Editorial for Special Issue "Advanced Materials in Catalysis and Adsorption".

This Special Issue aims to cover the latest research on the design and development of advanced materials for adsorption and catalytic applications [...].

Efficient Production of Segmented Carbon Nanofibers via Catalytic Decomposition of Trichloroethylene over Ni-W Catalyst.

The catalytic utilization of chlorine-organic wastes remains of extreme importance from an ecological point of view. Depending on the molecular structure of the chlorine-substituted hydrocarbon (presence of unsaturated bonds, intermolecular chlorine-to-hydrogen ratio), the features of its catalytic decomposition can be significantly different. Often, 1,2-dichloroethane is used as a model substrate. In the present work, the catalytic decomposition of trichloroethylene (C2HCl3) over microdispersed 100Ni and 96Ni-4W with the formation of carbon nanofibers (CNF) was studied. Catalysts were obtained by a co-precipitation of complex salts followed by reductive thermolysis. The disintegration of the initial bulk alloy driven by its interaction with the reaction mixture C2HCl3/H2/Ar entails the formation of submicron active particles. It has been established that the optimal activity of the pristine Ni catalyst and the 96Ni-4W alloy is provided in temperature ranges of 500-650 °C and 475-725 °C, respectively. The maximum yield of CNF for 2 h of reaction was 63 g/gcat for 100Ni and 112 g/gcat for 96Ni-4W catalyst. Longevity tests showed that nickel undergoes fast deactivation (after 3 h), whereas the 96Ni-4W catalyst remains active for 7 h of interaction. The effects of the catalyst's composition and the reaction temperature upon the structural and morphological characteristics of synthesized carbon nanofibers were investigated by X-ray diffraction analysis, Raman spectroscopy, and electron microscopies. The initial stages of the carbon erosion process were precisely examined by transmission electron microscopy coupled with elemental mapping. The segmented structure of CNF was found to be prevailing in a range of 500-650 °C. The textural parameters of carbon product (SBET and Vpore) were shown to reach maximum values (374 m2/g and 0.71 cm3/g, respectively) at the reaction temperature of 550 °C.

Comparative Study on Carbon Erosion of Nickel Alloys in the Presence of Organic Compounds under Various Reaction Conditions.

The processes of carbon erosion of nickel alloys during the catalytic pyrolysis of organic compounds with the formation of carbon nanofibers in a flow-through reactor as well as under reaction conditions in a close volume (Reactions under Autogenic Pressure at Elevated Temperature, RAPET) were studied. The efficiency of the ferromagnetic resonance method to monitor the appearance of catalytically active nickel particles in these processes has been shown. As found, the interaction of bulk Ni-Cr alloy with the reaction medium containing halogenated hydrocarbons (1,2-dichloroethane, 1-iodobutane, 1-bromobutane) results in the appearance of ferromagnetic particles of similar dimensions (~200-300 nm). In the cases of hexachlorobenzene and hexafluorobenzene, the presence of a hydrogen source (hexamethylbenzene) in the reaction mixture was shown to be highly required. The microdispersed samples of Ni-Cu and Ni-Mo alloys were prepared by mechanochemical alloying of powders and by reductive thermolysis of salts-precursors, accordingly. Their interaction with polymers (polyethylene and polyvinyl chloride) under RAPET conditions and with ethylene and 1,2-dichloroethane in a flow-through reactor are comparatively studied as well. According to microscopic data, the morphology of the formed carbon nanofibers is affected by the alloy composition and by the nature of the used organic substrate.

Synthesis of Chlorine- and Nitrogen-Containing Carbon Nanofibers for Water Purification from Chloroaromatic Compounds.

