Power-to-SNG technologies by hydrogenation of CO2 and biomass resources: A comparative chemical engineering process analysis

Power to Synthetic-Natural-Gas (SNG) technology consists of two main steps: water electrolysis and methanation; the primary energy input is usually surplus power from renewable energy sources, while the electrolytic hydrogen and carbon oxides from different CO_x sources are converted into methane that can be fed in the natural gas grid. We focus on methanation technology, where the main criteria are the complexity of process setup and reactor sizes to achieve production and SNG quality for gas-grid injection. The processes are simulated using a plug-flow model for the reactors and a pseudo-homogeneous kinetic law describing the reaction of CO₂ (that is rate limiting). The results show that feeding biogas or syngas (instead of CO₂) for methanation has remarkable effects regarding the operation and design of the processes; it is concluded that Power-to-SNG technologies that use methane rich streams are favorable in terms of biogas upgrading, H₂ requirements, reactor volumes and process simplicity, as far as these resources are available: e.g., using a typical composition (60% CH₄) the required inputs are 0.96 kmol of biogas, 1.54 kmol of H₂ and 0.26 m³ of reactors (two adiabatic beds with recirculation, R/F = 0.695) per kmol/min of pipeline quality dry gas product (95% CH₄), which means 60% hydrogen saving, less than 26% reaction volumes and near 62% reduction of process throughput, when compared to the methanation process that uses pure CO₂; conversion of syngas can be also favorable, but it requires high recirculation due to the large proportions of CO_x; e.g. for syngas (47.3%H₂-25.9%CO-17.2%CO₂-9.6%CH₄), the required values mean a 53% hydrogen saving and less than 25% reaction volumes, but only 11% reduction of process throughput.     

Unsupported cobalt nanoparticles as catalysts: Effect of preparation method on catalytic activity in CO2 methanation and ethanol steam reforming

Cobalt nanoparticles (10–50 nm) have been prepared by different procedures. Materials produced by reduction of cobalt chloride and nitrate by NaBH₄ contain B impurities as borates or borides. They are very active in ethanol steam reforming at 673–773 K with up to 85% hydrogen yield at 773 K. B-free samples obtained by thermal decomposition of Co₂(CO)₈ is slightly less selective to hydrogen, due to its activity in ethanol cracking to methane which is probably poisoned by boron impurities on the other catalysts. B-containing samples are inactive in CO₂ methanation and have weak activity in the reverse water gas shift (RWGS) reaction to CO. B-free nanoparticles have high activity in both CO₂ methanation and RWGS. However, methanation activity is reduced fast by growth of encapsulating carbon species. These particles however also show quite stable activity in RWGS to CO, attributed to CoO impurities.     

Coal char supported Ni catalysts prepared for CO2 methanation by hydrogenation

Catalytic CO₂ methanation is a potential solution for conversion of CO₂ into valuable products, and the catalyst plays a crucial role on the CO₂ conversion and CH₄ selectivity. However, some details involved in the CO₂ methanation over the carbon supported Ni catalysts are not yet fully understood. In this work, commercial coal char (CC) supported Ni catalysts were designed and prepared by two different methods (impregnation-thermal treatment method and thermal treatment-impregnation method) for CO₂ methanation. Effects of the preparation conditions (including the thermal treatment temperature and time, the mass ratio of CC:Ni and the preparation method), as well as the reaction temperature of CO₂ methanation, were investigated on the catalyst morphology, reducibility, structure and catalytic performance. Fibrous Ni-CC catalyst is achieved and shows high CO₂ conversion (72.9%–100%) and CH₄ selectivity (>99.0%) during the 600-min methanation process. Adverse changes of the catalyst surface and textural properties, reducibility, particle size and morphology are the potential factors leading to the catalyst deactivation, and possible solutions resistant to the deactivation were analyzed and discussed. The CO₂ methanation mechanism with the CO route was proposed based on the oxidation-reduction cycle of Ni in this work.     

