Silicotungstic Acid Research Articles

H4SiW12O40-catalyzed cyclization of epoxides/aldehydes and sulfonyl hydrazides: An efficient synthesis of 3,4-disubstituted 1H-pyrazoles

A simple and efficient method for the synthesis of pyrazoles through a silicotungstic acid (H4SiW12O40)-catalyzed cyclization of epoxides/aldehydes and sulfonyl hydrazides has been developed. Various epoxides/aldehydes were smoothly reacted with sulfonyl hydrazides to furnish regioselectivity 3,4-disubstituted 1H-pyrazoles. The application of such an earth-abundant, readily accessible, and nontoxic catalyst provides a green approach for the construction of 3,4-disubstituted 1H-pyrazoles. A plausible reaction mechanism has been proposed on the basis of control experiments, GC-MS and DFT calculations.

Oxidative Synthesis of Acid Blue 7 Dye Catalyzed by CuO/Silicotungstic Acid in Water-Phase.

A catalytic oxidation reaction for Acid Blue 7 dye synthesis was evaluated in water. Without lead oxide or manganese oxide derivatives as oxidants, polyoxometalate catalysts were investigated to reduce the usage of harmful heavy metal. A catalyst was prepared by mixing silicotungstic acid with copper oxide, and aqueous hydrogen peroxide (30%) was used as an oxidizing agent. This reaction proceeded to produce Acid Blue 7 from the corresponding leuco acid after 45 min at 95 °C and was viable for a 10 g-scale synthesis.

One pot synthesis of aluminum pillared intercalated layered clay supported silicotungstic acid (STA/Al-PILC) catalysts

One pot synthesis of silicotungstic acid (STA) containing aluminum pillared intercalated layered clay (STA/Al-PILC) catalysts is carried out by addition of STA to aluminum pillared clay synthesis media. STA-Al Keggin type pillar agents which are formed by charge interaction among them are inserted between clay layers. Effect of parameters on catalyst structure such as pH of clay suspension, STA quantity, addition step and its isolation in buffer solution are investigated. STA addition step has a crucial role on properties of catalysts. Conservation of the layered structure of Al-PILC support in the presence of STA is seen from X-ray powder diffraction (XRD) patterns and transmission electron microscopy (TEM) images. Basal spacing values do not show much difference with respect to that of Al-PILC support which is measured as 1.85 nm. The catalyst which owes the best structural properties has 217 m2/g surface area, 0.20 cm3/g pore volume, 0.44 nm average micropore size and 3.90 nm average mesopore size with high STA loading success. Lewis acidity is dominant acid character in all catalysts. Preservation of Keggin structure of STA in PILC structures is seen by X-ray photo electron spectroscopy (XPS) with a clear W4f7/2 and W4f5/2 spin orbital doublet. The increase in STA amount leads no additional increase in STA loading. Agglomeration, which is seen clearly in TEM images, occurs when STA is added either as its powder form to Al-pillar agent media or after isolating it within the buffer solution to Al-pillar agent-clay suspension. The proposed model which assumes the placement of pillar agents between clay layers, either after coupling with each other or alone, explains effects of STA addition steps on structural properties.

Synthesis of Butadiene from Formaldehyde and Propylene on Cesium Salts of Silicotungstic Heteropoly Acid

Synthesis of Butadiene from Formaldehyde and Propylene on Cesium Salts of Silicotungstic Heteropoly Acid

Conversion of bioplatform molecule, succinic acid to value-added products via esterification over 12-tungstosilicic acid anchored to MCM-22

The model bioplatform molecule succinic acid, via esterification with n-butanol, leads to succinate esters, promising fuel additives and value-added products. In the present article, the potential application of heterogeneous catalyst comprising silicotungstic acid (SiW12) and MCM-22 (SiW12-MCM-22) was exploited for esterification of succinic acid with n-butanol. Performance of the catalyst was examined by carrying out a detailed optimization study, focusing on the synthesis of diester (one of the excellent fuel additives) and kinetic experiments at different reaction time and temperatures. The experimental results exhibit synergistic effect of SiW12 and MCM-22, yielding 97% conversion of acid with 59% selectivity of diester, TON of 1214 and activation energy of 68 kJmol-1. Experiments to demonstrates the effectiveness of High Gravity approach were also performed. The green metrics, atom economy (86.47%) (for desired diester) with E-factor (0.69) were calculated. The catalyst was recovered and used for consecutive three catalytic cycles, exhibiting remarkable regenerative activity to synthesize esters and contribute new routes for industrial scale.

