Oxidation state surface

Silvery, shiny, and hard. Unique metal, gives off an odor as it forms volatile 0s04 on the surface (oxidation states 81). Osmium is the densest element (22.6 g cm3 record ). Was replaced in filaments (Osram) by the cheaper tungsten. Used in platinum alloys and as a catalyst. Haber s first catalyst in ammonia synthesis was osmium, which fortunately could be replaced by doped iron. The addition of as little as 1 to 2 % of this expensive metal increases the strength of steel (e.g. fountain-pen tips, early gramophone needles, syringe needles). 

Work is continuing to correlate the formation of surface oxidation states with changes in the photoconduction of films of PVCa. The relationship between energy transfer and photoconductivity is being investigated. 

Two final concerns must be addressed surface oxidation state and temperature dependence. Whenever one deposits a redox-active species on a metal surface, the oxidation state of the adsorbate (and therefore the OMTS bands) may change. One example is the adsorption of a biaxially substituted dicyano cobalt phthalocy-anine salt, MCoPc(CN)2 (where M = K or Cs), on gold to form the reduced species CoPc [111]. A second example is provided by the adsorption of TCNE on gold, silver, and copper. In that order, the charge state of TCNE on the surface ranges from 0 to 3, and the OMTS reflects these changes. 

Role of Ciystallographic Shear Planes This area is tied to the subject of surface oxidation state. In redox kinetics it is believed that sites for hydrocarbon oxidation are different from that for reoxidation, and crystallographic shear planes (CSP) have been suggested to assist bulk oxygen movement between the sites 44,45,46,47), There have been a few studies of this phenomenon. In WO2.95 WO2.9 it has been shown CSPs are involved in oxygen transfer but... 

J. F. Surface oxidation states of germanium. Surface Science 172, 455-65 (1986). 

The reactions of UO2 in aqueous solutions are of importance to the long-term storage of fission reactor spent-fuel. In particular, the leaching and dissolution mechanisms of UO2 in water will determine nuclide release rates in cases where fuel cladding fails (410. In order to determine the reactivity of UO2, a number of studies have been done including XPS work by McIntyre et al (1 4). Part of the objective of their work was to determine the variations in surface oxidation state of UO2 upon exposure to aqueous solution in an effort to understand how the reactivity of UC>2 would change. 

Lev et al. reported images of a Ni foil. They revealed flat terraces, 2-3 nm high. The authors noted the influence of the surface oxidation state on the tunneling current increase while the tip was engaged, and they explained this effect by the resistance of the oxide layer. 

Furthermore, the O/Mn ratio in the rams-Mn02 and the nsu-Mn02 samples are identical this implies that they present exactly the same oxidation state (0/Mn=1.95). The py-Mn02 sample initially contains a slightly more oxidised Mn (0/Mn=1.96). But XPS shows that the surface oxidation state becomes identical to that of the other forms under the reaction conditions (XPS Mn 3s shake up satellite = 4,9 + 0.1 eV). The variation of activity reported above cannot be linked to differences in the Mn mean oxidation state. In addition, as mentioned in the introduction, Py-Mn02, nsu-Mn02 and rams-Mn02 are so closely related structurally that the first coordination sphere of the Mn ions is the same in these 3 phases. 

The surface oxidation state of the transition metal and the availability of vacancies and/or adsorbed oxygen play a central role in defining the catalytic behavior of the oxides for this and other reactions. Particularly enlightening is fig. 25 which shows how the catalytic activity increases with the increasing average oxidation number (AON) of copper. 

The adsorption was measured by two methods (a) from the change of the capacitance of the electrode and (b) from the decrease of the oxidation charge of the electrode surface as measured by the charge associated with reduction peaks in a cathodic sweep taken from high (1.8 2.2 V) potentials. The surface oxide state that is influenced by adsorption of organic molecules is that which is reduced at the most cathodic potentials, 0.2 V, over the potential range that is normally associated with H underpotential deposition. 

Transition from an osciiiating surface oxide state to a permanentiy oxidised sampie during gas phase osciiiation... 

