Precious metal three-way catalyst as well as preparation method and application thereof

Abstract

The invention relates to a precious metal three-way catalyst as well as a preparation method and application thereof. The precious metal three-way catalyst comprises an alumina carrier, a cerium-zirconium solid solution and an active component M1, metal M2 is also loaded on the alumina carrier; the cerium-zirconium solid solution covers the surface of the alumina carrier, and the active component M1 is dispersed on the surface of the cerium-zirconium solid solution; the active component M1 comprises any one or a combination of at least two of Rh, Ir or Ru; the metal M2 comprises a combination of at least two of Pd, Pt, Rh or Au; the active component M1 and the metal M2 comprise at least three different elements. The noble metal three-way catalyst provided by the invention is used for degrading CO, NOx and CH3OH in an equivalent combustion mode, and is good in low-temperature activity, good in hydrothermal stability, relatively small in performance difference after hydrothermal aging, and wide in application prospect.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a noble metal three-way catalyst, its preparation method, and its uses. Background Technology

[0002] For stoichiometric combustion, three-way catalytic converters are an effective means of controlling emissions of pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Precious metal three-way catalytic converters are widely used in gasoline and natural gas vehicles. However, methanol combustion produces high levels of unconventional pollutants such as methanol and formaldehyde in engine exhaust. Especially when using M100 methanol engines, unconventional pollutant emissions during the cold start phase account for over 70%, making it difficult for traditional three-way catalytic converters to effectively purify this portion of pollutants.

[0003] Three-way catalysts (TWCs) are a core component of internal combustion engine exhaust aftertreatment systems, primarily used to simultaneously catalyze the purification of three main pollutants in gasoline vehicle exhaust: carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). x Its working principle is to oxidize CO and HC into carbon dioxide and water through a redox reaction under conditions close to the stoichiometric air-fuel ratio, while simultaneously reducing NO. x It is reduced to nitrogen. Since its first large-scale application in the 1970s, the three-way catalytic converter has become the mainstream technology for controlling gasoline vehicle exhaust emissions worldwide, playing a key role in reducing air pollution and meeting increasingly stringent emission regulations.

[0004] In existing technologies, three-way catalysts are usually based on honeycomb ceramic or metal supports, with an active coating having a high specific surface area. The active components mainly include noble metals (such as platinum, palladium, and rhodium), co-catalysts (such as rare earth oxides such as cerium, zirconium, and lanthanum), and stabilizer materials. In recent years, in order to further improve catalytic efficiency and durability, researchers have made a lot of improvements in materials and structures, mainly including: (1) developing cerium-zirconium composite oxide materials with high specific surface area and high thermal stability to improve oxygen storage capacity and anti-sintering performance; (2) optimizing the distribution and ratio of noble metals, such as using palladium to partially replace platinum to reduce costs, or designing core-shell structures to improve the utilization rate of noble metals; (3) introducing new co-catalysts (such as lanthanum, barium, and yttrium) to enhance the interaction between the coating and the support and suppress the high-temperature deactivation of active components; (4) improving the support structure, such as using gradient channel design or multilayer coating technology to optimize the mass transfer process and reduce back pressure.

[0005] However, despite significant progress, existing three-way catalyst technology still faces several key problems: (1) High dependence on precious metals: Catalyst performance is still highly dependent on precious metals such as platinum, palladium, and rhodium, which are scarce, expensive, and fluctuate wildly, resulting in high costs. (2) Insufficient high-temperature durability: Under long-term high-temperature operation conditions (especially above 900℃), active components are prone to sintering and agglomeration, and the cerium-zirconium solid solution phases separate, resulting in a decrease in oxygen storage capacity and rapid catalyst deactivation. (3) Cold start emission problem: During the cold start phase of the vehicle, the catalyst temperature is low and the activity is insufficient, resulting in a high proportion of pollutants emitted in the initial stage of total emissions, making it difficult to meet stricter low-temperature emission regulations. (4) Limited air-fuel ratio window: The catalyst has a narrow high-efficiency working window and requires extremely high precision in air-fuel ratio control, making it difficult to maintain the best conversion efficiency in actual driving cycles. (5) Poor adaptability to complex operating conditions: Under transient operating conditions such as frequent start-stop, high speed and high load, the catalyst's dynamic response capability to the simultaneous conversion of multiple pollutants still needs to be improved.

[0006] Therefore, how to develop a low-cost, highly active, high-temperature stable, and wide-operating-window three-way catalyst to further reduce the energy consumption and carbon emissions of methanol vehicles has become a pressing technical challenge in the field of exhaust gas purification. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a noble metal three-way catalyst, its preparation method, and its applications. The noble metal three-way catalyst of the present invention possesses excellent catalytic activity, low-temperature stability, and hydrothermal aging stability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a noble metal three-way catalyst, the noble metal three-way catalyst comprising an alumina support, a cerium-zirconium solid solution and an active component M1; the cerium-zirconium solid solution covers the surface of the alumina support, the active component M1 comprises any one or a combination of at least two of Rh, Ir or Ru; the metal M2 comprises a combination of at least two of Pd, Pt, Rh or Au; the active component M1 and the metal M2 comprise at least three different elements.

[0010] The noble metal three-way catalyst provided by this invention introduces a variety of different noble metals. Some of the noble metals are loaded on the surface of an alumina support, and the cerium-zirconium solid solution serves as an anchoring point for the active component M1. This can fully anchor the noble metals while reducing their agglomeration. Furthermore, the cerium-zirconium solid solution has a good crystal structure, oxygen storage capacity, and redox properties, which maximizes the optimization of the low-temperature performance of the noble metals in the stoichiometric combustion mode, while also exhibiting excellent hydrothermal stability.

[0011] This invention optimizes the metal-support interaction, allowing the active component to exist in the form of nanoparticles with high dispersion. It also regulates the electronic structure of noble metals and the oxygen defect concentration on the surface, thereby improving the low-temperature performance and thermal stability of the catalyst and achieving the goal of enhancing catalyst performance.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] In some embodiments, the general chemical formula of the cerium-zirconium solid solution is Ce. x Zr y O2, where 0.2≤x≤0.8, x+y=1. x can be, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, but is not limited to the listed values. Other unlisted values ​​within the range also apply.

[0014] In some embodiments, the mass ratio of the cerium-zirconium solid solution to alumina is (1-2):1, for example, it can be 1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] In some embodiments, based on a total mass of 100wt% of the noble metal three-way catalyst, the total mass fraction of the active component M1 and the metal M2 is 0.5wt%-1wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9% or 1.0wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Due to the high price of precious metals, this invention further controls the total mass fraction of active component M1 and metal M2 to 0.5wt%-1wt%, ensuring good catalyst activity without increasing the manufacturing cost of the catalyst.

[0017] In some embodiments, the total dispersion of the active component M1 and the metal M2 is 40%-60%, for example, it can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58% or 60%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] In some embodiments, the molar ratio of the active component M1 to the metal M2 is 1:(1-5), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] This invention further controls the molar ratio of active component M1 to metal M2 to be 1:(1-5). This molar ratio affects the dynamic equilibrium and synergistic efficiency of the redox reaction on the catalyst surface. If the proportion of active component M1 (e.g., Rh) is too large and the proportion of metal M2 (e.g., Pd, Pt) is too small, there will be an excess of carbon monoxide and hydrocarbons in the catalyst. In this atmosphere of excess CO and HC, CO and HC will compete for adsorption and poison the active sites of Rh. Simultaneously, this slightly oxygen-rich environment will inhibit NO... x The need for a low-oxygen environment is restored, resulting in a narrowing of the overall triple-effect purification window, NO x The low-temperature range for conversion is limited. If the proportion of active component M1 (e.g., Rh) is too small and the proportion of metal M2 (e.g., Pd, Pt) is too large, then nitrogen oxides will be in excess. The scarce rhodium metal sites cannot meet the NO requirements. x The conversion requirement. Meanwhile, the reactive oxygen species generated by excess Pd / Pt metal sites during the oxidation reactions of CO and CH3OH can further induce peroxidation and deactivation of Rh sites, and may also cause NO to... x Incomplete reduction to the greenhouse gas N2O leads to catalyst degradation in NO. x The reduced conversion selectivity leads to a significant increase in the overall catalyst ignition temperature.