Impacts of Sn(II) doping on the Keggin heteropolyacid-catalyzed etherification of glycerol with tert-butyl alcohol

In this work, phosphomolybdic acid salts were synthesized exchanging their protons by the Sn(II) cations (i.e., H3-xSnx/2PMo12O40; x = 0.0, 1.0, 2.0, 3.0), and evaluated in the etherification reactions of glycerol with tert-butyl alcohol (TBA). The catalytic activity of the phosphomolybdate salts containing a variable load of Sn(II) ions was further compared to phosphotungstic and silicotungstic acid salts (i.e., H3-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 3.0 and H4-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 4.0, respectively). The integrity of the Keggin anion after the synthesis was confirmed by infrared spectroscopy analysis. Physical properties were determined through thermal analyses, powder X-Rays diffraction patterns, N2 adsorption-desorption isotherms, and scanning electron microscopy. The acidity properties were analyzed by adsorbed pyridine FT-IR spectroscopy, NH3-programmed-temperature desorption, and potentiometric titration. Among all the Sn(II) heteropoly salts tested, the Sn3PMo12O40 was the most active and selective catalyst toward glyceryl ethers. The highest activity of Sn3PMo12O40 was assigned to the greater Lewis acidity strength. Modeling, simulation, and economic analysis allowed to evaluate the viability of the process. An annual capacity of 30,000 metric tons was developed, and the process is feasible with a return on investment (ROI) of 30.7%.

Efficient One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones via a Three-Component Biginelli Reaction.

Multicomponent reactions are considered to be of increasing importance as time progresses due to the economic and environmental advantages such strategies entail. The three-component Biginelli reaction involves the combination of an aldehyde, a β-ketoester and urea to produce 3,4-dihydropyrimidin-2(1H)-ones, also known as DHPMs. The synthesis of these products is highly important due to their myriad of medicinal properties, amongst them acting as calcium channel blockers and antihypertensive and anti-inflammatory agents. In this study, silicotungstic acid supported on Ambelyst-15 was used as a heterogeneous catalyst for the Biginelli reaction under solventless conditions. Electron-poor aromatic aldehydes gave the best results. Sterically hindered β-ketoesters resulted in lower reaction yields. The reaction was carried out under heterogeneous catalysis to allow easy recovery of the product from the reaction mixture and recycling of the catalyst. The heterogeneity of the reaction was confirmed by carrying out a hot filtration test.

A 2D Cd-containing Keggin-type heteropolyoxometalate with electro-catalytic behaviors

A layer compound, [Cd2(bibp)2.5(DMA)3(DMF) 2 (SiW12O40)]n (1), which was synthesized via a self-assembly procedure by the reaction of silicotungstic acid, cadmium ion and bichelate-bridging ligand (4,4′-bis(imidazolyl)biphenyl, bibp) in the solution of DMF and DMA, has been characterized by IR, elemental analysis, TGA, X-ray single crystal diffractometer and electrochemistry. Single crystal structure analysis shows that the structure for 1 represents hoop-club chains by the cadmium ions and the bibp ligands, extends to layers by the [SiW12O40]4− polyanions and further spreads to 3D by hydrogen bond via the bridge oxygen atoms in [SiW12O40]4− units. The electrochemical investigation shows that compound 1 exhibits POM-based electro-catalytic behavior for the reduction of nitrite.

General Synthesis of Ordered Mesoporous Carbonaceous Hybrid Nanostructures with Molecularly Dispersed Polyoxometallates.

Hybrid nanomaterials with controlled dimensions, intriguing components and ordered structures have attracted significant attention in nanoscience and technology. Herein, we report a facile and green polyoxometallate (POM)-assisted hydrothermal carbonization strategy for synthesis of carbonaceous hybrid nanomaterials with molecularly dispersed POMs and ordered mesopores. By using various polyoxometallates such as ammonium phosphomolybdate, silicotungstic acid, and phosphotungstic acid, our approach can be generalized to synthesize ordered mesoporous hybrid nanostructures with diverse compositions and morphologies (nanosheet-assembled hierarchical architectures, nanospheres, and nanorods). Moreover, the ordered mesoporous nanosheet-assembled hierarchical hybrids with molecularly dispersed POMs exhibit remarkable catalytic activity toward the dehydration of tert-butanol with the high isobutene selectivity (100 %) and long-term catalytic durability (80 h).

