Optimized mixed reforming of biogas with O2 addition in spark-discharge plasma

Adding O₂ into biogas to achieve partial oxidation and CO₂ mixed reforming can not only increase H₂ + CO concentration, but also reduce energy cost for H₂ production. In this study, optimized mixed reforming of biogas with O₂ addition in spark-discharge plasma was pursued in combination with thermodynamic-equilibrium calculation. With respect to mixed reforming of biogas with O₂ addition in spark-discharge plasma, combination coefficients of independent reactions were given to quantitatively evaluate the mixed extent at various O₂/(CH₄–CO₂) ratios. Compared thermodynamic-equilibrium with experimental results, it can be concluded that the optimal O₂/(CH₄–CO₂) ratio for optimized mixed reforming of biogas in spark-discharge plasma was about 0.7. When total-carbon conversion was relatively high (>75%), H₂ + CO concentration on wet basis was the highest and energy cost for H₂ production was the lowest at O₂/(CH₄–CO₂) = 0.7, and their experimental results were closest to their thermodynamic-equilibrium values.     

Microwave-assisted dry reforming of methane

The microwave-assisted dry reforming of methane over an activated carbon, which acted as catalyst and microwave receptor, was investigated. As a preliminary study, the CO₂ reforming of CH₄ was carried out using conventional heating and microwave heating in order to compare both heating devices. Higher conversions of CH₄ and CO₂ were achieved by microwave heating. Under microwave heating, various operating variables were studied in order to determine the best conditions for performing dry reforming with high conversions and the most suitable H₂/CO ratio. Thus, the dry reforming reaction was studied at different temperatures. An optimum range of working temperatures (between 700 °C and 800 °C) was established. In this range of temperatures, the dry reforming reaction is believed to take place as a combination of CH₄ decomposition and CO₂ gasification. Carbonaceous deposits from CH₄ decomposition are gasified by CO₂ and, as a result, active centres for the dry reforming reaction are constantly regenerated. The effect of the proportion of CO₂ fed in on the CH₄ and CO₂ conversions was also investigated. Small increases in the percentage of CO₂ fed in gave rise to large increases in both conversions, but especially in the case of CH₄. The volumetric hourly space velocity was also studied. It was found that the lower the space velocity, the higher the conversions obtained.     

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.     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Highly-efficient hydroxyapatite-supported nickel catalysts for dry reforming of methane

Ni-based catalysts were prepared using two hydroxyapatites (Ca-HA1, S_BET = 7 m²/g and Ca-HA2, S_BET = 60 m²/g) with different physico-chemical properties. The objective of the study was to evaluate the performance of these two materials as promising supports for dry reforming reaction (DRM) as well as to investigate the influence of different process parameters, such as temperature, pressure, time and catalyst pretreatment on the performance of these two catalysts. Thermodynamic calculations were performed to determine the conditions that would limit solid carbon deposit and favor the reactants conversion. Then, an experimental parametric study was carried out to investigate the impact of the temperature, pressure, catalyst pretreatment and support thermal treatment on the catalysts performance. The results showed that the catalyst pretreatment allowed the reduction of the nickel particles in a higher extent, which resulted in better catalytic performance when compared to the catalysts without pretreatment. High temperatures around 700 °C and low pressures around 1.6 bar were required to attain high CH₄ and CO₂ conversions around 70–80% as well as high H₂ and CO selectivity around 90% for 90 h of time on stream. In all cases, Ni/Ca-HA2 catalyst presented better catalytic performance than Ni/Ca-HA1 due to the presence of smaller nickel particles (10–20 nm), stronger basicity, higher density of basic sites (0.23 mmol g⁻¹) as well as higher specific surface area (S_BET = 60 m²/g) of the Ca-HA2 support. Ni/Ca-HA2 catalyst was highly active (initial methane conversion: 75%) and relatively stable during 90 h of TOS and its catalytic behavior was comparable with the performance of Ni-based catalysts prepared with conventional supports reported in the literature.     

Ethanol dry reforming over Ni supported on modified ceria-zirconia catalysts– the effect of Ti and Nb dopants

In this work complex metal-oxide catalysts with the general formula 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ were synthesized by the solvothermal method using supercritical alcohols followed by nickel deposition. The catalysts were characterized and studied in ethanol dry reforming reaction (EDR) in the temperature range 600–750 °C. XRD and TEM showed that the synthesis method provides incorporation of doping cations into the ceria-zirconia fluorite structure, leading to mixed oxides formation. The effect of doping cations on structural and surface properties of 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ and activity in the EDR reaction was investigated. Oxygen deficiency δ increases with the introduction of titanium and niobium cations, which contributes to the bifunctional reforming mechanism implementation with rapid oxidation of coke precursors and activation of СО₂ at surface oxygen vacancies. TPO-O₂ analysis after reaction showed no carbon formation above 700 °C, and a few carbon deposits (not exceeding 4%) even after significant catalyst deactivation at 600 °C.     

