Adsorption of CH4 and CO2 on Zr-metal organic frameworks

Zirconium-metal organic frameworks (Zr-MOFs) were synthesized with or without ammonium hydroxide as an additive in the synthesis process. It was found that addition of ammonium hydroxide would change the textural structure of Zr-MOF. The BET surface area, pore volume, and crystal size of Zr-MOF were reduced after addition of ammonium hydroxide. However, the crystalline structure and thermal stability were maintained and no functional groups were formed. Adsorption tests showed that Zr-MOF presented much higher CO(2) adsorption than CH(4). Zr-MOF exhibited CO(2) and CH(4) adsorption of 8.1 and 3.6 mmol/g, respectively, at 273 K, 988 kPa. The addition of ammonium hydroxide resulted in the Zr-MOF with a slight lower adsorption of CO(2) and CH(4), however, the selectivity of CO(2)/CH(4) is significantly enhanced.     

H2 storage and CO2 capture on a nanoscale metal organic framework with high thermal stability

A nanoscale aluminium-based metal organic framework (NMOF) with high thermal stability has been synthesized, which shows high H(2) and CO(2) uptake capacities and an excellent selectivity for CO(2) over N(2) and O(2).     

An ionic porous coordination framework exhibiting high CO2 affinity and CO2/CH4 selectivity

An ionic porous coordination polymer possessing partially exposed uncoordinated nitrogens exhibits strong interaction with CO(2) and high CO(2)/CH(4) selectivity, and the adsorption mechanism is illustrated by the structure of its CO(2)-loaded single-crystal.     

Adsorption of ethane, ethylene, propane, and propylene on a magnesium-based metal-organic framework

Separation of olefin/paraffin is an energy-intensive and difficult separation process in petrochemical industry. Energy-efficient adsorption process is considered as a promising alternative to the traditional cryogenic distillation for separating olefin/paraffin mixtures. In this work, we explored the feasibility of adsorptive separation of olefin/paraffin mixtures using a magnesium-based metal-organic framework, Mg-MOF-74. Adsorption equilibria and kinetics of ethane, ethylene, propane, and propylene on a Mg-MOF-74 adsorbent were determined at 278, 298, and 318 K and pressures up to 100 kPa. A dual-site Sips model was used to correlate the adsorption equilibrium data, and a micropore diffusion model was applied to extract the diffusivities from the adsorption kinetics data. A grand canonical Monte Carlo simulation was conducted to calculate the adsorption isotherms and to elucidate the adsorption mechanisms. The simulation results showed that all four adsorbate molecules are preferentially adsorbed on the open metal sites where each metal site binds one adsorbate molecule. Propylene and propane have a stronger affinity to the Mg-MOF-74 adsorbent than ethane and ethylene because of their significant dipole moments. Adsorption equilibrium selectivity, combined equilibrium and kinetic selectivity, and adsorbent selection parameter for pressure swing adsorption processes were estimated. The relatively high values of adsorption selectivity suggest that it is feasible to separate ethylene/ethane, propylene/propane, and propylene/ethylene pairs in a vacuum swing adsorption process using Mg-MOF-74 as an adsorbent.     

Adsorption of pyridine onto the metal organic framework MIL-101

The adsorption of pyridine onto the metal organic framework MIL-101 was investigated by experimental and theoretical methods. The amount of pyridine adsorbed on MIL-101 was extraordinarily large at 20 °C, corresponding to about 950 mg/g of dried MIL-101 and approximately half of the voids being filled. Most of the pyridine that had filled the voids was rapidly removed by evacuation at room temperature, but some of the pyridine was so strongly adsorbed that it was retained even under evacuation at 150 °C. Although IR spectra of the adsorbed pyridine indicated the adsorption of pyridine as pyridinium ions and coordinated pyridine at low temperatures, increasing the adsorption temperature induced partial cleavage of the pyridine rings. The high stabilization energy of pyridine on the coordinative unsaturated sites (CUS) of MIL-101, obtained by theoretical calculation, -103 kJ/mol, supported the strong adsorption of pyridine on the CUS.     

