CH4 Adsorption Research Articles

Decoding the zeolite cage effect in one-step ethylene purification from CO2/C2H2/C2H4 mixtures

Utilizing physical adsorption for ethylene purification from complex mixtures can significantly reduce the energy cost for production. The purification of multi-component systems through a single adsorption process presents a considerable challenge, largely stemming from the absence of customized strategies and thorough investigations into adsorption behaviours. We aim to understand adsorbents through a unique cage recognition approach and leverage these insights to develop an effective purification adsorbent, with the successful synthesis of SSZ-16 zeolite meeting requirements for multi-component purification. This zeolite, featuring a long aft supercage and a narrow gme cage construct two adsorption cages. The dense π-electron cloud of C2H2 enables a stronger interaction in aft cage, while CO2 is selectively captured within the environmentally compatible gme cage, demonstrating significantly higher C2H2 and CO2 adsorption capacity. The separation experiments reveal that SSZ-16 exhibits exceptional performance, with an unprecedented polymer-grade C2H4 productivity of 2099.16 L/kg from the CO2/C2H2/C2H4 mixture.

Mechanochemical "Cage-on-MOF" Strategy for Enhancing Gas Adsorption and Separation through Aperture Matching.

Post-modification of porous materials with molecular modulators has emerged as a well-established strategy for improving gas adsorption and separation. However, a notable challenge lies in maintaining porosity and the limited applicability of the current method. In this study, we employed the mechanochemical "Cage-on-MOF" strategy, utilizing porous coordination cages (PCCs) with intrinsic pores and apertures as surface modulators to improve the gas adsorption and separation properties of the parent MOFs. We demonstrated the fast and facile preparation of 28 distinct MOF@PCC composites by combining 7MOFs with 4 PCCs with varying aperture sizes and exposed functional groupsthrough a mechanochemical reactionin 5 mins. Only the combinations of PCCs and MOFs with closely matched aperture sizes exhibited enhanced gas adsorption and separation performance. Specifically, MOF-808@PCC-4 exhibited a significantly increased C2H2 uptake (+64%) and a longer CO2/C2H2 separation retention time (+40%). MIL-101@PCC-4 achieved a substantial C2H2 adsorption capacity of 6.11 mmol/g. This work not only highlights the broad applicability of the mechanochemical "Cage-on-MOF" strategy for thefunctionalization of a wide range of MOFs but also establishes potential design principles for the development of hybrid porous materials with enhanced gas adsorption and separation capabilities, along with promising applications in catalysis and intracellular delivery.

One-step purification of ethylene from ternary mixtures in an ultra-microporous interpenetrating MOF with unique constriction channels and F sites

The industrial importance of efficient purification of C2H4 from ternary C2H6/C2H4/C2H2 mixtures using a single adsorbent is significant, yet few adsorbents can achieve this challenging separation because of their very similar physical properties. Herein, we fabricated a robust metal–organic framework (MOF) that possessed unique constriction channels based on wide pockets and narrow windows as well as rich F sites and showed one-step C2H4 purification from C2H6/C2H4/C2H2 mixtures. The constriction channel restricts the adsorption of C2H4 in a degree, leading to high adsorption selectivity for both C2H6/C2H4 (1.9) and C2H2/C2H4 (2.9). Breakthrough experiments demonstrated that the material could efficiently separate C2H4 from C2H6/C2H4/C2H2 mixtures to produce highly pure C2H4 (>99.9%). Theoretical calculations provided a deep insight into the sorption mechanism, which revealed stronger multiple interactions between C2H6 or C2H2 molecules and pore walls compared to C2H4 molecules.

Molecular Insight into the Electric Field Regulation of N2 and CH4 Adsorption in the Trapdoor ZSM-25 Zeolites.

