Deposition Of Amorphous Carbon Research Articles

Polyethylene glycol promoted Cs/Zr-SiO2 bifunctional catalyst for aldol condensation of methyl propionate and formaldehyde to methyl methacrylate

The production of methyl methacrylate (MMA) via one-step gaseous aldol condensation of methyl propionate (MP) and formaldehyde (FA) has received wide attention. Herein, series of polyethylene glycol (PEG) promoted Cs-Zr/SiO2 catalysts were developed and characterized by XRD, FT-IR, HR-TEM, BET, NH3–/CO2-TPD and Py-IR etc. The dispersion of active acid and base sites and their balance in catalyst could be significantly improved with the addition of PEG, which facilitated the activation of reactants and conversion towards product MMA. Furthermore, the relationship between the acid-base properties and catalytic performance was revealed, the acid and base sites were responsible for the decomposition of trioxane, which was used as the source of FA, and transformation of MP, respectively. The in-situ DRIFTS experiments unraveled two catalytic pathways through the synergistic effects between the acid and base sites during the aldol condensation of MP with FA to MMA. Kinetic studies revealed that the activation energy of this aldol condensation on the optimal catalyst is 97.9 kJ/mol, with the reaction order of 0.98 and 1.18 corresponding to MP and FA. Deactivation behavior studies demonstrated that the decrease of catalytic activity as a function of time-on-stream was resulting from the deposition of predominant amorphous carbon instead of the loss of active components.

Analysis of the synergetic effect of process parameters of hydrogenated amorphous carbon deposition in plasma-enhanced chemical vapor deposition using machine learning

The synergetic effects of process parameters on hydrogenated amorphous carbon (a-C:H) films properties were quantitatively analyzed in plasma-enhanced chemical vapor deposition. Predictive models, created from experimental datasets and machine learning, indicate a synergetic effect between the H2 ratio and ion energy impacting on the substrate. At a H2 ratio of 75 %, etch rates of 200 nm/min were predicted, regardless of radio frequency (RF) bias. These rates decreased to 120–140 nm/min at lower H2 ratios, primarily depending on RF bias. Quadrupole mass spectrometry and Raman scattering were used to investigate the underlying mechanisms. High H2 ratios led to a greater presence of low-mass hydrogen-rich molecules in the plasma. The C2H3 radical intensity at a 75 % H2 ratio was 15 times greater than that at 0 % at an RF bias of 50 W, and similar trends were observed for other low-mass neutrals. The synergetic effects of H2 ratio and RF bias decreased the film's hydrogen content. Machine learning and those diagnostics revealed that ion bombardment induces dehydrogenation of a-C:H, influenced by hydrogen-rich species. This study demonstrates that machine learning can uncover complex plasma processes and optimize material synthesis.

Investigation of the removal mechanism in amorphous carbon chemical mechanical polishing for achieving an atomic-scale roughness

Amorphous carbon is replacing conventional hard masks in semiconductor fabrication due to its exceptional etching selectivity towards silicate. After amorphous carbon deposition, a chemical mechanical polishing (CMP) is essential for planarizing the surface locally and globally. This study investigated the chemical oxidation and mechanical abrasion of amorphous carbon based on several factors, including pH, polishing pressure, and oxidants. Oxidants promoted the formation of C-O, C=O, and –COOH. Mechanical abrasion accelerates carbon surface oxidation and the removal of oxidized film. In addition, slurries containing three potent oxidants were evaluated: ferric nitrate with hydrogen peroxide, potassium permanganate, and cerium ammonium nitrate (CAN). These oxidants accelerated C–C breakage and increased the removal rate. In comparison, the slurry containing 1 wt% CAN exhibited a maximum removal rate of 480 Å/min and an atomic-scale roughness of 0.056 nm.

SEM Electron-Beam-Induced Ultrathin Carbon Deposition Layer on Cu Substrate: Improved Dry Oxidation Protection Performance than CVD Single Layer Graphene.

