Selective Adsorption Of CO2 Research Articles

Diamine-appended metal-organic framework for carbon capture from wet flue gas: Characteristics and mechanism

Due to the superior CO2 adsorption capacity and selectivity, amine-functional solid adsorbents have received increasing attention. Nevertheless, amine-functionalized polyporous materials have a large performance deviation when considering carbon removal capacity under wet flue gas. Therefore, a variety of metal–organic frameworks (MOFs) with amine functionality are synthesized in this work by appending diamine with a propylene linker to Mg2(dobpdc) (dobpdc4- = 4,4′-dioxido-3,3′-biphenyldicarboxylate) and screened under the simulated flue gas environment with a high water content (7 v%). The results indicate that ndmpn-grafted Mg2(dobpdc) (ndmpn = N,N-dimethyl-1,3-propanediamine) has a high CO2 adsorption capacity of 1.72 mmol/g at 60 °C with an extremely low regeneration heat (2.26 GJ/ton CO2 at the desorption temperature of 145 °C). Adsorption property of ndmpn-Mg2(dobpdc) at high humidity is even more excellent than that of another well-reported diaminopropene-appended MOF, dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine). Herein, van der Waals (vdW)-corrected density functional theory (DFT) calculations are used to quantitatively analyze binding strengths and water effects on it between diamine-appended Mg2(dobpdc) and CO2. It is revealed that the addition of water makes ammonium carbamate chains produced in ndmpn-Mg2(dobpdc) more stable. These chemisorption structures under humid conditions have also been disclosed by using 15N solid-state nuclear magnetic resonance (NMR) spectroscopy experiments and DFT calculation. To conclude, we unveil the binary adsorption characteristics and mechanism of ndmpn-Mg2(dobpdc). It enables a thorough understanding of this compound and highlights its potential as a promising adsorbent under humid conditions for post-combustion applications.

Amidoxime Modified UiO-66@PIM-1 Mixed-Matrix Membranes to Enhance CO2 Separation and Anti-Aging Performance.

Mixed matrix membranes (MMMs) generally have some fatal defects, such as poor compatibility between the two phases leading to non-selective pores. In this work, PIM-1 was chosen as the polymer matrix, and UiO-66 modified with amidoxime (UiO-66-AO) was used as the filler to prepare the MMMs. In the MMMs, the amino and hydroxyl groups on UO-66-AO form a rich hydrogen bond network with the N and O atoms in the polymer PIM-1 chain to improve the compatibility between the polymer matrix and the filler. In addition, the selective adsorption of CO2 by the amidoxime group can promote the transport of CO2 in the membrane, which enhances the gas selectivity. The CO2 permeability and CO2/N2 selectivity of UiO-66-AO@PIM-1 MMMs are increased by 35.2% and 45.2% compared to pure PIM-1 membranes, reaching 7535.5 Barrer and 26.9, surpassing the Robeson Upper Bound (2008) and close to the 2019 Upper Bound. After 38 days of the aging experiment, the CO2 permeability is approximately 74% of the original. The results show that the addition of UiO-66-AO has an obvious effect on improving the aging properties of the membrane. The UiO-66-AO@PIM-1 MMMs have a bright prospect for CO2 separation in the future.

An anionic MOF as a multifunctional platform for selective adsorption of CO2, separation of organic dyes and ionic conductivity

It is a very effective strategy to capture and separate carbon dioxide by incorporation of alkali cations into MOFs. Presented here is an anionic metal-organic framework (MOF) (Me2NH2)2Co(tpta)·2H2O (1), in which the exchange of alkali ions (Li+ and Na+) took place with H2N(Me)2+ cations. As expected, CO2/N2 selectivity of the framework was improved significantly and reached 61.6 due to the inclusion of Li + using the ideal adsorbed solution theory (IAST) model. The enhancement of its CO2 uptake capability and selectivity has been mainly attributed to the charge-quadrupole interaction. For the CO2/N2 system, it is found that the inclusion of Li+ rather than Na+ favors higher selectivity. Additionally, it successfully separated cationic dye crystal violet (CV+) from anionic dye methyl orange (MO−) by the column-chromatography. Evidently, the enhancement of the electrostatic interaction greatly improves the separation performance of the framework.

