Catalytic conversions of chloroolefins over iron oxide nanoparticles 2. Isomerization of dichlorobutenes over iron oxide nanoparticles stabilized on the surface of ultradispersed poly(tetrafluoroethylene)

Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene) (UPTFE) granules were synthesized by the thermal destruction of iron formate in boiling bed of UPTFE on the surface of heated mineral oil. The particle size of nanoparticles (∼6 nm) containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to polymer ratio. The metal state is determined by the synthesis conditions. The nanoparticles synthesized at 280 °C consist mainly of the Fe₃O₄ and Fe₂O₃ phases. The samples obtained at 320 °C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested in dichlorobutene isomerization. Unlike isomerization on the iron oxide nanoparticles supported on silica gel, reaction over the UPTFE supports proceeds without an induction period. The sample with 10 wt.% Fe containing magnetically ordered γ-Fe₂O₃ nanoparticles possesses the highest catalytic activity. Fast electron exchange between the iron ions in different oxidation states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic activity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1383–1390, June, 2005.     

Synthesis and Characterization of Iron Oxide Nanoparticles by Solid State Chemical Reaction Method

The iron oxide nanoparticles were synthesized by solid state chemical reaction method. The synthesized powders were characterized by XRD, SEM, EDAX and TG-DTA techniques. An average grain size of 10–20 nm for Maghemite and 80–85 nm for Hematite was calculated using XRD line broadening and SEM. The effect of different parameters such as annealing temperature, milling time, Fe⁺³:Fe⁺² concentration ratio have been investigated on the particle size and phase formation. Heat treatment of the produced powders in which Fe⁺³:Fe⁺² ratio equal to 2:1, resulted in tetragonal (Maghemite) and rombohedral (Hematite) structures at 300 and 600 °C, respectively. It was found that by changing Fe⁺³:Fe⁺² ratios from 2:1 to 1:2, hematite phase and from 2:1 to 1:1, Maghemite phase were formed at 300 °C. In addition with increasing milling time, the iron oxide particle size decreases, but there was no changing in the kind of phase.     

Influence of the conditions of manufacture of nanomeric zirconium dioxide,stabilized with yttrium oxide,on its catalytic properties in the oxidation of CO

The morphological and catalytic properties of samples of nanomeric zirconium dioxide, stabilized with yttrium oxide, manufactured via the effect of a UHF field during the process of drying precipitated zirconium hydroxide and calcination at temperatures from 300 to 1000 °C, were studied. It was shown that the highest activity in the oxidation of CO occurred with 40 nm particles of zirconium dioxide prepared at 1000 °C. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 96–101, March–April, 2007.     

Activity of copper–cerium–zirconium catalysts in oxidation of hydrogen

We have studied the catalytic properties in oxidation of hydrogen for copper–cerium oxide systems deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300–1000 °C. We have shown that the catalytic activity of the samples obtained depends on the specific surface area of the original supports and the amount of reduced copper within the composition of the catalyst. In samples whose support has high specific surface area, the content of reduced metallic copper is greater and the catalytic activity is higher.     

Formation and properties of the nanocluster structure of iron oxides

Nanostructures based on iron oxide clusters 1–300 nm in size were synthesized and studied. Thermodynamic models of nanocluster nucleation resulting in the formation of both primary nanoclusters and nanocluster aggregates with the sizes up to 70–80 nm were considered. Models of heat capacity of the nanoclusters were examined, and the twofold increase in the heat capacity of the iron oxide clusters 2–3 nm in size compared to that of the bulk iron oxide samples was found. The size of the primary nanoclusters and the intercluster interaction make it possible to vary the magnetic properties of the nanostructures in a wide range from paramagnetic to magnetically ordered α-Fe₂O₃-γ-Fe₂O₃ nanostructures with the first-order magnetic phase transitions, magnetic twinning, and a strong magnetic field (10 Oe) effect on the magnetization increase at low temperatures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1693–1704, October, 2006.     

On the nature of decrease in the particles size of nanostructured nickel oxide obtained by the sol-gel method in the presence of surfactants

A processes of formation of nanostructured powders of nickel oxide by annealing in the temperature range of 200–700°C of the nickel hydroxide obtained by the sol-gel method at 80°C from solutions of nickel nitrate by precipitation with alkali in the presence of surfactant AF-12 (polyethylene oxide alkylphenyl ether) was investigated. The formation of nanostructured powders of nickel oxide in the presence of a surfactant reduces the size of nanoparticles to 20–25 nm, which is 1.5 times smaller than the particles obtained without a surfactant. The effective influence of surfactant on the particle size begins in the temperature range of its decomposition and evaporation equal 350–400°C.     

Cu-Co-Fe oxide catalysts supported on carbon nanotubes for the oxidation of CO

The catalytic activity and adsorption characteristics of the surface of catalysts in the form of carbon nanotubes produced on nickel and cobalt oxides with the Cu-Co-Fe oxide system as supported active phase were studied. At carbon nanotubes produced on nickel oxide with (10 + 10) wt.% of the catalytically active phase total conversion of CO to CO₂ is realized at 47 °C. This sample has high specific surface area and a large volume of mesopores. It was shown that the increase in catalytic activity correlates with the increase in the amount of the α₂ form of CO₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 222–226, July–August, 2006.     

