WO2008063038A1

WO2008063038A1 - Catalytic coating production method

Info

Publication number: WO2008063038A1
Application number: PCT/LT2006/000010
Authority: WO
Inventors: Aleksander Pavlovich Khinsky; Kristina Klemkaite; Nerijus Laurinaitis; Avelino Corma; Eduardo Polomares
Original assignee: Uab 'norta'
Priority date: 2006-11-23
Filing date: 2006-11-23
Publication date: 2008-05-29

Abstract

The invention relates to methods for producing catalytic coatings by thermally spraying a powder material and can be used in different branches of chemistry, power engineering and in automobile production. The aim of the invention is to obtain a catalytic double-sided coating on a metal strip, which apart from high catalytic properties in nitrogen oxides reducing and hydrocarbon oxidation reactions, exhibit high mechanical and operating properties, namely a high adhesion to a metal substrate and a high resistance to contamination in the atmosphere of sulphur dioxide gases and water vapour. For this purpose, the inventive method for thermally spraying a powder material to a metal strip consists in using a special composite powder which comprises an aluminium metal core, an intermediate aluminium hydroxide layer and a cobalt hydrotalcite coating on a particle surface, which is applied to the intermediate layer. The qualitative and quantitative composition of the composite powder is also disclosed. The inventive catalytic coating is sprayed according to a method consisting in thermally spraying to a metal strip, in mechanically processing said strip and in forming an article.

Description

METHOD FOR PRODUCING CATALYTIC COATING

FIELD OF THE INVENTION

The invention relates to methods for coating by spraying a material in a molten state and may find application in various fields of chemistry, energy. State of the art

Known methods for applying protective coatings using compositions based on aluminum compounds by methods of thermal spraying. Aluminum oxide is most widely used as a powder material for spraying coatings based on aluminum. As a rule, thermal spraying of ceramic coatings is carried out on a previously applied metal sublayer. Powder materials in pure form and / or their compounds - oxides, carbides, nitrides, etc. are used to spray coatings by thermal spraying methods. Often, sprayed powders are composite materials, for example, nickel particles coated with aluminum, tungsten, molybdenum.

The composition of the metal core and the thin coating layer is dictated by the need to take into account many factors, including a set of mechanical and special properties (adhesion strength of the coating to the substrate, porosity, corrosion resistance, erosion resistance, abrasion and wear resistance), as well as economic factors (production cost) .

In the process of thermal spraying, the powder material, as a rule, undergoes some transformation. This is due to the obligatory stage of the passage of powder materials in a jet of gas plasma (with plasma spraying) or in a stream of combustion products (with flame spraying).

Depending on the temperature of the gas stream, its length and speed, the particles of the sprayed material are heated to various temperatures, which causes various kinds of transformation in the particles - from surface heating and melting to complete melting and even transfer of the material into gas

phase. The choice of the optimal spraying mode is often sharply limited by the capabilities of the equipment and therefore the choice and optimization of the sprayed powders by chemical and phase composition, their structure and size is often the most important factor in successfully solving a technical problem, in particular thermal spraying of catalytic coatings on a metal substrate.

In the process of thermal spraying of powder materials onto a metal substrate, the following tasks must be simultaneously solved: - ensuring reliable mechanical contact of the sprayed layer with the metal substrate,

- providing a high density coating (reliable surface overlap)

- providing the necessary substructure of the coating. The first and third tasks are polar opposites, since to ensure reliable contact with the substrate, it is desirable to completely melt the particles during their passage in the gas stream - this ensures reliable adhesion of the coating to the substrate, but the shape of the particles is lost and the substructure of the coating changes. In order to simplify the technological problems that arise during thermal spraying, the process is often carried out in two or more stages. In this case, at the first stage, a special thin intermediate layer (sublayer) is sprayed, which, on the one hand, provides reliable adhesion to the substrate, and on the other hand, provides a good adhesion of the main layer, which is sprayed onto its surface.

As materials for spraying, powders, powder mixtures and special compositions of powders are used. As such compositions, powders are often used with a coating applied to their surface (the coating can be multilayered), powders with small particles of another material attached to their surface, and powders combined into whole complexes of particles connected to each other in a specific, ordered manner.

A known method of forming metal particles with an oxide coating for a plasma spraying process (US6582763, Рrеssеs fоrrrоdusіpg okhide soаtеd fme metal rаtсlеs). The fundamental difference from the usual surface oxidation process is the fact that a thin layer of oxides of those metals that are not part of the metal core is formed on the surface of metal particles. The process of applying an oxide coating includes the following stages - mixing a metal powder with an oxide, then feeding the mixture of powders into the thermal plasma stream to obtain a vapor phase; and finally, quenching (hardening) to fix the oxide layer on the surface of the particles.

There is also a known method of coating aluminum hydroxide particles in the form of lamellas with a ratio of thickness / length of 1:50 (JP2005089277, Wellcoated Composite Roller Apd Auxuus dispersion containing it). An aqueous suspension containing titanium, zirconium, cerium and tungsten in an amount of 0.01-2.5% is used to deposit hydroxide particles on the surface.

There is a method of forming metal particles with an inorganic coating (JP2005068508, Metal rover coater with Iporpur superfme rapplic apd its product method). The coating, which contains particles of aluminum oxide, aluminum hydroxide or their complex compounds, boron or phosphorus, in the form of a gel is deposited on the surface of metal powder particles. The final formation of the inorganic coating occurs during the heat treatment of the coated powder.

There is a known method of forming a precursor (WO2005040309, Method for Formula and Fisher-Torsch uspg and fight Suprt material) by contacting boehmite with a catalytic mixture containing the necessary catalytic materials. There is also a known method for the formation of spherical particles of a catalytic support (WO0222263, Catalust apd method method of microprocessor sizer randomized), which involves impregnation of a porous carrier with metals or metal oxides followed by dissolution of the carrier and the formation of spherical particles. For the manufacture of powder materials of the types mentioned above, various methods of physical and chemical deposition in the liquid and gas phase are used, as well as methods of mechanical coating, for example, when the powder is abraded in attritors of various types, etc.

A known method for the production of powder with a titanium coating (RU2178341, Titapium roverdrodustiop rocess), in which during the joint grinding of a metal powder with a titanium sponge, a thin layer of titanium is applied to the surface of the powder.

There is also known a method of forming a powder (US5561832, Metod for mapupuripg vapadium sarbide rover addad to stel rover bu milliproppress, apd the method for manufacturing parts therewith) when co-processing a metal powder with vanadium carbide by grinding.

A known method of forming a powder for thermal spraying

(US5530050, Theppl sprau arabadable rover for high temperature arrlicatiops), in which the formation of a layer of zirconium particles on the surface of a plastic metal particle occurs when they are jointly abraded in the attritor.

Thermal spraying methods are usually used to obtain coatings that provide mechanical (increase in surface hardness, decrease in friction coefficient and increase in wear resistance), physical and chemical (increase corrosion resistance in water and gas, gas erosion, increase radiation resistance) and special ( in particular catalytic) properties.

