IR SPECTROSCOPY STUDY OF CO ADSORPTION AND OF THE INTERACTION BETWEENCO AND HYDROGEN ON ALUMINA-SUPPORTED COBALT

IR spectroscopy was used to study CO adsorption on two samples of 5%Co /Al2O3. By variation of sample pretreatment, CO pressure, contact time and mode of hydrogen coadsorption, several surface species were ident ified: CO adsorbed on cobalt ions of different oxidation state, CO on metallic cobalt and polycarbonyls. Three species were distinguished wh ich gave rise to bands in the 2050-2060 cm-1 region and could coexist on the catalyst, depending on the experimental conditions: CO linearly adsorbed on Co atoms with partial positive charge (Co delta+), hydroc arbonyl (Co drop HCO) and polycarbonyl [Co(CO)n]. The thermal stabilit y and reactivity to hydrogen of the various species were studied and C O-Co0 was found to be the most stable.