CH4+CO2H2+CO

将廉价的碳源(CO2)转化为化石燃料可缓解由于温室气体引起的气候问题.CH4/CO2重整(CRM)是CO2转化利用的有效途径之一,要实现这个过程的关键是研制高效的光响应催化剂.本文采用WO3负载的第VIII族金属催化剂、引入光照能量来活化CO2,利用光热协同催化CRM.研究结果表明,光学材料WO3负载的第VIII族金属催化剂在可见光辅助下的催化活性是热驱动条件下的1.4～2.4倍,与等离子体金催化剂的活性增强率(1.7倍)相当.进一步以不同波段的可见光为光源,对WO3负载的第VIII族金属催化剂上催化活性提高的原因进行了研究.结果表明,活性增强率与WO3在可见光区域的吸光趋势并不吻合,说明并非WO3提高了其负载的第VIII族金属催化剂上CRM活性.除WO3外, WO3-x亦可作为光催化剂吸收可见光,因此,本文通过X射线光电子能谱、X射线衍射及紫外-可见分光光度法等进行表征.结果表明,在还原型CRM反应气氛下, WO3部分原位还原为WO3-x,并且活性增强率与WO3-x在可见光区域的吸光趋势相吻合,说明导致可见光辅助下活性增强的是WO3-x而不是WO3.热力学分析及原位电子顺磁共振波谱法结果表明, CO2的活化是CRM的速控步,该步骤吸热,在500 oC时不能自发进行.在可见光的辅助下, CO2可以被WO3-x通过Mars-vanKrevelen机理进行活化,提高速控步的反应速率,进而提高了催化活性.综上,本文为提高光催化活性提供了一条有效途径.     

Adsorption of CO2, CH4, and N2 on Zeolitic Imidazolate Frameworks: Experiments and Simulations

Experimental measurements and molecular simulations were conducted for two zeolitic imidazolate frameworks, ZIF‐8 and ZIF‐76. The transferability of the force field was tested by comparing molecular simulation results of gas adsorption with experimental data available in the literature for other ZIF materials (ZIF‐69). Owing to the good agreement observed between simulation and experimental data, the simulation results can be used to identify preferential adsorption sites, which are located close to the organic linkers. Topological mapping of the potential‐energy surfaces makes it possible to relate the preferential adsorption sites, Henry constant, and isosteric heats of adsorption at zero coverage to the nature of the host–guest interactions and the chemical nature of the organic linker. The role played by the topology of the solid and the organic linkers, instead of the metal sites, upon gas adsorption on zeolite‐like metal–organic frameworks is discussed.     

A DFT study on the selective adsorption and separation of CO2/CH4 on the Mg-decorated 2-D covalent organic framework (COF-5)

Covalent organic frameworks (COFs), an emerging class of crystalline polymeric materials, have garnered growing interest due to their ideal chemical and thermal stability and ordered microporous architectures, which make them effective agents for selective CH₄/CO₂ separation. In this work, adsorption and separation of methane and carbon dioxide molecules on the two-dimensional pristine and Mg-decorated COF-5 (MgCOF-5) was investigated using density functional theory, employing B3LYP. Both CH₄ and CO₂ molecules were found to weakly adsorbed through van der Waals interactions to the bare sheet via physisorption, releasing energies ranging from -3.8 to -5.6 and -8.7 to 12.8, respectively and the sheet's electrical characteristics don't alter all that much. To overcome this weak selectivity/sensitivity, multiple Mg atoms were decorated atop aromatic rings of COF-5. Our results show that up to four CO₂ molecules can be adsorbed on each Mg atom exothermically, whereas E_ad of CH₄ is near zero so the theoretical CO₂ capacity of a full Mg-covered sheet is 0.51 gCO₂/g MgCOF-5. Also, the decorating of Mg atoms on the surface of COF-5 induces certain changes in the sheet's electrical characteristics and that the sheet's E_g changes up to 80% following the adsorption of several CO₂ molecules, making it a potential candidate for CO₂ detection.     

Separation of CO2 and CH4 by a DDR membrane

The permeation of CO₂ and CH₄ and their binary mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a high permeance and maintains a very high selectivity for CO₂. At a total pressure of 101 kPa, the highest selectivity for CO₂ in a 50∶50 feed mixture was found to be over 4000 at 225 K. This is ascribed to the higher adsorption affinity, as well as to the higher mobility for the smaller CO₂ molecules in the zeolite, preventing the bypassing of the CH₄ through the membrane. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The feasibility of DDR membranes as applied to CO₂ removal from natural gas or biogas is anticipated.     