The hypothesis of an oscillation mechanism controlled by the catalyst bulk state is supported by the experiment with variable heat conductivity of the gas phase the branch of the phenomenon which is heat-dissipation independent indicates that a significantly larger sample volume than the near-interface region which should always be in thermal equilibrium with the gas phase is taking part. Therefore, it is assumed that the oscillation characterised by long cycle times and large amplitudes are controlled by a bulk process. Moreover, it is most probable that the oscillation of the macroscopic surface oxidation state namely metal or oxide as seen by visible inspection is only a secondary process that does not control the oscillating mechanism. 

In establishing the chemical state of the catalysts, XPS was used to determine the surface oxidation state of the metallic clusters and supports. As most of the atoms in nanocluster particle are surface atoms, it is expected that the measured oxidation state well reflects the bulk oxidation state. Pt4f and Cis spectra for the chemical-treated CBs-supported Pt catalysts are shown in Figures 4 and 5. The binding energies (BE) and relative peak areas are summarized in Table 5. 

The reasons for the deterioration of ceU performance can be distinguished in reversible and irreversible power loss. Inevitable irreversible performance loss is caused by carbon oxidation, platinum dissolution, and chemical attack of the membrane by radicals [7]. Reversible power loss can be caused by flooding of the cell, dehydration of the membrane electrode assembly (MEA), or change of the catalyst surface oxidation state [8]. If corrective actions are not started immediately, reversible effects lead to irreversible power loss that we define as degradation. In this chapter, we focus on the degradation of the catalyst layer due to undesired side reactions. 

The HPLP apparatus has been used to study the hydrogenation of carbon monoxide on iron and rhodium polycrystalline specimens as well as on sit e crystals and various rhodium compounds." Postreaction surface analysis revealed the presence of a catalytically active carbonaceous layer on all the samples investigated. In addition, precise control of the rhodium surface oxidation state by oxygen pretreatment in the UHV chamber was found to have a marked effect on the product distribution of the rhodium catalyzed reaction. 

The surface oxidation state would be changed by the control of a partial oxidation of non-oxides. Carbonitrides of group 4 and 5 elements were used as precursors for a partial oxidation. Carbonitrides form a complete solid solution of carbide and nitride. A partial... 

Lee, WH Reucroft, PJ. Vapor adsorption on coal- and wood-based chemically activated carbons (1) Surface oxidation states and adsorption of H2O. Carbon, 1999, 37, 7-14. 

Spark sensitivity values for a series of pyrotechnic compositions are given in Table 6.1. It can be seen that these values tend to be considerably greater than 0.10 J, unless a line metal powder (such as aluminum) is used. Keep in mind that spark sensitivities can vary greatly for a given oxidizer-fuel mixture, with the particle size and surface oxidation state of the fuel often playing a very significant role. A manufacturer cannot rely on spark sensitivity results other than those obtained on compositions produced by his company. 

Results discussed in this section reveal important trends in the stability of Pt nanoparticles. They identify the surface tension as a valid descriptor of nanoparticle stability. The surface tension must play an important role in the kinetic modeling of nanoparticle dissolution (Rinaldo et al., 2010, 2012). However, the main kinetic mechanisms that contribute to Pt nanoparticle dissolution proceed via formation and reduction of surface oxide intermediates at Pt. This well-founded observation suggests that stability studies, reported here for bare Pt nanoparticles evaluated in vacuo, should be expanded to Pt nanoparticles of varying surface oxidation state as well as conditions that mimic electrochemical conditions that the fuel cell catalyst is exposed to. 

In nanoparticle electrocatalysis, the area that Michael entered just some time ago in Munich, he and his coworkers rationalized the sensitivity of electrocatalytic processes to the stmcture of nanoparticles and interfaces. Studies of catalytic effects of metal oxide support materials revealed intriguing electronic structure effects on thin films of Pt, metal oxides, and graphene. In the realm of nanoparticle dissolution and degradation modeling, Michael s group has developed a comprehensive theory of Pt mass balance in catalyst layers. This theory relates surface tension, surface oxidation state, and dissolution kinetics of Pt. 

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