[en] Highlights: •Na-Mg double salt-based sorbent was used for high-temperature CO₂ sorption. •Divided section packing concept was applied to the SE-WGS reaction. •High-purity H₂ was produced from the SE-WGS reaction with divided section packing. •High-purity H₂ productivity could be further enhanced by modifying packing method. -- Abstract: Hydrogen is considered a promising environmentally benign energy carrier because it has high energy density and produces no pollutants when it is converted into other types of energy. The sorption-enhanced water gas shift (SE-WGS) reaction, where the catalytic WGS reaction and byproduct CO₂ removal are carried out simultaneously in a single reactor, has received considerable attention as a novel method for high-purity hydrogen production. Since the high-purity hydrogen productivity of the SE-WGS reaction is largely dependent on the performance of the CO₂ sorbent, the development of sorbents having high CO₂ sorption capacity is crucial. Recently, a Na-Mg double salt-based sorbent has been considered for high-temperature CO₂ capture since it has been reported to have a high sorption capacity and fast sorption kinetics. In this study, the SE-WGS reaction was experimentally demonstrated using a commercial catalyst and a Na-Mg double salt-based sorbent. However, the SE-WGS reaction with a one-body hybrid solid, a physical admixture of catalyst and sorbent, showed poor reactivity and reduced CO₂ sorption uptake. As a result, a divided section packing concept was suggested as a solution. In the divided section packing method, the degree of mixing for the catalyst and sorbent in a column can be controlled by the number of sections. High-purity hydrogen (<10 ppm CO) was produced directly from the SE-WGS reaction with divided section packing, and the hydrogen productivity was further improved when the reactor column was divided into more sections and packed with more sorbent.

[en] Layered double hydroxide (LDH), one of representative high-temperature CO_2 sorbents, has many advantages, including stable CO_2 sorption, fast sorption kinetics, and low regeneration temperature. However, CO_2 sorption uptake on LDH is not high enough for practical use; thus it is usually enhanced by impregnation with alkali metals such as K_2CO_3. In this study, LDH was impregnated with Na_2CO_3, and analyses based on scanning electron microscopy, N_2 gas physisorption, in situ X-ray diffraction, and Fourier transform infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO_2 sorption. Although the surface area of LDH decreased after Na_2CO_3 impregnation, CO_2 sorption uptake was greatly enhanced by the additional basicity of Na_2CO_3. The crystal structure of Na_2CO_3 in the Na_2CO_3-impregnated LDH changed from monoclinic to hexagonal with increasing temperature, and the sorbed-CO_2 was stored in the form of carbonate. Thermogravimetric analysis was used to measure CO_2 sorption uptake at 200-600 .deg. C. The sample of Na_2CO_3 : LDH=0.35 : 1 weight ratio had the largest CO_2 sorption uptake among the tested sorbents, and the CO_2 sorption uptake tended to increase even after 400 .deg. C

[en] Petroleum coke (PC)-derived porous carbons were developed through chemical activation using KOH and applied to adsorb Cu(II) ions from aqueous solutions. The effects of KOH/PC mass ratio and activation temperature on the preparation and physical properties of porous carbon were studied. Also, the effects of the initial solution pH, contact time, operating temperature, dosage of adsorbent, and initial Cu(II) concentration on adsorption were investigated in detail. A maximum Cu(II) ion adsorption capacity of 89.85 mg g⁻¹ was attained at 30 °C using PCK3-450, the porous carbon sample prepared using a KOH/PC mass ratio of 3:1 at 450 °C. Adsorption isotherms were analyzed using the Langmuir, Freundlich, and Temkin models, and the experimental data fit well with the Freundlich model. Pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion models were used to describe the adsorption kinetics, and the rate of adsorption conformed to the pseudo second-order kinetic model. The activation energy of Cu(II) ion adsorption on PCK3-450 was estimated at 29.61 kJ mol⁻¹, and thermodynamic parameters were discussed. The porous carbon adsorbents developed in this study are inexpensive and effective for Cu(II) ion removal from aqueous solutions.

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[en] Resonant X-ray scattering measurements for a GdB4 single crystal have been carried out at Gd L3- and L2-edges. Branching ratios between x-ray scattering intensities at two x-ray energies are different for resonance peaks. Their analysis shows different anisotropic characters of 5d electron states of Gd ions corresponding to the peaks.

[en] Strongly intertwined interaction among spin, orbital and charge degrees of freedom is the essence to induce emergent materials properties, and the investigation to understand their interplay has been actively pursued. In particular, resonant X-ray scattering technique has demonstrated powerful applications in unveiling their long-range ordering behavior with its enhanced sensitivity to the aforementioned degree of freedom. Here, we further demonstrated the spectroscopic application of the technique by providing experimental evidence to reveal spin polarizations in 4f and 5d orbital of the magnetic Tm ions with the orbital-selectivity, which introduced a route to understand fundamental mechanism of spin polarization in the compound. The enhanced sensitivity of the resonant X-ray scattering to various electric multipole transitions expects to find strong applications in studying various spin and polar ordering in materials to include high-order moments.

