Loss Of Pore Volume Research Articles

Fine quantitative characterization of high-H2S gas reservoirs under the influence of liquid sulfur deposition and adsorption

In order to clarify the influence of liquid sulfur deposition and adsorption to high-H2S gas reservoirs, three types of natural cores with typical carbonate pore structures were selected for high-temperature and high-pressure core displacement experiments. Fine quantitative characterization of the cores in three steady states (original, after sulfur injection, and after gas flooding) was carried out using the nuclear magnetic resonance (NMR) transverse relaxation time spectrum and imaging, X-ray computer tomography (CT) of full-diameter cores, basic physical property testing, and field emission scanning electron microscopy imaging. The loss of pore volume caused by sulfur deposition and adsorption mainly comes from the medium and large pores with sizes bigger than 1 000 μm. Liquid sulfur has a stronger adsorption and deposition ability in smaller pore spaces, and causes greater damage to reservoirs with poor original pore structures. The pore structure of the three types of carbonate reservoirs shows multiple fractal characteristics. The worse the pore structure, the greater the change of internal pore distribution caused by liquid sulfur deposition and adsorption, and the stronger the heterogeneity. Liquid sulfur deposition and adsorption change the pore size distribution, pore connectivity, and heterogeneity of the rock, which further changes the physical properties of the reservoir. After sulfur injection and gas flooding, the permeability of Type I reservoirs with good physical properties decreased by 16%, and that of Types II and III reservoirs with poor physical properties decreased by 90% or more, suggesting an extremely high damage. This indicates that the worse the initial physical properties, the greater the damage of liquid sulfur deposition and adsorption. Liquid sulfur is adsorbed and deposited in different types of pore space in the forms of flocculence, cobweb, or retinitis, causing different changes in the pore structure and physical property of the reservoir.

Stress sensitivity of carbonate gas reservoirs and its microscopic mechanism

In order to evaluate the stress sensitivity of carbonate reservoirs, a series of rock stress sensitivity tests were carried out under in-situ formation temperature and stress condition. Based on the calibration of capillary pressure curve, the variable fractal dimension was introduced to establish the conversion formula between relaxation time and pore size. By using the nuclear magnetic resonance (NMR) method, the pore volume loss caused by stress sensitivity within different scales of pore throat was quantitatively analyzed, and the microscopic mechanism of stress sensitivity of carbonate gas reservoirs was clarified. The results show that fractures can significantly affect the stress sensitivity of carbonate reservoirs. With the increase of initial permeability, the stress sensitivity coefficient decreases and then increases for porous reservoirs, but increases monotonously for fractured-porous reservoirs. The pore volume loss caused by stress sensitivity mainly occurs for mesopores (0.02–0.50 μm), contributing more than 50% of the total volume loss. Single high-angle fracture contributes 9.6% of the stress sensitivity and 15.7% of the irreversible damage. The microscopic mechanism of the stress sensitivity of carbonate gas reservoirs can be concluded as fracture closure, elastic contraction of pores and plastic deformation of rock skeleton.

Graphene Aerogel‐Supported Phase‐Change Material for Pyroelectric Energy Harvesting: Structural Modification and Form Stability Analysis

3D porous graphene aerogel (GA) has a capability to infiltrate plenty of phase‐change materials (PCM) into the internal pore. Since carbon‐based materials can offer excellent solar light absorption and conversion of thermal energy, they are widely used as container‐like supporting materials. In general, the GA shows a volume shrinkage problem due to the capillary force during the infiltration process, thus causing a loss in pore volume, that is, PCM weight loss. The PCM amount is proportional to both the absorbed and released thermal energies. Herein, cysteamine is introduced to bind GA. The PCM composite can reduce the volume shrinkage and have an excellent form stability even under the external force. Two kinds of PCMs are connected to a pyroelectric electrode to generate electrical energy. In addition, finite‐element method estimates the temperature profile and electrical peaks to confirm experimental results.

