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INVENTION
Russian Federation Patent RU2275962

METHOD FOR PREPARING CATALYST FOR TREATING EXHAUST internal combustion engine and the catalyst obtained in this way

Name of the inventor: Drobaha Elena A. (RU); Drobaha Gregory S. (RU); Solntsev Konstantin
The name of the patentee: Institute of Physical and Chemical Problems of Ceramic Materials, Russian Academy of Sciences (IPC RAS)
Address for correspondence: 119361, Moscow, ul. Ozernaya, 48, IPC RAS, Director K.A.Solntsevu
Starting date of the patent: 2004.12.09

The invention relates to a method of preparing the catalyst and the catalyst on the ceramic block and a metal honeycomb carrier for cleaning exhaust gases of internal combustion engines. Discloses a process for preparing a catalyst for purifying exhaust gases of internal combustion engines, comprising a preliminary calcination inert honeycomb block carrier, the simultaneous application to the surface of an intermediate coating of a modified aluminum oxide and the active phase of one or more platinum group metals from aqueous-alcoholic suspension containing the following components ., by mass% boehmite - 15-30, aluminum nitrate - 1.2, cerium nitrate - 4.8, 25% ammonium hydroxide solution - 10-20, one or more inorganic salts of metals of the platinum group metal, based on - 0,020-0,052, water-alcohol in a weight ratio of 1: 5-1: 10 - the rest, drying and reconstitution. And discloses a catalyst prepared by the above method, having the following characteristics: specific surface coatings - 100-200 m ² / g, the content of Al ₂ O ₃ - 5-13 wt%, CeO ₂ content - 0.5-1.3 wt. .% active phase based on platinum group metals - 0,12-0,26 wt% carrier -. the balance to 100 wt.%. Technical effect - the simplification of technology by reducing the number of process steps, the time of their implementation, to obtain a highly efficient catalyst.

DESCRIPTION OF THE INVENTION

The invention relates to methods of preparing catalysts and exhaust gas purification catalysts (exhaust gas) of the internal combustion engine (ICE).

Known methods for preparing catalysts on carriers of honeycomb structure with a plurality of apertures in the direction of gas stream flow. The initial specific surface area of such carriers is small block (0,01-0,65 m ² / g) and based on these catalysts have a low catalytic activity.

To increase the surface area of the original metal and ceramic block is widely used carrier substrate intermediate coating based on aluminum oxide with high specific surface (100-200 ^m2 / g), which was then deposited on one or more platinum group metals (platinum, palladium, rhodium) as the active ingredient, as high temperature stabilizers and additives are introduced into the catalyst of rare earth metal oxides (cerium, lanthanum and others.). The deposition of noble metals and the rare earth is predominantly of aqueous solutions of inorganic salts, followed by drying and reduction catalyst.

ICE known exhaust purification catalyst carriers for the block structure obtained by various methods.

A method is known, comprising a high-temperature pre-processing block carrier in the temperature range 800-1050 ° C, applying to the carrier a layer of aluminum hydroxide from an aqueous solution of potassium hydroxide in the presence of aluminum metal in the solution at a temperature of 20-25 ° C, separation of the carrier with a layer of aluminum hydroxide said solution, forming an alumina layer by thermal dehydration of aluminum hydroxide, the introduction of one or more substances alumina temperature stabilizers, one or more catalyst materials (RU 2190470 C2, 6/10/2002). A disadvantage of the method is the duration of the coating - from 24 to 70 hours and a multistage process, a and unsuitability for preparation of a catalyst on a ceramic carrier block. Prolonged exposure media, such as cordierite in a solution of potassium hydroxide to obtain the desired coating thickness and increasing the temperature of the solution during application (up to 40-50 ° C) lead to swelling of the ceramic material, and cracking during heat treatment.

According to the known method (US 4587231, 06.05.1986), in order to obtain a block of ICE exhaust purification catalyst monolithic carrier gas source repeatedly treated with alumina slurry in which the dispersed alumina powder containing cerium oxide, and cerium oxide is formed by pre-impregnating aluminum oxide powder solution cerium salt and then calcining. media treated slurry and calcined aluminum oxide coating is applied to the active substance - the platinum group metals. For this purpose, an intermediate coating is applied to an aqueous solution of each compound of the deposited noble metal (platinum, rhodium) and separately subjecting it to thermal decomposition. The disadvantages of the above-described suspension method include low coupling strength of the alumina coating to the original metal surface, thereby reducing the service life of the catalyst due to delamination of the intermediate coating with the active substances. Furthermore, a separate deposition of noble metals on a carrier with an intermediate coating technique significantly complicates and increases the time of preparing the catalyst, and does not increase the catalyst activity.

European Patent (EP 1438135 A3, 21.07.2004) discloses a method of preparing the supported catalyst of the honeycomb structure, which is formed on the surface of the alumina layer, followed by the known methods of stabilizing and modifying additions of aluminum oxide and catalytic components. For high surface intermediate coating deposition process of alumina suspension is repeated several times and after each operation performed drying medium, which leads to additional energy costs. A disadvantage of the method is its significant energy consumption and multistage without increasing catalyst activity.

The closest to the technical nature of the present invention is a process for preparing the catalyst, the catalyst for purification of exhaust gas according to ICE RU 2169614 C1, 27.06.2001. According to this known solution the catalyst preparation method includes the preliminary calcining the inert carrier cell block, which is a block of an aluminum foil, at a temperature of 850-920 ° C in a stream of air or oxygen for 12-15 hours, applying to the surface of the intermediate coating modified alumina from aqueous alcoholic suspension consisting of aluminum hydroxide, cerium nitrate, and then the resulting carrier after heat treatment at a temperature of 500-550 ° C, deposition of the active phase of one or more platinum group metals, drying and reconstitution. Thus the coating of the slurry is carried out at the following ratio of components, wt%: aluminum hydroxide - 22-32, aluminum nitrate - 2.4, cerium nitrate - 2.5 water-alcohol in the ratio 1: 1. Using 100. suspension of the above composition allows for a one time (single immersion) applied to the support block 7 to 14 wt.% of alumina as an intermediate coating. If necessary to further increase the coating weight of the intermediate stage in the dipping medium is repeated suspension.

The catalyst prepared by known solution consists of an inert carrier metal honeycomb block, which has an intermediate surface coating of alumina modified with applied thereto an active phase of platinum-group noble metals, and the catalyst of the following characteristics:

• the content of Al ₂ O ₃ catalyst - 7-14 wt%.
• the specific surface area _of Al ₂ O ₃ - 120-130 m ² / g,
• CeO ₂ content in the Al ₂ O ₃ - 8-15 wt.%.

The described method of preparing the catalyst is a multistage and energy-intensive. For example, the pre-heat treatment of the carrier at a temperature of 850-920 ° C in a stream of heated air even require unreasonable high, in our opinion, to create energy on the surface of an aluminum-steel foil germ adsorption centers. However, when the above-described metallic heat-resistant tape heat treatment mode, the partial migration of Al atoms to the surface of the belt due to the low processing temperature, and formation of an inhomogeneous composition of the oxide layer composed mainly of iron oxides, which deteriorates the adhesion of the coating and causes it to peel (especially at 14 wt .% deposited in one step), despite the additional step of wilting carrier before the heat treatment. Separate application of noble metal on the carrier with an intermediate coating technique significantly complicates and increases the time of catalyst preparation and often leads to an increase in the catalytic activity of catalysts supported thin layer.

The disadvantage of this method is the use as the basis of aluminum hydroxide slurry with a low specific surface area and adhesion, which requires the addition of aluminum nitrate plasticizer.

The object of the present invention is to speed and simplify the technology of preparation of block ICE exhaust purification catalyst, improving its strength and coating adhesion to the surface of the support block without reducing catalytic activity.

To solve this object, a the present method of preparing the catalyst for purification of combustion engine exhaust, including a preliminary calcination inert honeycomb block carrier, the simultaneous application to the surface of an intermediate coating of a modified aluminum oxide and the active phase of one or more platinum group metals from aqueous-alcoholic suspension containing . The following components in wt%: boehmite - 15-30, aluminum nitrate - 1.2, cerium nitrate - 4.8, 25% ammonium hydroxide solution - 10-20, one or more inorganic salts of platinum group metals, calculated as metals - 0,020-0,052, water-alcohol in a weight ratio of 1: 5-1: 10 - the rest, drying and reconstitution.

According to the proposed method for applying the coating is performed from a slurry comprising boehmite with an initial surface area of at least 300-350 m ² / g. The metal used as a carrier medium of corrugated and rolled into a steel strip and block its calcination is conducted at a temperature of 1000-1125 ° C, or the ceramic block using a carrier selected from the group consisting of cordierite, hematite, rutile, silicon carbide, and the calcination is carried out at temperature of 500-1000 ° C.

