Chan Hyun Lee

Hydrothermal Synthesis of K2CO3-Promoted Hydrotalcite from Hydroxide-Form Precursors for Novel High-Temperature CO2 Sorbent

In many materials for CO2 sorption, hydrotalcite is attracting substantial attention as a high temperature (200-500 °C) CO2 sorbent because of its fast sorption/desorption kinetics and easy regenerability. However, the CO2-sorption capacity of conventional hydrotalcite is relatively low for large-scale commercial use. To enhance CO2-sorption capacity, hydrotalcite is conventionally impregnated with alkali metals such as K2CO3. Although K2CO3-impregnated hydrotalcite has high CO2-sorption capacity, the preparation method takes long time and is inconvenient because hydrotalcite synthesis step and alkali metal impregnation step are separated. In this study, K2CO3-promoted hydrotalcite was newly synthesized from hydroxide-form percursors by a simple and eco-friendly method without a solvent-consuming washing step. Analysis based on X-ray diffraction indicated that the prepared samples had structures of well-defined hydrotalcite crystalline and un-reacted Mg(OH)2 precursor. Moreover, K2CO3 was successfully incorporated in hydrotalcite during the synthesis step. The prepared K2CO3-promoted hydrotalcite showed high CO2-sorption capacity and had potential for use as a high-temperature CO2 sorbent.

Electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite in acid media

Abstract The electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite (BPG) in acid media was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. A simple electrodeposition method of ruthenium oxide layer on BPG electrode was established in this study. Ruthenium oxide layer, which was prepared by a simple electrodeposition method in acidic ruthenium chloride solution, stable in the potential range between −0.3 and 0.9 V vs. saturated calomel electrode (SCE) but stripped at high potential range between 1.0 and 1.7 V . According to XPS analysis, the layer presented more than two different peaks, which showed the oxidation states of ruthenium between Ru (2+) and Ru (4+). A peak current of 260 μA at 1.0 V was observed for the electrooxidation of methanol on ruthenium oxide layer.

Secondary Crystal Growth on a Cracked Hydrotalcite-Based Film Synthesized by the Sol–Gel Method

The sol-gel synthesis method is an attractive technology for the fabrication of ceramic films due to its preparation simplicity and ease of varying the metal composition. However, this technique presents some limitations in relation to the film thickness. Notably, when the film thickness exceeds the critical limit, large tensile stresses occur, resulting in a cracked morphology. In this study, a secondary crystal growth method was introduced as a post-treatment process for Mg/Al hydrotalcite-based films synthesized by the sol-gel method, which typically present a cracked morphology. The cracked hydrotalcite-based film was hydrothermally treated for the secondary growth of hydrotalcite crystals. In the resulting film, hydrotalcite grew with a vertical orientation, and the gaps formed during the sol-gel synthesis were filled with hydrotalcite after the crystal growth. The secondary crystal growth method provides a new solution for cracked ceramic films synthesized by the sol-gel method.

Predictive Guide for Collective CO2 Adsorption Properties of Mg−Al Mixed Oxides

Although solid adsorption processes offer attractive benefits, such as reduced energy demands and penalties compared with liquid absorption processes, there are still pressing needs for solid adsorbents with high adsorption capacities, thermal efficiencies, and energy-intensive regeneration in gas-treatment processes. The CO2 adsorption capacities of layered double oxides (LDOs), which are attractive solid adsorbents, have an asymmetric volcano-type correlation with their relative crystallinities. Furthermore, new collective adsorption properties (adsorption capacity, adsorptive energy and charge-transfer amount based on the adsorbent weight) are proposed based on density functional theory (DFT) calculations and measured surface areas. The correlation of these collective properties with their crystallinities is in good agreement with the experimentally measured CO2 adsorptive capacity trend, providing a predictive guide for the development of solid adsorbents for gas-adsorption processes.