Bimodal Pore Size Distribution Research Articles

Mesoporous zirconia-modified clays supported nickel catalysts for CO and CO2 methanation

The Ni catalysts supported on a new structure with zirconia nanoparticles highly dispersed on the partly damaged clay layers has been prepared by the incipient wetness impregnation method and the new structure of the support has been prepared in one pot by the hydrothermal treatment of the mixture of the clay suspension and the ZrO(NO3)2 solution. The catalytic performances for the CO and CO2 methanation on the catalysts have been investigated at a temperature range from 300 °C to 500 °C at atmospheric pressure. The catalysts and supports have been characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). It is found that the zirconia-modified clays have the typical bimodal pore size distribution. Most of the pores with the sizes smaller than 10 nm are resulted from the zirconia pillared clays and the mesopores with the sizes larger than 10 nm and the macropores with the sizes larger than 50 nm are resulted from the partly damaged clay layers. The bimodal pore structure is beneficial to the dispersion of Ni on the layers of the zirconia-modified clays and the increase in Ni loading. The zirconia nanoparticles are highly dispersed on the partly damaged clay layers. Nickel oxide in cubic phase is the only Ni species that can be detected by XRD. The nickel oxide nanoparticles with the sizes of 12 nanometers or more are well dispersed on the zirconia-modified clay layers, which are observed to be buried in the stack layers of zirconia. The presence of nickel oxide in six different forms could be perceived on the new structure. Five of them except the Ni species that forms the spinel phase with Al in clays can be reduced to the active Ni species for the CO and CO2 methanation. But the activity of the Ni species is different, which is associated with the chemical environment at which the Ni species is located. The catalyst with the higher zirconia content, which also has the larger specific surface area and pore volume, exhibits the better catalytic performance for the CO or CO2 methanation. Zirconia in the catalyst is responsible for the dispersion of the Ni species, and it prevents the metallic Ni nanoparticles from sintering during the process of the reaction. In addition, it is also responsible for the reduction of the inactive carbon deposition. The catalyst with 15 wt.% zirconia content has the highest CO conversion of about 100% and the highest methane selectivity of about 93% at 450 °C for CO methanation, and the catalyst with 20% zirconia content has the CO2 conversion of about 80% and the highest methane selectivity of about 99% for CO2 methanation at 350 °C. The catalyst with 15 wt.% zirconia possesses promising stability and no distinct deactivation could be perceived after reaction for 40 h. This new catalyst has great potential to be used in the conversion of the blast furnace gas (BFG) and the coke oven gas (COG) to methane.

SAWCal: A user-friendly program for calculating soil available water quantities and physical quality indices

Conventional plant available water (PAW), least limiting water range (LLWR), integral water capacity (IWC) and integral energy (EI) are different approaches to quantify the soil water availability for plants. The PAW, the soil water between field capacity (FC) and permanent wilting point (PWP), is based merely on the soil matric potential. The LLWR in addition considers oxygen deficit and high soil penetration resistance limitations for plant growth excluding some of the restrictions of the PAW concept. The IWC approach adapts better with natural phenomena since it considers that the impacts of soil physical limitations on water uptake by plants are gradual and not in a cut-off form. Nevertheless, its calculation is laborious and time-consuming. The EI quantifies the energy required by plants to remove a unit amount of water from the soil over the available water range. As more attention is given to new soil available water (SAW) approaches nowadays, developing an algorithm and computer graphical user interface (GUI) for calculation of these indices (especially the IWC) would help to popularize the approaches’ application. Here we report the development of a software called SAWCal (Soil Available Water Calalculator) for calculating PAW, LLWR, IWC, and EI and related quantities. It also calculates the soil physical quality index (S), the slope of the water retention curve at its inflection point, proposed by Dexter (2004a,b,c). This software only needs the parameters of soil water retention and soil penetration resistance models. The C#, being an evolution of C++, as an object-oriented programming (OOP) was employed to develop the program. The parameters of single-porosity van Genuchten (1980) and dual-porosity Durner (1994) models are used to characterize the water retention and hydraulic conductivity functions for the soils with uni- and bi-modal pore size distributions, respectively. For establishing a continuous function of soil penetration resistance vs. matric suction, SAWCal uses a modified van Genuchten (1980) model or a power model depending on the user’s choice. When needed, the integration is performed numerically. SAWCal is a help-assisted user-friendly GUI to guide the user step-by-step through the procedures. It is also possible to export the program outputs in ASCII format compatible with MS Office and text-editing programs. The software is provided as a free supplementary material to this paper.