General Synthesis of Ordered Mesoporous Carbonaceous Hybrid Nanostructures with Molecularly Dispersed Polyoxometallates

AbstractHybrid nanomaterials with controlled dimensions, intriguing components and ordered structures have attracted significant attention in nanoscience and technology. Herein, we report a facile and green polyoxometallate (POM)‐assisted hydrothermal carbonization strategy for synthesis of carbonaceous hybrid nanomaterials with molecularly dispersed POMs and ordered mesopores. By using various polyoxometallates such as ammonium phosphomolybdate, silicotungstic acid, and phosphotungstic acid, our approach can be generalized to synthesize ordered mesoporous hybrid nanostructures with diverse compositions and morphologies (nanosheet‐assembled hierarchical architectures, nanospheres, and nanorods). Moreover, the ordered mesoporous nanosheet‐assembled hierarchical hybrids with molecularly dispersed POMs exhibit remarkable catalytic activity toward the dehydration of tert‐butanol with the high isobutene selectivity (100 %) and long‐term catalytic durability (80 h).

Development of New Cellulose-Based Hydrogel Membranes for Aqueous Electrochemical Capacitors

A rapidly growing interest in renewable energy resources requires efficient energy storage systems as well as a need to elaborate a greater number of eco-friendly components. Electrochemical double-layer capacitors (EDLCs), also known as supercapacitors are a class of energy storage devices that store the energy due to the separation of oppositely charged ions at in the electrical field resulting the formation of electrical double layer (EDL) at the porous carbon electrode/electrolyte interface. EDLCs consist of two porous carbonaceous electrodes pre-soaked with electrolyte and separated with a membrane (separator). The simple electrostatic mechanism of energy storage, lack of chemical changes and faradaic transitions during operation results in high electrical capacitance with respect to classical capacitors, significantly higher power density in comparison to batteries, and practically unlimited life span. Currently, the commercially produced EDLCs typically rely on organic solvents such as acetonitrile or propylene carbonate with the addition of conductive salts. However, such drawbacks as their low conductivity, toxicity flammability and high cost, led to the growth of interest in aqueous electrolytes such as KOH, H2SO4 or simple inorganic salts. Among main advantages of aqueous solvents such features as their higher ionic conductivity, lower viscosity, increased safety, lower cost and ease of assembly under ambient atmosphere, should be underlined.Modern and technologically advanced charge storage devices often require flexible and deformable devices for specific applications. Therefore, a lot of research is held into the development of alternatives for currently used liquid (aqueous and organic) electrolytes, which suffer from two prominent drawbacks — (i) the possibility of electrolyte leakage and (ii) high standards of technology to safely encapsulate electrolyte in the device. To overcome these limitations, the solid-state EDLCs using an ionically-conductive polymer or hydrogel membrane, serving as both the separator and the electrolyte, are under the spotlight. In this respect, a cellulose, built of β-(1→4)-linked D-glucose units, is one of the most prevalent and easily degradable biopolymer. Albeit the wide availability, biodegradability and low cost, the usage of cellulose is limited due to insolubility in most common solvents. The recent alternative, to toxic and flammable organic compounds, such as N,N- Dimethylformamide/N2O4, N-methylmorpholine oxide (NMMO), are ionic liquids (ILs), that have been gaining lately a lot of attention in energy storage systems. Various ILs based on imidazolium, pyridinium and ammonium cation paired with strongly basic anion (e.g., OAc-, HCOO-) were also recently used to dissolve cellulose [1]. However, the requirements of high-purity syntheses and the cost of some of the cations/anions may affect a large scale application.Therefore, our research refers to an alternative route of chemical processing of microcrystalline cellulose, i.e. its dissolution using various wt% ratio of aqueous NaOH/urea mixtures, and further processing into a hydrogel membrane in the presence of cross-linking agents, such as glutaraldehyde and citric acid. The cellulose-based hydrogel membranes will be used as a support for various aqueous electrolytes, including H2SO4, KOH, K2SO4, i.e. most commonly used for aqueous EDLCs. Also, the alternative solutions will be used, i.e. based on polyoxometalates, or more precisely Keggin-type heteropolyacids (such as H4SiW12O40) which according to our recent results seem to be promising candidates to replace conventional acidic/neutral electrolytes [2]. The thickness of the membranes will be adjusted to introduce the minimum volume of electrolyte, i.e. necessary to fill the porosity and all void spaces in the electrode material and to avoid the electrolyte excess. A structure and morphology will be characterized with SEM/EDX, AFM, AT-FTIR, XRD and TGA. The ionic conductivity will be determined using impedance spectroscopy over wide range of temperatures. The designed systems will be compared, in terms of energy, power and cycleability, with their analogues using conventional polypropylene separator in the presence of excess of liquid electrolyte. Acknowledgement Financial support was provided by the National Centre for Research and Development (NCBR, Poland) under Techmatstrateg Grant no. 347431/14/NCBR/2018.[1] D. Kasprzak, I. Stepniak, M. Galinski, Electrodes and hydrogel electrolytes based on cellulose: fabrication and characterization as EDLC components, J. Solid State Electrochem. 22 (2018) 3035–3047, https://doi.org/10.1007/s10008-018-4015-y[2] N.H. Wisinska, M. Skunik-Nuckowska, S. Dyjak, P.J. Kulesza, Factors affecting performance of electrochemical capacitors operating in Keggin-type silicotungstic acid electrolyte, Appl. Surf. Sci. 530 (2020) 147273, https://doi.org/10.1016/j.apsusc.2020.147273.

