Role Of Pore Structure Research Articles

Adsorption in Pyrene-Based Metal-Organic Frameworks: The Role of Pore Structure and Topology.

Pore topology and chemistry play crucial roles in the adsorption characteristics of metal-organic frameworks (MOFs). To deepen our understanding of the interactions between MOFs and CO2 during this process, we systematically investigate the adsorption properties of a group of pyrene-based MOFs. These MOFs feature Zn(II) as the metal ion and employ a pyrene-based ligand, specifically 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy). Including different additional ligands leads to frameworks with distinctive structural and chemical features. By comparing these structures, we could isolate the role that pore size, the presence of open-metal sites (OMS), metal-oxygen bridges, and framework charges play in the CO2 adsorption of these MOFs. Frameworks with constricted pore structures display a phenomenon known as the confinement effect, fostering stronger MOF-CO2 interactions and higher uptakes at low pressures. In contrast, entropic effects dominate at elevated pressures, and the MOF's pore volume becomes the driving factor. Through analysis of the CO2 uptakes of the benchmark materials ─some with narrower pores and others with larger pore volumes─it becomes evident that structures with narrower pores and high binding energies excel at low pressures. In contrast, those with larger volumes perform better at elevated pressures. Moreover, this research highlights that open-metal sites and inherent charges within the frameworks of ionic MOFs stand out as CO2-philic characteristics.

Influence of pore structure on thermal stress distribution inside coal particles during primary fragmentation

Thermal stress is an important reason of coal particle primary fragmentation, during which the role of pore structure is ambiguous. Thermal stress induced fragmentation experiments were conducted with low volatile coal/char particles, and the results show that the fragmentation severity enhances with increasing porosity. Various porous thermal stress models were developed with finite element method, and the influences of the pore shape, size, position and porosity on the thermal stress were discussed. The maximum thermal stress inside particle increases with pore curvature, the pore position affects the thermal stress more significantly at the particle center and surface. The expectation of the maximum tensile thermal stress linearly increases with porosity, making the particles with higher porosity easier to fragment, contrary to the conclusion deduced from the devolatilization theory. The obtained results are valuable for the analysis of different thermal processes concerning the thermal stresses of the solid feedstocks.

Experimental and DFT investigations on adsorption–regeneration performance and deactivation mechanism over engineered carbon fiber: role of pore structure and functional groups

Technology based on adsorption of porous carbon is a promising and cost-effective strategy for the recovery of high-value volatile organic compounds (VOCs) or removal of worthless VOCs.

Role of pore structure on resistance to physical crystallization damage of calcium sulfoaluminate belite (CSAB) cement blends

The resistance to physical sulfate damage was tested for a variety of cementitious mixtures including ordinary portland cement, calcium sulfoaluminate belite (CSAB) cement, a CSAB-fly ash blend and an air-entrained CSAB. Mortar bars were exposed to DI water or 5 % sodium sulfate solutions under cyclical wet-dry conditions. The expansions of the specimens were measured after each wetting cycle. A water sorptivity test, thermogravimetric analysis, x-ray diffraction analysis, mercury intrusion porosimetry method, and micro-computed tomography were applied to study differences in expansion and cracking in the mixtures. The results showed that the incorporation of fly ash into the CSAB matrix reduced cumulative pore volumes and slightly increased micropore sizes – both of which contributed to failure of the CSAB-fly ash systems. Use of the air-entraining agent in CSAB produced more, smaller, and more uniform pores, but did not influence the performance of CSAB. Both the CSAB and air entrained CSAB mixtures showed good resistance to physical sulfate damage. Samples with average pore diameters <15 nm prevented infiltration of sulfate ions and slowed the onset of salt crystalization damage.

Synthesis of Hierarchically Ordered Porous Silica Materials for CO2 Capture: The Role of Pore Structure and Functionalized Amine

Hierarchically ordered porous silica materials (HSMs) with a micro/mesoporous structure were successfully prepared with the sol-gel method using dextran, dextran/CTAB, and CTAB as templates. The obtained hierarchically structured silica was successfully modified with amine groups through post-grafting and one-pot methods. Their architectural features and texture parameters were characterized by XRD, N2 adsorption–desorption isotherms, SEM, TEM, FTIR, and TGA techniques. The results demonstrated that the pore structure depended on the reaction temperature and the amount of CTAB added in the synthesis procedure. A series of porous silica with hierarchical pore structures possessed abundant micropores, ordered mesopores, and a tunable surface area and pore volume. After modification, the ordered structure of the hierarchical porous silica almost disappeared due to the presence of amine groups in the pore channel. Furthermore, to explore the effect of pore structures and amine groups on CO2 adsorption performance, before and after amine modification of HSMs, adsorbents were evaluated regarding the capacity of collecting CO2 for comparison. According to these results, the varying microporous content, pore size distribution, and density of the amine groups were important factors determining the capacity of CO2 capture.

