Platinum clusters oxygen

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

Platinum clusters, n = 2-11 react with di oxygen at a rate that is within an order of magnitude of gas kinetic. There is no distinct size selective behavior. Products of these gas phase reactions observed with 7.87 eV ionization laser, are PtpO where for m=l,... 

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

It has also been well established that metals in the very finely divide state are unusually reactive. For example, Parmigiani and co-workers [72] have demonstrated that at low oxygen pressure, supported platinum clusters oxidize at room temperature, whereas the bulk metal reacts at the same pressure only around 800 K. Clearly, the active sites, based on small particle sizes and high defect densities, have implications aside from electrochemistry. 

Li, T., Balbuena, P.B. Oxygen reduction on a platinum cluster. Chem. Phys. Lett. 2003,367,439-47. 

With this method, Andersson and Rosen [169] recently investigated the adsorption of hydrogen or deuterium and oxygen on neutral platinum clusters and discovered the catal3dic water formation on the free clusters. Figure 1.30 displays mass spectra obtained with different partial pressures of hydrogen and oxygen in the separate collision gas cells. Panel a in Fig. 1.30 shows a mass spectrum of pure Pt clusters with no reactive gas in the collision cells. The mass spectrum in panel b was sampled after the cluster ions passed reaction cell 1 filled with 0.14 Pa of O2. The additional peaks in the mass spectrum... 

Molecular Oxygen Binding Energies, BE, and Optimized Pt—O and O—O Distances (Rr o and / 0 0), and Perpendicular Distance from the O Atom Closer to the Plane of the Platinum Cluster (D) for Different [Pt(111)]1802 and [Pt(100)]1802 Configurations at Equilibrium Potential... 

Monodispersed platinum clusters are prepared on a MgO(lOO) film by deposition of size-selected platinum cluster ions followed by neutralization. Subsequently, the deposited clusters are exposed to an isotopic oxygen gas until about twenty 02 molecules per platinum atom are adsorbed on the platinum clusters. Temperature-programmed-reaction proves that (carbon dioxide) molecules are produced, when C 0... 

Li, T. Balbuena, P. B. Computational studies of the interactions of oxygen with platinum clusters. J. Phys. Chem. B 2001,105, 9943-9952. 

Yamamoto K, Imaoka T, Chun WJ, Enoki O, Katoh H, Takenaga M, Sonoi A (2009) Size-specific catalytic activity of platinum clusters enhances oxygen reduction reactions. Nat Chem... 

In the case of the Pt(lOO) surface the interaction potential is derived from semiempirical quantum chemical calculations of the interactions of a water molecule with a 5-atom platinum cluster [35]. The lattice of metal atoms is flexible and the atoms can perform oscillatory motions described by a single force constant taken from lattice dynamics studies of the pure platinum metal. The water-platinum interaction potential does not only depend on the distance between two particles but also on the projection of this distance onto the surface plane, thus leading to the desired property of water adsorption with the oxygen atoms on top of a surface atom. For more details see the original references [1,2]. This model has later been simplifled and adapted to the Pt(lll) surface by Berkowitz and coworkers [3,4] who used a simple corrugation function instead of atom-atom pair potentials. 

Nesselberger, M., Roefzaad, M., Fay cal Hamou, R., Ulrich Biedermann, R, Schweinberger, F. E, Kunz, S., Schloegl, K., Wiberg, G. K. H., Ashton, S., Heiz, U., Mayrhofer, K. J. J., Arenz, M. (2013). The effect of particle proximity on the oxygen reduction rate of size-selected platinum clusters. Nature Materials, advance online pubhcation. doi 10.1038/nmat3712. 

In a carbon-supported metal electrocatalyst, the electronic interaction between metal and carbon support has a significant effect on its electrochemical performance [4], For carbon-supported Pt electrocatalyst, carbon could accelerate the electron transfer at the electrode-electrolyte interface, leading to an accelerated electrode process. Typically, the electrons are transferred from platinum clusters to the oxygen species on the surfece of a carbon support material and the chemical bond formation or the charge transfer process occurs at the contacting phase, which is considered to be beneficial to the enhancement of the catalytic properties in terms of activity and stability of the electrocatalysts. Experimentally, the investigation into the electron interaction between metal catalyst and support materials could be realized by various physical, spectroscopic, and electrochemical approaches. The electron donation behavior of Pt to carbon support materials has been demonstrated by the electron spin resonance (ESR) X-ray photoelectron spectroscopy (XPS) studies, with the conclusion that the electron interaction between Pt and carbon support depends on their Fermi level of electrons. It is considered that the electronic structure change of Pt on carbon support induced by the electron interaction has positive effect toward the enhancement of the catalytic properties and the improvement of the stability of the electrocatalyst system. However, the exact quantitative relationship between electronic interaction of carbon-supported catalyst and its electrocatalytic performance is still not yet fully established [4]. 

This direct reduction gave very poor dispersion because the neutral hydride is very mobile and favors transport processes leading to metal agglomeration in large particles. A calcination step, preferably in pure oxygen, must be conducted to decompose the complex prior to H2-reduction to obtain well-dispersed platinum clusters [74]. This requirement is valid for all other ammino cations of platinum group metals (see Sect. 3 for case studies). The only exception is ru-... 

The rhenium interacts strongly with the oxygen atoms of the support and also with platinum platinum interacts less strongly with the support than rhenium. One is tempted to generalize that when one of the metals in a supported bimetallic cluster is noble and the other oxophihc, the oxophUic metal interacts more strongly with the support than the noble metal if the bimetalhc frame of the precursor is maintained nearly intact, then this metal-support interaction helps keep the noble metal highly dispersed. 

Zhang J, Sasaki K, Sutter E, Adzic RR. 2007b. Stabilization of platinum oxygen reduction electrocatalysts using gold clusters. Science 315 220-222. 

Zhang, J., K. Sasaki, E. Sutter, and R. R. Adzic. Stabilization of Platinum Oxygen-Reduction Electrocatalysts Using Gold Clusters. Sci-... 

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