Preparation method of A-site cerium-doped double perovskite catalyst and application of A-site cerium-doped double perovskite catalyst in catalytic oxidation of toluene

Abstract

The invention relates to a preparation method of an A-site cerium-doped double perovskite catalyst and an application of the A-site cerium-doped double perovskite catalyst in catalytic oxidation of toluene, and belongs to the technical field of environmental catalytic materials. Aiming at the technical defects that a traditional noble metal catalyst is high in cost and the oxygen mobility of a perovskite material is insufficient, the double perovskite material is designed through A-site Ce < 3 + > / Ce < 4 + > doping and B-site Co / Mn bimetal collaboratively, and the chemical general formula is La2-xCexCoMnO6 (x is greater than or equal to 0 and less than or equal to 0.3). The catalyst shows remarkable advantages in catalytic oxidation of toluene: under the conditions that the mass space velocity is 18000 mL. (g.h) <-1 > and the toluene concentration is 2000 mg. M <-3 >, T50 (50% conversion rate temperature) is 223 DEG C, T90 (90% conversion rate temperature) is 243 DEG C, and the catalyst is superior to an undoped sample La2CoMnO6 catalyst. The preparation method of the catalyst is simple, the product selectivity is high, the stability is good, and the catalyst is especially suitable for efficient low-temperature catalytic degradation of methylbenzene.

Description

Technical Field

[0001] This application belongs to the technical field of catalytic materials, and particularly relates to a double perovskite catalyst constructed by a doping strategy of rare earth elements at the A site, and its application in the catalytic oxidation treatment of volatile organic compounds (VOCs), especially suitable for the efficient low-temperature catalytic degradation of toluene. Background Art

[0002] With the rapid development of industrialization and urbanization, volatile organic compound (VOC) pollution has become a global environmental problem. According to statistics, the annual global VOC emissions exceed 150 million tons, and benzene series compounds (such as toluene and xylene) account for more than 30%. As a typical toxic and harmful VOC, toluene not only participates in photochemical reactions to generate ozone and secondary organic aerosol (SOA), but also has significant harm to the human central nervous system and hematopoietic function. At present, VOC treatment technologies mainly include adsorption, condensation, biodegradation, and catalytic oxidation. Among them, catalytic oxidation technology is regarded as the most promising treatment method due to its mild reaction conditions, high purification efficiency, and no secondary pollution. However, existing catalysts still face bottlenecks such as insufficient low-temperature activity (T 90 > 300 °C), poor anti-coking performance, and dependence on precious metals (such as Pt / Pd).

[0003] ABO3-type perovskite materials (such as LaMnO3 and LaCoO3) have become research hotspots due to their adjustable redox properties and thermal stability. However, traditional single perovskite materials have defects such as low specific surface area and insufficient oxygen migration rate. Double perovskite (AA'BB'O6) can optimize the electronic structure through A / B-site bimetal design. However, existing research mainly focuses on the doping of single transition metals (such as Ni and Fe), and the mechanism of the synergistic effect between rare earth elements (such as Ce) and transition metals (Co / Mn) has been insufficiently studied. La 2-x Ce x CoMnO6 has achieved significant breakthroughs in catalytic activity, stability, and cost control through rare earth-transition metal co-doping and structure design, providing an innovative solution for the efficient treatment of VOCs. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an A-site cerium-doped double perovskite catalyst La 2-x Ce x CoMnO6 (0 ≤ x ≤ 0.3), and investigate its catalytic oxidation performance for toluene. Using La(NO3)3·6H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, and 50% Mn(NO3)2 as raw materials, La 2-x Ce xCoMnO6 (0 ≤ x ≤ 0.3). Doping with rare earth element Ce can improve the catalytic activity by inducing oxygen vacancies and enhancing the covalent nature of the metal-oxygen bond.

[0005] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] A preparation method of A-site cerium-doped double perovskite catalyst La 2-x Ce x CoMnO6 (0 ≤ x ≤ 0.3), characterized by comprising the following steps:

[0007] (1) The double perovskite catalyst is prepared by the sol-gel method with citric acid as a complexing agent. Appropriate amounts of La(NO3)3·6H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O, 50% Mn(NO3)2 and citric acid are dissolved in 50 mL of ultrapure water in a beaker.

