Highly Selective Photocatalytic CO₂ Reduction to C₂H₆ via Nanocluster-Single Atom-Vacancy on Ceria: Synergistic Mechanism and Orbital Effects

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The photocatalytic reduction of CO₂ to high-value C₂ products involves sluggish multiple proton-electron couplings, resulting in low efficiency and selectivity. This study demonstrates that palladium (Pd) single-atom (PdSA)- and Pd nanocluster (PdNCs)-loaded CeO₂ with abundant oxygen vacancies (Ov) synergistically enhance photocatalytic CO₂-to-ethane (C₂H₆) conversion effectively and selectively. The PdSA+NCs/CeO₂ photocatalyst achieves 80.4% electron selectivity for C₂H₆ production with an electron consumption rate of 206.3 μmol gcat⁻¹ h⁻¹ in pure water, representing a 172.4-fold enhancement over pristine CeO₂. PdNCs interact with neighboring PdSA and Ov to form a Fermi level with the continuous characteristics of discrete energy levels, improving the charge distribution in local spatial electric fields. This enhancement favors electron migration from the π to σ orbital of COCO*, promoting C-C coupling. Our findings provide new insights to rationally design synergistic interactions between SA, NCs, and Ov to achieve high selectivity toward C₂ products.