Breaking the activity-selectivity trade-off for acetylene semihydrogenation by Pd2 dual-atom site

Acetylene semihydrogenation is a critical process in the polyolefin industry by selectively removing trace acetylene from ethylene-rich reformate. However, this reaction is generally limited by the inherent activity-selectivity trade-off due to the thermodynamic advantage of overhydrogenation. Herein, we develop a facile and straightforward strategy to construct Pd2 dual-atom sites anchored on defect-rich surface-graphitized nanodiamond (ND@G) via the solvent-mediated dispersion of palladium carboxylate driven by the chelation of palladium precursors via carboxylate anion. Cs-corrected HAADF-STEM images coupled with XAS analysis unambiguously manifest the successful architecting of Pd2 dual-atom sites. Compared to Pd1 single-atom sites, the obtained Pd2/ND@G sample demonstrates superior catalytic performance in acetylene semihydrogenation, with the corresponding TOF values increased from 0.151 s−1 to 1.953 s−1, without the obvious decline of ethylene selectivity (93.2%, at full acetylene conversion). C2H2/C2H4-TPD, H2-D2 exchange reaction, isotope-labeled TPSR combined with DFT calculations confirm the effective co-activation of C2H2/H2 on Pd2 dual-atom sites while maintaining the weak adsorption of ethylene similar to that on its single-atom sites, which can break the activity-selectivity trade-off in acetylene semihydrogenation. Removing trace acetylene from ethylene is vital for plastic production, yet catalysts often overreact and waste the product. This work reveals that palladium dual-atom catalyst on carbon greatly speeds the reaction while keeping ethylene intact.