Effects of the Thermal Stability and the Fine Structure Changes of Strontium Hydroxyapatites Ion-Exchanged with Lead on Methane Oxidation in the Presence and Absence of Tetrachloromethane

Sugiyama, Shigeru; Iguchi, Yoshimasa; Nishioka, Hitoshi; Minami, Toshimitsu; Moriga, Toshihiro; Hayashi, Hiromu; Moffat, J.B.

doi:10.1006/jcat.1998.1992

Cited by 32 publications

(17 citation statements)

References 41 publications

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“…The starting materials were regent grade chemicals Wako Pure Chem., Ind., Co., Japan , NH 4 was separately poured into a different reaction chamber to get the HAp stoichiometric composition. These solutions were mixed at room temperature and then heated to desired temperature.…”

Section: Methodsmentioning

confidence: 99%

“…3 In the oxidation of methane, the addition of a small quantity of lead to Sr HAp resulted in the conversion and the selectivity to ethylene. 4 In the apatite structure, the Ca ions occupy two types of nonequivalent sites: the M 1 sites are at the fourfold symmetry4 f position and the M 2 sites are at the sixfold symmetry 6 h position. 5 The apatite structure has a high flexibility, so that many metal ions can incorporate in the structure.…”

Section: Introductionmentioning

confidence: 99%

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Hydrothermal Synthesis and Crystallographic Study of Sr-Pb Hydroxyapatite Solid Solutions

Zhu

Yanagisawa

Shimanouchi

et al. 2007

J. Ceram. Soc. Japan

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A continuous series of solid solutions in the system of strontium and lead hydroxyapatite, Pb x Sr 1 x HAP x 0-1 , was successfully synthesized by low-temperature mixing method LTMM at 160? C for 12 h under hydrothermal conditions. The samples were characterized by chemical analysis, electron microscopic observation and X-ray powder-pattern fitting. The site of the metal ions in the solid solutions was analyzed by the Rietveld method. The lattice constants of the prepared solid solutions varied linearly with Pb contents. It was found that Pb 2 ions in the solid solutions preferentially occupied the M 2 site in the apatite structure.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydrothermal Synthesis and Crystallographic Study of Sr-Pb Hydroxyapatite Solid Solutions

Zhu

Yanagisawa

Shimanouchi

et al. 2007

J. Ceram. Soc. Japan

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“…1,2 It has been reported that PdO microcrystals supported on χ-Al2O3 show a high catalytic activity in methane oxidation below 300˚C when CeO2 coexists altogether with PdO on the support (PdO/CeO2 catalysts). [3][4][5] Thus, PdO/CeO2 catalysts have the capability to ignite combustion at moderate temperatures as well as other advantages; colorless and transparent to visible light, which enables the catalyst to be utilized in various fields.…”

mentioning

confidence: 99%

Direct Detection of a Phase Change in PdO/CeO2 Supported on χ-Al2O3 by Means of in situ High-Temperature Measurements of XRD and FTIR

Kanezaki

Tanaka²,

Murai

et al. 2004

ANAL. SCI.

