Showing papers on "Phosphotungstic acid published in 2014"

Insight into Proton Transfer in Phosphotungstic Acid Functionalized Mesoporous Silica-Based Proton Exchange Membrane Fuel Cells

Abstract: We have developed for fuel cells a novel proton exchange membrane (PEM) using inorganic phosphotungstic acid (HPW) as proton carrier and mesoporous silica as matrix (HPW-meso-silica) . The proton conductivity measured by electrochemical impedance spectroscopy is 0.11 S cm^(–1) at 90 °C and 100% relative humidity (RH) with a low activation energy of 14 kJ mol^(–1). In order to determine the energetics associated with proton migration within the HPW-meso-silica PEM and to determine the mechanism of proton hopping, we report density functional theory (DFT) calculations using the generalized gradient approximation (GGA). These DFT calculations revealed that the proton transfer process involves both intramolecular and intermolecular proton transfer pathways. When the adjacent HPWs are close (less than 17.0 A apart), the calculated activation energy for intramolecular proton transfer within a HPW molecule is higher (29.1–18.8 kJ/mol) than the barrier for intermolecular proton transfer along the hydrogen bond. We find that the overall barrier for proton movement within the HPW-meso-silica membranes is determined by the intramolecular proton transfer pathway, which explains why the proton conductivity remains unchanged when the weight percentage of HPW on meso-silica is above 67 wt %. In contrast, the activation energy of proton transfer on a clean SiO_2 (111) surface is computed to be as high as 40 kJ mol^(–1), confirming the very low proton conductivity on clean silica surfaces observed experimentally.

Phosphotungstic acid encapsulated in the mesocages of amine-functionalized metal–organic frameworks for catalytic oxidative desulfurization

Abstract: Highly dispersed Keggin-type phosphotungstic acid (H3PW12O40, PTA) encapsulated in the mesocages of amine-functionalized metal-organic frameworks MIL-101(Cr)-NH2 has been prepared by an anion-exchange method. PTA anions (PW12O40(3-)) are stabilized in the mesocages via the electrostatic interaction with amino groups of the MIL-101(Cr)-NH2. The obtained catalyst (denoted PTA@MIL-101(Cr)-NH2) exhibits high catalytic activity in the extractive and catalytic oxidative desulfurization (ECODS) system under mild conditions. Moreover, it can be easily recovered and recycled several times without leaching and loss of activity.

Phosphotungstic Acid Immobilized on Ionic Liquid-Modified SBA-15: Efficient Hydrophobic Heterogeneous Catalyst for Oxidative Desulfurization in Fuel

Abstract: A heterogeneous catalyst system was synthesized by immobilizing phosphotungstic acid on ionic liquid-modified mesoporous silica SBA-15 and applied in oxidative desulfurization. Structure and properties of catalyst were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the contact angle. The results demonstrated that the synthesized catalyst possessed ordered mesopore structure and high special surface area. Due to the introduction of imidazole-based ionic liquid, the catalyst exhibited good wettability for model oil, which had significant contribution to desulfurization activity. Both DBT and 4,6-DMDBT could be removed completely at mild conditions (60 °C, 40 min). The removal of BT also can reach 81.3% within 60 min. Furthermore, the catalyst was recovered and reused in four reaction runs with a slight decrease in activity.

Mesoporous Polyoxometalate-Based Ionic Hybrid As a Triphasic Catalyst for Oxidation of Benzyl Alcohol with H2O2 on Water

Abstract: A self-assembled mesoporous polyoxometalate-based ionic hybrid catalyst [TMGHA]2.4H0.6PW was prepared by combination of alcohol amino-tethered guanidinium ionic liquid [TMGHA]Cl with Keggin phosphotungstic acid H3PW12O40 (PW). Nitrogen sorption experiment validated the formation of mesostructure with moderate BET surface area, and scanning and transmission electron microscopy (SEM and TEM) showed a fluffy coral-shaped morphology for the hybrid. The contact angle test displayed that the hybrid owned hydrophilic–hydrophobic balanced surface that exhibited well wettability for both water and organic substrate like benzyl alcohol. Therefore, the hybrid can efficiently catalyze the water-mediated triphasic oxidation of benzyl alcohol with H2O2. During the reaction, the triphase catalytic system showed a special “on water” effect mainly due to the suitable mesostructure and surface wettability, thus providing some clues for the preparation of green heterogeneous catalyst.

