Medium-sized Pores Research Articles

Selective hydroisomerization of n-dodecane over platinum supported on zeolites

In this study, in order to develop catalysts for the selective isomerization of higher paraffin, the hydroisomerization reaction of n-dodecane was performed as a model reaction. Pt/ZSM-48, Pt/HZSM-5, Pt/HY, and Pt/SAPO-11 were examined for the selective hydroisomerization of n-dodecane. The catalysts were characterized via X-ray powder diffraction, N2 adsorption, and the temperature-programmed desorption of ammonia. Among the catalysts studied, the Pt/HZSM-48 catalyst exhibited the best isomerization selectivity in the hydroisomerization reaction of n-dodecane, which is attributed to the moderate acid sites and medium-sized pores present in the HZSM-48. The highest iso-dodecane yield was obtained at a reaction temperature of 280 °C in the Pt/HZSM-48 catalyst. The optimal selectivity of the n-dodecane hydroisomerization over the Pt/SAPO-11 catalyst was obtained at approximately 300 °C, which was slightly higher than that of the Pt/HZSM-48 catalyst.

A preliminary study of pores on epidermal ridges: Are there any sex differences and age related changes?

The pore characteristics on the epidermal friction ridges are individualistic and thereby useful in the process of identification when used along with other minutiae details. The present work was undertaken with the objective of studying the sex difference and influence of age on the pore morphology. The study included 230 Indians belonging to various age groups. There was no significant difference in the pore characteristics between both the sexes. The average number of pores per centimeter of friction ridge was 8.40 in males and 8.83 in females. The closed type was the commonest type of pores seen. The size of pores varied from 69 μm to 284 μm in males and 66 μm–287 μm in females. The medium-sized pores were more common than the small and large-sized pores. The majority of the pores were situated in the periphery of the ridge. The commonest shape of pores seen was circular and oval shaped pores. As the age advances, the number of pores does not significantly vary. But, the size gradually increases, and the position and shape of pores changes with the age.

Gold Nanostructures for Surface-Enhanced Raman Spectroscopy, Prepared by Electrodeposition in Porous Silicon.

Electrodeposition of gold into porous silicon was investigated. In the present study, porous silicon with ~100 nm in pore diameter, so-called medium-sized pores, was used as template electrode for gold electrodeposition. The growth behavior of gold deposits was studied by scanning electron microscope observation of the gold deposited porous silicon. Gold nanorod arrays with different rod lengths were prepared, and their surface-enhanced Raman scattering properties were investigated. We found that the absorption peak due to the surface plasmon resonance can be tuned by changing the length of the nanorods. The optimum length of the gold nanorods was ~600 nm for surface-enhanced Raman spectroscopy using a He–Ne laser. The reason why the optimum length of the gold nanorods was 600 nm was discussed by considering the relationship between the absorption peak of surface plasmon resonance and the wavelength of the incident laser for Raman scattering.

Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications

Dihydrogen, methane, and carbon dioxide isotherm measurements were performed at 1-85 bar and 77-298 K on the evacuated forms of seven porous covalent organic frameworks (COFs). The uptake behavior and capacity of the COFs is best described by classifying them into three groups based on their structural dimensions and corresponding pore sizes. Group 1 consists of 2D structures with 1D small pores (9 A for each of COF-1 and COF-6), group 2 includes 2D structures with large 1D pores (27, 16, and 32 A for COF-5, COF-8, and COF-10, respectively), and group 3 is comprised of 3D structures with 3D medium-sized pores (12 A for each of COF-102 and COF-103). Group 3 COFs outperform group 1 and 2 COFs, and rival the best metal-organic frameworks and other porous materials in their uptake capacities. This is exemplified by the excess gas uptake of COF-102 at 35 bar (72 mg g(-1) at 77 K for hydrogen, 187 mg g(-1) at 298 K for methane, and 1180 mg g(-1) at 298 K for carbon dioxide), which is similar to the performance of COF-103 but higher than those observed for COF-1, COF-5, COF-6, COF-8, and COF-10 (hydrogen at 77 K, 15 mg g(-1) for COF-1, 36 mg g(-1) for COF-5, 23 mg g(-1) for COF-6, 35 mg g(-1) for COF-8, and 39 mg g(-1) for COF-10; methane at 298 K, 40 mg g(-1) for COF-1, 89 mg g(-1) for COF-5, 65 mg g(-1) for COF-6, 87 mg g(-1) for COF-8, and 80 mg g(-1) for COF-10; carbon dioxide at 298 K, 210 mg g(-1) for COF-1, 779 mg g(-1) for COF-5, 298 mg g(-1) for COF-6, 598 mg g(-1) for COF-8, and 759 mg g(-1) for COF-10). These findings place COFs among the most porous and the best adsorbents for hydrogen, methane, and carbon dioxide.

