Carbon Nanotube Support Research Articles

Influence of a carbon nanotube support and supercritical fluid reaction medium on Fe-catalyzed Fischer-Tropsch synthesis

To investigate the influence of a supercritical fluid reaction medium on nanoparticle-catalyzed Fischer-Tropsch synthesis (FTS), Fe-based nanoparticle catalysts supported on carbon nanotubes were prepared and tested under both gas phase and supercritical FTS operating conditions. The nanoparticle catalysts displayed high activity, low CH4 selectivity, and elevated oxygenate selectivity. Conversion and selectivity towards heavy, unhydrogenated products were elevated under supercritical operation. With K promotion, aldehydes were produced under both gas phase and supercritical conditions. This study demonstrated the necessity of K promotion for aldehyde production and demonstrated that appreciable amounts of aldehydes can be produced in gas phase, Fe-catalyzed FTS.

Synergistic effect of potassium hydroxide and steam co-treatment on the functionalization of carbon nanotubes applied as basic support in the Pd-catalyzed liquid-phase oxidation of ethanol

Surface functionalization of carbon nanotubes (CNTs) was achieved by a thermal treatment in the presence of pre-adsorbed potassium hydroxide and steam at 350–550 °C. The generated oxygen-containing functional groups were more basic and thermally stable compared with conventional acid-generated groups. The influence of the KOH-steam co-treatment conditions on the functionalization of CNTs was systematically investigated. Residual K species were found to intercalate in the inner graphene layers of the CNTs providing additional Brønsted basicity. Owing to the favorable basic properties and high thermal stability of the generated functional groups, Pd nanoparticles supported on the co-treated CNTs were found to be strongly anchored leading to a high degree of Pd dispersion and a high resistance to sintering. The Pd nanoparticles on the co-treated CNT support produced at 450 °C and 550 °C showed the highest activity and yields of acetic acid in the aerobic oxidation of aqueous ethanol reaching almost full conversion after 5 h in the absence of additional base. In addition, the KOH-steam co-treatment was found to enhance the recyclability of the Pd/CNT catalysts.

Fischer–Tropsch Synthesis: Influence of Acid Treatment and Preparation Method on Carbon Nanotube Supported Ruthenium Catalysts

The influences of nitric acid treatment on a carbon nanotube (CNT) support and the preparation method, incipient wetness impregnation (IWI) versus chemical vapor deposition (CVD), on catalytic performance during Fischer–Tropsch (FT) synthesis were examined using a slurry phase reactor. Acid treated CNT (ACNT) supported Ru catalysts exhibited higher activities compared to Ru supported on untreated CNTs (UCNTs). The acid-treated CVD catalyst had higher initial CO conversion (smaller average Ru particle size) but sintered more due to a greater tendency for Ru to be deposited exterior to CNT channels relative to IWI. After the initial decline and leveling off period, the ACNT IWI catalyst had the highest steady activity among the catalysts tested. The ACNT IWI catalyst also displayed greater oxygenate selectivity (∼17%) compared to ACNT CVD (∼12%) and UCNT IWI (∼10%) catalysts at similar conversions. Acid treatment created adsorption sites on the CNT surface that anchor Ru precursors and promote CO insertion ...

Multidimensional Thin Film Hybrid Electrodes with MoS2 Multilayer for Electrocatalytic Hydrogen Evolution Reaction.

Hybrid electrodes are widely used in various energy storage and conversion devices. However, conventional fabrication methods like simple mixing allow only limited control over the internal electrode structure, and it is often difficult to elucidate the structure-property relationship among the electrode components. Taking advantage of the versatile layer-by-layer (LbL) assembly method, herein we report the preparation of electrocatalytic thin film electrodes for hydrogen evolution reaction (HER), highlighting the importance of nanoscale composition in multidimensional hybrid electrodes. The fabrication utilized the electrostatic interaction between the two components: catalytically active two-dimensional MoS2 nanosheets and conductive, one-dimensional multiwalled carbon nanotube (MWNT) support. The electrocatalytic activity was found to be highly tunable by adjusting the thickness of the electrode, suggesting structural dependence of electron transfer and mass transport between the electrolyte and electrode, which is otherwise difficult to investigate in electrodes fabricated by simple conventional methods. Furthermore, the detailed mechanism of HER on the hybrid electrode was also investigated, revealing the fine balance between the catalytic activity of MoS2 and conductivity of MWNT. We anticipate that this unique approach will offer new insights into the nanoscale control of electrode architecture and the development of novel electroactive catalysts.

