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 24 th abundance of the elements in the Earth’s crust 3.Voisey Bay --- One of the Richest Ni Mine in the World 28 Ni (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 CH 2 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 First Character: Orientation of Carboxylic acid group 0º0º Cis Trans 180º

Second Character: Orientation of hydroxyl group 180º 0º0º PA monomers transcis

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 Diffraction Auger 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: Principle: ΔE = h  = E impact – E scattered Active Inactive Selection Rules:

Adsorption geometries of organic acids on metal

PPA/Ni(100) 300 K δ s (COO) 640 cm -1 γ(CH 3 )1050 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )2910 cm -1

PPA/Ni(100) 450 K ν (NiO)405 cm -1 δ s (COO)640 cm -1 δ(CH) in acetylide (-C≡CH) 785 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )2910 cm -1 Decomposition of adsorbed PPA Ref: T. Yuzawa, et al., J. Mol. Struct (1997) 307 TPD PPA/Ni(110)

PPA/Ni(100) 550 K ν(CO) at bridge site 1805 cm -1 δ s (COO)640 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )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 >CH 2 to >C=O PA

PA/Ni(100) 300 K ν(C=O)1710 cm -1 γ(C=O), γ(CH 3 )640 cm -1 γ(CH 3 )1050 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )2955 cm -1

Na Pyruvate v.s. PA/Al 2 O 3 S.S. Tavale, et al., Acta. Cryst. 14 (1961) 1281 (CH 3 COCOO)NaPA/Al 2 O 3 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(CH 3 )640 cm -1 γ(COO)780 cm -1 γ(CH 3 )1050 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )2910 cm -1 Decomposition above 400 K.

PA/Ni(100) 575 K ν(CO) at bridge site 1835 cm -1 ν (NiO)410 cm -1 γ(C=O), γ(CH 3 )640 cm -1 γ(COO)780 cm -1 δ as (CH 3 ), ν s (COO)1405 cm -1 ν(CH 2 ), ν(CH 3 )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