Solar-driven novel methane reforming with carbon looping for hydrogen production

As a renewable source, solar energy plays an important role in meeting energy demand for human beings and in relieving global warming. In this paper, the concentrated solar heat is utilized to drive the high-endothermic methane reforming with carbon looping. In so doing, the process increases the utilization of CO₂ and reduces the carbon emissions as well as saves the extra fuel consumption for combustion, leading to high efficiency of energy utilization. By optimizing this proposed system, the energy efficiency can reach approximate 67.13% with simultaneously reducing CO₂ emissions by 34.98% compared with SMR process. Exergy analysis is used to assess the location of irreversibility within process. The maximal part of exergy destroyer was localized in reformer with a contribution of 68%. In addition, the effects of hourly variation of direct normal irradiation on thermodynamic performance and methane conversion on the four typical days (spring equinox, summer solstice, autumn equinox, winter solstice) were analyzed in this work. The current work might be insightful for solar-hydrogen production field.     

Dry reforming of methane for hydrogen production over NiCo catalysts: Effect of NbZr promoters

Ni/Al₂O₃, NiCo/Al₂O₃MgO and NiCo/Al₂O₃MgO/NbZr nanocatalysts were prepared by the sol-gel technique with citric acid and tested in the dry reforming of methane (DRM). In this paper, the effects of Nb and Zr addition as promoters in Al₂O₃MgO supported catalysts on the physicochemical characteristics and the reaction performance in the DRM were investigated. The NbZr promoters are expected to enhance the activity and performance of the catalyst due to its high thermal stability and also improvement in the metal dispersion of the catalyst. The catalysts samples were characterized by FESEM, BET, XRD, TEM, H₂-TPR and CO₂-TPD techniques. FESEM results demonstrated that NiCo/Al₂O₃MgO/NbZr has more uniform and well-dispersion of metal than NiCo/Al₂O₃MgO. The BET results unravel that the addition of NbZr promoters increase the surface area of the synthesized catalyst due to the high surface area of the promoters. There is a formation of MgAl₂O₄ spinel-type solid solution proved by the XRD and CO₂-TPD analysis due to the interaction between alumina lattice and magnesium metal which has high resistance to carbon formation. The DRM reaction is performed in the tubular furnace reactor at 1073.15 K, 1 atm and a CH₄/CO₂ ratio of unity. The sol-gelled NiCo/Al₂O₃MgO/NbZr was found to be the most proper choice for DRM which illustrates much higher conversion (86.96% for CH₄ conversion and 87.84% for CO₂ conversion) compared to the other catalysts. This is due to the strong interaction between active metals and supports, resistance to coke formation and higher stability in DRM reaction.     

Boosted methane dry reforming for hydrogen generation on cobalt catalyst with small cerium dosage

Metal-support interface influences the catalytic activity and physical properties of heterocatalysts dramatically. Herein, the effect of cerium on material properties and catalytic activity of cobalt over gamma-alumina applied in dry reforming of methane (DRM) was investigated. The dispersion of cobalt over gamma-alumina was noticeably improved with low cerium dosages ranging from 0.1 to 0.5 wt%. In addition, the presence of Ce promoter on catalyst surface led to an enhancement in reducibility of cobalt oxide to cobalt metal in the catalyst activation. Using CO₂-temperature programmed desorption technique, the catalyst basicity was found to increase proportionally with cerium loading. At an optimal dosage of 0.3–0.5 wt%, the cerium promoted cobalt supported on gamma catalyst displayed outstanding performance in DRM with noticeable conversion improvements up to 11% in both methane and carbon dioxide.     

Improvements in hydrogen production from methane dry reforming on filament-shaped mesoporous alumina-supported cobalt nanocatalyst

The mesoporous gamma-alumina (γ-Al₂O₃) synthesized via evaporation-induced self-assembly method (EISA) using inorganic salt, Al(NO₃)₃·9H₂O precursor and water-ethanol solvent mixture was implemented as a support for Co catalyst in methane dry reforming at 973–1073 K under 1 atm. The γ-Al₂O₃ support possessed filament-shaped morphology with surface area of 173.4 m² g^?1 and cobalt nanoparticles were successfully dispersed on support with small crystallite size of 7.8 nm. The stability of 10%Co/Al₂O₃ was evident for CH₄ and CO₂ conversions at 1023 and 1073 K. CH₄ conversion could reach to 76.2% while 81.6% was observed for CO₂ conversion at 1073 K. Although graphitic and amorphous carbons were unavoidably formed on used catalyst, 10%Co/Al₂O₃ exhibited an outstanding performance comparable to noble metals with the desired ratio of H₂/CO for downstream Fischer-Tropsch process.     

