BF3 adsorption on alpha-Cr2O3 (10(1)over-bar-2): Probing the Lewis basicity of surface oxygen anions

Acid/base characterizations of metal oxide surfaces are used often to expla in their catalytic behavior. BF3, a strong Lewis acid, is used in this inve stigation as a probe molecule to interrogate the basicity of well-defined C r2O3 (10 (1) over bar2) surfaces. BF3 clearly probes differences in oxide i ons of different coordination on Cr2O3 (10 (1) over bar2). The heat of adso rption of BF3 shows that terminal chromyl oxygens are stronger Lewis bases than three-coordinate oxygen anions on the nearly stoichiometric surface. T he trends in basicity found with BF3 are the opposite of those found from t he heat of adsorption Of CO2, a,common probe molecule used to investigate t he basicity of oxide surfaces. The use of BF3 as a probe molecule is compli cated by some dissociation and the,slow build up of surface boron and fluor ine during consecutive thermal desorption runs.