Acid catalysis by heteropoly acids

Timofeeva, Maria N.

doi:10.1016/s0926-860x(03)00386-7

Cited by 392 publications

(188 citation statements)

References 45 publications

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“…in the catalyst bulk and have extremely high proton mobility. 30 Their catalytic reactions occur not only on the surface, but also in the bulk of the crystalline HPA. Due to this unique characteristic of the polar solution, solid HPAs behave as a highly concentrated solution as such all HPAs protons, not only the surface proton sites, participate in the catalytic reaction.…”

Section: Catalytic Performances Studiesmentioning

confidence: 99%

“…Due to this unique characteristic of the polar solution, solid HPAs behave as a highly concentrated solution as such all HPAs protons, not only the surface proton sites, participate in the catalytic reaction. [30][31][32][33] This phenomenon, which is unusual in heterogeneous acid catalyst, is called as "pseudoliquid phase". [30][31][32][33] The HPAs used in this work were cesium 2.50 heteropoly acid (Cs 2.50 HPA) and cesium 1.87 heteropoly acid (Cs 1.87 HPA).…”

Section: Catalytic Performances Studiesmentioning

confidence: 99%

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Selective synthesis of PEG-monoester using cesium heteropoly acid as heterogeneous catalyst

et al. 2017

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Esterification of oleic acid with polyethylene glycol 600 (PEG-600) to produce polyethylene glycol monooleate (PEG-monooleate) and polyethylene glycol dioleate (PEG-dioleate) as by-product has been studied in the presence of heterogeneous acid catalysts, i.e. cesium heteropoly acid (Cs HPA). The results are compared with those obtained from a classical homogeneous acid catalyst; p-toluene sulphonic acid (p-TSA). The reaction was conducted under nitrogen flow with vigorous stirring at 130 °C and 150 °C. The catalyst loading kept at 4% and the reaction was monitored at 1, 3, 7 and 24 hours. Reaction samples were analyzed using high performance liquid chromatography (HPLC) equipped with evaporative light scattering detector (ELSD). The results obtained showed that Cs HPAs exhibit 100% selectivity of PEG-monooleate from the first hour until 24 hours. However, this does not happen with homogeneous p-TSA, where formation of by-product; PEG-dioleate is observed in the initial stage. It is also showed that the mole ratio is the most important parameter not only to produce high yield of monoester but also to maintain it along the reaction. Chemical and physical properties of catalysts were characterized using Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Tranmittance Infra-Red (FTIR), ammonia temperature programmed desorption (NH 3 -TPD) and X-ray Diffraction (XRD).

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Section: Catalytic Performances Studiesmentioning

confidence: 99%

Section: Catalytic Performances Studiesmentioning

confidence: 99%

Selective synthesis of PEG-monoester using cesium heteropoly acid as heterogeneous catalyst

et al. 2017

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“…According to data, generally, HPAs are much stronger than H 3 PO 4 and also than the usual inorganic acids (HCl, H 2 SO 4 , HNO 3 , and HBr) and even such strong acids as HClO 4 and CF 3 SO 3 H. It is notable that sulfuric acid ranks 2-5 units of pKa below HPAs (29).…”

Section: Hpasmentioning

confidence: 99%

Heteropoly acids-catalyzed organic reactions in water: doubly green reactions

Heravi

Fard

Faghihi

2013

Green Chemistry Letters and Reviews

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The organic reactions in water, as the most significant green solvent, have attracted much attention due to their unique properties over conventional organic ones. In the catalytic area, heteropoly acids (HPAs) are also promising green solid acids to replace environmentally harmful liquid acid catalysts. Herein, we wish to report the organic reactions catalyzed by HPAs, their salt, and polyoxometalates (POMs) in aqueous systems.

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“…Their very strong Brønsted acidity allows them to be potentially good candidates for acid catalysis. Unfortunately, their low specific surface area in the solid state (1-10 m 2 /g) and their high solubility in polar solvents are obstacles to their development in heterogeneous catalysis [2][3][4]. These problems can be overcome by two ways: either by immobilizing them onto high surface area supports to improve the dispersion of the active phase or through the direct synthesis of acidic porous salts.…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-Heteropolyacids (HPA) immobilized onto SBA-15 silica were prepared by two different ways using either impregnation or encapsulation methodologies. Two Keggin-type HPA, H 3 PW 12 O 40 and H 4 SiW 12 O 40 were considered in this study. The resulting hybrid materials were fully characterized by N 2 adsorption-desorption isotherms, XRD, FT-IR, Raman, diffuse reflectance UV-Vis spectroscopies and 31 P MAS NMR. All characterization methods showed that at room temperature the catalysts contained well-dispersed and intact Keggin units throughout the solid. The catalytic activity of these solids was investigated in the isomerization of n-hexane. The impregnated and encapsulated phosphotungstic catalysts performed similarly in catalysis showing that the amount of active sites was nearly the same in both catalysts. On the contrary, the tungstosilicic encapsulated material was completely inactive while its impregnated counterpart was even more active than the phosphotungstic derived catalysts. The acidity of the solids was measured by various methods: microcalorimetry of ammonia adsorption, ammonia desorption followed by Temperature Programmed Desorption (TPD) and DRIFT/GC-MS and pyridine adsorption followed by infrared spectroscopy. Only pyridine adsorption and ammonia desorption followed by DRIFT/GC-MS agreed with the catalytic data. Ammonia adsorption followed by microcalorimetry was not able to differentiate between the four catalysts while the TPD experiments led to unreliable results, as not only the evolved ammonia but also other molecules such as water were taken into account in the measurements. The behavior difference between the encapsulated silico-and phosphotungstic acids was explained by a more pronounced encapsulation in the case of silicon. de préparation. L'activité catalytique de ces matériaux a ensuite été étudiée dans l'isomérisation du n-hexane.

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Acid catalysis by heteropoly acids

Cited by 392 publications

References 45 publications

Selective synthesis of PEG-monoester using cesium heteropoly acid as heterogeneous catalyst

Selective synthesis of PEG-monoester using cesium heteropoly acid as heterogeneous catalyst

Heteropoly acids-catalyzed organic reactions in water: doubly green reactions

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

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