Homogeneous Ni Single-Atom Sites in the NiZn Intermetallic Nanostructure for Efficient Semihydrogenation of Acetylene

Catalytic semihydrogenation of acetylene is crucial for ethylene purification but still faces a grand challenge in circumventing deep hydrogenation and oligomerization so far, especially for the cost-effective catalysts. Herein, two Ni-based intermetallic nanocatalysts with different atomic arrangements were subtly constructed via controlling the reduction temperature of ZnO-supported NiO particles. The one reduced at 400 °C is L12-type intermetallic Ni3Zn with separated Ni3 trimers (denoted as Ni/ZnO-R400 or Ni3Zn/ZnO); another reduced at 600 °C is L10-type intermetallic NiZn with the homogeneous Ni single atoms completely isolated by Zn atoms (denoted as Ni/ZnO-R600 or NiZn/ZnO). The systematical evaluations validate NiZn/ZnO as an outstanding noble metal-free catalyst for acetylene semihydrogenation, showing a significantly enhanced selectivity toward ethylene relative to Ni3Zn/ZnO (87.5 vs −275.4% at 200 °C) through suppressing not only the unselective hydrogenation to ethane but also carbon deposition. According to catalytic evaluations with or without ethylene, microcalorimetry, and density functional theory calculations, the superior selectivity of NiZn/ZnO stems from the noncompetitive adsorption between the moderately σ-bonded acetylene over two neighboring Ni single atoms and weakly π-bonded ethylene on Ni single-atom sites due to its unique Ni–Zn–Ni ensemble.