Structural evolution of TiN catalysts during mechanocatalytic ammonia synthesis.

Mechanocatalytic ammonia synthesis is a novel approach toward ammonia synthesis under mild conditions. However, many open questions remain about the mechanism of mechanocatalytic ammonia synthesis, as well as the structure of the active catalysts during milling. Herein, the structural evolution of an in situ synthesized titanium nitride catalyst is explored during extended milling. The yield of ammonia bound to the catalyst surface was found to strongly correlate with an increase in catalyst surface area during milling, although a lower surface concentration of ammonia at earlier milling times suggests a delay in ammonia formation, corresponding to the conversion of the titanium metal pre-catalyst into the nitride. Small pores develop in the catalyst during milling due to interstitial spaces between agglomerated titanium nitride nanoparticles, as shown by SEM and TEM. In the first 6 h, the titanium is both converted to a nitride and fractured to smaller particles, before an equilibrium state is reached. After 18 h of milling, the catalyst nanoparticles appear to crystallize into a denser material, resulting in a loss of surface area and pore volume.

Experimental Characterization of Anisotropic Mechanical and Thermal Properties of Gas Diffusion Layers

Gas diffusion layer (GDL) is a vital component in proton exchange membrane fuel cells (PEMFC) due its main functions to conduct electrons and heat between the adjacent fuel cell components, provide preferential pathways for product water removal and to provide uniform reactant gas flow distribution to the electrode surface. Because of the anisotropic GDL microstructure, the transport properties vary in the through-plane and in-plane direction. Furthermore, during fuel cell stack assembly pressures exerted on the flowfield land compress the GDL under land cause changes of the GDL microstructure. While moderate compression increases GDL thermal conductivity due to increased fiber-fiber contacts, excessive compression may impede diffusive and liquid water transport due to loss of GDL pore volume. Detailed knowledge of how thermal conductivity is affected by the anisotropic nature of gas diffusion layers under compression is imperative in order to provide a better understanding on how thermal gradients influence two-phase transport during PEMFC operation. Previous research efforts have focused on steady-state methods for measuring effective through-plane GDL thermal conductivity [1][2][3][4] and effective in-plane GDL thermal conductivity [5][6] but to the best of our knowledge no studies have been conducted to measure effective in-plane GDL thermal conductivity for a variety of different GDL types under compression.This study attempts to fill that gap by using specially designed in-house tools to characterize the influence of GDL anisotropy on effective thermal conductivity as a function compression for different GDL types. Furthermore, a comprehensive ex-situ mechanical study is conducted to characterize the compliance matrix for different GDL types. Early results indicate a highly non-linear compressive behaviour in the GDL through-plane direction with large variations for the different GDL types. Moreover, the flexural modulus is found to be highly anisotropic where stiffness in the GDL machine direction (MD) is consistently larger compared to stiffness in GDL cross machine direction (CMD). This work will provide a foundation for a numerical study to couple an anisotropic GDL structural model with a non-isothermal two-phase model to investigate the effects of inhomogenous compression on two-phase transport. Keywords: GDL, PEMFC, ex-situ, anisotropy, modulus, microstructure, mechanical, compression, characterization, MD, CMD, through-plane, in-plane, thermal conductivity[1] G. Karimi, X. Li, P. Teertstra, Electrochim. Acta (2010).[2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I. V. Zenyuk, O.S. Burheim, J. Electrochem. Soc. 165 (2018) F514–F525.[3] G. Unsworth, N. Zamel, X. Li, Int. J. Hydrogen Energy (2012).[4] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[5] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[6] N. Alhazmi, D.B. Ingham, M.S. Ismail, K.J. Hughes, L. Ma, M. Pourkashanian, Int. J. Hydrogen Energy (2013).