Hydrophilic magnetic polymer latexes. 1. Adsorption of magnetic iron oxide nanoparticles onto various cationic latexes

With a view to preparing monosized hydrophilic functional magnetic latex particles based on a two-step strategy using anionic iron oxide and cationic polymer latexes, the adsorption step was systematically investigated for a better control of the subsequent encapsulation step. The iron oxide nanoparticles were first obtained according to the classical precipitation method of ferric and ferrous chloride salt using a concentrated sodium hydroxide solution, whereas the polystyrene (PS), P(S/N-isopropylacrylamide (NIPAM)) core–shell and PNIPAM latexes were produced via emulsion and precipitation polymerizations, respectively. The polymer and inorganic colloids were then characterised. The adsorption of iron oxide nanoparticles onto the three types of polymer latexes via electrostatic interaction was studied as a function of iron oxide particle concentration, charge density and the cross-linking density of the hydrophilic layer. The maximum amounts of magnetic nanoparticles adsorbed onto the various latexes were found to increase in the following order: PS < P(S/NIPAM) < P(NIPAM). This significant difference is discussed by taking into account the charge distribution in the hydrogel layer and diffusion phenomena inside the cross-linked hydrophilic shell. Received: 28 December 1998 Accepted in revised form: 15 April 1999     

Small-size ZnO/MgO quantum systems with zinc oxide nanoparticles of controlled size

A method is proposed for the preparation of nanosized ZnO/MgO systems by the deposition of previously formed zinc oxide nanoparticles onto a support from a colloidal solution and for determination of the size of the deposited ZnO particles from the electronic spectra. The morphology of composites containing zinc oxide nanoparticles was investigated by electronic spectroscopy and transmission electron microscopy. The possibility of synthesizing solid-phase ZnO/MgO quantum systems with controllable size characteristics was demonstrated. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 183–188, May–June, 2007.     

Synthesis of iron oxide nanoparticles using chitosan and starch templates

Natural polymers like chitosan and starch have been employed as templates for the preparation of iron oxide nanoparticles. The templates offer selective binding sites for Fe(II) under aqueous conditions. Controlled drying and subsequent removal of the template backbone enables the synthesis of spatially separated iron oxide nanoparticles. The crystalline character of the iron oxide and near narrow particle size distribution pattern have been confirmed through powder XRD, Photon Correlation Spectroscopy, and TEM measurements. The crystallite sizes of the particles were found to be 26–35 nm irrespective of the nature of the template.     

Synthesis and characterization of Fe doped mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> by sol–gel method and its use in trichloroethylene combustion

Two mesoporous alumina samples were synthesized using the sol–gel method, and these samples were tested as catalysts in trichloroethylene combustion reaction. One alumina sample was doped with Fe to study the influence of a small amount of this agent on the characteristics and properties of alumina as a catalyst. Both catalysts (pure alumina and alumina doped with Fe) were thoroughly characterized by different techniques, such as DTA/TGA, FT-IR, XRD, SEM and TEM, and the porous characterization was conducted using a N₂ physisorption technique. The doping agent presented a particular influence on the morphology and textural porosity in the alumina catalyst and therefore, it exhibited different catalytic behavior than the pure alumina catalyst. For both catalysts, the crystalline phase of γ-alumina was reported using XRD technique, and the crystallite size ranged from 7.8 to 12.8 nm. Using TEM images, the alumina catalyst doped with Fe revealed to contain a mixture of three types of iron oxide (maghemite, magnetite and hematite), mainly as roughly spherical nanoparticles. For both alumina catalysts, trichloroethylene catalytic combustion was conducted on a packed bed reactor in air at a temperature range of 50 to 600 °C. The alumina catalyst doped with Fe showed a higher catalytic activity than pure alumina, mainly due to the presence of micropores and grain morphology of flat faces.     

Synthesis and characterization of sol–gel derived bioactive CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses containing magnetic nanoparticles

Magnetic bioglasses in the system CaO–SiO₂–P₂O₅ were prepared by interaction of acetic acid vapors with iron nitrate dispersed on the surface of sol–gel derived porous silicate network. Upon pyrolysis, the created iron acetate species transform into magnetic iron oxide nanoparticles. X-ray diffraction (XRD), FT-infrared (FT-IR) spectroscopy and surface area measurements (BET) were employed to monitor the evolution of glass structural features during the synthetic pathway as well as the structure and the texture of the resultant glasses. XRD, Raman spectroscopy and vibration magnetic measurements (VSM) revealed the features of magnetic phases, developed in the form of γ-Fe₂O₃ and magnetite. The obtained glasses exhibit in vitro bioactivity, expressed by spontaneous formation of hydroxyapatite on their surface after immersion in SBF at 37 °C, confirmed with μ-Raman and FT-IR spectroscopies.     

