A lanthanum iron perovskite catalyst, a preparation method and application thereof

Abstract

The present application relates to the technical field of catalyst preparation, in particular to a lanthanum-iron perovskite catalyst, a preparation method and application thereof.The catalyst contains iron and lanthanum; the content of the iron is 14-20wt%, and the content of the lanthanum is 76-80wt% based on the total weight of the catalyst; the single lanthanum-iron perovskite catalyst is in the shape of a cube, the average length of the side of the lanthanum-iron perovskite catalyst is 90-160nm; the specific surface area of the lanthanum-iron perovskite catalyst is 70-100m 2 / g, and the average particle size is 10-30nm.The catalyst provided by the present application has high catalytic soot combustion reaction activity and high stability, and the catalyst is a single crystal surface, which can expose surface atoms to provide a platform for studying the reaction mechanism.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a lanthanum-iron perovskite catalyst, a preparation method and application thereof. BACKGROUND

[0002] Diesel vehicles are widely used because of their high efficient and durable power source, good economic benefits and low CO2 emissions. However, the soot particles emitted by diesel vehicles are the main components of fine particulate matter (PM2.5) in the atmosphere, which not only causes serious pollution to the atmosphere, but also harms people's production and life and physical and mental health. Therefore, reducing the emission of motor vehicle exhaust pollutants, especially diesel vehicle exhaust, is the primary task of serving the blue sky defense and the air pollution prevention and control campaign, and the research on exhaust purification has important environmental protection significance.

[0003] Among the strategies for exhaust purification, catalytic aftertreatment is widely considered as the most effective purification method. Among them, catalytic soot purification is a purification process of heterogeneous oxidation reaction, which occurs at the contact interface of soot (solid)-catalyst (solid)-reaction gas (NO and O2), therefore, the effective contact between catalyst and soot, catalyst and reaction gas is crucial.

[0004] In recent years, a large number of catalyst materials have been used in the research of catalytic soot conversion reaction, such as transition metal oxides, alkali metal oxides, perovskite oxides and noble metal supported oxides. Perovskite oxides (ABO3) have excellent catalytic soot conversion performance, which has attracted widespread attention from researchers. Among them, cation A can be lanthanide elements, alkali metal or alkaline earth metal cations, and cation B is mainly transition metal elements, and the oxidation / reduction characteristics of metal cation B is the main factor for the catalytic activity of perovskite catalysts.

[0005] However, the process of catalytic soot oxidation with perovskite oxides as catalyst has not been fully studied, because the traditional perovskite oxide catalyst usually exposes multiple crystal surfaces, making the reaction mechanism more complex. Single crystal lanthanum-iron perovskite can expose specific surface atoms, which can be used to optimize the performance of the catalyst, and also provides a platform for studying the reaction mechanism.

[0006] CN107626319A discloses a method for preparing a flower-like lanthanum ferrite photocatalyst. The method involves first adding lanthanum nitrate and ferric nitrate in a 1:1 molar ratio to an ethanol solution, then transferring the solution to a hydrothermal reactor and reacting at 160-180℃ for 8-12 hours. After washing, drying, and grinding, the solution is then calcined at 700-900℃ for 2-4 hours under a nitrogen atmosphere at a heating rate of 1-3℃ / min to obtain a lanthanum ferrite photocatalyst with a flower-like structure and a particle size of 5-10 μm, assembled from layered lanthanum ferrite. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of low catalyst activity and instability in the existing technology of catalyst-catalyzed combustion of soot.

[0008] To achieve the above objectives, a first aspect of the present invention provides a lanthanum-iron perovskite catalyst containing iron and lanthanum.

[0009] Based on the total mass of the catalyst, the iron content is 14-20 wt% and the lanthanum content is 76-80 wt%.

[0010] Each of the lanthanum-iron perovskite catalysts is cubic in shape, and the average length of the side of the lanthanum-iron perovskite catalyst is 90-160 nm.

[0011] The specific surface area of ​​the lanthanum-iron perovskite catalyst is 70-100 m². 2 / g, with an average particle size of 10-30nm;

[0012] The lanthanum-iron perovskite catalyst has an average pore size of 1-10 nm and an average pore volume of 0.1-0.6 cm³. 3 / g.