Evaluating the Ability of Bone Char/nTiO2 Composite and UV Radiation for Simultaneous Oxidation and Adsorption of Arsenite

The reuse of waste materials for water treatment purposes is an important approach for promoting the circular economy and achieving effective environmental remediation. This study examined the use of bone char/titanium dioxide nanoparticles (BC/nTiO2) composite and UV for As(III) and As(V) removal from water. The composite was produced via two ways: addition of nTiO2 to bone char during and after pyrolysis. In comparison to the uncoated bone char pyrolyzed at 900 °C (BC900), nTiO2 deposition onto bone char led to a decrease in the specific surface area and pore volume from 69 to 38 m2/g and 0.23 to 0.16 cm3/g, respectively. However, the pore size slightly increased from 14 to 17 nm upon the addition of nTiO2. The composite prepared during pyrolysis (BC/nTiO2)P had better As removal than that prepared after pyrolysis with the aid of ultrasound (BC/nTiO2)US (57.3% vs. 24.8%). The composite (BC/nTiO2)P had higher arsenate oxidation than (BC/nTiO2)US by about 3.5 times. Arsenite oxidation and consequent adsorption with UV power of 4, 8 and 12 W was examined and benchmarked against the composite with visible light and BC alone. The highest UV power was found to be the most effective treatment with adsorption capacity of 281 µg/g followed by BC alone (196 µg/g). This suggests that the effect of surface area and pore volume loss due to nTiO2 deposition can only be compensated by applying a high level of UV power.

Macroscopic and Mesoscopic Deterioration Behaviors of Concrete under the Coupling Effect of Chlorine Salt Erosion and Freezing-Thawing Cycle.

The aim of this study was to reveal the macroscopic and mesoscopic deterioration behaviors of concrete under the coupling effect of chlorine salt erosion and the freezing–thawing cycle. The rapid freezing–thawing test was carried out in a 5% chlorine salt environment. The macroscopic characteristics of concrete were analyzed by testing the mass, the relative dynamic modulus of elasticity, and the compressive strength of concrete under different freezing–thawing cycles. Using CT scanning technology and three-dimensional reconstruction technology, the pore structure, CT value, and surface deviation of concrete before and after freezing–thawing were analyzed. Based on the changes of solid volume, pore volume, and solid CT value of concrete, the calculation method of relative CT value was proposed, and the damage model was established with relative CT value as the damage variable. The results demonstrate that the mass loss rate decreases in the beginning and then increases in the process of chlorine salt erosion and freezing–thawing, and the smaller the concrete size, the greater the mass loss rate. The relative dynamic modulus of elasticity decreases gradually, slowly at the initial stage and then at a faster rate, and the compressive strength loss rate increases gradually. The pore quantity, porosity, and volume loss rate of concrete increase in a fluctuating manner, whereas the relative CT value decreases. The comprehensive analysis shows that the chlorine salt frost resistance of concrete is negatively related to the water-cement ratio when the freezing–thawing cycle is fixed. The damage model could better reflect the freezing–thawing damage degree of concrete with different water cement ratios, and the damage evolution process is well described by the Weibull function.

Insights in the phenomena involved in deactivation of industrial hydrocracking catalysts through an accelerated deactivation protocol

A representative accelerated experimental deactivation procedure was developed to understand the activity loss of bifunctional vacuum gasoil (VGO) hydrocracking catalysts over time. Experiments were performed in an up-flow fixed-bed pilot unit with a typical vacuum gas oil feedstock. The deactivation was measured by tracking the decrease of VGO conversion (370 °C+) with time on stream. The catalyst consisted of nickel-molybdenum sulfide particles dispersed on a carrier containing USY zeolite. The impact of temperature, liquid hourly space velocity (LHSV), hydrogen to hydrocarbon (H2/HC) ratio and organic nitrogen (Norg) on the catalyst deactivation rate was first studied. The variables with the most significant impact on conversion loss were temperature and space velocity. Temperature directly influences the production rate of coke precursors, whereas space velocity affects the local concentration of feed contaminants along the reactor. Based on these results, the following operating conditions were selected to establish the final accelerated deactivation experimental protocol: T = 418 °C, LHSV = 3 h−1, H2/HC = 1500NL/L, P = 14 MPa, organic nitrogen content (Norg) = 150 ppm weight, total nitrogen content = 2500 ppm weight and a total time on stream of 30 days. Spent samples from this procedure presented similar properties to some industrial catalysts submitted to cycle lengths between 12 and 18 months. Both types of samples yield similar values of surface area and pore volume loss as well as a similar amount and nature of coke deposits. These results led to the qualitative validation of the protocol representativeness. This experimental procedure was then used to get more insight into the deactivation phenomenon. It was found that the organic nitrogen content of the feedstock is crucial, as it determines the ratio between available metal and acid sites. This ratio determines the reactions that take place and, therefore, the type of coke produced.

