LT4869B - METHOD OF RECOVERY OF COMPOSITE CATALYTIC COATINGS - Google Patents

Abstract

The invention is in the field of a manufacturing method for compositional catalytic surfaces, when the surface is formed by spraying a molten substance and can be used in various fields - chemical industry, energetics, ecology and other spheres for different catalytic elements, that would enable the chemical industry, metallurgy, thermal power plants, gas pumping stations, internal combustion engines, diesel and stationary power plants to neutralise their exhaust gases. The composite catalytic surface is made by plasmic spraying of the powder mix at the component ratio in mass percentage: metal aluminium and/or titanium 1-7, aluminium and/or titanium oxides 0.1-12, transition metal oxides 1-30, aluminium and/or titanium hydroxide - the remaining amount. Vanadium, chromium, molybdenum, wolfram, manganese, iron, cobalt, nickel and copper oxides are used as transition metal oxides here. The dispersion of the new powder mix is not less than 100 microns. The invention makes it possible to obtain surfaces with good catalytic properties - full conversion of carbon dioxide takes place at not more than 300 degrees C, and the catalyst burning point - the activity indictor of the catalyst - is in the range of 150-180 degrees C.

Description

The method of obtaining a composite catalytic coating is realized by the method of plasma spraying of a powder mixture onto a substrate, with the following composition of components, % by mass:

metallic aluminum and/or titanium 1-7 aluminum and/or titanium oxides 0.1-12 transition metal oxides 1-30 aluminum and/or titanium hydroxides remainder

The oxides used as transition metal oxides are vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper. The powder dispersion of the resulting mixture is at least 100 microns.

The invention allows obtaining coatings on a solid substrate with good catalytic properties - the temperature of complete conversion of carbon monoxide does not exceed 300 °C, and the catalyst ignition temperature, which can be read as a characteristic of the catalyst activity, is within 150-180 °C.

The invention relates to methods for producing composite catalytic coatings, where the coating is formed by spraying molten materials onto a substrate, and can be used in various areas of the chemical industry, energy, ecology, etc. for various types of catalytic elements that would ensure the neutralization of exhaust gas components from the chemical and metallurgical industries, thermal power plants, gas pumping stations, as well as from internal combustion engines and diesel engines of motor vehicles and stationary energy installations.

There are known methods for obtaining coatings on a metal or ceramic substrate by the gas thermal spraying method using compositions based on aluminum compounds. Aluminum oxide is most widely used as a powder for spraying composite coatings on an aluminum basis (see Metallic and Ceramic Coatings. Production, High Temperature Properties and Application. M.G.Hocking, V.Vasantasree and P.S.Sidky. Materials Department, Imperial College, 1990, London.).

A known method of forming coatings (see former USSR author's certificate No. 2026890, TPK C 25 D, 1992) involves applying to the base a sublayer of a molten Zn - Cu - Al - B alloy, then a main layer based on aluminum compounds containing Al, Cu, Mg, Mn, which is then oxidized by micro-arc in an alkaline electrolyte.

The above methods are quite complex, requiring a lot of labor and additional labor-intensive operations: undercoating, oxidation, or constant control of the substrate and coating temperature.

A known method for obtaining a multilayer coating (see former USSR patent No. 2049827, TPK C 23 C 4/00, 1995) involves spraying a layer in an environment of inert gas with the addition of dissociated hydrogen. In this case, composite Al - Ni powders are sprayed as a sublayer, which form hydrated forms of aluminum oxides in an environment of inert gas with the addition of hydrogen ions. The main layer is sprayed using composite powders or mixtures thereof based on aluminum or nickel and a chemically inert additive with a layered structure, such as boron nitride or carbon. The layer obtained in this way contains aluminum, hydrated forms of aluminum hydroxide (such as gibbsite and/or boehmite) and boron nitride or carbon additives. The latter are solid lubricants and ensure wear resistance.

The disadvantages of this method are that the resulting coating is quite expensive due to the large number of intermediate operations and expensive materials used for spraying, such as aluminum nickel powder. In addition, the coating does not have a sufficiently high wear resistance and porosity, which makes it unsuitable for use as a base for impregnation with various mixtures, i.e. non-universal.

