Micropore Surface Area Research Articles

Effect of adsorbed moisture on the pore size distribution of marine-continental transitional shales: Insights from lithofacies differences and clay swelling

The variation in pore water distribution within gas shale reservoirs has a significant effect on gas content, and thus on resource evaluation. However, the characteristics of water micro-distribution and its effects on pore parameters are still not well understood due to the mixed wettability of shale and the complexity of the pore structure. In this study, six lower Permian transitional shale samples from the southern North China Basin, humidified at four levels up to a relative humidity of 98%, were selected for moisture-equilibrated experiments and low-pressure N2 gas adsorption measurements. The results indicate that the adsorbed moisture in transitional clay-rich shales can be divided into capillary condensation water in the micropores and monolayer–multilayer adsorbed water in the non-micropores. Moreover, thermal maturity (VRo), total organic carbon, clay, and carbonate are positively correlated with the adsorbed moisture and micro-/mesopores, indicating that water in shales could be hosted in inorganic pores as well as in organic pores. Furthermore, the distribution of adsorbed moisture is mainly controlled by the VRo, component wettability (i.e., organic matter, clay, pyrite, and carbonate), and pore structure (micro-/mesopore distribution). In addition, a subtle adsorbed moisture may significantly reduce both the pore volume (PV) and specific surface area (SSA) of micropores, and the effect on micropores and SSA is more pronounced than that on the respective non-micropores and PVs. Additionally, the mechanism of clay swelling and pore expansion in clayey shale can provide certain insights for water–methane competitive adsorption, identifying clay type and pore size, and the formation of organo-mineral complexes.

Hydrothermal Activation of Porous Nitrogen-Doped Carbon Materials for Electrochemical Capacitors and Sodium-Ion Batteries.

Highly porous nitrogen-doped carbon nanomaterials have distinct advantages in energy storage and conversion technologies. In the present work, hydrothermal treatments in water or ammonia solution were used for modification of mesoporous nitrogen-doped graphitic carbon, synthesized by deposition of acetonitrile vapors on the pyrolysis products of calcium tartrate. Morphology, composition, and textural characteristics of the original and activated materials were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared spectroscopy, and nitrogen gas adsorption method. Both treatments resulted in a slight increase in specific surface area and volume of micropores and small mesopores due to the etching of carbon surface. Compared to the solely aqueous medium, activation with ammonia led to stronger destruction of the graphitic shells, the formation of larger micropores (1.4 nm vs. 0.6 nm), a higher concentration of carbonyl groups, and the addition of nitrogen-containing groups. The tests of nitrogen-doped carbon materials as electrodes in 1M H2SO4 electrolyte and sodium-ion batteries showed improvement of electrochemical performance after hydrothermal treatments especially when ammonia was used. The activation method developed in this work is hopeful to open up a new route of designing porous nitrogen-doped carbon materials for electrochemical applications.

Microelectrochemical Smart Needle for Real Time Minimally Invasive Oximetry.

A variety of brain disorders such as neural injury, brain dysfunction, vascular malformation, and neurodegenerative diseases are associated with abnormal levels of oxygen. Current methods to directly monitor tissue oxygenation in the brain are expensive and invasive, suffering from a lack of accuracy. Electrochemical detection has been used as an invasiveness and cost-effectiveness method, minimizing pain, discomfort, and injury to the patient. In this work, we developed a minimally invasive needle-sensor with a high surface area to monitor O2 levels in the brain using acupuncture needles. The approach was to directly etch the iron from stainless steel acupuncture needles via a controlled pitting corrosion process, obtaining a high microporous surface area. In order to increase the conductivity and selectivity, we designed and applied for the first time a low-cost coating process using non-toxic chemicals to deposit high surface area carbon nanoparticle, catalytically active laccase, and biocompatible polypyrrole. The physicochemical properties of the materials were characterized as well as their efficacy and viability as probes for the electrochemical detection of PO2. Our modified needles exhibited efficient electrocatalysis and high selectivity toward O2, with excellent repeatability. We well engineered a small diagnostic tool to monitor PO2, minimally invasive, able to monitor real-time O2 in vivo complex environments.

