A diesel oxidation catalyst with enhanced NO oxidation capacity, and a preparation method and application thereof

Abstract

This invention relates to a diesel oxidation catalyst that enhances NO oxidation capacity, its preparation method, and its application. The diesel oxidation catalyst comprises layered and regionalized coatings A, B, C, and optionally D. Based on the weight content of precious metals per unit volume, the sum of the loadings of platinum and palladium, the active components of precious metals, in coating B is greater than or equal to the sum of the loadings of platinum and palladium, the active components of precious metals, in coating A, and the sum of the loadings of platinum and palladium, the active components of precious metals, in coating C is greater than the sum of the loadings of platinum and palladium, the active components of precious metals, in coating B. This structural design significantly improves the low-temperature NO conversion capacity. The inclusion of coating C ensures stable fuel ignition performance, while coating D regulates the exhaust gas flow field. This catalyst has a simple preparation process, excellent performance, and can achieve a high NO conversion rate while meeting fuel ignition requirements under low precious metal loading conditions, making it suitable for industrial production applications.

Description

Technical Field

[0001] This invention belongs to the field of diesel engine exhaust gas purification catalysts, specifically relating to a diesel engine exhaust gas oxidation catalyst, its preparation method, and its application. Background Technology

[0002] With increasingly stringent global diesel engine emission regulations, diesel oxidation catalysts (DOCs) have become a key component of aftertreatment systems. Their core functions include: firstly, oxidizing NO to NO2, providing a high NO2 / NO2 ratio for downstream SCR (Selective Catalytic Reduction) or DPF (Diesel Particulate Filter). x Firstly, it improves the efficiency of low-temperature denitrification and passive regeneration of the DPF. Secondly, it oxidizes HC and CO, reducing harmful gas emissions and providing heat to promote downstream catalytic reactions. Thirdly, it has a fuel ignition function; in diesel engine after-injection strategies, DOC needs to quickly ignite high-concentration hydrocarbons to release heat for the DPF to complete active regeneration. However, precious metals platinum and palladium (Pt and Pd) are the main active components of DOC, and their prices are high and fluctuate drastically. To reduce vehicle costs, OEMs are constantly reducing the amount of precious metals used in DOC, while requiring it to still have a high NO conversion rate and reliable fuel ignition performance at low temperatures (200-250 ℃). This forces catalyst suppliers to strike a balance between low precious metal loading, high activity, and high stability. Therefore, developing new DOC products with both excellent catalytic performance and lower cost has become an inevitable choice for enterprises to enhance competitiveness, meet end-customer needs, and comply with environmental policy requirements, and is also an important trend driving the upgrading of diesel engine exhaust after-treatment technology.

[0003] To address these challenges, academia and industry have proposed several strategies: First, element doping and additive optimization: introducing alkaline earth metals (Ba and Sr), rare earth elements (Ce, Y, and Zr), or transition metals (Mn and Bi, etc.) into the support or preparation process to improve the thermal stability and sulfur resistance of the catalyst; second, zoned and layered coating design: rationally distributing precious metals according to the airflow axial gradient to achieve rapid oxidation combustion heat release and NO oxidation at the front end, while also controlling costs; third, adjusting the coating length and loading: optimizing the flow field and reaction zone; and fourth, optimizing the platinum-palladium ratio: adjusting the Pt / Pd ratio of the catalyst according to different engine characteristics to balance the NO oxidation and CO / HC oxidation performance.

[0004] WO2022069465A1 discloses a bismuth-containing diesel oxidation catalyst in which a bismuth-containing Pt catalytic coating (Bi2O3 or Bi-Al / Si composite oxide) is arranged in region B near the exhaust outlet to improve the efficiency of NO oxidation to NO2 and improve CO / HC oxidation at low temperature, while reducing the amount of Pt used.

[0005] Patent WO2021154701A1 discloses a yttrium-doped oxidation catalyst composition suitable for diesel engine exhaust treatment. Its core component is a platinum group metal (preferably Pt or Pt / Pd), manganese, and yttrium (or lanthanum, tin, magnesium, cerium, titanium, etc.) supported on a high-surface-area refractory metal oxide such as alumina. Zeolite can be further introduced, and the design can be optimized through layered or partitioned coatings. This structure significantly improves the low-temperature NO2 / NO2 ratio. x It also enhances stability after high-temperature hydrothermal aging, thereby simultaneously achieving the emission of HC, CO, and NO under cold start and long-term operation conditions. x Highly efficient conversion.