Optimizing acido-basic profile of support in Ni supported La2O3+Al2O3 catalyst for dry reforming of methane

The increasing alarm of global warming always draws interest in reactions like dry reforming of methane (DRM) where both global warming gases (CO2 and CH4) are converted into value-added chemical building blocks, such as syngas. Nickel catalyst active sites along with support acid-base profiles play a key role in DRM. Herein, xLa2O3+(100-x) Al2O3 (x = 0, 10, 15, 20%) supports are prepared and followed by NiO dispersion over the produced support by impregnation method. It was tested for DRM reaction and characterized with TGA, XRD, TEM, IR, Surface area and porosity measurement, H2-TPR, CO2-TPD and NH3-TPD techniques. Upon increasing the basic lanthana proportion in the acidic alumina support, the crystallinity of alumina and acidity of total support decline. Up to 15% Lanthana addition in support claims a low acid and rich basic surface including super basic sites (related to unidentate carbonates) which governed optimum catalytic performance 64% CH4 conversion, 79% CO2 conversion and H2/CO ~ 1 up to 460-min in time on stream test. 20% lanthanum oxide loading led to inferior performance due to rapid loss of surface area, pore-volume, pore diameter, acidity and medium basic strength sites. Fine-tuning of acid-base lanthana-alumina support with dispersed Ni species are a means for understanding DRM.

Paramagnetic Ionic Liquid/Metal Organic Framework Composites for CO2/CH4 and CO2/N2 Separations.

Global warming is arguably the biggest scientific challenge of the twenty-first century and its environmental consequences are already noticeable. To mitigate the emissions of greenhouse gases, particularly of CO2, there is an urgent need to design materials with improved adsorbent properties. Five different magnetic ionic liquids were impregnated into the metal–organic framework ZIF-8. The composites were produced by a direct-contact method, and their performance as sorbents for gas separation applications was studied. The impact of the ionic liquid anion on the sorption capacity and ideal CO2/CH4 and CO2/N2 selectivities were studied, focusing on understanding the influence of metal atom and ligand on the adsorbent properties. Reproducible methodology, along with rigorous characterization, were established to assess the impact of the ionic liquid on the performance of the composite materials. Results show that the ionic liquid was well-impregnated, and the ZIF-8 structure was maintained after ionic liquid impregnation. The produced composites were of microporous nature and were thermally stable. CO2, CH4, and N2 adsorption–desorption isotherms were obtained at 303 K and between 0 and 16 bar. The adsorption-desorption data of the composites were compared with that obtained for original ZIF-8. The general trend in composites is that the increased gas uptake per available pore volume compensates the pore volume loss. Adsorption data per unit mass showed that composites have reversible sorption, but inferior gas uptake at all pressure ranges. This is due to the observed total pore volume loss by the ionic liquid pore occupation/blockage. In most cases, composites showed superior selectivity performance at all pressure range. In particular, the composite [C4MIM]2[MnCl4]@ZIF-8 shows a different low-pressure selectivity trend from the original MOF, with a 33% increase in the CO2/N2 selectivity at 1 bar and 19% increase in the CO2/CH4 selectivity at 10 bar. This material shows potential for use in a post-combustion CO2 capture application that can contribute to greenhouse gas mitigation.

