CH4 Cracking Research Articles

Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 °C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N2 adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal efficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O-containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C–H and aliphatic C–H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring components. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH4 cracking. AAEMs have a catalytic activity on CH4 cracking. K is particularly effective in improving tar conversion and hydrogen production of biochar.

High syngas selectivity and near pure hydrogen production in perovskite oxygen carriers for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) provides an attractive route for hydrogen and syngas co-production through two successive steps of methane oxidation and steam splitting. However, there is also carbon formation through CH4 cracking which hampers the production of syngas (H2 and CO) and the following production of pure H2. This work prepared the perovskites La0.95Ce0.05NixFe1-xO3 (x = 0, 0.2, 0.5, 0.8, 1.0) as oxygen carriers for CL-SMR. The methane activation and steam splitting were investigated based on reactivity tests on a fixed-bed reactor and various characterizations. Results showed that La0.95Ce0.05Ni0.2Fe0.8O3 and La0.95Ce0.05Ni0.5Fe0.5O3 reached a high syngas selectivity (94.8%, 89.0%) accompanied with good methane conversion (93.1% and 95.7%) for methane partial oxidation, and near 100% hydrogen concentrations (higher than 99.6% and 99.5%) for steam splitting, indicating that additional separation step for pure hydrogen acquisition can be omitted. The H2/CO molar ratio was maintained at the optimal value of 2.0 throughout the methane partial oxidation process. Characterizations and density functional theory calculations demonstrated that methane partial oxidation was promoted via an oxygen vacancy-mediated Mars-van-Krevelen type mechanism and the partial oxidation ability of the oxygen carrier is restricted by its content of oxygen vacancy and lattice oxygen migration rate. The proper amount of Ni doping forming the NiFe synergetic effects also contributed highly to methane partial oxidation. Afterward, the deeply reduced metals combined with the oxygen vacancies provided active sites for steam splitting, hence generating pure H2.

Combination of Methyl from Methane Early Cracking: A Possible Mechanism for Carbon Isotopic Reversal of Overmature Natural Gas

In this study, a methane (CH4) cracking experiment in the temperature range of 425–800°C is presented. The experimental result shows that there are some alkane and alkene generation during CH4 cracking, in addition to hydrogen (H2). Moreover, the hydrocarbon gas displays carbon isotopic reversal ( δ 13 C 1 > δ 13 C 2 ) below 700°C, while solid carbon appears on the inner wall of the gold tube above 700°C. The variation in experimental products (including gas and solid carbon) with increasing temperature suggests that CH4 does not crack into carbon and H2 directly during its cracking, but first cracks into methyl (CH3⋅) and proton (H+) groups. CH3⋅ shares depleted 13C for preferential bond cleavage in 12C–H rather than 13C–H. CH3⋅ combination leads to depletion of 13C in heavy gas and further causes the carbon isotopic reversal ( δ 13 C 1 > δ 13 C 2 ) of hydrocarbon gas. Geological analysis of the experimental data indicates that the amount of heavy gas formed by the combination of CH3⋅ from CH4 early cracking and with depleted 13C is so little that can be masked by the bulk heavy gas from organic matter (OM) and with enriched 13C at R o < 2.5 % . Thus, natural gas shows normal isotope distribution ( δ 13 C 1 < δ 13 C 2 ) in this maturity stage. CH3⋅ combination (or CH4 polymerization) intensifies on exhaustion gas generation from OM in the maturity range of R o > 2.5 % . Therefore, the carbon isotopic reversal of natural gas appears at the overmature stage. CH4 polymerization is a possible mechanism for carbon isotopic reversal of overmature natural gas. The experimental results indicate that although CH4 might have start cracking at R o > 2.5 % , but it cracks substantially above 6.0% R o in actual geological settings.

