Three-way catalyst for lean-burn natural gas engine, preparation method and application

Abstract

The present invention relates to the field of catalysts, and specifically provides a three-way catalyst for a lean-burn natural gas engine, a preparation method and an application. The three-way catalyst comprises a substrate, a first catalyst coating material and a second catalyst coating material; the first catalyst coating material comprises a first carrier material and a first active component, the first carrier material comprises one or more of CeO2-ZrO2-La2O3-Nd2O3, La2O3-Al2O3, and CeO2-Al2O3, and the first active component comprises Pd; the second catalyst coating material comprises a second carrier material and a second active component, the second carrier material comprises CeO2, CeO2-ZrO2-La2O3-Y2O3, CeO2-ZrO2-La2O3-Pr6O 11 The second active component comprises Pt and / or Ni. The catalyst has high catalytic performance in rich combustion and lean combustion modes.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a three-way catalyst for a lean-burn natural gas engine, a preparation method and an application thereof. Background Art

[0002] Compared with gasoline and diesel, using natural gas as automobile fuel can effectively reduce the emission of automobile exhaust pollutants such as hydrocarbons (HC), nitrogen oxides (NOx), CO and greenhouse gas CO2, and natural gas vehicles have great development potential. Natural gas engines can adopt equivalent ratio combustion or lean combustion mode. When using equivalent ratio combustion, only three-way catalysts can be used to convert HC, NOx and CO into non-toxic CO2, H2O and N2 at the same time. The after-treatment device is simple in composition, so natural gas vehicles currently generally adopt equivalent ratio combustion mode. In recent years, in response to climate change and energy crises, countries have issued more stringent fuel consumption and emission regulations, explicitly requiring a significant improvement in automobile fuel economy. Since lean combustion has less heat loss and higher engine efficiency, the use of lean combustion mode can greatly reduce fuel consumption rate, which is an effective solution to reduce fuel consumption.

[0003] When natural gas engines use lean combustion, methane oxidation catalysts (MOC) can be used to oxidize and remove HC and CO, but NOx cannot be effectively reduced under oxygen-rich conditions, and additional catalyst units need to be added to remove NOx. Selective catalytic reduction (Urea-SCR) technology using urea as a reducing agent has been widely used in diesel vehicle NOx emission control. This technology can be used to solve the NOx emission problem of lean combustion natural gas engines. However, due to the large size of urea storage and delivery devices, which occupy a lot of space, and the risk of NH3 leakage in urea injection devices, an additional ammonia oxidation catalyst (ASC) needs to be installed to eliminate the leaked NH3, which will undoubtedly greatly increase the size and cost of the after-treatment device.

[0004] In recent years, a technical route for exhaust aftertreatment of lean-burn gasoline engines has been proposed: three-way catalyst (TWC) + passive selective catalytic reduction (PSCR) technology. The principle of this technical route is: in rich combustion mode, the three-way catalyst produces NH3, which is stored on the PSCR catalyst; in lean combustion mode, NOx reacts with the NH3 stored on the PSCR catalyst to undergo SCR reaction and is converted. This technical route uses a three-way catalyst as the NH3 source, eliminates the urea injection system, reduces the size of the aftertreatment device, and reduces the cost. However, this technical route is not yet mature, and there are still some technical problems that need to be solved. One of the technical problems is related to TWC. This technical route requires that the three-way catalyst can efficiently catalytically convert HC, CO and NOx in rich combustion mode, and can produce a large amount of NH3 to reduce the rich combustion mode time. At the same time, it requires that the three-way catalyst must also have excellent HC and CO oxidation capabilities in lean combustion mode. However, existing three-way catalysts, especially those used in natural gas vehicles, can only effectively eliminate HC, CO and NOx near the equivalence ratio. In rich combustion mode, the conversion efficiency of HC and CO is reduced, and in lean combustion mode, HC conversion is difficult.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a three-way catalyst for a lean-burn natural gas engine, a preparation method and an application thereof, so as to solve the problems that the existing three-way catalyst can only effectively eliminate HC, CO and NOx near the equivalence ratio, has low HC and CO conversion efficiency in rich combustion mode, and has difficulty in converting HC in lean combustion mode.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] In a first aspect, the present invention provides a three-way catalyst for a lean-burn natural gas engine, comprising a substrate, a first catalyst coating material and a second catalyst coating material, wherein the first catalyst coating material and the second catalyst coating material are coated on the substrate in sections;

