Multi-element rare earth oxide composite catalyst as well as preparation method and application thereof

Abstract

The invention relates to a multi-element rare earth oxide composite catalyst as well as a preparation method and application thereof. The catalyst comprises a carrier and a ternary composite material loaded on the carrier, the mass ratio of the carrier to the ternary composite material is (4: 6)-(7: 3); wherein the carrier is gamma-Al2O3 (aluminum oxide); the ternary composite material is composed of a La2O3 phase and an Nd-O solid solution phase, the proportion of the La2O3 phase is 20%-40%, and the proportion of the Nd-O solid solution phase is 60%-80%. The Nd element in the Nd-O solid solution phase has two valence states of Nd < 3 + > and Nd < 4 + >, and the molar ratio of the two valence states is as follows: Nd < 3 + > accounts for 35%-70%, and Nd < 4 + > accounts for 30%-65%. According to the obtained catalyst, the oxygen storage capacity and thermal stability of the catalyst are optimized by adjusting the La / Nd ratio and Nd valence state distribution, and the catalyst meets various vehicle catalysis requirements.

Description

Technical Field

[0001] This invention relates to a multi-element rare earth oxide composite catalyst, its preparation method, and its application in automotive exhaust catalysis. Background Technology

[0002] Amid the increasingly severe global energy crisis and environmental pollution, promoting the transition to clean energy has become a strategic priority for countries worldwide. With the continuous increase in the number of motor vehicles, exhaust pollution poses a growing threat to the ecological environment and public health, making the development of efficient exhaust purification technologies imperative. While currently widely used precious metal catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh) have some effectiveness, their scarcity and high cost make them unsuitable for large-scale applications. Therefore, developing novel ternary purification materials that combine high catalytic performance with low cost has become a key research direction for solving the problem of harmful gas pollution.

[0003] Rare earth oxides, due to their unique electronic structure, possess excellent optical, electrical, and magnetic properties, demonstrating great potential in material modification. Currently, catalytic applications of rare earth oxides mainly focus on La2O3, Ce2O3, or simple composites thereof, such as CN 107537488 A. This patent ball-mills zirconium oxide, cerium oxide, lanthanum powder, and alumina into nanocomposite powders, prepares a slurry, loads it onto a support, centrifuges it, impregnates it with palladium solution, and then produces a catalyst through a single-step calcination process. Because direct mixing and ball milling makes it difficult for the components to achieve simultaneous nanoscale uniform dispersion, the homogeneity of the composite system affects its intrinsic properties. Summary of the Invention

[0004] The purpose of this invention is to address the limitations of current technologies by providing a multi-element rare earth oxide composite catalyst, its preparation method, and its applications. This catalyst uses La₂O₃ and Nd-based oxides as raw materials, and achieves Nd oxidation state recombination through a solid-state reaction and valence state rearrangement under a specific oxygen partial pressure and high temperature and high pressure environment. 3+ To Nd 4+ The controlled oxidation and proportional conversion of rare earth oxides enhance the reactivity of the composite catalyst. The catalyst obtained by this invention can meet the catalytic requirements of different vehicle models, forming a formulation adapted to the catalytic requirements of various vehicles.

[0005] The technical solution of this invention is as follows: A multi-element rare earth oxide composite catalyst, comprising a support and a ternary composite material supported thereon; the support is γ-Al2O3, and the ternary composite material is a La2O3 phase and an Nd-O solid solution; The mass ratio of the carrier to the ternary composite material is 4:6 to 7:3. In the ternary composite material, the La2O3 phase accounts for 20wt%-40wt%, and the Nd-O solid solution phase accounts for 60wt%-80wt%; the Nd-O solid solution phase contains Nd 3+ / Nd 4+ Two valence states, the molar ratio of the two valence states is: Nd 3+ 35%-70%, Nd 4+ It accounts for 30%-65%.

