Carbon Nanotube Support Research Articles

A novel and active ruthenium based supported multiwalled carbon nanotube tungsten nanoalloy catalyst for sodium borohydride hydrolysis

At present, a novel and active catalyst, RuW/MWCNT catalyst, was successfully synthesized to complete the hydrolysis reaction of sodium borohydride (NaBH4). The activity of Ru catalyst was increased by adding tungsten (W) to ruthenium (Ru) on multi-walled carbon nanotube (MWCNT) support. Surface characterization of the catalyst was performed with scanning electron microscope (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmissing electron microscope (TEM) analysis methods. SEM-EDX revealed that RuW (95:5) catalyst metal ratio was obtained at desired nominal ratio. XRD characterization revealed that W addittion to the Ru structure increased its activity by forming an alloy. W addition Ru altered the electronic structure of the Ru. Parameters affecting the hydrolysis performance of RuW/MWCNT catalyst such as temperature, amount of catalyst, NaBH4 concentration and sodium hydroxide (NaOH) concentration were investigated. Adding NaOH to the reaction vessel reduced the activity of the RuW/MWCNT catalyst. From the hydrolysis measurements, the activation energy of RuW(95–5)/MWCNT catalyst was found to be 16.327 kjmol−1, the reaction order as 0.61 and the initial rate as 95,841,4 mL H2gcatmin−1. The stability of the RuW/MWCNT catalyst was tested using 5 times and it was observed that this novel RuW/MWCNT catalyst could complete the hydrolysis reaction despite repeated use.

Understanding the importance of N−doping for CNT-supported Ni catalysts for CO2 methanation

The N−doping of carbon nanotubes (CNTs) is widely accepted as an effective way to enhance the catalytic performance of CNT-supported Ni catalysts for CO2 methanation. To demonstrate, in a direct systematic comparison, the importance of N−doping for producing high-performance CO2 methanation catalysts, we developed two catalysts composed of 15 wt% Ni on pristine (Ni/CNT) and N−doped CNT (Ni/CNT−N) and correlated their catalytic performance with their properties. Compared to Ni/CNT, Ni/CNT−N achieved a higher XCO2 of 81.2% with SCH4 = 99.2% at a lower temperature of 400 °C, exhibiting excellent stability over 48 h time-on-stream testing. Our comprehensive comparative study demonstrated that the N−doped CNT support featured a better distribution of the Ni sites that were strongly interacting with the support, even with atomically dispersed Ni being observed by HAADF-STEM. This higher dispersion, enabled by the anchoring sites provided by the N−doping, is one of the main reasons for the enhanced performance of Ni/CNT−N, because it increases the H2 uptake capacity.

Chemically Modified Chitosan Supports for Phosphine-free Pd-catalyzed Crosscoupling Reaction of Arylboronic Acids with Acid Chlorides

Backgroung:Phosphine-free Pd-catalytic platforms, i) combination with chitosan- Schiff base (CS-Py/Pd), ii) immobilized on chitosan-Schiff base (CS-Py@Pd), and iii) anchored to modified carbon nanotube support (CNT@CS-Py@Pd),Methods:They were evaluated regarding a novel pathway for the cross-coupling reaction of arylboronic acids with acid chlorides.Results:The CS-Py@Pd platform had the highest catalytic efficiency of the three platforms, yielding moderate to excellent yields of diaryl ketones.Conclusion:The catalytic activity of the Pd-catalyst was highly dependent upon the manufacturing process and type of support.

Enhancing the Methanol Oxidation Reaction of Precious Metal Catalysts on Carbon Nanotube Support with a Thin Hydrogenated TiO2 Shell

