Speciation of Molybdates under Hydrothermal Conditions

Noack, Joachim; Rosowski, Frank; Schlögl, Robert; Trunschke, Annette

doi:10.1002/zaac.201400439

Cited by 23 publications

(27 citation statements)

References 46 publications

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“…39-363), and by the Raman band at 947 cm −1 assigned to the presence of Mo7O24 6− . At pH = 3-6 Mo7O24 6− [38,55] and Mo2O7 2− are the stable polymolybdate species in aqueous solution depending on the temperature [52], which agrees well with the Raman spectra of the solid phase. Bi1Mo1_pH5 exhibited a Bi/Mo bulk ratio of 1.1, which corresponds to the applied ratio and resulted in the largest surface area (32 m 2 /g, Table 1) among the different bismuth molybdates.…”

Section: Characterization Of the Samples Synthesized With Bi/mo = 1/1supporting

confidence: 78%

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

et al. 2015

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A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and Raman spectroscopy. The pH value during synthesis had a strong influence on the catalytic performance. Synthesis using a Bi/Mo ratio of 1/1 at pH ≥ 6 resulted in γ-Bi2MoO6, which exhibited a better catalytic performance than phase mixtures obtained at lower pH values. However, a significantly lower catalytic activity was observed at pH = 9 due to the low specific surface area. γ-Bi2MoO6 synthesized with Bi/Mo = 1/1 at pH = 6 and 7 exhibited relatively high surface areas and the best catalytic performance. All OPEN ACCESSCatalysts 2015, 5 1555 samples prepared with Bi/Mo = 1/1, except samples synthesized at pH = 1 and 9, showed better catalytic performance than samples synthesized with Bi/Mo = 2/3 at pH = 4 and 9 and γ-Bi2MoO6 synthesized by co-precipitation at pH = 7. At temperatures above 440 °C, the catalytic activity of the hydrothermally synthesized bismuth molybdates started to decrease due to sintering and loss of surface area. These results support that a combination of the required bismuth molybdate phase and a high specific surface area is crucial for a good performance in the selective oxidation of propylene.

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Section: Characterization Of the Samples Synthesized With Bi/mo = 1/1supporting

confidence: 78%

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

et al. 2015

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“…In this work, the phase transitions of tungstates initiated by acidification and increasing temperature up to 170 °C, were investigated by in situ Raman spectroscopy . Additionally, microwave‐assisted hydrothermal synthesis experiments combined with ex situ analysis by X‐ray diffraction and SEM were performed to in particular analyze the effect of pH on morphology and phase composition of the final product after extended isothermal crystallization time, reduced from 17 hours in the Raman‐autoclave to 2 hours in the microwave methodology.…”

Section: Introductionsupporting

confidence: 60%

Effect of Temperature and pH on Phase Transformations in Citric Acid Mediated Hydrothermal Growth of Tungsten Oxide

et al. 2018

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The temperature-dependent composition of suspension during citric acid mediated crystallization of tungsten trioxide (WO 3 ) from sodium tungstate was studied by in situ Raman spectroscopy. Additionally, microwave-assisted hydrothermal synthesis experiments combined with ex situ analysis by X-ray diffraction and SEM were performed to analyze the effect of pH on the eventually, isothermally, obtained crystal phase and morphology. The Raman results suggest that WO 3 ·2H 2 O precipitates from the tungstate solution upon acidification to pH 0.5 at room temperature. This is first transformed to WO 3 ·H 2 O initi- [a]

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“…13B) and trimolybdates [Mo VI 3 O 10 ] 2À (Fig. 13D) are preferentially formed, 158 whereas heptamolybdate {Mo 7 } dominates under ambient pressure at 25 1C (Fig. 11).…”

Section: Comparison Of Ipomos In Solution and The Solid Statementioning

confidence: 99%