Selective N-Formylation of amines using CO2 and H2 over NiCo Bimetallic Catalysts with Tunable Metal-Metal Hydroxide Species

The efficient conversion of carbon dioxide (CO₂) into value-added chemicals is crucial for sustainable development. Herein, we designed and synthesized a series of NiCo/NiCo-OH@NC-T catalysts via a hydrothermal-pyrolysis method for the N-formylation of amines with CO₂ and H₂. The relationship between their structure, activity, and the reaction mechanism was systematically investigated. Comprehensive characterization revealed that the pyrolysis temperature critically modulates the surface composition, finely tuning the ratio between metallic (Ni/Co) and hydroxide NiCo-OH species. The optimal NiCo/NiCo-OH@NC-450 catalyst, which features a balanced metal-hydroxide species and strong bimetallic synergy, demonstrated exceptional performance in the model reaction with morpholine, achieving complete conversion and 96% selectivity. A distinct volcano-shaped correlation was observed between catalytic activity and pyrolysis temperature, which is directly linked to the catalyst's hydrogen activation capacity and CO₂ adsorption strength. Mechanistic studies, including in situ DRIFTS, identified a surface-adsorbed formate (HCOO*) as the pivotal C1 intermediate, providing direct evidence for the reaction pathway. This work underscores the significance of engineering multifunctional interfaces in bifunctional catalysts for efficient CO₂ hydrogenation and provides fundamental insights into the underlying structure-activity relationship.