Concurrent Production of Carbon Monoxide and Manganese(II) Oxide through the Reaction of Carbon Dioxide with Manganese

This study introduces the simultaneous production of manganese oxide (MnO (II)) and carbon monoxide (CO) from the reaction of carbon dioxide (CO₂) with manganese (Mn) at ambient pressures. The reaction results showed that Mn oxidation in the presence of CO₂ creates highly pure MnO (99.4 mol %) and a small portion of another manganese oxide (Mn₃O₄ (III)) with the evolution of CO. It is striking that the oxidation path of manganese under CO₂ environments is totally reverse compared to that under oxygen (O₂) environments, and it produces MnO at much lower temperature (around 700 °C) than the temperature (1700 °C) from the O₂ oxidation path. The different patterns of Mn oxidation by both CO₂ and O₂ can arise from the differences in thermodynamic stability and reactivity of CO₂ and O₂. Additionally, mass spectroscopic measurements revealed that CO generation originates from the CO₂ reduction. Above 700 °C, more CO was produced by the reverse Boudouard reaction occurring between the carbon deposited on the manganese oxide surface and CO₂. This Mn–CO₂ reaction system provides an opportunity for producing more valuable products such as MnO and CO by utilizing the greenhouse gas

Abnormal Proton Positioning of Water Framework in the Presence of Paramagnetic Guest within Ion-Doped Clathrate Hydrate Host

The unique host–guest interactions of ionic clathrate hydrates, as distinct from those of other nonionic clathrate hydrates, need to be investigated to understand their inherent physicochemical features, but direct observation of ionic host geometry has not yet been attempted. In this study, we first report the distortions of the water–water connection in the charged cages caused by orbital mixing between a paramagnetic guest and an ion-doped host, and by electrostatic repulsion between the cationic host and guest via the direct observation with using synchrotron high-resolution powder diffraction analysis. The present findings well explain the mechanisms of unique phenomena occurring in ionic clathrate hydrates with paramagnetic guests

Tuning Behaviors of Methane Inclusion in Isoxazole Clathrate Hydrates

In this study, the inclusion of methane (CH₄) gas in isoxazole (C₃H₃NO) clathrate hydrates was investigated through spectroscopic observations, such as powder X-ray diffraction (PXRD) and Raman spectroscopy. PXRD patterns of isoxazole clathrate hydrates having two different mole fractions of water were analyzed, and Raman spectroscopy was used to understand the CH₄ inclusion behaviors in the hydrate cavities. Raman spectra indicated that CH₄ can be captured in both small and large cavities of structure II hydrate in the C₃H₃NO with 34H₂O system, while CH₄ can be entrapped in only small cavities of structure II hydrate in the C₃H₃NO with 17H₂O system. The PXRD result showed both clathrate hydrate samples exhibit the same cubic <i>Fd3m</i> structure II hydrate as expected. However, the structure II hydrate in the C₃H₃NO with 34H₂O system includes a small amount of hexagonal ice and structure I CH₄ hydrate. The phase equilibrium conditions of the binary (isoxazole + CH₄) clathrate hydrate were also identified through high-pressure micro differential scanning calorimetry (MicroDSC), and the equilibrium temperatures of the binary (isoxazole + CH₄) clathrate hydrate at given pressures are higher than those of the structure I CH₄ hydrate

Synergetic Effect of Ionic Liquids on the Kinetic Inhibition Performance of Poly(<i>N</i>‑vinylcaprolactam) for Natural Gas Hydrate Formation

