Highly dispersed Pd species active in the Suzuki-Miyaura reaction.

Structures of Pd/zeolites immersed in solvents were measured by in situ X-ray absorption fine structure (XAFS). Systematic studies revealed that the selection of an appropriate support (USY-zeolite), thermal treatment temperature of USY, solvent (o-xylene), H(2) partial pressure (6%), and the use of a Pd amine complex affect the structure of Pd. As a result, we found that monomeric Pd can be obtained in the USY support with H(2) bubbling in o-xylene. The structural properties of Pd correlate well with its catalytic performance in the Suzuki-Miyaura coupling reactions; a very high TON of up to 11,000,000 was obtained over the monomeric Pd.

Change in local environment upon quasicrystallization of Zr-Cu glassy alloys by addition of Pd and Pt.

The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr(70)Cu(30) glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.

Evaluation of the local environment for nanoscale quasicrystal formation in Zr(80)Pt(20) glassy alloy using Voronoi analysis.

The local atomic structure of nano-quasicrystal-forming Zr(80)Pt(20) binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q∼17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystalforming Zr(70)Pd(30) glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.