[0020] The molar ratio of M1 to M2 was controlled within the optimized range of 1:(1-5) to regulate the oxidation of CO / HC and NO. x The reduction reaction rate enables simultaneous and efficient purification of multiple pollutants in methanol vehicle exhaust.

[0021] In some embodiments, in the noble metal three-way catalyst, the active component M1 is Rh, and the metal M2 is Pd and Pt.

[0022] The present invention further preferably uses Rh as the active component M1 and Pd and Pt as the metal M2. In this case, the noble metal three-way catalyst has better catalytic activity and stability.

[0023] The noble metals Pd and Pt are highly efficient at oxidizing CO and CH3OH; the noble metals Rh, Ir, and Ru have excellent performance on NO and CO, especially on NO.

[0024] In some embodiments, the alumina is γ-Al2O3.

[0025] In some embodiments, the noble metal triple-effect catalyst further includes an additive.

[0026] In some embodiments, common additives include rare earth elements, alkaline earth metals, or transition metals.

[0027] The rare earth elements (such as Ce, Zr, Y, La, Nd, etc.) are mainly used to improve oxygen storage capacity, thermal stability, and promote the dispersion of noble metals. The alkaline earth metals (such as Ba, Sr, Ca, etc.) are commonly used to stabilize alumina coatings and adjust surface acidity. The transition metals (such as Fe, Mn, Ni, Co, etc.) can partially regulate catalytic activity and selectivity.

[0028] The additive is any one or a combination of at least two of the above elements, wherein the amount of additive added is 1wt.%-5wt.%, for example, it can be 1wt.%, 1.5wt.%, 2wt.%, 2.5wt.%, 3wt.%, 3.5wt.%, 4wt.%, 4.5wt.% or 5wt.%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0029] This invention adds an additive to a noble metal triple-effect catalyst to further improve the catalyst's high-temperature stability and lifespan. If the amount added is too small, the additive metal ions cannot stabilize the support, resulting in poor anti-sintering ability. Furthermore, only a very small number of noble metal particles come into contact with the additive metal species and undergo electronic interactions, leaving most of the noble metal unmodified and resulting in poor low-temperature activity enhancement. If the amount added is too large, the excess additive metal particles cannot enter the cerium-zirconium solid solution or alumina lattice. Instead, they precipitate as independent additive oxides on the catalyst surface or at grain boundaries. This not only blocks the catalyst's pores, leading to a decrease in the catalyst's specific surface area, but also covers the noble metal active sites, resulting in a decrease in catalytic activity.

[0030] In a second aspect, the present invention provides a method for preparing a noble metal three-way catalyst as described in the first aspect, the method comprising the following steps:

[0031] (1) A salt solution of mixed metal M2 and aluminum oxide are subjected to a first ultrasonic treatment and a first calcination to obtain M2 / Al2O3 powder;

[0032] (2) Mix cerium salt, zirconium salt and solvent to obtain cerium-zirconium mixed solution, mix cerium-zirconium mixed solution and M1 / Al2O3 powder obtained in step (1), add alkaline solution to adjust pH, react and calcine a second time to obtain CeZr / M2 / Al2O3 powder;

[0033] (3) The salt solution of active component M1 is impregnated into CeZr / M2 / Al2O3 powder, and after a second ultrasonic treatment and calcination, the M1 / CeZr / M2 / Al2O3 noble metal three-way catalyst is obtained.

[0034] The noble metal three-way catalyst provided by this invention is prepared by a multi-step impregnation method plus a co-precipitation method and ultrasound assistance. The co-precipitation method is used to generate more cerium-zirconium solid solution, rather than cerium-zirconium oxide or cerium dioxide or zirconium dioxide alone. Finally, the active component is further loaded on CeZr / M2 / Al2O3 powder. Ultrasonic dispersion is used during the impregnation of noble metal to reduce the migration speed of noble metal ions, reduce noble metal agglomeration, and fully anchor them at the sites. This makes the noble metal impregnation in the support more uniform, avoids the agglomeration of active components, and improves the dispersion, which is more conducive to the improvement of catalyst activity.

[0035] In step (1) of this invention, the synthesis of M2 / Al2O3 involves ultrasonic-assisted impregnation of a noble metal onto alumina. Ultrasound can disperse the metal salt precursor, promoting the diffusion and adsorption of the metal salt into the pores of Al2O3. Impregnating the noble metal M2 onto alumina allows for high dispersion and uniform distribution of the metal on the pure alumina surface.

[0036] In step (2) of this invention, the synthesis of CeZr / M2 / Al2O3 involves co-precipitation to precipitate the CeZr (CZ) solid solution onto M2 / Al2O3. A mixed solution containing cerium and zirconium salts is mixed with M2 / Al2O3 powder and then ultrasonically dispersed to ensure uniform adsorption of metal ions onto the carrier surface. During precipitation with added alkaline solution, the locally elevated OH- ions... - Concentration promotes the formation of Ce / Zr hydroxyl species. The abundant hydroxyl groups on the M2 noble metal particles and Al2O3 surface provide numerous heterogeneous nucleation sites, significantly lowering the heterogeneous nucleation energy barrier. CeZr nuclei preferentially and selectively form on the M2 / Al2O3 surface, rather than spontaneously nucleating and growing in solution. After nucleation, the Ce / Zr precursor continues to deposit and grow. Subsequent second calcination dehydrates and crystallizes the amorphous precursor, transforming it into a fluorite-structured CeZr solid solution. This process stabilizes the CeZr crystalline phase.

[0037] In step (3) of this invention, the synthesis of M1 / CeZr / M2 / Al2O3 is carried out using a conventional impregnation method, in which the Rh salt solution is loaded onto the pre-constructed CeZr / M2 / Al2O3 composite support. Ultrasound is used to promote the dispersion of the Rh precursor within the complex pores. Finally, loading the Rh salt onto CeZr / M2 / Al2O3 achieves the unique electronic structure of the Rh noble metal and its catalytic selectivity for NO. This minimizes the formation of alloys between Pd-Pt and Rh, preventing the loss of the noble metal's active centers.

[0038] The preparation method provided by this invention is reliable and has low loss of precious metals.

[0039] The difference and advantage of this invention compared to existing technologies lies in the following: This invention alters the impregnation sequence of precious metals and the introduction sequence of CeZr. Alumina (Al2O3) support possesses a high specific surface area and abundant acidic sites, making it an excellent adsorption and reforming center for CH3OH. CeZr is coated onto the alumina surface because Al2O3, as the support, is responsible for providing a stable platform with a high specific surface area. CeZr solid solution is an excellent oxygen storage material, capable of dynamically storing and releasing oxygen, balancing fluctuations in carbon monoxide (CO) and nitrogen oxides (NOx) in exhaust gases. x The oxidation-reduction cycle of the two processes each has its own function, which can produce perfect cerium-zirconium solid solution oxygen storage materials, stable high-temperature resistant alumina carriers, and precise division of labor for precious metal active sites.