Meso- and microporosity characteristics of Miocene lignite and subbituminous coals in the Kınık coalfield (Soma Basin, W. Turkey)

Three Miocene-age coal seams - a lower seam (kM2, subbituminous), a middle seam (kM3, subbituminous), and an upper seam (kP1, lignite) - in the Kınık coalfield, located in the southwesternmost part of the Soma Basin in western Turkey, and factors controlling mesoporosity and microporosity characteristics, were investigated using low-pressure N2 and CO2 adsorption techniques, respectively. In addition, this study is also aimed to compare controlling factors on meso- and microporosity characteristics of Soma Basin and Late Carboniferous Zonguldak, and Late Miocene-Pliocene Dombayova Basins. It is found that distinct differences with regard to meso- and microporosity exist among the three seams (kM2, kM3 and kP1) investigated in the Kınık coalfield. Specifically, samples from kP1 have greater mesopore surface areas and volumes than those from kM3. In addition, samples from the upper part of kM2 have significantly lower mesopore surface area and volume than from the lower part of this seam and from kM3 and kP1. Samples from the lower part of kM2 have higher meso- and micropore surface area and volume values than kM3 and kP1 samples. The increase in mesopore surface area and volume, along with the increase in ash yield toward the lower part of kM2, suggests that mesoporosity characteristics in this seam appear to be controlled mainly by mineral matter content. The results of this study show that meso- and micropore surface area and volume of Miocene subbituminous coal (kM2) in Kınık and Eynez coalfields of the Soma Basin have higher values than lignite from the Dombayova Basin and bituminous coal from the Zonguldak Basin. The differences in mesopore characteristics between the Soma and the Zonguldak Basins could be related to differences in rank. In addition, the mesoporosity of coal seams in the Dombayova Basin is more similar to seams in the Zonguldak Basin. These conflicting data suggest that rank might not be a controlling factor on the meso- and micropore characteristics of the basins investigated in this paper. Nevertheless, the common presence of structured huminite macerals in the Soma Basin seems to have caused relatively higher microporosity surface area and volume values, whereas the common presence of illite, particularly in the lower parts of kM2, resulted in higher values of mesopore surface area and volume in the Soma Basin samples. Consequently, maceral and mineralogical compositions of the studied Turkish coals seem to exert major controls on meso- and micropore characteristics.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

Author(s): Mao, H; Tang, J; Xu, J; Peng, Y; Chen, J; Wu, B; Jiang, Y; Hou, K; Chen, S; Wang, J; Lee, HR; Halat, DM; Zhang, B; Chen, W; Plantz, AZ; Lu, Z; Cui, Y; Reimer, JA | Abstract: Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming. 2 2

Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin

Biogenic gas shales, predominantly microbial in origin, form an important class of organic-rich shale reservoirs with a significant economic potential. Yet large gaps remain in the understanding of their gas generation, storage, and transport mechanisms, as previous studies have been largely focused on mature thermogenic shale reservoirs. In this study, the pore structure of 18 Antrim Shale samples was characterized using gas adsorption (CO2 and N2). The results show that most of the Antrim Shale samples are rich in organic matter content (0.58 wt.% to 14.15 wt.%), with highest values found in the Lachine and Norwood members. Samples from the Paxton Member, characterized by lower organic content, have smaller micropore surface area and micropore volume but larger meso-macro pore surface area and volume. The deconvolution results of the pore size distribution from the N2 adsorption indicate that all of the tested Antrim Shale samples have similar pore groups. Organic matter in the Antrim Shale hosts micro pores instead of meso-macro pores, while clay minerals host both micro and meso-macro pores. Mineral-related pores play a primary role in the total porosity. The biogenic Antrim Shale, therefore, has different pore structures from other well-studied thermogenic gas shales worldwide.

Simultaneous control of the pore volume and the surface wettability in porous carbons prepared by carbonization of iodine-treated cellulose derivatives

Microporous carbon was prepared by carbonization of carboxymethylcellulose and its sodium salt introduced various amounts of iodine. The iodine introducing treatment was performed by exposing raw materials to iodine vapor. Interaction between the carbon and water molecules was investigated by several methods related to water adsorption. The iodine treatment gave the porous carbons without reducing their char yield. The treatment on the sodium salt to I/Na molar ratio ≈ 1 gave the carbon both the largest microporous surface area of ca. 900 m2/g and the amount of acidic surface functional groups of ca. 1.81 mmol/g in the carbon which led to a higher interaction with water. The introduced acidic functional groups contributed to an increase in active site of water adsorption. It was expected that a porous carbon with simultaneous and suitable improving of char yield, porosity, and surface wettability would be achieved by the simple processing of iodine treatment and carbonization from cellulose-based resources.

