Spectroscopic study of carbon monoxide adsorption on cobalt(II) oxide-magnesium oxide solid solutions. 2. Carbon monoxide adsorption on isolated cobalt ions located on edges and steps

Abstract

The room-temperature surface chemistry of diluted MgO-CoO solid solutions toward CO is totally accounted for by the selective adsorption of CO on edges and steps whereby the Mg/sup 2 +/, Co/sup 2 +/ and O/sup 2 -/ coordinately unsaturated ions primarily react as O/sub 2//sup -/Mg/sup 2 +/O and/or O/sup 2 -/Co/sup 2 +/O/sup 2 -/ triplets to form C/sub 2/O/sub 2//sup 2 -/ (ketenic-like) and ((CO/sub 2/)/sub 2/CoCO)/sup 2 -/ (carbenoid-carbonylic) species whose relative concentrations depends upon the cobalt oxide mole fraction. Besides these species, also Mg/sup 2 +/-CO (sigma-bonded) and Co/sup 2 +/(CO/sub 3/) (sigma-..pi..-bonded) complexes are contemporarily detected. The simultaneous presence in fixed ratios of both Co/sup 2 +/, Mg/sup 2 +/ and (O/sup 2 -/Mg/sup 2 +/O/sup 2 -/), (O/sup 2 -/Co/sup 2 +/O/sup 2 -/) reactive ions and groupings of ions in the same surface regions is considered as a fingerprint manifestation of the edge chemistry and has been interpreted on the basis of a simplified geometric (unrelaxed) model of the edge regions. The vibrational assignments of all the surface structures have been made on the basis of a complete set of /sup 12/CO/sup 13/CO isotopic substitution experiments.