Competitive adsorption equilibria of CO2 and CH4 on a dry coal

Gases like CO₂ and CH₄ are able to adsorb on the coal surface, but also to dissolve into its structure causing the coal to swell. In this work, the binary adsorption of CO₂ and CH₄ on a dry coal (Sulcis Coal Province, Italy) and its swelling behavior are investigated. The competitive adsorption measurements are performed at 45?°C and up to 190 bar for pure CO₂, CH₄ and four mixtures of molar feed compositions of 20.0, 40.0, 60.0 and 80.0% CO₂ using a gravimetric-chromatographic technique. The results show that carbon dioxide adsorbs more favorably than methane leading to an enrichment of the fluid phase in CH₄. Coal swelling is determined using a high-pressure view cell, by exposing a coal disc to CO₂, CH₄ and He at 45 and 60?°C and up to 140 bar. For CO₂ and CH₄ a maximum swelling of about 4 and 2% is found, whereas He shows negligible swelling. The presented adsorption and swelling data are then discussed in terms of fundamental, thermodynamic aspects of adsorption and properties which are crucial for an ECBM operation, i.e. the CO₂ storage capacity and the dynamics of the replacement of CH₄ by CO₂.     

Molecular Simulations of CO2/CH4, CO2/N2 and N2/CH4 Binary Mixed Hydrates

Colloid Journal - Grand canonical Monte Carlo simulations were performed to study the occupancy of structure I multicomponent gas hydrates by CO2/CH4, CO2/N2, and N2/CH4 binary gas mixtures with...     

CO catalytic oxidation by a metal organic framework containing high density of reactive copper sites

A new metal organic framework containing high density of active Cu sites demonstrates 100% oxidative conversion of CO to CO(2).     

PAN-based activated carbon nanofiber/metal oxide composites for CO2 and CH4 adsorption: influence of metal oxide

In the present study, we successfully prepared two different electrospun polyacrylonitrile (PAN) based-activated carbon nanofiber (ACNF) composites by incorporation of well-distributed Fe₂O₃ and Co₃O₄ nanoparticles (NPs). The influence of metal oxide on the structural, morphological, and textural properties of final composites was thoroughly investigated. The results showed that the morphological and textural properties could be easily tuned by changing the metal oxide NPs. Even though, the ACNF composites were not chemically activated by any activation agent, they presented relatively high surface areas (S_BET) calculated by Brunauer–Emmett–Teller (BET) equation as 212.21 and 185.12 m²/g for ACNF/Fe₂O₃ and ACNF/Co₃O₄ composites, respectively. Furthermore, the ACNF composites were utilized as candidate adsorbents for CO₂ and CH₄ adsorption. The ACNF/Fe₂O₃ and ACNF/Co₃O₄ composites resulted the highest CO₂ adsorption capacities of 1.502 and 2.166 mmol/g at 0 °C, respectively, whereas the highest CH₄ adsorption capacities were obtained to be 0.516 and 0.661 mmol/g at 0 °C by ACNF/Fe₂O₃ and ACNF/Co₃O₄ composites, respectively. The isosteric heats calculated lower than 80 kJ/mol showed that the adsorption processes of CO₂ and CH₄ were mainly dominated by physical adsorption for both ACNF composites. Our findings indicated that ACNF-metal oxide composites are useful materials for designing of CO₂ and CH₄ adsorption systems.     

不同粒径的Ni/SiO2催化剂上CH4和CO2吸附活化的漫反射傅里叶变换红外光谱研究

 采用原位漫反射傅里叶变换红外光谱研究了CH4和CO2在不同粒径的Ni/SiO2催化剂上的吸附及活化. 结果表明,在不同粒径的催化剂上,检测到有CH4解离生成的CHx(x=1～3)物种,以及催化剂表面吸附的CHx物种与表面-OH 作用生成的CHx-O物种. CH4的裂解强烈依赖于催化剂表面Ni颗粒的大小,在粒径8 nm左右的Ni颗粒上, CH4较易解离; CO2难以直接在Ni/SiO2催化剂表面发生解离吸附,但CH4解离生成的吸附H对CO2的解离吸附具有明显的促进作用; CH4与CO2共吸附时,较小粒径的Ni可以促进CO2与表面氧物种发生反应,生成单齿表面碳酸盐物种.     