[0013] A second aspect of the present invention provides a method for preparing the lanthanum-iron perovskite catalyst described in the first aspect, the method comprising the following steps:

[0014] S1: In the presence of a solvent, a lanthanum source, an iron source, and ethylene glycol are subjected to a first reaction to obtain a preparative solution; the molar ratio of the lanthanum source (calculated as lanthanum element), the iron source (calculated as iron element), and ethylene glycol is 1:1:0.5-4.

[0015] S2: The prepared solution is placed in a reaction vessel for hydrothermal reaction to obtain the precursor; the conditions for the hydrothermal reaction are at least: temperature 100-180℃, time 12-48h;

[0016] S3: The precursor is calcined to obtain a lanthanum iron perovskite catalyst; the calcination conditions shall at least meet the following requirements: temperature of 400-600℃, time of 3-7h, and heating rate of 1-5℃ / min.

[0017] A third aspect of the present invention provides a lanthanum-iron perovskite catalyst prepared by the method described in the second aspect of the present invention.

[0018] The fourth aspect of the present invention provides the application of the lanthanum-iron perovskite catalyst described in the third aspect in the catalytic combustion reaction of soot.

[0019] The lanthanum-iron perovskite catalyst provided by this invention is a cubic structure assembled from lanthanum ferrite along a certain direction. Furthermore, the catalyst has suitable specific surface area, pore size, pore volume, and average particle size, thereby endowing it with high catalytic activity and high stability in the combustion of soot. Attached Figure Description

[0020] Figure 1 This is a graph showing the catalytic activity test results of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention, which was repeatedly used to catalyze the conversion of particulate matter into carbon soot five times.

[0021] Figure 2 These are X-ray diffraction analysis images of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention before and after being repeatedly used to catalyze the conversion of particulate matter into carbon soot five times.

[0022] Figure 3 These are SEM images of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention before and after being repeatedly used to catalyze the conversion of particulate matter into soot five times.

[0023] Figure 4 This is a SEM (scanning electron microscope) image of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention;

[0024] Figure 5 This is an X-ray diffraction analysis diagram of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention;

[0025] Figure 6 This is the EDS energy dispersive spectroscopy (EDS) analysis diagram of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention;

[0026] Figure 7 These are activity test graphs of carbon soot particulate matter conversion without catalyst and the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention for carbon soot particulate matter conversion. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] In this invention, unless otherwise stated, terms such as "average particle size" are used according to the Scherrer formula. The calculations show that "D" represents the average thickness of the grain perpendicular to the crystal plane (i.e., the average grain size described in this invention), β represents the half-peak width or integral width of the diffraction peak in the measured sample, θ represents the Bragg diffraction angle (2θ = 32.222), and Y represents... K is 0.943.

[0029] As mentioned above, a first aspect of the present invention provides a lanthanum-iron perovskite catalyst containing iron and lanthanum.

[0030] Based on the total mass of the catalyst, the iron content is 14-20 wt% and the lanthanum content is 76-80 wt%.

[0031] Each of the lanthanum-iron perovskite catalysts is cubic in shape, and the average length of the side of the lanthanum-iron perovskite catalyst is 90-160 nm.

[0032] The specific surface area of ​​the lanthanum-iron perovskite catalyst is 70-100 m². 2 / g, with an average particle size of 10-30nm;

[0033] The lanthanum-iron perovskite catalyst has an average pore size of 1-10 nm and an average pore volume of 0.1-0.6 cm³. 3 / g.

[0034] It should be noted that the pores of the lanthanum-iron perovskite catalyst are formed by the accumulation of lanthanum-iron perovskite catalysts during the catalyst preparation process.

[0035] Preferably, based on the total mass of the catalyst, the iron content is 18-20 wt% and the lanthanum content is 78-80 wt%.

[0036] In a preferred embodiment, the average length of the side of the lanthanum-iron perovskite catalyst is 100-150 nm.

[0037] More preferably, the specific surface area of ​​the lanthanum-iron perovskite catalyst is 90-100 m². 2 / g, with an average particle size of 26-30nm.