[0006] WO2024028567A1 proposes an improved diesel oxidation catalyst and its manufacturing method. The improvement is achieved through a "two-step heat treatment + secondary coating at the inlet end" method: first, a Pt / Pd layer is coated along the entire length and aged at high temperature to stabilize NO oxidation performance; then, a fresh PGM layer is coated only at the inlet end (10-40% of the length) and subjected to a secondary heat treatment at a lower temperature. This reduces the performance difference between fresh and aged catalysts, lowers the regeneration temperature requirement, and simultaneously ensures CO / HC conversion and exothermic capabilities.

[0007] The patent WO2023122414A1 adopts a partitioned / layered design, placing the first refractory oxide layer containing Pt / Pd and optional molecular sieves in the front-end region, and the second layer containing Pt-Mn in the downstream region. This improves the NO conversion rate with a lower amount of precious metals, promotes the regeneration of downstream SCR and DPF, and improves the low-temperature CO / HC activation performance.

[0008] While existing technologies have made some progress in additive introduction, zonal and stratified design, and precious metal optimization, there are still shortcomings in balancing low-temperature activity, fuel ignition performance, and hydrothermal stability while reducing precious metal loading. Therefore, new diesel oxidation catalysts and their preparation methods are still needed to achieve a further balance between performance and cost. Summary of the Invention

[0009] The purpose of this patent is to address the significant challenge of simultaneously achieving high NO conversion efficiency and fuel ignition performance in diesel oxidation catalysts with low precious metal loadings. This invention provides a diesel oxidation catalyst that enhances NO conversion, its preparation method, and its application, and the catalyst can provide stable fuel ignition performance.

[0010] To achieve the above objectives, the present invention provides a diesel oxidation catalyst that enhances NO oxidation capacity. The catalyst includes a support and a catalyst coating coated on the surface of the support. The support is a flow-through carrier with a honeycomb structure and has an axial length, and includes a front end and a rear end in the direction of gas flow. The catalyst coating includes coating A, coating B, coating C, and optionally coating D. Coating A, coating B, and coating C contain noble metal active components, while coating D does not contain noble metal active components.

[0011] In this invention, the diesel oxidation catalyst adopts a partitioned and layered structural design, including coating A, coating B, coating C, and coating D when necessary. Each coating has its own function. Coating C is a precious metal coating, which is mainly responsible for the ignition of fuel. Coating A and coating B are also precious metal coatings, which together undertake the NO conversion function and control hydrocarbon leakage during the fuel ignition process. Coating D is an alumina coating without precious metals, which is mainly used to regulate exhaust gas diffusion, further improve NO conversion rate and reduce hydrocarbon leakage.

[0012] The diesel oxidation catalyst has coating A applied to the front end of the carrier, with a coating length of 20% to 70% (preferably 30-60%) of the axial length of the carrier, extending from the front end to the rear end. Coating B is applied to the rear end of the carrier, with a coating length of 30% to 100% (preferably 40-80%) of the axial length of the carrier, extending from the rear end to the front end. Coating C is applied on top of coating A, with a coating length of 1% to 20% (preferably 3-15%) of the axial length of the carrier, extending from the front end to the rear end. If coating A is completely covered by coating B, then coating C is applied on top of coating B, extending from the front end to the rear end. In particular, if coating D is present, it is applied on top of coating A or coating B or coatings A and B, directly contacting the carrier, with a coating length of 0% (excluding 0%) to 100% (preferably 20-80%) of the axial length of the carrier, extending from the front end to the rear end, or from the rear end to the front end. In an embodiment of the diesel oxidation catalyst according to the present invention, coatings A, B and D can all be in direct contact with the carrier.

[0013] An important feature of the diesel oxidation catalyst is the loading of the noble metal active components platinum and palladium in coating B (weight of noble metal elements per unit volume, g / ft). 3The sum of the amounts of the coating A and its active components (platinum and palladium) is greater than or equal to the sum of their loadings. The NO conversion process is kinetically controlled in the low-temperature region (below 350 °C) and thermodynamically controlled in the high-temperature region. Current technical challenges primarily lie in improving the NO conversion rate in the low-temperature region. Diesel exhaust gas has a complex composition, and the NO oxidation to NO2 reaction involves multiple effects, including NO self-inhibition, hydrocarbon and carbon monoxide inhibition, and NO2 inhibition. These factors limit the improvement of NO conversion rate under low-temperature conditions. The structural design proposed in this invention can effectively balance these inhibition effects, thereby improving NO conversion performance in the low-temperature region. Simultaneously, considering stable fuel ignition performance, coating A also plays a crucial role in the fuel ignition process; excessively low precious metal loading may affect ignition performance. To this end, the present invention first controls the noble metal loading of coating A within a reasonable range; secondly, the sum of the loading of the noble metal active components platinum and palladium in coating C is greater than the sum of the loading of the noble metal active components platinum and palladium in coating B. By enhancing the ignition function of coating C, a higher temperature rise is obtained in the early stage of the reaction to compensate for the negative impact that the reduced loading of coating A may cause; at the same time, the hydrothermal stability of coating A is improved by process optimization, and the dispersion of noble metals after aging is improved.