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Since combustion starts at a temperature as low as 300˚C with iron oxides, one of the combustion catalysts, the evolution of toxic dioxins on the combustion is suppressed. 1,2 It has been reported that PdO microcrystals supported on χ-Al2O3 show a high catalytic activity in methane oxidation below 300˚C when CeO2 coexists altogether with PdO on the support (PdO/CeO2 catalysts). [3][4][5] Thus, PdO/CeO2 catalysts have the capability to ignite combustion at moderate temperatures as well as other advantages; colorless and transparent to visible light, which enables the catalyst to be utilized in various fields. We have reported that the Pd metal phase is observed in the X-ray absorption fine structure (XAFS) after treating the catalysts in an O2-deficient atmosphere at high temperature, and have suggested that a phase change between PdO and Pd takes place in the PdO/CeO2 catalysts. 4,5 In this work, in situ hightemperature measurements of XRD (in situ HTXRD) of the PdO/CeO2 catalysts and FT-IR (in situ HTFT-IR) of PdO microcrystals were made in order to verify the phase change in the temperature range where the catalysts work. The in situ high-temperature measurements allow us to have an accurate insight into the thermal change of the catalytic-active PdO under the condition of operation in which PdO catalyzes methane oxidation. Experimental ChemicalsThe synthesis of the PdO/CeO2 catalysts supported on χ-Al2O3 has been published. 4,5 In a small volume of an aqueous solution of Ce(NO3)3·6H2O, a weighed portion of Al(OH)3 (gibbsite) was suspended and admixed by vigorous stirring for 30 min. An aqueous solution of Pd((NO3)2 was added to the mixture in various atomic ratios of R = Ce/Pd. The mixture was stirred for 1 h, dried in air for 15 h and finally calcined at 500˚C in an electric furnace. The calcined solid was crushed, sieved to obtain a component of 10 -24 mesh in diameter, and was used in the measurements. In this experiment, we tested three kinds of catalysts with loading ratios of PdO and CeO2 vs. χ-Al2O3; 0.12 g/g and 0 g/g for the catalyst of R = 0, 0.18 g/g and 0.12 g/g for that of R = 1, 0.12 g/g and 0.84 g/g for that of R = 5, respectively. Three thermal events were observed in the thermogravimetry (TG) of a dried mixture of gibbsite, Ce(NO3)3·6H2O and Pd((NO3)2 below 500˚C: a large endotherm due to the formation of χ-Al2O3 located at 311˚C, an exotherm due to the formation of PdO at 240˚C, and that due to the formation of CeO2 at around 268˚C. Therefore, no other materials than χ-Al2O3, CeO2 and PdO are present in the PdO/CeO2 catalysts supported on χ-Al2O3 after calcination at 500˚C. ApparatusThe catalytic activity was tested in a fix-bed continuous-flow quartz reactor operated at atmospheric pressure, where the details of the experimental condition and the reactor design have been described previously.4,5 A small portion (0.5 g) of the catalyst was loaded in the reactor through which the mixed reactive gas and helium gas were passed when the pressures of methane and oxygen were 3.4 kPa and 20.3 kPa, ...

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“…In the oxidation of methane, the addition of a small quantity of Pb to Sr-HAp resulted in the selectivity conversion of ethylene [4].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and crystallographic study of Pb–Sr hydroxyapatite solid solutions by high temperature mixing method under hydrothermal conditions

Zhu

Yanagisawa

Shimanouchi

et al. 2009

Materials Research Bulletin

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Abstract:The solid solutions in the system of Pb and Sr hydroxyapatite, Sr 10-x Pb x HAp (x= 0-10), were successfully synthesized by high-temperature mixing method (HTMM) at 160ºC for 12 hours under hydrothermal conditions. The samples were characterized by X-ray diffraction, chemical analysis and electron microscopic observation, and the site of the metal ions in the solid solutions was analyzed with the Rietveld method.The lattice constants, both a and c, of the solid solutions varied linearly with Pb content. It was found that Pb ions in the solid solutions preferentially occupied the M (2) site in the apatite structure. HTMM gives Sr-Pb HAp solid solutions much better crystallization. However, due to the formation of intermediate compound of

show abstract

Effects of the Thermal Stability and the Fine Structure Changes of Strontium Hydroxyapatites Ion-Exchanged with Lead on Methane Oxidation in the Presence and Absence of Tetrachloromethane

Cited by 32 publications

References 41 publications

Hydrothermal Synthesis and Crystallographic Study of Sr-Pb Hydroxyapatite Solid Solutions

Hydrothermal Synthesis and Crystallographic Study of Sr-Pb Hydroxyapatite Solid Solutions

Direct Detection of a Phase Change in PdO/CeO2 Supported on χ-Al2O3 by Means of in situ High-Temperature Measurements of XRD and FTIR

Synthesis and crystallographic study of Pb–Sr hydroxyapatite solid solutions by high temperature mixing method under hydrothermal conditions

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