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

The transformations and the state of cobalt species during steam reforming of ethanol over Co/CeO2 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 Co3O4-rich or a Co0-rich surface, respectively. While Co3O4 was found to be inactive for ethanol steam reforming, gradual activation of the oxidation-pretreated catalyst with temperature through reduction in Co3O4 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.