CN116196972A - Diesel oxidation catalyst and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a diesel oxidation catalyst and a preparation method thereof, wherein the diesel oxidation catalyst comprises a carrier, a bottom coating coated on the carrier and a catalyst coating coated on the bottom coating; the carrier is a honeycomb ceramic carrier with a square pore canal structure; the bottom coating is a refractory material without a catalyst; the catalyst coating comprises a noble metal catalyst; the catalyst has high utilization efficiency, achieves the same catalytic effect, and can reduce the use amount of noble metal.

Description

A kind of diesel oxidation catalyst and preparation method thereof

technical field

The invention belongs to the technical field of catalysts, and in particular relates to a diesel oxidation catalyst and a preparation method thereof.

Background technique

The diesel oxidation catalyst is DOC. In the treatment of diesel engine exhaust, in order to meet the emission standards of China VI and above, a wall-flow diesel particulate filter DPF must be used. The regeneration of DPF is divided into active regeneration by burning fuel oil and passive regeneration by using NO2. During active regeneration, the fuel mainly burns on the DOC, and the precious metal content determines the combustion performance. As the price of precious metals increases, it is imperative to reduce the amount of precious metal used in catalyst design. The purpose of this design is therefore to reduce the amount of precious metal used in the catalyst. Experimental data show that the precious metal content in DOC can be reduced by more than 20%.

Since the pore shape of the current mainstream honeycomb ceramic carrier is square, and the gas flow pore is circular after catalyst coating, a large number of catalyst coatings are coated on the four corners of the square pore. However, under the condition of high gas flow velocity, it is difficult for the reaction gas to diffuse to the four corners of the carrier, thus resulting in a decrease in the utilization rate of the catalyst coating.

Contents of the invention

The technical problem solved by the invention is to provide a diesel oxidation catalyst, which has high utilization efficiency, achieves the same catalytic effect, and can reduce the usage amount of precious metals. Another technical problem solved by the present invention is to provide a preparation method of the above-mentioned diesel oxidation catalyst.

The present invention will solve the above problems through the following technical solutions:

A diesel oxidation catalyst, comprising a carrier, a primer coating applied on the carrier, and a catalyst coating coated on the primer coating; the carrier is a honeycomb ceramic carrier with a square pore structure; the The primer coating is a catalyst-free refractory material; the catalyst coating contains a noble metal catalyst.

Further, the primer coating includes one or more refractory materials among alumina, silica, zirconia, beta zeolite, SAPO34, SSZ13, and ZSM5.

Further, the pore volume of the refractory material is greater than 0.6ml/g, and the particle diameter D50 is not less than 7um.

Further, the coating amount of the primer coating is 20g/L-90g/L.

Further, the distribution of the primer coating in the axial direction includes uniform distribution and non-uniform distribution.

Further, the distribution of the catalyst coating in the axial direction includes uniform distribution and non-uniform distribution.

The present invention provides the preparation method of the above-mentioned diesel oxidation catalyst, comprising the following steps: uniformly coating the primer coating on a honeycomb ceramic carrier with square channels, and coating the catalyst coating on the aforementioned primer coating after drying It is obtained after drying and calcining on the honeycomb ceramic carrier.

The present invention also provides the application of the above-mentioned diesel oxidation catalyst in a diesel exhaust aftertreatment system.

The beneficial effect of the present invention is that the coating is firstly coated with a coating that does not contain precious metals, and the purpose is to coat the four corners of the carrier to form a circular channel structure. Then a noble metal-containing slurry is coated on this basis, and finally the noble metal-containing catalyst coating is ring-shaped. The gas flow channels are also circular, so the utilization efficiency of the catalyst coating containing precious metals is improved, which also means that the same catalytic effect can be achieved, and the amount of precious metals used can be reduced.

Description of drawings

Fig. 1: Electron micrograph of the diesel oxidation catalyst described in the present invention.

Detailed ways

The present invention will be further described below in combination with specific implementation methods and accompanying drawings, but the present invention is not limited thereto. The methods involved in the present invention are methods commonly used in the art unless otherwise specified, and the reagents involved can be obtained from common commercial channels unless otherwise specified.

A diesel oxidation catalyst provided by the present invention comprises a carrier, a primer coating applied on the carrier, and a catalyst coating coated on the primer coating; the carrier has a square pore structure A honeycomb ceramic carrier; the bottom coating is a catalyst-free refractory material; the catalyst coating contains a noble metal catalyst.

