Precise Manipulation of Co3+ Spin-State in Co3O4 via Cu doping for efficient CO oxidation

Cu content tunes site occupancy (octahedral or tetrahedral) for active site design. • Cu-Co 3 O 4 -7% induces higher spin Co 3+ , weakens Co–O, boosts O latt reactivity. • Cu-Co 3 O 4 -7% achieves complete CO conversion at 150 °C via O latt -mediated mechanism. • Linking occupancy, spin, bond length to performance for O latt catalyst design. Metal doping represents an effective strategy for modulating the electronic structure of cobalt spinel oxides and tailoring catalytic performance. However, the precise site occupancy of dopants in Co 3 O 4 lattice, octahedral versus tetrahedral, remains a subject of debate, hindering a mechanistic understanding of the promotional role of metal doping. In this study, by adjusting the doping amount of Cu (Cu-Co 3 O 4 -x%, x represents the amount of doped Cu), site-specific incorporation of Cu into either octahedral or tetrahedral sites of Co 3 O 4 was precisely controlled. The resulting Cu-Co 3 O 4 -7% achieves the highest CO oxidation activity under a high gas hourly space velocity. It is revealed that Cu doped in octahedral sites promotes the transition of Co 3+ from low spin to higher spin states. This spin-state transition weakens the Co 3d−O 2p interaction, facilitates lattice oxygen mobility, optimizes CO adsorption, and collectively enhances CO oxidation. This work provides a targeted approach for regulating the Co 3+ spin state and elucidates its critical role in molecular activation processes.