Layer-by-layer self-assembly of Nafion–[CS–PWA] composite membranes with suppressed vanadium ion crossover for vanadium redox flow battery applications

Abstract: A novel polymer–inorganic composite membrane, Nafion–[CS–PWA]n (n = the number of bilayers), was prepared by a layer-by-layer self-assembly technique with polycation chitosan (CS) and negatively charged phosphotungstic acid (PWA) for vanadium redox flow battery applications. The UV-visible spectra and SEM results showed that the CS–PWA multilayer was successfully fabricated on the surface of the Nafion membrane, and the FTIR result showed that there was a strong interaction between the CS and PWA molecules. The obtained Nafion–[CS–PWA]n showed much lower vanadium ion permeability compared with the pristine Nafion membrane. Accordingly, the VRFB with the Nafion–[CS–PWA]3 membrane exhibited higher coulombic efficiency (CE) and energy efficiency (EE) together with a slower self-discharge rate than that of the pristine Nafion212 system.

Phosphotungstic Acid Immobilized on Amine-Grafted Graphene Oxide as Acid/Base Bifunctional Catalyst for One-Pot Tandem Reaction

Abstract: In this study, phosphotungstic acid immobilized on amine-grafted graphene oxide (GOAP) was prepared successfully by silylanization and electrostatic interaction. The obtained GOAP was characterized by Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), zeta potential measurements, and X-ray photoelectron spectroscopy (XPS). Systematic studies demonstrated that GOAP had excellent catalytic activities and robustness in the one-pot tandem deacetalization–nitroaldol reaction. The key role of the acid/base ratio in the catalytic performance of this bifunctional catalyst was also revealed by preliminary kinetic studies. This bifunctional catalyst might find promising applications in green chemistry, as it can not only reduce costs and waste by saving separation/purification steps and solvents/reagents, but also increase the yield by avoiding the separation of intermediate products.

Novel catalyst by immobilizing a phosphotungstic acid on polymer brushes and its application in oxidative desulfurization

Abstract: In the study, an HPW–PDMAEMA–SiO2 (phosphotungstic acid (HPW); poly-N,N-dimethylaminoethyl methacrylate (PDMAEAM)) catalyst was successfully synthesized. The synthesized HPW–PDMAEMA–SiO2 catalyst was characterized via XRD, TEM, FT-IR, TGA, and ICP-AES. The results show that the HPW active species retained its Keggin structure after immobilizing into polymer brushes. At optimal reaction conditions, the oxidative desulfurization conversion of dibenzothiophene reached 100%, and there was no significant catalytic performance decrease after six recycles. The excellent recoverability of the catalyst was attributed to the decreased leaching of the HPW active species caused by the strong interaction between the negative [PW12O40]3− ions and positive ammonium ions in the PDMAEMA polymer brushes.

Graphene Oxide as Support for the Immobilization of Phosphotungstic Acid: Application in the Selective Oxidation of Benzyl Alcohol

Abstract: Graphene oxide functionalized with gama-aminopropyltriethoxysilane, is used as support for the immobilization of homogeneous heteropoly phosphotungstic acid. It is synthesized and characterized by SEM, XPS, XRD, 31P NMR and Raman. The effects of catalyst parameters and reaction conditions on the oxidation reaction of benzyl alcohol are systematically investigated. Under optimal conditions, the catalyst exhibit remarkably enhanced catalytic activity (conversion 76 % and selectivity 99 %). And the catalyst could be separated conveniently. Moreover, the loss of PW12O40 3− anion from the support under the reaction conditions is responsible for the deactivation of the catalyst. SEM images of a GO, b GO–N, c GO–N–PW (inset XPS spectrum of carbon), d GO–N–PW reused (inset XPS spectrum of carbon). The mechanism of deactivation was testified using the SEM images and the XPS spectrums in c (inset) and d (inset) .

