Composite three-way catalyst and method for increasing surface adhesive force of three-way catalyst particles

Abstract

The invention provides a composite three-way catalyst and a method for increasing the surface adhesive force of three-way catalyst particles. The composite three-way catalyst comprises a three-way catalyst, the aluminum oxide layer is coated on the surface of the three-way catalyst, and the thickness of the aluminum oxide layer is 0.1-0.5 nm. The composite catalyst is coated with the aluminum oxide layer, so that the surface adhesive force of the composite catalyst is improved, and the problem that active components of the catalyst fall off due to vibration in the moving process of an automobile can be effectively avoided.

Description

Technical Field

[0001] The invention belongs to the field of coating active components of three-way catalysts in tailpipes of pure gasoline vehicles and hybrid vehicles, and particularly relates to a composite three-way catalyst and a method for increasing surface adhesion of three-way catalyst particles. Background Art

[0002] Automobile exhaust, due to its presence of harmful substances such as incompletely burned carbon monoxide, hydrocarbons, and nitrogen oxides, has become a major source of air pollution, posing a serious threat to the environment and human health. To effectively address this pressing issue, the scientific and industrial communities have widely adopted three-way catalysts for automobile exhaust purification. These catalysts can simultaneously catalyze and convert these harmful gases, significantly reducing their emissions, making them a key component of current environmental protection technologies.

[0003] The purification effect of a catalyst depends not only on its initial activity and activity after hydrothermal aging, but also on its ability to remain stable on the carrier without loss. Because the particles of the active components of a three-way catalyst are small, when the catalyst moves significantly with the vehicle, it is easily lost from the carrier, resulting in a decrease in catalyst activity. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a composite three-way catalyst and a method for increasing the surface adhesion of three-way catalyst particles. The composite three-way catalyst has a large surface adhesion, which can effectively prevent the catalyst from falling off the carrier, thereby increasing the service life of the catalyst.

[0005] The present invention provides a composite three-way catalyst, comprising a three-way catalyst;

[0006] and a 0.1-0.5 nm aluminum oxide layer coated on the surface of the three-way catalyst.

[0007] Preferably, the thickness of the aluminum oxide layer is 0.2-0.4 nm.

[0008] Preferably, the aluminum oxide layer is an amorphous coating layer.

[0009] Preferably, the three-way catalyst is a three-way catalyst for purifying carbon monoxide, hydrocarbons and nitrogen oxides.

[0010] Preferably, the three-way catalyst is a doped or undoped cerium-zirconium solid solution loaded with one or more noble metals selected from platinum, palladium and rhodium.

[0011] Preferably, the three-way catalyst is a platinum-palladium-rhodium based three-way catalyst.

[0012] The present invention provides a method for preparing the composite three-way catalyst described in the above technical solution, comprising the following steps:

[0013] A composite three-way catalyst is obtained by periodically and alternately passing trimethylaluminum, nitrogen, water vapor and nitrogen on the surface of the three-way catalyst by atomic layer deposition.

[0014] Preferably, the three-way catalyst is heated to 280-320° C., kept at this temperature for 55-65 minutes, and then trimethylaluminum, nitrogen, water vapor, and nitrogen are periodically and alternately passed through the surface by atomic layer deposition.

[0015] Preferably, the three-way catalyst is heated to 290-310° C. and kept at this temperature for 58-62 minutes.

[0016] Preferably, the adhesion between the surface of the three-way catalyst and the cordierite support or the iron-based support is increased.

[0017] The present invention provides a composite three-way catalyst comprising a three-way catalyst and a 0.1-0.5 nm thick aluminum oxide layer coated on the surface of the three-way catalyst. The aluminum oxide coating enhances the surface adhesion of the composite catalyst, effectively preventing the loss of active catalyst components due to vibration during vehicle movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the initial activity and activity after hydrothermal aging of the three-way catalyst;

[0019] Figure 2 The initial activity and activity after hydrothermal aging of the three-way catalyst coated with an alumina layer;

[0020] Figure 3 This is the change in surface adhesion of the three-way catalyst before and after coating with the alumina layer. DETAILED DESCRIPTION

[0021] The present invention provides a composite three-way catalyst, comprising a three-way catalyst;

[0022] and a 0.1-0.5 nm aluminum oxide layer coated on the surface of the three-way catalyst.