[0006] The carrier is γ-Al2O3 with a size of 0.5-2μm. The ternary composite material agglomerates on the surface of the carrier to form fluffy particles, and the thickness of the ternary composite material attached to its surface is 0.1-0.5μm. The preparation method of the multi-element rare earth oxide composite catalyst includes the following steps: Step 1, (1) Add La2O3 and Nd2O3 to a ball mill jar with a ratio of 20wt%-40wt% for La2O3 and 60wt%-80wt% for Nd2O3 and stir to mix. Then put it into a muffle furnace and preheat it at 650-750℃ for 3-4 hours. (2) Seal the pretreated material into a HIP container and fill it with 90-110MPa of Ar and 0.1-0.5MPa of O2. Then keep it at 900-1150℃ for 2-3 hours and let it stand at room temperature to take out the La-Nd composite powder. When the O2 pressure is 0.2 ≤ P ≤ 0.5 MPa, the Nd element, Nd 4+ It accounts for 50%-65%, with the remainder being Nd. 3+ When the O2 pressure is 0.1 ≤ P < 0.2 MPa, the Nd element... 3+ It accounts for 60%-70%, with the remainder being Nd. 4+ ; Step two, The sintered La-Nd composite material powder was placed in a mortar and ground to less than 1 mm. It was then ball-milled in a ball mill at a ball-to-material ratio of 10:1 and a speed of 400-500 rpm for 5-6 hours to obtain La-Nd composite material powder with a particle size of 60-80 nm. Step 3, The La-Nd composite material powder obtained in step two was stirred with γ-Al2O3 slurry to obtain a mixed slurry; then PEG-PVA colloid was added and mixed, and dried at 80-90℃ for 6-12h to obtain a composite gel. Further, 50-100nm γ-Al2O3 powder is added to a 50%-75% concentration ethanol solution and ultrasonically dispersed for 30-60 minutes to form a γ-Al2O3 slurry with a concentration of 10-30wt%. Furthermore, 10-30g of composite material is added to every 100g of γ-Al2O3 slurry; Furthermore, PEG / PVA is mixed at a mass ratio of 3-5:1 to form a PEG-PVA colloid; the total colloid concentration reaches 3-10 wt%. Furthermore, the volume ratio of the mixed slurry to the PEG-PVA colloid is 1:0.5-1.5; Step 4, Stepped calcination process: (1) First stage: The composite gel obtained in step three is placed in a quartz tube and sealed. It is then placed in a tube furnace and heated at 15-25℃ / min to 300-400℃ and kept at that temperature for 2-3 hours. (2) Second stage: Continue heating in the tube furnace at 10-18℃ / min until it reaches 400-500℃, and hold for 4-5 hours; (3) Third stage: Continue to heat in the tube furnace at 0.5-1℃ / min to 700-800℃, hold for 10-13h, and cool naturally to room temperature to obtain a multi-element rare earth oxide composite catalyst with a diameter of 0.6-2.5μm and a fluffy microstructure. After stepwise calcination, the catalyst as a whole forms a clustered structure with the support as the core and the ternary composite material as the fluffy outer layer. This structure has a high specific surface area and a large number of exposed active sites, which can effectively adsorb and catalyze gaseous organic pollutants.

[0007] The aforementioned multi-element rare earth oxide composite catalyst is used as a catalyst for purifying automobile exhaust.

[0008] Specifically, for heavy-duty diesel vehicles: Nd 4+ The atomic ratio is 55%-65%; For traditional gasoline vehicles: Nd 3+ The atomic ratio is 60%-70%; For plug-in hybrid vehicles and similar models: Nd 3+ With Nd 4+ The atomic ratio is 45%-55%.

[0009] The essential features of this invention are: In this invention, La₂O₃ and Nd₂O₃ undergo a solid-state reaction and valence state rearrangement under a high-temperature and high-pressure environment with oxygen partial pressure. NdO₂ (Nd 4+ ) and Nd2O3 (Nd 3+ Electron transfer occurs between Nd and Nd, with some Nd... 3+ It is oxidized and reacts with La in the La2O3 lattice. 3+ A substitution reaction occurs, forming a La-Nd-O solid solution. The reaction pathway can be described as follows:

[0010] The resulting solid solution contains a mixed valence state structure of neodymium ions (i.e., Nd). 3+ / Nd 4+ (Coexistence) can achieve targeted catalytic performance for different exhaust gas environments.

[0011] The beneficial effects of this invention are: The catalyst prepared by this invention is a multi-element rare earth composite catalyst. By regulating the Nd valence state distribution and the La / Nd ratio, the catalytic ability of the catalyst is greatly enhanced, making the catalyst suitable for different vehicle models and possessing important application value in the field of automotive exhaust gas treatment technology.