SiC formation and SiO reactivity of methane at high temperatures

Methane (CH4) is a carbon source currently not in use in the production of silicon. Using a gaseous carbon source instead of conventional solid carbon sources presents an opportunity to rethink silicon production. Preliminary research into this topic has shown CH4 to have a very high SiO reactivity and it might even be a step on the way towards a closed silicon furnace. In this study SiC formation from SiO gas in CH4 containing atmospheres is investigated. A reference gas of pure Ar was compared to H2, CH4 and CO gases. SiC was produced by passing CH4 containing process gases through a layer of SiO producing pellets gas at 1650 °C and 1750 °C. A thermocouple, which measured the process gas temperature, was used to look for signs of thermal cracking of CH4. CH4 contents up to 8% was tested, the lack of a correlation between CH4 content and temperature showed that CH4 does not crack in the current setup despite the temperature being in the range 1650 °C–1750 °C. With a CH4 containing process gas, most of the SiC formed around the gas inlets and within the SiO producing raw material layer. The reaction between SiO and CH4 occurred instantaneously when the two gases met, and appeared to be favored over thermal cracking of CH4. At 1650 °C in H2 or CO containing process gases a thick layer of whiskers formed around the rim of the crucible. The whiskers were examined with STEM using EDS and EELS, which determined the whiskers to be made of SiC. These results suggest that relatively high CH4 pressures can be metastable at temperatures far away from the thermodynamic equilibrium. They also indicate CH4 to exhibit a very high SiO reactivity, which makes it a promising alternative for current carbon sources in the production of silicon.

Highly Dispersed NixGay Catalyst and La2O3 Promoter Supported by LDO Nanosheets for Dry Reforming of Methane: Synergetic Catalysis by Ni, Ga, and La2O3.

A highly active and stable Ni-based catalyst is the focal point for research on dry reforming of methane (DRM). Here, NixGay/La2O3-LDO catalysts composed of highly dispersed NixGay and La2O3 nanoparticles supported by the MgO/Al2O3 layered double oxide (LDO) nanosheets were synthesized by chemical methods. According to transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), CO2-TPD, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermal gravitational analysis (TGA), a synergistic reaction mechanism was proposed to explain the superior performance of the Ni0.8Ga0.2/La2O3-LDO catalyst. The NixGay alloy catalyst provides an effective way to balance the speed of CH4 cracking and CO2 disassociation, and the La2O3 promoter enriched the CO2 and ensured the generation of active O in time. They worked together to inhibit carbon accumulation and significantly improve the catalyst's activity and stability.

Enhanced activity of Co catalysts supported on tungsten carbide-activated carbon for CO2 reforming of CH4 to produce syngas

Carbon materials are widely used as catalysts or supports due to their excellent properties. In this paper, the tungsten carbide-activated carbon (WC-AC) composite support was successfully prepared by in-situ carburizing on AC matrix, which is characterized by the covalent anchoring of WC on the AC support. The active metal Co was supported on WC-AC for dry reforming of methane (DRM). Samples were analyzed by N2 physisorption measurements, XRD, XPS, H2-TPR, H2-TPD, CH4&CO2-TPSR, TG-DTG. The WC-AC stabilizes the disturbance of C in AC, alleviates the gasification effect of CO2 and increases the active sites for CH4 cracking. Moreover, WC provides a resistance-less bridge suitable for the Co3+ → Co2+, resulting in a high Co2+/Co3+ ratio on the catalyst surface. This enhances the interaction between the Co species and the WC-AC, thereby enhancing the CH4 activation. In the process of WC-AC promoting Co3+→Co2+, the catalyst surface is accompanied by the generation of oxygen vacancies. This can enhance the dissociative adsorption of CO2 on surface of the WC-cobalt oxide, and at the same time increase the relative proportion of adsorbed oxygen on the catalyst surface, thereby effectively inhibiting the formation of coke. However, the small amount of graphitic carbon generated due to the strong coupling of WC and Co is the main reason for deactivation of Co/WC-AC.

Mechanism of coke formation and corresponding gas fraction characteristics in biochar-catalyzed tar reforming during Corn Straw Pyrolysis

Formation of coke deposition is the main problem that restricts the development of tar reforming and even biomass thermal conversion. Biochar, prepared from gasification at 800 °C, was used for the catalytic reforming of biomass pyrolysis tar at 650 °C, monitoring the syngas formation during coke deposition. The principal consequences and conclusions are as follows: the coke yield increases from 10.9% to 18.9%, and the tar removal efficiency decreases from 89.0% to 56.7% when the feeding time of biomass is extended (10–50 min). The number of O-containing groups on the biochar surface decreases, and the proportion of minor aromatic rings increases. Biochar is more efficient in the catalytic removal of aliphatic components from tar than aromatic components. Catalytic reforming leads to the development of tar in the direction of increased aromatization. The addition of biochar has essentially no effect on CO yield and CO2 yield, while the CH4 yield decreases and the H2 yield increases. In addition to tar reforming, CH4 cracking is one of the pathways for coke generation on the biochar surface. The number of physical adsorption sites (nN2) and adsorption equilibrium constant (b) of biochar are obtained based on the N2 adsorption test.

