Impact of the Surface Carbonates on the Interaction between CO and ZnO Nanomaterials

Xinyu Xia 1Jennifer Strunk 1Raoul Naumann 1Yuemin Wang 1,2Christof Woell 2Martin Muhler 1

1. Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetstrasse 150, Bochum 44780, Germany
2. Physical Chemistry, Ruhr-University Bochum, Universitaetstrasse 150, Bochum 44780, Germany

Abstract

The adsorption of CO on ZnO nanomaterials samples after different pretreatment procedures was investigated with microcalorimetry. The interaction between CO and ZnO nanomaterials became much stronger after the adsorption and partial desorption of CO2. On carbonate-free ZnO surfaces, the CO equilibrium coverage is less than 0.1 micro mol/m2 for p = 100 Pa, and the differential heat of adsorption (qdiff) is only 40 kJ/mol for this coverage (at coverage < 0.05 micro mol/m2, qdiff may be extremely high due to the active sites).

After the adsorption sites on ZnO were partly covered by CO2 (after CO2 adsorption, the sample is evacuated at room temperature overnight), the equilibrium coverage for CO reaches 0.8 micro mol/m2 at p = 100 Pa, and qdiff is higher than 60 kJ/mol. The adsorption rate also became faster. This strong adsorption is due to the existence of surface bidentate carbonates on the mostly exposed ZnO (10-10) faces, which increase the Lewis acidity of Zn2+ on this faces, as also shown by TPD and HREELS studies on ZnO (10-10).

Corresponding to similar results for CO adsorption on sulphate-doped TiO2, it can be concluded that these acid anions generally increase the Lewis acidity of the transition metal ions exposed on metal oxides.

Contact: muhler@techem.rub.de

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Presentation: Oral at E-MRS Fall Meeting 2006, Symposium B, by Xinyu Xia
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-08 12:11
Revised:   2009-06-07 00:44
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