We designed core-Pd/shell-Ag nanocomposite catalyst (Pd@Ag) for highly selective semihydrogenation of alkynes. The construction of the core−shell nanocomposite enables a significant improvement in the low activity of Ag NPs for the selective semihydrogenation of alkynes because hydrogen is supplied from the core-Pd NPs to the shell-Ag NPs in a synergistic manner. Simultaneously, coating the core-Pd NPs with shell-Ag NPs results in efficient suppression of overhydrogenation of alkenes by the Pd NPs. This complementary action of core-Pd and shell-Ag provides high chemoselectivity toward a wide range of alkenes with high Z-selectivity under mild reaction conditions (room temperature and 1 atm H 2 ). Moreover, Pd@Ag can be easily separated from the reaction mixture and is reusable without loss of catalytic activity or selectivity.

In single-atom catalysis, the atomic structure and local electronic states of single atoms on a supporting material remain a fundamental question. We experimentally and theoretically solved these problems for single Pt atoms dispersed on freestanding graphene using plasma sputtering. Electron microscopy revealed the atomic arrangements of Pt atoms binding to carbon atoms at the step edges of nanographene flakes. X-ray photoelectron spectroscopy revealed a large binding energy shift of the Pt 4f state of a single Pt atom. First-principles calculations elucidated that the Pt 5d xy -orbital in the step edge plays a crucial role in the formation of chemical bonds to C atoms and in the considerable charge transfer from Pt to C atoms, resulting in the large binding energy shift of the Pt 4f state.

Isolated single metal atoms have attracted significant attention as catalytic materials with maximum surface areas as well as high activity and selectivity. However, a dense dispersion of single atoms on supported materials has not been achieved. We applied plasma sputtering in N2 atmosphere to disperse single Pt atoms on graphene. Scanning transmission electron microscopy observations confirmed the high-density dispersion of single Pt atoms, without widespread sintering into three-dimensional nanoparticles. X-ray photoelectron spectroscopy measurements revealed that pyridinic nitrogen was selectively doped in graphene during the sputtering. Our novel method provides a simple approach to synthesize high-density single Pt atoms on graphene.

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The atomic structures of Au25(SC2H4Ph)18, Au25(SePh)18, and Au144(SC2H4Ph)60, for which the crystal structures have been solved, were examined by aberration-corrected transmission electron microscopy (ACTEM). Time-lapse ACTEM images of Au25(SePh)18 exhibited characteristic patterns for the I h Au13 core more frequently compared to Au25(SC2H4Ph)18 at a dose rate (DR) = 4 pA/cm2. In contrast, time-lapse images of Au144(SC2H4Ph)60 randomly showed two types of patterns for the I h and fcc cores at DR = 4 pA/cm2, indicating that Au144(SC2H4Ph)60 can be interconverted between the two isomeric forms without fragmentation. We proposed that the I h isomer is more stable than the fcc isomer in Au144(SC2H4Ph)60 based on population analysis of the images of individual isomers.