An amorphous carbon deposition layer (CDL) with nanoscale thickness induced by scanning electron microscope (SEM) electron beam is studied as a carbon-based protective layer on copper (Cu). CDL is prepared by inducing the deposition of pollutants or hydrocarbons in the cavity of SEM through electron beam irradiation (EBI). Wrinkles and cracks will not form and the interfacial spacing of CDL/Cu is smaller than Graphene/Cu (Gr/Cu). The thickness and coverage of the interfacial oxide layer of CDL/Cu are all smaller than that of the Gr/Cu after the same oxidation conditions. Characterization of Raman mapping also demonstrates that CDL shows better oxidation inhibition effects than graphene. The structure of CDL is determined to be C = C and C = O, CH3- and C-O can be loaded vertically on CDL. Density functional theory (DFT) is employed for demonstrating the smaller interfacial gap of CDL/Cu, less wrinkles and cracks and larger adsorbing energy of water/oxygen compared with Gr/Cu. Molecular dynamic (MD) simulation also indicates that the diffusion of water or oxygen into CDL/Cu is more difficult and the oxidation of Cu covered by CDL is well suppressed. This work provides a new approach for the study of carbon-based antioxidant materials on Cu.

A promising method for promoting interfacial adhesion of aramid/rubber composite using atmospheric pressure plasma surface modification

AbstractToday, aramid fibers are well known as a high‐performance and ideal material for reinforcement purposes in rubber product manufacturing including hoses, tires, cables, and conveyors composites. However, surface modification of aramid fiber is necessary to solve poor interfacial adhesion between aramid fibers and the rubber matrix. Accordingly, in the present study, the effect of the surface modification of aramid fibers using atmospheric pressure plasma treatment with different precursors on adhesion to the rubber matrix was investigated. For that, the plasma coating was conducted using argon as the main working gas, and toluene, acetonitrile, tetraethyl orthosilicate (TEOS), and hexamethyldisiloxane (HMDSO) as liquid precursors. The physical–chemical characterization of the layer confirmed the successful deposition of amorphous carbon, amorphous nitride‐carbon, SiO2, and Polydimethylsiloxane (PDMS)‐like coating layers on the surface of aramid fibers by using toluene, acetonitrile, TEOS, and HMDSO as precursors, respectively. Overall, the result showed that the plasma surface modifications with acetonitrile precursor leads to the increase in interfacial adhesion of aramid/rubber composite, while retaining the tensile strength, and flame resistance properties of aramid as original fibers. Notably, the results of this study confirm the potential use of atmospheric pressure plasma for surface modification of aramid yarn to produce functional aramid for use in rubber composites.Highlights The plasma‐coated aramid using HMDSO, TEOS, toluene, and acetonitrile precursors was prepared; and its effect on the tensile properties of aramid fiber as well as interfacial adhesion between aramid/rubber composite was investigated. The positive effect of atmospheric pressure plasma coating using HMDSO precursor on the tensile properties of aramid fiber was revealed. The positive effect of atmospheric pressure plasma coating using toluene and acetonitrile on the interfacial adhesion between aramid/rubber composite was revealed. The positive effect of atmospheric pressure plasma coating using TEOS precursor on the flam resistance property of aramid fiber was revealed. This study provides valuable insights into the effect of the different plasma‐coated organosilicon and hydrocarbon precursors on the interfacial adhesion between aramid/rubber composite.

Analytical Py-GC/MS study on conversion behaviors and reaction mechanism of biochar-mediated catalytic upgradation of primary pyrolytic products from lignocellulosic biomass

