Hydrogen storage in carbon fibers activated with supercritical CO2: Models and the importance of porosity

In this work we studied the adsorption of H₂ at 77 K and 0.0–0.12 MPa onto carbon fibers activated with supercritical CO₂ (ACFs) and with different burn-offs (10–53%). The highest amount of H₂ stored was 2.45 wt% in an ACF with a burn-off of 51% at 0.12 MPa. The measured isotherms were analyzed using an equilibrium model derived by analogy with a multiple-site Langmuir-type adsorption model. The different equilibria correspond to adsorption in pores of different sizes. The experimental results fitted a model with two different adsorption sites satisfactorily, allowing such sites to be related to the microporous structure of the ACFs. Thus, a high-energy adsorbent–adsorbate interaction site, associated with very small micropores, accessible only to very small molecules such as H₂, and another lower-energy site associated with larger pores can be proposed. The model also predicts the adsorption behavior under equilibrium conditions at higher pressures, allowing the maximum adsorption capacity of the ACFs to be determined. The results show that the ACFs adsorb most of the H₂ molecules at low equilibrium pressures, and that they become almost saturated at pressures around 1.0 MPa. The maximum H₂ storage capacity in these ACFs lies between 1.50 and 3.15 wt%.     

Activated carbons with appropriate micropore size distribution for hydrogen adsorption

We measured hydrogen storage on five well-known commercial carbon materials (CCMs) and we compared their performances to those obtained on our lab-made activated carbons (ACs). H₂ uptake of our lab-made ACs was always higher than that of CCMs of similar S_BET, our best AC reached 6 wt.% H₂ excess adsorption at 77 K and 4 MPa. We calculated the contribution of four ranges of pores (<0.5 nm; 0.5-0.7 nm, 0.7-2 nm and >2 nm) to the H₂ excess adsorption for the 14 carbon materials considered in this study. We clearly demonstrated that: (i) the superiority in H₂ excess adsorption of lab-made ACs over the CCMs is related to their pore size distribution; (ii) H₂ uptakes higher than 3 wt.% are due to pores with diameter wider than 0.7 nm.     

Separation of H2/CH4 gas mixture through graphenylene membrane with functionalized nanopore: A computational study

Using molecular dynamics (MD) simulations, we investigated the performance of graphenylene membrane with functionalized nanopore in the H₂/CH₄ separation. In the present work, we studied the impact of functionalized nanopore, system temperature (298, 323, and 348 K), applied difference pressure (up to 2 MPa), and feed composition on the H₂/CH₄ separation performance. The passage of gas molecules across the nanopore was monitored within the simulations, and the permeance was determined under applied conditions. The results revealed that the size of gas molecules and its interaction with the membrane nanopore are two important factors in the separation performance of H₂/CH₄ gas mixture. It is also found that H₂ molecules can easily pass through the studied membranes, whereas no CH₄ molecule was seen in the permeate side, which confirms the ultrahigh selectivity of H₂ over CH₄. Furthermore, the maximum H₂ permeance of 1.95 × 10⁵ GPU through the pore 1 was obtained at 1.5 MPa, which was higher than that of 1.93 × 10⁵ GPU through pore 2. The results also demonstrated that the system temperature doesn't have any effect on the membrane performance. To this end, the permeance of H₂ molecules through the studied membranes obviously increased with raising the ration of H₂ molecules in the feed composition. Due to high selectivity and permeance, the graphenylene membrane with functionalized nanopore is expected to have promising applications in hydrogen separation from H₂/CH₄ mixed gas.     

