Au-Ni and Au-Fe heterometallic systems: an X-ray photoelectron spectroscopy study

Results of X-ray photoelectron spectroscopy (XPS) studies of Au-Ni and Au-Fe bimetallic nanoparticles (in the form of black and supported on SiO₂) are considered and systematized. The nanoparticles studied were prepared by metal-vapor synthesis. XPS studies on the chemical compositions, structures, and electronic states of heterometallic nanocomposites carried out both in the traditional and differential charging mode with a bias voltage applied to the sample holder are analyzed. The effect of the composition and electronic state of the Au-Ni heterometallic system on its catalytic activity is studied. It was shown that the variable differential charging mode allows one to identify and characterize species of different nature in multi-component heterometallic nanostructured materials. A state which correlates with the catalytic activity of the Au-Ni/SiO₂ system was identified in the Au 4f photoelectron spectra.     

X-ray photoelectron spectra of some Ni mono- and polynuclear complexes

The core-level photoelectron spectra for Ni(bpy)₂(OOCCMe₃)₂, Ni₂(H₂O)bpy₂(OOCCMe₃)₄, Nibpy(OOCCMe₃)₂, Ni(C₁₀H₄(CH₃)₂N(SO₂C₆H₄(CH₃), Ni₂(2,4-Lut)₂(OOCCMe₃)₄, and (2,4-Lut is 2,4-lutidine) are reported and discussed, and the role of ligands in their appearance is determined. X-ray irradiation of some complexes was found to induce removal of some pyridyl rings and oligomerization both at room and liquid nitrogen temperature. The dependence of composition on temperature was used to find correlation between ligand surrounding and the spectra.     

Asymptotics ast → ∞ of the solutions of nonlinear equations with nonsmall initial perturbations

A new method is proposed for finding asymptotics ast → ∞ of the solutions of the Cauchy problem for nonlinear evolution equations with nonsmall initial data. Translated fromMatematicheskie Zametki, Vol. 59, No. 6, pp. 855–864, June, 1996. This research was supported by the Russian Foundation for Basic Research under grant No. 93-011-134 and by the International Science Foundation under grant No. BX000.     

Induced super-halogen behavior of metal moieties in halogen-doped clusters: LinI(-) and AlnI(-), n = 13, 1, 2, 3

A comparative density functional theory (DFT) study of a series of neutral and negative-ionic lithium and aluminum clusters doped with iodine atom is presented. The I atom is found to preserve the same position at Li13 with and without the negative charge and Li13 to vary its shape from prolate to oblate with changing spin state of Li13I. Both the Mulliken and natural charges are considered, the natural-charge separation between the metal and halogen moieties being generally much larger (except for Al13I-). In LinI-, the additional electron is strongly localized on the metal moiety starting from n = 1, even though the electron affinity of Lin is much smaller than that of I. Such a super-halogen behavior of Lin is induced by highly electronegative iodine making the two components charged in LinI and leading to a charge-dipole interaction with the additional electron. In AlnI-, similar factors result in Aln being more negative than I already for n = 3, even though the electron affinity of I is higher, the effect escalating for n = 13.     

A quadratic quasi-linear Klein–Gordon equation in two space dimensions

We consider the quasi-linear Klein–Gordon equations in two space dimensions $$\left(\partial_{t}^{2} - \Delta + 1\right) u=\mathcal{N} (u)$$ in ${(t, x) \in \mathbf{R} \times \mathbf{R}^{2}}$ with a quadratic nonlinearity ${\mathcal{N} (u)}$ , which is linear with respect to the second-order derivatives of unknown functions.     

Thermochemical studies of 4-tert-butylbiphenyl and 4,4′-di-tert-butylbiphenyl

The standard massic energies of compounds of 4-tert-butylbiphenyl and 4,4′-di-tert-butylbiphenyl were measured at T = 298.15 K by static-bomb combustion calorimetry. The standard enthalpies of vaporization, fusion and sublimation were measured in a Calvet microcalorimeter, or by differential scanning calorimetry. The standard molar enthalpies of formation in the condensed and gaseous states were obtained from these data. The tert-butyl group increments for the substitution of one hydrogen atom in a position “4” in biphenyl molecule were calculated.     

The influence of plasma chemical treatment of a platinum catalyst on its activity in the dehydrogenation of cyclohexane

The influence of plasma chemical treatments on the catalytic activity of 0.64 wt % Pt/SiO₂ and 1.0 wt % Pt/SiO₂ platinum catalysts in the dehydrogenation of cyclohexane was studied. The state of the surface of the catalysts was examined using X-ray photoelectron spectroscopy. Temperature hysteresis caused by the formation of active carbon was observed in flow experiments. It was shown that the reaction on the initial catalysts occurred on neutral and positively charged Pt particles, and that the active centers contained carbon. After catalyst treatment with a high-frequency plasma in H₂, its activity increased by many times because of the formation of a large number of low-activity centers on positively charged platinum particles also containing carbon. Glow discharge plasma in Ar sharply decreased catalytic activity, and the reaction then predominantly occurred on centers localized on neutral Pt particles, whereas centers on positive Pt particles were blocked. The state of the substrate (silica gel) did not change under the action of plasmas of both kinds.