Controlling gas admission by regulating pore accessibility in porous materials has been a topic of extensive research. Recently, the electric field (E-field) has emerged as an external stimulus to alter the adsorption behavior of some microporous adsorbents. However, the mechanism behind this phenomenon is not yet fully understood. Here, we demonstrate the crucial role of the trapdoor cations of zeolite molecular sieves in E-field-regulated gas adsorption. The E-field activation caused framework expansion and cation deviation, significantly reducing the energy barrier for gas molecules passing through the pore aperture gated by the trapdoor cation. This led to an increase in the N2 adsorption capacity of ZSM-25 and a 60% improvement in N2/CH4 selectivity in the quest for nitrogen rejection for natural gas processing. By combining experimental and computational approaches, we elucidated the influence of E-field activation as a concurrent effect of the reduced heat of adsorption caused by framework expansion and the decrease in the energy barrier resulting from promoted cation oscillation. These findings pave the way for the material design of E-field-regulated adsorption and its application in molecular separation.

Metal-enhanced carbon-nitrogen material for selective detection of hazardous gases: Insights from interface electronic states

In this study, utilizing density functional theory, the C3N1 monolayer modified by Ir, Pd, Pt, and Rh atoms (Ir/Pd/Pt/Rh-C2N1) was chosen for selective adsorption of C2H2 amidst multiple gases (H2O, C2H2, and C4H10O2). According to the results of cohesive energy and ab initio molecular dynamics simulations, it is indicated that precious metal atoms can be stably anchored on the monolayer while enhancing the conductivity of the material The analysis of the electrostatic potential and work function determined the highly active sites and electron release capacity. In addition, the adsorption energy and distance disclosed the gas-solid interface structure of multiple gases on the Ir/Pd/Pt/Rh-C2N1 monolayer. Importantly, C2H2 exhibits strong responses to p-type semiconductor Pt-C2N1 and n-type semiconductor Ir-C2N1, respectively. Crystal Orbital Hamilton Population reveals the difference in adsorption energy due to modifications involving four precious metals. Interestingly, for the first time, the density of states calculation reveals that under the coexistence of multiple gases, the Pt/Ir-C2N1 monolayer effectively eliminates the interference of other gases and has a unique response only to C2H2. In real situations, with the basis of Gibbs free energy and Einstein's law of diffusion, it was determined that Pt-C2N1 and Ir-C2N1 showed excellent hydrophobicity, a wider temperature range, and a low diffusion activation energy barrier. In summary, Pt-C2N1 and Ir-C2N1 detect C2H2 without interference, maintaining fundamental principles, responsiveness, stability, and versatility unaffected by external factors.

Efficient recovery of acetylene from quaternary mixture by a pillar-layer framework with abundant Lewis basic sites

The efficient recovery of C2H2 from the gas mixtures comprising CO2 and other light hydrocarbons is the key to realize its further value-added production. In view of their similar physical properties, reasonable design of porous physical adsorbents is expected. Here, we report a metal–organic framework bpy-NH2-CuZrF6, which possesses the suitable aperture size and abundant Lewis basic sites derived from the modified amino groups and fluorinated anions, making it the first example of achieving the efficient recovery of C2H2 from a C2H2/C2H4/C2H6/CO2 quaternary mixture. This porous material possesses an excellent C2H2 adsorption capacity (138.9 cm3/g, 298 K and 1 bar) along with considerable IAST selectivities for equimolar C2H2/CO2 (6.6), C2H2/C2H4 (6.3), and C2H2/C2H6 (6.3) simultaneously. Combined with the adsorption heats and theoretical calculations, the preferential binding with C2H2 is demonstrated. And further breakthrough experiments show that the material can efficiently purify C2H2 not only from various binary mixtures (50/50 C2H2/CO2, 50/50 C2H2/C2H4, and 50/50 C2H2/C2H6), but also from the ternary (33.3/33.3/33.3 C2H2/C2H4/CO2) and even quaternary (25/25/25/25 C2H2/C2H4/C2H6/CO2) mixtures. As a result, 32.1 L/kg and 21.9 L/kg C2H2 with fuel-grade (purity ≥ 98 %) are recovered successfully after desorption for ternary (33.3/33.3/33.3 C2H2/C2H4/CO2) and quaternary (25/25/25/25 C2H2/C2H4/C2H6/CO2) mixtures respectively. Further combined with the green scalable synthesis, good recyclability, and high stability, this microporous material is expected to have a promising prospect for practical applications.