[0014] The coating material of coating A of the diesel oxidation catalyst may or may not contain molecular sieves, including one or more of β molecular sieves, ZSM-5, MOR and Y molecular sieves; the coating material of coating D does not contain molecular sieves.

[0015] This invention also relates to a method for preparing a diesel oxidation catalyst with enhanced NO oxidation capacity. The method involves feeding and preparing a slurry according to the coating structure ratio of coating A, coating B, coating C, and coating D, followed by sequential grinding and coating processes to prepare a diesel oxidation catalyst with the aforementioned multi-layered coating structure. This invention provides a method for preparing a diesel oxidation catalyst with enhanced NO oxidation capacity. This catalyst is applied to the catalytic oxidation reaction of engine exhaust gas, preferably for the oxidation treatment of diesel engine exhaust gas, and more preferably for the active regeneration process of a diesel particulate filter (DPF).

[0016] Beneficial effects

[0017] This invention provides a diesel oxidation catalyst with enhanced NO oxidation capacity and its preparation method. It adopts a unique structural design and combines a preparation process that improves the hydrothermal aging resistance of precious metals in each region. Under low precious metal loading conditions, it simultaneously meets the requirements of fuel ignition performance and achieves a high NO conversion capacity. Attached Figure Description

[0018] Figure 1 This is a design diagram of the coating structure of the diesel oxidation catalyst according to the first embodiment of the present invention.

[0019] Figure 2 This is a design diagram of the coating structure of the diesel oxidation catalyst according to the second embodiment of the present invention.

[0020] Figure 3 This is a design diagram of the coating structure of the diesel oxidation catalyst according to the third embodiment of the present invention.

[0021] Figure 4 This is a design diagram of the coating structure of the diesel oxidation catalyst according to the fourth embodiment of the present invention.

[0022] Figure 5 This is a coating structure design diagram of the diesel oxidation catalyst according to the fifth embodiment of the present invention.

[0023] Figure 6 This is a design diagram of the coating structure of the diesel oxidation catalyst according to the sixth embodiment of the present invention.

[0024] Figure 7 The NO oxidation capacity (NO2 / NO2 ratio) of the diesel oxidation catalysts of the first, second, and third embodiments of the present invention and Comparative Example 1 at different inlet temperatures. x The test results. Detailed Implementation

[0025] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] In this invention, the support can be any material commonly used in catalyst preparation, preferably comprising a ceramic or metal honeycomb structure, and can be a straight-through or wall-flow support. Ceramic supports are made of refractory materials, such as cordierite, cordierite-alumina, alumina, magnesium oxide, silicon nitride, silicon carbide, zirconium mullite, spodumene, alumina-silica, zirconium silicate, sillimanite, magnesium silicate, and aluminosilicates. Metallic supports are composed of one or more metals or metal alloys. In this invention, the support may contain up to approximately 900 or more channels or passages per square inch of cross-section for the flow of engine exhaust gases. For example, the support may have approximately 50 to 600, more typically approximately 200 to 400 cells per square inch (cpsi: channels per square inch). The cells may have a square, rectangular, circular, elliptical, hexagonal, or other polygonal cross-section. Flow-through supports typically have a wall thickness of 0.002 to 0.1 inches.

[0027] In this invention, the “front end” and “back end” of the carrier or catalyst are defined by the order in which they come into contact with the diesel engine exhaust gas. The end that comes into contact with the gas first is the front end, and the end that comes into contact with the gas last is the back end.

[0028] In this invention, the load is expressed as dry weight per unit volume; for example, the load of precious metals is expressed in g / ft. 3 (Refers to the loading of elemental precious metal per unit volume), the loading of coatings or coating materials is expressed in g / L or g / in. 3 .

[0029] In this invention, unless otherwise specified, "platinum and palladium" refers to "the elemental state of platinum and palladium".

[0030] In an embodiment of the diesel oxidation catalyst of the present invention, the present invention provides a diesel oxidation catalyst that enhances the NO oxidation capacity. The catalyst includes a support and a catalyst coating coated on the surface of the support. The support is a flow-through support with a honeycomb structure and has an axial length, and includes a front end and a rear end in the direction of gas flow. The catalyst coating includes coating A, coating B, coating C, and possibly coating D. Coating A, coating B, and coating C contain noble metal active components, while coating D does not contain noble metal active components.

