MOF-Derived SiO2 Confinement Strategy for Regenerable CrO x Catalysts in Moderate-Temperature Chemical Looping Oxidative Dehydrogenation of Ethylbenzene

Abstract High-loading chromium oxide catalysts are attractive for the dehydrogenation of ethylbenzene (EB) to styrene (ST), but the migration, aggregation, and irreversible restructuring of Cr species during high-temperature calcination and reaction often reduce active-site accessibility and accelerate catalyst deactivation. Herein, we report a reverse double-solvent strategy to construct a shape-preserving mesoporous SiO2 framework within a Cr-MOF precursor, yielding a Cr@Si-6 catalyst in which Cr3+-rich nanoscale Cr2O3 domains and highly dispersed chromate-like Cr6+ species are stabilized within a silica cage-like network. This architecture integrates three complementary structural features: the homogeneous Cr distribution inherited from the MOF precursor, physical confinement by the mesoporous SiO2 framework, and chemical anchoring with electronic regulation through Cr–O–Si interfacial linkages, thereby reconciling high Cr loading with high dispersion. Structural and spectroscopic characterizations show that the SiO2 skeleton suppresses long-range Cr migration, aggregation, and the development of bulk-like Cr2O3 domains, while Cr–O–Si interfacial coupling regulates the local coordination and electronic environment of the Cr species and strengthens their resistance to reduction-induced restructuring. In the chemical looping oxidative dehydrogenation of ethylbenzene (EB-CL-ODH), lattice oxygen participates in EB conversion during the reduction step, followed by regeneration of the reduced catalyst in a separate O2 oxidation step. Cr@Si-6 achieves 80% EB conversion, 91% ST selectivity, and 73% ST yield at the moderate temperature of 450 °C, outperforming directly calcined Cr-MOF-600 and conventional Cr/SiO2, while maintaining an ST selectivity above 90% with no obvious decay in EB conversion over 40 redox cycles. Postreaction XRD, Raman, TG/DTG, GC–MS/TIC, and SEM/EDS analyses further show that the confined Cr2O3/SiO2 architecture is largely preserved and that reaction-induced carbonaceous and heavy organic deposits can be substantially removed through oxidative regeneration. This work demonstrates that integrating MOF-derived Cr distribution, mesoporous silica confinement, and Cr–O–Si interfacial regulation provides an effective strategy for constructing high-loading, highly dispersed, and regenerable Cr-based oxygen carriers for moderate-temperature EB-CL-ODH.