Catalytic characteristics of various rubber-reinforcing carbon blacks in decomposition of methane for hydrogen production

Carbon black has recently been reported to act as an effective catalyst for methane decomposition and to exhibit stable catalytic behavior despite carbon deposition, and thus it can be used for CO₂-free production of hydrogen from natural gas. In this work, various carbon blacks with different primary particle size were investigated with respect to methane decomposition under atmospheric pressure from 1123 to 1223 K. Catalytic characteristics, such as activity, activation energy and reaction order, were investigated and compared. It was observed that with decreasing primary particle size (or increasing specific surface area), the specific activity increased and the activation energy decreased. The reaction orders for various pelletized, rubber-reinforcing carbon blacks were 0.6–0.7, about the same regardless of the primary particle size, while they were near 1 for fluffy carbon blacks. Fluffy carbon black showed higher activity and activation energy than the pelletized carbon black of the same primary particle size. Changes of the surface morphology during carbon deposition were observed by TEM. Variations of the number of active sites were discussed in regard of the primary particle size, carbon deposition and binder. The presence of different types of active sites was also suggested.     

Radiative transfer in a solar chemical reactor for the co-production of hydrogen and carbon by thermal decomposition of methane

Radiation heat transfer in a solar chemical reactor for the co-production of hydrogen and carbon by thermal decomposition of CH₄ is analyzed by the Monte Carlo ray-tracing method. The solar chemical reactor features a vortex flow of CH₄ confined to a cavity and laden with carbon particles that serve simultaneously as radiant absorbers and nucleation sites for the heterogeneous decomposition reaction. The reactor is treated as a 3D non-isothermal non-gray absorbing-emitting-scattering gas/particle suspension directly exposed to concentrated solar irradiation. The analysis includes coupling to conduction/convection heat transfer and chemical kinetics. Calculated temperature distribution and chemical conversion are compared with the experimentally measured values obtained with a 5 kW prototype reactor tested in a solar furnace.     

Catalytic decomposition of methane and methane/CO2 mixtures to produce synthesis gas and nanostructured carbonaceous material

Methane and CO₂ are the main components of biogas; therefore its direct conversion into a higher added value gas as syn-gas (mixture of CO and H₂) is a very interesting alternative for the valorisation of such renewable resource. In this work, firstly a thermodynamic analysis of the decomposition of CH₄:CO₂ mixtures at different temperatures and CH₄:CO₂ ratios simulating the biogas composition, has been carried out. Secondly, the decomposition of a mixture with a molar ratio of 1:1 has been studied in a fixed-bed reactor by using a Ni/Al₂O₃ based catalyst, at the temperature range in which according to the thermodynamic study, carbon formation is favoured. Results obtained have been compared to those of methane decomposition carried out under the same experimental conditions. Co-feeding of CO₂ and CH₄ avoids catalyst deactivation substantially, allowing to obtain a syn-gas with H₂:CO ratio close to 1. Moreover, the carbon obtained from mixtures of CH₄ and CO₂ is deposited as fishbone carbon nanofibres at 600 °C and ribbon carbon nanofibers at 700 °C, both being materials with high added value which can be used in multiple applications.     

Co-production of hydrogen and multi-wall carbon nanotubes from ethanol decomposition over Fe/Al2O3 catalysts

The co-production of hydrogen and carbon nanotubes (CNTs) from the decomposition of ethanol over Fe/Al₂O₃ at different temperatures and feeding rates of ethanol was investigated systematically. The results indicated that Fe/Al₂O₃ was a quite active catalyst for the co-production of hydrogen and CNTs and that its activity and stability depended strongly on the Fe loading. Among all catalysts tested, 10 mol% Fe/Al₂O₃ was the most effective catalyst based on the ratio of hydrogen production, the total H₂ yield, and the quality of the CNTs formed. The efficiency of hydrogen production from ethanol decomposition over 10 mol% Fe/Al₂O₃ reached a maximum of 80% at 800 °C and the yield of CNTs with well-oriented growth and uniform diameter was 141%. In addition, the reaction of hydrogen and CNTs co-produced from ethanol decomposition was proposed.     