[en] Structural transitions of the spinel CuV₂S₄ have been studied by means of X-ray diffraction using synchrotron radiation. The temperature dependence of reflections forbidden in a cubic spinel structure of Fd3m suggests that there are order-disorder transitions of 3d²(t_2g) orbitals of V³⁺ ions at about 75 and 210 K. An incommensurate superlattice reflection of (2+3/4,2,2+3/4) shows the structural phase transition occurring at about 90 K, in addition to the superlattice structural modulation at about 30-35 and 55 K. A reduced wavevector q=(3/4-δ,0,3/4-δ) shows the temperature dependence of the δ value from 0.015 to -0.025. A lock-in of δ=0.0 and a crossover of the δ value occur in the region of 40 to 50 K. The incommensurate structural modulation along [110], [011], and [101] directions appearing below about 90 K affects a paramagnetic spin order of V³⁺ ions at about 30-35 and 55 K, in addition to the 90 K structural transition. The paramagnetic behavior is interpreted mainly by the structural deformation and the (d_xy,d_yz,d_zx) orbitals in the VS ₆ octahedral chains sited along [110], [011], and [101] directions. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Highlights: • Porous carbons were prepared from cellulose via hydrothermal carbonization and ZnCl₂ activation. • A facile and effective CuCl loading method resulted in high CO adsorption performance. • Copper-loaded porous carbon exhibited good cyclic stability using vacuum regeneration. • Density functional theory calculations correlated the experimental results. CO is used as a raw material to produce valuable chemicals. Adsorption using solid materials can be employed to separate and recover CO from gas mixtures. In this study, cellulose-based, porous carbons were prepared via hydrothermal carbonization and ZnCl₂ activation. The prepared porous carbons were used for CO separation after CuCl loading by a facile solid-state dispersion method to induce π-complexation and eventually enhance the affinity toward CO. The sample with the highest CO uptake of 3.62 mmol g⁻¹ at 298 K and 101 kPa had a carbon:CuCl loading ratio of 1:1. This is the highest reported CO adsorption on porous carbons using CuCl as a π-complexation-inducing material. In addition, several factors, including the selectivity of CO against CO₂ and the cyclic stability using vacuum regeneration, demonstrated the potential for industrial applications. Density functional theory (DFT) calculations theoretically elucidated that the presence of small and well-dispersed CuCl clusters induce excellent CO-selective adsorption performance, which is in accordance with the experimental results.

[en] Highlights: • The optimal η_K was 87.62% by once N₂ limewater wash, followed by twice CO₂ water washes. • The CO₂ captured from produced syngas can improve the η_K. • The X_C adopting recovered potassium catalyst was well-described by RPM. • The recovered potassium catalyst had same catalytic activity as fresh K₂CO₃. • The recovered potassium catalyst shows a good lifecycle. - Abstract: In this study, after conducting K₂CO₃-catalyzed steam gasification in a bench-scale bubbling fluidized bed reactor, the bench-scale recovery process of potassium catalyst was investigated by changing washing methods and operating parameters. The optimal potassium catalyst recovery efficiency (η_K) from MSJ gasified residue was 87.62%, achieved by utilizing a combined washing method in which the first wash was performed with N₂ limewater (0.25 mol ratio of Ca/K) and the last two washes were with CO₂ water. The recovered potassium catalyst was re-loaded with MSJ coal and then was utilized for conducting the catalytic steam gasification in a lab-scale fixed bed reactor, in order to evaluate the performance of the recovered potassium catalyst from both experimental and kinetic aspects. Compared with the results obtained from fresh K₂CO₃, not only the trends of carbon conversion (X_C) were similar at each gasifying temperature, but also there was no obvious difference in volume percentage of gases produced. When the random pore model (RPM) was adopted, both reaction rate constant (k_RPM) and activation energy (Ea) remained similar. In addition, the lifecycle of the recovered potassium catalyst was studied. Finally, it can be concluded that the potassium catalyst was effectively and efficiently recovered from gasified residue and the recovered potassium catalyst had the same catalytic activity as fresh K₂CO₃, promoting the commercialization and development of the catalytic gasification process.

[en] Vanadium redox flow batteries (VRFBs) have attracted considerable attention for potential use in the development of large-scale energy storage systems. However, the commercialization of VRFBs is still challenging because of their various overpotentials, which are due to the poor reversibility and electrochemical activity of graphite felt (GF) electrodes. In this study, we fabricated a NiO-decorated GF electrode that exhibited a clear electrocatalytic effect on the V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox reactions. Vanadium ions preferentially attached to each NiO site because of strong electrostatic affinity to the local negatively charged O²⁻ species. In particular, a significant amount of NiO bound to graphite by replacement of hydrogen from the hydroxyl groups with nickel ion, leading to an increase in the ratio of carboxyl groups to hydroxyl groups. The increase in the number of carboxyl groups also improved the VRFB performance, since the carboxyl functional group on GF surface acts as effective catalyst for the vanadium redox reactions. Furthermore, NiO nanoparticles enhanced the mass-transfer property of vanadium ions by the increased area and hydrophilicity of the electrode surface. To optimize the electrode structure for high electrochemical performance, the crystallinity and morphology of the NiO catalyst on GF were controlled via the operating temperature and precursor concentration. When optimized NiO/GF₃₀₀ was applied to VRFBs, it exhibited high energy efficiency (74.5%) at a high current rate (125 mA cm⁻²), compared with GF without the catalyst (55.4%). Moreover, NiO-decorated GF exhibited durability and stability in acidic electrolyte during long-term operation for 300 cycles.

[en] A new route via the coating of layered ammonium nickel molybdate with oleic acid was developed to prepare an oil-soluble bimetallic dispersed catalyst for the hydrocracking reaction of heavy oil. The layered ammonium nickel molybdate, termed Ni-LTM precursor, was synthesized by precipitation, and the NiMo oleate complex was prepared with the oleic acid serving as an organic ligand. The prepared materials were characterized with X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It was found that the oleic acid is chemisorbed as a carboxylate onto the Ni-LTM nanoparticles, specifically on Ni-O bond. Also, the catalytic activities were compared between the NiMo oleate complex and other ordinary monometallic dispersed catalysts. The NiMo oleate complex showed excellent catalytic activity, demonstrating its potential to be applied as a novel dispersed catalyst.