Increased CO2 Adsorption Research Articles

Study of CO2 adsorption on iron oxide doped MCM-41

Carbon dioxide adsorption behaviors of iron oxide doped mesoporous silica (MCM-41) were investigated. The iron oxide doped on MCM-41 samples were prepared by impregnation method with iron concentrations of 0.10, 0.25, 0.50, 0.75 and 1.0 wt%. The XRD patterns indicate highly dispersed forms of iron oxide on MCM-41. The results from N2 adsorption-desorption showed that there was no difference in mesoporous structure upon the addition of iron oxide and that the morphology of doped adsorbent was slightly distorted from its original spherical shape. Adsorption isotherm indicated that modifying MCM-41 with iron oxide can increase CO2 adsorption with the best result being achieved with 0.50 wt%Fe/MCM-41. Good correlations between the adsorption extent and the surface area were observed. Interaction between CO2 and Fe atoms were studied by X-ray absorption near edge structure (XANES). XANES spectra indicated the transfer of metal d-electrons to CO2 π*-antibonding orbital giving rise to additional adsorption. Stronger bonding between CO2 and the adsorbent was indicated by the increase of the isosteric heat of adsorption.

KOH-activated graphite nanofibers as CO2adsorbents

Porous carbons have attracted much attention for their novel application in gas storage. In this study, porous graphite nano-fiber (PGNFs)-based graphite nano fibers (GNFs) were prepared by KOH activation to act as adsorbents. The GNFs were activated with KOH by changing the GNF/KOH weight ratio from 0 through 5 at 900°C. The effects of the GNF/ KOH weight ratios on the pore structures were also addressed with scanning electron microscope and N2 adsorption/desorption measurements. We found that the activated GNFs exhibited a gradual increase of CO2 adsorption capacity at CK-3 and then decreased to CK-5, as determined by CO2 adsorption isotherms. CK-3 had the narrowest micropore size distribution (0.6–0.78 nm) among the treated GNFs. Therefore, KOH activation was not only a significant method for developing a suitable pore-size distribution for gas adsorption, but also increased CO2 adsorption capacity as well. The study indicated that the sample prepared with a weight ratio of ‘3’ showed the best CO2 adsorption capacity (70.8 mg/g) as determined by CO2 adsorption isotherms at 298 K and 1 bar.

Tuning the performance of CO2 separation membranes by incorporating multifunctional modified silica microspheres into polymer matrix

In this study, three types of modified silica microspheres were functionalized with carboxyl, sulfonic acid group and pyridine group via a facile distillation-precipitation polymerization method, respectively. Each type of functionalized silica microspheres was incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate mixed matrix membranes (MMMs) for gas separation. Scanning electron microscopy (SEM) characterization indicated that all the three types of functionalized silica microspheres could disperse homogenously within the SPEEK matrix via tuning the polymer-particle interaction. The incorporation of silica microspheres and sulfonic acid functionalized silica microspheres resulted in increased free volume cavity (r3) in MMMs, whereas the pyridine functionalized silica microspheres led to decreased r3. The relation between r3 and gas diffusion coefficient was revealed: the higher r3 displayed higher gas diffusion coefficient. The functionalized silica microspheres could construct CO2 transport pathways due to the increased CO2 adsorption, imparting MMMs with remarkably enhanced CO2 separation performance. In particular, the pyridine functionalized silica microspheres loaded MMMs showed the optimum gas separation performance with CO2/CH4(N2) selectivity of 64.5 (68.3) and CO2 permeability of 2043 Barrer at loading of 20wt% in humidified state, surpassing the Robeson upper bound reported in 2008, while the pristine SPEEK membrane exhibited CO2/CH4(N2) selectivity of 26.7 (35.1) and CO2 permeability of 525 Barrer.

