Chemical Vapor Deposition Of Ethylene Research Articles

Selective hydrodesulfurization of FCC naphtha over carbon coated alumina supported CoMoS catalysts

Herein, carbon coated alumina (C@Al2O3) samples obtained by chemical vapor deposition of ethylene have been proposed as supports for CoMoS hydrodesulfurization (HDS) catalysts of full-range FCC naphtha. Various degree of support graphitization (from 30 to 74%) was achieved by changing the treatment time of alumina in ethylene from 15 to 120 min. The influence of the alumina graphitization on the state and morphology of the sulfide component and catalytic performance of CoMoS catalysts has been studied in detail. The dispersion of sulfide particles and the CoMoS phase content is found to increase with the growth of the graphitization degree. This is accompanied by an increase in the selectivity of the CoMoS/C@Al2O3 catalysts in the HDS of FCC naphtha, whereas the reverse trend is observed for the activity. Thus, by changing the support graphitization degree, the selectivity of CoMoS catalysts in FCC naphtha HDS can be tuned. An increase in the support graphitization degree to 74% made it possible to reduce the sulfur content in FCC naphtha from 238 to 10 ppm, with a total loss in octane number of less than 1.5 units, which demonstrates the great potential of CoMoS/C@Al2O3 catalysts for commercial application in selective HDS of FCC naphtha.

Graphitization of alumina as a way to stabilize its textural characteristics under hydrothermal conditions

Gamma alumina is a widely used support for catalysts of various processes. However, in the case of aqueous-phase processes, hydrothermal conditions result in transformation of γ-Al 2 O 3 to boehmite, which is accompanied by degradation of the porous structure and leads to rapid catalyst deactivation. Here, we demonstrate a simple approach to stabilize the textural characteristics of γ-Al 2 O 3 under hydrothermal conditions, based on preliminary graphitization of its surface by chemical vapor deposition of ethylene. Different duration (5–240 min) revealed the optimal degree of alumina surface coverage with carbon, ensuring the preservation of its textural characteristics from collapse during hydrothermal treatment (HTT) at 200 °C. Materials characterization was performed by X-ray diffraction, transmission electron microscopy, nitrogen physisorption, and Raman spectroscopy. It is shown that initial γ-Al 2 O 3 during HTT transforms into boehmite with a dramatic decrease in the surface area from 217 to 42 m 2 /g. Whereas the preliminary graphitization of its surface maintains high surface area of the material after HTT, which is achieved by forming a C@boehmite composite (294 m 2 /g). The presented approach makes it possible to modify the surface of alumina supports with a layer of graphite-like carbon and can be used to improve or maintain the catalysts activity. • C@Al 2 O 3 samples were obtained by ethylene CVD for 5–240 min. • Graphitization degree of Al 2 O 3 surface varied from 6 to 100%. • Nanocrystalline graphite with graphene fragment size less than 5 nm is formed in C@Al 2 O 3 . • Monolayer carbon coating prevents Al 2 O 3 texture collapse in hydrothermal conditions. • Mesoporous C@boehmite composite with high surface is formed by hydrothermal treatment of C@Al 2 O 3 .

Fabrication of a CNT/Ag potentiometric sensor for redox reactions via catalytic chemical vapor deposition

This work reports the fabrication of a robust and high-performance CNT/Ag composite electrode via catalytic chemical vapor deposition of ethylene. The fabricated electrode showed the formation of aligned CNTs with strong adhesion to the Ag substrate. It was successfully applied to zero-current potentiometry and sequential injection analysis of ascorbic acid. The CVD-fabricated CNT/Ag composite electrode showed an excellent response, a fast equilibrium, good sensitivity and reproducibility, as well as durability for long term use.

MgO/carbon nanofibers composite coatings on porous ceramic surface for CO2 capture

Ceramic materials modified by hybrid MgO/carbon nanofibers systems are synthesized and characterized. Disordered carbon nanofibers were obtained via catalytic chemical vapor deposition of ethylene over nickel nanoparticles supported on the starting porous ceramic substrate. The carbon nanofibers were functionalized by acid treatment to increase the number of carbonyl and carboxyl groups on their surface. The hybrid samples were prepared by a deep coating method using Mg (OH)2 nanoparticles. After calcination, the obtained hybrid system attained a specific surface area of 242 m2·g−1 and a pore volume of 0.8 cm3·g−1. The hybrid material shows significantly enhanced sorption capacity towards carbon dioxide (4.9 mmol·g−1 CO2 uptake) under 367 K and 1 bar partial pressure of CO2.

