RU2413573C1 - Nanocomposite material and method of producing said material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to inorganic chemistry, particularly to synthesis of porous nanostructures. Disclosed is a composite material containing an active phase in form of a heteropolyacid and/or its salt, which is incorporated into a matrix of a porous inorganic carrier in which the active phase has the form of nanoparticles, the heteropolyacid anion of which is bonded to structure-forming elements of the matrix through an ion bond and is incorporated into the matrix during its synthesis in situ. The invention also discloses a method of producing the material, according to which incorporation of the heteropolyacid into pores of the carrier takes place during synthesis of the matrix of the porous carrier in situ through reaction of an alkoxide of the structure-forming element of the synthesised matrix with the heteropolyacid and/or its salt in the presence of a salt of the same or of another structure-forming element of the matrix, homogenisation of the system to obtain a sol, gelling the sol, maturing the sol and thermal treatment of the sol.

EFFECT: invention enables to obtain stabilised nanocomposite material with high thermal stability and high acidity, the active phase of which is tightly bound to the carrier.

13 cl, 3 tbl, 3 dwg, 21 ex

Description

The invention relates to the field of inorganic chemistry, in particular to the synthesis of porous sorption-active nanostructures containing heteropoly acids, which can be used in various fields of chemical technology.

Heteropoly acids and their salts are complex compounds, the main structural element is the octahedral groups of MeO ₆ , with metal atoms (Me) at the center of the octahedrons, and oxygen atoms at the vertices of the octahedra. Heteropoly acids and their salts have ion-exchange and sorption properties with respect to multivalent ions of heavy and non-ferrous metals, including radioactive, therefore they are used as sorbents and ion exchangers. In addition, these compounds exhibit catalytic activity in a number of chemical reactions.

Known methods for producing sorbents based on heteropolyacids both in crystalline form and in the form of coarse-grained particles or granules, as well as in the form of an active phase deposited on an inert carrier (V.V. Pushkarev, A.F. Nikiforov "Sorption of radionuclides by salts of heteropolyacids" Moscow, 1982, pp. 60-61).

The most convenient to use materials containing heteropoly acids deposited on a carrier.

Known, for example, is a material containing a heteropoly acid compound deposited on silica gel, which is obtained by impregnating and / or precipitating onto silica gel granules pretreated with water vapor of at least one heteropoly acid selected from the group: tungsten phosphoric, tungsten-silicon, molybdenum-silicon (molybdenum phosphor) 2006/032843, 03/30/2006).

A known method for producing a composite material containing two active components: a transition metal of group VIII and heteropoly compounds or their derivatives. The method of obtaining the material involves applying two active components to the surface of inert carriers, such as silica gel, aluminosilicates, carbon. Conventional application methods are used, in particular, impregnation, adsorption, and precipitation procedures can be used. The application procedure can be carried out once, while the carrier is treated with a solution containing both components, or the application is carried out by successive treatments, first with a solution of a group VIII metal compound, then with a heteropoly compound solution or in the reverse order. After drying, the material is subjected to heat treatment at a temperature of 100-600 ° C either in air or in a stream of nitrogen (RU 2205688, 03/10/2003).

A known method for producing a composite material, including dissolving a heteropoly acid in distilled water, mixing the resulting mixture with the required amount of silica gel to obtain a suspension, mixing the suspension to obtain uniform impregnation, drying the suspension in air at a temperature of 200-250 ° C from 0.5 to 1.5 hours, further heating the suspension at a temperature of from 300 to 400 ° C from 0.5 to 1.5 hours and cooling the resulting product to room temperature. According to another variant of the method, the heteropoly acid is mixed with a binder selected from the series: silica, alumina, silica-alumina, clay, silica gel (RU 2328343, 02/10/2008).

