Natural Fe-based catalysts for the production of hydrogen and carbon nanomaterials via methane decomposition

Tierga and Ilmenite Fe-based ores are studied for the first time in the catalytic decomposition of methane (CDM) for the production of carbon dioxide-free hydrogen and carbon nanomaterials. Tierga exhibits superior catalytic performance at 800 °C. The effect of the reaction temperature, space velocity and reducing atmosphere in the catalytic decomposition of methane is evaluated using Tierga. The highest stability and activity (70 vol% hydrogen concentration) is obtained at 850 °C using methane as a reducing agent. Reduction with methane causes the fragmentation of the iron active phase and inhibits the formation of iron carbide, improving its activity and stability in the CDM. Hybrid nanomaterials composed of graphite sheets and carbon nanotubes with a high degree of graphitization are obtained. Considering its catalytic activity, the carbon quality, and the low cost of the material, Tierga has a competitive performance against synthetic iron-catalysts for carbon dioxide-free hydrogen and solid carbon generation.     

Hydrogen production from COx-Free thermocatalytic decomposition of methane over the mesoporous iron aluminate spinel (FeAl2O4) nanopowder supported nickel catalysts

In the present study, the thermocatalytic decomposition of methane (TDM) was performed over the NiO(x)/FeAl₂O₄ catalysts with various contents of nickel oxide. The FeAl₂O₄ catalyst support with mesoporous structure and high S_BET (80.26 m² g^?1) was synthesized according to the carbonate-based mechanochemical method. The calcined catalysts were characterized by the XRD, BET, H₂-TPR, CO₂-TPD, TPO, and FESEM analyses. The obtained results demonstrated that the S_BET of the synthesized catalysts reduced from 62 to 26 m² g^?1 by increasing the nickel loading from 20 to 60 wt.%, which is ascribed to the blockage of FeAl₂O₄ support pores. Furthermore, the activity results showed that the catalytic activity improved by increasing the nickel content from 20 to 50 wt.% due to the rise of active site concentration. However, the methane conversion was reached to 40% at 600 °C over the NiO(50)/FeAl₂O₄ catalyst. The more increment of nickel content decreased the catalytic efficiency due to the decline in active phase dispersion. Moreover, the increment amount of deposited carbon was seen by increasing the weight percentage of NiO. Therefore, the catalyst with 50 wt.% of NiO possessed excellent catalytic potential in the TDM process under the hard operating conditions (GHSV = 50,000 ml.h^?1.g^?1_cat). The influence of GHSV, feed ratio (CH₄:N₂), calcination temperature, and reduction temperature on the textural properties and catalytic activity of the NiO(50)/FeAl₂O₄ catalyst were also evaluated in detail.     

Mild temperature hydrogen production by methane decomposition over cobalt catalysts prepared with different precipitating agents

Hydrogen production by methane decomposition has been studied using different cobalt catalysts obtained by reduction of cobalt oxide precursors synthesized in ethylene glycol and using three different precipitating agents: sodium carbonate, ammonium hydroxide and urea. The physicochemical properties of the catalysts precursors vary with the precipitating agent, which shows a significant influence in their catalytic performance. Thus, the catalysts obtained from precursors precipitated with Na₂CO₃ or CO(NH₂)₂ show remarkable catalytic activity at lower temperatures, which in both cases has been assigned to the lower particle size and aggregation degree of the final metallic Co phase. Accordingly, the use of urea as precipitating agent led to the catalyst with the highest H₂ production at 600 °C after 12 h of time on stream. Likewise, it is worth mentioning that the catalyst prepared using Na₂CO₃ shows significant activity in this reaction even at temperatures as low as 400 °C.     

Evaluation of the economic impact of hydrogen production by methane decomposition with steam reforming of methane process

There has been considerable interest in the development of more efficient processes to generate hydrogen. Currently, steam methane reforming (SMR) is the most widely applied route for producing hydrogen from natural gas. Researchers worldwide have been working to invent more efficient routes to produce hydrogen. One of the routes is thermocatalytic decomposition of methane (TCDM) - a process that decomposes methane thermally to produce hydrogen from natural gas. TCDM has not yet been commercialized. However, the aim of this work was to conduct an economic and environmental analysis to determine whether the TCDM process is competitive with the more popular SMR process. The results indicate that the TCDM process has a lower carbon footprint. Further research on TCDM catalysts could make this process economically competitive with steam methane reforming.     