[0040] On the other hand, the preparation method of the present invention effectively inhibits Al 3+ Doping into the CeZr lattice ensures the integrity of the CeZr fluorite structure and its oxygen storage capacity. Loading M2 metal onto Al2O3 and M1 metal onto CeZr essentially designs specialized "workshops" for different types of chemical reactions. This results in excellent low-temperature catalytic activity of pollutants in stoichiometric combustion mode. In contrast, traditional processes use cerium-zirconium-aluminum as a support, and in the process of direct co-precipitation to form CeZrAl, Al... 3+ Ions (ionic radius 0.0535 nm) readily enter Ce. x Zr 1-x O2 lattice, replacing Ce 4+ (0.097nm) or Zr 4+ (0.084 nm). This severely interferes with the fluorite structure of CeZr, inhibiting its oxygen storage capacity and redox properties. Al 3+ The incorporation of [a substance] causes lattice shrinkage, increases the formation energy of oxygen vacancies, and obstructs oxygen ion migration channels.

[0041] In some embodiments, the duration of the first ultrasound in step (1) is 0.5h-2h, for example, it can be 0.5h, 1h, 1.5h or 2h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] In some embodiments, the alumina in step (1) is pretreated before use.

[0043] The pretreatment steps include: mixing ammonia and alumina, stirring, separating solid and liquid, drying, and then keeping at 500℃-600℃ for 2h-4h to obtain pretreated alumina.

[0044] This invention utilizes ammonia water to treat γ-Al2O3, thereby constructing surface defects and hydroxyl functional groups in alumina and simultaneously regulating the pore structure. This stable porous structure is more conducive to the reaction and improves the dispersion of metal M2.

[0045] In some embodiments, the temperature of the first roasting in step (1) is 500℃-600℃, for example, it can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ or 600℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] In some embodiments, the first roasting time in step (1) is 2h-4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] In some embodiments, the salt solution of metal M2 in step (1) includes a salt of metal M2 and a solvent.

[0048] In some embodiments, the total concentration of metal ions in the salt solution of metal M2 in step (1) is 2.5 mmol / L-11.5 mmol / L, for example, it can be 2.5 mmol / L, 3 mmol / L, 3.5 mmol / L, 4 mmol / L, 4.5 mmol / L, 5 mmol / L, 5.5 mmol / L, 6 mmol / L, 6.5 mmol / L, 7 mmol / L, 7.5 mmol / L, 8 mmol / L, 9.5 mmol / L, 9 mmol / L, 9.5 mmol / L, 10 mmol / L, 10.5 mmol / L, 11 mmol / L or 11.5 mmol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] In some embodiments, the total concentration of cerium-zirconium ions in the cerium-zirconium mixed solution in step (2) is 0.15 mol / L-0.85 mol / L, for example, it can be 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L or 0.85 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] In some embodiments, the total concentration of metal ions in the salt solution of active component M1 in step (3) is 1 mmol / L-6 mmol / L, for example, it can be 1 mmol / L, 1.5 mmol / L, 2 mmol / L, 2.5 mmol / L, 3 mmol / L, 3.5 mmol / L, 4 mmol / L, 4.5 mmol / L, 5 mmol / L, 5.5 mmol / L or 6 mmol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In some embodiments, the salt solution of active component M1 in step (3) includes a salt of active component M1 and a solvent.

[0052] In some embodiments, the solvent includes water.

[0053] In some embodiments, the salt of the active component M1 includes any one or a combination of at least two of rhodium, iridium, or ruthenium salts.

[0054] In some embodiments, the salt of the metal M2 includes any one or a combination of at least two of palladium salts, platinum salts, rhodium salts, or gold sources.

[0055] In some embodiments, the rhodium salt comprises any one or a combination of at least two of rhodium nitrate, rhodium sulfate, rhodium chloride, or rhodium acetate. Typical but non-limiting combinations include combinations of rhodium nitrate and rhodium sulfate, combinations of rhodium sulfate and rhodium chloride, combinations of rhodium chloride and rhodium acetate, combinations of rhodium nitrate and rhodium chloride, combinations of rhodium sulfate, rhodium chloride, and rhodium acetate, or combinations of rhodium nitrate, rhodium sulfate, rhodium chloride, and rhodium acetate, preferably rhodium nitrate.

[0056] In some embodiments, the iridium salt includes any one or a combination of at least two of iridium nitrate, iridium sulfate, iridium chloride, or iridium acetate. Typical but non-limiting combinations include combinations of iridium nitrate and iridium sulfate, combinations of iridium sulfate and iridium chloride, combinations of iridium chloride and iridium acetate, combinations of iridium nitrate and iridium chloride, combinations of iridium sulfate, iridium chloride, and iridium acetate, or combinations of iridium nitrate, iridium sulfate, iridium chloride, and iridium acetate, preferably iridium nitrate.

[0057] In some embodiments, the ruthenium salt includes any one or a combination of at least two of ruthenium nitrate, ruthenium sulfate, ruthenium chloride, or ruthenium acetate. Typical but non-limiting combinations include combinations of ruthenium nitrate and iridium sulfate, combinations of ruthenium sulfate and ruthenium chloride, combinations of ruthenium chloride and ruthenium acetate, combinations of ruthenium nitrate and ruthenium chloride, combinations of ruthenium sulfate, ruthenium chloride, and ruthenium acetate, or combinations of ruthenium nitrate, ruthenium sulfate, ruthenium chloride, and ruthenium acetate, preferably ruthenium nitrate.

[0058] In some embodiments, the palladium salt comprises any one or a combination of at least two of palladium nitrate, palladium sulfate, palladium chloride, or palladium acetate. Typical but non-limiting combinations include combinations of palladium nitrate and palladium sulfate, combinations of palladium sulfate and palladium chloride, combinations of palladium chloride and palladium acetate, combinations of palladium nitrate and palladium chloride, combinations of palladium sulfate, palladium chloride, and palladium acetate, or combinations of palladium nitrate, palladium sulfate, palladium chloride, and palladium acetate, preferably palladium nitrate.

[0059] In some embodiments, the platinum salt comprises any one or a combination of at least two of platinum nitrate, platinum sulfate, platinum chloride, or platinum acetate. Typical but non-limiting combinations include combinations of platinum nitrate and platinum sulfate, combinations of platinum sulfate and platinum chloride, combinations of platinum chloride and platinum acetate, combinations of platinum nitrate and platinum chloride, combinations of platinum sulfate, platinum chloride, and platinum acetate, or combinations of platinum nitrate, platinum sulfate, platinum chloride, and platinum acetate, preferably platinum nitrate.

[0060] In some embodiments, the gold source includes chloroauric acid, gold nitrate, or gold chloride.

[0061] In some embodiments, the cerium salt in step (2) includes any one or a combination of at least two of cerium nitrate, cerium sulfate, cerium chloride, or cerium acetate. Typical but non-limiting combinations include combinations of cerium nitrate and cerium sulfate, combinations of cerium sulfate and cerium chloride, combinations of cerium chloride and cerium acetate, combinations of cerium nitrate and cerium chloride, combinations of cerium sulfate, cerium chloride, and cerium acetate, or combinations of cerium nitrate, cerium sulfate, cerium chloride, and cerium acetate, preferably cerium nitrate.

[0062] In some embodiments, the zirconium salt in step (2) includes any one or a combination of at least two of zirconium nitrate, zirconium oxynitrate, zirconium sulfate, zirconium chloride, or zirconium acetate. Typical but non-limiting combinations include combinations of zirconium nitrate and zirconium oxynitrate, combinations of zirconium oxynitrate and zirconium sulfate, combinations of zirconium nitrate and zirconium sulfate, combinations of zirconium chloride and zirconium acetate, combinations of zirconium oxynitrate, zirconium sulfate, zirconium chloride, and zirconium acetate, preferably zirconium oxynitrate.