Catalyst for purifying internal combustion engine exhaust gas comprising an inert carrier block cell whose surface has a coating of alumina modified with an active phase of one or more platinum group metals, the resulting proposed method described above has the following characteristics:

• Specific surface coating - 100-200 m ² / g,
• Al ₂ O ₃ -. 5-13% by weight,
• CeO ₂ content - 0.5-1.3% by weight.
• active phase, based on the platinum group metals - 0,12-0,26% by weight.
• carrier - balance to 100 wt.%.

The technical result is achieved by:

- A carrier block prebaking in air to create an aluminum surface steel belt layer aluminas alpha- and gamma-modification, removal of adsorbed moisture from the surface of the ceramic block carriers of cordierite, hematite and rutile, and the starting composition and to stabilize the carrier block of silicon carbide, whose composition often includes residual carbon, which leads to increased adhesion of the deposited slurry coating method of a ceramic based on aluminum oxide;

- The use of certain chemical composition suspension, allowing one process cycle to obtain thermostable durable catalytic coating high surface area capable of generating particles of platinum group metal ultrafine nanometer order;

- Introduction of the aqueous-alcoholic suspension sequentially aluminum hydroxide in the form of its modification AlOOH (boehmite), Ce (NO _3)2, ammonium hydroxide and H ₂ PtCl _6, PdCl ₂ or RhCl ₃ of inorganic salts of noble metals in the form of solutions directly into the suspension leads to reduced time of the process and the resulting increase in strength of the catalytic coating, without altering the specific catalytic activity of the catalyst block.

Using the boehmite slurry of high surface area promotes the synthesis of ultrafine particles of noble metals as formed during thermal treatment of cerium oxide thermally stabilized gamma alumina impedes sintering of conglomeration and that leads to the possibility of obtaining high-gas purifying catalysts.

The carrier is heat treated to impart a carrier and its surface properties (adhesion improvement and stabilization of the surface) required for durable adhesion of the secondary catalytic coating: metal support - temperatue at 1000-1125 ° C, the ceramic - at a temperature of 500-1000 ° C.

The suspension is, in wt.%:

• Boehmite - 15-25,
• aluminum nitrate - 1-2,
• cerium nitrate - 4-8,
• 25% ammonium hydroxide solution - 10-20
• one or more inorganic salts of platinum group metals, (e.g., H ₂ PtCl _6, PdCl ₂ or ₃ RhCl) based metal - 0,020-0,052,
• water: alcohol = 1: 1 5 ÷ 10 - the rest.

Using the proposed suspension allows for a one time (one dive) applied to the block media from 6-13 wt.% Of aluminum oxide as an intermediate coating, which significantly reduces the time of preparation of the catalyst. The introduction of ammonium hydroxide solution to reduce the pH of the solution, which is extremely important when dealing with the steel carrier, and improve adhesion of the coating due to the formation of aluminum hydroxide gel directly in the preparation of the slurry.

Residues suspensions removed by centrifugation to provide a more uniform coating on the carrier block than when removing a slurry with compressed air, which occurs in the known solution, and immediately dried at stepwise raising the temperature from 50 to 120 ° C and heat treated at a temperature of 500-550 ° C, followed by reduction of the platinum metals, for example, in hydrogen at 350 ° C.

Yield after this regime leads to deterioration of the intermediate coating parameters, namely to reduce the strength of its coupling with the original carrier.

Composition of the slurry directly related to quality and quantity of the applied intermediate coating. The coating may be too thin, then the surface will be insufficiently developed to obtain a highly active catalyst, or uneven, with the possible occurrence of cracks during the heat treatment, that further lead to partial coating shattering. These temperature parameters and sequence of steps provide optimal structural characteristics values, particularly the specific surface area catalysts.

If necessary, the catalyst in the introduction of several noble metals, such as Pt-Rh, Pt-Pd and Pt-Pd-Rh, suspensions of the starting compounds are introduced all at once.

The invention is illustrated by the following examples.

