Pd-Ni alloys were recently found to be effective for the catalytic decomposition of chlorine-substituted organic compounds with the formation of carbon nanofibers. Decomposition of trichloroethylene over a Pd0.80Ni0.20 alloy resulted in the appearance of two types of such nanofibers. It was assumed that at least two kinds of active metal nanoparticles should coexist and catalyze the growth of carbon nanofibers of two types. Therefore, the present research aimed to study the behavior of the initially homogeneous Pd0.80Ni0.20 alloy in the medium containing trichloroethylene and hydrogen. As found, the particles of type I are of 100-300 nm in diameter and enriched with Pd (similar to 90 %). The particles of type II contain similar to 70 % Ni, and their size is about 10-20 nm. The driving forces of the segregation process appear to be the formation of carbides and hydrides of nickel and palladium, whose stabilities differ.

The paper presents an approach to the conditioning of associated petroleum or natural gas. The method is based on the process of catalytic pyrolysis of light hydrocarbons С 1 -С 4 on multicomponent alloy particles. As a result of such a process it is possible to obtain mainly a mixture of СH 4 +H 2 , since it is the fraction of С 2 -С 4 that is subjected to pyrolysis with the formation of hydrogen and carbon nanofibers (CNF). Equiatomic alloy [CoFeNi] promoted by addition of 7 at.% Cu ([CoFeNi]Cu 7 ) shows the highest activity in decomposition of C 2 -C 4 mixture. The maximum yield of CNF at 650 °C was 106 g/g cat in 30 min. It is shown that such an alloy can be successfully used for catalytic decomposition of С 2 -С 4 fraction in a mixture with methane. The dependence of CNF yield on the concentration of С 2 -С 4 fraction in the model mixture has been determined. It was found that at pyrolysis of the mixture with the volume ratio С 2 -С 4 /СH 4 = 10/90 within 30-180 min there is no appreciable deactivation of the catalyst. The yield of CNF after 180 min of reaction was 160 g/g cat . The average conversion of the С 2 -С 4 fraction in one pass reaches 20 %. The morphology and structure of the obtained CNF were studied by scanning and transmission electron microscopy and low-temperature nitrogen adsorption.

Joint exploding wires is a suitable method to produce multicomponent alloys in the form of dispersed powders with the target composition. In this research, three-, four-, and five-component alloys based on iron-triad metals (Ni, Co, and Fe) were prepared by exploding wires of different compositions, twisted in appropriate ratios. The collected spherical particles were examined by X-ray diffraction analysis and transmission electron microscopy. As found, the obtained samples are mainly fcc substitutional solid solutions based on nickel, while some compositions additionally contain a bcc phase. The powder samples were used as catalysts for the pyrolysis of C2-C4 hydrocarbons to produce nanostructured carbon materials. The [NiFeCo]CrCux alloys, where x = 6–20 wt%, exhibit appropriate activity up to a temperature of 750 °C. At the copper content of up to 20 wt%, the carbon yield reached 55–67 g/gcat after 15 min of the process. A correlation between the activity and structural and electronic properties of alloys has been found. Morphological features and textural characteristics of the carbon nanomaterials were explored by electron microscopy and low-temperature nitrogen adsorption. Depending on the composition of the initial alloy, the morphology of the carbon nanomaterials can vary from disordered feathery-like nanofibers to highly ordered nanotubes, and the specific surface areas of these materials are 290 and 60 m2/g, respectively. Thus, the proposed approach is quite simple, easily tunable, and scalable. The results obtained provide an important platform for the target synthesis of highly efficient multicomponent catalysts for the production of carbon nanomaterials.