[0063] In some embodiments, the alkaline solution in step (2) includes ammonia and ammonium carbonate.

[0064] In some embodiments, the concentration of the ammonia solution is 2 mol / L to 5 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] In some embodiments, the concentration of ammonium carbonate is 0.2 mol / L to 1 mol / L, for example, it can be 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] In some embodiments, step (2) involves adding an alkaline solution to adjust the pH of the reaction system to 9-10, for example, 9, 9.2, 9.5, 9.8 or 10, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] In some embodiments, the reaction time in step (2) is 3h-5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] In some embodiments, after the reaction in step (2) is completed and before the second calcination, solid-liquid separation and drying are also performed.

[0069] In some embodiments, the second calcination temperature in step (2) is 500℃-600℃, for example, it can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ or 600℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] In some embodiments, the second calcination time in step (2) is 2h-4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] In some embodiments, the duration of the second ultrasound in step (3) is 0.5h-2h, for example, it can be 0.5h, 1h, 1.5h or 2h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the calcination temperature in step (3) is 650℃-850℃, for example, it can be 650℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 750℃, 780℃, 800℃, 820℃ or 850℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0073] This invention further controls the calcination temperature in step (3) to be 650℃-850℃. The calcination temperature affects the dispersion state of the active components, the metal-support interaction, and the surface oxygen defect concentration, thus significantly affecting the low-temperature performance and thermal stability of the catalyst. If the calcination temperature is too high, the noble metal species will undergo significant sintering and aggregation, the particle size of the noble metal nanoparticles will increase significantly, the specific surface area will decrease sharply, the number of active sites will decrease, and the dispersion of noble metals will decrease. At the same time, excessive lattice stress will cause phase separation and structural collapse of the CeZr solid solution, resulting in insufficient surface oxygen vacancies, thereby reducing the low-temperature activity and high-temperature thermal stability of the catalyst. If the calcination temperature is too low, the noble metal species will mainly exist in the form of highly dispersed but not highly active noble metal species, and the crystallinity of the CeZr solid solution will be insufficient, the oxygen defect concentration will be low, and the stability will be poor, resulting in low initial activity and poor high-temperature durability of the catalyst, and the formation of stable and efficient noble metal-support interface active centers will be impossible.

[0074] In some embodiments, the calcination time in step (3) is 2h-4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0076] (1) Mix ammonia water and alumina, stir, filter and dry, and keep warm at 500℃-600℃ for 2h-4h to obtain pretreated alumina; immerse the pretreated alumina in the salt solution of metal M2, sonicate for 0.5h-2h, and calcine at 500℃-600℃ for 2h-4h to obtain M2 / Al2O3 powder;

[0077] (2) Mix cerium salt, zirconium salt and solvent to obtain cerium-zirconium mixed solution. Mix cerium-zirconium mixed solution and M1 / Al2O3 powder obtained in step (1), add alkaline solution to adjust pH to 9-10, stir, let stand for 3-5 hours, separate solid and liquid and dry, and calcine at 500℃-600℃ for 2-4 hours to obtain CeZr / M2 / Al2O3 powder;

[0078] The alkaline solution comprises ammonia water with a concentration of 2 mol / L to 5 mol / L and ammonium carbonate with a concentration of 0.2 mol / L to 1 mol / L, in a volume ratio of 1:(1-3).

[0079] (3) The salt solution of active component M1 is impregnated onto CeZr / M2 / Al2O3 powder, subjected to second sonication for 0.5h-2h, and calcined at 650℃-850℃ for 2h-4h to obtain M1 / CeZr / M2 / Al2O3 noble metal triple-effect catalyst.

[0080] Thirdly, the present invention provides an application of the precious metal three-way catalyst as described in the first aspect, wherein the precious metal three-way catalyst is used for methanol vehicle exhaust treatment.

[0081] The noble metal three-way catalyst provided by this invention is used to degrade CO and NO in methanol vehicle exhaust under stoichiometric combustion mode. x CH3OH exhibits good low-temperature activity and hydrothermal stability, with minimal performance differences after hydrothermal aging, indicating broad application prospects. This invention provides specialized treatment for methanol vehicle exhaust, expanding the application scenarios of three-way catalysts. Furthermore, it features a low low-temperature ignition temperature, good high-temperature stability, and low total precious metal loading, providing theoretical guidance for exhaust purification in emerging low-carbon power systems such as methanol vehicles, methanol hybrids, and marine methanol engines.

[0082] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0083] Compared with the prior art, the present invention has at least the following beneficial effects:

[0084] (1) The noble metal three-way catalyst provided by this invention introduces a variety of different noble metals. Some of the noble metals are loaded on the surface of an alumina support, and then a co-precipitation method is used to precipitate cerium-zirconium solid solution on M2 / Al2O3. The cerium-zirconium solid solution serves as an anchoring point for the active component M1, which can fully anchor the noble metal while reducing its agglomeration. Furthermore, the cerium-zirconium solid solution has a good crystal structure, oxygen storage capacity, and redox properties, maximizing the optimization of the low-temperature performance of the noble metal in the stoichiometric combustion mode, and also possessing excellent hydrothermal stability. By optimizing the metal-support interaction, the active component exists in the form of nanoparticles with high dispersion, regulating the electronic structure of the noble metal and the oxygen defect concentration on the surface, thereby improving the low-temperature performance and thermal stability of the catalyst, achieving the goal of improving catalyst performance.

[0085] (2) The noble metal three-way catalyst provided by this invention is prepared by a multi-step impregnation method plus a co-precipitation method and ultrasound assistance. The co-precipitation method is used to generate more cerium-zirconium solid solution, rather than cerium-zirconium oxide or cerium dioxide or zirconium dioxide alone. Finally, the active component is further loaded on CeZr / M2 / Al2O3 powder. Ultrasonic dispersion is used during the impregnation of noble metals to reduce the migration speed of noble metal ions, reduce noble metal agglomeration, and fully anchor them at the sites, making the noble metal impregnation in the support more uniform, avoiding the agglomeration of active components, and improving the dispersion, which is more conducive to the improvement of catalyst activity. The preparation method provided by this invention is reliable and has low noble metal loss.

[0086] (3) The noble metal triple-effect catalyst provided by the present invention is used to degrade CO and NO in stoichiometric combustion mode. x CH3OH exhibits good low-temperature activity and hydrothermal stability, with minimal performance differences after hydrothermal aging, making it a promising catalyst for a wide range of applications. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the structure of the noble metal three-way catalyst prepared in Example 1 of the present invention;

[0088] Figure 2 These are the XRD patterns of the noble metal three-way catalysts prepared in Examples 1-3 of this invention;

[0089] Figure 3 These are Raman diagrams of the noble metal three-way catalysts prepared in Examples 1-3 of this invention;

[0090] Figure 4 These are H2-TPR diagrams of the noble metal three-way catalysts prepared in Examples 1-3 of this invention;

[0091] Figure 5 This is a diagram showing the total dispersion of noble metals in the noble metal three-way catalysts prepared in Examples 1-3 of this invention.

[0092] Figure 6 This is a graph showing the CO conversion rate of fresh and aged noble metal triple-effect catalysts prepared in Examples 1-3 of this invention.

[0093] Figure 7 This is a graph showing the NO conversion rate of fresh and aged noble metal three-way catalysts prepared in Examples 1-3 of this invention.

[0094] Figure 8 This is a graph showing the CH3OH conversion rate of fresh and aged noble metal triple-effect catalysts prepared in Examples 1-3 of this invention.

[0095] Figure 9 This is a graph showing the CO conversion rate of fresh and aged noble metal triple-effect catalysts prepared in Example 1 and Comparative Example 2 of this invention.

[0096] Figure 10 This is a graph showing the NO conversion rate of fresh and aged noble metal three-way catalysts prepared in Example 1 and Comparative Example 2 of this invention.

[0097] Figure 11 This is a graph showing the CH3OH conversion rate of fresh and aged noble metal triple-effect catalysts prepared in Example 1 and Comparative Example 2 of this invention. Detailed Implementation

[0098] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0099] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0100] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0101] Example 1

[0102] This embodiment provides a noble metal triple-effect catalyst, the structural schematic diagram of which is shown below. Figure 1 As shown, the noble metal triple-effect catalyst comprises a γ-Al₂O₃ support loaded with metals Pd and Pt, and a cerium-zirconium solid solution Ce. 0.5 Zr 0.5 O2 and active component Rh;

[0103] The mass ratio of the cerium-zirconium solid solution to alumina is 1.5:1; based on the total mass of the noble metal triple-effect catalyst being 100wt%, the total mass fraction of the active component Rh and the metals Pd and Pt is 1wt%; the molar ratio of Pd / Pt / Rh is 5:2:3.

[0104] The preparation method of the noble metal three-way catalyst provided in this embodiment includes the following steps:

[0105] (1) Mix ammonia and alumina, stir, filter and dry, and keep warm at 550℃ for 3h to obtain pretreated alumina; immerse the pretreated alumina in aqueous solution of Pd(NO3)2 and Pt(NO3)2, stir for 2h, sonicate for 0.5h, and calcine at 550℃ for 3h to obtain Pd-Pt / Al2O3 powder;

[0106] (2) Mix Ce(NO3)2·6H2O, ZrO(NO3)2 and water to obtain a cerium-zirconium mixed solution. Mix the cerium-zirconium mixed solution and the Pd-Pt / Al2O3 powder obtained in step (1), add alkaline solution to adjust the pH to 9.5, stir for 0.5h, let stand for 4h, separate solid and liquid and dry, and calcine at 550℃ for 3h to obtain CeZr / Pd-Pt / Al2O3 powder;

[0107] The alkaline solution comprises ammonia water with a concentration of 3 mol / L and ammonium carbonate with a concentration of 0.5 mol / L, in a volume ratio of 1:1.

[0108] (3) The Rh(NO3)3 aqueous solution is impregnated onto CeZr / Pd-Pt / Al2O3 powder, subjected to a second ultrasonic treatment for 0.5 h, and calcined at 750 °C for 3 h to obtain the noble metal triple-effect catalyst, which can be denoted as Rh / CeZr / Pd-Pt / Al-750.

[0109] Example 2

[0110] This embodiment provides a noble metal three-way catalyst. The only difference from Example 1 is that when preparing the noble metal three-way catalyst, the calcination temperature in step (3) is replaced by 650°C instead of 750°C. The other steps remain unchanged. It can be denoted as Rh / CeZr / Pd-Pt / Al-650.

[0111] Example 3

[0112] This embodiment provides a noble metal three-way catalyst. The only difference from Example 1 is that when preparing the noble metal three-way catalyst, the calcination temperature in step (3) is replaced by 850°C instead of 750°C. The other steps remain unchanged. It can be denoted as Rh / CeZr / Pd-Pt / Al-850.

[0113] Example 4

[0114] This embodiment provides a noble metal three-way catalyst, which includes a γ-Al2O3 support and a cerium-zirconium solid solution Ce. 0.6 Zr 0.4 O2 and active component Rh; the alumina support is also loaded with metals Pd and Pt;

[0115] The mass ratio of the cerium-zirconium solid solution to alumina is 1.2:1; based on the total mass of the noble metal triple-effect catalyst being 100wt%, the total mass fraction of the active component Rh and the metals Pd and Pt is 0.5wt%; the molar ratio of Pd / Pt / Rh is 4:2:4.

[0116] The preparation method of the noble metal three-way catalyst provided in this embodiment includes the following steps:

[0117] (1) Mix ammonia and alumina, stir, filter and dry, and keep warm at 550℃ for 3h to obtain pretreated alumina; immerse the pretreated alumina in aqueous solution of Pd(NO3)2 and Pt(NO3)2, stir for 2h, sonicate for 0.5h, and calcine at 500℃ for 4h to obtain Pd-Pt / Al2O3 powder;

[0118] (2) Mix Ce(NO3)2·6H2O, ZrO(NO3)2 and water to obtain a cerium-zirconium mixed solution. Mix the cerium-zirconium mixed solution and the Pd-Pt / Al2O3 powder obtained in step (1), add alkaline solution to adjust the pH to 9, stir for 0.5 h, let stand for 4 h, separate solid and liquid and dry, and calcine at 500℃ for a second time for 4 h to obtain CeZr / Pd-Pt / Al2O3 powder;

[0119] The alkaline solution comprises ammonia water with a concentration of 2 mol / L and ammonium carbonate with a concentration of 0.5 mol / L, in a volume ratio of 1:2.

[0120] (3) The Rh(NO3)3 aqueous solution is impregnated onto CeZr / Pd-Pt / Al2O3 powder, subjected to a second ultrasonic treatment for 0.5 h, and calcined at 750 °C for 3 h to obtain the noble metal triple-effect catalyst, which can be denoted as Rh / CeZr / Pd-Pt / Al-750.

[0121] Example 5

[0122] This embodiment provides a noble metal three-way catalyst, which includes a γ-Al2O3 support and a cerium-zirconium solid solution Ce. 0.3 Zr 0.7 O2 and active component Rh, the cerium-zirconium solid solution Ce 0.3 Zr 0.7 The O2 also contains the additive Fe; the alumina support also contains metals Pd and Pt.

[0123] The mass ratio of the cerium-zirconium solid solution to alumina is 2:1; based on the total mass of the noble metal three-way catalyst being 100wt%, the total mass fraction of the active component Rh and metals Pd and Pt is 1wt%; the molar ratio of Pd / Pt / Rh is 2:6:2, and the total mass fraction of the auxiliary agent Fe is 2wt%.

[0124] The preparation method of the noble metal three-way catalyst provided in this embodiment includes the following steps:

[0125] (1) Mix ammonia and alumina, stir, filter and dry, and keep warm at 550℃ for 3h to obtain pretreated alumina; immerse the pretreated alumina in aqueous solution of Pd(NO3)2 and Pt(NO3)2, stir for 2h, sonicate for 0.5h, and calcine at 600℃ for 2h to obtain Pd-Pt / Al2O3 powder;

[0126] (2) Mix Ce(NO3)2·6H2O, ZrO(NO3)2 and water to obtain a cerium-zirconium mixed solution. Mix the cerium-zirconium mixed solution and the Pd-Pt / Al2O3 powder obtained in step (1), add alkaline solution to adjust the pH to 10, stir for 0.5 h, let stand for 4 h, separate solid and liquid and dry, and calcine at 600℃ for 2 h to obtain CeZr / Pd-Pt / Al2O3 powder;

[0127] The alkaline solution comprises ammonia water with a concentration of 5 mol / L and ammonium carbonate with a volume ratio of 1:1;

[0128] (3) Rh(NO3)3 aqueous solution and Fe(NO3)3·9H2O are impregnated onto CeZr / Pd-Pt / Al2O3 powder, subjected to a second ultrasonic treatment for 0.5 h, and calcined at 750 °C for 3 h to obtain the noble metal triple-effect catalyst, which can be denoted as Rh-Fe / CeZr / Pd-Pt / Al-750.

[0129] Example 6

[0130] This embodiment provides a noble metal three-way catalyst, which differs from Example 1 only in that the molar ratio of Pd / Pt / Rh is 1:5:1, and the preparation method is adapted accordingly.