Hydrogen Production from Methane Cracking in Dielectric Barrier Discharge Catalytic Plasma Reactor Using a Nanocatalyst

The study experimentally investigated a novel approach for producing hydrogen from methane cracking in dielectric barrier discharge catalytic plasma reactor using a nanocatalyst. Plasma-catalytic methane (CH4) cracking was undertaken in a dielectric barrier discharge (DBD) catalytic plasma reactor using Ni/MgAl2O4. The Ni/MgAl2O4 was synthesised through co-precipitation followed customised hydrothermal method. The physicochemical properties of the catalyst were examined using X-ray diffraction (XRD), scanning electron microscopy—energy dispersive X-ray spectrometry (SEM-EDX) and thermogravimetric analysis (TGA). The Ni/MgAl2O4 shows a porous structure spinel MgAl2O4 and thermal stability. In the catalytic-plasma methane cracking, the Ni/MgAl2O4 shows 80% of the maximum conversion of CH4 with H2 selectivity 75%. Furthermore, the stability of the catalyst was encouraging 16 h with CH4 conversion above 75%, and the selectivity of H2 was above 70%. This is attributed to the synergistic effect of the catalyst and plasma. The plasma-catalytic CH4 cracking is a promising technology for the simultaneous H2 and carbon nanotubes (CNTs) production for energy storage applications.

Catalytic CO2 reforming of CH4 over MgAl2O4 supported Ni-Co catalysts for the syngas production

Ni, Co and Ni–Co bimetallic catalysts of different ratios were synthesized by the Incipient Wetness Impregnation Method (IWI) over Magnesium Aluminate support, keeping the total metal loading 15 wt.%, characterized and tested for the reforming of methane with carbon dioxide at 873 K and 1 atm pressure. Magnesium Aluminate supported catalysts were also compared with Al2O3 supported Ni catalysts with similar metal loading. The results obtained revealed that MgAl2O4 exhibited excellent thermal stability as compared to Al2O3 as support at higher temperatures. Ni–Co catalyst, with an explicit Ni:Co (3:1) ratio for the 75Ni25Co/MgAl2O4 provided the highest CH4 conversion and was about 1.82 times that of the 100Ni/MgAl2O4; CO2 conversion also followed similar trends. Co-existence of Ni and Co with synergic effect in an explicit Ni:Co (3:1) ratio reduced the reduction temperature and increased the amount of metal in 75Ni25Co/MgAl2O4. CH4 and CO2 conversions, TOFDRM, H2: CO ratios and catalyst deactivations were related to the concentrations of the Ni–Co and particularly an explicit ratio of 3:1 for the Ni:Co in 75Ni25Co/MgAl2O4 catalyst provided the best initial & final conversions, TOFDRM and H2:CO ratio. Detail carbon analysis suggested that the type of coke deposited on 75Ni25Co/MgAl2O4 after the DRM reaction is of the same nature and are originating from the CH4 cracking reaction and are of reactive type.

Methane cracking within shale rocks: A new explanation for carbon isotope reversal of shale gas

