Metal Catalyst Precursor Research Articles

CARBON NANOSTRUCTURES OBTAINING FROM POLYMER MATERIALS

As part of the expansion of raw material base used in the development of technological and productive methods for the synthesis of carbon nanostructures (CNS) and solving the problem of environmentally friendly and economical polymer recycling, the results of investigation of microwave (MW) catalytic pyrolysis of macromolecular compounds from the range of polystyrene, polypropylene, polyethylene terephthalate, polyvinyl alcohol are presented. The information about existing approaches to solving these problems is briefly considered, and the prospects for MW processing of polymers are shown. The process was carried out by microwave treatment of a mixture of polymer raw materials acting as a carbon donor and substances-precursors of metal catalysts – cobalt and nickel compounds, their mixtures, as well as metal iron and nickel. Graphite and carbon fiber were used as temperature regulator. Experiments have demonstrated that effective conversion of the studied compounds occurs only in the presence of MW energy absorbers-converters, regardless of the nature of metal catalyst precursor. According to electron microscopy data, the resulting materials are a mixture of carbon nanostructures of disordered morphology with the predominant content of carbon nanotubes (CNTs) in the reaction products for experiments with polystyrene, polypropylene and polyethylene terephthalate. The use of polypropylene and polyvinyl alcohol leads to the production of carbon nanostructures containing only a small amount of CNTs. X-ray phase analysis data confirm the formation of multi-walled carbon nanotubes as the main structural component of the obtained carbon nanomaterials. It has been suggested that transformation pathways of the investigated hydrocarbons are similar, despite the difference in pyrolysis temperatures, which may be related to the simultaneous processes of polymer cracking, carbonization of decomposition products and CNS synthesis due to the rapid growth of reaction mass temperature during microwave treatment. The efficiency of different precursors of catalytic systems based on transition metals in the processes examined is substantiated. It has been shown that the high carbon content in feedstock promotes the formation of carbon nanostructures, but is not decisive for carbon nanotubes obtaining. For citation: Zaritovskii A.N., Kotenko E.N., Grishchuk S.V. Carbon nanostructures obtaining from polymer materials. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 99-106. DOI: 10.6060/ivkkt.20246705.6957.

Features of the noble metals impregnation into the polymeric matrix of hyper-cross-linked polystyrene

Commercial hyper-cross-linked polystyrene (HCLPS) was shown to be a promising support for the development of heterogeneous catalysts intended for fine organic synthesis. This paper summarizes the results of multiyear studies on the creation of heterogeneous Pd-, Ptand Ru-containing catalysts based on MN100 and MN270 HCLPS. Data obtained by characterization of HCLPS and the related catalysts using various physical and physicochemical methods are reported. It was shown that commercial HCLPS can be used in the catalyst synthesis as spherical grains or as a powder. The form of HCLPS, along with the features of the metal catalyst precursor, essentially affect the distribution of Pd, Pt and Ru compounds and the sizes of metal-containing nanoparticles formed in the polymer environment. In addition, this is the first study that considers in detail the effect of catalyst treatment in flowing hydrogen at 300 °C on the surface chemical composition of the MN100 powder samples impregnated with Pd, Pt and Ru compounds.

Features of the noble metals impregnation into the polymeric matrix of hyper-cross-linked polystyrene

Commercial hyper-cross-linked polystyrene (HCLPS) was shown to be a promising support for the development of heterogeneous catalysts intended for fine organic synthesis. This paper summarizes the results of multiyear studies on the creation of heterogeneous Pd-, Ptand Ru-containing catalysts based on MN100 and MN270 HCLPS. Data obtained by characterization of HCLPS and the related catalysts using various physical and physicochemical methods are reported. It was shown that commercial HCLPS can be used in the catalyst synthesis as spherical grains or as a powder. The form of HCLPS, along with the features of the metal catalyst precursor, essentially affect the distribution of Pd, Pt and Ru compounds and the sizes of metal-containing nanoparticles formed in the polymer environment. In addition, this is the first study that considers in detail the effect of catalyst treatment in flowing hydrogen at 300 °C on the surface chemical composition of the MN100 powder samples impregnated with Pd, Pt and Ru compounds.

