I. O. Volkov

X-ray photoelectron spectra and structure of composites prepared via deposition of Au, Ni, and Au + Ni nanoparticles on SiO2 from colloidal solutions in triethylamine

Monometallic (Au and Ni) and bimetallic (Au + Ni) nanoparticles deposited on SiO2 from colloidal solutions in triethylamine have been studied by x-ray photoelectron spectroscopy (XPS). The solutions were prepared through vapor-phase metal synthesis. We have determined the basic parameters of the core-level and valence-band XPS spectra of the Au/SiO2, Ni/SiO2, and Au-Ni/SiO2 systems. The results indicate that the Au in these systems is in the Au(0) state, while Ni is oxidized to Ni(II). The Au/SiO2 and Au-Ni/SiO2 samples differ little in the shape of the Au 4f peak. In the Au-Ni/SiO2 system, the Ni 2p3/2-Au 4f7/2 binding energy difference is 0.3 eV larger and the Ni 2p3/2 peak is narrower than those in the monometallic samples. The effects characteristic of the bimetallic system may be due to the interaction between Ni and Au or may be interpreted as evidence that the Au particles level off the potential relief on the SiO2 surface.

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.

Cyclohexane Dehydrogenation on a Copper-Platinum Catalyst

The reaction of the dehydrogenation of cyclohexane on a copper-platinum catalyst supported by silica gel (1 wt % Pt + 0.15 wt % Cu)/SiO2 was studied. The state of the catalyst surface was investigated using X-ray photoelectron spectroscopy. It was established that under both flow and static conditions, the activity of the copper-platinum catalyst is higher than the activity of a catalyst containing 1 wt % Pt/SiO2. The rise in activity as a result of the introduction of copper, due to a decrease in the activation energy, is explained by an increase in the fraction of carbon in the composition of active centers localized on particles of neutral (Ptm0) and positively charged (Ptn+δ) platinum, and by the formation of centers with increased activity as a result of the adsorption of Cu+δ on particles of Ptm0. It was demonstrated that treating the copper-platinum catalyst with the plasma of a glow discharge in argon and oxygen increases its activity, while treatment in high-frequency H2 plasma reduces it. The indicated changes in the activity are associated with the alteration of the activation energies and the number of active centers, revealed by X-ray photoelectron spectroscopy, that depend on changes in the catalyst surface composition.

Structure of mono- and bimetallic heterogeneous catalysts based on noble metals obtained by means of fluid technology and metal-vapor synthesis

Monometallic nanocomposites are obtained with the use of supercritical carbon dioxide (fluid technique) and metal-vapor synthesis (MVS), while bimetallic nanocomposites of Pt and Au noble metals and γ-Al2O3 oxide matrix are synthesized by a combination of these two methods. The structures, concentrations, and chemical states of metal atoms in composites are studied by means of small-angle X-ray scattering (SAXS), transparent electron microscopy (TEM), X-ray fluorescent analysis (XFA), and X-ray photoelectron spectroscopy (XPS). The neutral state of metal atoms in clusters is shown by XPS and their size distribution is found according to SAXS; as is shown, it is determined by the pore sizes of the oxide matrices and lies in the range of 1 to 50 nm. The obtained composites manifest themselves as effective catalysts in the oxidation of CO to CO2.

X-ray photoelectron and Mössbauer spectroscopy studies of bimetallic 57Fe-Pd nanocomposites prepared by metal-vapor synthesis

X-ray photoelectron and Mössbauer spectroscopy were used to study the composition and structure of 57Fe-Pd bimetallic black and 57Fe-Pd/SiO2 nanocomposites prepared by metal-vapor synthesis. The main parameters of the core level photoelectron spectra of 57Fe-Pd systems were determined. The bimetallic system was shown to be a disordered amorphous structure consisting of Pd particles, superparamagnetic γ-Fe2O3 nanoparticles with size 8–10 nm, and a Fe-O-Pd solid solution. Considerable broadening of Pd 3d peaks in 57Fe-Pd/SiO2 and an increase in the O 1s-Si 2p energy interval by 0.4 eV with respect to the spectrum of initial SiO2 were observed; this was evidence of the interaction of Pd with the support. The binding energy of Fe 2p3/2 peak in the nanocomposite spectrum was close to that of Fe2O3, but had a smaller width of the satellite peak and a larger spin-orbit splitting, which was indicative of a considerable amount of FeOOH on the surface compared with the other iron oxides.

Magnetodielectric composites based on functionalized polyphenylene sulfides containing iron nanoparticles

Preparation of iron-filled polyaminophenylene sulfides and polyhydroxyaminophenylene sulfides by the metal vapor procedure was studied. Nanocomposites based on these metal-containing polymers and epoxy-isopropylidenediphenol oligomers (ED-20) were prepared and their composition, properties, and structure were studied by X-ray diffraction and thermogravimetric analyses, and thermomechanical methods. The magnetic and dielectric properties of the materials were determined.

Dehydrogenation of isopropyl alcohol on modified cobalt catalyst

The effects of plasmochemical processing and of Ce, K, and Hf additives on the rate of dehydrogenation for isopropyl alcohol on a 5 wt % Co/SiO2 catalyst is studied under static and flow conditions. Glow discharge plasma in O2 and Ar and high-frequency electrodeless plasma in H2 (HF-H2) are used. Except for one sample containing Hf, an increase in catalytic activity is observed due to the formation of new active centers. The change in the composition of the initial catalyst’s surface after treatment with Ce and with oxygen, argon, and HF-H2 plasmas is determined by means of X-ray photoelectron spectroscopy. The change in the size and shape of Co particles after treating the catalyst with HF-H2 plasma and Ce is determined via X-ray phase analysis. It is suggested that the new catalytic centers formed after treatment in O2 and Ar plasma contain carbon atoms with C1s bond energies of 282.1 eV; after treatment with HF-H2 plasma, active centers contain hydrogen and carbon atoms with C1s bond energies of 282.5 eV; with cerium, the C1s bond energy is 297.7 eV.

Gold- and silver-containing fibroporous polytetrafluoroethylene obtained under laser irradiation, supercritical carbon dioxide treatment, and metal-vapor synthesis

A combined approach to the synthesis of functional nanocomposite materials based on fibroporous polytetrafluoroethylene (PTFE) prepared by the CO2 laser irradiation of the block PTFE sample (fluoroplastic-4) has been developed. Fibroporous materials (FPM) such as cotton and felt were modified by supercritical carbon dioxide treatment to create nano- and micropores in the surface layers of FPM fibers. The gold- and silver-containing fibroporous nanocomposites have been obtained by processing the nano-structured FPM with the organosols of the metal nanoparticles in isopropanol prepared by metal-vapor synthesis. The composition and structure of the metal-containing fluoropolymers have been investigated by X-ray analysis and electron microscopy.

Studying the structure of siloxane-urethane-ethylene oxide block copolymers

The structure of siloxane-urethane-ethylene oxide block copolymers is studied by means of atom force microscopy (AFM) and scanning electron microscopy (SEM). The degree of copolymer crystallinity is determined by X-ray diffraction. A correlation between the obtained results is established.

Studying the structure of nanocomposites obtained via the chemical decomposition of metal siloxanes in polymer matrices

The structure of polymer nanocomposites containing CuS clusters is studied by atom force (AFM), scanning (SEM), and transmission (TEM) electron microscopy, and by narrow-angle X-ray scattering (SAXS). The results point to the existence of spherical nanoparticles of 3–50 nm in diameter and larger agglomerates of sizes 1–5 μm in the studied nanocomposites (NCs). The morphology of NCs depends on the conditions of synthesis.