Stability evaluation of ethanol dry reforming on Lanthania‐doped cobalt‐based catalysts for hydrogen‐rich syngas generation

Catalytic stability with time‐on‐stream is an important aspect in ethanol dry reforming (EDR) since catalysts could encounter undesirable deterioration arising from deposited carbon. This work examined the promotional effect of La on 10%Co/Al₂O₃ in terms of activity, stability, and characteristics. Catalysts were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman, and X‐ray photoelectron spectroscopy (XPS) measurements whilst catalytic EDR performance of La‐promoted and unpromoted 10%Co/Al₂O₃ prepared via wet impregnation technique was investigated at 973 K for 72 h using a stoichiometric feed ratio (C₂H₅OH/CO₂ = 1/1). La promoter substantially enhanced both metal dispersion and metal surface area from 0.11% to 0.64% and 0.08 to 0.43 m² g^?1, respectively. Ethanol and CO₂ conversions appeared to be stable within 50 to 72 h after experiencing an initial activity drop. The conversion of C₂H₅OH and CO₂ for La‐promoted catalyst was about 1.65 and 1.34 times greater than unpromoted counterpart in this order. The carbonaceous deposition was considerably decreased from 55.6% to 36.8% with La promotion due to La₂O₂CO₃ intermediate formation. Additionally, 3%La‐10%Co/Al₂O₃ possessed greater oxygen vacancies acting as active sites for CO₂ adsorption and hence increasing carbon gasification. Even though graphitic and filamentous carbons were formed on used catalyst surface, La‐addition diminished graphite formation and increased the reactiveness of amorphous carbon.     

Pressurization effect on dry reforming of biogas in kilohertz spark-discharge plasma

To produce high-concentration syngas (CO + H₂) from biogas, the effect of pressurization on dry reforming of biogas (CH₄/CO₂ = 60%/40%) in kilohertz spark-discharge plasma was reported for the first time by elevating the pressure from 1 bar to 2 bar. It was found that elevating the pressure could not only increase the reactant conversions, but also reduce energy cost and increase fuel-production efficiency at the same specific energy input (SEI). In particular, pressurization exhibited a significantly positive effect on increasing CO₂ conversion and decreasing energy cost for converting CO₂. Syngas concentration as high as 83% (H₂/CO = 1.4) was achieved with a ratio of the flow rates of product gas (dry basis) to feeding gas, 1.7, at 2 bar and SEI = 753 kJ/mol. The by-product, H₂O, was produced with only about 5% of hydrogen-based selectivity in this work. At 2 bar, the effect of SEI was investigated by varying the power and flow rate, respectively. Compared with those at 1 bar, with the increase in SEI, reactants conversion increased fast, energy cost rose slowly and fuel-production efficiency decreased slowly at 2 bar.     

H2-rich syngas production from biogas reforming: Overcoming coking and sintering using bimetallic Ni-based catalysts

Dry reforming of methane is a very appealing catalytic route biogas (mainly composed by greenhouse gases: carbon dioxide and methane) conversion into added value syngas, which could be further upgraded to produce liquid fuels and added value chemicals. However, the major culprits of this reaction are coking and active phase sintering that result in catalysts deactivation. Herein we have developed a highly stable bimetallic Ni–Rh catalyst supported on mixed CeO₂–Al₂O₃ oxide using low-noble metal loadings. The addition of small amounts of rhodium to nickel catalysts prevents coke formation and improves sintering resistance, achieving high conversions over extended reaction times hence resulting in promising catalysts for biogas upgrading.     

Recent advances during CH4 dry reforming for syngas production: A mini review

Given the continuing issues of environment and energy, methane dry reforming for syngas production have sparked interest among researchers, but struggled with the process immaturity owing to catalyst deactivation. This review summarizes the recent advances in the development of efficient and stable catalysts with strong resistance to coking and metal sintering, including the application of novel materials, the assessment of advanced characterizations and the compatibility to improved reaction system. One feasible option is the crystalline oxide catalysts (perovskite, pyrochlore, spinel and LDHs), which feature a fine metal dispersion and surface confinement effect via a metal exsolution strategy and exhibit superior reactivity and stability. Some new materials (h-BN, clays and MOFs) also extend the option because of their unique morphology and microstructure. It also is elaborated that progresses were achieved in advanced characterizations application, leading to success in the establishment of reaction mechanisms and attributions to the formed robust catalysts. In addition, the perspective described the upgrade of reaction system to a higher reaction efficiency and milder reaction conditions. The combination of efficient reaction systems and robust catalysts paves a way for a scaling-up application of the process.     