[0038] Preferably, the average pore diameter of the pores is 8-10 nm, and the average pore volume of the pores is 0.5-0.6 cm³. 3 / g.

[0039] As previously described, a second aspect of the present invention provides a method for preparing the lanthanum-iron perovskite catalyst described in the first aspect of the present invention, the method comprising the following steps:

[0040] S1: In the presence of a solvent, a lanthanum source, an iron source, and ethylene glycol are subjected to a first reaction to obtain a preparative solution; the molar ratio of the lanthanum source (calculated as lanthanum element), the iron source (calculated as iron element), and ethylene glycol is 1:1:0.5-4.

[0041] S2: The prepared solution is placed in a reaction vessel for hydrothermal reaction to obtain the precursor; the conditions for the hydrothermal reaction are at least: temperature 100-180℃, time 12-48h;

[0042] S3: The precursor is calcined to obtain a lanthanum iron perovskite catalyst; the calcination conditions shall at least meet the following requirements: temperature of 400-600℃, time of 3-7h, and heating rate of 1-5℃ / min.

[0043] Preferably, in step S1, the lanthanum source is lanthanum nitrate.

[0044] According to a particularly preferred embodiment of the present invention, in step S1, the lanthanum source is lanthanum nitrate hexahydrate.

[0045] Preferably, in step S1, the iron source is ferric nitrate.

[0046] According to a particularly preferred embodiment of the present invention, in step S1, the iron source is ferric nitrate nonahydrate.

[0047] Preferably, in step S1, the solvent is water.

[0048] The present invention does not impose any particular limitation on the amount of solvent used, as long as it meets the requirements of the present invention. For example, the amount of solvent used is 50-60 mL relative to 1 mol of the lanthanum source (calculated as lanthanum element).

[0049] Preferably, in step S1, the molar ratio of the lanthanum source (calculated as lanthanum element), the iron source (calculated as iron element), and ethylene glycol is 1:1:2-4. The inventors of this invention have discovered that the lanthanum-iron perovskite catalyst prepared under these conditions exhibits better catalytic performance and stability in catalytic soot oxidation, and its application in the catalytic soot combustion reaction can significantly reduce the reaction temperature.

[0050] Preferably, in step S1, the conditions for the first reaction are at least: rotation speed of 300-600 rpm, temperature of 20-40℃, and time of 4-6 h.

[0051] This invention does not impose any particular limitation on the type of reactor; any type known in the art can be used, as long as it meets the requirements of this invention. Exemplarily, the reactor is a high-pressure reactor with a polytetrafluoroethylene liner. Further details of this invention will not be elaborated upon here, and those skilled in the art should not construe this as a limitation of the invention.

[0052] In a preferred embodiment, in step S2, the hydrothermal reaction conditions at least satisfy the following: temperature 120-160°C and time 12-48 h. The inventors of this invention have discovered that the lanthanum-iron perovskite catalyst prepared under these reaction conditions exhibits superior catalytic activity and good catalytic stability.

[0053] More preferably, in step S3, the method further includes: cooling the precursor before performing the calcination treatment, and then sequentially performing separation treatment, washing treatment, and drying treatment on the cooled precursor.

[0054] This invention does not particularly limit the separation process in step S3; any method known in the art can be used, as long as it meets the requirements of this invention. For example, in step S3, the separation process is centrifugation. Further details are omitted here, and those skilled in the art should not construe this as a limitation of the invention.

[0055] More preferably, in step S3, the separation process conditions must at least satisfy: a rotation speed of 3000-5000 rpm and a time of 3-5 min.

[0056] This invention does not particularly limit the washing method in step S3; any method known in the art can be used, as long as it meets the requirements of this invention. For example, in step S3, the washing process is performed using detergent. Further details are omitted here, and those skilled in the art should not construe this as a limitation of the invention.

[0057] Preferably, in step S3, the washing process involves washing with detergent A and detergent B 3-5 times each, and the conditions for each washing process are at least: a rotation speed of 3000-5000 rpm and a time of 3-5 min.

[0058] According to a preferred embodiment, in step S3, detergent A is deionized water and detergent B is ethanol.