[0012] This invention uses a stepped calcination process to form a fluffy spherical microstructure, which increases the contact area between the catalyst and the exhaust gas, improves catalytic performance, avoids the use of precious metals, and saves costs. Attached Figure Description

[0013] Figure 1 The image shown is a transmission electron microscope (TEM) image of the catalyst powder obtained in Example 1, with a scale bar of 1 μm.

[0014] Figure 2 XPS measurements of the Nd 3d orbitals obtained in Example 1 without O2 pressure.

[0015] Figure 3 XPS measurements of the Nd 3d orbital obtained in Example 1 when the O2 pressure is 0.2≤P≤0.5MPa. Detailed Implementation

[0016] Example 1: 1) Preparation method (1) Add La2O3 and Nd2O3 to a ball mill jar and mix them in a ratio of 20wt% La2O3 and 80wt% Nd2O3. (2) Place the ball mill jar into a muffle furnace and preheat it at 750°C for 4 hours; (3) The material obtained above was sealed in a HIP container and filled with a mixed gas of 110 MPa Ar and 0.4 MPa O2. It was kept at 900 °C for 2 hours to obtain a material with the following molar proportions of Nd: Nd 4+ 55% of the total, Nd 3+ La-Nd composite powder comprising 45%; (4) Place the La-Nd composite material powder into a mortar and grind it to less than 1 mm. Then, continuously ball mill it for 6 hours at a ball-to-material ratio of 10:1 and a rotation speed of 500 rpm to reduce the particle size to less than 80 nm. (5) Place 100g of 50-100nm γ-Al2O3 powder in a beaker, add 271ml of 75wt% ethanol aqueous solution, and ultrasonically disperse for 50 min to prepare a 30wt% uniform and stable carrier slurry. (6) Take 100g of 30wt% carrier slurry and 20g of La-Nd composite material powder with a particle size of 60-80nm and stir them together in a beaker; (7) 8.0g of polyethylene glycol (PEG) and 1.6g of polyvinyl alcohol (PVA) were combined and added to 86.4mL of deionized water. The mass ratio of PEG to PVA was 5:1 and the concentration of the colloidal system was 10wt%. The mixture was ultrasonically dispersed for 35min. (8) Take 100 mL of the mixed material obtained in (6) and mix it with 100 mL of the PEG-PVA colloid obtained in (7) in a beaker, place it in a drying oven, and dry it at 90°C for 12 h; (9) First stage, degumming and structural relaxation: The composite gel obtained in (8) is placed in a quartz tube and placed in a tube furnace. The temperature is increased to 400°C at a rate of 25°C / min and kept at that temperature for 3 hours. (10) Second stage, purification and micropore shaping: continue to heat to 500℃ in the tube furnace at 18℃ / min and hold for 5h; (11) Third stage, reconstruction and self-assembly of fluffy morphology: Continue to slowly heat to 800℃ in a tube furnace at 1℃ / min, hold for 13h, and obtain a La2O3 phase content of 17wt% and an Nd-O solid solution phase content of 83wt%, of which Nd 3+ Nd accounts for 45% of the total number of Nd atoms. 4+ A spherical ternary tail gas treatment catalyst that accounts for 55% of the total number of Nd atoms.

[0017] The ratio of the three components was determined using XPS. Figure 2 and Figure 3 XPS spectrum comparison analysis shows that the present invention successfully achieved the control of the valence state of Nd; wherein, Figure 2 In the Nd 3d orbital spectrum of the (untreated Nd2O3 precursor), the binding energy characteristic peaks mainly correspond to Nd... 3+ In stark contrast, Figure 3 In the spectrum (after treatment with a mixture of 110 MPa Ar and 0.4 MPa O2 at 900℃ for 2 h), a clear Nd group appeared at a significantly higher binding energy position. 4+ Characteristic peaks, calculated for Nd 4+ , accounting for 55%, Nd 3+ The proportion is 45%. This controllable mixed valence state (Nd) 3+ / Nd 4+These components constitute the redox centers of the catalyst, significantly enhancing its resistance to NO. x The adsorption and activation capabilities of [the substance] are demonstrated in Example 1, where it exhibited a high NO removal rate of 92.6% in the treatment of heavy-duty diesel vehicle exhaust. x The fundamental reason for conversion rate. Figure 1 The particle surface outline exhibits a spherical structure resembling clusters of fluff. The fluffy particles are black, and the overall diameter of the fluffy particles (the fluffy protrusions growing on the skeleton surface, shown as the black part) is 0.6-2.5 μm. The outer layer is attached with a ternary composite material with a total thickness of 0.2 μm. The fluffy structure can significantly increase the specific surface area of ​​the catalyst, resulting in high catalytic activity and efficiency.