Multistep filling of porous silicon with conductive polymer by electropolymerization

The filling of porous silicon with polypyrrole by electropolymerization was investigated. The filling with polypyrrole proceeded preferentially along the porous silicon wall, leading to the formation of tubular structures. By repeating the porosification, the pore filling and the additional porosification, through-tubes of polypyrrole were formed in macropores. The technique to form through-tube was also applied to medium-sized pores. A double layer with polypyrrole was produced by the repetition of porosification and pore filling twice. The immobilization of glucose oxidase was performed by electropolymerization in an aqueous solution containing glucose oxidase and pyrrole. Glucose oxidase was immobilized physically in the polypyrrole film. In the double layer, the sensitivity of glucose oxidase was measured by electrochemical oxidation of hydrogen peroxide, which was produced by the enzymatic reaction of glucose oxidase to gluconolactone. When glucose oxidase was immobilized in the upper layer, glucose was detected sensitively. On the other hand, when glucose oxidase was immobilized in the lower layer, the sensing current showed a slow and a low response. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fine-tuning in size and surface morphology of rod-shaped polypyrrole using porous silicon as template

We investigated electropolymerization of polypyrrole into porous silicon template. We used three types of porous silicon templates, i.e., porous silicon with ordered macro pores, medium-sized pores and meso pores. Polypyrrole was electropolymerized from pore bottoms to pore tops in all the porous silicon templates. After removal of the templates we obtained rod-shaped polypyrrole arrays. Changing the porous silicon templates easily controlled the size of the rod-shaped polypyrrole. We also used dendritic medium-sized pores for template, and then polypyrrole rod having a roughened surface was obtained. Here we demonstrated that the size and the surface morphology of polypyrrole rod were easily tuned using porous silicon.

Effect of preparation conditions on the pore structure of tricalcium phosphate and on the kinetics of its reaction with the lead ion in solution

The kinetics of the reaction of differently prepared tricalcium phosphate samples with the lead ion are considered. As distinct from mesoporous samples, samples with a mixed pore structure dominated by large and medium-sized pores are highly reactive toward the lead ion.

Electrochemical Formation of Porous Silicon with Medium-Sized Pores

Medium-sized pores of which diameter was over 100 nm were successfully prepared by anodization in 3 wt% HF aqueous solution containing KMnO4 and surfactant. The presence of an appropriate oxidizing agent and a surfactant was indispensable for the formation of medium-sized pores, but the concentration dependence was not significant. Similar method was applied to the p+-type silicon and led to the pore widening.

In situ SANS study of pore microstructure in YSZ thermal barrier coatings

Air plasma sprayed yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) were investigated by means of SANS. The measurements were performed in situ at different temperatures up to 1200 °C and ex situ after annealing at 1200 °C up to 100 h. Scattering curves were described by three populations of pores. The parameters of nanometric and medium-sized (20 nm) pores were determined. Specimens produced under different spray parameters showed qualitatively similar behaviour of nanometric and medium-sized pores during thermal exposure at elevated temperatures. The population of nanopores increased strongly at about 800 °C. The evolution of volume and size of nanopores and medium-size pores at 1200 °C indicated their sintering. The elimination of these pores coincides with the increase of Young's modulus.

Neovascularization of poly(ether ester) block-copolymer scaffolds in vivo: long-term investigations using intravital fluorescent microscopy.

