Showing papers on "Phosphotungstic acid published in 2006"
TL;DR: In this paper, the performance of the proton exchange membrane fuel cell (PEMFC) with composite Nafion-inorganic additives such as silicon oxide (SiO2), TiO2, tungsten oxide (WO3), and SiO2/phosphotungstic acid (PWA) has been studied for the operation of temperature of above 100 degrees C.
154 citations
TL;DR: The formation of active oxygen species such as the O2-*/ HO2* and *OH are proposed to be responsible for the degradation of dyes, and the K3PW12040 catalyst is very stable and very easily separated from the reaction system for reuse.
Abstract: Microporous solid K3PW12O40 is prepared by precipitation of phosphotungstic acid and potassium ion, followed by calcination. Using this material as photocatalyst, a series of dye pollutants, such as rhodamine B, malachite green, rhodamine 6G, fuchsin basic, and methyl violet, were efficiently degraded in the presence of H2O2 under visible light irradiation (λ > 420 nm). The photocatalyst was characterized via SEM, BET surface area, FT-IR, and XRD. The photocatalyst has relative large surface area, and the Keggin structure of phosphotungstic ions is intact during the precipitation and calcination. The degradation kinetics, TOC changes, degradation products, ESR detection of active oxygen species, and the effect of radical scavengers are also investigated to clarify the degradation process and the reaction pathway. The dyes can be facilely bleached and mineralized (ca. 40% of TOC removal for RhB), and the main degradation products of RhB detected, besides CO2, are the small organic acids. They are released ...
154 citations
TL;DR: A series of pyrazolylbisindole derivatives have been synthesized by reacting substituted pyrazole aldehydes with substituted indoles using phosphotungstic acid, a Keggin type heteropoly acid as catalyst exhibiting excellent anti-fungal activity.
122 citations
TL;DR: A combined amphiphilic catalyst of octadecyltrimethylammonium bromide (STAB) and phosphotungstic acid was formed directly in a reaction system Deep desulfurization of dibenzothiophene (DBT) with h
Abstract: A combined amphiphilic catalyst of octadecyltrimethylammonium bromide (STAB) and phosphotungstic acid was formed directly in a reaction system Deep desulfurization of dibenzothiophene (DBT) with h
88 citations
TL;DR: SBA-15 was synthesized using non-ionic surfactant as the structure directing agent at 40°C and was then impregnated with different loadings (10, 30, 50 and 70%) of phosphotungstic acid as mentioned in this paper.
Abstract: SBA-15 was synthesized using non-ionic surfactant as the structure directing agent at 40 °C. It was then impregnated with different loadings (10, 30, 50 and 70%) of phosphotungstic acid. They were characterized by XRD, N 2 adsorption, FT-IR and DRIFT techniques. The physicochemical characterization revealed that SBA-15 could accommodate discrete phosphotungstic acid due to its large pore volume and high surface area. The catalytic activity of these materials was examined in the vapour phase tert -butylation of phenol using tert -butyl alcohol as the alkylating agent. The influence of reaction parameters such as reaction temperature, reactant feed ratio, WHSV and time on stream was studied, and the results were correlated with physicochemical characteristics of the catalysts. 4- tert -Butyl phenol was observed as the major product with high selectivity. Among the catalysts, 30% phosphotungstic acid supported SBA-15 showed high phenol conversion under optimum conditions, which is significantly higher than either phosphotungstic acid loaded mesoporous AlPO or AlMCM-41.
68 citations
TL;DR: Using HPW on graphite walls as an electrostatic and acid anchor, positively charged titania nanoparticles and albumin molecules were successfully assembled around CNTs without altering their delocalized π-electron system.
Abstract: In this work, we developed a convenient and efficient method for solubilization, purification and functionalization of carbon nanotubes (CNTs) using a versatile reagent (phosphotungstic acid (HPW)). Because HPW can spontaneously attach to graphite walls as polyanions and provide static repulsion, CNT aggregates were divided into individual and small bundles of CNTs and turned into a stable solution by sonication in the presence of HPW. Amorphous carbon impurities and metal catalysts in the raw CNTs were removed by centrifugation and filtration. Finally, purified CNTs with a yield of 82 wt% were obtained. Using HPW on graphite walls as an electrostatic and acid anchor, positively charged titania nanoparticles and albumin molecules were successfully assembled around CNTs without altering their delocalized π-electron system. The versatility of this simple approach could be extended beyond inorganic nanoparticles and proteins, to other systems with desired properties.
