Dual-Atom-Site Sn-Cu/C3N4 Photocatalyst Selectively Produces Formaldehyde from CO2 Reduction

The solar-driven catalytic reduction of CO₂ to value-added chemicals is under intensive investigation. The reaction pathway via *OCHO intermediate (involving CO₂ 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 C₃N₄ 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 CO₂ photoconversion using heteronuclear dual-atom-site catalyst to generate an uncommon product (HCHO) of CO₂ reduction.