CO2 adsorption on alpha-Cr2O3 (1012) surfaces

The basicity of oxide surfaces is often associated with surface lattice oxy gen anions. CO2 is the standard probe molecule for investigating surface ba sicity, but limited information is available in the surface science literat ure concerning its interaction with well-defined (single crystal) oxide sur faces. On stoichiometric. Cr2O3 (10 (1) over bar2), CO2 interacts with cati on/anion site pairs to form bidentate carbonates that are stable at room te mperature. This site pair consists of five-coordinate Cr3+ cations and thre e-coordinate O2- anions on the clean, stoichiometric, nonpolar (10 (1) over bar2) surface. Terminating the surface cations with chromyl oxygen (Cr=O) via dissociative O-2 chemisorption breaks the interaction and gives rise to a weakly bound CO2 moiety, tentatively identified as a "monodentate" CO2 a dsorbate bound to terminal chromyl oxygen sites. Differences in the coordin ation of these species make the heats of adsorption a poor measure of the b asicity of surface oxide ions. Terminating the surface cations with chlorin e adatoms blocks the interaction between CO2 and the surface, and no uptake is observed.