Infrared Study of Carbon Monoxide Adsorption on Calcium and Strontium Oxides

Abstract

CO adsorption on CaO and SrO takes place, as on MgO, via a disproportionation reaction leading to both surface carbonates and unusual surface species with a complex vibrational spectrum in the low-frequency range. These are thought to be negatively charged CO polymers, the simplest ones being (CO)2–2. A strong electrostatic interaction between negative species and surface cations accounts for the marked dependence of the infrared signal on the lattice parameter of the solids. The increasing basicity along the series MgO, CaO, SrO causes: (i) a marked increase in the total adsorptive capacity; (ii) an increase in the relative population of polymers with respect to dimers; (iii) an increase in the importance of a Boudouart-like reaction upon desorption.