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.