[0059] The present invention does not impose any particular limitation on the amount of detergent used, as long as it meets the requirements of the present invention. For example, the amount of detergent used is 30-50 mL.

[0060] In a preferred embodiment, in step S3, the drying conditions must at least meet the following requirements: temperature of 80-100°C and time of 10-12 hours.

[0061] Preferably, in step S3, the calcination conditions at least satisfy the following: temperature of 400-500℃, time of 4-6h, and heating rate of 2-4℃ / min. The inventors of this invention have discovered that the lanthanum-iron perovskite catalyst prepared under these reaction conditions exhibits excellent catalytic performance, high CO2 selectivity, and good catalytic stability.

[0062] Preferably, in step S3, the calcination process is carried out under a protective atmosphere, and the protective atmosphere is at least one of air atmosphere and nitrogen atmosphere.

[0063] As previously stated, the third aspect of the present invention provides a lanthanum-iron perovskite catalyst prepared by the method described in the second aspect of the present invention.

[0064] As previously stated, the fourth aspect of the present invention provides the application of the lanthanum-iron perovskite catalyst described in the third aspect of the present invention in the catalytic combustion reaction of soot.

[0065] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are all commercially available products.

[0066] Lanthanum source:

[0067] Lanthanum nitrate hexahydrate, purchased from Beijing Innocare Technology Co., Ltd.

[0068] Tieyuan:

[0069] Ferric nitrate nonahydrate was purchased from Beijing Xinbaohai Chemical Technology Co., Ltd.

[0070] The high-pressure reactor with a polytetrafluoroethylene liner was purchased from Shanghai Yanzheng Experimental Instrument Co., Ltd., model YZHR-25.

[0071] The SEM scanning electron microscope was purchased from Kunshan Bolian Optics Co., Ltd., model SU8010 cold field emission scanning electron microscope;

[0072] The X-ray diffraction analyzer was purchased from Hangzhou Yingxin Instrument Co., Ltd., model Bruker D8Focus.

[0073] The BET specific surface area analyzer was purchased from Best Instrument Co., Ltd., model number 3H-2000BET-A.

[0074] The fixed-bed microreactor-gas chromatography detection system was purchased from Shanghai Linghua Instrument Co., Ltd., model GC9890B.

[0075] The room temperature is 25±2℃.

[0076] Example 1

[0077] This embodiment provides a method for preparing lanthanum-iron perovskite catalysts according to the formulations and process parameters in Table 1. The method includes the following steps:

[0078] S1: In the presence of a solvent, lanthanum source, iron source and ethylene glycol are reacted in the first reaction to obtain a preparative solution;

[0079] S2: The preparative solution is placed in a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction to obtain the precursor;

[0080] S3: The precursor is cooled to room temperature and then subjected to separation, washing, drying and calcination processes in sequence to obtain a lanthanum-iron perovskite catalyst.

[0081] Unless otherwise specified, Examples 2 and 3 follow the same process as Example 1, but with different process parameters, as detailed in Table 1.

[0082] Example 4

[0083] This embodiment prepares a lanthanum-iron perovskite catalyst according to the method of Example 1. The difference is that in step S1, the molar ratio of the lanthanum source (calculated as lanthanum), the iron source (calculated as iron), and ethylene glycol is 1:1:1. The remaining steps and parameters are the same as in Example 1.

[0084] Example 5

[0085] This embodiment prepares a lanthanum-iron perovskite catalyst according to the method of Example 1. The difference is that in step S2, the temperature of the hydrothermal reaction is 180°C, and the remaining steps and parameters are the same as in Example 1.

[0086] Example 6

[0087] This embodiment prepares a lanthanum-iron perovskite catalyst according to the method of Example 1. The difference is that in step S3, the calcination temperature is 600°C, and the remaining steps and parameters are the same as in Example 1.

[0088] Comparative Example 1

[0089] This comparative example prepares a lanthanum-iron perovskite catalyst according to the method of Example 1, except that in step S1, the molar ratio of the lanthanum source (calculated as lanthanum), the iron source (calculated as iron), and ethylene glycol is 1:0.5:4. The remaining steps and parameters are the same as in Example 1.

