Jung Tae Lim

Highly activated K-doped iron carbide nanocatalysts designed by computational simulation for Fischer–Tropsch synthesis

Although the reaction results of numerous iron-based Fischer–Tropsch synthesis catalysts containing various promoters have been reported, the research on their theoretical foundation is still insufficient. In the present work, highly activated K-doped χ-Fe5C2/charcoal nanocatalysts were designed using calculations based on density functional theory (DFT), and then prepared using a melt-infiltration process and a subsequent incipient-wetness method of K precursors. The catalyst at K/Fe = 0.075 in an atomic ratio that bears small iron carbide nanoparticles of ∼18 nm showed the highest activity (1.54 × 10−4 molCO gFe−1 s−1) and the best hydrocarbon yield (1.41 × 10−3 gHC gFe−1 s−1), as well as a good selectivity for gasoline-range (C5–C12) hydrocarbon products in the high-temperature Fischer–Tropsch reaction.

Investigation of magnetic properties of non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5Fe12O22

Ba2Mg0.5Co1.5Fe12O22 (non-doped) and non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5(Fe0.99M0.01)12O22 (M-doped) polycrystalline samples were prepared by the solid-state reaction method. The crystal structures and magnetic properties of samples were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The crystal structures of non-doped and M-doped samples were determined as hexagonal structures with R-3m space group by the Rietveld refinement. The unit cell volume (Vu) of non-doped sample was Vu = 1298.0 A3, while those of M-doped samples (M = Al, Ga, In) were Vu = 1295.7, 1296.7, and 1299.9 A3, respectively. From the magnetic hysteresis curves at room temperature, the saturation magnetization (Ms) and coercivity (Hc) of non-doped sample were found to be Ms = 28.0 emu/g and Hc = 255.4 Oe, but those of M-doped samples (M = Al, Ga, In) were Ms = 24.7, 28.4, 28.6 emu/g, and Hc = 222.0, 215.9, 190.7 Oe, respectively. From the temperature dependence ...

Magnetic properties of Zn doped Co2Y hexaferrite by using high-field Mössbauer spectroscopy

The polycrystalline samples of Ba2Co2−xZnxFe12O22 (x = 0.5, 1.0, 1.5) were synthesized by using solid-state-reaction method. From the XRD patterns, analyzed by Rietveld refinement, the prepared samples are found to be single-phased with rhombohedral structure (R-3m). The magnetic properties of samples were investigated with vibrating sample magnetometer, and high-field Mossbauer spectrometer. From the zero-field-cooled curves under 100 Oe between 4.2 and 740 K, we observe that the samples show spin transition from helicalmagnetic to ferrimagnetic order. With increasing Zn ion concentration, the spin transition temperature (Ts) and Curie temperature (TC) decrease linearly. We have obtained Zero-field Mossbauer spectra of all samples at various temperatures ranging from 4.2 to 650 K, and analyzed the spectra below TC as six-sextets for Fe sites. From the temperature dependence of hyperfine field (Hhf), we have noticed an abrupt change in Hhf at Ts. In addition, Mossbauer spectra of all samples at 4.2 K were...

Investigation of site preference of Zn doped Ba3Co2−xZnxFe24O41 by Mössbauer spectroscopy

The polycrystalline Ba3Co2−xZnxFe24O41 (x = 0.0, 0.5, 1.0) samples were prepared by using solid-state-reaction method. The crystal structures and magnetic properties of samples were investigated with x-ray diffractometer, vibrating sample magnetometer, and Mossbauer spectroscopy. The crystal structure of Ba3Co2−xZnxFe24O41 (x = 0.0, 0.5, 1.0) samples was determined to be a hexagonal structure with P63/mmc space group at 295 K, and the saturation magnetization (Ms) of Ba3Co2−xZnxFe24O41 (x = 0.0, 0.5, 1.0) samples were found to be Ms = 50.9, 53.1, 55.0 emu/g, respectively. From the temperature dependence of magnetization curves under 100 Oe between 4.2 and 740 K, we were able to observe the spin transition, and both spin transition temperature (Ts) and Curie temperature (TC) decrease with increasing Zn concentration. Mossbauer spectra of all samples were obtained and analyzed at various temperatures ranging from 4.2 to 295 K. With ten-sextets for Fe sites corresponding to the Z-type hexagonal crystallograp...