Direct methane cracking using a mixed conducting ceramic membrane for production of hydrogen and carbon

The direct cracking of methane can be used to produce CO_x and NO_x-free hydrogen for proton exchange membrane fuel cells. Recent studies have been focused on enhancing the hydrogen production using the direct thermocatalytic decomposition of methane as an attractive alternative to the conventional steam reforming process. We present the results of a systematic study of methane direct decomposition using a mixed conducting oxide, Y-doped BaCeO₃, membrane. A dense disk-shaped BaCe_0.85Y_0.15O₃ membrane was successfully prepared and covered with Pd film, as the catalyst for the methane decomposition. For the methane thermocatalytic decomposition, the methane gas was employed as reactant on the membrane side with a pressure of 10² kPa and rate of 70 ml/min at the reaction temperatures of 600, 700, and 800 °C. The hydrogen was selectively transported through the mixed conducting oxide membrane to the outer side. In addition, the carbon, which is a by-product after methane decomposition, showed the morphologies of sphere-shaped nanoparticles and the transparent sheets.     

Production of hydrogen and carbon nanofibers through the decomposition of methane over activated carbon supported Pd catalysts

Hydrogen has been produced by decomposing methane thermocatalytically at 1123 K in the presence of activated carbon supported Pd catalysts (Samples coded as Pd5 and Pd10 respectively) procured from SRL Chemicals, India. The studies indicated that the Pd10 catalyst has higher catalytic activity and life for methane decomposition reaction at 1123 K and volume hourly space velocity (VHSV) of 1.62 L/hr?g. An average methane conversion of 50 mol % has been obtained for Pd10 catalyst at the above reaction conditions. SEM and TEM-EDXA images of Pd10 catalyst after methane decomposition showed formation of carbon nanofibers. XRD of the above catalyst revealed, moderately crystalline peaks of Pd which may be responsible for the increase in the catalytic life and the formation of carbon nanofibers.     

High temperature iron-based catalysts for hydrogen and nanostructured carbon production by methane decomposition

The production of hydrogen and filamentous carbon by means of methane decomposition was investigated in a fixed-bed reactor using iron-based catalysts. The effect of the textural promoter and the addition of Mo as a dopant affects the catalysts performance substantially: iron catalyst prepared with Al₂O₃ showed slightly higher catalytic performance as compared to those prepared with MgO; Mo addition was found to improve the catalytic performance of the catalyst prepared with MgO, whereas in the catalyst prepared with Al₂O₃ displayed similar or slightly poorer results. Additionally, the influence of the catalyst reduction temperature, the reaction temperature and the space velocity on the hydrogen yield was thoroughly investigated. The study reveals that iron catalysts allow achieving high methane conversions at operating temperatures higher than 800 °C, yielding simultaneously carbon nanofilaments with interesting properties. Thus, at 900 °C reaction temperature and 1 l g⁻¹_cat h⁻¹ space velocity, ca. 93 vol% hydrogen concentration was obtained, which corresponds to a methane conversion of 87%. Additionally, it was found that at temperatures higher than 700 °C, carbon co-product is deposited mainly as multi walled carbon nanotubes. The textural and structural properties of the carbonaceous structures obtained are also presented.     

Hydrogen production by catalytic methane decomposition over yttria doped nickel based catalysts

Catalytic methane decomposition can become a green process for hydrogen production. In the present study, yttria doped nickel based catalysts were investigated for catalytic thermal decomposition of methane. All catalysts were prepared by sol-gel citrate method and structurally characterized with X-ray powder diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Brunauer, Emmet and Teller (BET) surface analysis techniques. Activity tests of synthesized catalysts were performed in a tubular reactor at 500 ml/min total flow rate and in a temperature range between 390 °C and 845 °C. In the non-catalytic reaction, decomposition of methane did not start until 880 °C was reached. In the presence of the catalyst with higher nickel content, methane conversion of 14% was achieved at the temperature of 500 °C. Increasing the reaction temperature led to higher coke formation. Lower nickel content in the catalyst reduced the carbon formation. Consequently, with this type of catalyst methane conversion of 50% has been realized at the temperature of 800 °C.     

