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Pd icosahedra with sizes controlled in the range of 5-35 nm were synthesized in high purity through a combination of polyol reduction and seed-mediated growth. The Pd icosahedra were obtained with purity >94 % and uniform sizes controlled in the range of 5-17 nm by using ethylene glycol as both the reductant and solvent. The studies indicate that the formation of Pd nanocrystals with an icosahedral shape was very sensitive to the reaction kinetics. The success of this synthesis relies on the use of HCl to manipulate the reaction kinetics and thus control the twin structure and shape of the resultant nanocrystals. The size of the Pd icosahedra could be further increased up to 35 nm by seed-mediated growth, with 17 nm Pd icosahedra serving as seeds. The multiply twinned Pd icosahedra could grow into larger sizes, and their shape and multiply twinned structure were preserved. Thanks to the presence of twin defects, the Pd icosahedra showed a catalytic current density towards formic-acid oxidation that was 1.9 and 11.6 times higher than that of single-crystal Pd octahedra, which were also fully covered by {111} facets, and commercial Pd/C, respectively., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Monodisperse CoPd nanoparticles (NPs) were synthesized and studied for catalytic formic acid (HCOOH) oxidation (FAO). The NPs were prepared by coreduction of Co(acac)(2) (acac = acetylacetonate) and PdBr(2) at 260 °C in oleylamine and trioctylphosphine, and their sizes (5-12 nm) and compositions (Co(10)Pd(90) to Co(60)Pd(40)) were controlled by heating ramp rate, metal salt concentration, or metal molar ratios. The 8 nm CoPd NPs were activated for HCOOH oxidation by a simple ethanol wash. In 0.1 M HClO(4) and 2 M HCOOH solution, their catalytic activities followed the trend of Co(50)Pd(50) > Co(60)Pd(40) > Co(10)Pd(90) > Pd. The Co(50)Pd(50) NPs had an oxidation peak at 0.4 V with a peak current density of 774 A/g(Pd). As a comparison, commercial Pd catalysts showed an oxidation peak at 0.75 V with peak current density of only 254 A/g(Pd). The synthesis procedure could also be extended to prepare CuPd NPs when Co(acac)(2) was replaced by Cu(ac)(2) (ac = acetate) in an otherwise identical condition. The CuPd NPs were less active catalysts than CoPd or even Pd for FAO in HClO(4) solution. The synthesis provides a general approach to Pd-based bimetallic NPs and will enable further investigation of Pd-based alloy NPs for electro-oxidation and other catalytic reactions., (© 2012 American Chemical Society)

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pdδ+ (0<δ<2) that has greatly enhanced activity for methane oxidation: T50 lowered by up to 130 °C and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pdδ+ site is related to its oxygen‐deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions. [ABSTRACT FROM AUTHOR]

Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br−, Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties. Creating predictable, controllable nanoparticles relies on a mechanistic understanding of their synthesis. Here, through integrated in situ liquid microscopy and first-principles calculations, the authors elucidate the atomistic details involved in the formation of colloidal core-shell nanoparticles. [ABSTRACT FROM AUTHOR]

We have synthesized Pd icosahedra with uniform, controllable sizes in plug reactors separated by air. The oxygen contained in the air segments not only contributed to the generation of a reductant from diethylene glycol in situ, but also oxidized elemental Pd back to the ionic form by oxidative etching and thus slowed down the reduction kinetics. Compared to droplet reactors involving silicone oil or fluorocarbon, the use of air as a carrier phase could reduce the production cost by avoiding additional procedures for the separation of products from the oil. The average diameters of the Pd icosahedra could be readily controlled in the range of 12-20 nm. The Pd icosahedra were further employed as seeds for the production of Pd@Pt2-3L core-shell icosahedra, which could serve as a catalyst toward the oxygen reduction reaction with greatly enhanced activity. We believe that the plug reactors could be extended to other types of noble-metal nanocrystals for their scale-up production. [ABSTRACT FROM AUTHOR]

Palladium wavy nanowires with an ultrathin diameter of 2 nm are synthesized using the polyol method without the involvement of any template. The success of this synthesis relies on the use of a suitable precursor that could be reduced instantaneously to generate a large number of small Pd nanoparticles. Due to a quick depletion of precursor, the small nanoparticles were unable to grow in size through atomic addition. In the case of low surface charges and high surface energies, these small nanoparticles were forced to coalesce into ultrathin nanowires with a wavy morphology via an attachment mechanism. Thanks to the unique structure and involvement of twin defects, the as-obtained Pd ultrathin nanowires show a catalytic current density of 2.5 times higher than the conventional Pd/C catalyst towards formic acid oxidation. This work not only offers a powerful route to the synthesis of nanowires through attachment-based growth but also opens the door to the rational design and fabrication of novel metal nanostructures with enhanced properties. [ABSTRACT FROM AUTHOR]

The Front Cover shows a polymer tube containing a continuous flow of plug reactors used for the synthesis of colloidal metal nanocrystals. In their Full Paper, Wang et al. report how such plug reactors can be applied to the continuous and scalable production of palladium icosahedral nanocrystals with uniform and controllable sizes. More information can be found in the Full Paper by Wang et al. on page 1658 in Issue 9, 2016 (DOI: 10.1002/cctc.201600060). [ABSTRACT FROM AUTHOR]