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