Vapor Phase Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Catalyst Supported on Niobia

Abstract: The vapor phase dehydration of glycerol was carried out on niobia-supported phosphotungstic acid (PTA) catalysts. The catalysts were prepared by varying the active component PTA loadings ranging from 10 to 40 wt% on the support. The catalysts were characterized by powder X-ray diffraction, laser Raman spectroscopy, temperature programmed desorption of ammonia, ex-situ FT-IR spectra of adsorbed pyridine, BET surface area and pore size distribution. The XRD results suggest that the active phase of phosphotungstic acid was found to be highly dispersed at lower PTA loadings on the support. The findings of Raman spectra reveals that the catalyst with 30 PTA/Nb-400 clearly exhibit the primary structure of Keggin ion of hetropolyacid on the niobia support. NH3-TPD experiments confirm that the acidity of the catalyst increases with increase of PTA loading and decreases at higher loadings. The nature of acidic sites on the catalyst surface was investigated by the ex-situ pyridine adsorbed FT-IR spectroscopy and the results suggest that the catalyst with 30 PTA/Nb has shown stronger Bronsted acidic sites. Pore size distribution reveals that 30 PTA/Nb-400 exhibited lager average pore diameter than the other loadings. The Nb2O5-supported PTA catalysts have shown remarkable catalytic performance during the dehydration of glycerol to acrolein. The catalytic properties during glycerol dehydration are related to the surface acidic functionality of the catalyst.

Heterogeneous Fenton-like degradation of 4-chlorophenol using a novel FeIII-containing polyoxometalate as the catalyst

Abstract: Fenton-like degradation of 4-chlorophenol (4-CP) in aqueous solution was studied over a novel Fe III -containing polyoxometalate (POM) as heterogeneous catalyst. The POM, assigned as Fe III AspPW 12 , was synthesized via precipitation reaction of phosphotungstic acid (PW 12 ) with the complex of ferric ion and aspartic acid (Asp) in aqueous solution. The catalyst displays high activity and good reusability for oxidation of 4-CP by hydrogen peroxide in the range from acidic to circumneutral pH values. The enhanced oxidation of 4-CP was observed when the reaction system was irradiated by a high pressure mercury lamp. Under the conditions of H 2 O 2 20 mM, Fe III AspPW 12 0.2 g/L, temperature 25 ± 2 °C and pH 6.5, the complete total organic carbon (TOC) removal for 100 mg/L 4-CP solution could be achieved in both dark and irradiation systems within 120 and 60 min, with H 2 O 2 utilization of 77% and 83% respectively. It is speculated that the catalysis may possibly undergo the redox cycles of Fe III ⇌ Fe II and POM ⇌ POM − on the surface of Fe III AspPW 12 , accompanied by hydroxyl radical formation from H 2 O 2 , and the oxidation of 4-CP consequently.

Heteropolyanion-based sulfated ionic liquid catalyzed formamides synthesis by grindstone chemistry

Abstract: A novel heteropolyanion-based sulfated ionic liquid (HIL-[Ch-OSO3H]3W12PO40) was prepared by pairing sulfate functionalized cholinium cation [N,N,N-trimethyl-2-(sulfooxy)ethanaminium] with catalytically active phosphotungstic acid anion (W12PO403−). It was characterized by 1H NMR, FT-IR, EDX, XRD, TGA and elemental analysis. Catalytic activity of thus prepared HIL was studied in N-formylation of amines under solvent-free grinding condition. The methodology provided cleaner conversion over shorter reaction time with high turnover frequency (TOF) and chemoselectivity.

In situ synthesis of nanocomposite membranes: comprehensive improvement strategy for direct methanol fuel cells.

Abstract: In situ synthesis is a powerful approach to control nanoparticle formation and consequently confers extraordinary properties upon composite membranes relative to conventional doping methods. Herein, uniform nanoparticles of cesium hydrogen salts of phosphotungstic acid (CsPW) are controllably synthesized in situ in Nafion to form CsPW–Nafion nanocomposite membranes with both improved proton conductivity and methanol-crossover suppression. A 101.3% increase of maximum power density has been achieved relative to pristine Nafion in a direct methanol fuel cell (DMFC), indicating a potential pathway for large-scale fabrication of DMFC alternative membranes.