Dual‐Atom‐Site Sn‐Cu/C 3 N 4 Photocatalyst Selectively Produces Formaldehyde from CO 2 Reduction

The solar‐driven catalytic reduction of CO 2 to value‐added chemicals is under intensive investigation. The reaction pathway via *OCHO intermediate (involving CO 2 adsorbed through O‐binding) usually leads to the two‐electron transfer product of HCOOH. Herein, a single‐atom catalyst with dual‐atom‐sites featuring neighboring Sn(II) and Cu(I) centers embedded in C 3 N 4 framework is developed and characterized, which markedly promotes the production of HCHO via four‐electron transfer through the *OCHO pathway. The optimized catalyst achieves a high HCHO productivity of 259.1 µmol g −1 and a selectivity of 61% after 24 h irradiation, which is ascribed to the synergic role of the neighboring Sn(II)–Cu(I) dual‐atom sites that stabilize the target intermediates for HCHO production. Moreover, adsorbed *HCHO intermediate is detected by in situ Fourier transform infrared spectroscopy (CO stretches at 1637 cm −1 ). This study provides a unique example that controls the selectivity of the multi‐electron transfer mechanisms of CO 2 photoconversion using heteronuclear dual‐atom‐site catalyst to generate an uncommon product (HCHO) of CO 2 reduction.