Catalytic Decomposition Of CH4 Research Articles

COx -free H2 Production via Catalytic Decomposition of CH4 over Fe Supported on Tungsten oxide-activated Carbon Catalyst: Effect of Tungsten Loading

Production of COx-free H2 from CH4 (a major global warming contributor) over cheap catalysts is a dominant task for the scientific community to accomplish environmental-friendly clean H2 energy sources. Herein, a tungsten oxide-activated carbon-supported Fe catalyst is prepared by impregnation method, characterized by X-ray diffraction, surface area-porosity measurement, temperature programmed reduction/oxidation and thermogravimetry analysis. 30wt.%Fe supported tungsten oxide incorporated activated carbon catalyst is found superior to 30 wt% Fe supported on activated carbon incorporated tungsten oxide due to higher surface area and high concentration of reducible catalytic active sites. 30wt.%Fe impregnated over 25 wt%WO3-75 wt%activated carbon support catalyst has the highest concentration of reducible surface-active species and it had excellent performance among other tungsten oxide incorporated catalysts. The catalyst showed 66.04% CH4 conversion, 63.12% H2 yield and YH2 /CCH4 > 0.9 initially which didn’t fall below 35 % up to 160-minutes. Improper matching between the rate of carbon formation and the rate of diffusion over a highly crystalline 30Fe50W50Ac catalyst resulted in rapid deactivation.

Formation of carbon nanofibers with Ni catalyst supported on a micro-mesoporous glass

The Ni/SiO2 system is one of the most interesting to produce COx-free H2 and valuable carbon nanofibers (CNFs) by the catalytic decomposition of CH4. SiO2 is one of the most effective support while Ni catalyst displays long life and high activity. We studied the catalytic chemical vapor deposition (CCVD) process of CH4 within Ni/glass system at relatively low temperature (600 °C) during long times (3 h), varying the amount of the catalyst (2.3–17.8% Ni(%)) and the carbon source (100:200 to 100:0, CH4:N2). As the amount of Ni and CH4 increases, the formation of CNFs is enhanced giving as a result CNFs/glass materials with more amount, longer and thicker CNFs. The initial microstructure of the glass support and the way of Ni catalyst is deposited play a decisive role. Pristine porous glass displays a microstructe of interconnected mesopores which are progressively filled with Ni, producing ink-bottle pores with open ends. After the CCVD process as the amount of Ni or CH4 increases, the porosity of the Ni-doped glass is reduced due to the progressively filling of the mesopores (4 nm) with CNFs. Furthermore, due to the formation of large entanglements of CNFs new pores appear (20–70 nm) depending on the processing conditions. Fish-bone with hollow core and bamboo-like CNFs are found over the surface and also inside the porous glass support. It is observed a base-growth mechanism due to the strong interaction between the catalyst and the support, which prevents the Ni deactivation enhancing its activity for long times.

Constructing different categories of heterostructured magnetic nanoparticles@carbon nanotubes-reduced graphene oxide, and their tunable excellent microwave absorption capabilities

In order to simultaneously effective utilization of interface engineering, dielectric loss and magnetic loss attenuation mechanisms, we elaborately constructed and synthesized the mixed-dimensional magnetic nanoparticles (NPs)@carbon nanotubes (CNTs)-reduced graphene oxide (RGO) van der Waals heterostructures (VDWHs) through the catalytic decomposition of C2H2 over FeOOH-RGO. By controlling the decomposition time, different categories and CNTs contents of heterostructured nanohybrids such as Fe3O4@CNTs-RGO, Fe@Fe3C@CNTs-RGO and Fe@Fe2C@CNTs-RGO, which consisted of two-dimensional (2-D) RGO nanosheets, zero-dimensional (0-D) magnetic NPs and one-dimensional (1-D) CNTs, could be selectively synthesized. The obtained results indicated that the as-prepared mixed-dimensional magnetic NPs@CNTs-RGO VDWHs displayed the excellent microwave absorption capabilities, which were proved to be attributed to the quarter-wavelength matching model and good impedance matching. Moreover, because of the improved dielectric loss abilities, values of attenuation constant, defects and/or multiple interfacial polarizations, the obtained Fe@Fe2C@CNTs-RGO samples exhibited evidently enhanced microwave absorption performances. Therefore, a simple and effective route was proposed to synthesize the mixed-dimensional magnetic NPs@CNTs-RGO VDWHs, which provided a new platform for the designing and production of high performance microwave absorption materials.