Effect of catalyst on carbon nanotubes synthesis on titanium diboride via chemical vapor deposition

AbstractCarbon nanotubes (CNTs) were in situ synthesized on titanium diboride (TiB2) substrates using different catalysts (Fe, Co, and Ni) via ethylene chemical vapor deposition (CVD). The effects of various catalysts on the quality and quantity of grown CNTs were investigated using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman characterization techniques. Next, as‐received powders were sintered by spark plasma sintering to obtain compact bulk composites. The effects of the metallic catalysts as sintering aids on the microstructural and mechanical properties of TiB2‐based composites were also studied. Results show that metal Ni not only plays a significant role in the catalyst to produce larger numbers of CNTs but also promotes the densification of TiB2 ceramics in sintering and has been shown to provide good reinforcement. Maximum values of flexural strength (1093 ± 19 MPa) and toughness (13.9 ± 0.3 MPa ·m1/2) were obtained using the Ni catalyst, which were significantly higher than the same values for Fe and Co catalysts.

Au nanoparticle@hollow mesoporous carbon with FeCo/graphitic shell nanoparticls as a magnetically recyclable yolk\u2013shell nanocatalyst for catalytic reduction of nitroaromatics

We have developed a highly stable and magnetically recyclable yolk–shell nanocatalyst for catalytic reduction of nitroaromatics. This nanocatalyst is composed of a ~13 nm Au nanoparticle encapsulated in a hollow mesoporous carbon (hmC) shell with a diameter of ~120 nm and a thickness of ~15 nm. The hmC shell contains ~6 nm FeCo/graphitic carbon shell (FeCo/GC) nanoparticles. We have synthesized the Au@hmC-FeCo/GC nanocatalyst by thermal decomposition of Fe and Co precursors in silica of a solid core/mesoporous shell structure containing a Au nanoparticle within the core, subsequent ethylene chemical vapor deposition (CVD), and then removal of the silica by treatment with aqueous HF. The Au@hmC-FeCo/GC has superparamagnetism and high saturation magnetization (29.2 emu g−1) at room temperature. It also shows a type IV sorption isotherm, typical for mesoporous carbon (pore diameter = 3.5 nm), thereby ensuring ready accessibility to the Au core by substrates. We have shown that the Au@hmC-FeCo/GC catalyses the reduction of 4-nitrophenol and 4-nitrotoluene more efficiently than Au nanoparticles do, can be separated very quickly from the reaction mixture using an magnet, and can be reused for the same reduction reaction at least five times without loss of the initial level of catalytic activity.

Dehydrogenation of ethanol over carbon-supported Cu–Co catalysts modified by catalytic chemical vapor deposition

A bimetallic copper–cobalt catalyst supported on activated carbon fibrous (ACF) material was prepared by the incipient wetness impregnation of the support with an aqueous solution of corresponding nitrates. Reference monometallic Cu/ACF and Co/ACF samples were synthesized analogously. In order to enhance the metal-support interaction and stabilize the dispersion of active components, the Cu–Co/ACF catalyst was subjected to catalytic chemical vapor deposition of ethylene at 600 °C with the formation of carbon nanofibers (CNF). As a result, the catalytic system consisting of Cu–Co particles anchored on carbon–carbon composite was obtained. All samples were characterized by a set of physicochemical methods. The catalytic performance of pristine and CNF-modified samples was studied in the ethanol dehydrogenation reaction. The activity of Cu–Co/CNF/ACF catalyst was shown to be two times higher compared with the unmodified bimetallic sample.

Chemical vapor deposition growth of bilayer graphene in between molybdenum disulfide sheets

Direct growth of flat micrometer-sized bilayer graphene islands in between molybdenum disulfide sheets is achieved by chemical vapor deposition of ethylene at about 800°C. The temperature assisted decomposition of ethylene takes place mainly at molybdenum disulfide step edges. The carbon atoms intercalate at this high temperature, and during the deposition process, through defects of the molybdenum disulfide surface such as steps and wrinkles. Post growth atomic force microscopy images reveal that circular flat graphene islands have grown at a high yield. They consist of two graphene layers stacked on top of each other with a total thickness of 0.74nm. Our results demonstrate direct, simple and high yield growth of graphene/molybdenum disulfide heterostructures, which can be of high importance in future nanoelectronic and optoelectronic applications.

