Preferential Adsorption Of CO2 Research Articles

2D-Mn2C12: An Optimal Electrocatalyst with Nonbonding Multiple Single Centers for CO2-to-CH4 Conversion.

The CO2 reduction reaction (CO2RR) is a promising method that can both mitigate the greenhouse effect and generate valuable chemicals. The 2D-M2C12 with high-density transition metal single atoms is a potential catalyst for various catalytic reactions. Using an effective strategy, we screened 1s-Mn2C12 as the most promising electrocatalyst for the CO2RR in the newly reported 2D-M2C12 family. A low applied potential of -0.17 V was reported for the CO2-to-CH4 conversion. The relative weak adsorption of H atom and H2O in the potential range of -0.2 to -0.8 V, ensures the preferential adsorption of CO2 and the following production of CH4. The different loading amounts of Mn atoms on γ-graphyne (GY) were also investigated. The Mn atoms prefer doping in the nonadjacent triangular pores instead of the adjacent ones due to the repulsive forces between d-orbitals when the Mn loading is less than 32.3 wt % (5Mn). As the Mn concentration further increases, adjacent Mn atoms begin to appear, and the Mn@GY becomes metallic or half-metallic. The presence of four adjacent Mn atoms increases the d-band center of Mn@GY, particularly the dz2 center involved in CO2 adsorption, thereby enhancing the adsorption capacity for CO2. These findings indicate that 1s-Mn2C12 with high Mn atomic loadings is an excellent CO2RR electrocatalyst, and it provides new insights for designing efficient CO2RR electrocatalyst.

Octa- and Tetradecanuclear Mixed-Valent Vanadium(III/IV) Malates with Triazoles: Gas Adsorptions, Chiral Interface Recognition, and In Situ Decarboxylation.

Spontaneous resolution has been found for a pair of cage-like octanuclear mixed-valent vanadium(III/IV) malate enantiomers [Δ-VIII4VIV4O5(R-mal)6(Hdatrz)6]·44.5H2O (ΔR-1) and [Λ-VIII4VIV4O5(S-mal)6(Hdatrz)6]·38.5H2O (ΛS-1, H3mal = malic acid; Hdatrz = 3,5-diamino-1,2,4-triazole). Their racemic reduced product K7[VIII5VIV3O5(R,S-mal)6(trz)6]·17H2O (2) and tetradecanuclear species K11[VIII3VIV11O11(R,S-mal)12(atrz)6]·45.5H2O (3) (Htrz = 1,2,3-triazole, Hatrz = 3-amino-1,2,4-triazole) have also been obtained. In situ decarboxylation happens for 3-amino-1,2,4-triazole-5-carboxylic acid (H2atrzc) to yield 3-amino-1,2,4-triazole under hydrothermal conditions. Both 1 and 2 show an interesting bicapped-triangular-prismatic {V8O5(mal)6} building block, which further decorates symmetrically with three [VIV2O2(R,S-mal)2]2- units to construct a pinwheel-like {V14}-cluster, 3. Bond valence calculation sum (BVS) analyses manifest that the oxidation states of bicapped V atoms are +3 in 1-3, while the other V atoms in the {V6O5} core are ambiguous between +3 and +4 states with strong electron delocalization. Intriguingly, the triple helical chains in 1 associate in parallel to generate an amine-functionalized chiral polyoxovanadate (POV)-based supramolecular open-framework. The diameter of the interior channel is 13.6 Å, showing preferential adsorption of CO2 over gases N2, H2, and CH4. Importantly, homochiral framework ΔR-1 is capable of performing chiral interface recognition for R-1,3-butanediol (R-BDO) through host-guest interactions, as confirmed by the structural analysis of the host-guest complex ΔR-1·3(R-BDO). There are six R-BDO molecules in the channel of ΔR-1.