[0090] Comparative Example 2

[0091] This comparative example prepares a lanthanum-iron perovskite catalyst according to the method of Example 1, except that in step S1, the molar ratio of the lanthanum source (calculated as lanthanum), the iron source (calculated as iron), and ethylene glycol is 1:1:6, and the remaining steps and parameters are the same as in Example 1.

[0092] Comparative Example 3

[0093] This comparative example prepared a lanthanum-iron perovskite catalyst according to the method of Example 1, except that in step S1, ethanol was used instead of ethylene glycol in the same weight proportions, and the remaining steps and parameters were the same as in Example 1.

[0094] Comparative Example 4

[0095] This comparative example prepares a lanthanum-iron perovskite catalyst according to the method of Example 1, except that in step S2, the temperature of the hydrothermal reaction is 200°C, and the remaining steps and parameters are the same as in Example 1.

[0096] Comparative Example 5

[0097] This comparative example prepared a lanthanum-iron perovskite catalyst according to the method of Example 1, except that in step S3, the calcination temperature was 800°C, and the remaining steps and parameters were the same as in Example 1.

[0098] Comparative Example 6

[0099] The lanthanum-iron perovskite catalyst was prepared using the steps and process parameters of Example 1 in publication number CN107626319A.

[0100] The parameters and conditions in the above embodiments and comparative examples are listed in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] In Table 1, K1 is the molar ratio of the lanthanum source, the iron source, and ethylene glycol, calculated as lanthanum element, and K2 is the molar ratio of the lanthanum source, the iron source, and ethanol, calculated as lanthanum element.

[0105] Continued from Table 1

[0106]

[0107]

[0108] In Table 1, K1 is the molar ratio of the lanthanum source, the iron source, and ethylene glycol, calculated as lanthanum element, and K2 is the molar ratio of the lanthanum source, the iron source, and ethanol, calculated as lanthanum element.

[0109] Test Example 1

[0110] The lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention were subjected to BET specific surface area tests to obtain the specific surface area, average pore size, and average pore volume of the catalysts. The average particle size of the catalysts was calculated using the Scherrer formula, and the results are shown in Table 2.

[0111] Table 2

[0112] Specific surface area, m 2 / g]] Average pore size, nm Average pore volume, cm3 / g 3 / g]]> Average particle size, nm Example 1 99.6 10 0.6 30 Example 2 94.3 9 0.5 28 Example 3 90.1 8 0.6 26 Example 4 89.4 8 0.5 24 Example 5 86.8 7 0.4 25 Example 6 84.3 6 0.5 27 Comparative Example 1 56.3 4 0.3 21 Comparative Example 2 53.2 4 0.2 18 Comparative Example 3 50.4 5 0.3 12 Comparative Example 4 49.6 3 0.2 15 Comparative Example 5 45.3 3 0.2 16

[0113] As can be seen from the results in Table 2, the lanthanum-iron perovskite catalyst prepared using the embodiments of the present invention has significantly more suitable specific surface area, pore size, pore volume, and particle size, which is the basis for subsequent efficient catalytic conversion of particulate matter.

[0114] Test Example 2

[0115] The lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention were subjected to EDS energy dispersive spectroscopy analysis to obtain the iron and lanthanum content of the catalysts. The results are shown in Table 3.

[0116] Table 3

[0117]

[0118]

[0119] As can be seen from the results in Table 3, the lanthanum-iron perovskite catalyst prepared by the embodiments of the present invention has a high iron content and lanthanum content. In the lanthanum-iron perovskite formed, both iron and lanthanum are in high valence states, which have excellent oxidation performance and are the basis for subsequent efficient catalytic conversion of particulate matter.

[0120] Test Example 3

[0121] The lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention were tested for their catalytic activity in converting particulate matter into carbon soot, with the catalysts without the addition of catalyst serving as the control group. The specific test results are shown in Table 4.