Subsurface multiphase reactive flow in geologic CO2 storage: Key impact factors and characterization approaches

Subsurface multiphase reactive flow in geologic CO2 storage: Key impact factors and characterization approaches

Effect of pore structure on Ni/Al2O3 microsphere catalysts for enhanced CO2 methanation

An understanding of the support effect is fundamental for guiding the rational design of heterogeneous catalysts. Herein, the role of pore structure on metal dispersion and catalytic performance was comprehensively investigated using Ni/Al2O3 catalysts. Three different Al2O3 supports, including Al2O3 microspheres prepared in microchannels and two commercially available Al2O3 supports named Sample 1 and Sample 2, were used and the Ni/Al2O3 catalysts were prepared by wetness impregnation method. X-ray diffraction, transmission electron microscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, N2 adsorption–desorption, and H2 pulse chemisorption analyses combined with a sintering kinetic model were used to investigate the effect of the support pore structure. The narrow pore size distribution (3–15 nm) of Al2O3 microspheres and Sample 1 led to a uniform NiO dispersion for the calcined catalysts. Moreover, the high specific surface area (291 m2/g) and large pore volume (1.0 mL/g) of the Al2O3 microspheres were beneficial for the deposition of NiO particles inside mesopore to obtain a stronger metal–support interaction. Owing to the smaller NiO nanoparticles and stronger metal–support interaction, the reduced Ni/Al2O3 microspheres exhibited an average Ni particle size of 10.2 nm under 36 wt% nickel loading, whereas the average Ni particle size loaded on Sample 1 and Sample 2 were 12.6 nm and 13.2 nm, respectively. The optimized CO2 conversion of 87.0% at 300 °C under atmospheric pressure was attributed to the large pore volume and uniform Ni dispersion of Ni/Al2O3 microsphere catalysts while the same value for Sample 1 and Sample 2 catalysts was 81.5% and 55.0%, respectively. This work provides valuable guidelines for designing effective CO2 methanation support and proves the potential application of Al2O3 microspheres for CO2 methanation.

The development of intermittent multiphase fluid flow pathways through a porous rock

Intermittent fluid flow has recently been identified as an important transport mode for processes involving subsurface multiphase fluids such as CO2 storage and natural gas production. However, due to experimental limitations, it has not been possible to identify why intermittency occurs at subsurface conditions and what the implications are for upscaled flow properties such as relative permeability. We address these questions with observations of nitrogen and brine flowing at steady-state through a carbonate rock. We overcome previous imaging limitations with high-speed (1s resolution), synchrotron-based X-ray micro-computed tomography combined with pressure measurements recorded while controlling fluid flux. We observe that intermittent fluid transport allows the non-wetting phase to flow through a more ramified network of pores, which would not be possible with connected pathway flow alone for the same flow rate. The volume of fluid intermittently fluctuating increases with capillary number, with the corresponding expansion of the flow network minimising the role of inertial forces in controlling flow even as the flow rate increases. Intermittent pathway flow sits energetically between laminar and turbulent through connected pathways. While a more ramified flow network favours lowered relative permeability, intermittency is more dissipative than laminar flow through connected pathways, and the relative permeability remains unchanged for low capillary numbers where the pore geometry controls the location of intermittency. However, as the capillary number increases further, the role of pore structure in controlling intermittency decreases which corresponds to an increase in relative permeability. These observations can serve as the basis of a model for the causal links between intermittent fluid flow, fluid distribution throughout the pore space, and the upscaled manifestation in relative permeability.

The role of pore structure and nitrogen surface groups in the adsorption behavior of formaldehyde on resin‐based carbons

This study focused on the role of pore structures and nitrogen surface functional groups in the formaldehyde (HCHO) adsorption on the carbonized resin‐based materials (UFC). After comparing the optimal sample UFAC‐700 obtained by the activation of UFC at 700°C with the commercial activated carbon (CAC) and other UFC, the HCHO adsorption capacity for UFAC‐700 (12.30 mg g−1) is more than three times and 10 times of that for CAC and UFC, respectively. Abundant pore structures could provide more adsorption sites for the initial stage of HCHO adsorption. Moreover, according to the density functional theory (DFT) calculations, pyrrolic‐N could enhance the adsorption energy and polar interaction of HCHO due to electrostatic force between the positively charged H attached to the nitrogen group and the negatively charged O atoms in the HCHO molecule. This study introduced a novel way to specifically design the surface modifications for volatile organic compounds (VOCs) adsorption.