If it is necessary to ensure sufficiently high catalytic properties of the coating on a material with a high density (complete absence of pores on the surface), whether metal or ceramic, they usually face a very specific problem.

The catalytic activity of a material is determined by a number of factors, both chemical and technological. Among the technological factors that determine the degree of catalytic activity is, in particular, the degree of development of the catalytic surface (Farrauto, RJ., Vartholom, CH, 1997. Pharmaceuticals Industrial Technologies Рrеssеsδ, 78-86: 122-134). This term describes a parameter characterizing the total surface area of one gram of coating. In the case of conventional coatings, this parameter is 0.01-0.1 m ² / g, while in the case of special, catalytic coatings, it reaches 100-400 m ² / g. Such a catalytic surface allows the placement of a proportionally larger volume of catalytic material. Therefore, the increase in the specific free surface, ceteris paribus, is proportional to the increase in the catalytic activity of the coating. A specific problem that must be solved by thermal spraying of catalytic coatings is the need to ensure a high specific surface. One of the solutions to this problem may be to increase the porosity of the coating during the spraying process. High porosity of the coating for conventional coatings is undesirable, as it causes deterioration adhesion to the substrate, as well as a decrease in the physicochemical characteristics of the coating. In some cases, for example, in the case of an anti-corrosion coating, high porosity is absolutely unacceptable, since it leads to the formation of ulcers and fistulas in the coating during the operation of products in a corrosive environment, and sometimes to catastrophic consequences.

In the case of catalytic coatings, a decrease in the adhesion strength of the sprayed layer to the substrate is also undesirable, since catalytic materials and products with a catalytic coating are often subjected to rather harsh operating conditions, accompanied by intense gas erosion, severe thermal cycles, etc.

On the other hand, an increase in the porosity of the coating is limited by the specific conditions of the thermal spraying process, and an increase in porosity is only achievable only up to values of about 4-5%. Taking into account the latent porosity (pores inside the coating that do not have access to the surface), an increase in the free surface practically does not occur and this way, from our point of view, is absolutely hopeless.

There is another concept for producing a catalytic coating with a developed surface by thermal spraying. In this case, the sprayed powder materials are a mixture of powders, including catalytic materials (metal oxides), aluminum hydroxides, in particular gibbsite and boehmite, which ensure the development of the free surface of the coating during and / or after spraying and a metal binder, usually aluminum which provides adhesion of the sprayed particles to each other and to the substrate.

As an example, a method for forming a catalytic coating is proposed (RU2126717C1, A method for manufacturing a catalytic unit for neutralizing gas emissions), in which a powder mixture consisting of aluminum - 0.5-5% and aluminum hydroxide is applied to the surface of a metal strip with high electrical resistance by plasma spraying with natural accompanying impurities. As a plasma-forming gas, air or another oxygen-containing mixture is used. In the process of spraying, it is proposed to maintain regulated energy regimes that ensure, on the one hand, the melting of aluminum particles, but excluding the thermal decomposition of aluminum hydroxide. The specified method allows you to get on the surface of a metal tape carrier thin composite layer with high adhesive strength. High adhesion strength is ensured due to the fact that during the spraying process as a result of the separation of powders in a plasma jet, an aluminum sublayer is formed on the surface of the tape, on which the main layer of aluminum hydroxide is formed. 5 The aluminum sublayer is characterized by high adhesion due to unsteady diffusion on the substrate directly during the deposition process.

The authors refer to an example of the application of this method, in which aluminum powders with a fineness of less than

10 40 microns and aluminum hydroxide (gibbsite) dispersion less than 10 microns. At the same time, aluminum hydroxide (gibbsite) does not require chemical treatment, but is used with natural (technological) impurities - sodium, potassium, calcium, silicon, etc. - which are in this case thermostabilizing elements and provide an additional increase in thermal stability

15 catalytic coating.

A known method of manufacturing a composite coating (RU97101513A, a Method of manufacturing a composite coating), in which a porous coating comprising a metal oxide and a metal binder is applied to the initial substrate by plasma spraying. As starting material for

20 plasma spraying use a mixture of powders, including aluminum oxide and / or titanium, aluminum as a metal binder and additionally aluminum hydroxide and / or titanium.

Similar methods are also proposed for preparing a catalytic coating based on hydrated titanium oxide (US2001014648, Catalust formed

25 bu srrauipg and titapium hudrohide material, US6228801, Rrosess for rrodusipg and satalust, KR2000022062, Satalutis sopverter apd method for mapufasturipg satalutis sopverter) in which said hydroxide (in the form of titanium metahydroxide) by thermal deposited on a substrate, primarily retaining its structure. The final formation of a catalytic coating with a developed surface

30 based on titanium oxides is carried out in the process of thermal decomposition of said titanium hydroxide with the formation of titanium oxide in the modification, mainly anatase.

As one of the coating options, thermal spraying of a mixture of powders of titanium metahydroxide and aluminum hydroxide with subsequent receipt, after decomposition of the sprayed layer, a mixture of titanium oxide (in the modification of anatase) and alumina gamma modification. The value of the specific free surface after decomposition of the sprayed layer is 50-70 m ² / g of coating. A known method of applying a porous coating to metal and ceramic materials by plasma spraying (US6254938B1, Sprauipg metod for arrluipg and porous coatigot substitute). In this case, a powder mixture is used, which includes aluminum hydroxide, aluminum oxide and / or titanium, glass powder, as a component forming a microstructure, aluminum metal powder and / or titanium as a metal binder. During plasma spraying, various components of the sprayed powder are introduced into different areas of the plasma flow. So, for example, aluminum hydroxide is introduced into the colder zone of the stream, and metals - aluminum and titanium - into the hotter one. The resulting coating, according to the authors, is characterized by high adhesion to the metal substrate and high porosity.

As studies in the field of thermal spraying of catalytic coatings with a developed surface show, to successfully solve these problems, it is necessary to form an intermediate layer, which should provide strong adhesion to the surface of the metal strip on the one hand and the catalytic coating that will be applied to this intermediate layer on the other.

To solve these two problems at the same time, the intermediate layer (sublayer) must, firstly, have a thermal expansion coefficient (ctr) as close to the ctp of the substrate, and, secondly, be as integrated as possible into the structure substrates, i.e. atoms of the coating material should form metallic bonds with atoms of the substrate material. If the first condition can be quite easily satisfied by selecting the material of the intermediate layer with a c.t.p. as close as possible to the c.t.

In plasma sputtering, such conditions can be realized only under conditions of high-temperature annealing after sputtering, and the temperature range during annealing should provide effective mutual diffusion of atoms of the material of the sublayer and the substrate. Since these temperatures are quite high, then usually there is a significant degradation of the coating itself, which is expressed in abnormal grain growth, high segregation of impurities and in the oxidation of grain along its boundaries. Carrying out such high-temperature annealing is undesirable for the above reasons. To ensure reliable adhesion of the sublayer with the coating applied to its surface, it must have a highly developed surface - the relative free surface in this case should be at least 10 m ² / g (this means that one gram of the coating must have a total surface of 10 square meters), which should provide high adhesion of the sprayed coating. However, recalculation of the maximum open porosity established for the intermediate layers sprayed in the usual way by the value of the relative free surface shows that the latter in this case does not exceed a value of the order of 1-2 m ² / g, which is clearly not enough.

