Methanation Reaction Research Articles

Reaction of methane with benzene and CO on Cu-modified ZSM-5 zeolite investigated by 13C MAS NMR spectroscopy

Three types of methoxy-like intermediates were generated at methane interaction with Cu-loaded ZSM-5 zeolite, containing copper in the form of either Cu2+ cations (Cu2+/H-ZSM-5) or [Cu3(µ-O)3]2+ oxo-clusters (CuO/H-ZSM-5). The methoxy species were tested for the reaction with benzene and carbon monoxide. 13C MAS NMR spectroscopy reveals that the methoxy species formed on CuO/H-ZSM-5 easily interact with benzene yielding toluene, whereas the methoxy species on Cu2+/H-ZSM-5 are less effective for benzene methylation. At the same time, the methoxy species on Cu2+/H-ZSM-5 can interact with CO forming surface acetate species, while strong adsorption of CO by [Cu3(µ-O)3]2+ oxo-clusters of CuO/H-ZSM-5 inhibits the reaction.

The ignition characteristics of dual-fuel spray at different ambient methane concentrations under engine-like conditions

In the present study, dual-fuel ignition process of pilot diesel spray injection into a natural gas-air mixture under engine-like conditions is numerically investigated via large-eddy simulation (LES). Methane and n-dodecane are considered as surrogates for natural gas and diesel fuels, respectively. This study aims to provide understandings of kinetic interactions for dual-fuel spray during the ignition process. The effects of ambient methane concentration on the ignition delay times (IDTs), product distributions, and heat release rates (HRRs) during dual-fuel ignition process are emphasized. The results show that methane prolongs the IDT of n-dodecane, especially for the first-stage IDT. Kinetic analyses reveal that the competition for OH between the dehydrogenation reactions of methane (CH4 + OH <=> CH3 + H2O) and n-dodecane (RH + OH <=> R + H2O) results in the increasing first-stage IDT of pilot spray. Moreover, it is found that the retarding effect positively correlates with the methane concentration. For product distributions, it is observed that the transition of CH2O from fuel-lean to fuel-rich regions is inhibited in the first-stage ignition. In the second-stage ignition, the concentration of CO is decreased as the methane concentration increases and the area with high CO concentration is gradually shifted to the downstream of the spray. In addition, HRRs of low-temperature exothermic reactions appear at the radial periphery as well as the head of the spray front; HRRs of high-temperature exothermic reactions are gradually shifted from the head to the center of the spray with the increase of ambient methane concentration. The HRRs of low- and high-temperature reactions are decreased with increasing ambient methane concentration, and the major reactions for heat release at various ambient methane concentrations are different.

Evaporating water-cooled methanation reactor for solid-oxide stack-based power-to-methane systems: Design, experiment and modeling

The power-to-methane process using a solid-oxide electrolyser, followed by an exothermic methanation reactor, is effective for the production of an energy carrier (synthesis methane) that can be readily stored and transported at a large scale. A significant gain of the coupling is the steam generation from the heat produced by the methanation reaction for the more effective steam electrolysis (compared to liquid water electrolysis). This paper investigates, both theoretically and experimentally, the system integrability and operability of an evaporating water-cooled methanation reactor designed for thermal coupling with a solid-oxide electrolyser. The results show that the pressurized steam generation directly by the reactor’s cooling system improves the flexibility of the system design. Under certain conditions, an increase in overall power-to-methane efficiency of more than 3 % can be obtained from the use of a superheater and a turbine located after the evaporation process. The parametric study of the methanation reactor indicates that decreasing the flowrate of the H2 and CO2 mixture, increasing the reaction gas pressure and increasing the cooling system pressure (saturation temperature) shifts the hot spot towards the inlet and improves the H2 conversion rate, which can reach above 97 %. It was determined that, under steady-state operation, the steam generation can be sufficiently stable for injection into the solid-oxide electrolyser; rapid pulsations with a standard deviation under 10% were measured. The calibrated 1D pseudo-homogeneous plug flow reactor model captures many of the trends, though, the assessment is limited without the exact kinetic model of the catalyst pellets.