Poly(ether ester) block-copolymer scaffolds of different pore size were implanted into the dorsal skinfold chamber of balb/c mice. Using intravital fluorescent microscopy, the temporal course of neovascularization into these scaffolds was quantitatively analyzed. Three scaffold groups (diameter, 5 mm; 220-260 thickness, microm; n = 30) were implanted. Different pore sizes were evaluated: small (20-75 microm), medium (75-212 microm) and large pores (250-300 microm). Measurements were performed on days 8, 12, 16, and 20 in the surrounding normal tissue, in the border zone, and in the center of the scaffold. Standard microcirculatory parameters were assessed (plasma leakage, vessel diameter, red blood cell velocity, and functional vessel density). The large-pored scaffolds showed significantly higher functional vessel density in the border zone and in the center (days 8 and 12) compared with the scaffold with the small and medium-sized pores. These data correlated with a larger vessel diameter and a higher red blood cell velocity in the large-pored scaffold group. Interestingly, during the evaluation period the microcirculatory parameters on the edge of the scaffolds returned to values similar to those found in the surrounding tissue. In the center of the scaffold, however, neovascularization was still active 20 days after implantation. Plasma leakage and vessel diameter were higher in the center of the scaffold. Red blood cell velocity and functional vessel density were 50% lower than in the surrounding tissue. In conclusion, the dorsal skinfold chamber model in mice allows long-term study of blood vessel growth and remodeling in porous biomedical materials. The rate of vessel ingrowth into poly(ether ester) block-copolymer scaffolds is influenced by pore size and was highest in the scaffold with the largest pores. The data generated with this model contribute to knowledge about the development of functional vessels and tissue ingrowth into biomaterials.

A BEAUTIFUL MELD

WHETHER PLANT BREEDER or chemist, hybridizers hope to blend the best features of the parents into optimal offspring. That's what a team of scientists in Japan has accomplished with the creation of a benzene-silica hybrid that assembles itself into a crystalline mesoporous material. The new material exhibits the periodic array of medium-sized pores that have made inorganic mesoporous molecular sieves so useful. Most striking, the pore walls themselves are completely regular, composed of orderly layers of benzene rings linked to alternating layers of silicate chains. The benzene rings can be functionalized, opening the door to the vast range of organic transformations that can lead to specially tailored properties { Nature , 416 ,304(2002)}. To date, all conventional mesoporous materials have had amorphous pore-wall structures that restrict their applications, notes chemist Shinji Inagaki, leader of the Frontier Research Group at Toyota Central R&D Laboratories, Nagakute. Inagaki synthesized and character...

Influence of tile synthesis parameters on the structural and textural properties of precipitated manganese oxides

A systematic study has been conducted in order to compare the structural and morphological properties as well as the genesis course of manganese oxides prepared by a precipitation-calcination method under different conditions. In particular, the roles of the precursor salt, the pH, the precipitating agent and thermal treatment were investigated. It was found that calcination at 873 K of the starting materials gives rise in all cases to crystalline bixbyite. However, the phases formed at lower temperatures are quite different and depend largely on the synthesis conditions. The systems prepared from a Mn(III) ionic salt present maximum specific surface areas according to a greater development medium-sized pores.

Decalin and Tetralin as Probe Molecules for Cracking and Hydrotreating the Light Cycle Oil

Cracking of tetralin and decalin was carried out over several zeolites to establish the effect of the pore topology of the catalyst on product distribution. These molecules were chosen as probe molecules, because they indicate which catalyst is the best for cracking or hydrotreating the light cycle oil (LCO) fraction, which is obtained directly from fluid catalytic cracking units. A set of zeolites with medium-sized (ZSM-5, MCM-22, ITQ-2), large (USY, Beta), and ultralarge pores (UTD-1), as well as a mesoporous MCM-41, were used as catalysts at 723 K. The results demonstrate that pore size and topology have a strong influence on diffusion, and consequently, on activity and selectivity in reactions such as ring opening, dealkylation, transalkylation, hydride transfer, and coke formation. UTD-1 generally has the highest activity per framework Al owing to the pore size and topology of this zeolite that enables flat molecules to diffuse easily inside the pores. According to the results, zeolites with medium-sized pores are adequate in combination with large-pore zeolites to crack naphthenes and fused aromatic–naphthenic rings, of the type present in LCO, to produce propene. Large-pore zeolites show good selectivity for naphthenic ring opening and appear to be better suited for hydrotreating LCO. Beta zeolite is a catalyst that is especially suitable for both processes.

