Dual-production of nickel foam supported carbon nanotubes and hydrogen by methane catalytic decomposition

Uniformly dispersed Ni catalysts supported on SiO₂ wash-coated Ni foams were synthesized by the wet impregnation method and successfully applied for methane catalytic decomposition (MCD) at atmospheric pressure. All the prepared catalysts exhibited high catalytic stability. The effects of reaction temperature, space velocity, Ni loading on the MCD performance and the morphologies of the as-prepared CNTs were investigated. The results show that high reaction temperature, low space velocity, and high Ni loading enhanced the hydrogen concentration in the outlet gases. Additionally, SEM and TEM observations indicate that the size (diameter) distribution of the as-prepared CNTs became broader with increasing reaction temperature and Ni loading, respectively. The uniform nickel-foam-supported CNTs and relatively high concentration of hydrogen were obtained simultaneously at 650 °C and at a weight hourly space velocity of 1 L g⁻¹_cat h⁻¹ by the catalyst with 20 wt% Ni. Raman spectroscopy reveals that the uniform MCNTs had a high degree of amorphization.     

In situ generation of nickel/carbon catalysts by partial gasification of coal char and application for methane decomposition

Catalytic methane decomposition (CMD) has a good potential to develop environmentally friendly hydrogen economy, and the catalyst plays a vital role on its applications. In this work, a novel strategy was proposed to fabricate efficient and effective nickel/carbon catalysts for CMD by introducing some additional nickel and K₂CO₃ into partial steam gasification of coal char. The gasification process is conducive to in situ synthesize nickel crystallites with high reduction degree (the value of Ni⁰/(Ni⁰+Ni²⁺) up to 76%–81%) on the catalyst surface, and it is competent for co-generation of hydrogen-rich gas and nickel/carbon hybrids with large surface areas (around 86–149 m²/g after washing off the residual potassium salts). The nickel/carbon hybrid as the gasification residue could serve as the catalyst for CMD, showing high and stable methane conversion (up to 80%–87%) at 850 °C. It is observed that co-production of hydrogen and filamentous carbons can be achieved in the 600-min process of CMD, thanks to the positive effect of K₂CO₃ on formation and activity improvement of the nickel/carbon catalyst.     

Tailored hydrotalcite-based Mg-Ni-Al catalyst for hydrogen production via methane decomposition: Effect of nickel concentration and spinel-like structures

Thrive for the CO_x-free hydrogen production via methane decomposition has gained much interest owing to its feasibility and environmental friendliness. Herein, ahydrotalcite based Nickel catalyst was synthesized via co-precipitation method by varying the amount of Nickel concentration and tested for methane decomposition reaction in a fixed bed reactor. In addition, the effect of calcination temperature in the development of the spinel-like structure of as-developed catalyst was comprehensively discussed. It was found that the hydrotalcite based Nickel catalyst prepared at 40% Nickel concentration has the highest performance of above 80% conversion for 7 h of methane decomposition which was owing to its effective diffusion of carbon particles and its spinel-like structure, evidently from the XRD and FESEM analysis. The profound performance monitored here was attributed to the formation of carbon nanofibers (CNFs) on the surface of the catalyst which levitates the active Ni^ospecies on its tips, results in more available active sites for the chemisorptions of the methane molecules. Nevertheless, the excessive of Nickel concentration leads to the detrimental methane decomposition performance, hencepromotes the formation of large particle size and successive development of bulk NiO phases during the reduction process, consequently abnegate the overall methane decomposition reaction. The aforementionedfindingsshow that the spinel-like structure is the key factor in the growth of long uniform CNFs and elevation of active sites on the fibre tips.     

Production of hydrogen from methane decomposition using nanosized carbon black as catalyst in a fluidized-bed reactor

Nanosized carbon black (NCB) was employed as catalyst for methane decomposition to produce hydrogen in a fluidized-bed reactor. The carbon atoms of the surface defects of NCB act as active sites in this reaction. The activity of NCB is improved after more defects in the surface of NCB are generated after the treatment in nitric acid and calcination in nitrogen gas. The loading of small amounts of Ni and Co can obviously increase the initial activity of NCB, however, their activity deceases very quickly after the reaction begins due to the encapsulation of the corresponding metal particles inside amorphous carbon produced from methane decomposition. After reaction, the formed carbon was found to grow into carbon flakes and cover the surface of NCB. The investigation with TEM and SEM indicates that they may form from a new carbon crystallite, not build upon the existing hexagon layer in the surface defects of NCB.     