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, ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ and exhibited an optimum at ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO₂ conversion was observed with growing ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$. 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.     

Effect of base promoter on activity of MCM-41-supported nickel catalyst for hydrogen production via dry reforming of methane

Dry reforming of methane (DRM) is considered a promising reforming technology that converts natural gas in the Natuna Sea into synthesis gas, which can be further utilized to produce beneficial chemicals such as olefins, alcohols, and liquid hydrocarbons. However, the challenges in commercializing the DRM process are carbon deposition and sintering of the catalyst at high temperatures, because of which the catalyst is easily deactivated. This study aimed to test the activity and stability of MCM-41-based catalysts for the DRM; determine the effect of promoter type on the activity and stability of MCM-41-based catalysts; and determine the effect of base promoter addition on the amount of carbon deposition. MCM-41-based catalysts were synthesized using incipient wetness impregnation method. XRD, N₂ Physisorption, H₂-TPR, CO₂-TPD, and TGA analysis were conducted to determine the physicochemical properties of the catalysts. The catalysts activity was tested in a fixed-bed reactor, under atmospheric pressure at 700 °C. Overall, all catalysts exhibited good stability for 240 min. Moreover, catalysts with Mg and Ca promoters showed the highest CH₄ and CO₂ conversion among all catalysts. Ni–Mg/MCM-41 catalyst yielded 72% CH₄ conversion and 54% CO₂ conversion, meanwhile Ni–Ca/MCM-41 yielded 69% CH₄ conversion and 55% CO₂ conversion. Furthermore, MCM-41-based catalysts with base promoter produced small amount of carbon deposition.     

Ni/MgAl2O4 catalyst for low-temperature oxidative dry methane reforming with CO2

Oxidative dry reforming of methane has been performed for 100 h on stream using Ni supported on MgAl₂O₄ spinel at different loadings at 500–700 °C, CO₂/CH₄ molar ratio of 0.76, and variable O₂/CH₄ molar ratio (0.12–0.47). Syngas with an H₂/CO ratio of 1.5–2.1 has been produced by manipulating reforming feed composition and temperature. The developed oxidative dry reforming process allowed high CH₄ conversion at all conditions, while CO₂ conversion decreased significantly with the lowering of the reforming temperature and increasing O₂ concentration. When considering both greenhouse gas conversions and H₂/CO ratio enhancement, the optimal reforming condition should be assigned to 550 °C and O₂/CH₄ molar ratio of 0.47, which delivered syngas with H₂/CO ratio of 1.5. Coke-free operation was also achieved, due to the combustion of surface carbon species by oxygen. The 3.4 wt% Ni/MgAl₂O₄ catalyst with a mean Ni nanoparticle diameter of 9.8 nm showed stable performance during oxidative dry reforming for 100 h on stream without deactivation by sintering or coke deposition. The superior activity and stability of MgAl₂O₄ supported Ni catalyst shown during reaction trials is consistent with characterization results from XRD, TPR, STEM, HR-STEM, XPS, and CHNS analysis.     

IR spectroscopic measurement of hydrogen production kinetics in methane dry reforming

Dry reforming of methane (DRM) is a reaction that converts two greenhouse gases, CH₄ and CO₂, to syngas (H₂ + CO). Gas chromatography (GC) is almost exclusively used to evaluate catalyst performance. In order to measure the hydrogen production rate with GC, an inert gas with a constant flow rate is usually fed into the system as an internal standard. In this work, an IR spectroscopy-based method is used to achieve the same technical goal with much higher time resolution and much smaller measurement errors. IR measures the molar fractions of CH₄, CO₂, CO and H₂O in the reaction effluent. By applying general mass balance principle and the relevant reaction stoichiometries, H₂ production rate is successfully measured without an internal standard. The results are quite close to those obtained by GC with much higher time resolution, making it possible to observe fast reaction kinetics.     

Effect of oxygen addition on catalytic performance of Ni/SiO2·MgO toward carbon dioxide reforming of methane under periodic operation

This work investigates the catalytic performance of an industrial steam reforming Ni/SiO₂·MgO catalyst toward dry reforming of CH₄ under periodic operation. The effects of cracking/regeneration temperatures and O₂ addition during regeneration on the catalyst stability and activity were determined and various characterizations i.e. BET, SEM, XRD, and TPO were employed to relate the catalyst performance with its physical properties. It was found that, without O₂ addition, the catalyst showed good stability at 650 °C but observed high deactivation at 750 °C due to the formation of encapsulating carbon. The addition of O₂ along with CO₂ can eliminate all deactivation at 750 °C and no significant loss of catalyst activity was observed for at least 12 cracking/regeneration cycles. The optimal performance for periodic operation was found at the condition with 5 min of the cracking step followed by 5 min of the regeneration step at 750 °C with CO₂/O₂ ratio of 7/3.     