3D designed and printed chemical generators for on demand reagent synthesis

Modern science has developed well-defined and versatile sets of chemicals to perform many specific tasks, yet the diversity of these reagents is so large that it can be impractical for any one lab to stock everything they might need. At the same time, isssues of stability or limited supply mean these chemicals can be very expensive to purchase from specialist retailers. Here, we address this problem by developing a cartridge -oriented approach to reactionware-based chemical generators which can easily and reliably produce specific reagents from low-cost precursors, requiring minimal expertise and time to operate, potentially in low infrastructure environments. We developed these chemical generators for four specific targets; transition metal catalyst precursor tris(dibenzylideneacetone)dipalladium(0) [Pd2(dba)3], oxidising agent Dess-Martin periodinane (DMP), protein photolinking reagent succinimidyl 4,4’-azipentanoate (NHS-diazirine), and the polyoxometalate cluster {P8W48}. The cartridge synthesis of these materials provides high-quality target compounds in good yields which are suitable for subsequent utilization.

Preparation of high-purity straight silicon nanowires by molten salt electrolysis

Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process. Using nickel formate as a metal catalyst precursor, straight silicon nanowires (65–150 nm in diameter) were directly prepared by electrolysis from the Ni/SiO2 porous pellets with 0.8 wt% nickel content in molten CaCl2 at 900 °C. Benefiting from their straight appearance and high purity, the silicon nanowires therefore offered an initial coulombic efficiency of 90.53% and specific capacity of 3377 mAh/g. In addition, the silicon nanowire/carbon composite exhibited excellent cycle performance, retaining 90.38% of the initial capacity after 100 cycles. Whilst further study on the charge storage performance is still ongoing, these preliminary results demonstrate that nickel formate is an efficient and effective metal catalyst precursor for catalytic preparation of high purity straight silicon nanowires via the molten salt electrolysis, which is suitable for large-scale production.

Effect of nickel precursor and catalyst activation temperature on methanation performance

This work studied an effect of anionic precursor on the preparation of active and fine nickel metal catalysts for syngas methanation. Nickel catalysts were pr¬epared by impregnation-co-precipitation method. Nickel hydrate salts of Ni(NO3)2·6H2O, NiSO4·6H2O and NiCl2·6H2O were used as a metal catalyst precursor, and the obtained catalysts were named as Ni/Al (N), Ni/Al (S) and Ni/Al (Cl), respectively. Methanation synthesis of carbon monoxide was carried out in a fixed bed stainless reactor. Prior to experiment, the catalyst powder was pressed into tablets, then crushed and sieved to use 0.5-0.9 mm particles. Reactions were performed at the temperature of 350 °C in the pressure of 3 atm of H2:CO syngas (the molar ratio of 3:1) with the GHSV of 3000 h-1. In the present methanation conditions, the Ni/Al (N), Ni/Al (S) and Ni/Al (Cl) catalysts gave the CH4 selectivity of 93%, 18% and 91% (vol.), respectively. The XRD and ICP-OES analysis clarified that although the Ni/Al (S) catalyst contained a similar nickel amount of 17.4 wt % to other two catalysts, its metal distribution was poor. Also the low activity of the Ni/Al (S) catalyst was caused by the contamination of remained sulfur from sulfate precursor. This work also examined an influence of catalyst activation temperature pre-synthesis. The Ni/Al (N) catalyst was reduced by pure hydrogen gas at different temperatures of 350 ºС, 400 ºС or 450 ºС. The catalyst activated at 400 ºС produced the highest CH4 amount of 0.087 mmol·g-1cat for the duration of 1h methanation. An initial temperature of methane formation was the lowest for the Ni/Al (N) catalyst which was activated at 400 ºС among three catalysts.

