IR spectroscopy study of CO adsorption and of the interaction between CO 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 identified: CO adsorbed on cobalt ions of different oxidation state, CO on metallic cobalt and polycarbonyls. Three species were distinguished which 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+), hydrocarbonyl (Co drop HCO) and polycarbonyl [Co(CO)n]. The thermal stability and reactivity to hydrogen of the various species were studied and CO-Co0 was found to be the most stable.