Graphene and carbon nanotubes by CH4 decomposition over Co Al catalysts

Abstract Catalysts containing Co and Al were prepared to obtain graphene and carbon nanotubes (CNTs) via the catalytic decomposition of CH4. The catalysts were prepared by co-precipitation with molar percentages of Co between 50 and 100%. The effects on the formed carbon of the catalyst composition, reaction temperatures of 500–900 °C, and activation with hydrogen were evaluated. The carbon that formed during the reactions was analyzed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed oxidation (TPO). The Raman spectra of the samples containing Al were characteristic of CNTs, with the IG/ID ratio increasing as the Co/Al ratio and reaction temperature increased. The Co100 sample presented a Raman spectrum indicative of few-layer graphene. The TPO analysis revealed cobalt carbide oxidation for the Co100 sample, and this phase was related to the formation of graphene. CNTs were favored by Co Al mixed oxides and reaction temperatures of 500–700 °C. Graphene was favored by the Co3O4 phase and higher reaction temperatures.

Enhanced Electromagnetic Wave Interference by Nanoscale Mixed-Dimensional C-MoS2 Magnetic van der Waals Heterostructures

It is generally believed that the matching of electromagnetic (EM) impedance or making the best of the interface polarization is an efficient way to achieve a good EM wave absorbing capability. Herein, the mixed-dimensional C-MoS2 based magnetic van der Waals heterostructures (vdWHs) were elaborately designed and successfully synthesized through the catalytic decomposition of C2H2 over Fe3O4–MoS2. By controlling the pyrolysis temperature, “3-0-2” type heterostructured C–Fe3O4–MoS2 ternary nanohybrid consisting of three-dimensional (3-D) carbon layers, zero dimensional (0-D) magnetite particles, and two-dimensional (2-D) MoS2 nanosheets (NSs) and “1-0-2” type CNTs-Fe@Fe3C-MoS2 vdWHs consisting of 1-D carbon nanotubes (CNTs), 0-D Fe and Fe3C nanoparticles, and 2-D MoS2 NSs were selectively synthesized. Compared to “0-2” type Fe3O4–MoS2, the obtained results demonstrated clearly that the introduction of carbon to form the mixed-dimensional C-MoS2 based magnetic vdWHs could greatly enhance the EM wave absorpt...

Decomposition of methane over Co3−xAlxO4 (x=0–2) coprecipitated catalysts: The role of Co phases in the activity and stability

High-purity hydrogen is an environmentally friendly source of alternative energy. Co3−xAl3O4 catalysts were evaluated for the production of H2 through the catalytic decomposition of CH4. The catalysts were prepared by co-precipitation and characterized by N2-physisorption analysis, TPR, XRD, and TPO. Activity tests were performed in a fixed-bed tubular reactor. The samples were either reduced with H2 at temperatures of 500 and 700 °C before the reactions or they were activated using CH4. Samples with Co/Al ratios of 1–2.3 showed higher surface area and exhibited the properties of mixed oxides derived from hydrotalcites. Six reducible phases were identified: three corresponding to the reduction of Co3O4 bulk oxide and three corresponding to mixed oxides represented by Co3−xAlxO4 with x varying from 0.5 to 2. The reduction temperature increased with x. The activation of the catalyst influenced the activity, the type of carbon produced, and the deactivation rate. Catalysts with Co/Al ratios of 1–2.3 showed the best results at 500 °C and required an induction time when they were activated with CH4. The stability of these catalysts was related to the Co3−xAlxO4 mixed oxides. The activation with H2 at 700 °C caused excessive reduction of the Co3O4 phase, and all samples were deactivated by sintering in the reaction at 700 °C. For samples activated with CH4, the amount of amorphous carbon produced was more important than sintering for deactivation at 700 °C.

