Interaction of CO with Alpha-Cr2O3 Surface - a FTIR and HRTEM Study

Microcrystals of alpha-Cr2O3 sintered at high temperature are single crystals with a well defined habit. By means of HRTEM and computer graphics techniques the indexes and the structure of the most frequently exposed (0112BAR), (2116BAR) and (1120BAR) faces are determined. The IR spectra of CO adsorbed on them show that the interaction is electrostatic in nature and that also a sigma charge transfer to the substrate may contribute to the detected adsorption-induced blue-shift of the CO frequency. Furthermore a small d-pi overlap contribution (primarly affecting the dynamic polarizability) is present for CO adsorbed on five-fold coordinated Cr3+ sites of the (0112BAR) and (2116BAR) faces.