• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.90-95
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• 2000

The ferrites, CuFe2O4 and SrFe12O129, were applied to decompose H2O for H2 generation. The ferrites prepared by the coprecipitation were reduced by CH4 gas to make the oxygen deficient ferrite. H2O was decomposed to form H2 by the oxygen deficient iron oxide, and the decomposition reactions were accelerated by the addition of divalent metals such as Cu and Sr in the ferrites. The spinel type CuFe2O4 containing a relatively large amount of divalent metals was more effective to H2 generation than magnetoplumbite type SrFe12O19 in H2O decomposition.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.164-167
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• 2000

Flue gases in the iron foundry consist of 15~20% CO2 as an air pollution gas whose emission should be mitigated in order to protect the environment. In the present study, ultrafine powders of NixZn1-xFe2O4 as a potential catalyst for the CO2 decomposition were prepared by the coprecipitation methods. Oxygen deficient ferrites (MeFe2O4-$\delta$) can decompose CO2 as C and O2 at a low temperature of about 30$0^{\circ}C$. The XRD result of synthesized ferrites showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with initial molar ratios of the mixed solution prior to reaction. The BET surface area of the (Ni, Zn)-ferrites was about 77~89.5$m^2$/g and their particle size was observed about 10~20 nm. The CO2 decomposition efficiency of the oxygen deficient (Nix, Zn1-x)-ferrites was the highest at x=0.3, and the ternary (Ni, Zn)-ferrites was better than that of binary Ni-ferrites.

• Journal of Hydrogen and New Energy
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• v.15 no.1
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• pp.32-38
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• 2004

Thermal behaviors of $(Cu_{0.5}Mn_{0.5})Fe_2O_4$, prepared by a solid method, were investigated for $H_2$ production by a thermochemical cycle. The thermal reduction of $(Cu_{0.5}Mn_{0.5})Fe_2O_4$ started from $300^\circ{C}$ and the weight loss was 1.3 wt% up to 1200. XRD shows the prepared ferrite has the spinel structure with a lattice constant of $8.414{\AA}$ and changed to the oxygen deficient structure by thermal reduction. Oxygen and hydrogen can be separately produced by the cycles of thermal reduction and water oxidation of the oxygen deficient ferrite.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.410-416
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• 2004

In this study, we fabricated magnetite coated on a cordierite honeycomb which has complex shape by ultrasound-enhanced ferrite plating. The effects of the plating condition on the formation of the magnetite and its microstructure were investigated. The magnetite coated on the honeycomb became an oxygen-deficient ferrite by H$_2$ gas reduction, then the effects of the molar concentrations of ammonium acetate for $CO_2$ gas decomposition have been studied. As the molar concentration of a pH buffer($CH_3$COONH$_4$, 0.1946∼0.3892 M) solution increased, the average particle size increased about 200∼250 nm. The magnetite coated on the honeycomb was reduced by H$_2$ gas for 2 h at 30$0^{\circ}C$. The inner pressure change in the cell began to occur at 315∼34$0^{\circ}C$. The H$_2$-Reduced magnetite coated on the honeycomb at 35$0^{\circ}C$ contained an oxygen deficient magnetite and $\alpha$-Fe phase. The thermogravimetric analysis with H$_2$ reduction and $CO_2$ decomposition were carried out with the magnetite coated on the honeycomb. A weight loss in process of H$_2$ reduction occurred between 32$0^{\circ}C$ and 34$0^{\circ}C$, while a weight gain was observed during the $CO_2$ decomposition.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.223-226
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• 2000

The oxygen deficient ferrites $(Ni_x,\; Zn_{1-x})Fe_2O_{4-{\delta}}$ can decompose $CO_2$ as C and $O_2$ at a low temperature of about $300^{\circ}C$. Ultra powders of $(Ni_x,\; Zn_{1-x})Fe_2O_4$ for the $CO_2$ decomposition were prepared by the hydrothermal methods. The XRD result of synthesized ferries showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with the starting molar ratios of the mixed solution prior to reaction. The BET surface area of the synthesized(Ni, Zn)-ferrites was above $110\textrm{m}^2/g$ and its particle size was very as small as about 5~10 nm. The $CO_2$ decomposition efficiency of the oxygen deficient ferrites($(Ni_x,\;Zn_{1-x})Fe_2O_{4-{\delta}}$) was almost independent with composition and the $CO_2$ decomposition efficiency of ternary (Ni, Zn)-ferrites was better than of binary Ni-ferrites.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.801-806
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• 2002

