The nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr0.5O2 solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm-1 which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce4+ and Zr4+ ions, and thus affecting the P-O and W=Oterminal bonds. The IR study indicates the formation of interfacial Ce4+-O-W and Zr4+-O-W bonds. The chemisorbed Keggin molecular layers on Ce0.5Zr0.5O 2 show activity towards conversion of acetophenone to styrene by Meerwein-Ponndorf-Verley reduction followed by dehydration. The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm -1 of the perturbed Keggin molecular layers. © 2007 Springer Science+Business Media, LLC.

Gangavarapu Ranga Rao

Department Of Chemistry

CERIUM COMPOUNDS

Chemisorption

Fourier transform infrared spectroscopy

infrared radiation

Negative ions

Phosphoric acid

Styrene

KEGGIN IONS

KEGGIN MOLECULAR LAYERS

LEWIS SITES

TUNGSTOPHOSPHORIC ACID

Solid solutions

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Catalysis Letters

12-Tungstophosphoric acid supported on montmorillonite K10 (PWA/mont-K10) catalysed Pechmann condensation reaction was reported. The catalyst was characterized by XRD, FTIR, UV-Vis DRS, surface area and pore size analysis, TGA and acidity by DRIFTS using pyridine. The morphology of the catalyst was studied by SEM. The activity of mont-K10, mont-KSF, SO 2- 4/ZrO 2, 12-tungstophosphoric acid, and PWA/mont-K10 was investigated by condensation reaction of resorcinol with ethyl acetoacetate in the absence of solvent. Effect of molar ratio, amount of catalyst, reaction temperature and time on the yield of 7-hydroxy-4-methylcoumarin had been investigated on PWA/mont-K10. PWA/mont-K10 catalysed condensation of ethyl acetoacetate with phenol and a few substituted phenols had also been carried out to yield corresponding coumarins. The recycled catalyst showed reduced activity after single use. 15 wt% PWA on mont- K10 was found to be effective for synthesis of coumarin derivatives without employing any solvent. © Springer Science+Business Media, LLC 2011.

Journal of Porous Materials

PWA/montmorillonite K10 catalyst for synthesis of coumarins under solvent-free conditions

A molecular salt with formula [BmIm]3[PMo12O40]3- has been prepared using room temperature ionic liquid and phosphomolybdic acid. The material is characterized by single-crystal X-ray diffraction. The compound crystallizes in orthorhombic system with space group Pca21. It is also characterized by CHN analysis, 31P MAS NMR, UV-vis DRS and near-IR methods. Thermal stability of the compound is investigated by TGA, IR and PXRD methods. Near-IR shows the loss of water of crystallization by the Keggin ions of phosphomolybdic acid bonded with ionic liquid. © 2008 Elsevier Masson SAS. All rights reserved.

Solid State Sciences

Synthesis and characterization of 1-butyl 3-methyl imidazolium phosphomolybdate molecular salt

A solid hybrid molecular material containing 1-butyl 3-methyl imidazolium cations and Keggin anions of phosphotungstic acid has been synthesized. It is fully characterized by CHN analysis, FTIR, XRD, UV-Vis-NIR DRS, 31P MAS NMR, TGA and SEM. The FTIR spectrum of the compound shows the fingerprint vibrational bands of both Keggin molecular anions and imidazolium cations. The aromatic C-H stretch region (2700-3250 cm-1) of imidazolium cation is split due to the interaction between the ring C-H and bulky Keggin anion. The red-shift in the UV-Vis spectra and the downfield 31P MAS NMR chemical shift also confirm the electrostatic interaction between the ions in the compound. Near IR spectral region (1000-2500 nm) shows the elimination of water in the compound which is hydrophobic. © Indian Academy of Sciences.

Fulltext

Journal of Chemical Sciences

Investigation of hybrid molecular material prepared by ionic liquid and polyoxometalate anion

The interaction of 20 wt% 12-tungstophosphoric acid with Cex Zr1 - x O2 solid solutions has been studied by PXRD, FTIR, FT-Raman, H2-TPR, NH3-TPD, diffuse reflectance UV-vis-NIR, and 31P MAS NMR techniques. The study indicates that the Keggin anions are attached to Lewis metal ion centres and anion vacancies on Cex Zr1 - x O2 supports through W{double bond, long}O terminal bonds. The Keggin units at the interface are chemically perturbed as indicated by non-intrinsic IR bands observed at 958 cm-1 (W{double bond, long}Oter bond), and 1052, 1102 cm-1 (P{single bond}O bond). NH3-TPD shows that the Keggin anions fixed to Lewis sites and/or oxygen ion vacancies decrease the ammonia uptake on Cex Zr1 - x O2 solid solutions. H2-TPR shows modified redox behaviour of Cex Zr1 - x O2 solid solutions due to the simultaneous reduction of ceria, decomposition of Keggin anions and the reduction of WO3. The broadening of 31P MAS NMR and DR-UV-vis-NIR spectra demonstrate the existence of chemical interactions between the Keggin anions and Cex Zr1 - x O2 supports. © 2008 Elsevier Inc. All rights reserved.

Journal of Colloid and Interface Science

Interaction of Keggin anions of 12-tungstophosphoric acid with Cex Zr1 - x O2 solid solutions

A white colour IL-SiWA hybrid molecular material has been synthesized using 1-butyl 3-methyl imidazolium bromide ionic liquid and silicotungstic acid. The material is found to dissolve in polar organic solvent such as DMSO, but not in water. It is characterized by CHN analysis, FTIR, XRD, UV-vis DRS, TGA and SEM. The FTIR spectra indicate the formation of a hybrid compound showing fingerprint vibrational bands of both Keggin ions of silicotungstic acid and imidazolium ions. There is a strong evidence of interaction between the Keggin anions and imidazolium cations from the UV-vis DR spectra and the splitting of imidazolium C-H bands in the IR spectrum of the IL-SiWA. The near IR shows loss of crystallization water from heteropoly acid when it reacts with ionic liquid forming the hybrid molecular material. © 2008 Elsevier B.V. All rights reserved.

Materials Chemistry and Physics

Synthesis and characterization of hybrid molecular material prepared by ionic liquid and silicotungstic acid

CeO2-ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV-vis-NIR diffuse reflectance, SEM and acid-base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid-base properties facilitating the dehydrogenation process. At low ceria content, the CeO2-ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)-ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2-ZnO catalysts for reactions involving acid-base sites. © 2005 Elsevier B.V. All rights reserved.

Journal of Molecular Catalysis A: Chemical

Promoting effect of ceria on the physicochemical and catalytic properties of CeO2-ZnO composite oxide catalysts

A series of ceria-incorporated zirconia (Ce1-xZrxO2, x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard's law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce3+ ← O2- and Ce4+ ← O2- charge transfer transitions. The two vibrational bands in 6960 cm-1 and 5168 cm-1 in the NIR region indicate the presence of surface hydroxyl groups on these materials.

Proceedings of the Indian Academy of Sciences: Chemical Sciences

XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

Microporous and Mesoporous Materials

Mesoporous silica-supported 12-tungstophosphoric acid catalysts for the liquid phase dehydration of d-xylose

Progress in Materials Science

Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates

Journal of Catalysis

Selective Meerwein–Ponndorf–Verley reduction of α,βα,β-unsaturated aldehydes over Zr-zeolite beta

Investigation of 12-tungstophosphoric acid supported on Ce 0.5Zr0.5O2 solid solution

Journal	Catalysis Letters
ISSN	1011372X
Open Access	No