Kinetics and mechanistic studies of methane dry reforming over Ca promoted 1Co–1Ce/AC-N catalyst

The mechanism and kinetic features of dry reforming with methane (DRM) over Ca promoted 1Co–1Ce/AC-N catalyst was investigated. The mechanistic pathway studies have conducted by FTIR and XPS analysis, structure-activity correlations demonstrated the CH₄ and CO₂ could adsorb on catalyst active sites and generate intermediate CH_x, OH and CH_xO, continue to generate CO and H₂ and then desorbed from active sites. Moreover, CH₄ could also oxidized by Ce⁴⁺ and CO₂ reduced by Ce³⁺, the same content of Ce⁴⁺ and Ce³⁺ on promoted catalyst greatly improved the reaction rate. The kinetic of dry reforming with methane was examined for temperature between 650 and 850 at 800 °C. The research was carried out by changing the CH₄/CO₂ ratios between 0.3 and 3.0. The obtained experiment data were fitted by three typical kinetic models (Power Law, Eley-Rideal and Langmuir-Hinshelwood), the fitting results demonstrated that the best prediction of reforming rates can provided by Langmuir-Hinshelwood model for the reaction temperatures between 650 and 800 °C. Moreover, activation energies of methane and carbon dioxide consumption were ?117 and ?47 kJ/mol, indicating that much higher energy barrier is needed for methane activation compared to carbon dioxide.     

Influence of the operating parameters over dry reforming of methane to syngas

The influence of operating parameters over dry reforming of methane reaction was evaluated using a Ni-based catalyst obtained after calcination of a hydrotalcite-like precursor. The studied variables were mass to flow ratio (W/F), reaction temperature and CO₂/CH₄ ratio. Maximum methane and carbon dioxide conversions were achieved at W/F ratios above 0.21 g h L⁻¹. The higher the W/F ratio was, the lower amount of water was formed, which led to a higher H₂/CO ratio. The increase in reaction temperature produced an increase in conversions. Water concentration in the outlet stream showed a maximum at 600 °C. At this temperature, reverse water–gas-shift reaction (RWGS) was favoured because it is endothermic. However, steam reforming and carbon gasification were also favoured and they consumed great part of the water produced. CO₂/CH₄ ratios above 1 led to a higher CH₄ conversion but selectivity to hydrogen decreased because RWGS reaction was favoured. When CO₂/CH₄ was below unity, CH₄ conversion decreased but less amount of water was produced so a higher H₂ selectivity was achieved. The catalyst exhibited good stability over dry reforming of methane under all the tested conditions, which may be ascribed to its high basicity. This property improved CO₂ adsorption and then RWGS reaction and carbon gasification.     

Syngas methanation with municipal solid waste char supported Ni catalyst: Choice of key parameters and catalyst's response

The low quality municipal solid wastes (MSW) derived char has a potential to be used as a methanation catalyst to achieve low-cost methanation of the syngas derived from MSW, and its performance with varying reaction parameters should be explored for better application. In this study, a MSW char supported Ni-based catalyst (Ni-MSWC) was prepared by impregnation; the influences of CO₂ and CH₄ impurities in the raw syngas on methanation and the feasibility of conducting methanation in a low-pressure condition were investigated, then the catalyst's response to the changing parameters was identified. The results showed that the presence of low concentration CO₂ in the H₂-rich syngas is favorable to the gasification of the char carrier and activates Ni-MSWC catalyst. However, it also promotes F–T synthesis reaction and leads to a decrease in the methane yield (Y_CH4). The decrease in reaction pressure causes a decrease in Y_CH4 and results in coke formation; but inhibits F–T synthesis reaction and increases methane selectivity (S_CH4). A higher reaction pressure increases system complexity and accelerates char carrier consumption. Moreover, presence of methane by 2.8% (vol.) promotes the methanation of CO₂ through the methane dry reforming reaction, but it inevitably causes coke formation and affects the catalyst's stability. Based on Y_CH4 and Ni-MSWC's responses, CO:CO₂ ≥ 3:2 and reaction pressure of 1 MPa (gauge pressure) are recommended, which help to inhibit the side reactions and maintain a high Y_CH4 (>95%).     

