Adsorption and Reaction of ortho-carborane on Pt(111) Final Report David Siap August 3, 2006 REU Program Advisors: Professor Trenary Aashani Tillekaratne University of Illinois at Chicago Department of Chemistry
ortho-carborane adsorbed on Pt(111) ortho-carborane, more commonly o-carborane C 2 H 12 B 10 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% H 2 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
Ultra High Vacuum (UHV) Pressure = 10-11 torr Needed for well-defined surface conditions Apparatus M ass Spectrum of carborane Mass Spectrum of carborane sample at 10-7 torr Carborane peaks 0 2 0 4 0 6 0 8 0 1 00 1 20 1 40 Mass (amu) XPS of 5 L carborane on Pt(111) surface 1 L =1 x 10-6 torr sec ~1 molecular layer Photoelectric Intensity B C XPS of carborane on Pt(111) 5 L C2 H 12B 10 x20 0 L C2 H 12B 10 x20 0 L C2 H 12B 10 200 400 600 800 1000 Binding Energy (ev)
RAIRS Thermal Evolution of ortho-carborane on RAIRS spectra as a function of temperature Pt(111) ΔR R 2L C2H12B10 90 K 3087 90 K molecular adsorption 2584 2638 2606 2626 150 K 200 K 250 K No reaction 90-250 K New surface species with BH bonds at 300 K Loss of all BH bonds by 400 K 300 K 2519 2507 2507 400 K.003 2400 2600 2800 3000 3200 Wavenumber (cm -1 ) InSb Detector Wavenumbers 1880-4000
RAIR SPECTRA OF ortho-carborane AS FUNCTION OF EXPOSURE 0.1 L 90K 0.5 L 90K 1 L 90K Δ R R 1.5 L 90K 2.0 L 90K 4.0 L 90K Similar Intensity of BH bonds indicate formation of monolayer at 1.5 L 6.0 L 90K 2586 2612 2638 8.0 L 90K 2400 2600 2800 WAVELENGTH[cm -1 ]
TPD (Temperature Programmed Desorption) TPD of H 2 Desorption Rate 294 294 β = 2Κ/s Supports IR data, consistent with shift observed at 300 K, as well as thermal stability to 250 K 130 485 H 2 TPD of 2 L C2H 12B 10 200 400 600 800 1000 Temp (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 H 2 after annealing to 300 K Determine if D 2 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
NSF Acknowledgements 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
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