Direct Methanol Fuel Cells (DMFCs) has drawn widespread research interests due to the low cost, higher energy density (6.08 kWh/kg) and ease in handling of methanol. In DMFCs, methanol is oxidized to CO2 at the anode and oxygen is reduced to water at the cathode to produce electricity. Platinum (Pt) is the state-of-the-art electro catalyst for methanol oxidation reaction (MOR). However, the high cost of Pt, sluggish MOR kinetics and CO poisoning on Pt surface impedes the commercialization of DMFCs. In addition, the methanol crossover from the anode side through polymer electrolyte membrane to the cathode side prevents the high concentration or pure methanol from being used. This causes the deliverable power density substantially lower than the theoretical value. Therefore, proper design of MEA and development of more efficient anode catalysts are necessary to achieve higher power density in DMFCs using high-concentration methanol fuels. General strategies adopted to overcome the issues of CO poisoning is to alloy oxophilic metals such as Ru, Sn and Rh with Pt or incorporate metal oxides such as TiO2, CeO2, MnO2, etc. as catalyst supports. These components provide abundant -OH species to efficiently oxidize CO to CO2 and improve the MOR kinetics. However, these strategies have been explored and are proven to work well in half-cell studies and their application in a full DMFC cell is lacking.Here in, we demonstrate a promising MOR catalyst based on a novel anode architecture with dual roles as the catalyst support and the microporous layer (MPL) in enhancing the MOR kinetics. A conformal thin layer of TiO2 shell has been successfully deposited on the oxygen functionalized nitrogen-doped carbon nanotube (O-NCNT) support to facilitate the formation of stable PtRu nanoparticles. Our synthesis approach involves the utilization of microwave heating and post-synthesis thermal annealing in H2 environment to form alloyed PtRu nanoparticles, denoted as PtRu/TiO2/ONCNTs. The synthesized catalyst shows improved MOR kinetics, enhanced CO oxidation and excellent stability compared to commercial PtRu/C anode catalyst in half-cell studies. The thin layer of hydrogenated TiO2 provide improved stability due to strong metal-support interaction, which reduces the nanoparticle agglomeration during high temperature annealing and further increases the oxophilicity of the catalyst, leading to enhanced CO oxidation. Alongside, this catalyst is used as an anode in a DMFC prototype single cell (5 cm2 active area MEA) to study the parameters that influence the peak power density of the catalyst. Our preliminary full cell results show that the catalysts synthesized using the NCNT support has very different mass transport comparing to the commercial PtRu/C anode. This new anode architecture requires different optimization in DMFCs before realizing the highly catalytic activities at high-concentration methanol to achieve high power densities.

High oxygen reduction reaction activity and durability of Pt catalyst photo-deposited on SnO2-coated and uncoated multi-walled carbon nanotubes

• Acid-treated CNTs were coated with SnO 2 by chemical method. • Platinum was photo-deposited on CNTs and SnO 2 -CNT supports. • Surface morphology was investigated by SEM and HAADF-STEM. • Pt/CNT and Pt/SnO 2 -CNT showed high oxygen reduction activity in acid media. Platinum nanoparticles were photo-deposited on acid-treated multi-walled carbon nanotubes (CNTs) and SnO 2 -coated CNTs. The SnO 2 -CNT nanocomposite was synthesised by a chemical method. Scanning and scanning transmission electron microscopy results indicated that the CNTs surface is partially covered by the SnO 2 layer. The surface morphology of the Pt catalyst depends on the nature of the support material. For instance, porous Pt aggregates of various sizes are formed at specific nucleation sites on the CNT surface, while a selective deposition of Pt was observed on the metal oxide part of the SnO 2 -CNT. Cyclic voltammetry and CO stripping investigations in 0.1 M HClO 4 solution confirmed different surface electrochemistry of the Pt catalysts. It is revealed that photo-deposition induces the formation of Pt-Sn nanoalloys due to increased interaction at the oxide interfaces. Both Pt/CNT and Pt/SnO 2 -CNT catalysts showed remarkable activity towards the electroreduction of oxygen in acid media. Durability measurement showed that photo-deposited Pt nanoparticles are more resistant to degradation. The corrosion-resistant nature of the SnO 2 -CNT support further improves the catalysts stability. Pt/CNT and Pt/SnO 2 -CNT catalysts retained 86% and 88% of the initial surface area respectively, after 10,000 potential cycles between 0.6 and 1.2 V RHE .

Electrocatalytic activity of bimetallic PtPd on cerium oxide-modified carbon nanotube for oxidation of alcohol and formic acid

