Heteropoly Compounds Research Articles

Application of heteropoly compounds with Keggin structure in corrosion protection and Ni-MH cell technology

Application of heteropoly compounds with Keggin structure in corrosion protection and Ni-MH cell technology

ОСОБЕННОСТИ ВЗАИМОДЕЙСТВИЯ ГЕМИНА И ZnII-КОМПЛЕКСА ТЕТРА(4 ПИРИДИЛ) ПОРФИРИНА С ГЕКСАМОЛИБДЕНОНИКЕЛАТ-ПОЛИАНИОНОМ В ВОДНЫХ СРЕДАХ

This work presents a method for producing new hybrid supramolecular organic-inorganic systems based on tetrapyrrole compounds (natural and artificially synthesized porphyrins) and hexamolibdenonicelate anion to create highly ordered supramolecular complexes based on porphyrins with the possibility of using them in medicine. In particular, the reaction of natural porphyrin (hemin) and the ZnII-complex of tetra(4-pyridyl)porphyrin with the heteropoly compound sodium hexamolibdenonicelate crystalline hydrate Na4[Ni(OH)6Mo6O18]·8H2O in an aqueous medium is considered. This heteropoly compound due to its physicochemical and biological properties can be considered as a part of photochromic materials and pharmacological agent. The optical absorption spectra of the obtained hybrid supramolecular organic-inorganic systems were investigated with the help of electronic absorption spectroscopy. Both the transformation of the bands which are the characteristics of porphyrins and the appearance of new bands indicating the formation of hybrid supramolecular organic-inorganic complexes are observed in the electron absorption spectra. The work traces the role of structural features of porphyrins in the process of their interaction with the heteropolyanions. Differences in the spectral behavior of the two metalloporphyrins when interacting them with the heteropoly compound have been shown and explained by variability in their structure. The data obtained will be useful when developing new hybrid materials as antibacterial components for medical use.

Cationic Effect in the Formation of Toxic and Antiviral Properties of Keggin Heteropoly Compounds

Cationic Effect in the Formation of Toxic and Antiviral Properties of Keggin Heteropoly Compounds

Synthesis and Properties of Rubidium Salts of Phosphotungstic Acid

The work is devoted to the study of the influence of synthesis conditions on the properties of water-insoluble rubidium salts of phosphotungstic acid (PTA). Such heteropoly compounds have a wide range of applications, including in the field of electrocatalysts and solid electrolytes for various electrochemical devices. The acid salts of PTA with high activity of acid sites on the particle surface are of particular interest. It is known that the properties of water-insoluble PTA salts strongly depend on synthesis conditions, such as the ratio of reagents, temperature, concentrations, and other parameters. The work examines the influence of the ratio and concentration of reagents on the sizes of crystallites and agglomerates, specific surface area (SSA), porosity, water content, and ionic conductivity of the synthesized PTA salts. The SSA value of the obtained samples varied in the range of 84–123 m2 g−1, and the ionic conductivity was 13–90 mS cm−1 at room temperature and 75% RH. An increase in the acid concentration and the degree of proton substitution led to an increase in SSA, accompanied by an increase in particle sizes without changing the size of crystallites. The results of the work may be useful for the development of new materials based on the obtained salts in many fields, including hydrogen energy.

Use of the Peroxide Method for Vanadium Activation to Obtain Mixed Keggin-Type Heteropoly Compounds

Use of the Peroxide Method for Vanadium Activation to Obtain Mixed Keggin-Type Heteropoly Compounds

Recent Contributions on Heteropoly Compounds as Suitable Catalysts in Selective Oxidation of Organic Substrates

Abstract: Organic transformations under suitable environment-friendly conditions have a great impact on the Green Chemistry area. In this context, heteropoly compounds (HPCs) have received considerable attention due to their ability to act as solid catalysts, with the advantage of being used and reused for different organic transformations without appreciable loss of their catalytic activity. In this review article, we report the recent results (2010-2022) obtained for the selective oxidation of organic substrates using a clean oxidant, such as oxygen or aqueous hydrogen peroxide, and HPCs as catalysts. Some of the investigated substrates correspond to the families of hydrocarbons, alcohols, phenols, aldehydes, ketones, amines, and sulfides, among others.

