Nanoscale ABO3 type rare earth-based perovskite catalyst and preparation method thereof

Abstract

The invention discloses a nanoscale ABO3 type rare earth-based perovskite catalyst and a preparation method thereof, the nanoscale ABO3 type rare earth-based perovskite catalyst has nanoscale grain size and high specific surface area, can be used for gasoline engine tail gas purification treatment, and belongs to the technical field of catalytic materials. According to the nanoscale ABO3 type rare earth-based perovskite catalyst prepared by the method disclosed by the invention, the thermal stability and low-temperature catalytic activity of the catalyst are improved, and a remarkable effect on treatment of automobile exhaust can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite oxide catalytic materials, and in particular to an ABO3 type rare earth-based perovskite catalyst with nano-scale grain size and high specific surface area that can be used for gasoline engine exhaust purification and a preparation method thereof. Background Art

[0002] Perovskite oxides have stable structures and diverse components. The valence, ratio and vacancy content of the elements can be adjusted over a wide range. They are widely used in the catalytic purification of motor vehicle exhaust. Literature research shows that the catalytic performance of perovskite materials is not only related to the grain size, specific surface area and carrier of the material, but also can be affected by adjusting the surface structure to reconstruct the performance. Due to the diversity of its constituent elements, the catalytic performance of perovskite materials varies greatly. Yildiz et al. (J.Am.Chem.Soc.2013,135,7909-7925) studied La 0.8 D 0.2 The cation segregation phenomenon of MnO3 (D=Ca, Sr, Ba) was found that the cation size mismatch, oxygen vacancies and cation vacancy distribution drive the segregation of dopants on the perovskite surface by affecting the elastic potential energy and electrostatic interaction, respectively, which directly affects the reaction performance and stability of the cathode in ORR. Wu et al. (Angew. Chem. 2017, 129, 9952-9956) controlled the termination site on the perovskite surface to regulate the reaction selectivity, used different treatment methods to enrich Sr or Ti on the SrTiO3 surface, and changed the selectivity of 2-propanol dehydrogenation products by adjusting the acidity and alkalinity of the catalyst. From the above studies, it can be seen that regulating the distribution of surface elements will significantly affect the reaction activity of perovskite catalysts. Since perovskite materials need to be calcined at high temperature (generally >800℃) during the synthesis process, high temperature will cause the perovskite grains to sinter, resulting in a rapid decrease in the surface area of ​​the catalyst, uneven particle distribution, and reduced activity. Reducing the perovskite grain size is an effective way to solve the problem of severe high-temperature sintering and poor anti-sintering performance of the catalyst. Conventionally, a perovskite catalyst with a core-shell structure is prepared by a template method, which can increase the loading amount and increase the specific surface area, but the shell material will cover the surface active sites, resulting in performance degradation. Alternatively, a nanoscale perovskite catalyst is obtained at a relatively low temperature by a mechanical ball milling method, which effectively increases the specific surface area of ​​the catalyst, but there is a problem of high initial activity and rapid sintering during the reaction. Therefore, in the present invention, we propose a step-by-step aging method to synthesize a rare earth-based perovskite catalyst material with an ABO3 configuration, which has a grain size of nanometers (generally not more than 50nm), a uniform grain distribution, and improves the thermal stability and low-temperature catalytic activity of the catalyst, which can play a significant role in the treatment of automobile exhaust.

[0003] The ideal perovskite-type oxide is a cubic crystal with cations at the A or B sites as nodes. The metal ions at the A site are coordinated with 12 adjacent oxygen atoms to form a cubic structure. At the same time, the metal ions at the B site are coordinated with oxygen to form a regular octahedral structure of BO6 inside the cubic structure. The tolerance factor (abbreviated as t, see the attached drawings in the specification Figure 3 ) is a fundamental parameter for measuring the stability of the perovskite structure. It was first proposed by Goldschmidt in 1926: Ions with a smaller tolerance factor have a higher degree of ion substitution and are prone to forming solid solutions. Under the condition that the tolerance factor 0.75 < t < 1 is satisfied, partial substitution at the A and B sites does not change the overall perovskite crystal structure, and the perovskite structure is the most stable at this time. Among them, r A and r B represent the atomic (ionic) radii of the A and B sites respectively, while r O represents the oxygen ion radius. Summary of the Invention

[0004] A nano-scale ABO3-type rare earth-based perovskite catalyst, the catalyst components can be abbreviated as A (1-i-j) A′ i A ″ j B (1-m-n) B′ m B ″n O3.