Improving the Selectivity and Stability of Supported Cobalt Catalysts via Static Bi-Doping and Dynamic Trace CO2 Co-Feeding During Propane Dehydrogenation.

Simultaneously enhancing selectivity and stability on supported propane dehydrogenation (PDH) catalysts remains a formidable challenge. Here, we report a combined static and dynamic strategy to address these issues synergistically. Firstly, we demonstrate a feasible sol-gel method for preparing atomically-dispersed Bi-decorated metal nanoparticle catalysts (MBi/Al2O3, M=Fe, Co, Ni, and Zn). In PDH testing, the total selectivity of by-products (CH4 and C2H6) significantly decreases to 4 % for CoBi catalysts due to the static Bi-doping, compared with 16 % for Co-supported catalysts. Secondly, to enhance catalytic stability, we introduce a dynamic trace CO2 co-feeding route. 10CoBi/Al2O3 catalysts exhibit superior durability against coke formation for 330 hours in PDH under a 40 % C3H8 atmosphere followed by pure C3H8 conditions at 600 °C while maintaining propylene selectivity at 96 %. Notably, introducing trace CO2 leads to a remarkable 6-fold decrease in the deactivation rate constant (kd). Multiple characterizations and density functional theory calculations reveal that charge transfer from atomically-distributed Bi to Co nanoparticles benefits lowering the energy of C3H6 adsorption thereby suppressing by-products. Furthermore, the dynamic co-feeding of trace CO2 facilitates coke removal, suppressing catalyst deactivation. The static Bi-doping and dynamic trace CO2 co-feeding strategy contributes simultaneously to increased selectivity and stability on supported PDH catalysts.

Improving the Selectivity and Stability of Supported Cobalt Catalysts via Static Bi‐Doping and Dynamic Trace CO2 Co‐feeding during Propane Dehydrogenation

Simultaneously enhancing selectivity and stability on supported propane dehydrogenation (PDH) catalysts remains a formidable challenge. Here, we report a combined static and dynamic strategy to address these issues synergistically. Firstly, we demonstrate a feasible sol‐gel method for preparing atomically‐dispersed Bi‐decorated metal nanoparticle catalysts (MBi/Al2O3, M= Fe, Co, Ni, and Zn). In PDH testing, the total selectivity of by‐products (CH4 and C2H6) significantly decreases to 4% for CoBi catalysts due to the static Bi‐doping, compared with 16% for Co‐supported catalysts. Secondly, to enhance catalytic stability, we introduce a dynamic trace CO2 co‐feeding route. 10CoBi/Al2O3 catalysts exhibit superior durability against coke formation for 330 hours in PDH under a 40% C3H8 atmosphere followed by pure C3H8 conditions at 600 °C while maintaining propylene selectivity at 96%. Notably, introducing trace CO2 leads to a remarkable 6‐fold decrease in the deactivation rate constant (kd). Multiple characterizations and density functional theory calculations reveal that charge transfer from atomically‐distributed Bi to Co nanoparticles benefits lowering the energy of C3H6 adsorption thereby suppressing by‐products. Furthermore, the dynamic co‐feeding of trace CO2 facilitates coke removal, suppressing catalyst deactivation. The static Bi‐doping and dynamic trace CO2 co‐feeding strategy contributes simultaneously to increased selectivity and stability on supported PDH catalysts.

