Oxidation states of active catalytic centers in ethanol steam reforming reaction on ceria based Rh promoted Co catalysts: An XPS study

• Rh promoter enhances the reducibility of Co on ceria.
• In the presence of Rh the H2 selectivity is higher in SRE reaction.
• It is assumed that both metallic and oxidized Co play an important role in SRE.
• Strongly bonded carbide species in the case of Co/CeO2 catalyst was detected, which was absent in the presence of Rh.

X-ray photoelectron spectroscopic (XPS) investigations were carried out to study the oxidation states of CeO2 and CeO2 supported Co–Rh catalysts during the temperature programmed stream reforming of ethanol reaction (SRE). Gas chromatography also was used to analyze the product composition. An initial re-oxidation of the pre-reduced catalysts was observed by water reactant and our results revealed a tendency of the oxidized monometallic catalysts to promote aldol condensation-type reactions. It was found that Rh enhances the reduction of Co during the pretreatment, and the highest H2 selectivity was obtained with the bimetallic catalyst in SRE reaction. Moreover, acetone formation was negligible on this sample. Enhanced CC bond scission and hydrogen production were detected from 650 K. In contrast to pure ethanol decomposition, during the EtOH + H2O reaction minor but important changes could be detected on the Ce 3d spectra. It was concluded that the accumulation of strongly bonded carbide species in the case of Co/CeO2 catalyst can contribute to the decreasing activity. This type of carbon was absent in the presence of a trace amounts of Rh, therefore the catalyst was more stable.

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