A co-doped perovskite catalyst of Fe and Co and a preparation method thereof

Abstract

The application belongs to the technical field of catalytic oxidation of firedamp, and discloses a Fe and Co synergistically doped perovskite catalyst and a preparation method thereof. x Fe y Co 1‑x‑y O3, wherein 0.7<=x<=1, 0<=y<=0.3, and the preparation method comprises two stages. In the first stage, a powder type perovskite catalyst material is prepared by using a two-step calcination preparation method. A precursor powder is obtained by first-stage calcination in a muffle furnace at a temperature of 350-400 DEG C, and Fe and Co doped perovskite powder type catalyst material is obtained by second-stage calcination at a temperature of 700-850 DEG C. In the second stage, a monolithic Fe and Co doped perovskite catalyst is prepared. In the first stage, the preparation parameters of the perovskite are accurately controlled by using different calcination temperatures, and the process is simple and easy to control, and is more suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ventilation air methane catalytic oxidation, and relates to development and synthesis of high-efficiency composite metal oxides, in particular to a Fe-Co synergistic double-doped perovskite catalyst for catalytic oxidation of low-concentration methane and a preparation method thereof. BACKGROUND

[0002] Natural gas with CH4 as the main component has become the most promising "fourth generation energy" due to its rich reserves, excellent combustion performance, high heat value and low emission. At present, natural gas is widely used as power fuel in vehicles and other mechanical equipment to replace gasoline or diesel, or used as power generation fuel in the chemical industry and power generation industry to replace coal. Coal mine gas is a kind of unconventional natural gas, and the coal mine gas extraction amount in China is as high as 19.4 billion cubic meters, accounting for about one third of the global coal mine gas emission amount, of which more than 70% is discharged in the form of coal mine ventilation air methane. Ventilation air methane, also known as ventilation air methane, is the gas discharged with the ventilation system after the gas generated in coal mining is diluted by air, and the average methane concentration is between 0.5-0.75%. The concentration is far below the flammable limit concentration of methane, which makes it impossible to directly utilize or oxidize the gas without adding supplemental fuel. In addition, considering the influence of a series of conditions such as gas concentration, ventilation volume and coal mining amount in the process of coal mining, the methane concentration and discharge flow of ventilation air methane are extremely unstable, which greatly increases the economic cost and technical difficulty of efficient utilization under conventional conditions.

[0003] At present, the utilization of ventilation air methane at home and abroad is mainly based on pressure swing adsorption, molecular membrane filtration and low-temperature liquefaction technologies, which are separated and purified before being utilized. However, such separation and purification technologies have the disadvantages of complex process and high cost, which leads to a generally low utilization rate of ventilation air methane, and a large amount of ventilation air methane is discharged, which not only causes serious pollution and damage to the environment, but also wastes a large amount of energy resources. In comparison, the heat reverse flow regenerative oxidation technology which utilizes the high-temperature environment in the combustion chamber to oxidize ventilation air methane to generate heat can achieve environmental protection discharge without waste water and solid waste, is more efficient and reliable, and has lower operating cost. In order to make the regenerative oxidation more energy-saving and environmentally friendly, a new ventilation air methane utilization technology, i.e. regenerative catalytic oxidation technology, is formed by combining the low-temperature catalytic oxidation technology on the basis of the regenerative oxidation device.

[0004] The core of low-temperature catalytic oxidation technology is to develop high-efficiency and stable catalysts, which are applied to the reaction of waste gas, and are efficient and environmentally friendly, which has extremely important scientific significance and potential application prospect for promoting the development of new technologies for coalbed methane development and utilization. The noble metals such as palladium, platinum and rhodium are the mainstream catalysts at present, because the catalysts have good performance for catalytic combustion of methane, but they are not only expensive and scarce in resources, but also easy to agglomerate, sinter and produce more toxic pollutants under high temperature conditions, thereby preventing oxygen migration to the active site and inhibiting the catalytic reaction. Therefore, the non-noble metal catalyst represented by perovskite has attracted great research interest of scholars at home and abroad due to its abundant reserves and low price. Compared with single transition metal oxides, perovskite composite metal oxides have better catalytic oxidation due to their diverse structures and compositions and more ion migration rates. Therefore, many technologies related to perovskite materials have emerged in recent years. For example, perovskite catalysts can be prepared by high-temperature self-dissolution method and used for catalyzing VOCs, or the intercalation of montmorillonite and the doping of iron can improve the catalytic activity of perovskite.