Influencing mechanism of carbon monoxide on the hydrogen absorption performance of Zr2Fe

Zr2Fe is considered as the promising hydrogen isotopes trapping material to control the quantity of tritium generated in deuterium–tritium fusion reaction. However, the vulnerability to poisoning by impurity gases such as carbon monoxide is the bottleneck for their applications. In this study, we show from our DFT calculations that the Zr2Fe(101) surface is saturated with 13CO molecules and the hollow site is the most stable CO adsorption site. The adsorption energy of CO is much lower than that of hydrogen, resulting in the preferential adsorption of CO on Zr2Fe(101). The dependence of the Gibbs free energies of CO on the temperatures under UHV conditions were also obtained. The climbing-image nudged elastic band results reveal that CO pre-coverage would block the hydrogen adsorption sites and affect the hydrogen diffusion. The Sieverts analysis demonstrates that even the low concentration CO is a fatal poison to the hydrogenation process of Zr2Fe at ambient temperature. Hydrogen absorption may occur at a higher temperature with a lower absorption rate and capacity, as CO starts to desorpt from Zr2Fe(101) with the increase of temperature and thus making H2 absorption possible, even though the H diffusion energy barriers are relatively high. Our results provide the basis for exploring the influence mechanisms of the impurity gas CO on the hydrogen adsorption properties of the Zr-based alloys, which would be beneficial for the applications of metal getter of tritium-containing waste gas.

PEG-templated synthesis of ultramicroporous n-ZIF-67 nanoparticles with high selectivity for the adsorption and uptake of CO2 over CH4 and N2

Challenges remain concerning the development of rapid and low-cost adsorbents that combine good separation performance with high adsorption capacity, especially for CO2. Herein, we report for the first time a new polyethylene glycol templated synthesis method to obtain a nanocrystalline zeolitic imidazolate framework (n-ZIF-67) at room temperature in 5 min. The n-ZIF-67 nanoparticles were characterized using X-ray powder diffraction with Rietveld refinement (space group = I-43 m, a = 17.0545(4) Å), Fourier-transform infrared, transmission electron microscopy, thermogravimetric analysis, and N2 adsorption (Brunauer-Emmett-Teller) measurements and exhibited excellent properties, including a total pore volume of 0.86 cm3/g, a high surface area equal to 1891 m2/g, and 0.64 nm size ultramicropores.). The highly porous ZIF-67 nanoparticles were explored for the adsorption and desorption of CH4, CO2, and N2 gases at pressures up to 40 bar and isotherm temperatures of 273, 298, 323, and 353 K. The adsorption isotherms revealed a high capacity for CO2 of 681 mg/g at 298 K and an adsorption enthalpy of 29.19 to 34.44 KJ/mol, in part linked to the ultramicroporous structure. The n-ZIF-67 particles exhibited gas uptake values for CH4 and N2 of 241 mg/g and 219 mg/g, respectively. As far as the authors are concerned, these are the highest capacities ever reported for zeolitic framework metal organic frameworks such as ZIF-67 and ZIF-8. The Langmuir adsorption isotherm was employed to obtain the maximum adsorption capacity, qm, and adsorption equilibrium constant, KL. The isosteric heat of adsorption data sheds light on a CO2 physisorption process. The n-ZIF-67 also exhibited high CO2/N2 and CO2/CH4 mixed gases selectivity, with the preferential adsorption of CO2 over N2 or CH4 confirmed by breakthrough experiments. The n-ZIF-67 with ultramicropores is therefore an effective new adsorbent for greenhouse gas capture with high CO2 gas selectivity over competing gases. Zeolitic framework MOFs merit further development as low-cost and easy-to-synthesize adsorbents to help address the pressing need to mitigate CO2 emissions.

Atomistic Origins of Reversible Noncatalytic Gas-Solid Interfacial Reactions.

Noncatalytic gas-solid reactions are a large group of heterogeneous reactions that are usually assumed to occur irreversibly because of the strong driving force to favor the forward direction toward the product formation. Using the example of Ni oxidation into NiO with CO2, herein, we demonstrate the existence of the reverse element that results in the NiO reduction from the countering effect of the gaseous product of CO. Using in situ electron microscopy observations and atomistic modeling, we show that the oxidation process occurs via preferential CO2 adsorption along step edges that results in step-flow growth of NiO layers, and the presence of Ni atoms on the flat NiO surface promotes the nucleation of NiO layers. Simultaneously, the NiO reduction happens via preferential step-edge adsorption of CO that leads to the receding motion of atomic steps, and the presence of Ni vacancies in the NiO surface facilitates the CO-adsorption-induced surface pitting. Temperature and CO2 pressure effect maps are constructed to illustrate the spatiotemporal dynamics of the competing NiO redox reactions. These results demonstrate the rich gas-solid surface reaction dynamics induced by the coexisting forward and reverse reaction elements and have practical applicability in manipulating gas-solid reactions via controlling the gas environment or atomic structure of the solid surface to steer the reaction toward the desired direction.