Spectroscopic Fingerprints of Carbon Monomers and Dimers on Ir(111): Experiment and Theory

By combining high-resolution photoelectron spectroscopy and ab initio calculations, we show that different carbon clusters can be formed on Ir(111) upon low temperature molecular beam epitaxy using a solid state carbon source. Besides carbon monomers, also dimers, trimers, and larger clusters are detected through C 1s core level measurements. The spectroscopic signal of carbon monomers is then used as a fingerprint to detect their presence during the early stages of graphene growth by ethylene chemical vapor deposition at high temperature. We demonstrate that our spectroscopic approach can be employed to investigate the role of carbon monomers and dimers in the nucleation and growth of graphene on different metal surfaces.

The Study of Porous Geometry Design for Capacitive Deionization Devices through Vertically-Aligned Carbon Nanotube Electrodes

In the face of an increasing water crisis, we are developing tools to optimize capacitive deionization (CDI) for brackish water desalination. CDI can be a competitive technology for brackish water treatment due to its higher energy efficiencies compared to reverse osmosis and its more inherent resistance to fouling [1]. However, CDI is still a developing technology where adsorption capacity and salt removal rates into porous, tortuous carbon electrodes is still low. We have designed vertically-aligned carbon nanotube (VA-CNT) electrodes, with minimal tortuosity, to investigate the role of porous geometry on the performance of flow-by CDI devices, specifically examining changes in diffusion resistance, salt adsorption rate and capacity. Previously, a breadth of carbon materials have been investigated for CDI including activated carbon, carbon aerogels, ordered mesoporous carbons, carbide-derived carbons, and carbon nanotubes, among many others [2]. High salt adsorption capacities have been attributed to the presence of micropores (< 2 nm), [3] and optimal materials seem to have a presence of macroporous pathways with microporous structures. [4, 5] However, many carbon materials have tortuous pores making it challenging to decouple the role of pore diameter on salt adsorption rate. VA-CNTs are an exciting material for investigating this issue due to the ability to manipulate the inter-CNT spacing, to study changes in the ion transport rate as a function of geometry, while maintaining mininimal tortuosity and intrinsic capacitance. In this work, we synthesize VA-CNT electrodes that are sparse (inter-CNT spacings upto 100 nm), and more dense CNTs (inter-CNT spacings upto 25 nm). These CNTs are grown using a standard chemical vapor deposition of ethylene on silicon wafers with iron catalyst. By varying the partial pressure of ethylene and the oxygen content in the furnace, we synthesize CNTs of varying densities. The VA-CNT forests is delaminated from the substrate with a high-temperature oxygen etch, seperating the carbon from the corrosive catalyst. The free-standing films are mounted against Ti metal plates serving as the current collectors, and constrained by a PEEK porous mesh (200 μm window, 40 μm wire diameter). We use a flow-by CDI experimental set up to study the role of varying voltages, electrode thicknesses, CNT densities, and chemical functionalization on desalination performance. We find that in a 1mM NaCl solution, CNT electrodes can adsorb from 5-15 mg salt/g carbon, at rates of 0.2-1 mg/g-min. Through densification, we maintain gravimetric performance, but increase our volumetric salt adsorption capacity from 0.2 to 0.3 g/cm3. We achieve charge efficiencies upto 80% for these systems. We combine this experimental investigation with an electric double layer model for macroporous electrodes to inform the design of carbon electrode materials for optimal ion adsorption and throughput in a flow-by CDI device. [1] T. Humplik, J. Lee, S. O'Hern, B. Fellman, M. Baig, S. Hassan, et al., Nanotechnology, 22, 292001 (2011). [2] S. Porada, R. Zhao, A. v. d. Wal, V. Presser, and P. M. Biesheuvel, Progress in Materials Science, 58, 8 (2013). [3] S. Porada, L. Weinstein, R. Dash, A. v. d. Wal, M. Bryjak, Y. Gogotsi, et al., ACS applied materials & interfaces, 4, 3 (2012). [4] M. Suss, T. Baumann, W. Bourcier, C. Spadaccini, K. Rose, et al., Energy & Environmental Science, 5, 11 (2012). [5] C. Tsouris, J. Mayes, K. Sharma, S. Yiacoumi, et al., Environmental Science & Technology, 45, 23 (2011).