[0005] The molar ratio of elements A and B is 7:10 to 13:10, where A includes element A and its substitutable elements A′ and A″; B includes element B and its substitutable elements B′ and B″.

[0006] Among them, element A and its substitutable elements A′ and A″ are one or two of the rare earth lanthanide elements.

[0007] Among them, element B and its substitutable elements B′ and B″ are one to three of alkaline earth metals and transition metals.

[0008] The catalyst has a typical perovskite crystal structure, and its primary grain size is less than 50 nm.

[0009] The catalyst can be a rare earth-based perovskite compound with a cubic crystal system, a hexagonal crystal system, or an orthorhombic crystal system configuration.

[0010] A preparation method of a nano-scale ABO3-type rare earth-based perovskite catalyst, the method includes:

[0011] 1) dispersing one of the metal oxides, carbonates, chlorides and nitrates corresponding to element B in deionized water, adding a certain amount of HNO3, H2SO4 and H2O2 thereto, and aging the mixture at a temperature of 150 to 200° C. with continuous stirring for 24 to 48 hours to form an oxide polymer suspension;

[0012] 2) The pH value of the oxide polymer suspension prepared above is less than 3.0;

[0013] 3) adding the metal salt of element A to the oxide polymer suspension prepared in 2);

[0014] 4) According to the specific selected elements, ammonia water or sodium hydroxide is added to the solution obtained in 3) through a T-type micro mixer to adjust the pH to 8-12;

[0015] 5) separating the suspension obtained in 4) into solid and liquid, washing the obtained solid part with deionized water until the conductivity of the washing water is lower than 10 μS / cm, and collecting the filter cake after washing;

[0016] 6) dispersing the filter cake obtained in 5) in deionized water, and adding dispersant D to obtain a suspension, wherein the dispersant D is a saturated fatty acid;

[0017] 7) The suspension obtained in 6) is continuously stirred at a temperature of 150 to 200° C. for 24 to 48 hours for aging to obtain an aged suspension;

[0018] 8) subjecting the aged suspension obtained in 7) to solid-liquid separation, and fully filtering to remove water, so that the water content of the filter cake is less than 50%, to obtain a hydrated hydroxide wet filter cake;

[0019] 9) The hydrated hydroxide wet cake obtained in 8) is heat treated at a temperature of 500 to 600° C. for 0.5 to 3 hours.

[0020] The applications of the catalyst include: as a closed-coupled catalyst close to the engine of a motor vehicle equipped with a gasoline engine, as an under-floor catalyst, and as a catalyst coating of a gasoline engine exhaust particulate filter.

[0021] The nanoscale ABO3 rare earth-based perovskite catalyst according to claim 1 is characterized in that the application of the catalyst includes: being used as a catalyst coating for DOC, DPF and ASC of a motor vehicle equipped with a gasoline engine.

[0022] advantage:

[0023] The ABO3 type rare earth-based perovskite catalyst disclosed by the present invention has nano-scale grain size and high specific surface area, can be used for gasoline engine exhaust purification, and belongs to the technical field of catalytic materials. The nano-scale ABO3 type rare earth-based perovskite catalyst prepared by the method of the present invention improves the thermal stability and low-temperature catalytic activity of the catalyst, and can play a significant role in the treatment of automobile exhaust. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the SEM picture of the comparative example and the example sample;

[0025] Figure 2 It is the XRD curve spectrum of comparative example and embodiment sample;

[0026] Figure 3 Schematic diagram of the gold Schmidt tolerance factor of the perovskite structure. DETAILED DESCRIPTION

[0027] Example 1

[0028] 152.5g of MnSO4 powder was dissolved and dispersed in 5.5L of deionized water, and stirred continuously at room temperature at a stirring speed of 150rpm. 0.5L of 1mol / L HNO3 solution and 0.25L of 1mol / L H2SO4 solution and 0.3L of 30% H2O2 solution were added thereto, and stirred continuously at a temperature of 150℃ at a stirring speed of 150rpm, and aged for 24hrs. 1.0L of 1mol / L La(NO3)3 solution was then added to the aged solution, and stirred continuously at a temperature of 150℃ at a stirring speed of 150rpm, and aged for 24hrs. 0.01mol C8 or C 10 or C 12 The saturated fatty acid is used as dispersant D, and then 0.3L of 28% ammonia water is added, the pH value is adjusted to 9, and the mixture is stirred continuously at 150°C with a stirring speed of 150rpm for aging for 24 hours. The aged suspension is subjected to solid-liquid separation, fully washed, and the moisture content of the final wet cake is controlled at about 45%, and the wet cake is collected. The obtained wet cake is calcined at 500°C for 2 hours to obtain a final product, which is a lanthanum-based perovskite compound with a molecular formula of LaMnO3, where La:Mn=1:1.