Molecular simulation of CO2/N2 injection on CH4 adsorption and diffusion

As an efficient and clean energy, coalbed methane development and utilization have deep significance in promoting energy conservation and emission reduction, reducing greenhouse gas emissions. Therefore, molecular simulation was utilized to study the influence of N2/CO2 on the adsorption and diffusion of methane in coal under different gas injection methods and to elucidate the influence of varying gas injection methods on the efficiency of coalbed methane extraction, which provides a basis for the efficient development of coalbed methane. The results show that the adsorption effect of gases in coal decreases with the increase of temperature and increases with the rise of pressure, and the adsorption performance of the three gases in coal shows the law of CO2 > CH4 > N2. In addition, the injection of CO2/N2 had an obvious inhibition effect on CH4 adsorption, and the inhibition effect of CO2 was more significant, and the inhibition effect on CH4 adsorption reached the maximum when the two gases were mixture injected. In terms of diffusion, compared with separate injection, mixed injection of N2 + CO2 promotes CH4 diffusion more effectively, which can be reflected in the relative concentration distribution and velocity distribution. The injection of N2 helps to increase the porosity of coal, and the injection of CO2 and N2 + CO2 will lead to the decrease of porosity, but the mixed gas injection has less effect than the injection of CO2 alone.

A Multitechnique Study of C2H4 Adsorption on a Model Single-Atom Rh1 Catalyst.

Single-atom catalysts are potentially ideal model systems to investigate structure-function relationships in catalysis if the active sites can be uniquely determined. In this work, we study the interaction of C2H4 with a model Rh/Fe3O4(001) catalyst that features 2-, 5-, and 6-fold coordinated Rh adatoms, as well as Rh clusters. Using multiple surface-sensitive techniques in combination with calculations of density functional theory (DFT), we follow the thermal evolution of the system and disentangle the behavior of the different species. C2H4 adsorption is strongest at the 2-fold coordinated Rh1 with a DFT-determined adsorption energy of -2.26 eV. However, desorption occurs at lower temperatures than expected because the Rh migrates into substitutional sites within the support, where the molecule is more weakly bound. The adsorption energy at the 5-fold coordinated Rh sites is predicated to be -1.49 eV, but the superposition of this signal with that from small Rh clusters and additional heterogeneity leads to a broad C2H4 desorption shoulder in TPD above room temperature.

Theoretical Study of CH4 and CO2 Separation by IRMOFs.

Porous materials such as isoreticular metal-organic frameworks (IRMOFs) can be applied in several areas that explore the physical adsorption. An area that has gained prominence is fuel gas storage, as it provides the storage of a large amount of gas at low pressure and the purification of combustible gas due to the selectivity of the different chemical environments of its pores. IRMOFs represent an ideal study group due to their wide range of pore sizes resulting from the use of different organic ligands. In this context, exploring IRMOFs that adsorb more efficiently stands out, mainly for optimizing the ligand, pressure, and temperature. This work focused on the adsorption and separation of CH4 and CO2 using various IRMOFs. The results suggest that IRMOF-6 is the most suitable for separation and purification and that enhanced purification occurs when the temperature is reduced and the system pressure is increased. This better performance is associated with the higher adsorption energies for this MOF, with CO2 being higher than CH4, which tends to become even more evident when the system pressure increases.

Pore structure and adsorption capability of marcolithotypes in the Weizhou mining area, western margin of Ordos Basin

Differences in the pore and fracture systems of four marcolithotypes (bright，semi‐bright, semi‐dull and dull) in coal reservoirs affect the quality of coalbed methane (CBM) and constrain exploration and development of CBM. In this paper, vitrinite reflectance (RO), maceral composition, proximate analysis, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), low‐field nuclear magnetic resonance (NMR) and high‐pressure isothermal adsorption experiments and the mathematical method of fractal dimension were carried out on high‐rank coal samples of different marcolithotypes from the Weizhou mining area in the western margin of Ordos Basin. The results show that from bright coal to dull coal, the RO and vitrinite content gradually decrease, while the mineral content and Aad gradually increase. SEM images show that the bright and semi‐bright coals develop open fractures, whereas semi‐dull and dull coals develop closed fractures. According to pore size distribution established by MIP and NMR, the proportion of seepage pores gradually increased from bright coal to dull coal, and MIP fractal dimension of seepage pores (DM2; 2.3352, 2.3532, 2.3755 and 2.4727, respectively) and NMR fractal dimension of seepage pores (DN2; 2.8767, 2.9142, 2.9297 and 2.9981, respectively) show that the structure of the seepage pore is progressively more complex from bright coal to dull coal. In addition, percentage of NMR adsorption pores progressively increases from bright coal to dull coal (64.96%, 76.64%, 82.04% and 89.67%, respectively), but total porosity of bright coal (6.74%) is much greater than that of dull coal (1.34%), which results in that bright coal also has the strongest CH4 adsorption capability (Langmuir volume is 22.898 cm3/g).

