Upgrading CO ₂ and H ₂ O to Analytical-Grade Propanal via an Electrocatalysis–Thermal Catalysis Relay on Single-Atom Catalysts

Sustainable synthesis of analytical-grade propanal from CO 2 and H 2 O via an electro-thermal cascade process is highly attractive but remains challenging due to the limited selectivity of CO 2 electroreduction to gaseous products (CO/C 2 H 4 ) and the sluggish kinetics of the subsequent thermal catalytic step at ambient pressure. In this work, we demonstrate a new pathway for the direct synthesis of purification-free analytical-grade propanal via electroreduction–hydroformylation cascade conversion of CO 2 and H 2 O over rationally designed single-atom catalysts (SACs). The Sn 1 Cu single-atom alloy (SAA) catalyst exhibits an exceptional potential-dependent CO 2 electroreduction selectivity toward C 2 H 4 and CO, with the C 2 H 4 to CO ratio increasing by 2 orders of magnitude in the potential range from −0.6 to −2.3 V (vs RHE). Results from in situ/operando characterizations and density functional theory (DFT) calculations reveal that the enhanced ethylene selectivity over Sn 1 Cu SAA arises from the high *CO coverage generated over a single-Sn-atom-modified Cu site, which promotes the symmetric *CO–*CO coupling, thereby significantly enhancing the electrochemical CO 2 reduction to ethylene. The resulting C 2 H 4 /CO/H 2 mixture is directly converted in a fixed-bed hydroformylation reactor over a triphenylphosphine-modified Rh SAC (PPh 3 -Rh 1 /ZnO), achieving an optimized ethylene-to-propanal selectivity of up to 98%. Analytical-grade propanal (∼99%) is obtained without further purification, and stable production was maintained for 200 h with a maximum C 3 H 6 O rate of 3.8 mg h –1 cm –2 under ambient pressure. This work establishes a general framework for integrating electrochemical and thermal catalysis to convert CO 2 and H 2 O into value-added aldehydes, offering a sustainable route for synthesizing value-added chemicals from basic feedstocks.