Novel issues of morphology, size, and structure of Pt nanoparticles in chemical engineering: surface attachment, aggregation or agglomeration, assembly, and structural changes (original) (raw)
Related papers
Journal of Colloid and Interface Science, 2011
In this article, polyhedral and non-polyhedral Pt nanoparticles were prepared by modified polyol method using AgNO 3 as a good structuremodifying agent. Their TEM and HRTEM images showed the particle size in the range of 8-16 nm for both the above cases. The structures and properties of the surfaces of Pt nanoparticles were investigated through cyclic voltammetry in dilute perchloric acid (HClO 4 ) electrolyte solution. A comparison of the electrocatalytic property in methanol electrooxidation was made. Here, the effects of polyhedral and nonpolyhedral morphologies on their catalytic properties were studied. The results revealed that the special catalytic activity of quasi-sphere non-polyhedral Pt nanoparticles is higher than that of polyhedral Pt nanoparticles. In addition, Pt nanoparticles of unsharp and quasi-sphere morphologies exhibit the tolerance to poisoning species better than that of Pt nanoparticles of sharp and polyhedral morphologies due to the various morphologies of the catalyst surfaces in the chronoamperometric plots. Therefore, these experimental evidences showed the morphology-dependent catalytic property according to the various morphologies and complexity of their catalyst surfaces.
Control of Morphology of Pt Nanoparticles and Pt-Pd Core-Shell Nanoparticles
In this paper, poly(vinylpyrrolidone) (PVP) protected Pt and Pt-Pd nanoparticles were synthesized by the reductions of H 2 PtCl 6 and Na 2 PdCl 4 in ethylene glycol (EG) using AgNO 3 as a structure-controlling agent. Transmission electron microscopy (TEM) and high resolution (HR)TEM were employed to study the morphology and size of Pt and Pt-Pd nanoparticles. The results showed that the size and morphology of Pt nanoparticle was precisely controlled by addition of AgNO 3 . Accordingly, only under the selection of the appropriate chemicals and experimental conditions, Pt-Pd nanoparticles with their core-shell morphology were precisely controlled.
Crystal size and shape analysis of Pt nanoparticles in two and three dimensions
2006
Abstract. The majority of industrial catalysts are high-surface-area solids, onto which an active component is dispersed in the form of nanoparticles that have sizes of between 1 and 20 nm. In an industrial environment, the crystal size distributions of such particles are conventionally measured by using either bright-field transmission electron microscope (TEM) images or X-ray diffraction.
From Self-Assembly of Platinum Nanoparticles to Nanostructured Materials
Small, 2005
One-dimensional (1D) nanostructures of metals, semiconductors and conductive polymers, such as nanowires and nanorods, are very attractive because of their unique electrical, optical, magnetic, and mechanical properties, as well as their potential applications in nanodevices. The synthesis of these nanostructures has been explored by many processes, which are all based on point-initiated uniaxial growth of the crystal or the polymer. One-dimensional arrangements of metal nanoparticles using templates, such as DNA or polymers, have been generated successfully. Nickel nanochains were, for instance, synthesized in a solution of poly-(vinyl pyrrolidone). Because of dipolar magnetic interactions, 1D self-assembly is typical for magnetic nanoparticles. We recently reported that Chini clusters (of general formula [Pt 3 (CO) 6 ] m 2À , m = 6) when deposited on flat sup-ports, self-assemble into nanowires. On the other hand, porous hard templates and liquid crystalline phases have been widely used to obtain nanostructured materials. In this communication, we first report the 1D self-assembly of platinum nanoparticles in very dilute solution and then show that the organization of much more concentrated nanoparticles into larger nanostructures (fibers or lamellae) can be controlled by using liquid crystals as templates.
Shape-Dependent Catalytic Properties of Pt Nanoparticles
Journal of The American Chemical Society, 2011
Tailoring the chemical reactivity of nanomaterials at the atomic level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the atomic level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al 2 O 3 . Nanoparticles with analogous average size distributions (∼0.8-1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidation of 2-propanol. A correlation between the number of undercoordinated atoms at the nanoparticle surface and the onset temperature for 2-propanol oxidation was observed, demonstrating that catalytic properties can be controlled through shape-selective synthesis.