First principles study of enhanced CO2 adsorption on MOF-253 by salt-insertion

We investigated the basic electron variation in salt-chelated MOF-253 and revealed increased CO2 adsorption by chelating PdCl2 and Cu(BF4)2 through the DFT-D2 method. The two N atoms preferentially orient to opposite side of the 2,2′-bipyridine (bpy) in bare MOF-253 to yield a CO2 adsorption energy of −0.15eV, which mainly contributes to the experimentally determined isotopic heat energy of −0.24eV. Following salt insertion, the two pyridine rings rotate to the same side to hold the salt that binds on NN atoms. While PdCl2 insertion does not significantly enhance CO2 adsorption, dipole polarization creates multiple adsorption sites by adding a PdCl bond and co-linker site, thereby increasing the adsorption capacity of the resultant material. Cu(BF4)2 chelation significantly increases the CO2 adsorption energy to −0.49eV, which is ascribed to the large positive charge of the Cu ion inducing significant electrostatic interactions with the O atom of CO2. Our calculation results demonstrate the effect of inherent electron distribution during salt insertion on CO2 adsorption and clearly explain the observed 7kJ/mol enhancement in CO2 absorption upon loading of Cu(BF4)2 on MOF-253. This study provides new insights into the selection of an ideal salt for chelation with the open bpy linker to improve gas uptake and illustrates the potential application of catalysis by MOF-253 to gas conversion.

ZnO:Ca nanopowders with enhanced CO2 sensing properties

Calcium doped ZnO (CZO) nanopowders with [Ca]/[Zn] atomic ratios of 0, 0.01, 0.03 and 0.05 were prepared via a sol-gel route and characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Characterization data showed that undoped and Ca-doped ZnO samples have a hexagonal wurtzite structure with a slight distortion of the ZnO lattice and no extra secondary phases, suggesting the substitution of Ca ions in the ZnO structure.Chemo-resistive devices based on a thick layer of the synthesized CZO nanoparticles were fabricated and their electrical and sensing properties towards CO2 were investigated. Sensing tests have demonstrated that Ca loading is the key factor in modulating the electrical properties and strongly improving the response of ZnO matrix towards CO2. An increased CO2 adsorption with Ca loading has been also evidenced by FT-IR, providing the basis for the formulation of a plausible mechanism for CO2 sensing operating on these sensors.

Nitrogen-doped porous aromatic frameworks for enhanced CO2 adsorption

Recently synthesized porous aromatic frameworks (PAFs) exhibit extremely high surface areas and exceptional thermal and hydrothermal stabilities. Using computer-aided design, we propose new PAFs, designated as NPAFs, by introducing nitrogen-containing groups to the biphenyl unit and predict their CO2 adsorption capacities with grand canonical Monte Carlo (GCMC) simulations. Among various NPAFs considered, one with imidazole groups shows the highest adsorption capacity for CO2 (11.5wt% at 1bar and 298K), in comparison with 5wt% for the parent PAF (PAF-1) at the same condition. At higher pressures (around 10bar), however, another NPAF with pyridinic N groups performs much better than the rest due to its greater pore volume in addition to the N functionality. This study suggests that adding N functionality to the organic linkers is a promising way to increase CO2 adsorption capacity of PAFs at ambient condition.

Cover Picture: Electrocatalytically Switchable CO2 Capture: First Principle Computational Exploration of Carbon Nanotubes with Pyridinic Nitrogen (ChemSusChem 2/2014)

Carbon nanotubes/graphene with specific nitrogen doping can contribute to a controllable, highly selective, and reversible CO2 capture, as illustrated by the front cover image. Carbon recycling represents a fundamental aspect of the global carbon balance, with CO2 capturing the first key concept of this cycle. Prof. Zhonghua Zhu and co-workers use long range dispersion-corrected density functional theory calculations to reveal that pyridinic nitrogen on carbon nanotubes/graphene leads to an increased CO2 adsorption strength in the presence of injected electrons, and, hence, a highly selective adsorption of CO2 over N2. This functionality can induce intrinsically reversible CO2 adsorption by switching the charge carrying state of the system on/off. More detail is given in the Full Paper by Jiao et al. on page 435, while more information about the research group is available in the Cover Profile (DOI: 10.1002/cssc.201301349).