[0031] In an embodiment of the diesel oxidation catalyst according to the present invention, coatings A, B and C are made of noble metal active components and coating materials, and coating D is made of coating materials; The noble metal active components of coatings A, B and C include platinum and palladium, which are loaded on the coating material; The coating materials of coatings A, B, C, and D are inorganic porous materials or mixtures of various inorganic porous materials, containing heat-resistant materials, such as one or more selected from metal oxides, non-metal oxides, and molecular sieves. The metal oxides are selected from at least one of alumina, strontium oxide, titanium dioxide, manganese oxide, zirconium oxide, barium oxide, lanthanum oxide, cerium oxide, and antimony oxide; the non-metal oxides are selected from silicon oxide; and the molecular sieves are selected from one or more of β-molecular sieves, ZSM-5, MOR, and Y-molecular sieves. Inorganic porous materials may be, for example, one or more of the following: alumina, alumina-silicon oxide, alumina-strontium oxide, alumina-strontium oxide-silicon oxide, alumina-titanium dioxide, alumina-titanium dioxide-silicon oxide, alumina-manganese oxide, alumina-zirconium oxide, alumina-barium oxide, alumina-barium oxide-silicon oxide, alumina-lanthanum oxide, alumina-cerium oxide, alumina-antimony oxide, alumina-antimony oxide-silicon oxide, and molecular sieves; particularly preferred are alumina, alumina-silicon oxide, alumina-barium oxide, alumina-barium oxide-silicon oxide, alumina-strontium oxide, and alumina-strontium oxide-silicon oxide.

[0032] When the coating material contains silicon oxide, barium oxide and strontium oxide, the content of silicon oxide, barium oxide or strontium oxide is 1% to 9% of the weight of aluminum oxide in the coating material, more preferably 3% to 6%.

[0033] In an embodiment of the diesel oxidation catalyst according to the present invention, coating A is applied to the front end of the carrier, and its coating length is 20% to 70%, preferably 30% to 60%, or 35% to 50% of the axial length of the carrier, extending from the front end to the rear end of the carrier. In an embodiment of the diesel oxidation catalyst according to the present invention, coating B is applied to the rear end of the support, and the coating length is 30% to 100%, preferably 40% to 80%, or 50% to 60% of the axial length of the support, extending from the rear end to the front end of the support. In an embodiment of the diesel oxidation catalyst according to the present invention, coating C is applied on top of coating A, and its coating length is 1% to 20%, preferably 3% to 15%, or 3% to 10% of the axial length of the carrier, extending from the front end to the rear end of the carrier. In an embodiment of the diesel oxidation catalyst according to the present invention, if coating D is present, it is coated on top of coating A or coating B or coatings A and B, in direct contact with the carrier, and its coating length is 0% to 100%, preferably 20% to 80%, or 40% to 60% of the axial length of the carrier, extending from the front end to the rear end of the carrier, or from the rear end to the front end of the carrier.

[0034] In an embodiment of the diesel oxidation catalyst according to the present invention, coatings A, B and D can be in direct contact with the carrier.

[0035] In an embodiment of the diesel oxidation catalyst according to the present invention, the loading of the coating material in coating A is 45 to 100 g / L, preferably 50-75 g / L, the weight ratio of the noble metal active components platinum and palladium in coating A is 2:1 to 8:1, and the sum of the weights of platinum and palladium is 0.1 wt% to 1.5 wt%, preferably 0.3 wt% to 1.0 wt% of the coating material in coating A; the loading of the coating material in coating B is 45 to 100 g / L, preferably 60-85 g / L, the weight ratio of the noble metal active components platinum and palladium in coating B is 4:1 to 12:1, and the sum of the weights of platinum and palladium is 0.2 wt% to 2.0 wt%, preferably 0.4 wt% to 1.5 wt% of the coating material in coating B; the loading of the coating material in coating C is 30 to 120 g / L, preferably 40-100 g / L. The weight ratio of the noble metal active components platinum and palladium in coating C is 1:1 to 5:1, and the sum of the weights of platinum and palladium is 2.0 wt% to 6.0 wt% and 3.0 wt% to 5.0 wt% of the coating material in coating C, respectively; the loading of the coating material in coating D is 10-60 g / L; preferably 20-40 g / L.

[0036] In an embodiment of the diesel oxidation catalyst according to the present invention, particularly preferably, the loading of the noble metal active components platinum and palladium of coating B, based on the noble metal weight content per unit volume (g / ft), is... 3 The sum of these values ​​is greater than or equal to the sum of the loading amounts of the noble metal active components platinum and palladium in coating A.