2012
In our facile synthesis method, poly(vinylpyrrolidone)-protected Pt and Pt−Pd bimetallic nanoparticles with controllable polyhedral core−shell morphologies are precisely synthesized by the reduction of Pt and Pd precursors at a certain temperature in ethylene glycol with silver nitrate as structure-controlling agent. The Pt nanoparticles exhibited well-shaped polyhedral morphology with highly fine and specific nanostructures in the size range of 20 nm. Important evidences of core−shell configurations of the Pt−Pd core−shell nanoparticles were clearly characterized by high-resolution transmission electron microscopy (HRTEM) measurements. The results of HRTEM images showed that the core−shell Pt−Pd nanoparticles in the size range of 25 nm with polyhedral morphology were synthesized with the thin Pd shells of ∼3 nm in thickness as the atomic Pd layers grown on the Pt cores. Very interesting characteristics of surface structure of Pt nanostructures and Pt−Pd core−shell nanostructures with surface defects were observed. The high-resolution TEM images of Pt−Pd bimetallic nanoparticles showed that the Frank−van der Merwe and Stranski−Krastanov growth modes coexist in the nucleation and growth of the Pd shells on the as-prepared Pt cores. It is predicted that the FM growth becomes the main favorable growth compared with the SK growth in the formation of the thin Pd shells of Pt−Pd core−shell nanoparticles. The experimental evidence of the deformations of lattice fringes and lattice-fringe patterns was found in Pt and Pt−Pd core−shell nanoparticles. The interesting renucleation and recrystallization at the attachments between the nanoparticles are revealed to form a good lattice match. In addition, our novel ideas of the largest surface-area superlattices and promising utilization of them are proposed for next generations of various fuel cells with low cost. Finally, the products of Pt−Pd core−shell nanoparticles can be potentially utilized as highly efficient catalysts in the realization of polymer electrolyte membrane fuel cell and direct methanol fuel cell using the very low Pt loading with better cost-effective design.
Nanotechnology, 2010
In this paper, Pt nanoparticles with good shapes of nanocubes and nano-octahedra and wellcontrolled sizes in the range 5-7 and 8-12nm, respectively, have been successfully synthesized. The modified polyol method by adding silver nitrate and varying the molar ratio of the solutions of silver nitrate and H2PtCl6 has been used to produce Pt nanoparticles of the size and shape to be controlled. The size and morphology of Pt nanoparticles have been studied by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results have shown that their very sharp and good shapes exist in the main forms of cubic, cuboctahedral, octahedral and tetrahedral shapes directly related to the crystal nucleation along various directions of the {100} cubic, {111} octahedral and {111} tetrahedral facets during synthesis. In particular, various irregular and new shapes of Pt nanoparticles have been found. Here, it is concluded that the role of silver ions has to be considered as an important factor for promoting and controlling the development of Pt nanoparticles of {100} cubic, {111} octahedral and {111} tetrahedral facets, and also directly orienting the growth and formation of Pt nanoparticles. © IOP Publishing Ltd.
Shape evolution of carbon supported Pt nanoparticles: From synthesis to application
Applied Catalysis B: Environmental, 2016
In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to synthesize carbon supported Pt catalysts. Varying the concentration of HCl caused changes in the shape of obtained nanoparticles, i.e. preferential growth of certain facets. Addition of catalyst support in the synthesis process facilitated the cleaning procedures necessary to remove the surfactant residues. Prepared catalyst powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis indicated the influence of HCl addition on the crystallite size and crystal habit. TEM revealed that addition of higher amounts of the capping agent led to the formation of a noticable amount of particles with concave cubic or branched-like structures. Influence of the catalyst particles shape on its electrochemical properties was tested in the oxidations of CO ads , ammonia and formic acid. The latter one was examined in terms of both activity and stability of as prepared and oxide-annealed (electrochemically treated) catalysts. The results clearly demonstrate that even small changes in the nanoparticle surface structure give rise to distinct modifications in their properties. Concave cubic particles, in comparison to other catalysts, show improved catalytic properties and the contribution of their preferentially oriented {100} facets is electrochemically detectable.