Showing papers on "Phosphotungstic acid published in 2023"

Thermocatalysis enables photocatalytic oxidation of methane to formic acid at room temperature beyond the selectivity limits

Abstract: Direct conversion of methane into fuels and chemicals remains a major challenge in modern science. Formic acid is one of the most promising platform molecules. Photocatalysis proposes an attractive route for methane partial oxidation under mild conditions. The radical mechanism of methane photocatalytic oxidation restricts the selectivity to target products. In this article, we propose a strategy to break conventional limitations of methane photocatalytic oxidation by adding a thermocatalyst and conducting the process in a one-pot reactor. In this strategy, the methane selective conversion into formic acid proceeds first over cesium salt of phosphotungstic acid on titania, which photocatalytically oxidizes methane into a mixture of C1 oxygenates. These oxygenates are then selectively converted into formic acid over a heterogeneous alumina-supported ruthenium catalyst. All reactions occur at room temperature in the same reactor. A selectivity to formic acid of 85% and a productivity of 5 mmol g−1photocatalyst are achieved.

Phosphotungstic acid catalysed bioethylene synthesis under industrially relevant conditions

Abstract: Among the different routes of ethylene production, the most plausible way to obtain it from renewable sources nowadays is the dehydration of bioethanol, which can be obtained from biomass or...

Polyoxometalate Archetype-Boosted Stability and Charge Storage of 2D Graphene Nanosheets

Abstract: In this study, the potential of impregnation of phosphotungstic acid (PTA), a polyoxometalate in enhancing specific capacitance (C sp) and diminishing the well-known restacking phenomenon of graphene nanosheets was explored. Graphene nanosheets were prepared chemically from graphite powder through the formation of graphene oxide (GO) and then the subsequent reduction of GO to the reduced GO (rGO). Impregnation of PTA in rGO-PTA (rGP) composites was carried out by simply dispersing rGO and PTA derived from tungstic acid. Scanning electron microscopy, X-ray diffraction analysis, UV–vis reflectance spectroscopy, and Fourier-transform infrared spectroscopy were used to analyze the elemental composition, microstates, and morphology of the composites. The charge-storing capacity and stability of the prepared rGP composites casted on a graphite electrode were examined with cyclic voltammetric, chronopotentiometric, and electrochemical impedance techniques. The effect of ions on the charging capacity of the electrodes was verified using electrolytes with different ion sizes. About 100% enhancement of C sp of rGO with 87% capacitance retention for 2000 charging-discharging cycles was achieved by impregnating rGP composites with only 1% PTA.

Preparation and characterization of novel proton conducting membranes for thin film fuel cell

Abstract: This paper reports on the preliminary results concerning the possible functioning of novel composite membranes based on Porous Anodic Alumina in a H₂/O₂ fuel cell. The Anodic Alumina Membranes (AAM) supports are suitable for applications in miniaturized or thin film fuel cells. In fact they offers the possibility to reduce the fuel cell structure to micrometer sizes, thanks to the micromachining technology.
The thin film fuel cells have been fabricated by impregnation of anodic porous alumina membranes (AAM) with Cesium Hydrogen Sulphate, Nafion^® and Phosphotungstic acid (PWA).
Porous alumina supports (50 µm thick and pore diameter of 200 nm) were filled with the proton conductor and characterized by means of Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and thermal analysis (DTA).
The electrochemical characterization of impregnated AAM was carried out by recording the polarization curves of a hydrogen-oxygen fuel cell working at intermediate temperatures (160 °C) for AAM/CsHSO₄ membranes and at low temperatures (25÷80 °C) in humid atmosphere for AAM/PWA and AAM/ Nafion^® membranes.

Effect of TiO2 and Al2O3 Addition on the Performance of Chitosan/Phosphotungstic Composite Membranes for Direct Methanol Fuel Cells

Abstract: Composite chitosan/phosphotungstic acid (CS/PTA) with the addition of TiO2 and Al2O3 particles were synthesized to be used as proton exchange membranes in direct methanol fuel cells (DMFCs). The influence of fillers was assessed through X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, liquid uptake, ion exchange capacity and methanol permeability measurements. The addition of TiO2 particles into proton exchange membranes led to an increase in crystallinity and a decrease in liquid uptake and methanol permeability with respect to pristine CS/PTA membranes, whilst the effect of the introduction of Al2O3 particles on the characteristics of membranes is almost the opposite. Membranes were successfully tested as proton conductors in a single module DMFC of 1 cm2 as active area, operating at 50 °C fed with 2 M methanol aqueous solution at the anode and oxygen at the cathode. Highest performance was reached by using a membrane with TiO2 (5 wt.%) particles, i.e., a power density of 40 mW cm−2, almost doubling the performance reached by using pristine CS/PTA membrane (i.e., 24 mW cm−2).