Graphene monolayer produced on Pt reusable substrates for transparent conductive electrodes applications

We developed a growth process by chemical vapour deposition (CVD) allowing high quality single layer graphene using a microelectronic industrial tool able to deposit graphene on 200 mm substrates. Growth was achieved by catalytic decomposition of CH4 at a very low CH4/H2 flow rate ratio to decrease the nucleation density of graphene on platinum (Pt) and favour large graphene grains. Graphene production with a high nucleation control is obtained on Pt thin film substrates at 800°C compared to 1000°C for Cu. In these conditions, grains with typically 10th of µm size are obtained. Each grain is formed with high quality single crystal(s) without any obvious atomic defect as verified by high resolution transmission electron microscopy (HRTEM). To better assess the graphene quality, Raman spectra and mapping were performed. The intensity ratio (IG/I2D) and linewidth (G and 2D band) attested that the deposited graphene is made of a single layer at least on the tested mapped area. We devised a new electrochemical transfer method which should allow re-using the Pt substrates. Graphene sheets transferred by electrochemistry are of high quality: the density of defects such as cracks and holes is minimised. The sheet resistance of a monolayer of graphene transferred onto glass by the electrochemical process is around RS = 1300 Ω/square (four point method). By improving this route we hope to produce high quality contaminant-free graphene grade material.

Experimental Comparative Study of Carbon Nanotubes Synthesized from CO and CH<sub>4</sub> by Flame Pyrolysis Method

In this paper, carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis of CO and CH4 using flame pyrolysis method. The effects of using the two different carbon sources to the preparation of CNTs with all other conditions being equal were comparatively studied. The results showed that: the morphology of CNTs synthesized from different carbon source gases had certain difference. Higher yield of carbon nanotubes could be synthesized using CH4 as carbon source than using CO. At the same time, the former had less number of tube walls and the vascular bundles arranged more neatly. Synthetizing CNTs via catalytic decomposition of CH4 had more advantages than using CO by flame pyrolysis method.

Influence of La on reduction behaviour and Ni metal surface area of Ni–Al2O3 catalysts for COx free H2 by catalytic decomposition of methane

A series of Ni:Al:La mixed oxides derived from hydrotalcite precursors with varying La/Al mole ratio were examined for COx free H2 production by catalytic decomposition of CH4. The physico-chemical characteristics of Ni:Al:La were determined by XRD, UV-DRS, SEM, TEM, Raman spectroscopy, BET-surface area, TPR and O2 pulse chemisorption measurements. Addition of La to Ni–Al improved the Ni metal surface area and the reduction behaviour of NiO particles is dramatically changed. Particle size of Ni was similar to the size of carbon nano fibre in the deactivated catalyst. A direct correlation between Ni metal surface area and the CH4 decomposition activity was observed.

Investigation of low and mild temperature for synthesis of high quality carbon nanotubes by chemical vapor deposition

The low reaction temperature for synthesis of carbon nanotubes (CNTs) with high quality was investigated by Ni/MgO catalytic decomposition of CH4 using a home-designed micro-fluidized bed reactor. It was found that the low and mild temperature at 500∼550°C would bring the dynamic equilibrium between the rate of CH4 decomposition and the rate of carbon diffusion over Ni catalyst for continuous precipitation of CNTs in the micro-fluidized bed condition. The CNTs synthesized at the corresponding conditions exhibited high quality with relatively small and mean outer diameter, less defect, and high purity.

The effect of synthesis conditions on the growth of carbon nanofilaments using intermetallic copper-tin catalysts

We report for the first time the synthesis of carbon nanofilaments using intermetallic Cu–Sn catalysts. The synthesis was achieved by the catalytic decomposition of C2H2 over a mixture of SnO2 and CuO particles. Also, we have investigated the effect of synthesis conditions on the morphology of carbon nanofilaments and the role of Cu–Sn catalysts in the growth mechanism. The weight ratio of SnO2 and CuO determined the phase of the Cu–Sn intermetallic compound. Favorable growth of carbon nanofilaments was observed at a weight ratio of approximately 1:2, which induces the formation of intermetallic Cu41Sn11 nanostructures. Structures observed at different synthesis pressures and temperatures included carbon nanofibers, carbon nanotubes (CNTs), and catalyst-filled CNTs. This morphological change of carbon nanofilaments was because of the change in C2H2 concentration in the reactor and the phase change of the Cu41Sn11 nanostructures. The observation of the growth of carbon nanofilament with increasing synthesis time confirmed the evolution of intermetallic Cu41Sn11 catalysts and the tip-growth mechanism of carbon nanofilaments. This synthesis methodology could be extended for similar syntheses using Sn-based alloy catalysts and direct growth of carbon nanofilaments on 3D substrates such as carbon fiber papers and a Cu foam, showing its potential for practical applications.