Microstructural Investigation of Coke Deposition in Pelleted Catalyst during Downhole Catalytic Upgrading of Heavy Crude Oil Using Porosimetry and X-ray Computed Tomography

Catalyst pore evolution due to coke and metals (e.g., Ni, V, etc.) deposition from heavy oil catalytic upgrading is studied using nitrogen adsorption–desorption, mercury porosimetry, X-ray computed tomography and Scanning electron microscope (SEM) techniques. These techniques probe the impact of coking on the global pore size distribution and the pore-scale connectivity of pores of different sizes. 24wt% coked NiMo/Al2O3 catalyst was studied. Coke deposition caused active site coverage and pore-mouth blockage making the core pore network inaccessible to reactants as reflected in the nearly loss of total surface area and pore volume observed from porosimetry, while the x-ray computed tomography image shows scanty coke deposits within the microstructure. The SEM image confirmed that pore-mouth blockage due to large coke deposition in the early hours of the upgrading reactions at the outer layer of the catalyst pellets is the major cause of deactivation. The spent catalyst experienced more than 90% drop in surface area with coke deposition on the outer layer of the catalyst far higher than in the centre. Therefore, one of the ways to enhance intra-particle diffusion and limit the impact of coke deposition on the outer layer of the catalyst is either to use nano-catalyst or engineered pore sizes.

Phase development and pore stability of yttria‐ and ytterbia‐stabilized zirconia aerogels

AbstractHigh‐porosity yttria‐ and ytterbia‐stabilized zirconia aerogels offer the potential of extremely low thermal conductivity materials for high‐temperature applications. Yttria‐ and ytterbia‐doped zirconia aerogels were synthesized using a sol‐gel approach over the dopant range of 0‐20 atomic percent. Surface area, pore volume, and morphology of the as‐dried aerogels and materials thermally exposed for short periods of time to temperatures up to 1200°C were characterized by nitrogen physisorption, scanning and transmission electron microscopy, and X‐ray diffraction. The aerogels as supercritically dried all were X‐ray amorphous. At a 5% dopant level, a tetragonal structure with a smaller monoclinic phase developed on thermal exposure. Mixed tetragonal and cubic phases or predominantly cubic materials were observed at higher dopant levels, depending on the dopant level, temperature and exposure time. The formation of crystalline phases was accompanied by loss of surface area and pore volume, although some mesoporous structure was maintained on short‐term exposure to 1000°C. Incorporation of the smaller Yb atom into the lattice structure resulted in smaller lattice dimensions on crystallization than was seen with Y doping and favored a more highly equiaxed structure. Aerogels synthesized with 15% Y maintained the smallest particle size without evidence of sintering at 1100°C. Largest shrinkage and loss of pore volume occurred on crystallization from the amorphous phase, with further loss of pores at temperatures above 1000°C attributable to changes in lattice parameters.

Distribution of sorbed water in the pore network of mudstones assessed from physisorption measurements

Abstract Nitrogen- and carbon dioxide physisorption isotherms were measured on three mudstone samples which were each moisture equilibrated to five different relative humidities (11, 32, 56, 75 and 97% RH at 303 K). Moisture equilibration was realized in desiccators using the deliquescent points of saturated salt solutions. Systematic testing and reproducibility tests indicate no pore structure alteration and validate the experimental approach. Traditional physisorption theories were employed for analysing the experimental data. The data reveals a decreasing trend in sorption capacity, Gurvich total pore volume, in the specific surface area from the Brunauer-Emmett-Teller theory and in the limiting micropore volume from the Dubinin-Astakhov theory. A combination of Barrett-Joyner-Hallenda and Dubinin-Astakhov theory was applied to compute cumulative pores size distributions disclosing that preadsorbed water is located in pore throats or narrow mesopores. However, no direct correlation between pore size and relative humidity is observed for relative humidities below 97%, suggesting no singular pore size control with respect to sorption mechanism. This contradicts the capillary condensation theory of water in which pores fill sequentially but supports the assumption that water sorption in mudstones is rather surface chemistry controlled. Discrepancies between the loss of Gurvich total pore volume caused by the adsorption of water and the volume of the adsorbed water itself were identified and denote that some of the preadsorbed water is located in parts of the pore system which are not accessible by nitrogen. Water sorption into the interlayers of expandable clay minerals may provide an explanation for the observed volume imbalances, as calculated interlayer water volumes, are within in the same order of magnitude as the volume imbalance. Carbon dioxide physisorption isotherms of moisture equilibrated mudstones show the same decreasing trend in sorption capacity and limiting micropore volume as the nitrogen physisorption isotherms.

