Abstract

The activation of CO2 on clean and hydroxylated ZnO nanoparticles has been studied by ultrahigh vacuum FTIR spectroscopy (UHV-FTIRS). Exposing the clean ZnO powder samples to CO2 at 300 K leads to the formation of a number of carbonate-related bands. A detailed assignment of these bands was carried out using isotope-substitution experiments with C18O2.

On the basis of vibrational and thermal stability data for ZnO single crystal surfaces, a consistent description of the interaction of CO2 with ZnO powder particles can be provided: on the mixed-terminated ZnO(101j0) facets, a tridentate carbonate is formed; on the polar, O-terminated (0001j) facets, a bidentate carbonate species is formed via CO2 activation at oxygen vacancy sites; and additional monodentate or polydentate carbonate species are formed at defect sites such as steps, edges, kinks, and vacancies. The formation of carbonate-related vibrational bands is observed at an exposure temperature as low as 100 K, thus demonstrating the high activity of ZnO nanoparticles with regard to CO2 activation.

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