Production of Alkyl Levulinates from Carbohydrate-Derived Chemical Intermediates Using Phosphotungstic Acid Supported on Humin-Derived Activated Carbon (PTA/HAC) as a Recyclable Heterogeneous Acid Catalyst

Abstract: This work reports a straightforward and high-yielding synthesis of alkyl levulinates (ALs), a class of promising biofuel, renewable solvent, and chemical feedstock of renewable origin. ALs were prepared by the acid-catalyzed esterification of levulinic acid (LA) and by the alcoholysis of carbohydrate-derived chemical platforms, such as furfuryl alcohol (FAL) and α-angelica lactone (α-AGL). Phosphotungstic acid (PTA) was chosen as the solid acid catalyst for the transformation, which was heterogenized on humin-derived activated carbon (HAC) for superior recyclability. Using HAC as catalyst support expands the scope of valorizing humin, a complex furanic resin produced inevitably as a side product (often considered waste) during the acid-catalyzed hydrolysis/dehydration of sugars and polymeric carbohydrates. Under optimized conditions (150 °C, 7 h, 25 wt.% of 20%PTA/HAC-600 catalyst), ethyl levulinate (EL) was obtained in an 85% isolated yield starting from FAL. Using the general synthetic protocol, EL was isolated in 88% and 84% yields from LA and α-AGL, respectively. The 20%PTA/HAC-600 catalyst was successfully recovered from the reaction mixture and recycled for five cycles. A marginal loss in the yield of ALs was observed in consecutive catalytic cycles due to partial leaching of PTA from the HAC support.

Fabrication of PVC Enrofloxacin-Selective Electrodes for Estimating Enrofloxacin in Pure Form and as Preparation Formula

Abstract: This study explored the development and qualities of the response of electrochemical properties of enrofloxacin-selective electrodes using precipitation based on producing phosphotungstic, after utilizing a matrix of polyvinyl chloride (PVC) and dibutyl phthalate or dibutyl phosphate as a plasticizer. The resulting membrane sensors were an enrofloxacin-phosphotungstic electrode (sensors 1) and an ENR-DOP-PTA electrode (sensors 2). Linear responses of (ENR-DBPH-PTA) and (ENR-DOP-PTA) within the concentration ranges of 2.1×10-6-10-1 and 3.0×10-6-10-2 mol. L-1, respectively, for both sensors were observed. Slopes of 51.61±0.24 and 39.40± 0.16 mV/decade and pH ranges equal to 2.5-8.5 and 2.0-9.0 were observed for sensors 1 and 2, respectively. The coefficients of selectivity of the created sensors demonstrated phenomenal selectivity for ENR. The proposed sensors showed useful scientific properties for the assurance of ENR in drug dosage and pure form.

Dehydration of bioethanol over phosphotungstic acid immobilized onto nanoporous activated carbons: thermodesorption and catalytic studies

Abstract: Phosphotungstic acid (PTA) was immobilized onto the porous structures of three nanoporous activated carbons (NACs), including oxidized, thermally treated, and pristine NACs. The PTA-NAC catalysts with different oxygen-containing functional groups on the carbon surface were obtained. The prepared catalysts can catalyze the reaction of bioethanol dehydration; they stimulate the formation of diethyl ether and ethylene. These catalysts showed high diethyl ether yields of up to 65% and excellent selectivities of up to 93% at 130–160 °С. The conversion of bioethanol to ethylene increased with increasing reaction temperature, and the ethylene yield reached almost 100% with about 100% selectivity at 190–220 °С.

Phosphotungstic acid immobilized over SnO2 mesoporous material as a heterogeneous catalyst for fructose to 5-hydroxymethylfurfural conversion

Abstract: 5-Hydroxymethylfurfural (HMF) is regarded as an essential platform chemical due to its flexible nature that could be converted into a variety of value-added compounds including production of liquid fuels and fine chemicals. We have developed a phosphotungstic acid (PTA) immobilized over SnO2 mesoporous material by hydrothermally employing Pluronic P123 as a structure directing agent (SDA) to obtain a heterogeneous catalyst for fructose to HMF conversion, and the catalyst is designated as MSnPTA. The powder X-ray diffraction patterns in low angle region, type IV isotherm and fringes of the catalyst confirmed the mesoporosity of the material. The catalyst is comprised of BET surface area of 85.86 m2/g and average pore diameter of 7.9 nm. Spherical shape through worm like structure formed small particles facilitated the large surface area of the MSnPTA catalyst that prefer to occur the catalytic reaction. The uniform elemental distribution of PTA over SnO2 ascribed more active sites, resulting in high acidity of the catalyst as measured by TPD of ammonia, which increased the conversion of fructose to high yield of HMF in a short reaction time. The yield of the HMF increased as increasing the amount of catalyst and temperature as expected.

