Search

A one-step preparation method for hybrid electromagnetic nanomaterials based on polydiphenylamine (PDPA) and bimetallic Co–Fe particles in the absence and presence of single-walled carbon nanotubes (SWCNT) was proposed. During IR heating of PDPA in the presence of Co(II) and Fe(III) salts in an inert atmosphere at T = 450–600 °C, the polycondensation of diphenylamine (DPA) oligomers and dehydrogenation of phenyleneamine units of the polymer with the formation of CN bonds and reduction of metals by evolved hydrogen with the formation of bimetallic Co–Fe particles dispersed in a polymer matrix occur simultaneously. When carbon nanotubes are introduced into the reaction system, a nanocomposite material is formed, in which bimetallic Co–Fe particles immobilized on SWCNT are distributed in the matrix of the polymer. According to XRD data, reflection peaks of bimetallic Co–Fe particles at diffraction scattering angles 2θ = 69.04° and 106.5° correspond to a solid solution based on the fcc-Co crystal lattice. According to SEM and TEM data, a mixture of particles with sizes of 8–30 nm and 400–800 nm (Co–Fe/PDPA) and 23–50 nm and 400–1100 nm (Co–Fe/SWCNT/PDPA) is formed in the nanocomposites. The obtained multifunctional Co–Fe/PDPA and Co–Fe/SWCNT/PDPA nanomaterials demonstrate good thermal, electrical and magnetic properties. The saturation magnetization of the nanomaterials is MS = 14.99–31.32 emu g−1 (Co–Fe/PDPA) and MS = 29.48–48.84 emu g−1 (Co–Fe/SWCNT/PDPA). The electrical conductivity of the nanomaterials reaches 3.5 × 10−3 S cm−1 (Co–Fe/PDPA) and 1.3 S cm−1 (Co–Fe/SWCNT/PDPA). In an inert medium, at 1000 °C the residue is 71–77%.

Carbon material (CM) based on shadbush CAm (Amelanchier) wood pulp and a mixture of CAm + AMS, where AMS is aluminum magnesium spinel, are used as a support for a Fe-containing catalyst promoted by Bi (0.6 wt %) for the hydrogenation of CO. The dynamics of the formation of iron carbides during the activation of iron oxides supported on the CM and CM–aluminum magnesium spinel mixture is studied, along with the effect bismuth has on this process. It is found that they already have nonzero magnetization at the stage of preparing the catalysts. It is shown that with Fe/CAm, only Hagg carbide forms in a medium of CO/H2 (1 : 1), while a mixture of Hagg carbides and e'-Fe2.2C forms when using Fe/(CAm + AMS). The promotion of the Fe/(CAm + AMS) catalyst by bismuth substantially increases the amount of formed Hagg carbide and affects the amount of e'-Fe2.2C negligibly.

Carbon material (СAm), prepared on the basis of shadbush (Amelanchier) wood is used as a support of bismuth-promoted (0.6 wt %) Fe-containing catalyst of CO hydrogenation. Structural, morphological, and physicochemical characteristics of the systems are studied. It is established via IR spectroscopy that sub-carbonyl and bridge forms of absorption are observed when bismuth is present on a surface of Fe/СAm during calcination in a stream of CO. At the same time, only iron oxide particles form, substantially facilitating the process of catalyst reduction afterward.

Condensed products are obtained via the partial oxidation of iron(II) cations using potassium permanganate, and their physicochemical properties are studied. Samples obtained at a potassium permanganate-to-iron(II) molar ratio close to stoichiometric in a preparation of magnetite have the greatest relative magnetic susceptibility. It is shown that the initial rate of formation of relative magnetic susceptibility in the range of 30–70°C depends linearly on the inverse thermodynamic temperature. Sedimentation of the synthesized products upon exposure to an external magnetic field is complete within 1–1.5 min. Diffractometry shows that crystalline magnetite samples form at a KMnO4 : Fe(II) molar ratio of 0.08–0.18. Magnetic granulometry reveals they have superparamagnetic properties. Under conditions of static sorption, the degree of extraction of chromate ions is 98.7%.