[0122] The lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention were subjected to catalytic activity tests for the conversion of particulate matter into carbon soot. The test methods are as follows:

[0123] (1) Weigh 0.01g of soot particles and 0.1g of the prepared catalyst, and mix them thoroughly to ensure that the catalyst and soot particles are in full contact to obtain a mixture;

[0124] (2) The mixture is placed in the quartz tube reactor of the fixed bed microreactor-gas chromatography detection system, and O2, NO and N2 with a volume ratio of 1:0.2:18.8 are introduced, wherein the total volume flow rate of O2, NO and N2 is 50 mL / min, and the mixture is heated. Sampling is performed every 5 min, and the concentrations of CO and CO2 at the temperature point are recorded respectively.

[0125] The conditions for the heat treatment must at least meet the following: starting temperature of 25°C, ending temperature of 650°C, and heating rate of 2°C / min.

[0126] The conversion of particulate matter in soot was detected without the addition of a catalyst, and this control group was used as the experimental group. The detection method is as follows:

[0127] 0.01 g of particulate matter was weighed and placed in the quartz tube reactor of a fixed-bed microreactor-gas chromatography detection system. O2, NO, and N2 were introduced in a volume ratio of 1:0.2:18.8, with a total volume flow rate of 50 mL / min. The mixture was heated and sampled every 5 min. The concentrations of CO and CO2 at each temperature point were recorded.

[0128] The conditions for the heat treatment must at least meet the following: starting temperature of 25°C, ending temperature of 650°C, and heating rate of 2°C / min.

[0129] The formula for calculating CO2 selectivity when CO2 concentration is at its maximum is as follows:

[0130] Formula for calculating the conversion rate of particulate matter from soot:

[0131] Where t0 is the initial temperature at which the mixture is heated, in °C.

[0132] tm is the temperature at which the CO2 concentration is at its maximum during the heat treatment of the mixture, in °C.

[0133] t1 is the temperature at a certain moment when the mixture is heated, in °C.

[0134] t2 is the final temperature (°C) of the heat treatment of the mixture.

[0135] The CO2 concentration, in ppm, is recorded during the heat treatment of the mixture.

[0136] C CO The CO concentration, in ppm, is the concentration recorded during the heat treatment of the mixture.

[0137] Among them, the ignition temperature T of particulate matter is 10 The temperature T corresponding to a 50% conversion rate of particulate matter in soot. 50 The temperature T corresponding to a 90% conversion rate of particulate matter in soot 90 The concentrations of CO and CO2 produced by the combustion of particulate matter were integrated separately, and the results were calculated as 10%, 50%, and 90% of the sum of the areas of CO2 and CO concentrations.

[0138] Based on the above detection methods and calculation formulas, the following parameters were obtained during the catalytic conversion of particulate matter by lanthanum-iron-perovskite catalysts prepared in the embodiments and comparative examples of the present invention: the ignition temperature of particulate matter, the temperature corresponding to a conversion rate of 50% for particulate matter, the temperature corresponding to a conversion rate of 90% for particulate matter, and the conversion rate of particulate matter.

[0139] Table 4

[0140]

[0141]

[0142] As can be seen from the results in Table 4, the lanthanum-iron perovskite catalyst prepared using the embodiments of the present invention has the performance of highly efficient catalytic conversion of carbon soot particulate matter.

[0143] Specifically, compared with the control group and the comparative example, the catalyst obtained in the embodiments of the present invention exhibits a lower ignition temperature for soot particles during the catalytic conversion process, a lower temperature corresponding to a soot particle conversion rate of 50%, and a lower temperature corresponding to a soot particle conversion rate of 90%. Furthermore, the maximum selectivity of CO2 reaches over 90%, indicating that the catalyst obtained in the present invention has excellent selectivity. This also further demonstrates that the catalyst obtained in the present invention has high catalytic performance for soot particle conversion.

[0144] Test Example 4

[0145] The lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention were subjected to catalytic stability tests for the conversion of particulate matter into carbon soot. The test methods are as follows:

[0146] (1) Weigh 0.01g of soot particles and 0.1g of the prepared catalyst, and mix them thoroughly to ensure that the catalyst and soot particles are in full contact to obtain a mixture;

[0147] (2) The mixture is placed in the quartz tube reactor of the fixed bed microreactor-gas chromatography detection system, and O2, NO and N2 with a volume ratio of 1:0.2:18.8 are introduced, wherein the total volume flow rate of O2, NO and N2 is 50 mL / min, and the mixture is heated. Sampling is performed every 5 min, and the concentrations of CO and CO2 at the temperature point are recorded respectively.