Application of Carbon Nanotubes Doped with Silicon As the Anode Electrode for Lithium Ion Battery

It is well known that the structural modification of carbon nanotubes (CNT) with heteroatoms, could modify their physical and chemical properties. These modifications open the possibilities to improve the electrochemical performance of CNT thus enhancing their application in batteries for storage of lithium ions. However, to achieve such characteristics it is important to control its structure, morphology and chemical composition during synthesis. In this work, the CNT were modified in situ by the intercalation of silicon (CNT-Si) in the graphitic carbon network to be used as an anode electrode in lithium ion battery. CNT-Si were synthesized by a modified chemical vapor deposition; toluene, ferrocene and triphenylsilane were used as carbon source, metal catalyst and silicon precursor, respectively. The effect of doping and temperature was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X ray photoelectron spectroscopy (XPS). The microscopy results showed that the CNT-Si were structurally modified with various forms of roughness, distortions and defects not only in the inner walls but also on outer walls. The elevated synthesis temperature had the most significant effect in the graphitic carbon network. According to the Raman scattering, the CNT-Si presented greater structural disorder due to the integration of silicon atoms in the carbon, which increased the disorder in hexagonal network. Elemental analysis composition by XPS indicated that the silicon was intercalated preferably at a higher temperature with a concentration of 0.76±10 at. %, clearly showing that silicon was successfully linked in the carbon network as Si-C. In order to examine the electrochemical properties of the materials, CNT-Si were used as an anode electrode for galvanostatic charge and discharge tests, as well as for cyclic votammetry curves. The results highlighted that temperature played a very important role on the electrocatalytic characteristics of materials and the insertion of the silicon in the carbon structure provided more sites for the diffusion and storage of lithium. The processes of alloying and de-alloying lithium in the CNT-Si matrix, charge and discharge capacity, as well as its cyclic performance will be discussed.

Fuel Sulfur and Iron Additives Contribute to the Formation of Carbon Nanotube-like Structures in an Internal Combustion Engine

Recent work has indicated the presence of carbon nanotubes (CNTs) in laboratory diesel and gasoline exhaust, in ambient air, and in lung samples of children exposed to traffic exhaust. While it is already known that certain processes will produce some carbonaceous particles of fullerene-like crystallinity, the conditions responsible for their formation remain unknown. On the basis of a standard process for the gas-phase synthesis of CNTs, we hypothesized that the presence of a metal catalyst precursor and high levels of fuel sulfur would impact CNT formation in a diesel engine. A diesel engine was doped with varying concentrations of fuel-borne sulfur and ferrocene to produce conditioned iron (Fe) particles that acted as seed catalysts. Results showed that in the presence of Fe nuclei resulting from 36 ppm ferrocene doping, 4500 ppm of fuel sulfur produced CNT-like structures in 31% of images analyzed by transmission electron microscopy. The precursor concentrations required for high rates of CNT growth a...

Formic Acid Dehydrogenation Catalysed by Tris(TPPTS) Ruthenium Species: Mechanism of the Initial “Fast” Cycle

AbstractWater‐soluble ruthenium m‐triphenylphosphinetrisulfonate (TPPTS) complexes are excellent catalysts for formic acid dehydrogenation. Interestingly, the choice of metal catalyst precursor has a direct influence on initial activities. The reaction with hexaaquaruthenium(II) tosylate directly yields bisphosphine complexes in the presence of TPPTS and formic acid, whereas trisphosphine adducts are involved if the reaction starts with ruthenium(III) chloride. We present the results of a series of manometric and spectroscopic experiments that reveal the true nature of these highly active species, and subsequently propose a rational “fast” cycle mechanism explaining this peculiar activity profile.

