High-performance Ni–SiO2 for pressurized carbon dioxide reforming of methane

The SiO₂ and Ni–SiO₂ were synthesized via the complex-decomposition method by using different organic acids as the complexing agent and fuel. The Ni-supported SiO₂ from different sources was prepared by the incipient impregnation method. The Ni–SiO₂ and Ni/SiO₂ were comparatively evaluated for carbon dioxide reforming of methane (CDR) under severe conditions of CH₄/CO₂ = 1.0, T = 750 °C, GHSV = 53200 mL g⁻¹ h⁻¹, and P = 0.1–1.0 MPa. The materials were fully characterized by XRD, XPS, TEM, TG-DSC, H₂-TPR, and N₂ adsorption-desorption at −196 °C. It was found that the complexing agent and preparation method of the catalyst significantly affected its surface area, the size and dispersion of Ni, the reduction behavior, and the coking and sintering properties, which determine the activity and stability of the catalyst for CDR. As a result, a highly active and stable Ni–SiO₂ for pressurized CDR was obtained by optimizing the complexing agent.     

One-pot sol–gel synthesis of Ni/TiO2 catalysts for methane decomposition into COx free hydrogen and multiwalled carbon nanotubes

A series of mesoporous Ni/TiO₂ catalysts with different loadings of nickel from 10 to 50 wt% was successfully prepared via a facile one-pot sol–gel route; characterized for its structural, textural and redox properties; and tested for the non-oxidative thermocatalytic decomposition of undiluted methane for the first time. The characterization results reveal the presence of both NiO and NiTiO₃ and metallic nickel as active metal phase in the fresh and reduced catalysts, respectively. Spherical catalyst particles were found to be highly inter-aggregated and to provide a porous texture to the catalyst. All of the prepared catalysts exhibited high catalytic activity and stability for methane decomposition. It is due to the fine dispersion of active nickel nanoparticles on the surface of the TiO₂ support with proper metal-support interaction. Moreover, with increasing nickel loading and reaction temperature, the yields of hydrogen and nanocarbon were found to be significantly increased. A maximum hydrogen yield of 56% and a final carbon yield of 1544% were obtained for the 50% Ni/TiO₂ catalyst at 700 °C with an undiluted methane feed of 150 ml/min for 360 min of time on stream. The catalyst showed high catalyst stability, for a period of 960 min of time on stream and ～24% hydrogen yield was observed at the end of long-term run using the 50% Ni/TiO₂ catalyst. Moreover, irrespective of the nickel loading involved, bulk amount of multiwalled carbon nanotubes were deposited on the surface of the catalyst. XRD and Raman analyses of the spent catalysts showed that the crystallinity of nanocarbon increased with increasing nickel loadings, whereas the graphitization degree remained unaffected, with an I_D/I_G value of 0.88.     

Preparation of activated carbon supported Fe–Al2O3 catalyst and its application for hydrogen production by catalytic methane decomposition

Activated carbon (AC) supported Fe–Al₂O₃ catalysts were prepared by impregnation method and used for catalytic methane decomposition to hydrogen. The XRD and H₂-TPR results showed that ferric nitrate on AC support was directly reduced to Fe metal by the reducibility of carbon at 870 °C. The loading amount and Fe/Al₂O₃ weight ratio affect the textural properties and catalytic methane decomposition. The surface area and pore volume of the catalyst decrease with the loading of Fe and Al₂O₃. Mesopores with size of about 4.5 nm can be formed at the loading of 20–60% and promote the catalytic activity and stability. The mesopores formation is thought that Fe accelerates burning off of carbon wall and enlarging pore sizes during the pretreatment. When the Fe/Al₂O₃ ratio is 16/24 to 24/16 at the loading of 40%, the resultant catalysts show narrow mesopore distributions and relative high methane conversion. Al₂O₃ as the promoter can improve catalytic activity and shorten transitional period of AC supported Fe catalyst.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Combination of CO2 reforming and partial oxidation of methane to produce syngas over Ni/SiO2 and Ni–Al2O3/SiO2 catalysts with different precursors

Ni/SiO₂ and Ni–Al₂O₃/SiO₂ catalysts were prepared by incipient wetness impregnation using citrate and nitrate precursors and tested with a reaction of combination of CO₂ reforming and partial oxidation of methane to produce syngas (H₂/CO). The catalytic activity of Ni/SiO₂ and Ni–Al₂O₃/SiO₂ greatly depended on interaction between NiO and support. NiO strongly interacted with support formed small nickel particles (about 4 nm for NiSC which is abbreviation of Ni/SiO₂ prepared with Nickel citrate precursor) after reduction. The small nickel particles over NiSC catalysts exhibited a good catalytic performance.     