• Bimetallic PtPd nanoparticles on CeO 2 modified CNT were prepared by reduction . • Effective catalysts provide better electrocatalytic performance towards oxidations. • High current density and durability compared to commercial Pt/C were found. This paper proposes an approach for the fabrication of an anode electrocatalyst for application as a fuel cell catalyst. It comprises three components, multiwall carbon nanotube (CNT), ceria oxide (CeO 2 ), and metal (i.e., Pt and/or Pd), using the reduction method for preparation. The characterization of the prepared catalysts was determined by transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy. The electrocatalytic performance of the prepared catalysts was examined by electrochemical measurements, e.g., cyclic voltammetry, chronoamperometry and CO stripping voltammetry. Among the catalysts, the obtained 1Pt1Pd − CeO 2 /CNT electrocatalyst provides a high electrochemical surface area, as well as high oxidation activity and durability for the oxidation of methanol, ethanol, and formic acid. The enhancement of the catalytic activity is attributed to changes in the surface electronic structures of Pt, Pd, and CeO 2 on the CNT surface that incrementally effect the active sites for oxidation. A required catalytic performance for these oxidations were observed with small-size and high-dispersion of the metal i.e.1Pt1Pd (3.34 nm) on the CeO 2 /CNT support nanocomposite. The results also show substantial improvement in the kinetics for oxidations and mass transfer efficiency owing to the catalyst structure. Therefore, the prepared catalysts have promising potential for application in low-temperature fuel cells.

Effect of Temperature, Syngas Space Velocity and Catalyst Stability of Co-Mn/CNT Bimetallic Catalyst on Fischer Tropsch Synthesis Performance

The effect of reaction temperature, syngas space velocity, and catalyst stability on Fischer-Tropsch reaction was investigated using a fixed-bed microreactor. Cobalt and Manganese bimetallic catalysts on carbon nanotubes (CNT) support (Co-Mn/CNT) were synthesized via the strong electrostatic adsorption (SEA) method. For testing the performance of the catalyst, Co-Mn/CNT catalysts with four different manganese percentages (0, 5, 10, 15, and 20%) were synthesized. Synthesized catalysts were then analyzed by TEM, FESEM, atomic absorption spectrometry (AAS), and zeta potential sizer. In this study, the temperature was varied from 200 to 280 °C and syngas space velocity was varied from 0.5 to 4.5 L/g.h. Results showed an increasing reaction temperature from 200 °C to 280 °C with reaction pressure of 20 atm, the Space velocity of 2.5 L/h.g and H2/CO ratio of 2, lead to the rise of CO % conversion from 59.5% to 88.2% and an increase for C5+ selectivity from 83.2% to 85.8%. When compared to the other catalyst formulation, the catalyst sample with 95% cobalt and 5% manganese on CNT support (95Co5Mn/CNT) performed more stable for 48 h on stream.

Ruthenium nanoparticles supported on carbon oxide nanotubes for electrocatalytic hydrogen evolution in alkaline media

“Cracking” water is of great significance to develop (HER) catalysts with high catalytic performance for non-platinum hydrogen evolution under alkaline conditions. In this paper, we prepared a ruthenium nanoparticle catalyst on oxidized carbon nanotubes (Ru@OCNT) support. Electrochemical tests showed that Ru@OCNT-700 exhibited excellent catalytic performance and good stability under alkaline conditions (1 M KOH). When the current density reached 10 mA cm−2, it only needed an overpotential of 13.2 mV. The Tafel slope was 45.4 mV/dec−1. Due to its excellent HER performance, Ru@OCNT electrocatalyst could have broad applicability in large-scale hydrogen production.

Catalytic Property and Stability of Subnanometer Pt Cluster on Carbon Nanotube in Direct Propane Dehydrogenation

Main observation and conclusionThe stability of nanosized platinum catalyst in direct propane dehydrogenation reaction is one of most critical challenges, which hinders the further improvements of catalytic performance. The cokes from side reaction covering the active site seriously undermine the catalyst stability. In this work, first principles calculations are performed to explore the catalytic properties of supported subnanometer platinum cluster on carbon nanotube support and focus is put on the inhibition of deep dehydrogenation. The reactivities of metal, interface, and tin promoter are investigated at the same footing. The whole reaction pathway from propane adsorption to propene desorption is revealed for different sites. It turns out that the C—H bond activation in propane is not the catalytic step with the largest barrier. Instead, the desorption of propene is more difficult. The comparison between different sites indicates that the interface between metal and support and Sn promoter is helpful to curb the propene deep dehydrogenation. Moreover, a descriptor is proposed to screen the potential effective propane direct dehydrogenation catalyst. The current work provides important insights on the development of new dehydrogenation catalyst.