[0037] In an embodiment of the diesel oxidation catalyst according to the present invention, the coating material of coating A may or may not contain molecular sieves, and the molecular sieves include one or more of β molecular sieves, ZSM-5, MOR and Y molecular sieves; the coating material of coating D does not contain molecular sieves.

[0038] This invention also relates to a method for preparing a diesel oxidation catalyst with enhanced NO oxidation capacity. The method involves feeding and preparing a slurry according to the coating structure ratio of coating A, coating B, coating C, and coating D, followed by grinding and coating processes, and then drying and calcination to prepare a diesel oxidation catalyst with the multi-layer coating structure.

[0039] The drying and calcination processes are as follows: after coating, the carrier is dried at 100-180 °C for 30-180 min, and then calcined at 400-600 °C under a nitrogen atmosphere for 0.5-5 h. Preferably, the drying is carried out at 120-150 °C for 60-90 min, and the calcination is carried out at 500-600 °C under a nitrogen atmosphere for 1-2 h; more preferably, the drying is carried out at 150 °C for 60 min, and the calcination is carried out at 550 °C under a nitrogen atmosphere for 1 h.

[0040] The diesel oxidation catalyst of this invention is applied to the catalytic oxidation reaction of engine exhaust gas, preferably for the oxidation treatment of diesel engine exhaust gas, and more preferably for the active regeneration process of diesel particulate filter (DPF) to improve NO conversion rate, promote the downstream SCR low-temperature denitrification efficiency, and enhance the regeneration reliability and overall emission control performance of DPF.

[0041] The technical solution of the present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited by the embodiments.

[0042] Example 1 Steps for preparing a diesel oxidation catalyst that enhances NO oxidation capacity: 1. Preparation and application of slurry for coating A a) Platinum nitrate and platinum nitrate are made into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=4:1 (weight ratio), and the sum of the weights of platinum and palladium is 0.40% of the coating material in coating A; stir evenly to form a slurry for coating.

[0043] b) Cylindrical straight-through cordierite carrier for coating: 7.5 inch × 4 inch, 400 cpsi (channelsper square inch), wall thickness 0.004 inch; Coating A extends from the front end to the rear end of the carrier. The coating action is completed by vacuuming material from the front end of the carrier to a certain height and then blowing it off; the coating length is 50% of the axial length of the carrier.

[0044] c) The carrier coated with coating A was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 72 g / L.

[0045] 2. Preparation and application of slurry for coating B d) Platinum nitrate and platinum nitrate are made into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=6:1 (weight ratio), and the sum of the weights of platinum and palladium is 0.8wt% of the coating material in coating B; stir evenly to form a slurry for coating.

[0046] e) Apply coating B using the carrier that has been coated with coating A; coating B extends from the rear end to the front end of the carrier. The material is sucked up from the rear end of the carrier to a certain height using a vacuum and then blown away to complete the coating action; the coating length is 50% of the axial length of the carrier.

[0047] f) The carrier coated with coating B was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0048] 3. Preparation and application of slurry for coating C g) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=2.5:1 (weight ratio), and the sum of the weights of platinum and palladium is 3.0 wt% of the coating material in coating C; stir evenly to form a slurry for coating.

[0049] h) Apply coating C using the carrier that has been coated with coatings A and B; coating C extends from the front end to the rear end of the carrier and is on top of coating A; use vacuum to suck material from the front end of the carrier to a certain height and then blow it to complete the coating action; the coating length is 5% of the axial length of the carrier.

[0050] i) The carrier coated with coating C was dried at 150 °C for 30 min, and then calcined at 550 °C for 1 h. The coating loading was 110 g / L. The diesel oxidation catalyst of Example 1 was thus prepared.

[0051] Example 2 Steps for preparing a diesel oxidation catalyst that enhances NO oxidation capacity: 1. Preparation and application of slurry for coating A a) Platinum nitrate and platinum nitrate are made into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=4:1 (weight ratio), and the sum of the weights of platinum and palladium is 0.40 wt% of the coating material in coating A; stir evenly to form a slurry for coating.

[0052] b) Cylindrical straight-through cordierite carrier for coating: 7.5×4 inch, 400 cpsi, wall thickness 0.004 inch; Coating A extends from the front end to the rear end of the carrier. The coating action is completed by vacuuming material from the front end of the carrier to a certain height and then blowing it off; the coating length is 50% of the axial length of the carrier.

[0053] c) The carrier coated with coating A was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 72 g / L.