Synthesis and photochemical modification of monolayer thin MOF flakes for incorporation in defect free polymer composites.

Metal-organic frameworks (MOFs) with benzophenone linker molecules are characterized by their ability to undergo photochemical postsynthetic modification. While this approach opens up almost unlimited possibilities for tailoring materials to specific applications, the processability of the large particles is still lacking. In this work, we present a new approach to fabricate micro flakes of the stable Zr-bzpdc-MOF (bzpdc = benzophenone-4-4'-dicarboxylate) with a thickness of only a few monolayers. The crystalline and nanoporous flakes form dispersions in acetone that are stable for months. Embedding the flakes in polymer composites was investigated as one of many possible applications. Zr-bzpdc-MOF micro flakes were decorated with poly(dimethylsiloxane) (PDMS) via a photochemical postsynthetic modification and incorporated into silicon elastomers. The PDMS functionalization allows covalent cross-linking between the MOF and the polymer while maintaining the porosity of the MOF. The resulting hybrid materials provide defect-free interfaces and show preferential adsorption of CO2 over CH4, making them attractive for gas separation or sensing applications. The work should serve as a basis for bringing bzpdc-MOFs into real-world applications - in polymeric membranes, but also beyond.

Preferential CO2 adsorption over cadmium-based Porous Metal-organic Framework

Preferential CO2 adsorption over cadmium-based Porous Metal-organic Framework

Direct utilization of crude and waste H2 via CO-tolerant hydrogenation

Direct utilization of crude and waste H2 via CO-tolerant hydrogenation

Increased CO2 Affinity and Adsorption Selectivity in MOF-801 Fluorinated Analogues.

The novel ZrIV-based perfluorinated metal–organic framework (PF-MOF) [Zr6O4(OH)4(TFS)6] (ZrTFS) was prepared under solvent-free conditions using the commercially available tetrafluorosuccinic acid (H2TFS) as a bridging ditopic linker. Since H2TFS can be seen as the fully aliphatic and perfluorinated C4 analogue of fumaric acid, ZrTFS was found to be isoreticular to zirconium fumarate (MOF-801). The structure of ZrTFS was solved and refined from X-ray powder diffraction data. Despite this analogy, the gas adsorption capacity of ZrTFS is much lower than that of MOF-801; in the former, the presence of bulky fluorine atoms causes a considerable window size reduction. To have PF-MOFs with more accessible porosity, postsynthetic exchange (PSE) reactions on (defective) MOF-801 suspended in H2TFS aqueous solutions were carried out. Despite the different H2TFS concentrations used in the PSE process, the exchanges yielded two mixed-linker materials of similar minimal formulae [Zr6O4(μ3-OH)4(μ1-OH)2.08(H2O)2.08(FUM)4.04(HTFS)1.84] (PF-MOF1) and [Zr6O4(μ3-OH)4(μ1-OH)1.83(H2O)1.83(FUM)4.04(HTFS)2.09] (PF-MOF2) (FUM2– = fumarate), where the perfluorinated linker was found to fully replace the capping acetate in the defective sites of pristine MOF-801. CO2 and N2 adsorption isotherms collected on all samples reveal that both CO2 thermodynamic affinity (isosteric heat of adsorption at zero coverage, Qst) and CO2/N2 adsorption selectivity increase with the amount of incorporated TFS2–, reaching the maximum values of 30 kJ mol–1 and 41 (IAST), respectively, in PF-MOF2. This confirms the beneficial effect coming from the introduction of fluorinated linkers in MOFs on their CO2 adsorption ability. Finally, solid-state density functional theory calculations were carried out to cast light on the structural features and on the thermodynamics of CO2 adsorption in MOF-801 and ZrTFS. Due to the difficulties in modeling a defective MOF, an intermediate structure containing both linkers in the framework was also designed. In this structure, the preferential CO2 adsorption site is the tetrahedral pore in the “UiO-66-like” structure. The extra energy stabilization stems from a hydrogen bond interaction between CO2 and a hydroxyl group on the inorganic cluster.