Carbon oxides methanation in equilibrium; a thermodynamic approach

Global warming and greenhouse gases as two main threat to human societies due to increasing carbon oxides, such as CO and CO₂ and lack of energy storages results in challenges efforts to controlling these atmospheric pollutions in various ways and methods. Carbon oxides methanation was considered as chemical process to conversion carbon oxides to their products as syngas. Various parameters can be effective on this process such as temperature, pressure and equivalence ratio of feeding products specially H₂/CO₂ and H₂/CO. In this study, three various equivalence ratio of feeding products were investigated against pressure and temperature in equilibrium condition to determine concentration of main products. Five various pressures applied to system of equilibrium, i.e. 1, 5, 10, 25, 50 atm beside temperature change from 200 K to 1500 K. Moreover, fugacity effects also were investigated in Soave–Redlich–Kwong equation of state in comparison with ideal gas. Results revealed that fugacity was completely changes the results especially for water production and hydrogen consumption. According to the results, carbon di and monoxides conversion were increased during pressure increasing where methane selectivity also increased. In maximum condition of coke formation there was 0.1 mol fraction of it in both CO and CO₂ methanation. Although, higher equivalence ratio of each carbon oxides combination feeding products ascended CH₄ selectivity and yield but in high equivalence ratio (ER = 6) CH₄ yield decreased about 8% for both investigated methanation process. In lower equivalence ratio (lower than stoichiometric) condition, methane yield replaced with mainly carbon yield.     

Optimization of VPSA-EHP/C process for high-pressure hydrogen recovery from Coke Oven Gas using CO selective adsorbent

The production of hydrogen through conventional pathways and recovery from by-products typically utilize pressure swing adsorption (PSA) technology as final purification step. Dual-layered PSA columns packed with conventional activated carbon and molecular sieve 5A material exhibit relatively low selectivity for O₂, N₂ and CO in particular. Therefore, eliminating CO (and other poisons) using conventional PSA to acceptable concentrations for EHP/C is only achievable with lower recovery rates. To improve recovery rates, there is a need for a highly efficient purification process that is highly selective for these hydrogen contaminants without compromising the product quality. Here we report an optimization study where vacuum PSA (VPSA) and electrochemical hydrogen purification and compression (EHP/C) technology is utilized for purification and compression of hydrogen from Coke Oven Gas (COG). The VPSA columns were packed with activated carbon and CuCl(7.0)-activated carbon to selectively retain poisonous CO₂ and CO, respectively. The optimal operating conditions were determined with surrogate models produced via non-linear regression of known sample input-output data points, by varying the adsorbent layering ratio (0.30–0.84), adsorption pressure (0.38–0.78 MPa), purge to feed ratio (P/F-ratio) (1–10%), adsorption step time (100–1500 s) and the EHP/C stack current per cell (37–52 A) in the original models. The two-bed VPSA system obtained 90.5% recovery and retained CO and CO₂ below their thresholds at 0.84 layering ratio, 0.78 MPa adsorption pressure, 840s adsorption time and 5.3% P/F-ratio, at the expense of H₂ purity (77.1%) by breakthrough of CH₄, N₂ and O₂. Hydrogen purity was upgraded to >99.999% by EHP/C, which recovered 90.0% of hydrogen and simultaneously compressed to 20 MPa, which required 3.2 kWh/kg H₂. The overall VPSA-EHP/C recovery rate in this configuration was 81.5%. By utilizing the EHP/C retentate gas as VPSA purge gas, overall VPSA-EHP/C recovery rates may reach 87.3% and consume less energy due to a decrease in adsorption pressure. We show that adsorption columns designed to function as poisonous component eliminator are an effective strategy to pre-condition hydrogen synthesis gases prior to further processing with EHP/C. Although the EHP/C was exposed to significant concentrations of methane, nitrogen and oxygen by their advancement through VPSA, the performance was only slightly affected. The VPSA-EHP/C method is applicable to a wide range of hydrogen gas mixtures that require further purification and compression. Traditional PSA for purification from primary and by-product (COG, annealing, chlor-alkali and flat/float glass manufacturing) hydrogen sources can be changed to a VPSA-EHP/C systems for hydrogen purification and simultaneous compression.     

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.     

Hydrogen and/or syngas production by combined steam and dry reforming of methane on nickel catalysts

Two alumina supported Ni catalysts with pore sizes of 5.4 nm and 9 nm were synthetized, characterized and tested in the Combined Steam and Dry Reforming of Methane (CSDRM) for the production of hydrogen rich gases or syngas. The reaction mixture was designed to simulate the composition of real clean biogas, the addition of water being made in order to have molar ratios of H₂O:CO₂ corresponding to 2.5:1, 7.5:1 and 12.5:1. Structural and functional characterization of catalysts revealed that Ni/Al₂O₃ with larger pore size shows better characteristics: higher surface area, lower Ni crystallite sizes, higher proportion of stronger catalytic sites for hydrogen adsorption, and higher capacity to adsorb CO₂. At all studied temperatures, for a CH₄:CO₂:H₂O molar ratio of 1:0.48:1.2, a (H₂+CO) mixture with H₂:CO ratio around 2.5 is obtained. For the production of hydrogen rich gases, the optimum conditions are: CH₄:CO₂:H₂O = 1:0.48:6.1 and 600 °C. No catalyst deactivation was observed after 24 h time on stream for both studied catalysts, and no carbon deposition was revealed on the used catalysts surface regardless the reaction conditions.     