[0009] The first catalyst coating material includes a first carrier material and a first active component, the first carrier material includes one or more of CeO2-ZrO2-La2O3-Nd2O3, La2O3-Al2O3, CeO2-Al2O3, and the first active component includes Pd;

[0010] The second catalyst coating material includes a second carrier material and a second active component, wherein the second carrier material includes CeO2, CeO2-ZrO2-La2O3-Y2O3, CeO2-ZrO2-La2O3-Pr6O 11One or more of the above, wherein the second active component includes Pt and / or Ni.

[0011] Furthermore, the CeO2 content in the CeO2-ZrO2-La2O3-Nd2O3 is 20-30wt%, the ZrO2 content is 60-75wt%, the La2O3 content is 2-9wt%, and the Nd2O3 content is 3-7wt%;

[0012] The La2O3-Al2O3 has a La2O3 content of 3-5wt% and an Al2O3 content of 95-97wt%;

[0013] The CeO2 content in the CeO2-Al2O3 is 3-5wt%, and the Al2O3 content is 95-97wt%.

[0014] Furthermore, the CeO2 content in the CeO2-ZrO2-La2O3-Y2O3 is 60-70wt%, the ZrO2 content is 20-30wt%, the La2O3 content is 2-9wt%, and the Y2O3 content is 2-13wt%;

[0015] The CeO2-ZrO2-La2O3-Pr6O 11 The CeO2 content is 60~70wt%, the ZrO2 content is 20~30wt%, the La2O3 content is 2~9wt%, and the Pr6O 11 The content is 2~7wt%.

[0016] Furthermore, the CeO2 content in the first catalyst coating material is 0~30 wt%, and the first active component content is 0.5~2.5wt%; the CeO2 content in the second catalyst coating material is 60~100wt%, and the second active component content is 0.5~15wt%.

[0017] Furthermore, the first catalyst coating material is coated on an end of the substrate close to the engine; and the second catalyst coating material is coated on an end of the substrate away from the engine.

[0018] In a second aspect, the present invention provides a method for preparing the above-mentioned three-way catalyst for a lean-burn natural gas engine, comprising the following steps:

[0019] S1, loading the precursor solution of the first active component on the first carrier material by an impregnation method, and obtaining the first catalyst coating material after drying and calcining;

[0020] S2, loading the precursor solution of the second active component on the second carrier material by an impregnation method, and obtaining the second catalyst coating material after drying and calcining;

[0021] S3, ball-milling the first catalyst coating material and the binder, and applying the mixture to the front 50% area of ​​the substrate close to the engine, and obtaining a semi-finished catalyst after drying and calcining;

[0022] S4. The second catalyst coating material is mixed with a binder by ball milling and then coated on the rear 50% area of ​​the substrate away from the engine, and a finished catalyst is obtained after drying and calcining.

[0023] Furthermore, the precursor solutions in S1 and S2 include nitrate solution, acetate solution, hydrochloride solution or ammonium salt solution.

[0024] Furthermore, the binder in S3 and S4 is one or more of aluminum sol, silica sol and zirconium sol.

[0025] Furthermore, in S1-S4, the drying condition is 100-120° C. for 3-5 h, and the calcination condition is 500-600° C. for 2-5 h.

[0026] In a third aspect, the present invention provides an application of a three-way catalyst for a lean burn natural gas engine in the treatment of exhaust gas from a natural gas vehicle, wherein the three-way catalyst for a lean burn natural gas engine is the above-mentioned three-way catalyst for a lean burn natural gas engine, or a three-way catalyst for a lean burn natural gas engine prepared by the preparation method of the above-mentioned three-way catalyst for a lean burn natural gas engine.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The three-way catalyst for a lean-burn natural gas engine provided by the present invention comprises a substrate, a first catalyst coating material and a second catalyst coating material, wherein the first catalyst coating material and the second catalyst coating material are coated on the substrate in sections, wherein the first catalyst coating material comprises a specific first carrier material and a specific first active component, and the second catalyst coating material comprises a specific second carrier material and a specific second active component. The catalyst can effectively remove HC, CO and NOx in a rich-burn mode and produce a large amount of NH3, and also has high HC and CO catalytic oxidation performance in a lean-burn mode. The catalyst is used in the TWC+PSCR technical route of a lean-burn natural gas engine, and can achieve a good exhaust pollutant purification effect. DETAILED DESCRIPTION

[0029] The embodiments of the present invention will be described in detail below in conjunction with examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer.