Effects of reaction conditions and organic sulfur compounds on coke formation and HZSM-5 catalyst performance during jet propellant fuel (JP-8) cracking

Coke formation and catalytic performance under various conditions, such as reaction period, temperature, presence of carrier gas and organic sulfur compounds in the feed, were investigated for JP-8 cracking over HZSM-5 catalysts. The spent HZSM-5 catalysts were characterized by N2 adsorption/desorption, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscope (FT-IR), Temperature programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS). A significant loss of surface area and pore volume appeared in the initial period of the cracking reaction, owing to coke formation. Complex, aromatic structured coke formed and deposited on the surface the HZSM-5 catalyst. This resulted in high carbon content, carbon burn-off at higher temperatures, and a change in morphology to less well-defined shapes. As the reaction temperature increased, the aromaticity of the coke species increased, thereby resulting in the coke species having more carbon content and a lower H/C ratio. Furthermore, the absence of a carrier gas gave rise to faster catalyst deactivation and lower LPG yield. Surrogate JP-8 fuel experiments revealed that the aromatic sulfur compounds in the feed do not degrade the catalytic activity by sulfur poisoning, but rather by accelerated coke formation.

Evaluating Fracture Volume Loss During Flowback and Its Relationship to Choke Size: Fastback vs. Slowback

Summary In this study we estimated the initial effective fracture pore volume (Vfi) and fracture volume loss (dVef) for 21 wells completed in the Montney and Eagle Ford formations. We also evaluated the relationship between dVef and choke size. First, we applied rate-decline analysis to water-flowback data of candidate wells to estimate the ultimate water recovery volume, approximated as Vfi. Second, we estimated dVef using a fracture compressibility relationship to evaluate the fracture volume loss of the Eagle Ford wells. Third, we investigated the effect of choke size on dVef for the Eagle Ford fastback and slowback wells. Semilog plots of flowback water rate vs. cumulative water volume show straight-line trends, representing a harmonic decline. The estimated Vfi accounts for approximately 84 and 26% of the total injected water volume (TIV) of the Montney and Eagle Ford wells, respectively. The results show that approximately 10% of the fracture volume is lost during flowback. This loss in fracture volume predominantly happens during the early flowback and becomes minimal during the late flowback period. The results show a relatively higher dVef for fastback (a flowback process with a relatively large choke size) wells compared with that for slowback (a flowback process with a relatively small choke size) wells. In this study we proposed a method to estimate the initial fracture volume and investigated the loss in fracture volume during the flowback process. Analyses of the field data led to an improved understanding of the factors that control water flowback and the effective fracture volume.

