Effects of O₂ and H₂O in the Oxidative Steam-Reforming Reaction of Ethanol on Rh Catalysts

With both real-world catalyst Rh/CeO₂ and model-system Rh(111), we investigated how oxygen and water play effective roles in the oxidative steam-reforming (OSR) reaction of ethanol. The results show that atomic oxygen (O∗) on Rh surfaces enhanced significantly the decomposition probability of ethanol and altered the reaction path from one via cleavage of the C-H_β bond forming an oxametallacycle to another via cleavage of the C-H_α bond forming an acetaldehyde; this alternation highly promoted the production of H₂, along with side products CO, CH₄, and H₂O. The reaction path shifted to acetate intermediates with the oxygen content greater than 0.08 ML, which suppressed the production of H₂ but promoted that of CO₂. The effect of hydroxyl (OH∗) resembled that of O∗, whereas OH∗ further enhanced the reaction probability of ethanol on Rh surfaces precovered with O∗ but slightly affected the reaction path. The intermolecular hydrogen bonding between surface O∗ or OH∗ and ethanol or its fragments accounts for the enhanced reaction probability and the altered reaction path. The mechanistic results yield clues for a rational optimization of the OSR reaction of ethanol, through tuning the quantities of O₂ and H₂O, the production of H₂, and less poisoning carbon species.