This article presents a novel strategy for the synthesis of well-defined diatomic catalysts (DACs) for the efficient photoconversion of CO₂ into ethylene (C₂H₄). The study introduces an "up-bottom ion-cutting" approach to fabricate CuAu-DAs (diatomic Au-Cu sites) supported on TiO₂, achieving a highly ordered structure with a compact heteroatomic spacing of 2-3 Å. This structure significantly reduces the C-C coupling energy barrier, enabling high-efficiency production of C₂H₄ with excellent sustainability. The CuAu-DAs structure consists of Cu single atoms (Cu-SAs) and Au single atoms (Au-SAs), where Cu-SAs are responsible for *CO generation, while Au-SAs act as *CO coupling centers, synergistically promoting the photoconversion of CO₂ into C₂H₄. The catalyst demonstrates a remarkable production rate of 568.8 μmol·g⁻¹·h⁻¹ without any sacrificial agents and maintains stability over 120 hours of photocatalytic testing. The study highlights the importance of precise atomic-level control in bimetallic solid catalysts for optimizing catalytic performance and understanding reaction mechanisms. The proposed up-bottom ion-cutting strategy allows for the controlled synthesis of well-defined DACs, overcoming the limitations of traditional bottom-up methods that lead to disordered heteronuclear sites. The CuAu-DAs-TiO₂ composite exhibits superior structural stability and resistance to CO poisoning, attributed to the synergistic effect of Cu and Au sites, which facilitate efficient *CO generation and coupling. The catalyst's performance is further supported by detailed structural characterization, including XANES, EXAFS, and DRIFTS analyses, which confirm the unique atomic configuration and reaction mechanisms. The study also explores the photocatalytic performance of CuAu-DAs-TiO₂ in the reduction of CO₂, demonstrating its ability to produce C₂H₄ with high selectivity and efficiency. The catalyst's stability is further validated through long-term testing and CO-TPD analysis, which show minimal CO poisoning and excellent CO adsorption capacity. The results indicate that the CuAu-DAs structure effectively balances activity and stability, making it a promising candidate for efficient CO₂ reduction in the context of sustainable energy and chemical production.This article presents a novel strategy for the synthesis of well-defined diatomic catalysts (DACs) for the efficient photoconversion of CO₂ into ethylene (C₂H₄). The study introduces an "up-bottom ion-cutting" approach to fabricate CuAu-DAs (diatomic Au-Cu sites) supported on TiO₂, achieving a highly ordered structure with a compact heteroatomic spacing of 2-3 Å. This structure significantly reduces the C-C coupling energy barrier, enabling high-efficiency production of C₂H₄ with excellent sustainability. The CuAu-DAs structure consists of Cu single atoms (Cu-SAs) and Au single atoms (Au-SAs), where Cu-SAs are responsible for *CO generation, while Au-SAs act as *CO coupling centers, synergistically promoting the photoconversion of CO₂ into C₂H₄. The catalyst demonstrates a remarkable production rate of 568.8 μmol·g⁻¹·h⁻¹ without any sacrificial agents and maintains stability over 120 hours of photocatalytic testing. The study highlights the importance of precise atomic-level control in bimetallic solid catalysts for optimizing catalytic performance and understanding reaction mechanisms. The proposed up-bottom ion-cutting strategy allows for the controlled synthesis of well-defined DACs, overcoming the limitations of traditional bottom-up methods that lead to disordered heteronuclear sites. The CuAu-DAs-TiO₂ composite exhibits superior structural stability and resistance to CO poisoning, attributed to the synergistic effect of Cu and Au sites, which facilitate efficient *CO generation and coupling. The catalyst's performance is further supported by detailed structural characterization, including XANES, EXAFS, and DRIFTS analyses, which confirm the unique atomic configuration and reaction mechanisms. The study also explores the photocatalytic performance of CuAu-DAs-TiO₂ in the reduction of CO₂, demonstrating its ability to produce C₂H₄ with high selectivity and efficiency. The catalyst's stability is further validated through long-term testing and CO-TPD analysis, which show minimal CO poisoning and excellent CO adsorption capacity. The results indicate that the CuAu-DAs structure effectively balances activity and stability, making it a promising candidate for efficient CO₂ reduction in the context of sustainable energy and chemical production.