Size-dependent catalytic and melting properties of platinum-palladium nanoparticles

Institute of Mechanics, Materials and Civil Engineering, Catholic University of Louvain, 2 Place Sainte Barbe, 1348 Louvain-La-Neuve, Belgium. .
Nanoscale Research Letters (Impact Factor: 2.78). 05/2011; 6(1):396. DOI: 10.1186/1556-276X-6-396
Source: PubMed


While nanocatalysis is a very active field, there have been very few studies in the size/shape-dependent catalytic properties of transition metals from a thermodynamical approach. Transition metal nanoparticles are very attractive due their high surface to volume ratio and their high surface energy. In particular, in this paper we focus on the Pt-Pd catalyst which is an important system in catalysis. The melting temperature, melting enthalpy, and catalytic activation energy were found to decrease with size. The face centered cubic crystal structure of platinum and palladium has been considered in the model. The shape stability has been discussed. The phase diagram of different polyhedral shapes has been plotted and the surface segregation has been considered. The model predicts a nanoparticle core rich in Pt surrounded by a layer enriched in Pd. The Pd segregation at the surface strongly modifies the catalytic activation energy compared to the non-segregated nanoparticle. The predictions were compared with the available experimental data in the literature.

65.80-g; 82.60.Qr; 64.75.Jk

  • Source
    • "The distinct properties of such nanomaterials have led to revolutionary applications in a wide variety of fields such as optoelectronics [1], energy conversion and storage [2], medicine [3] [4], and catalysis among many others [5] [6] [7] [8] [9]. The behavior and performance of nanomaterials in general for the aforementioned applications are highly dependent on the particle size, shape, and size distribution as well as the surrounding environment [8] [10] [11]. This has brought a tremendous interest on developing methods that allow a control over the synthesis parameters and, therefore a better control over the final characteristics of the nanomaterials [12]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: In this work a new approach to synthesize iridium nanoparticles on reduced graphene oxide is presented. The nanoparticles were directly deposited and grown on the surface of the carbonbased support using a single step reduction method through gamma irradiation. In this process, an aqueous isopropanol solution containing the iridium precursor, graphene oxide, and sodium dodecyl sulfate was initially prepared and sonicated thoroughly to obtain a homogeneous dispersion. The samples were irradiated with gamma rays with energies of 1.17 and 1.33 MeV emitted from the spontaneous decay of the 60Co irradiator. The interaction of gamma rays with water in the presence of isopropanol generates highly reducing species homogeneously distributed in the solution that can reduce the Ir precursor down to a zero valence state. An absorbed dose of 60 kGy was used, which according to the yield of reducing species is sufficient to reduce the total amount of precursor present in the solution. This novel approach leads to the formation of 2.3 ± 0.5 nm Ir nanoparticles distributed along the surface of the support. The oxygenated functionalities of graphene oxide served as nucleation sites for the formation of Ir nuclei and their subsequent growth. XPS results revealed that the interaction of Ir with the support occurs through Ir-O bonds.
    Full-text · Article · Sep 2015 · Applied Surface Science
  • Source
    • "Figure 8 shows a plot of temperature versus particle size constructed for noble-metal nanoparticles enclosed in a laurite-type mineral host. The thick red curve in this phase diagram represents the coarsening threshold for nanoparticles or diffusional boundary growth, which is broadly constrained here using recent datasets on noble-metal nanoparticles (Hills et al. 2003; Alyousef et al. 2010; So et al. 2010; Guisbiers et al. 2011; Cornish and Chown 2011). The lower limit (lower red curve) is defined by the temperature at which Os–Ir–Ru(–Pt) nanoalloys are stable during controlled heating (i.e. "
    [Show abstract] [Hide abstract]
    ABSTRACT: event, confirming previous thermodynamic predictions. Understanding these complex features is of particular interest due to the fact that changes in temperature and variable degrees of fluid/rock interaction during metamorphism and intrusion have also significantly affected the chromite-hosted IPGE carrier phases. Here, we propose that the metamorphic fluids involved in the hydrous metamorphism have caused the desulphurization of laurite RuS 2 , releasing minute particles of Ru–Os–Ir alloys <50 nm in diameter. The following short-lived thermal event that promoted dehydration in the chromitite had the opposite effect on nanoparticle stability, producing a significant coarsening of metal nanoparticles to dimensions larger than a micron. Based on such observations, we argue that IPGE nanoparti-cles can be exsolved and grown (or coarsen) from sulphide matrices during prograde metamorphism or heating and not exclusively upon cooling under magmatic conditions as it has been previously suggested. These results provide new insights on the relevant role of temperature and nanopar-ticle–host interaction phenomena in natural systems, shedding new light on the kinetic controls of nano-to micron-scale IPGE particle distributions during metamorphism. Abstract The Loma Baya complex in southwestern Mexico is a volume of chromitite-bearing oceanic mantle that records a complex metamorphic history, defined by a first stage of hydrous metamorphism overprinted by a short-lived thermal event associated with an Eocene granite intrusion. During the hydrous metamorphism, the primary magmatic chromite–olivine assemblage was replaced by a secondary, porous intergrowth of Fe 2+-rich chromite and chlorite. The heat supplied by an Eocene-age granite intrusion reversed the hydration reaction, producing chro-mite rims with perfectly developed crystal faces. This third-generation chromite is in equilibrium with highly mag-nesian (neoformed) olivine and defines a chemical trend analogous to the original magmatic one. The preservation of both reactions in the Loma Baya chromitite provides compelling evidence that the hydration of chromite can be reversed by either prograde metamorphism or any heating
    Full-text · Article · Jul 2015 · Contributions to Mineralogy and Petrology
  • Source
    • "This consideration cannot explain all of the phenomena for R3, but the authors strongly consider the micro-structural change of the ALD Pt layer to be the main parameter leading to such results. Although porous Pd used as a current collecting layer may also agglomerate in a hightemperature atmosphere, the micro-structural change of porous Pd was not considered as a parameter that had an impact on the reaction kinetics due to its relatively low surface energy [25]. Meanwhile, it was recently shown that an ultra-thin Pt thin film fabricated by ALD can also serve as an electrode catalyst without an additional current collecting layer [12], which indirectly means that the porous palladium current collecting layer used in this study may have a negative effect on the diffusion of the fuel. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nano-thin platinum (Pt) films with a dense microstructure for low-temperature solid oxide fuel cells (LT-SOFCs) were fabricated by atomic layer deposition (ALD) and were charac-terized in terms of their micro-structural properties and electrochemical performance. Pt thin films with a purity level of w99% were achieved by controlling the O 2 pulsing time. The agglomeration behavior of the ALD Pt thin films was characterized by the annealing temperature, becoming extremely severe above 550 C. An LT-SOFC with a 25 nm thick dense ALD Pt cathode layer exhibited a peak power density of w110 mW/cm 2 at 450 C.
    Full-text · Article · Aug 2014 · International Journal of Hydrogen Energy
Show more