[0005] However, there are still some problems in such technologies at present. For example, the modification of perovskite is mostly single-element doping at A and B sites, which has limited improvement of the catalytic activity of perovskite. At the same time, the modified perovskite has defects such as small specific surface area, small pore size and easy deactivation at high temperature, so its catalytic performance still cannot meet the efficient utilization of waste gas. In addition, the perovskite doped with multiple elements is easy to agglomerate during preparation, so that the active centers of the catalyst are less exposed, which greatly inhibits the catalytic activity. Moreover, the preparation of perovskite by traditional sol-gel method has a long cycle, and the heat treatment time is generally more than 12h, which has high time cost. The above problems seriously hinder the industrial production and practical application of perovskite catalysts, so it is urgent to solve the problems by novel and simple technical solutions. SUMMARY

[0006] To solve the existing technical problems, the present application provides a Fe, Co synergistic double-doped perovskite, which modifies the perovskite by doping two B-site ions of Fe and Co, embeds multiple elements into the ABO3 perovskite lattice, and forms a LaMn x Fe y Co 1-x-y O3 type perovskite structure. The perovskite structure benefits from the synergistic effect between different transition metal ions at B site, and has more excellent catalytic performance, more surface ion migration rate, variable oxidation state and structural defects compared with single perovskite material.

[0007] The present application is realized by the following technical solutions:

[0008] A Fe, Co synergistic double-doped perovskite catalyst, which has a chemical formula of LaMn xFe y Co 1-x-y O3, wherein 0.7≤x≤1, 0≤y≤0.3.

[0009] The technical scheme adopts Fe and Co metal to cooperatively dope LaMnO3 perovskite, wherein the synergistic effect among the Fe, Co and Mn metals in the B position can induce the cell structure distortion and the lattice ion valence change, greatly increases the active center exposure of the catalyst, and thus improves the redox property of the perovskite.

[0010] The application further provides a preparation method of the Fe and Co cooperatively double-doped perovskite catalyst, which comprises two stages, the first stage is to prepare a powder type perovskite catalyst material by using a two-step calcination preparation method, and the second stage is to prepare a monolithic Fe and Co double-doped perovskite catalyst.

[0011] The application is achieved by the following technical scheme:

[0012] A preparation method of a Fe and Co cooperatively double-doped perovskite catalyst, comprising the following steps:

[0013] Step 1: according to the stoichiometric ratio of LaMnxFeyCo1-x-yO3, lanthanum nitrate, manganese nitrate, iron nitrate, cobalt nitrate and a complexing agent are weighed and dissolved in deionized water to configure a precursor solution;

[0014] Step 2: ammonia water or industrial strong alkali is added dropwise to the precursor solution, and the solution pH value is 1.5-3.0;

[0015] Step 3: the solution is placed in a room temperature water bath magnetic stirrer, a thickening agent is added, the water bath temperature is raised to 80-95 DEG C, a dispersing agent is added, and stirring is performed until a viscous state is obtained to obtain a wet material;

[0016] Step 4: the wet material is placed in a muffle furnace for first step calcination to obtain a precursor powder, and the calcination temperature is 350-400 DEG C;

[0017] Step 5: the precursor powder is subjected to second step calcination in a muffle furnace, the calcination temperature is 700-850 DEG C, and after cooling, a Fe and Co double-doped perovskite powder type catalyst material is obtained.

[0018] The above steps are steps for preparing a powder type perovskite catalyst material by using a two-step calcination preparation method.