Fabrication of Carbon Nanofiber and Silicon Carbonitride Ceramic Nanomposites by <i>In Situ</i> Growth during Ceramic Formation

Carbon nanofiber (CNF) and silicon carbonitride (SiCN) ceramic nanocomposites (SiCN/CNF) are fabricated by in-situ growth of CNFs in SiCN ceramics during ceramic transformation of polymeric precursors of polysilazanes (PSZ). Metal catalyst precursors are mixed into the polysilazane liquid forming metal particles from decomposition under heating during the pyrolysis. At certain temperatures, ethylene was introduced as a carbon source to induce the growth of CNFs over the metal particles in the ceramic body followed by heating to higher temperatures to complete the pyrolysis. In this way, bulk nanocomposites of SiCN/CNF are obtained as crack-free bodies although some pores are left in the sample. Scanning electron microscopy (SEM) analysis performed on the cross-section of nanocomposites revealed the distribution of needle-like nanofibers of diameter ~ 200 nm and exposed length of ~ 2 μm. The CNFs exhibited the unique multiscale nanostructure in micron hollow tubes with branched nanofiber walls. Energy dispersive X-ray spectrometer (EDX) detected carbon as the major element from the nanofibers confirming the formation of carbon nanofibers. Moreover, clusters of nanoparticles are formed on the ceramic surface from carbon depositions. The in-situ growth of CNFs in SiCN ceramics provides a one-step process potentially to be developed for fabrication of structural and functional SiCN/CNF nanocomposites.

Carbon nanotube–nanopipe composite vertical arrays for enhanced electrochemical capacitance

The newly-designed vertical array structure of carbon nanotubes (CNTs) surrounding carbon nanopipes (CNTs@CNPs) was fabricated, which includes the formation of the primary CNP (ca. 200nm in diameter) arrays in virtue of the anodic aluminum oxide (AAO) membrane template with infiltration of polymer solution containing metal catalyst precursor, followed by carbonization and CVD growth of the secondary CNTs (20nm in diameter). The secondary CNTs with controllable density/length are grown both inside and outside the primary CNPs, which not only induce the four times increase of the specific surface areas for the samples, but also largely enhance the interconnection between the vertical CNPs for good electric conductance. The unique CNTs@CNPs arrays significantly improve the electrochemical capacitance per unit area with great long-term stability, indicating the promise as new material platform for development of advanced energy-storage devices.

In Situ Carbon Nanotube Formation in Templated Pores of Polymer‐Derived Ceramics

AbstractMulti‐walled carbon nanotubes (MWCNTs) have been formed in situ in porous, polymer derived ceramics, using polystyrene (PS) microbeads as pore formers. The microbeads were coated with nickel acetate, as a transition metal catalyst precursor, and then introduced into the preceramic polymer methylphenylpolysiloxane (PMPS). The PMPS served as a precursor for the ceramic matrix and as carbon source for CNT formation. The PS microbead burnout was observed between 200 and 400 °C, leaving behind nickel nanoparticles at the surface of the templated pore walls. Thermal conversion of the precursor to ceramic was carried out in the temperature range between 500 and 1 200 °C. MWCNTs were formed in the templated pores during the pyrolysis step by converting the carbon from the decomposition of PMPS. The oxidation resistance of these composites has been studied and an interesting catalytic oxidation phenomenon was observed that may be quite important for the oxidation of carbon nanotubes.

A Review of Recent Advances on the Effects of Microstructural Refinement and Nano-Catalytic Additives on the Hydrogen Storage Properties of Metal and Complex Hydrides