Near‐Net‐Shape Fabrication of Ti3SiC2‐based Ceramics by Three‐Dimensional Printing

This paper focuses on the preparation of near‐net‐shaped dense Ti3SiC2‐based materials via an indirect three‐dimensional printing (3D printing) and postreactive melt infiltration (RMI) processes. TiC preforms with bimodal pore size distribution were fabricated through 3D printing, followed by the infiltration of Si melt and Al–Si alloy (Al40Si60 and Al70Si30). Dense composites with density of ~4.1 g/cm3 were obtained after the infiltration. No volume shrinkage was obtained after the reactive infiltration with Al–Si alloy. The participation of Al during the infiltration process promoted the formation of Ti3SiC2. The as‐fabricated Ti3SiC2‐based materials showed enhanced mechanical and electromagnetic interference shielding properties.

Preparation of poly(γ-glutamic acid)/hydroxyapatite monolith via biomineralization for bone tissue engineering

A hybrid monolith of poly(γ-glutamic acid) and hydroxyapatite (PGA/HAp monolith) was prepared via biomineralization and used as a macroporous cell scaffold in bone tissue engineering. The PGA monolith having a bimodal pore size distribution was used as a substrate to induce biomineralization. The PGA/HAp monolith was obtained by immersing the PGA monolith in simulated body fluid. Pretreatment with CaCl2 enhanced the apatite-forming ability of the PGA monolith. Murine osteoblastic MC3T3-E1 cells efficiently attached and proliferated on the PGA/HAp monolith. MTT assay showed that both the PGA and PGA/HAp monolith did not have apparent cytotoxicity. Moreover, the PGA and PGA/HAp monoliths adsorbed bone morphogenetic protein-2 (BMP-2) by electrostatic interaction which was slowly released in the medium during cell culture. The PGA/HAp monolith enhanced BMP-2 induced alkaline phosphatase activity compared to the PGA monolith and a polystyrene culture plate. Thus, these PGA/HAp monoliths may have potential in bone tissue engineering.

Porous carbon material based on petroleum pitch

The samples of granulated (2–4 mm) porous carbon material with unimodal and bimodal poresize distributions were prepared. The sample with a unimodal porous structure was prepared via the mixing of soot and petroleum pitch followed by carbonization (the first stage). At the second stage, the carbon material obtained was ground to a particle size smaller than 0.2 mm, mixed with petroleum pitch, and also subjected to carbonization. The porous structures of these materials were studied by scanning electron microscopy and mercury porosimetry. It was established that the predominant pore size (20–1000 nm) of the samples with the unimodal structure depends on the used soot grade. At the second stage of the process, a considerable volume of pores in a range of 4–12 μm is formed in the production of bidisperse material. As compared with a sample with the monodisperse structure, porous carbon material with a bimodal distribution of pores was characterized by a lower crushing strength of granules and comparable specific surface areas, total pore volumes, and ash contents.

Enhanced CO Tolerance of PEFC Anode Catalyst by Optimized Degree of Activation of Resorcinol-Formaldehyde Carbon Support