Three-dimensional porous Mn–Ni/Al2O3 microspheres for enhanced low temperature CO hydrogenation to produce methane

CO methanation has attracted much attention because it transforms CO in syngas and coke oven gas into CH₄. Here, porous Al₂O₃ microspheres were successfully used as catalyst supports meanwhile the Mn was used as a promoter of Ni/Al₂O₃ catalysts. The as-obtained Ni/Al₂O₃ and Mn–Ni/Al₂O₃ samples display a micro-spherical morphology with a center diameter near 10 μm. Versus the Ni/Al₂O₃ catalyst, the 10Mn–Ni/Al₂O₃ catalyst exhibits a high specific surface area of 92.5 m²/g with an average pore size of 7.0 nm. The 10Mn–Ni/Al₂O₃ catalyst has the best performance along with can achieve a CO conversion of 100% and a CH₄ selectivity of 90.7% at 300 °C. Even at 130 °C, the 10Mn–Ni/Al₂O₃ catalyst shows a CO conversion of 44.0% and a CH₄ selectivity of 84.1%. The higher low-temperature catalytic activity may be since the catalyst surface contains more CO adsorption sites and thus has a stronger adsorption performance for CO. Density functional theory (DFT) calculations confirm that the Mn additive enhances the adsorption of CO, especially for the 10Mn–Ni/Al₂O₃ catalyst with the strongest adsorption energy.     

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.     

Gibbs free energy minimization as a way to optimize the combined steam and carbon dioxide reforming of methane

Gibbs free energy minimization was applied to study thermodynamic equilibrium of the combined steam and carbon dioxide reforming of methane. Coke deposition, the content of methane and carbon dioxide in syn-gas as well as H₂/CO ratio were investigated as a function of CO₂/CH₄ and H₂O/CH₄ mole ratios at different temperatures and pressures. The ranges of the molar ratios CH₄/CO₂/H₂O in the feed with H₂/CO = 2.1-2.2 were identified at which reforming of methane is not complicated by coke deposition. For each range optimized CH₄/CO₂/H₂O molar ratios characterized by the lowest content of methane and carbon dioxide in syn-gas were found.     

Facile synthesis of hybrid porous composites and its porous carbon for enhanced H2 and CH4 storage

The anticipated energy crisis due to the extensive use of limited stock fossil fuels forces the scientific society for find prompt solution for commercialization of hydrogen as a clean source of energy. Hence, convenient and efficient solid-state hydrogen storage adsorbents are required. Additionally, the safe commercialization of huge reservoir natural gas (CH₄) as an on-board vehicle fuel and alternative to gasoline due to its environmentally friendly combustion is also a vital issue. To this end, in this study we report facile synthesis of polymer-based composites for H₂ and CH₄ uptake. The cross-linked polymer and its porous composites with activated carbon were developed through in-situ synthesis method. The mass loadings of activated carbon were varied from 7 to 20 wt%. The developed hybrid porous composites achieved high specific surface area (SSA) of 1420 m²/g and total pore volume (TPV) of 0.932 cm³/g as compared to 695 m²/g and 0.857 cm³/g for pristine porous polymer. Additionally, the porous composite was activated converted to a highly porous carbon material achieving SSA and TPV of 2679 m²/g and 1.335 cm³/g, respectively. The H₂ adsorption for all developed porous materials was studied at 77 and 298 K and 20 bar achieving excess uptake of 4.4 wt% and 0.17 wt% respectively, which is comparable to the highest reported value for porous carbon. Furthermore, the developed porous materials achieved CH₄ uptake of 8.15 mmol/g at 298 K and 20 bar which is also among the top reported values for porous carbon.     

