Pd Single-Atom Catalysts on Nitrogen-Doped Graphene for the Highly Selective Photothermal Hydrogenation of Acetylene to Ethylene.

The selective hydrogenation of acetylene to ethylene in an ethylene-rich gas stream is an important process in the chemical industry. Pd-based catalysts are widely used in this reaction due to their excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single-atom catalysts on nitrogen-doped graphene (Pd1 /N-graphene) by a freeze-drying-assisted method is reported. The Pd1 /N-graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C2 H2 with H2 in the presence of excess C2 H4 under photothermal heating (UV and visible-light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C2 H4 hydrogenation. Importantly, the Pd1 /N-graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar-driven photothermal catalyst systems based on single-atom active sites for selective hydrogenation reactions.