1. Introduction Carbon monoxide contaminations in hydrogen reforming from hydrocarbon can cause a serious problem for PEFC performance [1]. Even a commercial platinum–ruthenium alloy catalyst which well-know as the highest CO tolerance cannot accept H2 with CO contamination higher than 300 ppm. The highly dispersed and high-alloy degree Pt2Ru3/C was found to be much higher CO tolerance than that of commercial Pt2Ru3/C [2]; however, effect of carbon support was still unclear. Resorcinol-formaldehyde Carbon gel is attracting more attention for its high electrical conductivity, high surface area and mesoporosity; moreover, pore characters are adjustable by vary of synthesis condition [3]. In this work, effect of porosity of carbon support on CO tolerance was investigated. 2. Experiment Resorcinol-formaldehyde carbon was prepared at a fixed R/C ratio of 1400, and degrees of activation were 0%(no activation), 42% and 58%, Rc1400 ac0, ac37 and ac58, respectively. Pt2Ru3 was deposited on RC1400 by rapid quenching method (30wt%Pt-25wt%Ru/C) [2]. The catalysts were characterized by XRD, BET surface area, STEM. The anodes were tested in 5 cm2 membrane electrode assemblies (MEA). The CO tolerance experiments were performed at constant current density mode (0.2 A/cm2) First, pure H2 flow for one hour and then introduce 100 ppm of CO in H2for 2 hours, followed by 500 ppm, 1000 ppm, and 2000 ppm in every 2 hours. 3. Results Rc1400 ac42 and ac58 have meso-micro pore structure with bimodal pore size distribution. In Table 1 , it showed that an increase in degrees of activation from ac0 to ac42, only mesopore increases with maintaining regular mesopore structure of Rc1000, and not much micropore increased (compare with later result) resulting in increase in BET surface area. But form ac42 to ac 58, degree of activation increased with micropore volume from 0.471 to 1.576 cm3g-1. Crystallite size of metal particle also depend on density of micropore, Pt2Ru3/RC1400ac0 showed biggest crystallite size at 4.2 nm. Following by commercial Pt2Ru3/C but other two catalysts was 2.3-2.5 nm. It can be seeing that surface area have direct relation to crystallite size but after some point there are not much effect. As in case of Pt2Ru3/RC1400ac42 and Pt2Ru3/RC1400ac58, even surface area was very different (1215 m2g-1) but the crystallite size was not much diffent (0.2 nm) As shown in Fig. 1, cell voltage at 0.2 A/cm2 drops from 0.76 to 0.59 V (24.4%) for Pt2Ru3/Rc1400ac58 while the voltage drops from 0.75 to 0.4 (46.7%) for commercial Pt2Ru3/C. Pt2Ru3/RC1400ac37 catalysts have superior CO tolerance to commercial Pt2Ru3/C. Pt2Ru3/Rc1000ac42 and Pt2Ru3/Rc1000ac0 has lower efficiency and CO tolerance than commercial Pt2Ru3/C. These results indicate that small Pt2Ru3particles and higher density of the mesopores is important for CO tolerance. In the other hand, surface area and micropore density does not much influent CO tolerance of PEFC anode catalyst.These studies could lead to significant knowledge of metal support interaction, and Resorcinol-Formaldehyde carbon gel can be a promising support for future development of CO tolerance catalyst for PEFC. Table 1 Physical properties of Pt2Ru3/Rc1400 catalysts compare with commercial Pt2Ru3/C catalystPt2Ru3/RC 1400Surface area of support (m2g-1)Micro- pore Volume (CM3g-1)Mesopore Volume (CM3g-1)Crystallite size by XRD (nm)Ac 0Ac 42Ac 58 619193327480.2310.4711.5760.1750.4670.4674.22.52.3CommercialCatalyst827--3.4 Figure 1 F igure 1 Effect of CO concentration on cell voltage at 0.2 A/cm2. Cell temp.: 70oC; Electrolyte: Nafion® NRE 212; Cathode: Pt/C (0.5 mg/cm2 ); O2 humidified at 70oC; Flow rate: 80 mL/min; Anode: Pt2Ru3/C (0.5 mg-PtRu/cm2 ); H2 containing 0-2000 ppm CO humidified at 70oC; Flow rate: 80 mL/min.

Degradation of benzene on Zr-doped TiO2 photocatalysts with a bimodal pore size distribution

Zr-doped TiO2 was prepared from TiOSO4 and ZrOCO3 by a co-precipitation method using NH3·H2O as the precipitation agent. The Zr-doped TiO2 was characterized by X-ray diffraction (XRD), low temperature N2 adsorption–desorption measurement, and UV–Vis diffuse reflectance spectroscopy technology. Appropriate amounts of ZrO2 addition can greatly improve the TiO2 microstructure properties and its photocatalytic activities. In addition, polyethylene glycol (PEG) was used as a surfactant for templating the pore structure of samples. A bimodal pore structure can be controlled using PEG6000 and PEG20000 surfactants simultaneously during the preparation. The rate constant of benzene degradation over the Zr-doped TiO2 linearly decreases with the increase of photocatalytic reaction temperature and decreases in a polynomial relation with the benzene concentration. Moreover, it increases approximately linearly with the increase of the illumination intensity or area.