This study aims to demonstrate the general carbocatalytic conversion behaviors and reaction mechanisms of representative biomass-derived primary pyrolytic products towards product upgradation. Specifically, 4-Ethylguaiacol (4-EGC) and 5-hydroxymethylfurfural (5-HMF) were selected as lignin- and cellulose/hemicellulose-derived model compound, respectively, to elucidate the origin of products under different temperatures and biochar-reactant mixing ratios. Three reaction routes were distinguished, including side-chain elimination, ring opening and recombination, with each route exhibiting unique characteristics in terms of initiation temperature and selectivity. For 4-EGC, elimination of side-chains began at 500 °C, accompanied by alkyl transfer reactions to generate multi-alkyl-substituted phenols, while ring-opening started at 700 °C, and aromatics could be simultaneously produced. Biochar did not change the initiation temperature of each route but significantly influenced the product distribution. Comparing the biochar-reactant mixing ratio of 0 and 10:1, at 600 °C the selectivity towards phenols increased from 20.52 % to 54.98 %, and at 800 °C the selectivity towards aromatics increased from 14.28 % to 53.01 %. For 5-HMF, the elimination of side chains already began at 400 °C, and the ring-opening started at around 600 °C, but recombination products (phenols and aromatics) would not notably emerge until 700 °C. Biochar could both lower the initiation temperature of each reaction route and change the conversion efficiency for 5-HMF owing to the lower stability of furan ring. However, the impact of biochar on selectivity towards aromatics was less pronounced compared to 4-EGC. Even at 800 °C, the relative content of aromatics only reached 28.88 % with a biochar-reactant mixing ratio of 10:1 for 5-HMF. Comparative investigations on biochar structure before and after co-pyrolysis reactions further revealed that, at 600 °C, biochar maintained its structural integrity, but at 800 °C, it underwent significant changes, including amorphous carbon deposition covering the surface. Raman spectra analysis supported these findings, showing that biochar becomes more amorphous after reactions at 600 °C, while at 800 °C, larger aromatic ring systems form on the biochar, reducing defect sites.

Ni0+ particle size-dependent pyrolytic reforming of toluene over Ni/Al2O3 for the co-production of hydrogen and CNTs

Pyrolytic reforming of toluene over Ni-based catalysts loaded on nano-sized and micro-sized γ-Al2O3 is investigated in a fixed bed reactor under the temperature from 500 °C to 800 °C. The physicochemical properties of γ-Al2O3 and Ni/Al2O3 catalysts were characterized by HRTEM, XPS, XRD and H2-pulse chemisorption. The metal Ni loaded on micro-sized γ-Al2O3 gave the steady toluene conversion of more than 80% and graphite yield of 87.3% after 1 h of reforming reaction. The rapid decrease of H2 yield from 5.2 mmol/g-toluene to 0.4 mmol/g-toluene over Ni/nano-Al2O3 was obtained during the 1 h of reforming reaction at 500 °C. The particle size of metal Ni over nano-sized and micro-sized γ-Al2O3 were centered at 7.8 nm and 28.8 nm, respectively. The metastable NiCx crystallites were observed over the spent Ni/nano-Al2O3 catalyst, while only metal Ni were obtained over the spent Ni/micro-Al2O3 catalyst. Ni0+ particle size-dependent crystalline phase was evidenced by MD simulations, where incorporation of more carbon atoms was achieved on small Ni particles. The energy barrier for –CH2 dehydrogenation over Ni32C, Ni4C and Ni3C were estimated to be 90.2, 105.1 and 116.0 kJ/mol through the DFT simulation, respectively. It can be concluded that the crystalline Ni phase was maintained over Ni/micro-Al2O3 with large Ni particle size, prolonging the catalytic endurance and promoting the CNTs (Carbon Nanotubes) growth without the deposition of unexpected amorphous carbon.

Temperature-dependent synthesis of dimethyl ether (DME) from methanol over beta zeolite: a novel approach to a sustainable fuel.

Crystalline beta zeolite molecular sieve with SiO2/Al2O3 molar ratio of 28.5 was synthesized by the hydrothermal crystallization method and examined for methanol dehydration reaction. The micro-mesoporous beta zeolite was active between 280 and 450°C. Dimethyl ether (DME) was observed as the predominant product at all reaction temperatures, with a maximum selectivity of 47.9% at 300°C and a methanol turnover frequency (TOFMeOH) of 741.9 h-1. At increased reaction temperatures, beta zeolite showed enhanced strong acid site fraction, promoting higher hydrocarbon formation following the olefin-based cycle. It was revealed that the crystallinity, porosity and acidity of beta zeolite change in the reaction environment. Amorphous carbon deposition occurred on beta zeolite, which involved a loss in crystallinity to some extent. The temperature increase showed a pore-broadening phenomenon at elevated temperature regions. Regeneration cycle testing demonstrated beta zeolite activity maintained stable throughout a 280 h time-on-stream period.