Characterisation and modelling of polypropylene/carbon nanofibre nanocomposites

In this paper we describe the production of a polypropylene (PP)/carbon nanofibre (CNF) nanocomposite, and subsequent characterisation of the structure and properties of the nanocomposite material at various stages of blending. Dispersion of the CNF throughout the matrix PP was monitored by scanning electron microscopy (SEM), and analysis of the lengths of the individual CNF was estimated using dynamic light scattering (DLS). This latter technique enabled a comparison to be made between the measured Young's modulus of the material and that predicted by micromechanical modelling, using the fibre length as determined by DLS. The temperature performance of the nanocomposite material was determined, and this behaviour has also been modelled.     

Carbonaceous materials as catalysts for decomposition of methane

Thermo-catalytic decomposition of methane over different carbonaceous materials was studied by monitoring the mass gain with time. The initial decomposition rates as well as the long-term behaviour of the catalyst (i.e. the carbon mass that the catalyst can accumulate before deactivation occurs) were determined for a wide range of carbon blacks (CB) with different textural properties and surface chemistry, and for a commercial activated carbon (AC). The commercial carbon black BP2000 showed the highest amount of carbon deposited, 6.13 g C_dep/g C_o before deactivation while the higher initial carbon formation rate (r_o) among the different samples tested was obtained for the activated carbon CG Norit (85.9 mg C_dep/g C_o min). The relationship between the characteristics of the carbonaceous materials and their efficiency as catalysts were also evaluated. The amount of carbon deposited until deactivation shows a linear relationship with the total pore volume of the fresh catalysts. A good correlation is also found between the initial reaction rate and the concentration of oxygenated groups desorbed as CO after a temperature-programmed desorption (TPD) experiment.     

Effect of micropores diffusion on kinetics of CH4 decomposition over a wood-derived carbon catalyst

In order to optimise hydrogen production from biomass gasification, catalytic conversion of methane contained in a surrogate biomass syngas (CH₄ 14%; CO 19%; CO₂ 14%; H₂ 16%; H₂O 30%; N₂ 7%) is investigated over a fixed bed of porous wood char as a function of temperature (800–1000 °C) and space time (1.6–6.2 min g L⁻¹). Determination of Thiele modulus evidences a change of kinetic regime from chemically- to diffusion-controlled when the temperature increases; this finding is particularly relevant when porous chars having an average pore width of 1 nm are used as catalysts. Mass diffusion transfers are accounted for by a model introducing an internal effectiveness factor. Knudsen diffusion in micropores is shown to limit the conversion rate of methane per unit mass of catalyst, and explains why such a rate is not proportional to the BET surface area, especially when the latter is higher than typically 300 m²/g. It is concluded that diffusion limitations in micropores should be taken into account, otherwise underestimated activation energy and intrinsic kinetic constant are obtained in some experimental conditions.     

Hydrogen production by catalytic decomposition of methane over carbon catalysts in a fluidized bed

A fluidized bed reactor made of quartz tube with an I.D. of 0.055 m and a height of 1.0 m was employed for the thermocatalytic decomposition of methane to produce CO₂ — free hydrogen. The fluidized bed was used for continuous withdrawal of the carbon products from the reactor. Two kinds of carbon catalysts — activated carbon and carbon black — were employed in order to compare their catalytic activities for the decomposition of methane in the fluidized bed. The thermocatalytic decomposition of methane was carried out in a temperature range of 800–925°C, using a methane gas velocity of 1.0–3.0 U _mf and an operating pressure of 1.0 atm. Distinctive difference was observed in the catalytic activities of two carbon catalysts. The activated carbon catalyst exhibited higher initial activity which decreased significantly with time. However, the carbon black catalyst exhibited somewhat lower initial activity compared to the activated carbon catalyst, but its activity quickly reached a quasi-steady state and was sustained over time. Surfaces of the carbon catalysts before and after the reaction were observed by SEM. The effect of various operating parameters such as the reaction temperature and the gas velocity on the reaction rate was investigated.     

Production of hydrogen and carbon nanotubes from methane decomposition in a two-stage fluidized bed reactor

Methane decomposition over a Ni/Cu/Al₂O₃ catalyst is studied in a two-stage fluidized bed reactor. Low temperature is adopted in the lower stage and high temperature in the upper stage. This allows the fluidized catalysts to decompose methane with high activity in the high temperature condition; then the carbon produced will diffuse effectively to form carbon nanotubes (CNTs) in both low and high temperature regions. Thus the catalytic cycle of carbon production and carbon diffusion in micro scale can be tailored by a macroscopic method, which permits the catalyst to have high activity and high thermal stability even at 1123 K for hydrogen production for long times. Such controlled temperature condition also provides an increased thermal driving force for the nucleation of CNTs and hence favors the graphitization of CNTs, characterized by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and XRD. Multistage operation with different temperatures in a fluidized bed reactor is an effective way to meet the both requirements of hydrogen production and preparation of CNTs with relatively perfect microstructures.     