The influence of the structural properties of the aluminum magnesium spinel (AMS) support with different specific surface areas on the physicochemical properties and dynamics of the activation of Fe–K-containing catalysts in syngas atmosphere is studied. On the activation of Fe/AMS and Fe–K/AMS in a flow of CO/H2 (1 : 1), Hagg carbide χ-Fe5С2 is formed with a Curie temperature Tθ = 257°С for all catalysts. However, using the magnetometric method in situ, it is found that the amount of carbide formed is different for aluminum magnesium spinel with different specific surface areas.

Iron-containing catalysts promoted with potassium supported on a carbon carrier were prepared by changing the sequence of the introduction of components (iron and potassium) into the carrier (activated carbon) using an impregnation method. After calcination, the catalysts contained hematite and magnetite; in this case, the particle sizes of iron oxides depended on the sequence of the introduction of a potassium promoter. A minimum particle size was observed upon the subsequent introduction of initially potassium from nitrate and then iron. The activation of all of the catalysts in a flow of CO/H2 resulted in the formation of Hagg carbide (Fe5C2). It was shown that the catalyst with the smallest carbide particle size was the most active in the hydrogenation of CO.

For the first time, under the conditions of in situ oxidative polymerization, a hybrid dispersed magnetic material based on poly-3-amine-7-methylamine-2-methylphenazine (PAMMPh) is obtained in which nanoparticles Fe3O4 are dispersed in an electroactive polymer matrix. According to the results of TEM and SEM, Fe3O4 nanoparticles have sizes of 4 nm < d < 11 nm. Using IR spectroscopy it is established that the chain propagation proceeds via the addition of C–N between 3-amine groups and the para position of phenyl rings relative to nitrogen. The chemical structure, phase composition, and the magnetic and thermal properties of the nanomaterials versus the synthesis conditions are investigated. It is shown that the Fe3O4/PAMMPh nanocomposite material is superparamagnetic and thermally stable.

The kinetics of the formation of iron carbides during the activation of iron-coated catalyst for Fischer–Tropsch synthesis promoted by copper and potassium, and by carbon monoxide and syngas, is studied. It is established that the presence of copper lowers the initial temperature of hematite reduction to magnetite and leads to the formation of carbide in both CO and СО/Н2. Potassium slows the rate of magnetite formation, but it accelerates the formation of iron oxide. It is shown that the rate of carbide formation during magnetite reduction for catalysts is half that in the reaction of hematite reduction to magnetite in both CO and СО/Н2.

A study was made of the effect of synthesis conditions on the properties of a magnetoactive compound obtained by the interaction of iron(II) sulfate with potassium chromate. It was found that, in the formation of the magnetoactive compound, chromium is almost completely coprecipitates with the solid phase. To produce the magnetoactive compound with high relative magnetic susceptibility, it is necessary to precipitate it from the initial solution in no less than 10 min after its preparation at a K2CrO4: FeSO4 molar ratio of 0.16–0.18.

The influence of the molecular-weight parameters of the polymer on the functional properties of metal–carbon nano-materials (MCN) was revealed for the first time. A difference in the phase composition of iron-containing nanoparticles was established employing high and low molecular weight poly-acrylonitrile, which determines the magnetic characteristics of the MCN.

Hybrid iron-containing nanocomposite materials based on polyphenoxazine (PPOA) were synthesized for the first time via chemical transformations of PPOA in the presence of iron(III) salt (FeCl3·6H2O, Fe(NO3)3·6H2O or Fe(CH3COCH=C(CH3)O)3) in an inert atmosphere under IR radiation in the temperature range of 350–600 °С. The developed hybrid nanocomposites were characterized by means of FTIR spectroscopy, X-ray diffraction (XRD), transmission (TEM) and scanning (SEM) electron microscopy, X-Ray fluorescence spectroscopy (XRF), Inductively coupled plasma atomic emission spectroscopy (ICP-AES), atomic absorption spectrometry (AAS), elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and magnetometry. The dependence of phase composition, magnetic and thermal properties of hybrid nanocomposites, as well as the size and shape of nanoparticles on synthesis temperature, Fe concentration and the nature of iron(III) salt was demonstrated.