Synthesis, characterization and catalytic performances of Ce-SBA-15 supported nickel catalysts for methane dry reforming to hydrogen and syngas

A series of Ce-incorporated SBA-15 mesoporous materials were synthesized through direct hydrothermal synthesis method and further impregnated with 12 wt.% Ni. The samples were characterized by ICP-AES, XRD, N₂ physisorption, XPS, TPR, H₂ chemisorption, TGA, temperature-programmed hydrogenation (TPH) and TEM measurements. The low-angle XRD and N₂ physisorption results showed the Ce successfully incorporated into the framework of SBA-15. The catalytic properties of these catalysts were investigated in methane reforming with CO₂. The Ce/Si molar ratio had a significant influence on the catalytic performance. The highest catalytic activity and long-term stability were obtained over the Ni/Ce-SBA-15 (Ce/Si = 0.04) sample. The improved catalytic behavior could be attributed to the cerium impact in the framework of SBA-15, where cerium promoted the dispersion of nano-sized Ni species and inhibited the carbon formation. In comparison with the effect of CeO₂ crystallites in SBA-15, cerium in the framework of SBA-15 promoted the formation of the nickel metallic particles with smaller size. The XRD and TGA results exhibited that carbon deposition was responsible for activity loss of Ni/SBA-15 and Ni/Ce-SBA-15 (Ce/Si = 0.06) catalysts. TEM results showed that the hexagonal mesopores of SBA-15 were still kept intact after reaction and the pore walls of SBA-15 prevented the aggregation of nickel.     

Simulative optimization of catalyst configuration for biogas dry reforming

Biogas dry reforming is a promising technology for converting biomass into high-value products and reducing greenhouse gas emissions. Recent improvements to biogas reforming have mainly focused on the preparation of functional catalysts; however, little attention has been paid to the effects of catalyst configuration in plug flow reactors. In this study, a Ni/MgO catalyst for biogas reforming was synthesized via the wet impregnation method. Parameters were optimized using an experimental rig and then simulations were performed using an Aspen HYSYS reaction simulator. We simulated loading the same amount of catalyst into 1, 2, 3, or 10 zones inside the reactor and compared performance parameters, including H₂ yield, CO yield, CH₄ conversion, and CO₂ conversion. The results of simulations showed that a 2-zone configuration with a catalyst ratio of 1:4 was optimal, with 88.2% H₂ yield, 83.5% CO yield, 96.4% CH₄ conversion, and 91.7% CO₂ conversion. Catalyst zone number, catalyst distribution, and catalyst zone position all had significant effects on catalytic behavior. The findings of this study provide new insights into the processes of biogas reforming and other heterogeneous catalysis reactions.     

A review on reforming bio-ethanol for hydrogen production

Bio-ethanol is a prosperous renewable energy carrier mainly produced from biomass fermentation. Reforming of bio-ethanol provides a promising method for hydrogen production from renewable resources. Besides operating conditions, the use of catalysts plays a crucial role in hydrogen production through ethanol reforming. Rh and Ni are so far the best and the most commonly used catalysts for ethanol steam reforming towards hydrogen production. The selection of proper support for catalyst and the methods of catalyst preparation significantly affect the activity of catalysts. In terms of hydrogen production and long-term stability, MgO, ZnO, _CeO2${\mathrm{CeO}}_2$, and _La2O3${\mathrm{La}}_2{\mathrm{O}}_3$ are suitable supports for Rh and Ni due to their basic characteristics, which favor ethanol dehydrogenation but inhibit dehydration. As Rh and Ni are inactive for water gas shift reaction (WGSR), the development of bimetallic catalysts, alloy catalysts, and double-bed reactors is promising to enhance hydrogen production and long-term catalyst stability. Autothermal reforming of bio-ethanol has the advantages of lesser external heat input and long-term stability. Its overall efficiency needs to be further enhanced, as part of the ethanol feedstock is used to provide low-grade thermal energy. Development of millisecond-contact time reactor provides a low-cost and effective way to reform bio-ethanol and hydrocarbons for fuel upgrading. Despite its early R&D stage, bio-ethanol reforming for hydrogen production shows promises for its future fuel cell applications.     

