Molybdosilicic Acid Research Articles

Synthesis and characterization of alumina supported molybdosilicic acid (SiMo12/Al2O3): Efficient solid acid catalyst for the synthesis of pyranopyrazole derivatives

A series of highly reusable heterogeneous catalysts (10-40 wt.% SiMo12/Al2O3), consisting of molybdosilicic acid (SiMo12) impregnated on alumina (Al2O3) support was synthesized by the wetness impregnation method. The physicochemical properties of synthesized catalyst were studied using FT-IR, XRD, SEM, EDX, TEM, BET and TG-DTA analysis techniques. The study proves that the synthesized SiMo12 catalyst efficiently incorporated on the surface of Al2O3. The catalytic activity of prepared catalyst was investigated for the synthesis of pyranopyrazole(6-amino-4-phenyl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5carbonitrile) via cyclocondensation reaction of aldehydes, malononitrile, hydrazine hydrate and ethyl-acetoacetate under solvent-free conditions. Among different catalysts, 30% SiMo12 supported on to Al2O3 showed the highest catalytic activity. High yield, shorter reaction time, operational simplicity, solvent-free conditions and reusability of the catalyst are the distinct features of this protocol.

MoSiA를 이용한 수전해용 공유가교 SPEEK/Cs-MoSiA/Ceria복합막의 제조 및 성능 연구

>> To improve the electrochemical and mechanical characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The SPEEK organic-inorganic blended composite membranes were prepared by sol-gel casting method. It was loaded with the highly dispersed ceria and cesium-substituted molybdosilicic acid (Cs-MoSiA) and 1,4-diiodobutane which was cross-linking agent contents of 10 μL. Cs-MoSiA was added to increase proton conductivity. Ceria (CeO2) was used as a free radical scavenger which degrade the membrane in polymer electrolyte membrane water elctrolysis (PEMWE). In conclusion, CL-SPEEK/Cs-MoSiA/Ceria 1% composite membrane showed high proton conductivity 0.2104 S/cm at 25°C which was better than Nafion 117 membrane.

Influence of pH on immobilization of molybdosilicic acid on hollow silica spheres and promotion of hydrolytic dehydrogenation of ammonia borane

In this work, we investigated the influence of the pH condition during the impregnation process on the immobilization of molybdosilicic acid on hollow silica spheres and their activity for hydrolytic dehydrogenation of ammonia borane. To adjust the pH, amino acids such as L-aspartic acid and L(+)-arginine were added to the impregnating solution. Transmission and scanning electron microscopy showed that samples prepared at lower pH consist of homogeneous hollow silica spheres while those prepared at higher pH include collapsed hollow spheres. The activity for hydrogen evolusion from aqueous NH3BH3 solution depends on the catalyst; the molar ratios of the hydrolytically generated hydrogen to the initial NH3BH3 were 2.0, 1.3, 1.3, and 1.0 at pH = 4.0, 6.0, 8.0, and 9.7, respectively. After the reaction, the sample prepared at lower pH had a higher valence value of Mo species according to results from X-ray photoelectron spectroscopy, and the corresponding amount of Mo species in the reaction solution was also lower. The results indicated that the molybdosilicic acid supported on homogeneous hollow silica spheres had a higher valence value of Mo species and the effectively immobilized acid had a higher activity for hydrogen evolusion from aqueous NH3BH3 solution.

Reduced Molybenum‐Oxide‐Based Core–Shell Hybrids: “Blue” Electrons Are Delocalized on the Shell

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo72Fe30} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, Mössbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo72Fe30}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including 31P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo72Fe30}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by FeII being of interdisciplinary including catalytic interest (the MoVI/MoV and FeIII/FeII couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.

Methoxylation of α-pinene over heteropolyacids immobilized in silica

The methoxylation of α-pinene was studied using heteropolyacids immobilized on silica as catalysts, at 60 °C, being the α-terpinyl methyl ether the main product. Tungstophosphoric acid (PW), molybdophosphoric acid (PMo), tungstosilicic acid (SiW) and molybdosilicic acid (SiMo) were immobilized on silica by sol–gel method. It was observed that the catalytic activity of the silica-supported heteropolyacids decreases in the series: PW2_S > SiW_S > PMo_S > SiMo_S. A series of PW immobilized on silica with different PW loading were prepared. It was observed that the catalytic activity increases with the amount of PW immobilized on silica. However, at high amount of PW on silica, a decrease of the catalytic activity was observed. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained with all catalysts. Catalytic stability of the PW2_S was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. It was observed that the kinetic model fits the experimental concentration data quite well.