Effective Hydrodeoxygenation of Stearic Acid and Cyperus Esculentus Oil into Liquid Alkanes over Nitrogen‐Modified Carbon Nanotube‐Supported Ruthenium Catalysts

AbstractNitrogen‐modified carbon nanotube‐supported ruthenium catalyst was demonstrated to be effective in the conversion of crude cyperus esculentus oil into linear liquid alkanes. The model compound stearic acid was nearly quantitatively converted into liquid alkanes, and the yields of n‐heptadecane and n‐octadecane were 89.5 % and 8.5 %, respectively. The mass yield of liquid alkanes from crude cyperus esculentus oil was 76.6 %, which was very close to the theoretical yield. The catalyst could be reused at least six times without loss of catalytic activity during the conversion of oil. We found that the nitrogen modification of the carbon nanotube support was beneficial to form more Ru0 species, which exhibited excellent catalytic activity and stability towards the hydrodeoxygenation of stearic acid and plant oil.

The tunable effect of nitrogen and boron dopants on a single walled carbon nanotube support on the catalytic properties of a single gold atom catalyst: a first principles study of CO oxidation

Doping of supports is a practical strategy to tune the catalytic performance of a single Au atom in CO oxidation.

Chemical Strategies for Enhancing Activity and Charge Transfer in Ultrathin Pt Nanowires Immobilized onto Nanotube Supports for the Oxygen Reduction Reaction

Multiwalled carbon nanotubes (MWNTs) represent a promising support medium for electrocatalysts, especially Pt nanoparticles (NPs). The advantages of using MWNTs include their large surface area, high conductivity, as well as long-term stability. Surface functionalization of MWNTs with various terminal groups, such as -COOH, -SH, and -NH2, allows for rational electronic tuning of catalyst-support interactions. However, several issues still need to be addressed for such systems. First, over the course of an electrochemical run, catalyst durability can decrease, due in part to metal NP dissolution, a process facilitated by the inherently high surface defect concentration within the support. Second, the covalent functionalization treatment of MWNTs adopted by most groups tends to lead to a loss of structural integrity of the nanotubes (NTs). To mitigate for all of these issues, we have utilized two different attachment approaches (i.e., covalent versus noncovalent) to functionalize the outer walls of pristine MWNTs and compared the catalytic performance of as-deposited ultrathin (<2 nm) 1D Pt nanowires with that of conventional Pt NPs toward the oxygen reduction reaction (ORR). Our results demonstrated that the electrochemical activity of Pt nanostructures immobilized onto functionalized carbon nanotube (CNT) supports could be dramatically improved by using ultrathin Pt nanowires (instead of NPs) with noncovalently (as opposed to covalently) functionalized CNT supports. Spectroscopic evidence corroborated the definitive presence of charge transfer between the metal catalysts and the underlying NT support, whose direction and magnitude are a direct function of (i) the terminal chemistry as well as (ii) the attachment methodology, both of which simultaneously impact upon the observed electrocatalytic performance. Specifically, the use of a noncovalent π-π stacking method coupled with a -COOH terminal moiety yielded the highest performance results, reported to date, for any similar system consisting of Pt (commercial NPs or otherwise) deposited onto carbon-based supports, a finding of broader interest toward the fabrication of high-performing electrocatalysts in general.

Selective Hydrogenation of 2‐Methylfuran and 2,5‐Dimethylfuran over Atomic Layer Deposited Platinum Catalysts on Multiwalled Carbon Nanotube and Alumina Supports

Abstract2‐Methylfuran (2MF) and 2,5‐dimethylfuran (DMF) were hydrogenated in the vapor phase to the corresponding tetrahydrofurans, linear 2‐ketones, and alcohols over Pt nanoparticles supported on multiwalled carbon nanotubes (MWCNTs) and alumina by atomic layer deposition. The hydrogenation behavior of sub‐nanometer Pt deposited on alumina was influenced by the acidity of the support. Relative to a commercial Pt/C catalyst, the Pt/MWCNT catalyst was found to contain similarly sized Pt nanoparticles that display a broader size distribution and significantly more n‐alkanes than oxygenates during hydrogenation of these alkyl‐substituted furans.

