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.