COx-free hydrogen production from ammonia decomposition over sepiolite-supported nickel catalysts

Sepiolite, a clay mineral, was utilized as a support for nickel-based catalysts for CO_x-free hydrogen production from ammonia decomposition. First, the physical and chemical properties of sepiolite were changed by calcining it at temperatures varying from 500 to 1000 °C, then nickel was impregnated on these calcined supports and tested for ammonia decomposition at various temperatures following reduction at 650 °C. Results indicated that even though the catalysts contained almost the same amount of nickel, they showed different hydrogen production performance. Detailed characterization of the catalysts before and after reaction illustrated that the support obtained by calcining sepiolite at 700 °C shows good basic properties with a high surface area offering a high degree of nickel dispersion. These properties lead to promising hydrogen production rates which are on par, if not higher, than most of the nickel-based catalysts prepared on supports, which are either not cheap or require tedious preparation procedures.     

Methane catalytic decomposition over ordered mesoporous carbons: A promising route for hydrogen production

Methane decomposition offers an interesting route for the CO₂-free hydrogen production. The use of carbon catalysts, in addition to lowering the reaction temperature, presents a number of advantages, such as low cost, possibility of operating under autocatalytic conditions and feasibility of using the produced carbons in non-energy applications. In this work, a novel class of carbonaceous materials, having an ordered mesoporous structure (CMK-3 and CMK-5), has been checked as catalysts for methane decomposition, the results obtained being compared to those corresponding to a carbon black sample (CB-bp) and two activated carbons, presenting micro- (AC-mic) and mesoporosity (AC-mes), respectively. Ordered mesoporous carbons, and especially CMK-5, possess a remarkable activity and stability for the hydrogen production through that reaction. Under both temperature programmed and isothermal experiments, CMK-5 has shown to be a superior catalyst for methane decomposition than the AC-mic and CB-bp materials. Likewise, the catalytic activity of CMK-5 is superior to that of AC-mes in spite of the presence of mesoporosity and a high surface area in the latter. The remarkable stability of the CMK-5 catalyst is demonstrated by the high amount of carbon deposits that can be formed on this sample. This result has been assigned to the growth of the carbon deposits from methane decomposition towards the outer part of the catalyst particles, avoiding the blockage of the uniform mesopores present in CMK-5. Thus, up to 25 g of carbon deposits have been formed per gram of CMK-5, while the latter still retains a significant catalytic activity.     

Kinetic and autocatalytic effects during the hydrogen production by methane decomposition over carbonaceous catalysts

The reaction kinetics of methane decomposition to yield hydrogen and carbon has been investigated comparing different types of carbonaceous catalysts: two ordered mesoporous carbons (CMK-3 and CMK-5) and two commercial carbon blacks (CB-bp and CB-v). The evolution of the reaction rate along the time has been analyzed concluding that it is governed by different and opposite events: reduction of active sites by carbon deposition, autocatalytic effects of the carbon deposits and pore blockage and diffusional constraints. A relatively simple kinetic model has been developed that fits quite well the experimental reaction rate curves in spite of the complexity of the involved phenomena.     

Microwave-assisted catalytic decomposition of methane over activated carbon for -free hydrogen production

The aim of this work was to combine microwave heating with the use of low-cost granular activated carbon as a catalyst for the production of CO₂-free hydrogen by methane decomposition in a fixed bed quartz-tube flow reactor. In order to compare the results achieved, conventional heating was also applied to the catalytic decomposition reaction of methane over the activated carbon. It was found that methane conversions were higher under microwave conditions than with conventional heating when the temperature measured was lower than or equal to . However, when the temperature was increased, the difference between the conversions under microwave and conventional heating was reduced. The influence of volumetric hourly space velocity (VHSV) on the conversion tests using both microwave and conventional heating was also studied. In general, there is a substantial initial conversion, which declines sharply during the first stages of the reaction but tends to stabilise with time. An increase in the VHSV has a negative effect on CH₄ conversion, and even more so in the case of microwave heating. Nevertheless, the conversions obtained in the microwave device at the beginning of the experiments are, in general, better than the conversions reported in other works which also use a carbonaceous-based catalyst. Additionally, the formation of carbon nanofibres in one of the microwave experiments is also reported.     