Exergy analysis of hydrogen production via biogas dry reforming

Among the alternative pathways for hydrogen production, the use of biogas from organic waste via dry reforming of methane (DRM), water gas shift reaction and pressure swing adsorption (PSA) is often seen as an interesting option. In this work, the thermodynamic performance of this type of biohydrogen energy system –additionally including a combined-cycle scheme that satisfies the electricity and steam requirements of the process– is evaluated through exergy analysis. The main data needed for the analysis are acquired from a predictive simulation model implemented in Aspen Plus^®. The system shows an exergetic efficiency of 55%, with the DRM and the power generation subsystems arising as the main sources of irreversibility. Furthermore, given the significant influence found for the PSA off-gas on the thermodynamic performance of the system, two alternative process configurations based on the use of this stream are evaluated. In this regard, full recirculation of the PSA off-gas to the DRM reactor is found to improve the system's exergetic performance.     

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.     

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.     

Impact of impurities on biogas valorization through dry reforming of methane reaction

Biogas is mainly composed of methane, carbon dioxide as well as other compounds such as water and volatile organic compounds (VOCs). In this study, the composition of a biogas produced in a landfill is determined using gas chromatography. CH₄ and CO₂ represent 60% of its composition, rendering a valorization via the dry reforming of methane (DRM) reaction very promising. Moreover, H₂O and VOCs represent respectively 1.5% and 1500 ppm of biogas, which may affect the catalytic efficiency. The performance of CoNiMgAl catalysts derived from hydrotalcites is studied in the presence of toluene, water and a combination of both. The presence of toluene causes a progressive increase in the catalytic activity as well as higher carbon deposition. The addition of water decreases CO₂ conversion and carbon formation and increases the H₂/CO to values closer to 1. When both molecules are added, the catalytic activity remains stable, confirming that DRM is possible in the presence of both compounds.     

Combined dry reforming and partial oxidation of methane to synthesis gas on noble metal catalysts

In this paper CO₂ reforming of methane combined with partial oxidation of methane to syngas over noble metal catalysts (Rh, Ru, Pt, Pd, Ir) supported on alumina-stabilized magnesia has been studied. The catalysts were characterized by using BET, XRD, SEM, TEM, TPR, TPH and H₂S chemisorption techniques. The H₂S chemisorption analysis showed an active metal crystallite size in the range of 1.8-4.24 nm for the prepared catalysts. The obtained results revealed that the Rh and Ru catalysts showed the highest activity in combined reforming and both the dry reforming and partial oxidation of methane. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50 h of reaction. In addition, the H₂/CO ratio was around 2 and 0.7 over different catalysts for catalytic partial oxidation and dry reforming, respectively.     

Internal reforming SOFC running on biogas

Direct feeding of biogas to SOFC, which is derived from municipal organic wastes, has been investigated as a carbon-neutral renewable energy system. CH₄/CO₂ ratio in the actual biogas fluctuated between 1.4 and 1.9 indicating biogas composition is strongly affected by the kinds of organic wastes and the operational conditions of methane fermentation. Using anode-supported button cells, stable operation of biogas-fueled SOFC was achieved with the internal reforming mode at 800 °C. Cell voltage above 0.8 V was recorded over 800 h at 200 mA cm⁻². It has been revealed that air addition to actual biogas reduced the risk of carbon formation and led to more stable operation without compromising cell voltage due to the lowering of anodic overvoltage.     

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

In recent times, glycerol has been employed as feedstock for the production of syngas (H₂ and CO) with H₂ as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al₂O₃ catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L g_cat⁻¹ h⁻¹). Ag (3)-Ni/Al₂O₃ gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H₂ production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al₂O₃, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O₂.     

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.     