Enhanced catalytic activity of methane dry reforming by the confinement of Ni nanoparticles into mesoporous silica

Nickel nanoparticles were immobilized in mesoporous silica by a polyethyleneimine (PEI)-aided route and their catalytic performance was evaluated in dry reforming of methane. NH₂ terminal groups of PEI strongly interacted with surface silanol groups of mesoporous silica and then, Ni-chelating PEIs were highly dispersed inside its ordered channel. The steric hindrance of PEI with a long hydrocarbon chain also restricted the aggregation of Ni-PEI complexes anchored in the porous framework. The catalysts prepared by the PEI-aided route showed the stable activity at 750 °C for 40 h because Ni particles were confined inside the pore and therefore, cannot be sintered more than the pore diameter of their parent support. The carbon deposit is much smaller in the catalyst prepared by the PEI-aided route than the reference catalyst synthesized via a traditional impregnation method, suggesting that the sintering of Ni particles is a main contribution to the generation of graphitic carbon.     

Improvement of steam methane reforming via in-situ CO2 sorption over a nickel-calcium composite catalyst

Optimization of steam methane reforming (SMR) reaction by CO₂ sorption enhancement was investigated. In this study, the sorption-enhanced steam methane reforming reaction (SESMR) was conducted to maximize hydrogen production via suitable adjustments in the operating conditions of the reaction, which include the molar ratio of steam to CH₄, space velocity, and temperature. The reforming catalysts were prepared by a physical mixture of 20 wt% Ni/Al₂O₃ and CaO. The results reveal that there are significant differences in CH₄ conversion between the SMR and the SESMR from 18% to 108%; this conversion strongly depended on the reaction conditions. High-purity H₂ products (98.9%) with <0.1 ppmv CO were obtained by SESMR under the suitable conditions of 2600 cm³/g/h, steam/CH₄ molar ratio of 4 and 823 K. This implies that the high-quality H₂ produced through the SESMR process could be directly used for the proton-exchange membrane fuel cell.     

Experimental studies on hydrogen generation by methane autothermal reforming over nickel-based catalyst

This paper presents the experimental studies on the hydrogen generation by methane autothermal reforming method. An experimental system was built in-house for this study. The temperature profile along the axis of the reformer was measured and discussed. The peak temperature of the reformer appeared in the part of 1/4 to 2/4 of the reformer length from inlet to outlet. The maximum hydrogen yield, hydrogen mole numbers generated per mole of methane consumed of 2.71, was achieved at molar oxygen-to-carbon ratio of 1.68 and molar steam-to-carbon ratio of 2.5. Under this condition, the energy conversion efficiency of the reforming process reached 81.4% based on the lower heating values.     

Molecular simulation of methane steam reforming reaction for hydrogen production

By means of advanced techniques of molecular simulations, we have studied the chemical equilibrium of methane steam reforming reaction. We have computed the conversion of CH₄, yield and selectivity of H₂, etc. in the gas phase by reactive canonical Monte Carlo (RCMC) method and compared with those from Gibbs energy of formation method. The consistency of the two methods encourages us to use the RCMC method to optimize the operating conditions. We found that under low pressure 0.1 MPa, high temperature 1073 K and high water-gas ratio H₂O/CH₄ = 5, the CH₄ conversion, H₂ yield and selectivity were the highest, with the values of 99.93%, 3.51 mol/molCH₄ and 99.98%, respectively. In addition, the pore size of activated carbon significantly affects the chemical equilibrium composition in the pores. Since low pressure and high temperature are not conducive to the adsorption of reactive components by activated carbon, the chemical balance in the pores cannot be improved. At 773 K, 3.0 MPa and pore width is less than 2 nm, the pores are mainly occupied by CH₄ and H₂O reactant molecules. Further increasing the temperature can increase the H₂ content in the pores, but the adsorption capacity in the pores will decrease. We use activated carbon to adsorb and separate CO and H₂ (CO:H₂ = 1:3), the main components after the gas phase reaction reaches equilibrium. At 298 K, 7.5 MPa and the optimal pore width of 0.76 nm, the CO/H₂ selectivity is 28.3 and the CO adsorption capacity is 8.45 mmol/cm³.     