Comparative life cycle assessment of power-to-methane pathways: Process simulation of biological and catalytic biogas methanation

Power-to-Methane (P2M) pathways are proposed as an innovative solution to utilize surplus renewable electricity for long-term and long-distance storage. This electricity can produce hydrogen using electrolysis and, with the input of CO2 from biogas, be further used for the production of synthetic methane. The methanation reaction can be done with a biocatalyst or nickel catalyst, each with a different pathway of pre- and post-treatment steps. To date, only a limited number of studies have analysed the environmental impact of P2M pathways using life cycle assessment, and no study has directly compared the biological and catalytic P2M pathways. The goal of this research is to close this knowledge gap by quantifying the environmental impact of synthetic methane production and identifying differences between both pathways. Mass and heat balances of both pathways were simulated with AspenPlus and used as basis for a thorough life cycle inventory of the material and energy demand. The global warming potential per MWh synthetic CH4 is similar for the biological and catalytic pathways, but the impact is differently distributed between the processes. The catalytic pathway requires more sulfur removal, compression power and cooling demand. In the biological pathway, the bioreactor has a large impact due to its electricity and nutrient demand, whereas the catalytic reactor's impact is almost negligible.

Ultra-stable porous yolk-shell Ni catalysts for the steam reforming of methane with alkali poisoning

Hydrogen, a clean energy carrier, can be produced from renewable sources such as biomass and waste, but it is needed to develop new catalysts with high resistance against impurities. Ni/Al2O3 yolk-shell catalysts were prepared by different procedure for the steam reforming of methane reaction with alkali poisoning. Yolk-shell (ys) and porous yolk-shell (pys) materials were synthesized using a spray pyrolysis process. The physicochemical and structural properties of the prepared catalysts on the reaction performance and alkali resistance were investigated. All the yolk-shell catalysts exhibited high resistance to carbon deposition. The Ni/pys-Al2O3 catalyst showed the highest CH4 conversion and the best stability at a gas hourly space velocity of 932,492 mL·g−1·h−1 even upon exposure to alkali hydroxide vapor. It also showed strong resistance to sintering, whereas the structures of the ys-Ni-Al2O3 and Ni/ys-Al2O3 catalysts were relatively degraded under the same conditions.

Prediction model for methanation reaction conditions based on a state transition simulated annealing algorithm optimized extreme learning machine

Methanation is the core process of synthetic natural gas, the performance of the entire reaction system depends on precise values of the reaction condition parameters. Accurate predictions of the CO conversion rate of the methanation reaction can eliminate time-consuming and complex steps in experiments and speed up the discovery of the best reaction conditions. However, the methanation reaction is an uncertain, highly complex, and highly nonlinear process. Thus, this paper proposes a machine learning prediction model for the methanation reaction to facilitate the subsequent search for optimal reaction conditions. The reaction temperature, pressure, hydrogen–carbon ratio, water vapor content, CO2 content, and space velocity were selected as the condition variables. The CO conversion rate was the optimization objective. An extreme learning machine (ELM) was selected as a prediction model. Because the input weights and bias matrices of the ELM are randomly generated, an ELM based on a state transition simulated annealing (STASA-ELM) algorithm is proposed. The STASA algorithm was used to optimize the ELM to improve the accuracy and stability of the model. Five additional sets of experimental data were designed for the experiment, and the error between the experimental and predicted values was small. Thus, the STASA-ELM algorithm can accurately predict the conversion of CO for different values of reaction conditions.

Computational study of CO2 methanation over two-dimensional molybdenum carbide catalysts

Two-dimensional molybdenum carbide (2D-Mo2C) is thought to be promising for catalytic hydrogenation of CO2 to CH4, but little is known about its catalytic reaction mechanism. In this work, we investigate the hydrogenation of CO2 to CH4 on 2D-Mo2C using density functional theory. Our calculations show that Mo on the surface can efficiently decompose CO2 to CO and O, and also H2 to H. The hydrogenation of CO produces CHO that is readily deoxygenated to CH, and CH is selectively hydrogenated to produce CH4. Interestingly, the embedded Ir1 on 2D-Mo2C can act as a single-atom promoter to improve the performance of CO2 methanation, while on the other hand maintaining its high selectivity for CH4. This work provides insight into the mechanism of 2D-Mo2C-catalyzed CO2 methanation reactions and suggests a strategy to improve the performance of such catalysts through single-atom promoters.