Methane thermocatalytic decomposition to COx-free hydrogen and carbon nanomaterials over Ni–Mn–Ru/Al2O3 catalysts

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO_x-free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al₂O₃ catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N₂ adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al₂O₃ catalyst using Ru(NO)(NO₃)_x(OH)_y(x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/g_cat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al₂O₃ catalysts.     

Kinetics of methane decomposition to COx-free hydrogen and carbon nanofiber over Ni–Cu/MgO catalyst

Kinetic modeling of methane decomposition to CO_x-free hydrogen and carbon nanofiber has been carried out in the temperature range 550–650 °C over Ni–Cu/MgO catalyst from CH₄–H₂ mixtures at atmospheric pressure. Assuming the different mechanisms of the reaction, several kinetic models were derived based on Langmuir–Hinshelwood type. The optimum value of kinetic parameters has been obtained by Genetic Algorithm and statistical analysis has been used for the model discrimination. The suggested kinetic model relates to the mechanism when the dissociative adsorption of methane molecule is the rate-determining stage and the estimated activation energy is 50.4 kJ/mol in agreement with the literature. The catalyst deactivation was found to be dependent on the time, reaction temperature, and partial pressures of methane and hydrogen. Inspection of the behavior of the catalyst activity in relation to time, led to a model of second order for catalyst deactivation.     

Hydrogen production by methane decomposition using bimetallic Ni–Fe catalysts

The catalytic methane decomposition is the leading method for CO_x-free hydrogen and carbon nanomaterial production. In the present study, calcium-silicate based bimetallic Ni–Fe catalysts have been prepared and used to decompose the methane content of the ‘product gas’ obtained in the biomass gasification process for increasing total hydrogen production. Al₂O₃ was used as secondary support on calcium silicate based support material where Ni or Ni–Fe were doped by co-impregnation technique. The activity of catalysts was examined for diluted 6% methane-nitrogen mixture in a tubular reactor at different temperatures between 600 °C and 800 °C under atmospheric pressure, and data were collected using a quadrupole mass spectrometer. Catalysts were characterized by XRD, SEM/EDS, TEM, XPS, ICP-MS, BET, TPR, and TGA techniques. The relation between structural and textural properties of catalysts and their catalytic activity has been investigated. Even though the crystal structure of catalysts had a significant effect on the activity, a direct relation between the BET surface area and the activity was not observed. The methane conversion increased by increasing temperature up to 700 °C. The highest methane conversion has been obtained as 69% at 700 °C with F3 catalyst which has the highest Fe addition, and the addition of Fe improved the stability of catalysts. Moreover, carbon nanotubes with different diameter were formed during methane decomposition reaction, and the addition of Fe increased the formation tendency.     

Ni–Fe–B catalysts for NaBH4 hydrolysis

A series of Ni–Fe–B catalysts with different Fe/(Fe + Ni) molar ratios, used for the hydrolysis of NaBH₄, were prepared by chemical reduction of NiCl₂ and FeCl₃ mixed solution with NaBH₄. The measurements revealed that the catalysts with the molar ratio of Fe/(Fe + Ni) (30%) exhibited the highest catalytic activity, and the optimal reduction temperature is 348 K. In addition, the effects of the concentration of NaBH₄, NaOH and the hydrolytic temperature of NaBH₄ were discussed in detail. The results show that the reaction rate of hydrolysis first rises up and then goes down subsequently with the increase of NaBH₄ concentration, as well as the concentration of NaOH. The activation energy of the hydrolysis for Ni–Fe–B catalysts is fitted to 57 kJ/mol. The maximum value of hydrogen generation is 2910 ml/(min g) at 298 K.     

Characterization and catalytic behavior of hydrotalcite-derived Ni–Al catalysts for methane decomposition