Activated carbon from polyurethane residues as molecular sieves for kinetic adsorption/separation of CO2/CH4

Activated carbon-based molecular sieves were synthetized, characterized and their kinetics of adsorption were evaluated to be used in separation processes of CO2/CH4 mixtures. Polyurethane (PU) foams were used as carbon precursors and the PU-derived carbons were physical activated with CO2. All the samples present a preferential adsorption of CO2 over methane in kinetic adsorption experiments. Samples activated at 800 ºC during 6 h exhibited the highest selectivity due to the absence of methane adsorption at lower resident times, which makes those samples very interesting for industrial processes of natural gas purification. Kinetic studies were performed to explain the kinetic profiles obtained, confirming that in the samples with smallest pore size, intraparticle diffusion was the limiting step, evidencing that certain oxygen groups favour CO2 adsorption, whereas adsorption was the limiting step in the samples with wider pores.

Adsorptive removal and catalytic performance of metal-organic frameworks containing mixed azolium-bipyridine ligand

Two ligands, 1, 3-bis(4-carboxyphenyl)imidazolium chloride and 4, 4-bipyridine, were employed to prepare nickel and zinc azolium based MOFs, Ni-MOF and Zn-MOF by the mixed ligand solvothermal approach. The positively charged azolium moieties in the imidazolium linker resulted in a charged environment in the as-synthesized frameworks. As a result, Ni-MOF and Zn-MOF demonstrated preferential adsorption of CO2 over methane molecules in the gas phase adsorption due to the higher quadruple moment of CO2, which interacts more with the positively charged frameworks. Besides, in aqueous media, Ni-MOF and Zn-MOF exhibited incredible adsorption efficiency for anionic dyes. In the following, Ni-MOF was metallated at the carbene site of the azolium linker to generate the novel heterogeneous catalyst Pd/Ni-MOF, which was successfully applied for Sonogashira and Suzuki-Miyaura coupling reactions without losing its activity after three cycles.

CO2/CH4 mixed-gas separation through carbon nitride membrane: A molecular dynamics simulation

We performed molecular dynamics simulations to study the performance of a pristine carbon nitride (C2N) membrane for separation of CO2/CH4 gas mixture. The influences of system temperature (298, 323, and 348 K), applied pressure difference (up to 2000 kPa), and feed composition on the CO2/CH4 separation were also explored. The permselectivity of the C2N membrane for separation of CO2/CH4 mixture was theoretically determined. The highest CO2 permeance of 1.32 × 106 GPU in the absence of applied external pressure was achieved. It is demonstrated that CO2 molecules can easily diffuse through the membrane, while no CH4 molecule was seen on the permeate side. Thus, an ultrahigh selectivity of CO2 over CH4 was achieved. The membrane indicated a superior performance, which easily exceeds the Robeson’s upper bound. The investigation of the gas permeation mechanism revealed that the preferential adsorption of CO2 and suitable size of this molecule owing to proper orientation are two important factors for efficient separation of CO2 from CH4 by the C2N membrane. In fact, CO2 molecules tend to reorient themselves close to the membrane nanopores to diffuse perpendicularly through. To this end, the density map and the potential of the mean force analysis were also conducted, which confirmed the simulation results.

Strain boosts CO oxidation on Ni single-atom-catalyst supported by defective graphene

In order to realize the sulfur and water resistance and facilitate the CO oxidation reactions, the effects of strain on the adsorption of CO, O2, SO2 and H2O molecules on Ni single-atom-catalyst supported by single-carbon-vacancy graphene (Ni-SG) have been studied based on first principles calculations. It shows that the compressive strain increases the adsorption energies of all above mentioned molecules on Ni-SG, where SO2 is adsorbed more strongly on Ni-SG than CO. However, in the presence of tensile strain, the adsorption energies decreases significantly when the molecules (O2 and SO2) obtain electrons from Ni-SG, while the adsorption energies just slightly decrease when the molecules (CO and H2O) lose electrons to Ni-SG, which finally achieves the preferential adsorption of CO and O2 molecules on Ni-SG by tensile strain. In addition, with tensile strain increasing to 10%, the rate-limited energy barrier along Eley-Rideal (ER) path monotonically increases from 0.77 eV to 0.98 eV, while the rate-limited energy barrier along Langmuir-Hinshelwood (LH) path monotonically decreases from 0.54 eV to 0.44 eV, indicating that the tensile strain can facilitate the LH mechanism while imped the ER mechanism on Ni-SG. The Hirshfeld charge and orbital levels of O2 and CO molecules are modulated by the tensile strain, which plays an important role for the decreasing of energy barriers for CO oxidation. Overall, the tensile strain can enhance the sulfur and water resistance of Ni-SG, as well as boost the CO oxidation reactions.