Selective Methacrolein Oxidation Catalyzed with Heteropoly Compounds: Effect of the Oxidation State Modulated with Hydrogen Pretreatment

Selective Methacrolein Oxidation Catalyzed with Heteropoly Compounds: Effect of the Oxidation State Modulated with Hydrogen Pretreatment

Improvement of So2 Resistance of Cu-Ssz-13 with Heteropoly Compounds in Selective Catalytic Reduction of No

Improvement of So2 Resistance of Cu-Ssz-13 with Heteropoly Compounds in Selective Catalytic Reduction of No

Epoxidation of Allyl Chloride in the Presence of Tungsten Oxo–Peroxo Heteropoly Compounds of P(V), As(V), and Si(IV) Under Phase-Transfer Catalysis Conditions

Epoxidation of Allyl Chloride in the Presence of Tungsten Oxo–Peroxo Heteropoly Compounds of P(V), As(V), and Si(IV) Under Phase-Transfer Catalysis Conditions

Studying the Stability of Supported Heteropoly Compounds Using Data from Diffuse Reflectance Infrared Spectroscopy

Studying the Stability of Supported Heteropoly Compounds Using Data from Diffuse Reflectance Infrared Spectroscopy

Selective Oxidation of Isobutane to Methacrylic Acid and Methacrolein: A Critical Review

Selective oxidation of isobutane to methacrolein (MAC) and methacrylic acid (MAA) has received great interest both in the chemical industry and in academic research. The advantages of this reaction originate not only from the low cost of the starting material and reduced process complexity, but also from limiting the use of toxic reactants and the production of wastes. Successive studies and reports have shown that heteropolycompounds (HPCs) with Keggin structure (under the form of partially neutralized acids with increased stability) can selectively convert isobutane to MAA and MAC due to their strong and tunable acidity and redox properties. This review hence aims to discuss the Keggin-type HPCs that have been used in recent years to catalyze the oxidation of isobutane to MAA and MAC, and to review alternative metal oxides with proper redox properties for the same reaction. In addition, the influence of the main reaction conditions will be discussed.

Studying the States of Platinum in Deposited Heteropoly Compounds via Diffuse Reflection IR Spectroscopy

Studying the States of Platinum in Deposited Heteropoly Compounds via Diffuse Reflection IR Spectroscopy

Catalytic Conversion for Hydrogen Sulfide

In this study, a series of transition metal mono-substituted heteropoly compounds H7PMo11MO39 (M = Co2+, Mn2+, Ni2+ and Zn2+) (HPMo11M) and single-absent heteropoly compounds H3PMo11O39 (HPMo11) were prepared for highly effective removal of hydrogen sulfide (H2S) from gas stream. The heteropoly compounds were characterized Fourier transform infrared spectroscopy (FT-IR), elemental analysis and scanning electron microscopy (SEM). The results confirmed that the transition metal ions successfully replaced the Mo atom. H7PMo11CoO39 showed that the outstanding desulfurization capacity and the H2S removal efficiency can reach more than 90% for 3 h. Besides, after regeneration, the desulfurization capacity of H7PMo11CoO39 towards H2S only a drop of 5.11% of the initial desulfurization capacity. Optimization experiments demonstrated that H7PMo11CoO39 had the ideal desulfurization performance under the condition of low H2S concentration or high dosage of H7PMo11CoO39. An appropriate temperature of 25°C is necessary for high removal efficiency. The optimum pH value for desulfurization is 5. The kinetic data can be well described by pseudo-first-order kinetic model. The desulfurization products were proved to be S and SO42– based on X-ray photoelectron spectroscopy (XPS) characterization results.

Experimental Investigation of Simultaneous Removal of SO2 and NOx Using a Heteropoly Compound

ABSTRACT Aiming at developing a simple, feasible method for SO2 and NOx removal, in this work, various doping amounts of heteropolyacid and heteropolyacid salts were prepared and used in wet absorption for simultaneous removal of SO2 and NO. The desulfurization and denitrification performance was evaluated by investigating dynamic SO2 and NO absorption in a simulated reactor containing a heteropoly compound (HPC) solution along with various factors influencing the reaction. The results demonstrate that this system had a high removal efficiency of SO2 and modest NO removal. The amount of Wolfram (W) doping and the pH of the solution affecting the removal performance was studied, and a stable SO2 removal efficiency higher than 95% was obtained for HPW1Mo at a pH value of 5.5. In addition, the desulfurization performance of NaPWMo with a 50% removal efficiency was higher than that of the HPWMo solution (20%) after a 60 min reaction time. A high concentration of the NaPWMo solution and the presence of O2 were beneficial to desulfurization at room temperature. In addition, the removal efficiency of SO2 or NO by NaPWMo was only affected by its own gas concentration rather than their mutual influences on each other. This work should be beneficial to the optimization leading to the development of simultaneous desulfurization and denitrification systems in practical applications.