Optimization of preparation of NaA zeolite from fly ash for CO2 capture.

The green synthesis method of fly ash-based NaA zeolite was explored to reduce the synthesis cost and environmental hazards. For the prepared NaA samples, the effects of crystallization time, solid-liquid ratio, and Si/Al ratio were systematically studied. CO2 adsorption isotherm is used for adsorption model fitting analysis and adsorption selectivity determination. According to the experimental results, the optimized NaA zeolite synthesis conditions are as follows: the Si/Al ratio of NaA zeolite is 1.4, the solid-liquid ratio is 10, and the crystallization time is 6 h. The green synthesis method reported in this study can successfully prepare NaA zeolite and exhibit excellent CO2 adsorption performance, reaching 4.34 mmol/g, with high CO2 selective adsorption ability, reaching 89.2 for N2, 257.1 for O2, and 45.8 for CH4. The adsorbed CO2 can be released for further utilization, and NaA zeolite also has strong adsorption and regeneration performance, with a ten cycle adsorption capacity only decreasing by 1.17%. In addition, the use of cheap raw materials synthesis methods will promote the large-scale industry application of green synthesis technology in the future.

Selective Gas Sensing under a Mixed Gas Flow with a One-Dimensional Copper Coordination Polymer.

Structural changes of the coordination polymer associated with gas adsorption (gate opening-type adsorption) can be linked to bulk physical properties such as magnetism, electrical conductivity, and dielectric properties. To enable real-space sensing applications, it is imperative to have a system where the selective adsorption of mixed gases can be correlated with physical properties. In this report, we demonstrate that a crystalline sample of one-dimensional (1D) coordination polymer exhibits selective CO2 adsorption while simultaneously displaying dielectric switching behavior in a mixed N2/CO2 gas environment. In the crystal of {[Cu2(2-TPA)4(pz)]·CH3CN}n (1·CH3CN), where 2-TPA and pz are 2-thiophencarboxylate and pyrazine, respectively, paddle wheel-type units of [Cu2(2-TPA)4] are bridged by pz, forming a 1D chain structure. One of the two crystallographically independent 2-TPA units was interacted with the pz moiety of the adjacent 1D chain by π···π interactions, forming a two-dimensional (2D) layer parallel to the ab plane. Activated 1 shows selective CO2 adsorption by a gate opening-type adsorption mechanism, indicating that the CO2 adsorption process is accompanied by a structural change. The change in the real part of dielectric permittivity (ε') under the mixed N2/CO2 gas flow is a result of the selective CO2 adsorption, which was supported by the enthalpy changes (ΔH) associated with CO2 adsorption in two methods: CO2 adsorption isotherms and temperature-dependent measurements of ε' under a mixed N2/CO2 gas flow. The calculated ΔH values were found to be in good agreement across both methods. The CO2 ratio in the mixed N2/CO2 gas flow increased, and the switching ratio of ε' (Δε') also increased. Notably, Δε' exhibited a marked increase beyond the pressure required for gate opening adsorption.

Solid–solid thermal synthesis of bimetallic Ni/Zn embedded in N-doped porous carbon for efficient adsorptive separation based on CO2 adsorption at low pressure