Thus, to obtain a porous coating with high adhesion strength, the sprayed layer must be dense (on the side adjacent to the substrate), which should provide high adhesion to the substrate, and, therefore, high thermomechanical characteristics of the coating, and, at the same time , the sprayed layer must be highly porous (on its surface) to ensure special, including catalytic, properties. This contradiction is resolved due to the specific chemical composition of the sprayed powders and the original technology of their spraying.

To simplify, consider the spraying scheme of a three-component powder mixture consisting of aluminum hydroxide powder, silicate glass powder and aluminum powder (US6254938B1, Srааупg method for fоrррlуiпг а ророус соатипг то substitute). In this model composition, metal aluminum performs, firstly, the role of the metal sublayer, providing high adhesion strength of the sprayed layer to the substrate, and, secondly, the role of the metal bond to fix the particles of the porous surface of the sprayed layer. Silicate glass powder provides the development of the macrostructure of the sprayed coating. When spraying silicate glass powder, according to the authors, partial melting of particles from the surface is ensured for reliable adhesion, on the one hand, with sprayed aluminum and, on the other hand, with aluminum hydroxide powder, which is deposited on the surface of a composite layer formed from molten aluminum and particles of glass. Powder aluminum hydroxide plays the role of a substance that provides a ceramic coating based on aluminum oxide with a highly developed porous surface (i.e., provides the development of the coating microstructure). This problem can be achieved by thermal decomposition of aluminum hydroxide (520-600 ⁰ C) due to the following reaction: 2Al (OH) ₃ = Al ₂ O ₃ + 2H ₂ O (1)

However, to obtain a porous coating, it is necessary that the thermal decomposition of aluminum hydroxide proceeds already on the surface of the sprayed layer and the hydroxide particles are rigidly fixed in the layer. This can only be achieved if, during the plasma spraying process, it is possible to avoid the dissociation of hydroxide particles in the plasma jet (which has a temperature of 5000-8000 ⁰ C). In this case, in order to increase the affinity for aluminum, it is necessary to provide a partial melting of hydroxide particles from the surface.

Thus, in the process of plasma spraying of the model composition, when the particles of the powder pass through the plasma jet, the melting of aluminum metal particles, partial melting from the surface of the glass particles, and prevention of complete thermal decomposition of aluminum hydroxide particles are simultaneously ensured. This is achieved by supplying powders to various areas of the plasma jet - aluminum hydroxide is supplied to the colder zone, aluminum metal to the hotter zone. In addition, during the spraying process, priority is given to the passage of aluminum particles to the surface of the substrate in order to ensure strong adhesion of the sprayed layer to the substrate. This is achieved by selecting the fractional composition of the sprayed powders. Thus, for example, aluminum and silicate glass particles have a predominantly large mass, and therefore acquire a high velocity when passing through a plasma jet, which in turn ensures their predominant passage to the surface of the sprayed substrate.

Thus, during the deposition process, a composite layer is formed, consisting of aluminum, melted in a plasma jet and forming a plastic sublayer on the surface of the substrate. Glass particles partially melted from the surface are embedded in this layer, which ensures their strong adhesion to the layer. And finally, particles of aluminum hydroxide, which did not decompose during passage through the plasma jet, were introduced into the surface of this layer. The composite coating obtained in this way is not the final product, because, firstly, it is not porous, and secondly, its phase composition does not meet the requirements for special coatings (for example, for using the coating in catalysis gamma and theta modifications of aluminum oxides should be predominantly on its surface) and, thirdly, the residual thermal stresses (the result of the plasma spraying process itself) are quite high. Obtaining the necessary physical and chemical properties of the sprayed composite coating is achieved by conducting heat treatment in an oxidizing environment, mainly in air. During the decomposition of aluminum hydroxide in the temperature range 480-660 ° C during the heat treatment, the formation of aluminum oxide with a highly developed microporous surface occurs in accordance with reaction (1).

Thus, the process of heat treatment of the sprayed composite layer in an oxidizing medium provides, according to the authors, the preparation of the necessary chemical and phase composition on the surface with the simultaneous formation of a specific macro- and microstructure of the surface layer.

The method of thermal spraying described in detail above for the preparation of catalytic coatings has a number of significant drawbacks, the main of which is the problem of preventing thermal decomposition of aluminum hydroxide during its passage in a plasma jet.

The means proposed by the authors to prevent the thermal decomposition of aluminum hydroxide during thermal spraying are reduced to the separate introduction of aluminum and aluminum hydroxide powders into different zones of the plasma jet, the hydroxide being introduced into the colder zone. This should really reduce the risk of partial or complete decomposition of the hydroxide, however, this reduces the path size of the hydroxide particles in the plasma stream and, therefore, reduces the speed of the particles, which in turn leads to an increase in the probability of decomposition of the particles during the deposition process. In the event that the colder zone of the plasma jet is determined, any change in the mass of particles, air pressure in the plasmatron, or a small change in the electrical parameters of the source during the deposition process will lead to a change in the trajectory of the particles, and, therefore, to decomposition of particles in the process of spraying, or to their underheating - in this case, they simply will not adhere to the substrate.

Therefore, it seems reasonable to use complex powder materials structurally combined in the volume of one particle for thermal spraying. In this case, many problems that pose serious or even insoluble problems when spraying mixed powder compositions can be simultaneously solved. In particular, in this case, the problem of protecting the surface of the particles by applying a special coating of refractory and heat-resistant metal or alloy can be solved, as well as the problem of increasing the adhesion of the coating by increasing the mass of the particles (increasing kinetic energy) and special coatings of various types that increase the adhesion strength of the sprayed layer.

The next step in the development of the thermal spraying of catalytic coatings is the development of complex powder materials, which in the catalysis are called precursors. A precursor is usually understood as a substance that contains the necessary catalytic materials and, after its application to the surface of the carrier, can be converted, after a series of procedures, into a catalyst (Farutauto, RJ., Pharmaceutical, C.H., 1997, Industrial Chemical Industrial Chemicals). As such procedures, heating, irradiation or other activation of the surface of the catalytic coating can be used.

The use of complex powder materials as precursors can also solve a number of specific problems associated with the deposition of catalysts. Consider, as an example, a spraying option using a mixed composition consisting of aluminum metal, aluminum oxide and hydroxides. The proposed process allows to obtain a catalytic coating characterized by a relatively high free surface (50-70 m ² / g) and a statistically uniform distribution of catalyst particles. However, the optimal operation of the catalyst is possible only when the catalytic particles are on the surface of a special catalytic carrier, the role of which is played by gamma and theta alumina, as well as aluminum hydroxide in the form of gibbsite and / or boehmite. Moreover, the catalytic activity of the catalyst is higher, the higher the degree of development surface. In the case described above, when applying the powder mixture composition, the thermal spraying process is constructed in such a way that aluminum hydroxide is applied to the surface of the product in an undecomposed or partially decomposed state. Subsequent heat treatment leads to thermal decomposition of the hydroxide and a strong increase in the free surface. However, an increase in the free surface does not lead to migration and redistribution of catalyst particles on the surface of the catalytic carrier (see Fig. L).

