpectroscopyLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 4guiding decapolequadrupolemass filter90° deflectortime-of-flightmass spectrometer(product ions)- IR FELIX (40-3333.3 cm-1)- OPO/OPA cooled 12 K RF ion trap (He or buffer gas mix)- accumulate & thermalize ionsIon detector AB+∙Rg AB+ + Rg (Rg = He, Ne)(single photon photodissociation spectra)
5. Results: Experimental IR SpectraLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 5[(CeO2)(VO2)]+•He [(CeO2)(V2O4)]+•Ne [(Ce2O3)(VO2)]+•Ne Asmis et al. J. Chem. Phys. 120, 6461 (2004). V2O4+V=O stretchterminalO-V-ObackboneWhat are these modes?
6. IR Spectra: Exp. vs TheoryLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 6Computational:B3LYP/def-TZVPP(Turbomole) [(CeO2)(VO2)]+ The effect of rare-gas is negligible.Agrees with the experiment.V2O4+123451: terminal V=O2: terminal Ce=O asym O-Ce-O-V backbone3: terminal Ce=O sym O-Ce-O-V backbone4: asym O-V-O backbone 5: sym O-V-O backbone1B1C1A•HeCeV1AO [(CeO2)(V2O4)]+ [(Ce2O3)(VO2)]+ [(CeO2)(VO2)]+
7. Electronic Structures of Ce-V Oxide ClustersCe4+V5++ Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 7[(CeO2)(VO2)]+ [(CeO2)(VO2)2]+ + [(Ce2O3)(VO2)]+ Fully oxidizedPartially oxidizedCe3+ (4f1)Ce3+ (4f1)Ce3+ (4f1)V5+spin density Ce4+ is reduced first, consistent with bulk model study.
8. Reduction on Different Metal Site in [(MO2)(V2O4)]+ Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 8Relative to V5+, the reducibility of “support” metal atoms:Ce4+ > Ti4+ > Si4+Relative reactivity of supported VOx: CeO2 > TiO2 > SiO2Ce-VSi-VTi-V0.0 kJ/mol -71.3 kJ/mol 0.0 kJ/mol -20.1 kJ/mol 0.0 kJ/mol +112.7 kJ/mol V4+Ti3+V4+Si3+“Support” metal atom is reducedCe3+V4+Vanadium atom is reduced
9. ConclusionsLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 9IRPD spectroscopy combined with DFT allows to identify geometric and electronic structure of binary metal oxide clusters. 2) B3LYP with suitable basis set can properly calculate cerium-containing clusters. 3) The high reducibility of cerium atom implies an active role of CeO2 in supported catalysts.
10. AcknowledgmentsLing Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 10Fritz-Haber Institute:Collaborators: Staff at FELIX (FOM Institute Rijnhuizen, Netherlands) for assistanceFinancial support: Alexander von Humboldt Foundation European Community's Seventh Framework ProgrammeGerard MeijerTorsten WendeNadja HeineKnut R. AsmisPeter Lievens, Pieterjan ClaesSoumen Bhattacharyy(Katholieke Universiteit Leuven) Joachim Sauer, Marek Sierka(Humboldt University)
11. Gas-phase IR spectra of VO1-3+ and V2O2-6+Asmis et al. J. Chem. Phys. 120, 6461 (2004). Determination of Scale Factor