Infrared and Thermal Analysis Studies of Heteropoly Acids

Southward, Barry W. L.; Vaughan, J; O’Connor, C.T.

doi:10.1006/jcat.1995.1131

Cited by 64 publications

(39 citation statements)

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“…IR spectroscopy was chosen as the method of analysis, because unlike calorimetry or TPD, it gives information on the nature of the sites and with the right probes is fairly sensitive to small energetic differences between sites. IR spectroscopy has been applied extensively for the structural characterization of heteropoly compounds at various temperatures and degrees of dehydration [62,63,64,65,66,67,68,69]. This method in addition delivers information on the structure of a sample after each treatment by investigating the lowfrequency range of the IR spectrum.…”

Section: Acid-base Properties Under Relevant Conditionsmentioning

confidence: 99%

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

Jentoft

Klokishner

Kröhnert

et al. 2003

Applied Catalysis A: General

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The present study focuses on the evidence about the existence of Keggin ions under various reactive conditions. The stability of the hydrated parent heteropoly acid (HPA) phases is probed in water, by thermal methods in the gas phase, by in situ X-ray diffraction and in situ EXAFS. An extensive analysis of the in situ optical spectra as UV-Vis-NIR in diffuse reflectance yields detailed information about the activated species that are clearly different from Keggin ions but are also clearly no fragments of binary oxides in crystalline or amorphous form. Infrared spectroscopy with CO as probe molecule is used to investigate active sites for their acidity. Besides -OH groups evidence for electron-rich Lewis acid sites was found in activated HPA. All information fit into a picture of a metastable defective polyoxometallate anion that is oligomerised to prevent crystallisation of binary oxides as the true nature of the "active HPA" catalyst. The as-synthesized HPA crystal is thus a pre catalyst and the precursor oxide mixture is the final deactivated state of the catalyst.

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Section: Acid-base Properties Under Relevant Conditionsmentioning

confidence: 99%

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

Jentoft

Klokishner

Kröhnert

et al. 2003

Applied Catalysis A: General

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“…As shown in Fig.2 Table 3 Infrared spectral data* (cm -1 ) of heteropolyoxometalates (CTMA) 4 Fig.2 The comparison of absorption bands are due to the decomposition of the anhydrous heteropolyoxometalates. Their DTA curves exhibit a small endothermic peaks at about 100 and three strong exothermic peaks between 300 and 580 , which is attributed to the removal or dissociation of CTMA molecule and its fragment with simultaneous collapse of Keggin-type structure [8][9][10] . The final products of the thermal decomposition are the mixture of WO 3 , MoO 3 and SiO 2 [5,[7][8][9][10][11][16][17][18] .…”

Section: Xrd Of the Heteropolyoxometalatesmentioning

confidence: 99%

“…For comparison, the thermal decomposition of organoammonium polyoxometalates was investigated, but the thermal behavior of these compounds was briefly described for identification purposes [11] . Studies on the thermal analysis of the transition-metal-substituted tungstophosphates or tetrabutylammonium salts [9] had also been reported,but concerning cetyltrimethylammonium (CTMA) of molybdotungstosilicic acids was hardly focused. [11][12][13][14] .…”

Section: Introductionmentioning

confidence: 99%

“…The knowledge of the thermal behavior and thermodynamic data are useful and essential for promoting the applications of polyoxometalates. In previous papers, the thermal properties of the polyoxometalate anion [5][6][7] , especially the parent Keggin-type anions, have been reported [8][9][10] . Thermal analysis studies of heteropoly acids were reported by Southward B W L et al [9] .…”

Section: Introductionmentioning

confidence: 99%

“…In previous papers, the thermal properties of the polyoxometalate anion [5][6][7] , especially the parent Keggin-type anions, have been reported [8][9][10] . Thermal analysis studies of heteropoly acids were reported by Southward B W L et al [9] . Román P et al [5] reported the synthesis and thermal behavior of t-butylammonium polymolybdates.…”

Section: Introductionmentioning

confidence: 99%

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Preparation and properties of the heteropolyoxometalates of large organic cation with molybdotungstosilicic acids

Wang

Fang

Wei

2008

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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Some new heteropolyoxometalates of large organic cations with molybdotungstosilicic acids (general formula: (CTMA) 4 SiMo x W 12-x O 40 •mH 2 O•nDMF, x=0,2,4,6,8,10,12) were prepared by the reaction of cetyltrimethylammonium bromide (CTMAB,C 16 H 33 N(CH 3 ) 3 Br) with H 4 SiMo x W 12-x O 40 (x=0,2,4,6,8,10,12) in aqueous solution and recrystallization in DMF, and characterized by elemental analysis, IR spectra,TG-DTA and XRD techniques. The IR spectrum confi rms the presence of Keggin structure and organic cations in these compounds, and it is indicated that the stretching vibration of the M-Od, M-Ob-M and Si-Oa becomes more red-shifted when molybdenum is gradually substituted for the tungsten atom. In particular, the thermal decomposition of the heteropolyoxometalates was studied in nitrogen atmosphere. The TG-DTA curves show that their thermal behaviors not only contain the release of water molecule, DMF molecule, CTMA and its fragments but also contains simultaneous collapse of Keggin anion. Their end products of the thermal decomposition are the mixture of WO 3 , MoO 3 and SiO 2 . And from the final decomposition temperature of view, it is found that the thermal stability of these compounds gradually is decreased when the number of molybdenum atoms is increased.

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Assembly of Heteropoly Acid Nanoparticles in SBA‐15 and Its Performance as an Acid Catalyst

Wang

Chen

et al. 2005

Chemistry A European J

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Keggin-type 12-tungstophosphoric acid (TPA) nanocrystals have been assembled inside the pores of mesoporous silica through a vacuum impregnation method by using large-pore SBA-15 as a nanoreactor. The product was characterized by Brunauer-Emmet-Teller particle size distribution (BET-PSD), NMR and FT-IR spectroscopy, X-ray diffraction (XRD), tranmsission electron microscopy (TEM), differential thermal analysis (DTA) and FT-IR of adsorbed pyridine. The experimental results illustrate that the TPA nanocrystals are excellent Brønsted acid catalytic materials at room temperature.

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Infrared and Thermal Analysis Studies of Heteropoly Acids

Cited by 64 publications

References 0 publications

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

Preparation and properties of the heteropolyoxometalates of large organic cation with molybdotungstosilicic acids

Assembly of Heteropoly Acid Nanoparticles in SBA‐15 and Its Performance as an Acid Catalyst

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