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.