Adsorption of CO2 on the perovskite-type oxide LaCoO3

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 O2– ions and O2 adsorbs on surface metal ions.