High-efficient adsorptive materials for carbon dioxide (CO2) capture and separation of a gas mixture are vital for energy consumption and emission reduction but are still a substantial challenge. A facile synthesis of bimetallic nickel/zinc embedded in N-doped carbon (Ni/Zn@NC) through the solid–solid thermal method (SST) is developed herein. The SST method is a straightforward procedure with the advantage that the materials are obtained in a single step and solvent-free conditions. Thermal analysis and material characterization were used to investigate the synthesis mechanism during the SST process. The results revealed that an intermediate material, initially obtained at a low thermal temperature, was sacrificed to generate Ni/Zn@NC at high temperatures of the SST method. The resulting robust carbon structure, decorated with heteroatoms (Ni, Zn, N), exhibits a potential for efficient CO2 adsorption during the capture and separation of biogas (CO2/CH4), off-gas (CO2/N2), and natural gas (CH4/ N2). The synergetic effect of Ni in the materials enhances the selectivity of SCO2/CH4, SCO2/N2, and SCH4/N2. The improved selectivities by effective sites were confirmed by computational modeling. Significantly, the Ni/Zn@NC material obtained through a mild yet simple synthesis method (SST) exhibits substantially higher CO2 adsorption capacity and selectivity when compared to commercial carbon (activated charcoal).

Exquisitely Constructing a Robust MOF with Dual Pore Sizes for Efficient CO2 Capture.

Developing metal-organic framework (MOF) adsorbents with excellent performance and robust stability is of critical importance to reduce CO2 emissions yet challenging. Herein, a robust ultra-microporous MOF, Cu(bpfb)(bdc), with mixed ligands of N, N'-(1,4-phenylene)diisonicotinamide (bpfb), and 1,4-dicarboxybenzene (bdc) was delicately constructed. Structurally, this material possesses double-interpenetrated frameworks formed by two staggered, independent frameworks, resulting in two types of narrow ultra-micropores of 3.4 × 5.0 and 4.2 × 12.8 Å2, respectively. The above structural properties make its highly selective separation at 273~298 K with a CO2 capacity of 71.0~86.2 mg/g. Its adsorption heat over CO2 and IAST selectivity were calculated to be 27 kJ/mol and 52.2, respectively. Remarkably, cyclic breakthrough experiments corroborate its impressive performance in CO2/N2 separation in not only dry but also 75% RH humid conditions. Molecular simulation reveals that C-H···OCO2 in the pores plays a pivotal role in the high selectivity of CO2 adsorption. These results point out the huge potential application of this material for CO2/N2 separation.

Bimetallic Metal Organic Framework Composites for Carbondioxide Capture

Maintaining breathable air in human space flight missions is a challenge since there will be a gradual increase in the concentration of CO2 due to the exhalation of the spacecraft crew. Modern air revitalization technology for space missions uses temperature swing adsorption with zeolite-based materials as the adsorbent. However, the major drawbacks of zeolites are difficulty in regenerating used adsorbent and low selectivity towards CO2. Besides, frequent replacement of adsorption beds is necessary because of their low adsorption capacity towards CO2. This requires carrying a few spare beds in the spacecraft, which is not preferred because of the low-weight requirements for space missions. Hence, shifting to alternate materials with more selectivity and adsorption capacity toward CO2 becomes essential. Metal-organic frameworks (MOFs) are a class of crystalline materials found to be potential adsorbents for CO2 capture. Due to their ultra-high porosity, tunable pore characteristics, selective capture, and synergistic performance, they could replace the existing zeolite-based adsorbents. Further enhancement in the adsorption capacity could be achieved by introducing a secondary metal into the framework. This will bring heterogeneity in the structure, creation of defects, and open metal sites, thus enhancing the adsorption behavior. Incorporating a secondary metal into the framework and an additional filler material like activated carbon, making a BMOF composite, would lead to an exemplary improvement in the adsorption activity. The addition of filler material will lead to an increase in pore volume, which will enhance the adsorption capacity. In the current work, activated carbon was synthesized from sawdust via chemical activation method using KOH as the activating agent. It was carried out at low temperatures to boost the porous structure formation. Then the composite of Cu-Ni bimetallic MOF with activated carbon was prepared through one-pot solvothermal synthesis. The incorporation of activated carbon created an additional number of pores in the system leading to enhanced adsorption. N2 adsorption-desorption analysis was carried out to find the surface area. The results showed that the surface area of activated carbon and Cu-Ni-Activated carbon BMOF composite was found to be 576 m2/g and 1321 m2/g, respectively. The analysis also revealed the presence of microporous system in the material. Several characterization techniques, such as IR, SEM, XRD etc., were used to study morphology and characteristic features. The SEM shows that the incorporation of nickel and activated carbon have made a profound modification on the octahedral morphology of copper.CO2 adsorption studies were carried out at 1 bar, 25°C. The BMOF composite adsorbent was found to adsorb ~4.52 mmol/g of CO2 whereas the as-synthesized activated carbon and ZSM-5 were found to adsorb ~2.71 mmol/g and ~1.68 mmol/g respectively. To understand the level of microporosity in the supermicropores range, CO2 adsorption analysis at 1 bar and 0°C was carried out since N2 adsorption at -196°C have limitations due to kinetic diffusion related problems at low temperatures. It revealed a micropore volume (<1.066nm) of 0.252 cm3 /g and a pore size range of 4-10 angstroms, which is ideal for selective CO2 adsorption. Also, the BMOF composite was found to adsorb ~8.27 mmol/g at 0°C, which showed that adsorption capacity increases with a decrease in temperature. Hence, the BMOF composites could serve as a promising adsorbent for selective CO2 capture. Figure 1