Study of the deactivation mechanism of carbon blacks used in methane decomposition

Carbon blacks have recently gained attention as suitable catalysts for the CO_x-free hydrogen production by thermo-catalytic decomposition of methane (TCD) because of their stability and efficiency. In the present work, several commercial carbon blacks were studied as catalysts for the TCD of methane by varying the temperature and the methane space velocity. The BP2000 carbon black sample, which showed the highest activity in methane decomposition per mass of catalyst, was studied more thoroughly. Despite BP2000 exhibiting stable activity in the TCD of methane during several hours on stream, a long duration run carried out at 950 °C revealed that it finally became deactivated. The changes in the physicochemical properties (textural properties, surface chemistry and crystallinity) of the BP2000 sample at different stages of the catalyst lifetime were measured, and the main results obtained are presented here. The paper also discusses the potential of the production of a wide range of hydrogen–methane mixtures, which can be directly fed to an internal combustion engine, by means of TCD with carbonaceous catalysts.     

Cathodic hydrogen recovery and methane conversion using Pt coating 3D nickel foam instead of Pt-carbon cloth in microbial electrolysis cells

A cheap but efficient electrode material is required to explore and apply to microbial electrolysis cell (MEC) with high hydrogen evolution reaction (HER) efficiency and low over-potential loss. Pt coating carbon cloth (Pt/CC) was one of the most efficient catalyst for hydrogen production in current lab research, but it is difficult to be applied in practice because of expensive cost and week strength from the base material (carbon cloth). Thus a cheap and effective supporting base material is worth to evaluate on hydrogen recovery and loss to methane for the MEC future application. In this study, nickel foam (NF) was used as an alternative to expensive carbon cloth, and NF coated with Pt (Pt/NF) was applied and evaluated through catalytic performance, hydrogen production efficiency and economic assessment in comparison with Pt/CC. The Pt/NF showed a competitive HER performance to Pt/CC. The highest hydrogen yield was reached 0.71 ± 0.03 m³/m³·d by Pt/NF under 0.8 V, which exceeded 6%, 10% over Pt/CC and NF, respectively. The energy efficiency relative to the electrical energy input was 127% for Pt/NF and 123%, 110% for Pt/CC and NF, respectively. For fifteen cycles, the methane content of Pt/NF got the lowest due to its higher hydrogen evolution activity. The economic analysis showed a 56% reduction when using Pt/NF as supporting base in place of carbon cloth to achieve similar performance. The linear sweep voltammetry (LSV) showed the possibility to further reduce input voltage in a long term operation.     

Decomposition of methane in the presence of ethanol over activated carbon catalyst

The interest in hydrogen as a potential fuel of the future has stimulated development of new technologies of its production. The main method of hydrogen production is based on the process of steam reforming of methane, but recently increasing attention has been paid to the catalytic decomposition of methane (CDM) whose advantage is its pro-ecological character. This reaction, besides hydrogen, produces also catalytically low-active carbonaceous deposit which settles on the surface of the catalyst and leads to its deactivation. The study reported is an attempt at suppressing the catalyst deactivation by developing a method leading to formation of carbonaceous deposit potentially active in CDM process. For this purpose, it was proposed that the reaction system would contain methane and ethanol. Simultaneous decomposition of these two substances was performed in parallel at three temperatures of 750, 850 or 950 °C. The catalyst was activated carbon obtained from the hazelnut shells. The addition of ethanol was found to have a positive effect on the course of CDM, leading to an increase in the amount of hydrogen produced and to stabilisation of the catalyst activity at a high level.     