[0030] In one aspect, the present invention provides a three-way catalyst for a lean-burn natural gas engine, comprising a substrate, a first catalyst coating material and a second catalyst coating material, wherein the first catalyst coating material and the second catalyst coating material are coated on the substrate in sections;

[0031] The first catalyst coating material includes a first carrier material and a first active component, the first carrier material includes one or more of CeO2-ZrO2-La2O3-Nd2O3, La2O3-Al2O3, CeO2-Al2O3, and the first active component includes Pd;

[0032] The second catalyst coating material includes a second carrier material and a second active component, wherein the second carrier material includes CeO2, CeO2-ZrO2-La2O3-Y2O3, CeO2-ZrO2-La2O3-Pr6O 11 One or more of the above, wherein the second active component includes Pt and / or Ni.

[0033] It should be noted that in the present invention, CeO2-ZrO2-La2O3-Nd2O3 refers to a composite material composed of CeO2, ZrO2, La2O3, and Nd2O3, La2O3-Al2O3 refers to a composite material composed of La2O3 and Al2O3, CeO2-Al2O3 refers to a composite material composed of CeO2 and Al2O3, CeO2-ZrO2-La2O3-Y2O3 refers to a composite material composed of CeO2, ZrO2, La2O3, and Y2O3, CeO2-ZrO2-La2O3-Pr6O 11 It refers to CeO2, ZrO2, La2O3, Pr6O 11 Composite materials composed of.

[0034] The above-mentioned three-way catalyst for lean-burn natural gas engine includes a substrate, a first catalyst coating material and a second catalyst coating material, wherein the first catalyst coating material and the second catalyst coating material are coated on the substrate in sections, wherein the first catalyst coating material includes a specific first carrier material and a specific first active component, and the second catalyst coating material includes a specific second carrier material and a specific second active component. The catalyst can effectively remove HC, CO and NOx in rich combustion mode and produce a large amount of NH3, and also has high HC and CO catalytic oxidation performance in lean combustion mode. The catalyst is used in the TWC+PSCR technical route of lean-burn natural gas engines and can achieve a good exhaust pollutant purification effect.

[0035] In an optional embodiment, the CeO2-ZrO2-La2O3-Nd2O3 has a CeO2 content of 20-30wt%, a ZrO2 content of 60-75wt%, a La2O3 content of 2-9wt%, and a Nd2O3 content of 3-7wt%;

[0036] The La2O3-Al2O3 has a La2O3 content of 3-5wt% and an Al2O3 content of 95-97wt%;

[0037] The CeO2 content in the CeO2-Al2O3 is 3-5wt%, and the Al2O3 content is 95-97wt%.

[0038] The CeO2 content in the above-mentioned CeO2-ZrO2-La2O3-Nd2O3 is typically but not limited to 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%; the ZrO2 content is typically but not limited to 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt% or 75wt%; the La2O3 content is typically but not limited to 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt% or 9wt%. The La2O3 content in the above La2O3-Al2O3 is typically but not limited to 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%; the Al2O3 content is typically but not limited to 95wt%, 95.5wt%, 96wt%, 96.5wt% or 97wt%. The CeO2 content in the above CeO2-Al2O3 is typically but not limited to 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%; the Al2O3 content is typically but not limited to 95wt%, 95.5wt%, 96wt%, 96.5wt% or 97wt%. Studies have found that when the content of each component in each component of the first carrier material is within the above range, the catalyst effect is better.

[0039] In an optional embodiment, the CeO2-ZrO2-La2O3-Y2O3 has a CeO2 content of 60-70wt%, a ZrO2 content of 20-30wt%, a La2O3 content of 2-9wt%, and a Y2O3 content of 2-13wt%;

[0040] The CeO2-ZrO2-La2O3-Pr6O 11 The CeO2 content is 60~70wt%, the ZrO2 content is 20~30wt%, the La2O3 content is 2~9wt%, and the Pr6O 11 The content is 2~7wt%.