Optimization of methane production in a swine manure–rice straw anaerobic co-digestion process with sycamore sawdust biochar application

Anaerobic co-digestion has been widely applied to re-utilize livestock manure; however, the low methane yield is still a key issue. Biochar could play an important role in anaerobic digestion. This study aims to produce and characterize sycamore sawdust biochar (SSB), determine the promoting effect on the swine manure–rice straw co-digestion system by applying the SSB, and obtain the optimal digesting conditions by using a Box–Behnken design of response surface methodology (RSM). The results showed that SSB had a porous structure composed of micropores and mesopores. The micropore surface area reached 162.87 m2/g, and the mesopore volume accounted for 43.67% of the total pore volume. SSB was also rich in C=O surface functional groups, and the BET specific surface area was up to 276.67 m2/g. Application of SSB could improve the pH value and the stability of the co-digestion system, and eventually improve the cumulative methane yield. The maximum cumulative methane yield in this test was 217.99 mL/(g VS) when 4% SSB was added. According to the response surface optimization analysis, the cumulative methane yield could be 247.20 mL/(g VS) under the optimal conditions: 94.54% swine manure, 8.78% TS and 5.49% SSB.

Goethite-humic acid coprecipitate mediated Fenton-like degradation of sulfanilamide: The role of coprecipitated humic acid in accelerating Fe(III)/Fe(II) cycle and degradation efficiency

While extensive studies found that dissociative and iron mineral-adsorbed humic acid (HA) could either stimulate or inhibit Fenton-like processes, little was known about the influence of iron mineral-coprecipitated HA on Fenton-like reactions. Here, goethite and HA (Gt-HA) coprecipitates having different C:Fe molar ratios (C:Fe = 0.16–0.99) were biologically prepared, and for the first time, investigated for their abilities of H2O2 activation and catalytic degradation of sulfanilamide. For system containing Gt-HA with the optimal C:Fe ratio of 0.30, over 91.1% of sulfanilamide (10 mg/L) was removed in 2 h, which was 46.2% higher than that of the control Gt system. Additionally, H2O2 decomposition, •OH production, and organic carbon removal in Gt-HA systems were all more efficient than those in Gt system. Higher carbon moieties stability and lower micropore surface area of Gt-HA decreased the competition for •OH and H2O2, thus helped to improve degradation efficiency. Electrochemical analysis, quenching experiments, and Fe species detection showed that the coprecipitated HA could serve as electron shuttle and complex with Fe(III) mainly via carboxyl groups at octahedral sites to improve Fe(III)/Fe(II) transformation. This study improved our understanding of Fe(III)/Fe(II) cycling in Fe‒C coprecipitates and demonstrated the potential of developing Fe‒C coprecipitates as efficient catalysts in Fenton-like processes.

Activated carbon microspheres derived from hydrothermally treated mango seed shells for acetone vapor removal

Mango fruit seed shells were used as starting materials to produce activated carbons for the capture of acetone, a typical volatile organic compound (VOC), from gaseous streams. This fruit waste presents high volatiles and low ashes contents, as expected for the lignocelulosic materials commonly used for the preparation of activated carbons. The starting material was hydrothermally treated at 180 or 250 °C for 5 h and the obtained hydrochars were activated with KOH solutions. The carbon samples were characterized by SEM, EDX, TG/DTA, Raman spectroscopy and textural analysis by physisorption. The adsorption capacity and adsorption cycles were investigated by TG. The hydrochars presented spherical morphology and the activated carbons derived from them presented heterogeneous micropore structures allowing to high capacity of acetone vapor removal, namely 472 mg/g, at 30 °C and 363 mg/g, at 50 °C. The results indicate that the adsorption capacity of the activated carbons is directly related to their Dubinin-Astakhov micropore surface areas and microporous volumes determined by NLDFT. The adsorption of acetone vapor showed a pseudo-first order kinetics and both external and intra-particle transport contributed for the overall process. Highly efficient and stable acetone vapor removal was observed over the activated carbons after five cycles.

Iodide ion containing ionic liquid mixture based asymmetrical capacitor performance

Abstract Development of high efficiency energy storage systems is increasingly important as these systems enable utilize energy from renewable sources and reduce greenhouse gas evolution caused by fuel combustion technologies in the same time. Electricity storage in the supercapacitor containing neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid or mixture of ionic liquids (EMImBF4 with addition of 5 wt% 1-ethyl-3-methylimidazolium iodide (EMImI)) has been studied in the two- and three-electrode systems using high porosity carbon electrode material with specific surface area of 2090 m2 g-1, micropore surface area of 2060 m2 g-1 and total pore volume of 1.085 cm3 g-1. Based on electrochemical characterization data (cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power discharge), the asymmetrical capacitor with ionic liquid mixture of 5 wt% EMImI in EMImBF4 shows increase in cell capacitance 5 F g-1 and specific energy about 3.5 W h kg-1 as well as in specific power, compared with the data for symmetrical capacitor system based on neat EMImBF4. However, electrochemical stability, i.e. the potential region of ideal polarizability for the ionic liquid mixture based capacitor is lower and therefore the coulombic and energy efficiencies calculated are also smaller.