Facile Synthesis of Efficient Pentaethylenehexamine-Phosphotungstic Acid Heterogeneous Catalysts for Oxidative Desulfurization

Abstract: The ultra-deep desulfurization of oil needs to be solved urgently due to various problems, including environmental pollution and environmental protection requirements. Oxidative desulfurization (ODS) was considered to be the most promising technology. The facile synthesis of highly efficient and stable HPW-based heterogeneous catalysts for oxidative desulfurization is still a challenging task. In this paper, pentamethylene hexamine (PEHA) and phosphotungstic acid (HPW) were combined by a simple one-step method to prepare a heterogeneous catalyst of PEHA-HPW for the production of ultra-deep desulfurization fuel oil. The composite material exhibited excellent catalytic activity and high recyclability, which could reach a 100% dibenzothiophene (DBT) removal rate in 30 min and be recycled at least 5 times. Experiments and DFT simulations were used to better examine the ODS mechanism of PEHA-HPW. It was proved that the rich amino groups on the surface of PEHA-HPW play a crucial role. This work provides a simple and feasible way for the manufacture of efficient HPW-based catalysts.

Oxidative desulfurization using nanocomposites of heterogeneous phosphotungstic acid over natural zeolites; optimization by central-composite design

Abstract: Abstract In this research, the phosphotungstic acid (PTA) was impregnated on natural zeolites of clinoptilolite (Clin), mordenite (Mord), ferrierite (Ferr), and natrolite (Nat) and was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX. The synthesized heterogeneous nanocomposites were used for oxidative desulfurization of dibenzothiophene (DBT). Among samples, PTA-Ferr has removed the most amount of DBT (82.02%) from model fuel and PTA-Nat, PTA-Clin, and PTA-Mord indicated 56.00%, 73.62%, and 67.05% removal of initial DBT, respectively. PTA-Ferr had a high surface area of 293.6 m2/g, agglomeration-free particles with an average size of 10.2 nm. To study the effect of operating parameters such as reaction time, reaction temperature and DBT concentration on the ODS activity of PTA-Ferr, a central composite design (CCD) was used. Optimized conditions for the highest DBT removal (94.39%) were obtained at a reaction time of 55 min, the temperature of 60 °C and a DBT concentration of 250 ppm.

Preparation and Photocatalytic Properties of Phosphotungstic Acid SiC Composites

Abstract: Four kinds of PTA SiC photocatalysts with different proportions of PTA were prepared by impregnation from phosphotungstic acid (PTA) and SiC. The photocatalyst was characterized by UV-Vis diffuse reflectance spectroscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Rhodamine B (RHB) was used as degradation substrate to investigate the photocatalytic degradation performance of the photocatalyst. The results show that the prepared photocatalyst maintains both the support structure of SiC and the Keggin structure of PTA. PTA SiC with 40% mass fraction of PTA had the best photocatalytic degradation performance. When exposed to light for 180 min, RHB can reach 66% of the degradation efficiency and the photodegradation reaction rate constant was 5.21×10−3 min−1. As an active substance, hydroxyl radical plays a decisive role in photocatalytic degradation of RHB.

Catalysis Research of PDMSUr-PWA Films: Aspects to be Considered

Abstract: PU/PDMS based co-polymers present as drawbacks low hardness and tenacity. By this reason, they are reinforced with silicate structure like ormosil, which is acting as a reinforcement agent. In turn, these ormosil can act as a suitable matrix to host polyoxometalates like phosphotungstic acid (H3PW12O40/ PWA). Thus, PDMSUr-PWA films (containing PDMS, Urethanes, Polyurethanes, Silicates and PWA), which constitute hybrid materials exhibit interesting mechanical and chemical properties, looking to satisfy part of the demand of thermal and electrical insulators and anticorrosive coatings also. For the applications of these materials are necessary the correlation among structure, composition, and properties. From results of XPS and ATR FT-MIR analysis constitute evidence of the presence of molecular ([PW12O40]3–) and atomic (W) Tungsten at top Surface (10 nm of depth) of these materials. Furthermore, considering features that PDMSUr-PWA films exhibit e.g. elasticity and hardness, one can infer that these materials could constitute a structural support for PWA in applications of heterogeneous catalysis in many chemical reactions. PDMSUr-PWA film containing 35 w/w% of PWA approximately (content at which the W concentration is maxima), the Tungsten segregation at surface of these films is predominant. Additionally, if it is taken in consideration the significant Bromine presence at surface at the concentration of PWA mentioned above, one could deduct that this sample is candidate for application as anticorrosive coatings. Finally, taking advantage of the Proton conductivity of PWA, this sample also could be considered as a mixed conductor (of protons and electrons), which in the form of membranes fulfill the requirements in order to be used as fuel cells.