Chlorine- and nitrogen-containing carbon nanofibers (CNFs) were obtained by combined catalytic pyrolysis of trichloroethylene (C2HCl3) and acetonitrile (CH3CN). Their efficiency in the adsorption of 1,2-dichlorobenzene (1,2-DCB) from water has been studied. The synthesis of CNFs was carried out over self-dispersing nickel catalyst at 600 °C. The produced CNFs possess a well-defined segmented structure, high specific surface area (~300 m2/g) and high porosity (0.5-0.7 cm3/g). The addition of CH3CN into the reaction mixture allows the introduction of nitrogen into the CNF structure and increases the volume of mesopores. As a result, the capacity of CNF towards adsorption of 1,2-DCB from its aqueous solution increased from 0.41 to 0.57 cm3/g. Regardless of the presence of N, the CNF samples exhibited a degree of 1,2-DCB adsorption from water-organic emulsion exceeding 90%. The adsorption process was shown to be well described by the Dubinin-Astakhov equation. The regeneration of the used CNF adsorbent through liquid-phase hydrodechlorination was also investigated. For this purpose, Pd nanoparticles (1.5 wt%) were deposited on the CNF surface to form the adsorbent with catalytic function. The presence of palladium was found to have a slight effect on the adsorption capacity of CNF. Further regeneration of the adsorbent-catalyst via hydrodechlorination of adsorbed 1,2-DCB was completed within 1 h with 100% conversion. The repeated use of regenerated adsorbent-catalysts for purification of solutions after the first cycle of adsorption ensures almost complete removal of 1,2-DCB.

Effect of Pretreatment with Acids on the N-Functionalization of Carbon Nanofibers Using Melamine.

Nowadays, N-functionalized carbon nanomaterials attract a growing interest. The use of melamine as a functionalizing agent looks prospective from environmental and cost points of view. Moreover, the melamine molecule contains a high amount of nitrogen with an atomic ratio C/N of 1/2. In present work, the initial carbon nanofibers (CNFs) were synthesized via catalytic pyrolysis of ethylene over microdispersed Ni-Cu alloy. The CNF materials were pretreated with 12% hydrochloric acid or with a mixture of concentrated nitric and sulfuric acids, which allowed etching of the metals from the fibers and oxidizing of the fibers' surface. Finally, the CNFs were N-functionalized via their impregnation with a melamine solution and thermolysis in an inert atmosphere. According to the microscopic data, the initial structure of the CNFs remained the same after the pretreatment and post-functionalization procedures. At the same time, the surface of the N-functionalized CNFs became more defective. The textural properties of the materials were also affected. In the case of the oxidative treatment with a mixture of acids, the highest content of the surface oxygen of 11.8% was registered by X-ray photoelectron spectroscopy. The amount of nitrogen introduced during the post-functionalization of CNFs with melamine increased from 1.4 to 4.3%. Along with this, the surface oxygen concentration diminished to 6.4%.

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 Co1-xPtx 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/gcat), 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/gcat for Co0.75Pt0.25 sample. The local composition of the active alloyed particles and the structural features of CNF were explored.

Comparative analysis of the characteristics of carbonaceous material obtained via single-staged steam pyrolysis of waste tires.

