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 C r2O3(0001) film as well as on samples of polycrystalline alpha-Cr2O3. The C r2O3(0001) film has been grown on the (110) surface of a chromium single cr ystal. Upon CO2 dosage, two chemisorbed and two weakly bound adsorption sta tes are identified. We associate the strongly bound carbon dioxide with car boxylates, bent CO2delta- species adsorbed on top of the chromium ions of t he 'polar' (0001) surface. An assignment to surface carbonate formed upon a dsorption on surface oxygen ions is not compatible with the vibrational dat a. 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: c onsider different modes of coordination elf the CO2 chemisorbates. In parti cular, bidentate carbonate species are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.