Investigation of 12-Tungstophosphoric Acid Supported on Ce0.5Zr0.5O2 Solid Solution
TL;DR: In this paper, the nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr 0.5O2 solid solution has been investigated.
Abstract: 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 Ce0.5Zr0.5O2 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.
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TL;DR: A white colour IL-SiWA hybrid molecular material has been synthesized using 1-butyl 3-methyl imidazolium bromide ionic liquid and silicotungstic acid as discussed by the authors.
Abstract: 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.
115 citations
TL;DR: A group of ionic liquid (IL)-based polyoxometalate (POM) salts were prepared via anion exchange of imidazolium IL precursors tethered by different carbon chain alkyls with various Keggin POMs as mentioned in this paper.
Abstract: A group of ionic liquid (IL)-based polyoxometalate (POM) salts were prepared via anion-exchange of imidazolium IL precursors tethered by different carbon chain alkyls with various Keggin POMs. The ...
98 citations
TL;DR: A molecular salt with formula [BmIm]3[PMo12O40]3− has been prepared using room temperature ionic liquid and phosphomolybdic acid.
Abstract: 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.
95 citations
TL;DR: In this paper, highly uniformed SBA-15 catalysts functionalized with 12-tungstophosphorus acid (HPW) were synthesized via direct synthesis method, and their characteristics were investigated using BET surface analysis, NH 3 -TPD, FTIR, SEM, TEM, EDS and TGA.
Abstract: Via direct synthesis method, highly uniformed SBA-15 catalysts functionalized with 12-tungstophosphorus acid (HPW) were synthesized. Their characteristics were investigated using BET surface analysis, NH 3 -TPD, FTIR, SEM, TEM, EDS and TGA. Surface defects were found in catalysts with high HPW loading (30–40 wt.%). High loadings also caused the deposition of HPW on the external surface and subject to oxidative decomposition to WO 3 that affected their acidity. HPW in mesopores had better thermal stability. High lauric acid conversion (70%) and monolaurin yield (50%) were shown in 6 h at 160 °C by the catalyst with 20 wt.% HPW. Lower yield was achieved at higher temperature. Its ordered mesoporosity evidently resulted in shape selectivity effect to suppress by-products formation. Effects of reaction temperature (150–170 °C), reactant ratios (1:1–5:1) and catalysts loadings (1–5 wt.%) were thoroughly elucidated.
93 citations
TL;DR: A polyoxometalate-based lanthanide-organic framework was achieved using the Ho(4)(dpdo)(8)(H(2)O)(16)BW(12)O(40) nanocage as a secondary building block for the heterogeneous catalysis of phosphodiester cleavage in an aqueous solution.
Abstract: A polyoxometalate-based lanthanide−organic framework was achieved using the {[Ho4(dpdo)8(H2O)16BW12O40] (H2O)2}7+ nanocage as a secondary building block for the heterogeneous catalysis of phosphodiester cleavage in an aqueous solution.
91 citations
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TL;DR: The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by success in large-scale applications and by promising laboratory results as mentioned in this paper.
Abstract: Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.
1,047 citations
TL;DR: In this paper, it is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample.
Abstract: Temperature-programmed reduction in a H2/Ar mixture of Rh-loaded CeO2-ZrO2 solid solutions with a ZrO2 content varying between 10 and 90% mol and of monoclinic, tetragonal, and cubic structures is reported. It is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample. The promotion of the bulk reduction results in high oxygen storage capacity (OSC) as measured by oxygen uptake. A structural dependence of both reduction and oxidation processes is observed which is attributed to a higher oxygen mobility in the cubic structure compared to the tetragonal and monoclinic ones.
854 citations
TL;DR: In this paper, the properties of solid heteropoly catalysts are described, together with important principles required for the understanding and design of solid Heterpoly(oxometalates) catalysts.
Abstract: Fundamental and superior characteristics of heteropoly
compounds (heteropolyoxometalates) in the solid state that make them
suitable for catalyst design at the atomic/molecular levels are described,
together with important principles required for the understanding and
design of solid heteropoly catalysts. First, the molecular nature of
heteropolyanions (metal oxide clusters), which can be preserved in the
solid state, enables control of the acid and redox properties over a wide
range. Second, the presence of hierarchical structures (primary, secondary
and tertiary structures) can lead to three catalysis
modes—surface-type, pseudoliquid (or bulk-type I) and bulk-type II.
Precise control of pore size is possible through the understanding of the
microstructure, which results in unique shape selectivity observed for
various reactions. Heteropoly compounds are green catalysts functioning in
a variety of reaction fields and efficient bifunctional catalysts when
combined with other components. The elucidation of catalytic processes is
also possible at the atomic/molecular level due to their molecular nature.
The positions and dynamic nature of protons as well as organic reaction
intermediates in the pseudo-liquid phase can be clarified by spectroscopic
techniques. Various reactions promoted by solid heteropoly catalysts are
collected from recent publications to illustrate the usefulness of the
above ideas and of heteropoly catalysts themselves.
521 citations
TL;DR: In this paper, an attempt is made to rationalise the various factors and the interconnections to the structure, the texture, and the effects of the nanometre scale, which all contribute to the properties of these materials.
Abstract: Nanostructured CeO2–ZrO2 mixed oxides have attracted great interest in the past 10 years, in particular as redox or oxygen storage promoters in the three-way catalysts. However, it has now became clear that both the chemistry of the simple oxides and the complex metal–CeO2-based oxide interactions can play a critical role in developing novel and highly active materials for a number of processes, ranging from catalysts for H2 production from fuels up to ceramic materials and solid state conductors for fuel cells. Despite the apparent simplicity of these systems, extreme variability of their chemical and textural properties has been observed. An attempt is made here to rationalise the various factors and the inter-connections to the structure, the texture, and the effects of the nanometre scale, which all contribute to the properties of these materials.
409 citations