Graphene Growth on Pt(111) by Ethylene Chemical Vapor Deposition at Surface Temperatures near 1000 K

The nucleation and growth of graphene islands on a Pt(111) surface were examined at temperatures near 1000 K. Graphene was grown by chemical vapor deposition of ethylene, and a low-energy electron microscope (LEEM) was used to image the growing graphene islands with resolution of 10 nm and to perform spatially localized electron diffraction. It is shown that graphene grows bidirectionally over the step edges of Pt, and its formation can induce substantial changes in the platinum surface morphology. Average size and density of graphene islands strongly depend on surface temperature during deposition. Postdosing Auger electron spectroscopy was employed as a complementary macroscopic technique to measure the total carbon deposited as a result of ethylene dissociative sticking and decomposition. The initial dissociative sticking coefficient S0(Tg = 300 K, Ts) for ethylene was found to decrease with increasing surface temperature until a temperature of Ts = 850 K was reached whereupon it increased with temperature.

Healing of graphene on single crystalline Ni(111) films

The annealing of graphene layers grown on 150 nm thick single crystal Ni(111) films was investigated in situ by low energy electron microscopy and photoemission electron microscopy. After growth, by means of chemical vapor deposition of ethylene, the graphene layers consist of several domains showing different orientations with respect to the underlying Ni surface and also of small bilayer areas. It is shown that, in a controlled process, the rotated domains can be transformed into lattice-aligned graphene, and the bilayer areas can be selectively dissolved, so that exclusively the aligned monolayer graphene is obtained. The ordering mechanism involves transport of C atoms across the surface and solution in the bulk.

Growth of single and multi-layer graphene on Ir(1 0 0)

We report on the high temperature chemical vapor deposition of ethylene on Ir(100) and the resulting development of single and multi-layer graphene films. By employing X-ray photoemission electron spectromicroscopy, low energy electron microscopy and related microprobe methods, we investigate nucleation and growth of graphene as a function of the concentration of the chemisorbed carbon lattice gas. Further, we characterize the morphology and crystal structure of graphene as a function of temperature, revealing subtle changes in bonding occurring upon cooling from growth to room temperature. We also identify conditions to grow multi-layer flakes. Their thickness, unambiguously determined through the analysis of the intensity of the Ir 4f and C 1s emission, is correlated to the electron reflectivity at very low kinetic energy. The effective attenuation length of electrons in few-layer graphene is estimated to be 4.4 and 8.4Å at kinetic energies of 116 and 338eV, respectively.

Synthesis of Multi-Walled Carbon Nanotubes by Fluidized-Bed Chemical Vapor Deposition over Co/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

Synthesis of multi-walled carbon nanotubes (MWCNTs) was accomplished by catalytic chemical vapor deposition of ethylene over Co/Al2O3 in a fluidized-bed. The reaction temperature and ethylene concentration, as the molar percentage (mol%), were both found to be crucial factors determining the solid carbon conversion level and selectivity of MWCNT formation, but had no significant effect on the size distribution of the obtained MWCNTs. Amorphous carbon and carbon nanofibers (CNFs) were the main products obtained at a reaction temperature of 550°C. Amorphous carbon was also formed when using ethylene at a high concentration (62.5 mol%), which possibly deactivated the catalyst. Increasing the reaction temperature from 550 to 650°C resulted in better graphitized MWCNTs. The average diameters of the synthesized MWCNTs were in the range of 7–8 nm independent of the reaction temperature or ethylene concentration. The selectivity of alkane production decreased considerably at reaction temperatures above 675°C, resulting in a higher productivity of MWCNTs. The activation energy for MWCNT formation was found to be 65.3 kJ/mol, which matched well with that previously reported for carbon diffuusion in liquid cobalt.

Spectroscopic characterization of graphene films grown on Pt(111) surface by chemical vapor deposition of ethylene

This work reports the peculiar properties of a graphene film prepared by the chemical vapor deposition of ethylene in high vacuum on a well oriented and carefully cleaned Pt(111) crystal surface maintained at high temperature. In‐situ and ex‐situ characterization techniques (low‐energy electron diffraction, high‐resolution electron energy loss spectroscopy, scanning electron microscopy and Raman micro‐spectroscopy) used here indicate the prevalence of single‐layer regions and the presence of two different orientations of the graphene sheets with respect to the Pt(111) substrate. In most of the deposited area, evidence is found of a compressive stress for the graphene lattice, as a net result of the growth process on a metal substrate. This graphene film grown on Pt(111) exhibits a lower degree of order and of homogeneity with respect to the exfoliated graphene on Si/SiO2, as it is found generally for graphene on metals, but several characterization techniques indicate a better quality than in previous deposition experiments on the same metal substrate. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Growth Kinetics of Vertically Aligned Carbon Nanotube Arrays in Clean Oxygen-free Conditions