Preparation and evaluation of monolithic poly(N-vinylcarbazole-co-1,4-divinylbenzene) capillary columns for the separation of small molecules.

Short-term polymerization or the so-called low-conversion polymerization was applied for the preparation of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) monolithic capillary columns. The synthesis was carried out by thermally initiated free radical copolymerization under the influence of inert micro- (toluene) and macroporogen (1-decanol) and α,α'-azoisobutyronitrile (AIBN) as radical initiator. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen adsorption, and mercury intrusion porosimetry (MIP). The copolymerization process was studied by monomer conversion measurements. This approach led to increased porosity and specific surface area. A specific surface area above 400m(2)/g of the monolith and a distinct bimodal pore size distribution were obtained. The chromatographic performance was determined in terms of theoretical plate heights and number of theoretical plates. The lowest plate height value was found to be 3.9μm (corresponding to ≈256,000 plates per meter) applying methylparaben utilizing an 80mm × 0.2mm i.d. monolithic capillary. The developed NVC/DVB monolithic supports showed high separation efficiency towards small molecules, which was exemplified applying reversed-phase (RP) separation of alkylbenzenes, beta-blockers, flavanoids, parabens, and phenones. The loading capacity was analyzed for isocratic separation of seven alkylbenzenes and was found to be up to 77ng total mass of alkylbenzenes. Furthermore, a long-term stability test of 1,000 consecutive runs was performed and resulted in a maximum variance of 0.97, 0.85, and 0.16% RSD for resolution, peak width at half height, and retention times, respectively. The material was proven to have a high permeability of 1.11E-14m(2), applying water as a mobile phase.

Synthesis of carbon with bimodal porosity by simultaneous polymerization of furfuryl alcohol and phloroglucinol

Carbon materials with bimodal porosity have shown enhanced performance in a wide variety of applications including catalysis, energy storage and fluid separation. Presence of mesoporosity is essential to lower the mass transfer limitation imposed by the microporous nature of the carbons. The synthesis approaches used to prepare bimodal carbons with controlled micro/mesopore size and narrow pore size distribution, usually involve multi step processes and the use of harsh chemicals and solvents. Herein, we present a simple one step method that can be used to synthesize carbon with bimodal pore size distribution. Simultaneous polymerization of furfuryl alcohol and phloroglucinol-formaldehyde in the presence of a structure-directing agent (Pluronic F-127) was carried out and the resultant polymer was pyrolyzed to yield the bimodal carbon. Effect of polymerization conditions such as concentrations of monomer, initiator and surfactant on the bimodal pore size distribution of the carbon was studied in detail. Pyrolyzed precursors form carbons with narrow mean micropore size of 0.5nm and mean mesopores ranging from 3.5 to 6nm. The range of the mesopore size could be altered by varying the polymerization parameters (acid and surfactant concentration) as well as selective oxidation using CO2 gas.

Bimodal pore size distribution of a high-plasticity compacted clay

The microstructure of compacted clay plays an important role in its hydraulic and mechanical behaviour. However, little experimental evidence is available for high-plasticity clay compacted on the wet side of the standard Proctor optimum water content. The results of an oedometric and microstructural investigation (mercury intrusion porosimetry) on reconstituted and compacted high-plasticity clay are presented. The microstructural results indicate that a bimodal pore size density function is not limited to clays compacted on the dry side of the standard Proctor optimum. The compacted clay prepared on the wet side can display a bimodal pore size distribution dependent on the level of compaction, current void ratio and degree of saturation. The bimodal distribution of the compacted clay can be lost by compression to high vertical stress accompanied by an increase in the degree of saturation. In this case the compression path ultimately approaches the normal compression line of the reconstituted saturated material. The results demonstrate that the observed behaviour of the compacted clay can be interpreted with reference to the reconstituted clay.