Impact of Ce/Zr Ratio in the Nanostructured Ceria and Zirconia Composites on the Selective CO2 Adsorption.

High surface-area, mesoporous CeO2, ZrO2, and Ce-Zr composite nanoparticles were developed using the hydrothermal template-assisted synthesis method. Samples were characterized using XRD, N2 physisorption, TEM, XPS, and FT-IR spectroscopic methods. The CO2 adsorption ability of the obtained materials was tested under dynamic and equilibrium conditions. A high CO2 adsorption capacity in CO2/N2 flow or CO2/N2/H2O was determined for all studied adsorbents depending on their composition flow. A higher CO2 adsorption was registered for Ce-Zr composite nanomaterials due to the presence of strong O2- base sites and enriched surface oxygen species. The role of the Ce/Zr ratio is the process of the formation of highly active and selective adsorption sites is discussed. The calculated heat of adsorption revealed the processes of chemisorption and physisorption. Experimental data could be appropriately described by the Yoon-Nelson kinetic model. The composites reused in five adsorption/desorption cycles showed a high stability with a slight decrease in CO2 adsorption capacities in dry flow and in the presence of water vapor.

Sustainable preparation of hierarchical porous carbon from discarded shells of crustaceans for efficient CO2 capture

The improved CO2 adsorption capacity and selectivity is the focus of research on the carbon-based CO2 adsorbent, while nitrogen-containing groups on the surface of adsorbent have an important effect on the CO2 adsorption. In this study, nitrogen self-doped hierarchical porous carbon was prepared from three kinds of crustacean shells, namely, hairy crab shell, crayfish shell and greasyback shrimp shell. It revealed that the pore structure of porous carbon can be regulated well with the varied activation temperature and the amount of KOH. With the favorable activation temperature of 800℃ and the mass ratio of activator to carbon (A/C) of 1:1, the obtained porous carbon with different carbon precursors exhibited relatively high specific surface area (1430.63–1734.64 m2/g), large pore volume (0.70–1.48 cm3/g) and developed pore-size distribution. Consequently, among the three kinds of hierarchical porous carbon tested, that prepared form greasyback shrimp displayed the excellent CO2 adsorption of 5.144 and 4.325 mmol/g at 1 bar, 273 K and 298 K and the highest CO2/N2 selectivity was observed of 32.32, attributed to the volume of mesopore and micropore and the type of nitrogen-containing groups. The effects of nitrogen-containing groups in porous carbon on the CO2 adsorption and CO2/N2 selectivity were analyzed, and it revealed that the CO2/N2 selectivity of porous carbon was positively correlated with pyrrolic N. In conclusion, the porous structures and nitrogen-containing groups of porous carbons both contribute to the CO2 adsorption and selectivity. The porous carbon with well recycling performance in this study presented a practical application prospect.