The closest in technical essence and the achieved result is a composite material containing the active phase in the form of a heteropoly acid and / or its salt, impregnated in a matrix of a mesoporous inorganic carrier and occupying from 50 to 95% of the pore volume. A method for producing this material involves impregnating a heteropoly acid compound into the pores of a carrier in two stages, first, the carrier is treated with a salt precursor containing a metal cation, after which the impregnated carrier is heated and then treated with a second precursor containing a heteropoly acid anion (US 6815392, November 9, 2004).

Common disadvantages of the known technical solutions are as follows:

- leaching of heteropoly acids due to the lack of a chemical bond with the carrier;

- low dispersion of the applied heteropoly acids;

- low thermal stability;

- low acidity of heteropolyacid systems.

The present invention is to obtain a composite material with high dispersion, thermal stability and high acidity, in which the heteropoly acid compound is associated with the matrix of the carrier in such a way that it is not washed out of the pores by solvents.

The problem is solved by the described composite material containing the active phase in the form of a heteropoly acid and / or its salt, introduced into the matrix of a porous inorganic carrier, while the active phase is in the form of nanoparticles, the heteropoly acid anion of which is connected with the structure-forming elements of the matrix by an ionic bond and introduced into the matrix at the stage its in situ synthesis. The claimed material contains an active phase in the form of nanoparticles that are not washed out of the carrier by solvents.

As a porous carrier, the material may contain aluminosilicates or their analogues with substituted cations of silicon and / or aluminum in oxygen tetrahedra.

As a porous carrier, the material may also contain oxides selected from the group: alumina, titanium dioxide, zirconia, silicon dioxide.

Preferably, as compounds with a heteropoly acid anion, the material contains acids selected from the range: 12-phosphor tungsten, 12-tungsten-silicon, 12-phosphoformolybdenum, 12-molybdenum, or salts of the acids mentioned.

The problem is also solved by the described method for producing a composite material containing the active phase in the form of a heteropoly acid and / or its salt in a matrix of a porous inorganic carrier, comprising introducing into the carrier matrix a compound containing a heteropoly acid anion, according to which the introduction is carried out at the stage of matrix synthesis in situ by interaction alkoxide of the structural element of the synthesized matrix with a heteropoly acid and / or its salt in the presence of a salt of the same or another structure binder matrix element system homogenization to obtain a sol, gelling the sol gel maturation and its heat treatment.

Preferably, tetraethoxysilane, tetrabutoxytitanium, isopropoxide aluminum, or iron, or gallium, preferably in the form of an alcoholic solution, is supplied as an alkoxide of the structure-forming element of the synthesized matrix.

Preferably, salts of metals selected from the series aluminum, iron, gallium, titanium, zirconium in the form of their aqueous solutions are fed as a salt of the structure-forming element of the matrix.

Preferably, as compounds with a heteropoly acid anion, acids selected from the range of: 12-phosphor tungsten, 12-tungsten-silicon, 12-phosphoformolybdenum, 12-molybdenum, or salts of the above acids are fed into the reaction.

Advantageously, the interaction is carried out when acid or alkali is added to the system in an amount providing synthesis of the carrier of a predetermined composition.

Preferably, the heat treatment is carried out by drying the gel at 50-120 ° C and subsequent calcining in air at 300-400 ° C.

Below are examples of the implementation of the claimed invention and comparative characteristics of the materials obtained by the claimed and known methods (example 2 - comparative).

Example 1

A nanocomposite material based on heteropoly acid and porous aluminosilicate is prepared as follows. A solution containing 30 ml of water, 28 ml of ethanol, 22 g of TEOS (tetraethoxysilane), 0.68 g of 12-phosphor tungsten acid and 2 g of aluminum nitrate are homogenized and a solution of 0.6 g of 40% HF and 2 ml of 1 M HNO _{3 is} added to it. in 25 ml of water. The system is thoroughly mixed and left to gel. The product is dried at a temperature of 110 ° C and calcined in air at 350 ° C for 3 hours. The result is 6.5 g of a nanocomposite material containing 10.5 wt.% Heteropoly acid encapsulated in an aluminosilicate matrix with a ratio of Si / Al = 10.