Hybrid metal-polymer nanocomposite materials based on polyphenoxazine (PPhOA) and Fe 3 O 4 nanoparticles were obtained for the first time via two methods: in situ oxidative polymerization of phenoxazine (PhOA) in an aqueous solution of isopropyl alcohol with nanoparticles of Fe 3 O 4 being present; chemical transformations of PPhOA subjected to IR heating at 400–450 °Ði in the presence of FeCl 3 ·6H 2 O in an inert atmosphere. Obtained hybrid Fe 3 O 4 /PPhOA nanomaterials were characterized by means of Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectrometry (ААS), elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), as well as by vibrating sample magnetometry. The chemical structure, phase composition, magnetic and thermal properties of obtained nanocomposites were investigated in relation to the synthesis conditions.

A simple method for preparation of hybrid magnetic nanocomposites consisting of bimetallic Co–Fe nanoparticles and polyphenoxazine (PPOA) is described. The nanocomposites were prepared by IR heating of precursors based on PPOA, cobalt (II) acetate, and iron (III) chloride in an inert atmosphere at T = 400–600 °C in a short time (2–10 min). Hybrid nanomaterials were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, transmission and field emission scanning electron microscopy, atomic absorption spectrometry, and vibrating sample magnetometry. Based on the value of hysteresis loop squareness (k S = 0.021–0.034), it was concluded that almost 100% of Co–Fe nanoparticles in the nanocomposite are superparamagnetic.

Aspects of the physicochemical properties of a hydrocarbon material based on seabuckthorn (Hippophae rhamnoides) sawdust are studied. The use of a hydrocarbon material based on sea buckthorn sawdust as a structural promoter of Со/CHip cobalt catalyst in the reaction of CO hydrogenation is shown to require an additional cycling stage in the mode of reduction and oxidation. The resulting mean size of the Co particles is found to be 18–19 nm and is considered acceptable for the synthesis of С5+ liquid hydrocarbons.

The reduction of Fe2O3/SiO2 catalysts in flowing CO and CO + H2 in the temperature-programmed and isothermal modes has been investigated by in situ magnetization measurements. The process takes place in two steps, successively yielding magnetite and Hagg carbide. The carbide concentration in the case of reduction with CO is higher than in the case of reduction with the CO + H2. This is assumed to be due to the formation of Fe2SiO4 in the reduction of the catalysts with CO + H2.

This study is devoted to the reduction of Fe2O3 supported on silica gel in H2 in the temperature range of 290–600 °C. A continuous magnetization measurement method was used to obtain the temperature programmed reduction (TPR) profile. The influence of the external magnetic field on the dynamics of the process is investigated. It was shown that the TPR profile depends both on the magnitude of the applied field and on the particle size of hematite.

Polymer-metal-carbon hybrid nanomaterials based on thermostable electroactive poly-3-amine-7-methylamine-2-methylphenazine (PAMMP), single walled carbon nanotubes (SWCNT), and magnetite (Fe₃O₄) nanoparticles were synthesized for the first time. Hybrid Fe₃O₄/SWCNT/PAMMP nanomaterial synthesis was carried out via in situ chemical oxidative polymerization of 3-amine-7-methylamine-2-methylphenazine hydrochloride in the presence of metal-carbon Fe₃O₄/SWCNT nanocomposites. Fe₃O₄/SWCNT nanocomposites were obtained by the immobilization of magnetite nanoparticles on the SWCNT surface in the course of Fe₃O₄ nanoparticles synthesis in alkaline medium. The developed nanocomposite materials were characterized by FTIR spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission (FE-SEM) scanning electron microscopy, atomic absorption spectrometry (AAS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and magnetometry. The chemical structure and phase composition, magnetic and electrical properties, and thermal stability of the obtained multifunctional nanomaterials, depending on synthesis conditions, were investigated.