Methanation reactions for chemical storage and purification of hydrogen: Overview and structure-reactivity correlations in supported metals

The drastic effects associated with climate changes, mainly induced by the increasing carbon emissions, challenge our modern society and mandate immediate solutions. This requires in the first place, accelerating the introduction of green alternatives for the standing carbon-based energy technologies, and simultaneously increasing the contribution of the carbon-free renewables to our energy sector. Among a few catalytic processes, the methanation of carbon oxides is currently envisaged as a cornerstone in the renewable energy concepts. On one hand, the methanation of CO is intensively studied for ultra-purification of reforming-generated hydrogen feed gases used in the low-temperature hydrogen fuel cells and in the production of ammonia. This involves the selective methanation of CO in CO₂-rich H₂ fuels to lower CO concentration from about 5000 ppm down to <5 ppm. The other major application involves the solo or the total methanation of CO and CO₂. This involves the conversion of syngas or the methanation of air-captured CO₂ using green hydrogen produced from renewable energies (power-to-gas). These aspects revive the importance of Sabatier reactions and presents them as an essential part of the cycle of renewable-energy applications. In this review, we will focus on the recent advancements of the methanation of CO and CO₂ on oxide supported Ni and Ru catalysts in the frame of their use in the abovementioned applications. After an overview of different catalytic processes related to hydrogen production, we will basically concentrate on the structure-reactivity relationships of CO and CO₂ methanation in different applications, highlighting limitations and advantages of different catalytic systems. Basically, we will map out the interplay of different electronic and structural features and correlate them to the catalytic performance for CO and CO₂ methanation. This includes the discussion of metal particle size effect, nature of the support, and the effect of reaction gas atmospheres. Clarifying the interplay of these parameters will help us to further understand the metal-support interaction (MSI) based on structural (SMSIs) and electronic (EMSIs) aspects which is essential for steering the catalytic performance of these catalysts for a specific reaction pathway.     

Optimization of content of components over activated carbon catalyst on CO2 reforming of methane using multi-response surface methodology

To accurately and efficiently optimize the component content of the catalyst is one important strategy to fabricate robust catalysts. By multi-response surface methodology (RSM), this study chose promising metal components (Co, Ce, and W) supported over activated carbon as a catalyst to investigate the catalytic activity of CO₂–CH₄ reforming. First, the center point of the center-complex design (CCD) based on RSM was determined by single-factor experiment, Co, W and Ce were loaded with 10.1 wt%, 9.7 wt%, and 9.2 wt%, respectively. Then, the three-factor and five-level CCD was exhibited. Four well-matched quadratic regression models (R² is close to 1) were developed to gain a better understanding of the effects of the individual component content and their interactions on CH₄ conversion, CO₂ conversion, H₂ yield, and CO yield. The results showed that W content was the most important negative parameter affecting the conversion of CH₄ and CO₂, while the Co and Ce content played a significant positive role in the catalyst performance. The interactive effects of all different component content imposed a significant effect on the CO₂ conversion and CO yield. At last, the content optimization suggested that the optimal catalytic activity was achieved at the content of Co, W, and Ce of 10.6 wt%, 6.5 wt%, and 8.6 wt%, respectively, which was validated by a mean error of less than 2.2%.     

Hydrogen production from CH4 dry reforming over Sc promoted Ni / MCM-41

The activity of Ni supported on MCM-41 catalyst with/without scandium promoter was investigated for hydrogen production. The performance of the catalysts with different Sc loadings (0.00, 0.10, 0.25, 0.50, 0.75, 1.00 and 3.00 wt%) was examined. N₂ adsorption-desorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the characterization of the catalytic materials. The prepared catalysts were tested in dry reforming of methane. The effect of Sc addition on activity, hydrogen yield, H₂/CO ratio and stability are discussed. CH₄ and CO₂ conversions were measured under atmospheric pressure at 800 °C. Low Sc loading (<0.75 wt%) showed a positive effect on H₂ yield, CH₄ and CO₂ conversions. Addition of Sc strengthened the interaction of Ni with support and also increased the basicity which in turn affected the amount of CO₂ adsorbed on the surface of the catalyst. Notably, promoting with Sc almost suppressed the carbon formation leading to outstanding catalytic stability; thus 17% carbon deposition reduction was attained. The effect of different reaction temperatures, GHSV and CH₄:CO₂ ratio was also investigated.     

