The Mechanism of Steam-Ethanol Reforming on Co13/CeO2–x: A DFT Study

In the present work, density functional theory calculations are performed to study mechanisms of ethanol steam reforming reactions on the Co13/CeO2–x model. The related adsorption situations and reaction cycles were clarified. Ethanol will convert into CH3CO species through dehydrogenation steps on the Cox+ site, followed by coupling with hydroxyl from water dissociation on CeO2–x, yielding acetic acid on the interface. The acetic acid will spread to the Co0 site to cleave C–C and then convert to CO2. H2 forms on the Cox+ site. The coke formation is mainly caused by CH accumulation on the Co0 site and could be released by CH oxidation on the Cox+ site. The oxidation state of Co on the surface affects the activity of ESR reactions. A higher oxidized Co site, featured with a lower ensemble size of Co, facilitates recombination reactions (e.g., H2, acetic acid formation, and CH oxidation). On the contrary, a more reduced Co site favors dissociation reactions (e.g., C–C scission). The Cox+ site is the most favorable site for the dehydrogenation of ethanol into CH3CO. CeO2–x will promote H2O dissociation via oxygen vacancy and lattice oxygen. On the hydroxylated CeO2–x surface, mobile O on CeO2–x has a higher tendency of oxidizing Co, while mobile OH is mainly responsible for releasing carbon deposition. In the experiment, keeping a high Co0/Co2+ ratio can gain high proportions of Co0 and Cox+ site, contributing to high ESR activity. Metal–oxide interaction should be strengthened to promote the spread of mobile OH. Enhancing metal–oxide interface formation is essential for CH3COOH formation. The redox property of CeO2 needs to be increased through doping with other elements, contributing to more oxygen vacancies. Adding O2 could help release carbon deposition.