Example 2

The material is obtained in two stages. In the first stage, an aluminosilicate without heteropoly acid is produced analogously to Example 1 in an amount of 6 g. In the second stage, 0.65 g of 12-phosphor tungsten acid is dissolved in 9 g of water. Aluminosilicate is impregnated with this solution. Then dried at a temperature of 110 ° C and calcined in air at 350 ° C for 3 hours. The result is a sample containing 10.5 wt.% Heteropoly acid deposited on aluminosilicate with a ratio of Si / Al = 10.

Example 1 illustrates the preparation of a nanocomposite material by encapsulating a heteropoly acid in an aluminosilicate porous carrier at the stage of its in situ synthesis. Example 2 illustrates the preparation of known materials with heteropoly acids supported on previously prepared porous carriers. Comparison of the nanocomposite material obtained in example 1 with a known material based on heteropolyacids and porous aluminosilicate (example 2) showed that it has a number of distinctive properties.

1) In the nanocomposite material obtained by the claimed method (pr. 1), the heteropoly acid interacts (chemically bonded) with the carrier, which is confirmed by NMR and IR spectroscopy. Figure 1 shows the NMR spectra with rotation at a magic angle (VMU) on the nuclei ³¹ P (a), ²⁷ Al (b) and ²⁸ Si (c). The ³¹ P NMR spectrum of the initial heteropoly acid has a main peak in the region of -16 ppm. The signal in the same region, but broader, has the spectrum of the sample of Example 2. At the same time, the obtained nanocomposite material has a peak in the region of -13 ppm, which indicates a strongly distorted structure of the heteropoly acid anion. The ²⁷ Al NMR method suggests that the deposition of a heteropoly acid on aluminosilicate by impregnation does not change the ratio of octahedral (0 ppm) and tetrahedral Al (60 ppm) in the sample. However, the obtained nanocomposite material has a significantly larger contribution of octahedral aluminum, which indicates the interaction of Al with a heteropolyacid anion. The ²⁹ Si NMR method shows that the nanocomposite material contains tetrahedral Si, surrounded by exclusively silicon (-Si (OSi) ₄ - signal -110 ppm) and Si, associated with 3 silicon-oxygen tetrahedra and one aluminum-oxygen tetrahedron (-Si (OSi) ₃ OAl-signal -100 ppm). At the same time, the aluminosilicate and the sample of example 2 obtained by impregnating aluminosilicate have one wide signal, which is associated with the inhomogeneous environment of Si in their structure. Apparently, the coordinated Al heteropolyacid anion in the nanocomposite material is embedded in the lattice with the formation of homogeneous centers and a close environment for silicon.

The results confirm the study using IR spectroscopy (figure 2). It can be seen that sample 2 is characterized by the same position of the bands corresponding to stretching vibrations W = O and deformation vibrations W-O-W, as well as an individual heteropoly acid. On the contrary, in the spectrum of sample 1, a significant broadening of the vibrational band W = O and its shift to lower frequencies are observed. This suggests stretching the bond W = O due to strong interaction with the aluminosilicate lattice.

2) In the nanocomposite material obtained by in situ encapsulation, in contrast to the deposited systems, the heteropoly acid is not washed out from the carrier, which is confirmed by chemical analysis data. Table 1 shows the chemical analysis data of Examples 1-2 before and after washing the samples with water and acid. It can be seen that the heteropoly acid is rigidly fixed on the carrier only in sample 1. In the sample coated with the heteropoly acid (Example 2), it is easily washed off even after washing with water. The absence of leaching of the heteropoly acid using HNO ₃ from the obtained material indicates the encapsulation of the heteropoly acid in the carrier.

Table 1 The HPA content in the samples before and after washing Samples GPA content, wt.% before washing after washing with water after washing with 30% HNO ₃ one 10.7 10.5 10,4 2 10.7 0.5 0.2

3) Nanocomposite material obtained by the claimed method, in contrast to known systems, has a high dispersion and, due to the high dispersion of the heteropoly acid component and its interaction with the carrier, acquires high acidity. Figure 3 shows the data of thermoprogrammed desorption of ammonia, allowing to determine the number of acid centers and their distribution in strength. It can be seen that the number and strength of acid sites increases significantly for sample 1.

