Infrared, laser-Raman and X-ray diffraction investigation of MoO3/ZrO2 and the oxidation of (Z)-but-2-ene

Miyata, Hisashi; Tokuda, Shoji; Ono, Takehlko; Ohno, Takashi; Hatayama, Fumikazu

doi:10.1039/ft9908602291

Cited by 46 publications

(30 citation statements)

References 20 publications

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“…The shift of the bands at 945 and 973 cm -1 to higher frequencies reflects the dehydration of the sample at 673 K; physisorbed H 2 O weakens ModO bonds and it causes the ν(ModO) in MoO x species to shift to lower frequencies. [45][46][47][48][49] The shift of the 897 cm -1 band to 905 cm -1 for isolated tetrahedral MoO 4 species on Al 2 O 3 was attributed by Jeziorowski et al 42 and Wang et al 44 to interactions with the Al 2 O 3 . Treatment at 723 K caused the 905 cm -1 band to weaken gradually and the 833 cm -1 band to become more intense until it emerged as the most intense band in the 800-900 cm -1 region ( Figure 8B,C).…”

Section: Resultsmentioning

confidence: 99%

“…The radial structure function shows a scattering peak with a maximum at 3.37 Å (curve c in Figure 5B) 14,[41][42][43][44][45] These studies have concluded that the structure of supported MoO x species depends strongly on the identity of the oxide support, on the Mo content, and on the treatment temperature, but only weakly on the solution pH and on the type of soluble Mo precursor used. Since hydration of supported MoO x samples by exposure to ambient moisture can alter their Raman spectra, [45][46][47][48][49] all spectra in our study were obtained after in situ treatment at the specified temperatures within the Raman cell.…”

Section: Resultsmentioning

confidence: 99%

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Structural Characterization of Molybdenum Oxide Supported on Zirconia

et al. 2000

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X-ray diffraction and X-ray absorption and Raman spectroscopies were used to determine the structure of dispersed and crystalline structures in MoO x /ZrO 2 catalysts useful in the oxidative dehydrogenation of alkanes. The MoO x surface density on ZrO 2 was varied over a wide range (0.35-50 Mo/nm 2 ) by changing the Mo content (1-44 wt % MoO 3 ) and the treatment temperature (393-973 K). Raman spectra showed that MoO x / ZrO 2 samples with low surface density (<5 Mo/nm 2 ) treated at temperatures below 873 K initially contain isolated tetrahedral MoO x species; these species oligomerize to form two-dimensional structures with bridging MosOsMo bonds as the surface density increased to values typical for a polymolybdate monolayer (∼5 Mo/nm 2 ). An increase in surface density led to a shift in the ν(ModO) Raman band to higher frequencies and to changes in the near-edge X-ray absorption spectra. Both of these are consistent with the growth of these polymolybdate domains with increasing Mo surface density, as also suggested by the concurrent decrease in the UV-visible absorption energy. Thermal treatment at 973 K led to the dissociation of MosOsMo bonds and to the formation of tetragonal-pyramidal OdMoO 4 species. For MoO x /ZrO 2 samples with Mo surface densities greater than 5 Mo/nm 2 , MoO 3 and Zr(MoO 4 ) 2 were detected by Raman and for larger crystallites also by X-ray diffraction. Treatment of these samples in air at 723 K led to the predominant formation of MoO 3 , while higher temperatures led to a solid-state reaction between MoO 3 and ZrO 2 to form Zr(MoO 4 ) 2 . This structural evolution was confirmed by the evolution of pre-edge and near edge features in the X-ray absorption spectra of these high surface density samples. Zr(MoO 4 ) 2 contains Mo 6+ cations in a distorted tetrahedral coordination with one oxygen bonded only to molybdenum and the other three shared by Zr and Mo atoms. The Raman bands observed for Zr(MoO 4 ) 2 at 750, 945, and 1003 cm -1 were assigned to ν sym (OsMosO), ν asym (OsMosO), and ν(ModO) vibrational modes, respectively, based on the analysis of the Raman bands observed after 18 O 2 exchange with lattice oxygen atoms. Bridging O atoms in MosOs Mo species exchanged with gas phase 18 O 2 more readily than terminal ModO species.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Structural Characterization of Molybdenum Oxide Supported on Zirconia

et al. 2000

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“…The precipitate of Zr(OH) 4 was obtained by adding aqueous ammonia slowly into an aqueous solution of zirconium oxichloride (Aldrich) at room temperature with stirring until the pH of aqueous solution reached about 8. [21][22][23] The precipitate was washed thoroughly with distilled water until chloride ion was not detected with AgNO 3 solution, and was dried at room temperature for 12 h. The dried precipitate was powdered (100 mesh) by grinding.…”

Section: Methodsmentioning

confidence: 99%

“…These systems are active for various reactions, such as partial oxidation of hydrocarbons and alcohols, [1][2][3][4][5] hydrogenolysis and hydrodesulfurization of crude oil, 6,7 metathesis of alkenes, 8 hydrogenation of benzene, 9 and cracking of hydrocarbons. 10 The conventional way to prepare the catalysts is to impregnate the high surface area support oxide with an aqueous solution of ammonium heptamolybdate followed by calcining the solid in air.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Studies on ZrO₂Modified with MoO₃and Activity for Acid Catalysis

2003

Bulletin of the Korean Chemical Society

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Zirconia modified with MoO 3 was prepared by impregnation of powdered Zr(OH) 4 with ammonium heptamolybdate aqueous solution followed by calcining in air at high temperature. Spectroscopic studies on prepared catalysts were performed by using FTIR, Raman, XRD, and DSC and by measuring surface area. Upon the addition of molybdenum oxide to zirconia up to 15 wt%, the specific surface area increased in proportion to the molybdate oxide content, while acidity measured by irreversible chemisorption of ammonia exhibited a maximum value at 3 wt% of MoO 3 . Since the ZrO 2 stabilizes the molybdenum oxide species, for the samples equal to or less than 30 wt%, molybdenum oxide was well dispersed on the surface of zirconia and no phase of crystalline MoO 3 was observed at any calcination temperature above 400 o C. The catalytic activities for cumene dealkylation were roughly correlated with the acidity of catalysts measured by ammonia chemisorption method, while the catalytic activities for 2-propanol dehydration were not correlated with the acidity because weak acid sites are necessary for the reaction.

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“…promoted catalysts which are considered to be green catalysts [12][13][14][15][16]. Molybdenum and tungstate based zirconia catalysts are used for several organic reactions such as acetylation, alkylation, esterification, transesterification, 1,3-dioxalanes, biphenyl urea, etc.…”

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confidence: 99%