Parametric, kinetic, and thermodynamic studies of microwave-assisted esterification of Kusum oil

In this research, non-edible Kusum oil was used to convert the free fatty acid into its methyl esters using a silicotungstic acid catalyst. The microwave as a heat source was used to fasten the rate of esterification of Kusum oil. The parametric study of the effect of methanol to oil molar ratio, catalyst amount, temperature, and time was carried out to obtain the reasonable conversion of free fatty acid. The study revealed that 9:1 molar ratio, 65 °C, 3.6 wt% catalyst, and 13 min of reaction time gave 92% free fatty acid (FFA) conversion. Further, the present study also estimates the kinetic and thermodynamic parameters of Kusum oil esterification. The kinetic study was performed at four temperatures with a pre-optimized 9:1 molar ratio of methanol to oil, 3.6 wt.% Silicotungstic acid for different time intervals. The kinetic study revealed that microwave-assisted acid-catalyzed esterification reaction is pseudo-first-order having activation energy 38.82 kJ.mol−1 and pre-exponential factor 219,037 min−1, respectively. The higher value of pre-exponential factor and lower activation energy in the kinetic study indicates the non-thermal effect associated with microwave heating. The rate constant and Gibbs’ free energy change at 65 °C was 0.224 min−1 and 98.89 kJ.mol−1. The values of Enthalpy and Entropy changes were 36.06 kJ.mol−1 and −0.185 kJ.mol−1.K − 1. It shows the reaction is non-spontaneous and endergonic by nature.

Analyzing esterification kinetics of model bio-oil with ethanol catalyzed by a green catalyst

Fast pyrolysis of biomass is a potential method for the production of bio-oils as a renewable liquid fuel. Bio-oils contain a large number of organic compounds, particularly carboxylic acids, which cause corrosiveness and instability that are troublesome for storage and for the transportation of fuel. Upgrading is an important process to transform bio-oils into high-quality biofuels. Contained organic acids are treated with alcohol to convert them into esters by esterification which may be considered as a good intermediate bio-oil upgrading method. This work presents a kinetic study for 12-tungstosilicic acid (a type of heteropoly acid, HPA) catalyzed esterification of a model bio-oil with ethanol. The main compound of the agro-residue-derived bio-oil was illustrated by oleic acid. The kinetic study was investigated under the molar ratio between ethanol to oleic acid of 9.11:1 and catalyst loading of 10 wt% condition with the varied reaction temperature in the range of 35-75°C. The result showed that a pseudo-first-order was suitable to represent the kinetic model for esterification of the model bio-oil. By fitting between the experimental results and kinetic model, the activation energy (Ea) and the pre-exponential factor (A) were found to be 31.5 kJ/mol and 432 min−1, respectively. This comparatively low activation energy equated to other catalytic esterification proved that the HPA catalyst (12-tungstosilicic acid) considered here was an assured green catalyst for esterification in the bio-oil upgrading process.

A recyclable cucurbit[6]uril-supported silicotungstic acid catalyst used in the esterification reaction

The esterification reaction used to prepare butyl paraben (BP) and propyl gallate (PG) catalyzed using a cucurbit[6]uril-supported Keggin-type silicotungstic acid (Q[6]-STA) catalyst has been investigated. The Q[6]-STA catalyst has been characterized using FTIR spectroscopy, XRD, SEM, EDS, thermal analysis, and surface area studies. Q[6]-STA was easy to prepare in high yield and exhibited some advantageous properties, such as high catalytic activity and its convenient recovery. Moreover, a reusability study showed that the Q[6]-STA catalyst was stable and active.

