Catalytic Site Engineering for Photocatalytic Ethylene Synthesis.

Ethylene (C2H4) is a key platform chemical that is conventionally produced through energy-intensive, fossil-dependent thermal processes. Photocatalysis offers a green alternative by enabling the directional conversion of diverse carbon-based precursors into C2H4 under mild conditions, although the inertness of these precursors and the difficulty of controlling C-C coupling and selectivity remain major obstacles. Unlike previous reviews that focus on a single feedstock, this review systematically surveys the photocatalytic synthesis of C2H4 from four representative precursors, namely CO2, methane, ethane, and ethanol. Using catalytic site engineering as a unifying thread, it discusses how tailoring the microenvironment of active sites mitigates the intrinsic inertness and kinetic barriers of precursor molecules and steers key intermediates toward selective C2H4 formation. The four conversion routes are further compared in terms of their core challenges, design strategies, and industrial potential, and the key scientific and engineering gaps are highlighted to guide the rational design of efficient photocatalytic C2H4 synthesis systems.