[0008] (2) The solution obtained after mixing in step (1) is vigorously stirred until completely dissolved, and then placed in a water bath at a certain temperature, and the solution is evaporated until a gel-like substance is formed.

[0009] (3) After the gel-like substance obtained in step (2) is dried and kept warm in a forced-air drying oven for a period of time, it is naturally cooled to obtain a precursor material.

[0010] (4) The precursor material dried in step (3) is ground, placed in a crucible with a lid, and then heated in a muffle furnace to a specified temperature at a certain rate, kept warm for a period of time, and then naturally cooled. After grinding, the material is obtained, denoted as La 2- x Ce x CoMnO6 (0 ≤ x ≤ 0.3).

[0011] Further, in step (1), the total metal:citric acid = 1:1.2.

[0012] Further, the specific dosages of La(NO3)3·6H2O and Ce(NO3)3·6H2O in step (1) are determined according to different Ce doping amounts (0 ≤ x ≤ 0.3).

[0013] Further, the stirring time in step (2) is 30 min.

[0014] Further, the temperature of the water bath in step (2) is 80 °C.

[0015] Further, the temperature for keeping warm in the forced-air drying oven in step (3) is 120 °C, and the time is 12 h.

[0016] Furthermore, the crucible with a lid in step (4) remains in a semi-closed state, and the calcination atmosphere is air.

[0017] Furthermore, the heating rate in step (4) is 5 °C / min, the holding reaction temperature is 600 °C, and the time is 5 h.

[0018] The present invention also provides the application of the above-mentioned A-site cerium-doped double perovskite catalyst in the catalytic oxidation of toluene.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The preparation method of the A-site cerium-doped double perovskite catalyst La 2-x Ce x CoMnO6 (0 ≤ x ≤ 0.3) of the present invention can significantly improve the catalytic activity. In the catalytic oxidation of toluene, the La 1.8 Ce 0.2 CoMnO6 catalyst of the present invention has a T -1 (50% conversion temperature) of 223 °C and a T 50 (90% conversion temperature) of 243 °C under the condition of a mass space velocity of 18000 mL·(g·h) 90 , showing an approximately 11% increase in activity compared to undoped La2CoMnO6 (T 90 = 273 °C).

[0021] 2. The A-site cerium-doped double perovskite catalyst prepared by the present invention has the advantages of controllable oxygen vacancy concentration and synergistic effect of double active sites.

[0022] 3. The raw materials provided by the present invention are inexpensive, the preparation method of the catalyst is simple, and the stability is good, which is expected to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 SEM (scanning electron microscope) images of the Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4;

[0024] Figure 2 XRD (X-ray diffraction) patterns of the Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4;

[0025] Figure 3 H2-TPR (temperature-programmed reduction) profiles of the Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4;

[0026] Figure 4EDS (Energy Dispersive X-ray Spectroscopy) pattern of the Ce 0.2 catalyst prepared in Example 3;

[0027] Figure 5 Activity diagrams of the Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4; Detailed implementation manners

[0028] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. However, it should not be construed as a limitation of the present invention. On the contrary, the purpose of providing these examples is to make the understanding of the disclosed content of the present invention more thorough and comprehensive.

[0029] Example 1:

[0030] A preparation method of a double perovskite catalyst La2CoMnO6:

[0031] (1) Dissolve 4.33 g of La(NO3)3·6H2O, 1.4552 g of Co(NO3)2·6H2O, 1.162 mL of 50% Mn(NO3)2, and 5.0434 g of citric acid in 50 mL of ultrapure water in a beaker. Stir the resulting mixed solution vigorously for 30 min until completely dissolved, then place it in a water bath at 80 °C, and evaporate the solution until a gel-like substance is formed. Put the gel-like substance in an oven at 120 °C and dry it for 12 h, and then cool it naturally to obtain a precursor material.

[0032] (2) Grind the dried precursor material, put it into a crucible with a lid, and then heat it in a muffle furnace at a rate of 5 °C / min to 600 °C. After holding for 5 h, cool it naturally, and then grind it to obtain a material, denoted as Ce 0.

