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IR spectroscopy was used to study CO adsorption on two samples of By variation of sample 5%Co/Al 2 O 3 . pretreatment, CO pressure, contact time and mode of hydrogen coadsorption, several surface species were identiÐed : CO adsorbed on cobalt ions of di †erent oxidation state, CO on metallic cobalt and polycarbonyls. Three species were distinguished which gave rise to bands in the 2050È2060 cm~1 region and could coexist on the catalyst, depending on the experimental conditions : CO linearly adsorbed on Co atoms with partial positive charge (Cod`), hydrocarbonyl and polycarbonyl The thermal stability and (Co † OE H CO) [Co(CO) n]. reactivity to hydrogen of the various species were studied and COwCo0 was found to be the most stable.

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Two-component Co-Ce samples deposited onto SiO 2 have been prepared, characterized and tested in the reaction of complete n-hexane and CO oxidation. It was established that cerium enhanced the catalytic activity of cobalt in the reaction of n-hexane oxidation, although this depended on the sequence of cobalt and cerium introduction. Co-impregnation of Co and Ce resulted in a close interaction between Co 3 O 4 and CeO 2 leading to more surface oxygen species available and, therefore, a better reactivity.