CO2 Adsorption Behaviors of Biomass-Based Activated Carbons Prepared by a Microwave/Steam Activation Technique for Molecular Sieve.

In this study, the activated carbon was prepared with superior CO2 selective adsorption properties using walnut shells, a biomass waste, as a precursor. The activations were conducted at various times using the microwave heating technique in a steam atmosphere. The surface morphology and chemical composition of activated carbon were analyzed using a scanning electron microscope and energy-dispersive X-ray spectroscopy. The textural properties were investigated using the N2/77K isothermal method, and the structural characteristics were examined using X-ray diffraction analysis. The CO2 and H2 adsorption properties of activated carbon were analyzed using a thermogravimetric analyzer and a high-pressure isothermal adsorption apparatus, respectively, under atmospheric and high-pressure conditions. Depending on the activation time, the specific surface area and total pore volume of the activated carbon were 570-690 m2/g and 0.26-0.34 cm3/g, respectively. The adsorption behaviors of CO2 of the activated carbon were different under atmospheric and high-pressure conditions. At atmospheric pressure, a significant dependence on micropores with diameters less than 0.8 nm was observed, whereas, at high pressure, the micropores and mesopores in the range of 1.6-2.4 nm exhibited a significant dependence. However, H2 adsorption did not occur at relatively low pressures. Consequently, the prepared activated carbon exhibited superior selective adsorption properties for CO2.

Surface Heterogeneity Affects Adsorption Selectivity for CO2 Over CH4 in Bare Mesostructured Silica with 2D Hexagonal Symmetry and Different Pore Size

AbstractMesoporous silica‐based materials are used as sorbents and supports in many fields. The ordered pore architecture of MCM‐41, and the absence of interconnections, make it suitable as a model system. The surface is natively functionalized by many silanol groups, endowing the material with a polar surface to directly interact with the target species or to mount additional functional groups. Either bare or functionalized, surface silanol arrangement is crucial to material performance. In the case of CO2 capture with amine‐functionalized silica, silanol groups are responsible for fundamental H‐bonds during chemisorption, but they also modulate the effect and weight of humidity on the material performance. In addition, the silanol groups can also tune the weight of physisorption over chemisorption. The relationship between these aspects and the textural features of mesostructured silica has not been addressed in detail. In this study, computer models are employed to investigate the adsorption capacity and selectivity of bare mesostructured silica with three different pore sizes. Results are rationalized in terms of silanol surface density and pore curvature. The importance of the energetic inequivalence between Q3 and Q2 sites on the silica surface is emphasized, as this causes adsorption behavior to deviate from ideality.

Electronic Properties and CO2-Selective Adsorption of (NiB)n (n = 1~10) Clusters: A Density Functional Theory Study.

In this study, we investigated the electronic properties and selective adsorption for CO2 of nickel boride clusters (NiB)n, (n = 1~10) using the first principles method. We optimized the structures of the clusters and analyzed their stability based on binding energy per atom. It was observed that (NiB)n clusters adopt 3D geometries from n = 4, which were more stable compared to the plane clusters. The vertical electron affinity, vertical ionization energy, chemical potential, and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap were calculated. Our results revealed that (NiB)6 and (NiB)10, with high chemical potential, exhibit a higher affinity for CO2 adsorption due to a charge delivery channel that forms along the Ni→B→CO2 path. Notably, (NiB)10 demonstrated a more practical CO2 desorption temperature, as well as a broader window for the selective adsorption of CO2 over N2. The density of states analysis showed that the enhanced CO2 adsorption on (NiB)10 can be attributed to the synergistic effect between Ni and B, which provides more active sites for CO2 adsorption and promotes the electron transfer from the surface to the CO2 molecule. Our theoretical results imply that (NiB)10 should be a promising candidate for CO2 capture.