Precise control of the number of walls formed during carbon nanotube growth using chemical vapor deposition

We demonstrate a one-step approach for selecting the number of walls formed during carbon nanotube (CNT) growth by catalytic decomposition of CH4 over Fe–Mo/MgO catalysts. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), thermal gravimetric analysis (TGA) and Raman spectroscopy analyses indicate that high purity single-walled, double-walled and triple-walled carbon nanotubes can be synthesized by tuning the Fe:Mo atomic ratio of catalysts. The results reveal that the concentration of Mo in the catalyst plays an important role in the size of catalyst particles and in the deposition rate of carbon atoms during CNT growth. Thus, the wall numbers of CNTs can be controlled precisely.

A Facile Synthesis of Carbon Nanobelts over Mo/Fe/MgO Catalysts

Carbon nanobelts(CNBs) with high purities (over 90%) have been successfully synthesized by catalytic decomposition of CH4 over Mo/Fe/MgO catalysts at 1173 K. The CNBs have thickness of about 8.0nm, width of about 50-200nm.with few defects and amorphous. It has been found that the addition of component Mo in catalysts plays a key role to synthesize the carbon nanobelts at high yields. The graphitic sheets increased with the increase of Mo content in catalysts.

Growth of single and double walled carbon nanotubes over Co/V/MgO catalysts

High quality single walled carbon nanotubes (SWCNTs) and double walled carbon nanotubes (DWCNTs) were synthesized on Co/V/MgO catalysts by catalytic decomposition of CH 4 in H 2. Raman spectroscopy data revealed that the diameters of as-prepared SWCNTs are 1.28 and 0.73 nm. The diameter value of DWCNTs from Raman analysis also showed a narrow diameter distribution. Using field emission transmission electron microscopy (TEM), it was found that the diameter of carbon nanotubes can be controlled mainly by adjusting the molar ratio of Co–V versus the MgO support. The structure properties of catalysts were examined by X-ray diffraction (XRD). The formation of C 7V 8 may play an important role in preserving carbon in the catalyst particle and favoring the dissociation balance of CH 4.

Efficient Growth of Horizontally Aligned Single-Walled Carbon Nanotubes by Chemical Vapor Deposition Over MgO-Supported Bimetallic Co-Based Catalysts

A series of supported cobalt-based catalysts (Co-X, where X = Mn, V, W, Gd, Mo) has been investigated for the growth of single-walled carbon nanotubes via catalytic decomposition of CH4. At 850 degrees C, Mn, W and Gd promoted Co-catalysts produce SWNTs while Mo and V do not yield any SWNTs. Furthermore, Co-Gd catalysts produce high quality SWNTs with very few defects, and also narrow diameter and chirality distributions (approximately 1 nm). The growth of horizontally aligned SWNTs (approximately 1 mm long) using the Co-Gd catalyst is also demonstrated.

Decomposition of metal carbides as an elementary step of carbon nanotube synthesis

The role of catalyst components in catalysts containing molybdenum, Mo/M/MgO (M Ni, Co, and Fe), as well as Mo-free catalysts, M/MgO (M Ni, Co, and Fe), for carbon nanotube (CNT) synthesis have been investigated by TEM, XRD, and Raman spectroscopy. CNT synthesis by the catalytic decomposition of CH 4 over M/MgO catalysts can proceed at reaction temperatures higher than the decomposition temperature of the metal carbides (Ni 3C, Co 2C, and Fe 3C), which indicates that carbon in the CNT originates from the graphitic carbon formed on the catalyst surface by the decomposition of metal carbides. For all catalysts containing Mo, thin CNT formation starts at an identical temperature of 923 K, corresponding to the decomposition temperature of MoC 1− x into Mo 2C. The significant effect of the addition of Mo is concerned with the formation of Mo 2C in a catalyst particle during CNT synthesis at high reaction temperatures. The presence of a stable Mo 2C phase leads to the formation of thin CNT with better crystallinity at high reaction temperatures. The role of Ni, Co, and Fe in the Mo/M/MgO catalysts is ascribed to the dissociation of CH 4.