Shale gas with carbon isotope reversal (δ13Cmethane > δ13Cethane), as a promising indicator for resource “sweet-spot”, tends to occur at high-over maturity shales with high gas dryness index (Cmethane/(Cmethane + Cethane) > 0.97). However, the cause for this reversal is still controversial and remains an open question. In the present work, we propose methane cracking within high-over matured shale rocks, as one of the possible mechanisms, to explain this reversal, which will further enhance the knowledge about carbon isotope reversal of shale gas. In order to validate this hypothesis, methane pyrolysis experiments were carried out in closed gold-tube system to investigate the mechanism of occurrence of carbon isotope reversal in shale gas. From the pyrolysates, the cracking of CH4 and the generation of higher number hydrocarbons like C2H4, C2H6, and C3H8 were detected. The CH4 cracking and the subsequent formation of C2H6 led to the residual CH4 being enriched in 13C whereas the produced C2H6 is depleted in 13C. Based on our experimental results and the data analysis of 583 samples from shale gas reservoirs from different regions of the world, we suggest that CH4 will be cracked and combined into C2H6 in high-over matured shales. When the contribution from methane-derived C2H6 is sufficiently massive, the commonly found order of δ13Cmethane < δ13Cethane will change with increasing maturity (e.g. vitrinite reflectance, Ro > ~2.0%) and a carbon isotope reversal will occur for the shale gas. The Barnett shale from Fort Worth Basin, USA, as the application representative shale gas reservoir, cover the evolution scope of the increase and subsequent decrease of δ13Cethane along with increase of δ13Cmethane and thus the beginning of the carbon isotope reversal.

Thermodynamic sensitivity analysis of CO2 reforming of methane based on equilibrium predictions

Thermodynamic sensitivity analysis was conducted to evaluate the selectivity dry reforming of methane (DRM) with respect to other competing side reactions in terms of Gibbs energy minimization and equilibrium reactor compositions. Spontaneity of each reaction was evaluated by their corresponding changes in Gibbs energy as a function of reactor temperature from 100 – 1000 °C. At temperatures above 700 °C, all reactions considered with the exception of the Boudouard reaction are spontaneous due to their negative deltaG values. Equilibrium compositions were computed for 40 kmol of feed (CO2 + CH4) to determine its sensitivity to occurrence of reverse water-gas-shift (RWGS) reaction and changes in feed CO2/CH4 ratio. The presence of RWGS reaction results to higher reactant conversion accompanied by more severe carbon formation. The H2/CO ratio was however not affected by its occurrence. At CO2/CH4 feed ratio of 2, the product ratio was barely affected and at minimal carbon formation while CO2/CH4 ratio value of 0.5 produced a lot of carbon especially at high temperatures due to the prevalence of CH4 cracking. DRM is thus more preferable at temperatures above 700 °C, devoid of RWGS and high feed CH4.

Enhanced dry reforming of methane over mesostructured fibrous Ni/MFI zeolite: Influence of preparation methods

Dry reforming of methane is acknowledged to be an environmentally benign route for conversion of CO2 and CH4 into syngas (CO and H2). Herein, unique mesostructured fibrous MFI support was synthesized by microemulsion method, and Ni incorporation via double solvent, physical mixing and wetness impregnation methods. Results revealed wetness impregnation catalyst had the highest activity and stability. Activation energy of reactants showed a reliance on acidity, where moderate acidity impeded deactivation by CH4 cracking. Furthermore, degree of catalyst deactivation was negligible compared to what is attainable on conventional zeolite catalysts. Thus, fibrous morphology, microscopic dispersion and moderate acidity played a positive role in boosting reactants accessibility to active Ni sites which results in preservation of activity under the harsh conditions of DRM process.

Effect of Oxidants on Syngas Synthesis from Biogas over 3 wt % Ni-Ce-MgO-ZrO2/Al2O3 Catalyst

The utilization of fossil fuels has led to a gradual increase in greenhouse gas emissions, which have accelerated global climate change. Therefore, there is a growing interest in renewable energy sources and technologies. Biogas has gained considerable attention as an abundant renewable energy resource. Common biogases include anaerobic digestion gas and landfill gas, which can be used to synthesize high-value-added syngas through catalytic reforming. Because syngas (CO and H2) is synthesized at high reaction temperature, carbon is generated by the Boudouard reaction from CO and CH4 cracking; thus, C blocks the pores and surface of the catalyst, thereby causing catalyst deactivation. In this study, a simulation was performed to measure the CH4 and CO2 conversion rates and the syngas yield for different ratios of CO2/CH4 (0.5, 1, and 2). The simulation results showed that the optimum CO2/CH4 ratio is 0.5; therefore, biogas reforming over the 3 wt% Ni/Ce-MgO-ZrO2/Al2O3 catalyst was performed under these conditions. CH4 and CO2 conversion rates and the syngas yield were evaluated by varying the R values (R = (CO2 + O2)/CH4) on the effect of CO2 and O2 oxidants of CH4. In addition, steam was added during biogas reforming to elucidate the effect of steam addition on CO2 and CH4 conversion rates. The durability and activity of the catalyst after 200-h biogas reforming were evaluated under the optimal conditions of R = 0.7, 850 °C, and 1 atm.