The catalyst particle is rigidly fixed in the sprayed layer after thermal spraying and its position does not change during the decomposition of aluminum hydroxide. Therefore, an increase in the free surface is not accompanied by a proportional increase in catalytic activity.

A sharp increase in the level of catalytic activity is possible only when a special precursor is used for the thermal spraying process. Such a solution is proposed in the patent (EP1449581, Satalust for steam refoimipg soptaiped piskel, magpesium apd alumipium, rrosess for rrodusipg the satalust, apd the rrosess for rrodusipg hudrogep usipg the satalust), wherein the method of forming the precursor comprises calcining the composite particles of aluminum hydroxide, consisting of a core - particles of a hydroxide and a composite hydroxide layer on the surface of said core containing magnesium, nickel and aluminum, and subsequent reduction by heating. During recovery, according to the authors, a redistribution of the reduced nickel particles in the volume of the particles occurs with their predominant placement on the surface of porous oxide particles, which ensures high catalytic properties. There is also proposed a method of forming a precursor for the subsequent preparation of a catalyst (US2004 / 0127587A1, Method for Formation and Fisher-Uspag and battle-in-material), in which aluminum powder is used as a carrier powder for the catalyst (one of boehmite transforming aluminum powder (one of when heated). The formation of boehmite occurs when Gibbsite is heated in the temperature range of 170-180 ° C and is accompanied by an increase in its porosity. The formation of the precursor occurs upon impregnation of boehmite, which has a certain crystallite size, namely, in the range of 4-30 nanometers. As solutions for coating formation, aqueous solutions of salts and organic solvents are used. A method for forming a precursor (EP 1462475 Al, Mg-Zn-

Albased bakedite-resin and resin composition containing theme), in which the composite Mg-Zn-Al layer is formed on the surface of the core, consisting of Mg-Al hydrotalcite. The particle size of the precursor is 0.1-1.0 microns.

A method for producing a precursor is also proposed (JP2004255245, the Wellbearing method, the method of the method, the method consists of the aluminum, the surface is the hydrothermal method, which includes the aluminum surface and magnesium nickel. This precursor is subjected to heat treatment in a reducing medium, where nickel oxide is reduced to nickel and its uniform distribution on the particle surface is ensured.

A known method for the manufacture of composite coatings (WO2004079035, Method for production and co-production) with plasma spraying. The composite coating obtained in accordance with this method can be used as a substrate for applying various coatings, for example, polymer, as well as impregnation with various compositions, including catalytic ones. The proposed method consists in the fact that in the sprayed powder, providing the development of the microstructure of the coating, enter the composite powder with a coating of the type hydrotalcite (composite precursor). A coating of this composition is sprayed onto a metal or ceramic substrate, then machining and heat treatment are carried out by annealing. The aim of the invention described above is to obtain a catalytic coating having enhanced characteristics, namely, the adhesion strength of the coating to the substrate and a high free surface.

To achieve this goal, a coating is applied to the substrate by thermal spraying, which includes a mixture of alumina powders, aluminum metal as a binder metal, glass powder, as a material for the formation of the coating macrostructure, as well as a composite precursor with a coating of hydrotalcite type.

At the same time, it is proposed to choose the components of the powder mixture for spraying from the ratio, wt.%: Aluminum 1-7

Alumina 0.1-12

Glass powder 1-3

Composite powder (precursor) rest. As a composite powder in a coating according to the invention, an aluminum hydroxide-based powder material is used with a hydrotalcite type coating applied to its surface.

Aluminum hydroxide in the modification of gibbsite or boehmite is used as the carrier of the composite powder. Gibbsite Al (OH) ₃ has a monoclinic crystal lattice and dissociates in the temperature range

200-300 ⁰ C with the formation of boehmite, AlO (OH), which, in turn, decomposes in the temperature range 520-580 ° C.

The introduction of a composite powder based on aluminum hydroxide with a hydrotalcite coating into the mixture ensures the development of the coating microstructure and allows obtaining a highly effective catalytically active coating surface with high microporosity.

Hydrotalcite is usually understood to mean a natural mineral represented by the formula Mg ₆ Al ₂ (OH) ₂ .16CO ₃ . 4H ₂ O. The structure of hydrotalcite is derived from brucite Mg (OH) ₂ , where magnesium ions form octahedra that line up in an infinite layer. These layers are superimposed on one another and are held together due to hydrogen bonds. When a part of divalent magnesium cations is replaced by trivalent cations of close radius, for example, aluminum cations, the layer receives an additional positive charge, which is compensated by the introduction of divalent CO ₃ anions located between the layers.

The so-called hydrotalcite-type materials are isomorphic analogues in which the cations of magnesium and aluminum are partially replaced by divalent and trivalent metal cations with a close ionic radius. The decomposition of materials such as hydrotalcite occurs, as a rule, in three stages.

At the first stage - about 200 ⁰ C, the so-called crystallization water is released from hydrotalcite, which is retained in the structure during crystallization. At the second stage, in the temperature range 350-450 ° C, anions are separated from the structure, which are located between the cation layers and provide electrostatic equilibrium of the material. The departure of anions is accompanied by the release of interplanar space and the primary development of the surface of the material. In this case, there is no destruction of the structure of the material, and it can be restored by holding the material in an atmosphere of saturated steam.

In the third stage, at temperatures above 650 ° C, irreversible destruction of the structure of the material with the formation of oxides of magnesium, aluminum and other metals occurs. This process is accompanied by a repeated, more significant development of the free surface. On average, the free surface is 200 to 400 m ² / g. With a further increase in the annealing temperature - over 750 ° C, spinel formation occurs.

A typical x-ray decomposition of the classical hydrotalcite of the Mg-Al system with the formation of the corresponding oxides and spinels (see figure 2).

The main advantages of synthetic hydrotalcites in comparison with hydroxides are the following:

- decomposition of hydrotalcites occurs in three stages, which opens up great opportunities for multi-stage heat treatment, - within the second stage of hydrotalcite decomposition (350-450 ° C), its structure can be completely restored in an atmosphere of saturated steam,

- the temperature of the interval of the third stage of decomposition of hydrotalcite is 650-750 ⁰ C, which significantly exceeds the temperature range of the decomposition of aluminum hydroxide, which is 500-560 ⁰ C, - the free surface after the complete decomposition of hydrotalcite is 200-400 m ² / g.

The most important fundamental difference between hydrotalcites and aluminum hydroxides is their ability to replace aluminum and magnesium cations with trivalent and, accordingly, divalent cations of most metals, the oxides of which are widely used in catalysis, provided that their ionic radius is not much different from the ionic radii of aluminum and magnesium. This allows one to introduce such metals directly into the structure of hydrotalcites and, thus, use the main features of their decomposition to obtain catalysts the necessary chemical composition in the form of a mixture of oxides or complex oxides

(spinel) with a high free surface.

