Co and Mo Co-doped Fe₂O₃ for Selective Ethylene Production via Chemical Looping Oxidative Dehydrogenation

In this study, we investigate Co and/or Mo doped Fe₂O₃ (Co_xMo_1–x/Fe₂O₃, x = 0, 0.2, 0.3, 0.4, and 1) as redox catalysts for chemical looping oxidative dehydrogenation (CL-ODH) of ethane. Under the cyclic redox reaction mode, the five as-prepared samples behave differently toward ethane conversion. Among the five redox catalysts, CoFe₂O₄ (x = 1) is highly reactive and tends to overoxidize ethane into CO₂, while Mo/Fe₂O₃ (x = 0) exhibits promising ethylene selectivity but inferior H₂ removal capability. By tuning the molar ratio of Co/(Co + Mo), 87.4% ethylene selectivity at 56.2% ethane conversion can be achieved by the Co_0.3Mo_0.7/Fe₂O₃ (x = 0.3) redox catalyst at 825 °C and 6000 h^–1. C₂H₆-TPR results show that the selectivity of Co_0.3Mo_0.7/Fe₂O₃ alters as the ODH reaction proceeds due to the dynamic change of surface properties of the redox catalyst in the reaction. XPS results indicate that a relatively low Fe content as well as a high Mo content at the near-surface of the redox catalyst is beneficial for its ethylene selectivity in CL-ODH of ethane. DFT calculations reveal that Co cations in the Co_0.3Mo_0.7/Fe₂O₃ structure are responsible for the activity and H₂ combustion capability of the redox catalyst, while Mo plays a key role in tuning the ethylene selectivity.