Versatile Flow Injection System for Spectrophotometric Determination of Silicon in Agronomic Samples

A versatile flow injection system for spectrophotometric determination of silicon (Si) in agronomic samples is proposed. For plant and slag analysis (1.0–10.0 mg L−1 Si), the method involves monitoring the yellowish molybdosilicic acid at 410 nm. Soil, fertilizer, water, and sugarcane juice analysis (0.5–5.0 mg L−1 Si) were accomplished by adding a reducing agent, and the molybdenum blue compound that formed was monitored at 735 nm. Flexibility of the method allows determination in a variety of matrices involving a wide range of concentrations. Beer's law is followed up to 20.0 mg L−1 Si (r<0.9997; n=6) for analysis at 410 nm and up to 10.0 mg L−1 Si (r<0.9998; n=6) at 735 nm. For the yellow‐color and blue‐color methods, the detection limits were estimated as 0.5 and 0.1 mg L−1 Si. Measurement frequency for both methods is approximately 75 h−1 using 48 mg of ammonium heptamolybdate, 80 mg of oxalic acid, and 24 mg of ascorbic acid per determination. Results are precise (r.s.d.>0.1%, n=10) and in agreement with inductively coupled plasma–optical emission spectroscopy (ICP‐OES). Statistical differences between data sets were not confirmed after applying the Student's ttest at the 95% confidence level (texp=0.195>ttab=2.57) related to n=6.

Synthesis of plant sterol esters catalyzed by heteropolyacid in a solvent‐free system

The synthesis of phytosteryl esters is of importance due to their recent recognition and application as cholesterol-lowering agents in the food and nutraceutical industries. In this study, a synthetic route potentially useful for the large-scale production of food-grade phytosteryl esters with high yield and purity in a solvent-free system was investigated. To examine the feasibility of replacing sodium methylate by heteropolyacid, four heteropolyacids, tungstosilicic acid, tungstophosphoric acid, molybdosilicic acid and molybdophosphoric acid, were evaluated to determine the best catalyst and the optimum conditions for the esterification reaction between various fatty acids and phytosterols. The results suggested that tungstosilicic acid was more selective towards butyric acid and caprylic acid than towards lauric acid, palmitic acid, and oleic acid. However, there was no significant discrimination in terms of the tungstosilicic acid catalyst's selectivity to stearic acid, oleic acid, linoleic acid and alpha-linolenic acid, all with C18 chains, in the esterification reaction. The yield of phytosteryl ester was higher than 90% when the esterification reaction was carried out at 150 °C, with phytosterols and fatty acids in a molar ratio of 1 : 1.5, and catalyzed by 0.2% tungstosilicic acid in silica gel. The catalysts recovery experiments suggested that the immobilized tungstosilicic acid did not significantly lose its activity in six operation runs. As a result, the immobilized tungstosilicic acid would be a promising catalyst for replacing sodium methylate, to synthesize phytosteryl esters with fatty acids and phytosterols as the starting materials in a commercial production.

Preparation and characterization of H4SiMo12O40/poly(vinyl alcohol) fiber mats produced by an electrospinning method

AbstractFor the first time, high‐percentage molybdosilicic acid fiber mats (20–80% H4SiMo12O40) were prepared using the electrospinning technique. The fiber mats were characterized by IR, XRD, and DSC. The results indicated that poly(vinyl alcohol) was changed from a semicrystalline to an amorphous state with an increasing molybdosilicic acid content. The results from scanning electron microscopy (SEM) showed that the average diameter of the fibers was about 285–600 nm. The effects of the viscosity and conductivity of the H4SiMo12O40/poly(vinyl alcohol) solution on the morphologies of the fiber mats were investigated. The swelling properties of the fiber mats in water were also studied.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1573–1578, 2003

One-Pot Reactions with Sol-Gel Entrapped Catalysts, Acids and Bases

Silica sol-gel entrapped acids, bases and organometallic catalysts are used successfully in one-pot reactions without interfering with each other. Both physically and covalently entrapped acids and bases were employed in these processes, including polystyrene sulfonic acid, 1-propane sulfonic acid, molybdosilicic acid (SiO2-MoO3), poly[(vinylbenzyltrimethyl)ammonium] hydroxide and 1,5,7-triazabicyclo[4.4.0]decene. The entrapped metal-based catalysts are Rh2Co2(CO)12 and RuCl2(PPh3)3. The one-pot reactions carried out with these heterogenized reagents and catalysts include formation of alkenes under acidic and basic conditions, C—C bond formation by condensation reactions with an α-carbon to a carbonyl, hydroformylation and hydrogenation.