[0029] Example 2

[0030] 152.5g of MnSO4 powder was dissolved and dispersed in 5.5L of deionized water, and stirred continuously at room temperature at a speed of 120rpm. 0.5L of 1mol / L HNO3 solution and 0.25L of 1mol / L H2SO4 solution, as well as 0.3L of 30% H2O2 solution were added thereto, and stirred continuously at a temperature of 60°C at a speed of 120rpm, and aged for 48hrs. Then 0.5L of 1mol / L La(NO3)3 solution and 0.5L of 1mol / L Ce(NO3)3 solution were added to the aged solution, and stirred continuously at a temperature of 60°C at a speed of 120rpm, and aged for 24hrs. 0.01mol C8 or C 10 or C 12 The saturated fatty acid was used as dispersant D, and then 0.3L of 28% ammonia water was added, the pH value was adjusted to 9, and the mixture was stirred continuously at 60°C with a stirring speed of 120rpm and aged for 24 hours. The aged suspension was separated into solid and liquid, and washed thoroughly. The moisture content of the final wet cake was controlled at 45%, and the wet cake was collected. The obtained wet cake was calcined at 500°C for 2 hours to obtain a final product, which was a lanthanum-cerium-based perovskite compound with a molecular formula of La 0.5 Ce 0.5 MnO3, where La:Ce:Mn=0.5:0.5:1.

[0031] Example 3

[0032] 153.5g FeSO4 powder was added to 5.5L deionized water to dissolve and disperse, and stirred continuously at room temperature at a stirring speed of 150rpm. 0.5L of 1mol / L HNO3 solution and 0.25L of 1mol / L H2SO4 solution and 0.3L of 30% H2O2 solution were added thereto, and stirred continuously at a temperature of 90°C at a stirring speed of 150rpm, and aged for 36hrs. Then 0.5L of 1mol / L La(NO3)3 solution and 0.5L of 1mol / L Sr(NO3)2 solution were added to the aged solution, and stirred continuously at a temperature of 90°C at a stirring speed of 150rpm, and aged for 24hrs. A T-type micro mixer was used, and 0.3L of 28% ammonia water was slowly injected into one inlet, and the mixed solution in the reactor was circulated and injected into the other inlet. The feed flow rate of the two materials was consistent at 100ml / min. 0.01mol C8 or C 10 or C 12The saturated fatty acid was used as dispersant D, and the pH value was adjusted to 9. The mixture was stirred continuously at 90°C with a stirring speed of 150 rpm and aged for 24 hours. The aged suspension was separated into solid and liquid, washed thoroughly, and the moisture content of the final wet cake was controlled at 45%. The wet cake was collected. The obtained wet cake was calcined at 500°C for 2 hours. The final product was a lanthanum-strontium-based perovskite compound with a molecular formula of La 0.5 Sr 0.5 FeO3, where La:Sr:Fe=0.5:0.5:1.

[0033] Comparative Example 1

[0034] Dissolve 152.5g FeSO4 powder in 5.5L deionized water, stir continuously at room temperature, add 0.5L 1mol / L HNO3 solution and 0.25L 1mol / L H2SO4 solution, and 0.3L 30% H2O2 solution, age at 150℃ for 24hrs, add 1L 1mol / L La(NO3)3 solution to the mixture, age at 150℃ for 24hrs. Add 0.3L 28% ammonia water, adjust pH to 9, age at 150℃ for 24hrs. Separate the aged suspension into solid and liquid, and calcine the solid part at 500℃ for 2hrs. The final product is a lanthanum-based perovskite compound, the molecular formula of which is LaFeO3, where La:Fe=1:1.