Templating synthesis of hierarchically meso/macroporous N-doped microalgae derived biocarbon as oxygen reduction reaction catalyst for microbial fuel cells

N-doped carbons have been hailed as cost effective catalysts for the large-scale commercialization of microbial fuel cells (MFCs). In this paper, we developed a hierarchically meso/macroporous N-doped biocarbon by templating approach using Chlorella pyrenoidosa as precursor. The results showed that graphitic-N was the dominating functional group contributing to oxygen reduction reaction (ORR) performance. In addition, the role of pore structure was identified and the results suggested that mesopores exhibited a nearly linear correlation with limiting current density and half-wave potential, while electrochemical surface area almost linearly varied with macropores in the carbon materials. These results implied that mesopores play a dominating role in facilitating ion and oxygen supply and creating accessible active sites for ORR, while macropores mainly served as an electrolyte buffering reservoir shortening the electrolyte diffusion distances in the prepared catalysts. The optimized meso/macro pore structure enhanced the accessibility of the active sites and facilitated the mass transport of ion and oxygen, and consequently improved ORR performance of catalyst. The as-prepared catalyst exhibited a remarkably higher power generation than that of the commercial Pt/C in MFCs. This paper offered an insight into the effect of pore structure on the ORR performance of catalysts, and also provided an alternative avenue for synthesizing meso/macroporous carbon catalysts for the applications of MFCs.

Transalkylation of 1,2,4-trimethylbenzene with toluene over large pore zeolites: Role of pore structure and acidity

Effects of pore structure and acidity over Beta and Y zeolites with a range of Brønsted and Lewis acid sites on their catalytic behaviour in the transalkylation reaction were investigated. The tests were conducted for a time-on-stream (TOS) of 50 h in a fixed-bed reactor at 400 °C, 10 bar, H2/HC = 4, and WHSV=5 h−1 with a 50:50 wt. % toluene:124-TMB mixture as feedstock. While initial (TOS ≤3 h) TMBs conversion was similar, wide differences were evident as the effects of partial deactivation became apparent with TOS. Zeolite Beta (Si/Al = 12.5) exhibited highest conversion and xylenes yield. As the Si/Al ratio of zeolite Beta is increased, the performance dropped whereas an opposite trend was observed for Y zeolites underscoring the importance of optimum level of dealumination depending on the zeolite structure. Isomerization of 124-TMB was observed over Beta which was not sustained by Y. The existence of separate active sites for TMB isomerization and its transalkylation with toluene in Beta is suggested.

Factors governing soil water repellency under tillage management: The role of pore structure and hydrophobic substances

AbstractSoil water repellency (SWR) has significant effects on soil degradation by changing some soil processes (e.g., carbon sequestration and soil erosion). Understanding the influence factors of SWR under conservation agriculture are playing a vital role in the sustainable development for improving soil quality. However, how soil pore structure influence on SWR remains unclear. We aim to assess the impact of hydrophobic substances and pore structure on SWR. Here we conducted two long‐term experimental fields with three treatments: conventional tillage (CT), reduced tillage (RT), and no‐tillage (NT). X‐ray tomography and the sorptivity method were used to measure soil pore structure and SWR, respectively. We found that soil organic carbon (SOC) and microbial biomass carbon (MBC) were higher in RT and NT treatments than in CT. MBC had significant influences on soil water sorptivity (Sw) and water repellency index (RI; p &lt; 0.001), whereas SOC had no influence on Sw (p &gt; 0.05). MBC also showed a closer relationship with SWR than SOC in redundancy analysis. The RT and NT increased the porosity of 55–165 μm that had a positive relationship with ethanol sorptivity and RI (p &lt; 0.05). Ethanol sorptivity increased with an increase in soil pore porosity and connectivity under RT and NT treatments. However, increasing the pore surface area could decrease Sw due to enhance contact area between hydrophobic substances and soil water. Overall, the RT and NT treatments increased the water repellency index, which was a result of the interactions between pore structure and hydrophobic substances.