Encapsulated Cobalt Oxide on Carbon Nanotube Support as Catalyst for Selective Continuous Hydrogenation of the Showcase Substrate 1‐Iodo‐4‐nitrobenzene

AbstractA carbon nanotube supported catalyst containing cobalt/cobalt oxide (Co/Co3O4) nanoparticles encapsulated within a shell of nitrogen‐doped graphene layers (Co3O4/NGr@CNT) was prepared. It shows excellent chemoselectivity in the hydrogenation of 1‐iodo‐4‐nitrobenzene, which contains an iodine substituent highly sensitive against hydrodehalogenation. In contrast to traditional activated charcoal‐supported catalysts such as Pt‐V/C or the closely related Vulcan carbon black supported Co3O4/NGr@C, the advantageous morphological properties of the CNT support allow for the application of the new Co3O4/NGr@CNT as a fixed bed catalyst in a continuous flow reactor. Under optimized conditions, no dehalogenation side products could be detected. This remarkable selectivity in combination with its mechanical stability under operation conditions render Co3O4/NGr@CNT a catalyst particularly relevant for application in continuous processes based on a packed bed reactor.magnified image

Atmospheric Pressure Ammonia Synthesis Using Non-thermal Plasma Assisted Catalysis

This paper described a novel and green approach on catalytic ammonia synthesis using non-thermal plasma (NTP). The process studied in this paper involves the synthesis and absorption of ammonia under atmospheric pressure and low temperature. The effects of operational parameters including applied voltage, frequency, gas component and flow rate on ammonia synthesis under NTP conditions are studied in this paper. In addition, different selected catalysts and absorbents were investigated under different conditions of NTP treatment and the ammonia efficiency was reported and analyzed. Ru catalyst with carbon nanotube support, along with Cs promoter and micro porous absorbents including Molecular Sieve 13X and Amberlyst 15 yield the highest ammonia efficiency in this process. Results further indicated that frequency and applied voltage of 10,000 Hz and 6000 V, with N2:H2 feed ratio of 3:1 provided the optimized efficiency of ammonia synthesis of 2.3 gNH3/kWh.

Polymer- and Carbon Nanotube-Supported Heterogeneous Catalysts for the Synthesis of Carbamates from Halides, Amines, and CO2

A series of tetraalkylammonium catalysts immobilized on polystyrene or carbon nanotubes were investigated in a reaction between alkyl halides, amines, and CO2. The yield of carbamates was up to 85 % at 100 °C and 1 MPa of CO2 after 3 h (first stage 25 °C, 1 h) in the presence of Cs2CO3 and DMF as a solvent. The best results were achieved in the case of large ammonium substituents (C4 and C6) in the catalyst, benzyl amine, and benzyl chloride as reagents. The catalysts retained their activity after at least five cycles when carefully dried between cycles. Both polymer and carbon nanotube supports were equally effective, but the latter were less prone to deactivation.

Enhanced Hydrogen Evolution Catalysis Based on Cu Nanoparticles Deposited on Carbon Nanotubes at the Liquid/Liquid Interface

AbstractCopper nanoparticles were electrodeposited in situ on a conductive multi‐walled carbon nanotubes (MWCNT) support at a free‐standing water/1,2‐dichloroethane interface. The Cu/MWCNT nanocomposites act as highly active hydrogen evolution catalysts at the interface in the presence of lipophilic decamethylferrocene as the reducing agent.

Carbon Coated Metal Nanoparticles for Electrocatalysis

To promote the performance of nanoparticle electrocatalysts, a facile hydrothermal method is developed to generate core–shell nanocomposites with a metal catalyst core and a carbon shell. In this method, glucose serves as the reducing agent and carbon precursor while cetyltrimethylammonium surfactants serve as both pore structure-directing agents and nanoparticle capping agent. The accessibility of the metal catalyst core was examined by gas-phase ethylene hydrogenation and the electrocatalytic activity was tested by formic acid oxidation (FOR). The selection of halide counter ions used during the synthesis was found to be critical. The optimized sample of Pd-carbon nanocomposite exhibits a FOR current density of 2.55 mA/cm2, which is higher than that of un-coated Pd nanoparticles with no support (0.89 mA/cm2) and with carbon nanotube support (1.08 mA/cm2).

