Volumetric Gas Adsorption Research Articles

Hydrogen storage and selective carbon dioxide capture in a new chromium(iii)-based infinite coordination polymer

A new chromium(III)-based infinite coordination polymer (ICP) was synthesized under solvothermal conditions. The morphology, particle size and the textural porosity of the resulting solids could be monitored and controlled by adjusting the volume ratio of the solvent mixture (1,4-dioxane/N,N′-dimethylformamide). Two differently textured samples were further compared using powder X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, solid-state UV-Vis spectroscopy and thermogravimetric analysis. Their sorption capacities for H2, CO2 and CH4 were measured by using volumetric gas adsorption, while the isosteric heats of adsorption for the same gasses were calculated based on gas sorption data at different temperatures. Both samples showed a remarkable selectivity for CO2 over CH4 at 273 K. H2 and CO2 sorption capacities, (respectively 16.9 mg g−1 at 77 K and 817 mm Hg and 168 mg g−1 at 273 K and 760 mm Hg) of the sample composed of the nanosized particles, are comparable or even superior to values reported for most MOFs and ZIFs under similar conditions.

Hydrogen Storage Behavior of Amorphous Carbon Nanotubes at Low Pressure and Room Temperature

Amorphous carbon nanotubes (ACNTs) were produced by a temperature-controlled arc discharging furnace with a mixture powders of Co-Ni (1:1wt%) alloy as catalyst and hydrogen as buffer gas. As-grown and treated ACNTs with a mean diameter of about 14nm for hydrogen storage and release experiments were studied in this paper. The test experiments of hydrogen uptake and release were carried out by a volumetric gas-adsorption measurement system. The results indicated that the hydrogen storage capacity of ACNTs was 1.1wt% at the pressure of 2.45MPa and room temperature. Around 50% of the adsorbed hydrogen gas of ACNTs could be released under a standard pressure and at room temperature.

Pore structure and water adsorptivity of petroleum coke-derived activated carbon for adsorption heat pump–Influence of hydrogen content of coke

Abstract In order to achieve high cooling output performance of adsorption heat pump (AHP) by improving water adsorptivity of an adsorbent, we have been developing activated carbon (AC) prepared from petroleum coke with potassium hydroxide chemical activation. In particular, this research dealt with the effect of hydrogen content of coke on pore structure, surface chemistry and water vapor adsorptivity of AC prepared. Three petroleum cokes with H/C molar ratios ranging from 0.266 to 0.417 were employed as a raw carbonaceous material, and activated at 773 K for 1 h under various weight ratios of KOH/coke, R . Pore structure, such as BET surface area and pore size distribution, was estimated by N 2 and CO 2 adsorption isotherms. Amount of adsorbed water vapor on AC was measured by a volumetric gas adsorption apparatus. The total content of acidic surface functional groups was determined by the Boehm titration method. As a result, it was found that development of pores was promoted at higher hydrogen content and higher KOH/coke weight ratio. Further, the pores were mainly consisted of micropore. Concerning water vapor adsorption, the same trend as N 2 adsorption could be observed; i.e. amount of water adsorbed on AC increased as increasing H/C molar ratio of coke. In the operation relative pressure range of AHP ranging from 0.11 to 0.38, the adsorptivity of water vapor on AC prepared from coke with H/C = 0.417 at R = 5 achieved about 1.2 times higher than that of commercial silica gel, which is 0.19 kg/kg of water adsorptivity. It was also suggested that a steep increase in water adsorptivity at relative pressure over 0.2 was attributed to a well-developed micropore greater than 0.5 nm and high hydrophilicity of activated carbon prepared.

High-Performance Pd-Based Hydrogen Spillover Catalysts for Hydrogen Storage

High surface area carbon materials are promising for low-temperature storage of hydrogen by physisorption. To achieve acceptable hydrogen capacities at ambient temperature, chemisorption must come into play. The dispersion of transition metal catalysts to carbon materials can enhance the ambient temperature adsorption capacity of the carbon materials via the hydrogen spillover mechanism. In this study, three different hydrogen dissociation catalysts (Pd, PdAg, and PdCd nanoparticles) were dispersed onto surfaces of activated carbon. The surface composition of these metal-dispersed carbon materials was analyzed using X-ray photoelectron spectroscopy (XPS) and the specific surface areas, and pore sizes were measured using N2 adsorption/desorption. The effect of the dispersed catalysts on the hydrogen adsorption properties of the activated carbon was systemically investigated at 77 K and room temperature (295 K) using a volumetric gas adsorption technique. At 77 K, the catalysts have no effect, and the hydro...