Ni–Cu–Zn/MCM-22 catalysts for simultaneous production of hydrogen and multiwall carbon nanotubes via thermo-catalytic decomposition of methane

Pure hydrogen and carbon nanotubes were produced via thermo-catalytic decomposition (TCD) of methane over Ni-loaded MCM-22 catalysts in a vertical fixed-bed reactor. The effect of reaction temperature, gas hourly space velocity (GHSV), Cu/Zn promoter and time on stream on the methane conversion, hydrogen and carbon yields were studied over the synthesized catalysts. The catalytic performance of the 50%Ni–5%Cu–5%Zn/MCM-22 catalyst was found to be highly stable compared to other catalysts. The highest conversion of methane over 50%Ni–5%Cu–5%Zn/MCM-22 catalyst reached 85% with 947% carbon yield. Methane conversion increased on increasing the reaction temperature up to 750 °C and decreased thereafter at higher temperatures. XRD and TEM analysis of the carbon byproduct revealed that graphitic carbon appeared as a major crystalline phase during the reaction. HRTEM results revealed that most of the Ni particles were located on the tip of the carbon nanofibers/nanotubes formed on the spent catalysts. The carbon nanofibres have an average outer diameter of approximately 20–40 nm with an average length of 450–500 nm. Four types of carbon nanofibers were detected and their formation strongly depended on the reaction temperature, time on stream and degree of the interaction between the metallic Ni particle and support. The optimum conditions for CNT production within the experimental ranges were found at a reaction temperature of 750 °C.     

Ni/Ce-MCM-41 mesostructured catalysts for simultaneous production of hydrogen and nanocarbon via methane decomposition

For the first time, simultaneous production of hydrogen and nanocarbon via catalytic decomposition of methane over Ni-loaded mesoporous Ce-MCM-41 catalysts was investigated. The catalytic performance of the Ni/Ce-MCM-41 catalysts is very stable and the reaction activity remained almost unchanged during 1400 min steam on time at temperatures 540, 560 and 580 °C, respectively. The methane conversion level over these catalysts reached 60–75% with a 100% selectivity towards hydrogen. TEM observations revealed that most of the Ni particles located on the tip of the carbon nanofibers/nanotubes in the used catalysts, keeping their exposed surface clean during the test and thus remaining active for continuous reaction without obvious deactivation. Two kinds of carbon materials, graphitic carbon (C_g) as major and amorphous carbon (C_A) as minor were produced in the reaction, as confirmed by XRD analysis and TEM observations. Carbon nanofibers/nanotubes had an average diameter of approximately 30–50 nm and tens micrometers in length, depending on the reaction temperature, reaction time and Ni particle diameter. Four types of carbon nanofibers/nanotubes were detected and their formations greatly depend on the reaction temperature, time on steam and degree of the interaction between the metallic Ni and support. The respective mechanisms of the formation of nanocarbons were postulated and discussed.     

Promotional effect of addition of ceria over yttria-zirconia supported Ni based catalyst system for hydrogen production through dry reforming of methane

The idea of hydrogen production through dry reforming of methane (DRM) is simply outstanding as it is related to decrease the concentration of green-house gases. Yttria-Zirconia supported Nickel catalyst has thermal stability and mobile lattice oxygen but poor oxygen replenishment by CO₂ to the reduced sites. Promotional addition of ceria adds catalytic merit as quick availability of lattice oxygen, good oxygen replenishment by CO₂ to the reduced sites, and reducing bandgap. Herein, 1-3 wt% Ce promoted yttria-zirconia supported Ni catalyst is investigated and characterized by X-ray Diffraction (XRD), Raman, Infrared and UV–vis spectroscopy, CH₄-temperature programmed surface reaction (CH₄-TPSR) and cyclic H₂TPR-CO₂TPD-H₂TPR experiment. The addition of 2 wt% ceria causes lower crystallinity of metallic nickel (than 1 wt% ceria) which facilitates wide range of CH₄ decomposition sites (confirmed by CH₄-TPSR). It additionally cultivates the mixed cerium zirconium oxide for resultant mixed potential and additional oxygen mobility. It ensures about 79% H₂ yield.     

Life cycle assessment of hydrogen production by methane decomposition using carbonaceous catalysts

Methane decomposition to yield hydrogen and carbon (CH₄ ? 2H₂ + C) is one of the cleanest alternatives, free of CO₂ emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.