[0019] Further, the following steps are further included:

[0020] Step 6: the powder type perovskite, aluminum sol or silicon sol is weighed and dissolved in deionized water, a dispersing agent is added, stirring is performed until a slurry state is obtained, and then ball milling treatment is performed;

[0021] Step 7: immerse the coptis matrix in a boiling oxalic acid solution, then place it in a ventilated drying oven at 105 DEG C for 1h, and then calcine it in a muffle furnace at a high temperature;

[0022] Step 8: immerse the coptis matrix treated in step 7 in deionized water, immerse it for 30s, take it out, repeat 3 times, and then immerse the coptis matrix in the perovskite coating slurry in step 6 to obtain a wet catalyst;

[0023] Step 9: place the wet catalyst obtained in step 8 in a muffle furnace and calcine it.

[0024] The above steps are steps for preparing the monolithic Fe and Co double-doped perovskite catalyst based on the powder perovskite catalyst material.

[0025] Further, the complexing agent in step 1 is a mixture of citric acid and glucose, the molar ratio of citric acid to glucose is 8:2, and the molar ratio of the complexing agent to the total metal ions is 1.5:1-2:1.

[0026] Further, the total nitrate content in the precursor solution is 14-18wt.%.

[0027] Further, in step 3, the thickening agent is hydroxymethyl cellulose, and the content is 0.1-0.3wt.%; the dispersing agent is polyethylene glycol, and the content is 1-5wt.%.

[0028] Further, in steps 4 and 5, the heating and cooling rates of the muffle furnace are both 10 DEG C / min, oxygen or air is continuously introduced during the calcination process, the flow rate is 30-60ml / min, the calcination time in step 4 is 30-40min, and the calcination time in step 5 is 1.5-2h.

[0029] Further, in step 7, the oxalic acid solution has a content of 30-50wt.% and is immersed for 1h, and the calcination temperature and time are 450-550 DEG C and 1h, respectively.

[0030] Further, in step 8, the loading amount of the perovskite on the coptis is 80-150g / L.

[0031] The addition amount, mixing order, process conditions and other parameters of the catalyst components in the present application are all based on the results of repeated experiments and optimization.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] (1) The application adopts Fe, Co metal to cooperatively dope LaMnO3 perovskite, wherein the synergistic effect among B-site Fe, Co and Mn metals can induce cell structure distortion and lattice ion valence change, greatly increasing the exposure of active centers of the catalyst, thereby improving the redox properties of the perovskite.

[0034] (2) The application adopts a mixture of citric acid and glucose as a complexing agent for the complexing reaction, compared with the traditional single citric acid as a complexing agent, glucose contains five hydroxyl groups, which is easy to form ester groups with the carboxyl groups of citric acid, and is conducive to the occurrence of complexing reaction among metal ions. At the same time, glucose is neutral in pH, which can replace part of citric acid, on the one hand, it can avoid too small pH value of the solution, thereby reducing the subsequent ammonia consumption and reducing the preparation cost. On the other hand, the combustion products of glucose are CO2 and H2O, which can avoid the generation of acidic substances.

[0035] (3) The application adopts a mixture of citric acid and glucose as a complexing agent for the complexing reaction, and adds a thickening agent and a dispersant before the complexing reaction, which can ensure the integrity of the complexing reaction while improving the reaction rate, and effectively improve the component purity, crystallinity and particle size uniformity of the catalyst.

[0036] (4) The traditional heat treatment method of drying first and then calcining usually has a drying temperature of more than 100 degrees, which is carried out in a ventilated drying box or a vacuum drying box. The obtained dry gel after drying has a volume of 5-10 times of the original volume. Therefore, the dry gel cannot be prepared in large quantities at one time in industry, and the dry gel after drying still contains un-decomposed nitrate, which must be removed through the calcination heating process in a muffle furnace.

[0037] The two-step calcination method of the application replaces the traditional heat treatment method of drying first and then calcining. The two-step calcination is directly carried out in a muffle furnace, and two temperature segments are set, one is low temperature 350-400 DEG C, and the other is high temperature 700-850 DEG C. The two-step calcination can be carried out in sequence according to the program. The total preparation time of the two-step calcination method is not more than 3h, which is much higher than the efficiency of the traditional drying method, and is more suitable for industrial application. Moreover, the perovskite precursor obtained after the first low-temperature calcination is agglomerated oxide, and the volume change is small. This is due to the fact that the carbonates in the sol are decomposed at a very fast speed at a high temperature of 300 degrees, and the agglomerated oxide is La, Fe, Co oxide. Therefore, the preparation efficiency is improved, and the process of moving the dry gel from the drying box to the muffle furnace can be eliminated, the growth rate of the perovskite crystal is improved, the heat treatment reaction time is shortened, and the generation of impurities is inhibited.