Measurements of Hydrogen Spillover in Platinum Doped Superactivated Carbon

Hydrogen uptake was measured for platinum doped superactivated carbon at 296 K where hydrogen spillover was expected to occur. High pressure adsorption measurements using a Sieverts apparatus did not show an increase in gravimetric storage capacity over the unmodified superactivated carbon. Measurements of small samples (∼0.2 g) over long equilibration times, consistent with the reported procedure, showed significant scatter and were not well above instrument background. In larger samples (∼3 g), the hydrogen uptake was significantly above background but did not show enhancement due to spillover; total uptake scaled with the available surface area of the superactivated carbon. Any hydrogen spillover sorption was thus below the detection limit of standard volumetric gas adsorption measurements. Due to the additional mass of the catalyst nanoparticles and decreased surface area in the platinum doped system, the net effect of spillover sorption is detrimental for gravimetric density of hydrogen.

Thermodynamics of hydrogen adsorption on calcium-exchanged faujasite-type zeolites

Abstract A combination of variable-temperature infrared spectroscopy with volumetric gas adsorption measurements was used to study the thermodynamics of hydrogen adsorption, at a low temperature, on calcium-exchanged zeolites X and Y. Two adsorption regimes were considered: (i) localized adsorption of dihydrogen molecules on Ca 2+ cation sites, and (ii) delocalized hydrogen adsorption following saturation of the Ca 2+ adsorbing centres. For localized adsorption, the corresponding enthalpy change was found to be in the range of −12 to −15 kJ mol −1 , while the isosteric heat of delocalized adsorption was found to be in the range of 4.5–5.5 kJ mol −1 . These experimental results are discussed in the broader context of corresponding data for other alkaline zeolites, with a focus on correlation between adsorption enthalpy and entropy for the localized adsorption regime.

Determination of multi-component gas and water equilibrium and non-equilibrium sorption isotherms in carbonaceous solids from early-time measurements

A rapid method is presented for determination of the multi-component gas and water sorption isotherms on carbonaceous solids from the non-equilibrium sorption data. This approach alleviates the long-time data requirement of the traditional volumetric gas adsorption technique used to construct gas isotherms requiring a series of equilibrium sorption measurements by successive pressure increments, particularly resorted in the coalbed methane industry. This is accomplished by the application of the non-equilibrium thermodynamics, multi-component material balance, gas sorption, and dissolution kinetic considerations for the gas adsorbed by carbonaceous solids and the gas dissolved in water under the effect of pressure, temperature, and grain size. The capabilities of the new technique in reducing the time required for construction of an isotherm are demonstrated by analyzing a series of the non-equilibrium sorption measurements and projecting the results to the equilibrium case. Moreover, it is demonstrated that the present model enables constructing both the equilibrium and non-equilibrium multi-component gas and water sorption isotherms in any carbonaceous solids and particularly coals simultaneously in relatively shorter time and with higher accuracy.

High Precision Volumetric Gas Adsorption Apparatus

We have developed a new volumetric gas adsorption apparatus into which the dead volume measurement cell (dVd cell) is incorporated (cf. Fig. 1). The dVd cell measures continuously the change of dead volume during adsorption measurement. The dead volume at every step of adsorption measurement is used in calculation of adsorbed amount of nitrogen gas. Introduction of the dVd cell makes the level-control system of liquid nitrogen unnecessary, and enables the adsorption error due to the minute fluctuation of liquid–nitrogen level small. The sensitivity and reproducibility of our new adsorption apparatus have been examined using some certified materials (cf. Fig. 4).