Fe-Substituted Mullite Powders for the In Situ Synthesis of Carbon Nanotubes by Catalytic Chemical Vapor Deposition

Powders of iron-substituted mullite were prepared by combustion and further calcination in air at different temperatures. A detailed study involving notably Mössbauer spectroscopy showed that the Fe3+ ions are distributed between the mullite phase and a corundum phase that progressively dissolves into mullite upon the increase in calcination temperature. Carbon nanotube−Fe−mullite nanocomposites were prepared for the first time by a direct method involving a reduction of these powders in H2−CH4 and without any mechanical mixing step. The carbon nanotubes formed by the catalytic decomposition of CH4 on the smallest metal particles are mostly double-walled and multiwalled, although some carbon nanofibers are also observed.

Catalytic decomposition of CH 4 over NiO–Al 2O 3–SiO 2 catalysts: Influence of catalyst preparation conditions on the production of H 2

This paper presents the synthesis and characterization of NiO–Al 2O 3–SiO 2 catalysts prepared by co-precipitation method and the catalytic activities estimated for the production of H 2 by CH 4 decomposition. The physico-chemical characteristics are evaluated by XRD analysis, TPR and O 2 pulse chemisorption, XPS, CHNS, SEM/EDAX, TEM and BET-surface areas of fresh and used forms of catalysts. XRD studies revealed the presence of hydrotalcite-like precursors in oven dried form and produced dispersed NiO species upon calcination in static air at 450 °C. The catalyst compositions for NiO–Al 2O 3–SiO 2 system are optimized based on various parameters such as varying Ni loadings, change in Al/Si ratios, precipitation at different pH and finally choice of precursors on CH 4 decomposition activities. Based on the results it is concluded that the composition of NiO–Al 2O 3–SiO 2 and preparation conditions played a key role in the decomposition of CH 4. The optimized compositions are established for the production of H 2 that can be utilized in fuel cell applications.

H 2 production from CH 4 decomposition: Regeneration capability and performance of nickel and rhodium oxide catalysts

Nickel–lanthanum (LaNiO 3) and nickel–rhodium–lanthanum (LaNi 0.95Rh 0.05O 3) perovskite-type oxide precursors were synthesized by different methodologies (co-precipitation, sol–gel and impregnation). They were reduced in an H 2 atmosphere to produce nickel and rhodium nanoparticles on the La 2O 3 substrate. All samples were tested in the catalytic decomposition of CH 4. Methane decomposed into carbon and H 2 at reaction temperatures as low as 450 °C—no other reaction products were observed. Conversions were in the range of 14–28%, and LaNi 0.95Rh 0.05O 3 synthesized by co-precipitation was the most active catalyst. All catalysts maintained sustained activity even after massive carbon deposition indicating that these deposits are of the nanotube-type, as confirmed by transmission electron microscopy (TEM). The reaction seems to occur in a way that a nickel or rhodium crystal face is always clean enough to expose sufficient active sites to make the catalytic process continue. The samples were subjected to a reduction–oxidation–reduction cycle and in situ analyses confirmed the stability of the perovskite structure. All diffraction patterns showed a phase change around 400 °C, due to reduction of LaNiO 3 to an intermediate La 2Ni 2O 5 structure. When the reduction temperatures reach 600 °C, this structure collapses through the formation of Ni 0 crystallites deposited on the La 2O 3. Under oxidative conditions, the perovskite system is recomposed with nickel re-entering the LaNiO 3 framework structure accounting for the regenerative capability of these solids.

Catalytic decomposition of CH 4 over Ni-Al 2O 3-SiO 2 catalysts: Influence of pretreatment conditions for the production of H 2

This article reports the production of CO x free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al 2O 3-SiO 2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si (4:0.5:1.5) catalyst reduced with hydrazine hydrate produced better H 2 yields of ca. 1815 mol H 2/mol Ni than the catalyst reduced with 5% H 2/N 2.