The recent advances on the effects of microstructural refinement and various nano-catalytic additives on the hydrogen storage properties of metal and complex hydrides obtained in the last few years in the allied laboratories at the University of Waterloo (Canada) and Military University of Technology (Warsaw, Poland) are critically reviewed in this paper. The research results indicate that microstructural refinement (particle and grain size) induced by ball milling influences quite modestly the hydrogen storage properties of simple metal and complex metal hydrides. On the other hand, the addition of nanometric elemental metals acting as potent catalysts and/or metal halide catalytic precursors brings about profound improvements in the hydrogen absorption/desorption kinetics for simple metal and complex metal hydrides alike. In general, catalytic precursors react with the hydride matrix forming a metal salt and free nanometric or amorphous elemental metals/intermetallics which, in turn, act catalytically. However, these catalysts change only kinetic properties i.e. the hydrogen absorption/desorption rate but they do not change thermodynamics (e.g., enthalpy change of hydrogen sorption reactions). It is shown that a complex metal hydride, LiAlH4, after high energy ball milling with a nanometric Ni metal catalyst and/or MnCl2 catalytic precursor, is able to desorb relatively large quantities of hydrogen at RT, 40 and 80 °C. This kind of behavior is very encouraging for the future development of solid state hydrogen systems.

Methylaluminum dichloride as a cocatalyst for Ni(II) α-diimine complexes catalyzed ethylene polymerization

Diimine Ni(II) catalysts have attained special interest due to their tunable polymerization activity and polymer microstructure by simple modification of the ligand architecture. 1,2 Technical process for olefin polymerization requires the use of suitable cocatalysts to transform inactive but readily prepared and handled catalyst precursors into the active species. The activity of methylaluminoxane (MAO) or its derivatives as cocatalysts is generally unmatched by other organoaluminum reagents. The ability of these substances to activate many kinds of catalytic precursors has been demonstrated for a wide range of transition metal catalyst precursors. However the practical use of MAO also poses some important drawbacks. For example, they are relatively expensive reagents that have to be used in large excess to achieve their optimum efficiency. Recently we have reported the polymerization/oligomerization behavior of late transition metal catalysts in combination with common alkyl aluminums like ethylaluminum sesquichloride (EAS). 3,4 In the present study we explore the use of methylaluminum dichloride (MADC) as a potential alternative for MAO towards the polymerization of ethylene with Ni(II) α-diimine catalysts.

Different carbon nanostructured materials obtained in catalytic chemical vapor deposition

Different carbon nanostructured materials, such as nanotubes, nanofibers, nanosprings and nanooctopus, were grown by changing the metal catalyst and experimental parameters of the thermal chemical vapor deposition process. These experiments were performed using a tubular furnace and methane or acetylene as carbon feedstock gases. Thin films of Ni or Cu were deposited onto a SiO2/Si substrate and employed as catalysts. The effect of the growth temperature, metal catalyst and carbon gas precursor (methane or acetylene) on the final carbon nanoestructured material was studied by scanning electron microscopy, Raman spectroscopy and grazing incidence X-ray diffraction. Growth of multiwall carbon nanotubes (MWCNTs) was observed using both metal films and carbon precursor gases, whereas partially oxidized Ni films promoted formation of nanosprings. Experiments with reduced supply of methane resulted in octopus-like carbon nanostructures when a Cu film was used as a catalyst.

Nitrogen in highly crystalline carbon nanotubes

Multiwall carbon nanotubes (MWCNTs) with an unprecedented degree of internal order were synthesised by chemical vapour deposition (CVD) adding a nitrogen-containing compound to the hydrocarbon feedstock. Ferrocene was used as the metal catalyst precursor. The remarkable crystallinity of these nanotubes lies both in the isochirality and in the crystallographic register of their walls, as demonstrated by electron diffraction and high resolution electron microscopy experiments. High resolution transmission electron microscopy analysis shows that the walls of the nanotubes consist of truncated stacked cones, instead of perfect cylinders, with a range of apex angles that appears to be related to the nitrogen concentration in the synthesis process. The structure of armchair, zigzag and chiral nanotubes is modelled and discussed in terms of density of topological defects, providing an interesting comparison with our microscopy experiments. A growth mechanism based on the interplay of base- and tip-growth is proposed to account for our experimental observations.