A green and reusable catalytic system based on silicopolyoxotungstovanadates incorporated in a polymeric material for the selective oxidation of sulfides to sulfones

Two vanadium-containing Keggin silicopolyoxotungsto compounds K5SiVW11O40 and K6SiV2W10O40 were synthesized and characterized. They were incorporated in a superporous hydrogel constitute by prop-2-enamide and propenoic acid as initial monomers and bis-acrylamide as cross-linking moiety. Materials were characterized by several techniques. According to FTIR and 51V MAS-NMR, the (SiVxW12-xO40)(4+x)- anions are the main species present in the hybrid materials. Additionally, they do not decompose during the preparation of the composite. XRD and SEM-EDX results suggest that (SiVxW12-xO40)(4+x)- anions were well dispersed in the support or present as amorphous phases. These materials were evaluated as catalysts in the oxidation of sulfides to sulfones, using an eco-friendly oxidant and mild reaction conditions. The hybrid materials with higher content of the heteropoly compound displayed a remarkable catalytic behaviour in the oxidation of diphenyl sulfide. Materials also exhibited a stable catalytic performance through consecutive reuses. Optimum reaction parameters established were subsequently translated to the oxidation of a sulfide of interest (dapsone) due to its pharmacological activities.

Study on the Synthesize, Characterization, and Conductive Performance of Nickelzircomolybdnum Heteropoly Acid Salt with Keggin Structure

A novel heteropoly acid salt, Na6[Ni(Mo11ZrO39)]·20H2O, has been synthesized by the means of acidification and adding the reactants into the solution step by step. The heteropoly compound was characterized by elemental analysis, TGA/DSC, infrared spectrum, ultraviolet spectrum, X-ray diffraction, and SEM. Its protonic conduction was measured by the means of the electrochemical impedance spectrum. The results showed that it belongs to the Keggin type, and its conductivity value was 1.23 × 10–2 S/cm at 23°C when the relative humidity was 60%, and the conductivity enhanced with the elevated temperature. Its proton conduction mechanism was in accordance with vehicle mechanism, and the activation energy was 27.82 kJ/mol.

Эффективность использования гетерополисоединений типа (NH4)2[Co(H2O)4]2[Mo8O27]∙6H2O в качестве катализаторов для получения этилена

Carrying out heterogeneous acid catalysis with the use of heteropoly compounds has received considerable attention due to the great economic and environmental benefits. In spite of this, its industrial application is limited as there are difficulties in catalyst regeneration (settling) caused by its relatively low thermal stability. The aim of present work was to search and select catalysts related to the class of heteropoly compounds for propane cracking, to test the selectivity of the prosses as well as to discuss possible approaches for solving the problem of catalyst deactivation, that can contribute to achieve stable characteristics of solid heteropoly catalysts. Among these approaches are: the development of new catalysts with high thermal stability, the modification of catalysts to promote coke combustion, the inhibition of coke formation on heteropoly compound catalysts during the process, carrying out the reactions in supercritical media and also the cascade reactions using a multifunctional heteropoly catalyst. The obtained catalyst was also studied by physicochemical methods to get deep knowledge about which features of these compounds influence on the catalytic activity. A highly active and selective catalyst for ammonium octomolybdenocobaltate(II) ammonium (NH4)2[Co(H2O)4]2[Mo8O27]∙6H2O was synthesized for cracking associated petroleum gases. The qualitative, quantitative, and structural composition as well as the specific surface area of the obtained catalyst was established by the methods of X-ray diffraction, X-ray phase and fluorescence analysis. It was revealed that ammonium octomolybdenocobaltate(II) crystallizes in a triclinic syngony with cell parameters: а = 8.6292(9) Å b = 9.4795(10) Å c = 12.2071(13) Å α = 104.326(2)° β = 109.910(2)° γ = 100.820(2)°.

Lanthanum Exchanged Keggin Structured Heteropoly Compounds for Biodiesel Production

La-exchanged 12-tungstophosphoric acid (LaxTPA) and 12-molybdophosphoric acid (LaxMPA) salts (x = 0.25, 0.50, 0.75 and 1.00) were prepared via an ion exchange method. The physico-chemical characteristics of the materials were analyzed by using elemental analysis, X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), N2-physical adsorption, X-ray photoelectron spectroscopy (XPS), and acidity-basicity measurements. The results indicated that La was introduced into the secondary structure of heteropolyacid (HPA) and have not influenced the primary structure, which effectively improved the surface area and pore size. Acidity-basicity studies indicated that incorporation of La resulted in a decrease in the number of acid sites and an increase in the number of basic sites. The catalytic activity of samples was studied in transesterification of glyceryl tributyrate with methanol and LaxTPA samples which exhibited high activity compared to LaxMPA samples due to having more active basic sites and a larger surface area. Calcined LaxTPA samples showed excellent stability, outstanding recyclability, and high activity for one pot transesterification and esterification processes. This outcome was attributed to the presence of balanced acidic and basic sites.