66 citations
TL;DR: In this article, the performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PtWO x /C and phosphotungstic acid (PTA) impregnated Pt/C electrocatalysts.
65 citations
TL;DR: In this paper, two types of poly(phenylene oxide) (PPO) membranes were prepared: one by chemical modification through sulfonation using chlorosulfonic acid and another by physical incorporation with a heteropolyacid (HPA), viz., phosphotungstic acid.
63 citations
TL;DR: In this paper, a novel catalytic membrane has been prepared by linking phosphotungstic acid H3PW12O40 (W12), a polyoxometalate having interesting properties as photocatalyst, on the surface of plasma-modified membranes.
Abstract: Novel catalytic membranes have been prepared by linking phosphotungstic acid H3PW12O40 (W12), a polyoxometalate having interesting properties as photocatalyst, on the surface of plasma-modified membranes. Porous flat-sheet membranes made of polyvinylidene fluoride (PVDF) have been prepared by a phase-inversion technique induced by a nonsolvent. These membranes have been modified by plasma treatments on the surface to graft N-containing polar groups that are able to act as binding sites with W12 (PVDF−NH2−W12). A comparison of the surface and bulk properties of the native and modified PVDF membranes has been reported. Catalytic activity of the PVDF−NH2−W12 membranes has been evaluated in the aerobic degradation reaction of phenol in water. Catalytic tests have been carried out in a membrane reactor operating in continuous mode. Better catalytic performances have been observed for the W12 heterogenized on PVDF membrane than for W12 in a homogeneous phase. Moreover, PVDF−NH2−W12 membranes have given proof of...
58 citations
TL;DR: In this paper, a proton-conducting composite material was synthesized from 1-butyl-3-methyl-imidazolium chloride (BMImCl) and 12-phosphotungstic acid (PWA).
52 citations
TL;DR: In this article, a solvent casting technique has been used, which allows the nanofiller to be delaminated by an ultrasonic pre-treatment, as confirmed by TEM and XRD analysis.
TL;DR: In this paper, the authors examined the mechanisms of hydride transfer and alkylation over phosphotungstic acid using ab initio density functional theory methods and found that the barrier for alkylations is intrinsically lower than that for hydrides transfer, thus providing a favorable path to the buildup of heavy hydrocarbons on acid surface.
TL;DR: In this article, the synthesis of mesoporous TiO2 particles using PWA assisted sol-gel method was investigated, where anatase TiO 2 materials with the BET surface area of ∼150m2/g were successfully prepared via PWA-assisted hydrolysis and polycondensation reactions of tetrabutyl titanate.
TL;DR: In this paper, the photochromic process of nanocomposite film containing nanometer-sized Keggin type phosphotungstic acid uniformly dispersed in polyacrylamide matrix was studied by in situ AFM and spectroscopy.
TL;DR: In this article, a mesoporous Al-MCM-41 (Si/Al = 20) molecular sieve was synthesized hydrothermally and characterized by X-ray diffraction, nitrogen-sorption studies and 27Al and 29Si MAS-NMR spectroscopies.
Abstract: Mesoporous Al-MCM-41 (Si/Al = 20) molecular sieve was synthesized hydrothermally and characterized by X-ray diffraction (XRD), nitrogen-sorption studies and 27Al and 29Si MAS-NMR spectroscopies. 10, 20 and 40 wt% phosphotungstic acid (PW) (H3PW12O40) were supported on Al-MCM-41 and the resulting catalysts were characterized by XRD, FT-IR, nitrogen-sorption, DRIFT, 1H and 31P MAS-NMR and DRS UV–vis spectral techniques. 1H MAS-NMR spectra of PW/Al-MCM-41 revealed leveling of the acidity of PW protons to Al-MCM-41. Their catalytic activities were evaluated in the esterification of succinic anhydride with ethanol in the temperature between 60 and 120 °C. Monoethyl succinate (MES) and diethyl succinate (DES) were obtained as products. The effects of alcohol/anhydride molar ratio and temperature were studied. Unsymmetrical alcoholysis of succinic anhydride with methanol and 1-butanol was also carried out successfully.