According to the preparation method of a kind of diesel oxidation catalyst of the present invention, be prepared into embodiment 1-4 and comparative example 1-2, concrete preparation method is as follows:

Example 1:

Add 20g of SAPO34 zeolite and 20g of SSZ13 zeolite into the container, add water and stir to mix, then add 50g of 40% silica sol, add water to adjust viscosity and solid content; apply the slurry on the blank ceramic honeycomb carrier of NGK, the carrier diameter is 5.66 inches, 3 inches in length, mesh number 400, wall thickness 4mm, coating weight (dry weight) 60g/L; dry at 100-150°C to form a bottom layer that does not contain precious metals.

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, ensure that the Pt metal concentration coated on the honeycomb carrier is 20g/ft ³ , and the Pd metal content is 10g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, and add water to adjust the solid content and viscosity of the slurry. Coating was carried out on the carrier coated with the bottom layer catalyst, and the coating amount (dry weight) was 95 g/L. After coating, it is dried in an air stream at 100°C-150°C, and then the catalyst is calcined at 550°C.

Embodiment 2;

Add 20g of SAPO34 zeolite and 20g of SSZ13 zeolite into the container, add water and stir to mix, then add 50g of 40% silica sol, add water to adjust viscosity and solid content; apply the slurry on the blank ceramic honeycomb carrier of NGK, the carrier diameter is 5.66 inches, 3 inches in length, mesh number 400, wall thickness 4mm, coating weight (dry weight) 60g/L; dry at 100-150°C to form a bottom layer that does not contain precious metals.

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, and ensure that the Pt metal concentration coated on the honeycomb carrier is 16g/ft ³ , and the Pd metal content is 8g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, and add water to adjust the solid content and viscosity of the slurry. Coating was carried out on the carrier coated with the bottom layer catalyst, and the coating amount (dry weight) was 95 g/L. After coating, it is dried in an air flow at 100°C-150°C, and then the catalyst is calcined at 550°C.

Example 3:

Add 30g of SAPO34 zeolite and 30g of SSZ13 zeolite into the container, add water to stir and mix, then add 75g of 40% silica sol, add water to adjust viscosity and solid content; apply the slurry on the blank ceramic honeycomb carrier of NGK, the carrier diameter is 5.66 inches, length 3 inches, mesh number 400, wall thickness 4mm, coating weight (dry weight) 90g/L; dry at 100-150°C to form a coating that does not contain precious metals at the bottom.

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, and ensure that the Pt metal concentration coated on the honeycomb carrier is 16g/ft ³ , and the Pd metal content is 8g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, and add water to adjust the solid content and viscosity of the slurry. Coating was carried out on the carrier coated with the bottom layer catalyst, and the coating amount (dry weight) was 95 g/L. After coating, it is dried in an air flow at 100°C-150°C, and then the catalyst is calcined at 550°C.

Example 4:

Add 20g of SAPO34 zeolite and 20g of SSZ13 zeolite into the container, add water and stir to mix, then add 50g of 40% silica sol, add water to adjust viscosity and solid content; apply the slurry on the blank ceramic honeycomb carrier of NGK, the carrier diameter is 5.66 inches, 3 inches in length, 400 mesh, 4mm wall thickness. The coating direction is the inlet direction of the gas flow, and the coating length is 1.5 inches. The coating amount (dry weight) is 60g/L; it is dried at a temperature of 100-150°C to form a coating with no precious metal in the bottom layer.

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, and ensure that the Pt metal concentration coated on the honeycomb carrier is 16g/ft ³ , and the Pd metal content is 8g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, and add water to adjust the solid content and viscosity of the slurry. Coating was carried out on the carrier coated with the bottom layer catalyst, and the coating amount (dry weight) was 95 g/L. After coating, it is dried in an air stream at 100°C-150°C, and then the catalyst is calcined at 550°C.

Comparative example 1:

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, ensure that the Pt metal concentration coated on the honeycomb carrier is 20g/ft ³ , and the Pd metal content is 10g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, and add water to adjust the solid content and viscosity of the slurry. The slurry is coated on the blank ceramic honeycomb carrier of NGK, the diameter of the carrier is 5.66 inches, the length is 3 inches, the mesh number is 400, and the wall thickness is 4mm. After coating, it is dried in the air flow of 100°C-150°C. The catalyst is then calcined at 550°C.

