Bebensee, F.

Buchholz, M.

Nefedov, A.

Weidler, P.G.

Wöll, C.

English

Weidler, P. G.

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association • dielectric surfaces: both s- and p-polarized light couple to adsorbate vibrations. • Reduction in reflectivity (positive bands), but also to an enhancement of reflectivity (negative bands). • s-polarized light: bands will always be negative • p-polarized light: bands can be negative or positive depending on the incidence angle θ and the refractive index n of the substrate.  Institute of Functional Interfaces, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein – Leopoldshafen Maria Buchholz, Peter G. Weidler, Fabian Bebensee, Alexei Nefedov, Christof Wöll Institute of Functional Interfaces Helmholtz Research School „Energy-related catalysis“ References [1]      Y. Wang, R. Kováčik, B. Meyer, K. Kotsis, D. Stodt, V. Staemmler, H. Qiu, F. Traeger, D. Langenberg, M. Muhler, C. Wöll, Angew. Chem.Int. Ed. 2007, 5624-5627. [2]      H. Noei, H. Qiu, Y. Wang, M. Muhler, C. Wöll, ChemPhysChem 2010, 3604-3607. [3]      M. Buchholz, P. G. Weidler, F. Bebensee, A. Nefedov, C. Wöll, „Carbon dioxide on ZnO (10-10): Tridentate carbonate orientation proved by infrared reflection            absorption spectroscopy”, Phys. Chem. Chem. Phys. 2013, DOI: 10.1039/C3CP54643H.    • Transmission measurements on powder samples and reflection measurements on flat samples are possible • Cooling to 100 K (LN2), in IR- chamber to 30 K (LHe), heating to 1300 K UHV-IR/XPS-chamber at IFG „THEO“. ZnO (1010 )single crystal  on sample holder. Preparation Sputtering: Ar 1·10-6 mbar, 1 kV, 6 mA Annealing: 800 K Check quality with LEED and/or XPS  CO2-dosing directly in IR-chamber @ 110 K LEED: (2x1) – Phase of CO2 on ZnO (1010 ) 540,0 535,5 531,0 526,5 522,0530.75  Binding energy [eV]O 1sRT  Intensity [cps] 1026,0 1022,2 1018,4 1014,61021.8  Binding energy [eV]Zn 2p3/2RT  Intensity Carbon dioxide on ZnO (1010)  The analysis of azimuth- and polarisation dependences allow us to get the information about the adsorption geometry of adsorbates on the oxide surface.  Such knowledge will allow to improve the real catalyst, e.g the structure and the particle size.           . Phase diagram of CO2 on ZnO (1010)[1] Reflectivity calculation Calculated spectra of possible configurations: Comparison: Calculation vs. Experiment Conclusion Motivation • ZnO (1010):Lowest energy facet of ZnO and most dominant on particles  Catalyst:  ZnO (till 1960)   Cu/ZnO(/Al2O3) today  CO   +  2H2     CH3OH ΔE= - 92 kJ/mol CO2  +  3H2    CH3OH + H2O  ΔE= - 50 kJ/mol Production: 30 Mio  tons per year (2000) 1 cm 100 nm  XPS: ZnO (1010 ) Heterogeneous catalysis refers to the form of catalysis where the phase of the catalyst differs from that of the reactants. Most of the heterogeneous catalysts are solids and the great majority of reactants are gases or liquids.   • One or more of the reactants are  adsorbed on to the surface of the catalyst at active sites. These active sites are mainly on the surface. The investigation of the interaction between the adsorbed species and the substrate is therefore from great interest.   • The surface science approach is using model systems to simplify these complex systems.   • Ultra-high vacuum is used, because there is no contamination by adsorption of gases from the air, and so the pure reaction between the catalyst and the reactant can be studied.  

Infrared reflection absrption scpectroscopy on metal oxide single crystals

https://publikationen.bibliothek.kit.edu/220095222/3816519

Infrared reflection absrption scpectroscopy on metal oxide single crystals

Abstract

Similar works

Full text

Available Versions

KITopen