Permeability of the rat small intestinal epithelium along the villus-crypt axis: Effects of glucose transport

The aim of this study was to elucidate the permeability characteristics of the epithelium along the villus-crypt axis and investigate the effect of glucose transport on these characteristics along this axis. The disappearance rates of (14)C-mannitol and (51)Cr-EDTA or (3)H-inulin were determined as clearance (Cl(x)) from a recirculating perfusion system of the jejunal lumen in anesthetized rats. Net fluid transport was varied over a large range by exchanging mannitol with glucose in the perfusate solution and by inhibition of nervously mediated secretory processes with hexamethonium. The perfusion rate was 0.5 or 0.2 mL/min. Cl(Man) enhanced significantly with increasing net fluid transport (secretion 8.50+/-1.88, to absorption 16.72+/-1.75 microL x min(-1) x g(-1)) and with glucose perfusates. Cl(Cr-EDTA) was constant irrespective of net fluid transport and was reduced to insignificant values at a perfusion rate of 0.2 mL/min. Cl(In) was not different from zero. The absorbing apical part of the villus contains small pores (radius, <6 A) allowing passive transport via solvent drag of, e.g., monosaccharides, whereas the pores in the crypts are large (50-60 A) and inaccessible to the luminal content. The basal part of the villus contains medium-sized pores (10-15 A) through which no solvent drag occurs. Active glucose transport in the rat mainly increases the number of small pores accessible for passive transport, whereas the size of these pores seems to stay constant.

The fractal dimension of pore distribution patterns in variously-compacted soil

Pore-size distribution pattern significantly alters many soil properties affecting water movement and root growth. The distribution is largely influenced by soil compaction but information on how to describe this effect is very limited. In this study we used the fractal dimension to characterize pore distribution patterns in variously-compacted soil. The soil used was an Orthic Luvisol (Lublin Region, Poland). The various soil compaction was obtained by wheel traffic treatments: unwheeled (L); moderately compacted, 3 tractor passes (MC); strongly compacted, 8 tractor passes (SC). Pore distribution patterns of all pores (>0.3 mm) and water-conducting pores were analyzed with an image analyzer and the two-dimensional fractal dimension was estimated. All pores were analyzed on the drawings obtained from the polished surfaces of soil blocks 8×9×2 cm. To analyze the water-conducting pores, soil cores were taken in cylinders of length 20 cm and diameter 21.5 cm from the plots on which methylene blue solution was applied. The pores were analyzed on horizontal cuts at 2 cm depth intervals. Mean values of fractal dimensions for all pores ( D p2) in the horizontal plane of surface soil in L, MC and SC were 1.69, 1.42 and 1.35, respectively. In the vertical plane, the corresponding values were 1.48, 1.35 and 1.29. In L the fractal dimension reflected pores of different size ranging from a few tenths of a millimetre to a dozen or so millimetres with rather smooth walls. In MC the contribution of large pores decreased whereas that of medium-sized pores considerably increased forming net-like patterns. However in SC, the largest area was of massive structure with longitudinal cracks and scarce and unevenly-distributed larger pores. The D p2 was linearly correlated with areal porosity ( R=0.965) and the arithmetic mean of the areas of pores ( R=0.914). Mean values of fractal dimensions for the blue staining patterns ( D s2) in the plough layer ranged from 1.06 to 1.12 in L and MC whereas it decreased to 0.94 in SC. The wide range of D s2 values for 2 cm layers of upper soil in L reflected the high variability of pore structures in this treatment. In the subsoil, the D s2 varied from 1.03 to 1.09 and reflected mostly the distribution pattern of earthworm channels. The values of fractal dimensions for roots ( D r2) reflected different branching and root growth in variously-compacted soil. This study showed that fractal analysis provides a relevant quantification of the changes of pore and root structure in relation to soil compaction.

