• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.566-572
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• 2007

Two hybrid catalysts for the direct synthesis of DME were prepared and the catalytic activity of these catalysts were investigated. The hybrid catalyst for the direct synthesis of DME was composed as the catalytic active components of methanol synthesis and dehydration. The methanol synthesis catalyst was formed from the precursor contained Cu and Zn, the methanol dehydration catalyst was used ${\gamma}-Al_2O_3$. As PM-CZ+D and CP-CZA/D, Two hybrid catalysts were prepared by physical mixing method (PM-CZ+D) and precipitation method (CP-CZA/D), respectively. PM-CZ+D was prepared by physically mixing methanol synthesis catalyst and methanol dehydration catalyst, CP-CZA/D was prepared by depositing Cu-Zn or Cu-Zn-Al components on ${\gamma}-Al_2O_3$. The crystallinity and the surface morphology of synthesized catalyst were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) to investigate the physical property of prepared catalyst. And BET surface area by $N_2$ adsorption and the surface area of Cu by $N_2O$ chemisorption were investigated about the hybrid catalysts. In addition, catalytic activity of these hybrid catalysts was examined with varying reaction conditions. At that time, the reaction temperature of $250{\sim}290^{\circ}C$, the reaction pressure of 50~70 atm, the $[H_2]/[CO]$ mole ratio of 0.5~2.0 and the space velocity of $1,500{\sim}6,000h^{-1}$ were investigated the catalytic activity. From these results, it was confirmed that the reactivity of CP-CZA/D was higher than that of PM-CZ+D. When the conditions of reaction temperature, pressure, $[H_2]/[CO]$ ratio and space velocity were $260^{\circ}C$, 50 atm and 1.0, $3,000h^{-1}$ respectively, CO conversion using CP-CZA/D hybrid catalyst was 72% and the CO conversion of CP-CZA/D was more than 20% compared with the CO conversion of PM-CZ+D. It was known that Cu surface area of CP-CZA/D hybrid catalyst was higher than that of hybrid PM-CZ+D catalyst using $N_2O$ chemisorption. It was assumed that the catalytic activity was improved because Cu particle of hybrid catalyst prepared by precipitation method was well dispersed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.235-242
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• 2018

High temperature electrical conductivity of Aluminum Nitride (AlN) ceramics sintered with $Y_2O_3$ as a sintering aid has been investigated with respect to various sintering conditions and MgO-dopant. When magnesium oxide is added as a dopant, liquid glass-film and crystalline phases such as spinel, perovskite are formed as second phases, which affects their electrical properties. According to high temperature impedance analysis, MgO doping leads to reduction of activation energy and electrical resistivity due to AlN grains. On the other hand, the activation energy and electrical resistivity due to grain boundary were increased by MgO doping. This is a result of the formation of liquid glass film in the grain boundary, which contains Mg ions, or the elevation of schottky barrier due to the precipitation of Mg in the grain boundary. For the annealed sample of MgO doped AlN, the electrical resistivity and activation energy were increased further compared to MgO doped AlN, which results from diffusion of Mg in the grains from grain boundary as shown in the microstructure.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.2
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• pp.95-102
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• 2019

In order to investigate the effect of water treatment on activity of WGS catalyst, $Cu/ZnO/MgO/Al_2O_3$ (CZMA) catalysts were synthesized by co-precipitation method. The prepared catalysts were water-treated at two different temperature (250, $350^{\circ}C$). Synthesized catalysts were characterized by using BET, SEM, $N_2O$ chemisorption, XRD, $H_2-TPR$ and XPS analysis. The catalytic activity tests were carried out at a GHSV of $28,000h^{-1}$ and a temperature range of $180-320^{\circ}C$. The reduction temperature decreased with water treatment and CZMA_250 catalyst showed the lowest reduction temperature and retained a large amount of $Cu^+$. Water-treated catalysts showed increased reactivity compared to untreated catalyst and the CZMA_250 catalyst showed higher catalytic activity on WGS reaction.

