surface chemistry of propionic acid and pyruvic acid on ni(100) xiang yang department of chemistry...
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Surface Chemistry of propionic acid and pyruvic acid
on Ni(100)
Xiang Yang
Department of Chemistry
University of Waterloo, Waterloo, Ontario, Canada
?NICKEL
1.Inexpensive catalyst
2.Ranked 24th abundance of the elements in the Earth’s crust
3.Voisey Bay--- One of the Richest Ni Mine in the World
28
Ni58.6934(2)
Nickel(100)
DISTANCE: Ni-Ni =2.49 Angstroms for 2-fold Bridge
Far Ni-Ni = 3.52 Angstroms for 4-fold Bridge
Motivation -- 1
• No direct evidence on the bonding of PPA with Ni(100), our study will focus on the bonding between PPA and Ni(100).
• Extending the database of the adsorption of carboxylic acids on Ni(100).
• Good reference for the adsorption study of PA on Ni(100)
• The effects of replacement the CH2 group in PPA with the keto group in PA on the adsorption on Ni(100)
Motivation -- 2
Everything Looks Good
Let’s Go For It
Trouble !!!
Tasks of the thesis
• Determination of the stable conformations of PA monomers
• Investigate the adsorption of PPA and PA on Ni(100) by EELS
• Conclusion & Outlook
PA monomers - - 1
First Character: Orientation of Carboxylic acid group
0º
CisTrans
180º
Second Character: Orientation of hydroxyl group
180º0º
PA monomers - - 2
trans cis
Third Character: Orientation of methyl group
eclipsed and staggered
Total possible conformers: 2*2*2 = 8
Stability vs. Total Energy (<< 0)
Stability vs. Vibrational Frequencies
Imaginary Frequencies
Energy
stability
•E (Staggered Structures) >> E (eclipsed structure)
•All Staggered Structures have imaginary frequencies.
E
Cte Tte
Cce
Tce
Imaginary Frequencies.
PA radical
Tasks of the thesis
• Determination of the stable conformations of PA monomers
• Investigate the adsorption of PPA and PA on Ni(100) by EELS
• Conclusion & Outlook
Low Energy Electron DiffractionAuger Electron Spectroscopy
Electron Energy Loss Spectroscopy
Temperature Programmed Desorption
Ion Gun
Electron gun
EELS
H. Yu, PhD thesis, 1998
Vibrational Electron Energy Loss Spectroscopy
From: http://www.chembio.uoguelph.ca/educmat/chm729/eels/eels0.htm
Principle:
ΔE = h = E impact – E scatteredActive Inactive
Selection Rules:
Adsorption geometries of organic acids on metal
PPA/Ni(100)300 K
δs(COO)640 cm-1
γ(CH3)1050 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2910 cm-1
PPA/Ni(100)450 K
ν (NiO)405 cm-1
δs(COO)640 cm-1
δ(CH) in acetylide (-C≡CH) 785 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2910 cm-1
Decomposition of adsorbed PPARef: T. Yuzawa, et al., J. Mol. Struct. 413- 414 (1997) 307
TPDPPA/Ni(110)
PPA/Ni(100)550 K
ν(CO) at bridge site1805 cm-1
δs(COO)640 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2910 cm-1
Conclusions:
1. Dehydrogenation
2. Bidentate or Bridge mode
3. Decomposition above 400 K
4. Decompose to CO above 550 K
5. Decompose to C and O above 600 K
PPA
From >CH2 to >C=O
PA
PA/Ni(100)300 K
ν(C=O)1710 cm-1
γ(C=O), γ(CH3)640 cm-1
γ(CH3)1050 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2955 cm-1
Na Pyruvate v.s. PA/Al2O3
S.S. Tavale, et al., Acta. Cryst. 14 (1961) 1281
(CH3COCOO)Na PA/Al2O3
S. Devdas, et al., Surf. Sci. 326 (1995) 327
Possible adsorption Configurations
PA/Ni(100)450 K
ν(C=O)1710 cm-1
ν (NiO)410 cm-1
γ(C=O), γ(CH3)640 cm-1
γ(COO)780 cm-1
γ(CH3)1050 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2910 cm-1
Decomposition above 400 K.
PA/Ni(100)575 K
ν(CO) at bridge site1835 cm-1
ν (NiO)410 cm-1
γ(C=O), γ(CH3)640 cm-1
γ(COO)780 cm-1
δas(CH3), νs(COO) 1405 cm-1
ν(CH2), ν(CH3)2910 cm-1
Conclusions:
1. Dehydrogenation
2. Bidentate and 5-member chelate mode
3. Decomposition above 400 K
4. Decompose to CO above 575 K
5. Decompose to C and O above 600 K
Summary• Pyruvic acid has 3 stable monomer conformers• Both propionic acid and pyruvic acid undergo
dehydrogenation upon adsorption on Ni(100) at room-temperature
• Both propionic acid and pyruvic acid undergo decomposition above 400 K and further decompose to CO above 550 K and C or O above 600 K.
Outlook• Temperature Programmed Desorption
• Modified Ni surfaces (purity gap)
• High pressure reaction cell (pressure gap)
• Computational work on larger Ni cluster and Ni surface.
Acknowledgements
• Supervisor ---- Prof. Tong Leung
• All group members
• Advisory Committee members
• Natural Sciences and Engineering Research Council of Canada