FeMTiOx Mixed Metal Oxides (M = Ni, Sn, Co, Mn, Ce) for Chemical Looping-Based Oxidative Dehydrogenation of C₂H₆ and Successive CO₂ Activation

Chemical looping (CL)-based oxidative dehydrogenation (CL-ODH) of ethane (C2H6) and successive CO2 activation to form CO were investigated on FeMTiOx catalysts (M = Ni, Sn, Co, Mn, Ce metal oxide), and a proper reduction extent of active metal oxides was found to be well correlated with C2H6 conversion as well as the amount of oxidized COx formation during the C2H6 activation step. The easily reducible FeCeTiOx showed a higher C2H6 conversion of 19.6% and an ethylene (C2H4) selectivity of 73.4% due to the higher redox property of the CeO2 promoter, which also showed a higher CO2 activation to CO with its productivity of 0.130 mmol/g due to the presence of abundant oxygen vacant sites with smaller crystallite sizes of active metal oxides. The fast oxygen transfer rate and thermal stability of Ce-incorporated FeTiOx were responsible for an enhanced ethylene productivity. The newly formed MnTiO3 phases with coexisting FeTiO3 phases on FeMnTiOx were found to be active sites for the CL-ODH reaction due to an increased number of stable lattice oxygens with the highest C2H4 selectivity of 80%. However, easy reducibility and facile aggregation of NiO and Co3O4 phases on FeNiTiOx and FeCoTiOx revealed a higher selectivity to COx in the range of 18.3–18.9% compared to the optimal FeCeTiOx with a lower COx selectivity of 14.4%. The lower C2H6 conversion on FeSnTiOx was also attributed to the suppressed redox properties of active metal oxides.