CO2 CH4 Research Articles

Molecular guest exchange and subsequent structural transformation in CH4 – CO2 replacement occurring in sH hydrates as revealed by 13C NMR spectroscopy and molecular dynamic simulations

This study adopted experimental and computational approaches to investigate CH4 – CO2 replacement in the structure H (sH) CH4 + methylcyclopentane (MCP) hydrate for its dual functions of CH4 recovery and CO2 sequestration. Hydrate phase equilibria, 13C NMR spectra, and molecular dynamics (MD) simulations of CH4 + MCP – CO2 replacement were examined and compared with those of CH4 + neohexane (NH) – CO2 replacement to elucidate the molecular guest exchange behaviors in both systems. The structure I (sI) hydrates were thermodynamically favored in CO2-rich gas mixtures (CH4 + CO2 + MCP systems), and a structural transformation from sH to sI occurred when CO2 composition in the feed gas was higher than 20 %. The 13C NMR spectra indicated that the CO2 molecules preferred to occupy the large (51262) cages of sI and the medium (435663) cages of sH compared to the small (512) cages of both sI and sH during replacement. Following CO2 injection into the sH CH4 + MCP hydrate, the initial sH hydrate transformed to the sI hydrate with CH4 recovery of approximately 78 %. The MD simulations also demonstrated that structural transformation in the CH4 + MCP – CO2 replacement would occur at the lower CO2 enclathration ratio compared to the CH4 + NH – CO2 replacement, thereby leading to a lower CO2 concentration in the newly formed sI hydrate. This is the first study to provide both experimental and computational evidence of guest-dependent structural transformation in sH CH4 + liquid hydrocarbons – CO2 replacement.

Microscopic Insights and Optimization of the CH4-CO2 Replacement in Natural Gas Hydrates.

Using the CO2 replacement method to exploit natural gas hydrates and store CO2 has great significance in energy access and environmental protection. Herein, the molecular dynamic method is utilized to analyze and evaluate the CH4-CO2 replacement at different constant temperatures and pressures. For optimization, various temperature oscillations are introduced in the CH4-CO2 replacement. It illustrates that increasing the temperature can improve the amounts of CH4 escape and CO2 capture but is unfavorable to the long-term CO2 storage and hydrate stability. The effects of pressure are not as significant and definite as those of temperature. Appropriate temperature oscillations can achieve comprehensive improvements, which benefit from both the deep diffusion of CO2 in the higher temperature stage and the rapid rebuilding of CO2 hydrate within just nanoseconds caused by the memory effects in the lower temperature stage. The results also reveal that the optimal lower temperature duration and frequency should be moderate. Decreasing the lower temperature value can distinctly enhance CO2 capture and hydrate stability. This study can help understand the mechanisms of CH4-CO2 replacement under different temperature and pressure conditions, especially at temperature transitions, and proposes a potentially effective method to achieve large-scale carbon sequestration in the hydrate.

Stability of submarine slopes during replacement of methane in natural gas hydrates with carbon dioxide

Replacement of methane (CH4) in natural gas hydrates (NGHs) with carbon dioxide (CO2) can sequestrate CO2 in the seabed while developing the natural gas, so it is an environmental-friendly energy production and carbon sequestration mode. A dynamic evolution model for the mechanical parameters of a NGH reservoir during CH4–CO2 replacement was established. Then, the finite element method was adopted to build a temperature-seepage-stress-saturation multi-field coupling model for CH4–CO2 replacement in the NGH reservoir to study the evolution of physical parameters of strata and the slope stability in the replacement process. Results demonstrate that mechanical parameters including the peak strength, elastic modulus, and cohesion of NGH and CO2 hydrate (CDH) bearing sediment samples are all positively correlated with the saturation. The generation of CDHs leads to a decrease in permeability of the reservoir during CH4–CO2 replacement, and the CO2 injection rate gradually slows down with the prolonging injection time of CO2. During CH4–CO2 replacement, the slope is more prone to failure with the increasing submarine slope angle, decomposition range of NGHs, reservoir thickness, and initial saturation; with the enlargement of the generation range of CDHs and the thickness of overlaying strata, the slope is more stable.