Using ligand regulation, metal replacement, and ligand doping strategies on Zr-FUM to improve methane separation from coalbed gas

Developing adsorbents suitable for industrial applications that can effectively enhance the separation of methane (CH4) from nitrogen (N2) in coalbed gas is crucial to improve energy recovery and mitigate greenhouse gas emissions. In this study, three modification strategies were implemented on Zr-FUM, including ligand regulation, metal replacement, and ligand doping, to synthesize Zr-FDCA, Al-FUM, and Zr-FUM-FA, with the aim of improving the performance of CH4/N2 separation under humid conditions. The results demonstrated that the promotion of robust orbital overlap and strengthened electrovalent bonding on adsorbents can selectively enhance CH4 adsorption. As a result, Zr-FUM-FA achieved a saturated CH4 adsorption capacity of 1.37 mmol/g, a CH4 working window of 307 s, and a CH4/N2 sorbent selection parameter (Ssp) of 47.31, exceeding the performance of most reported adsorbents. Analyses of the pore structure, surface morphology, and functional groups revealed that the presence of an ultramicropore proximity to CH4, reduced static resistance, and enhanced electrovalent bond were key factors for CH4 separation. Grand Canonical Monte Carlo and Density Functional Theory studies indicated that the introduction of -C-H- in FA played a crucial role in enhancing CH4 adsorption. Optimization of adsorption parameters using the Aspen adsorption package showed that in a dual-adsorbent bed system, the recovery and purity of CH4 in Zr-FUM-FA reach 99.5% and 97.3%, respectively, providing important theoretical support for the improvement of CH4 recovery in the pressure swing adsorption process from coalbed gas.

Understanding pore features of pillar-layered MOFs on one-step C2H4 purification from C2H6/C2H4 mixtures

Purification of ethylene from ethane through adsorption separation is a key industrial process in present chemical field, since the similar physical properties of both C2H4 and C2H6 that makes them difficult to separate. Therefore, constructing C2H6-selective adsorbents and clarifying its structure–activity relationship is a very difficult undertaking. In this study, 3D pillar-layered metal organic frameworks (MMOF-kgm (M = Zn, Co, Ni) and NiMOF-sql) with different topologies, kagome and square lattice, were constructed by using the cheap ligands (1,4-benzenedicarboxylic acid and triethylenediamine). The effect of pore features on C2H6/C2H4 separation performance and the separation mechanism were systematically investigated by the above two isomeric MOFs. In particular, NiMOF-kgm with kagome topology provides narrower triangular pore shows notably adsorption of C2H6 over C2H4, which is validated by gas adsorption, IAST selectivity and breakthrough measurements. The selective adsorption mechanisms of MOF with kagome topology were further revealed through DFT calculations. This study provides in-depth insights into optimizing the pore structure of MOFs to enhance C2H6/C2H4 separation performance, offering new design strategies for developing efficient materials for ethane-selective adsorbent for one-step ethylene purification.