[0038] In addition, based on the repeated experimental optimization results, the present application improves the adding amount of each component, the mixing order and the process conditions in the preparation process. Therefore, compared with the traditional sol-gel method, the preparation method adopted by the present application is simple and easy to control, has short heat treatment time, low preparation cost, and is more suitable for industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0039] The specific embodiments of the present application will be further illustrated below in combination with the drawings.

[0040] Figure 1 LaMn x Fe y Co 1-x - y XRD pattern of O3-type perovskite, wherein, Figure 1 (a) is a whole figure; Figure 1 (b) is a local enlarged view;

[0041] Figure 2 LaMn x Fe y Co 1-x-y H2-TPR pattern of O3-type perovskite;

[0042] Figure 3 LaMn x Fe y Co 1-x-y O2-TPD pattern of O3-type perovskite;

[0043] Figure 4 Methane catalytic efficiency diagram of each perovskite catalyst prepared by the present application. DETAILED DESCRIPTION

[0044] In order to more clearly express the present application, the present application will be further illustrated below in combination with the drawings and specific examples.

[0045] Example 1

[0046] The present embodiment provides a Fe and Co synergistically double-doped perovskite catalyst, which has a chemical general formula of LaMn x Fe y Co 1-x-y O3, wherein 0.7≤x≤1 and 0≤y≤0.3.

[0047] The preparation of the above Fe and Co synergistically double-doped perovskite catalyst mainly includes two stages, the first stage is to prepare a powder type perovskite catalyst material, and the second stage is to prepare a whole type Fe and Co double-doped perovskite catalyst.

[0048] The first stage of the preparation of the powder type perovskite catalyst adopts a two-step calcination preparation method, and the preparation method comprises the following steps:

[0049] Step 1: according to the stoichiometric ratio of LaMn x Fe y Co 1-x-y O3, lanthanum nitrate, manganese nitrate, iron nitrate, cobalt nitrate and a complexing agent are weighed and dissolved in deionized water to prepare a precursor solution;

[0050] In this step, the complexing agent is a mixture of citric acid and glucose, and the molar ratio of the two is 8:2; the molar ratio of the complexing agent to the total metal ions is 1.5:1-2:1.

[0051] Step 2: Under stirring conditions, ammonia water or industrial strong alkali is added dropwise to the precursor solution, and the pH value of the solution is 1.5-3.0;

[0052] In this step, stirring is carried out at room temperature, and the stirring speed is 100-200 r / min; in order to shorten the complexing reaction and improve the preparation efficiency, the total nitrate content in the precursor solution is 14-18 wt.%.

[0053] Step 3: The solution is placed in a room temperature water bath magnetic stirrer, a thickening agent is added under stirring conditions, the water bath temperature is raised to 80-95℃, and after the temperature is constant, a dispersing agent is added, and the stirring is continued until a viscous state is obtained, and a wet material is obtained;

[0054] In this step, the thickening agent is hydroxymethyl cellulose, and the content is 0.1-0.3 wt.%; the dispersing agent is polyethylene glycol, and the content is 1-5 wt.%; the continuous stirring speed is 300-600 r / min, and the stirring time is 2-3 h.

[0055] In this step, hydroxymethyl cellulose is added as a thickening agent, and polyethylene glycol is added as a dispersing agent, which is beneficial to the formation of a stable solution dispersion system and shortens the complexing reaction process and improves the preparation efficiency.

[0056] Step 4: The wet material obtained in step 3 is placed in a muffle furnace at a higher temperature for first-step calcination, and after being kept at the temperature for a period of time, a precursor powder is obtained;

[0057] In this step, the first-step calcination temperature is 350-400℃, the muffle furnace has a temperature rising and falling rate of 10℃ / min, the calcination time is 30-40 min, and oxygen or air is continuously introduced during the calcination process, and the flow rate is 30-60 ml / min.