Adsorption of CO2 on Zeolites at Moderate Temperatures

Pressure swing adsorption (PSA) and temperature swing adsorption (TSA) are potential techniques for removing carbon dioxide (CO2) from high-pressure fuel gas streams. Zeolites are suitable candidate sorbents for use in these processes; however, the systems would be even more energy efficient if the sorbents were operational at moderate or high temperatures, especially for the removal of CO2 from high-pressure gas streams, such as those from integrated gasification combined-cycle (IGCC) systems. Competitive gas adsorption tests with gas mixtures representing both coal combustion and coal gasification gas streams were conducted in an atmospheric flow reactor with five zeolites at 120 °C. Promising results of preferential adsorption of CO2 were observed with two of these zeolites. However, the CO2 adsorption capacity was significantly lower at 120 °C than at ambient temperature. Volumetric gas adsorption tests of CO2 and nitrogen (N2) on these two zeolites were conducted at 120 °C, up to a pressure of 300 ps...

Characterisation of the Surface Activity of Carbon Blacks

In order to gain a better understanding of the reinforcement mechanism of fillers, the surface activity of a selection of industrial carbon blacks produced by different procedures with varying average particle sizes (spec. N2 surface area) and aggregate structure (DBP number) were investigated using the volumetric gas adsorption method. The adsorption isotherms for polymer-like gases were used to determine the particles’ geometrical surface roughness and the distribution functions of energetically different bonding sites for polymers on the surfaces on atomic length scales. The influence of the surface activity on the reinforcement of elastomers is demonstrated using examples of vulcanisates.

Adsorption of CO2, N2, and O2 on Natural Zeolites

Pressure swing adsorption (PSA) and temperature swing adsorption are potential techniques for removing CO2 from high-pressure fuel gas streams. Natural zeolites are suitable candidate sorbents for use in the PSA process. Studies of volumetric gas adsorption of CO2 ,N 2, and O2 on three natural zeolites, with different major cations, were conducted at 25 °C up to a pressure of 300 psi (2 10 6 Pa). Preferential adsorption of CO2 was observed with all three zeolites. The natural zeolite with the highest sodium content and highest surface area showed the highest CO2 adsorption capacity. Competitive gas adsorption studies also showed that the zeolite with the highest sodium content gave the best separation of CO2 from the gas mixtures. Contact time did not affect the extent of adsorption of the zeolites. Temperature-programmed desorption studies indicated that the majority of the physically adsorbed CO2 was desorbed at room temperature, while some strongly bound CO2 was desorbed at 115 °C.

Surface energy distribution of carbon black measured by static gas adsorption

The energetic surface heterogeneity of various carbon blacks has been investigated by means of volumetric gas adsorption techniques. From the adsorption isotherms of ethene at a coverage of about 0.001 up to 1 monolayer the energy distribution functions of adsorption sites are evaluated. Four discrete species of energetic adsorption sites are identified on all carbon black surfaces irrespective of morphology. The fraction of the different adsorption sites is found to depend significantly on the microstructure and primary particle size and on manufacturing conditions as well.

Hydrogen storage in carbon nanostructures

Carbon nanotubes have been known for more than 10 years. It is a challenge to fill their unique tubular structure with metals and gases. Especially, the absorption of hydrogen in single wall nanotubes has attracted many research groups worldwide. The values published for the quantity of hydrogen absorbed in nanostructured carbon materials varies between 0.4 and 67 mass%. With the assumption that the hydrogen condenses in the cavity of the nanotube or forms an adsorbed monolayer of hydrogen at the surface of the tube, the potential of nanotubes as a host material for hydrogen storage can be estimated. The hydrogen storage density due to condensed hydrogen in the cavity of the tube depends linearly on the tube diameter and starts at 1.5 mass% for a 0.671 nm single wall carbon nanotube. The surface adsorption of a monolayer of hydrogen leads to a maximum storage capacity of 3.3 mass%. We have investigated a large number of nanostructured carbon samples, i.e. high surface area graphite, single wall and multiwall nanotubes, by means of volumetric gas adsorption, galvanostatic charge/discharge experiments and temperature programmed desorption spectroscopy. The reversible hydrogen capacity of the carbon samples measured in an electrochemical half-cell at room temperature correlates with the specific surface area (BET) of the sample and is 1.5 mass% /1000 m 2/ g .