[0054] 2. Preparation and application of slurry for coating B d) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=6:1 (weight ratio). The total weight of platinum and palladium is 0.8 wt% of the coating material in coating B. BaO is added according to the loading amount of BaO being 3.0 g / L. Stir evenly to form a slurry for coating.

[0055] e) Apply coating B using the carrier that has been coated with coating A; coating B extends from the rear end to the front end of the carrier. The material is sucked up from the rear end of the carrier to a certain height using a vacuum and then blown away to complete the coating action; the coating length is 50% of the axial length of the carrier.

[0056] f) The carrier coated with coating B was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0057] 3. Preparation and application of slurry for coating C g) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=2.5:1 (weight ratio), and the sum of the weights of platinum and palladium is 3.0 wt% of the coating material in coating C; stir evenly to form a slurry for coating.

[0058] h) Apply coating C using the carrier that has been coated with coatings A and B; coating C extends from the front end to the rear end of the carrier and is on top of coating A; use vacuum to suck material from the front end of the carrier to a certain height and then blow it to complete the coating action; the coating length is 5% of the axial length of the carrier.

[0059] i) The carrier coated with coating C was dried at 150 °C for 30 min, and then calcined at 550 °C for 1 h, with a coating loading of 110 g / L. The diesel oxidation catalyst of Example 2 was thus prepared.

[0060] Example 3 Steps for preparing a diesel oxidation catalyst that enhances NO oxidation capacity: 1. Preparation and application of slurry for coating D a) Add the alumina-silica material to water, then add the necessary additives and stir evenly to form a slurry, which is then ready for coating.

[0061] b) Cylindrical straight-through cordierite carrier for coating: 7.5×4 inch, 400 cpsi, wall thickness 0.004 inch; Coating D extends from the rear end to the front end of the carrier, and the coating action is completed by vacuuming the material from the rear end of the carrier to a certain height and then blowing it off; the coating length is 67% of the axial length of the carrier.

[0062] c) The carrier coated with coating D was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0063] 2. Preparation and application of slurry for coating A d) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=5:1 (weight ratio), and the sum of the weights of platinum and palladium is 0.50 wt% of the coating material in coating A; stir evenly to form a slurry for coating.

[0064] e) Apply coating A using a carrier that has already been coated with coating D; coating A extends from the front end to the rear end of the carrier. The material is sucked up from the front end of the carrier to a certain height using a vacuum and then blown away to complete the coating action; the coating length is 50% of the axial length of the carrier.

[0065] f) The carrier coated with coating A was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0066] 3. Preparation and application of slurry for coating B g) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=5:1 (weight ratio), and the sum of the weights of platinum and palladium is 0.50 wt% of the coating material in coating B; stir evenly to form a slurry for coating.

[0067] h) Apply coating B using the carrier that has completed coatings D and A; coating B extends from the rear end of the carrier h to the front end, and the material is sucked up from the rear end of the carrier to a certain height using a vacuum and then blown away to complete the coating action; the coating length is 50% of the axial length of the carrier.

[0068] i) The carrier coated with coating B was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0069] 4. Preparation and application of slurry for coating C j) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=2.8:1 (weight ratio), and the sum of the weights of platinum and palladium is 4.3 wt% of the coating material in coating C; stir evenly to form a slurry for coating.

[0070] k) Apply coating C using a carrier that has already been coated with coatings D, A, and B; coating C extends from the front end to the rear end of the carrier and is on top of coating A; use a vacuum to suck material from the front end of the carrier to a certain height and then blow it off to complete the coating action; the coating length is 5% of the axial length of the carrier.

[0071] l) The carrier coated with coating C was dried at 150 °C for 30 min, and then calcined at 550 °C for 1 h, with a coating loading of 73 g / L. The diesel oxidation catalyst of Example 3 was thus prepared.

[0072] Comparative Example 1 1. Preparation and application of slurry for coating A a) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=4.7:1 (weight ratio), and the sum of the weights of platinum and palladium is 1.05 wt% of the coating material in coating A; stir evenly to form a slurry for coating.

[0073] b) Cylindrical straight-through cordierite carrier for coating: 7.5×4 inch, 400 cpsi, wall thickness 0.004 inch; Coating A extends from the front end to the rear end of the carrier. The coating action is completed by vacuuming the material from the front end of the carrier to a certain height and then blowing it off; the coating length is 42.5% of the axial length of the carrier.

[0074] c) The carrier coated with coating A was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h, with a coating loading of 61 g / L.

[0075] 2. Preparation and application of slurry for coating B d) Platinum nitrate and platinum nitrate were prepared into an aqueous solution and then added to the coating material alumina-silica slurry, with a Pt:Pd ratio of 5:1 (by weight). The total weight of platinum and palladium was 0.22 wt% of the coating material in coating B. The mixture was stirred evenly to form a slurry for coating.