Vertically aligned carbon nanotubes (CNTs) are an important technological system, as well as a fascinating system for studying basic principles of nanomaterials synthesis; yet despite continuing efforts for the past decade many important questions about this process remain largely unexplained. We present a series of parametric ethylene chemical vapor deposition growth studies in a "hot-wall" reactor using ultrapure process gases that reveal the fundamental kinetics of the CNT growth. Our data show that the growth rate is proportional to the concentration of the carbon feedstock and monotonically decreases with the concentration of hydrogen gas and that the most important parameter determining the rate of the CNT growth is the production rate of active carbon precursor in the gas phase reaction. The growth termination times obtained with the purified gas mixtures were strikingly insensitive to variations in both hydrogen and ethylene pressures ruling out the carbon encapsulation of the catalyst as the main process termination cause.

Single Terrace Growth of Graphene on a Metal Surface

The epitaxial growth of graphene by chemical vapor deposition of ethylene on a Ru(0001) surface was monitored by high-temperature scanning tunneling microscopy. The in situ data show that at low pressures and high temperatures the metal surface facets into large terraces, leading to much better ordered graphene layers than resulting from the known growth mode. Density functional theory calculations show that the single terrace growth mode can be understood from the energetics of the graphene-metal interaction.

Carbon nanofiber based catalyst supports to be used in microreactors: Synthesis and characterization

Carbon nanofiber (CNF) layers have been synthesized on flat fused silica and silicon substrates, as well as inside flow channels of silicon-technology based microreactors by thermal catalytic chemical vapor deposition of ethylene using nickel thin-film catalyst. These CNF layers are to be used as structured catalyst support. The influence of the ethylene concentration and addition of hydrogen to the carbon-containing gas on the morphology of CNF layers was studied. Very low amount of CNFs were produced at low ethylene concentrations (<25%) due to the restricted supply of carbon species. Addition of hydrogen during the CNF growth resulted in significant enhancement of the CNF-yield, producing thicker layers of CNFs and CNFs with smaller diameters. Channels containing silicon micropillars covered with these CNFs have a significantly enhanced surface-to-volume ratio compared to bare microreactor channels (3–4 orders of magnitude). Deposition of well-distributed platinum nanoparticles was carried out on these CNF layers, exemplifying their functionality as structured catalyst support to be used in microreactors.

Effect of the type of carbon nanotubes on tribological properties of polyamide 6

AbstractMultiwalled carbon nanotubes have been synthesized by catalytic chemical vapor deposition of ethylene, using two different catalysts in order to obtain nanotubes with average diameters of 24 and 58 nm, and different lengths. Polyamide 6 (PA6) was reinforced by melt‐mixing in an extruder with 2 wt% functionalized and unfunctionalized carbon nanotubes (CNTs). The nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, and sliding wear determination (SWD). SWD results show a reduction of the residual depth in a scratch test. The reduction is larger in the presence of unfunctionalized CNTs. A further reduction is obtained when decreasing the nanotubes diameter, an effect which is related to larger interfaces between the nanotube and polymeric matrix. CNTs enhance the crystallinity of the polymer and act as nucleation sites, thus increasing the crystallization temperature in respect to neat PA6. The addition of carbon nanotubes helps the formation of PA6 in α‐crystalline form, which is thermodynamically more stable that the γ‐form. CNTs also can act as heterogeneous nucleation sites, hampering the movement of the polymer chains and increasing the crystallization temperature. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Electrical Double-Layer Capacitance of Zeolite-Templated Carbon in Organic Electrolyte

Porous carbon materials have been prepared using chemical vapor deposition of ethylene and acetonitrile on zeolite Y templates with the subsequent removal of the template. The use of zeolite templates enabled tuning of the carbon chemistry, microstructure, and specific surface area while maintaining ordered pores and similar pore-size distribution. Evaluation of the performance of the templated carbons in electrochemical capacitors with tetraethylammonium tetrafluoroborate salt solution in acetonitrile showed a high gravimetric capacitance of up to and a short time constant of up to , indicating fast charge/discharge capability. Nitrogen doping limited the capacitor performance at high current densities without enhancing the energy-storage characteristics at low current densities. Specific capacitance at a constant pore size was found to linearly depend on the surface area, suggesting a potential for further improvements. Carbons produced by zeolite-templating method are promising for use in high-energy, high-power electrochemical capacitors employing organic electrolytes.