[0023] The composite three-way catalyst provided by this invention coats the surface of the catalyst with an alumina layer. This layer does not affect the catalyst's activity but significantly improves its surface adhesion, allowing the catalyst to adhere more tightly to a support (such as a cordierite support or an iron-based support) and prevent it from falling off. Experimental results show that adhesion is improved by up to 300%.

[0024] In the present invention, the thickness of the aluminum oxide layer is 0.1-0.5 nm, specifically 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm or 0.5 nm.

[0025] The present invention adopts an atomic layer deposition method to achieve uniform deposition of an aluminum oxide layer, and the formed aluminum oxide layer is an amorphous coating layer.

[0026] In the present invention, the three-way catalyst is a three-way catalyst for purifying carbon monoxide, hydrocarbons, and nitrogen oxides. Specifically, the three-way catalyst is a doped or undoped cerium-zirconium solid solution loaded with one or more precious metals selected from platinum, palladium, and rhodium. The three-way catalyst is a palladium-rhodium-based three-way catalyst, more specifically, a cerium-zirconium solid solution loaded with platinum, palladium, and rhodium.

[0027] The present invention provides a method for increasing the surface adhesion of three-way catalyst particles, comprising the following steps:

[0028] A composite three-way catalyst is obtained by periodically and alternately passing trimethylaluminum, nitrogen, water vapor and nitrogen on the surface of the three-way catalyst by atomic layer deposition.

[0029] The three-way catalyst of the present invention is heated to 280-320°C and held at this temperature for 55-65 minutes, and then trimethylaluminum, nitrogen, water vapor, and nitrogen are periodically and alternately passed over the surface using atomic layer deposition. The heating temperature can be 280°C, 290°C, 300°C, 310°C, or 320°C, and the holding time is 55 minutes, 56 minutes, 57 minutes, 58 minutes, 59 minutes, 60 minutes, 61 minutes, 62 minutes, 63 minutes, 64 minutes, or 65 minutes. The three-way catalyst is preferably heated to 290-310°C and held at this temperature for 58-62 minutes.

[0030] The number of periodic alternations is 1 to 6 times, specifically 1 time, 2 times, 3 times, 4 times, 5 times or 6 times.

[0031] The invention increases the adhesion between the surface of the three-way catalyst and the cordierite carrier (used in the automotive field) or the iron-based carrier (used in the motorcycle field) by arranging an alumina layer.

[0032] The present invention performs aging treatment on a composite three-way catalyst. In the present invention, the aging temperature is 900-1000° C., specifically 900° C., 910° C., 920° C., 930° C., 940° C., 950° C., 960° C., 970° C., 980° C., 990° C. or 1000° C.; the aging time is 19-21 hours, specifically 19 hours, 19.5 hours, 20 hours, 20.5 hours or 21 hours; and the volume fraction of water vapor during aging is 8-12%, and can be 8%, 9%, 10%, 11% or 12%.

[0033] The modification method of the three-way catalyst of the present invention will not affect the initial activity of the catalyst (T 90 ); and activity after aging at 950℃ and 10% water vapor for 20h (T 90 ).

[0034] To further illustrate the present invention, a composite three-way catalyst and a method for increasing the surface adhesion of three-way catalyst particles provided by the present invention are described in detail below with reference to examples. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0035] Example 1

[0036] 120 g of a palladium-rhodium-based cerium-zirconium solid solution as a three-way catalyst was placed in an atomic layer deposition apparatus, evacuated, heated to 300°C, and held for 1 hour; trimethylaluminum, nitrogen, water vapor, and nitrogen were alternately passed over the catalyst surface five times. After cooling, the three-way catalyst was removed from the atomic layer deposition apparatus to obtain a composite three-way catalyst having an amorphous alumina coating layer with a thickness of 0.4 nm;

[0037] The composite three-way catalyst with the coating layer was aged for 20 hours at 950° C., with a volume fraction of 10% water vapor and air as the balance gas, to obtain a hydrothermally aged three-way catalyst with the coating layer.