[0076] e) Apply coating B using the carrier that has been coated with coating A; coating B extends from the rear end to the front end of the carrier. The material is sucked up from the rear end of the carrier to a certain height using a vacuum and then blown away to complete the coating action; the coating length is 57.5% of the axial length of the carrier.

[0077] f) The carrier coated with coating B was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h. The coating loading was 80 g / L.

[0078] 3. Preparation and application of slurry for coating C g) Platinum nitrate and platinum nitrate are prepared into an aqueous solution and then added to the coating material alumina-silica slurry, Pt:Pd=2.8:1 (weight ratio), and the sum of the weights of platinum and palladium is 3.0 wt% of the coating material in coating C; stir evenly to form a slurry for coating.

[0079] h) Apply coating C using the carrier that has been coated with coatings A and B; coating C extends from the front end to the rear end of the carrier and is on top of coating A; use vacuum to suck material from the front end of the carrier to a certain height and then blow it to complete the coating action; the coating length is 5% of the axial length of the carrier.

[0080] i) The support coated with coating C was dried at 150 °C for 30 min and then calcined at 550 °C for 1 h, with a coating loading of 107 g / L. The diesel oxidation catalyst of Comparative Example 1 was thus prepared.

[0081] Test example: Engine bench test Before testing, the diesel oxidation catalyst samples prepared in Examples 1, 2, 3, and Comparative Example 1 were first subjected to aging treatment in a hydrothermal furnace. The aging conditions were: continuous aging at 650 °C in a 10% H2O atmosphere for 80 h. After the above aging treatment, the resulting catalyst samples were used for subsequent bench performance comparison tests.

[0082] In the specific test, the catalyst sample used had a diameter of 7.5 inches, a length of 4 inches, a pressure of 400 cpsi, and a wall thickness of 0.004 inches. It was installed downstream of the exhaust pipe of a 5 L diesel engine. The test items included: (1) determining the NO2 / NO2 ratio in the engine exhaust gas under different temperature conditions. x The scale and test conditions were: temperature 275-400 ℃, space velocity 80000 h⁻¹. -1 NO x The original emissions were 600-1500 ppm, THC was 40-70 ppm, and CO was 35-50 ppm; the test results are listed in Table 1; (2) Test of fuel ignition performance. Test conditions: ① DOC inlet temperature 260 ℃, space velocity 80000 h -1 ② DOC inlet temperature 280 ℃, space velocity 100000 h -1 ③ DOC inlet temperature 350 ℃, space velocity 160000 h -1 Test procedure: Fuel was injected by in-cylinder post-injection. The temperature (T5) and hydrocarbon slip value at the DOC outlet were measured. The lower the T5 temperature and the lower the hydrocarbon slip value, the better the fuel ignition performance. The test results are listed in Table 2.

[0083] Table 1 NO2 / NO2 ratio for different diesel oxidation catalysts x

[0084] Table 2. Fuel ignition performance of different diesel oxidation catalysts

[0085] From Table 1 and Figure 7 The test results show that the NO2 / NO2 ratio of the diesel oxidation catalysts in Examples 1, 2, and 3 of this invention is... x All examples showed significantly better performance than Comparative Example 1, especially exhibiting higher NO oxidation capacity in the low-temperature range of 275-350 °C; Example 2 showed the best NO oxidation capacity. The test results in Table 2 further demonstrate that, under inlet temperatures of 260 °C, 280 °C, and 350 °C, and high space velocities, the catalysts of the present invention also exhibited highly efficient fuel ignition performance compared to the comparative examples, with hydrocarbon leakage values ​​all within acceptable ranges. In summary, the diesel oxidation catalyst of the present invention significantly improves low-temperature NO conversion while ensuring fuel ignition performance, demonstrating superior overall performance compared to existing technologies and possessing outstanding application value.

[0086] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A diesel oxidation catalyst that enhances NO oxidation capacity, said catalyst comprising a support and a catalyst coating applied to the surface of the support, characterized in that: The carrier is a flow-through carrier with a honeycomb structure and has an axial length, and includes a front end and a rear end according to the direction of airflow. The catalyst coating includes coating A, coating B, and coating C; And optional coating D; Coatings A, B, and C contain precious metal active components, while coating D does not contain precious metal active components.

2. The diesel oxidation catalyst according to claim 1, characterized in that, Coatings A, B, and C are made of noble metal active components and coating materials, while coating D is made of coating materials. The noble metal active components of coatings A, B and C include platinum and palladium, which are loaded on the coating material; The coating materials of coatings A, B, C and D are mixtures of one or more inorganic porous materials, containing heat-resistant materials; the inorganic porous materials are selected from one or more of metal oxides, non-metal oxides and molecular sieves.