CH4 Cracking over the Cu–Ni/Al-MCM-41 Catalyst for the Simultaneous Production of H2 and Highly Ordered Graphitic Carbon Nanofibers

The Cu-Ni bimetallic catalysts dispersed on various silica supports were examined for catalytic cracking of CH4 to produce pure H2 with near zero COx emissions and fine quality carbon nano fibers. The 27Al MAS NMR spectra of Al containing MCM-41 samples revealed the existence of framework and extra framework decorated Al species. Insertion of Al species into the framework of MCM-41, significantly improved the accessible active surface Ni sites, which was confirmed from the simultaneous H2 and N2O pulse titration techniques. NH3 TPD measurements demonstrated a high ratio of moderate and strong acid sites upon Al- insertion into the silica matrix. The framework tetrahedral -Al in MCM-41 stabilized the surface Cu-Ni alloy sites and protected from the sintering and fragmentation of Ni consequently enhanced the H2 yields of 270 Nm3/(molNi)-1 were obtained with Si/Al ratio = 150 with catalyst. The better performance of the Cu-Ni/Al-MCM-41 (Si/Al = 150) was rationalized using the physicochemical characteristics ...

H2 production from a plasma-assisted chemical looping system from the partial oxidation of CH4 at mild temperatures

A plasma-assisted chemical looping system for the production of H2 (PCLH) was investigated in this study. This system allows the partial oxidation of CH4 at mild temperatures (573–773 K). Four active oxygen carriers: Fe2O3, NiO-impregnated Fe2O3 (NiO/Fe2O3), SrFeO3−δ and NiO-impregnated SrFeO3−δ (NiO/SrFeO3−δ) were compared, each working both as a packed material for the plasma reactor and an oxygen source for the partial oxidation of CH4. Similar conversions of CH4, and low yields of H2 were obtained in Fe2O3 and SrFeO3−δ. It was concluded that in these cases, H2 was mainly produced from direct cracking of CH4 by plasma. In contrast, when using NiO/Fe2O3 and NiO/SrFeO3−δ, substantial production of H2 was achieved. It is proposed that there is a synergistic effect between the catalyst and the oxygen carrier; the presence of the metallic Ni phase was responsible for catalysing the production of H2, and the oxygen from the support helped prevent the build-up of coke. As a result, the activity of Ni was continuously maintained for H2 production. The chemical loop is closed with the oxygen carriers being regenerated in air with plasma and then used in the next looping cycle. The high H2 production capability in NiO/Fe2O3 was repeatable; whilst, NiO/SrFeO3−δ deactivated in the second and third cycles. Amongst the temperatures studied, NiO/Fe2O3 at 673 K resulted in the best performance for H2-rich gas production. A further increase in the operating temperature led to a total combustion of CH4.

Methane decomposition and carbon deposition over Ni/ZrO2 catalysts: Comparison of amorphous, tetragonal, and monoclinic zirconia phase

The influence of crystal phase of ZrO2 on the catalytic performance of methane decomposition and the properties of deposited carbon on Ni/ZrO2 catalysts was investigated. Ni/ZrO2 catalysts were prepared by incipient-wetness impregnation method with 5% Ni loading, using amorphous, monoclinic, and tetragonal ZrO2 as supports. It was found that Ni/am-ZrO2 exhibited high activity and superior stability for carbon dioxide reforming of methane during 50 h of TOS, which could be attributed to the smaller Ni particle size and the lower coking rate. Additionally, the results of O2-TPO/TPH/CO2-TPO showed that the nature of carbon deposition via CH4 decomposition on Ni/ZrO2 catalysts was strongly influenced by both the Ni particle size and the crystal phase of zirconia. The lowest coking rate on Ni/am-ZrO2 for carbon dioxide reforming of methane was due to the lower CH4 decomposition rate and the higher gasification rate of carbon species by CO2. Carbon deposited on Ni/am-ZrO2 could be greatly removed by CO2, due to the presence of large amount of adsorbed oxygen species on the surface of amorphous ZrO2. For comparison, the imbalance of CH4 cracking and removal of coke by CO2 resulted in the accumulation of coke, leading to the deactivation of catalysts.

