Hydrochlorination of acetylene on single-atom Pd/N-doped carbon catalysts: Importance of pyridinic-N synergism

Alternative palladium (Pd)-based catalysts to toxic mercuric chloride catalysts in vinyl chloride manufacture via acetylene hydrochlorination is currently limited by the lack of efficient and durable active sites. Here, the catalytic behavior of Pd-based catalysts with tunable nanostructures and coordination bonds were investigated. The evolution of Pd entities were precisely regulated by controlled thermal treatment. Pyridinic nitrogen is shown to regulate the nanostructures and coordination bonds of Pd sites, improve the thermal stability of Pd atoms, promote the adsorption of acetylene and enrich hydrogen chloride. These results indicate that Pd single-atom is more active than Pd nanoparticle or Pd cluster. The catalytic performance of Pd single-atom catalyst can be further improved by substituting Pd-Cl bond with Pd-N bond, with PdN2 identified as the efficient and durable active sites. Furthermore, the enrichment of hydrogen chloride enables the Pd single-atom catalysts to produce vinyl chloride via a non-hydrogen chloride excess method, which is a breakthrough in the existing industrial system. Our strategy for controlling the catalytic behavior of Pd sites is of a broad application prospect for the precise control and design of metal active sites.