[0041] The CeO2 content in the above CeO2-ZrO2-La2O3-Y2O3 is typically but not limited to 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt% or 70wt%; the ZrO2 content is typically but not limited to 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt% ; The La2O3 content is typically but not limited to 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt% or 9wt%; The Y2O3 content is typically but not limited to 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt% or 13wt%. The above CeO2-ZrO2-La2O3-Pr6O 11 The CeO2 content is typically but not limited to 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt% or 70wt%; the ZrO2 content is typically but not limited to 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%; the La2O3 content is typically but not limited to 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt% or 9wt%; the Pr6O 11 The content is typically but not limited to 2wt%, 3wt%, 4wt%, 5wt%, 6wt% or 7wt%. Studies have found that when the content of each component in each component of the second carrier material is within the above range, the catalyst effect is better.

[0042] In an optional embodiment, the CeO2 content in the first catalyst coating material is 0~30 wt%, and the first active component content is 0.5~2.5wt%; the CeO2 content in the second catalyst coating material is 60~100wt%, and the second active component content is 0.5~15wt%.

[0043] The CeO2 content in the above-mentioned first catalyst coating material is typically but not limited to 0, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 28wt% or 30wt%; the content of the first active component is typically but not limited to 0.5wt%, 1wt%, 1.5wt%, 2wt% or 2.5wt%. The CeO2 content in the above-mentioned second catalyst coating material is typically but not limited to 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, 96wt%, 98wt% or 100wt%; the second active component content is typically but not limited to 0.5wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt% or 15wt%. Studies have found that when the CeO2 content and the first active component content in the first catalyst coating material are within the above ranges, and the CeO2 content and the second active component content in the second catalyst coating material are within the above ranges, the catalyst effect is better.

[0044] In an optional embodiment, the first catalyst coating material is coated on the end of the substrate close to the engine; the second catalyst coating material is coated on the end of the substrate away from the engine. Coating the first catalyst coating material on the end of the substrate close to the engine (also called the "front end") rather than the end away from the engine (also called the "rear end") can generate more NH3 in the rich combustion mode.

[0045] In an optional embodiment, the substrate includes a cordierite, mullite or silicon carbide honeycomb ceramic substrate.

[0046] On the other hand, the present invention also provides a method for preparing the above-mentioned three-way catalyst for a lean-burn natural gas engine, comprising the following steps:

[0047] S1, loading the precursor solution of the first active component on the first carrier material by an impregnation method, and obtaining the first catalyst coating material after drying and calcining;

[0048] S2, loading the precursor solution of the second active component on the second carrier material by an impregnation method, and obtaining the second catalyst coating material after drying and calcining;

[0049] S3, ball-milling the first catalyst coating material and the binder, and applying the mixture to the front 50% area of ​​the substrate close to the engine, and obtaining a semi-finished catalyst after drying and calcining;

[0050] S4. The second catalyst coating material is mixed with a binder by ball milling and then coated on the rear 50% area of ​​the substrate away from the engine, and a finished catalyst is obtained after drying and calcining.

[0051] The above preparation method has scientific process and the prepared catalyst has stable and reliable performance.

[0052] In an optional embodiment, the precursor solutions in S1 and S2 include nitrate solution, acetate solution, hydrochloride solution or ammonium salt solution.

[0053] In an optional embodiment, the binder in S3 and S4 is one or more of aluminum sol, silica sol and zirconium sol.

[0054] In an optional embodiment, the drying conditions in S1-S4 are drying at 100-120°C for 3-5 h, and the roasting conditions are roasting at 500-600°C for 2-5 h. The temperature in the above drying conditions is typically but not limited to 100°C, 105°C, 110°C, 115°C or 120°C; the drying time is typically but not limited to 3 h, 3.5 h, 4 h, 4.5 h or 5 h. The temperature in the roasting conditions is typically but not limited to 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C; the roasting time is typically but not limited to 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h.

