Selective hydrogenation of acetylene on Cu-Pd intermetallic compounds and Pd atoms substituted Cu(111) surfaces

The selective hydrogenation of acetylene was studied on the ordered Cu-Pd intermetallic compounds (L1₀-type CuPd, L1₂-type Cu₃Pd, and L1₂-type CuPd₃) and Pd-modified Cu(111) surfaces through first-principles calculations. The catalytic selectivity and activity of Cu-Pd alloy catalysts are closely related to the crystal structure and composition of Cu-Pd intermetallic compounds and the size of Pd ensembles of Cu-based dilute alloy surface for the selective hydrogenation of acetylene to ethylene. Significantly, we found that the ordered Cu-Pd alloy surface containing isolated Pd atoms (i.e., L1₂-type Cu₃Pd(111) surface) is highly efficient for the selective hydrogenation reaction of C₂H₂ + H₂→ C₂H₄. The contiguous Pd atom ensembles (Pd dimer and trimer) are catalytically active towards C₂H₂ + H → C₂H₃ and C₂H₃ + H → C₂H₄ reactions than the single Pd atom on a Pd-decorated Cu(111) surface. However, the small Pd ensembles on Cu(111) present a low chemical activity for H₂ dissociation compared with the ordered Cu-Pd intermetallic compounds. Our theoretical results provide a strategy of crystal phase and composition control for enhancing the selectivity and activity of Cu-Pd catalysts towards acetylene selective hydrogenation.