Recent advances in biogas purifying technologies: Process design and economic considerations

Biogas is a promising renewable energy source that is produced from biowaste and can potentially replace conventional energy resources. The economic value of biogas, which is primarily comprised of CH4, CO2, and other impurities (e.g. H2S, and N2) can be increased by upgrading and purification. This study presents the techno-economic feasibility of the cryogenic biogas upgrading process (CBioUP) based on product purities, biomethane selling prices and different refrigeration systems over 25 years of lifetime. The proposed CBioUPs is comprised of compression, refrigeration, and separation sections. Compressed biogas was liquefied in two refrigeration systems (propane pre-cooled mixed refrigerants and optimized cascade technologies) followed by a distillation separation unit. CBioUP proved its flexibility in terms of the number of distillation columns to produce low-grade CH4 (≈94.58 mol%), high-grade CH4 (≈97.13 mol%), and liquid CO2 by-product. The process's robustness to varying biogas feed composition revealed higher CO2 content would necessitate additional duty and/or equipment to enhance separation efficiency, whereas a CH4 content of ≥70% generated biomethane with a purity >99.6 mol% even in a single distillation column. CBioUP demonstrated its suitability for producing different grades of CH4 with a promising net present value (NPV) of $28.3 and $30.9 billion for low/high-grade biomethane.

Harnessing the structural attributes of NiMg-CUK-1 MOF for the dual-function capture and transformation of carbon dioxide into methane

Carbon capture and conversion into chemical fuels are often considered distinct processes, whereby a sorbent is responsible for enriching a CO2 stream while a catalyst facilitates transformation into value-added commodities. Herein, we implement NiMg-CUK-1, a metal–organic framework (MOF) possessing the characteristics of both adsorbent and catalyst for the sequential capture and conversion of CO2 to methane (CH4). By harnessing the disparity in thermal stability between Ni- and Mg-CUK-1 analogues, Ni nanoparticles are preferentially generated throughout the preserved Mg portion of the framework. Tuning the Ni:Mg ratio and the NiMg-CUK-1 treatment temperature maximizes catalytic performance while preserving a substantial portion of the CO2 capture functionality inherent to the MOF. The optimized NiMg-CUK-1 is deployed in a dual-mode reactor system that alternates between ambient temperature CO2 capture and methanation under mild reaction conditions (250 °C). After five cycles, the optimal NiMg-CUK-1 reaches a levelled-out performance of 1.46 ± 0.24 mmol CO2 captured g−1, and 1.52 ± 0.23 mmol CH4 produced g−1, surpassing similar sorbent-based catalysts reliant on the chemical looping of metal oxides and carbonates. The introduced approach paves the way for combined capture and conversion of CO2 using a single dual-functional material capable of both low-temperature CO2 desorption and CH4 production.

An approach to the high efficient exploitation of nature gas hydrate and carbon sequestration via injecting CO2/H2 gas mixture with varying composition

The combined technology integrating CO2/H2 injection and CH4 production with in situ steam reformation of CH4 has provided a promising way to address green energy production and CO2 storage. However, how to break through the mutual constraints between CH4 recovery and CO2 storage remains a big challenge. Here, we explored changing the composition of the injected gas at different stages to simultaneously achieve high CO2 sequestration and high CH4 recovery. The experimental results exhibit the high-level CH4 recovery ratios of 83–89 %. Meanwhile, this variable composition gas injection mode presented good performance in CH4 concentration of produced gas and gas injection-production ratio, and showed outstanding H2 utilization efficiency. All these mean that the variable composition gas injection has better economics than other gas injection modes. Further calculation results of hydrate saturation and solid shrinkage volume suggest that adopting fixed CO2-containing (55 %) gas can realize non-destructive hydrate mining with a final CH4 recovery of 58 %; while the varying gas composition is to first enhance gas recovery and then repair the sediments with a basic repair ratio of > 70 %. Thus, we were able to keep hydrate saturation in the reservoir within safe thresholds and repair the reservoir before the possible occurrence of wellbore and formation damages by changing the gas composition of the injected gas. Therefore, this approach is greatly promising for high-efficient and safe exploitation of gas hydrate.