In this work, carbon nanofibers characterized by a bimodal structure and elastic strain were obtained by catalytic decomposition of trichloroethylene over palladium‑nickel alloys in the presence of hydrogen and argon at 600 °C. The bimetallic catalysts Pd100-xNix, where x = 10–50 at.%, were found to be more efficient in the production of carbon nanofibers compared with the pure nickel reference sample (Ni100). Contrarily, pure palladium (Pd100) exhibited almost no activity under the given reaction conditions. After 1 h of the experiment, the highest carbon yield of 35 g/gcat was observed for the Pd90Ni10 alloy. The obtained Pd100-xNix@CNF materials possess a three-dimensional macroscopic structure composed of at least two types of fibers, which differ in thickness. Surprisingly, these bimodal carbon materials are characterized by elastic strain. Such behavior was never observed before for the carbon nanofibers produced using other catalyst compositions or pure nickel. According to electron microscopy data, the Pd100-xNix@CNF samples consist predominantly of long fibers with a dense, segmented structure and a diameter of hundreds of nanometers. Additionally, helical fibers of 50–100 nm in diameter are found in all these samples. Raman spectroscopy analysis revealed that both the La values and the fraction of amorphous carbon are higher in cases of carbon nanofibers grown over bimetallic catalysts. As a result, the specific surface area of the Pd100-xNix@CNF materials lies in the range of 276–433 m2/g and exceeds that of Ni100@CNF (115 m2/g). The produced materials exhibit high efficiency in the selective hydrogenation of acetylene.

The search for new active catalysts for the pyrolysis of hydrocarbons to produce carbon nanofibers remains an urgent task. In the present work, a series of porous Co-Pd(x) alloys, where x = 2–12 at%, were synthesized and studied. The synthesis of the alloys was performed by reductive thermolysis of multicomponent precursors obtained by co-precipitation of ammonia complex salts of cobalt and palladium in acetone. The composition of the prepared alloys corresponded to that specified during the synthesis. As was revealed by X-ray diffraction analysis, the alloy samples are mixtures of solid solutions based on the hcp and fcc phases of cobalt. The alloys are characterized by a branched 3D microstructure, formed by grains ranging in size from 1 to 3 microns and connected by bridges. The carbon productivity of Co-Pd alloys in the ethylene pyrolysis process exceeded that of pure cobalt by more than two orders of magnitude. Note that the monometallic palladium sample is not active at all under the applied conditions. The maximum carbon yield, exceeding 200 g/gcat, was achieved over the alloy containing 7 at% Pd. The obtained alloys demonstrated a significant short-time productivity compared to the systems reported earlier. The synthesized composite material is represented by carbon nanofibers with a developed specific surface area (∼ 300 m2/g) and containing dispersed particles of the initial Co-Pd alloy embedded in their structure. The set of unique properties of the obtained Co-Pd/CNF materials allows one to consider them a potential candidate for future catalytic studies.

Production of hydrogen from natural gas remains to be an actual task. In a present study, a series of NiO-CuO-Al (OH)3 catalysts was prepared using a mechanochemical activation method under varied conditions. Among the considered parameters are centrifugal acceleration value (an), the motion mode of the milling balls, and their diameter. Although these parameters did not affect the phase composition of the obtained powders noticeably, they influenced the dispersion and distribution uniformity of the components and, thus, affected the catalytic activity in the catalytic chemical vapor deposition of methane. At an = 40 G, the prepared powders possessed the maximum possible dispersion and distribution uniformity of metal oxides. In the case of the optimized preparation conditions, the achieved hydrogen productivity was as high as 215 Nm3/(kgcat x h). Carbon nanofibers, which are the solid-phase product of the process, possess a stacked and coaxial-conical structure and have a diameter of 10-120 nm.

A series of nickel-tin alloys was prepared by mechanochemical alloying of nickel and tin metal powders in a planetary mill. The evolution of morphology and phase composition of these alloys depending on the tin content and the duration of the alloying procedure was studied using X-ray diffraction analysis and scanning electron microscopy. The conditions providing the formation of Ni1-xSnx solid solutions based on the face-centered cubic lattice of nickel were determined. Based on the obtained results, the main stages of the mechanochemical alloying process have been proposed. The prepared nickel-tin alloys were tested as catalysts for the production of carbon nanofibers via catalytic chemical vapor deposition of C2-C4 hydrocarbons at 650 degrees C. An optimal value of the mechanochemical alloying duration in terms of carbon yield was found to be 5 min. Another key factor affecting the catalytic performance is the tin content in the alloy composition. Thus, when tin was introduced in the amount of 0.5-3 at.%, the carbon yield after 30 min of reaction exceeded 120 g/gcat. Moreover, the tin content also influences the morphology and the diameter of carbon nanofibers, as well as the character of their growth. Depending on the tin content, the carbon filament diameter can be varied in the range from 20 to 500 nm. All carbon materials synthesized using NiSn alloys possess a high specific surface area of >= 250 m2/g and a total pore volume > 0.4 cm3/g. Such textural characteristics make these materials attractive for use as sorbents or catalyst supports.