Example 1. For the preparation of the catalyst block used corrugated steel strip and rolled in unit diameter and 25 mm height. The calcining furnace metal block carrier is calcined in air at a temperature of 1000-1125 ° C for 8-10 hours. After cooling unit is weighed (weight block of 10 g) and immersed in a suspension of the following composition: wt% boehmite (specific surface area 350 m ² / g) - 15, aluminum nitrate - 1, nitrate cerium - 4, ammonium hydroxide solution (25%. ethyl) - 10 salt _of H ₂ PtCI ₆ .6H ₂ O and RhCI ₃ · 3H ₂ O, based on metals - 0.02 (including Pt - 0,016, Rh - 0,004) , water: alcohol weight ratio 1:10 - rest.

Block is then removed, drained for 1-2 minutes at a rotation speed of 1500 rev / min. Next, the block was dried at stepwise raising the temperature from 50 to 120 ° C and heat treated at a temperature of 500-550 ° C, followed by reduction of the platinum metals in hydrogen at 350 ° C. Then unload the unit and the gravimetric method determines the mass of supported catalyst coating. The resultant catalyst has the following composition in wt%: Al ₂ O ₃ - 5.6 CeO ₂ - 0.5, Pt - 0.1, Rh - 0.02, the carrier - the rest.. The specific surface of the coating, determined by the BET method of nitrogen adsorption at low temperature, was 100 m ² / g Al ₂ O _3.

Example 2. Analogously to Example 1, but the oxidized metal block weighing 10 g is immersed into a suspension of the following composition, wt.%: Boehmite (specific surface area 300 m ² / g) - 30, aluminum nitrate - 2, cerium nitrate - 8 25% NaOH solution was ammonium - 20 salt PdCI ₂ · 4H ₂ O and RhCI ₃ · 3H ₂ O, based on metals - 0,052 (including Pd - 0,05, Rh - 0,002) , water: ethanol in a weight ratio of 1: 5 - rest.

Further according to Example 1. The resultant catalyst has the following composition in wt%: Al ₂ O ₃ - 11, CeO ₂ - 1.0, Pd - 0.25, Rh - 0.01, the carrier - the rest.. Specific surface coating - 170 m ² / g Al ₂ O _3.

Example 3. To prepare the catalyst is a cylindrical block of cordierite with longitudinal through channels. The calcining furnace block carrier is calcined in air at 500-550 ° C for 5-8 hours. Next, 10 g block was treated according to Example 1. The resultant catalyst has the following composition in wt%:. Al ₂ O ₃ - 6.5 CeO ₂ - 0.6, Pt - 0.1, Rh - 0.02, medium - rest. The surface area of the coating was 125 m ² / g Al ₂ O _3.

Example 4. Analogously to Example 3, but block weighing 10 g were placed in suspension and worked up as in Example 2. The resulting catalyst had the following composition in wt%: Al ₂ O ₃ - 13 CeO ₂ - 1,3, Pd - 0,25, Rh -. 0.01, the carrier - the rest. Specific surface coating - 200 m ² / g Al ₂ O _3.

Example 5. To prepare the catalyst is a cylindrical block of hematite with longitudinal through channels. Block carrier is calcined in air at 500-550 ° C for 5-8 hours. After cooling unit (weighing 10 g) was immersed in a suspension of the following composition: wt% boehmite (specific surface area 350 m ² / g) - 15 -1 aluminum nitrate, cerium nitrate - 4, 25% ammonium hydroxide 10. salts PdCI ₂ · 4H ₂ O and RhCI ₃ · 3H ₂ O, based on metals - 0,052 (including Pd - 0,05, Rh - 0,002) , water: ethanol in a weight ratio of 1:10 - the rest.

Further according to Example 1. The resultant catalyst has the following composition in wt%: Al ₂ O ₃ - 5,5, CeO ₂ - 0.5, Pd - 0.25, Rh - 0.01, the carrier - the rest.. Specific surface coating - 125 m ² / g Al ₂ O _3.

Example 6. To prepare the catalyst is cylindrical blocks of rutile with longitudinal through channels. Prebaking unit is carried out analogously to Example 5. Then, the unit weight of 10 g was immersed in the suspension of the following composition, wt.%: Boehmite (specific surface area 300 m ² / g) - 30, aluminum nitrate - 2, cerium nitrate - 8 25% ammonium hydroxide - 20 salt H ₂ PtCI ₆ .6H ₂ O and RhCI ₃ · 3H ₂ O, based on metals - 0.02 (including Pt - 0,016, Rh - 0,004) , water: alcohol weight ratio 1: 5 - the rest.

Further according to Example 1. The resultant catalyst has the following composition in wt%:. Al ₂ O ₃ - 12.5, CeO ₂ - 1.1, Pt - 0.1, Rh - 0.02, the carrier - the rest. Specific surface coating - 185 m ² / g Al ₂ O _3.

Example 7. To prepare the catalyst is cylindrical blocks of silicon carbide with a longitudinal through-channels. Block carrier is calcined in air at 550-1000 ° C for 5-8 hours. Unit weight 10 g was treated in Example 5 hereinafter.

The resultant catalyst has the following composition in wt%: Al ₂ O ₃ - 5, CeO ₂ - 0.5, Pd - 0.25, Rh - 0.01, the carrier - the rest.. The surface area of the coating was about 100 m ² / g Al ₂ O _3.

Example 8. Analogously to Example 7, but block weighing 10 g was further treated according to Example 6.

The resultant catalyst has the following composition in wt%: Al ₂ O ₃ - 9,5, CeO ₂ - 0.9, Pt - 0.1, Rh - 0.02, the carrier - the rest.. Specific surface coating - 145 m ² / g Al ₂ O _3.

Example 9. On metallic blocks made of steel H23YU5 brand tape using a procedure described in the prior art (RU 2169614) method of preparation of the carrier and the composition of the slurry: Al (OH) ₃ - 32 wt%, Al (NO ₃₎₃ - 4 wt%, Ce (NO.. . ₃₎₂ - 5 wt%, the rest is water: ethanol in a weight ratio of 1: 1 was obtained a catalyst having the following composition in wt%:. Al ₃ O ₃ - 14, CeO _2, Al ₂ O ₃ - 8, Pd - 0,25, Rh - 0,01, the carrier - the rest. Specific surface coating was - 130 m ² / g.

Example 10 Analogously to Example 9, the catalyst prepared with the following composition: Al ₂ O ₃ - 13 wt%, CeO _2, Al ₂ O ₃ - 10 wt%, Pt - 0,1 wt%, Rh - 0,02 wt.... %. Specific surface coating was - 120 m ² / g.

For comparison, the catalyst obtained was tested in the reaction of CO oxidation by oxygen to CO ₂ on a laboratory flow unit under the following conditions: gas mixture - CO 1 vol% O ₂ - 2% by volume, balance nitrogen, the volumetric gas flow rate - 30000 h ^{-.. 1.}

Experiments showed that the catalytic activity of the catalyst samples prepared according to the claimed method, above ₍₉₀ T = 175-200 ° C) or equal (T ₉₀ = 205 ° C) the catalyst activity according to the prototype. At the same time, the inventive method can significantly reduce the process time for preparing a catalyst by reducing the number of processing steps, reduce power consumption and labor, which in turn will significantly reduce the cost of the catalyst and to obtain a highly efficient internal combustion engine exhaust gas purification catalyst. The experimental results are shown in Table.

CLAIM

1. A process for preparing a catalyst for purifying exhaust gases of internal combustion engines, comprising a preliminary calcining the inert carrier cell block, drawing on the surface of a modified intermediate coating of alumina hydroalcoholic suspension comprising aluminum hydroxide, cerium nitrate, deposition of the active phase of one or more platinum group metals, drying and reduction, characterized in that applying the intermediate coating and the active phase is carried out simultaneously from a slurry comprising boehmite as aluminum hydroxide, with the following ratio of its components, wt.%:

2. The method of claim 1, wherein the intermediate coating deposition is carried out from a suspension containing the starting boehmite with a specific surface area of at least 300-350 m ² / g.

3. A method according to claim 1, characterized in that as carrier medium of a metallic corrugated and rolled into a steel strip and block its calcination is carried out at a temperature of 1000-1125 ° C.

4. A method according to claim 1, characterized in that as carrier ceramic block using a carrier selected from the group consisting of silicon carbide, cordierite, hematite, rutile, and its calcination is carried out at 500-1000 ° C.

5. A catalyst for purifying exhaust gases of internal combustion engines, comprising an inert carrier block cell whose surface has a coating of alumina modified with an active phase of one or more platinum group metals, characterized in that it is obtained by the method according to any one of claims 1 4 and has the following characteristics: specific surface coating - 100-200 m ² / g, the content of Al ₂ O ₃ - 5-13% by weight of CeO ₂ content - 0.5-1.3 wt%, the active phase.. based on platinum group metals - 0,12-0,26 wt% carrier -. the balance to 100 wt.%.

print version
Publication date 07.04.2007gg

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