Promoting Effect of Co, Cu, Cr and Fe on Activity of Ni-Based Alloys in Catalytic Processing of Chlorinated Hydrocarbons

A Hybrid Nanocomposite Based on the T-Shaped Carbon Nanotubes and Fullerenes as a Prospect Material for Triple-Value Memory Cells

Relying on empirical and quantum chemical methods, a hybrid nanocomposite based on the T-shaped carbon nanotube (CNT) junction and internal fullerene C₆₀ is proposed as a potential triple-value memory cell. The T-shaped CNT provides three potential wells where the internal fullerene can be located. The fullerene can move between these wells under the periodic external electric field, whose strength and frequency parameters are identified. The process of the fullerene's motion control corresponds to the memory cell write operation. The read operation can be realized by determining the fullerene's position inside the CNT by estimation of the charge transfer between a fullerene and the CNT's walls. Calculations took into account such external factors as temperature and air environment.

Porous Co-Pt Nanoalloys for Production of Carbon Nanofibers and Composites

The controllable synthesis of carbon nanofibers (CNF) and composites based on CNF (Metals/CNF) is of particular interest. In the present work, the samples of CNF were produced via ethylene decomposition over Co-Pt (0-100 at.% Pt) microdispersed alloys prepared by a reductive thermolysis of multicomponent precursors. XRD analysis showed that the crystal structure of alloys in the composition range of 5-35 at.% Pt corresponds to a fcc lattice based on cobalt (Fm-3m), while the CoPt (50 at.% Pt) and CoPt₃ (75 at.% Pt) samples are intermetallics with the structure P4/mmm and Pm-3m, respectively. The microstructure of the alloys is represented by agglomerates of polycrystalline particles (50-150 nm) interconnected by the filaments. The impact of Pt content in the Co_1-xPt_x samples on their activity in CNF production was revealed. The interaction of alloys with ethylene is accompanied by the generation of active particles on which the growth of nanofibers occurs. Plane Co showed low productivity (~5.5 g/g_cat), while Pt itself exhibited no activity at all. The addition of 15-25 at.% Pt to cobalt catalyst leads to an increase in activity by 3-5 times. The maximum yield of CNF reached 40 g/g_cat for Co_0.75Pt_0.25 sample. The local composition of the active alloyed particles and the structural features of CNF were explored.

Scaling up the Process of Catalytic Decomposition of Chlorinated Hydrocarbons with the Formation of Carbon Nanostructures

Catalytic processing of organochlorine wastes is considered an eco-friendly technology. Moreover, it allows us to obtain a value-added product—nanostructured carbon materials. However, the realization of this process is complicated by the aggressiveness of the reaction medium due to the presence of active chlorine species. The present research is focused on the characteristics of the carbon product obtained over the Ni-Pd catalyst containing 5 wt% of palladium in various quartz reactors: from a lab-scale reactor equipped with McBain balance to scaled-up reactors producing hundreds of grams. 1,2-dichloroethane was used as a model chlorine-substituted organic compound. The characterization of the materials was performed using scanning and transmission electron microscopies, Raman spectroscopy, and low-temperature nitrogen adsorption. Depending on the reactor type, the carbon yield varied from 14.0 to 24.2 g/g(cat). The resulting carbon nanofibers possess a segmented structure with disordered packaging of the graphene layers. It is shown that the carbon deposits are also different in density, structure, and morphology, depending on the type of reactor. Thus, the specific surface area changed from 405 to 262 and 286 m2/g for the products from reactor #1, #2, and #3, correspondingly. The main condition providing the growth of a fluffy carbon product is found to be its ability to grow in any direction. If the reactor walls limit the carbon growing process, the carbon product is represented by very dense fibers that can finally crack the reactor.

Dynamic State and Active Structure of Ni-Co Catalyst in Carbon Nanofiber Growth Revealed by in Situ Transmission Electron Microscopy

Alloy catalysts often show superior effectiveness in the growth of carbon nanotubes/nanofibers (CNTs/CNFs) as compared to monometallic catalysts. However, due to the lack of an understanding of the active state and active structure, the origin of the superior performance of alloy catalysts is unknown. In this work, we report an in situ transmission electron microscopy (TEM) study of the CNF growth enabled by one of the most active known alloy catalysts, i.e., Ni-Co, providing insights into the active state and the interaction between Ni and Co in the working catalyst. We reveal that the functioning catalyst is highly dynamic, undergoing constant reshaping and periodic elongation/contraction. Atomic-scale imaging combined with in situ electron energy-loss spectroscopy further identifies the active structure as a Ni-Co metallic alloy (face-centered cubic, FCC). Aided by the molecular dynamics simulation and density functional theory calculations, we rationalize the dynamic behavior of the catalyst and the growth mechanism of CNFs and provide insight into the origin of the superior performance of the Ni-Co alloy catalyst.

