RU2640412C1 - Method of applying catalytic coating on ceramic neutralizer unit of internal combustion engine worked gases - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves forming a substrate of γalumina with a high specific surface area on the surface of a ceramic carrier by immersion in an aqueous suspension containing aluminium hydroxide (boehmite) and aluminium nitrate, followed by drying and heat treatment at 500-550°C, applying a catalytically active coating on the formed substrate from a solution of metal salts of variable valence in an organic solvent, drying and heat treating. The suspension for depositing the substrate further comprises aluminium hydroxide. The catalytically active coating is applied from a solution of the mixed copper salt of lower carboxylic acids, and the amount of solution necessary for a single application of the catalytic coating is evaluated in advance, the drying of the applied coating to a constant weight is carried out at 110-115°C, and its subsequent heat treatment is carried out in a current of air at a temperature of 500-600°C for 60-80 minutes.

EFFECT: reducing the energy intensity of the method and reducing the time required for its implementation while ensuring efficiency.

4 cl, 2 dwg, 1 tbl, 2 ex

Description

The invention relates to the field of catalysis and can be used to reduce the harmfulness of exhaust gases of internal combustion engines by cleaning and neutralizing them.

In most countries, the requirements for the toxicity of exhaust gases are tightened every year and new standards are introduced, which makes catalytic converters of exhaust gases an increasingly important element in the engine and car. The catalytic oxidation of products of incomplete combustion and the catalytic reduction of nitrogen oxides currently remains the main way to neutralize exhaust gases of internal combustion engines (ICE), while the requirements for the catalytic converters themselves, their physical and chemical properties are also increasing.

One of the main factors of catalyst efficiency along with the composition and quality of the working layer is the developed structure of its substrate. However, metallic supports made of fechral smooth and corrugated foil, and ceramic ones made of cordierite or mullite ceramics, have an underdeveloped surface. On ceramic carriers, to increase it, a substrate layer with a developed structure and open pores is formed from materials with a high specific surface.

A known method of preparing a catalyst for purification of exhaust gases of internal combustion engines (RU 2190470, publ. 2002.06.10), comprising applying to a ceramic carrier layer of aluminum hydroxide at a temperature of 20-25 ° C in an aqueous solution of potassium hydroxide when dissolving aluminum metal powder in it, forming alumina layer by thermal dehydration of aluminum hydroxide; the introduction of substances, thermostabilizing alumina, impregnation with aqueous solutions of salts of cerium, platinum, rhodium, drying and restoration in an aqueous solution of sodium borohydride. The disadvantages of the method are the duration and multi-stage. In addition, long exposure of the carrier, for example, from cordierite in a solution of potassium hydroxide leads to swelling of the ceramics and its cracking during heat treatment, which does not allow to achieve high quality of the catalyst.

A known method of preparing a catalyst for purification of exhaust gases of internal combustion engines (RU 2275962, publ. 2006.05.20), comprising pre-calcining an inert honeycomb block carrier with simultaneous application of an intermediate coating of modified alumina and the active phase of one or more platinum metals on its surface groups from a water-alcohol suspension containing the following components, wt. %: boehmite 15-30, aluminum nitrate 1-2, cerium nitrate 4-8, 25% solution of ammonium hydroxide 10-20, one or more inorganic salts of platinum group metals, in terms of metals - 0.020-0.052, water-alcohol in mass ratio of 1: 5-1: 10 - the rest, drying and recovery. According to the known method, the coating is carried out from a suspension containing boehmite with an initial specific surface area of at least 300-350 m ² / g, while in one of its embodiments, a block ceramic carrier selected from the group consisting of cordierite, hematite, is used as a carrier, rutile, silicon carbide, and calcination is carried out at a temperature of 500-1000 ° C. However, a highly efficient catalyst obtained by a known method has a high cost; in addition, it detects an insufficient service life when using domestic fuels due to the instability of noble metals to catalytic poisons (sulfur, lead, iron compounds) and the tendency to intense burning when combustible substances reach the catalyst surface above normal , which greatly limits its use.

Closest to the claimed is a method for producing nanostructured catalytic coatings on ceramic supports for neutralizing exhaust gases of internal combustion engines (RU 2515727, publ. 2014.05.20), according to which ceramic supports are calcined for two hours in a muffle furnace at a temperature of 400-600 ° C for cleaning from organics, after cooling, they are immersed in a 4-5% suspension of aluminum oxide-hydroxide (boehmite) with a high-temperature binder - 1-3% aluminum nitrate, then, after drying, the coatings are calcined for 6 hours in a muffle second oven at a temperature of 500-550 ° C. A block with a formed substrate is immersed in a solution of metal salts of variable valency (nitric copper, cobalt nitrate) in a mixture of organic solvents with a suspension of titanium dioxide and boehmite, after extraction, the excess solution is removed by blowing air or centrifugation, dried with a stepwise rise in temperature from 50 to 120 ° C and heat treated at 600-650 ° C for 240 min to convert metal salts to oxides.

The known method requires a number of energy-intensive auxiliary operations, while it provides a catalytic coating that is designed to neutralize the exhaust gases of diesel engines and is effective, in particular, for automotive diesel engines.

The objective of the invention is to provide a method of manufacturing a highly efficient catalytic converter of the exhaust gas of a gasoline internal combustion engine.

The technical result of the method consists in reducing the energy intensity of the method and reducing the time for its implementation while ensuring the effectiveness of the converter when cleaning the exhaust gases of gasoline engines.

The specified technical result is achieved by the method of producing catalytic coatings on ceramic supports for neutralizing exhaust gases of internal combustion engines, comprising forming on the surface of the ceramic support a substrate of γ-alumina with a high specific surface by immersion in an aqueous suspension containing aluminum oxide-hydroxide (boehmite) and aluminum nitrate, followed by drying and heat treatment at 500-550 ° C, application of a catalytically active coating on the formed substrate Existence from a solution of metal salts of variable valency in an organic solvent, drying and heat treatment, according to which, in contrast to the known one, the suspension for coating the substrate additionally contains aluminum hydroxide, a catalytically active coating is applied from a solution of a mixed copper salt of lower carboxylic acids, while previously experimentally estimate the amount of solution required for a single application of a catalytically active coating, drying the applied coating to a constant wire weight out at 110-115 ° C, and its subsequent heat treatment is carried out in air at a temperature of 500-600 ° C for 60-80 minutes.

In an advantageous embodiment of the method, the catalytic coating is applied from a solution in an organic solvent of a mixed copper salt of two low molecular weight short-chain carboxylic acids selected from the group consisting of butyric C ₃ H ₇ COOH, formic HCOOH, valerianic C ₄ H ₉ COOH acid, in a concentration providing a copper content of 20-60 g / l in terms of metal.

The substrate containing γ-alumina is formed from a suspension containing, g / l: aluminum hydroxide - 10-20, aluminum hydroxide oxide - 100-200, aluminum nitrate - 5-10.

Optimal is the double deposition of a catalytic coating from a solution of a mixed copper salt of two carboxylic acids, followed by drying and heat treatment, which provides the maximum value of the conversion of CO and CH.

The method is as follows.

A modified aluminum oxide substrate with a high specific surface, which is formed from an aqueous suspension containing aluminum hydroxide and aluminum hydroxide oxide (boehmite), as well as aluminum nitrate (high temperature binder) at the stated content of components, is applied to the cordierite block of the exhaust gas neutralizer of the internal combustion engine.

The suspension impregnated block is dried at a temperature of 110-115 ° C for 30-40 minutes, then calcined at 500-550 ° C for 100-150 minutes.

Divalent copper oxide, which is a catalytically active component, is applied from a solution containing its precursor - a mixed copper salt of two carboxylic acids: butyric C ₃ H ₇ COOH and formic HCOOH or valerian C ₄ H ₉ COOH and formic in an organic solvent, mainly in benzene n-butanol.

The impregnation of the block with the above solution is as follows:

- the unit is installed in the nozzle-clamp made of low-pressure polyethylene and placed in an airtight container equipped with a flexible hose with a shut-off valve connected to the second container;

- the calculated volume of the solution of a given concentration is poured into the second container and the hose is lowered into it;

- in a sealed container with a block create a vacuum, as a result of which the solution from the second tank fills all the channels and voids of the block;

- after a short (3-5 min) exposure, the vacuum is removed, the solution is drained and the block is purged.

The amount of solution required for a single impregnation of the block is pre-set using the control impregnation of the block, carried out as described above, while a measured amount of solution is poured into the second container, and the volume of solution absorbed by the block is calculated by the amount of solution remaining after impregnation.

A solution of a catalytically active copper oxide precursor is used - a mixed organic salt of divalent copper with a content providing a copper concentration of 20-60 g / l in terms of metal, and in each case this content is adjusted taking into account the amount of solution required for impregnation of the cordierite block. The impregnation of the block with a solution introducing the calculated amount of the catalytically active component ensures optimal and stable efficiency of the catalytically active layer of the exhaust gas neutralizer.

After impregnation, the cordierite block is dried under an extract in air at ordinary temperature, and then in a drying cabinet at a temperature of 110-150 ° C to constant weight.

The dried block is annealed at a temperature of 500-600 ° C for 60-80 minutes in an air stream, which ensures the conversion of the organic copper salt into oxide and the removal of organic radicals and solvent residues.

If necessary, to verify the correctness of the calculation of the applied amount of the active component, a control weighing of the block is carried out and an increase in its mass is determined.

Examples of specific implementation of the method

The effectiveness of the obtained catalysts was checked in accordance with GOST R52033-2003 “Cars with gasoline engines. Emissions of pollutants with exhaust gases ”by measuring the toxicity of exhaust gases at a reduced crankshaft speed (850 rpm) and increased (2200, 2500, 3000 rpm).

During the tests used "Engine exhaust gas neutralizer" with a detachable housing (patent RU 130629 for utility model, publ. 2013.07.27), designed for research.

The conversion activity of CO and CH cordierite neutralizers with the resulting coating was evaluated on a bench represented by a 110 hp four-cylinder gasoline engine. at 6000 rpm ^-1 , with a torque of 145 Nm at 4800 rpm.

To study the composition of the obtained coating, an AVG-4 gas analyzer was used, designed to measure the volume fraction of carbon monoxide CO, total hydrocarbons CH, carbon dioxide CO ₂ , oxygen O ₂ in the exhaust gases of cars with gasoline engines.

Example 1

Cordierite block with a total volume of 291.4 cm ³ with a γ-alumina substrate deposited from a suspension containing, g / l: aluminum hydroxide 20, aluminum hydroxide (boehmite) 100, aluminum nitrate 5. Drying 30 min, calcining 100 min at 500 ° C. Catalytically active coating once. As previously established, for complete impregnation of the cordierite block, uniform filling of all its channels and impregnation of the substrate, 250 ml of solution is sufficient. A solution of copper formbutyrate (a mixed salt of butyric and formic acid) with a content of 125 g of salt per 1 liter of n-butanol was used. Calcination is carried out at 500 ° C for 80 minutes

Example 2

Substrate applied from a suspension containing, g / l: aluminum hydroxide 10, boehmite 200, aluminum nitrate 10. Drying 40 min, calcination at 550 ° C for 2.5 hours. The results of the preliminary impregnation, as in example 1, is 250 ml. Double application of a catalytically active coating. A solution of copper formvalerate (a mixed salt of valerianic and formic acid) in benzene with a content of 199 g of salt per 1 liter of benzene was used. Calcination at 600 ° C for 60 minutes

The test results of the coated catalyst obtained in example 2 are presented in the form of diagrams of changes in the content of CO (Fig. 1) and CH (Fig. 2) in the exhaust gases.

Symbols on the diagrams: empty - block without catalytic coating; Cu 2.2 - block with a catalytic coating (double application) according to example 2.

The effectiveness of the resulting coatings was also evaluated by the magnitude of the conversion of CO and CH.

The results of using a catalyst with catalytic coatings deposited by the proposed method according to examples 1 and 2, with different (underestimated and overstated) the number of revolutions of the crankshaft are presented in table form.

The data in the table are the average of the sum of 6 experiments conducted with a time interval of 10 minutes.

The results show that with an increase in the number of revolutions of the engine crankshaft and, consequently, with an increase in the flow of exhaust gases, the degree of conversion remains practically unchanged. The catalyst with a catalytic coating deposited by the proposed method has a significant service life.

Claims (4)

1. A method of producing catalytic coatings on ceramic supports for neutralizing exhaust gases of internal combustion engines, comprising forming a γ-alumina substrate with a high specific surface on the surface of the ceramic support by immersion in an aqueous suspension containing aluminum oxide-hydroxide (boehmite) and aluminum nitrate , followed by drying and heat treatment at 500-550 ° C, applying a catalytically active coating from a solution of variable metal salts to the formed substrate valencies in an organic solvent, drying and heat treatment, characterized in that the suspension for applying a substrate additionally contains aluminum hydroxide, a catalytically active coating is applied from a solution of a mixed copper salt of lower carboxylic acids, while the amount of solution required for a single application of a catalytic coating is previously estimated experimentally drying the coating to a constant weight is carried out at 110-115 ° C, and its subsequent heat treatment is carried out in a current of air and at a temperature of 500-600 ° C for 60-80 minutes. 2. The method according to p. 1, characterized in that the catalytically active coating is applied from a solution in an organic solvent of a mixed copper salt of two low molecular weight short-chain carboxylic acids selected from the group consisting of butyric C ₃ H ₇ COOH, formic HCOOH, valerian C ₄ H ₉ COOH acid, the concentration of which provides a copper content of 20-60 g / l in terms of metal. 3. The method according to p. 1, characterized in that the substrate containing γ-alumina is formed from a suspension containing, g / l: aluminum hydroxide - 10-20, aluminum hydroxide oxide - 100-200, aluminum nitrate - 5- 10. 4. The method according to p. 1, characterized in that the deposition of a catalytically active coating with drying and heat treatment is carried out twice.

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