Orbital symmetry matching-mediated synergistic N2/CO2 activation on Cu-Co3O4 for photocatalytic urea synthesis

Cu optimizes Co 3 O 4 d-orbital occupancy for symmetry-matched interactions with N 2 and CO 2 . • Cu-Co 3 O 4 reduces C − N coupling barrier from 2.34 to 1.19 eV. • Cu-Co 3 O 4 exhibits superior performance, ranking among the highest reported for photocatalytic urea synthesis. Photocatalytic CO 2 /N 2 co-reduction to urea is a green route for carbon‑nitrogen cycle closure, yet it is severely limited by the disparate orbital symmetry requirements of CO 2 /N 2 that impede synergistic activation on a single catalyst. Herein, Co 3 O 4 is doped with Fe/Cu/Ni to tailor the d -orbital configuration of its active sites, and Cu-Co 3 O 4 emerges as the optimal catalyst. It delivers a high urea yield of 25 μmol g −1  h −1 and a solar-to-urea conversion efficiency of nearly 0.035%, which ranks among the top efficiencies for photocatalytic urea synthesis. In situ diffuse reflectance infrared Fourier transform spectroscopy identifies *N 2 CO as the key reaction intermediate, while projected density of states calculations reveal that Cu 2+ ( d 9 ) optimizes d orbital occupation of catalyst to realize symmetry-matched adsorption of CO 2 /N 2 and strengthen orbital coupling. Density functional theory calculations further demonstrate that *N 2 CO formation is the rate-limiting step for urea synthesis, with Cu-Co 3 O 4 lowering the C − N coupling barrier to 1.19 eV (vs. 2.34 eV for pristine Co 3 O 4 ). This work establishes orbital symmetry matching between the d -orbitals of catalytically active sites and the π orbitals of reactants as a critical determinant for the selectivity of multi-molecule co-reduction reactions, thereby providing a general design principle for the development of high-performance photocatalysts. A Cu-doped Co 3 O 4 photocatalyst is rationally engineered, where incorporated Cu 2+ ( d 9 ) optimizes the occupation of active d xy / d xz orbitals in Co 3 O 4 , enabling symmetry-matched interactions with CO 2 and N 2 and reducing the C − N coupling barrier. This catalyst achieves a high urea yield of 25 μmol g −1  h −1 and a solar-to-urea conversion efficiency of ~0.035%, ranking among the top-performing systems for photocatalytic urea synthesis to date. Download: Download high-res image (115KB) Download: Download full-size image