Comments on the ring-opening polymerization of morpholine-2,5-dione derivatives by various metal catalysts and characterization of the products formed in the reactions involving R2SnX2, where X = OPriand NMe2and R = Bun, Ph and p-Me2NC6H4

(3S,6S)-3-Isopropyl-6-methyl-morpholine-2,5-dione (1), and (3S,6S)-3,6-dimethyl-morpholine-2,5-dione (2), do not enter into ring-opening polymerization reactions with metal catalyst precursors commonly employed for lactides, and with Sn(II) octanoate, only low molecular weight oligomers are obtained. Reactions with R2SnX2 compounds, where R = Ph, Bu(n) and p-Me2NC6H4 and X = OPr(i) or NMe2, reveal that ring-opening of the morpholine-2,5-diones does occur, but that polymerization is terminated by the formation of kinetically-inert products such as {Ph2Sn[mu,eta(3)-OCH(Me)CONCH(Pr(i))COOPr(i)]}2 (3), and {[Bu(n))2Sn[mu,eta(3)-OCH(Me)CONCH(Me)CONMe2]}2 (4), with elimination of HX. Ph3SnOPr(i) is seen to react reversibly with morpholine-2,5-diones in toluene-d8 by 1H NMR spectroscopy while (Bu(n))3SnNMe2 reacts by ring opening to give (Bu(n))3SnOCH(Me)C(O)NHCHMeC(O)NMe2. The new organotin compounds have been characterized by 1H, 13C{1H} and 118Sn NMR spectroscopy and compounds 1, 2, 3 and 4 by single crystal X-ray crystallography.

NEXAFS and X-ray scattering study of structure changes after post-annealing treatments of aligned MWNTs

The control of the crystallization degree is an important issue for carbon nanotube applications. In this context, we present the evolution of the structure after post-annealing treatment of multiwalled carbon nanotubes (MWNT), obtained by the aerosol pyrolysis process, involving liquid aerosols containing both hydrocarbon source and the metal catalyst precursor. The alignment and the degree of crystallinity of the raw and annealed carbon nanotubes have been quantified by X-ray diffraction measurements also used to analyze the metallic phases inside the nanotubes. The Near-Edge X-ray Absorption Fine Structure (NEXAFS) studies were performed at the C K-edge in order to follow the evolution of the electronic structure with the local structure and the degree of crystallinity of the nanotubes. We confirm that this chemical vapour deposition synthesis method enables to produce well-aligned multiwalled carbon nanotubes. The effect of post-annealing temperature both on local ordering and graphitization degree of nanotube walls are described. The results are compared to the previous observations of individual nanotubes by HRTEM concerning the structural changes occurring during annealing treatments.

Synthesis of multi-walled carbon nanotubes and nano-fibres using the aerosol method with metal-ions as the catalyst precursors

We report on MWNTs synthesised using the aerosol method. The catalyst particles are formed by dissolving metal salts in organic solvents. This solution is sprayed as aerosols into a furnace. The active catalyst is formed in-situ, using H 2 as carrier gas and as reducing agent of the metal ions. This synthesis route gives possibilities for using a uniquely wide range of metal catalyst precursors and carbon sources. Using this approach, the size of the active catalyst particles can be calculated. MWNTs, prepared using Co(NO 3) 2 · 6H 2O as precursor and tetrahydrofuran, serving as solvent and carbon source demonstrate the reliability of these predictions.

New Tandem Catalysis: Preparation of Cyclic Enol Ethers Through a Ruthenium‐Catalyzed Ring‐Closing Metathesis—Olefin Isomerization Sequence.

Tandem reactions that proceed with a single metal catalyst precursor offer novel opportunities for developing efficient new reaction sequences. In this regard, reaction conditions have been identified that allows for a tandem ring-closing metathesis−olefin isomerization sequence catalyzed by a common ruthenium precursor. Specifically, the tandem process generates cyclic enol ethers from a variety of readily available acyclic dienes in a single reaction vessel using Grubbs' ruthenium alkylidene.