Electrochemical glucose biosensor based on an osmium redox polymer and glucose oxidase grafted to carbon nanotubes: A design-of-experiments optimisation of current density and stability

Enzymatic glucose electrodes based on mediated electron transfer have potential for application as semi-implantable or implantable sensors. Enzyme electrodes consisting of adsorbed osmium-based redox polymer crosslinked with a glucose oxidising enzyme are promising systems for continuous glucose monitoring, but suffer from signal output magnitude and long-term stability issues. The inclusion of carbon nanosupports such as multiwalled carbon nanotubes (MWCNTs) into these sensors tends to increase characteristics such as current density and surface coverage of enzyme or mediator. However, large quantities of nanomaterials are often necessary to see significant effects. Grafting of the enzyme to the surface of the MWCNTs improves dispersibility of the nanosupport aiding enzyme electrode fabrication, and increases enzyme activity. Here we report on a design of experiments (DoE) approach to determine the optimum amount of each component in enzyme electrodes, using glucose oxidase grafted to carbon nanotube support, to maximise current density and stability for application to continuous use glucose biosensing. Using the DoE approach while considering current density and stability responses delivers a set of component amounts where both responses are optimised. Thus far stability has not been investigated as a response to be optimised using a DoE approach. The optimised enzyme electrodes show a current density of 3.18 ± 0.30 mA cm−2, representing a 146% increase in current density in 50 mM phosphate-buffered saline at 37 °C containing 5 mM glucose when compared to similar systems where enzyme and nanosupport are not grafted to each other. Using the predictive DoE model, component amounts were then modified to minimise the quantity of the nanoconjugate while showing similar electrochemical behaviour and current density to the optimised system, using 93% less of the nanoconjugate. However, the operational stability under continuous use was moderate with only ≈ 50% amperometric current retained after 12 hr use. Overcoating with a Nafion protective layer improved stability to 72–75% over the same period. The coupling of adsorbed films to the electrode surface, use of additional perm-selective membranes, and/or use of pulsed potentials to implement intermittent sampling of glucose levels, rather than continuous amperometry, is proposed to improve operational stability.

High lithium storage performance of CoO with a distinctive dual-carbon-confined nanoarchitecture.

Herein, a distinctive dual-carbon-confined nanoarchitecture, composed of an inner highly conductive, robust carbon nanotube (CNT) support and outer well-designed porous carbon (PC) coating, was demonstrated to efficiently improve the electrochemical properties of CoO nanoparticles for the first time, and the CoO nanoparticles were confined between the CNTs and porous carbon. The well-designed porous carbon coating showed significant superiority compared to common non-porous carbon coatings, due to its distinctive characteristics such as high flexibility, rich free space and open tunnel-like structure. Therefore, the synergistic effects of the CNT core and the porous carbon sheath endowed the CoO-based composite (CNTs@CoO@PC) with improved electrochemical reaction kinetics, large pseudocapacitive contribution and superior structural stability. As a result, the CNTs@CoO@PC showed outstanding performance with 1090, 571 and 242 mA h g-1 at 200, 1000 and 5000 mA g-1 after 300, 600 and 1000 cycles, respectively. Furthermore, this strategy may be used to improve other metal oxide anode materials for lithium storage.

Effect of CNTs Support in CL of PEMFC on the Structure of Ionomer Ultra-Thin Film

Proton Exchange Membrane Fuel Cell (PEMFC) is an energy converter with high power density, no carbon emissions, and features of quick start-up. It has extremely broad application prospects. However, despite these advantages, there are still several obstacles that hinder the performance improvement of PEMFC. Among them, the ionomer film in the catalyst layer (CL) and the catalyst constitute a multi-phase nano-scale structural morphology, which is essential for the transportation of protons and water, and the improvement of the utilization rate of the catalyst. In order to improve the material transport capacity of the above-mentioned parts, the water transport performance can be optimized by improving the structure of carbon support.A classic molecular dynamics simulation was conducted to established a model of platinum particles on carbon nanotubes (CNTs),which explore the effect of the carbon surface on the molecular level structure of the ionomer film, and the corresponding structure−property relationships. the following simulations is mainly conducted: 1) the influence of CNTs on the self-assembly process of ionomer on its surface, 2) the effect of ionomer ratio on film morphology, 3) structural composition around CNTs with different water contents，4) the influence of the presence of nano-platinum particles on the structure of the ionomer film around the CNTs. At the same time, the above model was used to compare the morphology of the water area inside the nano-thick ionomer film formed under different conditions，the formation process of the water area around the CNTs, and the proton transport capacity of the corresponding structure. These results provide a molecular basis for the study of the morphology of the nanostructures inside the CL, and give the way in which the CNTs affect the ionomer film structure and water transport capacity. Figure 1

CO2 reforming of methane to syngas over multi-walled carbon nanotube supported Ni-Ce nanoparticles: effect of different synthesis methods.

