Citric acid regulated mesoporous lanthanum manganese perovskite catalyst, preparation method and application

Abstract

The invention discloses a citric acid regulated mesoporous lanthanum manganese perovskite catalyst, a preparation method and application, in the preparation method, lanthanum salt, manganese salt and citric acid are used as raw materials, a one-step fusion pyrolysis method is adopted for preparation, and the molar ratio of the lanthanum salt to the manganese salt to the citric acid is 1: (0.9-1.1): (1-3). The perovskite catalyst can catalytically degrade toluene waste gas with relatively high concentration, and relatively high toluene removal rate and mineralization rate can be obtained under the condition of low-temperature catalytic oxidation.

Description

Technical Field

[0001] The present invention relates to the field of VOCs waste gas treatment catalysts, and in particular to a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst, a preparation method and applications thereof. Background Art

[0002] With the rapid development of industrialization, volatile organic compound (VOC) pollution has become an increasingly serious problem. Toluene, a typical aromatic hydrocarbon pollutant, poses a significant threat to human health and the environment. Catalytic oxidation technology, due to its high efficiency and environmental friendliness, has become a mainstream method for treating VOCs. Perovskite-type oxides (ABO3) exhibit great potential in this field due to their excellent redox properties and thermal stability.

[0003] Perovskite catalyst preparation methods primarily include solid-phase, sol-gel, and hydrothermal methods. While the solid-phase method offers simplicity, the resulting catalyst particles are coarse and inactive. While the sol-gel method can yield products with high surface areas, it suffers from complex preparation processes and poor thermal stability. The hydrothermal method offers high purity and good dispersion, but with low yields and prolonged reaction times. Furthermore, existing methods struggle to precisely control both the catalyst pore structure and the valence state of the active sites, limiting their effectiveness in the catalytic oxidation of VOCs.

[0004] In recent years, melt pyrolysis has attracted attention due to its advantages such as simplicity and low energy consumption. However, the existing technology still faces the following technical bottlenecks: (1) uneven mixing of precursors leads to deviations from the stoichiometric ratio of product components; (2) limited means of controlling pore structure make it difficult to form an ideal mesoporous structure. In particular, for the catalytic oxidation of difficult-to-degrade VOCs such as toluene, the low-temperature activity of existing catalysts still needs to be improved. Summary of the Invention

[0005] The present invention aims to provide a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst, a preparation method and an application thereof. The perovskite catalyst can catalytically degrade toluene waste gas with a relatively high concentration, and can achieve a relatively high toluene removal rate and mineralization rate under low-temperature catalytic oxidation conditions.

[0006] In order to solve the above technical problems, the specific scheme adopted in the present invention is: a preparation method of a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst, which uses lanthanum salt, manganese salt and citric acid as raw materials and is prepared by a one-step melt pyrolysis method, and the molar ratio of lanthanum salt, manganese salt and citric acid is 1: (0.9-1.1): (1-3).

[0007] Preferably, the method comprises the following steps:

[0008] 1) Grind the lanthanum salt, manganese salt and citric acid into powder and mix them evenly to prepare a mixed powder;

[0009] 2) calcining the mixed powder for 1.5-2.5 hours to obtain a calcined product;

[0010] 3) Grinding the calcined product to obtain the lanthanum manganese perovskite catalyst.

[0011] Preferably, in step 1), the lanthanum salt, manganese salt and citric acid are ground in an agate mortar for 30-60 minutes.

[0012] Preferably, in step 2), the calcination temperature range is from room temperature to 750° C., and the heating rate is 2-3° C. / min.

[0013] Preferably, in step 3), after the calcined product is ground, tableting and sieving are performed to obtain a 40-60 mesh lanthanum manganese perovskite catalyst.

[0014] Preferably, the molar ratio of lanthanum salt, manganese salt and citric acid is 1:1:1.

[0015] Preferably, the lanthanum salt is lanthanum nitrate, and the manganese salt is manganese acetate.

[0016] A citric acid-regulated mesoporous lanthanum manganese perovskite catalyst is prepared by any one of the above-mentioned methods for preparing the citric acid-regulated mesoporous lanthanum manganese perovskite catalyst.

[0017] The above-mentioned citric acid-regulated mesoporous lanthanum manganese perovskite catalyst is used in toluene degradation.

[0018] Preferably, the toluene degradation reaction is carried out in a fixed bed reactor using a mesoporous lanthanum manganese perovskite catalyst regulated by citric acid as a degradation catalyst; the reaction conditions are: reaction temperature 180-280 ° C, space velocity 60000 mL·(g·h) - 1. Toluene concentration 500-2000ppm.