Study on hydrogen-rich syngas production by dry autothermal reforming from biomass derived gas

In this study, the H₂-rich syngas (H₂ + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO₂/CH₄ and O₂/CH₄ molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO₂ concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H₂/CO molar ratio between 1 and 2 was achieved by varying CO₂/CH₄ molar ratio. However, the syngas concentrations were affected by CO₂/CH₄ and O₂/CH₄ molar ratio.     

Optimization of boron dispersion on fibrous-silica-nickel catalyst for enhanced CO2 hydrogenation to methane

There are numerous reports regarding boron-containing catalysts for hydrogen-related reactions from CO₂ including dry reforming of methane and methanation. Besides enhancing the productivity, boron also improved nickel activity and stability. However, the detailed mechanistic study, particularly in explaining the starring role of boron in the enhanced reactions, is still lacking. Thus, herein we loaded boron on fibrous-silica-nickel and investigated their physicochemical properties and mechanistic route by means of in-situ FTIR for enhanced CO₂ methanation. It was found that the appropriate dispersion of boron surrounds the nickel particles is an important factor to improve the adsorption of CO₂ before interacting with split hydrogen atom from the nickel sides to form intermediates which are subsequently dehydrated, and then serial hydrogenation gave the final product of methane. Boron also accelerated the methanation and restricted coke formation. A hybrid approach on optimization via a face-centered central composite design and a response surface methodology showed that reaction using H₂/CO₂ ratio of 6, GHSV of 10,500 mL g^?1 h^?1, at 500 °C gave the highest percentage of CH₄ of 84.3%. To indicate the error, the predicted values were compared to the experimental values, yielding an accurately minimal error ranging from 0 to 11%. As a result, the empirical models generated for CO₂ hydrogenation to methane were reasonably accurate, with all actual values for the confirmation runs fitting within the 94% prediction interval.     

Numerical study of syngas production via CH4–H2S mixture partial oxidation

The detailed kinetic mechanism of pyrolysis and oxidation of the H₂S–CH₄ mixture was developed. The mechanism was validated on experimental data on the ignition delay, laminar flame velocity, conversion degree of H₂S and CH₄, as well as on the yield of main conversion products – H₂ and CO. The developed mechanism was used for a numerical study of the conversion degree of H₂S and CH₄, the syngas yield and syngas composition during partial oxidation of the H₂S–CH₄ mixture with H₂S/CH₄ = 1/9, 1/4 and 3/1 in a plug flow reactor of 1 m in length in the wide range of initial temperature (T₀ = 600–1400 K) and fuel-to-air equivalence ratio (ϕ = 1–30). It is shown that the maximum relative yield of syngas can be obtained at ϕ = 3–5 depending on T₀ and the H₂S/CH₄ ratio in the fuel. The mole fraction of H₂ in syngas is higher than that of CO. For the mixture with H₂S/CH₄ = 3/1, the mole fraction of H₂ can be greater than the equilibrium value in a certain range of ϕ∼6–10. The reasons for this effect are analyzed. The mole fraction of CO in conversion products rapidly decreases with increasing ϕ. As a result, the ratio γ_H2/γ_CO increases fast with the growth of ϕ. Besides H₂ and CO, the conversion products can contain S₂ and NO (at ϕ∼2), CS (at ϕ∼3), CS₂ (at 3 < ϕ < 10), unburned hydrocarbons (at ϕ > 3) and other species. The least amount of conversion byproducts is observed at ϕ = 3–3.5 when there is the maximum syngas yield. Syngas selectivity turned out maximal at ϕ = 2.5–3. Therefore, ϕ∼3 seems to be the most optimal value for carrying out the conversion of H₂S–CH₄ mixtures.     