Therefore, it is precisely synthetic hydrotalcites with partially substituted magnesium and aluminum ions that are advisable to use as a material ensuring the creation of a highly efficient catalytically active surface with high microporosity.

In the above patent, when using a composite precursor, a high level of catalytic properties is achieved due to the fact that the precursor is a porous particle of aluminum hydroxide (gibbsite or boehmite), on the surface of which a thin layer of hydrotalcite is deposited. In the process of thermal decomposition after sputtering, the precursor core, consisting of gibbsite or boehmite, transforms into aluminum oxide, and hydrotalcite on its surface into a mixture of oxides or, depending on the processing temperature, spinel. The fundamental difference from the process of decomposition of the powder mixture coating is that, with this technology, on the surface of the carrier particle, in the process of its development, there is always a layer of hydrotalcite, which also decomposes with an increase in the free surface of the coating. In the process of joint decomposition of the core and the coating, the corresponding effects are multiplied, which sharply increases the degree of surface development.

An example is the attempt to reproduce the plasma spraying technology of a catalytic coating on a metal substrate in accordance with the patent WO2004079035 described above. A thin (40 μm) strip of heat-resistant chromium-aluminum steel grade OC404 (Sandvik) was used as a substrate. Plasma spraying was performed using an APP-403 type current source and an air plasma torch. Air was used as a plasma-forming gas. The electrical parameters corresponded to those cited in the aforementioned patent, namely, voltage of 210 volts, current of 150 amperes. The regulation of these parameters was carried out in a rather narrow range (voltage within 200-220 volts, current within 140-160 amperes). Going beyond the boundaries of these ranges led to a breakdown of the spraying process. The distance between the cut of the plasma torch nozzle and the sprayed surface was 100 mm. A decrease in this distance leads to overheating, and an increase leads to insufficient heating of the sprayed surface. AT the first and second cases, the echo led to a sharp decrease in adhesion of the sprayed layer. The air pressure that was used as the plasma-forming gas was maintained at 0.07 MPa. A decrease in air pressure can lead to overheating of the plasma torch during the deposition process, an increase in pressure leads to an increase in voltage between the anode and cathode - in this case, the stability of the plasma torch decreases and the probability of its failure sharply increases.

The only parameters that can be widely controlled with plasma spraying are the speed and flow rate of the sprayed powders. The powder can be supplied in two ways - by introducing the powder into the plasma torch and feeding along the axial line in the plasma jet (to the most warmed up zone) and feeding directly to the peripheral (colder zone) plasma jet.

In our experiment, we used four options for feeding powder into a plasma jet.

For spraying, a mixture of powders was used, including, according to the patent, 85% of the composite powder (boehmite coated with hydrotalcite), 10% alumina of gamma modification, 3% aluminum and 2% glass powder (all powders with a fineness of less than 60 microns). A mixture of powders was supplied:

Option 1 - into the interior of the plasma torch along its longitudinal axis,

Option 2 - into the peripheral zone of the plasma jet 30 mm from the nozzle exit,

Option 3 - in the peripheral zone of the plasma jet 70 mm from the nozzle exit,

Option 4 - separate feed: a mixture of aluminum and glass powders into the peripheral zone of the jet 30 mm from the nozzle exit (hotter zone), a mixture of composite powder and aluminum oxide into the peripheral zone of the jet 70 mm from the nozzle exit (cooler zone).

In the first case, when the powder mixture passed through the nozzle of the plasma torch, the aluminum particles (the most low-melting component) melted and after 30-40 seconds the output of the plasma torch was blocked. Thus, the first embodiment of the powder supply is not acceptable in this case.

In the second case, when the powder mixture was fed into the peripheral zone of the plasma jet at a distance of 30 mm from the nozzle exit, a coating was obtained with satisfactory properties about 10 microns thick. However when serving powder mixture in the peripheral zone was observed, as shown by weight analysis, an extremely irrational flow rate of the sprayed powder. The amount of powder deposited was not more than 3-5% of the total amount of powder supplied. In the third case, when the powder mixture was supplied to the peripheral zone of the plasma jet at a distance of 70 mm from the nozzle exit, the powder did not have time to warm up when passing through the plasma and did not form a coating on the surface of the carrier. Thus, the third embodiment of the powder supply is not acceptable.

In the fourth case, when two mixtures were separately fed into different zones of the plasma jet, a coating was obtained with satisfactory properties about 15 microns thick. However, in this case, as in the second case, an irrational consumption of the sprayed powder was observed. The amount of deposited powder was about 8-10% of the total amount of deposited powder. From the above results of the reproduction of the aforementioned patent it can be seen that this method of obtaining composite coatings has a number of disadvantages that severely limit the possibility of its application. The fact is that the thermal spraying method provides, to one degree or another, the passage of powder particles in a plasma jet, which ensures full or partial melting of the particles, which, in turn, ensures their reliable adhesion to a metal substrate. In the case when the powder materials are sprayed to provide a dense coating, this is acceptable and even desirable, however, when spraying the complex precursors described in the above invention, this leads to a number of serious problems.

The main problem is that although the particle diameter of the composite precursor is large enough (reaches 100 microns), their mass is insufficient for effective incorporation into the intermediate layer deposited on the surface of the substrate to increase adhesion. On the other hand, aluminum particles included in the composition of the powder mixture are effectively embedded in the intermediate layer, capturing part of the sprayed particles and thereby increasing the efficiency of the process. However, most of the powder - from 80 to 90% - does not spray and goes to waste, thereby reducing the efficiency of the spraying process. In connection with the foregoing, it seems reasonable to significantly increase the particle mass of the composite precursor by introducing additional materials that are used in the spraying process and which, at least, will not reduce the level of catalytic properties of the coating. This will provide a sharp increase in the density of the deposited layer, and, consequently, the level of catalytic properties, as well as a reduction in the unproductive expenditures of the powder of the composite precursor by reducing losses during sputtering.

This problem can be solved by creating a composite precursor in which a metal aluminum particle is a core on which an intermediate layer of aluminum hydroxide is deposited, firmly adhered to the metal core and having a developed surface on which a layer of hydrotalcite is deposited.

Fig.Z is a diagram of the sequential development of the concept of a precursor. The diagram shows the evolution of the precursor concept - starting with a hydrotalcite particle, through a composite powder in which aluminum hydroxide plays the role of a core (gibbsite or boehmite), and hydrotalcite is used as a coating, and to a precursor, which is a composition of an aluminum core, an intermediate hydroxide layer aluminum and hydrotalcite coatings. Let us consider successively the requirements for individual components of the precursor and the possibility of their implementation in practice.

The aluminum particle, which is the core of the precursor, should have a size of 60-100 microns, which is due to the possibilities of feeding the powder from the dispenser and its passage through the plasma torch. The process of creating an aluminum hydroxide layer on the particle surface is a rather complicated task, since it must ensure that the following conditions are met:

- high porosity of the layer to ensure uniform distribution of hydrotalcite deposited on its surface, - uniform distribution of the porous layer over the surface of the particle and a complete coating of the surface of the aluminum particle,

- high adhesion of the porous layer to the surface of the aluminum particles. To accomplish this task, methods of chemical vapor deposition and methods of joint mechanical processing in attritors can be used. Chemical vapor deposition methods provide a continuous coating with a sufficiently good adhesion, but they cannot provide a porous layer of a sufficiently large thickness (about 5-10 microns). Joint processing methods in attritors provide a porous layer of a sufficiently large thickness, but they do not provide a continuous coating and reliable adhesion. Very simple and effective are the methods of oxidation of aluminum powders in air.

