Synergistic Effects of Crystal Phase and Strain for N2 Dissociation on Ru(0001) Surfaces with Multilayered Hexagonal Close-Packed Structures.

The synergistic effects of strain and crystal phase on the reaction activity of nitrogen molecule dissociation have been studied using density functional theory calculations on Ru(0001) surfaces with multilayered hexagonal close-packed structures. The phase transformation from hexagonal close-packed phase (2H) to face-centered cubic (3C) phase or unconventional phases (4H, DHCP, 6H1, and 6H2) would occur under the uniaxial tensile strain loaded along the c axis. The close-packed surfaces of unconventional crystal phases show an enhanced chemical reactivity for N adsorption due to the upshifted d-band center of Ru. However, the N2 adsorption energy is almost independent of the applied strain and crystal phase. The optimized catalytic activity of Ru(0001) surfaces with the unconventional phases is found for the N2 dissociation through breaking the scaling relationships between the reaction barrier and reaction energy. Our results indicate that the strain-induced phase transformation is an effective method to improve the catalytic activity of noble metal catalysts toward the N2 dissociation reaction.

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.