Electrocatalytically Switchable CO2 Capture: First Principle Computational Exploration of Carbon Nanotubes with Pyridinic Nitrogen

Carbon nanotubes with specific nitrogen doping are proposed for controllable, highly selective, and reversible CO2 capture. Using density functional theory incorporating long-range dispersion corrections, we investigated the adsorption behavior of CO2 on (7,7) single-walled carbon nanotubes (CNTs) with several nitrogen doping configurations and varying charge states. Pyridinic-nitrogen incorporation in CNTs is found to induce an increasing CO2 adsorption strength with electron injecting, leading to a highly selective CO2 adsorption in comparison with N2 . This functionality could induce intrinsically reversible CO2 adsorption as capture/release can be controlled by switching the charge carrying state of the system on/off. This phenomenon is verified for a number of different models and theoretical methods, with clear ramifications for the possibility of implementation with a broader class of graphene-based materials. A scheme for the implementation of this remarkable reversible electrocatalytic CO2 -capture phenomenon is considered.

Synthesis and Low-Temperature CO2 Capture Properties of a Novel Mg–Zr Solid Sorbent

Mesoporous Mg–Zr solid solutions with different nominal Mg/Zr atomic ratios (0, 0.25, 0.5, 0.75, 1) were synthesized by a coprecipitation method, and the performance of CO2 adsorption/desorption was studied in a fixed-bed reactor under different conditions. In the synthesis process, Mg2+ was introduced successfully into the ZrO2 lattice and formed a maximum number of new Mg–O–Zr basic sites at Mg/Zr = 0.5. The CO2-temperature-programmed desorption (TPD) results showed the basic strength of the basic sites was Zr–O–Zr < Mg–O–Zr < Mg–O–Mg and the relatively weak basic strength of Mg–O–Zr was a benefit for regeneration of the sorbent. In the process of adsorption, high surface area (269 m2/g) and pore volume (0.63 m3/g) as well as appropriate basic sites of Mg–O–Zr made the Mg–Zr solid sorbent increase CO2 adsorption capacity by more than 5 times compared to pure MgO. The CO2 adsorption capacity of the sorbent increased in the presence of water vapor. Typically, the CO2 capacity of Mg–Zr solid sorbent had a maximum CO2 capture of 1.28 mmol/g at 30 °C without water vapor and 1.56 mmol/g sorbent under 10 vol % moist conditions at 60 °C, respectively. Results of a reutilization test suggested that the sorbent was stable for cyclic adsorption.

Development of efficient amine-modified mesoporous silica SBA-15 for CO2 capture

A novel CO2 sorbent was prepared by impregnating mesoporous silica, SBA-15, with acrylonitrile (AN)-modified tetraethylenepentamine (TEPA) in order to increase CO2 adsorption capacity and improve cycling stability. The mesoporous silica with pre- and post-surface modification was investigated by X-ray diffraction characterization (XRD), N2 adsorption–desorption test (N2-BET), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The adsorption/desorption performance of S-TN (TN: AN modified TEPA) and S-TEPA was studied by dynamic adsorption. Test results showed that the solid base-impregnated SBA-15 demonstrated high CO2 adsorption capacity (180.1mgg−1-adsorbent for 70% amine loading level). Compared to S-TEPA (24.1% decrease of initial capacity), S-TN with 50% amine loading exhibited improved cycling stability, 99.9% activity reserved (from initial 153.0mgg−1 to 151.3mgg−1) after 12 cycles of adsorption/desorption at 100°C. A mechanism of molecular structure of the loaded amine was attributed to the improved performance.

Carbon Dioxide Adsorption by Calcium Zirconate at Higher Temperature

The CO2 adsorption by calcium zirconate was explored at pre- and post- combustion temperature condition. The several samples of the calcium zirconate were prepared by different methods such as sol-gel, solid-solid fusion, template and micro-emulsion. The samples of the calcium zirconate were characterized by measurement of surface area, alkalinity/acidity, and recording the XRD patterns and SEM images. The CO2 adsorptions by samples of the calcium zirconate were studied in the temperature range 100 to 850 oC and the CO2 adsorptions were observed in the ranges of 6.88 to 40.6 wt % at 600 0C and 8 to 16.82 wt% at in between the temperatures 200 to 300 oC. The effect of Ca/Zr mol ratio in the samples of the calcium zirconate on the CO2 adsorption and alkalinity were discussed. The adsorbed moisture by the samples of the calcium zirconate was found to be useful for the CO2 adsorption. The promoted the samples of the calcium zirconate by K+, Na+, Rb+, Cs+, Ag+ and La3+ showed the increased CO2 adsorption. The exposure time of CO2 on the samples of the calcium zirconate showed the increased CO2 adsorption. The samples of the calcium zirconate were found to be regenerable and reusable several times for the adsorption of CO2 for at the post- and pre-combustion temperature condition. © 2012 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Increasing Selective CO2 Adsorption on Amine-Grafted SBA-15 by Increasing Silanol Density