Steam reforming of methane over unsupported nickel catalysts

This paper describes a study of steam reforming of methane using unsupported nickel powder catalysts. The reaction yields were measured and the unsupported nickel powder surface was studied to explore its potential as a catalyst in internal or external reforming solid oxide fuel cells. The unsupported nickel catalyst used and presented in this paper is a pure micrometric nickel powder with an open filamentary structure, irregular ‘fractal-like’ surface and high external/internal surface ratio. CH₄ conversion increases and coke deposition decreases significantly with the decrease of CH₄:H₂O ratio. At a CH₄:H₂O ratio of 1:2 thermodynamic equilibrium is achieved, even with methane residence times of only ∼0.5 s. The CH₄ conversion is 98 ± 2% at 700 °C and no coke is generated during steam reforming which compares favorably with supported Ni catalyst systems. This ratio was used in further investigations to measure the hydrogen production, the CH₄ conversion, the H₂ yield and the selectivity of the CO, and CO₂ formation. Methane-rich fuel ratios cause significant deviations of the experimental results from the theoretical model, which has been partially correlated to the adsorption of carbon on the surface according to TEM, XPS and elemental analysis. At the fuel: water ratio of 1:2, the unsupported Ni catalyst exhibited high catalytic activity and stability during the steam reforming of methane at low-medium temperature range.     

Computational screening of metal-organic frameworks with open copper sites for hydrogen purification

With the increasing demand for environmental protection worldwide, metal-organic frameworks (MOFs) have been pivotal in the clean energy domain. Due to the high surface areas, large porosities and structural tunability, they are promising for the adsorption separation of H₂/CH₄ mixtures. High-throughput computational screening was adopted to identify the optimal adsorbents for hydrogen purification from 502 MOFs with open copper sites. Firstly, the adsorption performance of H₂/CH₄ mixture in 440 MOFs, which exhibit non-zero surface area and over -3.8 Å largest cavity diameter (LCD), was calculated using grand canonical Monte Carlo (GCMC) simulations at 300 K and various pressures. Secondly, we identified the top 9 high-performance MOFs by evaluating the ranking of candidate adsorbent performance according to a combination metric of adsorption performance score (APS, the product of adsorption capacity of CH₄ and selectivity of CH₄ over H₂) and percent regenerability (R%). PCN-39 and MOF-505 exhibit high APS of 101 mol kg⁻¹ and 67.9 mol kg⁻¹, respectively, promising for hydrogen purification. Subsequently, the breakthrough curves of H₂/CH₄ mixture through the fixed bed packed with some optimal MOFs were predicted to evaluate their effects in practical hydrogen purification. UMODEH08 or UMOBEF04 exhibits the long dimensionless residence time over 30 of CH₄ for the H₂/CH₄ separation. Finally, we also explored the behaviors of the radial distribution functions (RDF) and adsorption equilibrium configurations to further demonstrate how the selected MOFs differentiate CH₄ from H₂. The investigation on all these observations at molecular level will pave the way for the development of new materials for clean energy applications.     

Flowerlike microspheres catalyst NiO/La2O3 for ethanol-H2 production

Catalysts of nano-sized nickel oxide particles based on flowerlike lanthanum oxide microspheres with high disperse were prepared to achieve simultaneous dehydrogenation of ethanol and water molecules on multi-active sites. XRD, SEM, 77K N₂ adsorption were used to analyze and observe the catalysts’ structure, morphology and porosity. Catalytic parameters with respect to yield of H₂, activity, selectivity towards gaseous products and stability with time-on-stream and time-on-off-stream were all determined. This special morphology NiO/La₂O₃ catalyst represented more than 1000 h time-on-stream stability test and 500 h time-on-off-stream stability test for hydrogen fuel production from ethanol steam reforming at 300 °C without any deactivation. During the 1000 h time-on-stream stability test, ethanol–water mixtures could be converted into H₂, CO, and CH₄ with average selectivity values of 57.0, 20.1, 19.6 and little CO₂ of 3.2 mol%, respectively, and average ethanol conversion values of 96.7 mol%, with H₂ yield of 1.61 mol H₂/mol C₂H₅OH. During the 500 h time-on-off-stream stability test, ethanol–water mixtures could be converted into H₂, CO, CH₄ and CO₂ with average selectivity values of 65.1, 17.3, 15.1 and 2.5 mol%, respectively, and average ethanol conversion values of 80.0 mol%. For the ethanol-H₂ and petrolic hybrid vehicle (EH–HV), the combustion value is the most important factor. So, it was very suitable for the EH–HV application that the low temperature ethanol steam reforming products’ distribution was with high H₂, CO, CH₄ and very low CO₂ selectivity over the special NiO/La₂O₃ flowerlike microspheres.     