Fabrication of heterogeneous photocatalysts for insight role of carbon nanofibre in hierarchical WO3/ MoSe2 composite for enhanced photocatalytic hydrogen generation

Mimicking the natural photosynthesis system, artificial photocatalysis facilitates effective utilization of solar energy for environmental sustainability and hydrogen energy production. In this work, the robust and efficient carbon fiber has been successfully incorporated into the interface between WO₃ nanodots and MoSe₂ needles using the facile hydrothermal and solvothermal method. The suitable interfacial contact of heterogeneous photocatalysts plays a significant role in the separation/transfer of interfacial photogenerated electron-hole pairs and hetero-junction. It seems an efficient approach for enhanced photocatalytic performance since the greater area of contact could improve the interfacial rate of charge transfer. The phase structure of prepared WO₃ nanodots changed from the monoclinic to hexagonal phase by the addition of co-catalyst. The experimental results exhibited that carbon fiber played a tri-functional role to boost up the photocatalytic activity over MoSe₂ nanostructures. It's not only act as operative co-catalyst but could also serve as the conductive electron bridges, rather than general cocatalyst, to accumulate electrons and encourage the hydrogen generation kinetics over the WO₃ photocatalysts. More interestingly, the WO₃?1% MoSe₂?1.5% carbon fiber and WO₃?1%MoSe₂ nanocomposites demonstrated the excellent rates of hydrogen evolution 438.7 and 356.2?mmol/g.h, which were 7.6 and 6.17 times higher when compared to that of pure MoSe₂, respectively. Under the visible light excitation, the atomically junction encourages fast electron transfer from nanofibers to MoSe₂ to suppress the rapid recombination kinetics within WO₃ nanodots and extend the lifetime of WO₃ charge carrier's, thereby releasing more photogenerated electrons with higher reducing power for hydrogen evolution. The current work can contribute with new perspectives and mechanistic insight for the design and development of heterogeneous photocatalysts WO₃ based nanostructures using the combination of MoSe₂ and trifunctional carbon nanofibers for environment and energy harvesting applications.     

Bi-metallic catalysts of mesoporous Al2O3 supported on Fe,Ni and Mn for methane decomposition: Effect of activation temperature

Methane decomposition reaction has been studied at three different activation temperatures (500 °C, 800 °C and 950 °C) over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts. On co-impregnation of Ni on Fe/Al₂O₃ the activity of the catalyst was retained even at the high activation temperature at 950 °C and up to 180 min. The Ni promotion enhanced the reducibility of Fe/Al₂O₃ oxides showing higher catalytic activity with a hydrogen yield of 69%. The reactivity of bimetallic Mn and Fe over Al₂O₃ catalyst decreased at 800 °C and 950 °C activation temperatures. Regeneration studies revealed that the catalyst could be effectively recycled up to 9 times. The addition of O₂ (1 ml, 2 ml, 4 ml) in the feed enhanced substantially CH₄ conversion, the yield of hydrogen and the stability of the catalyst.     

NiBa catalysts for CO2-reforming of methane

Ni–Ba catalysts supported on γ-Al₂O₃ for the dry reforming of methane were prepared, characterized and studied under reaction conditions. Ba incorporation inhibits the formation of Ni spinel. All the Ni–Ba catalysts studied are highly active for the CO₂-reforming of methane. However, the Ni–Ba catalyst with high Ba and Ni content was the most active and stable catalyst, due to the presence of accessible Ni particles stabilized by the formation of BaAl₂O₄.     