Two template removal methods were employed to create porosity in mesoporous silica SBA-15: ethanol extraction versus conventional high-temperature calcination. The resulting silicas were subjected to amine (3-aminopropyl) grafting and studied for their CO2 adsorption properties. The goal was to significantly increase the surface silanol density, and hence the grafted amine loading, leading directly to increased CO2 adsorption capacity and CO2/N2 selectivity. Thus, the silanol density was increased from 3.4 OH/nm2 for the calcined SBA-15 to 8.5 OH/nm2 for the SBA-15 by solvent extraction. Correspondingly, for these two samples, the grafted amine loading was increased from 2.2 to 3.2 mmol/g, and the CO2 adsorption capacity was increased from 1.05 to 1.6 mmol/g at conditions relevant to CO2 capture (0.15 bar and 25 °C), or a 52% increase. The CO2/N2 selectivity was increased from 46 to 131. The isosteric heats of adsorption, the sorbent stability during cyclic adsorption–desorption, and the (positive) effects of moisture on CO2 adsorption were also investigated and compared.

Functionalizing Porous Aromatic Frameworks with Polar Organic Groups for High-Capacity and Selective CO2 Separation: A Molecular Simulation Study

Porous aromatic frameworks (PAFs) were recently synthesized with the highest surface area to date; one such PAF (PAF-1) has diamond-like structure with biphenyl building blocks and exhibits exceptional thermal and hydrothermal stabilities. Herein, we computationally design new PAFs by introducing polar organic groups to the biphenyl unit and then investigate their separating power toward CO(2) by using grand-canonical Monte Carlo (GCMC) simulations. Among these functional PAFs, we found that tetrahydrofuran-like ether-functionalized PAF-1 shows higher adsorption capacity for CO(2) at 1 bar and 298 K (10 mol per kilogram of adsorbent) and also much higher selectivities for CO(2)/CH(4), CO(2)/N(2), and CO(2)/H(2) mixtures when compared with the amine functionality. The electrostatic interactions are found to play a dominant role in the high CO(2) selectivities of functional PAFs, as switching off atomic charges would decrease the selectivity by an order of magnitude. This work suggests that functionalizing porous frameworks with tetrahydrofuran-like ether groups is a promising way to increase CO(2) adsorption capacity and selectivity, especially at ambient pressures.

Characterization and Activity of K, CeO2, and Mn Promoted Ni/Al2O3Catalysts for Carbon Dioxide Reforming of Methane

Reforming of methane with carbon dioxide into syngas over Ni/γ-Al2O3 catalysts modified by potassium, MnO, and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by BET surface area, pore volume, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature-programmed studies, and pulse chemisorption. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed-bed reactor. Results of the investigation suggested that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by the addition of both potassium and CeO2 (or MnO) as promoters. The results of the various characterization techniques were used to relate the observed catalytic activity and stability to the catalyst property. The stability and lower amounts of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters, strong metal−support interaction (TPR, H2 pulse chemisorption, H2-TPD), and their increased CO2 adsorption (CO2-TPD). For the stable 13.5Ni−2K/10CeO2−Al2O3 catalyst, the effect of reaction temperature and contact time on conversion and product yield was studied. It was found that the conversion and product yield increased with increasing reaction temperature and W/FCH4,0 and reached equilibrium at W/FCH4,0 = 1.7 kg-cat·h/kgmethane. The mechanism of the CH4/CO2 reaction has been proposed, based on which a kinetic model was developed to estimate the kinetic parameters. The estimated kinetic parameters predicted the product yields satisfactorily. CH4 activation to form CHx and CHxO decomposition are suggested to be the rate-determining steps of the CH4/CO2 reaction over the 13.5Ni−2K/10CeO2−Al2O3 catalyst. The activation energy for methane adsorption and dissociation (Ek1L), CHxO decomposition (Ek7L), and reverse water gas shift reaction (Ekr) were estimated to be 113.8 ± 5.5, 119.3 ± 4.7, and 155.3 ± 7.0 kJ/mol, respectively.