First-principles study of the C2H4 adsorption on the small Ag-Cu clusters

The adsorption behaviors of the C2H4 molecule on the surface of the 7-atom Ag-Cu clusters are systematically investigated based on generalized gradient approximate density functional theory. The top site adsorption of C2H4 on the Ag7 cluster is physical adsorption, and the top site adsorption on the other clusters is chemical adsorption. The bridge site adsorption of C2H4 on Ag7 and Cu7 clusters is physical adsorption, while the chemical adsorption of C2H4 on the other clusters undergoes the transformation from the bridge site to the top site adsorption on the Cu atoms. In particular, the original structures of Ag5Cu2 and Ag4Cu3 clusters deformed significantly when C2H4 was adsorbed on their bridge sites. The adsorption of C2H4 on the bridge site of the Ag5Cu2 cluster is more stable than that on the top site, and the adsorption of C2H4 on the top site of the remainder clusters is more stable than that on the bridge site. Overall, the Ag2Cu5 cluster is the most stable for C2H4 adsorption configuration among all the studied clusters.

Selectively photocatalytic oxidation of methane to methanol promoted by Charge-Polarized Zn-Ti pairs

Photocatalysis offers an intriguing route for selective oxidation of CH4 to CH3OH under mild conditions. However, owing to the ultra-high stability of CH4 and the diversity of oxidative products, the activity of CH4 oxidation and the selectivity of CH3OH are still far from satisfactory. Herein, we report a dual-cocatalyst of Au and bimetallic oxide (Zn2Ti3O8) nanoparticles (NPs) modified TiO2 nanotube (Au/Zn2Ti3O8/TiO2) for highly active and selective photocatalytic oxidation of CH4 to CH3OH with O2 at room temperature. The introduction of Zn2Ti3O8 NPs is skillfully exploited the epitaxies of ZIF-8 on the surface of protonated titanate nanotubes (H-TNTs) and the followed thermal treatment with air. During photocatalytic CH4 oxidation, 1.7 %Au/Zn2Ti3O8/TiO2-4 achieved a formation rate of liquid oxygenates of 1200 μmol·gcat.–1·h−1 with a CH3OH selectivity of 91.5 %, which were much higher than those over 1.7 %Au/TiO2 and 1.7 %Au/ZnO. Mechanism investigation confirmed the presence of the strong electron interaction between Au NPs, Zn2Ti3O8 NPs and TiO2 nanotubes in 1.7 %Au/Zn2Ti3O8/TiO2-4, which intensified the charge polarization between Zn sites and Ti sites. These charge-polarized Zn-Ti sites were not only beneficial to the adsorption and activation of CH4, but also accelerated the further transformation of CH3OOH to CH3OH, as well as inhibited the excessive oxidation of CH3OH.

Two-way coupling dynamics of CH4 adsorption and coal matrix deformation: Insights from hybrid GCMC/MD simulations

CH4 adsorption can deform coal microporous structures, subsequently altering adsorption isotherms. To unravel this intricate interplay at a microscopic level, we use a hybrid Grand Canonical Monte Carlo/Molecular Dynamics (GCMC/MD) simulation at 313.15 K and pressures up to 500 bar on five independent amorphous coal matrix models. Our results reveal that CH4 adsorption increases pore volume and porosity primarily by generating additional pores of similar sizes to those present in coal matrices, thereby maintaining a consistent average pore size across different pressures. The volumetric strain has a linear correlation with CH4 loading, with volumetric swelling amount approximating the expansion of CH4-occupiable pore volume, but less than He-occupiable pore volume which results in increased matrix skeletal density. Local radial density distribution of carbon atoms indicates that the immediate environment around carbon atoms remains unchanged. In a flexible matrix, the energy released during CH4 adsorption is partially absorbed by matrix deformation, resulting in a lower isosteric heat of adsorption compared to a rigid matrix, which suggests easier desorption. This study provides new insights into the mutual relationship between CH4 adsorption and coal matrix deformation, shedding lights on the complex interactions of various hydrocarbons with geomaterials.