Influence of promoting Ni-based catalysts with ruthenium in the dry reforming of polypropylene plastics for syngas production

The catalytic dry reforming of plastic waste is conducted in two-stage fixed bed reactors. The pyrolysis of polypropylene plastics occurs in the first reactor, and the pyrolyzed gases undergo a reforming reaction with carbon dioxide over a catalyst in the second reactor. The wet impregnation method is used to synthesize Ru–Ni/Al₂O₃ catalysts, which are then calcined and reduced at 800 °C. The results show that as the nickel loading increases, the syngas production increases. Promoting the catalyst with a small quantity of ruthenium significantly improves the plastic conversion into syngas. The dry reforming of polypropylene over 1Ru15Ni/Al₂O₃ catalyst resulted in the maximum syngas yield (159 mmol_syngas/g_PP) at a 2:1 plastic to catalyst ratio. The catalytic dry reforming of plastics is promising for the production of synthesis gas.     

Syngas production from methane dry reforming over SmCoO3 perovskite catalyst: Kinetics and mechanistic studies

The kinetics of the methane dry (CO₂) reforming over the SmCoO₃ was investigated in the temperature ranged 973–1073 K by varying the CH₄ and CO₂ partial pressures. Based on detailed study of the reaction mechanism, a mechanistic model is proposed from which a kinetic model is derived. The mechanistic pattern assumes adsorption of CH₄ on reduced Co, followed by methane cracking and carbon deposition. CO₂ reacts with Sm₂O₃ to form Sm₂O₂CO₃ and the oxycarbonates react with carbon to produce CO. The power law and Langmuir–Hinshelwood kinetic model which is established on this mechanism were able to forecast the kinetic results.     

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.     

Development and validation of a Ni-based catalyst for carbon dioxide dry reforming of methane process coupled to solid oxide fuel cells

Recent studies propose dry reforming as a potential alternative to steam reforming. A number of advantages come mainly from the substitution of steam with CO₂, representing a potential strategy for CO₂ and waste heat reuse in both carbon-intensive industry (e.g. steel) and power generation applications (e.g. dry reforming coupling to solid oxide fuel cells).The objective of this study is the development, by means of an ultrasound assisted synthesis technique, of a novel 15%Ni -6%ZrO₂ –3%CaO -Al₂O₃ catalyst with high surface area and metal dispersion, to achieve high values of methane conversion and stable performance, obtained by significantly limiting carbon deposition at temperature in the range 700–750 °C. In this range, compatible with the dry reformer-SOFC thermal integration, conventional catalysts seriously suffer from coking tolerance issues.The catalyst exhibited very promising results with high methane conversion rates of 93% at 750 °C and 1.25 CO₂/CH₄ ratio at the reactor inlet (dilution: in SiC 4:1 in volume), stable over 450 h of operation, with no significant changes in outlet gas composition and relevant modifications on material structure as revealed by SEM/EDX, XRD and Raman, analysis.     

Plasma-assisted Ni catalysts: Toward highly-efficient dry reforming of methane at low temperature

Dry reforming of methane (DRM) reaction can convert primary greenhouse gases (CH₄ and CO₂) to value-added chemicals (H₂ and CO), but generally suffers from harsh reaction conditions (>700 °C) and inevitable deactivation of catalysts. In this work, we report supported Ni catalysts based on a topotactic transformation process from the layered double hydroxides (NiZnAl?LDHs) precursors. Structural characterizations (XRD, HRTEM, CO chemisorption) verify a uniform distribution of Ni nanoparticles (～7 nm) on the mixed metal oxides support with a high dispersion (denoted as Ni/MMO). With the assistance of non-thermal plasma (NTP), the optimal sample (Ni/MMO?S2) exhibits a good catalytic conversion of CH₄ (～69%) and CO₂ (～54%) at low temperatures (30–60 °C), which is comparable with the activity of thermocatalytic process at ～650 °C without NTP. The energy efficiency of NTP-assisted catalysis process is an order of magnitude higher than that of thermocatalytic process at ～650 °C and enhances by 80% relative to NTP-alone process at low temperatures. The Ni/MMO?S2 catalyst shows satisfactory stability after 600 min stability test, with a slight decrease in conversion (within ～1%). In addition, a combined study including catalytic evaluations, operando OES, XAFS and XPS verifies that metallic Ni species acts as active center, which can promote the dissociation of CH₄ and CO₂ into highly reactive intermediate species with the assistance of NTP. This synergistic effect between plasma and Ni catalyst remarkably decreases the apparent activation energy by ～50%, accounting for the high catalytic performance at low temperatures. This work demonstrates a promising synergistic catalysis strategy between plasma and catalysts at low temperatures, which can be extended to other reactions operated under harsh conditions.