The Pt Atom

In Figure 12a (Pd Pt = 1 2) and 12b (Pd Pt = 1 1), only the spectral feature of CO adsorbed on the Pt atoms, i.e., a strong band at 2068 cm and a very weak broad band at around 1880 cm was observed, while that derived from CO adsorbed on Pd atoms at 1941 cm is completely absent, which proved that the Pd-core has been completely covered by a Pt-shell. Recently we also characterized Au-core/Pd-shell bimetallic nanoparticles by the CO-IR [144]. Reduction of two different precious metal ions by refluxing in ethanol/ water in the presence of poly(A-vinyl-2-pyrrolidone) (PVP) gave a colloidal dispersion of core/shell structured bimetallic nanoparticles. In the case of Pd and Au ions, the bimetallic nanoparticles with a Au-core/Pd-shell structure are usually produced. In contrast, it is difficult to prepare bimetallic nanoparticles with the inverted core/shell, i.e., Pd-core/Au-shell structure. A sacrificial hydrogen strategy is useful to construct the inverted core/shell structure, where the colloidal dispersions of Pd cores are treated with hydrogen and then the solution of the second element, Au ions, is slowly... 

The stoichiometric Pt3Co(lll) surface has one-quarter of the Pt atoms replaced with Co atoms. Bulk Co is very reactive toward oxygen, on which O2 dissociation is probably non-activated. The Co atoms on the alloy surface are diluted by Pt, but... 

C222x Z = 4 Dx = 1.82 R = 0.061 for 3,313 intensities. The structure is isomorphous with the monosodium salt of 5 -IMP.184 The structure is a nonstoichiometric complex (—86% Pt occupancy). The 5 -IMP molecules (86% occupancy) liganded to the Pt exist as dianions, whereas the 5 -IMP molecules (0.14% occupancy) not involved in Pt coordination are monoprotonated (5 -IMPH). The coordination about the Pt atom is approximately square-planar two of the ligands are the N-7 atoms of the hypoxanthine base and the two ammonia molecules. In fact, the Pt atom... 

The two predominant features in Figure 3.24 are attributable to the 4f orbitals of the Pt electrode. The two peaks were deconvoluted as shown into a main peak and a smaller satellite peak. At potentials > 0.7 V vs. SCE, a peak at 77.1 eV was observed which was attributed to PtO. On the basis of these results, those of Kim et ai (1971), and the coulometric and ellipsometric data discussed above, Augustynski and Balsenc (1979) proposed that the signal attributed to the Pt 4f orbitals shifted via formation of PtO was only observed after the formation of the phase oxide, since it is only after this place exchange that the chemical environment of the Pt atoms is modified... 

MoOj. After this reduction the Pt atoms may form a surface complex with the partially reduced Mo ions. For the Pt-Mo/y-AljO catalysts which are used at temperatures < 600°C, the active complex may be the dispersed PtM.oOx (where X = 2-3), under the reducing conditions. For temperatures > 600°C, the catalyst can have the surface complex of PtMoOj where x ranges from 0 to 2 depending upon the temperature of reduction. 

Adsorbates may form ordered overlayers, which can have their own periodicity. The adsorbate structure is given with respect to that of the substrate metal. For simple arrangements the Wood notation is used some examples are given in Fig. A.3. The notation Pt (110) - c(2x2) O means that oxygen atoms form an ordered overlayer with a unit cell that has twice the dimensions of the Pt (110) unit cell, and an additional O in the middle. Note that this abbreviation does not specify where the O is with respect to the Pt atoms. It may be on top of the Pt atoms but also in bridged or fourfold sites, or in principle anywhere as long as the periodic... 

Platinum-195-NMR spectroscopy is an effective means to probe the electronic state of the Pt atoms in the compounds. The 196Pt nucleus,... 

The Ptm-Ptm bond in the alkyl complexes exhibits a unique character in that the Pt atom acts both as Ptn and PtIV or the intermediate through electron localization and delocalization along the Pt-Pt axis (1) coordination of olefin is a Pt11 character, since no olefin-Pt17 complex is known and (2) the very easy and rapid nucleophilic attack on the coordinated alkyl ce-carbon atoms is a PtIV character. Alkyl-Ptn complexes do not easily undergo nucleophilic attack unless the com-... 

Table 4. CASPT2 excitation energies for the Pt atom including the effect of spin-orbit coupling...

The XANES region of the Pt Lm and Ln absorption edges can be used to determine the fractional d-electron occupancy of the Pt atoms in the catalyst sample by a so-called white line analysis. Figure 2 shows the XAS spectrum collected at both Pt Lm and Lii absorption edges of Na2Pt(OH)e. The sharp features at the absorption edges are called white lines after the white line observed in early photographic film based XAS measurements. Mansour and coworkers have shown that comparison of the white line intensities of a sample with those of a reference metal foil provides a measure of the fractional d-electron vacancy, f, of the absorber atoms in the sample. is defined as follows ... 

Ru provides sites for water activation as well as having an electronic effect on the Pt atoms, such that CO is less strongly adsorbed. In situ XAS measurements have been used to determine the structure of PtRu catalysts, to assess the magnitude of any electronic effect that alloy formation may have on the Pt component of the catalyst, and to provide evidence in support of the bifunctional mechanism. 

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