• Clean Technology
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• v.23 no.4
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• pp.429-434
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• 2017

To investigate the effect of magnesium oxide addition, $Cu/ZnO/MgO/Al_2O_3$ (CZMA) catalysts were prepared using co-precipitation method with fixed molar ratio of Cu/Zn/Mg/Al as 45/45/5/5 mol% for low-temperature water gas shift reaction. Synthesized catalysts were characterized by using BET, $N_2O$ chemisorption, XRD, $H_2-TPR$ and $NH_3-TPD$ analysis. The catalytic activity tests were carried out at a GHSV of $28,000h^{-1}$ and a temperature range of $200{\sim}320^{\circ}C$. At the same condition, magnesium oxide added catalyst (CZMA 400) showed that the lowest reduction temperature and stable presence of $Cu^+$, that is active species and abundant weak acid site. Also magnesium oxide added catalysts (CZMA) showed higher catalytic activity at temperature range above $240^{\circ}C$ than the catalyst without magnesium oxide (CZA). Consequently, CZMA 400 catalyst is considered to be excellent catalyst showing CO conversion of 77.59% without deactivation for about 75 hours at $240^{\circ}C$, GHSV $28,000h^{-1}$.

• Clean Technology
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• v.21 no.1
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• pp.68-75
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• 2015

In this study, we investigated the structure and properties of a highly heat conductive metal-ceramic core-shell CoAl₂O₄@Al micro-composite for heterogeneous catalysts support. The CoAl₂O₄@Al was prepared by hydrothermal surface oxidation of Al metal powder, which resulted in the structure with a high heat conductive Al metal core encapsulated by a high surface area CoAl₂O₄ shell. For comparison, CoAl₂O₄ was also prepared by co-precipitation method and also utilized for a catalyst support. Rh catalysts supported on CoAl₂O₄@Al and CoAl₂O₄ were prepared by incipient wetness impregnation and characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), CO chemisorption, and temperature-programmed reduction (TPR). The properties of catalysts were investigated for glycerol steam reforming reaction for hydrogen production at 550 ℃. Rh/CoAl₂O₄@Al exhibited about 2.8 times higher glycerol conversion turnover frequency (TOF) than Rh/CoAl₂O₄ due to facilitated heat transport through the core-shell structure. The CoAl₂O₄@Al and CoAl₂O₄ also showed some catalytic activities due to a partial reduction of Co on the support, and a higher catalytic activity was also found on the CoAl₂O₄@Al core-shell than CoAl₂O₄. These catalysts, however, displayed deactivation on the reaction stream due to carbon deposition on the catalysts surface.

• New & Renewable Energy
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• v.4 no.4
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• pp.80-87
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• 2008

Steam reforming of LPG was investigated over spc-Ni/MgAl catalyst in a temperature range of $600{\sim}850^{\circ}C$, feed molar ratio of $H_2O/C=1.0{\sim}3.0$, space velocity of $10,000{\sim}90,000h^{-1}$ and at atmospheric pressure. spc-Ni/MgAl catalyst was prepared by a co-precipitation method, whereas Ni/MgO and $Ni/Al_2O_3$ catalysts were prepared by an incipient wetness method. The characteristics of catalysts were analyzed by N2 Physisorption, CO chemisorption, XRD, TOF-SIMS, SEM and TEM techniques. The Ni/MgO and $Ni/Al_2O_3$ catalysts were deactivated by the formation of carbon. However, the spc-Ni/MgAl catalyst showed higher conversion and $H_2$ selectivity than the other catalysts, even though carbon was formed on the surface of the catalyst during the reaction under the tested reaction conditions.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.564-568
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• 2006

AlO(OH) nano gel is used in precursor of ceramic material, coating material and catalyst. For use of these, not only physiochemical control for particle morphology, pore characteristic and peptization but also studies of synthetic method for preparation of advanced application products were required. In this study, AlO(OH) nano gel was prepared through the aging and drying process of aluminum hydroxides gel precipitated by the hydrolysis reaction of dilute NaOH solution and aluminum sulfate solution. In this process, optimum synthetic condition of AlO(OH) nano gel having excellent pore volume as studying the effect of water and aluminum sulfate mole ratio on gel precipitates has been studied. Water and aluminum sulfate mole ratio brought about numerous changes on crystal morphology, surface area, pore volume and pore size. Physiochemical properties were investigated as using XRD, TEM, TG/DTA, FT-IR, and $N_2$ BET method.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1158-1164
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• 1998