Predicting Adsorption of Methane and Carbon Dioxide Mixture in Shale Using Simplified Local-Density Model: Implications for Enhanced Gas Recovery and Carbon Dioxide Sequestration

Carbon dioxide (CO2) capture and storage have attracted global focus because CO2 emissions are responsible for global warming. Recently, injecting CO2 into shale gas reservoirs is regarded as a promising technique to enhance shale gas (i.e., methane (CH4)) production while permanently storing CO2 underground. This study aims to develop a calculation workflow, which is built on the simplified local-density (SLD) model, to predict excess and absolute adsorption isotherms of gas mixture based on single-component adsorption data. Such a calculation workflow was validated by comparing the measured adsorption of CH4, CO2, and binary CH4/CO2 mixture in shale reported previously in the literature with the predicted results using the calculation workflow. The crucial steps of the calculation workflow are applying the multicomponent SLD model to conduct regression analysis on the measured adsorption isotherm of each component in the gas mixture simultaneously and using the determined key regression parameters to predict the adsorption isotherms of gas mixtures with various feed-gas mole fractions. Through the calculation workflow, the density profiles and mole fractions of the adsorbed gases can be determined, from which the absolute adsorption of the gas mixture is estimated. In addition, the CO2/CH4 adsorption selectivity larger than one is observed, illustrating the preferential adsorption of CO2 over CH4 on shale, which implies that CO2 has enormous potential to enhance CH4 production while sequestering itself in shale. Our findings demonstrate that the proposed calculation workflow depending on the multicomponent SLD model enables us to accurately predict the adsorption of gas mixtures in nanopores based on single-component adsorption results. Following the innovative calculation flow path, we could bypass the experimental difficulties of measuring the multicomponent mole fractions in the gas phase at the equilibrium during the adsorption experiments. This study also provides insight into the CO2/CH4 competitive adsorption behavior in nanopores and gives guidance to CO2-enhanced gas recovery (CO2-EGR) and CO2 sequestration in shale formations.

Dual-function biomimetic carrier based facilitated transport mixed matrix membranes with high stability for efficient CO2/N2 separation

Realizing efficient carbon capture by high-performance CO2 separation membrane is significant to mitigate the increasing emissions of greenhouse gas CO2. Inspired by the extraordinary CO2 hydration ability of carbonic anhydrase (CA), a biomimetic MOF (CFA-1) which can mimic the CO2 hydration sites of CA but possesses better stability and the lower price was incorporated into Pebax to fabricated high-performance facilitated transport mixed matrix membranes. The optimal membrane has a CO2 permeability of 869 Barrer with a CO2/N2 ideal selectivity of 88.6 at 1 bar and 30 °C, which is 9.2 times and 2.8 times than the pristine Pebax membrane. Such superior CO2/N2 separation performance (far surpasses 2008 upper bound) is original from the dual-function of CFA-1: (1) provide extra pathways for gas diffusion and affinity sites for preferential CO2 adsorption; (2) facilitate CO2 transport in the membrane by efficiently catalyze CO2 hydration reaction. Furthermore, the Pebax/CFA-1 membranes fabricated can also exhibit excellent stability after being treated under high temperature and harsh pH, which is not available in the Pebax/CA membranes. Overall, such biomimetic dual-function MOFs may pave a new avenue to advance the high-performance CO2 facilitated transport membranes with excellent stability.