Excess-methane dry and oxidative reforming on Ni-containing hydrotalcite-derived catalysts for biogas upgrading into synthesis gas

The activity of Ni-containing hydrotalcite-derived catalysts was assayed in the excess-methane dry reforming of different CH₄-CO₂ mixtures, aiming to simulate biogas upgrading to hydrogen and/or syngas. These catalysts yielded methane conversions quite far away from the thermodynamically predicted values, pointing to the inhibition of important methane consuming reactions, such as direct methane decomposition (DMD). Adding oxygen to the gas mixture (12.5%) results in increased methane conversions. Almost constant H₂/CO ratios, around 1.5, were measured at any temperature (600–850 °C). However, solid carbon formation was found to take place to a higher extent. The intrinsic properties of the hydrotalcite-derived catalysts tested results in favored reverse water gas shift reaction, leading to CO₂ and H₂ conversion.     

Ordered mesoporous Fe-Al2O3 based-catalysts synthesized via a direct "one-pot" method for the dry reforming of a model biogas mixture

Biogas plays a vital role in the emerging renewable energy sector and its efficient utilization is attracting significant attention as an alternative energy carrier to non-renewable fossil fuel resources. Since biogas consists mainly of CH₄ and CO₂, dry reforming of methane arises as an appropriate process enabling its chemical conversion to high-quality synthesis gas (syngas: H₂ and CO mixtures). In this study, we synthesized via a direct "one-pot" method following an evaporation-induced self-assembly approach, ordered mesoporous Fe_10%, Ni_5% and Fe_x%Ni_(1-x) (x: 2.5, 5 or 7.5%) in Al₂O₃ as catalysts for syngas production via dry reforming of a model biogas mixture (CH₄/CO₂ = 1.8, at a temperature of 700 °C). Monometallic Fe_10%Al₂O₃ catalyst presented lower reactivity levels and slightly deactivated during catalysis compared to stable Ni_5%Al₂O₃. According to physico-chemical characterization techniques, the incomplete reduction of Fe₂O₃ into Fe₃O₄ rather than Fe⁰ nanoparticles (catalytically active) coupled with the segregation of Fe₃O₄ oxides were the main factors leading to the low performance of mesoporous Fe_10%Al₂O₃. These drawbacks were overcome upon the partial substitution of Fe by Ni (another transition metal) forming specifically bimetallic Fe_5%Ni_5%Al₂O₃ displaying reactivity levels close to thermodynamic expected ones. The formation of Fe-Ni alloys stabilized iron inside alumina matrix and protected it from segregation. Along with the confinement effect, spent catalyst characterizations showed high resistance towards coke deposition.     

Syngas production via the biogas dry reforming reaction over Ni supported on zirconia modified with CeO2 or La2O3 catalysts

The catalytic efficiency and bench scale time on steam stability of Ni dispersed on three commercially available catalytic supports (ZrO₂, La₂O₃–ZrO₂ and CeO₂–ZrO₂) has been studied for the dry reforming of methane (DRM) in the temperature range of 500–800 °C and a CH₄/CO₂ ratio equal to 1.5, simulating typical biogas quality. Ni supported on LaZr and CeZr carriers that obeyed enhanced basicity and oxygen ion lability values than Zr, exhibited superior catalytic efficiency and stability. A variety of techniques, namely N₂ physisorption-desorption (BET method), powder X-ray diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, potentiometric titration and inductively coupled plasma emission spectroscopy (ICP), were applied for the characterization of particles morphology, textural, structural and other physical properties of the materials, as well as the type of carbon deposited on the catalytic surface after exposure to DRM reaction conditions. Post-reaction analysis of the deposited carbon on the catalysts surfaces showed that the prominent trend of the carbon deposits on the Ni/Zr and Ni/LaZr samples was to have a filamentous tube like morphology (graphite-2H). In contrast, on the Ni/CeZr used catalyst, the formation of small amount of carbon tube-like architectures was detected. The enhanced basicity and Ni dispersion of the Ni/LaZr and Ni/CeZr samples as well as the high oxygen ion lability of the lattice oxygen in the latter, were considered to be the major factors involved in the superior efficiency and durability of these samples in comparison to Ni/Zr sample.     

