Impact of B-site cations of MgX₂O₄ (X=Cr, Fe, Mn) spinels on the chemical looping oxidative dehydrogenation of ethane to ethylene

Chemical looping oxidative dehydrogenation (CL-ODH) provides a multifunctional conversion platform that can take advantage of the selective oxidation of lattice oxygen in oxygen carrier to achieve high-valued ethane to ethylene conversion. In this study, we explored the effect of B-site element in MgX₂O₄ (X=Cr, Fe, or Mn) spinel-type oxygen carriers on the performance of ethane CL-ODH. The properties test and characterization of MgX₂O₄ spinel were tested by fixed bed and H₂-TPR, O₂-TPD, TG, in-situ Raman, SEM, and TEM. The results showed that because MgCr₂O₄ only released a small amount of adsorbed surface oxygen, it tended to catalyze the conversion of ethane to coke and hydrogen. MgFe₂O₄ facilitated the deep oxidation of ethane into CO₂ by providing more surface lattice oxygen. Meanwhile, since a significant amount of bulk lattice oxygen was released by the MgMn₂O₄ oxygen carrier, it could burn hydrogen in a targeted manner to advance the reaction and increased ethylene's selectivity. Thereby, MgMn₂O₄ achieved an ethane conversion of 73.72% with an ethylene selectivity of 81.46%. Furthermore, the MgMn₂O₄ catalyst demonstrated stable reactivity and an ethylene yield of about 62.00% in ethane CL-ODH over the 30 redox cycles. The screening tests indicated that the B-site elements in MgX₂O₄ spinel oxides could significantly influence their ability to supply lattice oxygen, thereby affecting their performance in ethane CL-ODH reaction.