Comparative example 2:

Add 90g of γ-Al ₂ O ₃ with water and stir evenly, add chloroplatinic acid solution and palladium acetate solution, ensure that the Pt metal concentration coated on the honeycomb carrier is 20g/ft ³ , and the Pd metal content is 10g/ft ³ . After stirring for 30 minutes, add 5% aqueous alumina, add 20g SAPO34 zeolite and 20g SSZ13 zeolite, and then add water to adjust the solid content and viscosity of the slurry. The slurry is coated on the blank ceramic honeycomb carrier of NGK, the diameter of the carrier is 5.66 inches, the length is 3 inches, the mesh number is 400, and the wall thickness is 4mm. After coating, it is dried in the air flow of 100°C-150°C. The catalyst is then calcined at 550°C.

The catalytic performance of Examples 1-4 of the present invention and Comparative Examples 1-2 used in the diesel exhaust after-treatment system was tested, and the gas conditions of the test are shown in the following table: the concentration unit of the unspecified gas concentration is ppm.

O ₂ CO ₂ CO ppm Propylene ppm ppm of toluene H ₂ O N ₂ Airspeed h ^-1 10% 8% 500 3000 1000 5% balance gas 120000

Utilize the gas in the above table to test the catalyst performance of Examples 1-4 of the present invention and Comparative Examples 1-2, feed the reaction gas at 150°C, raise the temperature to 500°C at a rate of 10°C/min, and test the total hydrocarbon content Conversion efficiency, the performance of the catalyst is evaluated by the temperatures T50 and T90 required to achieve 50% conversion efficiency and 90% conversion efficiency. The smaller the T50 and T90, the higher the performance of the catalyst.

Catalyst sample T50/℃ T90/℃ Example 1 198 232 Example 2 211 253 Example 3 220 264 Example 4 218 259 Comparative example 1 217 260 Comparative example 2 228 273

The results show that the T50 and T90 of Example 1 are the smallest, so the catalyst performance of this design is the highest. The T50 of Comparative Example 1 with the same precious metal content is about 20 degrees higher than that of Example 1. Therefore, coating the bottom layer with a coating that does not contain precious metals has a significant effect on improving the performance of the catalyst.

Judging from Example 2 and Comparative Example 1, the catalyst performances of the two are relatively close, but the noble metal content of Example 2 is 80% of that of Comparative Example 1. Therefore, the amount of precious metals can be reduced by more than 20%.

The properties of Example 3 and Example 4 are also close to those of Comparative Example 1. Therefore, the effectiveness of the design has been further proved.

It can be understood that the above specific embodiments are all further descriptions of the present invention, and are not intended to limit the protection scope of the present invention. For those skilled in the art, all other modifications and modifications obtained under the condition of no creative work, All belong to the protection scope of the present invention.

Claims (8)

1. a diesel oxidation catalyst is characterized in that, comprises carrier, is coated on the primer coating on described carrier, and is coated on the catalyst coating on described primer coating; Described carrier has square channel structure The honeycomb ceramic carrier; the bottom coating is a catalyst-free refractory material; the catalyst coating contains a noble metal catalyst. 2. The diesel oxidation catalyst according to claim 1, characterized in that, the primer coating comprises one or more refractory materials in alumina, silicon oxide, zirconia, beta zeolite, SAPO34, SSZ13, and ZSM5 . 3. The diesel oxidation catalyst according to claim 2, characterized in that the pore volume of the refractory material is greater than 0.6ml/g, and the particle diameter D50 is not less than 7um. 4. The diesel oxidation catalyst according to claim 1, characterized in that, the coating amount of the primer layer is 20g/L-90g/L. 5. The diesel oxidation catalyst according to claim 1, wherein the distribution of the undercoat layer in the axial direction includes uniform distribution and non-uniform distribution. 6. The diesel oxidation catalyst according to claim 1, wherein the distribution of the catalyst coating in the axial direction includes uniform distribution and non-uniform distribution. 7. a preparation method of the diesel oxidation catalyst as claimed in any one of claims 1-6, is characterized in that, comprises the following steps: undercoat is evenly coated on the honeycomb ceramic carrier with square channel, after drying The catalyst coating is coated on the above-mentioned honeycomb ceramic carrier coated with the primer coating, dried and calcined to obtain it. 8. An application of the diesel oxidation catalyst according to any one of claims 1-6 in a diesel exhaust aftertreatment system.

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