3. The diesel oxidation catalyst according to claim 2, characterized in that: The metal oxide is selected from at least one of alumina, strontium oxide, titanium dioxide, manganese oxide, zirconium oxide, barium oxide, lanthanum oxide, cerium oxide, and antimony oxide; the non-metal oxide is selected from silicon oxide; the molecular sieve is selected from one or more of β-molecular sieve, ZSM-5, MOR, and Y-molecular sieve; the mixture of inorganic porous materials is preferably one or more of alumina, alumina-silicon oxide, alumina-strontium oxide, alumina-strontium oxide-silicon oxide, alumina-titanium oxide, alumina-titanium oxide-silicon oxide, alumina-manganese oxide, alumina-zirconium oxide, alumina-barium oxide, alumina-barium oxide-silicon oxide, alumina-lanthanum oxide, alumina-cerium oxide, alumina-antimony oxide, alumina-antimony oxide-silicon oxide, and molecular sieve.

4. The diesel oxidation catalyst according to claim 1, characterized in that: Coating A is applied to the front end of the carrier, and its coating length is 20% to 70% of the axial length of the carrier, extending from the front end to the rear end of the carrier; Coating B is applied to the rear end of the carrier, and its coating length is 30% to 100% of the axial length of the carrier, extending from the rear end of the carrier to the front end. Coating C is applied on top of coating A or B, and its coating length is 1% to 20% of the axial length of the carrier, extending from the front end to the rear end of the carrier. Preferably, if coating D is present, it is applied to coating A or coating B or coatings A and B below, in direct contact with the carrier, and its coating length is 0% to 100% of the axial length of the carrier, extending from the front end to the rear end of the carrier, or from the rear end to the front end of the carrier. Preferably, coatings A, B and D can be in direct contact with the carrier.

5. The diesel oxidation catalyst according to any one of claims 1-4, characterized in that: The loading of coating material in coating A is 45 to 100 g / L, the weight ratio of the noble metal active components platinum and palladium in coating A is 2:1 to 8:1, and the sum of the weights of platinum and palladium is 0.1 wt% to 1.5 wt% of the coating material in coating A; The loading of coating material in coating B is 45 to 100 g / L, and the weight ratio of the noble metal active components platinum and palladium in coating B is 4:1 to 12:1, with the sum of the weights of platinum and palladium being 0.2 wt% to 2.0 wt% of the coating material in coating B. The loading of coating material in coating C is 30 to 120 g / L, the weight ratio of the noble metal active components platinum and palladium in coating C is 1:1 to 5:1, and the sum of the weights of platinum and palladium is 2.0 wt% to 6.0 wt% of the coating material in coating C; The loading of coating material in coating D is 10 to 60 g / L.

6. The diesel oxidation catalyst according to claim 4, characterized in that: Based on the precious metal content per unit volume, the sum of the loading of platinum and palladium, the active components of precious metals in coating B, is greater than or equal to the sum of the loading of platinum and palladium, the active components of precious metals in coating A, and the sum of the loading of platinum and palladium, the active components of precious metals in coating C, is greater than the sum of the loading of platinum and palladium, the active components of precious metals in coating B.

7. The diesel oxidation catalyst according to any one of claims 1-6, characterized in that: Coating A may or may not contain molecular sieves in its coating material, and the molecular sieves include one or more combinations of β molecular sieves, ZSM-5, MOR and Y molecular sieves; coating D does not contain molecular sieves in its coating material.

8. A method for preparing a diesel oxidation catalyst that enhances NO oxidation capacity, characterized in that: According to the coating structure ratio of coating A, coating B, coating C and coating D as described in any one of claims 1-7, the materials are fed and slurry is prepared. Then, the grinding and coating processes are completed in sequence according to the structural layer order of the coating. Then, the drying and calcination treatment is carried out to prepare a diesel oxidation catalyst with the multi-layer coating structure.

9. The method for preparing the diesel oxidation catalyst according to claim 8, characterized in that: The drying and calcination process is as follows: after coating, the carrier is dried at 120-180 ℃ for 30-180 min, and then calcined at 400-600 ℃ under a nitrogen atmosphere for 0.5-5 h.

10. The application of the diesel oxidation catalyst according to any one of claims 1 to 7 or the diesel oxidation catalyst prepared according to the preparation method of claim 8 or 9, specifically for the oxidation treatment of diesel engine exhaust gas, preferably for the active regeneration process of diesel particulate filter (DPF).

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