A highly sustainable hydrothermal synthesized MnO2 as cathodic catalyst in solar photocatalytic fuel cell

A unidirectional flow solar photocatalytic fuel cell (PFC) was successfully developed for the first time to offer alternative for electricity generation and simultaneous wastewater treatment. This study was focused on the synthesis of α-, δ- and β-MnO2 by wet chemical hydrothermal method for application as the cathodic catalyst in PFC. The crystallographic evolution was performed by varying the ratios of KMnO4 to MnSO4. The mechanism of the PFC with the MnO2/C as cathode was also discussed. Results showed that the catalytic activity of MnO2/C cathode was mainly predominated by their crystallographic structures which included Mn–O bond strength and tunnel size, following order of α- > δ- > β-MnO2/C. Interestingly, it was discovered that the specific surface areas (SBET) of different crystal phases did not give an impact on the PFC performance. However, the Pmax could be significantly influenced by the micropore surface area (Smicro) in the comparison among α-MnO2. Furthermore, the morphological transformation carried out by altering the hydrothermal duration demonstrated that the nanowire α-M3(24 h)/C with 1:1 ratio of KMnO4 and MnSO4 yielded excellent PFC performance with a Pmax of 2.8680 μW cm−2 and the lowest Rint of 700 Ω.

Reactivating Adsorption Capacities of Spent Bleaching Earth for Using in Crude Palm Oil Industry

The spent bleaching earth from the palm oil refining industries contains various contaminants, including free fatty acids and hazardous material. The conventional procedure is harmful to the environment. In this study, spent bleaching earth (SBE) was successfully regenerated by calcination and acid-activation process. The calcination process was performed at 500, 600 and 700°C for 2, 3 and 4 h. All samples were then mixed with CaCO3 and lastly activated with aqueous acid. The results showed the SBE color restored at calcination temperature higher than 500°C, even though the decomposition of the volatile compound was removed at 680°C according to thermal gravimetric analysis. Treatment affected the clay structure and mostly removed the impregnated organic matter. The primary phase of regenerated SBE is similar to virgin bleaching earth (VBE), implying the calcination and acid-activation is not alter the phase. Moreover, the adsorbent capacity of regenerated SBE was comparable with VBE, showing the regenerated SBE has promising potential for many applications, in particular for the palm oil refining industry. Regenerated SBE gave significantly larger specific surface area, microporous surface area and total pore volume with smaller the average pore diameter.

Effect of ultrasonic vibration-assisted pelleting of biomass on biochar properties

The objective of this research was to investigate the potential of ultrasonic vibration-assisted (UV-A) pelleting as pretreatment method to produce biochar with desired properties. In this study, poplar (PP), switchgrass (SG), and wheat straw (WS) were pretreated with UV-A pelleting process, then the biochar were produced in a muffle at atmosphere condition with a highest temperature treatment (HTT) at 300, 500, and 700 °C, respectively. Ultrasonic power had an obvious effect on the biochar yield and pH, a higher biochar yield and biochar pH were obtained from PP00, SG50, and WS50 and PP50, SG50, and WS00, respectively. The FTIR spectra showed that O–H stretching, C–H stretching, carbonyl bonds/CO stretching, C–H stretching, C–O–C, and C–C stretching were found in spectra of UV-A pretreated biomass, while disappeared in spectra of biochar, indicating the changes of functional groups. Although UV-A pelleting pretreatment did not show considerable effect on the C, H, N, and S content of biochar (less than 2%) under the same HTT, the formation of multi-layer and porous structure was observed on biochar surface. The specific surface area, micropore surface area, and total pore volume of biochar from UV-A pelleting increased with increasing of ultrasonic power. In addition, HTT and type of biomass also had different functions on the biochar properties. The results of this study showed that UV-A pelleting pretreatment has a great potential to produce biochar with desired chemical structures and physical properties.