The closest known (prototype) method for obtaining composite coatings (see Patent of the Republic of Lithuania No. 4456, TPK C 23 C 4/00, 1997), in which a porous coating containing a metal oxide and a metal binder is applied to the initial substrate by plasma spraying, in addition, as the initial material for plasma spraying, a powder mixture containing aluminum and/or titanium oxides, aluminum and/or titanium hydroxides is used, as a material forming the macrostructure of the coating, glass powder as a material ensuring the formation of the microstructure of the coating, and metallic aluminum and/or titanium as a metal bond, with the following composition of components, % by weight:

metallic aluminum and/or titanium 1-7 aluminum and/or titanium oxides 0.1-12 glass powder 2-45 aluminum and/or titanium hydroxides remaining quantity The dispersibility of the powder must be: aluminum and titanium oxides less than 30 pm aluminum and titanium hydroxides less than 8 pm glass powder less than 30 pm aluminum and titanium less than 50 pm

The disadvantages of this method are that although the coating produced by this method has sufficiently high adhesion resistance characteristics of the sprayed layer to the substrate, a homogeneous phase composition and a large free surface after heat treatment, the catalytic properties are very insignificant.

The aim of this invention is to obtain a catalytic layer on a solid substrate with pronounced catalytic properties.

The aim is achieved by mixing transition metal oxide powders (vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper) individually or in a mixture in the following composition of components, % by weight:

metallic aluminum and/or titanium 1 - 7 aluminum and/or titanium oxides 0.1-12 transition metal oxides 1 - 30 aluminum and/or titanium hydroxides remainder

From the description of the prototype, we see that the coating obtained using this technology can be further used for anti-corrosion coatings based on metal and polymers, anti-friction coatings, for applying varnish and paint coatings, and coatings with special properties, including coatings with catalytic properties.

This coating may indeed have some catalytic properties, since, after thermal treatment, the decomposition of sprayed aluminum and titanium hydroxides should form γ-modified aluminum oxides and anatase-modified titanium oxides, which have some catalytic properties in the oxidation and reduction reactions of exhaust gas components, such as carbon monoxide. However, the catalytic activity of the aforementioned oxides is usually so low that they are never used as a catalyst, but are practically always used as a catalytic carrier on which the catalyst is deposited in various ways. The most commonly used methods are impregnation with various salts, with subsequent drying and thermal decomposition of the salts, sol-gel methods, chemical vapor deposition methods, magnetron or ion plasma spraying, and other methods.

Catalysts are usually noble metals - platinum, palladium, rhodium, sometimes gold or silver, or metal oxides - oxides of iron, copper, nickel, cobalt, vanadium, tungsten, etc.

Catalysts in the form of metal oxides are widely used in various chemical industry processes, as well as for the decontamination of exhaust gases. Ceramic carriers based on complex oxides of the spinel, zeolite or other types are usually used as catalytic carriers. In addition, they usually contain aluminum oxide.

For example, a catalyst for the methanol synthesis process is known (see US Patent No. 5,767,039, TPK B 01 J 23/06, B 01 J 23/72, 1998 06 16). This synthetic catalyst based on aluminum, copper and zinc oxides is obtained by mixing copper and zinc with their subsequent precipitation together with aluminum from its salts.

A complex catalyst for neutralizing nitrogen oxides is also known (see US Patent No. 5,776,426, TPK C 01 F 1/00, B 01 D 11/00, 1998 07 07). It is a zeolite-type catalytic carrier with embedded active centers based on copper, cobalt and iron ions. The catalytic material contains 2 - 8% copper, 1 - 4% iron and 0.25 - 4% cobalt.

A catalyst for the production of methyl ethyl ketone based on copper and silicon oxides is also known (see US Patent No. 5,723,679, TPK C 07 C 45/00, 1998 03 03).

For the single-step reduction of copper oxides and oxidation of hydrocarbons, a catalyst made of spinel (a complex oxide based on alumina) containing copper and zinc ions is used (see US patent No. 5,750,460, TPK B 01 J 23/06, B 01 J 21/04, B 01 J 23/72, 1998 05 12).

Thus, in order to obtain a catalytic coating with high catalytic properties, a thin, as a rule, monomolecular layer of catalyst must be applied to the coating obtained according to the technology described in the prototype.

However, as studies have shown, the catalyst can be introduced into the catalytic layer and the catalyst carrier during the plasma spraying stage. In this case, one of the components of the sprayed composition, namely the hydroxide, is mixed with dispersed transition metal oxide powders (vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper) individually or in a mixture thereof.