A Joule-heated carbon nanofiber aerogel-supported catalyst for hydrogen production via methanol steam reforming

Copper (Cu)-containing catalysts are preferable in the methanol steam reforming (MSR) process because of their abundant sources, low cost, and high low-temperature activities. During operation, Cu-containing catalysts are typically heated by an external heat source and are most commonly used in their macroscopic powdered form, leading to uneven temperature distributions, nonuniform mass/heat transfer, slow heating rates, and difficult replacement. These issues must therefore be addressed in the design of specific catalysts for the MSR reaction. Herein, a three-dimensional Joule-heated carbon nanofiber aerogel (CNFA)-supported catalyst (Cu/CNFA-op10) was prepared by a facile one-pot method and followed by the catalytic evaluation. It was found that the even temperature distribution, effective heat/mass/electron transfer, and uniform distribution of the Cu nanoparticles, were responsible for the excellent catalytic activities. In addition, the deactivation of the CNFA-supported catalyst was also found and caused by the aggregation and sintering of Cu0/+ nanoparticles, the deposition of amorphous carbon on the surface of active sites, and the chemical state transition of the active particles. In this proof-of-concept demonstration, the high catalytic activity of the Joule-heating-driven catalyst provides a novel strategy for further designing and fabricating 3D monolithic catalysts related to the MSR reaction.

Imaging mechanism and contrast separation in low-voltage scanning electron microscopy imaging of carbon nanotube arrays on SiO2/Si substrate

Polymer-sorted high-density carbon nanotube (CNT) arrays have shown great potential to extend the silicon-based Moore's law. Imaging the CNT arrays on insulators like SiO2/Si using low-voltage scanning electron microscopy (LVSEM) to acquire array information like the alignment, density, and distribution of residual polymers is necessary. Such a task remains challenging due to the nanoscale CNT body (1–2 nm in diameter), nanoscale tube-to-tube separation (1–10 nm), the broadening of the apparent diameter, and the complex image contrast caused by the insulating substrate and polymer residues. In this study, the imaging mechanism for this system is investigated. Two methods are developed to separate the three dominant contrasts, i.e. topographic contrast, charge contrast, and material contrast, by selecting the take-off angle and energy of the emitted electrons as enabled by changing the working distance or the deceleration voltage. The contrast formation and separation mechanism is further confirmed by the dynamic contrast evolution due to the electron-beam-induced deposition of amorphous carbon. The contrast separation method is further applied to an individual CNT, reducing its apparent diameter from 36 nm to 6 nm. This result hints at the potential for LVSEM to count the density exceeding 150 CNTs/μm of CNT arrays. Finally, a comparative study of LVSEM and transmission electron microscopy confirms the failure of LVSEM to resolve CNTs in a bundle. The results suggest that the density of CNT arrays may be underestimated in reported SEM data. The proposed method can serve as a useful tool for further study and application of arrayed CNTs.

In Situ Electrical Detection of Methane Oxidation on Atomically Thin IrO2 Nanosheet Films Down to Room Temperature

AbstractActivation of the CH bond is the first step in converting methane into valuable chemicals. Herein, the successful induction and electrical detection of a methane oxidation reaction are reported at room temperature using IrO2 nanosheets, a 2D form of IrO2. A clear decrease in electrical resistance upon exposure to methane is observed by using atomically thin IrO2 nanosheet films. The resistance decrease disappears upon simultaneous exposure to oxygen, suggesting that methane is oxidized by consuming the lattice oxygen of the IrO2 nanosheets and that the oxygen vacancies generated are recovered by oxygen in the atmosphere. The resistance decrease is observed even at 300 K, indicating the high methane oxidation ability of the IrO2 nanosheets. These results are confirmed by a shift of the Ir 4f peaks in ambient pressure X‐ray photoelectron spectra. Furthermore, deposition of amorphous carbon, that is, methane oxidation products, on IrO2 nanosheets is also confirmed by Raman scattering spectroscopy after prolonged methane exposure at high temperatures in the absence of oxygen. This study demonstrates the ability of IrO2 nanosheets to oxidize methane at least down to 300 K and is an important example of the usefulness and simplicity of chemical reaction monitoring using electrical resistance changes.