A series of Ni catalysts were prepared from Ni–Al hydrotalcite-like compounds (HTlcs) by varying the Ni/Al molar ratio (1–4) and calcination temperature (773–1173 K) of HTlcs. The catalysts were reduced with H₂ at 1073 K and tested for CH₄ decomposition at 773–923 K on a thermal gravimeter. Various techniques including N₂ physical adsorption, XRD, H₂-TPR, XPS, HAADF-STEM, TEM, and Raman were applied to characterize the catalysts and the as-produced carbon. The characterizations show that calcination of Ni–Al HTlcs leads to Ni(Al)O solid solution and minor NiO and/or NiAl₂O₄ spinel may be formed depending on the Ni/Al ratio and calcination temperature; upon reduction at 1073 K, most nickel species are reduced to metallic Ni. In CH₄ decomposition, carbon yield shows a volcano-type dependence on the Ni content with the optimum Ni/Al ratio equal to 3. On the other hand, carbon yield is affected by the calcination temperature of the Ni₃Al HTlcs to a small extent. Carbon yield is also significantly affected by the reaction temperature, which decreases remarkably with a rise of temperature to 923 K. TEM and Raman indicate that fish-bone carbon nanofibers are formed at 773–823 K, whereas multi-walled carbon nanotubes are formed at 873–923 K.     

Molten salt-promoted Ni–Fe/Al2O3 catalyst for methane decomposition

Bimetallic Ni–Fe/Al₂O₃ catalysts were prepared by the molten salt method, and the catalytic performance of the Ni–Fe/Al₂O₃ catalysts with the KCl–NiCl₂ melt for methane decomposition was evaluated at 800 °C. The catalysts and carbon products were characterized by XRD, SEM/EDS, XRF and Raman spectroscopy techniques. The results show that molten salt-promoted Ni–Fe/Al₂O₃ catalysts exhibit high activity and long-term stability up to 1000 min time on stream without any deactivation. The carbon products over the molten salt-promoted Ni–Fe/Al₂O₃ catalysts are in the form of small granular particles instead of filamentous carbon for the catalyst without molten salt. The promotional effect of the molten salt may attribute to the higher wettability of the Fe–Ni alloy by molten salt, which can prevent the catalysts from deactivation due to carbon encapsulation.     

Iron incorporated Ni–ZrO2 catalysts for electric power generation from methane

On the purpose to perform as functional layer of SOFCs operating on methane fuel, NiFe–ZrO₂ alloy catalysts have been synthesized and investigated for methane partial oxidation reactions. Ni₄Fe₁–ZrO₂ shows catalytic activity comparable to that of Ni–ZrO₂ and superior to other Fe-containing catalysts. In addition, O₂-TPO analysis indicates iron is also prone to coke formation; as a result, most of NiFe–ZrO₂ catalysts do not show improved coking resistance than Ni–ZrO₂. Anyway, Ni₄Fe₁–ZrO₂ (Ni:Fe = 4:1 by weight) prepared by glycine-nitrate process shows somewhat less carbon deposition than the others. However, Raman spectroscopy demonstrates that the addition of Fe does reduce the graphitization degree of the deposited carbon, suggesting the easier elimination of carbon once it is deposited over the catalyst. Ni₄Fe₁–ZrO₂ has an excellent long-term stability for partial oxidation of methane reaction at 850 °C. A solid oxide fuel cell with conventional nickel cermet anode and Ni₄Fe₁–ZrO₂ functional layer is operated on CH₄–O₂ gas mixture to yield a peak power density of 1038 mW cm⁻² at 850 °C, which is comparable to that of hydrogen fuel. In summary, the Ni₄Fe₁–ZrO₂ catalyst is potential catalyst as functional layer for solid-oxide fuel cells operating on methane fuel.     

Stability improvements of Ni/α-Al2O3 catalysts to obtain hydrogen from methane reforming

Ni catalysts supported on commercial α-Al₂O₃ modified by addition of CeO₂ and/or ZrO₂ were prepared in the present work. Since the principal objective was to evaluate the behavior of these systems and the support effect on the stability, methane reforming reactions were studied with steam, carbon dioxide, partial oxidation and mixed reforming. Results show that catalysts supported on Ce–Zr–α-Al₂O₃ composites present better reforming activity and stability noticeably higher than in the case of the reference support. With respect to composites, the presence of mixed oxides of Ce_xZr_1−xO₂ type facilitates the formation of active phases with higher interaction. This fact reduces the deactivation by sintering conferring to the system a higher contribution of adsorbed oxygen species, favoring the deposited carbon elimination. These improvements resulted in being dependent on the Ce:Zr ratio of the composite, thus obtaining more stable catalysts for Ce:Zr = 4:1 ratios.     