TL;DR: Using a mild wet-chemical route, cage-like phosphotungstic acid (HPW) molecules of 1.2 mm diameter were successfully filled into opened carbon nanotubes (CNTs) with cavity diameter of 2 mm as mentioned in this paper.
TL;DR: In this article, a 15% STA (15 SZ-750) catalyst with different calcination temperatures (600-850°C) was prepared by suspending zirconium oxyhydroxide in methanol solution of STA followed by drying and calcination.
Abstract: Zirconia-supported silicotungstic acid (15% STA) catalyst with different calcination temperatures (600–850 °C) was prepared by suspending zirconium oxyhydroxide in methanol solution of STA followed by drying and calcination. These catalysts were characterized by XRD, FTIR pyridine adsorption and DRUV–vis spectroscopy. The catalysts showed both Bronsted as well as Lewis acidity and 15% STA on zirconia calcined at 750 °C (15 SZ-750) had the highest Bronsted acidity. Characterization of 15 SZ-750 catalyst by Raman spectroscopy showed the presence of zirconia-anchored mono-oxotungstate as the major tungsten species present in this catalyst. These catalysts were used in benzoylation of veratrole with benzoic anhydride and 15 SZ-750 catalyst showed the highest activity. For catalyst with support calcined at different temperatures before HPA impregnation, catalytic activity decreases as the support calcination temperature increases due to the decrease in Bronsted acidity. Comparison of the catalytic activity of 15 SZ-750 with that of zirconia-supported phosphotungstic acid (15%, calcined at 750 °C, 15 PZ-750) in benzoylation of veratrole with benzoic anhydride, acylation of anisole with acetic anhydride and in alkylation of diphenylether with 1-dodecene showed that 15 SZ-750 catalyst has higher activity and deactivation resistance due to its higher Bronsted acidity. The deactivated catalyst could be regenerated by calcination without appreciable loss in activity.
TL;DR: In this paper, the physicochemical properties of these composite membranes were studied by means of field-emission scanning electron microscopy (FSEM), X-ray diffraction (XRD) analysis, thermogravimetry analysis (TGA) and Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy.
TL;DR: Ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules, and it is concluded that the loss ofconstitutional water molecules is a plausible deactivation mechanism of the acid catalyst.
Abstract: Heterpolyacids (HPAs) demonstrate catalytic activity for oxidative and acid-catalyzed hydrocarbon conversion processes. Deactivation and thermal instability, however, have prevented their widespread use. Herein, ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules. The overall reaction energy and activation barrier are computed for the overall reaction HnXM12O40 → Hn-2XM12O39 + H2O. and subsequently used to predict the effect of HPA composition on thermal stability. For example, the desorption of a constitutional water molecule is found to be increasingly endothermic in the order silicomolybdic acid (H4SiMo12O40) < phosphomolybdic acid (H3PMo12O40) < silicotungstic acid (H4SiW12O40) < phosphotungstic acid (H3PW12O40), in agreement with the experimental ordering of their thermal stability. The presence of an adjacent Keggin unit may stabilize the structural defect created by the water de...
TL;DR: A new kind of inorganic-organic composite membranes based on sulfonated polyethersulfone cardo (SPES-C) with embedded phosphotungstic acid (PWA) was prepared by using FT-IR, XRD, TGA and SEM techniques.
TL;DR: In this paper, Rhodium-MonoPhos was successfully immobilised on four different anionic carrier materials: a mesoporous aluminosilicate (AlTUD-1), phosphotungstic acid on alumina (PWTUD), Nafion, and a nafion silica composite (SAC-13).
TL;DR: In this paper, a simple and efficient method was developed for the synthesis of quinaldines and lepidines by a one-pot reaction of anilines with crotonaldehyde or methyl vinyl ketone using phosphotungstic acid, a Keggins-type heteropoly acid, under both thermal and microwave irradiation conditions.
TL;DR: In this article, the authors describe a low-cost catalyzed one-pot condensation of aryl aldehydes, urea derivatives and β-diketones under microwave irradiation, which produces 3,4-dihydropyrimidin-2(1H)-ones in excellent yields and high purity.