Methane dry reforming using oil palm shell activated carbon supported cobalt catalyst: Multi-response optimization

Dry reforming of methane with carbon dioxide was investigated using oil palm shell activated carbon (OPS-AC) supported cobalt catalyst. The cobalt loaded OPS-AC catalysts were prepared by wet-impregnation method and characterized using SEM, FESEM, BET, TPR and TPD. Surface morphology of OPS-AC supported cobalt catalysts exhibited higher porosity, surface area and micropore volume with different densities of cobalt particles and support. Furthermore, greater amount of H₂ chemisorbed and acidity were observed with increasing cobalt contents. Response surface methodology (RSM) was employed to design the experiments based on factorial central composite design. Catalytic testing was performed using a micro reactor system by varying four variables: temperature, gauge pressure, CH₄/ CO₂ ratio and gas hourly specific velocity (GHSV). H₂ and CO yields were analyzed and quantified by gas chromatography with thermal conductivity detector (TCD). Both responses (H₂ and CO) yields were optimized simultaneously using desirability function analysis. Reaction temperature was the most influential variable with high desirability prevalent for both responses. The optimum response values of H₂ and CO yields corresponded to 903 °C, 0.88 bar(g), CH₄/ CO₂ = 1.31 and GHSV = 4,488 mL/h.g-catalyst.     

Thermodynamic analysis of aqueous phase reforming of three model compounds in bio-oil for hydrogen production

Thermodynamic analysis with Gibbs free energy minimization was performed for aqueous phase reforming of methanol, acetic acid, and ethylene glycol as model compounds for hydrogen production from bio-oil. The effects of the temperature (340-660 K) and pressure ratio Psys/PH₂O (0.1-2.0) on the selectivity of H₂ and CH₄, formation of solid carbon, and conversion of model compounds were analyzed. The influences of CaO and O₂ addition on the formation of H₂, CH₄, and CO₂ in the gas phase and solid phase carbon, CaCO₃, and Ca(OH)₂ were also investigated. With methanation and carbon formation, the conversion of the model compounds was >99.99% with no carbon formation, and methanation was thermodynamically favored over hydrogen production. H₂ selectivity was greatly improved when methanation was suppressed, but most of the inlet model compounds formed solid carbon. After suppressing both methanation and carbon formation, aqueous phase reforming of methanol, acetic acid and ethylene glycol at 500 K and with Psys/PH₂O = 1.1 gave H₂ selectivity of 74.98%, 66.64% and 71.38%, respectively. These were similar to the maximum stoichiometric hydrogen selectivity of 75.00% (methanol), 66.67% (acetic acid), and 71.43% (ethylene glycol). At 500 K and 2.90 MPa, as the molar ratio of CaO/BMCs increased, the normalized variation in H₂ increased and that for CH₄ decreased. Formation of solid carbon was effectively suppressed by addition of O₂, but this was at the expense of H₂ formation. With the O₂/BMCs molar ratio regulated at 1.0, oxidation and CO₂ capture increased the normalized variation in H₂ to 33.33% (methanol), 50.00% (acetic acid), and 60.00% (ethylene glycol), and the formation of solid carbon decreased to zero.     

Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO₃ and La_1−xCe_xNiO₃ (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H₂ + CO). The gaseous reactants consisted of CO₂ and CH₄ in a molar ratio of 1:1. At a GHSV of 10,000 hr⁻¹, CH₄ conversion over LaNiO₃ catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO₂ conversion increased from 51% to 92%. The achieved selectivities of CO and H₂ were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H₂ to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La₂O₂CO₃ phases after CO₂ reforming. The FE-SEM results reveal carbon whisker of the LaNiO₃ catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H₂-TPR results confirm that Ce metals can store and provide oxygen.     