Synthesis of fluorine doped tin oxide nanoparticles by sol–gel technique and their characterization

This article presents novel attempt to synthesis of fluorine doped tin oxide (FTO) nanoparticles by sol–gel technique. The synthesized FTO nanoparticles were obtained after calcination. Temperatures of calcination were 600 and 700 °C due to identify changes in the particles size growth. A DG/DTA and FTIR study identifies the oxide and formation of the nanopowders. The XRD studies confirm the tetragonal crystallite structure of fluorine doped tin oxide. The TEM image confirms the size of FTO particles in nanoscale. The electrical studies on FTO nanopowders results the decrease in resistivity profile with increasing calcinations. The optical band gap studies for sol–gel synthesis FTO nanoparticles is found to be in the range of 4.11–3.84 eV conforming decreasing optical band gap with increasing calcinating temperatures.     

Reactivity of nanoparticles; interaction between zinc and copper oxide nanoparticles and iron ions in an alkaline medium

The reactivity of zinc and copper oxide nanoparticles was investigated upon their interaction with iron oxides. It was ascertained that, depending on the reaction conditions, nanoparticles of zinc and copper ferrites (ZnFe₂O₄ and CuFe₂O₄) or core/shell nanoparticles (Fe₃O₄/ZnO) are produced. Size, composition, and structure of the resulting nanoparticles were determined by transmission electron microscopy and X-ray diffraction analysis. The average size of zinc and copper ferrite nanoparticles was ascertained to be 9–10 and 2–3 nm, respectively. For core/shell Fe₃O₄/ZnO nanoparticles, the average size is 20 nm. It was experimentally proved that the photoluminescence radiative characteristics of ZnO nanoparticles are retained in core/shell Fe₃O₄/ZnO nanoparticles.     

Effect of the means of preparation of nanodispersed CuO/MgO catalysts on their activity in the oxidation of CO

A method is proposed for obtaining copper-containing catalysts by means of mechanical mixing of previously formed monodispersed CuO nanoparticles (mean particle diameter 12 nm) with MgO. Higher activity was found for these catalysts in the oxidation of carbon monoxide than for the analogous copper-containing systems prepared by impregnation and deposition of cupric oxide nanoparticles from colloidal solution. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 165–169, May–June, 2008.     

Activation of methanol-tolerant carbon-supported RuSe<Subscript>x</Subscript> electrocatalytic nanoparticles towards more efficient oxygen reduction

An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSe_x nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSe_x catalytic centers with ultra-thin films of WO₃, the potential of oxygen reduction in 0.5 mol dm⁻³ H₂SO₄ (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO₃-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm⁻² (at 300 mA cm⁻²) has been observed upon utilization of WO₃-modified RuSe_x in polymer electrolyte membrane fuel cell at 80 °C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSe_x nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm⁻³ level. Dedicated to Professor Dr. Algirdas Vaskelis on the occassion of his 70th birthday.     

DFT Studies of Palladium Model Catalysts: Structure and Size Effects

An important task for theory is the multi-scale modeling of catalytic properties of nanocrystallites with sizes ranging from clusters of few metal atoms to particles consisting of 10³–10⁴ atoms. To explore catalytic properties of nanosized metal catalysts, we developed an approach based on three-dimensional symmetric model clusters of 1–2 nm (~100 metal atoms) with fcc structure, terminated by low-index surfaces. With this modeling technique one is able to describe at an accurate DFT level various catalytic and adsorption properties of metal nanoparticles in quantitative agreement with experimental studies of model catalysts deposited on thin oxide films. Metal nanocrystallites exhibit properties that can significantly vary with their size and shape.     

Preparation of the iron carbide-fullerene black nanostructured composite coating on the steel-45 surface

Fullerene black at 1150°C interacts with the surface of iron to form a nanostructured composite coating consisting of orthorhombic iron carbide crystallites of 60–100 nm size and dispersed islands of fullerene black. In the process of formation of the composite coatings both the fullerene black with a particle size of 40–50 nm and the carbon oxide formed in the process were involved. Under the conditions of the process, the content of hydrogen and oxygen in the structure of fullerene black decreased, straightening out curved surfaces occurred, and appeared a system of aromatic conjugation.     

Synthesis and properties of Co–Pt alloy silica core-shell particles

This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt nanoparticles were prepared from CoCl₂ (4.2 × 10⁻⁵ M), H₂PtCl₆ (1.8 × 10⁻⁵ M), citric acid (4 × 10⁻⁴ M) and NaBH₄ (1.2 × 10⁻² M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent, 3-aminopropyltrimethoxysilane (8 × 10⁻⁵ M), and a silica source, tetraethoxyorthosilicate (7.2 × 10⁻⁴ M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature. Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field.     

Effect of ZrO<Subscript>2</Subscript> morphology in copper–cerium–zirconium oxide systems on their catalytic properties in the reaction of co oxidation in hydrogen-rich mixtures

We studied the catalytic properties of copper–cerium oxide systems, deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300-1000 °C, in the reaction of selective oxidation of CO in a stream of hydrogen. We have shown that the catalytic activity of the samples obtained correlates with the activity of the original supports in the reaction of CO oxidation: the highest CO conversion is observed on catalysts with the highest and the lowest specific surface area. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 115-120, March-April, 2009.