Development of a kinetic model for CO2 methanation over a commercial Ni/SiO 2 catalyst in a differential reactor

Development of a kinetic model for CO2 methanation over a commercial nickel catalyst was performed to consider pathways of CO2 conversion via Sabatier and RWGS reactions. H2/CO2 ratio in the feed gas composition was varied at the stoichiometry of the Sabatier reaction assuming a fictitious CO2 conversion of 0 to 0.7. Non-stochiometric gas feeding and the addition of product gases, i.e., methane and steam, were also considered to examine reaction orders and inhibition effects. The kinetic tests were carried out at 300–350 °C and 0.1–0.9 MPa. GHSV corresponded to 37,494 h−1. The stable activity was achieved by forcibly stressing the catalyst under the equilibria at 500 °C for 35 h. The kinetic measurements were conducted at an isothermal differential fixed bed reactor in the absence of heat and mass transport limitations. The methanation reaction was first fitted with the power law and LH approaches by considering the Sabatier reaction. Then, the RWGS reaction was added to consider CO formation using the power law models. The results showed a better fitting of experimental observations by using the LH expression with the formation of formyl as RDS and the power law model with inhibiting influence of water.

Mechanism of Catalytic CO2 Hydrogenation to Methane and Methanol Using a Bimetallic Cu3Pd Cluster at a Zirconia Support.

For very small nanocluster-based catalysts, the exploration of the influence of the particle size, composition, and support offers precisely variable parameters in a wide material search space to control catalysts' performance. We present the mechanism of the CO2 methanation reaction on the oxidized bimetallic Cu3Pd tetramer (Cu3PdO2) supported on a zirconia model support represented by Zr12O24 based on the energy profile obtained from density functional theory calculations on the reaction of CO2 and H2. In order to determine the role of the Pd atom, the performance of Cu3PdO2 with monometallic Cu4O2 at the same support has been compared. Parallel to methane formation, the alternative path of methanol formation at this catalyst has also been investigated. The results show that the exchange of a single atom in Cu4 with a single Pd atom improves catalyst/s performance via lowering the barriers associated with hydrogen dissociation steps that occur on the Pd atom. The above-mentioned results suggest that the doping strategy at the level of single atoms can offer a precise control knob for designing new catalysts with desired performance.

Experimental and chemical kinetic modeling study of trimethoxy methane combustion

The use of oxymethylene ethers (OMEs) as alternative fuels or fuel-additives has motivated the present study on the combustion behavior of trimethoxy methane (TMM), which is a branched version of OMEs. A detailed chemical kinetic model for TMM combustion is provided, which is based on a recent model for the structurally similar dimethoxy methane (DMM) and recent elementary reaction kinetics studies. This model is validated against TMM ignition delay times measured in a shock tube at 20 and 40 bar, under fuel lean, stoichiometric, and fuel rich conditions. Further, the TMM model is validated against laminar burning velocities, which were measured in a heat flux setup for a variation of fuel/air ratios. A good agreement between the TMM model predictions and the measured ignition delay times and laminar burning velocities is observed. At fuel rich conditions in the shock tube, however, the model underestimates the reactivity of TMM by up to 60%, which could not be compensated by physically meaningful modifications of the TMM model. The analysis of the TMM model shows that at low temperatures, TMM is primarily consumed via H-atom abstraction by ȮH radicals, followed by classical β-scission and low-temperature chemistry. At higher temperatures, a significant fraction of TMM is consumed via unimolecular decomposition, leading to a higher reactivity compared to OME2. The present model and experiments lay the foundation for future kinetic modeling of TMM and other branched OME-like compounds.

Non-oxidative coupling reaction of methane to hydrogen and ethene via plasma-catalysis process

The plasma pyrolysis and plasma catalysis of methane coupling were performed under room temperature and atmosphere. The coupling of methane through gliding arc plasma with different H2/CH4 ratios and N2 flow rates exhibited conversion from 25% to 40% and high selectivity of acetylene above 90%. Plasma emission spectra displayed lowest IHβ/IHα ratio at H2/CH4 ratio of 3, while IHβ/IHα ratio decreased with increasing N2 feed rate from 0 to 2 L/min, which had similar variation with selectivity of acetylene. X-ray photoelectron spectra for reduced catalysts demonstrated that metallic Pd species (335.4 eV) were transferred to electron-rich Pd species (334.8eV and 334.1 eV) with increasing Pd loading and Ag/Pd ratio, corresponding to red shift of linear adsorbed CO stretching frequency from 2060 to 2068 cm−1 to 2055-2015 cm−1. Superior plasma catalytic behavior over 0.1Pd0.5Ag/Al2O3 catalyst has been reached with 86.5% selectivity of ethene and 36.2% conversion of methane.