The method is implemented as follows:

The composite coating is sprayed onto a solid metal or ceramic substrate. A powder composition based on aluminum hydroxide was used with the following composition of components, % by weight:

metallic aluminum and/or titanium aluminum and/or titanium oxide

1-7 0.1 -12 transition metal oxides 1 - 30 aluminum and/or titanium oxide remaining amount

Before spraying, the powder composition is activated in a ball mill according to a special mode, during which, due to the adhesion of aluminum hydroxide particles to oxide particles, a dispersed (at least 100 mp) composite powder is obtained, in which fine oxide particles are arranged on the surface of sufficiently large hydroxide particles.

Example.

The composite coating was sprayed onto a 40 micron thick steel substrate. An aluminum hydroxide-based powder composition was used with the following composition, % by weight:

aluminum metal - 6 vanadium oxide - 2 chromium oxide - 4 molybdenum oxide - 3 tungsten oxide - 3 aluminum hydroxide - remaining amount

For spraying, a PN-V1 plasmatron with a separate supply of powder components and an APR-403 current source were used. Atmospheric air was used as the plasma-forming gas. Spraying process parameters: voltage - 200V, current -170 A, nozzle cut distance from the base - lOOmm.

The thickness of the applied coating was 20-30 microns.

The resulting coating was thermally treated in a SNOL-type furnace at 560°C for 2 hours, and cooled in air.

Other examples of the method and the characteristics of the resulting coating are given in Tables 1 and 2.

The main operating characteristics of the catalyst are the catalyst ignition temperature and the carbon monoxide (CO) complete conversion temperature.

The main reaction used to determine the characteristics of a catalyst is the oxidation of carbon monoxide (CO) by oxygen (O2) to carbon monoxide (CO2). The ignition temperature of the catalyst is the temperature at which 50% of carbon monoxide (CO) is oxidized to carbon monoxide (CO2). The complete conversion temperature is the temperature at which 100% of carbon monoxide (CO) is oxidized to carbon monoxide (CO2). These characteristics can be determined by laboratory and bench tests. In our case, the characteristics were determined by bench tests.

Table 2 shows the test results of catalytic coatings containing various amounts of transition metal oxides in the carbon monoxide oxidation reaction.

The table shows that the use of transition metal oxides as catalysts is quite effective - the temperature of complete conversion of carbon monoxide does not exceed 300° C, and the catalyst ignition temperature, which can be read as a characteristic of the catalyst activity, is within 150 - 180° C (in the prototype - at least 250° C).

In addition, Table 2 shows that using a complex mixture of transition metal oxides increases the activity of the catalyst, which is evident from Examples 4, 5 and 6.

The high dispersity of the powder mixture used in the new invention (at least 100 microns) increases the powder utilization rate, while making its use much more economical.

*Table 7

Copper oxide, % by mass 1 o 1 m Ό cn Oh Nickel oxide, % by mass 1 cu 00 cu CU cu 1 Cobalt oxide, wt% 1 cn cu Iron oxide, mass % 1 00 00 1 cu there Manganese oxide, wt% t 1 v© Ό 1 1 1 Tungsten oxide, % by weight CO 1 1 m m cn o Molybdenum oxide, % by mass m 1 1 m m cn WHO Chromium oxide, mass % cu 1 1 cu 1 Vanadium oxide mass % CU 1 1 1 cu cu Aluminum hydroxide, wt% remaining quantity remaining quantity remaining quantity remaining quantity Remaining quantity remaining quantity remaining quantity Aluminum, mass % m ΙΛ o ,Λ .Λ &, N O ·£, - cu m Γ'-

CO complete conversion temperature °C 300 | 280 | 300 o o cu 260 260 290 Ignition temperature °C 081 1,170 | 170 o vO 165 150 180 Position from Table 1 - cu cn and o r-

Claims (3)

DEFINITION OF INVENTION 1. A process for the preparation of a composite catalytic coating comprising the step of depositing a porous coating of aluminum and / or titanium, aluminum and / or titanium oxides and aluminum and / or titanium hydroxides on a substrate by a plasma spraying process, characterized in that transition metal oxides are added to the powder composition. powder as a substance with catalytic properties at the following weight percentages: Aluminum and / or titanium metal 1 - 7 Oxides of aluminum and / or titanium 0,1-12 Oxides of transition metal 1 - 30 Hydroxides of aluminum and / or titanium Process for the preparation of a composite catalytic coating according to claim 1, characterized in that vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper are used as transition metal oxides. 3. A process for the preparation of a composite catalytic coating according to claims 1 and 2, wherein the resulting mixture has a powder dispersion of at least 100 microns.