This paper addresses the effect of promotion with copper and potassium on the carbidisation kinetics, structure and performance of silica supported iron catalysts for high temperature Fischer–Tropsch synthesis. The promotion with copper and potassium results in the enhancement of iron dispersion. Small hematite nanoparticles were uncovered in the calcined iron catalysts. Activation of the calcined catalysts in carbon monoxide or syngas results in the reduction of hematite to magnetite at 250–300 °C. The magnetite is then carbidised into Hagg iron carbide. The promotion with copper and potassium affects the rate of the iron reduction and carbidisation. Copper strongly enhances both hematite reduction and magnetite carbidisation in carbon monoxide and syngas. The presence of potassium hinders reduction of hematite to magnetite. Much higher reaction rates were observed on copper-promoted catalysts than on the potassium-promoted and unpromoted counterparts while the promotion with potassium had a stronger impact on the selectivity.

Size effects were found to influence the low-temperature oxidation of Co nanoparticles. These effects were likely caused by the predominant formation of oxide phase nuclei on edge and vertex Co nanocrystal atoms. The initial rate of oxidation was proportional to the degree of nanoparticle surface coverage with atomic oxygen. The magnetic method was used to determine the size of Co nanoparticles. The results were close to those obtained by transmission electron microscopy.

International audience

International audience; Low-temperature oxidation of carbon-supported cobalt nanoparticles leads to the size-dependent effects probably related to the selective nucleation of oxide at the edges and the corners of cobalt crystallites. The initial oxidation rate depends on the oxygen partial pressure. Magnetic measurements of particle size are in good agreement with the results of transmission electron microscopy.

International audience; The genesis of cobalt metal particles in silica-supported Fischer-Tropsch catalysts was studied using in situ Foner vibrating-sample magnetic method. The cobalt promoted and unpromoted catalysts were prepared by aqueous (co)-impregnation using cobalt nitrate or acetate, ruthenium nitrosyl nitrate or perrhenic acid followed by oxidative pre-treatment in air and reduction in hydrogen. In several catalyst preparations, sucrose was added to the impregnating solutions. The genesis of cobalt metal phases in these catalysts was monitored in situ by the magnetic method during the temperature-programmed reduction in pure hydrogen. A considerably higher extent of cobalt reduction was found in the catalysts prepared from cobalt nitrate than in those prepared from cobalt acetate. Promotion with ruthenium and rhenium results in a considerable decrease in the temperature of the emergence of cobalt metal phases. Small superparamagnetic, single-domain and multi-domain ferromagnetic cobalt metal particles were observed in the reduced catalysts by the magnetic method. It was found that lower temperature calcination of the cobalt catalysts prepared from cobalt nitrate and addition of sucrose to the impregnating solution lead to a decrease in the concentration of multi-domain cobalt ferromagnetic metal particles and to an increase in the fraction of superparamagnetic cobalt particles. Superparamagnetic cobalt particles smaller than 6-7 nm were detected in the reduced catalysts prepared from cobalt nitrate with sucrose addition and in the catalysts prepared from cobalt acetate. Catalyst characterization using X-ray diffraction and X-ray photoelectron spectroscopy has confirmed the results about cobalt dispersion and reducibility in the cobalt silica-supported catalysts obtained by the Foner magnetic method.

International audience; The promotion of Co/SiO2 catalysts with noble metals such as Ru and Re substantially decreased the mean size of Co particles and increased the fraction of superparamagnetic particles. The Langevin function was used to approximate the magnetic field dependence of magnetization. This allowed the size of Co nanoparticles to be estimated. A decrease in the temperature of the reduction of Co/SiO2 in the presence of Ru and Re decreased the probability of the encapsulation of Co particles in carrier pores.