ZSM-5/Silicalite-1 core-shell beads as CO2 adsorbents with increased hydrophobicity

Zeolites are commonly used for selective CO2 adsorption from biogas and flue gas. One of the biggest challenges for zeolites in this application is the presence of water vapour in the raw gas streams. While zeolites with low Si/Al ratio typically display high CO2 adsorption, they are hydrophilic and H2O competes for adsorption on the active sites. On the other hand, zeolites with high Si/Al ratio are hydrophobic, but display lower CO2 adsorption capacities. In order to overcome this limitation and to combine the high CO2 adsorption capacity of low Si/Al zeolites and the hydrophobicity of high Si/Al zeolites into a single material, we designed and synthesized novel core-shell zeolitic beads comprising a ZSM-5 core and a Silicalite-1 shell. Two different strategies were employed to synthesize these macroscopic core-shell beads. In both approaches, the initial step was the synthesis of binderless ZSM-5 beads with hierarchical porosity using resin beads as hard template. In the first strategy, a shell of Silicalite-1 was synthesized on the external surface of the calcined ZSM-5 beads, yielding Sil-ZSM-A core-shell beads (0.84 ± 0.12 mm). In the second strategy, the Silicalite-1 shell was synthesized without first removing the polymeric template from the ZSM-5 beads, resulting in core-shell composite beads that after calcination yielded Sil-ZSM-B core-shell beads (0.73 ± 0.14 mm). Characterization by SEM, XRD, XRF, ICP-AES and N2 physisorption indicated that both Sil-ZSM-A and Sil-ZSM-B beads displayed the desired zeolitic core-shell structure with hierarchical porosity. Both core-shell beads showed the anticipated increase in hydrophobicity. The most promising results were obtained with Sil-ZSM-A beads, which displayed a 40% decrease in H2O adsorption capacity at 20% relative humidity (RH) and a 28% decrease at max RH compared to the parent ZSM-5 beads. At the same time, their CO2 adsorption capacity (1.94 mmol/g at 1 bar) decreased only slightly compared to the parent ZSM-5 beads (2.13 mmol/g at 1 bar). These results indicate that these core-shell beads present the desired combination of the high CO2 adsorption capacity of the ZSM-5 core with the hydrophobicity of the Silicalite-1 shell. This is a promising feature for application in the adsorption of CO2 from water-containing streams.

Biomass Based N/O Codoped Porous Carbons with Abundant Ultramicropores for Highly Selective CO2 Adsorption

In this work, N/O codoped porous carbons (NOPCs) were derived from corn silk accompanied by Na2CO3 activation. The porous structures and surface chemical features of as-prepared carbon materials were tailored by adjusting the Na2CO3 mass ratio. After activation, the optimized sample (NOPC1) with abundant ultramicropores and pyrrolic N displays an enhanced CO2 adsorption capacity of 3.15 mmol g−1 and 1.95 mmol g−1 at 273 K and 298 K at 1 bar, respectively. Moreover, this sample also exhibited high IAST selectivity (16.9) and Henry’s law selectivity (15.6) for CO2/N2 at 298 K as well as moderate heat adsorption. Significantly, the joint effect between ultramicropore structure and pyrrolic N content was found to govern the CO2 adsorption performance of NOPCs samples.