Several multi-walled carbon nanotubes supported Ni-Ce catalysts were synthesized, and their performance in carbon dioxide reforming of methane (CDRM) for syngas production was evaluated. The attachment of Ni-Ce nanoparticles to the functionalized carbon nanotube (fCNT) support was carried out using four synthesis routes, i.e., impregnation (I), sol-gel (S), co-precipitation (C), and hydrothermal (H) methods. Results indicated that synthesis method influences the properties of the NiCe/fCNT catalysts in terms of homogeneity of metal dispersion, size of crystallites, and metal-support interaction. The activity of the catalysts followed the order of NiCe/fCNT(H) > NiCe/fCNT(S) > NiCe/fCNT(C) > NiCe/fCNT(I). The NiCe/fCNT(H) catalyst exhibited the highest catalytic activity with CH4 and CO2 conversions of 92 and 96%, respectively, and resulted in syngas product with consistent H2/CO ratio of 0.91 at reaction temperature of 800 °C without notable deactivation up to 30 h of reaction. Moreover, the growth of carbon on the spent catalyst was only 2% with deposition rate of 4.08 mg/gcat·h; this was plausibly due to the well-dispersed distribution of nanoparticles on fCNT surface and abundant presence of oxygenated groups on the catalyst surface.

Microfluidic Behavior of Alumina Nanotube-Based Pathways within Hydrophobic CNT Barriers.

The use of porous micro-and nanostructured materials within microfluidic devices results in unique fluid transport characteristics. In this paper, we investigate the microfluidic behavior of hybrid alumina nanotube-based pathways within the hydrophobic carbon nanotube (CNT) barriers. These hybrid systems provide unique benefits for potential liquid transport control in porous structures with real-time sensing of fluids. In particular, we examine how the alignment of the alumina nanostructures with high internal porosity enables increased capillary action and sensitivity of detection. Based on the Lucas and Washburn model (LW) and the modified LW models, the microfluidic behavior of these systems is detailed. The time exponent prediction from the models for capillary transport in porous media is determined to be ≤0.5. The experimental results demonstrate that the average capillary rise in the nanostructured media driven by a capillary force follows t0.7. The hydrophilic/electrically insulating and hydrophobic/electrically conductive patterned structures of the device are used for electronic measurements within the microfluidic channels. The device structure enables the detection of fluid samples of very low analyte concentrations (1 μM) that can be achieved due to the very high surface area of the hybrid structure combined with the electrical conductivity of the CNT support structure.

Thermal transport characteristics of supported carbon nanotube: Molecular dynamics simulation and theoretical analysis

With the rapid development of carbon nanotube (CNT)-based devices, thermal transport characteristics of CNT supported on substrate is to be urgently explored. Herein, we systematically study the thermal transport properties of supported single-wall CNT including length, temperature and substrate coupling strength dependence of thermal conductivity using molecular dynamics (MD) simulation. Interestingly, a theoretical model is proposed to describe the length dependent thermal conductivity of supported SWCNT, which matches well with our MD results. Moreover, the phenomenon of non-monotonic change of thermal conductivity with the variation of coupling coefficient is first discovered in supported CNT. The underlying mechanism is revealed by spectral energy density (SED), phonon transport and stress distribution analysis. Our study provides valuable insights towards the thermal dissipation performance of CNT-based electronic and photonic devices.

Three-dimensional electrochemical sensor with covalent organic framework decorated carbon nanotubes signal amplification for the detection of furazolidone

In this study, we developed a facile one-pot strategy for immobilizing a covalent organic framework (COF) on an amino-functionalized carbon nanotube (NH2-CNT) support at room temperature. The COF@NH2-CNT composite obtained possessed a high specific surface area (147.3 m2 g−1), and good conductivity when deposited on the glassy carbon electrode (GCE). The COF@NH2-CNT/GCE sensor offered excellent analytical performance for the detection of the nitrofuran antibacterial agent furazolidone. The sensor offered a wide range furazolidone detection range from 0.2 μM to 100 μM, with a low limit of detection of 7.75 × 10-8 M. The recovery test was performed in chicken and lamb samples with satisfactory recoveries ranged from 87.8%–126.9%. The furazolidone residues in beef and pork samples were determined using the COF@NH2-CNT/GCE sensor and high-performance liquid chromatography. There was no significant difference between the two methods. The ability of the COF to efficiently adsorb furazolidone was a key to high sensitivity and fast response of the sensor platform. Results encourage the wider use of COFs in electrochemical sensor development.

