N₈ stabilized single-atom Pd for highly selective hydrogenation of acetylene

Single-atom catalysts show a promising future in many reactions even though great challenges still remain such as facile synthesis and long stability. In this work, a single-atom Pd catalyst attached to a designed N₈ Lewis base species (Pd₁-N₈/CNT) is synthesized with cyclic voltammetry (CV) method. The catalyst demonstrates long stability and enhanced C₂H₄ selectivity in selective hydrogenation of acetylene at 40 °C. CV is carried out in a three-electrode setup with PdO/CNT as the working electrode in NaN₃ solution. HAADF-STEM confirms single-atom Pd sites are successfully isolated. XPS measurements and Bader charge calculations indicate N₈ is effectively synthesized on CNT substrate after CV treatment while single-atom Pd is stabilized by attaching to the end N of N₈. Acetylene-temperature programed desorption (C₂H₂-TPD) and density functional theory (DFT) calculations suggest C₂H₂ favors the π bonding on single Pd atom, while H₂ dissociates on the N atom (next to Pd) instead of conventionally on Pd. The synergistic effect favors C₂H₄ formation but prevents full hydrogenation of acetylene to C₂H₆. This work opens up a new perspective to design and synthesize more selective catalysts with isolated single-atom sites.