Role of pore structure on the activity and stability of sulfide catalyst

Effect of pore structure on the activity and stability of sulfide phase in hydrodesulfurization (HDS) of diesel were systematically investigated. A series of alumina with different pore structure were prepared by calcining pseudo boehmite at different temperatures. Various characterizations suggested that the surface concentration of OH groups and Lewis acid sites generally decreased with calcination temperature. The properties of sulfide phase in fresh and spent catalysts were analysis by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The results showed that the concentration of CoMoS species was greatly decreased after the reaction while the average length of MoS2 slabs was substantially increased. The concentration of preserved CoMoS species was proportional to the average pore size of support indicating that the strip-off of Co from CoMoS phase can be reduced when the average pore size is larger. Furthermore, the activity evaluation showed that larger pore structure of support is beneficial for the intrinsic activity and stability of CoMoS phase in the HDS of diesel. The reason was partially attributed to that the pore with larger diameter can reduce the coke deposition on the catalyst so that increase the intrinsic activity and stability of CoMoS sites.

The role of pore evolution during supersolidus liquid phase sintering of prealloyed brass powder

ABSTRACT The aim of this research is to study the pore structure as well as to assess the liquid phase sintering behaviour of Cu-28Zn powder specimens at different green density levels and temperatures. For this purpose, samples were compacted to obtain six different green densities and then sintered at 870°C, 890°C and in part at 930°C for 30 min. The results revealed that the spherical pores which are formed inside the grains can be swept by grain boundaries due to grain growth and join to primary pores so that secondary intragranular pores are eliminated and intergranular pores enlarged at higher temperatures. Also, the pores move upwards to the top of sample due to buoyancy forces. The role of pore structure in distortion is more tangible at higher temperatures (930°C) so that O-shape and X-shape distortions were observed at high and low green density samples, respectively.

Efficient removal of tetrabromobisphenol A using microporous and mesoporous carbons: The role of pore structure

Abstract Tetrabromobisphenol A (TBBPA) is a widely used flame retardant yet a persistent pollutant in the environment. In this study, various microporous and mesoporous carbon-based materials were synthesized and their adsorption performance toward TBBPA was systematically evaluated. The adsorbents were characterized by transmission electron microscope, scanning electron microscope, X-ray diffraction, Raman spectroscopy, N2 adsorption/desorption and Zeta potential measurements. TBBPA adsorption over coal-based activated carbon (F300), coconut-shell-based activated carbon (AC) and CMK-3 followed Freundlich adsorption model, while TBBPA adsorption over zeolite-templated carbon (ZTC), single-walled carbon nanotube (SWNT) and multiwalled carbon nanotube (MWNT) could be well described by both Freundlich model and Langmuir model. Compared with F300 and AC, TBBPA diffusion on ZTC and CMK-3 is faster because of their ordered pore structure and higher average pore size. The surface-area-normalized adsorption capacity of TBBPA was higher on ZTC, AC and F300 than on CMK-3, SWNT and MWNT, which can be attributed to the stronger micropore-filling effect with the microporous carbonaceous materials. The presence of humic acids had little effect on TBBPA sorption over ZTC, F300, CMK-3 and AC, while suppressed TBBPA adsorption on SWNT and MWNT were observed. In the column adsorption test, ZTC was capable of continuously treating synthetic wastewater stream, indicating that ZTC had great potential to be used as an effective adsorbent for TBBPA removal.

Role of pore structure in the percolation and storage capacities of deeply buried sandstone reservoirs: A case study of the Junggar Basin, China

Deeply buried sandstone reservoirs are characterized by their wide pore-throat distributions and varied storage and percolation capacities. An integrated analysis comprising casting thin section, scanning electron microscopy, X-ray computed tomography (micro-CT), high-pressure mercury intrusion (HPMI), and constant-rate mercury intrusion (CRMI) is performed on thirteen samples from the Jurassic Sangonghe Formation in the Junggar Basin to investigate the pore structures and their influence on the storage and percolation capacities. HPMI, CRMI, and micro-CT are combined to determine the full-range pore size distributions (FPSDs), which have multimodal distributions between 2.77 nm and 500 μm with three broad peaks. The right peak, ranging from 100 to 500 μm, is associated with residual and dissolution intergranular pores. The middle peak is mainly composed of dissolution intergranular and intragranular pores with radii between 10 and 100 μm. The left peak exhibited fluctuations and is characterized by dissolution intragranular and intercrystalline pores with radii of 37 nm–10 μm. According to the pore types, sizes, and proportions in the FPSD, the pores are classified as intercrystalline nanopores (<1 μm), intragranular micro-small pores (1–10 μm), mixed intergranular and intragranular mesopores (10–100 μm), and intergranular macropores (>100 μm). A storage capacity evaluation combining the classifications and FPSD indicates that the macropores and nanopores primarily contribute to porosity, albeit with contrasting influences on the storage capacity. The contents of macropores determine the storage capacity of a deeply buried sandstone reservoir, while the negative effects of nanopores become predominant with decreasing porosity. A percolation capacity evaluation on the basis of CRMI results suggests that the permeability contribution is dominated by nanopores in tight sandstone, controlled by micro-small pores in low-permeability sandstone, and dominated by mesopores in conventional sandstone. Mesopores always play a favorable role in percolation. However, the negative impacts of nanopores should be considered in low-permeability and tight sandstone. Micro-small pores have a negative influence on the permeability of conventional sandstone, but are favorable for the fluid percolation of most low-permeability and tight sandstone reservoirs. A new empirical equation indicates that r10 of the FPSD is the suitable as the proper pore-throat radius for the permeability estimation of deeply buried sandstone reservoirs.