Mixed oxygen ionic‐carbonate ionic conductor membrane reactor for coupling CO2 capture with in situ methanation

AbstractCO2 methanation is one of the vital reactions to utilize CO2 and realize power to gas process. To decrease the CO2 capture cost and alleviate the hot spots during the strong exothermic methanation reaction, here, we report a coupling of CO2 capture process with in situ CO2 methanation process through a ceramic‐molten carbonate (MC) dual phase membrane reactor over the Ni‐based catalyst. The performance of the membrane reactor was systematically investigated and compared with the traditional fixed‐bed reactor. The results show that the performance of the membrane reactor is higher than that of the fixed‐bed reactor, since the produced steam through the methanation process can be partially removed through the dual‐phase membrane, which promotes the reaction shift to right side. A stability test shows no obvious degradation within 32 h. These results indicate that the membrane reactor is promising for coupling CO2 capture with in situ methanation process.

CeO2 Nanorod@NiPhy Core‐shell Catalyst for Methane Dry Reforming: Effect of Simultaneous Sintering Prevention of CeO2 Support and Active Ni

AbstractPreventing the sintering of nano‐catalyst is crucial to maintain their performance especially for high‐temperature reactions such as CO2 reforming of methane (DRM) reaction. In this paper, we design CeO2 nanorod@Ni phyllosilicate (CeO2@NiPhy) catalysts with different NiPhy shell thickness to simultaneously preserve the morphology of CeO2 nanorod and prevent the sintering of Ni. Compared with Ni/CeO2 supported catalyst, CeO2@NiPhy core‐shell catalyst with a shell thickness of 9 nm exhibits much better performance for DRM with stable CH4 and CO2 conversions of 75 % and 80 % respectively and lower carbon deposition due to high Ni sintering resistance and higher thermal stability of CeO2 during calcination and DRM reaction thereby higher oxygen vacancies concentration. In‐situ diffuse reflectance infrared Fourier transform spectra result demonstrates that DRM reaction takes place with a bi‐functional mechanism on CeO2@NiPhy. This design strategy can be applied to prepare other nano‐catalysts with high sintering resistance of both active metal and catalyst support for high‐temperature applications.

Methane activation on metal oxide nanoparticles: spectroscopic identification of reaction mechanism

Currently, there is a lack of detailed knowledge about methane (CH4) reactions on metal oxide surfaces. This reaction involves in different processes such as chemical looping combustion and catalytic carbon dioxide (CO2) reforming of CH4. In this study, in situ diffuse reflectance infrared Fourier transform spectroscopy was used to investigate CH4 reaction on three transition metal oxides (CoO, CuO, and α-Fe2O3) which are commonly used in these processes at temperatures ranging from 100 °C to 700 °C. The results show that CH4 is adsorbed on the metal oxide surfaces as methoxy and formate, and then the methoxy group reacts with the metal oxide lattice oxygen forming bicarbonate. Under the effect of the used reaction temperature, the bicarbonate decomposes to CO2 and water vapor.

The bulk and supported perovskite-type catalysts for the CO2 reforming of methane: The effect of ceria and magnesia

BackgroundThe bulk or supported nickel catalysts are active in the dry reforming of methane to produce syngas. The nickel-based catalysts are deactivated quickly due to the metal sintering and coke deposition. Perovskite catalysts are stable, enhance the dispersion of the active sites, and resist metal sintering and coke deposition. The coke deposition is inhibited by increasing the CO2 adsorption and oxidation of the deposited coke. MethodsA series of ceria-doped perovskite catalysts La1-xCexNiO3, LaNi1-xCexO3 and magnesia-modified-alumina supported perovskite-type catalysts were prepared via the sol-gel method. The prepared catalysts were thoroughly characterized via state-of-the-art characterization techniques. Significant findingsThe incorporation of ceria assisted the supported catalysts in forming a dispersed phase at low loading and forming other NiO or NiO-MgO (solid solution) NiAl2O4 and MgAl2O4 (spinel phase). The catalytic activity for the CO2 reforming of methane reaction increased with the addition of magnesia and the substitution of La-ion with tetravalent metal cation (ceria). The doping of ceria increased the stability of the catalyst. The bulk catalyst La0.5Ce0.5NiO3 exhibited promising catalytic activity. The magnesia-modified-alumina-supported catalyst (50La0.5Ce0.5NiO3/8MgO-Al2O3) was more active than the alumina-supported or bulk-perovskite catalysts with low coke deposition and higher percent conversion of CH4 (97%) and CO2 (99%) at 1073 K.