[0148] The conditions for the heat treatment must at least meet the following: starting temperature of 25°C, ending temperature of 650°C, and heating rate of 2°C / min.

[0149] (3) After the reaction is completed, weigh the catalyst in the quartz tube reactor and record it as W1, and weigh 0.1W1 g of soot particles.

[0150] The formula for calculating CO2 selectivity when CO2 concentration is at its maximum is as follows:

[0151] Formula for calculating the conversion rate of particulate matter from soot:

[0152] Where t0 is the initial temperature at which the mixture is heated, in °C.

[0153] tm is the temperature at which the CO2 concentration is at its maximum during the heat treatment of the mixture, in °C.

[0154] t1 is the temperature at a certain moment when the mixture is heated, in °C.

[0155] t2 is the final temperature (°C) of the heat treatment of the mixture.

[0156] The CO2 concentration, in ppm, is recorded during the heat treatment of the mixture.

[0157] C CO The CO concentration, in ppm, is the concentration recorded during the heat treatment of the mixture.

[0158] Among them, the ignition temperature T of particulate matter is 10 The temperature T corresponding to a 50% conversion rate of particulate matter in soot. 50 The temperature T corresponding to a 90% conversion rate of particulate matter in soot 90The concentrations of CO and CO2 produced by the combustion of particulate matter were integrated separately, and the results were calculated as 10%, 50%, and 90% of the sum of the areas of CO2 and CO concentrations.

[0159] Repeat steps (1), (2), and (3) five times, and calculate the ignition temperature of soot particles, the temperature at which the soot particle conversion rate reaches 50%, the temperature at which the soot particle conversion rate reaches 90%, and the CO2 selectivity at the maximum CO2 concentration during each catalytic soot particle conversion process of the lanthanum iron perovskite catalyst prepared in the embodiments and comparative examples of the present invention.

[0160] Furthermore, X-ray diffraction analysis and morphology analysis were performed on the lanthanum-iron perovskite catalysts prepared in the embodiments and comparative examples of the present invention before catalyzing the conversion of particulate matter into carbon soot, and after being repeatedly used to catalyze the conversion of particulate matter into carbon soot five times.

[0161] For example, Figure 1 The figure shows the catalytic activity test results of the lanthanum iron perovskite catalyst obtained in Example 1 of the present invention being repeatedly used to catalyze the conversion of particulate matter into carbon soot five times. Figure 2 The X-ray diffraction analysis diagrams of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention before catalyzing the conversion of particulate matter into soot and after being repeatedly used to catalyze the conversion of particulate matter into soot five times are shown. Figure 3 The images shown are SEM (Scanning Electron Microscopy) images of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention before and after being repeatedly used to catalyze the conversion of particulate matter into soot particles five times.

[0162] Among them, from Figure 1 As can be seen, the lanthanum-iron perovskite catalyst prepared in Example 1 of this invention exhibits essentially unchanged catalytic activity after five cycles of testing, and the CO2 selectivity remains above 98% even at the highest CO2 concentration. This demonstrates that the lanthanum-iron perovskite catalyst prepared in Example 1 of this invention possesses excellent stability.

[0163] from Figure 2 As can be seen, comparing the X-ray diffraction patterns of the lanthanum-iron perovskite catalyst used in Example 1 of this invention before and after being repeatedly used to catalyze the conversion of particulate matter into soot, the diffraction peak positions of the catalyst after 5 cycles are consistent with those of the fresh sample before catalytic conversion, without any shift. Furthermore, no new diffraction peaks appeared, and the peak positions corresponded perfectly with those on the standard card, indicating that the catalyst maintained a good crystal structure during the catalytic cycle, i.e., it possesses high phase structure stability.

[0164] Among them, Figure 3In the image, (a) is a SEM (Scanning Electron Microscope) image of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention before catalyzing the conversion of particulate matter into soot; (b) is a SEM image of the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention after being repeatedly used to catalyze the conversion of particulate matter into soot five times. Figure 3 It can be seen that after five cycles of testing, the morphology of the catalyst remained consistent with that before the test, exhibiting a highly regular cubic shape. Moreover, the particle size of the catalyst did not change significantly, indicating that the catalyst possesses high mechanical stability due to its cubic morphology.