Hydrogen production by methane decomposition over Co-Al mixed oxides derived from hydrotalcites: Effect of the catalyst activation with H2 or CH4

This study examines the influence of catalyst activation for methane decomposition over Co-Al mixed oxides derived from hydrotalcites. Samples were prepared by coprecipitation and characterized by surface area measurements and temperature-programmed reduction. Spent catalysts and carbon produced in the reaction were characterized by X-ray diffractometry, temperature-programmed oxidation and scanning electron microscopy. Activity runs using previously reduced samples with H₂ or activated under CH₄ flow were carried out in a fixed-bed reactor between 500 and 750 °C using in-line gas chromatography analysis. The specific surface area decreases as the Co/Al ratio increases, which is related to the increased Co₃O₄ phase rather than Co-Al mixed oxides. The TPR results indicate the reduction of four types of Co species: Co³⁺ and Co²⁺ species from Co₃O₄, and Co from inverse spinel (Co₂AlO₄) and normal spinel (CoAl₂O₄). Reduction with hydrogen at 750 °C was very severe. Samples reduced with H₂ showed large Co° crystallites, which increased with the Co/Al ratio. Co-Al catalyst activation under methane flow leads to lower crystallite size and higher thermal stability for hydrogen production by methane decomposition.     

Hierarchical porous carbon catalyst for simultaneous preparation of hydrogen and fibrous carbon by catalytic methane decomposition

Direct coal liquefaction residue was used as the precursor for preparing hierarchical micro-/macro-mesoporous carbon by KOH activation with addition of Al₂O₃, and the resultant carbon AlRC was used as the catalyst for catalytic methane decomposition. The results indicate that the carbon AlRC shows excellent methane conversion, up to 61% after 10 h. Besides hydrogen production from methane decomposition, fibrous carbons were formed on the AlRC catalyst, which is different from other carbon catalysts. The investigations of the formation and growth of the fibrous carbon on the carbon catalyst and its catalytic performance indicated that the formed fibrous carbon contribute to the high methane conversion of AlRC catalyst.     

Effects of reaction conditions on hydrogen production and carbon nanofiber properties generated by methane decomposition in a fixed bed reactor using a NiCuAl catalyst

In this paper, the results obtained in the catalytic decomposition of methane in a fixed bed reactor using a NiCuAl catalyst prepared by the fusion method are presented. The influences of reaction temperature and space velocity on hydrogen concentration in the outlet gases, as well as on the properties of the carbon produced, have been investigated. Reaction temperature and the space velocity both increase the reaction rate of methane decomposition, but also cause an increase in the rate of catalyst deactivation. Under the operating conditions used, the carbon product is mainly deposited as nanofibers with textural properties highly correlated with the degree of crystallinity.     

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.     

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H₂ addition on CH₄ decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H₂ to CH₄ changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H₂ flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H₂, and when the H₂ flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H₂ to CH₄ and the catalyst deactivation is restrained. Filamentous carbon is obtained when H₂ is introduced into CH₄ reaction gas compared with the agglomerate carbon without H₂ addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.     

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.     

Effect of coexistence of H2S on production of hydrogen and solid carbon by methane decomposition using Fe catalyst

Biogas derived from livestock manure and food residue contains CO₂ and H₂S as well as methane. The effect of CO₂ and H₂S coexistence on the production of hydrogen and solid carbon by methane decomposition over iron oxide catalysts was investigated. The catalytic activity for methane decomposition was decreased by the coexistence of H₂S. Moreover, the activity decrease was aggravated by the coexistence of CO₂ as well as H₂S, and higher temperature was required to mitigate the activity decrease by the coexistence of CO₂. By increasing the amount of catalyst, the upstream catalyst was preferentially poisoned, but the downstream catalyst developed catalytic activity thanks to its sacrifice. With 2 g of catalyst, the maximum conversion of pure methane was about 85% at 840 °C, but it was slightly less than 80% in the presence of H₂S or H₂S + CO₂. When the catalyst amount was increased to 4 g, the conversion of pure methane was about 90% at 800 °C, but 84% in the presence of H₂S and 80% in the presence of H₂S + CO₂. The poisoning by H₂S was irreversible at low temperatures but became reversible at higher temperatures. Since H₂S is adsorbed by the deposited carbon, the procedure for further removal of H₂S may be omitted. The coexistence of H₂S also affected the shape of the deposited carbon. Although carbon-based catalysts are known to be effective for methane decomposition in the presence of H₂S, iron oxide catalysts have the advantage of superior methane conversion at low temperatures. By flowing methane with CO₂ and H₂S from the downstream side after the reaction flowing from the upstream side for a certain period of time, the catalytic lifetime was drastically extended and the amount of hydrogen and solid carbon produced was dramatically increased, compared to the case of flowing from upstream all the way.     

