Flexible Single-Atom Cesium Sites on Amorphous MgO Nano-Cushions for Enhanced CO₂-Involved Multi-Step Reactions

Single atomic sites (SAs) face challenges in catalyzing complex chemical processes involving multiple intermediates due to rigid coordination environments, steric hindrances, and limited activation behaviors. Herein, an alloying-mediated element repartition method is developed to synthesize flexible cesium single-atom catalysts, anchoring Cs single sites on precisely controlled amorphous-MgO/crystalline NbC hetero-phase nano-supports. The amorphousMgO(a-MgO) equipped Cs₁-a-MgO/NbC achieves 91% yield in the cyclization of CO₂ with 2-aminobenzonitrile within a complex gas-liquid-solid triphasic system, outperforming its counterpart fabricated with rigid crystalline MgO, Cs₁-c-MgO/NbC catalyst (only a yield of 23%). The Cs₁-a-MgO/NbC shows excellent tolerance to various functional groups in sustainable catalysis, especially removing the traditional requirement for high-pressure conditions and additives. Operando spectroscopic characterizations and theoretical calculations demonstrate that sandwich-structural Cs₁-a-MgO/NbC enhances the consecutive activation through vertically adsorbed configurations of intermediates during the C-N coupling and N-heterocyclic ring formation. Cs SAs supported by a-MgO nano-cushions allow for adaptability to the dynamic transformations of multiple intermediates via tensile Cs-O and compressive Mg─O bonds, ultimately reducing the energy barriers of critical rearrangement and isomerization steps. This study provides valuable insights into designing flexible SACs to overcome the limitations of rigid support interfaces, thereby enhancing performance toward multi-intermediate conversion in heterogeneous catalytic transformations.