Synthesis and Mechanistic Study of Palladium Nanobars and Nanorods

Abstract

This paper describes a simple and versatile method for growing highly anisotropic nanostructures of Pd, single-crystal nanobars bounded by {100} facets and single-crystal nanorods with their side surfaces enclosed by {100} and {110} facets. According to thermodynamic arguments, Pd atoms should nucleate and grow in a solution phase to form cuboctahedrons of spherical shape with their surfaces bounded by a mix of {111} and {100} facets. Anisotropic nanostructures can only form under kinetically controlled conditions, while the cubic symmetry is broken. In the present system, we found that one-dimensional growth could be induced and maintained through an interplay of the following processes: (i) speedy reduction of the precursor to ensure prompt addition of atoms to the seed; (ii) chemisorption of bromide on the seed to promote the formation of {100} and {110} facets; and (iii) localized oxidative etching on one specific face of the seed to initiate preferential growth on this face. Experimentally, the anisotropic growth can be achieved by varying the type and concentration of reducing agent, as well as by adjusting the reaction temperature. This methodology developed for Pd has also been extended to both Au and Pt. As expected for a kinetically controlled product, the anisotropic nanostructure evolved into the thermodynamically favored shape during an aging process.

Sub-10 nm Platinum Nanocrystals with Size and Shape Control: Catalytic Study for Ethylene and Pyrrole Hydrogenation

“…25 In the present approach, bromide ions were used as the shape directing agent. [26][27][28][29][30] The bromide-mediated strategy is more favorable catalytically because the bromide species are only on the nanocrystal surface and are easily removed after synthesis by washing. In general, the metal salts ( Pt(IV) and Pt(II) ), the surfactants (PVP), and the shape directing agent (bromide ions) were dissolved in ethylene glycol at room temperature to form a precursor solution.…”

Enhanced hydrothermal stability of high performance lean fuel combustion alumina-supported palladium catalyst modified by nickel

“…The Pd, Ni, NiO, and NiAl 2 O 4 crystal could be the face-centered cubic structures, and this nanospheres or near-spherical particles mostly show an FCC structure in the form of cuboctahedrons with their surfaces bounded by a mixture of (1 1 1) and (1 0 0) [53]. The Pd (1 1 1) and Pd (1 0 0) planes can match the corresponding planes of Ni, NiO or NiAl 2 O 4 without the angle distortion between them.…”

New insights into the growth mechanism and surface structure of palladium nanocrystals

“…Such defects are common features of an oriented attachment growth mechanism and have also been observed in the synthesis of nanorods and nanowires made of metals or metal sulfides [22,23]. In the previous studies, a mechanism based on the anisotropic growth of initially formed nanocubes via localized oxidative etching has been used to explain the formation of Pd nanobars with aspect ratios larger than unity [25,26]. As demonstrated in the current study, however, this type of Pd nanostructure seems to be formed via particle coalescence in a one-dimensional fashion even though the exact pathway for such growth is yet to be resolved.…”

“…The recrystallization process involves the migration of atomic species on the two-dimensional surface of a nanocrystal, giving rise to reconstruction of the surface and thus shape. During this shape focusing process, bromide ions seem to play a significant role in promoting the formation of {100} facets by lowering their surface energy through the preferential chemisorption [25][26][27], and thus inducing evolution of the shape into a nanobar.…”