Tailoring of 3D printed polyethylenimine functionalized MCM-41 based monoliths and scrutiny on CO2 adsorption characteristics

Amine functionalized mesoporous silica materials have emerged as promising adsorbents in terms of CO2 capture. Despite the noteworthy advancement in the development of novel adsorbents, commercial implementation of solid-gas contactors in real-time application is challenging. This is because, the conventional packed bed systems exhibit high-pressure drop, poor mass as well as heat transfer characteristics, attrition, and dusting issue. Therefore, it is pre-requisite to develop definite structured configurations in view of industrial applications. In the current work, 3D printing technique is used to fabricate PEI functionalized MCM-41 based structured configuration and their CO2 adsorption performance is investigated. In this study, MCM-41 is subjected to organic modification using PEI entities with different molecular weights (MW ∼ 600, 1200, 1800) and formulated into 3D printable ceramic ink using appropriate binders and plasticizers. The ceramic ink showed shear thinning behavior when the plasticizer is minimal in the formulation. The ceramic ink is then processed into three-dimensional configurations using pneumatic extrusion technique and their physicochemical characteristics are analyzed in addition to their powder counterparts. The current work aims to envisage the influence of molecular weight of organic moiety used for the functionalization of MCM-41 on the CO2 uptake capacity of 3D printed monoliths at different temperature conditions (30, 45, 60, 75, 90, 105 ℃). Through this study, we aim to tailor the design of 3D printed polyethylenimine functionalized MCM-41 based monoliths and assess their CO2 adsorption properties, selectivity, and stability across multiple cycles. By addressing these aspects, our research contributes to the field by advancing the understanding of tailored adsorbent materials for CO2 capture and highlighting the potential of 3D printing technology in fabricating structured adsorbents for industrial applications.

Investigating the selective adsorption of CO2 by MIL-101(Cr)-NH2 and modeling the equilibrium data using a new three-parameter isotherm

Compared to MIL-101(Fe)-NH2, MIL-101(Cr)-NH2 has considerably higher adsorption of CO2. On the other hand, the adsorption of CH4 and N2 by MIL-101(Cr)-NH2 is lower than the adsorption of these gases by MIL-101(Fe)-NH2 leading to a higher selectivity of CO2 to CH4 and N2 for MIL-101(Cr)-NH2. The chemisorption mechanism is more influential in higher temperatures and pressure, which can be attributed to the performance of amines which can adsorb more CO2 at higher temperatures and pressure. The isosteric heat of CO2 adsorption on MIL-101(Cr)-NH2 was estimated equal to − 31 kJ mol-1.MIL-101(Cr)-NH2 was synthesized and characterized by the BET, XRD, FESEM, TGA, and DTA methods. The BET surface area of the synthesized MOF was achieved equal to 1768 m2 g-1. The adsorption capacity of pure CO2, CH4, and N2 was estimated using the volumetric method. A new three-parameter equation was presented to model the experimental adsorption data including both types I and II isotherm shapes. Using the Ideal Adsorbed Solution Theory (IAST), the selectivity of CO2 to CH4 at high pressure, and CO2 to N2 at lower pressures was estimated equal to 4.1 and 4.7, respectively. In addition to 25 °C, the adsorption tests were performed at 18 and 30 °C to estimate the adsorption heat of CO2 on MIL-101(Cr)-NH2 achieved equal to − 31 kJ mol-1. The adsorption isotherm of CO2 at 25 and 30 °C have been almost identical showing the role of the chemisorption mechanism of CO2 by the amine functional group, especially at higher temperatures and pressures. Furthermore, the resistance of synthesized MOF to water was investigated by putting it in contact with water for 24 h. The result showed that MIL-101(Cr)-NH2 can be classified as thermodynamically stable to water.

Ab initio study of metal-decorated carbon and silicon prismanes as the selective CO2 adsorbents