[0058] Step 5: The precursor powder obtained in step 4 is coarsely ground and compacted, and then placed in a muffle furnace for second-step calcination, cooled to room temperature after the calcination is completed, and then subjected to a fine grinding process to obtain a Fe, Co double-doped perovskite powder type catalyst material.

[0059] In this step, the second step calcination temperature is 700-850℃, the muffle furnace heating and cooling rate is 10℃ / min, the calcination time is 1.5-2h, and nitrogen or argon is continuously introduced during the calcination process at a flow rate of 30-60ml / min.

[0060] Through the above preparation steps, the powder type catalytic material is prepared. The following steps are based on the preparation of the powder type catalytic material to obtain a monolithic Fe and Co double-doped perovskite, and the preparation method comprises the following steps:

[0061] Step 6: Weigh the powder type perovskite, aluminum sol or silicon sol, dissolve in deionized water, add dispersant under stirring conditions, continue stirring until it becomes a slurry, and then ball mill the catalyst slurry;

[0062] In this step, the solid content of the perovskite in the slurry is 60-85%, and the solid content of the aluminum sol or silicon sol is 3-10%; the stirring speed is 50-100r / min; and after ball milling, the particle size of the catalyst is 55-70um.

[0063] Step 7: Soak the coptite matrix in boiling oxalic acid solution, then dry it in a ventilated drying oven at 105℃ for 1h, and then calcine it in a muffle furnace at high temperature;

[0064] In this step, the oxalic acid solution contains 30-50wt.% of oxalic acid, and the soaking time is 1h; the calcination temperature and time are 450-550℃ and 1h, respectively.

[0065] Step 8: Soak the coptite treated in step 7 in deionized water, soak for 30s, repeat 3 times, and blow the coptite with an air gun; then soak the coptite in the perovskite coating slurry in step 6, blow the coptite channel with an air gun, and make the slurry load evenly to obtain a wet catalyst. Estimate the coptite loading based on the mass of the coptite, the water absorption and the solid content of the perovskite slurry. If the loading is insufficient, repeat the soaking and blowing of the coptite until the desired loading is reached, and then place it at room temperature for 30min;

[0066] In this step, the loading of perovskite on coptite is 80-150g / L.

[0067] Step 9: Calcine the wet catalyst obtained in step 8 in a 500℃ muffle furnace for 2h.

[0068] Specifically, the present embodiment provides a process for preparing a perovskite catalyst LaMn 0.8 Fe 0.15 Co 0.05 O3, which comprises the following steps:

[0069] (1) Weigh 14.724 g of lanthanum nitrate, 9.735 g of manganese nitrate (50% by mass), 2.092 g of iron nitrate, 0.495 g of cobalt nitrate, 4.640 g of glucose, and 21.542 g of citric acid into deionized water, and dropwise add ammonia water under stirring conditions until the pH value of the solution is 1.5;

[0070] (2) Place the solution in a room temperature water bath magnetic stirrer, and under stirring conditions, add 0.295 g of hydroxymethyl cellulose, and raise the water bath temperature to 80-95°C, and after the temperature is constant, add 0.532 g of polyethylene glycol, and continue stirring until it is viscous;

[0071] (3) Place the obtained wet material in a muffle furnace at 380°C for the first step of calcination for 30 min, and after coarse grinding and compaction, place it in a muffle furnace at 750°C for the second step of calcination, and the calcination time is 2 h; after the calcination is completed, cool to room temperature, and then perform fine grinding to obtain LaMn 0.8 Fe 0.15 Co 0.05 O3 type perovskite powder formula catalytic material.

[0072] Example 2

[0073] This example uses the method of Example 1 to prepare the perovskite catalyst LaMn 0.8 Fe 0.1 Co 0.1 O3, the difference is only that in step (1), 1.395 g of iron nitrate and 0.990 g of cobalt nitrate are added; and in step (2), 0.530 g of polyethylene glycol is added.

[0074] Example 3

[0075] This example uses the method of Example 1 to prepare the perovskite catalyst LaMn 0.8 Fe 0.05 Co 0.15 O3, the difference is only that in step (1), 0.697 g of iron nitrate and 1.484 g of cobalt nitrate are added; and in step (2), 0.293 g of hydroxymethyl cellulose and 0.528 g of polyethylene glycol are added.

[0076] Comparative Example 1

[0077] This comparative example provides a process for preparing a perovskite catalyst LaMnO3 by a traditional sol-gel method, which includes the following steps:

[0078] (1) Weigh 14.724 g of lanthanum nitrate, 9.735 g of manganese nitrate (50% by mass), 2.092 g of iron nitrate, 0.495 g of cobalt nitrate, 4.640 g of glucose, and 21.542 g of citric acid into deionized water, and dropwise add ammonia water under stirring conditions until the pH value of the solution is 1.5;

[0079] (2) The solution was evaporated to a gel at 85°C under stirring at a speed of 600 r / min, and then was placed in a constant temperature drying oven at 130°C for aging for 12 h. The obtained precursor was calcined at 900°C in an air atmosphere for 4 h to obtain a perovskite powder with a molecular formula of LaMnO3.

[0080] Comparative Example 2

[0081] This comparative example prepared a perovskite catalyst LaMn 0.8 Fe 0.2 O3 by the method of Comparative Example 1, with the only difference being that 14.724 g of lanthanum nitrate, 9.735 g of manganese nitrate (50% by mass), and 2.789 g of iron nitrate were added in step (1).

[0082] Comparative Example 3

[0083] This comparative example prepared a perovskite catalyst LaMn 0.8 Co 0.2 O3 by the method of Comparative Example 1, with the only difference being that 14.724 g of lanthanum nitrate, 9.735 g of manganese nitrate (50% by mass), and 1.979 g of cobalt nitrate were added in step (1).

[0084] As Figure 1 shown in the following table, LaMn x Fe y Co 1-x-y O3 type perovskite catalysts were prepared. Figure 1 As can be seen from (a), the LaMnO3 perovskite phase characteristic diffraction peaks belonging to rhombic symmetric crystal structure appeared at positions of 23.1°, 32.5°, 40.3°, 47.0°, 58.4°, and 68.9° in Example 1, 2, and 3, indicating that the prepared catalysts have complete perovskite crystal structures. At the same time, the catalyst samples have superstoichiometric oxygen, and the overall spectrum has no other obvious impurity peaks, thereby proving that the improved sol-gel method used in the present application can prepare high-purity perovskite type catalysts. For Comparative Examples 1, 2, and 3, the intensity of the main characteristic diffraction peak of the Fe-Co doped perovskite (Example 1, 2, and 3) at about 32.5° is reduced, and the peak type is broadened, which indicates that the crystallinity of the Fe and Co double metal co-doped catalyst is reduced, the particle size is smaller, and the degree of crystal structure distortion caused by double doping is greater. Figure 1 (b) is a partial enlarged view of (a), and the change of the XRD main peak can be seen from (b). Figure 1 (b) is a partial enlarged view of (a), and the change of the XRD main peak can be seen from (b). Figure 1 (b) is a partial enlarged view of (a), and the change of the XRD main peak can be seen from (b).

[0085] In order to further explore the LaMn 1-x-y Fe x Co yH2-TPR tests were performed to evaluate the redox properties of the O3 perovskites, see Figure 2 For the comparative example 1 perovskite, there are three typical reduction peaks, with the following characteristics: the first two low-temperature a, b reduction peaks at 345°C, 425°C, respectively, are attributed to the reduction of Mn 4+ to Mn 3+ and Mn 3+ to Mn 2+ The reduction peak at low temperature can be attributed to the consumption of non-stoichiometric oxygen and lattice oxygen; while the high-temperature g reduction peak at about 770°C is due to the reduction of weakly bound MnO to metallic Mn. The peak value of the g peak in comparative example 1 is significantly higher than that of the a, b peaks, indicating that the content of low-valence Mn accounts for a high proportion in comparative example 1. The a peak of comparative example 2, which is singly doped, slightly moves to a higher temperature, while the b peak moves in the opposite direction. Both reduction peaks are higher, and the peak shape is also more sharp. This is related to the reduction peaks of Fe 4+ to Fe 3+ at about 350°C and Fe 3+ to Fe 2+ at about 433°C. This phenomenon indicates that the doping of a small amount of Fe is beneficial to improving the low-temperature reducibility of Mn species. On this basis, the low-temperature reduction peak temperature of example 1 is further reduced, which can be attributed to the reduction of Co3O4 to CoO (g peak 250-320°C) and CoO to Co 0 (d peak 320-400°C) or Fe-Co promoting the increase of high-valence Mn 4+ , Mn 3+ content in the perovskite.