The effects of activation conditions on physical properties of activated carbon

Porous carbons with a high porosity were successfully produced from fast pyrolysis pine wood char via a thermochemical method in which KOH was used as chemical activator. The effects of various weight ratios of KOH to pyrolysis char (0.65:1, 0.7:1, 1.0:1, 1.35:1, and 1.7:1) on the physical properties of activated carbons were investigated. When the weight ratio of KOH to pyrolysis char was 1.35:1, the prepared activated carbon had the highest surface area of 1140 m2/g with a total pore volume of 0.71 cm3/g, a microporous surface area of 957 m2/g, and a microporous specific volume of 0.51 cm3/g. As the weight ratio of KOH to pyrolysis char increased from 0.65 to 1.35, the prepared activated carbon had increases in total surface area, total pore volume, microporous surface area, and specific volume of micropores. However, there was a reverse trend when the weight ratio of KOH to pyrolysis char was higher than 1.35. The use of nitrogen as a flow gas resulted in much more developed activated carbon than without nitrogen. The experiment results suggested that activated carbon with high surface area could be prepared from pyrolysis char by adjusting the activation conditions.

Poly(s-triazine) based porous carbon for CO2 sequestration

Nitrogen containing microporous materials are promising candidates for the efficient and selective CO2 capture. Triazine containing polyaminals are the potential precursors for the preparation of porous carbons. The various nitrogen moieties present in the materials are examined by XPS analysis. The FE-SEM and HR-TEM images of the materials and N2 sorption profile exhibit abundant microporous structure. Pore size distribution reveals the existence of narrow micropores in the materials. The prepared materials exhibit surface area up to 684 m2/g, microporous surface area up to 441 m2/g and CO2 capture up to 154 mg/g. CO2 isotherm data is well fitted with Langmuir and Freundlich isotherm models. Spontaneity of the CO2 adsorption process are demonstrated by thermodynamic parameters. The high CO2/N2 selectivity and considerable CO2/CH4 selectivity of the materials are calculated by initial slope method (Henry's law).

Effect of calcium dispersion and graphitization during high-temperature pyrolysis of beech wood char on the gasification rate with CO2

This paper presents thermal deactivation of beech wood chars during secondary pyrolysis in a drop-tube reactor. Pyrolysis temperature was varied between 1000 °C and 1600 °C at a constant residence time of 200 ms. The effect of pyrolysis conditions on initial conversion rate R0 during gasification, graphitization of the carbon matrix and ash morphology was investigated. Gasification experiments for the determination of R0 were conducted in a thermogravimetric analyzer using pure CO2 at 750 °C and isothermal conditions. A linear decrease in initial conversion rate R0 was observed between 1000 °C and 1400 °C. However, a strong increase of R0 at 1600 °C was encountered. Micropore surface area of the secondary chars showed no correlation with the initial conversion rate R0 during gasification with CO2. Graphitization of the carbon matrix was determined using X-ray diffraction and Raman spectroscopy suggesting the growth of aromatic clusters and graphite-like structures for increasing pyrolysis temperatures up to 1600 °C. Furthermore, CaO dispersion was analyzed quantitatively and qualitatively using temperature-programmed reaction at 300 °C as well as SEM/TEM. CaO dispersion DCaO decreases steadily between 1000 °C and 1400 °C whereas a strong increase can be observed at 1600 °C, which is in good accordance with the development of the initial conversion rate R0 as a function of pyrolysis temperature. SEM/TEM images indicate the formation of a thin CaO layer at 1600 °C that is presumably responsible for the strong increase in initial conversion rate R0 at this temperature. When excluding the catalytic activity of CaO via formation of the ratio R0DCaO−1, increasing graphitization degree has a linear negative influence on char reactivity at pyrolysis temperatures between 1000 °C and 1400 °C.

Characteristics of pore structures from the Lower Paleozoic shale gas reservoirs in northern Guizhou, South China