Mixed reforming of methane over Ni–K/CeO2–Al2O3: Study of catalyst performance and reaction kinetics

Syngas can be effectively produced by mixed reforming of methane (MRM). In this work, the performance of Ni–K/CeO₂–Al₂O₃ catalyst in this process was investigated in a fixed-bed reactor in the 923–1073 K range. Both potassium and ceria are renowned for improving the performance of Ni catalyst in the reforming process. The influence of reaction conditions (viz. temperature, space time, feed composition and time-on-stream) on the conversion of two reactants CH₄ and CO₂, yield of the products H₂ and CO and the H₂/CO ratio in syngas were studied. At T = 1073 K and W/Q₀ = 0.17 g-h/L (here, W and Q₀ denote catalyst mass and volumetric flow rate of feed), conversions of CH₄ and CO₂ were 91.2 and 80.1%. When S/C ratio (or steam-to-carbon ratio) in feed increased from 0.2 to 0.5 mol/mol, H₂/CO ratio at T = 1073 K changed from 1.32 to 2.14 mol/mol. The catalyst performed stably for 50 h of time-on-stream. Reaction kinetics was studied between 973 and 1073 K and power law kinetic model was suggested. The apparent activation energy values for consumption of CH₄ and CO₂ were found to be 33.3 and 45.5 kJ/mol, respectively. This work is expected to aid catalyst development and reactor design for the MRM process.     

Simultaneous production of hydrogen and carbon nanotubes from biogas: On the design of combined process

We introduced a novel combined process of CO₂ methanation (METH) and catalytic decomposition of methane (CDM) for simultaneous production of hydrogen (H₂) and carbon nanotubes (CNTs) from biogas. In this process, biogas is catalytically upgraded into CH₄-rich gas in METH reactor using Ni/CeO₂ catalyst, and the obtained CH₄-rich gas is subsequently decomposed into H₂ and CNTs in CDM reactor over CoMo/MgO catalyst. Among the three different process scenarios proposed, the combined process with a steam condenser equipped between METH and CDM reactors could greatly improve a CNTs productivity. The CNTs production yield increased by more than 2.5-fold, maximizing at 9.08 gCNTs/gCat with a CNTs purity of 90%. The deposited carbon product was characterized as multi-walled carbon nanotubes (MWCNTs) with a surface area of 136.0 m²/g, comparable with commercial CNTs of 199.8 m²/g. The remarkable I_G/I_D ratio of 2.18 confirms a superior portion of graphitic carbon in the synthesized CNTs upon the commercial CNTs with I_G/I_D = 0.74. Notably, the CH₄ conversion reached 94.5%, while the CO₂ conversion achieved 100%, resulting in the H₂ yield and H₂ purity higher than 90%. This combined process demonstrates a promising route for production of high quality CNTs and high purity H₂ with complete CO₂ conversion using biogas as abundant renewable energy resources. In addition, the test of raw biogas showed no deactivation of catalyst, justifying the implementation of the developed process for real biogas without purification.     

Zirconia-supported tungsten oxides for cyclic production of syngas and hydrogen by methane reforming and water splitting

ZrO₂-supported tungsten oxides were used for cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation). The reduction characteristics of WO₃ to WO₂ and WO₂ to W were examined at various temperatures (1073–1273 K) and reaction times. Significant portions of the tungsten oxides were also reduced by the produced H₂ and CO. The extent of reduction by H₂ varied greatly depending on temperature and WO₃ content and also on the reduction of either WO₃ or WO₂, while that by CO was consistently low. When the overall degree of reduction became sufficiently high, methane decomposition started to proceed rapidly, resulting in considerable carbon deposition and H₂ production. Consequently, the H₂/(CO + CO₂) ratio varied from around 1 to higher than 2. During the repeated cyclic operations with a proper reduction time at a given temperature, the syngas and hydrogen yields decreased gradually while the H₂/(CO + CO₂) ratio remained nearly constant and the carbon deposition was negligible.     

Production of hydrogen by partial oxidation with thermal plasma

The purpose of this paper is to investigate the characteristics and optimum operating conditions of the plasmatron-assisted CH₄ reforming reaction for the hydrogen-rich gas production. In order to increase the hydrogen production and the methane conversion rate, parametric screening study was conducted at various CH₄ flow ratio and steam flow ratio and with and without adding catalyst in the reactor. High-temperature plasma flame was made with air and arc discharge, and the air flow rate and the input power were set to 5.1  L/min and 6.4 kW, respectively.When the steam flow ratio was 30.2%, the hydrogen production was maximized and the optimal methane conversion rate was 99.7%. Under these optimal conditions, the following syngas concentrations were determined: H₂, 50.4%; CO, 5.7%; CO₂, 13.8%; and C₂H₂, 1.1%. H₂/CO ratio was 9.7 and the hydrogen yield was 93.7%.     

