Wet oxidation of ammonia was carried out in the presence of Ce-based composite oxide catalysts. Reaction proceeded rapidly in the high pH region, indicating that ammonia was more reactive than ammonium ion. The Co/Ce and /Ce composite oxides were remarkably active. The maximum percentage decrease in ammonia was attained at a Ce content around 20 mol % for Co/Ce and 20-50 mol % for /Ce, respectively. They exhibited high activity in the decomposition of hydrogen peroxide, which suggested that the high activity of these composite oxides in the oxidation of ammonia was due partly to their high redox property. It was found that their strong affinity toward ammonia also contributed to their high activity in the oxidation of ammonia. The ESR spectral analysis indicated that interactions between Co and Ce, and Mn and Ce, were present in these composite oxides. The activity of the /Ce catalysts was higher than that of water-soluble copper compounds which are known as the most active catalyst in the wet oxidation.

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Ti-doped and undoped CaFe 2 O 4 powders were prepared from a malic acid complex and their properties were evaluated using analytical instruments. According to an XRD measurement, there were no traces of impurity phases in 5 mol % Ti-doped CaFe 2 O 4 powder, while impurity phases such as ¡-Fe 2 O 3 and CaTiO 3 were observed for 10 mol % Ti-doped CaFe 2 [Received September 16, 2013; Accepted December 3, 2013] For several decades, the physical and chemical properties of calcium ferrite (CaFe 2 O 4 ) crystal have been researched widely because of its useful applications such as in gas absorbers, in electrochemical devices for high-temperature use, and as an oxidation catalyst.1)3) CaFe 2 O 4 has recently attracted considerable attention as a new photocatalyst material owing to its excellent photoreductive property for H 2 O and CO 2 . 4)9) In general, CaFe 2 O 4 is prepared by a solid-state reaction. Although a solidstate reaction is most frequently used because of ease and convenience, it has several problems such as changes in stoichiometric ratio and the ease of formation of impurity phases.10) This is because the starting materials must be repeatedly ground and calcined many times to prepare the intended crystal phase. As a result, the specific surface area of the product decreases and the catalytic activity has inevitably falls. Needless to say, a high surface area is an important property of surface functionality materials such as catalysts.Marcilly and co-workers have reported a new preparation method employing organic acids (citric, malic, tartaric, glycolic acids etc.) to obtain metal oxides. 11) They showed that H + in an organic acid with -OH or -COOH groups is replaced by the metal ion in the solution and the organic acid complex is easily formed. This complex is available for a precursor to prepare the objective material. Therefore, it is expected that the precursor is transformed to objective oxide at lower calcination temperature than the case of a solid-state reaction method and the resulting final product has a large surface-area and a high homogeneity.In the present study, we have examined the preparation of CaFe 2 O 4 powder with high specific surface area from a malic acid complex, instead of employing a solid-state reaction, and characterized the powder by X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), fluorescence X-ray spectrometry (XRF), scanning electron microscopy (SEM), surface area measurement, and UVvis spectrometry. Furthermore, the effect of Ti addition on the crystal phase, microstructure, specific surface area, and optical properties of CaFe 2 O 4 was investigated.CaFe 2 O 4 powder was synthesized by a malic acid complex method. Ca(NO 3 ) 2 ·4H 2 O, Fe(NO 3 ) 3 ·9H 2 O, and malic acid in a 1:2:3 molar ratio were dissolved in deionized water. The addition of Ti to CaFe 2 O 4 carried out using Ti[OCH(CH 3 ) 2 ] 4 . The amount of Ti doped set to 5 and 10 mol % to Fe. The solution was dehydrated and heated on a hot plate to prepare the precursor powder of CaFe 2...

Nanopowder of MgFe 2 O 4 was prepared from an organic acid complex method. Among three kinds of organic acids examined, it was found from an XRD measurement that the highest purity powder of MgFe 2 O 4 was obtained from a malic acid complex. SEM observation revealed that the powder is fluffy aggregates and each particle has irregular shape. The TGDTA and IR measurements show that thermolysis process of a malic acid complex in air was mainly constructed at two stages consisting of dehydration and ligand pyrolysis. Furthermore, it was confirmed from a VSM measurement that the saturation magnetization of MgFe 2 O 4 nanopowder is much smaller value than that of the bulk material.©2014 The Ceramic Society of Japan. All rights reserved.Key-words : MgFe 2 O 4 , Malic acid complex, TG-DTA, IR, XRD, SEM, BET, VSM [Received February 10, 2014; Accepted April 19, 2014] There has been a considerable interest in magnesium ferrite (MgFe 2 O 4 ) owing to their useful properties such as catalyst, gas sensor, microwave device, fuel cell, drug delivery, and so forth.1)7) In recent research, Mg ferrite has attracted attention as a photocatalyst because of smaller band gap energy than that of TiO 2 with anatase-type structure.8)10) In these applications, the synthesis of fine powders having high purity is indispensable. Generally, MgFe 2 O 4 is prepared from mixed oxides or carbonates by a solid-state reaction. Although a solid-state reaction is frequently used for ease and convenience, it has several problems such as change in stoichiometric ratio and ease of formation of impurity phases.11) Because the grinding and heating of starting materials must be repeated many times to prepare the intended crystal phase at a higher temperature. As a result, the particle size of the ferrites becomes very large and the specific surface area inevitably falls. Marcilly and co-workers have found a new preparation method via organic acids to obtain metal oxides. 12)In the organic acid process, H + in an organic acid with -OH or -COOH groups is replaced by the metal ion in the solution and the organic acid complex is easily formed. It is expected that the precursor is transformed to objective oxide at lower calcination temperature. For MgFe 2 O 4 , there are some reports which prepared the nanopowder using citric acid and tartaric acid as an organic acid.13)16) However, ¡-Fe 2 O 3 is included in these cases as an impurity and there are no reports for MgFe 2 O 4 nanopowder with single phase as far as our knowledge.In the present study, we have examined to prepare nanosized MgFe 2 O 4 powder without impurity by utilizing a malic acid complex. Then, the detailed characterization of obtained powder was carried out by thermal gravimetric-differential thermal analysis (TGDTA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffactometry (XRD), scanning electron microscopy (SEM), specific surface area measurement, and vibrating sample magnetrometry (VSM).MgFe 2 O 4 powder was prepared from an organic acid complex method. Mg(NO 3 ) 2 ·4H 2 O, Fe(...

La-added and pure MgFe 2 O 4 powders were prepared from a malic acid complex, and the effect of La-adding on the microstructure and specific surface area of MgFe 2 O 4 powder were examined. There were no traces of impurity phases for pure MgFe 2 O 4 powder in the X-ray diffraction measurement after calcination in the range of 600 to 800°C. When La atoms were added to MgFe 2 O 4 , the crystallite growth of MgFe 2 O 4 was suppressed remarkably, resulting in a higher specific surface area in comparison with the pure material, and the lattice volume increased. X-ray photoelectron spectroscopy measurements showed that the binding energies of Mg 2s, , and La 3+ valence states, respectively. Scanning electron microscopy observations revealed that MgFe 2 O 4 powder shows an aggregation of granular particles and that the individual particles are tightly interconnected with each other, whereas smaller particles compared with pure MgFe 2 O 4 were observed for the La-added powder. It was found from the N 2 adsorption measurement, moreover, that the amount of mesopore increases with La addition.