Influence of ethylene on carbon-catalysed decomposition of methane

Catalytic decomposition of methane is a much promising pro-ecological method of hydrogen production. However, the drawback of this method is fast deactivation of the catalyst by deposition of a low-active methane-originated carbon on its surface. In this study an attempt has been made to reduce the process of catalyst deactivation by adding admixture of ethylene to methane directed to the reactor. The study has been performed on the activated carbon obtained by Na₂CO₃ activation of pine wood and two commercial types of activated carbons. All the carbon types have been subjected to ultimate analysis, determination of the surface area and pore structure. It has been shown that ethylene also forms a carbonaceous deposit but in contrast to the methane-originated deposit the ethylene-originated one shows good catalytic properties in the reaction of methane decomposition. The addition of 20% ethylene seems to be optimum for ensuring high yield of hydrogen for a long time. The ethylene admixture addition is the more effective the higher the temperature of the process.     

Activity of NiCuAl catalyst in methane decomposition studied using a thermobalance and the structural changes in the Ni and the deposited carbon

Activity measurements of a NiCuAl catalyst for the thermal decomposition of methane have been carried out in a thermobalance at different operating temperatures and partial pressures of methane and hydrogen. The thermobalance allows, by gravimetry, a continuous record of the evolution of the deposited carbon during and at the end of the test and the extraction of a sufficient amount of homogenous sample to study the involved structural changes in Ni and the structural properties of the deposited carbon by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of the operating temperature, mainly derived from thermal sintering, on Ni particles and on the deposited carbon is highly significant. The effect of methane as a reactant and hydrogen as a reaction product is mostly derived from its influence on the reaction rate. Additionally, methane and hydrogen reduce the effect of thermal sintering on Ni lowering the surface energy by chemisorption. The study also shows that the deposited carbon on the Ni leading face probably diffuses to the Ni trailing face superficially, and not through bulk Ni as assumed by the present kinetic models.     

Facile fabrication of comb-like porous NiCo2O4 nanoneedles on Ni foam as an advanced electrode for high-performance supercapacitor

It is very desirable to develop the high-performance supercapacitors to meet the rapidly growing demands for energy-autonomous operation and miniaturization of devices. Herein, comb-like porous NiCo₂O₄ nanoneedles on the three-dimension (3D) nickel foam (NF) have been successfully synthesized through a facile pulsed laser ablation (PLA) approach without any post-treatments and surfactant (denoted as NiCo₂O₄-PLA). The influence of working solution during the fabricated process on the properties of NiCo₂O₄-PLA has been demonstrated in detail in terms of the crystalline structure, specific surface area, morphology, and electrochemical performance. Benefiting from the large specific surface (261.4 m² g⁻¹), abundant pores, and highly conductive scaffold, the NiCo₂O₄-PLA binder-free electrode exhibits an outstanding specific capacitance (1650 F g⁻¹ at a current density of 1 A g⁻¹) and eminent cycling performance (91.78% retention after a 12,000-cycle test at a current density of 10 A g⁻¹) compared with the control samples. The assembled asymmetric device (NiCo₂O₄-PLA//AC-ASCs) delivers the high specific capacitance of 126.9 F g⁻¹ at the current density of 1 A g⁻¹, the large energy density of 56.7 Wh kg⁻¹ at a power density of 756 W kg⁻¹, and the low internal resistance. The attractive results strongly prove that it is an ideal candidate for advanced supercapacitor application.