Role of Platinum Deposits on Titanium(IV) Oxide Particles: Structural and Kinetic Analyses of Photocatalytic Reaction in Aqueous Alcohol and Amino Acid Solutions

Photocatalytic reaction at 298 K by platinum-loaded titanium(IV) oxide (TiO2−Pt) particles suspended in deaerated aqueous solutions of 2-propanol or (S)-lysine (Lys) was investigated. The TiO2 catalysts with various amounts of Pt loadings were prepared by impregnation from aqueous chloroplatinic acid solution onto a commercial TiO2 (Degussa P-25) followed by hydrogen reduction at 753 K. The physical properties of deposited Pt, e.g., particle size, surface area, and electronic state, were studied respectively by transmission electron microscopy, volumetric gas adsorption measurement, and X-ray photoelectron spectroscopy as well as infrared spectroscopy of adsorbed carbon monoxide. The increase in Pt amount mainly resulted in an increase of the number of Pt deposits, not of their size. The catalysts were suspended in the aqueous solutions and photoirradiated at a wavelength >300 nm under an argon (Ar) atmosphere. The overall rate of photocatalytic reactions for both 2-propanol and Lys, corresponding to the rate of consumption of these substrates, was negligible without Pt loading, increased drastically with the loading up to ca. 0.3%, and was almost constant or a little decreased by the further loadings. However, the rate of formation of pipecolinic acid (PCA) from Lys was improved gradually with a increase of Pt loading up to ca. 2 wt %. These dependences were discussed as a function of Pt surface area, which is employed as a measure that includes the properties of both number and size of Pt deposits. For the photocatalytic dehydrogenation of 2-propanol, the rate dependence could be interpreted semiquantitatively with the model that only the TiO2 particles loaded with at least one Pt deposit can photocatalyze, but the reaction rate is independent of the number of Pt deposits. Therefore, the overall rate is proportional to the number of Pt-loaded TiO2 particles. On the other hand, for the interpretation of the rate of PCA and H2 productions, the number of Pt deposits on each TiO2 particle had to be taken into account. The efficient production of PCA at higher Pt loadings was attributed to the reduction of a Schiff base intermediate produced via oxidation of Lys with positive holes and subsequent intramolecular condensation at the Pt deposit that is close to the site for the oxidation. Otherwise, photoexcited electrons are consumed for H2 production and the intermediate remains unreduced or undergoes further oxidation. It was suggested that the intermediate produced at the TiO2 surface sites within a distance of several nanometers from the Pt deposit undergoes efficient reduction to PCA. Thus, the importance of the distribution of Pt deposits for the preparation of highly active and selective TiO2−Pt photocatalyst has been clearly demonstrated.

Studies on the Sulfur Poisoning of Ru–RuOx/TiO2Catalyst for the Adsorption and Methanation of Carbon Monoxide

The effects of sulfur poisoning on the chemisorption and on the methanation of carbon monoxide over Ru/TiO2catalyst were investigated by FTIR spectroscopy and volumetric gas adsorption measurements. The CS2molecules are η′ bonded to Ru sites through one of the sulfur atoms and decompose to the constituent elements on thermal activation. Each S atom may deactivate 3 to 10 metal sites even at low coverages, the effect being more pronounced on the chemisorption of hydrogen. The deposited sulfur (and possibly carbon also) sterically hinders the formation of certain multicarbonyl and monocarbonyl species (νCO in 2055–2140 cm−1region), which otherwise transform to methane via surface methylene groups in the presence of chemisorbed hydrogen and are found to play an important role in the low-temperature methanation activity of the studied catalyst. The Ru–CO species giving rise to lower-frequency vibrational bands are affected to a lesser extent. The presence of sulfur also results in the development of some new CO binding states which are weak and are identified with the CO and S coadsorbed at Ru sites of different oxidation states or of varying crystallographic nature. The CO adsorbed in these states is not reactive to hydrogen.

