Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 43: Oxides and Insulators: Adsorption II

O 43.1: Vortrag

Mittwoch, 28. März 2007, 15:45–16:00, H42

Coadsorption of CO and CO₂ on zinc oxide: from single crystal to powder particles — •Henshan Qiu¹, Yuemin Wang^1,2, Xinyu Xia², Martin Muhler², and Christof Wöll¹ — ¹Lehrstuhl für Physikalische Chemie I, Ruhr-Universität Bochum, D-44780 Bochum — ²Lehrstuhl für Technische Chemie, Ruhr-Universität Bochum, D-44780 Bochum

The interaction of CO and CO₂ with ZnO surfaces was studied using high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and microcalorimetry. Exposing the non-polar ZnO(10-10) surface to CO₂ results in the formation of an unusual tridentate carbonate species with the two carbon dioxide O-atoms being almost equivalently bound to two different Zn surface atoms. Two stable carbonate phases are found: a full (1x1) monolayer with a binding energy of 52 kJ/mol and a half monolayer with (2x1) structure and binding energy of 86 kJ/mol. With regard to CO adsorption on ZnO(10-10), the precoverage of CO₂ leads to an increase of CO binding energy from 30 to 55 kJ/mol and a slight blue-shift of the ν(C-O) peak by 1 meV. The amount of adsorbed CO increases first due to the existence of surfaces carbonates and then decreases because of site blocking effect. The co-adsorbed CO₂ leads also to stronger adsorption of CO on ZnO powder particles, giving rise to an adsorption energy distribution between 45-65 kJ/mol. The increase of interaction strength is attributed to the formation of tridentate carbonates on the most exposed ZnO(10-10) surfaces, which increases the Lewis acidity of the surface.