adsorption and reaction of ortho -carborane on pt(111 )
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Adsorption and Reaction of ortho-
Carborane on Pt(111)
David SiapAugust 3, 2006
REU Program
Advisors: Professor Trenary
Aashani Tillekaratne
University of Illinois at Chicago Department of Chemistry
Final Report
ortho-Carborane adsorbed on Pt(111)
■ ortho-Carborane, more commonly o-Carborane
C2H12B10
■ Present on surface of platinum, Miller Index 111
■ Boron Cage Structure
■ 8.3% Hydrogen by mass
Motivations Hydrogen Storage is a key challenge to
realizing a hydrogen economy DOE goal is a viable storage mechanism 9% H2 by mass by
2015 Metal catalyzed release and uptake of hydrogen in complex
hydrides is a promising approach Because boron is one of the lightest elements, boron
hydrides are good candidates for hydrogen storage
Catalytic surface chemistry of BH bonds has never been studied before
Characterize nature of bonding of carborane with Pt(111) Explore thermal evolution of molecule Study various other properties of molecule May lead to optimization of well known techniques using
carborane, such as thin film vapor deposition
Surface Science Methods
Reflection Absorption Infrared Spectroscopy
(RAIRS) If a bond is present it will
produce a “peak”
■ Mass Spectrometry
■ Temperature Programmed Desorption (TPD)
■ X-Ray Photoelectron Spectroscopy
Apparatus Ultra High Vacuum (UHV)
Pressure = 10-11 torr Needed for well-defined surface
conditions
Mass Spectrum of carborane sample at 10-7 torr
XPS of 5 L carborane on Pt(111) surface 1 L =1 x 10-6 torr sec ~1
molecular layer
Mass Spectrum of carborane
Mass (amu)0 20 40 60 80 100 120 140
Carborane peaks
XPS of carborane on Pt(111)
Binding Energy (eV)
200 400 600 800 1000
Photoelectric Intensity
x20CB
0 L C2H12B10
5 L C2H12B10
x20
0 L C2H12B10
RAIRS Thermal Evolution of ortho-Carborane on Pt(111)
InSb DetectorWavenumbers 1880-4000
RAIRS spectra as a function of temperature
Wavenumber (cm-1)
2400 2600 2800 3000 3200
2L C2H12B10 90 K
150 K
200 K
250 K
300 K
400 K
R R
30872638
2519
2507
2507
2626
2606
.003
2584
90 K molecular adsorption No reaction 90-250 K New surface species with BH
bonds at 300 K Loss of all BH bonds by 400 K
RAIR SPECTRA OF ortho-CARBORANE
AS FUNCTION OF EXPOSURE
2400 2600 2800
R R
WAVELENGTH[cm-1
]
6.0 L 90K
8.0 L 90K2586
2612
2638
4.0 L 90K
1 L 90K
1.5 L 90K
2.0 L 90K
0.5 L 90K
0.1 L 90K
Similar Intensity of BH bonds indicate
formation of monolayer at 1.5 L
TPD (Temperature Programmed Desorption)
s
294
130485
TPD of H2
Temp (K)200 400 600 800 1000
Desorption Rate
H2 TPD of 2 L C2H12B10
294
Supports IR data, consistent with shift observed at 300 K, as well as thermal stability to 250 K
Conclusions
ortho-Carborane is thermally stable on Pt(111) through 250 K
Chemical reaction at 300 K is indicated by a red shift, as well as a decrease in intensity at 300 K. This is supported by TPD results
ortho-Carborane forms a monolayer on Pt(111) at about a 1.5 L exposure
BH bonds broken at 400 K CH bonds broken at 300 K Pt(111) catalyzes thermal decomposition of
carborane
Future Directions
Fully Analyze Results Analyze MCT results for information on BB bonds Explain Lack of BH bonds after introduction of H2 after
annealing to 300 K Determine if D2 exchange is really what is occuring at
250 K Repeat Experiments Under Optimized Conditions Explore Avenues Not Possible with Current
Apparatus, more TPD and XPS
Acknowledgements•NSF
•DoD
•REU Site University of Illinois at Chicago
Entire Trenary Group
•Professor Trenary
•Aashani Tillekaratne
•Kumudu Mudiyanselage
•James Jones
•Dr. Rongping Deng
•Dr. Amy Asunskis
•Walter Kondratko
•Tapa Jash
•Danny Zavitz
•Dr. Eldad Herceg
References
P. Atkins and L. Jones. Chemistry. Molecules, Matter and Change, 3rdEd. W.H. Freeman, New York, 1997, Mass Spectrometry.
Leites, L.A. Chemical Reviews, 1991, 279
Leites, L.A.; Bukalov. S.S. Journal of Raman Spectroscopy, 7, 1978, 235
Baughman, Ray H. Journal of Chemical Physics, 53, 1970, 3773
Leffler, A.J.;Alexander,M.N. and Sagalyn, P.L.;Walker, N. Journal of Chemical Physics, 63, 1975, 3971
Trenary, M; Annu Rev Phys Chem, 51, 2000, 381
Trenary, M; Reversible Dehydrogenation of Boron Nanoclusters (Proposal to Department of Energy)
Zeng, Hong; Byun, Dongjin; Zhang, Jiandi; Vidali, G.; Onellion, M.; Dowben, P.A.; Surface Science, 313, 1994, 239
Riviere, J.C. Practical Surface Analysis (Second Edition), John Wiley and Sons Ltd, 1990
National Energy Policy, Report of the National Energy Policy Development Group, May 2001
Basic Research Needs for the Hydrogen Economy, Report of the Basic Energy Sciences Workshop on Hydrogen Production, Storage, and Use, May 2003
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