Tuning Lattice Oxygen of Fe-OMS-2 Oxygen Carriers for Chemical Looping Oxidative Dehydrogenation of Ethylbenzene

Chemical looping oxidative dehydrogenation of ethylbenzene to styrene is a key route to achieve its green and low-carbon production, and oxygen carriers with high activity and stability are the core of the industrialization of this process. This study investigated the regulation mechanism of hydrogen reduction pretreatment on the catalytic performance of Fe-OMS-2 oxygen carriers at 350 ℃. Combined with multi-dimensional characterization and activity tests, the structure-activity relationship was clarified. The results showed that hydrogen reduction could stepwise regulate the Mn valence state (Mn⁴⁺→Mn³⁺→Mn²⁺), among which Mn³⁺ was the core active species, and its lattice oxygen could efficiently activate the C-H bond of ethylbenzene and inhibit deep oxidation. Fe³⁺ stabilized the carrier by forming a Mn-O-Fe structure and promoted the directional reduction of Mn⁴⁺ to Mn³⁺. The Fe-OMS-2 reduced for 30 min exhibited the optimal performance: the ethylbenzene conversion rate was 71.7% and the styrene selectivity was 93.5% at 350 ℃, and it maintained stable performance in 40 redox cycles with a carbon deposition amount of only 1.5 wt%. This study reveals the regulation mechanism of hydrogen reduction and the synergistic stabilization effect of Fe³⁺, and proposes an oxygen storage-catalysis coupling mechanism for Fe-OMS-2 catalyzed chemical looping oxidative dehydrogenation of ethylbenzene, providing experimental and theoretical support for the design and modification of low-temperature, high-efficiency and stable oxygen carriers for chemical looping alkylarene oxidative dehydrogenation.