Adsorption separation of CO2 and N2 on MIL-101 metal-organic framework and activated carbon

In this work, the CO₂ and N₂ adsorption properties of MIL-101 metal-organic framework (MOF) and activated carbon (AC) were investigated using a standard gravimetric method within the pressure range of 0–30 bar and at four different temperatures (298, 308, 318 and 328 K). The dual-site Langmuir–Freundlich (DSLF) model was used to describe the CO₂ adsorption behaviors on these two adsorbents. The diffusion coefficients and activation energy E _a for diffusion of CO₂ in the MIL-101 and AC samples were estimated separately. Results showed that the isosteric heat of CO₂ adsorption on the MIL-101 at zero loading was much higher than that on the AC due to a much stronger interaction between CO₂ molecule and the unsaturated metal sites Cr³⁺ on MIL-101. Meanwhile, the dramatically decreased isosteric heats of CO₂ adsorption on MIL-101 indicated a more heterogeneous surface of MIL-101. Furthermore, the adsorption kinetic behaviors of CO₂ on the two samples can be well described by the micropore diffusion model. With the increase of temperature, the diffusion coefficients of CO₂ in the two samples both increased. The activation energy E _a for diffusion of CO₂ in MIL-101 was slightly lower than that in AC, suggesting that MIL-101 was much favorable for the CO₂ adsorption. The CO₂/N₂ selectivities on MIL-101 and AC were separately estimated to be 13.7 and 9.2 using Henry law constant, which were much higher than those on other MOFs.     

TiO2改性的镁基中温吸附剂及其CO2吸附性能的研究

采用沉淀法合成一系列TiO₂改性的镁基吸附剂,利用XRD、SEM和氮气吸附等方法对吸附剂进行表征,通过变温吸附-脱附动态循环实验考察其CO₂吸附性能。随着TiO₂含量的增加,样品的结晶度逐渐下降,同时由于焙烧后生成钛酸镁,样品比表面积逐渐减小。当TiO₂添加量为2%(质量分数),此时吸附剂呈直径为4.0~5.0μm的球形,局部为纳米片状结构,该吸附剂自第二次循环开始吸附能力无明显变化;经过50次变温吸附脱附循环实验后,动态吸附容量可达6.64%(质量分数),这是由于TiO₂改性后生成的钛酸镁为该吸附剂提供了刚性骨架,促进了活性组分的分散,并提高了吸附剂的稳定性。     

Adsorption of CO2 in metal organic frameworks of different metal centres: Grand Canonical Monte Carlo simulations compared to experiments

A Grand Canonical Monte Carlo study has been performed in order to compare the different CO₂ adsorption mechanisms between two members of the MIL-n family of hybrid metal-organic framework materials. The MIL-53 (Al) and MIL-47 (V) systems were considered. The results obtained confirm that there is a structural interchange between a large pore and narrow pore forms of MIL-53 (Al), not seen with the MIL-47 (V) material, which is a consequence of the presence of μ ₂-OH groups. The interactions between the CO₂ molecules and these μ ₂ OH groups mainly govern the adsorption mechanism in this MIL-53 (Al) material. The subsequent breaking of these adsorption geometries after the adsorbate loading increases past the point where no more preferred adsorption sites are available, are proposed as key features of the breathing phenomenon. After this, any new adsorbates introduced into the MIL-53 (Al) large pore structure experience a homogeneous adsorption environment with no preferential adsorption sites in a similar way to what occurs in MIL-47 (V).     

Adsorption of N,N-dimethylamine from aqueous solutions by a metal organic framework,MOF – 235

Water-resistant MOF-235 was used to adsorb N,N-dimethylamine (DMA) from aqueous solutions. It was synthesized from terephthalic acid and FeCl₃.6H₂O under air-free conditions and characterized by its crystalline structure, functional groups and temperature resistance. The kinetic data results were best adjusted to the pseudo-second order model (R²>0.963). The best-fit isotherm, Langmuir model, suggested the adsorption of DMA is localized on homogenously distributed active sites on the surface. This fit was confirmed by the value of β?=?1 on the Redlich-Peterson model. Our study suggests that the manipulation of novel materials such as MOF-235 promises new avenues for water treatment solutions.

Schematic structure of MOF-235 and its application as adsorbent.     

A microporous, moisture-stable, and amine-functionalized metal-organic framework for highly selective separation of CO2 from CH4

A new microporous amino-functionalized metal-organic framework has been synthesized by direct self-assembly, which exhibits high moisture-stability, acceptable capacity, and unprecedented high selectivity for CO(2) over CH(4), suggesting its potential application in gas separation processes like natural gas and biogas upgrading.