The effect of swelling pressure during coal carbonization on coke porosity

In cokemaking, the generation of swelling pressure is an important consideration since excessive pressures result in problems with pushing the coke and in extreme cases, damage to coke ovens may occur. In this investigation, the effect of swelling pressure generated during coal carbonization in coke ovens on coke porosity was studied. The swelling pressure was measured using a movable-wall test oven. The gas pressure in the plastic layer and the swelling pressure were monitored during the carbonization of coals in the test coke ovens. The porous structure of the resultant coke was assessed. The coke macropore structure was characterized using an optical microscope coupled with an image analyser and the micropore structure was characterized using a volumetric gas adsorption method. A method to determine the extent to which the macropores were distorted under unit pressure during the thermoplastic stage was also developed. It was shown that the macropores were compressed against the coke oven wall by the gas pressure in the plastic layer, resulting in the distortion of their shape; the extent of distortion varied greatly with the type of coal. The results suggested that the macropore distortion depended not only on the swelling pressure but also on the amount of distortion per unit pressure during the thermoplastic stage. Furthermore, the characteristics of the coke pore structure from a dangerously swelling coal varied considerably over the oven width. As the oven centre, where the gas pressure was extremely high, was approached, the macroporosity and the mean macropore diameter decreased, while the microporosity increased. The changes in the macroporosity and microporosity over the oven width are discussed in relation to the gas pressure in the plastic layer and the swelling pressure developed during carbonization.

A high-pressure volumetric gas adsorption system

A unique, all-metal, volumetric gas adsorption system has been described. This device was capable of facilitating precise and semiautomatic measurements which could be used to produce complete adsorption isotherms. Isotherm temperatures could be controlled and maintained at the boiling point of liquid nitrogen, argon, and oxygen. In addition, relatively high-pressure adsorption isotherms could be measured due to the all-metal construction of the adsorption system.

Open pore structure analysis of lithium bearing ceramics

The analysis of the open pore structure includes mercury porosimetry, helium stereopycnometry, gas permeability and specific surface area measurements. These methods were used in the analysis of different types of Li 2SiO 3 and Li 4SiO 4 specimens whose behaviour is tested under operation conditions in various irradiation experiments. Mercury porosimetry yielded density of the specimens, size distribution of the channels and amount of the open porosity. The correlation between mercury pressure and channel diameter was approximated by the Washburn equation. Density determinations by means of helium stereopycnometry demonstrated the existence of open pore volume below the mercury porosimetry detection. Additional information about the structure of open porosity was obtained by gas permeability measurements evaluated using the Carman relation, which is a generalization of the Hagen-Poiseuille law. This approach correlates structure parameters of the open porosity with permeability coefficients. The specific surface area was determined by applying the BET theory to volumetric nitrogen gas adsorption.

A chemical and physical characterization of alumina-supported Rh 6(CO) 16

The decarbonylation and carbonylation reactions of the metal cluster carbonyl Rh 6(CO) 16 supported on Al 2O 3 were investigated using volumetric gas adsorption measurements, ir spectroscopy, isotopic measurements, transmission electron microscopy, and EPR spectroscopy. Complete decarbonylation by O 2 and subsequent recarbonylation to Rh 6(CO) 16 could be achieved at room temperature provided sufficient physically adsorbed H 2O was present. A two-step reaction scheme is presented which accounts for the experimental data; it is suggested that the Rh 6 cluster remained intact during these reactions. When heated, in vacuo, above 250 °C, the catalyst lost its ability to undergo the reversible carbonylation/decarbonylation cycle, and the resulting material resembled a highly dispersed conventional Rh catalyst. TEM data showed that no larger crystallites (>10 Å) of Rh are formed even when heated in vacuo to 450 °C.

石炭の表面反応に関する研究

We estimated total surface area of some Japanese coal by the volumetric gas adsorption method. From these results, the relations between pore size and surface area in coals were clarified. For the confirmation of the relations in question, we used the Kelvin equation that based on the capillary condensation theory.Using the B.E.T. method, the surface areas of coals were derived from adsorption isotherms of nitrogen (at-196°C) and carbon dioxide (at-78°C).The results obtained are as follows.1) The surface areas determined with carbon dioxide, are greater than those with nitrogen.2) If we give the physical and chemical reactivity of coal by means of the surface area and pore size distribution, one of the most responsible coal is Oshima.3) The values of surface area do not always have definite connection with its pore size distribution. Namely, even if the coals have practically equal surface area, the pore size distribution of these coals are fairly different.