[0055] On the other hand, the present invention also provides an application of the above three-way catalyst for lean-burn natural gas engines in the treatment of exhaust gas from natural gas vehicles. The above three-way catalyst for lean-burn natural gas engines is applied to the treatment of exhaust gas from natural gas vehicles, which can effectively remove HC, CO and NOx in rich combustion mode and produce a large amount of NH3, and can also effectively remove HC and CO in lean combustion mode.

[0056] On the other hand, the present invention also provides a lean-burn natural gas engine exhaust aftertreatment device, comprising the above-mentioned three-way catalyst and a passive nitrogen oxide selective catalytic reduction catalyst, wherein the passive nitrogen oxide selective catalytic reduction catalyst is located downstream of the above-mentioned three-way catalyst.

[0057] The present invention is further described in detail below with reference to Examples and Comparative Examples.

[0058] Example 1

[0059] A three-way catalyst for lean-burn natural gas engines:

[0060] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0061] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0062] The catalyst is prepared by the following method:

[0063] S1. Add 4.95 g of CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 21 wt%, the ZrO2 content is 72 wt%, the La2O3 content is 2 wt%, and the Nd2O3 content is 5 wt%) and 4.95 g of La2O3-Al2O3 (wherein the La2O3 content is 4.5 wt%, and the Al2O3 content is 95.5 wt%) carrier powders into a palladium nitrate solution containing 0.1 g of Pd, stir rapidly and evenly, let stand for 3 h, then dry at 120 ° C for 4 h, and calcine at 550 ° C for 3 h to obtain a powder 1 with a Pd content of 1 wt%.

[0064] S2. Add 9.9 g of CeO2-ZrO2-La2O3-Y2O3 (wherein the CeO2 content is 60 wt%, the ZrO2 content is 30 wt%, the La2O3 content is 5 wt%, and the Y2O3 content is 5 wt%) carrier powder to a platinum nitrate solution containing 0.1 g Pt, stir quickly and evenly, let it stand for 3 h, then dry at 120 ° C for 4 h, and calcine at 550 ° C for 3 h to obtain powder 2 with a Pt content of 1 wt%.

[0065] S3. Add 9.8 g of CeO2 carrier powder to a nickel acetate solution containing 0.2 g of Ni, stir quickly and evenly, let stand for 3 hours, then dry at 110°C for 4 hours, and calcine at 550°C for 3 hours to obtain powder 3 with a Ni content of 2 wt%.

[0066] S4. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0067] S5. After powder 2 and powder 3 are mixed with a binder by ball milling to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0068] Example 2

[0069] A three-way catalyst for lean-burn natural gas engines:

[0070] Front section Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0071] The latter stage is Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0072] The catalyst is prepared by the following method:

[0073] S1. Powder 1, powder 2 and powder 3 were prepared by the same method as S1 to S3 in Example 1.

[0074] S2. After powder 2 and powder 3 are mixed with a binder by ball milling to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0075] S3. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0076] Example 3

[0077] A three-way catalyst for lean-burn natural gas engines:

[0078] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0079] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3;

[0080] The catalyst is prepared by the following method:

[0081] S1. Powder 1 and powder 2 were prepared by the same method as S1 and S2 in Example 1.

[0082] S2. After powder 1 and a binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0083] S3, after powder 2 and a binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0084] Example 4

[0085] A three-way catalyst for lean-burn natural gas engines:

[0086] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3;

[0087] Back stage Ni / CeO2;

[0088] The catalyst is prepared by the following method:

[0089] S1. Add 9.9 g of CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 21 wt%, the ZrO2 content is 72 wt%, the La2O3 content is 2 wt%, and the Nd2O3 content is 5 wt%) carrier powder to a palladium nitrate solution containing 0.1 g of Pd, stir quickly and evenly, let stand for 3 h, then dry at 120 ° C for 4 h, and calcine at 550 ° C for 3 h to obtain a powder 1 with a Pd content of 1 wt%.

[0090] S2. Powder 3 is prepared by the same method as S3 in Example 1.