Exergy analysis of hydrogen production via steam methane reforming

The performance of hydrogen production via steam methane reforming (SMR) is evaluated using exergy analysis, with emphasis on exergy flows, destruction, waste, and efficiencies. A steam methane reformer model was developed using a chemical equilibrium model with detailed heat integration. A base-case system was evaluated using operating parameters from published literature. Reformer operating parameters were varied to illustrate their influence on system performance. The calculated thermal and exergy efficiencies of the base-case system are lower than those reported in literature. The majority of the exergy destruction occurs due to the high irreversibility of chemical reactions and heat transfer. A significant amount of exergy is wasted in the exhaust stream. The variation of reformer operating parameters illustrated an inverse relationship between hydrogen yield and the amount of methane required by the system. The results of this investigation demonstrate the utility of exergy analysis and provide guidance for where research and development in hydrogen production via SMR should be focused.     

Co and Ni supported on CeO2 as selective bimetallic catalyst for dry reforming of methane

Co/CeO₂ (Co 7.5 wt.%), Ni/CeO₂ (Ni 7.5 wt.%) and Co–Ni/CeO₂ (Co 3.75 wt.%, Ni 3.75 wt.%) catalysts were prepared by surfactant assisted co-precipitation method. Samples were characterized by X-Ray diffraction, BET surface areas measurements, temperature programmed reduction and tested for the dry reforming of methane CH₄ + CO₂ → 2CO + 2H₂ in the temperature range 600–800 °C with a CH₄:CO₂:Ar 20:20:60 vol.% feed mixture and a total flow rate of 50 cm³ min⁻¹ (GHSW = 30,000 mL g⁻¹ h⁻¹). The bimetallic Co–Ni/CeO₂ catalyst showed higher CH₄ conversion in comparison with monometallic systems in the whole temperature range, being 50% at 600 °C and 97% at 800 °C. H₂/CO selectivity decreased in the following order: Co–Ni/CeO₂ > Ni/CeO₂ > Co/CeO₂. Carbon deposition on spent catalysts was analyzed by thermal analysis (TG-DTA). After 20 h under stream at 750 °C, cobalt-containing catalysts, Co/CeO₂ and Co–Ni/CeO₂, showed a stable operation in presence of a deposited amorphous carbon of 6 wt.%, whereas Ni/CeO₂ showed an 8% decrease of catalytic activity due to a massive presence of amorphous and graphitic carbon (25 wt.%).     

Production of hydrogen via methane reforming using atmospheric pressure microwave plasma

In this paper, results of hydrogen production via methane reforming in the atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen. Important advantages of the presented waveguide-based nozzleless cylinder-type MPS are: stable operation in various gases (including air) at high flow rates, no need for a cooling system, and impedance matching. The plasma generation was stabilized by an additional swirled nitrogen flow (50 or 100 l min⁻¹). The methane flow rate was up to 175 l min⁻¹. The absorbed microwave power could be changed from 3000 to 5000 W. The hydrogen production rate and the corresponding energy efficiency in the presented methane reforming by the waveguide-based nozzleless cylinder-type MPS were up to 255 g[H₂] h⁻¹ and 85 g[H₂] kWh⁻¹, respectively. These parameters are better than those typical of the conventional methods of hydrogen production (steam reforming of methane and water electrolysis).     

Biogas reforming for hydrogen enrichment by ceria decorated over nickel catalyst supported on titania and alumina

Catalytic dry reforming of biogas for hydrogen enrichment was studied over cerium oxide promoted nickel catalysts supported on titanium dioxide and aluminium oxide. The catalysts were prepared by wet impregnation method and characterized by H₂-TPR, XRD, BET and FESEM techniques. Their catalytic performance in the biogas dry reforming reaction was studied at temperature ranges from 650 to 850 °C, with a CH₄/CO₂ ratio of 1.5:1. The H₂-TPR results revealed that 11 wt % Ni impregnation on TiO₂ support makes the catalyst with strong metal-support interaction which moderates the metal sintering. Also, the addition of CeO₂ effectively improved the CH₄ and CO₂ conversions as well as H₂ enrichment. At 850 °C, 11 wt % Ni/TiO₂ catalyst leads to 70.5% CH₄ conversion with 32.0% H₂ enrichment, whereas, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) yielded high CH₄ conversion (84.9%) with 40.6% of H₂ enrichment. No significant change in the activity of the catalyst was observed with 8.8 wt % of carbon deposited on the Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst, after 7 h of continuous reforming. Moreover, under combined (dry and oxidative) reforming of biogas, the stoichiometric H₂/CO ratio (1.2) was observed at 0.47 O₂/CH₄ ratios with negligible carbon deposition. Thus, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst exhibited better activity and selectivity with high catalyst stability at 850 °C.