In Situ XRD and In Situ IR Spectroscopic Analyses of Structural Change of Goethite in Methane Oxidation

Katoh, Masahiro; Orihara, Masanao; Moriga, Toshihiro; Nakabayashi, Ichiro; Sugiyama, Shigeru; Tanaka, Suminori

doi:10.1006/jssc.2000.8992

Cited by 23 publications

(18 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 When the catalyst of R = 1 was used, the efficiency, CM, appeared from 200˚C, increased suddenly at 250˚C, and reached 100% at 340˚C. When the catalyst of R = 0 was used, however, the efficiency started increasing at a higher temperature than that of R = 1, and finally reached 100% at 350˚C.…”

Section: Resultsmentioning

confidence: 97%

“…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%

See 1 more Smart Citation

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.

Self Cite

View full text Add to dashboard Cite

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, ...

show abstract

Section: Resultsmentioning

confidence: 97%

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.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The absence of both carbon monoxide and C2 compounds (such as ethane) is consistent with previous work 5), 6) . CM(%) = 100[1 − CH4(P)/{CH4(P) + CO2(P)}] (1) where CH4(P) and CO2(P) are the molar amount of methane and that of carbon dioxide, respectively, measured at the exit of the reactor 3) . When the Fe/γ-Al2O3 catalyst was used, initial conversion appeared at 673 K, increased gradually with increasing temperature and reached 100% near 923 K. When the Fe/SiO2 _ Al2O3 catalyst was used however, the onset of conversion moved to a higher temperature (823 K) and finally reached 100% near 1073 K. On the other hand, the activity was negligible across the temperature range of Fig.…”

Section: Resultsmentioning

confidence: 99%

“…In recent studies of the catalytic properties of iron oxides in methane oxidation, we have reported that hematite (α-Fe2O3) is an active iron oxide which catalyzes methane oxidation effectively and that this solid phase is formed as the result of the phase transformation from the precursor goethite (α-FeOOH) at high temperature 3) . It has been reported that goethite loaded on some appropriate supporting materials should resolve potential disadvantages of the unsupported catalyst and, at the same time, will prove to be a precursor to produce an efficient catalyst for methane oxidation for practical use 3) .…”

Section: Introductionmentioning

confidence: 99%

“…It has been reported that goethite loaded on some appropriate supporting materials should resolve potential disadvantages of the unsupported catalyst and, at the same time, will prove to be a precursor to produce an efficient catalyst for methane oxidation for practical use 3) . Formation of goethite on the supporting materials γ-Al2O3, SiO2 _ Al2O3 and SiO2 is examined for this purpose and a critical comparison of the activities of these catalysts in methane oxidation is described in this study, as well as investigating their catalytic properties.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Catalytic Activity of Iron Oxides Supported on γ-Al<sub>2</sub>O<sub>3</sub> for Methane Oxidation

Tanaka

Nakagawa

Kanezaki

et al. 2005

J. Jpn. Petrol. Inst.

Self Cite

View full text Add to dashboard Cite

[Regular Paper] IntroductionIron oxides are abundant in our surroundings, both in the terrestrial environment -soil, rocks, and mineralsand sometimes in water resources, furthermore, they are inexpensive and less harmful to human beings. For these reasons, iron oxides are widely used as combustion catalysts. For example, a report has been released suggesting that addition of iron oxides to incinerators helps restrict dioxin, carbon monoxide, and nitrogen oxides in the exhaust fumes 1) .Dioxin discharged from incineration plants is produced by reactions of unburned granular carbon particles, reacting with dioxin precursors through de novo synthesis with materials such as inorganic chlorine, air and moisture 2) . It is also produced by decomposition or synthetic reactions of chlorobenzenes or chlorophenols. Accordingly it is believed that reduction of unburned granular carbon particles, together with achieving complete combustion in the incinerators, makes it possible to restrict dioxin generation.In recent studies of the catalytic properties of iron oxides in methane oxidation, we have reported that hematite (α-Fe2O3) is an active iron oxide which catalyzes methane oxidation effectively and that this solid phase is formed as the result of the phase transformation from the precursor goethite (α-FeOOH) at high temperature 3) .It has been reported that goethite loaded on some appropriate supporting materials should resolve potential disadvantages of the unsupported catalyst and, at the same time, will prove to be a precursor to produce an efficient catalyst for methane oxidation for practical use 3) . Formation of goethite on the supporting materials γ-Al2O3, SiO2 _ Al2O3 and SiO2 is examined for this purpose and a critical comparison of the activities of these catalysts in methane oxidation is described in this study, as well as investigating their catalytic properties. Experimental 1. MaterialsThree catalysts were obtained by means of the airoxidation of Fe 2+ in an aqueous alkaline suspension containing FeSO4, NaOH and one of three supporting materials, γ-Al2O3, SiO2 _ Al2O3 and SiO2. Prior to the Catalytic Activity of Iron Oxides Supported on γ-Al2O3for Methane Oxidation Three kinds of catalysts of goethites supported on γ-Al2O3 (Fe/γ-Al2O3), SiO2 _ Al2O3 (Fe/SiO2 _ Al2O3) and SiO2 (Fe/SiO2) were investigated in terms of the catalytic activity of methane oxidation. The specific surface areas of these catalysts were larger in common than the area of goethite with no supports. The Fe/γ-Al2O3 catalyst has the highest performance in the low-temperature activity of methane oxidation which started at 623 K and completed at 923 K. When the Fe-content in Fe/γ-Al2O3 was increased, the formation of goethite was observed by the X-ray analyses and the activity of this catalyst increased up to 6 mol%. After the catalytic methane oxidation at 823 K, it was observed that goethite in Fe/γ-Al2O3 transformed to hematite which has been known as an active iron oxide in methane oxidation. The activity of Fe/γ-Al2O3 was enhanced by t...

show abstract

Removal of tannins and polyhydroxy phenols by electro‐chemical techniques

Murugananthan

Raju

Prabhakar

2005

J of Chemical Tech & Biotech

View full text Add to dashboard Cite

The removal of tannins and their basic molecules such as catechol, pyrogallol, phloroglucinol and resorcinol was studied by electro-flotation and electro-oxidation techniques. Iron rods and triple oxide (TaO 2 /RuO 2 /IrO 2 ) coated titanium rods were used as electrodes for electro-flotation and electrooxidation respectively. Interaction of tannins and polyhydroxy phenols with iron oxy-hydroxide formed by anodic dissolution of iron was studied by UV-Visible, FT-IR and zeta-potential measurements. GC-MS was used to identify the intermediate compounds formed during electro-oxidation. Catechol, pyrogallol, phloroglucinol and resorcinol were found to be mineralized in the presence of triple oxide (TaO 2 /RuO 2 /IrO 2 ) coated titanium electrodes. Catechol and pyrogallol were found to form insoluble organo-metal complexes while resorcinol and phloroglucinol were found to adsorb on iron oxy-hydroxide. The sludge thus formed was simultaneously separated from the aqueous phase by hydrogen bubbles. It was observed that the power consumption is relatively high for electro-oxidation compared with electroflotation. The effects of pH and reaction time on their removal were also studied and the results are discussed.

show abstract

In Situ XRD and In Situ IR Spectroscopic Analyses of Structural Change of Goethite in Methane Oxidation

Cited by 23 publications

References 15 publications

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

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

Catalytic Activity of Iron Oxides Supported on γ-Al<sub>2</sub>O<sub>3</sub> for Methane Oxidation

Removal of tannins and polyhydroxy phenols by electro‐chemical techniques

Contact Info

Product

Resources

About