[0091] S3. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0092] S4. After the powder 3 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0093] Example 5

[0094] A three-way catalyst for lean-burn natural gas engines:

[0095] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / CeO2-Al2O3;

[0096] Back stage Pt / CeO2-ZrO2-La2O3-Pr6O 11 +Ni / CeO2;

[0097] The catalyst is prepared by the following method:

[0098] S1. Add 4.95g of CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 21 wt%, the ZrO2 content is 72wt%, the La2O3 content is 2wt%, and the Nd2O3 content is 5wt%) and 4.95g of CeO2-Al2O3 (wherein the CeO2 content is 4.5wt%, and the Al2O3 content is 95.5wt%) carrier powders into a palladium nitrate solution containing 0.1g of Pd, stir quickly and evenly, let stand for 3h, then dry at 120℃ for 4h, and calcine at 550℃ for 3h to obtain powder 1 with a Pd content of 1wt%.

[0099] S2, 9.9 g CeO2-ZrO2-La2O3-Pr6O 11 (CeO2 content is 60 wt%, ZrO2 content is 30 wt%, La2O3 content is 3 wt%, Pr6O 11 The carrier powder (with a content of 7wt%) was added to a platinum nitrate solution containing 0.1g Pt, quickly stirred and allowed to stand for 3h, then dried at 120℃ for 4h and calcined at 550℃ for 3h to obtain powder 2 with a Pt content of 1wt%.

[0100] S3. Powder 3 was prepared by the same method as S3 in Example 1.

[0101] S4. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0102] S5. After powder 2 and powder 3 are mixed with a binder by ball milling to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0103] Example 6

[0104] A three-way catalyst for lean-burn natural gas engines:

[0105] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0106] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0107] Different from Example 1, in this embodiment, CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 15 wt%, the ZrO2 content is 78 wt%, the La2O3 content is 1 wt%, and the Nd2O3 content is 6 wt%), La2O3-Al2O3 (wherein the La2O3 content is 6 wt%, and the Al2O3 content is 94 wt%), and CeO2-ZrO2-La2O3-Y2O3 (wherein the CeO2 content is 75 wt%, the ZrO2 content is 19 wt%, the La2O3 content is 5 wt%, and the Y2O3 content is 1 wt%). The content of each component in the above components is not within the preferred range of the present invention.

[0108] Example 7

[0109] A three-way catalyst for lean-burn natural gas engines:

[0110] Front section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0111] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0112] Different from Example 1, in this example, CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 80 wt%, the ZrO2 content is 14 wt%, the La2O3 content is 2 wt%, and the Nd2O3 content is 4 wt%), La2O3-Al2O3 (wherein the La2O3 content is 6 wt%, and the Al2O3 content is 94 wt%), and CeO2-ZrO2-La2O3-Y2O3 (wherein the CeO2 content is 55 wt%, the ZrO2 content is 35 wt%, the La2O3 content is 8 wt%, and the Y2O3 content is 2 wt%). The content of each component in the above components is not within the preferred range of the present invention, and the CeO2 content in the first catalyst coating material and the second catalyst coating material is not within the preferred range of the present invention.

[0113] Comparative Example 1

[0114] A three-way catalyst for lean-burn natural gas engines:

[0115] Full section Pd / CeO2-ZrO2-La2O3-Nd2O3+Pd / La2O3-Al2O3;

[0116] The catalyst is prepared by the following method:

[0117] S1. Powder 1 was prepared by the same method as S1 in Example 1.

[0118] S2. The powder 1 and the binder are ball-milled and mixed to prepare a slurry, which is then coated on a cordierite ceramic honeycomb substrate to obtain a final catalyst.

[0119] Comparative Example 2

[0120] A three-way catalyst for lean-burn natural gas engines:

[0121] Full section Pt / CeO2-ZrO2-La2O3-Y2O3;

[0122] The catalyst is prepared by the following method:

[0123] S1. Powder 2 was prepared by the same method as S2 in Example 1.

[0124] S2. After powder 2 and a binder are ball-milled and mixed to prepare a slurry, the slurry is coated on a cordierite ceramic honeycomb substrate to obtain a final catalyst.

[0125] Comparative Example 3

[0126] A three-way catalyst for lean-burn natural gas engines:

[0127] Front section Pt / CeO2-ZrO2-La2O3;

[0128] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0129] The catalyst is prepared by the following method:

[0130] S1. Add 9.9 g of CeO2-ZrO2-La2O3 (wherein the CeO2 content is 21 wt%, the ZrO2 content is 72 wt%, and the La2O3 content is 7 wt%) carrier powder to a platinum nitrate solution containing 0.1 g of Pt, stir quickly and evenly, let stand for 3 h, then dry at 120 ° C for 4 h, and calcine at 550 ° C for 3 h to obtain powder 1 with a Pt content of 1 wt%.

