IR investigations of CO2 adsorption on chromia surfaces: Cr2O3 (0001)/Cr(110) versus polycrystalline alpha-Cr2O3

The adsorption of carbon dioxide has been studied on a single-crystalline Cr2O3(0001) film as well as on samples of polycrystalline alpha-Cr2O3. The Cr2O3(0001) film has been grown on the (110) surface of a chromium single crystal. Upon CO2 dosage, two chemisorbed and two weakly bound adsorption states are identified. We associate the strongly bound carbon dioxide with carboxylates, bent CO2delta- species adsorbed on top of the chromium ions of the 'polar' (0001) surface. An assignment to surface carbonate formed upon adsorption on surface oxygen ions is not compatible with the vibrational data. The IR spectra of CO2 chemisorbed on polycrystalline alpha-Cr2O3 differ substantially from the IRAS spectra of the CO2/Cr2O3(0001)/Cr(110) system. As the faces of the microcrystals show mainly non-(0001) termination, we: consider different modes of coordination elf the CO2 chemisorbates. In particular, bidentate carbonate species are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.