Zeolite decorated highly porous acicular calcium silicate ceramics

Macrocellular calcium silicate (wollastonite) ceramic foams possessing ~86vol% total porosity were produced from commercial calcium silicate hydrate (xonotlite) nano-size acicular crystals and poly-methyl-methacrylate microbeads (PMMA) (used as sacrificial pore formers). Open cell wollastonite foams had a bi-modal pore size distribution with major modes located ~100nm due to interparticle porosity and ~100µm due to the sacrificial pore former. These macrocellular ceramics were then used as a scaffold for MFI type zeolite (silicalite-1) synthesis. Monolayer coffin shaped zeolite crystals (~3µm size, measured from the c-axis and ~300nm thickness) were observed with almost full coverage on the inner macro-cell walls. The specific surface area of the components increased from 9.6m2/g to 108.2m2/g via zeolite functionalization, leading to components possessing multiscale porosity.

Infiltrating sulfur into a highly porous carbon sphere as cathode material for lithium–sulfur batteries

Sulfur composite material with a highly porous carbon sphere as the conducting container was prepared. The highly porous carbon sphere was easily synthesized with resorcinol–formaldehyde precursor as the carbon source. The morphology of the carbon was observed with field emission scanning electron microscope and transmission electron microscope, which showed a well-defined spherical shape. Brunauer–Emmett–Teller analysis indicated that it possesses a high specific surface area of 1563m2g−1 and a total pore volume of 2.66cm3g−1 with a bimodal pore size distribution, which allow high sulfur loading and easy transportation of lithium ions. Sulfur carbon composites with varied sulfur contents were prepared by melt–diffusion method and lithium sulfur cells with the sulfur composites showed improved cyclablity and long-term cycle life.

Fabrication and Characterization of Graded Anodes for Anode-Supported Solid Oxide Fuel Cells by Tape Casting and Lamination

Graded anodes for anode-supported solid oxide fuel cells (SOFCs) are fabricated by tape casting and subsequent cold lamination of plates using different compositions. Rheological parameters are adjusted to obtain stable suspensions for tape casting. The conditions for the tape casting and lamination will be described. Flexural strength of the reduced cermets measured using three-point bending configuration is 468 ± 37 MPa. The graded anode supports are characterized by scanning electron microscope observations, mercury porosimetry intrusion, and resistivity measurements, showing an adequate and homogeneous distribution of nickel, zirconia, and pores. The laminated samples showed a total porosity of 18.7 % (in vol%) and a bimodal pore size distribution centered in 20 and 150 nm, and the measured electrical resistivity of this sample was 120 ± 12 μΩ cm. The novelty of the present work is the lamination of tapes at room temperature without using plasticizers. This is made by the combination of two different binders with varying Tg (glass transition temperature) which resulted in plastic deformation at room temperature. Those results indicate that the proposed process is a cost-effective method to fabricate anode-supported SOFCs.

Synthesis of a new ordered mesoporous NiMoO4 complex oxide and its efficient catalytic performance for oxidative dehydrogenation of propane

Highly ordered mesoporous NiMoO4 material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2 adsorption-desorption, Raman and FT-IR. The mesoporous NiMoO4 with the coexistence of α-NiMoO4 and β-NiMoO4 showed well-ordered mesoporous structure, a bimodal pore size distribution and crystalline framework. The catalytic performance of NiMoO4 was investigated for oxidative dehydrogenation of propane. It is demonstrated that the mesoporous NiMoO4 catalyst with more surface active oxygen species showed better catalytic performance in oxidative dehydrogenation of propane in comparison with bulk NiMoO4.

3D ordered nanoporous NiMoO4 for high-performance supercapacitor electrode materials

3D ordered nanocrystalline nanoporous NiMoO4 with high surface area and bimodal pore size distribution has been synthesized by nanocasting from mesoporous silica KIT-6, and applied as high-performance supercapacitor electrode material.