Dynamics of Co/Co2C redox cycle and their catalytic consequences in Fischer–Tropsch synthesis on cobalt–manganese catalysts

Fischer–Tropsch synthesis over CoMn oxides is a surface-catalyzed structure-sensitive reaction. Active site changes greatly alter product distribution. The dynamics and essence of the changes in Co species during the reaction have seldom been explored. Herein, multiple characterizations were applied to confirm that two types of active sites, i.e., Co and Co2C, coexist on CoMnOx under the reaction conditions. Apart from the direct participation of carbon species in the reaction, the steady-state isotopic transient kinetic analysis also suggested the mutual transformation of carbon species in Co2C. The ratio of the two paths altered with the temperature, thus leading to Co2C-rich and Co-rich surfaces at intermediate and high temperatures, respectively. Kinetic calculations and microkinetic modeling showed that Co2C-rich surfaces facilitated CO adsorption and suppressed hydrogen adsorption. This gave high carbon-chain growth activity. The Co-rich surfaces showed high vacancy and hydrogen coverages, lowering the CO activation and CH4 formation energies.

Towards efficient production of syngas via the CH4 bi-reforming with CO2 over Ni/xMgAl powder and monolithic catalysts

In this study, a promising monolithic catalyst composition for the production of syngas using bi-reforming (BRM) of CH4–CO2 mixture was proposed. The BRM performance was evaluated with N2/CH4/H2O/CO2 (1/1/0.8/0.4) mixture at 700–800 °C. First, the influence of MgO loading on the activity of 10 wt.% of Ni supported on xMgAl (x is MgO content, x = 10–40 wt.%) powder catalyst was studied. The addition of 10–20 wt.% of MgO leads to higher reforming performance, probably due to the formation of MgAl2O4 phase that enhance the Ni dispersion. At 800 °C, the CH4 conversion and H2 yield obtained with Ni/20MgAl are 1.7 and 1.5 times, respectively, higher than that of the Ni/Al catalyst. However, higher MgO loading causes a coverage of Ni active sites and decrease activity. Ni/20MgAl powder catalyst exhibit highest activity and this sample was then deposited on monolith substrate. The monolith catalyst shows higher BRM activity than powder form. Long-term test demonstrates high stability of monolith catalyst with less than 5% the losses in CH4 and CO2 conversions after 60 h time on stream. CH4 and CO2 conversion are 89% and 81%, respectively. The H2/CO ratio is near 2, which meets the requirement for methanol/Fischer–Tropsch fuel synthesis.

The synthesis and characterization of Ni-M-Tb/Al2O3 (M: Mg, Ca, Sr and Ba) nanocatalysts prepared by different types of doping using the ultrasonic-assisted method to enhance CO2 methanation

In the present study, Ni-M-Tb/Al2O3 (M: Mg, Ca, Sr and Ba) nanostructured catalysts with different ratios of the alkali metals were synthesized by the ultrasonic-assisted one-pot method. The catalytic performance was investigated in terms of CO2 conversion, CH4 selectivity, and stability via the H2-TPR analysis. The structural properties were delineated using XRD, SEM, TEM and BET equation. The results showed that the 2Ni-5Mg-5Tb/Al2O3 catalyst with a maximum CO2 conversion of 75.37% and CH4 selectivity of 100%, at the operating temperature of 400 °C in the molar ratio of H2:CO2:3.5 for 100 h, had the best performance. This could benefit from the particular electronic structure of Tb in combination with Mg and Ni, reducing agglomeration, as demonstrated by the SEM and BET results. Based on the current findings, novel catalysts with high conversion efficiency of CO2 to CH4 might be achieved by tuning a decent combination of alkaline and rear earth elements as the promoters of Ni-based catalysts.

SrTiO3 nanosheets decorated with ZnFe2O4 nanoparticles as Z-scheme photocatalysts for highly efficient photocatalytic degradation and CO2 conversion

Nanocomposite has attracted widespread attention for efficiently utilizing solar energy and improving conversion efficiency during wastewater purification and solar fuels evolution. In this study, Z-scheme ZnFe2O4-SrTiO3 nanocomposite was prepared and used as photocatalysts for tetracycline hydrochloride (TCH) degradation and CO2 conversion. The as-obtained ZnFe2O4-SrTiO3 system achieved drastically enhanced TCH degradation efficiency up to 84.56 % with respect to pure ZnFe2O4(13.81 %) and SrTiO3(49.66 %) under visible light irradiation. The influences of ZnFe2O4 content and co-existing ions on the photodegradation activities were investigated. In addition, ZnFe2O4-SrTiO3 nanocomposite exhibited outstanding CO2 photoreduction activity, the CO and CH4 evolution rate were 8.24 μmol/g/h and 2.51 μmol/g/h, which was 2.5 and 6.4 times higher than that observed for SrTiO3, respectively. The reinforced photocatalytic TCH degradation and CO2 conversion activities are mainly attributed to the obviously enhanced utilization of solar energy and the dramatically boosted electron-hole pair separation efficiency through a Z-scheme charge transfer model. In addition, a possible photocatalytic enhancement mechanism of ZnFe2O4-SrTiO3 nanocomposite is proposed in the light of trapping experiments, ESR and DFT calculations. Our studies implies that ZnFe2O4-SrTiO3 nanocomposite are expected to effectively realize wastewater purification and CO2 reduction to renewable solar fuels.