Синтез и исследование гексамолибдохромата пиридин-3-карбоновой кислоты состава (С6H5NO2)2[H3O]4[CrMo6O18(OH)6].4Н2О

The Chemistry of heteropoly compounds (HPC) is one of the modern direction of Coordination chemistry. In current times, the high importance in the development of HPC chemistry is the synthesis of new hybrid, organic-inorganic heteropolystructures with preassigned physicochemical properties as well as the determination of common factors of change in these properties depending on the composition and structure. The X-ray diffraction study of the obtained compounds has showed that the packing of molecules into crystals is carried out with the formation of through channels along the c axis, which can play a significant role, for example, during catalytic processes. The ability of natural nicotinic acid to form complexes with heteropolyanion [CrMo6(ОН)6O18]4- is known. The high biological activity of nicotinic acid, as well as the activity of a number of polymetallates to the suppression of certain types of viruses which was described in the literature, make it possible to consider hybrid materials based on these substances promising from the point of view of the consciousness of new pharmaceuticals. Based on this data, we have synthesized pyridine-3-carboxylic acid hexamolybdochromate of composition (С6H5NO2)2[H3O]4[CrMo6O18(OH)6].4Н2О. The compound was studied by chemical, X-ray diffraction, thermogravimetric, NMR and IR spectroscopic methods of analysis. It is established that the synthesized compound crystallizes in triclinic syngony with unit cell parameters: а = 9.1640(8)Å, b = 10.6441(11)Å, с = 10.8241(12)Å; α = 95.968(10)°, β = 109.864(12)°, γ = 105.059(11)°; calc .= 2.502 g/cm3, V = 937.2(2) Å3; Z = 1.

Multiphase Hydrodechlorination of 1,3,5-Trichlorobenzene on Palladium Catalysts Supported on Alumina: Effect of the Support Properties and Modification by Heteropoly Acid Based on Silicon and Tungsten

Catalytic systems 2 wt % Pd/Al2O3 were prepared using noncalcined boehmite (NC) and two types of alumina support: one was prepared by the calcination of boehmite at 600°C (C) and the other produced by Engelhard (E). To prepare 2 wt % Pd/HPC–Al2O3 samples, these supports were modified by impregnation by a heteropoly compound (HPC) (20 wt % Н8[Si(W2O7)6] ⋅ 6Н2О). The effect of the Al2O3 structure and its modification by the heteropoly compound on the physicochemical properties, activity, selectivity and stability of catalysts in the reaction of multiphase hydrodechlorination of 1,3,5-trichlorobenzene (TCB) was studied. All catalysts showed activity in the considered reaction with the predominant formation of benzene but were deactivated in the reaction medium. Modification by the heteropoly compound resulted in increased stability and was especially effective for catalyst supported on Al2O3(E). The method of scanning electron microscopy (SEM) was used to determine the morphological differences of supports. According to the data of transmission electron microscopy, all catalysts contained palladium in the form of particles less than 20 nm in size. The particle size and width of the size distribution increases in the series Pd/Al2O3(NC) < Pd/Al2O3(C) < Pd/Al2O3(E). Modification by the heteropoly compound was favorable for the decrease in the size of palladium particles. The method of temperature-programmed reduction with hydrogen (TPR-H2) showed that all catalysts included in their composition palladium hydride along with more strongly surface-bound metal forms that are reduced at elevated temperatures, and their content decreases after modification by the heteropoly compound and increases after catalytic tests. According to diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the deposition of a heteropoly compound leads to a change in the type of Lewis acid sites on the alumina surface and in the electronic state of palladium. According to the results of infrared spectroscopic studies of adsorbed CO, the relatively large particles of Pd0 are the main form on the surface of nonmodified catalysts. The catalysts modified by the heteropoly compound contain single Pd+ and Pd2+ cations, and the fraction of Pd0 is substantially smaller. The specific features of the Lewis acidity of the catalyst surface determine the possibility of 1,3,5-trichlorobenzene adsorption and activation on the support and the spillover of hydrogen from Pd0. An increase in the catalyst stability as a result of support modification by the heteropoly compound can be explained by the appearance of new active sites in the interaction of palladium with the heteropoly compound or its thermal decomposition products.