Mobility of protein through a porous membrane

The electrophoretic mobility of proteins in membrane pores has been investigated experimentally. When the size of the protein is small relative to the pore size, the protein mobility is identical to the free protein mobility. As the pore radius approaches the protein radius the mobility of the protein is significantly reduced. This phenomenon has been explained in terms of electrokinetic theory. Using a method of reflections, and taking into account the effect of the back-flow, an approximation has been developed for the average mobility in a closed system of a spherical particle moving under electrophoresis parallel to the axis of a cylindrical pore. This approximation assumes that the surface potential of the particle is low, and is valid for arbitrary double layer thickness relative to particle size, provided that there is minimal overlap between the double layers at the pore surface and around the particle. It is also predicted that when the protein and the membrane have surface potentials of the same sign, there can be a significant increase in protein mobility for medium-sized pores.

NOVEL EPOXIDATION CATALYST Titanium complex anchored inside zeolite

Scientists at the Davy Faraday Laboratory of the Royal Institution of Great Britain have created a new catalyst for epoxidizing olefins by anchoring titanium metal complexes to the inner walls of a mesoporous zeolite (with medium-sized pores). The work extends the advantages of zeolites' shape selectivity to molecules that are too big to fit into the smaller channels of microporous zeolites. And opens a new route for preparing novel catalysts with large concentrations of well-spaced and structurally welldefined catalytic sites. The new catalyst—developed by a group including Thomas Maschmeyer, Fernando Rey, and Gopinathan Sankar, under the direction of Sir John Meurig Thomas—has been successfully tested on cyclohexene and pinene [ Nature , 378 , 159 (1995)]. Thomas regards the work as some of the best he has been involved with in catalysis because it is a new strategy for producing high-performance, mesoporous inorganic catalysts. Industry observers express interest, but they are withholding judgment...

Wettability Literature Survey Part 5: The Effects of Wettability on Relative Permeability

The wettability of a core will strongly affect its waterflood behavior and relative permeability. Wettability affects relative permeability because it is a major factor in the control of the location, flow, and distribution of fluids in a porous medium. In uniformly or fractionally wetted porous media, the water relative permeability increases and the oil relative permeability decreases as the system becomes more oil-wet. In a mixed-wettability system, the continuous oil-wet paths in the larger pores alter the relative permeability curves and allow the system to be waterflooded to a very low residual oil saturation (ROS) after the injection of many PV's of water. The most accurate relative permeability measurements are made on native-state core, where the reservoir wettability is perserved. Serious errors can result when measurements are made on cores with altered wettability, such as cleaned core or core contaminated with drilling-mud surfactants.

Techniques for Mapping and Diagnosing EOR Processes

Diagnostic methods for tracking EOR processes have evolved considerably during recent years. Because each technique can provide different information about specific EOR processes, selection of the best technique for a problem must be done on a case-by-case basis. This paper describes techniques available for evaluating and diagnosing EOR processes and problems and presents selection criteria for each. Two examples are given to illustrate how a suite of techniques can be chosen.

Effect of air-drying and critical point drying on the porosity of clay soils

Samples from four surface and one subsurface horizons of clay-rich soils from Quebec were air-dried and critical point dried. In the latter samples, the total pore volume was 19–84% larger than in the former samples. The total pore volume, determined by mercury intrusion porosimetry and density measurements, was subdivided into large (&gt; 8.8 μm), medium, and small (&lt; 0.19 μm) pores. The effect of drying on these pores was estimated. Medium-sized pores were affected most by the drying technique, followed next by the large pores, and finally by the small pores. The modifications due to drying could not be explained adequately by shrinkage and it was assumed, from the pore-size distribution curves, that organic matter content had a buffer effect on particle reorganization. Keywords: critical point drying, clay soils, pore volume, pore-size distribution, organic matter.