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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 effect the structural properties of a support, magnesium aluminum spinel, with different structural characteristics has on the physicochemical properties of Fe–K-containing catalysts for the hydrogenation of CO is studied. It is shown that hematite is the main phase in Fe-containing catalysts. A highly disperse distribution of iron oxide on the surface of the substrate is observed in case of a bimodal distribution of meso-pores. It is shown via IR spectroscopy that Fe2+ cations and metallic iron are the main sites of adsorption. The introduction of potassium reduces the surface concentration of clusters (including Fe2+) in different coordination environments. A rise in the contribution from the subcarbonyl forms of adsorption to the spectrum of the absorption bands and a drop in the amount of oxidized iron on the surfaces of metallic iron particles are observed.

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.

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.

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.

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.

The effect a carrier’s nature has on the activation of supported iron catalysts in a stream of pure carbon monoxide CO is investigated. It is shown that iron is mainly present in the form of magnetite Fe3O4 in case of carbon supports and in the form of hematite Fe2O3 for silica gel supports. It is shown that all activated samples are chiefly made up of the Hagg carbide χ-Fe5C2, but its concentration is higher for the carbon supports.

The effect the nature of activated carbons prepared from natural renewable resources has on the metal particle size in cobalt- and iron-containing systems that can be used as catalysts in Fischer-Tropsch synthesis (FTS) is studied. The highest dispersity is observed for the Co3O4-WS (wood sawdust) system. The average particle size is 9.5 nm.

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.

The effect of external magnetic field on the kinetics of reduction of bulk Co3O4 and silica-supported cobalt oxide (Co3O4/SiO2) with hydrogen has been investigated. The magnetic field exerts an effect on the apparent activation energy of reduction of the bulk oxide and has no effect on the activation energy of reduction of Co3O4/SiO2. It is hypothesized that the changes in the kinetic parameters are due to the effect of the external magnetic field on the structure defects in the solid.

An experimental setup controlling the topochemical transformations in synthesis of ferromagnetic metal nanoparticles is described. The setup is based on a vibrating magnetometer. The range of operating temperatures in the reaction zone is 300–870 K. The required sensitivity is maintained by a magnetic field of up to 0.6 T. Gases (or gas mixtures) may be blown through the reactor at a flow rate as high as 150 cm3/min. The experimental results illustrating the capabilities of the setup are presented.

The size effects during the oxidation-reduction treatment (ORT) of Co nanoparticles in the Co/SiO2 catalyst were studied. The results of ORT on Co nanoparticles depended on the initial size distribution of nanoparticles; for small nanoparticles, ORT did not lead to further decrease in size. (The threshold size was obviously less than 10–15 nm.) The critical size of Co particles depended on the conditions of oxidation and reduction, i.e., the heating rate, the composition of the gas mixture, etc.

The dynamics and kinetics of formation of iron carbides in Fe/SiO2 catalysts during the hydrogenation of CO and in a topochemical reaction between Fe and CO was studied. The effective activation energy of carbide formation was found to increase as the size of iron particles decreased. Alternative hypotheses explaining the observed size effect are suggested.

A model of the heat-generating reaction of the low-temperature oxidation of nickel nanoparticles in nickel-supported catalysts is discussed. We use the continuous measurement of magnetization to estimate the heat effect of the reaction, allowing us to measure the heating of nickel nanoparticles in the support matrix, due to the temperature dependence of magnetization.

The most recent advances in magnetometric methods of investigation of supported Co-, Ni- and Fe-containing catalysts are outlined. Magnetic characteristics provide comprehensive information on (i) catalytic reactions, (ii) the size and distribution of ferromagnetic nanoparticles in topochemical reactions during the catalyst preparation and in the catalytic process and (iii) chemisorption on ferromagnets. The characteristic features and advantages of different magnetometric methods and their combinations with traditional methods of investigation of catalysts are considered.