Carbon dioxide reforming of methane in a SrCe0.7Zr0.2Eu0.1O3−δ proton conducting membrane reactor

Utilizing CO₂ for fuel production holds the promise for reduced carbon energy cycles. In this paper we demonstrate a membrane reactor, integrating catalytic CO₂ reforming of methane with in-situ H₂ separation, that results in increased CO₂ and CH₄ conversion and H₂ production compared to a Ni catalyst alone. The tubular proton-conducting SrCe_0.7Zr_0.2Eu_0.1O_3−δ membrane reactor demonstrates that the addition of the membrane improves CO₂ conversion, due to in-situ H₂ removal, by 10% and 30% at 900 °C for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1 feed ratios, respectively. It also improves total H₂ production at 900 °C by 15% and 18% for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1, respectively. Further, the H₂/CO in the reactor side effluent can be adjusted for subsequent desired Fischer-Tropsch products by combining CO₂ reforming and steam reforming of methane.     

Combined air partial oxidation and CO2 reforming of coal bed methane to synthesis gas over co-precipitated Ni-Mg-ZrO2 catalyst

The present study aims at exploring a concept which can convert coal-bed methane (containing methane, air and carbon dioxide) to synthesis gas. Without pre-separation and purification, the low-cost synthesis gas can be produced by coupling air partial oxidation and CO₂ reforming of coal bed methane. For this purpose, the co-precipitated Ni-Mg-ZrO₂ catalyst was prepared. It was found that the co-precipitated Ni-Mg-ZrO₂ catalyst exhibited the best activity and stability at 800 °C during the reaction. The conversions of CH₄ and CO₂ maintained at 94.8% and 82.1% respectively after 100 h of reaction. The effect of reaction temperature was investigated. The H₂/CO ratio in the product was mainly dependent on the feed gas composition. By changing O₂/CO₂ ratio of the feed gases, the H₂/CO ratio in the off-gas varied between 0.8 and 1.8. The experimental results showed that the high thermal stability and basic properties of the catalyst, and the strong metal-support interaction played important roles in improving the activity and stability of the catalyst. With the combined reactions and the Ni-Mg-ZrO₂ catalyst, the coal bed methane could be converted to synthesis gas, which can meet the need of the subsequent synthesis processes.     

Influence of CO2, CH4, and initial temperature on H2/CO laminar flame speed

The objective of this study is to investigate the impact of syngas composition by varying the H₂/CO ratio (1:3, 1:1, and 3:1 by volume), the CO₂ dilution (0%–40%), and methane addition (0%–40%) on laminar flame speed. Thus, laminar flame speeds of premixed syngas–air mixtures were measured for different equivalence ratios (0.8–2.2) and inlet temperatures (295–450 K) using the Bunsen-burner method. It was found that laminar flame speed increases with increasing H₂/CO ratio, while CO₂ dilution or CH₄ addition decreased it. The location of the maximum flame speed shifts to richer mixtures with decreasing H₂/CO ratio, while it shifts to leaner mixtures with the addition of CH₄ due to its inherent slower flame speed. The location of the maximum flame speed is also shifted towards leaner mixtures with the addition of CO₂ due to the preponderance of the reduction of the adiabatic flame temperature with increasing dilution. Comparison between experimental and numerical results shows a better agreement using a modified mechanism derived from GRI-Mech 3.0. A correlation, based on the experimental results, is proposed to calculate the laminar flame speed over a wide range of equivalence ratios, inlet temperatures, and fuel content.     

Alumina-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co_3-xAl_xO₄ and, for the silica-containing sample, of a segregated Co₃O₄ phase is evident. These catalysts have been tested in CO₂ hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523–773 K. Both catalysts are active in CO₂ hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO₂ hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al₂O₃, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO₂ hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH₄ selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon.