Heteropolyacid Salts Research Articles

Arylether-type polybenzimidazole-based composites containing imidazole-substituted heteropolyacid salts for high-temperature proton exchange membrane fuel cells

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes are one of the most promising candidates for practical applications in high temperature proton exchange membrane fuel cells. In the field of the proton exchange membranes, a key target is to develop the membranes possessing high proton conducting ability, and meanwhile maintaining good mechanical integrity. It is extremely hard for PBI-based membranes at a high acid doping level (ADL) to have good strength due to the strong “plasticization effect” caused by PA molecules to PBI backbones. In order to obtain high-proton-conductivity membranes with a good comprehensive performance, three imidazole-substituted heteropolyacid salts (imi-HPAs) were synthesized and then incorporated into an arylether-type polybenzimidazole (Ph-PBI) matrix to fabricate some composite membranes via a solution blending process. Since both Ph-PBI matrix and imidazole-substituted heteropolyacid salts contained the functional imidazole groups, some preferred mixed effects and performance enhancements of the organic-inorganic composite membranes were observed. The morphology of the composite membranes revealed that imidazole-substituted heteropolyacid salts were homogenously dispersed in the Ph-PBI matrix. The membrane Ph-PBI/imi-HPA-3–15 % at ADL∼290.4 % had the highest conductivity of 166.6 mS·cm-1 at 200 °C. A H2/O2 fuel cell based on one membrane showed a peak power density of 454 mW·cm-2 at 160 °C, without humidification.

Cerium(III)phosphotungstate: an efficient catalyst in esterification of fatty acids

In this report, a known heteropolyacid salt (HPAs) cerium (Ⅲ) phosphotungstate was synthesized in a volume ratio of 2:1:2 with a molar ratio of 1:1:1 of each ingredient. These HPAs are further utilized in form of a catalyst to generate biodiesel through the esterification of variable carbon chain length alcohols (methanol, ethanol, n-propanol, isopropanol, n-butanol) and stearic acid at different conditions of reaction. FTIR of the produced biodiesel was also done for the assurance of ester peaks in it. Analysis of some important biodiesel properties (density, dynamic viscosity, acid value, aniline point, boiling point, cloud and pour point, and flash and fire point) etc., to differentiate and validate the results. A large surface area of the catalyst i.e. 121.427 m2/g determined using the BET surface area analyser, supports the fact of outrageous catalytic action in the esterification reaction. The effect of additives was also studied on the properties of resultant biodiesel. The calorific value of the samples was measured at 7320 Kcal/kg without additive and 7512 Kcal/kg after adding toluene (as an additive) in the biodiesel generated in the study. The pour point temperature of the biodiesel with additives was observed even < 20℃.

Potentiometric Application of CeFeMoP and CeAlMoP in Zr(IV) Ions Analysis: A Comparative Study

Two cerium-based ionophores Cerium(III) ironmolybdophosphate (CeFeMoP) and Cerium(III) aluminomolybdophosphate (CeAlMoP), were synthesised, having ion exchange capacities of 5.76±0.1 and 5.6±0.2 meq/gm respectively. Electroanalytical studies of synthesised heteropolyacid salts have been done using epoxy resin as binder material to form membranes of variable compositions. The potentiometric observation supports the behaviour of 40% membrane in both cases. CeFeMoP-based electrode showed a linear range from concentration 1x10-6 to 1x10-1 M and a limit of detection 6.31×10-7 M. In contrast, these parameters in the case of CeAlMoP are of linear range from 1x10-7 M to 1x10-1 M, response time 22 seconds and a limit of detection 5.01 × 10-7 M. Membranes yielded a rapid response time of 15 seconds in the case of CeFeMoP. The membranes performed very well in the case of internal concentration variations of the same solution and several other types of non-aqueous media. The FIM method proves the selectivity of the electrode even in the presence of interfering ions. CeFeMoP based sensor performed over a constant potential behaviour in pH values ranging between 3.32-8.26 while CeAlMoP based electrode worked in the pH range of 3.25-10.54 for a constant internal concentration of Zr(IV) ions. The two sensors also performed well as indicator electrodes as well as in real-time sample analysis. Hence, it is concluded that these sensors derived from CeFeMoP and CeAlMoP are quite effective in analyzing the Zr(IV) ions in various samples with quick response time and a lifetime of around 8 and 7 months respectively. A real field study was also performed by using an ICP-MS analyzer.

Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts.

Phase Transfer Catalytic Oxidation of Cyclopentene to Glutaraldehyde by Vanadium Molybdenum Heteropolyacid Salts

Phase Transfer Catalytic Oxidation of Cyclopentene to Glutaraldehyde by Vanadium Molybdenum Heteropolyacid Salts

Cesium partially exchanged heteropolyacid salts: efficient solid catalysts to produce bioadditives from the levulinic acid esterification with alkyl alcohols

Cesium partially exchanged heteropolyacid salts: efficient solid catalysts to produce bioadditives from the levulinic acid esterification with alkyl alcohols

Preparation and photocatalytic properties of β2-SiW11Mn/TiO2 nanomaterials

With manganese substituted heteropoly tungstate β2-K6[SiW11Mn(H2O)O39]·xH2O as the active component, a composite photocatalyst β2-SiW11Mn/TiO2 was prepared by impregnation method. The composite catalyst was characterized by FT-IR, UV-Vis, XRD, SEM and X-ray photoelectron spectroscopy. The catalytic activity was evaluated by the degradation of malachite green solution. The results showed that the degradation of malachite green under ultraviolet light reached 92.7% and the degradation effect under sunlight is better than that under ultraviolet light, reaching 97.2%. This indicates that polyoxometalates and titanium dioxide produced a synergistic effect to make the light response range expanded and reduced the reaction requirements. The catalytic degradation performance of pure titanium dioxide, heteropoly acid salt β2-SiW11Mn and the prepared catalyst β2-SiW11Mn/TiO2 on malachite green were studied. The results showed that the composite photocatalyst exhibited the best photocatalytic activity, confirming the significance of the material being compounded. Finally, the kinetics of the reaction were studied, and the reaction is a first-order reaction.

Heteropolyacid salts as catalyst in the biodiesel production: A review

Heteropolyacids have been used as marvellous catalyst in various type of organic transformations such as oxidation/reduction and transesterification reactions etc. Many novel and exciting developments are going on in this research area attracting worldwide attention of the researcher as well as industrialists. In this review, we seek out to bring application of heteropolyacid as a catalyst in the production of biodiesel through esterification and transesterification reaction.

Copper phosphotungstate-catalyzed microwave-assisted synthesis of 5-hydroxymethylfurfural in a biphasic system

In this paper, we have described a novel route to produce 5-hydroxymethylfurfural (HMF), a valuable platform molecule obtained from biomass. Metal-exchanged Keggin heteropolyacid salts were used as catalysts, in microwave-assisted reactions carried out in a water-ethyl acetate biphasic system. To avoid the use of homogenous Brønsted acid catalysts, which are corrosive and difficult to be reused, we have exchanged the protons of the Keggin heteropolyacids with transition metal cations. These salts were evaluated in the fructose dehydration, being the Cu3/2PW12O40 the most active and selective catalyst, achieving 81% of HMF yield, after 15 min reaction at 413 K under microwave irradiation. The effects of metal cation, anion or heteropolyanion present in the catalyst were evaluated. The greatest efficiency of the Cu3/2PW12O40 was attributed to its high Lewis acidic strength which allows its coordinates with the water molecules, consequently generating H3O+ ions in the reaction medium. In addition, after assessing reactions of fructose dehydration in the presence of other Copper salts [i.e., CuCl2 or Cu(NO3)2], we conclude the anion plays too a key role. The higher softness of phosphotungstic anion should stabilize protonate intermediates better than chloride or nitrate anions, favouring this way the reaction. Finally, although the catalyst has been soluble, it was easily reused by removing the aqueous phase and adding a new load of the substrate dissolved in ethyl acetate. The runs were successfully repeated without the loss of activity of the catalyst. Graphical abstract

Esterification of levulinic acid over Sn(II) exchanged Keggin heteropolyacid salts: An efficient route to obtain bioaditives

Abstract In this paper, we describe a process to add value to the biomass derivatives (i.e., levulinic acid), converting it to bioadditives over solid Sn(II) exchanged Keggin heteropolyacid salts. These solid catalysts are an attractive alternative to the traditional soluble and corrosive Bronsted acid catalysts. Among Sn(II) heteropoly salts, the Sn1.5PW12O40 was the most active and selective catalyst, achieving high conversions (ca. 90 %) and selectivity (90–97 %) for alkyl esters and angelica lactone, the main reaction products. The impacts of the main reaction parameters (i.e., catalyst load, temperature, and the molar ratio of alcohol to acid) were investigated. The use of renewable raw material, and an efficient and recyclable catalyst are the main positive features of this process. The Sn1.5PW12O40 catalyst was easily recovered and reused without loss activity.

Hydrolysis of Cellulose in the Presence of Catalysts Based on Cesium Salts of Heteropoly Acids

Hydrolysis of Cellulose in the Presence of Catalysts Based on Cesium Salts of Heteropoly Acids

Extraction of lithium and aluminium from bauxite mine tailings by mixed acid treatment without roasting

Bauxite mine tailings can be used as the reserve resources of aluminium and lithium. In this study, a less energy consumption treatment method for extracting aluminium and lithium from bauxite mine tailings has been proposed, which used mixed acid to leach aluminium and lithium from tailings directly, avoided roasting for reducing energy consumption, and obtained effective results.The minerals in the tailings are kaolinite, diaspore, boehmite, anatase and illite, among others. The minerals have fine dissemination sizes and low liberation. Under the leaching conditions of Al and Li of an acid concentration of 60%, a liquid-solid ratio of 4 mL/g, a reaction temperature of 100 °C and a reaction time of 3 h, the highest leaching rates of Al and Li are 88.64% and 96.35%, respectively. In the leaching process, phosphoric acid reacts with Al and Li in the strong acidic environment provided by sulphuric acid to produce heteropoly acids or heteropoly acid salts that dissolve in the solution.

Monoterpenes etherification reactions with alkyl alcohols over cesium partially exchanged Keggin heteropoly salts: effects of catalyst composition

In this work, cesium partially exchanged Keggin heteropolyacid (HPA) salts were prepared, characterized, and evaluated as solid catalysts in monoterpenes etherification reactions with alkyl alcohols. A comparison of the activity of soluble HPAs and their insoluble cesium salts showed that among three different Keggin anions the phosphotungstate was the most efficient catalyst. Assessments on the effects of the level of the protons exchange by cesium cations demonstrated that Cs2.5H0.5PW12O40 solid salt was the most active and selective phosphotungstate catalyst, converting β-pinene to α-terpinyl methyl ether. The influences of the main reaction parameters such as reaction temperature, time, catalyst load, substrate nature (i.e., alcohols and monoterpenes) were investigated. We have demonstrated that the simultaneous presence of the cesium ions and protons in the catalyst plays an essential role, being the 2.5–0.5 the optimum molar ratio. The Cs2.5H0.5PW12O40 salt was efficiently recovered and reused without loss of catalytic activity.

Hydrolysis of Cellulose in the Presence of Catalysts Based on Cesium Salts of Heteropolyacids

The catalytic properties of cesium salts of heteropolyacids with the composition Cs4-хHхSiW12O40 (х = 3 and 3.5), Cs3-хHхPMo12O40 and Cs3-хHхPW12O40 (х = 2 and 2.5) were studied in the hydrolysis of cellulose to glucose at 180 °C in an argon atmosphere. Glucose was shown to be the main product of the reaction. The maximum yield reached 23% in the presence of Cs3HSiW12O40 for 1 h of the reaction. Specific surface area was supposed to affect the catalyst efficiency. It was found that in the presence of the indicated salts the reaction is heterogeneous and homogeneous, which is caused by leaching of the active component to the solution. The obtained materials were shown to be more efficient in comparison with the systems reported in the literature.

The main factors affecting the catalytic properties of Ru/Cs-HPA systems in one-pot hydrolysis-hydrogenation of cellulose to sorbitol

One-pot conversion of mechanically activated cellulose to sorbitol was investigated over bifunctional catalysts based on Ru (0.6, 1 and 3 wt.%) and cesium salts of heteropoly acids (HPA) Cs2.1H0.9PW12O40 and Cs3HSiW12O40 (Cs-PW and Cs-SiW, respectively). The maximal yield of sorbitol equal to 59 % and selectivity 94 % were achieved over the 1%Ru/Cs3HSiW12O40 catalyst. Physicochemical and catalytic data showed that the rate-determining step, i.e. the hydrolysis of cellulose, depended on the surface acidity of catalysts, whereas Ru content in catalyst affected both the hydrolysis and the hydrogenation steps. The kinetic parameters for one-pot conversion of cellulose were determined by mathematical modeling approach and were successfully used for the prediction of the yields of sorbitol and mannitol.

Cesium‐Exchanged Lacunar Keggin Heteropolyacid Salts: Efficient Solid Catalysts for the Green Oxidation of Terpenic Alcohols with Hydrogen Peroxide

AbstractIn this work, an innovative and green oxidative process to convert renewable and abundant raw material to more value‐added fine chemicals was developed. Hydrogen peroxide, an environmentally benign oxidant, was used in Cs–exchanged lacunar Keggin heteropolyacid salts‐catalyzed oxidation reactions of the terpenic alcohols (i. e., nerol was the model molecule). The activity of most outstanding catalyst (Cs8SiW11O39) was compared with various catalysts. Epoxides and aldehydes, which are an attractive feedstock for fragrance and pharmaceutical industries were selectively obtained. Lacunar Keggin heteropolyacid salts containing cesium as the counter ion (i. e., Cs7PW11O39, Cs7PMo11O39 and Cs8SiW11O39) were easily synthesized and characterized by infrared spectroscopy, powdered X‐rays diffraction, X‐rays dispersive spectroscopy, scanning electronic microscopy, thermal analysis, porosimetry analyses, diameter and pores distribution. The influences of the main reaction variables such as catalyst concentration, the stoichiometry of the reactants and reaction temperature were evaluated. The reaction scope was successfully extended to the other terpenic alcohols. The Cs8SiW11O39 was the most active and selective lacunar salt. After five cycles of successive reuse, no loss of catalytic activity or selectivity was observed.

Synthesis and catalytic properties of nickel salts of Keggin-type heteropolyacids embedded metal-organic framework hybrid nanocatalyst

Abstract Nickel salts of Keggin-type heteropolyacid on Zr(IV)-based metal-organic frameworks (UiO-66) has been synthesized via ion-exchange followed by a facile one-pot hydrothermal method. The synthesized catalysts underwent FT-IR, N2 adsorption-desorption, powder XRD, SEM and TEM analysis. The NiHSiW/UiO-66 catalyst was used as a new and effective solid acid in the catalytic transfer free fatty acid to biodiesel with an optimum conversion of 86.7%. The excellent activity of the NiHSiW/UiO-66 nanocatalyst was closely related to its high specific surface area, nano-sized catalyst, and the synergistic effects of NiHSiW salts and UiO-66 matrix. Importantly, a relatively stable catalytic performance was achieved for 8 repeated cycles. Finally, kinetics of the esterification reaction have been assumed to be of pseudo first order.

Fabrication and Properties of Hybrid Membranes Based on Poly (Vinyl Alcohol), Sulfosuccinic Acid and Salts of Heteropolyacid with or without Silica for Fuel Cells Applications

Fabrication and Properties of Hybrid Membranes Based on Poly (Vinyl Alcohol), Sulfosuccinic Acid and Salts of Heteropolyacid with or without Silica for Fuel Cells Applications

An ultrasound enhanced catalytic ozonation process for the ultra-deep desulfurization of diesel oil

An ultrasound enhanced catalytic ozonation process was applied for the desulfurization of diesel oil with some metal salts of Keggin-type heteropolyacids, H3PW12O40–Mx/nH3−xPW12O40 (abbreviated as Mx/nH3−xPW12O40), as catalysts.

One-pot synthesis at room temperature of epoxides and linalool derivative pyrans in monolacunary Na7PW11O39-catalyzed oxidation reactions by hydrogen peroxide.

In this work, we describe a new one-pot synthesis route of valuable linalool oxidation derivatives (i.e., 2-(5-methyl-5-vinyltetrahydrofuran-2-yl propan-2-ol) (1a)), 2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol (1b) and diepoxide (1c), using a green oxidant (i.e., hydrogen peroxide) under mild conditions (i.e., room temperature). Lacunar Keggin heteropolyacid salts were the catalysts investigated in this reaction. Among them, Na7PW11O39 was the most active and selective toward oxidation products. All the catalysts were characterized by FT-IR, TG/DSC, BET, XRD analyses and potentiometric titration. The main reaction parameters were assessed. Special attention was dedicated to correlating the composition and properties of the catalysts and their activity.