The kinetics of oxidation of Co nanoparticles used in heterogeneous catalysis in silica gels and alumina with various porous structures was studied at room temperature. A mathematical model describing processes in the system was suggested. The experimental observations were qualitatively explained.

Chromium and its compounds are widely used in various industries. Wastewater from industrial enterprises using chromium compounds are subject to complete disposal at treatment facilities. The possibility of synthesizing a magnetoactive compound by oxidizing part of Fe(II) cations with chromate-anions in the presence of lignosulfonates was investigated. The magnetic activity was measured on Gouy balance, magnetic characteristics were determined by the magnetic granulometry method. It has been shown that the interaction of Fe(II) cations with chromate-anions passes with the formation of an water soluble intermediate without redox transformations at pH 3.4. Using method of the isomolar series, it was determined that the ratio of chromate-ions and Fe(II) cations in the intermediate is 1:2.33. The intermediate solution is stable for a long time. Synthesized magnetoactive compound samples are ferrimagnets. The use of lignosulfonate and the synthesis with heating can achieve a higher magnetic activity of magnetoactive compound. The optimal lignosulfonate consumption is 0.7 g/g Fe.

Investigations in the field of the development of inexpensive catalysts for the production of environmentally safe fuels, based on synthesis-gas from biomass, have been performed. The influence of acidic (sulphuric and phosphorous acids) treatment on the specific surface of Russian (Voronezh and Krasnodar) origins of bentonitic clays was investigated. For the determination of the optimal conditions of acidic treatment, the method of extremal experiment planning has been applied. The full factor experiment was chosen as the plan; in such an experiment, all factor combinations are implemented on all levels used for investigations. The variable parameters were as follows: the acid concentration, and the temperature and time of the acid treatment. The average pore diameter and the specific surface of clays were chosen as the response functions. The response surface appearance is very complex.

The thermal decomposition of cobalt formate in a flow of an inert gas led to the formation of cobalt nanoparticles in pores of various substrates (silica gel, alumina, activated carbon, and montmorillonite). Electron microscopic studies showed that the particle-size distribution of cobalt depended on the external magnetic field strength; the average particle size and distribution variance decreased as the field strength increased. It was assumed that the external magnetic field affected the nucleation constant of cobalt nanoparticles.

The thermal decomposition of the cobalt complex with hexamethylenetetramine (NO3)2Co(H2O)6(HMTA)2 · 4(H2O) was studied by the methods of differential thermal analysis, thermogravimetry, mass spectrometry, X-ray diffraction analysis, and by the magnetic method. It was established that the thermal decomposition of the complex in a current of an inert gas is accompanied by a pronounced exothermic process and formation of Co nanoparticles. It was shown that the kinetics of this process and the chemical nature of the decomposition products depend on the initial density of the sample under study.

Oxidation of cobalt nanoparticles supported on montmorillonite was studied using transmission electron microscopy and temperature programmed reduction of the oxide particles. It has been shown that hollow shells of cobalt oxide were formed in this process, consisting of the mixture of CoO and Co3O4 oxides. A linear relationship between the thickness of shells and the initial particles size was established which suggests that both diffusion of cobalt ions through the oxide layer and diffusion of the oxygen into cobalt occur, but particles sintering is negligible compared with the reverse diffusion of cobalt. The lower critical diameter of cobalt particles was estimated, above which formation of hollow shells occurred. The hollow shells formation is suggested to be the reason for cobalt redispersion upon oxidation−reduction cycling of supported heterogeneous catalysts.

A high-resolution transmission microscopy study showed that the oxidation of Co nanoparticles deposited on montmorillonite resulted in the formation of nanoshells consisting of cobalt oxides and containing spherical voids. A linear dependence was found between the initial diameter of Co particles and the oxide shell thickness.