NixCoy Nanocatalyst Supported by ZrO2 Hollow Sphere for Dry Reforming of Methane: Synergetic Catalysis by Ni and Co in Alloy.

NixCoy/H-ZrO2 catalysts composed of highly dispersed NixCoy nanoparticles supported by mesoporous ZrO2 hollow sphere are synthesized by templating and impregnation processes. According to thermogravimetric analysis, X-ray photoelectron spectroscopy, and dry reforming results, a synergetic reaction mechanism is proposed to explain the better performance of alloy catalysts compared to Ni/H-ZrO2 or Co/H-ZrO2. In dry reforming of methane (DRM) reaction, Ni and Co act as catalysts for CH4 cracking and CO2 reduction, respectively, and the induced carbon deposits on Ni can be oxidized by the active oxygen left on Co, which regenerate the metal surface for the following reaction. Among all the alloy catalysts, the Ni0.8Co0.2/H-ZrO2 catalyst presents the highest activity and stability because the strong metal-support interaction prevents the sintering of nanocatalysts at high temperature and the hollow structure enhances the mass transportation of reactants and products. More importantly, Ni and Co can synergistically balance the speed of CH4 cracking and CO2 reduction, which effectively avoid coke accumulation/catalyst oxidation and ensure fast and stable conversion for DRM reaction.

Two-dimensional mechanistic Solid Oxide Fuel Cell model with revised detailed methane reforming mechanism

A revised mechanistic SOFC model is presented with two main important modifications compared to the current state-of-the-art mechanistic SOFC models: 1) current models are all developed based on the “CH4 adsorption mechanism”; this is one of the most critical reactions but studies have indicated that CH4 adsorbed dissociatively on nickel, which is considered in the present revised model; and 2) kinetic data in the current models are fitted, in particular those for critical reactions such as CH4 cracking, CO and CO2 surface reactions; in the present work, the activation energies for those reactions are taken from DFT calculations, while the pre-exponential factors are still fitted to experimental data. The results show that carbon distribution predicted by the revised model fits better the experimental observations reported in the literature and thus the proposed revised model represents a more realistic SOFC model operating with CH4 or CO fuel gas. Furthermore, the revised model was used to investigate the distributions of gas/surface species concentration and temperature effects under humidified CH4. The results show that Ni surface is covered mainly by H(s) and CO(s) where the electrochemical reactions take place, whereas there is a very high coverage of C(s) where electrochemical reactions are absent.

Carbon Co-Deposition During Gas Reduction of Water-Atomized Fe-Cr-Mo Powder

AbstractThe water atomization of iron powder with a composition of Fe-3Cr-0.5Mo (wt.%) at 1600°C and 150 bar creates an oxide layer, which in this study was reduced using a mixture of methane (CH4) and argon (Ar) gas. The lowest oxygen content was achieved with a 100 cc/min flow rate of CH4, but this also resulted in a co-deposition of carbon due to the cracking of CH4. This carbon can be used directly to create high-quality, sinter hardenable steel, thereby eliminating the need for an additional mixing step prior to sintering. An exponential relationship was found to exist between the CH4gas flow rate and carbon content of the powder, meaning that its composition can be easily controlled to suit a variety of different applications.

Syngas production from methane dry reforming over Ni/SBA-15 catalyst: Effect of operating parameters

The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH4/CO2 volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m2 g−1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H2 temperature-programmed reaction shows that NiO particles were reduced to metallic Ni0 phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH4 decomposition reaction. Both CH4 and CO2 conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO2 and CH4 partial pressure of 20 kPa. CH4 conversion improved with increasing CO2 partial pressure, PCO2 and exhibited an optimum at PCO2 of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO2 conversion was observed with growing PCO2. Additionally, CH4 and CO2 conversions decreased significantly with rising CH4 partial pressure because of increasing carbon formation rate via CH4 cracking in CH4-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement.