A method of obtaining a catalytically active oxide layer and a catalytically active material obtained by this method

 

(57) Abstract:

The invention relates to catalytic chemistry, namely a process for the production of catalytically active layers, and receive carriers of catalysts that can be used for deep oxidation of organic compounds and carbon monoxide in the exhaust gas chemistry, petrochemistry and internal combustion engines. Describes how to obtain a catalytically active oxide layers on a substrate made of a valve metal or its alloy mainly made of aluminum, by oxidation treatment of the substrate in the electrolyte. As the oxidation treatment using the process of the microarc oxidation in alkaline electrolyte with the addition of ultra-fine powders of metal oxides and transition metal salts. Obtained in this way the material has a high developed surface due to the resulting structure of oxide layers, as well as considerable heat resistance and wear resistance. 2 s and 5 C.p. f-crystals, 2 Il.

The invention relates to catalytic chemistry, namely a process for the production of catalytically active layers, and receive carriers of catalysts that can be used for GH internal combustion engines.

The known method [SU 1034762 A, 1983] preparation of a carrier for catalyst for oxidation of carbon monoxide by the manufacture of aluminum system in the form of two tape folding them and the subsequent anodizing. Anodizing is carried out in a 10% solution of oxalic acid at 20oC, current density of 5 A/DM2within 1.5 hours of the Proposed method of anodizing receive oxide layers with a thickness of 100 μm which does not have sufficient specific surface area.

The known method [SU 733717 A, 1980] preparation of the catalyst for purification of exhaust gases with increased activity and mechanical strength. In this method before applying the catalytically active layer anodize titanium plate in solutions of hydrochloric and sulfuric acids. This method allows you to obtain an oxide, a porous layer only on Titan.

As a prototype of the selected method of forming a porous oxide layer on the surface of the monolithic catalytic Converter is made of aluminum, by oxidation of the surface of the product in the electrolyte used for the subsequent deposition of the catalytically active components. Oxidative processes are conducted by passing a constant current density 96,2 a/m2when strain.

The obtained oxide layer has a negligible thickness (2-10 µm), low wear resistance and heat resistance, specific surface area of the obtained porous oxide layer is 30-150 m2/,

Also known catalyst, which consists of a layer of aluminum oxide with a specific surface area of 100-300 m2/g, formed on the surface of aluminum. On the surface of the first layer formed of the second layer of aluminum oxide with a specific surface area of 10-50 m2/g, which cause the catalytically active layer containing platinum, palladium and/or rhodium [JP N 3-49614 A, 1991].

Also known application of Japan [JP N 3-52556 A, 1991], which describes a substrate of aluminum or aluminum alloy. On the surface of the substrate formed by coating consisting of a contiguous surfaces of the barrier layer and the layer with needle structure. The holes in the porous layer are communicated with the external environment through the holes of the outer layer. The material is used as the sorbent.

The basis of the invention is to develop a method of obtaining a porous catalytically active oxide layers of considerable thickness, having wear resistance and heat resistance, as well as material made of vigodniy for use as a catalyst carrier.

The problem is solved in that, as in the known method, to obtain an oxide layer uses a process called oxidative treatment in the electrolyte is non-porous substrate made of a valve metal or its alloy, predominantly from aluminium.

What's new is that as the oxidation treatment using the process of the microarc oxidation in alkaline electrolyte with the addition of ultra-fine powders of oxides of aluminum and/or zirconium and transition metal salts selected from the group comprising Mn, Cr,Cu, Co, Fe or mixtures thereof.

In addition, the process of microarc oxidation in alkaline electrolyte with the addition of ultra-fine powder of aluminum oxide and/or zirconium and transition metal salts or mixtures thereof are in anode mode, when the pulse frequency 50 Hz, pulse duration 50-300 μs, the current density 10-120 A/DM2, voltage 200 - 520, for 1200-2400 C.

In addition, as the alkaline electrolyte is used an aqueous solution containing silicates, alkali metal hydroxide with the addition of ultra-fine powders of aluminum oxide and/or zirconium and transition metal salts or mixtures thereof, in the following ratio of components, g/l:

deposits and/or zirconium - 20-60

Salts of transition metals or mixtures thereof is 0.5 - 15

In addition, as ultra-fine powder of metal oxides using ultra-fine powders of aluminum oxide or zirconium oxide with a specific surface area not less than 100 m2/,

In addition, as the transition metal salts are used, for example, cobalt nitrate, chromate, potassium or sodium, potassium permanganate, ammoniagenes digitaltruth citrate hydrate or a mixture thereof.

In addition, the processed material from a valve metal or its alloy mainly made of aluminum, may have an initial oxide layer thickness of not less than 50 μm.

Obtained by this method of catalytically active material is made of at least one metal containing aluminum or its alloys with oxide, a porous film on its surface, which consists of at least two layers. The inner layer consists of two parts: the outer part, representing the aluminum oxide of a thickness of 10-20 μm, the inner part of the boundary: the oxide-metal thickness of 200 microns. The outer layer has a high specific surface area due to the resulting needle-like structure and contains transition metals, selected from the group including the ECC formation of oxide coatings on the surface of products, made of valve metals and their alloys, with the aim of protecting these products from wear, dermonecrotic, corrosion. In the proposed method the method used for coating on the surface of valve metals catalytically active porous oxide coatings, which can also serve as carriers for catalytically active layer applied is known in catalysis methods from solutions containing salts of metals from group VIII. The feature of the microarc oxidation is that in the same process on the metal anode is synthesized material, the components of which are components of the processed metal and the electrolyte, and processing of the resulting coating electrical discharges. The temperature in the discharge zone can reach 2000oC, under the action of high temperatures, the coating is formed of the components of the electrolyte ions and metal base, with the formation of oxygen-containing compounds (oxides, spinels). Therefore, by varying the electrolyte composition and processing conditions, it is possible to obtain coverage with the required properties. To obtain coverage in accordance with the task - thick, heat-resistant, wear-resistant, high is Ergani silicate is less than 20 g/l in solution, containing ultra-fine powders and salts of transition metals decreases the intensity of microarc process that affects the quality of the coating. The increase in the concentration of silicate is more than 50 g/l contributes to the formation of the coating, which dramatically reduced the content of transition metals and oxides of metals, at any concentration in solutions of salts of transition metals and oxides of metals and increases the content of silicon oxide to 90%. This reduces the catalytic activity of the coating and impairs their physical and mechanical properties. Introduction in the electrolyte salts of transition metals leads to the fact that in the process of deposition on the surface of the formed oxygen-containing compounds, providing a coating of catalytic activity. The content of transition metal salts in the solution is determined by the fact that at values of less than 0.5 g/l metal content in the coating on the level of impurities and is not observed its influence on the structure and catalytic properties of the coating. The increase in the concentration of more than 15 g/l begins to affect the stability of the flow microarc process, which affects the quality of the coating. It becomes loose and uneven. To ensure durability ZrO2), specific surface area which was 300 m2/, in Addition, the research found that the introduction into the electrolyte ultrafine powders with a developed surface leads to an increase in the content of oxygen-containing compounds in the coating. This is because the ions present in the solution, the charge present in solution the particles of the dispersed powders and transport them to the surface of the anode. Getting in the zone microarc discharge, the particles are embedded in the oxide barrier film. Under the influence of high temperatures (about 2000oC) they interact with the adsorbed ions. The concentration of the powders was 20-60 g/l Boundary concentrations are determined by the fact that at lower values does not increase the content of refractory oxides due to particles ultrafine powder, which affects the physico-mechanical properties of the coating. The increase in the concentration of more than 20 g/l leads to a decrease of the conductivity of the electrolyte. This affects the stability of the flow microarc processes on the electrode, and hence on the quality of the coating.

The invention is illustrated by the following graphic materials.

In Fig.1 shows fo the flanged portion of the inner layer, 2 - the outer layer of the coating.

In Fig. 2 shows a photograph illustrating the structure of the outer layer of the coating.

The formed coating is shown in Fig. 1, can be divided into two layers. The inner layer consists of two parts 1A and 1B, is formed within the first 0-300 with processing. Its first part (1A) is formed by oxidation of the metal with the formation of its oxide, the thickness of the layer is increased to 100-200 μm over the entire processing time of the sample due to the diffusion of oxygen into the metal. This reduces the conductivity of the metal and increases the electric field strength. Thus it creates the preconditions for the formation of the second part of the inner layer (16), which is formed from a metal oxide and the components of the electrolyte, the thickness of 10-20 μm, the time 300-600 C. the Formation of this layer leads to an increase of the voltage drop in the oxide, after which the electrical breakdown locally burn oxide layer. High temperature in the zone breakdown contribute to the synthesis of the outer coating layer 2, which together with the metal oxide substrate includes large quantities of groups of atoms or particles of the powders included in the composition of the electrolyte. The thickness of this layer coating composition is of metal in the coating is in the range 3-25% by weight of the total coating. The elemental composition of the coatings was determined by the method of electron microprobe analysis of the surface layers of the coating on the scanning electron microscope JSM - 84 with the prefix elemental analysis Link-860. The chemical composition of the surface layers of the samples was determined by three points located on the flat surface of the sample. The size of the analyzed area was approximately 3.5 mm2. It is established that the introduction of the electrolyte salts of transition metals in which the metal is present in the form of a cation or is included in an oxygen-containing anion, creates conditions for the formation of coatings with different structures. Thus, in the presence of metal cation (Co2+) formed a dense coating with minor porosity. The introduction of electrolyte compounds in which the metal is part of the oxygen-containing anion (CrO42-, MnO4-) leads to the formation of the coating, which has considerable porosity, which ensures an increase in its specific surface area. In addition, the content of transition metal in the coating is much larger (up to 25%) when it is part of the oxygen-containing anion, than when the metal in the electrolyte in the form of a cation (up to 5%).

Bure 610oC. To test the samples were heated at the above temperature for one hour, and then was rapidly cooled in water, the temperature of which was 20-30oC. Coating withstood 38-44 cycles without failure. In addition, tests showed that the coating can withstand heating at a temperature of 800oC for one hour and subsequent gradual cooling from 800 to 20oC. in Addition, examples of the coating obtained from an electrolyte containing salts of chromium, it has been experimentally established that the presence of ions of Cr6+in the resulting microarc oxidation coatings, provides the catalytic activity of the prepared products in the model reaction of methane oxidation, and the presence of porosity and the developed surface provided by the specific structure of the coating, capable of applying a surface coating of metals from the group VIII by known methods.

Example 1. The sample, made of aluminium alloy (Al-Cu-Mg) in the form of a cylinder with square 0,0003 DM2worked in the electrolyte containing Na2SiO3- 50 g/l, KOH - 2 g/l Al2O3(UDP)-20 g/l, Co(NO3)21 g/l Treatment was carried out in a pulsed mode with a pulse repetition rate of 50 Hz, UA= V square, the Affairs of 20-40oC. To maintain a stable temperature of the electrolyte was stirred, and used a bath with a cooling jacket. The resulting coating consists of two layers - an inner layer, the inner part of which is at the interface of the oxide-metal thickness of 200 μm, and the outer portion is 10 μm. The thickness of the second outer layer of 50 μm. It consists of components of the electrolyte, including aluminum - 13%, silicon - 38,61%, cobalt - 5%. Resistance to thermal shock - 40 cycles, when the heating of the samples at 610oC for 60 min and subsequent sudden cooling in water at a temperature of 20-40oC.

Example 2. The sample, made of the same material as in example 1 was treated in an electrolyte containing Na2SiO3- 50 g/l, KOH - 2 g/l Al2O3(UDP) -20 g/l, Na2CrO45 g/L. the processing Mode used is the same as in example 1. The resulting coating consists of an inner layer, the inner part of which is 200 μm. and the outer part is 20 μm. The thickness of the outer coating layer is 200 μm. In the coating composition includes: aluminum - 3,20%, silicon - 75,44%, chromium - 12%. Resistance to thermal shock - 40 cycles. Conditions of testing and research of the coating composition are the same as in example 1.

Example 3. The sample was processed in elec g/L. The processing mode is the same as in examples 1,2. The resulting coating consists of an inner layer, the inner part of which 190 μm, and the outer part 20 μm. The thickness of the outer coating layer 190 μm. In the coating composition aluminum - 4,1%, silicon 75%, zirconium 5,6% chrome - 14%. Resistance to thermal shock was 42 cycle. Conditions of testing and research of the coating composition are the same as in example 1.

Example 4. The sample was processed in the electrolyte, composed of: Na2SiO3- 50 g/l, KOH - 2 g/l Al2O3(UDP) - 20 g/l KMnO4to 1 g/L. the processing Mode is the same as in example 1. The resulting coating consists of an inner layer, the inner part of which 190 μm, and the outer part 10 μm. The thickness of the outer coating layer 110 μm. In the coating composition aluminum - 1,33%, silicon - 78,4%, Mn - 8,86%. Resistance to thermal shock 38 cycles. Conditions of testing and research of the coating composition are the same as in example 1.

Example 5. The sample was processed in the electrolyte, composed of: Na2SiO3- 50 g/l, KOH - 2 g/l Al2O3(UDP) - 20 g/l, 2C6H5O7FeC6H7NH4CO2+2H2O

The calculation of the conversion was carried out according to the formula

X% = (C1-C2/C1)100,

where X is the conversion of m is eakly was carried out at the temperature from 150 to 700oC and then when it drops from 700 to 150oC. the Investigated coating showed 50% conversion of CH4when the temperature is raised to 610oC and when the temperature was decreased to 520oC.

1. A method of obtaining a catalytically active oxide layers on a substrate made of a valve metal or its alloy mainly made of aluminum, by oxidation treatment of the substrate in the electrolyte, characterized in that the oxidation treatment using the process of the microarc oxidation in alkaline electrolyte with the addition of ultra-fine powders of oxides of aluminum and/or zirconium and transition metal salts selected from the group comprising Mn, Cr, Cu, Co, Fe or mixtures thereof.

2. The method according to p. 1, characterized in that the process of microarc oxidation in alkaline electrolyte with the addition of ultra-fine powder of aluminum oxide and/or zirconium and transition metal salts or mixtures thereof are in anode mode, when the pulse frequency 50 Hz, pulse duration of 50 to 300 μs, current density 10 - 120 A/DM2, voltage 200 - 520, for 1200 - 2400 S.

3. The method according to PP.1 and 2, characterized in that the alkaline electrolyte is used an aqueous solution containing silicates and perehodnik metals or mixtures thereof, in the following ratio of components, g/l:

The alkali metal silicate - 20 - 50

The alkali metal hydroxide - 1 - 2

Ultra-fine powder of aluminum oxide and/or zirconium - 20 - 60

Salts of transition metals or mixtures thereof is 1 to 10

4. The method according to p. 3, characterized in that the specific surface area of ultrafine powders of alumina and/or Zirconia is not less than 100 m2/,

5. The method according to p. 3, characterized in that as salts or their mixtures are used, for example, cobalt nitrate, chromate, potassium or sodium, ammoniacontaminated citrate hydrate or a mixture thereof.

6. The method according to p. 1, characterized in that the processed substrate made of valve metals or their alloys, predominantly of aluminum, may have an initial oxide layer thickness of not less than 50 μm.

7. The catalytically active material made of at least one metal containing aluminum or its alloys with a porous oxide film on its surface, which consists of at least two layers, wherein the inner layer consists of two parts: the outer part, representing the aluminum oxide with a thickness of 10 to 20 μm, the inner part at the interface of the oxide-mally, selected from the group comprising Mn, Cr, Cu, Co, Fe or mixtures thereof in the form of oxides.

 

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