Highly CO-selective Ni–MgO–CexZr1–xO2 catalyst for efficient low-temperature reverse water–gas shift reaction

High inertness of CO2 hinders its usage as a cost-effective C1 resource to produce value-added chemicals, and hence, reactive H2 are often employed for CO2 utilization. CO is a more reactive C1 building block that can be produced via the reverse water–gas shift (RWGS) reaction using CO2, but this requires a high temperature with robust catalysts that should endure the harsh endothermic conditions. Herein, Ni–MgO–CexZr1–xO2 (NMCxZ1–xO) catalysts with various Ce/Zr ratios, giving different strong metal–support interaction (SMSI) among metallic components, are investigated for low-temperature RWGS reaction to achieve high CO selectivity. The control of Ce/Zr ratios affords systematic changes in the oxygen storage capacity (OSC), acidity, and basicity, affording remarkable changes in the catalytic behaviors for CO2 conversion and CO selectivity. Among various NMCxZ1-xO catalysts, NMC0.6Z0.4O exhibited the highest resistance to change in reaction temperature, maintaining 100 % CO selectivity below 320 °C, whereas the CO2 conversion and CH4 selectivity of the other catalysts increased dramatically with increasing reaction temperature. The 100 % CO selectivity can be attributed to the high OSC and optimized balance of acidity and basicity of the NMC0.6Z0.4O catalyst, and its retention of catalytic activity owing to the SMSI among metallic components.

Efficient and facile preparation of pure silica CHA zeolite membranes by gel-less method

To bring zeolite membranes to commercial application, corresponding preparation technology must solve the following issues like low permeance, poor reproducibility, high manufacturing cost and scale-up etc., which is still a grand challenge. The imhomogeneous slurry-like mother liquor required by the preparation of pure silica CHA membrane makes this challenge even tougher. Herein, we realized facile and efficient preparation of pure silica CHA membrane for the first time. The use of an active silica source, ammonium hexafluorosilicate ((NH4)2SiF6), enabled facile membrane synthesis in a homogeneous mother liquor at mild temperature and ambient pressure. The replacement of conventional imhomogeneous slurry-like mother liquor with homogeneous mother liqour significantly improved the reproducibility of membrane synthesis and favored the formation of thin membrane. The high activity of (NH4)2SiF6 allowed low temperature synthesis at ambient pressure without sacrificing synthesis time. Moreover, gel-less synthesis significantly reduced material waste at no cost of selectivity and permeance. All these factors combined together resulted into a facile and reproducible preparation of thin pure silica CHA membrane with high material efficiency, energy efficiency and low equipment cost. Calcined pure silica CHA membrane exhibited outstanding CO2 permence of 2.9 × 10−6mol/(m2⋅s⋅Pa) and high CO2–CH4 selectivity ∼170. This efficient and facile preparation method has great potential for large scale synthesis.

Applying synchronous fluorescence spectra with Gaussian band fitting and two-dimensional correlation to characterize structural composition of DOM from soils in an aquatic-terrestrial ecotone

