1. Ling Jiang Department of Molecular Physics Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4-6, 14195 Berlin, Germany 65th International Symposium on Molecular Spectroscopy Vibrational Spectroscopy of Binary Metal Oxide Clusters IR Spectroscopy + Theory [(CeO 2 )(V 2 O 4 )] + Gas-phase model system Vanadium oxide Supported catalyst

2. Motivation: Supported Vanadium Oxide Catalysts Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 2 3) It is difficult to calculate cerium 4f electrons in the bulk. Can we use gas-phase IR spectroscopy to understand the supportactive site interactions? Enhanced reactivity is due to the ability of CeO 2 to stabilize the reduced Ce 3+. 2) Reactivity of VO x depends on support material: CeO 2 > TiO 2 > SiO 2 1) Vanadium oxide catalyst is very important in industry.

3. Gas-phase Model: Binary Ce-V, Ti-V, Si-V Oxide Clusters Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 3 1) Test system for benchmarking theory: [(CeO 2 )(VO 2 )] + : fully oxidized [(CeO 2 )(V 2 O 4 )] + : one unpaired electron (). [(Ce 2 O 3 )(VO 2 )] + : two unpaired electrons ( ). 2) To compare the reducibility of Ce 4+, Ti 4+, and Si 4+ : [(MO 2 )(V 2 O 4 )] + () M = Ce, Ti, Si Ce:4f 1 3d 1 4s 2 (Ce 4+ ) V:3d 3 4s 2 (V 5+ ) Ti:3d 2 4s 2 (Ti 4+ ) Si:3d 2 4s 2 (Si 4+ )

4. cluster source region - dual laser vaporization - electron ionization - ion spray high vacuum 10 -8 mbar D. J. Goebbert, G. Meijer, K. R. Asmis, AIP Conf. Proc. 1104, 22 (2008). Exp. Setup: Infrared Photodissociation Spectroscopy Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 4 guiding decapole quadrupole mass filter 90° deflector time-of-flight mass 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 ions Ion detector AB + ∙Rg  AB + + Rg (Rg = He, Ne) (single photon photodissociation spectra)

5. Results: Experimental IR Spectra Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 5 [(CeO 2 )(VO 2 )] + He [(CeO 2 )(V 2 O 4 )] + Ne [(Ce 2 O 3 )(VO 2 )] + Ne Asmis et al. J. Chem. Phys. 120, 6461 (2004). V2O4+V2O4+ V=O stretch terminal O-V-O backbone What are these modes?

6. IR Spectra: Exp. vs Theory Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 6 Computational: B3LYP/def-TZVPP (Turbomole) [(CeO 2 )(VO 2 )] + The effect of rare-gas is negligible. Agrees with the experiment. V2O4+V2O4+ 1 2 3 4 5 1: terminal V=O 2: terminal Ce=O asym O-Ce-O-V backbone 3: terminal Ce=O sym O-Ce-O-V backbone 4: asym O-V-O backbone 5: sym O-V-O backbone 1B 1C 1AHe Ce V 1A O [(CeO 2 )(V 2 O 4 )] + [(Ce 2 O 3 )(VO 2 )] + [(CeO 2 )(VO 2 )] +

7. Electronic Structures of Ce-V Oxide Clusters Ce 4+ V 5+ +  Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 7 [(CeO 2 )(VO 2 )] + [(CeO 2 )(VO 2 ) 2 ] + +   [(Ce 2 O 3 )(VO 2 )] + Fully oxidized Partially oxidized Ce 3+ (4f 1 ) V 5+ spin density Ce 4+ is reduced first, consistent with bulk model study.

8. Reduction on Different Metal Site in [(MO 2 )(V 2 O 4 )] + Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 8 Relative to V 5+, the reducibility of “support” metal atoms: Ce 4+ > Ti 4+ > Si 4+ Relative reactivity of supported VO x : CeO 2 > TiO 2 > SiO 2 Ce-V Si-V Ti-V 0.0 kJ/mol -71.3 kJ/mol 0.0 kJ/mol -20.1 kJ/mol 0.0 kJ/mol +112.7 kJ/mol V 4+ Ti 3+ V 4+ Si 3+ “Support” metal atom is reduced Ce 3+ V 4+ Vanadium atom is reduced

9. Conclusions Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 9 1)IRPD 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 CeO 2 in supported catalysts.

10. Acknowledgments Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 10 Fritz-Haber Institute: Collaborators: Staff at FELIX (FOM Institute Rijnhuizen, Netherlands) for assistance Financial support: Alexander von Humboldt Foundation European Community's Seventh Framework Programme Gerard Meijer Torsten Wende Nadja Heine Knut R. Asmis Peter Lievens, Pieterjan Claes Soumen Bhattacharyy (Katholieke Universiteit Leuven) Joachim Sauer, Marek Sierka (Humboldt University)

11. Gas-phase IR spectra of VO 1-3 + and V 2 O 2-6 + Asmis et al. J. Chem. Phys. 120, 6461 (2004). Determination of Scale Factor