[0035] Comparative Example 2

[0036] Dissolve 152.5g FeSO4 powder in 5.5L deionized water, stir continuously at room temperature, add 0.5L 1mol / L HNO3 solution and 0.25L 1mol / L H2SO4 solution, and 0.3L 30% H2O2 solution, then add 0.5L 1mol / L La(NO3)3 solution and 0.5L 1mol / L Ce(NO3)3 solution to the mixture. Add 0.3L 28% ammonia water, adjust the pH to 9, and age at 50°C for 24 hours. Separate the aged suspension into solid and liquid, and calcine the solid at 500°C for 2 hours. The final product is a lanthanum-cerium-based perovskite compound with the molecular formula La 0.5 Ce 0.5 FeO3, where La:Ce:Fe=0.5:0.5:1.

[0037] Table 1, Comparison of BET specific surface area test results of examples and comparative examples

[0038] BET test results <![CDATA[Specific surface area (m 2 / g)]]> Example 1 40 Example 2 45 Example 3 64 Comparative Example 1 9 Comparative Example 2 15

[0039] Table 2, grain sizes calculated by XRD test of samples of embodiments and comparative examples

[0040] XRD test results Grain size (nm) Example 1 17 Example 2 14 Example 3 8 Comparative Example 1 74 Comparative Example 2 39

Claims

1. A nano-scale ABO3 type rare earth-based perovskite catalyst, characterized in that: The catalyst component can be abbreviated as A (1-i-j) A′ i A ″j B (1-m-n) B′ m B ″n O3.

2. A nanoscale ABO3 type rare earth-based perovskite catalyst according to claim 1, characterized in that: The molar ratio of elements A and B is 7:10 to 13:10, wherein A includes element A and its replaceable elements A′ and A″; and B includes element B and its replaceable elements B′ and B″.

3. A nano-scale ABO3 type rare earth-based perovskite catalyst according to claim 2, characterized in that: The element A and its substitutable elements A′ and A″ are one or two of the rare earth lanthanide elements.

4. A nano-scale ABO3 type rare earth-based perovskite catalyst according to claim 2, characterized in that: The element B and its substitutable elements B′ and B″ are one to three of alkaline earth metals and transition metals.

5. The nanoscale ABO3 type rare earth-based perovskite catalyst according to claim 1, characterized in that: The catalyst has a typical perovskite crystal structure, and its primary crystallite size is less than 50 nm.

6. A nano-scale ABO3 type rare earth-based perovskite catalyst according to claim 1, characterized in that: The catalyst may be a rare earth-based perovskite compound having a cubic, hexagonal or orthorhombic crystal configuration.

7. A method for preparing the nano-scale ABO3 type rare earth-based perovskite catalyst as claimed in claim 1, characterized in that: The method includes: 1) dispersing one of the metal oxides, carbonates, chlorides and nitrates corresponding to element B in deionized water, adding a certain amount of HNO3, H2SO4 and H2O2 thereto, and aging the mixture at a temperature of 150 to 200° C. with continuous stirring for 24 to 48 hours to form an oxide polymer suspension; 2) The pH value of the oxide polymer suspension prepared above is less than 3.0; 3) adding the metal salt of element A to the oxide polymer suspension prepared in 2); 4) According to the specific selected elements, ammonia water or sodium hydroxide is added to the solution obtained in 3) through a T-type micro mixer to adjust the pH to 8-12; 5) separating the suspension obtained in 4) into solid and liquid, washing the obtained solid part with deionized water until the conductivity of the washing water is lower than 10 μS / cm, and collecting the filter cake after washing; 6) dispersing the filter cake obtained in 5) in deionized water, and adding dispersant D to obtain a suspension, wherein the dispersant D is a saturated fatty acid; 7) The suspension obtained in 6) is continuously stirred at a temperature of 150 to 200° C. for 24 to 48 hours for aging to obtain an aged suspension; 8) subjecting the aged suspension obtained in 7) to solid-liquid separation, and fully filtering to remove water, so that the water content of the filter cake is less than 50%, to obtain a hydrated hydroxide wet filter cake; 9) The hydrated hydroxide wet cake obtained in 8) is heat treated at a temperature of 500 to 600° C. for 0.5 to 3 hours.

8. The nanoscale ABO3 type rare earth-based perovskite catalyst according to claim 1, characterized in that: The applications of the catalyst include: as a closed-coupled catalyst close to the engine of a motor vehicle equipped with a gasoline engine, as an under-floor catalyst, and as a catalyst coating of a gasoline engine exhaust particulate filter.

9. The nano-scale ABO3 type rare earth-based perovskite catalyst according to claim 1, characterized in that: The application of the catalyst includes: being used as a catalyst coating of DOC, DPF and ASC of a motor vehicle equipped with a gasoline engine.

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