To identify the synergetic inhibition effects of ionic liquids (ILs) containing tetrafluoroborate anion (BF₄^–), various ILs, poly­(<i>N</i>-vinylcaprolactam) (PVCap), commercially available polymeric hydrate inhibitor, and their mixtures, were tested as kinetic hydrate inhibitors (KHIs) for natural gas hydrate formation. The experimental results revealed that PVCap–IL mixtures exhibited significantly higher KHI performance. In particular, the mixture of PVCap and 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF₄) showed the best hydrate inhibition effectiveness, even under higher pressures. As HMP-BF₄ also exhibited the highest hydrate-nucleation-inhibiting performance when it was used alone, further experiments were performed using the mixtures of PVCap and HMP-BF₄ at various combinational concentrations. As a result of the experiments, the combination of 1.0 wt % PVCap and 0.5 wt % HMP-BF₄ was found to provide the longest induction time. The excellent synergetic effect of the ILs on natural gas hydrate inhibition may arise from the prevention of methane-containing 5¹² cage formation by the ILs, inducing inhibition of metastable structure I hydrate formation

Synergetic Effect of Ionic Liquids on the Kinetic Inhibition Performance of Poly(<i>N</i>‑vinylcaprolactam) for Natural Gas Hydrate Formation

To identify the synergetic inhibition effects of ionic liquids (ILs) containing tetrafluoroborate anion (BF₄^–), various ILs, poly­(<i>N</i>-vinylcaprolactam) (PVCap), commercially available polymeric hydrate inhibitor, and their mixtures, were tested as kinetic hydrate inhibitors (KHIs) for natural gas hydrate formation. The experimental results revealed that PVCap–IL mixtures exhibited significantly higher KHI performance. In particular, the mixture of PVCap and 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF₄) showed the best hydrate inhibition effectiveness, even under higher pressures. As HMP-BF₄ also exhibited the highest hydrate-nucleation-inhibiting performance when it was used alone, further experiments were performed using the mixtures of PVCap and HMP-BF₄ at various combinational concentrations. As a result of the experiments, the combination of 1.0 wt % PVCap and 0.5 wt % HMP-BF₄ was found to provide the longest induction time. The excellent synergetic effect of the ILs on natural gas hydrate inhibition may arise from the prevention of methane-containing 5¹² cage formation by the ILs, inducing inhibition of metastable structure I hydrate formation

Rollable Microfluidic Systems with Microscale Bending Radius and Tuning of Device Function with Reconfigurable 3D Channel Geometry

Flexible microfluidic system is an essential component of wearable biosensors to handle body fluids. A parylene-based, thin-film microfluidic system is developed to achieve flexible microfluidics with microscale bending radius. A new molding and bonding technique is developed for parylene microchannel fabrication. Bonding with nanoadhesive layers deposited by initiated chemical vapor deposition (iCVD) enables the construction of microfluidic channels with short fabrication time and high bonding strength. The high mechanical strength of parylene allows less channel deformation from the internal pressure for the thin-film parylene channel than bulk PDMS channel. At the same time, negligible channel sagging or collapse is observed during channel bending down to a few hundreds of micrometers due to stress relaxation by prestretch structure. The flexible parylene channels are also developed into a rollable microfluidic system. In a rollable microfluidics format, 2D parylene channels can be rolled around a capillary tubing working as inlets to minimize the device footprint. In addition, we show that creating reconfigurable 3D channel geometry with microscale bending radius can lead to tunable device function: tunable Dean-flow mixer is demonstrated using reconfigurable microscale 3D curved channel. Flexible parylene microfluidics with microscale bending radius is expected to provide an important breakthrough for many fields including wearable biosensors and tunable 3D microfluidics

Superexchange-Like Interaction of Encaged Molecular Oxygen in Nitrogen-Doped Water Cages of Clathrate Hydrates

Clathrate hydrates are a highly prospective material in energy and environmental fields, but the inherent nature of inclusion phenomena occurring in the stacked water cages has not been completely resolved yet. Investigating the magnetism of guest molecules is a new experimental approach in clathrate hydrate research to open the possibility of icy magnetic applications as a novel material as well as to understand the unrevealed host–guest interactions in icy inclusion compounds. In this study, we observed an indirect spin coupling between encaged dioxygen molecules via a nonmagnetic water framework through the measurement of guest magnetization. This spin coupling is reminiscent of superexchange coupling between magnetic ions through intervening oxygens in antiferromagnetic oxides, such as MnO and CoO. Theoretical calculations revealed that OH– incorporated in the framework induced the mixing of perpendicular π* orbitals of two distant dioxygens and that ammonia doping into the hydrate cage leads to a longer lifetime of that orientation