[0019] The present invention proposes a method for preparing a lanthanum manganese perovskite catalyst with a controllable mesoporous structure by regulating the citric acid ratio. This method can efficiently catalyze the degradation of high-concentration toluene waste gas, achieving high toluene removal and mineralization rates under low-temperature catalytic oxidation conditions. The method employs a one-step melt pyrolysis process, which overcomes the cumbersome steps of traditional methods. The process is simple and has great potential for practical application.

[0020] In the present invention, citric acid, manganese salt and lanthanum salt are subjected to a one-step melt pyrolysis method to prepare lanthanum manganese titanium ore catalyst. First, citric acid can form a stable complex with metal ions to achieve uniform mixing at the atomic level and avoid component segregation; secondly, citric acid decomposes during high-temperature roasting to produce gas (CO2, H2O) to form a mesoporous structure. The higher the proportion of citric acid, the more gas produced by decomposition, and the larger the pore volume and pore diameter, but too high may cause the skeleton to collapse. In the most preferred embodiment of La: Mn: citric acid = 1:1:1, it can ensure that the metal ions are fully complexed, and the catalyst can produce the largest mesopore diameter and have a larger specific surface area; finally, the reducing atmosphere (CO, H2) generated by the combustion of citric acid can induce the formation of surface oxygen vacancies, promoting the formation of lattice oxygen (O 2- ) is activated into active oxygen (O - or O2 2- ), the high specific surface area of ​​the mesoporous structure exposes more active crystal faces, promoting the adsorption and dissociation of O2, thereby improving the catalytic oxidation performance of the catalyst for toluene. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The graph of toluene degradation and CO2 selectivity of the catalyst prepared in Example 1 of the present invention at different temperatures is shown;

[0022] Figure 2 The catalyst prepared in Example 2 of the present invention is a graph showing the degradation of toluene and CO2 selectivity at different temperatures;

[0023] Figure 3 The catalyst prepared in Example 3 of the present invention is a graph showing the degradation of toluene and CO2 selectivity at different temperatures;

[0024] Figure 4 BET and pore size distribution diagrams of the catalysts of Examples 1-3;

[0025] Figure 5 is the SEM image of the catalyst of Example 1-3; DETAILED DESCRIPTION

[0026] The present invention is described below by means of 3 embodiments:

[0027] Example 1

[0028] The preparation of the LaMnO3 catalyst in this embodiment 1 includes the following steps:

[0029] (1) 5 mmol of citric acid, 5 mmol of Mn(Ac)2·4H2O, and 5 mmol of La(NO3)3·6H2O were ground into powder in an agate mortar and mixed evenly.

[0030] (2) The powder mixed in step (1) was calcined at 750° C. for 2 h at a heating rate of 2.5° C. / min in an air atmosphere.

[0031] (3) Grinding, tableting, and sieving the calcined material from step (2) into 40-60 mesh particles to obtain 1-LaMnO3 catalyst.

[0032] Example 2

[0033] The preparation of the LaMnO3 catalyst in this embodiment 2 includes the following steps:

[0034] (1) Grind 10 mmol of citric acid, 5 mmol of Mn(Ac)2·4H2O, and 5 mmol of La(NO3)3·6H2O into powder in an agate mortar and mix them evenly.

[0035] (2) The powder mixed in step (1) was calcined at 750° C. for 2 h at a heating rate of 2.5° C. / min in an air atmosphere.

[0036] (3) Grinding, tableting, and sieving the calcined material from step (2) into 40-60 mesh particles to obtain a 2-LaMnO3 catalyst.

[0037] Example 3

[0038] The preparation of the LaMnO3 catalyst in this embodiment includes the following steps:

[0039] (1) Grind 15 mmol of citric acid, 5 mmol of Mn(Ac)2·4H2O, and 5 mmol of La(NO3)3·6H2O into powder in an agate mortar and mix them evenly.

[0040] (2) The powder mixed in step (1) was calcined at 750° C. for 2 h at a heating rate of 2.5° C. / min in an air atmosphere.

[0041] (3) Grinding, tableting, and sieving the calcined material from step (2) into 40-60 mesh particles to obtain a 3-LaMnO3 catalyst.