The following are other examples illustrating the claimed invention, but not limiting it. The synthesis conditions in examples 1-21 are summarized in table 3.

Example 3

Nanocomposite material is prepared as follows. To a solution containing 30 ml of water and 4 g of a block copolymer of EO ₂₀ PO ₇₀ EO ₂₀ (Pluronic PI 23), 120 g of a 2 M HCl solution, 0.9 g of aluminum nitrate, 0.278 g of 12-phosphor tungsten acid are added and stirred for 2 hours . After that, add 9 g of TEOS and stirred at 40 ° C for 24 hours, and then at 100 ° C for 48 hours. After that, the product is filtered off, dried at a temperature of 110 ° C and calcined in air at 350 ° C for 3 hours. The result is 2.6 g of a nanocomposite material containing 10.5 wt.% Heteropoly acid encapsulated in an aluminosilicate matrix with a ratio of Si / Al = 10.

Example 4

Nanocomposite material is prepared as follows. To a solution containing 10 ml of water, 20 g of TEOS, 0.2 g of aluminum nitrate and 0.62 g of 12-phosphor tungsten acid, 9 g of cetyltrimethylammonium bromide (CTMA), 6.6 g of HCl (36 wt.%) In 27 ml of water are added. . The solution was thoroughly stirred for 3 hours at room temperature. After that, the product is filtered off, dried at a temperature of 110 ° C. The resulting product was stirred for 1 hour in a solution of 0.05 M H ₂ SO ₄ / ethanol at 78 ° C, then filtered and dried at 110 ° C and calcined in air at 350 ° C for 3 hours. The result is 6 g of nanocomposite material containing 8 wt.% Heteropoly acid encapsulated in an aluminosilicate matrix with a ratio of S1 / Al = 14.

Samples 3-4 illustrate the possibility of varying pore size by adding a template. The study of the porous structure was carried out by the method of low-temperature nitrogen adsorption. Table 2 shows the data for the samples by surface area, pore volume and average pore diameter.

table 2 The porous characteristics of the samples Samples BET surface area, m ² / g Pore volume, cm ³ / g Pore Size, A Example 1 340 0.65 76 Example 3 710 1,04 one hundred Example 4 760 0.86 39

Example 5

Material prepared analogously to Example 1, but instead of the solution of HF + HNO ₃ is used as catalyst HNO _3.

Example 6

The material is obtained analogously to example 1, but instead of ethanol with water, isopropanol with water is used as a solvent.

Example 7

The material is obtained analogously to example 1, but the drying is carried out at 50 ° C instead of 110 ° C.

Example 8

The material is obtained analogously to example 1, but the calcination is carried out at 400 ° C instead of 350 ° C.

Examples 5-8 illustrate the variation of synthesis conditions. The results obtained indicate that the materials can be obtained in a wide range of conditions.

Example 9

The material is obtained analogously to example 1, but using 1.53 g of 12-phosphor tungsten acid instead of 0.68 g

Example 10

The material is obtained analogously to example 1, but using 1 g of aluminum nitrate instead of 2 g.

Example 11

The material is obtained analogously to example 1, but aluminum isopropoxide is used instead of TEOS.

Example 12

The material is obtained analogously to example 1, but instead of TEOS zirconium isopropoxide is used, and the sol is obtained by adjusting the pH to 4 using concentrated NH ₄ OH.

Example 13

The material is obtained analogously to example 1, but titanium tetrabutoxide is used instead of TEOS.

Example 14

The material is obtained analogously to example 1, but instead of aluminum nitrate, titanium sulfate is used.

Example 15

The material is obtained analogously to example 1, but iron (III) nitrate is used instead of aluminum nitrate.

Example 16

The material is obtained analogously to example 1, but instead of aluminum nitrate, gallium (III) nitrate is used.

