A rapid preparation method of a diesel engine exhaust treatment catalyst based on joule heat impact and application thereof

Abstract

The application discloses a kind of fast preparation method of diesel engine exhaust treatment catalyst based on Joule heat shock and application thereof.The method comprises the following steps: mixing catalytic active metal precursor, carrier precursor and conductive adjusting component to construct precursor system, after forming and pre-drying, high instantaneous current pulse is applied in inert or reducing atmosphere, and carrier structure reconstruction and active metal high dispersion anchoring are completed within millisecond to second level time.The method has high preparation efficiency, low energy consumption, can effectively inhibit metal sintering and enhance metal-carrier interaction.The prepared catalyst has excellent low-temperature activity and thermal stability, and is suitable for efficient purification of carbon monoxide, hydrocarbons and nitrogen oxides in diesel engine exhaust.

Description

Technical Field

[0001] This invention relates to a method for preparing a diesel engine exhaust gas treatment catalyst, and particularly to a Joule heating shock technology, which enables the rapid preparation of a diesel engine exhaust gas treatment catalyst with high dispersion and rapid anchoring of catalytically active metals within an ultra-short timescale of milliseconds to seconds, and simultaneously constructs a stable catalyst with strong metal-support interaction. Background Technology

[0002] Diesel engines are widely used in road transportation, construction machinery, agricultural machinery, and stationary power generation equipment due to their high thermal efficiency, fuel economy, and reliability. However, the exhaust gases emitted by diesel engines during operation typically contain carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). These pollutants are significant sources of photochemical smog and fine particulate pollution, harming human respiratory and cardiovascular health. With increasingly stringent emission regulations in various countries, diesel engine exhaust pollution control faces higher requirements. Therefore, diesel engines are typically equipped with exhaust aftertreatment systems, in which the diesel oxidation catalyst (DOC) is a key functional component for the efficient oxidation and removal of CO and HC. It also promotes the conversion of NO to NO2 to a certain extent, providing favorable conditions for subsequent denitrification or particulate capture processes. Existing DOCs typically use noble metals such as Pt and Pd as catalytically active components, supported on high specific surface area oxide carriers such as γ-Al₂O₃, CeO₂, and CeO₂-ZrO₂. The main industrial preparation method is equal volume impregnation or excessive impregnation-drying-high temperature calcination process. The above traditional preparation methods generally have the following shortcomings: (1) The preparation process is long and the energy consumption is high. The calcination temperature is high and the time usually takes several hours, resulting in low production efficiency; (2) Long-term high temperature calcination can easily lead to sintering and agglomeration of noble metal nanoparticles, which increases the size of metal particles, thereby reducing the metal dispersion and catalytic activity, and is especially unfavorable to the performance at low temperature; (3) The metal-support interaction mainly depends on the slow thermal equilibrium process to form. The means of interface structure regulation are limited, resulting in insufficient stability of the catalyst under high temperature or hydrothermal aging conditions and limited service life.

[0003] Joule thermal shock technology is a novel heat treatment technique that applies a large instantaneous current to a conductive material, causing a significant Joule heating effect within an extremely short time, resulting in ultra-high-speed heating and rapid cooling after power is cut off. This technology offers advantages such as extremely high heating rates, extremely short processing times, controllable local temperatures, and low overall energy consumption. It is beneficial for inhibiting prolonged grain growth, limiting particle migration, and inducing the formation of non-equilibrium crystalline phases or stable interface structures. However, existing technologies lack a mature solution for systematically applying Joule thermal shock technology to the preparation process of diesel engine exhaust gas treatment catalysts, simultaneously achieving high dispersion of active metals, rapid crystallization of the support, and synergistic construction of strong metal-support interactions within milliseconds to seconds. Summary of the Invention

[0004] To address the technical problems of traditional methods for preparing diesel engine exhaust gas treatment catalysts, such as long process times, high energy consumption, easy metal sintering, and limited control over metal-support interactions, this invention aims to provide a rapid preparation method for diesel engine exhaust gas treatment catalysts based on Joule thermal shock and its applications. This method utilizes the instantaneous Joule heating effect to simultaneously achieve rapid support crystallization / reconstruction and high dispersion and stable anchoring of the catalytically active metal within milliseconds to seconds, significantly shortening the preparation cycle, reducing energy consumption, and effectively enhancing the catalyst's low-temperature activity and high-temperature / hydrothermal stability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a diesel engine exhaust gas treatment catalyst based on Joule thermal shock includes the following steps: (1) Construction of precursor system: The catalytic active metal precursor, the support precursor and the conductivity regulating component are mixed in a predetermined ratio to obtain a precursor system with uniform composition; wherein, the catalytic active metal precursor is preferably loaded into the pores of the support precursor by impregnation method. The precursor system can form a continuous or quasi-continuous conductive path in the subsequent Joule thermal shock treatment process to ensure that the current passes through uniformly and generates an effective Joule thermal effect.