[0131] S2. Powder 2 and powder 3 were prepared by the same method as S2 and S3 in Example 1.

[0132] S3. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0133] S4. After powder 2 and powder 3 are mixed with a binder by ball milling to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0134] Comparative Example 4

[0135] A three-way catalyst for lean-burn natural gas engines:

[0136] Front section Pt / CeO2-ZrO2-La2O3-Nd2O3+Pt / Al2O3;

[0137] The latter stage is Pt / CeO2-ZrO2-La2O3-Y2O3+Ni / CeO2;

[0138] The catalyst is prepared by the following method:

[0139] S1. Add 4.95 g of CeO2-ZrO2-La2O3-Nd2O3 (wherein the CeO2 content is 21 wt%, the ZrO2 content is 72 wt%, the La2O3 content is 2 wt%, and the Nd2O3 content is 5 wt%) and 4.95 g of Al2O3 carrier powder to a platinum nitrate solution containing 0.1 g of Pt, stir quickly and evenly, let stand for 3 h, then dry at 120 ° C for 4 h, and calcine at 550 ° C for 3 h to obtain a powder 1 with a Pt content of 1 wt%.

[0140] S2. Powder 2 and powder 3 were prepared by the same method as S2 and S3 in Example 1.

[0141] S3. After the powder 1 and the binder are ball-milled and mixed to prepare a slurry, the slurry is coated on the front 50% area of ​​the cordierite ceramic honeycomb substrate close to the engine to obtain a semi-finished catalyst.

[0142] S4. After powder 2 and powder 3 are mixed with a binder by ball milling to prepare a slurry, the slurry is coated on the cordierite ceramic honeycomb substrate in the rear 50% area away from the engine to obtain the final catalyst.

[0143] Catalytic performance verification example

[0144] The catalysts prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated for catalyst activity on a simulated atmosphere evaluation system. The evaluation atmospheres included lean burn atmosphere and rich burn atmosphere. The lean burn atmosphere was: 10% CO2, 10% H2O, 5790ppm CO, 630ppm NO, 3160ppm CH4, 17627ppm O2, N2 as the balance gas, and the space velocity was 50000 h -1 The fuel-rich atmosphere is: 10% CO2, 10% H2O, 5790ppm CO, 630ppm NO, 3160ppm CH4, 17627ppm O2, N2 is the balance gas, and the air velocity is 50000h -1 The evaluation results are shown in Tables 1 to 3.

[0145] Table 1 Activity test results under lean combustion atmosphere conditions

[0146]

[0147] Note: 50 represents the catalyst bed temperature when the conversion rate of pollutants reaches 50%, T 90 Represents the catalyst bed temperature when the pollutant conversion rate reaches 90%. “ / ” represents that the pollutant conversion rate does not reach 90% even when the catalyst bed temperature is 550℃.

[0148] Table 2 Activity test results under fuel-rich atmosphere

[0149]

[0150] Table 3 NH3 generation in rich fuel atmosphere

[0151]

[0152] Comparison between Example 1 and Comparative Example 2 shows that adding the first catalyst coating containing Pd can effectively purify CH4 in the lean combustion mode.

[0153] Comparison between Example 1 and Example 2 shows that coating the first catalyst coating containing Pd on the front section of the substrate close to the engine rather than the rear section can generate more NH3 in the rich combustion mode.

[0154] Comparison between Example 1 and Example 3 shows that the second catalyst coating layer containing both Pt and Ni can improve the catalytic purification efficiency of CH4 and NO in the rich combustion mode and generate more NH3.

[0155] Comparison between Example 1 and Example 3 and Comparative Example 1 shows that adding a second catalyst coating containing Pt and / or Ni can effectively purify CH4 and NO and produce more NH3 in the rich combustion mode.