Carbon nanofibers were produced via catalytic decomposition of ethylene over porous Co-Pd alloys prepared by reductive thermolysis of bicomponent precursors. The Pd content in the alloy samples was varied from 0 to 10 at %. X-ray diffraction analysis of the prepared alloys showed that their crystal structure corresponds to fcc Co1-xPdx solid solutions based on a cubic cobalt lattice (Fm-3m) with an admixture of the hcp Co1-yPdy phase based on a hexagonal cobalt lattice (P63/mmc). The effect of the Pd content (x) in Co1-xPdx alloys on their performance in the catalytic pyrolysis of ethylene with the formation of carbon nanofibers was studied. As a result of ethylene interaction with Co-Pd alloys, the latter ones undergo rapid disintegration with the formation of active alloy particles functioning as sites for the growth of carbon nanofibers. Note that pure cobalt exhibited a low carbon yield of 10.5 g/gcat, while pure palladium is almost inactive. The addition of 2-10 at% Pd to cobalt increases its activity by more than 15 times. The maximum carbon yield of 196 g/gcat after 1 h of the reaction at 550 degrees C was reached over the Co-Pd (4) sample.

Multicomponent alloys attract growing attention to be applied in various fields of science and technology. In the present study, Ni52Fe22Cr15Cu11 alloy was produced via a single-stage method of electric explosion of wire. It was shown that this method makes it possible to obtain a phase-pure powder (solid solution with a fcc structure, a = 3.583 & Aring;) consisting of spherical nanoparticles with an average diameter of similar to 70 nm. According to chemical analysis data, the formed alloy nanoparticles are close in composition to the target ratio of metals. Depending on the treatment procedures such as reduction in hydrogen, heating in argon, calcination in air, and catalytic chemical vapor deposition of C-2-C-4 hydrocarbons, the alloy undergoes different changes. The evolution of the phase composition and magnetic properties of the alloy was monitored using X-ray diffraction analysis and ferromagnetic resonance spectroscopy. As found, the alloy exhibits the phase stability while treating in argon only. Its treatment in hydrogen at temperatures of 500 degrees C and above facilitates the damage of the solid solution. During the catalytic chemical vapor deposition process performed at 650 degrees C for 30 min, the carbon yield reached the value of 42 g/g(cat). According to transmission electron microscopy, the morphology of the deposited carbon is represented by a set of nanofibers with a mosaic structure. The resulting carbon nanofibers have a specific surface area of similar to 330 m(2)/g and a pore volume of similar to 0.8 cm(3)/g.

This paper reports the synthesis and characterization of carbon-carbon composites based on carbon xerogels with different porosity and carbon nanofibers. Initial carbon xerogels were prepared by pyrolysis in an inert atmosphere of organic xerogels synthesized via a resorcinol-formaldehyde polycondensation route. Carbon nanofibers were grown inside the xerogel matrix by means of catalytic chemical vapor deposition of ethylene on dispersed nickel particles. Two approaches, such as an incipient wetness impregnation and a one-pot synthesis, were used for doping carbon xerogels with nickel. The kinetics of the carbon accumulation were studied in a reactor equipped with McBain balances. The activation energy values estimated for two regions with different carbon accumulation rates were found to be 80 and 100 kJ/mol. In the second region, the higher activation barrier is explained by the deactivation of nickel particles due to their partial blockage by amorphous carbon deposits. The porous structure of initial carbon xerogels was found to affect both the carbon accumulation rate and the carbon yield. Thus, the carbon yield values of 47.1-58.5 g/gNi at 450-470 degrees C were obtained in the case of macroporous xerogel. The content of CNFs in the composites influences their textural characteristics. The optimal CNF loadings were found to be 25 wt% for CX-meso and 45 wt% for CX-macro. In these cases, the carbon deposition procedure should last 3 and 7 min, respectively. Since the grown carbon filaments are characterized by a coaxial- conical morphology, the carbon-carbon composite materials possess a more ordered structure than as-prepared xerogels.