[0006] (2) Molding and pre-drying treatment: The precursor system obtained in step (1) is prepared into solid structures such as blocks, sheets, granules or tablets, and dried at a temperature not higher than 200°C to remove solvent and / or physically adsorbed water, while maintaining the integrity of the precursor structure and the stability of the conductive network.

[0007] (3) Joule thermal shock treatment: In an inert or reducing atmosphere, a transient high current pulse is applied to the solid precursor obtained in step (2), so that it is rapidly heated to 800-1800℃ in a millisecond to second time through the Joule thermal effect, and then rapidly cooled after power is cut off, thereby completing the rapid crystallization or structural reconstruction of the carrier, and realizing the reduction, high dispersion and stable anchoring of the active metal. This rapid heating and quenching process effectively inhibits the long-term diffusion of metal atoms, thereby avoiding the sintering and growth of nanoparticles.

[0008] (4) Optional post-treatment steps: The material after Joule heat shock treatment is subjected to atmosphere control treatment at 300-500℃ to further stabilize the overall structure of the catalyst, adjust the valence state of the active metal, or optimize the surface properties.

[0009] Compared with the prior art, the present invention has the following beneficial effects: 1. High preparation efficiency and low energy consumption: The key heat treatment time of the catalyst is significantly shortened from hours in traditional processes to milliseconds to seconds, which significantly improves preparation efficiency and reduces energy consumption.

[0010] 2. High dispersion of active metal: The ultra-fast heating and cooling process effectively inhibits the migration and sintering of active metal nanoparticles at high temperatures, enabling them to be stably anchored on the support surface with high dispersion (average particle size <5 nm), thus exhibiting excellent low-temperature catalytic activity.

[0011] 3. Strong structural stability: The instantaneous high-temperature Joule thermal shock induces rapid reconstruction of the metal-support interface, forming a stable and strong metal-support interaction, which greatly improves the structural stability and service life of the catalyst under high temperature and hydrothermal aging conditions.

[0012] 4. The method has good versatility: It is applicable to various diesel engine exhaust gas treatment catalyst systems with Pt, Pd and other active components and oxides such as aluminum, cerium, zirconium and titanium as carriers, and has good industrial application and scale-up potential. Attached Figure Description

[0013] Figure 1 The Pt / Ce prepared in Example 1 0.5 Zr 0.5 TEM image of Pt nanoparticles (average particle size of approximately 3.71 nm) in O2 catalyst.

[0014] Figure 2 The image shows a TEM image of Pt nanoparticles (average particle size of approximately 6.64 nm) in the Pt / Al2O3 catalyst prepared in Comparative Example 1. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the implementation methods of this invention will be described in detail below with reference to the embodiments. However, the scope of protection of this invention is not limited to the following embodiments. Other embodiments obtained by those skilled in the art without departing from the concept of this invention are all within the scope of protection of this invention. Example 1