Impact of metal precursor and molar ratios on adsorption and separation of CO2 and CH4 by SOD-ZIF-67 prepared using green solvent-free synthesis

The subclass of metal-organic frameworks (MOFs) known as SOD-ZIF-67 (Sodalite Co (mIm)2, with mIm = 2-methylimidazole) has demonstrated exceptional performance in carbon dioxide (CO2) adsorption and separation. Traditional synthesis methods for SOD-ZIF-67 are often time-consuming and require significant quantities of organic solvents. This study introduces an enhanced, eco-friendly, solvent-free method for synthesizing SOD-ZIF-67. In this approach, SOD-ZIF-67 is produced within 1 h by mechanically grinding a cobalt (Co) metal precursor with an organic linker (mIm), eliminating the need for solvents. The properties of the synthesized SOD-ZIF-67 samples were confirmed through various characterization techniques. Thermal stability tests indicated that the synthesized SOD-ZIF-67 could endure temperatures up to 673 K. Among the samples prepared with different molar ratios, the SOD-ZIF-67 sample with a Co to HmIm molar ratio of 2:1 (denoted as Z-2) demonstrated the highest BET surface area and pore volume, measuring 1923 m2/g and 0.72 cm3/g, respectively. Z-2 exhibited uniform and narrow ultramicropores measuring 0.54 nm, and demonstrated a CO2 adsorption capacity of 91.52 mg (CO2)/g (2.08 mmol/g) at 298 K and 100 kPa. The material showed high selectivity for CO2 over N2 and CH4, with selectivities of 20.44 for CO2/N2 (0.15:0.85) and 4.28 for CO2/CH4 (0.5:0.5). Additionally, breakthrough experiments with CO2/N2 and CO2/CH4 mixtures validated its dynamic separation efficiency, underscoring Z-2′s suitability for selective CO2 capture from flue gases and natural gas purification.

Adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal based on in-situ diffuse reflectance FTIR

The adsorption mechanisms of CH4 and CO2 on the coal surface is the theoretical basis for CO2 sequestration with enhanced coalbed methane recovery (CO2-ECBM). Molecular simulation is the main method to study the adsorption mechanism at present, but the model used in the process of molecular simulation could not accurately characterize the coal macromolecular structure. Therefore, we used in-situ diffuse reflectance Fourier-transform infrared spectroscopy (FTIR) to study the adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal. The results showed that CO2 and CH4 were physisorbed on the aromatic rings, and the aromatic rings represented the primary competitive adsorption sites for CO2 and CH4, CO2 was preferentially adsorbed at the top of the aromatic ring compared to CH4. Both carboxyl and carbonyl groups were beneficial for CO2 adsorption but not for CH4 adsorption. Compared to aromatic rings, the adsorption affinity of carboxyl groups for CO2 were stronger. The results of this study revealed the adsorption mechanisms of CO2 and CH4 on the aromatic rings and oxygen groups, as well as the impact of oxygen groups on the gas adsorption capacity, providing a theoretical basis for applying CO2-ECBM in the medium-volatile bituminous coal reservoirs.

Comparative study of metal-organic frameworks synthesized via imide condensation and coordination assembly.

A series of metal-organic frameworks (1-XDI) have been synthesized by imide condensation reactions between an amine-functionalized pentanuclear zinc cluster, Zn4Cl5(bt-NH2)6, (bt-NH2 = 5-aminobenzotriazolate), and organic dianhydrides (pyromellitic dianhydride (PMDA), naphthalenetetracarboxylic dianhydride (NDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (HFIPA)). The properties of the 1-XDI MOFs have been compared with analogues (2-XDI) prepared using traditional coordination assembly. The resulting materials have been characterized by ATR-IR spectroscopy, acid-digested 1H NMR spectroscopy, elemental analysis, and gas adsorption measurements. N2 adsorption isotherm data reveal modest porosities and BET surface areas (30-552 m2 g-1). All of the new 1-XDI and 2-XDI MOFs show selective adsorption of C2H2 over CO2 while 2-PMDI and 2-BPDI exhibit high selectivity toward C3H6/C3H8 separation. This study establishes imide condensation of preformed metal-organic clusters with organic linkers as a viable route for MOF design.