Preparation of porous Co-Pt alloys for catalytic synthesis of carbon nanofibers

A simple and convenient procedure for the production of highly dispersed porous Co-Pt alloys to be used as catalysts for the synthesis of nanostructured carbon fibers (CNF) has been developed. The technique is based on the thermal decomposition of specially synthesized multicomponent precursors in a reducing atmosphere. A series of porous single-phase alloys Co-Pt (10-75 at% Pt) have been synthesized. The alloys containing 75 and 50 at% Pt were identified by the x-ray diffraction analysis as the intermetallics CoPt₃ and CoPt, respectively. Within the region of 10-35 at% Pt, the synthesized alloys are represented by Co_1-x Pt _x random solid solutions with face-centered cubic lattice. The alloys obtained are characterized by a porous structure consisting of assembled fragments with a size of 50-150 nm. The obtained alloys were tested in the catalytic chemical vapor deposition of the ethylene to CNF. A significant synergistic effect between Co and Pt in the synthesis of carbon nanomaterials (CNMs) was revealed. The yield of CNF (for 30 min reaction) for catalysts containing 25-35 at% Pt was 30-38 g(CNF)/g(cat), whereas those for Co (100%) and Pt (100%) samples were as low as 5.6 and >0.1 g(CNF)/g(cat), respectively. The produced CNM composed of fibers with a segmented structure was shown to be characterized by a rather high specific surface area (200-250 m² g^-1) and structural homogeneity.

Sol-Gel-Prepared Ni-Mo-Mg-O System for Catalytic Transformation of Chlorinated Organic Wastes into Nanostructured Carbon

The present work aimed to prepare Ni-Mo particles distributed within the MgO matrix. With this purpose in mind, a ternary Ni-Mo-Mg oxide system was synthesized by a sol-gel approach. The samples were studied by low-temperature nitrogen adsorption, X-ray diffraction analysis, and transmission electron microscopy equipped with energy dispersive X-ray analysis. Both the nickel and molybdenum species in the prepared samples were characterized by a fine and uniform distribution. The diffraction pattern of the ternary system was predominantly represented by the MgO reflections. The catalytic activity of the samples was tested in the decomposition of 1,2-dichloroethane used as a representative of the chlorinated organic wastes. The nanostructured carbon filaments resulting from the decomposition of the halogenated substrate were found to be characterized by a narrow diameter distribution, according to the transmission electron microscopy data, thus confirming the fine distribution of the active Ni-Mo particles. The results obviously show the advantages of the sol-gel technique for obtaining efficient catalysts.

Hybrid Materials Based on Carbon Nanotubes and Nanofibers for Environmental Applications

With the advances in material science, hybrid nanomaterials with unique mechanical, electrical, thermal and optical characteristics have been developed. Among them, hybrids based on filamentous forms of carbon, such as carbon nanotubes and carbon nanofibers, in combination with inorganic nanoparticles attract particular attention. Due to the structure and morphology, charge and energy transfer processes lead to synergistic effects that allow the use of less material with higher productivity. To clarify these issues, this review will summarize and discuss the relevant studies of the use of inorganic compounds of various chemical groups in modifying carbon nanomaterials for ecological applications.

Effect of Mo on the catalytic activity of Ni-based self-organizing catalysts for processing of dichloroethane into segmented carbon nanomaterials

A series of micro-disperse Ni-Mo alloys with the sponge-like structure was prepared by a simultaneous precipitation method followed by sintering of the sediment in H₂ atmosphere at 800 °C. According to XRD data, the formation of single-phase solid solution Ni_1-xMo_x took place for the samples with Mo content of 0.6–8.3 wt.%. Synthesized samples were studied in a process of the catalytic CVD of C₂H₄Cl₂ at 550–700 °C. In situ kinetic studies of carbon deposition process were carried out in a flow gravimetric setup equipped with McBain balances. An interaction of Ni-Mo alloys with C₂H₄Cl₂ is accompanied by their rapid disintegration with formation of disperse active particles catalyzing the growth of carbon nanomaterials (CNM). The strong boosting effect of Mo on the catalytic performance of Ni was revealed. The maximum yield of CNM product (8.3 wt.% Mo, 600 °C, 120 min) was as high as 45 g/g_M. The study on effect of the reaction temperature on the CNM yield allowed one to define an optimal temperature regime. The impact of Mo concentration upon the morphology, structural features and textural properties of the produced carbon fibers was investigated by means of SEM, TEM, Raman spectroscopy and low-temperature nitrogen adsorption. The role of chemisorbed chlorine species in a pulse-to-pulse regime of the segmented carbon filaments formation was discussed.