[0156] Although the present invention has been illustrated and described with specific embodiments, it will be appreciated that many other changes and modifications may be made without departing from the spirit and scope of the present invention. Therefore, it is intended to include all such changes and modifications within the scope of the present invention in the appended claims.

Claims

1. A three-way catalyst for a lean-burn natural gas engine, characterized in that: It comprises a substrate, a first catalyst coating material and a second catalyst coating material, wherein the first catalyst coating material and the second catalyst coating material are coated on the substrate in sections; The first catalyst coating material includes a first carrier material and a first active component, the first carrier material includes one or more of CeO2-ZrO2-La2O3-Nd2O3, La2O3-Al2O3, CeO2-Al2O3, and the first active component includes Pd; The second catalyst coating material includes a second carrier material and a second active component, wherein the second carrier material includes CeO2, CeO2-ZrO2-La2O3-Y2O3, CeO2-ZrO2-La2O3-Pr6O 11 One or more of the above, wherein the second active component includes Pt and / or Ni; The CeO2 content in the first catalyst coating material is 0-30 wt%, and the first active component content is 0.5-2.5 wt%; the CeO2 content in the second catalyst coating material is 60-100 wt%, and the second active component content is 0.5-15 wt%; The first catalyst coating material is coated on an end of the substrate close to the engine; the second catalyst coating material is coated on an end of the substrate away from the engine.

2. The three-way catalyst for a lean-burn natural gas engine according to claim 1, characterized in that: The CeO2-ZrO2-La2O3-Nd2O3 has a CeO2 content of 20-30wt%, a ZrO2 content of 60-75wt%, a La2O3 content of 2-9wt%, and a Nd2O3 content of 3-7wt%; The La2O3-Al2O3 has a La2O3 content of 3-5wt% and an Al2O3 content of 95-97wt%; The CeO2 content in the CeO2-Al2O3 is 3-5wt%, and the Al2O3 content is 95-97wt%.

3. The three-way catalyst for a lean-burn natural gas engine according to claim 1, characterized in that: The CeO2-ZrO2-La2O3-Y2O3 has a CeO2 content of 60-70wt%, a ZrO2 content of 20-30wt%, a La2O3 content of 2-9wt%, and a Y2O3 content of 2-13wt%; The CeO2-ZrO2-La2O3-Pr6O 11 The CeO2 content is 60~70wt%, the ZrO2 content is 20~30wt%, the La2O3 content is 2~9wt%, and the Pr6O 11 The content is 2~7wt%.

4. The method for preparing a three-way catalyst for a lean-burn natural gas engine according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, loading the precursor solution of the first active component on the first carrier material by an impregnation method, and obtaining the first catalyst coating material after drying and calcining; S2, loading the precursor solution of the second active component onto the second carrier material by an impregnation method, and obtaining the second catalyst coating material after drying and calcining; S3, ball-milling the first catalyst coating material and the binder, and applying the mixture to the front 50% area of ​​the substrate close to the engine, and obtaining a semi-finished catalyst after drying and calcining; S4. The second catalyst coating material is mixed with a binder by ball milling and then coated on the rear 50% area of ​​the substrate away from the engine, and a finished catalyst is obtained after drying and calcining.

5. The method for preparing a three-way catalyst for a lean-burn natural gas engine according to claim 4, characterized in that: The precursor solutions in S1 and S2 include nitrate solution, acetate solution, hydrochloride solution or ammonium salt solution.

6. The method for preparing a three-way catalyst for a lean-burn natural gas engine according to claim 4, characterized in that: The binder in S3 and S4 is one or more of aluminum sol, silica sol and zirconium sol.

7. The method for preparing a three-way catalyst for a lean-burn natural gas engine according to claim 4, characterized in that: The drying conditions in S1-S4 are 100-120° C. for 3-5 h, and the calcination conditions are 500-600° C. for 2-5 h.

8. Application of a three-way catalyst for a lean-burn natural gas engine in the treatment of exhaust gas from a natural gas vehicle, characterized in that: The three-way catalyst for a lean burn natural gas engine is the three-way catalyst for a lean burn natural gas engine as claimed in any one of claims 1 to 3, or a three-way catalyst for a lean burn natural gas engine prepared by the preparation method for a three-way catalyst for a lean burn natural gas engine as claimed in any one of claims 4 to 7.

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