One-pot Aerosol Synthesis of Carbon Nanotube-Zn2GeO4 Composite Microspheres for Enhanced Lithium-ion Storage Properties

Three-dimensional (3D) carbon nanotube (CNT)-multicomponent metal oxide composite microspheres with non-aggregation characteristics are prepared using a simple one-pot spray pyrolysis process, applying water-soluble metal salt and oxidized CNT fibers. The hierarchical porous 3D structure of the CNT is formed by networking the flexible CNTs with a high aspect ratio during the drying stage of a droplet. Subsequently, the Zn and Ge salts are deposited over the CNTs to form the ZnO-CNT and GeO2-CNT composite microsphere. Decomposition of Zn and Ge salts into their respective oxides and the conversion reaction to form Zn2GeO4 at 700°C, produce the Zn2GeO4-CNT composite microsphere. The initial discharge capacities of the Zn2GeO4, Zn2GeO4-CNT, ZnO-CNT, and GeO2-CNT microspheres, at a current density of 1.5Ag−1, are 1351, 1211, 1387, and 1631mAhg−1, respectively, and their discharge capacities at the 300th cycle are 415, 762, 261, and 480mAhg−1, respectively. The CNT-Zn2GeO4 composite microspheres, selected as the first target material, show electrochemical properties superior to those of the bare Zn2GeO4, CNT-ZnO, and CNT-GeO2 composite microspheres. The synergetic effect of the multicomponent composition of Zn2GeO4 and the CNT support result in excellent Li-ion storage properties of the Zn2GeO4-CNT composite microspheres.

Platinum nanoparticles on carbon-nanotube support prepared by room-temperature reduction with H2 in ethylene glycol/water mixed solvent as catalysts for polymer electrolyte membrane fuel cells

Polyol approach is commonly used in synthesizing Pt nanoparticles in polymer electrolyte membrane fuel cells. However, the application of this process consumes a great deal of time and energy, as the reduction of precursors requires elevated temperatures and several hours. Moreover, the ethylene glycol and its oxidizing products bound to Pt are difficult to remove. In this work, we utilize the advantages of ethylene glycol and prepare Pt nanoparticles through a room-temperature hydrogen gas reduction in an ethylene glycol/water mixed solvent, which is followed by subsequent harvesting by carbon nanotubes as electrocatalysts. This method is simple, facile, and time-efficient, as the entire room-temperature reduction process is completed in a few minutes. As the solvent changes from water to an ethylene glycol/water mix, the size of Pt nanoparticles varies from 10 to 3 nm and their shape transitions from polyhedral to spherical. Pt nanoparticles prepared in a 1:1 volume ratio mixture of ethylene glycol/water are uniformly dispersed with an average size of ∼3 nm. The optimized carbon nanotube-supported Pt electrocatalyst exhibits excellent methanol oxidation and oxygen reduction activities. This work demonstrates the potential use of mixed solvents as an approach in materials synthesis.

Biopolymer Stabilized Nanogold Particles on Carbon Nanotube Support as Sensing Platform for Electrochemical Detection of 5-Fluorouracil in-vitro

A fast and facile electrochemical sensor for the detection of an important anti-cancer drug, 5-fluorouracil, is fabricated using a gold nanoparticle decorated multiwall carbon nanotube (GNP-MWCNT) composite modified electrode. GNP-MWCNT composite has been prepared by a simple one-pot synthesis in the presence of chitosan, which acts as a reducing as well as stabilizing agent. Synthesized GNP-MWCNT is characterized by UV-Visible spectroscopy, Raman spectroscopy, XRD analysis and FESEM for the structural and chemical properties of nanocomposite, and the size of the gold nanoparticles is determined to be ∼30nm by different methods. The electrochemical capability of the fabricated GNP-MWCNT composite modified electrode for the detection of 5-FU is examined by cyclic voltammetry, electrochemical impedance analysis and differential pulse voltammetry. The nanoAu decorated carbon nanotube electrode is found to be efficient for electrocatalytic oxidation of 5-FU. Peak current of the DPVs exhibited a linear relationship against 5-FU over a wide concentration range of 0.03–10μM with a low-detection-limit (3σ/b) of 20nM, and the analysis time is as low as 25s. Practical utility of the developed GNP-MWCNT nanocomposite biosensor has been demonstrated for the detection of 5-FU directly from artificial urine and pharmaceutical formulations with good recovery limits.