Hydrogen production for fuel cells through methane reforming at low temperatures

Hydrogen production for fuel cells through methane (CH₄) reforming at low temperatures has been investigated both thermodynamically and experimentally. From the thermodynamic equilibrium analysis, it is concluded that steam reforming of CH₄ (SRM) at low pressure and a high steam-to-CH₄ ratio can be achieved without significant loss of hydrogen yield at a low temperature such as 550 °C. A scheme for the production of hydrogen for fuel cells at low temperatures by burning the unconverted CH₄ to supply the heat for SRM is proposed and the calculated value of the heat-balanced temperature is 548 °C. SRM with and/or without the presence of oxygen at low temperatures is experimentally investigated over a Ni/Ce–ZrO₂/θ-Al₂O₃ catalyst. The catalyst shows high activity and stability towards SRM at temperatures from 400 to 650 °C. The effects of O₂:CH₄ and H₂O:CH₄ ratios on the conversion of CH₄, the hydrogen yield, the selectivity for carbon monoxide, and the H₂:CO ratio are investigated at 650 °C with a constant CH₄ space velocity. Results indicate that CH₄ conversion increases significantly with increasing O₂:CH₄ or H₂O:CH₄ ratio, and the hydrogen content in dry tail gas increases with the H₂O:CH₄ ratio.     

Optimized global reaction mechanisms for H2, CO,CH4, and their mixtures

Global reaction mechanisms (GRMs) are widely used in combustion engineering. However, it is difficult to find GRMs commonly available for various mixtures of H₂, CO, and CH₄ (with air), which are likely to be the primary fuels in the future. In this study, a series of GRMs were optimized to follow the results of the five detailed reaction mechanisms (GRI 3.0, USC II, San Diego, FFCM-1, CRECK) for the essential fuels (H₂, CO, CH₄) and their mixtures (at 300 K and 1 bar). At first, a 1-step GRM of H₂+air (R1) and another of CO + air (R2), were optimized to reproduce their respective laminar burning velocities (LBVs). After that, an additional water-gas shift reaction (R3) was suggested to improve the prediction for the H₂+CO + air mixture. Similarly, a 1-step GRM (M1) was developed for the fuel-lean mixtures of CH₄+air, and a 2-step GRM (R1+M1) was proposed for the fuel-lean mixtures of H₂+CH₄+air. In the case of the mixture of H₂+CO + CH₄+air, an additional methane oxidation reaction (M1L) producing H₂ and CO was suggested, and a 4-step GRM (R1+R2+R3+M1L) showed reliable results in the fuel-lean conditions. However, to get reliable LBVs over all equivalence ratios, two additional reactions (M2+M3) were proposed to reflect the endothermic reaction. Furthermore, the pre-exponential factor of the methane oxidation reaction (M1R) varied as a function of the hydrogen concentration in the fuel. Conclusively, acceptable LBVs could be obtained for the H₂+CO + CH₄+air mixtures in a moderate temperature range (300 K–600 K).     

Dual application of Ti-catalyzed Li-RHC composite for H2 purification and CO methanation

2LiH + MgB₂ composite doped with TiO₂ (Li-RHC-Ti) is employed with a two-fold purpose: hydrogen purification under a H₂–CO (0.1 mol%) mixture and CO methanation. Upon dynamic cycling under CO–H₂ mixture, hydrogen release curves display a quite stable amount of pure hydrogen of about 10 wt%, short release times of around 60 min, and minor degradation. Gas analysis by Fourier transform infrared spectroscopy (FTIR) after a thermal dehydrogenation process of MgH₂ and LiBH₄ under CO evidence the conversion of CO to CH₄. Li-RHC-Ti dehydrogenated under CO shows the simultaneous formation of CH₄, CH₃OH, and B(CH₃)₃ in the gas phase. X-ray powder diffraction (XRPD) and FTIR characterizations of the solid phases of Li-RHC-Ti after both H₂–CO mixture and CO interactions demonstrate the formation of MgO, LiBO_2, and HCOO⁻ species. Li-RHC-Ti acts as a hydrogen source and promoter for the CO conversion. Reaction pathways are proposed based on experimental results and equilibrium composition calculations.