Dissolved organic matter (DOM), the primary participant of carbon and nitrogen cycle, has a great impact on the behavior and fate of organic pollutants and heavy metals in eutrophic lakes. The dynamic spectral properties of DOM fractions were revealed in an aquatic-terrestrial ecotone under the different types of land use. Composite soil samples of different depths (0–20, 20–40 and 40–60 cm) were collected from four different land uses along a disturbed-impact gradient in Taihu Lake, China, i.e., grassland (GRL), forest land (FOL), paddy field (PAF), and vegetable field (VEF). DOM mainly consisted of tyrosine-like material (TYLF), tryptophan-like material (TRLF), microbial humic-like material (MHLF), fulvic-like material (FLF) and humic-like material (HLF) within all soil profiles, where TRLF was the dominant component (61.30 %) using synchronous fluorescence spectroscopy (SFS) combined with principal component analysis and Gaussian band fitting. Based on two-dimensional correlation spectroscopy with SFS and Fourier transform infrared, the variation order of DOM fractions was FLF → MHLF → HLF → TRLF → TYLF within the GRL soil profile, and MHLF exhibited an oppositive change with aliphatic OH and amide I in protein. The order of DOM fractions was MHLF → FLF → HLF → TYLF → TRLF within the FOL soil profile, and the change trend of MHLF remained oppositive with aliphatic OH and CO in ester. The order of DOM within the PAF soil profile fractions was TRLF → MHLF → HLF → TYLF → FLF, and changing trends of TYLF were oppositive to aliphatic OH, CH bending vibration, CH bending vibration and CO in ester. The order of DOM fractions was HLF → TYLF → TRLF → FLF → MHLF within the VEF soil profile, where the changing trend TYLF remained oppositive to aliphatic OH, CH deformations in lignin and aliphatic group and amide I in protein. This study may provide important support for alleviating lake water eutrophication or pollution.

Deformation mechanism and displacement ability during CO2 displacing CH4 in coal seam under different temperatures

Liquid CO2 has the synergistic effect of low-temperature damage and displacing CH4 after injecting into the coal seam, which can effectively improve coalbed permeability and promptly promote the adsorbed CH4 to desorption state for preventing the coal and gas outburst disasters. The injected CO2 gets adsorbed at the surface of the coal pores, which causes the coal swelling. In this work, we developed a triaxial experimental platform to explore the features of CO2 displacing CH4 under different temperatures. The variation of coal swelling and segmentation features of the displacing concentration was elucidated. The seepage ability and mechanism of gas mitigation in the coal seam during LCO2-ECBM were revealed. The results showed that the coal samples displayed swelling deformation in the CH4 adsorption and CH4 displacement stages, and the strain curves can be divided into rapid and slow deformation phases. The strain in the CO2 displacing CH4 stage is notably larger than that in the CH4 adsorption stage. Three dominant results were obtained during the CH4 displacement: Free CH4 driving by CO2 injection, CH4 self-desorption, and CO2–CH4 competitive adsorption. The displacing flow rate increased swiftly in the initial stage, and then decreased to a stable tendency. The cumulative displacement volume of CH4 in different stages exhibited distinct functional relationships. The integrated contribution of the coal matrix shrinkage and thermal stress damage to gas seepage improvement was more prominent than that of the adsorption swelling to seepage inhibition in the coal seam.

Enhanced methane production in anaerobic co-digestion systems with modified black phosphorus

Black phosphorus (BP) and BP modified by hydrogen peroxide (MBP) were used as accelerants to enhance CH4 production and CO2 reduction in microbial electrolysis cells (MECs) coupled with anaerobic co-digestion systems (MEC-AcoD). The MEC-AcoD group with a voltage of 0.6 V and 0.03 wt.% of MBP accelerant (MEC0.6MBP0.03) had the largest CH4 yield (242.1 mL/g VS) and the smallest carbon dioxide yield (97.6 mL/g VS) compared with the control group (141.2 mL/g VS, 146.9 mL/g VS). The digestates that used MEC0.6MBP0.03 exhibited superior thermal stability (46.2 %) and total nutrient contents (44.5 g/kg). These improvements may be attributed to the superior electron exchange capacity and physicochemical properties of MBP. Herein, we propose a strategy to understand enhanced CH4 production and CO2 reduction in anaerobic co-digestion and MEC-AcoD systems using MBP accelerants. Notably, combining MBP and MEC could effectively promote anaerobic co-digestion performance.

Mechanochemical Synthesis of Bimetallic NiCo Supported on a CeO2 Catalyst with Less Metal Loading for Non-Thermal Plasma Catalytic CO2 Hydrogenation

Non-thermal plasma (NTP) catalysis is a promising technology for CO2 valorization with renewable H2, in which catalyst design is one of the key aspects to progress the hybrid technology. Herein, bimetallic NiCo supported on CeO2 catalysts, that is, NiCo/CeO2, were developed with less metal loading of ∼2 wt % using mechanochemical synthesis for NTP-catalytic CO2 methanation. During the synthesis, different addition orders of Ni and Co precursors were investigated, and the results show that the NiCo1/CeO2-I catalyst (which was prepared by the simultaneous addition of Ni and Co precursors, protocol I) exhibited the highest CO2 conversion (∼60%) and CH4 selectivity/yield (∼80%/∼50%), whereas the NiCo1/CeO2-II and NiCo1/CeO2-III catalysts (prepared by sequential addition protocols of II and III) showed very poor catalytic performance. Characterization results suggested that in protocol I, Ni and Co prefer to alloy, and concentrated oxygen vacancies on the CeO2 surface and high surface basicity are retained as well. Such properties of NiCo1/CeO2-I were responsible for CO2 activation and hydrogenation under NTP conditions, which was explained by the proposed mechanisms.