Nondestructive neutron imaging diagnosis of acidic gas reduction catalyst after 400-Hour operation in natural gas furnace

Residential natural gas furnaces are the primary space-heating devices in US homes, leading to substantial environmental impact caused by the acidic components in the furnace combustion gases. To experimentally demonstrate acidic gas reduction in a furnace, a monolithic catalyst was fabricated and was called the AGR. A commercially-available condensing furnace was retrofitted with the AGR, and a 400-hour reliability and durability test was conducted. The results showed that the AGR significantly reduced acidic gases in the flue gas and produced condensate with neutral pH. Challenges were also revealed: inappropriate condensate drainage caused incomplete combustion and amorphous carbon deposits. To nondestructively survey the internal state of the AGR, neutron computed tomography (NCT) was employed to produce spatially resolved 2D and 3D representations of the 2-L, aged AGR component. The NCT results confirm the integrity of the AGR component, which consists of two blocks, without deformation or damage to AGR channels. The distribution of the particle accumulation in the middle of the top block was visibly heavier than the entrance and exit of the top block. The representative cross-section views revealed significant aggregation in the central region but not at the rim. The spatially resolved details provide in-depth diagnosis, evaluation, and understanding of the AGR. The insights can enable new AGR designs that realize a uniform and self-cleaning flow pattern, alleviate significant particle aggregation, and thus enhance AGR-enabled furnace performance. The neutron imaging method demonstrates the good potential that can diagnose faults and improve the design, optimization, and production processes of novel catalysts and other components or systems with heavy metal shell.

Amorphous Carbon Coatings on Glass for High Voltage Protection

Radio frequency Hollow Cathode based hybrid process integrating both Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition was used for deposition of amorphous carbon on glass samples. The films were subjected to high voltage pulses and the performance was compared with uncoated glass samples to test the protection ability of the films, the ability to prevent the deteriorating effects of corona flashovers/arcs. In contrast to the uncoated glass the well adherent carbon films with thicknesses between 3.5 and 17 μm exhibited an excellent protection of the glass substrate against the flashovers/arc damages in both polarities of the electric field with voltages up to 300 kV.

Carbon Nanotube/Polymer Coaxial Cables with Strong Interface for Damping Composites and Stretchable Conductors

AbstractCarbon nanotube (CNT) fibers have the potential to serve as continuous nano‐fillers for structural and functional composite materials, yet there exists the interfacial problem that has hindered the development of continuous fiber reinforced composites for a long time. Here, a method to overcome this challenge by coating a thick CNT sponge around a single‐walled nanotube (SWNT) fiber is presented, and then infiltrating polymers into the sponge to construct a SWNT@polymer coaxial cable. It has been found that the residual stress‐induced deposition of amorphous carbon as an intermediate layer between the underlying SWNT fiber and the subsequently coated multi‐walled nanotube (MWNT) sponge plays a key role in interfacial properties, and together with well‐dispersed CNT in the polymer matrix, a superior interfacial shear strength (>12 MPa), enhanced tensile strength and toughness is achieved. These coaxial cables demonstrate high mechanical damping ability and can serve as stretchable conductors maintaining high electrical conductivity during large‐strain cyclic deformation. These results indicate a promising route toward developing continuous CNT fiber‐based composites with wide applications as structural and multi‐functional composite materials.

Growth of Single-Walled Carbon Nanotubes from Solid Carbon Nanoparticle Seeds via Cap Formation Engineering with a Two-Step Growth Process and Water Vapor Supply.