The decomposition and/or conversion of carbon dioxide to carbon have been studied using oxygen-deficient ferrites for the reduction of $CO_2$ emission to the atmosphere. In this work, the homogeneous precipitation method using urea decomposition was employed to induce in situ precipitation of Ni ferrite($Ni_{0.4}Fe_{2.6}O_4$) on the porous ceramic fiber support (50 mm diameter${\times}$10 mm thickness). Effects of ferrite loading conditions on the CO2 decomposition efficiency were discussed in this paper. Removal of residual chloride ions and urea by solvent exchange from the porous media after ferrite deposition apparently helps to form spinel ferrite, but does not increase the efficiency of $CO_2$ decomposition. Porous ceramic fiber composites containing 20 wt% (1g) ferrite samples showed 100% efficiency for $CO_2$decomposition during the first three minutes, but the efficiency decreased rapidly after the elapsed time of ten minutes. The characteristic reduction time for the $CO_2$ decomposition efficiency was estimated as about 3∼7 min.

• Journal of Hydrogen and New Energy
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• v.17 no.3
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• pp.309-316
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• 2006

Co-ferrite was synthesized by HEBM (High Energy Ball Milling) with a stoichiometric (Co/Fe=0.5/2.5) mixture of CoO and $Fe_2O_3$ powders. The effect of milling time on the phase transformation of the mixture was investigated by XRD. Mono-phase solid solution of Co-ferrite, which was milled for 4 h and then calcined at $900^{\circ}C$ in the Ar atmosphere, was confirmed by XRD analysis. The composition and thermal reduction behavior of Co-ferrite were analyzed by TGA and XRF. As a result, oxygen deficient Co-ferrite was synthesized by HEBM and the weight decrease of the Co-ferrite, which was oxidized at $600^{\circ}C$ for 10h by $H_2O$ vapor, was 2.41 wt% during thermal reduction at $1300^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.657-662
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• 2002

The reduced ferrites, reduced NiF $e_2$ $O_4$ and CuF $e_2$ $O_4$, by C $H_4$ were applied to $CO_2$ decomposition to avoid the greenhouse effects. At the reduction reaction above $700^{\circ}C$, $H_2$ and CO were generated by partial oxidation of C $H_4$ After the reduction reaction up to 80$0^{\circ}C$, the spinel structure ferrites changed to mixture of the oxygen deficient iron oxide (Fe $O_{(1-{\delta})}$(0$\leq$$\delta$$\leq$1)) and the metallic Ni or Cu. The rate and quantity of $CO_2$ decomposition with reduced CuF $e_2$ $O_4$ were larger than those with reduced NiFe $O_4$. The $CO_2$ gas was decomposed by oxidation of the oxygen deficient iron oxide. The metallic Cu and Ni were not oxidized and remained in a metallic state up to 80$0^{\circ}C$. The $CO_2$ decomposition reaction with the reduced ferrite by C $H_4$ gas is excellent process preparing useful gas such as $H_2$and CO and decomposing $CO_2$ gas.

• Journal of Hydrogen and New Energy
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• v.14 no.4
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• pp.298-304
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• 2003

The thermal behavior of $NiFe_2O_4$ prepared by a solid-state reaction was investigated for $H_2$ generation by the thermochemical cycle. The reduction of $NiFe_2O_4$ started from $800^{\circ}C$, and the weight loss was 0.2-0.3 wt% up to $1000^{\circ}C$. In the $H_2O$ decomposition reaction, $H_2$ was generated by oxidation of reduced $NiFe_2O_4$. The crystal structure of $NiFe_2O_4$ maintained during the redox reaction of 5 cycles. From this observation, the lattice oxygen in $NiFe_2O_4$ is released without the structural change during the thermal reduction and oxygen deficient $NiFe_2O_4$ can be restored to the spinel structure of $NiFe_2O_4$.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.185-189
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• 2011

In this work, nano-sized M-ferrites (M=Co, Ni, Cu, Zn) for the decomposition of carbon dioxide were synthesized by the chemical co-precipitation. From the thermogravimetric analysis, it was clear that the maximum weight loss of each sample took place below $350^{\circ}C$. High temperature calcination resulted in more systematic crystallines, smaller specific surface area and larger particle size. An analysis by FTIR in the range of $375{\sim}406cm^{-1}$ revealed the presence of chelates at the octahedral site, which implies the formation of spinel structure in the ferrites. The current work showed that a $500^{\circ}C$ is the optimum heat treatment temperature of metal ferrites for $CO_2$ decomposition reaction.