Role of silicotungstic acid on the catalytic performance over CeO2‐HSiW catalysts for selective catalytic reduction of NOx with NH3

The CeO2 modified by silicotungstic acid (impregnation method [SiW/CeO2] and one pot method [CeO2‐Si‐W]) was investigated in the NH3‐SCR reaction. The surface nitrate species and surface acid sites were improved by the introduction of silicotungstic acid into CeO2, which stopped forming stable nitrate, and then improved the N2 selectivity. The interaction between Ce and W species existed and caused the formation of Ce2(WO4)3 at CeO2‐Si‐W, resulting in the abundance of unsaturated W=O, which contributed to the generation of Brønsted acid sites and was responsible for the superior SCR performance. Thus, CeO2‐Si‐W exhibited the best NOx conversion and nearly 100% NOx conversion was obtained at 225–450°C.

Synthesis and characterization of WS2/SiO2 microfibers

Tungsten disulfide polycrystalline microfibers were successfully synthesized by a process involving electrospinning, calcination, and sulfidation steps. We used an aqueous solution of silicotungstic acid (H4SiW12O40) and polyvinyl alcohol as precursors for the synthesis of composite fibers by the needle-less electrospinning technique. The obtained green composite fibers (av. diam. 460 nm) were converted by calcination in air to tungsten oxide WO3 fibers with traces of SiO2 and a smaller diameter (av. diam. 335 nm). The heat treatment of the WO3 fibers under flowing H2/H2S/N2 stream led to conversion to tungsten disulfide WS2 with retention of the fibrous morphology (av. diam. 196 nm). Characterization of the intermediate and final fibers was performed by the XRD, SEM, TEM, HAADF STEM EDS, elemental analyses ICP-OES, and IR spectroscopy methods.

A μ-AsO4-Bridging Hexadecanuclear Ni-Substituted Polyoxotungstate.

A novel tetrahedral μ-AsO4-bridging hexadecanuclear Ni-substituted silicotungstate (ST) Na21H10[(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]·60H2O (1) was made by the reactions of trivacant [A-α-SiW9O34]10- ({SiW9}) units with Ni2+ cations and Na3AsO4·12H2O and characterized by IR spectrometry, elemental analysis, thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). 1 contains a novel polyoxoanion [(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]31- built by four trivacant Keggin [A-α-SiW9O34]10- fragments linked through an unprecedented [(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster, where the tetrahedral AsO4 acts as an exclusively μ2-bridging unit to link multiple Ni centers; such a connection mode appears for the first time in polyoxometalate chemistry. Furthermore, the electrochemical and catalytic oxidation properties of compound 1 have been investigated.

Hydrogenolysis of glycerol to propanediols over silicotungstic acid catalysts intercalated with CuZnFe hydrotalcite-like compounds

A series of catalysts derived from silicotungstic acid (SiW) intercalated with CuZnFe hydrotalcite-like compounds (HTLCs) via ion-exchange method was prepared and characterized by N2-physisorption, XRD, TEM, SEM, H2-TPR, FT-IR, and Py-IR spectra. The intercalation of SiW species into CuZnFe HTLCs was confirmed by these characterization techniques, while the catalytic performance was evaluated for glycerol hydrogenolysis. It was found that introduction of SiW significantly enhanced the selectivity towards 1,3-propanediols (1,3-PDO), owing to the increased Brønsted acid introduction, as demonstrated by Py-IR analysis. The catalyst intercalating 30 wt.% SiW showed the highest selectivity (22.4%) to 1,3-PDO at 68.9% glycerol transformation. The catalytic performance was discussed and correlated with the physicochemical properties of these catalysts. The present contribution provides an economical approach to convert surplus glycerol from biodiesel manufacture to valuable propanediols.

Hybrid Hairy Platelets with Tunable Structures by Inclusion Crystallization of Polyferrocene-Containing Block Copolymers and Silicotungstic Acid.

Herein, we report hybrid hairy platelets formed by block copolymers containing a poly(ethylene oxide) (PEO) midblock and polyferrocene end-blocks with silicotungstic acid (STA). As inclusion crystallization of PEO midblocks and STA clusters lead to crystalline lamellae in thin films at room temperature, the polyferrocene end-blocks that are excluded from the lattice will graft on the surface of the lamellae, giving rise to hybrid hairy platelets. The dependence of crystallographic structures and morphologies of platelets on the length of end-blocks is investigated. The presence of relatively long end-blocks induces the formation of an inclusion crystal with a tetragonal cell (termed as β-form), whereas an inclusion crystal with an orthorhombic cell (termed as α-form) can be formed with block copolymers with relatively shorter end-blocks.

Underwater Adhesive HPMC/SiW-PDMAEMA/Fe3+ Hydrogel with Self-Healing, Conductive, and Reversible Adhesive Properties

A reusable, underwater adhesive, self-healing, and conductive hydrogel was developed by the construction of an interpenetrating network structure consisting of a tungstosilicic acid (SiW) cross-lin...