The process of growing a porous layer on the surface of an aluminum particle consists in sequentially hydrating the oxide layer to form a porous structure, then again forming the oxide layer, hydrating it, etc. The process can be brought to a porous hydroxide layer of the required thickness or even complete hydration of the aluminum particle.

The series of articles (KINETICS AND CATALYSIS, 2000, volume 41, Xa 6, p.907-915, KINETICS AND CATALYSIS, 2000, volume 41, JV ° 6, p.916-924) describes the technology for producing porous cermet by forming aluminum particles coated with aluminum hydroxide on the surface and their subsequent pressing. The formation of a porous layer of aluminum hydroxide on the surface of the particles is carried out during the oxidation of aluminum particles in an autoclave with a controlled temperature and pressure. The basic laws of the kinetics of the formation of the surface layer of aluminum hydroxide (boehmite) during the oxidation of aluminum particles in the vapor phase (hydrothermal oxidation) are established in the articles. As established during the research, at the initial stage of the process, the formation of aluminum oxide occurs, which then, during hydration, turns into boehmite. The free surface of the boehmite layer, with its volume of less than 10%, is 200-250 m ² / g. With a further increase in the volume of the surface layer, the free surface decreases to 150-160 m ² / g.

A known method for producing aluminum hydroxides (WO 2004 / 071950A1, A method for producing hydroxides or oxides of aluminum and hydrogen and a device for its implementation) from a powder of finely dispersed aluminum with a particle size of not more than 20 μm, from which an aqueous suspension is prepared, which is fed to the reactor, where the suspension is sprayed with drops with a diameter of 5-100 microns in water under a pressure of 20-40 MPa at a temperature of 220-900 ° C.

The use of this method provides, according to the authors, obtaining:

- aluminum hydroxide (boehmite) at a temperature of 250-300 ⁰ C, a pressure of 32-35 MPa and an aluminum / water ratio of 8-12,

- aluminum hydroxide (bayerite) at a temperature of 220-330 ° C, a pressure of 30-33 MPa and an aluminum / water ratio of 12-14,

- a mixture of aluminum hydroxides (boehmite and bayerite) at a temperature of 280-330 ° C, a pressure of 30-33 MPa and an aluminum / water ratio of 1-12. A method for the production of hydroxides and aluminum oxides is also provided.

(US2758011, Roodustiof of alumipa) by oxidation in an aqueous medium under pressure.

The deposition of a hydrotalcite layer on the porous surface of aluminum hydroxide can be carried out by various methods, including methods of impregnation, coprecipitation, etc. (CN1483513, "sootipg"). SUMMARY OF THE INVENTION

The objective of the invention was to develop a complex precursor for thermal spraying of catalytic coatings. The complex precursor was supposed to be particles including an aluminum core, an intermediate coating of aluminum hydroxide and an outer layer of catalytic material based on synthetic hydrotalcite.

The catalytic coating obtained in the process of thermal spraying of a complex precursor should provide good adhesion to the substrate, a high specific free surface and high catalytic properties in the reaction of reduction of nitrogen oxides. DETAILED DESCRIPTION OF THE INVENTION

The essence of the invention consists in the fact that for the thermal spraying of catalytic coatings a special powder material is made - a precursor (resursor), each particle of which is a core of aluminum with an intermediate layer of aluminum hydroxide deposited on its surface and a surface layer of catalytic material deposited on the surface of the intermediate layer - synthetic hydrotalcite. For the preparation of the precursor, aluminum powder with a dispersion of 20-100 microns is used. The technological process for obtaining a precursor includes two stages:

Stage 1 Hydration of aluminum powder in water vapor to obtain a surface layer of aluminum hydroxide (gibbsite, boehmite and / or bayerite).

2 stage. Deposition of a layer of synthetic hydrotalcite onto the surface of hydrated aluminum powder.

For the production of the precursor, a technological process for hydration of aluminum powder (stage 1) was developed, which provides a porous intermediate layer of aluminum hydroxide on the surface of aluminum particles.

100 grams of aluminum powder, dispersion of less than 63 microns, were placed in a special autoclave with a volume of 6 liters, equipped with an electric heating element (2.4 kW power) and channels (working and emergency) for steam output. The autoclave was filled with 2 liters of distilled water, tightly closed and turned on. The steam outlet channel was adjusted so as to provide an excess pressure of about 1.5 bar, and the temperature was maintained at 100 ⁰ C using the electronic control unit. The formation of hydroxide in a vapor-air medium continued for 90 minutes. After completion of the process, the safety valve was open until the autoclave was completely cooled. Upon reaching a temperature of 35 ° C, the powder was recovered from the autoclave. The powder was dried in the open air at room temperature for 8-12 hours. In FIG. Figure 4 shows an X-ray diffraction pattern of an aluminum powder with a hydrated layer. In addition to the peaks corresponding to aluminum, peaks corresponding to aluminum hydroxides, namely boehmite and bayerite, are clearly visible. Thus, in this case, we have a mixed structure of the hydrated layer.

Figure 4 - x-ray aluminum powder with a hydrated layer. The development of the chemical and phase composition of synthetic hydrotalcite for the deposition of a surface catalytic layer on a precursor was carried out as follows. The development of the catalyst was carried out in relation to the task of reducing nitrogen oxides and oxidizing carbon monoxide in the exhaust gases of a diesel engine. This statement of the problem determined the requirements for both the catalyst and its operating conditions. The catalyst under development (based on hydrotalcite) should ensure the reduction of nitrogen oxides to molecular nitrogen and the oxidation of carbon monoxide to carbon dioxide. To ensure the task, hydrotalcites of the Mg-Al-Co system were selected with the possibility of introducing additional metal ions, such as sodium, vanadium, cerium, and / or ruthenium.

The catalyst obtained by the decomposition of hydrotalcites described above is active in the removal of nitrogen oxides at low temperatures and in the presence of oxygen, water vapor, and sulfur oxides, as well as in the oxidation of carbon-containing mixtures at low temperatures. Catalysts can be prepared by coprecipitation of solutions containing magnesium, aluminum and cobalt with an alkali solution for the synthesis of Mg-Al-Co hydrotalcite.

3 stage. A solution containing cobalt, magnesium and aluminum ions was obtained from the soluble salts of Mg (NO ₃ ) ₂ .6H ₂ O, A1 (NO ₃ ) ₃ .9H ₂ O and Co (NO ₃ ) ₂ .6H ₂ O. In the corresponding In solutions, the concentration of magnesium, aluminum, and cobalt ions, as well as the ratio (Mg + Co) / Al, can vary over a wide range without exceeding the solubility limit.