Nitrogen-doped carbon nanomaterials are often produced by the catalytic decomposition of various N-containing organic substrates over nickel-based catalysts. Generally, most such catalysts are ferromagnetic. In the present research, the effect of complete disappearance of ferromagnetic resonance spectra for similar systems during the heat treatment of a NiCu alloy with melamine or g-C3N4 in a closed reaction volume within the temperature range of 450-500 degrees C was observed for the first time. The X-ray diffraction method showed that the cause of the observed phenomenon is the formation of new products such as nickel nitrides (Ni3N and Ni4N) and a copper- enriched NiCu alloy, which do not possess ferromagnetism at the temperature of registration of their ferromagnetic resonance spectra. The resulting nickel nitrides decompose when the temperature rises above 550 degrees C to form nickel nanoparticles stable under reaction conditions up to 850 degrees C and detectable by ferromagnetic resonance spectroscopy.

Carbon nanofibers were produced via catalytic decomposition of ethylene over porous CoPd alloys prepared by reductive thermolysis of bicomponent precursors. The Pd content in the alloy samples was varied from 0 to 10 at%. X-ray diffraction analysis of the prepared alloys showed that their crystal structure corresponds to fcc Co1-xPdx solid solutions based on a cubic cobalt lattice (Fm-3m) with an admixture of the hcp Co1-yPdy phase based on a hexagonal cobalt lattice (P63/mmc). The effect of the Pd content (x) in Co1-xPdx alloys on their performance in the catalytic pyrolysis of ethylene with the formation of carbon nanofibers was studied. As a result of ethylene interaction with CoPd alloys, the latter ones undergo rapid disintegration with the formation of active alloy particles functioning as sites for the growth of carbon nanofibers. Note that pure cobalt exhibited a low carbon yield of 10.5 g/gcat, while pure palladium is almost inactive. The addition of 2–10 at% Pd to cobalt increases its activity by more than 15 times. The maximum carbon yield of 196 g/gcat after 1 h of the reaction at 550 °C was reached over the CoPd (4) sample.

Carbon nanofibers with specified textural characteristics, obtained via catalytic chemical vapor deposition of various hydrocarbons, attract growing interest from both scientists and industrialists. In the present work, the optimal hydrogen content in terms of the carbon accumulation rate, process selectivity, and productivity of the Ni-Cu catalyst was found to be in the range of 40-70 vol%. As was revealed by the X-ray diffraction analysis, the catalytic particles are represented by a solid Ni-Cu solution based on the fcc lattice of Ni, and their composition does not depend on the hydrogen concentration. As found, the introduction of an optimal hydrogen amount into the initial reaction mixture decreases AD/AG (from 2.59 to 2.43) and increases both specific surface area (from 127 to 165 m2/g) and total pore volume (from 0.15 to 0.26 cm3/g). Thus, the effect of hydrogen on the decomposition of ethylene over self-dispersing catalysts is studied for the first time.

Due to the widespread of lubricants, improving their tribological characteristics remains an important practical task. Among the promising modifying additives, carbon nanomaterials attract special attention. Such materials are found to improve the antifriction characteristics of lubricants and oils. In the present research, carbon nanofibers were synthesized via catalytic pyrolysis of a mixture of light hydrocarbons (C2-C4) over the Ni-Cu catalyst. In order to form functional groups on the surface of carbon nanofibers, they were treated with diluted acids HCl, HNO3, and H2SO4 as well as with concentrated HNO3. The functionalized samples were comprehensively characterized by a set of physicochemical methods including atomic absorption spectroscopy, scanning and transmission electron microscopies, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, temperature-programmed desorption/oxidation, and Raman spectroscopy. As defined, the surface oxygen concentration in the samples varies from 3.5 to 16.3 at.%. It was shown that the addition of modified carbon nanofibers to a motor oil leads to an improvement in its tribological characteristics. In particular, the most effective additive was the sample treated with diluted HNO3. The motor oil with this modifying additive exhibited the heating temperature decreased by 10 degrees C and the contact spot area on the stationary body decreased by 20 %.

Nickel and its alloys are widely used for the synthesis of carbon nanofibers via catalytic chemical vapor depo-sition of various hydrocarbons. In the present research, a series of Ni-Sn alloys with tin loading varied in a range from 0.1 to 25.0 at% were prepared and characterized. Alloying of nickel with a small amount of tin was found to accelerate significantly the catalytic process of ethylene decomposition accompanied by carbon deposition. For the NiSn(0.25) sample, the carbon yield reaches 195 g/gcat after 30 min at 550 degrees C. At the highest Sn loading (25.0 at%), the process is completely suppressed. A new mechanism explaining the observed interaction of ethylene with Ni-Sn alloys was proposed. Single-atom Sn species are responsible for the increased catalytic ac-tivity. A single-atom Ni-Sn alloy is considered an efficient catalyst with enhanced stability for the production of carbon nanofibers.