[0042] Characterization Test

[0043] 20 mg of each catalyst obtained in Examples 1-3 was used to measure the specific surface area and pore structure of the catalysts on a Belsorp-mini II instrument. Prior to testing, the samples were vacuum-pretreated at 300°C for 4 hours. Nitrogen adsorption isotherms were measured at 77 K, and the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The pore volume and average pore diameter were calculated using the Barret-Joyner-Halenda (BJH) method, as shown in Table 1. Table 1. Physical structure parameters of lanthanum manganese perovskite catalysts

[0044] Take 10 mg of each catalyst obtained in Examples 1-3 and test the surface morphology (SEM) of the catalyst using a Zeiss SIGMA instrument ( Figure 5 ).

[0045] Combined with Table 1 and Figure 4 、 5 It can be seen that the surfaces of the catalysts prepared with different citric acid ratios are all porous, forming a mesoporous structure. Example 2 has the smallest specific surface area and pore diameter; Example 3 has the largest specific surface area and a relatively large mesopore diameter; and Example 1 has the largest mesopore diameter and a larger specific surface area. Both the mesoporous structure and the larger specific surface area facilitate contact between exhaust gas and the active components of the catalyst surface, improving catalytic degradation efficiency.

[0046] Performance Testing

[0047] 100 mg of each catalyst obtained in Examples 1-3 was mixed evenly with quartz sand (ratio 1:4) and placed in a fixed bed reactor equipped with a quartz reactor for activity testing. The reaction gas composition was: 1000 ppm toluene, 60000 mL·(g·h) -1 、100mL·min -1 (10% O2 / N2). The toluene inlet and outlet concentrations were monitored online by gas chromatograph. The toluene conversion rate was calculated by calculating the toluene concentrations before and after degradation. The CO2 selectivity, or mineralization rate, was calculated by combining the CO2 outlet concentration with the toluene inlet concentration and the toluene conversion rate. The toluene conversion rates are shown in Tables 2 and 3: Table 2. Toluene conversion of lanthanum manganese perovskite catalyst Table 3. CO2 selectivity of lanthanum manganese perovskite catalysts

[0048] Combined with Table 2, Table 3 and Figure 1-3 As can be seen, the toluene conversion rate of Example 1 is over 90% at 250°C, while that of Example 3 is only greater than 90% at temperatures above 250°C. The toluene conversion rate of Example 2 is only around 80% at 280°C. Furthermore, the CO2 selectivity of Examples 1 and 3 is superior to that of Example 2. The catalyst of Example 1 has a wider active temperature window and a lower light-off temperature. Therefore, the catalysts obtained from Examples 1 and 3 exhibit superior low-temperature catalytic oxidation activity.

Claims

1. A method for preparing a mesoporous lanthanum manganese perovskite catalyst regulated by citric acid, characterized in that: The method is prepared by using lanthanum salt, manganese salt and citric acid as raw materials and adopting a one-step melt pyrolysis method. The molar ratio of lanthanum salt, manganese salt and citric acid is 1:(0.9-1.1):(1-3).

2. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 1, wherein: The following steps are involved: 1) Grind the lanthanum salt, manganese salt and citric acid into powder and mix them evenly to prepare a mixed powder; 2) calcining the mixed powder for 1.5-2.5 hours to obtain a calcined product; 3) Grinding the calcined product to obtain the lanthanum manganese perovskite catalyst.

3. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 2, wherein: In step 1), lanthanum salt, manganese salt and citric acid are ground in an agate mortar for 30-60 minutes.

4. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 2, wherein: In step 2), the calcination temperature range is from room temperature to 750° C., and the heating rate is 2-3° C. / min.

5. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 2, wherein: In step 3), after the calcined product is ground, tableting and sieving are performed to obtain a 40-60 mesh lanthanum manganese perovskite catalyst.

6. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 1, wherein: The molar ratio of lanthanum salt, manganese salt and citric acid is 1:1:

1.

7. The method for preparing a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 1, characterized in that: The lanthanum salt is lanthanum nitrate, and the manganese salt is manganese acetate.

8. A citric acid-regulated mesoporous lanthanum manganese perovskite catalyst, characterized by: The catalyst is prepared by the method for preparing any one of the citric acid-regulated mesoporous lanthanum manganese perovskite catalysts described in claims 1-7.

9. Use of the citric acid-regulated mesoporous lanthanum manganese perovskite catalyst according to claim 8 in toluene degradation.

10. Use of a citric acid-regulated mesoporous lanthanum manganese perovskite catalyst in toluene degradation according to claim 9, characterized in that: Toluene degradation was carried out in a fixed-bed reactor using a mesoporous lanthanum manganese perovskite catalyst regulated by citric acid as a degradation catalyst. The reaction conditions were: reaction temperature 180-280°C, space velocity 60000 mL·(g·h) - 1. Toluene concentration 500-2000ppm.

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