Unraveling the Complex Causality behind Sulfur-Ligated Gold Clusters in Acetylene Hydrochlorination

Vinyl chloride monomers are essential for manufacturing versatile thermoplastic polymers. Here, we present the Au₂₅/AC-300 composites, which were pretreated at 300 °C in air and demonstrate outstanding catalytic performance in the acetylene hydrochlorination process. At 180 °C, a gas hourly space velocity of 36 mL g^-1 h^-1 is achieved, resulting in an acetylene conversion of >94% and a vinyl chloride selectivity of >99%. In the same reaction conditions, the Au₂₅/AC-500 with big gold nanoparticles exhibits lower catalytic activity. The residual surface S species on gold cluster surfaces are responsible for the superior catalytic performance. These species can significantly inhibit the reduction of Au⁺ to metallic species and subsequently delay their aggregation, as confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction by hydrogen experiments, thereby preserving catalytic activity throughout the acetylene hydrochlorination process. Further, the [Au₂₅S]⁺ clusters exhibit strong bonds with acetylene molecules with a maximum of ∼11 adsorbed acetylene per cluster, determined by in situ ultraviolet photodissociation protocol, which is a rate-determining step during the nanogold catalyzed acetylene hydrochlorination.