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

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 (Pd_SA)- and Pd nanocluster (Pd_NCs)-loaded CeO₂ with abundant oxygen vacancies (O_v) synergistically enhance photocatalytic CO₂-to-ethane (C₂H₆) conversion effectively and selectively. The Pd_SA+NCs/CeO₂ photocatalyst achieves 80.4% electron selectivity for C₂H₆ production with an electron consumption rate of 206.3 μmol g_cat^-1 h^-1 in pure water, representing a 172.4-fold enhancement over pristine CeO₂. Pd_NCs interact with neighboring Pd_SA and O_v 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 O_v to achieve high selectivity toward C₂ products.