Impact of Brine/CO2 exposure on the transport and mechanical properties of the Mt Simon sandstone

Abstract When sandstone rocks are exposed to CO2-saturated brine, their transport and mechanical properties can change due to brine/CO2-induced chemical reactions. The present study investigates the change in the flow-through characteristics, porosity, and the mechanical behavior of Mt. Simon Sandstone samples caused by exposure to brine/CO2. The cores, extracted from a depth interval of 2110.4–2111.4 m (6924–6927 ft) in the Mt. Simon formation, were first characterized for their mechanical and transport properties, and then aged in CO2-saturated brine at pressures of 17.24 MPa (2500 psi) and temperature of 50 °C for one to two weeks. Following that, the changes in the transport and mechanical properties of the samples were analyzed using He pycnometry, flow perporometry and triaxial testing. Our experiments show that the porosity of the Mt. Simon samples slightly increases after exposure to CO2/brine, while the permeability increases more substantially depending on the stress state. Measurements of the flow-through pore size distribution (PSD) are indicative of the changes occurring and are consistent with the observed increases in permeability. Nitrogen adsorption tests (BET), before and after incubation, show a significant loss of pore volume in the mesoporous range that is indicative of clay dissolution. Weakening of the materials was observed based on the mechanical properties studied, a result that is consistent with the observed dissolution of clays that play a central role in the cementation of the quartz grains. Finally, the analysis of the brine compositions reveals an increase in concentration of most cations after incubation with the Mt. Simon cores. This is also consistent with mineral/clay dissolution, confirmed by the porosity, transport, and mechanical property measurements as well as electron microscopy analysis of the same samples.

Silylated Zeolites With Enhanced Hydrothermal Stability for the Aqueous-Phase Hydrogenation of Levulinic Acid to γ-Valerolactone.

A systematic silylation approach using mono-, di-, and trichlorosilanes with different alkyl chain lengths was employed to enhance the hydrothermal stability of zeolite Y. DRIFT spectra of the silylated zeolites indicate that the attachment of the silanes takes place at surface silanol groups. Regarding hydrothermal stability under aqueous-phase processing (APP) conditions, i.e., pH ≈ 2, 473 K and autogenous pressure, the selective silylation of the zeolite surface using monochlorosilanes has no considerable influence. By using trichlorosilanes, the hydrothermal stability of zeolite Y can be improved significantly as proven by a stability test in an aqueous solution of 0.2 M levulinic acid (LA) and 0.6 M formic acid (FA) at 473 K. However, the silylation with trichlorosilanes results in a significant loss of total specific pore volume and total specific surface area, e.g., 0.35 cm3 g−1 and 507 m2 g−1 for the silylated zeolite Y functionalized with n-octadecyltrichlorosilane compared to 0.51 cm3 g−1 and 788 m2 g−1 for the parent zeolite Y. The hydrogenation of LA to γ-valerolactone (GVL) was conducted over 3 wt.-% Pt on zeolite Y (3PtY) silylated with either n-octadecyltrichlorosilane or methyltrichlorosilane using different reducing agents, e.g., FA or H2. While in the stability test an enhanced hydrothermal stability was found for zeolite Y silylated with n-octadecyltrichlorosilane, its stability in the hydrogenation of LA was far less pronounced. Only by applying an excess amount of methyltrichlorosilane, i.e., 10 mmol per 1 g of zeolite Y, presumably resulting in a high degree of polymerization among the silanes, a recognizable improvement of the stability of the 3 PtY catalyst could be achieved. Nonetheless, the pore blockage found for zeolite Y silylated with an excess amount of methyltrichlorosilane was reflected in a drastically lower GVL yield at 493 K using FA as reducing agent, i.e., 12 vs. 34% for 3PtY after 24 h.