Effects of competitive adsorption on production capacity during CO2 displacement of CH4 in shale

During CO2 displacement of CH4 in shale, competitive adsorption results in reduced pore space used for gas flow in shale, which is closely associated with the production capacity of shale-gas reservoirs. Thus, the present work investigates the effects of CO2–CH4 competitive adsorption on production capacity. Herein, a slit–pore model is developed in terms of gas storage (CO2 and CH4) and graphene pores using molecular dynamics and implemented via large-scale atomic/molecular massively parallel simulator. The effects of CO2 injection pressure, temperature, and velocity and of pore size on CO2–CH4 displacement and competitive adsorption properties are simulated and examined. Hence, the displacement efficiency of CH4 and the adsorption layer thickness of the CO2–CH4 binary mixture are determined. Moreover, based on a basic seepage model of planar linear flooding, the effect of CO2–CH4 competitive adsorption on production capacity is analytically investigated. Results demonstrate that the production capacity with consideration of adsorption layer thickness is less than that without consideration of adsorption layer thickness, illustrating that CO2–CH4 competitive adsorption behaviors are closely connected with permeability, flow rate, and production capacity of shale-gas reservoirs, especially for shale-gas reservoirs containing large numbers of pores and slits.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.

Pd-Sb Rhombohedra with an Unconventional Rhombohedral Phase as a Trifunctional Electrocatalyst.

Crystal phase engineering is an important strategy for designing noble-metal-based catalysts with optimized activity and stability. From the thermodynamic point of view, it remains a great challenge to synthesize unconventional phases of noble metals. Here, a new class of Pd-based nanostructure with unconventional rhombohedral Pd20 Sb7 phase is successfully synthesized. Benefiting from the high proportion of the unique exposed Pd20 Sb7 (003) surface, Pd20 Sb7 rhombohedra display much enhanced ethanol oxidation reaction (EOR) and oxygen reduction reaction performance compared with commercial Pd/C. Moreover, Pd20 Sb7 rhombohedra are also demonstrated as an effective air cathode in non-aqueous Li-air batteries with an overpotential of only 0.24V. Density functional theory calculations reveal that the unique exposed facets of Pd20 Sb7 rhombohedra can not only reduce the excessive adsorption of CH3 CO* to CH3 COOH on Pd for promoting EOR process, but also weaken CO binding and CO poisoning. This work provides a new class of unconventional intermetallic nanomaterials with enhanced electrocatalytic activity.

Permeation of Ternary Mixture Containing H2S, CO2 and CH4 in Aquivion® Perfluorosulfonic Acid (PFSA) Ionomer Membranes.

Aquivion® E87-12S Perfluorosulfonated acid ionomer material (PFSA) has been studied as a membrane technology for natural gas sweetening from CO2, H2S due to its interesting chemical and mechanical stability and good separation performance for polar compounds in humid environments. In the present work, permeation of the H2S/CO2/CH4 ternary mixture in this short-side PFSA chain was investigated at pressures up to 10 bar, temperatures up to 50 °C, and in a range of relative humidity (RH) from 20% to 90%. The results obtained confirm the strong dependence of Aquivion® on water activity and temperature, and its ability to separate gases based on their water solubility without substantial differences between pure and mixed gas experiments. Indeed, even when tested in ternary mixture, the permeation behavior remains similar to that observed for pure components and binary mixtures. In particular, the permeability of H2S is higher than that of CO2 and methane CH4, reaching values of 500 Barrer at 50 °C and 80% RH, against 450 and 23 Barrer for the other two gases respectively. Additionally, when tested at higher pressures of up to 10 bar under humid conditions, the membrane properties remained largely unchanged, thus confirming the overall stability and durability of Aquivion® E87-12S in acid environments.