In this paper, we conducted comprehensive analysis of the selective adsorption of CO2 by carbon and silicon prismanes along with metal ions. The results of calculations from B3LYP/6-31G(d,p) and M06-2X/6-31G(d,p) levels of theory show that Be[Formula: see text], Mg[Formula: see text], Ca[Formula: see text] and Li[Formula: see text], Na[Formula: see text], K[Formula: see text] ions are bounded strongly enough to prismanes. The Be[Formula: see text] ion binds more strongly to the C8 H8 cubane with binding energy 9.66[Formula: see text]eV compared to Li[Formula: see text], Na[Formula: see text], K[Formula: see text], Mg[Formula: see text] and Ca[Formula: see text] ions having binding energies 1.26, 0.63, 0.51, 4.60 and 3.36[Formula: see text]eV, respectively. Similar results were obtained for larger prismanes C[Formula: see text]H[Formula: see text] and C[Formula: see text]H[Formula: see text]. Instead of binding energy, we determine the adsorption of gases on metal-ion prismane complex along with effect of temperature on different gas adsorption shows that C8H8_Mg[Formula: see text] and C8H8_Be[Formula: see text] are active adsorbents at temperatures above room temperature. It is also observed that in comparison to N2 and CH4, CO2 interacts more strongly with all prismanes decorated with metal ions. These non-covalent interaction plots are used to study the prismane and metal-ion interaction. Comparable study of silicon prismanes with M06 2X/6-31G (d, p) basis set, in terms of binding energy, adsorption of gases on prismane along with temperature effect, also possesses similar selectivity to CO2 molecule with even higher adsorption energies. Thus, beryllium-decorated prismanes can be considered as promising adsorbents of carbon dioxide with good selectivity and high adsorption energy.

Metal cation-exchanged LTA zeolites for CO2/N2 and CO2/CH4 separation: The roles of gas-framework and gas-cation interactions

Selective CO2 adsorption for efficient carbon capture from flue gas (CO2/N2 - 15/85, v/v) and biogas (CO2/CH4 - 50/50, v/v) is important for achieving global energy and climate goals but remains a challenge due to the lack of effective adsorbents. To address this issue, we attempted to develop zeolite adsorbents by systematically investigating the effect of different extra-framework metal cations (i.e., Na+, Ca2+, Mn2+, and Ce3+-exchanged in LTA zeolites) on selective CO2 adsorption from CO2/N2 and CO2/CH4. Analyzing the isosteric heat of adsorption results showed that CO2 adsorption at moderate pressure (e.g., 15 and 50 kPa relevant to the compositions of flue gas and biogas, respectively) is governed by the gas-framework interaction. On the other hand, the adsorption of N2 and CH4 was found to be dominated by the gas-cation interaction. Therefore, we concluded that metal cations with a small charge-to-size ratio are beneficial for selective CO2 adsorption from flue gas and biogas because they tend to induce strong CO2-framework interaction (due to the enhanced charge induction to zeolite framework O) and weak N2 or CH4-cation interaction (due to the weakened gas-cation electrostatic interaction). Specifically, LTA zeolites in the form of Na+, with the smallest charge-to-size ratio of cation in this study, exhibit the highest CO2 uptake and separation factor of CO2/N2 and CO2/CH4, as demonstrated by both static single-component adsorption and dynamic binary adsorption results. In addition, the potential of metal cation-exchanged LTA zeolites for VSA and PSA processes was evaluated. Our study provides valuable insights for designing small-pore zeolites as adsorbents for carbon capture.

Boosting the selectivity of Pt catalysts for cinnamaldehyde hydrogenation to cinnamylalcohol by surface oxidation of SiC support

The selective hydrogenation of cinnamaldehyde (CAL) is very important, but still remains challenging due to the coexistence of easily hydrogenated CC and CO bonds in CAL molecule. In this work, we report that employing partially oxidized SiC (SiC–O) as the support of Pt can evidently enhance the catalytic selectivity for the selective hydrogenation of CO in CAL. Further investigations show that the partially oxidized SiC surface can change the adsorption mode of CAL and facilitate the selective adsorption of CO in CAL. During the catalytic process, H2 was dissociated on Pt particles while CAL was mainly adsorbed and activated on the surface of support. The active H species generated on the Pt surface then spilled over to the support surface and reacted with the CO bond activated by the support surface to selectively form cinnamylalcohol. The present work revealed an important cooperative catalysis of metal and SiC, which would be helpful to design and application of more SiC-based catalysts.