Hollow core@mesoporous shell boron nitride nanopolyhedron-confined ammonia borane: a pure B–N–H composite for chemical hydrogen storage

Ammonia borane-derived boron nitride nanopolyhedra with a hollow core@mesoporous shell structure displaying a specific surface area of 200.5 m2 g−1, a total pore volume of 0.287 cm3 g−1 and a bimodal pore size distribution were successfully prepared and used as nanoscaffolds to improve the dehydrogenation properties of ammonia borane by an exclusive nanoconfinement effect.

Microstructural control of porous Al<sub>2</sub>TiO<sub>5</sub> by using various starches as pore-forming agents

Porous Al2TiO5 ceramics with various starches as pore-forming agents have been prepared by the reactive sintering method using fine-grained starting materials. Commercially available corn, potato and rice starches were used as the pore forming agents. TG–DTA and XRD studies revealed that the rice starch most promoted the formation of Al2TiO5 among the three starches, presumably due to its strong heat flow during the combustion. Al2TiO5 samples sintered with each starch contained a bimodal pore-size distribution, viz., slit-like pores with the size of <~20 µm, and continuous open-pores with the size of several µm. The thermal expansion behavior of the sample with 30 wt.% rice starch was similar to those without starch.

Mesoporous titania thin films as efficient enzyme carriers for paraoxon determination/detoxification: effects of enzyme binding and pore hierarchy on the biocatalyst activity and reusability.

In this work we demonstrate the efficient immobilization of histidine 6-tagged organophosphate hydrolase (His6-OPH), an organophosphate-degrading enzyme, on mesoporous titania thin films. This permits the use of the biocatalyst films as efficient tools in the detection/detoxification of paraoxon. His6-OPH was immobilized on mesoporous thin films with uniform (9 nm) and bimodal (13-38 nm) pore size distribution, through covalent attachment and physical adsorption. The biocatalyst films show good activity, and enhanced stability with respect to the free enzyme at extreme conditions of pH and temperature, especially around neutral pH and room temperature. In addition, the bioactive films can be easily separated from the reaction media and reused multiple times without significant loss of activity.

Bimodal porous gold opals for molecular sensing

We have fabricated bimodal porous gold skeletons by double-templating routes using poly(styrene) colloidal opals as templates. The fabricated gold skeletons show a bimodal pore-size distribution, with small pores within spheres and large pores between spheres. The templated bimodal porous gold skeletons were applied in Raman scattering experiments to study sensing efficiency for probe molecules. We found that the bimodal porous gold skeletons showed obvious enhancement of Raman scattering signals versus that of the unimodal porous gold which only has interstitial pores of several hundred nanometers.

Development of novel LSM/GDC composite and electrochemical characterization of LSM/GDC based cathode-supported direct carbon fuel cells

(La0.8Sr0.2)0.95MnO3−δ (LSM)–Gd0.1Ce0.9O2−δ (gadolinium-doped ceria, GDC) composite cathode material was developed and characterized in terms of chemical stability, sintering behaviour, electrical conductivity, mechanical strength and microstructures to assess its feasibility as cathode support applications in cathode-supported fuel cell configurations. The sintering inhibition effect of LSM, in the presence of GDC, was observed and clearly demonstrated. The mechanical characterization of developed composites revealed that fracture behaviour is directly affected by pore size distribution. The Weibull strength distribution showed that for bimodal pore size distribution, two different fracture rates were present. Furthermore, the contiguity of LSM and GDC grains was calculated with image analysis, and correlation of microstructural features with mechanical and electrical properties was established. Subsequently, an LSM/GDC-based cathode-supported direct carbon fuel cell (DCFC) with Ni/ScSZ (scandia-stabilised zirconia) anode was successfully fabricated via slurry coating and co-firing techniques. The microstructures of electrodes and electrolyte layers were observed to confirm the desired morphology after co-sintering, and a single cell was electrochemically characterized in solid oxide fuel cell (SOFC) and DCFC mode with ambient air as oxidant. The higher values of open-circuit voltage indicated that the electrolyte layer prepared by vacuum slurry coating is dense enough. The corresponding peak power densities at 850 °C were 450 and 225 mW cm−2 in SOFC and DCFC mode, respectively. Electrochemical impedance spectroscopy was carried out to observe electrode polarization and ohmic resistance.