Dependence of unsaturated chloride diffusion on the pore structure in cementitious materials

Conceptual analysis is performed to examine the effects of pore features on the water continuity in unsaturated porous systems. The roles of pore features in relative chloride diffusion coefficient (Drc) of mortar specimens at various degrees of water saturation (Sw) were studied based on mercury intrusion porosimetry and resistivity tests. It is found that the role of pore structure in the Drc-Sw relationship is a result of its effect on the water continuity. Porosity and tortuosity are not relevant to the Drc-Sw relationship. A finer pore size distribution or lower pore connectivity tends to result in a lower Drc. The pore size effect on the Drc is pronounced primarily at high Sw, while the Drc is dominated by the pore connectivity at low Sw. Cement mortar with a higher water-to-binder ratio shows larger chloride diffusion at high relative humidity levels but smaller chloride diffusion at low relative humidity levels.

Composite Membranes Derived from Cellulose and Lignin Sulfonate for Selective Separations and Antifouling Aspects.

Cellulose-based membrane materials allow for separations in both aqueous solutions and organic solvents. The addition of nanocomposites into cellulose structure is facilitated through steric interaction and strong hydrogen bonding with the hydroxy groups present within cellulose. An ionic liquid, 1-ethyl-3-methylimidazolium acetate, was used as a solvent for microcrystalline cellulose to incorporate graphene oxide quantum dots into cellulose membranes. In this work, other composite materials such as, iron oxide nanoparticles, polyacrylic acid, and lignin sulfonate have all been uniformly incorporated into cellulose membranes utilizing ionic liquid cosolvents. Integration of iron into cellulose membranes resulted in high selectivity (>99%) of neutral red and methylene blue model dyes separation over salts with a high permeability of 17 LMH/bar. With non-aqueous (alcohol) solvent, iron–cellulose composite membranes become less selective and more permeable, suggesting the interaction of iron ions cellulose OH groups plays a major role in pore structure. Polyacrylic acid was integrated into cellulose membranes to add pH responsive behavior and capacity for metal ion capture. Calcium capture of 55 mg Ca2+/g membrane was observed for PAA-cellulose membranes. Lignin sulfonate was also incorporated into cellulose membranes to add strong negative charge and a steric barrier to enhance antifouling behavior. Lignin sulfonate was also functionalized on the commercial DOW NF270 nanofiltration membranes via esterification of hydroxy groups with carboxyl group present on the membrane surface. Antifouling behavior was observed for both lignin-cellulose composite and commercial membranes functionalized with lignin. Up to 90% recovery of water flux after repeated cycles of fouling was observed for both types of lignin functionalized membranes while flux recovery of up to 60% was observed for unmodified membranes.

Hierarchically Porous Carbon Materials for CO2 Capture: The Role of Pore Structure

With advances in porous carbon synthesis techniques, hierarchically porous carbon (HPC) materials are being utilized as relatively new sorbents for CO2 capture applications. These HPC materials were used as a platform to prepare samples with differing textural properties and morphologies to elucidate structure–property relationships. It was found that high microporous content, rather than overall surface area, was of primary importance for predicting good CO2 capture performance. Two HPC materials were analyzed, each with near identical high surface area (∼2700 m2/g) and colossally high pore volume (∼10 cm3/g), but with different microporous content and pore size distributions, which led to dramatically different CO2 capture performance. Overall, large pore volumes obtained from distinct mesopores were found to significantly impact adsorption performance. From these results, an optimized HPC material was synthesized that achieved a high CO2 capacity of ∼3.7 mmol/g at 25 °C and 1 bar.

Mesoporous silica supported cobalt catalysts for gas phase hydrogenation of nitrobenzene: role of pore structure on stable catalytic performance

Mesoporous silica supported Co catalysts (Co/COK-12 and Co/SBA-16) are active for hydrogenation of nitrobenzene to aniline. The support pore architecture is decisive in maintaining stable catalytic performance.