The alkaline solution is formed by mixing alkaline hydroxides and carbonates, mainly NaOH and Na ₂ CO ₃ in adequate concentrations, ensuring complete precipitation of the components of the first solution.

Both solutions were thoroughly mixed. The resulting gel was aged from 3 to 20 hours at temperatures in the range of 60-100 ° C. After aging, the resulting material was filtered and washed to obtain a pH in the range of 6.8-7.5. After calcination at temperatures up to 300 ^° C, the resulting material was converted to Mg / Al / Co mixed oxides.

There are other methods described above for the preparation of hydrotalcites (Cavapi, F., Trrifiro, F., Vassari, A., Catal. Todau, 11 173 (1991); Miuata, S., Claus Clau Miper., 28, 50 ( 1980); Allmap, R., Jersep, HP, Neues Jähr. Mip., Moptsh., 544 (1969); Rehisle, WT, Chemteh, Jashu 58 (1986). The resulting material was impregnated with other metals, such as sodium, cerium, ruthenium and / or vanadium. Impregnation of said metal held in a temperature range of 10 -100 ° C, priemuschestvenno in the range of 20-40 ⁰ C, from salt solutions and, after calcination occurred the formation of a sodium cobalt oxide oxide Route Nia, cerium oxide or vanadium oxide. Percentages the ratio of the oxides of these metals in the catalyst is 0.1-30%, mainly 1-20%.

The catalytic properties of mixed oxides obtained by decomposition of hydrotalcites in the reaction of reduction of nitrogen oxides were carried out at a laboratory bench. The experiments were carried out in a special reactor, which is a quartz tube with a diameter of 22 mm and a length of 530 mm. Catalytic material, weighing 1 gram, in the form of particles with a size of 0.25-0.42 mm, was loaded into the reactor and heated to a temperature of 350 ° C with the passage of nitrogen or hydrogen. At this temperature, the material was aged for 30 minutes. After that, the desired reaction temperature was established and the supply of nitrogen oxides was ensured. The gases supplied were a mixture of 300 million ^"1 NO, 900 million ^{" 1} C ₃ H ₈ , as well as varying amounts of oxygen and nitrogen. The flow rate when the gas mixture was supplied was 650 ml / min. To assess the effect of water and SO ₂ on the reduction of nitrogen oxides, experiments were carried out with the introduction of water in the range of 0-10% and SO ₂ in the range of 0-60 ppm ^{. 1.} The concentration of nitrogen oxides in the outlet of the reactor was constantly monitored using a chemo-luminescent detector 951 A.

The catalytic activity of mixed oxides obtained after decomposition of hydrotalcite in the oxidation reaction of carbon-containing mixtures was determined in a special reactor, which is a quartz tube with a diameter of 22 mm and a length of 530 mm. Catalytic material, weighing 1 gram, in the form of particles with a size of 0.25-0.42 mm, was loaded into the reactor and heated to 350 ° C with the passage of nitrogen or hydrogen. At this temperature, the material was aged for 30 minutes. After that, the catalyst was cooled in a stream of nitrogen to 120 ^° C. A reaction mixture was supplied, which consisted of a mixture of gases, including 300 million ^" NO, 900 million ^{" 1} C ₃ H ₈ and 8% oxygen, the rest was nitrogen. The flow rate when the gas mixture was supplied was 650 ml / min. The gas mixture was heated from a temperature of 120 to 550 ° C at a rate of 5 ° C / min. Propane oxidation was monitored by CO ₂ content. Information confirming the possibility of carrying out the invention

Example 1. Preparation of a catalyst based on Mg / Al / Co hydrotalcite with a molar ratio of 65/20/15.

Aqueous solutions were prepared: 0.975M solution of magnesium nitrate, 0, 3M solution of aluminum nitrate and 0.225M solution of cobalt nitrate. They mixed when shaken with 3, 3M aqueous NaOH and IM Na ₂ CO ₃ until pH is obtained

13.

The resulting gel was ripened for 12 hours at 60 ⁰ C, then washed and filtered to obtain a pH of 7. Then the material was calcined at 650 ° C for 6 hours. After calcination, the material had a relative free surface of 165 m ² / g.

Example 2. Preparation of a catalyst based on Mg-Al-Co hydrotalcite with a molar ratio of 65/20/15 with Na and V.

To the catalyst described in Example 1 was added, by impregnation, an IM solution of the vanadium salt and NaOH to obtain 1% vanadium and 6% sodium. Then, the material was dried and calcined at 550 ^° C. After calcination, the material had a relative free surface of 55 m ² / g.

Example 3. Catalytic activity in the NOx reduction reaction of the catalyst described in Example 2. The catalyst described in Example 2 was used to remove NOx, as described above, at various temperatures. A 95% conversion of nitrogen oxides was obtained with an experiment duration of 1 hour at temperatures in the range of 100-400 ° C and in the presence of 8% oxygen.

Example 4. Catalytic activity in the oxidation reaction of carbon-containing mixtures of the catalyst described in example 1.

The catalyst described in example 1 was used to remove carbon-containing mixtures, as described above. It was found that in the presence of this catalyst, propane oxidation occurs at temperatures 120 ° C lower than without catalyst. The hydrotalcite compositions described above were applied to the intermediate layer of aluminum hydroxide on the surface of an aluminum particle (stage 2 of the preparation of a complex precursor) by the deposition method.

Example 5. The deposition of a layer of hydrotalcite on an intermediate layer of aluminum hydroxide (gibbsite / boehmite) in the production of a complex precursor. 50 g of aluminum powder with a layer of hydroxide on the surface

(processed according to the above technology) were placed in a glass vessel containing a solution of "B" (20 g of NaOH and 20 g of NaHCO ₃ in 250 ml of water). Then, with stirring, a solution of “A” (160 ml of IM Mg (NO ₃ ) ₂ x 6H ₂ O, 28 ml of IM Co (NO ₃ ) ₂ x 6H ₂ O and 64 ml of IM A1 (NO ₃ ) ₃ x 9H ₂ O). Process precipitation is accompanied by a strong exothermic reaction - the temperature rises to 90-95 ⁰ C. Precipitation takes about 3 hours. The resulting suspension was ripened for 24 hours at 80 ° C, then cooled to room temperature, filtered by distilled water, dried at room temperature and milled. Thus, a thin layer of hydrotalcite was deposited on the surface of particles with a porous layer based on aluminum hydroxides (Fig. 5).

Thus obtained precursor was used in the process of thermal spraying to obtain a catalytic coating. A steel strip made of heat-resistant steel 40 microns thick (Sandvik OC404) was used as a substrate for obtaining a catalytic coating. Spraying was carried out on both sides. When spraying, an APR-403 current source was used, as well as a plasma torch and dispensers of an original design, which provided a highly dispersed and light ceramic powder. The microstructure of the coating surface is presented in Fig.6.

After spraying, the samples were corrugated with a step of 3 mm and rolled up into catalytic blocks with a diameter of 40 mm and a length of 50 mm. The catalytic blocks thus obtained were heat-treated in the temperature range 650-850 ⁰ C to decompose the intermediate hydroxide layer and the surface layer of cobalt hydrotalcite. The heat treatment regime included slow heating (at a speed of no higher than 3 ° C min ^"1 ), holding for 3 hours in the temperature range 650-850 ° C and slow cooling (at a speed of no higher than 4 ⁰ C min ^{" 1} ) to room temperature .