Thermal Expansivity of Ionic Clathrate Hydrates Including Gaseous Guest Molecules

Although thermal expansion is a key factor in relation to the host−guest interaction of clathrate hydrates, few studies have investigated the thermal behavior of ionic clathrate hydrates. The existence of ionic species in these hydrates creates a unique host−guest interaction compared to that of nonionic clathrate hydrates. It was revealed that X-ray diffraction cannot be used for research of tetramethylammonium hydroxide clathrate hydrates due to damage of the cations by the X-ray, which results in abnormal thermal expansion of the ionic clathrate hydrates. Hence, in the present work, the thermal expansivities of binary sII Me4NOD·16D2O and sI DClO4·5.5D2O were measured by neutron powder diffraction (NPD) in order to shed light on their thermal behavior. General correlations for the thermal behaviors of given structures were established and lattice expansions depending on the guests were compared between ionic and nonionic clathrate hydrates. The peculiar change in the thermal expansivity of binary DClO4·5.5D2O was also considered in relation to the host−guest configuration

Atomically Dispersed Nickel Coordinated with Nitrogen on Carbon Nanotubes to Boost Electrochemical CO₂ Reduction

Single-atom catalysts (SACs) are being widely developed for the CO2 reduction reaction (CO2RR) because of their remarkable activity and selectivity. However, insufficient CO2RR performance and the poor long-term stability of the SACs remain obstacles to process scale-up. Herein, we explore Ni SACs (Ni-N/NCNT) under practical conditions using a zero-gap CO2 electrolyzer for CO production. We demonstrate that the CO2RR performance of the Ni-N/NCNT results from the suitable Ni–N–C, which enhanced electron transfer and increased CO2 adsorption. Furthermore, we propose a strategy for improving the CO2RR performance and long-term stability by focusing on the membrane electrode assembly (MEA) structure. A maximum Faradaic efficiency of 96.73% (at 2.1 V) and partial current density of 219.49 mA cm–2 (at 2.4 V) for CO production were obtained on the MEA with the Ni-N/NCNT catalyst and the Sustainion (Sust.) membrane. In addition, MEA with Sust. exhibited long-term stability at −100 mA cm–2 for over 60 h

Role of Binder in Cu₂O Gas Diffusion Electrodes for CO₂ Reduction to C₂₊ Products

The electrochemical CO2 reduction reaction (CO2RR) to form C2+ products was investigated to obtain high selectivity in liquid CO2-fed systems having the limitation of low current density. Over the past decade, flow cells with gas diffusion electrodes (GDEs) have emerged to achieve high current densities close to the industrial-relevance scale by overcoming gas diffusion limitations. However, key parameters of GDE design, including binders, were not sufficiently identified to enhance selectivity and current density for C2+ products. Nafion, FAA-3, and polypyrrole were used to explore the effects of binder type and content on GDE properties such as porosity (gas permeability), ion conductivity, and electron conductivity for the modulation of the CO2RR on the Cu2O catalyst. The Cu2O GDEs with high binder content showed poor selectivity for C2+ products because of their low exposure to the catalyst surface and decreased gas permeability. The anion exchange ionomer, FAA-3, showed high selectivity for C2+ products and electrode stability resulting from the C–C coupling increase and suppression of the hydrogen evolution reaction, which was induced by OH– conductivity. In contrast, the cation exchange ionomer, Nafion, exhibited low electrode stability due to the loss of gas products through the catholyte and due to its excessive wettability