Pore structure in shale is an important factor influencing the storage capacity of a shale gas reservoir and the effect of shale gas development. Taking the core and outcrop shale samples from the Lower Cambrian Niutitang Formation and Lower Silurian Longmaxi Formation as the object of the research, combined with the scanning electron microscope, high pressure mercury injection, CO2 and N2 gas adsorption experiments, we investigated the porosity, pore types, pore structure, and pore size distribution of the Lower Paleozoic shale gas reservoirs in northern Guizhou, South China. The results indicated that there are developed various genetic types of micro-nano pores in the Lower Paleozoic marine shale in northern Guizhou, which provide the main reservoir spaces for shale gas. The porosity of the Lower Paleozoic shale in northern Guizhou is 1.30%–13.37% in range, and the average is 4.56%. The inter-granular pore, organic matter pore and intra-granular pore are most common. Micropore (<2 nm) and mesopore (2–50 nm) are the main reservoir storage space for shale gas. The specific surface area of micropore plus mesopore in the Lower Paleozoic shale accounts for 94.3% of the total specific surface area, and their pore volume accounts for 59.1% of the total pore volume in northern Guizhou. The pore size of the Lower Paleozoic shale is mainly distributed in 0.4–0.7 nm, 3–10 nm and 0.05–200 μm. The pore structure is the parallel-plate pore with slit shape, two-ends-opened tube pore and ink-bottle shape pore. There are significant differences in the porosity and pore size between the Longmaxi Formation shale and the Niutitang Formation shale. The average porosity and average pore size of the Longmaxi Formation shale is 6.4% and 4.71 nm, while the Niutitang Formation shale is 5.3% and 4.23 nm, respectively. The pore structure of the Lower Paleozoic shale gas reservoir is mainly influenced by organic matter abundance, thermal maturity, mineral composition of shale. The porosity and micropore volume of shale show an increasing trend, with the increase of total organic carbon content and quartz content. The porosity and pore volume of shale have a decreasing trend, with the increase of thermal maturity level and clay mineral content.

Influences of supercritical carbon dioxide fluid on pore morphology of various rank coals: A review

Supercritical carbon dioxide is known to change the pore structure of coals and thus affect their carbon dioxide sequestration capacity. In this study, supercritical carbon dioxide dependence of pore morphology of coals was reviewed. Results indicated that the micropore surface area and volume of dry coals varied between –20% and 20% after exposure to supercritical carbon dioxide. Changes in the micropore size distribution of dry coals after supercritical carbon dioxide exposure were not found to be significant; however, the change in meso- and macropores with diameter of 2–8 nm was observed to be significant. Supercritical carbon dioxide and H2O exposure mainly influenced pores with diameters of 0.4–0.7, 0.7–0.9 and 2–8 nm. The variation in the pore fractal dimensions of the coals ranged from –0.5% to 0.5% after supercritical carbon dioxide exposure. Furthermore, the dependence of supercritical carbon dioxide on the pore structure of coals relies on the coal rank. The change in the pore structure of the coals after supercritical carbon dioxide exposure was observed to be related to the following aspects. First, supercritical carbon dioxide induced swelling in coal matrix, thus reducing the pore surface area and volume of the coal matrix and compressing the cleat system. Next, the extraction of supercritical carbon dioxide mobilised the small organic molecules dispersed in the coal matrix; this increased the pore volume, particularly of micropores. Finally, the mineral dissolution/precipitation also changed the pore structure of the coals. To further examine supercritical carbon dioxide dependence of coal pore morphology, the following studies should be performed. The characterisation of the chemical and pore structure of coals should be combined with existing coal structure models to account for the mechanism of supercritical carbon dioxide changing the pore structure of coals. Combination of physical experiments and numerical simulations is recommended to predict the changes in porosity and permeability of coals due to long-term carbon dioxide sequestration.

Effect of Manganese and zeolite composition on zeolite-supported Ni-catalysts for dry reforming of methane

This study examines the effects of manganese (Mn) on zeolite-supported Ni catalysts for dry reforming of methane (DRM). Three commercially-available zeolites (NH4-ZSM5, NH4-Y, Na-Y) were used as catalyst supports for the Ni (10 wt%) catalysts, and 4 different loadings of Mn (0-15 wt%) were used. The activities of the catalysts were screened, and selected catalysts were investigated for 24 hours in the DRM reaction. It was found that the effects of Mn on catalyst activity depends upon the type of zeolite support. Generally, however, Mn decreased the activity of the zeolite-supported Ni-based catalyst, but reactivity was more stable over a 24 -h reaction period. The beneficial effects of Mn as a promoter on NH4-ZSM5 and NH4-Y zeolites are to reduce carbon deposition, to decrease the crystal size of Ni, and to increase Ni dispersion on the zeolite. However, as Mn loading increases, the crystallinity of the zeolite structure and its micropore surface area generally decrease. Mn loading at 10 wt% and 15 wt% on Na-Y is detrimental to catalyst activity and to crystal structure, as it facilitates the destruction of the crystal structure of the Na-Y zeolite and significantly enhances sintering in a high temperature reducing atmosphere.