Hydrogen production from biogas reforming and the effect of H2S on CH4 conversion

Biogas produced during anaerobic decomposition of plant and animal wastes consists of high concentrations of methane (CH₄), carbon dioxide (CO₂) and traces of hydrogen sulfide (H₂S). The primary focus of this research was on investigating the effect of a major impurity (i.e., H₂S) on a commercial methane reforming catalyst during hydrogen production. The effect of temperature on CH₄ and CO₂ conversions was studied at three temperatures (650, 750 and 850 °C) during catalytic biogas reforming. The experimental CH₄ and CO₂ conversions thus obtained were found to follow a trend similar to the simulated conversions predicted using ASPEN plus. The gas compositions at thermodynamic equilibrium were estimated as a function of temperature to understand the intermediate reactions taking place during biogas dry reforming. The exit gas concentrations as a function of temperature during catalytic reforming also followed a trend similar to that predicted by the model. Finally, catalytic reforming experiments were carried out using three different H₂S concentrations (0.5, 1.0 and 1.5 mol%). The study found that even with the introduction of small amount of H₂S (0.5 mol%), the CH₄ and CO₂ conversions dropped to about 20% each as compared to 65% and 85%, respectively in the absence of H₂S.     

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.     

Nickel based catalysts for methane dry reforming: Effect of supports on catalytic activity and stability

Methane dry reforming (MDR) is a promising process for syngas production through the valorisation of two of the main Greenhouse gases. Despite the high endothermicity, it should be carried out at low temperature to directly use the syngas for Fischer-Tropsch reaction and oxygenated chemical production. The catalyst plays a key role in this process as it must encourage syngas formation by limiting coke deactivation. This work focusses the attention on the effect of different supports in the activity and stability of nickel-based catalysts. In particular, MDR has been studied at relatively low temperature, 500 °C, to deeply investigate how the support influences the reaction pathway. Ceria, zirconia, alumina, silica and titania were considered and the morphological and structural features of the materials were analysed via N₂-physisorption, AAS, TPR, XRD, CO₂-TPD, and SEM techniques. Moreover, by analysing the spent catalysts, it was possible to identify the causes of catalysts deactivation. Titania based catalyst is not active for MDR, while silica and zirconia present moderated activity due to the poor support stability. Most promising results are obtained with ceria and alumina-based catalysts; for these materials, 70-h reaction was carried out and alumina catalyst has proved to be the most stable towards MDR at low reaction temperature with a stable H₂ yield of 25% .     

Synthesis of NiO/MgO/ZrO2 catalyst for syngas production from partial oxidation and dry reforming of biogas

This work focuses on a facile NiO/MgO/ZrO₂ synthesis protocol for syngas production via partial oxidation and dry reforming of biogas. Herein, performance of the developed catalysts with different amounts of MgO (0–40 %wt. of support) and NiO (10–50 %wt.) on %CH₄ conversion, %CO₂ conversion, H₂/CO ratio, and carbon formation are studied. The results reveal the presence of monoclinic ZrO₂ and tetragonal ZrO₂ phases with 50%NiO/ZrO₂ catalyst synthesized by surface modification technique using carbon derived from urea. Addition of MgO in the catalyst shows ability to stabilize tetragonal ZrO₂ phase as well as enhance basic surface of the catalyst. These properties render the adsorption of CO₂ molecules on the surface, which subsequently are reduced by carbon, leading to CO production. Appropriated amount of NiO and MgO, which is 30 %wt. NiO and 20 %wt. MgO (relative to ZrO₂) can produce syngas having quality (H₂/CO molar ratio) of ca. 2.     

Ni supported on CaO-MgO-Al2O3 as a highly selective and stable catalyst for H2 production via the glycerol steam reforming reaction

A comparative study of the GSR performance for Ni/CaO-MgO-Al₂O₃ and Ni/Al₂O₃ catalysts is reported. Catalysts were synthesized applying the wet impregnation method at a constant metal loading (8 wt %). Synthesized samples were characterized by N₂ adsorption/desorption, ICP, BET, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, XPS, TEM, STEM-HAADF and EDS. The carbon deposited on their surface under reaction conditions was characterized by TPO, Raman and TEM. It was proven that the use of CaO-MgO as alumina modifiers leads to smaller nickel species crystallite size, increased basicity and surface amount of Ni⁰ phase. Thus, it increases the conversion to gaseous products favoring H₂ and CO₂ production to the detriment of CO formation, by enhancing the water gas-shift (WGS) reaction. No liquid products were produced by the Ni/modAl catalyst over 550 °C, whereas time on stream results confirmed that deactivation can be prevented, as apart from decreasing the amount of coke deposition the nature of carbon was altered towards less graphitic and more defective structures.     

