Ethanol steam reforming over Co-based catalysts: Investigation of cobalt coordination environment under reaction conditions

The transformations and state of cobalt species during steam reforming of ethanol were investigated over Co/CeO 2 catalysts pretreated with oxidation (O) and reduction (R) steps. Both catalysts were found to transform in situ to the same active phase under reaction conditions, exhibiting both CoO and Co 0 species at steady state. The reforming performance of the two catalysts also converged to the same level, giving similar product yields. [Display omitted] ► Ethanol steam reforming over Co/CeO 2 catalysts was studied. ► Coordination environment of Co was examined using in situ and controlled-atmosphere techniques. ► Catalysts converged to similar oxidation states and performance levels regardless of pretreatment. ► Active catalysts were found to be comprised of both CoO and Co 0 species. The transformations and the state of cobalt species during steam reforming of ethanol over Co/CeO 2 were investigated using in situ X-ray diffraction, controlled-atmosphere X-ray absorption fine structure, and X-ray photoelectron spectroscopy as well as steady state activity measurements. The catalyst was pretreated under an oxidizing or reducing atmosphere prior to characterization and activity testing to yield a Co 3O 4-rich or a Co 0-rich surface, respectively. While Co 3O 4 was found to be inactive for ethanol steam reforming, gradual activation of the oxidation-pretreated catalyst with temperature through reduction in Co 3O 4 took place under reaction conditions, and, over the activated catalyst, a mixture of both CoO and metallic Co were observed. Over the reduction-pretreated catalyst, metallic Co was partially oxidized to CoO during steam reforming of ethanol. The extent of cobalt reduction was observed to be independent of the initial state of the metal on the catalyst surface, and cobalt phase had the same composition under reaction above 450 °C.