The development of methods for purposeful modification of the polyethylene matrix with carbon nanostructures to create stronger and more durable pipe composites is an important direction in polymer science. Carbon nanofibers (CNFs) of three types, obtained via catalytic chemical vapor deposition of ethylene (Type I), trichloroethylene (Type II), and a mixture of ethylene and acetonitrile (Type III), were applied as modifying additives to improve the physical and mechanical characteristics of polyethylene. The polyethylene/CNF composites were prepared using a laboratory plasticizer. The introduction of CNFs (Type I) with a densely packed structure into the polymer matrix was found to provide the formation of a uniform fine-spherulitic structure that results in increased tensile strength, yield strength, elastic modulus, and abrasive wear. Such a positive effect is observed when the CNF content in the composite does not exceed 1.0 wt%. An increase in the abrasion resistance by a factor of 1.6 was observed.

A method for the synthesis of microdispersed Fe–Pd (0–10 atom

Multicomponent metal systems attract growing interest today, especially as catalysts for various processes. In the present work, a series of [CoFeNi]Pdx alloys (equal atomic content of base metals) doped with palladium in the amount of 0-10 at.% were synthesized via thermolysis of multicomponent precursors. The resulting [CoFeNi]Pdx alloys were found to be single-phase solid solutions with a fcc structure represented by agglomerates of grains fused. The performance of the alloys was explored in a mixture of saturated hydrocarbons (C2-C4) within the temperature range of 600-675 degrees C. As a result of interaction with the reaction mixture, spontaneous disintegration of the alloys containing above 2 at.% Pd occurs with the formation of dispersed particles responsible for the catalytic growth of carbon nanofibers (CNF). The dependence of the productivity of the [CoFeNi]Pdx alloys towards CNFs on the x parameter was studied. The highest CNF yield (YC = 25-46 g/gcat, 30 min) was achieved at an optimal Pd concentration of 8 at.% within the entire temperature range. According to TEM and EDX data, regardless of the reaction temperature and Pd concentration in the alloy, the catalyst particles have the same composition as defined at the synthesis of the alloys. The resulting CoFeNiPd@CNF composite can be considered as a catalyst for other heterogeneous catalysis processes.

In this research, a self-dispersing 92Ni-4Mo-4W catalyst showing high productivity towards the H 2-assisted synthesis of turbostratic carbon nanofibers was proposed. The effect of reaction temperature on the efficiency of 92Ni-4Mo-4W alloy in the decomposition of trichloroethylene was studied. It was found that in the temperature range of 580-620 degrees C, the most rapid destruction of the initial alloy followed by the growth of carbon material is realized. This is confirmed by the minimum induction period (9-11 min) and the maximum carbon yield (95-107 g/g cat ). As revealed, the catalytically active particles of submicron size contain uniformly distributed Ni, Mo, and W. It is demonstrated that the decomposition of trichloroethylene over the 92Ni-4Mo-4W catalyst results in the formation of a turbostratic carbon material with a segmented structure, containing a minimum quantity of amorphous carbon and possessing high textural characteristics (specific surface area of 330-410 m 2 /g; pore volume of 0.48-0.58 cm 3 /g).

In this study, the modified alkoxide sol–gel approach was used for the synthesis of ternary Ni–Ce–Mg–O oxide systems of variable composition. The prepared samples were characterized by thermal analysis, low-temperature nitrogen adsorption, transmission electron microscopy, X-ray diffraction, and temperature-programmed reduction. The presence of CeO2 in the oxide composition was found to affect such properties as texture, morphology, reducibility of Ni2+, and dispersion of Ni0 in the reduced samples. The catalytic properties of the Ni–Ce–Mg–O samples were examined with regard to dry reforming of methane (DRM) and catalytic pyrolysis of hydrocarbons with the formation of carbon nanofibers (CNF). It was found that the CeO2-containing samples demonstrate more stable performance in DRM and are less prone to coke formation. The Ni10Ce10 catalyst containing 10