Synergistic Interplay of Ni Single Atoms and Neighboring Mn ₂ Dual Atoms Enabling Selective Photocatalytic Reduction of CO ₂ to Propane

The photocatalytic conversion of CO₂ and H₂O into long carbon chain products (C_n, n ≥ 3) presents a sustainable strategy for synthesizing high-value fuels and chemicals. However, the synthesis of long carbon chain products under mild conditions still faces great challenges, largely due to sluggish multi-electron/proton transfer kinetics and the thermodynamically unfavorable C₁-C₁ and C₁-C₂ coupling processes. In this study, we developed tri-metal active sites composed of Ni single atoms and Mn₂ dual atoms anchored on NH₂-MIL-125(Ti) (Ni₁/Mn₂-MIL) for synergistic photocatalytic C₃H₈ production. The synthesized Ni₁/Mn₂-MIL catalyst achieved efficient CO₂ photoreduction (CO₂PR) in pure water, yielding 32.2 µmol g^-1 h^-1 of C₃H₈ with 81.3% electron-based selectivity, significantly outperforming Ni₁-MIL and Mn₂-MIL. Remarkably, the catalyst exhibited exceptional stability over 50 cycles without degradation. Integrated experimental and theoretical investigations revealed that the Ni₁ site activates CO₂ to form CO, while the adjacent Mn₂ site promotes the formation of *COCHO intermediates. Strong electronic interactions between Ni₁ and Mn₂ create charge-polarized active sites, which mitigate electrostatic repulsion between C₁ and C₂ intermediates, thereby promoting C-C coupling and subsequent formation of the *CH₂OCOCO intermediates. Consequently, both the selectivity and catalytic efficiency toward C₃H₈ production are significantly enhanced.