Solid carbon nanoparticles are promising growth seeds to prepare single-walled carbon nanotubes (SWCNTs) at high temperatures, at which the SWCNT crystallinity should be improved significantly but conventional metal catalyst nanoparticles are unstable and suffer from aggregation. The noncatalytic nature of solid carbon nanoparticles, however, makes SWCNT growth inefficient, resulting in a limited growth yield. In this study, we develop a two-step chemical vapor deposition process to efficiently synthesize high-crystallinity SWCNTs at high temperatures from solid carbon nanoparticles obtained from nanodiamond. Based on thermodynamic considerations, the growth conditions are separately adjusted to supply different growth driving forces which are suitable for the formation of the initial cap structures and for the stationary elongation of SWCNTs. This process, called cap formation engineering, improves the nucleation density of the cap structures. We examined the changes in crystallinity, amorphous carbon deposition, diameter, and yield of SWCNTs with respect to the synthesis conditions. By controlling the initial growth conditions, high-quality SWCNTs are grown with improved yield. With the addition of water vapor as the etchant, deposition of amorphous carbon at high temperatures was further prevented. The results provide a pathway for precise growth control of SWCNTs from unconventional solid growth seeds.

Degradation Comparison of Cyclic and Linear Siloxane Contamination on Solid Oxide Fuel Cells Ni-YSZ Anode

The solid oxide fuel cell (SOFC) nickel-yttria stabilized zirconia (Ni-YSZ) anode degradation due to different types of siloxane contamination is investigated. A cyclic structure siloxane, octamethylcyclotetrasiloxane (D4), and a linear structure siloxane, decamethyltetrasiloxane (L4), are mixed with H2+N2 as the fuel for SOFCs at 750°C. The electrochemical characterization results after stability experiments suggest that the SOFC contaminated with cyclic siloxane, D4, had higher degradation. Pure YSZ pellets with different surface hydroxylation extents were also tested to investigate the D4/L4 adsorption and deposition process. Postmortem SEM/WDS, XRD and Raman analysis all indicate that cyclic siloxane has more deposition than linear siloxane on the anode. Further analysis demonstrates that high adsorption and low desorption rates of cyclic siloxane on YSZ are linked to the degradation. Besides the silicon deposition, SiC and amorphous carbon deposition were also observed from the XRD and Raman analysis.

Investigation of MoOx/Al2O3 under Cyclic Operation for Oxidative and Non-Oxidative Dehydrogenation of Propane

A MoOx/Al2O3 catalyst was synthesised and tested for oxidative (ODP) and non-oxidative (DP) dehydrogenation of propane in a reaction cycle of ODP followed by DP and a second ODP run. Characterisation results show that the fresh catalyst contains highly dispersed Mo oxide species in the +6 oxidation state with tetrahedral coordination as [MoVIO4]2− moieties. In situ X-ray Absorption Spectroscopy (XAS) shows that [MoVIO4]2− is present during the first ODP run of the reaction cycle and is reduced to MoIVO2 in the following DP run. The reduced species are partly re-oxidised in the subsequent second ODP run of the reaction cycle. The partly re-oxidised species exhibit oxidation and coordination states that are lower than 6 but higher than 4 and are referred to as MoxOy. These species significantly improved propene formation (relatively 27% higher) in the second ODP run at similar propane conversion activity. Accordingly, the initial tetrahedral [MoVIO4]2− present during the first ODP run of the reaction cycle is active for propane conversion; however, it is unselective for propene. The reduced MoIVO2 species are relatively less active and selective for DP. It is suggested that the MoxOy species generated by the reaction cycle are active and selective for ODP. The vibrational spectroscopic data indicate that the retained surface species are amorphous carbon deposits with a higher proportion of aromatic/olefinic like species.

