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

[(CeO2)(V2O4)]+

Gas-phase model systemVanadium oxide

Supported catalyst

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 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 > SiO2

1) Vanadium oxide catalyst is very important in industry.

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:

[(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, Si

Ce:4f13d14s2

(Ce4+)

V:3d34s2

(V5+)

Ti:3d24s2

(Ti4+)

Si:3d24s2

(Si4+)

cluster source region

- dual laser vaporization- electron ionization- ion spray

high vacuum10-8 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-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 ions

Ion detector

AB+∙Rg AB+ + Rg (Rg = He, Ne)(single photon photodissociation spectra)

Results: Experimental IR Spectra

Ling 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 stretch

terminalO-V-Obackbone

What are these modes?

IR Spectra: Exp. vs Theory

Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 6

Computational:

B3LYP/def-TZVPP

(Turbomole)

[(CeO2)(VO2)]+

The effect of rare-gas is negligible.

Agrees with the experiment.

V2O4+

12

3

45

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

1A•He

CeV 1A

O

[(CeO2)(V2O4)]+ [(Ce2O3)(VO2)]+ [(CeO2)(VO2)]+

Electronic Structures of Ce-V Oxide Clusters

Ce4+ V5+

+

Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 7

[(CeO2)(VO2)]+

[(CeO2)(VO2)2]+

+

[(Ce2O3)(VO2)]+

Fully oxidized Partially oxidized

Ce3+ (4f1)

Ce3+ (4f1)

Ce3+ (4f1)

V5+ spin density

Ce4+ is reduced first, consistent with bulk model study.

Reduction on Different Metal Site in [(MO2)(V2O4)]+

Ling Jiang, Fritz-Haber-Institut Berlin, June 23, 2010 Symposium on Molecular Spectroscopy 8

Relative to V5+, the reducibility of “support” metal atoms:Ce4+ > Ti4+ > Si4+

Relative reactivity of supported VOx: CeO2 > TiO2 > SiO2

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

V4+Ti3+

V4+Si3+

“Support” metal atom is reduced

Ce3+ V4+

Vanadium atom is reduced

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 CeO2 in supported catalysts.

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 HeineKnut R. Asmis

Peter Lievens, Pieterjan ClaesSoumen Bhattacharyy(Katholieke Universiteit Leuven)

Joachim Sauer, Marek Sierka(Humboldt University)

Gas-phase IR spectra of VO1-3+ and V2O2-6

+

Asmis et al. J. Chem. Phys. 120, 6461 (2004).

Determination of Scale Factor