Fabrication of highly (110)-Oriented ZIF-8 membrane at low temperature using nanosheet seed layer

Preferred orientation represents a main concern for microstructure control and performance optimization of MOF membranes. To date, it remains a challenging task to precisely control preferred orientation of ZIF-8 membrane. Herein, we prepared highly (110)-oriented ZIF-8 membrane by oriented secondary growth. Among various elements, preparation of uniform ZIF-8 nanosheet seeds through thermal conversion of identically shaped ZIF-L precursors, spin-coating-assisted oriented deposition of (110)-oriented ZIF-8 seed layer, and controlled in-plane secondary growth at low temperature were found crucial for obtaining well-intergrown (110)-oriented ZIF-8 membrane whose H2/CO2 ideal selectivity exceeded H2/N2 and H2/CH4 under ambient conditions, owing to preferential CO2 adsorption capacity of not only PEI but also ZIF-8 nanosheets compared with their bulk counterparts. Our research highlighted the significance of preferred orientation regulation in tailoring the gas permeation behavior of MOF membranes.

Overview of the Adsorption and Transport Properties of Water, Ions, Carbon Dioxide, and Methane in Swelling Clays

It is quite challenging to understand the details of the complex mechanisms involved in the swelling processes of clays such as montmorillonite as a function of relative humidity (RH), and the adsorption and transport processes of CO2 and CH4 in swelling clays. Here we present a review of the molecular simulation results for the swelling clay systems which not only compare well with the experimental data but also provide deep insights into the details of these mechanisms. The presence of CO2 and CH4 hardly affects the distribution and mobility of the interlayer water and ions in these systems. Under all conditions, the stable basal d-spacing was mainly determined by the type of counterion present in the interlayer region and the amount of water in each hydration state was almost independent of the RH and the layer charge. The uptake of CH4 in the 1W state of the Na-clay was much smaller compared to that of CO2. The adsorbate mobility generally increased with increasing hydration/RH because of the associated swelling of the interlayer region. Interestingly, the uptake of CO2 in the high-charge clay was dramatically decreased, and the mobility of CO2 in each hydration state was almost independent of the type of cation. The preferential adsorption of CO2 over CH4 plays an important role in the diffusion processes. Such an understanding is important for the successful mitigation of climate change via storage of anthropogenic CO2 in geological formations.

Swelling response of anthracite coal during CH4-CO2 competitive adsorption by molecular simulation

Adsorption-induced swelling is a major concern for gas injection to promote recovery of coalbed methane, especially in the CH4-CO2 competitive adsorption process because it directly determines the permeability of the reservoir. In this work, adsorption isotherms and the swelling response of anthracite coal during CH4-CO2 competitive adsorption are investigated through molecular simulation. The results show that the adsorption capacity of CH4 is suppressed due to the preferential adsorption of CO2 on anthracite coal. The increase in the mole fraction of CO2 can increase the total adsorption capacity of the binary mixture. Moreover, as the fugacity increases from 0.1 to 10.1 MPa, the volumetric strain dominated by adsorption-induced swelling gradually increases. Also, the increase in the mole fraction of CO2 can increase the volumetric strain of the binary mixture. This research can provide guidance for coalbed methane recovery.

Preferential adsorption of CO2 on cobalt ferrite sites and its role in oxidative dehydrogenation of ethylbenzene

Preferential adsorption of CO2 on cobalt ferrite sites and its role in oxidative dehydrogenation of ethylbenzene

Cooperative defect tailoring: A promising protocol for exceeding performance limits of state-of-the-art MOF membranes

Preferred orientation control represents an effective method for grain boundary defect elimination at the mesoscopic scale and therefore, performance enhancement of MOF membrane. In contrast, tailoring the separation performance of MOF membrane via structural defect engineering at the microscopic scale remains elusive. In this work, we pioneered the fabrication of (111)-oriented UiO-66 membrane via oriented tertiary growth. The use of ZrS2 as metal source during solvothermal synthesis led to higher number of missing linkers within the framework and therefore, preferential adsorption of CO2 over N2. In comparison with secondary growth, both CO2/N2 selectivity and CO2 permeability of obtained UiO-66 membrane after tertiary growth were concurrently increased, thereby transcending both the 2008 Robeson upper bound and the separation performance limits of state-of-the-art polycrystalline MOF membranes for CO2/N2 gas pair.