Evaluation of the catalytic properties of the blocks was carried out at the stand of the original design. 7. The scheme of the stand is presented, which includes: a steam boiler 1, a gas inlet pipe 2, a gas outlet pipe 3, an EcoLipe 6000 gas analyzer 4, a filter 5, a counter 6, a pump 7, valves 8, a cylindrical furnace 9, and T9- thermocouples

T12

Evaluation of the catalytic properties of the coatings was carried out in the reaction of reduction of nitrogen oxides during the combustion of liquefied gas (LPG) in a domestic boiler, while passing combustion products having a concentration of:

NO _x : 30-40 ppm ^"1 ;

СО: 4000 - 5000 million ^"1 ;

O ₂ : -0.3% through two catalytic blocks with a diameter of 40 mm and a length of 50 mm with a speed of 2.8 l / min using a pump. Catalytic properties were evaluated using an EcoLipe 6000 gas analyzer.

Example 6. The manufacturing technology of the catalytic block (option 1). A powder precursor based on the aluminum / gibbsite / cobalt hydrotalcite composition was prepared as follows. Aluminum particles with a dispersion of 60-100 microns were oxidized in a thermostat in the vapor phase at a temperature of 340 ° C and a pressure of 32 MPa for 24 hours, which led to the formation of a porous layer of aluminum hydroxide (gibbsite) with a developed surface on the surface of aluminum particles. Then, in a special installation, aluminum hydrotalcite was precipitated with a cobalt content of about 15%. The obtained powder, after filtration, drying, and grinding, was sprayed by thermal spraying onto OC404 steel tape from two sides. Then the tape was corrugated, rolled into a cylinder (to form a catalytic block) and fixed by sliding it into a thin pipe (G, Fig. 8).

Example 7. The manufacturing technology of the catalytic block (option 2). The technology corresponded to that given in Example 6, differing only in that, in the manufacture of the precursor, aluminum fractions of 20-60 microns were used (2 ^?, Fig. 8). Example 8. The manufacturing technology of the catalytic block (option S).

The technology corresponded to that given in Example 6, differing only in that in the manufacture of the precursor, the oxidation of aluminum in the vapor phase was carried out at a temperature of 280 ° C and a pressure of 34 MPa, which led to the formation of an intermediate layer in the structure of boehmite (3 ^?, Fig. 8). Example 9. The manufacturing technology of the catalytic block (option 4).

The technology corresponded to that given in Example 6, differing only in that in the manufacture of the precursor, the oxidation of aluminum in the vapor phase was carried out at a temperature of 240 ° C and a pressure of 32 MPa, which led to the formation of an intermediate layer in the structure of bayerite (4 ', Fig. 8). Example 10. The manufacturing technology of the catalytic block (option 5).

The technology corresponded to that given in Example 6, differing only in that in the manufacture of the precursor, the oxidation of aluminum in the vapor phase was carried out at a temperature of 300 ° C and a pressure of 32 MPa, which led to the formation of an intermediate layer with a mixed structure of bayerite and boehmite (5 ', Fig. 8). Example 11. The manufacturing technology of the catalytic block (option 6).

The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, 0.2% cerium (6 ', Fig. 8). Example 12. The manufacturing technology of the catalytic block (option 7).

The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, 0.1% ruthenium (7 ', Fig. 8).

Example 13. The manufacturing technology of the catalytic block (option 8). The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, about 0.1% sodium (8 ', Fig. 8).

On l'-8 ', Fig. 8 presents the test results of samples (catalytic blocks) after various options for their manufacture and heat treatment.

Claims

CLAIM

1. A method of producing a catalytic material by thermal spraying of aluminum, aluminum oxide, aluminum hydroxide and hydrotalcite, characterized in that said materials are formed before spraying in the form of a composite powder, in which aluminum particles play the role of a core on which an intermediate layer of aluminum hydroxide is successively formed and surface layer of hydrotalcite.

2. The method according to p. 1, characterized in that the core of the particles of the composite powder is a particle of aluminum powder fraction 20-100 microns.

3. The method according to p. 1, characterized in that the intermediate layer of aluminum hydroxide is formed in the process of vapor-air oxidation of aluminum powder.

4. The method according to p. 1 and 3, characterized in that the intermediate layer of aluminum hydroxide is gibbsite.

5. The method according to p. 1 and 3, characterized in that the intermediate layer of aluminum hydroxide is bayerite.

6. The method according to p. 1 and 3, characterized in that the intermediate layer of aluminum hydroxide is boehmite.

7. The method according to p. 1 and 3, characterized in that the intermediate layer of aluminum hydroxide is a mixture of bayerite and boehmite.

8. The method according to p. 1 and 3, characterized in that the intermediate hydroxide layer has a thickness in the range of 0.01 - OD D, where D is the diameter of the aluminum core.

9. The method according to p. 1 and 3, characterized in that the surface layer of hydrotalcite is formed during its deposition on the surface of the intermediate hydroxide layer.

10. The method according to p. 1, 3 and 9, characterized in that the deposited hydrotalcite layer has a composition corresponding to the empirical formula XMgCoAl, where X is a metal or a combination of the following metals: cerium, ruthenium, vanadium and / or sodium; Mg is magnesium, Co is cobalt, and Al is aluminum.

11. The method according to p. 1 to 10, characterized in that the catalyst obtained after the decomposition of the deposited layer of hydrotalcite is active in the reaction of reduction of nitrogen oxides, which is a consequence of the presence of cerium, ruthenium, vanadium and / or sodium in the form of oxides and the consequence of the presence of Mg / Al / Co in the form of mixed oxides obtained by the decomposition of hydrotalcite.

12. The method according to p. 1 - 11, characterized in that cerium, ruthenium, vanadium and / or sodium are introduced into the Mg / Al / Co mixed oxides obtained by decomposition of the deposited hydrotalcite layer by impregnation and calcination of the catalyst at temperatures in the range of 350 - 800 ⁰ C for 1-20 hours.

13. The method according to p. 1 - 12, characterized in that Mg / Al / Co mixed oxides obtained by decomposition of hydrotalcite contain Al in the range of 5-50%, and the total content of Mg and Co is in the range of 50-95%.

14. The method according to p. 1 - 13, characterized in that for the introduction of cerium, ruthenium, vanadium and / or sodium, which by impregnation are introduced into the mixed oxides obtained by decomposition of hydrotalcite, aqueous solutions of salts are used, the concentration of these metals in the finished catalyst is in the range of 0.1-30%, mainly in the range of 1-20%.

15. The method according to p. 1 - 14, characterized in that the catalyst obtained by the decomposition of hydrotalcite is active in the removal of nitrogen oxides in the temperature range of 100 - 500 ° C in the presence of oxygen, water and sulfur oxide.

16. The method according to p. 1 - 15, characterized in that it is active in the oxidation reactions of carbon-containing compounds.