Investigation on modification of Ru/CNTs catalyst for the generation of COx-free hydrogen from ammonia

The modification of Ru/CNTs (CNTs denotes carbon nanotubes) with rare earth, alkali, and alkaline earth compounds were systematically studied. The loading of modifying agents leads to decrease in pore volume and surface area; but improvement in thermal stability of Ru/CNTs. The size and morphology of Ru particles are not affected by the modification. For the catalysts modified by metal nitrates, activities were found in the order of K–Ru>Na–Ru>Li–Ru>Ce–Ru>Ba–Ru>La–Ru>Ca–Ru>Ru, signifying that within the same groups (K, Na and Li; Ba and Ca), the higher the electronegativity of the promoter, the lower is the NH₃ conversion. Of all the potassium salts adopted, KNO₃, KOH, and KCO₃ show similar promotional effect, suggesting that KOH is the active promoter for catalytic activity. The maximum promotional effect was observed at an atomic ratio of K/Ru=2. The electron-withdrawing groups, F⁻¹, Cl⁻¹, Br⁻¹, SO₄²⁻, and PO₄³⁻ are inhibitors of Ru catalysts. The results of N₂-TPD investigation revealed that the promotional effects of a modifier is a combined result of: (i) enhancing combinative desorption of nitrogen atoms, and (ii) decreasing of the apparent activation energy of the decomposition reaction.     

The simultaneous activation of methane and carbon dioxide to C2 hydrocarbons under pulse corona plasma over La2O3/γ-Al2O3 catalyst

The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C₂ hydrocarbons and by-products were CO and H₂. Methane conversion and the yield of C₂ hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C₂ hydrocarbons decreased. The synergism of La₂O₃/γ-Al₂O₃ and plasma gave methane conversion of 24.9% and C₂ hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C₂ hydrocarbons changed by using Pd-La₂O₃/γ-Al₂O₃ catalyst, the major C₂ product was ethylene.     

Integrated methane decomposition and solid oxide fuel cell for efficient electrical power generation and carbon capture

This work proposes the application of methane decomposition (MD) as a fuel processor to replace methane steam reforming (MSR) for hydrogen production for a methane-fuelled solid oxide fuel cell (SOFC) system. In this work, comparison between the MD–SOFC and the MSR–SOFC was performed in terms of SOFC performances and economic analysis to demonstrate a benefit of using MD as a fuel processor. Energy analysis of SOFC system was evaluated based on thermally self-sufficient condition where no external energy is required for the system. Although the MD–SOFC system offers lower electrical efficiency than that of the MSR–SOFC as solid carbon is generated without being further combusted to generate energy; however, the MD–SOFC stack can be operated at higher power density due to high purity of hydrogen supplied to the fuel cell, resulting in smaller size of the system when compared to the MSR–SOFC. Moreover, the MD–SOFC system is less complicated than that of the MSR–SOFC as the CCS facility is not necessary to be included to reduce CO₂ emission. Economic analysis demonstrated that the SOFC system with MD is more competitive than the conventional system with MSR when considering the valuable by-products of solid carbon even with the low-valued carbon black. It is suggested that the success of this proposed SOFC system with MD relies on the technology development on cogeneration of hydrogen and valuable carbon products.     

Co/Al2O3 catalysts promoted with noble metals for production of hydrogen by methane steam reforming

The effect of noble metal addition on the catalytic properties of Co/Al₂O₃ was evaluated for the steam reforming of methane. Co/Al₂O₃ catalysts were prepared with addition of different noble metals (Pt, Pd, Ru and Ir 0.3 wt.%) by a wetness impregnation method and characterized by UV–vis spectroscopy, temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) of the reduced catalysts. The UV–vis spectra of the samples indicate that, most likely, large amounts of the supported cobalt form Co species in which cobalt is in octahedral and tetrahedral symmetries. No peaks assigned to cobalt species from aluminate were found for the promoted and unpromoted cobalt catalysts. TPO analyses showed that the addition of the noble metals on the Co/Al₂O₃ catalyst leads to a more stable metallic state and less susceptible to the deactivation process during the reforming reaction. The Co/Al₂O₃ promoted with Pt showed higher stability and selectivity for H₂production during the methane steam reforming.     

Catalytic decomposition of methane over a wood char concurrently activated by a pyrolysis gas

The catalytic activity of a wood char towards CH₄ decomposition in a pyrolysis gas was investigated in a fixed bed reactor for maximising hydrogen production from biomass gasification. Wood char is suggested to be the cheapest and greenest catalyst for CH₄ conversion as it is directly produced in the pyrolysis facility. The conversion of methane reaches 70% for a contact time of 120 ms at 1000 °C. Because steam and CO₂ are simultaneously present in the pyrolysis gas, the carbon catalyst is continuously regenerated. Hence the conversion of methane quickly stabilises. Such a phenomenon is shown to be possible through the oxidation of the char by CO₂ and H₂O at high temperature, which prevents the blocking of the mouth of pores by the concurrent pyrolytic carbon deposition. In the experimental conditions, oxygenated functional surface groups are continuously formed (by steam and CO₂ oxidation) and thermally decomposed. The active sites for CH₄ chemisorption and decomposition are suggested to be the unsaturated carbon atoms generated by the evolution of the oxygenated functions at high temperature.     