Investigation of Magnetic Properties of Zn Doped Y-Type Barium Ferrite

The Ba₂Co_2-xZn_xFe₁₂O₂₂ (x = 0.0

Hyperfine structure and magnetic properties of Zn doped Co2Z hexaferrite investigated by high-field Mössbauer spectroscopy

, 0.5, 1.0, 1.5, and 2.0) polycrystalline samples were synthesized by the solid-state reaction method. Based on the Rietveld refinement, the crystal structures of samples were found to be single-phased and determined to be rhombohedral with space group of R - 3m. The unit cell volume (V_u) of the samples increased with increasing Zn ion concentration. In the magnetic phase diagram of Ba₂Co_2-xZn_xFe₁₂O₂₂ system, samples with x ≤ 1.5 showed the spin transitions both at T_s and T_C. For x = 2.0 sample, we observed the disappearance T_s. The non-magnetic Zn ions preferentially occupy the tetrahedral sublattices of 6c_IV*, and 6c_IV* with down-spin site. At low temperature, this leads to the increase in M_s. However, the experimentally measured M_s at 295 K shows a slight decrease around x = 1.5. In - ddition, we have measured Mössbauer spectra of samples at various temperatures ranging from 4.2 to 750 K, which can analyzed with six-sextets for Fe sites corresponding to the 3b_VI, 6c_IV*, 6c_VI, 18h_VI, 6c_IV, and 3α_VI of the Y-type hexagonal crystallographic sites. From the Mössbauer spectra of 295 K, we observed the line-width broadening with increasing Zn concentration.

Microscopic evidence of magnetic and structure phase transition in multiferroic spinel FeV2O4

The polycrystalline samples of Ba3Co2−xZnxFe24O41 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were synthesized by the standard solid-state-reaction method. Based on the XRD patterns analyzed by Rietveld refinement, the structure was determined to be single-phased hexagonal with space group of P63/mmc. With increasing Zn ion concentration, the unit cell volume (Vu) of samples was increased, as the sites of Fe3+ ions changed from tetrahedral to octahedral sites. We have obtained zero-field Mossbauer spectra of all samples at various temperatures ranging from 4.2 to 750 K. The measured spectra below TC were analyzed with six distinguishable sextets due to the superposition of ten-sextets for Fe sites, corresponding to the Z-type hexagonal ferrite. Also, the hyperfine field (Hhf) and electric quadrupole shift (EQ) have shown abrupt changes around spin transition temperature (TS). In addition, Mossbauer spectra of all samples at 4.2 K were taken with an applied field ranging from 0 to 50 kOe, which indicates the decreas...

The crystalline and magnetic properties of Zn doped strontium Z-type hexaferrite synthesized by polymerizable complex method

We report the microscopic evidence for magnetic and structural phase transitions in multiferroic spinel FeV2O4 from the hyperfine magnetic interaction. FeV2O4 sample shows three different crystal structures with the phase transitions from tetragonal to orthorhombic structure around 70 K, from orthorhombic to tetragonal structure around 109 K, and from tetragonal to cubic structure around 140 K. Mossbauer spectra of FeV2O4, obtained at various temperatures, were analyzed with severely distorted 8-line below TC, and doublet at TC. Also, the Mossbauer spectra change from doublet to singlet around TJT ≅ 140 K due to the reduction of Jahn-Teller effect. The value of electric quadrupole splitting (ΔEQ) is 3.05 mm/s at 4.2 K, indicating the noncollinear spin structure with strong polarization from the gap energy of 5T2g band, Δ1 ≅ 0. Whereas, there is collinear spin structure between TS ≅ 70 K < T < TC ≅ 109 K, since Δ1 in this temperature range increases from the value when T < TS due to the non-degenerate ener...

Investigation of spin reorientation in YMn1−xFexO3 (x = 0.55, 0.6, 0.7, 0.8, 0.9, and 1.0) by Mössbauer spectroscopy

Polycrystalline samples of Sr3Co2-xZnxFe24O41 (x = 0.0, 0.5, 1.0, 1.5, 2.0) were synthesized by a polymerizable complex method. The crystallographic, and magnetic properties of samples were investigated using x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The crystal structures of all samples were determined to be hexagonal with the space group P63/mmc. The hysteresis curves under 10 kOe at 295 K showed that all samples were not saturated due to the high planar anisotropy of Sr ions. In addition, the coercivity (Hc) of samples decreased with increasing Zn ion contents. Mossbauer spectra of all samples were obtained at 295 K, and least-squares fitted below TC as six distinguishable sextets (4fIV, 4fIV*, 12kVI*, 4fVI*+ 4eIV, 12kVI, and 2dV + 2aVI + 4fVI + 4eVI).

Mössbauer Study of the Dynamics in BaFe 12 O 19 Single Crystals

YMn1−xFexO3 (x = 0.55, 0.6, 0.7, 0.8, 0.9, and 1.0) polycrystalline samples were prepared by the solid-state-reaction method. The crystal structure and magnetic properties of samples were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer, and Mossbauer spectroscopy. The XRD patterns at 295 K, analyzed by Rietveld refinement method, showed that all samples were single-phased orthorhombic of Pnma with both Bragg (RB) and structure (RF) factors less than 5%. Mossbauer spectra of all samples were obtained at various temperatures ranging from 4.2 to 500 K, and the spectra below TC were fitted by least-square method as a function of the Fe and Mn distribution. Isomer shift (δ) values of all samples indicated that the charge states were Fe3+. In addition, temperature-dependent hyperfine field (Hhf), averaged electric quadrupole shift 〈EQ〉, and averaged isomer shift 〈δ〉 have shown abrupt changes around TSR due to the change in the charge state of Mn ions.