Aluminium sulfate solution was prepared by sulfuric acid treatment from gibbsite. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was precipitated from aluminium sulfate solution by adding it into ethylalcohol. From XRD analysis as-prepared $Al_2(SO_4)_3$ · $nH_2O$ was confirmed to have mixed-crystalization water(n=18, 16, 12, 6). The average water of crystalization calculated from thermogravimetry(TG) was 14.7. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was thermally decomposed and converted to $Al_2(SO_4)_3$ at $800^{\circ}C$, $\gamma-Al_2O_3$ at $900-1000^{\circ}C$, and $\alpha-Al_2O_3$ at $1200^{\circ}C$. Ni-doped $\gamma-Al_2O_3$, was synthesized from the slurry of as-prepared $\gamma-Al_2O_3$, with the ratio of [Ni]/[Al]=0.5. The reaction conditions of synthesis were determined as initial pH 9.0 and temperature $80^{\circ}C$ The basicity(pH) of slurry was controlled by using urea and $NH_4OH$ solution. Urea was also used for deposition-precipitation. For determining termination of reaction, the data acquisition was performed by oxidation reduction potential(ORP), conductivity and pH value in the process of reaction. Termination of the reaction was decided by observing the reaction steps and rapid decrease in conductivity. On the other hand, BET(Brunauer, Emmett and Teller) and thermal diffusity of Ni- doped $\gamma-Al_2O_3$, with various content of Ni were measured and compared. Thermal stability of Ni- doped $\gamma-Al_2O_3$ at $1250^{\circ}C$ was confirmed from BET and XRD analysis. The surface state of Ni-doped $\gamma-Al_2O_3$ was investigated by X-ray photoelectron spectroscopy(XPS). The binding energy at $Ni2P_{3/2}$ increased with increasing the formation of $NiAl_2O_4$ phase.

• Clean Technology
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• v.17 no.2
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• pp.166-174
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• 2011

The xAl-yCe oxide catalysts with different mol ratios of Al/(Al+Ce) were prepared by a co-precipitation method and Pt supported on xAl-yCe oxide catalysts were synthesized by an incipient wetness impregnation method. The catalysts were characterized by X-ray Diffraction (XRD), $N_2$ sorption, and $H_2$/CO-temperature programmed reduction ($H_2$/CO-TPR) to correlate with catalytic activities in co oxidation. Among the catalysts studied here, Pt/1Al-9Ce oxide catalyst showed the highest activity in dry and wet reaction conditions and the catalytic activity showed a typical volcano-shape curve with respect to Al/(Al+Ce) mol ratio. When the presence of 5% water vapor in the feed, the temperature of $T_{50%}$ was shifted ca. $30^{\circ}C$ to lower temperature region than that in dry condition. From CO-TPR, the desorption peak of $CO_2$ on Pt/1Al-9Ce oxide catalyst showed the highest value and well correlated the catalytic performance. It indicates that the Pt/1Al-9Ce oxide catalyst has a large amount of active sites which can be adsorbed by co and easy to supplies the needed oxygen. In addition, the amount of pentacoordinated $Al^{3+}$ sites obtained through $^{27}Al$ NMR analysis is well correlated the catalytic performance.

• Clean Technology
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• v.20 no.3
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• pp.330-336
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• 2014

Mg-Al mixed oxides with molar ratio of Mg/Al = 1-3 were prepared by co-precipitation and characterized by using X-ray diffraction, scanning electron microscopy, BET surface area and pore volume measured by $N_2$ sorption analysis, and temperature programmed desorption of iso-propanol. As Al content in Mg-Al mixed oxide increased, the acidity and BET surface area proportionally increased. This increase of acidity directly influenced the catalytic activity of iso-propanol conversion and selectivity to propylene.