Preparations of Highly Stable RuCo/CNTs Electrocatalysts for Oxygen Reduction Reaction

The ruthenium-based chalcogenide catalysts such as ruthenium selenides have been shown to display good electrocatalytic activity toward oxygen reduction reaction (ORR) in acidic media. In this investigation, the carbon nanotubes (CNTs) supported RuCo alloyed nanoparticles (RuCo/CNTs) were prepared with different Ru/Co ratios (Ru/Co=0.5, 1.0, 2.0, 3.0) by impregnated method followed by heat treatments using less expansive metal chlorides as precursors. It was found that the RuCo nanoparticles were uniformly dispersed on the CNTs support and exhibited hexagonal alloyed phase with small amounts of metal oxides at the surface. The mean particle sizes were smaller than 10 nm and the potentials corresponding to oxygen reduction reaction were 0.67~0.73 V with the electron transfer numbers (n) of 3.0~4.0. The amounts of Co presented in the alloy significantly influenced the growth of nanoparticles and the defects of CNTs support. The best ORR activity with high stability in an acid solution was achieved with the RuCo/CNTs catalyst prepared with Ru/Co=2.0.

Fabrication of Fischer–Tropsch Catalysts by Deposition of Iron Nanocrystals on Carbon Nanotubes

The fabrication of supported catalysts consisting of colloidal iron oxide nanocrystals with tunable size, geometry, and loading—homogeneously dispersed on carbon nanotube (CNT) supports—is described herein. The catalyst synthesis is performed in a two‐step approach. First, colloidal iron and iron oxide nanocrystals with a narrow size distribution are produced. Second, the nanocrystals are attached to CNT grains serving as support structure. Important features, like iron loading and nanocrystal density on the CNT support, are controlled by changing the nanocrystal concentration and ligand concentration, respectively. The Fischer–Tropsch performance reveals these new materials to be active, selective toward lower olefins (60% C of hydrocarbons produced in the absence of promoters), and remarkably stable against particle growth.

Preparations of Highly Stable RuxCo/CNTs Electrocatalysts for Oxygen Reduction Reaction

The carbon nanotubes (CNTs) supported ruthenium cobalt alloy (Ru x Co) nanoparticles (Ru x Co/CNTs) were prepared with different Ru/Co ratios (x=Ru/Co=0.5, 1.0, 2.0, 3.0) by impregnated method using less expensive metal chlorides (CoCl2 and RuCl3) as precursors. The heat treatments were carried at the temperatures of 300°C, 400°C, 500°C and 700°C for comparison. It was found that the as prepared Ru x Co nanoparticles were uniformly dispersed on the CNTs support and exhibited mainly hexagonal alloyed phase with small amounts of metal oxides being presented at the surface. The mean particle sizes were smaller than 10 nm and the potentials corresponding to oxygen reduction reaction (ORR) were 0.67~0.73 V with the electron transfer numbers (n) of 3.0~4.0 by varying the Ru/Co ratios from 0.5 to 3.0. The amounts of Co presented in the alloy significantly influenced the growth of Ru x Co nanoparticles and the defects of CNTs support. The best ORR activity with high stability in an acid solution was achieved with the Ru2Co/CNTs when heat-treated at 400°C under H2 for 2 h.

Carbon/carbon nanotube-supported RuO2 nanoparticles with a hollow interior as excellent electrode materials for supercapacitors

Tailoring the internal structure of nanomaterials is an effective way to enhance their performance for a given application. Herein, a core–shell templated approach is demonstrated to fabricate carbon or carbon nanotube-supported hollow structured RuO2 nanoparticles as excellent electrode materials for supercapacitors. This strategy involves the synthesis of core–shell Ag–Ru nanoparticles, and subsequent loading on carbon or carbon nanotube support. Then the Ag component is removed from the core region using saturated aqueous Na2S solution to generate hollow structured Ru nanoparticles on carbon or carbon nanotube support, which are then converted into RuO2 with intact hollow structure by thermal treatment in air. In particular, the as-prepared carbon or carbon nanotube-supported hollow RuO2 nanoparticles for a supercapacitor adopting the H2SO4 electrolyte exhibit high specific capacitances of 817.1 and 819.9Fg−1, respectively, at a current density of 0.2Ag−1. The specific capacitances for hRuO2/C, hRuO2/CNT nanocomposites were maintained at 805.8 and 770.2Fg−1, respectively, at current density of 0.5Ag−1 with good cycle stability. The comparison in electrochemical performance between the hollow structured RuO2 and their core–shell counterparts for a capacitor manifests that the preparation of RuO2 nanoparticles with hollow interiors is favorable for the enhancement in their capacitive behavior.