SO3 decomposition over CuO–CeO2 based catalysts in the sulfur–iodine cycle for hydrogen production

The effect of several catalyst supports with large specific surface area (such as SiC, Al₂O₃, SiC–Al₂O₃–ball, and SiC–Al₂O₃) on catalytic activity was evaluated in this study. CuO–CeO₂ supported on SiC–Al₂O₃ exhibited high stability and activity, which was considerably close to the thermodynamic equilibrium curve at 625 °C during the stability test for 50 h. The SO₃ decomposition temperature decreased from 750 °C to 625 °C. SiC–Al₂O₃contained numerous micropores and mesopores and had a large specific area, indicating strong adsorption, as determined by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and nitrogen adsorption measurement. X-ray photoelectron spectroscopy (XPS) revealed that the surface of SiC–Al₂O₃consisted of Al₂O₃, SiC, and SiO₂ and that the cerium oxide surface had the largest number of defects. Temperature-programmed reduction (H₂-TPR) results indicated that the cerium–copper oxides on the surface of powdered SiC–Al₂O₃ had the strongest redox potential and that CuO had the lowest reduction temperature.     

Metallic and carbonaceous –based catalysts performance in the solar catalytic decomposition of methane for hydrogen and carbon production

Solar catalytic decomposition of methane (SCDM) was investigated in a solar furnace facility with different catalysts. The aim of this exploratory study was to investigate the potential of the catalytic methane decomposition approach providing the reaction heat via solar energy at different experimental conditions. All experiments conducted pointed out to the simultaneous production of a gas phase composed only by hydrogen and un-reacted methane with a solid product deposited into the catalyst particles varying upon the catalysts used: nanostructured carbons either in form of carbon nanofibers (CNF) or multi-walled carbon nanotubes (MWCNT) were obtained with the metallic catalyst whereas amorphous carbon was produced using a carbonaceous catalyst. The use of catalysts in the solar assisted methane decomposition present some advantages as compared to the high temperature non-catalytic solar methane decomposition route, mainly derived from the use of lower temperatures (600–950 °C): SCDM yields higher reaction rates, provides an enhancement in process efficiency, avoids the formation of other hydrocarbons (100% selectivity to H₂) and increases the quality of the carbonaceous product obtained, when compared to the non-catalytic route.     

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH₃ for hydrogen production was studied using Ni/La₂O₃ catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La₂O₃-450 > 10Ni/La₂O₃-550 > 10Ni/La₂O₃-650 ≈ 10Ni/La₂O₃-750 ≈ 10Ni/La₂O₃-850. The excellent activity (100%) of 10Ni/La₂O₃-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO₂-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH₃ conversion with the 40 wt% Ni formulation demonstrating complete NH₃ conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h⁻¹∙g_cat⁻¹).     

Metallic Ni monolith–Ni/MgAl2O4 dual bed catalysts for the autothermal partial oxidation of methane to synthesis gas

A dual bed catalyst system consisting of a metallic Ni monolith catalyst in the front followed by a supported nickel catalyst Ni/MgAl₂O₄ has been studied for the autothermal partial oxidation of methane to synthesis gas. The effects of bed configuration, reforming bed length, feed temperature and gas hourly space velocity on the reaction as well as the stability are investigated. The results show that the metallic Ni monolith in the front functions as the oxidation catalyst, which prevents the exposure of the reforming catalyst in the back to the very high temperature, while the supported Ni/MgAl₂O₄ in the back functions as the reforming catalyst which further increases the methane conversion by 5%. A typical 5 mmNi monolith–5mmNi/MgAl₂O₄ dual bed catalyst exhibits methane conversion and hydrogen and carbon monoxide selectivities of 85.3%, 91.5% and 93.0%, respectively, under autothermal conditions at a methane to oxygen molar ratio of 2.0 and gas hourly space velocity of 1.0 × 10⁵ h⁻¹. The dual bed catalyst system is also very stable.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Catalytic features of Ni/Ba–Ce0.9–Y0.1 catalyst to produce hydrogen for PCFCs by methane reforming

Methane reforming in steam (SR), auto-thermal (ATR) and partial oxidation (POX) conditions over Ni/Ba–Ce_0.9–Y_0.1 catalyst was investigated in the temperature range 500–700 °C. Catalyst presents a satisfying activity in POX condition only. BCY carrier was not stable in the presence of CO₂ and, irrespective of reaction conditions, it reacts with CO₂ giving rise to the formation of BaCO₃ and CeO₂. The very low activity observed in SR conditions was due to the negative role exerted by water strongly absorbed on catalyst surface, limiting so the accessibility and reduction state of Ni active sites. In POX condition catalyst is active and satisfying H₂ yield can be reached by operating at T = 700 °C. A significant reduction of coke formation was observed by operating in POX at 700 °C. On the contrary, in ATR condition at the same reaction temperature huge amount of filamentous coke was observed.