The Coordination Microenvironment Tailoring in 2D MOFs for Enhancing Photocatalytic Acetylene Semi-Hydrogenation

The semi-hydrogenation of acetylene (C₂H₂) to ethylene (C₂H₄) by photocatalytic is a new and clean strategy for removal of C₂H₂ impurities from raw C₂H₄ to produce polymer-grade C₂H₄. In the state-of-the-art, most of the studies on photocatalytic acetylene hydrogenation (PAH) were achieved by cobalt-based photocatalysts, while the studies on the influence of microenvironment of cobalt catalytic active sites remain limited. Herein, via coordination ligand modulation method, we chose three 2D metal organic framework (2D MOFs) with different coordinated atoms (N, O, and S) around cobalt center and afforded CoN₄ MOF, CoO₄ MOF, and CoS₄ MOF, respectively, for studying the influence of coordination environment of cobalt active sites on photocatalytic C₂H₂ reduction. As a result, CoO₄ MOF with O-coordinated cobalt sites exhibited the highest activity with C₂H₂-to-C₂H₄ yield of 852.68 µmol g^-1 h^-1 in C₂H₂ atmosphere. Interestingly, in simulated industry-relevant conditions gas with 1% C₂H₂ contained C₂H₄ mixture, CoN₄ MOF showed the optimal performance with near 100% conversion of low-concentrated C₂H₂. The photophysical, C₂H₂ adsorption characterization, in situ FTIR, and density functional theory (DFT) calculation were conducted to investigate the reaction mechanism. The results demonstrated that the O-coordinated Co sites behaved more favorably thermodynamically for *C₂H₂-to-*CH₂CH intermediate, which caused superior activity. In contrast, the N-coordinated Co sites showed highly efficient PAH in C₂H₄ rich conditions with low concentrated C₂H₂ due to the weak C₂H₄ competitive adsorption. This work is the first to explore the dependence of the active site coordination microenvironment for C₂H₂ photoreduction and provides a platform for constructing highly selective photocatalysts.