Electronic State Modulation of a Single-Cu Site on a Bimetallically Doped Titanium-Oxo Cluster to Enhance CO₂ Storage

While atomically monodisperse nanostructured materials with controllable heterometal dopants are highly desirable to unravel the structure-catalysis relationships, their controlled synthesis and atomic-level structural determination remain significant challenges. Here, we report on nanosized titanium-oxo clusters featuring two heterometallic sites, Ti₁₀M₂O₈Sal₆(HSal)₂(OCH₃)₁₆(CH₃OH)₄ (denoted as TiM₂; M₂ = MnCu, CaCu, Cu₂, Mn₂, Ca₂; Sal and HSal represent salicylate and 2-hydroxybenzoate, respectively), which were used for catalyzing and photocatalyzing the CO₂/epoxide cycloaddition to synthesize cyclic carbonates. Notably, the valence state of Cu is modulated by Mn in the TiMnCu cluster as Cu exists in the δ+ valence (1 < δ < 2), whereas in TiCu₂ and TiCaCu, Cu is + 2 valence. TiMnCu exhibited the highest catalytic activity and selectivity with 1 atm CO₂, and also effective activity using simulated flue gas. Experiments and density functional theory simulations revealed that CO₂ activation is the rate-determining step, with the reduced valence of Cu promoting CO₂ activation and positioning the adsorbed CO₂ closer to the epoxide, thereby facilitating the cyclization process. Our study underscores that in metal-oxide supports with heterometal centers, the modulation of electronic states by the different heterometals can significantly enhance catalytic performance.