Cover Feature: Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading (ChemNanoMat 7/2020)

The cover feature shows the controllable synthesis of nickel single atoms embedded in nitrogen-doped carbon nanotubes (NiSA−N-CNT) and graphene (NiSA−N-G). Addition of citric acid introduces amorphous carbon on the layered g-C3N4-Ni and, after annealing under the same conditions, NiSA−N-G was obtained instead of NiSA−N-CNT. NiSA−N-G with Ni atomic loading of ∼6 wt% catalysts shows better activity and stability for the CO2 reduction reaction than NiSA−N-CNT with Ni loading of ∼15 wt% due to the more open and exposed active sites in NiSA−N-G. The exposed active sites are most important for the electrocatalytic activity of single atom catalysts. More information can be found in the Full Paper by Chang Liu, Qianfan Zhang, San Ping Jiang et al.

Carbon nanotube-supported polyamide membrane with minimized internal concentration polarization for both aqueous and organic solvent forward osmosis process

We proposed a novel strategy for fabricating a high-performance forward osmosis (FO) membrane by forming a polyamide (PA) selective layer via interfacial polymerization on top of an interconnected porous carbon nanotube (CNT) network support. The fabricated CNT-PA membrane had a highly permeable and selective PA layer for fast water and solvents passage with efficient salt and solutes rejection, and an ultrathin CNT support that significantly reduced the internal concentration polarization in the FO process. Tested in the FO (e.g., active layer facing feed solution) mode using DI water as feed solution and 1.0 M NaCl as draw solution, the optimal CNT-PA membrane exhibited a water flux of as high as 139 L m−2 h−1(LMH)with comparable salt rejection, 686% higher than that of commercial FO membrane, outperforming the previously reported best FO membranes tested under similar conditions. Besides, the CNT-PA membrane also showed great capability to recover organic solvents such as ethanol (EtOH), dimethylsulfoxide (DMSO), dimethylformamide (DMF) and dimethylacetamide (DMAc) when used in the organic solvent forward osmosis (OSFO) process and to concentrate chemicals in organic solvents. Results present that the CNT-PA membrane exhibited a DMAc flux of around 20 LMH with near 100% rhodamine B dye rejection and a negligible reverse solute flux when using 2.0 M PEG400 as a draw solution. The contributions of the CNT support layer and the PA selective layer to the osmotic filtration performance of the CNT-PA membrane were investigated and discussed to provide insights on the FO membrane design and fabrication for the efficient separation in aqueous and organic solvent system.

Effect of Pressure, H2/CO Ratio and Reduction Conditions on Co–Mn/CNT Bimetallic Catalyst Performance in Fischer–Tropsch Reaction

The effects of process conditions on Fischer–Tropsch Synthesis (FTS) product distributions were studied using a fixed-bed microreactor and a Co–Mn/CNT catalyst. Cobalt and Manganese, supported on Carbon Nanotubes (CNT) catalyst were prepared by a Strong Electrostatic Adsorption (SEA) method. CNT supports were initially acid and thermally treated in order to functionalize support to uptake more Co clusters. Catalyst samples were characterized by Transmitted Electron Microscope (TEM), particle size analyzer, and Thermal Gravimetric Analysis (TGA). TEM images showed catalyst metal particle intake on CNT support with different Co and Mn loading percentage. Performance test of Co–Mn/CNT in Fischer–Tropsch synthesis (FTS) was carried out in a fixed-bed micro-reactor at different pressures (from 1 atm to 25 atm), H2/CO ratio (0.5–2.5), and reduction temperature and duration. The reactor was connected to the online Gas Chromatograph (GC) for product analysis. It was found that the reaction conditions have the dominant effect on product selectivity. Cobalt catalyst supported on acid and thermal pre-treated CNT at optimum reaction condition resulted in CO conversion of 58.7% and C5+ selectivity of 59.1%.

Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading

AbstractSingle‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C3N4, g‐C3N4−Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C3N4−Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C3N4‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO2 reduction reaction (CO2RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs.