Efficient Photocatalytic Semihydrogenation of 2-Butyne-1,4-diol over TiO₂ Supported Cu Single Atoms with Near-Unity Conversion and Selectivity

Selective thermocatalytic hydrogenation of 2-butyne-1,4-diol (BYD) to 2-butene-1,4-diol (BED) is vital for producing downstream fine chemicals like pharmaceuticals. However, the current thermocatalytic semihydrogenation typically requires elevated temperatures, excessive high-pressure H₂, and costly Pd-based catalysts or flammable Raney Ni. Here, we highlight a sustainable photocatalytic semihydrogenation of BYD to BED using Cu single atoms anchored on TiO₂ nanoparticles (Cu-SAs-TiO₂) with water as the hydrogen source under ambient conditions. Under the irradiation of simulated solar light, Cu-SAs-TiO₂ unprecedentedly achieves a BYD conversion of ∼100% with an exceptionally high BED selectivity of 99.4%, which substantially outperforms the previously reported thermocatalysts. Even in a large-scale photocatalytic system (6 L) and under outdoor sunlight irradiation of 22 h, Cu-SAs-TiO₂ still delivered a BYD conversion of ∼100%, a BED selectivity of 97.5%, and a BED production rate of 0.22 mmol_BED·g_cat^-1·h^-1. Isotope-labeling analyses, experiments on the kinetic isotope effect of hydrogen, in situ photochemical infrared spectra, and theoretical simulations together reveal that the Cu single atoms promote water dissociation and BED desorption, eventually contributing to a complete BYD conversion and a high BED selectivity.