Shape‐Selective Synthesis of Palladium Nanoparticles Stabilized by Highly Branched Amphiphilic Polymers

Abstract

Despite the current broad interest in such materials, the synthesis of defined structures in the size range of 10 nm to ca. 1 μm (“mesoscopic”) is challenging. Few routes shape‐selectively afford geometrically regular structures, other than the typical spherical metal particles of 1 to 10 nm. Moreover, these few routes are largely restricted to aqueous systems, however, for catalysis and other applications dispersions in organic solvents are desirable. Carbon monoxide reduction of a palladium(II) compound in combination with stabilization by (readily available) amphiphilic hyperbranched polymers surprisingly affords dispersions of hexagonal platelets selectively with average sizes of thirty to several hundred nanometers in toluene. The size can be controlled by the polymer composition. Transmission electron microscopy (TEM), electron diffraction, and extended X‐ray absorption fine structure (EXAFS) spectroscopy demonstrate these palladium(0) platelets to be extremely thin (1–2 nm). Despite this high aspect ratio, the platelets prove quite shear resistant.

Aqueous-Phase Hydrogenation of Succinic Acid to γ-Butyrolactone and Tetrahydrofuran over Pd/C, Re/C, and Pd–Re/C Catalysts

“…The fringe spacing of 2.35 Å in Figure a′ deviates distinctly from the Pd(111) lattice plane spacing (2.25 Å) with a face-centered-cubic (fcc) structure, which can be ascribed to the 1/3(422) reflection that is normally forbidden in an fcc structure. This observation is in good agreement with previous publications. − For the PdRe 0.6 /C catalyst, the particles are anomalous and asymmetrical, with some appearance of agglomeration in Figure b. Figure b′ shows the high-resolution TEM (HR-TEM) image of agglomerated particles on the edge of the support.…”

Formation and Growth of Pd Nanoparticles Inside a Highly Cross-Linked Polystyrene Support: Role of the Reducing Agent

“…In this respect, it has been recently reported that Pd nanoparticles exhibiting unusual triangular shapes are generated when palladacycle complexes or palladium acetate in solution are treated with CO at room temperature . Also CO reduction of Pd­(II) compounds in toluene in combination with stabilization by amphiphilic polymers was reported to selectively afford dispersions of hexagonal platelets . The phenomenon observed in our case is similar, although it occurs entirely at the solid/gas interface, and not in solution.…”

Zirconium and Hafnium Twin Monomers for Mixed Oxides

“…In contrast, ultrafine Pd NPs were observed to attach on the tube wall due to the absence of anchors, which play a nucleation role in the growth of Pd NPs as confirmed by the large Pd particle size in Pd–MWNT‐COOH. The clear lattice fringe of about 0.22 nm observed by HRTEM belongs to the (111) plane of fcc Pd, and is consistent with the spacing (0.238 nm) of fringes due to the kinetically forbidden reflections of Pd 1/3(422), which is expected to appear in thin films or platelets with (111) surfaces 35…”