[0033] Example 2:

[0034] A preparation method of a double perovskite catalyst La 1.9 Ce 0.1 CoMnO6:

[0035] (1) Dissolve 4.1136 g of La(NO3)3·6H2O, 0.2717 g of Ce(NO3)3·6H2O, 1.4552 g of Co(NO3)2·6H2O, 1.162 mL of 50% Mn(NO3)2, and 5.0434 g of citric acid in 50 mL of ultrapure water in a beaker. Stir the resulting mixed solution vigorously for 30 min until completely dissolved, then place it in a water bath at 80 °C, and evaporate the solution until a gel-like substance is formed. Put the gel-like substance in an oven at 120 °C and dry it for 12 h, and then cool it naturally to obtain a precursor material.

[0036] (2) Grind the dried precursor material, place it in a crucible with a lid, then heat it in a muffle furnace to 600 °C at a rate of 5 °C / min, keep it at this temperature for 5 h, then let it cool naturally. After grinding, the material obtained is denoted as Ce 0.1.

[0037] Example 3:

[0038] Preparation method of an A-site cerium-doped double perovskite catalyst La 1.8 Ce 0.2 CoMnO6:

[0039] (1) Dissolve 3.8971 g of La(NO3)3·6H2O, 0.4342 g of Ce(NO3)3·6H2O, 1.4552 g of Co(NO3)2·6H2O, 1.162 mL of 50% Mn(NO3)2 and 5.0434 g in 50 mL of ultrapure water in a beaker. Stir the resulting mixed solution vigorously for 30 min until completely dissolved, then place it in a water bath at 80 °C, and evaporate the solution until a gel-like substance is formed. Put the gel-like substance in an oven at 120 °C and dry it for 12 h, then let it cool naturally to obtain the precursor material.

[0040] (2) Grind the dried precursor material, place it in a crucible with a lid, then heat it in a muffle furnace to 600 °C at a rate of 5 °C / min, keep it at this temperature for 5 h, then let it cool naturally. After grinding, the material obtained is denoted as Ce 0.2.

[0041] Example 4:

[0042] Preparation method of an A-site cerium-doped double perovskite catalyst La 1.7 Ce 0.3 CoMnO6:

[0043] (1) Dissolve 3.6806 g of La(NO3)3·6H2O, 0.6513 g of Ce(NO3)3·6H2O, 1.4552 g of Co(NO3)2·6H2O, 1.162 mL of 50% Mn(NO3)2 and 5.0434 g in 50 mL of ultrapure water in a beaker. Stir the resulting mixed solution vigorously for 30 min until completely dissolved, then place it in a water bath at 80 °C, and evaporate the solution until a gel-like substance is formed. Put the gel-like substance in an oven at 120 °C and dry it for 12 h, then let it cool naturally to obtain the precursor material.

[0044] (2) Grind the dried precursor material, place it in a crucible with a lid, then heat it in a muffle furnace to 600 °C at a rate of 5 °C / min, keep it at this temperature for 5 h, then let it cool naturally. After grinding, the material obtained is denoted as Ce 0.3.

[0045] Toluene catalytic oxidation experiment:

[0046] The catalytic activity of 0.1g of catalyst for toluene oxidation is evaluated. Usually the catalyst is placed at the same height as the center of the heating furnace, and a 2000mg·m -3 The reaction flow of toluene and 21 vol% O2 / N2 was kept warm (115 °C) and then heated at 30 mL min -1 The total flow rate through the catalyst bed is 18000 mL·(g·h) -1 The concentration changes of toluene and CO2 were monitored by a gas chromatograph (GC) equipped with two hydrogen flame ionization detectors (FID). The temperature program set in the reaction device (170-350℃, 5℃·min -1 ) ensures full automatic coordination with the GC sampling interval (10 min), and takes six consecutive samples at each temperature point and takes the average value to calculate the toluene concentration to ensure that the activity of the catalyst is truly reflected.

[0047] Figure 1 The SEM (scanning electron microscope) images of Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4. After Ce doping, the catalyst morphology is significantly improved, and the catalyst surface becomes more loose and porous. 1.8 Ce 0.2 CoMnO6 has the largest pores.