[0016] This embodiment aims to demonstrate the feasibility of using a conductivity-regulating component content of 0.1% (mass fraction, lower limit) and a pulse duration of 1 millisecond (lower limit). First, cerium nitrate (Ce(NO3)3·6H2O) and zirconium nitrate (Zr(NO3)4·5H2O) were weighed in a molar ratio of Ce:Zr = 1:1 and dissolved in deionized water to prepare a mixed salt solution. Commercial pseudoboehmite powder was added to the above solution, and the salt solution was fully loaded into the pores of the carrier precursor using an equal-volume impregnation method, followed by drying at 80°C. The dried powder was then thoroughly ground and mixed with 0.1% (mass fraction) of conductive carbon black (Vulcan XC-72) to form a uniform precursor powder. The powder was pressed into discs with a diameter of 10 mm and a thickness of approximately 2 mm using a tablet press at a pressure of 10 MPa. The disc precursor was placed in a tube furnace, and under an argon atmosphere, a transient high-current pulse with a duration of 1 millisecond and a current density of 5 × 10³ A / cm² was applied to its two electrodes. After power was turned off, the material was allowed to cool naturally to room temperature in an atmosphere. Subsequently, the obtained sample was treated in air at 400°C for 30 minutes to remove residual carbon and stabilize the surface, yielding the target Pt / Ce. 0.5 Zr 0.5 O2 catalyst. For example, Figure 1 As shown, the Pt nanoparticles prepared by transmission electron microscopy (TEM) have an average particle size of approximately 3.71 nm and are uniformly dispersed on the CeZrO2 solid solution support. Example 2

[0017] This embodiment aims to demonstrate the feasibility of using a conductivity-regulating component content of 5% (mass fraction, upper limit) and a pulse duration of 10 seconds (upper limit). Using an equal-volume impregnation method, palladium nitrate (Pd(NO3)2) solution was impregnated onto commercial boehmite (γ-AlOOH) powder, and allowed to stand for 12 hours to allow the active component to fully penetrate the carrier pores. Subsequently, 5% (mass fraction) of multi-walled carbon nanotubes (MWCNTs) were added to the impregnated wet powder and thoroughly ground to achieve uniform mixing. After drying the mixture at 80°C for 12 hours, it was pressed into discs with a diameter of 10 mm using a tablet press at a pressure of 10 MPa. The disc precursor was placed in an argon-hydrogen mixed reducing atmosphere containing 5% H2 and subjected to Joule thermal shock treatment with a current pulse lasting 10 seconds and a current density of 3 × 10² A / cm². After treatment, the power was cut off, and the mixture was rapidly cooled in the atmosphere to directly obtain the Pd / γ-Al2O3 catalyst without additional post-treatment. TEM characterization showed that the average particle size of the Pd nanoparticles was approximately 4.0 nm, and they were tightly bound to the Al2O3 support. Example 3

[0018] This embodiment aims to demonstrate the preparation of a composite support catalyst using graphene as a conductivity modifier. First, zirconium oxychloride (ZrOCl2·8H2O) and tetrabutyl titanate were dissolved in an ethanol-water mixed solvent in a certain proportion. After hydrolysis and precipitation, the precipitate was washed and dried to obtain a ZrTi composite hydroxide support precursor powder. Platinum chloride (PtCl2) solution was loaded onto the above support precursor using an excess impregnation method, and after drying, a Pt-loaded precursor was obtained. This precursor was mixed with a 1.5% (w / w) aqueous solution of graphene oxide (GO), ultrasonically dispersed to form a uniform slurry, and then freeze-dried to obtain a fluffy composite precursor bulk material. In an argon atmosphere, a transient current pulse with a duration of 500 milliseconds and a current density of 1.5 × 10³ A / cm² was applied to the bulk material. This high-temperature shock process simultaneously achieved partial thermal reduction of GO, formation of the ZrTiO3 support, and reduction and anchoring of Pt nanoparticles. In the obtained Pt / ZrO2-TiO2 catalyst, the average particle size of Pt nanoparticles is about 2.8 nm. Example 4

[0019] This embodiment aims to demonstrate the preparation of particulate catalyst morphology and its application at high current densities. A CeZr composite hydroxide precursor powder loaded with chloroplatinic acid was prepared according to the method in Example 1. This powder was mixed with 0.5% acetylene black by mass fraction and extruded into short cylindrical particles with a diameter of approximately 2 mm, which were then dried at 100°C. Several particles were evenly distributed in a graphite boat with electrodes connected to both ends, ensuring contact between particles to form a conductive path. The particles were subjected to a high-current pulse with a duration of 100 ms and a current density of 8 × 10³ A / cm² (close to the upper limit) in a nitrogen atmosphere for impact treatment. The treated particulate catalyst was then air-treated at 400°C for 30 minutes. This particulate catalyst can be directly used in a fixed-bed reactor, and tests show that it exhibits excellent propane oxidation activity. Example 5

[0020] This embodiment aims to highlight the advantages of Joule thermal shock in inducing strong metal-support interaction (SMSI) through comparative experiments. Two identical CeO2 precursor powders loaded with platinum nitrate were prepared, each mixed with 1% carbon nanotubes.

[0021] Sample A (Joule thermal shock): After tableting, it was treated with a pulse with a duration of 2 seconds and a current density of 1×10³ A / cm² in a 5% H2 / Ar atmosphere.

[0022] Sample B (conventional heat treatment): After tableting, it was placed in the same 5% H2 / Ar atmosphere tube furnace and heated to 800℃ (equivalent to the peak temperature of Joule thermal shock) at 10℃ / min, and held at that temperature for 2 hours.

[0023] CO chemisorption and X-ray photoelectron spectroscopy (XPS) analyses were performed on both samples. The results showed that sample A exhibited significantly higher CO chemisorption than sample B, indicating a higher Pt dispersion. XPS analysis revealed a higher relative Ce³⁺ content in sample A, and a more significant electronic interaction at the Pt-CeO₂ support interface. This confirms that the Joule thermal shock process more effectively induced strong metal-support interaction (SMSI) with encapsulation characteristics, enhancing interfacial stability while achieving high metal dispersion.

[0024] Comparative Example 1: This comparative example demonstrates a traditional preparation method. Using an impregnation method, alumina is added to deionized water and stirred thoroughly to ensure uniform dispersion, forming a support suspension. A platinum precursor is dissolved in deionized water and added dropwise to the above-mentioned support suspension, with thorough stirring for 1 hour. Subsequently, an appropriate amount of citric acid solution is added to the mixture, and stirring continues for 2 hours. The mixture is then dried at 120°C and calcined at 600°C for 3 hours to obtain the DOC oxidation catalyst. Figure 2As shown, the average particle size of the prepared Pt nanoparticles is approximately 6.64 nm, as determined by transmission electron microscopy (TEM).

Claims

1. A method for preparing a diesel engine exhaust gas treatment catalyst based on Joule thermal shock, characterized in that, Includes the following steps: (1) Construction of precursor system: The catalytic active metal precursor, the support precursor and the conductivity regulating component are mixed in a predetermined ratio to obtain a precursor system with uniform composition. The catalytic active metal precursor is preferably loaded into the pores of the support precursor by impregnation method. The precursor system can form a continuous or quasi-continuous conductive path during the subsequent Joule thermal shock treatment. (2) Molding and pre-drying treatment: The precursor system is prepared into a solid structure with a specific shape and dried at a temperature not exceeding 200°C to remove solvent and / or physically adsorbed water; (3) Joule thermal shock treatment: In an inert or reducing atmosphere, a transient high current pulse is applied to the solid precursor after step (2) to raise its temperature to 800-1800℃ in a millisecond to second time through the Joule thermal effect, and then it is rapidly cooled after the power is cut off, thereby obtaining a diesel engine exhaust gas treatment catalyst. (4) Optional post-processing steps: subject the material after Joule heat shock treatment to atmosphere conditioning at 300-500℃.

2. The preparation method according to claim 1, characterized in that, The catalytically active metal precursor is selected from one or two soluble chlorides, nitrates, or organometallic salts of platinum and palladium; the support precursor is selected from oxides, hydroxides, nitrates, or any combination thereof of aluminum, cerium, zirconium, and titanium; the conductivity regulating component is selected from at least one of carbon nanotubes, graphene, conductive carbon black, and metal fibers, and its mass fraction in the precursor system is 0.1-5%.

3. The preparation method according to claim 1 or 2, characterized in that, The duration of the instantaneous high-current pulse is from 1 millisecond to 10 seconds, and the current density is 10²-10. 4 A / cm².

4. The preparation method according to claims 1 to 3, characterized in that, The solid precursor structure is blocky, sheet-like, granular, or compressed.

5. A diesel engine exhaust gas treatment catalyst, characterized in that, Prepared by the method of any one of claims 1 to 4, comprising an oxide support and catalytically active metal nanoparticles highly dispersed on the surface of the oxide support, wherein the average particle size of the nanoparticles is less than 5 nm, and a strong metal-support interaction is formed with the oxide support through Joule thermal shock treatment.

6. The diesel engine exhaust gas treatment catalyst according to claim 5, characterized in that, The catalyst is used to purify carbon monoxide, hydrocarbons and / or nitrogen oxides in diesel engine exhaust.

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