1. Reactions of unsaturated oxygenates on metal surfaces
Will Medlin
Department of Chemical and Biological Engineering
Colorado Center for Biorefining and Biofuels (C2B2)
University of Colorado
Graduate students: Andrea Loh (MS 07), Clay Horiuchi, Steve Marshall
Funding: National Science Foundation
(collaborative project with John Monnier, Univ. of S. Carolina)

2. Overall objective: Control selectivity in conversions of multifunctional oxygenates
Some probe molecules:
The catalyst: metallic and bimetallic surfaces

3. Reaction pathways for hydrogenation of EpB
n-butyraldehyde
Schaal et al. 2006

4. Selectivity to various products is a sensitive function of surface composition
Control metal catalyst composition (e.g. PtXAgY) using electroless deposition – Monnier and Williams
On supported Pd catalysts, selectivity to C=C products is higher

5. Surface science approaches used to understand EpB reactivity on metal surfaces?
Methods for studies on Pt(111), Pd(111), and Cu(111)
High Resolution Electron Energy Loss Spectroscopy (HREELS)
Temperature Programmed Desorption (TPD)
Density functional theory (DFT)

6. Ring-opening of EpB on Ag(110) results in oxametallacycle formation
2.46
2.29
2.27
2.36 Ag O C1 C2 C3 C4 C1 C3 C2 C4
1.67 O
2.81
2.54
2.44 Ag Ag Ag
Medlin, Barteau, and Vohs, J. Mol. Catal. (2000) 163, 129.
Medlin and Barteau, J. Phys. Chem. B (2001) 105,

7. DFT indicates other C4H6O adsorption structures may be stable on Pd(111) and Pt(111)
oxametallacycle
di-sigma

8. At low temperatures, EpB adsorbs through olefin function
Adsorbed through olefin O
Pt(111)
(C=C) stretch
Di-sigma bonded O
Pt(111)
(di-s C-H) stretch
Loh, Davis, Medlin, JACS 130 (2008) 5507.

9. EpB undergoes ring-opening on Pt(111) by 230 K Pt(111)
C1=O aldehyde
C1-H aldehyde
C1H2, C4H2
C3H
O-C1-C2
C4H2
C3-C4
C2H, C3H 1 2 3 4
Loh, Davis, Medlin, JACS 130 (2008) 5507.

10. Temperature programmed desorption confirms decarbonylation reaction
EpB 1 2 3 4
CrHO 1 2 3 4
At saturation, approximately ¾ of C3 undergoes complete dehydrogenation
Loh, Davis, Medlin, JACS 130 (2008) 5507.

11. Ring-opened EpB intermediate and crotonaldehyde have similar (but not identical) HREEL spectra1 2 3 4
Crotonaldehyde
C4H3 deformations
C4-H2 scissoring
EpB-derived
intermediate
C4-H2 stretching 1 2 3 4
Loh, Davis, Medlin, JACS 130 (2008) 5507.

12. Aldehyde formation predicted in one EpB geometry optimization on Pd(111)
Experimental
HREELS CO
DFT (IR)
Loh, Davis, Medlin, JACS 130 (2008) 5507.

13. HREEL spectra show clear differences between ring-opened EpB on Pt vs
HREEL spectra show clear differences between ring-opened EpB on Pt vs. Pd (111)
Aldehyde formation and decarbonylation clearly observed on both surfaces….
… but intermediate on Pd(111) is likely to be more highly-coordinated, consistent with catalysis studies
Marshall, Horiuchi, Zhang, Medlin, submitted.

14. EpB and Crotonaldehyde on Pd(111) annealed to 250K have nearly identical HREEL spectra3 4
EpB 1 2 3 4
CrHO
Marshall, Horiuchi, Zhang, Medlin, submitted.

15. Reaction pathways for hydrogenation of EpB
n-butyraldehyde
Schaal et al. 2006 15

16. Computational chemistry studies suggest favorable interaction of Cu/Ag with O end of molecule
2.46
2.29
2.27
2.36 Ag O C1 C2 C3 C4 Pt Pt Pt
Schaal, Hyman, Medlin, Monnier, to be submitted.

17. Parallels with adsorption and reaction of 2(5H)-furanone
EpB
2(5H)-furanone
Crotonaldehyde

18. Furanone also undergoes ring-opening and decarbonylation on Pd(111), but at higher temperatures
CO formation begins around 300 K
Furanone monolayer
Multilayers of condensed furanone

19. DFT helps in assigning vibrational modes, suggests furanone adsorbed in tilted configuration through olefin
C=O stretch C1 C4
doop(C-H) C2 C3
C-H stretch

20. TPD confirms decarbonylation and CO2 formation pathways on Pt(111)

21. Conclusions: reactions of unsaturated oxygenates on Pt-group metals
EpB reacts via ring-opening and C-H scission to form a surface aldehyde intermediate on Pt(111) and Pd(111)
Aldehyde formation pathway can be avoided by addition of Ag to surface of Pt
Adsorption and reaction of furanone shows numerous parallels with EpB chemistry, though ring-opening reaction is more activated C1 C2 C3 C4

22. As coverage increases, decomposition is delayed to higher temperatures
High-temp.
C3H6
Low-temp.
Loh, Davis, Medlin, JACS 130 (2008) 5507.