Example 17

The material is obtained analogously to example 13, but instead of aluminum nitrate, zirconyl chloride is used.

Example 18

The material is obtained analogously to example 1, but instead of 12-phosphor tungsten acid, the ammonium salt of 12-phosphor tungsten acid is used.

Example 19

The material is obtained analogously to example 1, but instead of 12-phosphor tungsten acid, 12-phosphoromolybdic acid is used.

Example 20

The material is obtained analogously to example 1, but instead of 12-phosphor tungsten acid, 12-tungsten-silicon is used.

Example 21

The material is obtained analogously to example 1, but instead of 12-phosphor tungsten acid, 12-molybdenum silicic acid is used.

Examples 9-21 illustrate the preparation of nanocomposite materials with different compositions of heteropoly acids and using a different carrier matrix. The properties of the materials obtained in examples 9-21 are similar to the properties of the material obtained in example 1. Thus, this method is universal in the preparation of a two-component support using alkoxide and a cation in the presence of heteropoly acid.

Claims (13)

1. A composite material containing the active phase in the form of a heteropoly acid and / or its salt in a matrix of a porous inorganic carrier, characterized in that it contains an active phase in the form of nanoparticles, the heteropoly acid anion of which is coupled to the structure-forming elements of the matrix by an ionic bond and introduced into the matrix at the stage its synthesis in situ. 2. The composite material according to claim 1, characterized in that it contains an active phase in the form of nanoparticles not washed out of the carrier by solvents. 3. The composite material according to claim 1, characterized in that as a porous carrier it contains aluminosilicates or their analogues with substituted cations of silicon and / or aluminum in oxygen tetrahedra. 4. The composite material according to claim 1, characterized in that as a porous carrier it contains oxides selected from the group: alumina, titanium dioxide, zirconia, silicon dioxide. 5. The composite material according to claim 1, characterized in that, as compounds with a heteropoly acid anion, it contains acids selected from the series: 12-phosphor tungsten, 12-tungsten-silicon, 12-phosphoformolybdenum, 12-molybdenum, or salts of the mentioned acids. 6. The composite material according to claim 1, characterized in that the pore diameter of the material is in the range of 5-500 Å. 7. A method of obtaining a composite material containing an active phase in the form of a heteropoly acid and / or its salt in a matrix of a porous inorganic carrier, comprising introducing into the carrier matrix a compound containing a heteropoly acid anion, characterized in that the introduction is carried out at the stage of matrix synthesis in situ by alkoxide interaction structure-forming element of the synthesized matrix with a heteropoly acid and / or its salt in the presence of a salt of the same or another structure-forming element of the matrix, system homogenization Sol production, gelation of the sol, gel maturation and heat treatment. 8. The method according to claim 7, characterized in that as the alkoxide of the structural element of the synthesized matrix, tetraethoxysilane, tetrabutoxy titanium, aluminum or iron, or gallium isopropoxide are fed into the interaction, mainly in the form of an alcohol solution. 9. The method according to claim 7, characterized in that as a salt of the structure-forming element of the matrix, metal salts selected from the series: aluminum, iron, gallium, titanium, zirconium in the form of their aqueous solutions are supplied for interaction. 10. The method according to claim 7, characterized in that as the compounds with the heteropoly acid anion, acids selected from the series: 12-phosphor tungsten, 12-tungsten-silicon, 12-phosphoformolybdenum, 12-molybdenum, or salts of the mentioned acids are fed into the reaction. 11. The method according to claim 7, characterized in that the interaction of the alkoxide of the structure-forming element of the synthesized matrix with a heteropoly acid and / or its salt is carried out in the presence of a pore-forming template with its subsequent removal. 12. The method according to claim 7, characterized in that the interaction is carried out when acid or alkali is added to the system in an amount providing synthesis of a carrier of a selected composition. 13. The method according to claim 7, characterized in that the heat treatment is carried out by drying the gel at 50-150 ° C and subsequent calcination in air at 300-400 ° C.

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