Kiyong Ahn

Catalytic Characteristics of Perovskite-type Oxides under Mixed Methane and Oxygen Gases

As the single chamber SOFC (SC-SOFC) showed higher prospect on reducing the operation temperature as well as offering higher design flexibility of SOFCs, lots of concerns have been given to investigate the catalytic activity of perovskite-type oxide in mixed fuel and oxidant conditions. Hence we thoroughly investigated the catalytic property of various perovskite-type oxides such as La 0.8 Sr 0.2 MnO₃ (LSM), La 0.6 Sr 0.4 CoO₃ (LSC), La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O₃ (LSCF), Sm 0.5 Sr 0.5 CoO₃ (SSC), and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 (BSCF) under the partial oxidation condition of methane which used to be given for SC-SOFC operation. In this study, powder form of each perovskite oxides whose surface areas were controlled to be equal, were investigated as functions of methane to oxygen ratios and reactor temperature. XRD, BET and SEM were employed to characterize the crystalline phase, surface area and microstructure of prepared powders before and after the catalytic oxidation. According to the gas phase analysis with flow-through type reactor and gas chromatography system, LSC, SSC, and LSCF showed higher catalytic activity at fairly lower temperature around 400℃~450℃ whereas LSM and BSCF could be activated at much higher temperature above 600℃.

Nonlinear echo cancellation using an expanded correlation LMS algorithm

Nonlinear echo cancellation in a hybrid telephone network is considered, whereby adaptive Volterra filtering is utilized along with an expanded correlation LMS (ECLMS) algorithm to compensate for nonlinear distortion in the echo path. Also, some simulation results are provided to demonstrate the validity of the proposed approach even in a double-talk situation.

Oxygen Vacancy Chain Formation in TiO2 under External Strain for Resistive Switching Memory

The electronic structure and vacancy formation energy of rutile TiO2 with ordered oxygen vacancies were calculated using the density functional theory with on-site Coulomb corrections between Ti 3d orbital and O 2p orbital (LDA+Ud+Up). The calculated band gaps are about 3 eV, using LDA+Ud+Up, and a hybrid functional proposed by Heyd–Scuseria–Ernzerhog. The ordered oxygen vacancies were introduced along the [001] direction within a 3×3×4 supercell of rutile TiO2-x that consisted of 72 Ti and 136 O atoms. Biaxial strain was induced in the rutile TiO2 along the x- and y-directions up to ±5%. The lowest formation energy of ordered oxygen vacancies was found in 5% compressive strain and deemed as a thermodynamically favorable structure.

Enhanced carbon tolerance of Ir alloyed Ni-Based metal for methane partial oxidation

Carbon plugging of active catalytic sites significantly degrades the performance of the hydrocarbon reformers. In this study, we show that small amount of Ir alloyed to Ni/CeO2 nanoparticle exhibit promising improvements to the carbon tolerance properties. XRD analysis indicates that the synthesized nanoparticles are comprised of independent NiO and CeO2 particulates and that the added Ir atoms tend to stay on the surface consistent with the theoretical calculation results of the proposed Ir-Ni alloy. The Ir rich samples show higher methane cracking rate and better carbon removal characteristics. Also, the CO selectivity result shows that adding Ir can prolong the lifetime of the Ni active sites despite a slight drop in the initial partial oxidization reforming rate. Our findings highlight the enhancement effects of Ir on the Ni-based metal carbon tolerance properties and bring us one step closer to finding a solution for the carbon plugging problem.

A Study of Methane Oxidation over Transition Metal (TM)/CeO 2 (TM=Ni, Co, Cu, Fe)

The properties of methane oxidation were studied in this research over transition metal containing (TM/, TM