Improved photocatalytic performance in Bi2S3-ZnSe nanocomposites for hydrogen production

One way to improve the rate of hydrogen production from water-splitting reactions is by the separation of photogenerated carriers. This separation process can be achieved with narrow bandgap semiconductors. ZnSe has a 2.7?eV bandgap, but its photocatalytic activity is very low due to a high recombination rate of the photogenerated carriers. Therefore, a combination of Bi₂S₃ and ZnSe may potentially produce a visible-light-active photocatalyst, utilizing bandgap engineering and the p-n junction effect. ZnSe, Bi₂S₃ and Bi₂S₃-ZnSe nanocomposites were prepared by a hydrothermal method. Bi₂S₃ at different weight percentages (3–15?wt%) was decorated with ZnSe nanoparticles. The hydrogen evolution reaction was conducted in the investigation of ZnSe, Bi₂S₃ and Bi₂S₃-ZnSe photocatalytic efficiency. The results demonstrate that photocatalytic efficiency was highly affected by the Bi₂S₃ weight percent. The optimal weight percent for Bi₂S₃ was 15?wt%, at which the rate of hydrogen evolution was 2600?μmol?g^?1 h^?1 within 240?min in the presence of 1.2?g/L photocatalyst.     

Catalytic combustion of natural gas as the role of on-site heat supply in rapid catalytic CO2---H2O reforming of methane

Development in highly active catalysts for the reforming of methane with H₂O, CO₂, and H₂O+CO₂, and partial oxidation of methane was conducted to produce hydrogen with high reaction rates. A Ni-based three-component catalyst such as Ni---La₂O₃---Ru or Ni---Ce₂O₃---Pt supported on alumina wash-coated ceramic fiber in a plate shape was very suitable for both reactions. The catalyst composition was set at 10 wt.-% Ni, 5.6 wt.-% La₂0₃, and 0.57 wt.-% Ru for example, or molar ratios of these components were 1:0.2:0.03. Even with such a low concentration, the precious metal enhanced the reaction rate markedly, and this synergistic effect was ascribed to the hydrogen spillover effect through the part of precious metal and it resulted in a more reduced surface of the main catalyst component. In particular, a marked enhancement in the reaction rate of CO₂-reforming of methane was observed by the modification of a low concentration Rh to the Ni---Ce₂0₃---Pt catalyst. Very high space-time yields of H₂ (i.e., 8300 mol/1 h in partial oxidation of methane at 600°C with a methane conversion of 37.5%, and 3585 mol/1 h in CO₂reforming of methane at 600°C with a methane conversion of 58%) were realized in those reactions. By combining the catalytic combustion reaction, methane conversion to syngas was markedly enhanced, and even with a very short contact time (10 ms) the conversion of methane increased more than that at 50 ms. The space-time yield of hydrogen amounted to 2,780 mol/1 h with a methane conversion of 90% at 700°C. Furthermore, in a reaction of CH₄---CO₂---H₂O---O₂ on the four components catalyst, an extraordinarily high space-time yield of hydrogen, 12 190 mol/1 h, could be realized under the conditions of very high space velocity (5 ms).     

Progress in low temperature hydrogen production with simultaneous CO2 abatement

A new process has recently been proposed and investigated for low temperature hydrogen production from hydrocarbons with simultaneous CO₂ abatement. It is based on a concept involving simultaneous hydrogen production and CO₂ removal, which uses a stationary catalyst phase and a continuously moving adsorbent phase for in situ removal of CO₂ and ex situ regeneration of adsorbent. This paper summaries the recent developments in the technology using methane (main composition of natual gas) and glycerol (main by-product of biofuels) as the model feedstocks and microsized hydrotalcite as the CO₂ adsorbent. The paper consists of an overview of the new technology, associated fundamental studies including dynamics of adsorption, hydrodynamics, solid hold-up and heat transfer, and chemical reactions. Challenges for further development of the technology and process optimisation are also briefly discussed.