Experimental and Theoretical Density Functional Theory Approaches for Desulfurization of Dibenzothiophene from Diesel Fuel with Imidazole-Based Heteropolyacid Catalysts

Abstract: Oxidative desulfurization (ODS) has been proved to be an efficient strategy for the removal of aromatic sulfur compounds from diesel oils, which are one of the main sources of air pollution. Heteropolyacid catalysts are highly active species for ODS, but the promotion of their catalytic activity and clarification of their catalytic mechanism remain an important issue. Herein, a series of novel imidazole-based heteropolyacid catalysts are prepared by a one-pot method for multiphase deep ODS of fuel with hydrogen peroxide as an oxidant. The experimental results show that the desulfurization performance of the prepared imidazole-based heteropolyacid catalysts is high up to 99.9% under mild conditions. The catalyst also possesses excellent recovery performance, and the desulfurization activity remains at 97.7% after being recycled seven times. Furthermore, density functional theory calculation is first employed to clarify the origin of the high desulfurization activity, and the results show that with the imidazole-based heteropolyacid (HPW-VIM) as the catalyst, the energy barrier is much lower than that with phosphotungstic acid (HPW) as the catalyst.

Anchoring HPW by amino‐modified MIL ‐101(Cr) to improve the properties of SPEEK in proton exchange membranes

Abstract: Incorporating phosphotungstic acid (HPW) in proton exchange membranes (PEMs) is an effective way to improve proton conductivity, but its leakage remains a problem. It can be solved by immobilizing acid in membranes to enhance the stability of PEMs. Herein, we proposed a novel sulfonated poly(ether ether ketone) (SPEEK) composite membrane (SPEEK/[email protected]) that was prepared by blending amino-modified MIL-101(Cr) to anchor HPW. In this work, HPW was anchored through hydrogen bond to minimize its leakage and enhance the overall compatibility. The incorporation of MIL-101(Cr)-NH2 also helped lower the swelling ratio and improve the dimensional stability. Compared with pristine SPEEK and SPEEK/MIL membrane, the proton conductivity of the SPEEK/[email protected] composite membrane increased by 26% and 14%, respectively. The superior performance recommended a promising conception for anchoring HPW in PEMs.

The Effect of Phosphotungstic Acid Filled on Carboxymethyl Cellulose/Polyvinyl Alcohol Matrix as the Polymer Electrolyte Membrane

Abstract: In this work, the researchers developed a new composite membrane based on Polyvinyl Alcohol (PVA) doped carboxymethyl cellulose (CMC) matrix to obtain mixed matrix membranes (MMMs) that showed a high methanol resistance and also applied the citric acid (CA) as a crosslinking agent. The addition of Phosphotungstic Acid (PTA) as filler into the CMC/PVA matrix aims to improve the performance of the membranes. The composite membranes were evaluated for chemical stability, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infra-red (FTIR), water uptake (WU), methanol uptake (MU), methanol permeability, and ion exchange capacity (IEC). The results showed the prominent value of oxidation stability according to its weight loss of 49.81 to 7.39% at 50 °C, the WU in the range of ± to 71.34%, the IEC of 0.17 to 0.72 mmol/g, the MU in the range 31.96 % to 4.38% and permeability of methanol in the range 17.28 × 10 -7 to 2.27 × 10 -7 cm 2 /s. The methanol permeability and uptake decreased along with the increase of the amount of PTA in the composite membrane. The addition of PTA increased the IEC and demonstrated significant positive effects in the composite membranes. In conclusion, the CMC/PVA/PTA membrane can be recommended as promising biomaterial for polymer electrolyte membrane direct methanol fuel cell (DMFC) applications.

Polyoxometalate/carbon black modified glassy carbon electrode for the detection of dopamine

Abstract: Abstract Dopamine (DA) is a crucial neurotransmitter in the central nervous system (CNS) of human and multicellular animal brains. In this paper, we report for the first time the synthesis of C/PWA composites by doping phosphotungstic acid (PWA) on carbon black nanoparticles by impregnation method. The synthesized materials were characterized and corroborated using high-resolution scanning electron microscopy, X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy. The synthesized C/PWA composite modified glassy carbon (GC) electrodes were used as selective electrocatalysts for dopamine (DA) oxidation process. The electrochemical redox behavior of DA was studied with cyclic voltammetry (CV). Under optimized conditions, DA was detected by differential pulse voltammetry (DPV) and the calibration plot showed linearity ( R 2 = 0.9988) over the range of DA concentrations of 10 µM-600 µM with a detection line of 0.1 µM. The sensor's capability to detect DA in commercial DA injections in real time has been successfully demonstrated.