[0131] Example 7

[0132] This embodiment provides a noble metal three-way catalyst, which differs from Example 1 only in that the molar ratio of Pd / Pt / Rh is 3:3:1, and the preparation method is adapted accordingly.

[0133] Example 8

[0134] This embodiment provides a noble metal three-way catalyst. The only difference from Example 1 is that when preparing the noble metal three-way catalyst, the calcination temperature in step (3) is replaced by 450°C instead of 750°C, while the other steps remain unchanged.

[0135] Example 9

[0136] This embodiment provides a noble metal three-way catalyst. The only difference from Example 1 is that when preparing the noble metal three-way catalyst, the calcination temperature in step (3) is replaced by 1200℃ instead of 750℃, while the other steps remain unchanged.

[0137] Comparative Example 1

[0138] This comparative example provides a noble metal catalyst, which is prepared by the following method, and the structure and composition of the obtained noble metal catalyst are determined by the method, which includes:

[0139] (a) Mix ammonia and alumina, stir, filter and dry, and keep warm at 550℃ for 3h to obtain the pretreated γ-Al2O3 support;

[0140] (b) A cerium-zirconium mixed solution was obtained by mixing Ce(NO3)2·6H2O, ZrO(NO3)2 and water. The cerium-zirconium mixed solution and γ-Al2O3 support were mixed, and an alkaline solution was added to adjust the pH to 9.5. The mixture was stirred for 0.5 h, allowed to stand for 4 h, separated by solid-liquid separation and dried, and then calcined at 550 °C for 3 h to obtain CeZr / Al2O3 powder. The alkaline solution consisted of ammonia water with a concentration of 3 mol / L and ammonium carbonate with a concentration of 0.5 mol / L in a volume ratio of 1:1.

[0141] (c) Impregnate CeZr / Al2O3 powder with an aqueous solution of Pd(NO3)2, Pt(NO3)2 and Rh(NO3)3, sonicate for 0.5 h, and calcine at 750 °C for 3 h to obtain the noble metal triple-effect catalyst, which can be denoted as Rh-Pd-Pt / CeZr / Al-750.

[0142] Comparative Example 2

[0143] This comparative example provides a noble metal catalyst, which differs from Example 1 in that it contains only the active component Rh. When preparing this noble metal catalyst, Pd(NO3)2 and Pt(NO3)2 are not added, but only an aqueous solution of Rh(NO3)3 is added in step (3). The remaining preparation steps remain unchanged, and the structure and composition of the obtained noble metal catalyst are determined by this method.

[0144] Comparative Example 3

[0145] This comparative example provides a noble metal catalyst, which differs from Example 1 in that it uses a cerium-zirconium solid solution (Ce). 0.5 Zr 0.5 O2 replaced with Ce 0.5 Ti 0.5 When preparing this noble metal catalyst, ZrO(NO3)2 in step (2) is replaced with an equimolar amount of TiCl4, while the other preparation steps remain unchanged. The structure and composition of the obtained noble metal catalyst are determined by this method.

[0146] Characterization tests:

[0147] (1) The XRD patterns of the noble metal three-way catalysts prepared in Examples 1-3 are as follows: Figure 2 As shown in the figure, all three noble metal three-way catalysts exhibit diffraction peaks near 2θ = 29.2°, which are attributed to the cubic fluorite structure of CeZr (JCPDSPDF#38-1436). Furthermore, none of the three catalysts showed obvious diffraction peaks representing pure CeO2 or ZrO2 species, indicating that all three catalysts exist primarily as CeZr solid solutions without significant phase separation. With increasing calcination temperature, the full width at half maximum (FWHM) of the CeZr solid solution characteristic peaks gradually narrowed, and the diffraction peaks gradually sharpened, indicating that high-temperature treatment significantly improved the crystallinity of the catalysts, and the grain size gradually increased.

[0148] The XRD pattern of Example 3 showed new diffraction peaks (2θ≈40°), possibly due to the agglomeration of noble metals caused by high-temperature calcination, resulting in large-particle noble metal species (PDF#46-1043, PDF#04-0802). In contrast, no obvious characteristic peaks of Pd / Pt / Rh were observed in the patterns of Examples 1 and 2, indicating a higher degree of noble metal dispersion. In Example 3, the increased size of the CeZr solid solution particles at high temperature led to particle migration and aggregation, resulting in a decrease in specific surface area and thus reduced reactivity.

[0149] (2) Raman diagrams of the noble metal three-way catalysts prepared in Examples 1-3 are shown below. Figure 3 As shown in the figure, the main Raman peak of the noble metal three-way catalysts prepared in Examples 1-3 is located at 472 cm⁻¹. -1 At this location, the vibrational peak can be attributed to the F-type of the cubic fluorite structure in the CeZr solid solution. 2g Vibration peak. 308cm -1 and 628cm -1 The vibrational peak at that location is attributed to the characteristic peak of (tetragonal) t-ZrO2. Additionally, γ-Al2O3 and Rh / RhO... x The substance does not have Raman activity.

[0150] The vibrational peak at 757 cm⁻¹ in the noble metal triple-effect catalyst obtained in Example 3 is attributed to the characteristic peaks of PdO and RhO₂ species. Compared to Example 2, the vibrational peak at 308 cm⁻¹ in Examples 1 and 3 is significantly different. -1 and 628cm -1 The diffraction peaks of t-ZrO2 are significantly stronger.

[0151] Example 1 at 472cm -1The diffraction peaks of the CeZr solid solution in Example 1 were significantly stronger than those in Examples 2 and 3, indicating that the CeZr solid solution content was the highest in Example 1. Examples 2 and 3 both showed varying degrees of t-ZrO2 presence, possibly because the CeZr solid solution in Example 2 was not yet fully stable. In Example 3, the CeZr solid solution structure was disrupted, and oxides began to precipitate. Noble metal aggregation was observed in Example 3, consistent with the characteristic peaks of Pd and Pt observed in the XRD of Example 3.

[0152] (3) The H2-TPR diagrams of the noble metal three-way catalysts prepared in Examples 1-3 are shown below. Figure 4 As shown, the effect of different calcination temperatures on the reduction performance of the catalyst was analyzed by H2-TPR. H2 consumption peaks appeared in the range of 0~50℃, corresponding to 36℃ (Example 2) and 30℃ (Example 1), respectively, which can be attributed to highly dispersed PdO. x Species reduction. Example 1 exhibited the lowest reduction temperature, corresponding to its optimal catalytic activity. Peaks appearing in the 50–100 °C range can be attributed to PdO. x PtO x RhO x Reduction of species. The peak in Example 2 was 76℃, the peak in Example 1 was 75℃, and the peak in Example 3 was 70℃. Generally, peaks in this range correspond to metal-support interactions. Excessively strong metal-support interaction (MSI) can cause active species to be "encapsulated" by the support or become too firmly "anchored," making reduction difficult and hindering reactant activation. This is manifested in the highest temperature of the H2-TPR main peak. Conversely, excessively weak metal-support interaction (MSI) can lead to migration and sintering of noble metals, which is also detrimental to the reaction and further reduces activity. Moderate metal-support interaction (MSI) can stabilize metal nanoparticles and prevent sintering and agglomeration without excessively inhibiting their reduction ability and reactivity. The peak values ​​of the reduction peaks, from lowest to highest temperature, are: 70℃ (Example 3) < 75℃ (Example 1) < 76℃ (Example 2). This indicates that Example 2 has the strongest metal-support interaction, Example 3 has the weakest, and Example 1 has a moderate metal-support interaction. Since the peak intensity after 200℃ is very small and can be almost ignored, this temperature range includes the interface Ce. 4+ The reduction of species, which can be attributed to metal-support interactions, can be used to assess the redox capacity of the catalyst. Peaks appearing in the 200–400 °C range are related to Ce. 4+ This is related to the weak reduction process, which typically originates from the Ce interface in close contact with precious metals. 4+These interfacial oxygen species are key elements in catalytic oxidation reactions. The peak values ​​within this range are 304.8℃ (Example 2), 298.4℃ (Example 1), and 283.6℃ (Example 3).

[0153] (4) The total dispersion diagram of noble metals of the noble metal three-way catalysts prepared in Examples 1-3 is shown in the figure. Figure 5 As shown in the figure, the total dispersion of noble metals (Pd, Pt, and Rh) on the surface of Examples 1-3 exhibited a trend of first increasing and then decreasing. With increasing calcination temperature, the dispersion increased from 43.58% to 53.53% and then decreased to 50.24%. This may be related to the migration-aggregation competition mechanism of metal particles. Calcination temperature has a regulatory effect on the texture characteristics of the catalyst and the metal dispersion behavior. The sample calcined at 750℃ (Example 1) achieved the optimal noble metal dispersion while maintaining the mesoporous structure. Combined with the trend of the catalyst activity first increasing and then decreasing, it can be seen that the noble metal dispersion is well correlated with the catalyst performance.

[0154] The noble metal triple-effect catalysts prepared in the examples and comparative examples were tested: The activity evaluation of the catalysts in this invention was carried out in a fixed-bed quartz tube reactor with an inner diameter of 5 mm. The total flow rate of the evaluation gas was 300 mL / min, the mass of catalyst used in each test was 54 mg, and the particle size of the catalyst used in the test was 40-60 mesh. The composition of the introduced gas was 0.03% CH3OH, 0.43% CO, 0.03% NO, 0.21% O2, 10% H2O, with N2 as the equilibrium gas. Water vapor was generated by the flowing N2 gas through a water bath bubbler. The total flow rate was 300 mL / min, the mass hourly space velocity during the activity test was 50000 mL / (g∙h), and the theoretical air-fuel ratio λ = 0.9986. The quartz tube used in the experiment had an inner diameter of 5 mm and a height of 430 mm. Quartz wool was placed at the bottom of the catalyst to prevent catalyst loss. The flow rate of the reactant gases is controlled by a mass control flow meter. The reactants during the reaction process include CH3OH, NO, NO2, CO, CO2, N2O, NH3, and NO. x Concentrations were continuously monitored using an Antaris IGS gas analyzer (ThermoFisher). The reaction temperature was controlled by a tube furnace. Activity testing was performed using a programmed temperature ramp-up method, increasing the temperature from 25°C to 500°C at a rate of 5°C / min.

[0155] Use T 50 and T 90 T represents the catalytic activity of a catalyst on its reactants. 50 T represents the reaction temperature at which the reactant conversion rate reaches 50%. 90 The reaction temperature indicates that the reactant conversion rate reaches 90%. The test results are shown in Table 1 below.

[0156] Hydrothermal aging reaction conditions: 10% H2O, water vapor is generated by flowing N2 gas through a water bath bubbler, with a total flow rate of 100 mL / min, heated to 900℃ at a heating rate of 10℃ / min, and held at that temperature for 10 h.

[0157] In all experiments, the formulas for calculating the exhaust gas conversion are as follows. The conversion rates of CH3OH, CO, and NO are defined as follows:

[0158] CH3OH conversion(%)={1-[CH3OH] out / [CH3OH] in}×100%;

[0159] CO conversion (%) = {1 - [CO]} out / [CO] in}×100%;

[0160] NO conversion(%) = {1 - [NO]} out / [NO] in}×100%;

[0161] Among them, [CH3OH] in and [CH3OH] out These represent the methanol concentrations at import and export levels, respectively, and [CO]. in and [CO] out These are the concentrations of imported CO and exported CO, [NO]. in and [NO] out These are the concentrations of nitric oxide imported and exported, respectively.

[0162] Figure 6 , Figure 7 , Figure 8 The figures show the conversion rates of CO, NO, and CH3OH of fresh and aged catalysts at the calcination temperatures of Examples 1-3, respectively. As can be seen from the figures, the catalysts exhibit good high-temperature stability after hydrothermal aging, and their activity does not decrease significantly.

[0163] Figure 9 , Figure 10 , Figure 11 The conversion rate curves of CO, NO, and CH3OH for Example 1 and Comparative Example 2 are shown respectively (calcination temperature 750℃). The figures show that the catalyst activity is enhanced under the synergistic effect of the three noble metals. The single noble metal catalyst exhibits poor activity.

[0164] Table 1:

[0165]

[0166] The test results show that:

[0167] (1) As can be seen from Examples 1-4, the present invention prepares a noble metal three-way catalyst by a multi-step impregnation method plus a co-precipitation method and ultrasound assistance. The co-precipitation method is used to generate more cerium-zirconium solid solution. Then, the active component is further loaded onto CeZr / M2 / Al2O3 powder. By optimizing the metal-support interaction, the active component exists in the form of nanoparticles, which have high dispersion. This regulates the electronic structure of the noble metal and the oxygen defect concentration on the surface, thereby improving the low-temperature performance and thermal stability of the catalyst, achieving the purpose of improving the catalyst performance. The noble metal three-way catalyst provided by the present invention is used to degrade CO and NO in stoichiometric combustion mode. x CH3OH exhibits good low-temperature activity and hydrothermal stability, with minimal performance differences after hydrothermal aging, making it a promising catalyst for a wide range of applications.

[0168] (2) As can be seen from Example 5, the present invention regulates the catalyst performance by further adding additives. By controlling the amount of additives added to be 1wt.%-5wt.%, the amount of additives added will affect the structural stability of the catalyst, the electronic valence state of the noble metal, and the metal-support interaction.

[0169] (3) A comparison of Example 1 and Examples 6-7 shows that by further controlling the molar ratio of active component M1 to metal M2 to 1:(1-5), the present invention can improve the dynamic equilibrium and synergistic efficiency of the oxidation-reduction reaction on the catalyst surface. If the proportion of active component M1 (such as rhodium) is too large and the proportion of metal M2 (such as platinum or palladium) is too small, there will be an excess of carbon monoxide and hydrocarbons in the reaction atmosphere. In this atmosphere of excess CO and HC, CO and HC will compete for adsorption and poison the active sites of Rh. At the same time, this slightly oxygen-rich environment will inhibit NO. x The need for a low-oxygen environment is restored, resulting in a narrowing of the overall triple-effect purification window, NO x The low-temperature range for conversion is limited. If the proportion of active component M1 (e.g., rhodium) is too small and the proportion of metal M2 (e.g., palladium, platinum) is too large, there will be an excess of nitrogen oxides in the reaction atmosphere. The scarce rhodium metal sites cannot meet the NO requirements. x The conversion requirement. Meanwhile, the reactive oxygen species generated by excess Pd / Pt metal sites during the oxidation reactions of CO and CH3OH can further induce peroxidation and deactivation of Rh sites, and may also cause NO to... x Incomplete reduction to the greenhouse gas N2O leads to catalyst degradation in NO. xThe decreased conversion selectivity led to a significant increase in the overall catalyst ignition temperature. Maintaining the molar ratio of M1 to M2 within the optimized range of 1:(1-5) aimed to regulate the CO / HC oxidation and NO conversion. x The reduction reaction rate enables simultaneous and efficient purification of multiple pollutants in methanol vehicle exhaust.

[0170] (4) By comparing Example 1 with Examples 8-9, it can be seen that by further controlling the calcination temperature in step (3) to 650℃-850℃, the calcination temperature affects the dispersion state of the active components, the metal-support interaction, and the surface oxygen defect concentration, thus significantly affecting the low-temperature performance and thermal stability of the catalyst. If the calcination temperature is too high, the noble metal species will undergo significant sintering and aggregation, the particle size of the noble metal nanoparticles will increase significantly, the specific surface area will decrease sharply, the number of active sites will decrease, and the dispersion of noble metals will decrease. At the same time, excessive lattice stress will cause phase separation and structural collapse of CeZr solid solution, resulting in insufficient surface oxygen vacancies, thereby reducing the low-temperature activity and high-temperature thermal stability of the catalyst. If the calcination temperature is too low, the noble metal species will mainly exist in the form of highly dispersed but not highly active noble metal species, and the crystallinity of CeZr solid solution will be insufficient, the oxygen defect concentration will be low and the stability will be poor, resulting in low initial activity and poor high-temperature durability of the catalyst, and it will be unable to form a stable and efficient noble metal-support interface active center.

[0171] (5) As can be seen from Example 1 and Comparative Example 1, if all active components are impregnated together instead of impregnated in steps, the division of labor of the active center cannot be achieved, the metal-support interaction of the catalyst is weakened, and the precious metals will be coated or formed into alloys, which weakens the number of active sites and makes it impossible to achieve the technical effects of low temperature ignition temperature, high anti-sintering ability, wide catalytic purification window and high utilization rate of precious metals.

[0172] (6) As can be seen from Example 1 and Comparative Example 2, if the active component is not impregnated on the surface of Al2O3, but only loaded on the surface of CeZr solid solution, the ignition temperature of HC will be high and the low-temperature conversion efficiency will be reduced. Furthermore, if there are only noble metal species that reduce NO, but no noble metal active species that deeply oxidize HC and CO, the reaction window of the three-way catalytic reaction will be narrowed, and the technical effect of deep oxidation of HC compounds cannot be achieved.

[0173] (7) As can be seen from Example 1 and Comparative Example 3, if the cerium-zirconium solid solution is replaced with the cerium-titanium solid solution, the cerium-titanium solid solution has insufficient oxygen storage capacity, poor high-temperature stability, and poor synergistic effect with the noble metal interface, and cannot achieve the technical effects of low low-temperature ignition temperature, good high-temperature stability, wide reaction window and high NO selectivity.

[0174] In summary, the noble metal three-way catalyst provided by this invention is used to degrade CO and NO in stoichiometric combustion mode. x CH3OH exhibits good low-temperature activity and hydrothermal stability, with minimal performance differences after hydrothermal aging, making it a promising catalyst for a wide range of applications.

[0175] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A noble metal triple-effect catalyst, characterized in that, The noble metal triple-effect catalyst comprises an alumina support, a cerium-zirconium solid solution, and an active component M1. The alumina support is further loaded with metal M2; the cerium-zirconium solid solution covers the surface of the alumina support, and the active component M1 is dispersed on the surface of the cerium-zirconium solid solution; The active component M1 includes any one or a combination of at least two of Rh, Ir, or Ru; The metal M2 includes a combination of at least two of Pd, Pt, Rh or Au; The active component M1 and metal M2 comprise at least three different elements.

2. The noble metal triple-effect catalyst according to claim 1, characterized in that, The general chemical formula of the cerium-zirconium solid solution is Ce. x Zr y O2, where 0.2≤x≤0.8, x+y=1; The mass ratio of the cerium-zirconium solid solution to alumina is (1-2):1; Based on a total mass of 100 wt% for the noble metal three-way catalyst, the total mass fraction of the active component M1 and metal M2 is 0.5 wt%-1 wt%. The total dispersion of the active component M1 and the metal M2 is 40%-60%; The molar ratio of the active component M1 to the metal M2 is 1:(1-5).

3. The noble metal triple-effect catalyst according to claim 1, characterized in that, The active component M1 is Rh, and the metal M2 is Pd and Pt; The alumina is γ-Al₂O₃; The noble metal three-way catalyst also includes an auxiliary agent, which includes any one or a combination of at least two of Ba, Sr, Ca, Ce, Zr, Y, La, Nd, Fe, Mn, Ni or Co.

4. A method for preparing a noble metal three-way catalyst as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) A salt solution of mixed metal M2 and aluminum oxide are subjected to a first ultrasonic treatment and a first calcination to obtain M2 / Al2O3 powder; (2) Mix cerium salt, zirconium salt and solvent to obtain cerium-zirconium mixed solution, mix cerium-zirconium mixed solution and M1 / Al2O3 powder obtained in step (1), add alkaline solution to adjust pH, react and calcine a second time to obtain CeZr / M2 / Al2O3 powder; (3) The salt solution of active component M1 is impregnated into CeZr / M2 / Al2O3 powder, and after a second ultrasonic treatment and calcination, the M1 / CeZr / M2 / Al2O3 noble metal three-way catalyst is obtained.

5. The preparation method according to claim 4, characterized in that, Step (1) The duration of the first ultrasound is 0.5h-2h; The alumina described in step (1) is pretreated before use; Step (1) The temperature of the first roasting is 500℃-600℃; Step (1) The first roasting time is 2h-4h.

6. The preparation method according to claim 4, characterized in that, The salt solution of metal M2 in step (1) includes a salt of metal M2 and a solvent; The salt solution of active component M1 in step (3) includes the salt of active component M1 and a solvent; The salts of the active component M1 and the metal M2 each independently include any one or a combination of at least two of palladium, platinum, rhodium, iridium, or ruthenium salts.

7. The preparation method according to claim 4, characterized in that, The alkaline solution in step (2) includes ammonia and ammonium carbonate; The concentration of the ammonia solution is 2 mol / L-5 mol / L; The concentration of the ammonium carbonate is 0.2 mol / L to 1 mol / L; Step (2) Add alkali solution to adjust the pH of the reaction system to 9-10; Step (2) The second roasting temperature is 500℃-600℃; Step (2) The second roasting time is 2h-4h.

8. The preparation method according to claim 4, characterized in that, Step (3) The duration of the second ultrasound is 0.5h-2h; The calcination temperature in step (3) is 650℃-850℃; The calcination time in step (3) is 2h-4h.

9. The preparation method according to claim 4, characterized in that, The preparation method includes the following steps: (1) Mix ammonia water and alumina, stir, filter and dry, and keep warm at 500℃-600℃ for 2h-4h to obtain pretreated alumina; immerse the pretreated alumina in the salt solution of metal M2, sonicate for 0.5h-2h, and calcine at 500℃-600℃ for 2h-4h to obtain M2 / Al2O3 powder; (2) Mix cerium salt, zirconium salt and solvent to obtain cerium-zirconium mixed solution. Mix cerium-zirconium mixed solution and M1 / Al2O3 powder obtained in step (1), add alkaline solution to adjust pH to 9-10, stir, let stand for 3-5 hours, separate solid and liquid and dry, and calcine at 500℃-600℃ for 2-4 hours to obtain CeZr / M2 / Al2O3 powder; The alkaline solution comprises ammonia water with a concentration of 2 mol / L to 5 mol / L and ammonium carbonate with a concentration of 0.2 mol / L to 1 mol / L, in a volume ratio of 1:(1-3). (3) The salt solution of active component M1 is impregnated onto CeZr / M2 / Al2O3 powder, subjected to second sonication for 0.5h-2h, and calcined at 650℃-850℃ for 2h-4h to obtain M1 / CeZr / M2 / Al2O3 noble metal triple-effect catalyst.

10. The use of a noble metal three-way catalyst as described in any one of claims 1-3, characterized in that, The precious metal triple-effect catalyst is used for methanol vehicle exhaust treatment.

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