[0165] To more clearly illustrate the lanthanum-iron perovskite catalyst prepared according to the present invention, by way of example, the present invention... Figure 4 The image shown is a SEM (scanning electron microscope) image of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention. Figure 5 The X-ray diffraction analysis pattern of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention is shown. Figure 6 The EDS energy dispersive spectroscopy (EDS) analysis diagram of the lanthanum-iron perovskite catalyst obtained in Example 1 of the present invention is shown. Figure 7 The diagram shows the activity test results of carbon soot particulate matter conversion without catalyst and the lanthanum-iron perovskite catalyst obtained in Example 1 of this invention for carbon soot particulate matter conversion.

[0166] Among them, from Figure 4 As can be seen, the lanthanum-iron perovskite catalyst prepared in Example 1 of this invention is cubic in shape and has a highly regular morphological structure. The cubic particles have high dispersion, and the side length of each particle is about 90-160 nm. The catalyst surface is flat and there are no rough or uneven areas, indicating that the obtained catalyst itself has few defects and is close to a perfect lanthanum-iron perovskite catalyst crystal.

[0167] from Figure 5 As can be seen, when the X-ray diffraction pattern of the lanthanum-iron perovskite catalyst obtained according to Example 1 of the present invention is compared with the standard card (PDF#01-070-7777), no other La2O3 and Fe2O3 diffraction peaks appear, confirming that the obtained lanthanum-iron perovskite catalyst is pure phase and isomorphic with the standard card, indicating that the lanthanum-iron perovskite catalyst prepared by the preparation method provided by the present invention has been successfully synthesized.

[0168] from Figure 6 As can be seen, in the lanthanum-iron perovskite catalyst obtained according to Example 1 of the present invention, based on the total mass of the catalyst, the iron content is 19.83 wt% and the lanthanum content is 78.87 wt%.

[0169] from Figure 7It can be seen that, compared with the case without the addition of a catalyst, the soot particulate matter conversion process has a higher ignition temperature and peak temperature. When the lanthanum iron perovskite catalyst obtained in Example 1 of this invention is used to catalyze the soot particulate matter conversion, the ignition temperature and peak temperature of the soot both shift to a lower temperature, indicating that the prepared lanthanum iron perovskite catalyst has excellent catalytic activity and good catalytic effect for soot particulate matter conversion.

[0170] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a lanthanum-iron perovskite catalyst for catalyzing the combustion reaction of soot, characterized in that, The method includes the following steps: S1: In the presence of a solvent, lanthanum source, iron source and ethylene glycol are reacted in the first reaction to obtain a preparative solution; The solvent is water; the amount of solvent used is 50 mL; The lanthanum source is lanthanum nitrate hexahydrate; the amount of the lanthanum source used is 1 mol; The iron source is ferric nitrate nonahydrate; The molar ratio of the lanthanum source (calculated as lanthanum element), the iron source (calculated as iron element), and the ethylene glycol is 1:1:

4. The conditions for the first reaction were: stirring speed of 600 rpm, temperature of 25°C, and time of 5 h. S2: The preparative solution is placed in a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction to obtain the precursor; The conditions for the hydrothermal reaction are: temperature 120℃, time 48h; S3: Cool the precursor to room temperature and sequentially perform separation, washing, drying and calcination to obtain a lanthanum iron perovskite catalyst. The separation process is centrifugation; the separation conditions are: rotation speed of 3000 rpm and time of 3 min. The washing process involves washing three times each with detergent A and detergent B; detergent A is deionized water; the amount of detergent A used is 30 mL; detergent B is ethanol; the amount of detergent B used is 40 mL; the washing conditions are: a rotation speed of 3000 rpm for each wash and a washing time of 4 min for each wash. The drying conditions are: temperature 80℃, time 12h; The calcination conditions are as follows: temperature 500℃, time 5h, heating rate 2℃ / min; the calcination is carried out under a protective atmosphere, namely air.

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