Tailoring Rh content on dendritic fibrous silica alumina catalyst for enhanced CO2 capture in catalytic CO2 methanation

Dendritic fibrous X%Rh/FSA catalysts were synthesized by the microwave-assisted microemulsion and wetness impregnation approaches. Catalytic CO2 methanation was performed at temperature ranging of 150‒500 °C and atmospheric pressure with stoichiometric feed composition. FESEM and TEM micrographs confirmed the spherical bicontinuous concentric lamellar morphology of FSA offering high accessibility of capturing CO2 to the active sites, thus promotion of heterogenous catalysis activity. H2-TPR and pyrrole adsorbed IR spectroscopy results reveals that the metal-support interaction and degree of basicity strength were enormously enhanced with the increasing Rh content. The 1%Rh appeared to be the optimal loading with respect to the CO2 conversion and CH4 formation rate as a function of temperature, accredited to its medium basicity strength and fibrous morphology. The in situ FTIR analyses showed that medium basic sites promoted the desired carbonate species that readily participate into hydrogenation compared to strong basic sites. In addition, CH4/CO2 ratio indicates that the rate of CO hydrogenation was superior to that of RWGS over Rh/FSA catalysts. The absence of graphitic carbon for all spent Rh/FSA catalysts in post-characterization analyses suggests that their excellent catalytic performance could be assigned to the preservation of most active sites owing to enhanced CO2 adsorption on catalyst surface which effectively remove amorphous carbon deposits via CO2 gasification process.

Synthesis of smooth low friction graphitic nanoparticle film by vacuum arc deposition

Formation of smooth low friction carbon onion nanoparticle film was carried out using vacuum arc deposition. Carbon onions were synthesized by the arc discharge of carbon rod as a cathode and deposited directly onto the substrate in a vacuum. The process of carbon onion synthesis and nanoparticle film growth was investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), and quadrupole mass spectrometer (QMS). It was observed that isolated carbon onions were successfully synthesized by pulsed arc discharge of the carbon rod as a cathode under relatively low pressure of 10−7 Pa. The synthesized isolated carbon onions around the cathode were in flight in vacuum and deposited onto the substrate. A smooth carbon onion nanoparticle film with surface roughness (Ra) of 0.37 nm was gradually formed on a graphite substrate by 100 pulse shots of the arc discharge. A smooth nanoparticle film was achieved due to the mixture of the deposition of carbon onions and amorphous carbon in this process, where amorphous carbons were filled between carbon onions interparticle. AFM friction measurements in the vacuum revealed that the synthesized nanoparticle film possessed lower friction coefficient than graphite, which was attributed to the low adhesive force and smooth surface roughness of the carbon onion nanoparticle film.

Promoting effects of Fe-Ni alloy on co-production of H2 and carbon nanotubes during steam reforming of biomass tar over Ni-Fe/α-Al2O3

Fe-modified Ni/Al2O3 catalysts with Fe/Ni molar ratios of 0, 0.5, 1 and 2 were prepared to promote the co-production of H2 and carbon nanotubes (CNTs) during steam reforming of toluene as a tar model compound. After the addition of Fe, toluene conversion increased from 55.1% of Ni/Al2O3 to 73.6% of F1N1A (Fe/Ni ratio of 1), and H2 yield over F1N1A reached the maximum of more than 2000 mmol/(g-cata). Multi-walled carbon nanotubes with average diameter of 10–30 nm were generated and follow tip-growth mechanism. Compared with Ni/Al2O3, the addition of Fe remarkably increased the amount and quality of CNTs which had longer length and less tortuosity. These dual promoting effects on H2 and CNTs after the addition of Fe were attributed to the strong interaction between Ni and Fe in Fe-Ni alloy. Fe-Ni alloy had the high activity for the decomposition performance of toluene and H2O to generate more H2 and intermediates for improving the reforming reaction. Meanwhile, the high catalytic decomposition activity supplied more carbon species and the formation of Fe-Ni alloy enhanced the generation of metal carbide for promoting CNTs growth. Besides, the deposition of amorphous carbon was suppressed and the interaction between Ni particle and catalyst support was weakened after the addition of Fe, which kept the activity of catalyst and promoted the tip-growth of CNTs.