Equilibrium Adsorption of Molybdosilicic Acid Solutions on Carbon and Silica: Basic Studies for the Preparation of Ecofriendly Acidic Catalysts

Molybdosilicic acid solutions acidified with HCl were impregnated on carbon and silica by the equilibrium adsorption technique. From the equilibrium adsorption isotherms performed at 20°C, it was established that the heteropolyacid amount adsorbed on carbon is higher than that on silica. Differences in shape and initial slope of the isotherm were observed. The interaction of the molybdosilicate anion was higher with carbon surface groups than with silanol groups. The physicochemical characterization of the solids has shown that the molybdosilicic acid presents an undegraded Keggin structure in the supported samples up to 250°C. The surface acidity, mainly related to heteropolyacid adsorbed amount, was higher for samples on carbon. However, the silica-supported acid showed a bulk acidity higher than that on carbon, due to its lower interaction degree.

A Portable Fiber-Optic Chemical Device for the Quantitative Determination of Carbon Monoxide from Automobile Exhaust Emissions

ABSTRACT A colorimetxic method for the quantitative determination of CO by diffuse reflectance is described. This method is based on the reduction by CO of Mo (VI) from the indicator reagent molybdosilicic acid (H8Si[Mo2O7]6). The reduction yielded a change of color from clear yellow to dark green on white disk filter chart paper wetted with reagent indicator solution. The gaseous mixture containing CO was forced to pass through this chart paper, initiating the reaction. The intensity of the color produced, measured by diffuse reflectance, was proportional to the CO concentration present in exhaust gases in the range from 0.02 to 12% volume/volume (v/v). A 650-nm light-emitting diode was used as a light source. A two-fiber-optic system carried the light from the source to the detection system, which was composed of a photodiode, an amplification circuit, and a digital display. The method was applied with success in field measurements for automobiles in the Otto cycle. In a previous paper, this method was used for the quantitative determination of exhaust emissions from diesel-fueled vehicles.1

フッ化物分離/モリブドケイ酸青吸光光度法による高純度アルミニウム中の微量けい素の定量

フッ化物分離/モリブドケイ酸青吸光光度法による高純度アルミニウム中の微量けい素の定量

Kinetic spectrophotometric determination of trace amounts of nitrite by its reaction with molybdosilicic acid blue

A new kinetic spectrophotometric method was developed to determine nitrite using molybdosilicic acid blue (MSAB) as a color reagent. This method is simple, rapid, sensitive and selective for the determination of trace amounts of nitrite ion. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at λ max=810 nm. The fixed time method was used. The limit of detection was 0.004 ppm. The relative standard deviations for the determination of 0.06 and 0.30 ppm of nitrite were 3.0% ( n=6) and 1.3% ( n=10), respectively. Two linear calibration graphs were observed (0.02–0.1 and 0.1–1.0 ppm). The method was applied to the determination of nitrite in well and waste waters.

Sorption-spectrometric determination of Copper, Mercury, and Amines using chemically modified Silica

Color reactions of copper(II) with 4-(2-pyridylazo)-resorcinol and Picramine E on silica chemically modified with iminodiacetic acid groups and the exchange reaction of mercury(II) with copper diethyldithiocarbamate in the phase of silica chemically modified with hexadecyl groups were studied. Test methods were developed for the determination of copper and mercury. It was demonstrated that long-chain amines can be determined as ion pairs with the reduced form of molybdosilicic acid at the surface of silica chemically modified with hexadecyl groups.