The two-stage technology of porous carbonaceous material obtained via pyrolysis in inert medium with subsequent activation by steam is well known. While steam could be a suitable substance for pyrolysis as well, single-staged technology for waste tire recycling is yet to be developed. A comparative analysis of the characteristics of the carbonaceous materials obtained by the single-staged steam pyrolysis of waste tires was carried out, which could provide a theoretical background for the development of such technology. The steam pyrolysis was performed in a tubular reactor in an overheated steam medium (500°C with 5 kg/h mass flow rate). The technical characteristics of the obtained samples were evaluated in the context of their potential for further application as absorbent and raw material for rubber production according to Chemical Abstracts Service No. 1333-86-4. The composition and physico-chemical properties of the obtained samples were studied using BET and thermogravimetric analysis, atomic emission, transmission and scanning electron microscopies, Raman, X-ray diffraction, and photoelectron spectroscopies. The results revealed that the structure and properties of all obtained carbonaceous material samples were similar. The samples consisted of amorphous carbon (with a disordered graphite lattice) and contained a significant amount of metal oxides. According to experimental data, zinc was present in the form of ZnO with a binding energy of 1022.4 eV, while sulfur was observed in the form of sulfide and oxysulfide with binding energies of 161.8 and 163.2 eV, respectively. According to electron microscopy, the morphology of samples was represented by a set of spherical agglomerates comprising nanosized particles. According to the BET analysis of the samples, the specific surface area varied in the range between 52.0 and 66.0 m2/g and the pore volume values were within a range of 0.53-0.87 cm3/g, while the average pore size varied from 412 to 527 Å.Implications: Our paper presents original research in the field of characterization of solid material obtained by single-staged steam gasification of waste tires, which were produced and exploited in conditions of Russia. Modern technology allows thermal utilization of waste tires by obtaining powders of carbonaceous material, which could be used as fuel, adsorbent, etc., but this process usually consists of two stages - pyrolysis in inert medium and activation in steam or carbon dioxide. One of the most promising directions of technological development is simplifying this process into single step, ensuring that the obtained material could be used as carbon black or adsorbent for gas steam cleansing. No data on suitability of carbonaceous material obtained by single-step steam pyrolysis of all-season waste tires to be adsorbent and/or carbon black is present in the literature. In order to evaluate the suitability of the obtained material to be adsorbent, the high specific surface area should be determined, while CAS technical standards specify many chemical and physical properties of industrial carbon black.The aim of the current article is to study the properties of carbonaceous material obtained during single-staged steam gasification of four different all-season tires (due to their widespread application worldwide) and evaluate its fitness as industrial-scale carbon black or adsorbent. The additional problem addressed was the evaluation of the variation in characteristics of carbonaceous material obtained due to different origins of tires. Experiments were conducted in a tubular lab reactor in order to simplify the experimental procedure while ensuring the applicability of the obtained results to practical conditions.The obtained results could be used for the development of the technology for closed-cycle tire processing (because black carbon is used for tire production) and adsorbent production. The characteristics of the materials obtained allow us to choose optimal parameters for such treatment and develop special policies and programs, which will integrate and regulate waste tire utilization via steam gasification.

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.

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 Co1-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.

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 Ni1-xMox 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/gM. 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.

CO Oxidation over Pd/ZrO2 Catalysts: Role of Support's Donor Sites.

A series of supported Pd/ZrO2 catalysts with Pd loading from 0.2 to 2 wt % was synthesized. The ZrO2 material prepared by a similar technique was used as a reference sample. The samples have been characterized by means of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), testing reaction of ethane hydrogenolysis (HGE), N2 adsorption, and electron paramagnetic resonance (EPR) spectroscopy. 1,3,5-trinitrobenzene was used as a probe molecule for the EPR spin probe method. The catalytic performance of samples was tested in the model reaction of CO oxidation. It was shown that the concentration of donor sites of support measured by EPR spin probe correlates with catalytic behavior during light-off tests. Low concentration of donor sites on a support's surface was found to be caused by the presence of the specific surface defects that are related to existence of coordinately unsaturated structures.

CF2Cl2 decomposition over nanocrystalline MgO: evidence for long induction periods.

CF(2)Cl(2) has been found to react with nanoscale MgO at 325 degrees C and higher temperatures. In excess of the halocarbon, the reaction results in the formation of MgF(2) as a predominant solid product, with CCl(4), and CO(2) formed as the main gaseous products. The kinetics of the process is characterized by a prolonged induction period, which is as long as 8.5 h at 325 degrees C. The length of the induction period decreases with temperature increase and becomes negligible at 500 degrees C. Complete CF(2)Cl(2) mineralization has been achieved in an excess of MgO at 450 degrees C. Detailed HRTEM and EDX analysis has shown that the induction period involves the formation of small amounts of magnesium halides on the oxide surface and results in its reconstruction leading to initial oriental ordering of the nanocrystals followed by substantial changes in the bulk composition of the nanoparticles. The reaction proved to be structurally sensitive. It has been found that deep fluoridation is possible only for nanoscale MgO samples. The use of samples with lower surface areas results in lengthening of the induction period and decrease of the reaction depth. The MgO transformation to MgF(2) has been found to result in a surface area decrease by more that an order of magnitude as a result of intense sintering of magnesium fluoride under the reaction conditions.