[0048] Figure 2 The XRD (X-ray diffraction) patterns of Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4. The 2θ values of all materials are 23°, 33°, 41°, 47°, 58°, 68°, and 78°, respectively, and are double perovskite crystals. 1.8 Ce 0.2 The diffraction peak intensity of CoMnO6 is relatively large, indicating that the material has a high degree of crystallinity and a relatively complete crystal structure, which may form a more stable double perovskite main phase and reduce the interference of amorphous phase or impurity phase.

[0049] Figure 3 The H2-TPR (temperature programmed reduction) diagrams of Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4. Generally speaking, catalysts that consume more hydrogen at lower temperatures tend to have better catalytic activity for toluene. 1.8 Ce 0.2 The H2-TPR peak area of CoMnO6 material is the largest, indicating that it has the strongest redox ability.

[0050] Figure 4 EDS (Energy Dispersive X-ray Spectroscopy) pattern of the La 1.8 Ce 0.2 CoMnO6 catalyst prepared in Example 3, indicating that the Ce element has been uniformly doped.

[0051] Figure 5 Activity diagrams of the Ce 0, Ce 0.1, Ce 0.2, and Ce 0.3 catalysts prepared in Examples 1, 2, 3, and 4. It can be seen that La 1.8 Ce 0.2 CoMnO6 has the strongest ability to catalytically oxidize toluene, with its T 90 being 241 °C, which is 27 °C lower than that of the material without Ce element doping. The T 90 of all A-site cerium-doped double perovskite catalysts is lower than that of the undoped catalysts, proving that the catalytic oxidation performance of A-site cerium-doped double perovskite catalysts for toluene has been significantly improved.

Claims

1. The present invention relates to a preparation method of an A-site cerium-doped double perovskite catalyst and its application in the catalytic oxidation of toluene, which mainly includes the following steps: S1, La 2-x Ce x Preparation of CoMnO6 precursor Dissolve appropriate amounts of La(NO3)3·6H2O, Ce(NO3)3·6H2O, Co(NO3)2·6H2O and 50% Mn(NO3)2 in a beaker with ultrapure water, and then add the corresponding citric acid as a complexing agent to the metal salt solution. Stir the solution vigorously for 30 min until completely dissolved, and then add it to a water bath at 80 °C. Evaporate the solution until a gel-like substance is formed, and immediately dry it in a blast drying oven at 120 °C for 12 h. S2, La 2-x Ce x Preparation of CoMnO6 After grinding the solid obtained in S1, it is calcined at 600 °C for 5 h to obtain La 2-x Ce x CoMnO6.

2. The preparation method of a Ce-doped double perovskite catalyst at the A-site and its application in catalytic oxidation of toluene according to claim 1, characterized in that, The A-site cerium-doped double perovskite catalyst is prepared by the sol-gel method.

3. The preparation method of a cerium-doped double perovskite catalyst at the A site and its application in the catalytic oxidation of toluene according to claim 1, characterized in that, In the step S1, the masses of La(NO3)3·6H2O and Ce(NO3)3·6H2O depend on different cerium doping amounts. The mass of Co(NO3)2·6H2O is 1.4552 g, the volume of 50% Mn(NO3)2 is 1.162 mL, and the volume of the ultrapure water solution is 50 mL.

4. The preparation method of a cerium-doped double perovskite catalyst at the A-site and its application in the catalytic oxidation of toluene according to claim 1, characterized in that, La 2-x Ce x For the CoMnO6 material x, the value range is 0.1 ≤ x ≤ 0.

3.

5. The preparation method of a cerium-doped double perovskite catalyst at the A site and its application in the catalytic oxidation of toluene according to claim 1, characterized in that, In the step S1, the molar ratio of metal ions to the complexing agent is 1:1.

2.

6. The preparation method of a Ce-doped double perovskite catalyst at the A-site and its application in the catalytic oxidation of toluene according to claim 1, characterized in that, In the step S2, the calcination temperature is 600 °C, the heating rate is 5 °C / min, and the calcination reaction time is 5 h.

7. The A-site cerium-doped double perovskite catalyst prepared by the preparation method according to any one of claims 1-6 is used in the field of catalytic oxidation of toluene.

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