Spectrophotometric determination of phosphate and silicate by sequential injection using molybdenum blue chemistry

This paper presents a spectrophotometric sequential injection (SI) determination of phosphate and silicate in environmental samples and cell cultivation medium using the molybdenum blue reaction. The interference of silicate in the determination of phosphate was eliminated by using a reagent composed of 5 mmol l −1 ammonium molybdate in 0.2 mol l −1 nitric acid, containing 0.25% (w/v) oxalic acid to avoid the formation of molybdosilicic acid. The interference of phosphate in the determination of silicate was avoided adding a 10% (w/v) oxalic acid solution to the reaction zone where the molybdophosphoric and molybdosilicic acids were previously formed, in order to destroy the molybdophosphoric acid. To perform this task in the single line SI system, obtaining a total sample and reagent zones penetration, it was used as a combination of sandwiching the sample zone between reagent zones and flow reversal through an auxiliary reaction coil. The method has a phosphate sampling frequency of 75 h −1, with a linear dynamic range between 0.2 and 7 mg l −1 and a detection limit of 0.1 mg l −1 PO 4 3=P. For silicate, the sampling frequency is 40 h −1 with a linear dynamic range between 5 and 50 mg l −1 and a limit of detection of 1 mg l −1 SiO 3 2=Si.

A Dihydrate Complex of Molybdosilicic Acid and Hexamethylphosphoramide, [{(CH3)2N}3PO]5[H4SiMo12O40].2H2O

The molybdosilicic acid residue, H4SiMo12O40, has the Keggin structure with M—O distances varying between 1.796 (4) and 2.112 (3) Å. In the hexamethylphosphoramide groups, all N atoms except one show a planar coordination.

A Sensitive Method for the Determination of Silicon by Molecular Absorption Spectroscopy

A sensitive molecular absorption spectrophotometric (MAS) method has been developed for the estimation of silicon in iron and steel samples. The method is based on the typical property of silicon to form molybdosilicic acid in the acid medium in which 1 silicon atom binds 12 molybdenum atoms. The molybdosilicic acid is extracted by n-butanol and the attached molybdenum is stripped and back extracted into aqueous phase using 1:1 NH 4OH. The stripped molybdenum is determined using a sensitive MAS method involving molybdenum–pyrocatecholviolet (PCV)–Cetyltrimethyl-ammoniumbromide (CTAB) ternary ion association complex ( 1). Phosphorus and arsenic interfere significantly but may be masked with tartaric acid.

Determination of trace silicon in high purity titanium and chromium by molybdosilicic acid blue spectrophotometry after fluoride separation.

高純度金属材料中の微量ケイ素の定量法として知られているフッ化物分離/モリブドケイ酸青吸光光度法を高純度チタン及び高純度クロムに応用することとし,そのために必要な諸条件を検討した.本法では試料量を1gまで増やすことが可能となり,その場合のケイ素の検出限界は0.07ppm,回収率はチタンで98%,クロムで97%であった.高純度チタン及び高純度クロムに本法を適用したところ良好な結果が得られ,ケイ素1ppm以下の試料について十分定量可能であることが分かった.

Detection of trace silicon in high purity iron by molybdosilicic acid blue spectrophotometry following fluoride separation.

近年,高純度鉄の物性研究が盛んに行われるようになり,高純度鉄の純度評価技術の確立が望まれている.高純度鉄中の微量ケイ素定量法として従来から用いられているフッ化物分離法では,マトリックスの鉄量が増えると硫酸鉄の沈殿が生じ,ケイ素の揮発分離が阻害される.そのため,用いる試料量に上限があり,ppmオーダーまでのケイ素の定量しかできない.そこでリン酸を用いて鉄をマスキングすることとし,微量ケイ素の定量に必要な諸条件を検討した.本法では試料量を1gまで増やすことが可能となり,その場合のケイ素の検出限界(3σ)は0.06ppm,回収率は約96%であった.更に,数種類の高純度鉄について本法を適用したところ良好な結果が得られ,ケイ素1ppm以下の試料についても十分定量可能であることが分かった.

Extraction voltammetric determination of silicon

A determination of silicon is described which utilizes the selective extraction of molybdosilicic acid with methyl-iso-butyl-ketone. The extract is mixed with iso-propanol. No additional electrolyte is necessary because sufficient sulphuric acid is coextracted and provides good conductivity. The 3s-limit of detection was found to be 4×10−8 mol l−1 Si. The method was applied to determine silicon in cereals.