Influence of silica promotion on NiCe/MgAlSi catalysts for the oxy-steam reforming of biogas to syngas

This work has exploited the effects of silica on magnesium aluminum silicate supported NiCe based catalysts (NiCe/MgAlSi) prepared using sol-gel method followed by incipient wetness impregnation for syngas production through oxy-steam reforming (OSR) of biogas. Measurements investigating the effects of increasing Si/Al molar ratio (0–5) on activity and carbon deposition were performed in a once-through flow reactor at atmospheric pressure and temperatures of 600, 700, and 800 °C with a fixed GHSV of 45,000 ml g_cat⁻¹ h⁻¹ and molar feed ratio of CH₄/CO₂/O₂/H₂O = 1/0.67/0.1/0.3. The catalysts were characterized by N₂-physisorption, XRD, SEM, HRTEM, TGA, Raman, and ICP-OES. In the results, the addition of silica has been found to increase Ni crystallite sizes and decrease carbon deposition. Thus, NiCe/MgAlSi with Si/Al = 5 is promising, exhibiting high conversions of CH₄ (91.7%), CO₂ (80.4%), and H₂/CO ratio of 1.6 without carbon deposition and good stability for 120 h at 800 °C.     

Experimental study of syngas production from methane dry reforming with heat recovery strategy

This study employed the concept of heat recovery to design a set of reformer to facilitate the methane dry reforming (MDR), through which syngas (H₂+CO) could be generated. The MDR involves an endothermic reaction and thus additional energy is required to sustain it. According to the concept of industrial heat recovery, the energy required to facilitate the MDR was recovered from waste heat. In addition, after the reforming reaction, the waste heat inside the reformer was used for internal heat recovery to preheat the reactants (CO₂+CH₄) to reduce the amount of energy required for the reforming reaction. Regarding the parameter settings in the experiments, the CH₄ feed flow rate was set at 1–2.5 NL/min and the mole ratio for CO₂/CH₄ was set at 0.43–1.22. Subsequently, an oven was used to simulate a heat recovery environment to facilitate the dry reforming experiment. The experimental results indicated that an increase in oven temperature could increase the reforming reaction temperature and elevate the energy for the reformer. H₂ and CO production could increase when the reformer gained more energy. The high-temperature gas generated from the reforming reaction was applied to facilitate internal heat recovery of reformer and preheat the reactants; thus, the efficiency of reforming and CO₂ conversion were evidently elevated. The theoretical equilibrium analysis indicated that the thermal efficiency of reforming increased with the increase of CO₂/CH₄ molar ratio. While, the thermal efficiency of reforming by experiments decreased with the increase of the CH₄ feed rate, but increased with the increase of CO₂/CH₄. In summary, the experimental results revealed that the overall H₂ was 0.017–0.019 mol/min. In addition, the reforming efficiency was 8.76%–78.08%, the CO₂ conversion was 53.92%–96.43%, and the maximum thermal efficiency of reforming was 102.3%.     

Effect of substitution by Ni in MgAl2O4 spinel for biogas dry reforming

Mesoporous nanocrystalline Mg_1-xNi_xAl₂O₄ (x = 0.10, 0.13, 0.17 and 0.20) with large surface area were synthesized via a simple one-step sol-gel method using nonprecious metals. The prepared Mg_1-xNi_xAl₂O₄ catalysts exhibit good catalytic performance towards methane and carbon dioxide dry reforming reaction. The catalysts were evaluated by various techniques, including XRD, BET, TPR, TPO, EPR, Chemisorption, SEM and TEM. All the Ni incorporated MgAl₂O₄ samples possessed high BET area (296–305 m² g^?1) and pore volume (0.47–0.56 cm³ g^?1) with small pore size (6.4–7.4 nm) in meso region after calcination at 700 °C. The TPR results suggested strong interaction effect in NiMg and the reducibility property of the catalysts improved with the increase of nickel doping. Mg_0.8Ni_0.2Al₂O₄ exhibited the highest activity for biogas dry reforming with 72.6% CH₄ and 80.7% CO₂ conversion at 700 °C. Electron paramagnetic resonance (EPR) results indicated that the incorporation of Ni in MgAl₂O₄ spinel lattice led to the lattice distortion and formed oxygen vacancies which are a benefit for the dry reforming reaction.     