[0018] 2) Applicable vehicle models: Heavy-duty diesel vehicles, targeting high NO x Emissions. These types of vehicles produce large amounts of NO under oxygen-rich combustion conditions. x (Accounting for 30-50% of exhaust gas composition), the exhaust gas is rich in oxygen and NO x The content is high; therefore, a La2O3 ratio of 20%-30% and an oxygen partial pressure of 0.2-0.5 MPa are used in the preparation to make Nd 4+ With a proportion of 55%-65%, this material utilizes the strong oxidizing properties of NdO2 to achieve NO oxidation within a working window of 300-550℃. x Transformation.

[0019] 3) Measurement methods and conditions: Catalytic experiments were conducted in a piston flow reactor system. 90 mg of 100-mesh powdered catalyst was loaded into a quartz tube, and a solution containing 500 ppm NO was used. x A synthesis gas mixture of 1200 ppm CO and 530 ppm HC, under a nitrogen flow rate of 260 sccm and in the presence of 3% water vapor by volume, was used to achieve a space velocity (GHSV) of 120 L / (g•h) for NO reaction. X Reduction Experiment. 90 mg of 100-mesh powdered catalyst was loaded into a quartz tube. A CO oxidation experiment was conducted using a nitrogen flow rate of 260 sccm, 3% water vapor, and 20% oxygen, with a space velocity (GHSV) of 120 L / (g•h). Finally, 90 mg of 100-mesh powdered sample was loaded into a quartz tube. A synthesis gas mixture containing 1200 ppm CO and 530 ppm HC was used, with a nitrogen flow rate of 260 sccm, 3% water vapor, and a GHSV of 120 L / (g•h), for HC reduction. The concentrations of reactants and products were measured using an online gas analyzer (MKS MultiGas 2030 FTIR).

[0020] Comparative Example 1: A one-stage calcination process was used for comparison, that is, the stepped calcination process in Example 1 was omitted, and the temperature was directly raised to 800°C at a heating rate of 20°C / min and held for 5 hours. Other process conditions were the same as in Example 1.

[0021] Comparative Example 2: Using the exact same raw material ratio and process as in Example 1, up to the step calcination stage, in the third stage of step calcination, the heating rate was increased from 1℃ / min to 5℃ / min, while other parameters remained unchanged.

[0022] Comparative Example 3: Using the exact same raw material ratios and processes as in Example 1, only PEG was used as a binder during the slurry mixing stage, and the total amount used was equivalent to the total amount of colloid in Example 1.

[0023] Table 1

[0024] Example 2: 1) Preparation method (1) Add La2O3 and Nd2O3 to a ball mill jar and mix them in a ratio of 34wt% La2O3 and 66wt% Nd2O3. (2) Place the ball mill jar into a muffle furnace and preheat it at 720°C for 3.5 hours; (3) The material obtained above was sealed in a HIP container and filled with a mixed gas of 104 MPa Ar and 0.1 MPa O2. It was kept at 1060 °C for 2.5 h to obtain a material with the following molar proportions of Nd: Nd 4+ 37% of Nd 3+ La-Nd composite powder accounts for 73%; (4) Place the La-Nd composite material powder into a mortar and grind it to less than 1 mm. Then, continuously ball mill it for 5.5 h at a ball-to-material ratio of 10:1 and a rotation speed of 460 rpm to reduce the particle size to less than 80 nm. (5) Place 100g of 50-100nm γ-Al2O3 powder in a beaker, add 360ml of 65wt% ethanol aqueous solution, and ultrasonically disperse for 50 min to prepare a 24wt% uniform and stable carrier slurry. (6) Take 100g of 24wt% carrier slurry and 24g of La-Nd composite material powder with a particle size of 60-80nm and stir them together in a beaker; (7) Combine 8.0g of polyethylene glycol (PEG) and 2.0g of polyvinyl alcohol (PVA) and add them to 120mL of deionized water. The mass ratio of PEG to PVA is 4:1, and the concentration of the colloidal system is 7.7wt%. Disperse by ultrasonication for 30min. (8) Take 100 mL of the mixed material obtained in (6) and mix it with 100 mL of the PEG-PVA colloid obtained in (7) in a beaker, place it in a drying oven, and dry it at 85°C for 9 h; (9) Place the composite gel obtained in (8) in a quartz tube, place it in a tube furnace, heat it to 350°C at a rate of 20°C / min, and keep it at that temperature for 2.5h; (10) Continue heating in the tube furnace at 15℃ / min to 450℃ and hold for 4.5h; (11) Continue to slowly heat to 760℃ in a tube furnace at 0.8℃ / min, hold for 12h, and obtain a La2O3 phase content of 30wt% and an Nd-O solid solution phase content of 70wt%, of which Nd 3+ Nd accounts for 63% of the total number of Nd atoms. 4+ A spherical ternary tail gas treatment catalyst that accounts for 37% of the total number of Nd atoms.

[0025] 2) Applicable vehicle models: Traditional gasoline vehicles, whose exhaust emissions are primarily CO (70-85%), have a narrow operating temperature range (250-500℃) and prioritize CO purification. Therefore, the preparation process uses a 30%-40% La2O3 ratio and a relatively low oxygen partial pressure of 0.1-0.2 MPa to allow Nd... 3+ The atomic ratio is 60%-70%, which enhances the reduction efficiency of CO.

[0026] 3) The electrochemical performance testing method is the same as that in Example 1.

[0027] Example 3: 1) Preparation method (1) Add La2O3 and Nd2O3 to a ball mill jar and mix them in a ratio of 27wt% La2O3 and 73wt% Nd2O3. (2) Place the ball mill jar into a muffle furnace and preheat it at 680°C for 3.5 hours; (3) The material obtained above was sealed in a HIP container and filled with a mixed gas of 97 MPa Ar and 0.2 MPa O2. It was kept at 980 °C for 2.5 h to obtain a material with the following molar proportions of Nd: Nd 4+ 50% of the total, Nd 3+ La-Nd composite powder comprising 50%; (4) Place the La-Nd composite material powder into a mortar and grind it to less than 1 mm. Then, continuously ball mill it for 5.5 h at a ball-to-material ratio of 10:1 and a rotation speed of 440 rpm to reduce the particle size to less than 80 nm. (5) Place 100g of 50-100nm γ-Al2O3 powder in a beaker, add 546ml of 60wt% ethanol aqueous solution, and ultrasonically disperse for 50 min to prepare a 17wt% uniform and stable carrier slurry. (6) Take 100g of 17wt% carrier slurry and 17g of La-Nd composite material powder with a particle size of 60-80nm and stir them together in a beaker; (7) Combine 8.0g of polyethylene glycol (PEG) and 2.0g of polyvinyl alcohol (PVA) and add them to 120mL of deionized water. The mass ratio of PEG to PVA is 4:1, and the concentration of the colloidal system is 7.7wt%. Disperse by ultrasonication for 30min. (8) Take 100 mL of the mixed material obtained in (6) and mix it with 100 mL of the PEG-PVA colloid obtained in (7) in a beaker, place it in a drying oven, and dry it at 85°C for 9 h; (9) Place the composite gel obtained in (8) in a quartz tube, place it in a tube furnace, heat it to 350°C at a rate of 20°C / min, and keep it at that temperature for 2.5h; (10) Continue heating in the tube furnace at 14℃ / min to 450℃ and hold for 4.5h; (11) Continue to slowly heat to 730℃ in a tube furnace at 0.8℃ / min, hold for 11h, and obtain a La2O3 phase content of 24wt% and an Nd-O solid solution phase content of 76wt%, of which Nd 3+ Nd accounts for 50% of the total number of Nd atoms. 4+ A spherical ternary tail gas treatment catalyst that accounts for 50% of the total number of Nd atoms.

[0028] 2) Applicable vehicle models: Plug-in hybrid electric vehicles. These vehicles experience large fluctuations in exhaust composition and temperature (150-600℃) due to intermittent engine operation, and simultaneously need to handle CO / HC in fuel mode and NO in the electric motor-assisted phase. x Only then can the CO / HC / NO balance be achieved. x Conversion; therefore, the oxygen partial pressure is controlled at 0.2 MPa during preparation, Nd 3+ With Nd 4+ Each 45%-55%, enhancing the control of CO and NO over a wide temperature range. x The redox efficiency.

[0029] 3) The electrochemical performance testing method is the same as that in Example 1.

[0030] Example 4: 1) Preparation method (1) Add La2O3 and Nd2O3 to a ball mill jar and mix them in a ratio of 40wt% La2O3 and 60wt% Nd2O3. (2) Place the ball mill jar into a muffle furnace and preheat it at 650°C for 3 hours; (3) The material obtained above was sealed in a HIP container and filled with a mixed gas of 90 MPa Ar and 0.1 MPa O2. It was kept at 900 °C for 2 h to obtain a material with the following molar proportions of Nd: Nd 4+ 30% of Nd 3+ La-Nd composite powder accounts for 70%; (4) Place the La-Nd composite material powder into a mortar and grind it to less than 1 mm. Then, continuously ball mill it for 5 hours at a ball-to-material ratio of 10:1 and a rotation speed of 400 rpm to reduce the particle size to less than 80 nm. (5) Place 100g of 50-100nm γ-Al2O3 powder in a beaker, add 985ml of 50wt% ethanol aqueous solution, and ultrasonically disperse for 30 min to prepare a 10wt% uniform and stable carrier slurry. (6) Take 100g of 10wt% carrier slurry and 10g of La-Nd composite material powder with a particle size of 60-80nm and stir them together in a beaker; (7) Combine 3.0g of polyethylene glycol (PEG) and 1.0g of polyvinyl alcohol (PVA) and add them to 120mL of deionized water. The mass ratio of PEG to PVA is 3:1, and the concentration of the colloidal system is 3.2wt%. Disperse by ultrasonication for 30min. (8) Take 100 mL of the mixed material obtained in (6) and 100 mL of the PEG-PVA colloid obtained in (7) and mix them in a beaker. Place the mixture in a drying oven and dry it at 80 °C for 6 h. (9) Place the composite gel obtained in (8) in a quartz tube, place it in a tube furnace, heat it to 300°C at a rate of 15°C / min, and keep it at that temperature for 2 hours; (10) Continue heating in the tube furnace at 10℃ / min to 400℃ and hold for 4h; (11) Continue to slowly heat to 700℃ in a tube furnace at 0.5℃ / min, hold for 10h, and obtain a La2O3 phase content of 36wt% and an Nd-O solid solution phase content of 64wt%, of which Nd 3+ Nd accounts for 70% of the total number of Nd atoms. 4+ A spherical ternary tail gas treatment catalyst that accounts for 30% of the total number of Nd atoms.

[0031] 2) Applicable vehicle models: Suitable for multi-power platform vehicles, this material achieves efficient exhaust gas treatment in a wide temperature range of 200-600℃ through the synergistic effect of the stability of La2O3, the oxidizing properties of NdO2, and the reducing properties of Nd2O3. It is particularly suitable for intelligent power systems with multiple operating modes.

[0032] 3) The electrochemical performance testing method is the same as that in Example 1.

[0033] Table 2

[0034] The above embodiments and data illustrate that, through the design and process optimization of the ratio of three rare earth oxides, La2O3, NdO2, and Nd2O3, this invention has successfully constructed an exhaust gas treatment system suitable for different vehicle models, greatly enhancing the treatment of NO. x The study investigated the redox properties of CO and CH compounds, and simultaneously addressed three major technical bottlenecks: the easy decomposition of NdO2, the difficulty in controlling the Nd valence state, and the difficulty in forming an ideal microstructure between the active components and the support.

[0035] Matters not covered in this invention are common knowledge.

Claims

1. A multi-element rare earth oxide composite catalyst, characterized in that, The catalyst consists of a support and a ternary composite material supported thereon; the support is γ-Al2O3, and the ternary composite material is a La2O3 phase and an Nd-O solid solution. The mass ratio of the carrier to the ternary composite material is 4:6 to 7:

3. In the ternary composite material, the La2O3 phase accounts for 20wt%-40wt%, and the Nd-O solid solution phase accounts for 60wt%-80wt%; the Nd element in the Nd-O solid solution phase is Nd 3+ / Nd 4+ Two valence states, the molar ratio of the two valence states is: Nd 3+ 35%-70%, Nd 4+ It accounts for 30%-65%.

2. The multi-element rare earth oxide composite catalyst as described in claim 1, characterized in that, The carrier is γ-Al2O3 with a size of 0.5-2μm. The ternary composite material agglomerates on the surface of the carrier to form fluffy particles, and the thickness of the ternary composite material attached to the surface is 0.1-0.5μm.

3. The preparation method of the multi-element rare earth oxide composite catalyst as described in claim 1, characterized in that, Includes the following steps: Step 1, (1) Add La2O3 and Nd2O3 to a ball mill jar with a ratio of 20wt%-40wt% for La2O3 and 60wt%-80wt% for Nd2O3 and stir to mix. Then put it into a muffle furnace and preheat it at 650-750℃ for 3-4 hours. (2) Seal the pretreated material into a HIP container and fill it with 90-110MPa of Ar and 0.1-0.5MPa of O2. Then keep it at 900-1150℃ for 2-3 hours and let it stand at room temperature to take out the La-Nd composite powder. When the O2 pressure is 0.2 ≤ P ≤ 0.5 MPa, the Nd element, Nd 4+ It accounts for 50%-65%, with the remainder being Nd. 3+ When the O2 pressure is 0.1 ≤ P < 0.2 MPa, the Nd element... 3+ It accounts for 60%-70%, with the remainder being Nd. 4+ ; Step 2: Place the sintered La-Nd composite material powder in a mortar and grind it to less than 1 mm, then ball mill it to obtain La-Nd composite material powder with a particle size of 60-80 nm. Step 3: Stir the La-Nd composite material powder obtained in Step 2 with γ-Al2O3 slurry to obtain a mixed slurry; then add PEG-PVA colloid and mix, and dry at 80-90℃ for 6-12h to obtain a composite gel. The method involves adding 10-30g of composite material to every 100g of γ-Al2O3 slurry; the volume ratio of the mixed slurry to PEG-PVA colloid is 1:0.5-1.5; PEG / PVA is mixed at a mass ratio of 3-5:1 to form PEG-PVA colloid; and the total colloid concentration reaches 3-10 wt%. Add 50-100nm γ-Al2O3 powder to a 50%-75% concentration ethanol solution and ultrasonically disperse for 30-60 minutes to form a γ-Al2O3 slurry with a concentration of 10-30wt%. Step 4, (1) First stage: Place the composite gel obtained in step 3 in a quartz tube and seal it. Place it in a tube furnace and heat it at 15-25℃ / min until it reaches 300-400℃. Keep it warm for 2-3 hours. (2) Second stage: Continue heating in the tube furnace at 10-18℃ / min until it reaches 400-500℃, and hold for 4-5 hours; (3) Third stage: Continue to heat in the tube furnace at 0.5-1℃ / min to 700-800℃, hold for 10-13h, and cool naturally to room temperature to obtain multi-element rare earth oxide composite catalyst.

4. The preparation method of the multi-element rare earth oxide composite catalyst as described in claim 3, characterized in that, The ball milling process involves: subsequently using ethanol as the medium, performing high-energy planetary ball milling for 5-6 hours at a ball-to-material ratio of 10:1 and a rotation speed of 400-500 rpm.

5. The application of the multi-element rare earth oxide composite catalyst as described in claim 1, characterized in that, Used as a catalyst for purifying automobile exhaust.

6. The application of the multi-element rare earth oxide composite catalyst as described in claim 5, characterized in that, For different vehicle models, the Nd content in the Nd-O solid solution phase... 3+ The atomic ratios are as follows: When used in heavy-duty diesel vehicles, Nd 4+ The atomic ratio is 55%-65%; Alternatively, when used in conventional gasoline vehicles, Nd 3+ The atomic ratio is 60%-70%; Alternatively, when used in plug-in hybrid vehicles, Nd 3+ With Nd 4+ The atomic ratio is 45%-55% each.

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