The oxidation of Co nanoparticles with water vapor and molecular oxygen was studied over the temperature range 10–200°C. Cobalt particles reacted with water vapor at pH2O = 18 torr. Preadsorbed hydrogen and CO had no pronounced influence on the oxidation rate of cobalt nanoparticles. Temperature-programmed reduction showed that, after the oxidation of cobalt nanoparticles with water vapor, oxidized cobalt was in the divalent state.

The physicochemical properties of Co-supported catalysts were studied, and the particle size of Co in Co/MgO/Al2O3 and Co-0.2% Ru/MgO/Al2O3 catalysts for the Fischer-Tropsch synthesis (FTS) was estimated using a magnetic method. It was found that a considerable fraction of superparamagnetic Co particles, which increase selectivity for C5+ hydrocarbons and decrease the yield of methane in the FTS, was present in a ruthenium-containing catalyst along with single-domain ferromagnetic particles. In this case, the catalyst activity increased by a factor of 10.

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.

The influence of various factors on the particle-size distribution of Co in Co-deposited catalysts is considered. The temperatures of drying and calcining and gas flow rate during calcining were found to substantially affect the mean radius of Co particles. The partial pressure of hydrogen during reduction influenced the form of the particle-size distribution of Co. The fraction of small particles increased as the partial pressure of hydrogen grew. Conversely, a decrease in the partial pressure of hydrogen caused the enrichment of the system in large-sized cobalt particles.

A magnetic method was proposed for evaluating the average particle size of cobalt metal in supported cobalt catalysts for the Fischer-Tropsch synthesis. This method includes a set of techniques such as in situ temperature-programmed reduction and in situ temperature-programmed oxidation with simultaneous magnetization measurements and the dependence of magnetization on magnetic field intensity (the field dependence method). It was found that cobalt supported on silica gel with a bimodal pore-size distribution exhibited a special behavior in topochemical processes: the majority of cobalt particles occurred in a superparamagnetic state, while a portion occurred in a multidomain state.

The effect of the size distribution of metal particles on the process kinetics was studied for the oxi- dation and reduction of cobalt nanoparticles (6-10 nm) in the Co/SiO 2 , Co/Al 2 O 3 , and Co/ZrO 2 systems in both isothermic and temperature-programmed regimes in the temperature range from 280 to 500 K. The average size of the cobalt particles was estimated by measurements of the coercive force and residual magnetization using a vibration magnetometer. It was found that the average particle size increases upon cobalt oxidation and decreases upon cobalt reduction due to changes in the fraction of nonsuperparamagnetic particles with sizes of at least 6.5 nm.

Processes occurring in the preparation of the Co/ZrO2 + 6% Y2O3 catalyst are studied by temperature-programmed reduction (TPR). The effects of the concentration of Co, the porosity of the support, and the calcination temperature on catalyst reduction were studied. As was shown by continuous magnetization measurements in the course of TPR, metallic cobalt appeared on the microporous support in two temperature ranges irrespective of the precalcination temperature and the concentration of supported cobalt. These factors affect the reduction rate but do not change the maximum temperatures of the corresponding peaks. It is suggested that the first maximum of the Co formation rate is due to the reduction of CoO particles on the surface of the support and within macropores, whereas the second maximum is due to the reduction of CoO particles located within support micropores. Only one temperature range of CoO reduction was found in the macroporous ZrO2 + 6% Y2O3. This effect is likely due to mass transfer in support micropores.

The influence of oxide–oxide interaction on the catalytic properties of cobalt in CO hydrogenation is investigated on the example of a Co/Al2O3 catalyst. Oxide–oxide interaction was prevented by modification of the alumina surface with magnesia. It has been shown that oxide–oxide interaction affects catalytic activity and the amount of carbon deposited on the catalyst surface.

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We outline the method for evaluation of the particle size distribution of the magnetic nanoparticles from the hysteresis loop measurements. We apply the method to study the ultrafine Co particles filling the porous silica gel matrix (SiO 2 ). The influence of the technological conditions of the sample preparation onto particle size distribution function is demonstrated.