A Review on the Different Aspects and Challenges of the Dry Reforming of Methane (DRM) Reaction.

The dry reforming of methane (DRM) reaction is among the most popular catalytic reactions for the production of syngas (H2/CO) with a H2:CO ratio favorable for the Fischer–Tropsch reaction; this makes the DRM reaction important from an industrial perspective, as unlimited possibilities for production of valuable products are presented by the FT process. At the same time, simultaneously tackling two major contributors to the greenhouse effect (CH4 and CO2) is an additional contribution of the DRM reaction. The main players in the DRM arena—Ni-supported catalysts—suffer from both coking and sintering, while the activation of the two reactants (CO2 and CH4) through different approaches merits further exploration, opening new pathways for innovation. In this review, different families of materials are explored and discussed, ranging from metal-supported catalysts, to layered materials, to organic frameworks. DRM catalyst design criteria—such as support basicity and surface area, bimetallic active sites and promoters, and metal–support interaction—are all discussed. To evaluate the reactivity of the surface and understand the energetics of the process, density-functional theory calculations are used as a unique tool.

CFD-DEM Simulation of Particle Fluidization Behavior and Glycerol Gasification in a Supercritical Water Fluidized Bed

In this study, a mathematical model of hydrogen production from glycerol gasification in supercritical water was established based on the CFD-DEM method. The fluidization process of a supercritical water fluidized bed and the effects of bed height and feed structure on particle distribution and residence time of feedstock were analyzed. Additionally, the temperature field in the fluidized bed, the reaction rate distribution of each reaction and the influence of wall temperature on gas yields were also studied. The simulation results show that the bubble channel is easy to form along the wall at one side of the feed inlet. When the initial bed height is high, and the double symmetric feed inlet structure is used, the residence time of the feedstock is prolonged. The pyrolysis of glycerol mainly occurs in the middle and lower part of the fluidized bed reactor, and the reaction rate of the water gas shift reaction and methanation reaction are highest near the outlet, and a high wall temperature is conducive to the glycerol gasification.

Alternative acid catalysts for the stable and selective direct conversion of CO2/CO mixtures into light olefins

Different acid catalysts (silicoaluminophosphates (SAPOs) -34, −18, and − 11, and HZSM-5 zeolite) were tested as components of In2O3-ZrO2/acid tandem catalysts in the direct synthesis of light olefins by hydrogenation of CO2, CO and their mixture. The conversion and olefins yield and selectivity evidence that the presence of the large amount of strongly acidic sites in SAPO-34 favors the extent of the reaction mechanism with methanol as intermediate, minimizing secondary methanation reactions. In addition, the shape selectivity of SAPO-34 boosts olefins selectivity (mainly of propylene), limiting the extent of the secondary reactions for the formation of other hydrocarbons. Using SAPOs as acid catalysts enhances olefins selectivity when co-feeding CO2 with CO. Despite all tandem catalysts undergo deactivation by coke deposition (mostly in the acid catalyst), a pseudo-steady state of stable remaining activity is acquired. From the study of the coke nature, soft and hard coke were discerned. For the complete regeneration of the SAPO-34 in the tandem catalyst, the stripping of the soft coke is not sufficient and the combustion at 500 °C of the hard coke (little developed) deposited on the micropores is required.

Modeling and estimating kinetic parameters for CO2 methanation from fixed bed reactor experiments

AbstractCO2 methanation, which converts CO2 and hydrogen into methane as fuel, is one of the promising candidates for the development of CO2 utilization technologies. Recently, a highly active catalyst made of Ni/ZrO2 for methanation has been developed, and is currently investigated as a potential use in a high‐performance reactor. However, design of reactor must be carried out carefully, since this reaction is highly exothermic, which may cause reactor runaway and deterioration of catalysts. For this problem, a mathematical model that can predict the behavior inside the reactor is necessary. In this work, we consider the methanation reaction of CO2 in a reactor model and estimate the kinetic parameters in the reaction rate model from experimental data. In the parameter estimation using literature values and Tikhonov regularization, eight kinetic parameters in the rate equations were identified from 64 data points with a wide range of conditions. We confirm that molar fractions at the reactor exit predicted by this reactor model are in good agreement with the experimental results. Furthermore, the developed model was validated to predict the compositions and temperature that were not used in the estimation. We expect the developed model will be a powerful tool for the reactor design.

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.