Preparation and improvement of the mesoporous nanostructured nickel catalysts supported on magnesium aluminate for syngas production by glycerol dry reforming

Dry reforming of glycerol is an interesting method for syngas production due to its H₂/CO ≈ 1 that is suitable for FT synthesis. In this study, the performance of the Ni/MgO.Al₂O₃ catalysts with different nickel contents was investigated in glycerol dry reforming. The MgO.Al₂O₃ carrier was prepared by a simple sol-gel method and the nickel-based catalysts were synthesized by the wet impregnation method. The prepared catalysts possessed high BET surface area and pore volume. The TPR analysis showed a strong interaction between Ni and the catalyst support. The results demonstrated that the glycerol conversion decreased by increasing in CO₂/glycerol (GRR) molar ratio. All the prepared samples showed high stability in glycerol dry reforming during 25 h of reaction, indicating the high resistance of the catalysts against carbon formation. Also, 10 wt%Ni/MgO.Al₂O₃ catalysts possessed the highest catalytic performance (52% of glycerol conversion at 750 °C) due to the high dispersion of nickel on the prepared carrier.     

Biogas dry reforming for hydrogen production over Ni-M-Al catalysts (M = Mg,Li, Ca,La, Cu,Co, Zn)

Biogas can be highlighted as a renewable raw material for the production of hydrogen. In this study, Ni-M-Al catalysts were evaluated to obtain hydrogen from the biogas reforming. The catalysts were synthesized by coprecipitation with Ni and Al with a molar percentage of 55 and 33%, respectively, varying the third component M = Mg, Li, Ca, La, Cu, Co, Zn, with a molar percentage of 11%. The reactions were carried out in a fixed bed tubular reactor using a synthetic biogas (70% of CH₄ and 30% of CO₂). The results showed that the CH₄ conversion increased with the temperature up to 700 °C for La11, Cu11, and Zn11 catalysts. CO₂ conversion increased for all catalysts in the range of 500–700 °C. The H₂/CO molar ratios observed in the reactions were higher than 1 due to the contribution of the CH₄ decomposition reaction. The catalyst containing La presented better stability in the reactions due to the stronger acid sites and high resistance to sintering. Carbon filaments were produced by all catalysts at 600 and 700 °C. Sintering was the main cause of deactivation of the catalysts, except for La11.     

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

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

Parametric study of catalytic dry reforming of methane for syngas production at elevated pressures

This study examined and elucidated the catalytic dry reforming of methane (DRM) for synthesis gas (syngas) production. The DRM performance was characterized using CH₄ and CO₂ conversions and product yields under various operating conditions and reactant compositions. A fixed-bed tubular reactor was used as the physical model and axisymmetric non-isothermal governing equations for the gas flow, energy transfer and species transport were solved numerically. The reactant inlet temperature was used as the primary parameter. Good agreement between the numerically predicted and experimentally measured data was obtained as the carbon formation reactions were included. A carbon-free reaction was obtained from the numerical model at high temperature which agreed with the thermodynamic equilibrium analysis. It was found that the DRM performance was degraded as the reaction pressure and reactant flow rate were increased. Under these conditions, carbon yield increases with the increase in pressure and reactant flow rate. It was also found that DRM performance can be enhanced by introducing excessive CO₂ into the reaction system. Carbon formation was suppressed by the excessive CO₂ supply. The numerical results also indicated that decreases in CO₂ and CH₄ partial pressures led to enhance the DRM performance. The addition of H₂ as one of the reactants suppresses CH₄ conversion and inhibited carbon formation while the addition of CO resulted in suppressing CO₂ conversion and enhancing carbon formation.     

A review on coke management during dry reforming of methane

The dry (CO₂) reforming of methane is a great promising technology, particularly because of its dual advantages of natural gas valorization and mitigating global warming via carbon dioxide sequestration. However, coke management is the most difficult problem in commercialization of the process. We have therefore examined in this paper the various catalytic systems being evaluated for the dry reforming with emphasis on operating parameters, activity, and coke deposition. Other factors such as the catalyst promoter, the reactor system, and the periodical regeneration were also critically reviewed. The benefits of utilizing methane from natural gas and other sources, where carbon dioxide is considered as an impurity component, are emphasized. Structured basic catalysts, with periodic regeneration certainties, are strong candidates for industrial applications. Therefore, efforts to build commercial scales for the benefit of global energy industries were highlighted. Copyright © 2015 John Wiley & Sons, Ltd.