TL;DR: In this paper, the catalytic performance of MCM-41 molecular sieve was examined in the vapour phase alkylation of phenol with tert-butyl alcohol (TBA) in the temperature range 190-275 °C.
TL;DR: In this article, a new class of proton conducting glass membranes for hydrogen fuel cell applications are developed using phosphotungstic acid, which showed good mechanical and thermal stability, and also found a maximum proton conductivity of 9.1 × 10 −2 ǫ s/cm at 90 −°C and 30% RH.
TL;DR: In this paper, a mixture of Heteropoly acid (HPA)-impregnated zirconium phosphate (ZrP) was prepared by an incipient wetness impregnation method by varying the wt.% of HPAs.
Abstract: Heteropoly acid (HPA)-impregnated zirconium phosphate (ZrP) was prepared by an incipient wetness impregnation method by varying the wt.% of HPAs like phosphotungstic acid (PWA), phosphomolybdic acid (PMoA), silicotungstic acid (SiWA) and silicomolybdic acid (SiMoA). All the samples were characterized by X-ray diffraction studies, FTIR, determination of acid sites and TG–DTA. The catalytic activities of all the samples were evaluated by carrying out the liquid phase bromination of phenol using KBr and hydrogen peroxide. The reaction products were analysed by GC through a capillary column. From the product analysis it was found that PWA/ZrP shows the highest conversion. Even so SiWA/ZrP heated at 110 °C shows the highest para- selectivity (in the range of 32–41%), higher than any other HPA/ZrP. The selectivity increases with an increase in the activation temperature up to 400 °C and thereafter it remains constant. The reaction proceeds through the formation of Br + (bromonium ion) which attacks the phenol ring, forming different brominated products.
TL;DR: In this paper, a composite membrane with a low amount of PWA embedding, showed lower methanol crossover in comparison to Nafion ®, but the added PWA in- creased the water retention of the composite membrane.
Abstract: Sulfonated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene- oxy-phenylene) (PEEK-WC) membranes with various degrees of sulfonation (DS) were pre- pared, and their electrochemical and thermal properties were studied. Composites were formed by adding the hydrated phosphotungstic acid (PWA). The membrane (DS = 0.96, PWA = 50 %) conductivity was increased to 3.5 × 10 -2 S cm -1 at room temperature and 6.0 × 10 -2 S cm -1 at 80 °C. The composite membrane with a low amount of PWA embed- ded, showed lower methanol crossover in comparison to Nafion ® . The addition of PWA in- creased the water retention of the composite membrane.
TL;DR: In this paper, a mixture of Heteropoly acid (HPA)-impregnated titanium phosphate (TiP) was prepared by an incipient wetness impregnation method by varying the weight percent of HPAs like phosphotungstic acid (PWA), phosphomolybdic acid (PMoA), silicotungstric acid (SiWA), and silicomolybic acid(SiMoA), and all the samples were characterized by XRD, FTIR, acid sites, pore size distribution, and TG-DTA
Abstract: Heteropoly acid (HPA)-impregnated titanium phosphate (TiP) was prepared by an incipient wetness impregnation method by varying the weight percent of HPAs like phosphotungstic acid (PWA), phosphomolybdic acid (PMoA), silicotungstic acid (SiWA) and silicomolybdic acid (SiMoA). All the samples were characterized by XRD, FTIR, acid sites, pore size distribution, and TG-DTA. The catalytic activities of all the samples were evaluated by carrying out the liquid phase bromination of phenol using KBr and hydrogen peroxide. The reaction products were analysed by GC through a capillary column. From the product analysis it was found that PWA/TiP, dried at 110 °C shows the highest conversion (98%). Even so SiWA/TiP dried at 110 °C shows the highest para-selectivity (30%), higher than any other HPA/TiP. The selectivity increases with an increase in the activation temperature up to 400 °C and thereafter it remains constant. The reaction proceeds through the formation of Br+ (bromonium ion) which attacks the phenol ring, forming different brominated products.
TL;DR: In this paper, density functional theory is used to examine the formation and transformation of adsorbed alkoxide intermediates to active carbenium-ion species over solid acid catalysts.
20 Oct 2006