Unraveling defect-modulated active sites in lamellar-stacked molybdenum oxide for atmospheric CO2 cycloaddition

Air-induced self-reduction creates abundant coupled Mo 5+ –oxygen vacancy pairs. • Poisoning experiments identify Lewis acidic Mo ions as the true active centers. • Lamellar-stacked architecture exposes high-density active sites for CO 2 conversion. • The catalyst displays excellent cycling stability and broad substrate adaptability. CO 2 cycloaddition provides a sustainable and atom-economical route for CO 2 utilization, yet the development of high-performance molybdenum-based catalysts is hampered by poorly controllable defect modulation and ambiguous active-site origins. Herein, we report a facile air calcination strategy to fabricate lamellar-stacked defective molybdenum oxide (Mo-MOF-500/2h) from a rod-shaped Mo-MOF precursor. Air-induced pyrolysis enables the in-situ formation of abundant Mo 5+ species along with oxygen vacancies, fundamentally different from the isolated inert oxygen vacancies in conventional MoO 3 . Selective chemical poisoning experiments and kinetic analysis resolve the long-standing controversy regarding active sites in Mo-based cycloaddition catalysis, verifying that Lewis acidic Mo 5+ /Mo 6+ centers rather than surface hydroxyl groups dominate epoxide activation, while adjacent oxygen vacancies modulate paired Mo 5+ centers to lower the apparent activation barrier. As a result, Mo-MOF-500/2h achieves a high carbonate yield of 96% for CO 2 cycloaddition with epichlorohydrin within 6 h at 80 °C under atmospheric CO 2 pressure, accompanied by good substrate adaptability and excellent long-term cycling durability. This work clarifies the morphology–defect–activity correlation of molybdenum oxides and provides feasible guidance for the design of high-efficiency CO 2 fixation catalysts. Download: Download high-res image (221KB) Download: Download full-size image