Adsorption of CO2 on the perovskite-type oxide LaCoO3

Abstract

Adsorption isotherms and i.r. spectra of CO₂ on the perovskite-type oxide LaCoCO₃ are given. Coverages at 50 mmHg are above half a monolayer. At 195 K the B.E.T. multilayer adsorption isotherm fits the data satisfactorily while at 623–673 K the Freundlich isotherm is obeyed. At lower temperatures (195–373 K) mainly physical adsorption, with a constant isosteric heat of 18.8 kJ mol^–1, takes place. Entropy calculations show this adsorbed species to be in a supermobile state with a vibration perpendicular to the surface at a frequency of 4.2 × 10¹¹ s^–1. At higher temperatures (373–673 K) chemisorption occurs; the heat of adsorption of the adsorbed species at 623–673 K was found to be 33.5 kJ mol^–1 for a coverage of 0.5. At 298 K i.r. bands at 1110, 1070 and 840 cm^–1 were observed. At 423, 573 and 773 K bands were found at 1770, 1635, 1465, 1355, 1105, 1060 and 850 cm^–1, attributed to carbonate species. Coadsorption data show that CO₂ and CO adsorb on the same sites while O₂ adsorbs on a different type of site. It is concluded that CO₂ adsorbs on O^2– ions and O₂ adsorbs on surface metal ions.