Cathode Carbon Corrosion and Electrode Layer Compaction in PEM Fuel Cells

PEM fuel cells (PEMFCs) show great promise to increase the fuel efficiency for transportation applications. However, cost reduction and improvement in durability is required for mass commercialization. To achieve high platinum dispersions, platinum is typically supported on high surface area carbon. However, elemental carbon is not the thermodynamically favored state under PEMFC operating conditions of acidity and potential. Catalyst support, e.g., carbon, corrosion occurs during fuel cell operation, which can be greatly exacerbated by SD/SU cycles when hydrogen/air fronts are present on the fuel cell anode. Carbon corrosion results in thinning of the catalyst layer and changes in surface hydrophobicity, contributing to degradation of the catalyst and accelerating performance losses. The high cost of the noble metal(s) used as the catalyst makes this a crucial area requiring durability improvement. Porous electrodes lose substantial porosity during PEMFC operation, which does not appear to correlate directly with loss of carbon during corrosion reactions. Compaction of the electrode layer reduces the pore volume within the electrode and can negatively impact performance due to increased mass transport losses. To examine the stability of electrode structures and further understand the combined effects of carbon corrosion on performance, we have tested various types of carbon support materials, as well as platinum and platinum-alloy catalysts under simulated drive-cycles and accelerated stress tests. Post characterization has included porosity measurements by mercury intrusion porosimetry (MIP), transmission electron microscopy (TEM) characterization of electrode cross-sections and 2D image analysis, and focus ion beam-SEM (FIB-SEM). Advanced alloy catalysts maintain their electrode structure for some period of time during ASTs, but eventually display similar pore collapse and loss as that observed for Pt-only catalysts supported on high-surface-area-carbons. The loss of pore volume is shown by impedance measurements to result in large increases in mass transport losses. The initial pore size distribution within the catalyst layer shows a range of sizes with an average pore diameter of 120 nm. This average pore diameter holds for up to 500 AST cycles; however, after 1000 AST cycles the average pore diameter is reduced to 40 nm. The initial pore sizes exhibit a distribution centered around 50-99 nm, but range in size up to ~ 300 nm (See Figure 1a). After the AST, most of the remaining pores are < 50 nm, with a few pores measured above 50 nm (See Figure 1b). During the carbon corrosion AST, PtCo alloy catalyst particles show a loss of Co, changing from 18 at.% Co initially to 14 at.% Co after the AST, further degrading the performance of the electrode. Acknowledgments The authors wish to acknowledge the financial support of the Fuel Cell Technologies Office and Fuel Cell Component R&D Team Lead: Dimitrios Papageorgopoulus and Technology Development Manager: Nancy Garland. The authors also wish to acknowledge General Motors and Ion Power, Inc. for supplying materials used in this study. Figure 1

Size exclusion chromatography with superficially porous particles

A comparison is made using size-exclusion chromatography (SEC) of synthetic polymers between fully porous particles (FPPs) and superficially porous particles (SPPs) with similar particle diameters, pore sizes and equal flow rates. Polystyrene molecular weight standards with a mobile phase of tetrahydrofuran are utilized for all measurements conducted with standard HPLC equipment.Although it is traditionally thought that larger pore volume is thermodynamically advantageous in SEC for better separations, SPPs have kinetic advantages and these will be shown to compensate for the loss in pore volume compared to FPPs. The comparison metrics include the elution range (smaller with SPPs), the plate count (larger for SPPs), the rate production of theoretical plates (larger for SPPs) and the specific resolution (larger with FPPs). Advantages to using SPPs for SEC are discussed such that similar separations can be conducted faster using SPPs.SEC using SPPs offers similar peak capacities to that using FPPs but with faster operation. This also suggests that SEC conducted in the second dimension of a two-dimensional liquid chromatograph may benefit with reduced run time and with equivalently reduced peak width making SPPs advantageous for sampling the first dimension by the second dimension separator. Additional advantages are discussed for biomolecules along with a discussion of optimization criteria for size-based separations.

Thermal stability of porous sol-gel phosphosilicates and their surface area stabilisation by lanthanum addition

The thermal stability of porous sol-gel phosphosilicates was studied by comparing the textural features upon calcination between 400 and 550°C. A significant loss of surface area and pore volume were observed; the first is due to thermal coarsening of the nanoparticles, and the pore volume reduction was ascribed to sintering of the most external nanoparticles producing less void volume. Lanthanum addition was investigated as thermal stabilizer. For the mesoporous phosphosilicate composition, lanthanum addition enhanced the surface area, showing a 45% and 50% improvement with respect to the La-free counterpart; the effect was much less visible for the macroporous composition.