[0038] Figure 1 is the initial activity and activity after hydrothermal aging of the three-way catalyst. After hydrothermal aging, T 90 =320°C. The reaction gas composition is [C3H8] = 300ppm, [C3H6] = 800ppm, [H2] = 0.2%, [CO] = 3.5%, [NO] = 800ppm, [O2] = air-fuel ratio of 1, [CO2] = 10%, [H2O] = 10%, N2 balance gas, space velocity 50000h -1 .

[0039] Figure 2 is the initial activity and activity after hydrothermal aging of the three-way catalyst coated with alumina layer. After hydrothermal aging, T 90 =320°C. The reaction gas composition is [C3H8] = 300ppm, [C3H6] = 800ppm, [H2] = 0.2%, [CO] = 3.5%, [NO] = 800ppm, [O2] = air-fuel ratio of 1, [CO2] = 10%, [H2O] = 10%, N2 balance gas, space velocity 50000h -1 .

[0040] Surface adhesion test method: Use the adhesion test function of the atomic force microscope (AFM) to test the adhesion of the catalyst before and after coating. First, the AFM tip touches the sample downward, and then gradually lifts the tip upward. The force required to separate the tip and the sample represents the magnitude of the sample surface adhesion. Figure 3 The surface adhesion of the three-way catalyst before and after being coated with an alumina layer increases by 3 times compared to the uncoated one.

[0041] As can be seen from the above examples, the present invention provides a composite three-way catalyst comprising a three-way catalyst and a 0.1-0.5 nm thick alumina layer coated on the surface of the three-way catalyst. The alumina coating enhances the surface adhesion of the composite catalyst, effectively preventing the loss of active catalyst components due to vibration during vehicle movement.

[0042] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A composite three-way catalyst, characterized in that: Includes three-way catalyst; and an aluminum oxide layer with a thickness of 0.1 to 0.5 nm coated on the surface of the three-way catalyst.

2. The composite three-way catalyst according to claim 1, characterized in that The thickness of the aluminum oxide layer is 0.2-0.4 nm.

3. The composite three-way catalyst according to claim 1, characterized in that The aluminum oxide layer is an amorphous coating layer.

4. The composite three-way catalyst according to claim 1, characterized in that The three-way catalyst is a three-way catalyst for purifying carbon monoxide, hydrocarbons and nitrogen oxides.

5. The composite three-way catalyst according to claim 1, characterized in that The three-way catalyst is a doped or undoped cerium-zirconium solid solution loaded with one or more noble metals selected from platinum, palladium and rhodium.

6. The composite three-way catalyst according to claim 1, characterized in that The three-way catalyst is a platinum-palladium-rhodium based three-way catalyst.

7. A method for increasing the surface adhesion of three-way catalyst particles, comprising the following steps: A composite three-way catalyst is obtained by periodically and alternately passing trimethylaluminum, nitrogen, water vapor and nitrogen on the surface of the three-way catalyst by atomic layer deposition.

8. The preparation method according to claim 7, characterized in that The three-way catalyst is heated to 280-320°C and kept warm for 55-65 minutes, and then trimethylaluminum, nitrogen, water vapor and nitrogen are periodically and alternately passed through the surface by atomic layer deposition.

9. The preparation method according to claim 8, characterized in that The three-way catalyst is heated to 290-310°C and kept warm for 58-62 minutes.

10. The preparation method according to claim 7, characterized in that Increase the adhesion between the surface of the three-way catalyst and the cordierite carrier or the iron-based carrier.

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