[0086] As shown in Figure 3 , the oxygen adsorption and desorption curves of LaMn 1-x-y Fe x Co y O3 perovskite catalysts were plotted to evaluate and analyze the oxygen species and their mobility. From the figure, three main oxygen desorption regions can be observed. The oxygen species desorbed in the first region (100-300°C) is O α , the oxygen species desorbed in the second region (300-500°C) is O β , and O γ in the third region (500-750°C). O α is attributed to the physical and chemical adsorption oxygen species with the weakest adsorption capacity on the catalyst surface, collectively referred to as adsorbed oxygen. O β is attributed to the chemisorbed oxygen adsorbed on the surface and subsurface oxygen vacancies of the catalyst, also known as vacancy oxygen, and the lattice oxygen O γThe oxygen desorption is related to the lattice oxygen on the surface or inside of the catalyst. In the first and second regions, the comparative example 1 shows a weak oxygen desorption peak, while the comparative example 2 and the example 1 show a strong desorption peak, which indicates that the doped perovskite has more oxygen species adsorbed on the surface, or compared with the comparative example 1, the doping makes the active oxygen species of the catalyst easily released from the surface or subsurface oxygen vacancies, which is consistent with the methane catalytic combustion performance of each catalyst. Similarly, in the third region, the oxygen desorption peak intensity of the doped perovskite is also higher than that of the comparative example 1. In addition, the peak fitting calculation of each desorption peak shows that the O α and O β amount of the Fe-Co double-doped perovskite group is the highest, which indicates that compared with the comparative examples 1 and 2, the double doping makes the perovskite have a better oxygen migration rate. At the same time, the total oxygen desorption amount of the catalyst is also the highest, which indicates that the active synergistic effect between Mn and Fe-Co in the catalyst can improve the oxygen activation ability of the catalyst more than the traditional single-element doping in the B site.

[0087] Comparing the H2-TPR and O2-TPD curves of different catalysts, the reduction and oxidation of the example 1 are higher than those of the comparative examples 1 and 2 prepared by the traditional sol-gel method, which indicates that there is a strong interaction between Fe-Co and Mn. This strong interaction promotes the lattice distortion of the perovskite, which in turn leads to the decrease of the crystallinity, the decrease of the particle size, and even the increase of the specific surface area of the catalyst. On the other hand, the synergistic doping increases the content of high-valence Mn in the perovskite and the oxygen species on the surface of the catalyst, which are all beneficial to the improvement of the low-temperature catalytic performance of the catalyst. In order to further compare the actual catalytic performance gap, the most difficult to oxidize methane in hydrocarbons is selected as the reactant for the catalytic combustion experiment.

[0088] Referring to Figure 4 , the difference in the methane catalytic performance of the different perovskite catalysts prepared by the present application is shown. The specific reaction temperatures at which the methane conversion rates are 10%, 50% and 90% are denoted as T 10 , T 50 and T 90 , respectively. T 10 is usually taken as the light-off temperature of the catalyst, and T 90 is the complete combustion temperature. The temperature range of the methane catalytic combustion characteristic experiment is set to be between 200 and 700℃. Under this temperature range, the conversion rate curves of all the perovskites are "S" type curves, that is, the catalytic reaction rate is fast in the low-temperature and high-temperature ranges, and is slow in the medium-temperature range. The light-off temperature and the complete combustion temperature of LaMnO3 (the comparative example 1) are 427.4℃ and 608.4℃, respectively. With the doping of Co, the CH4 conversion rate of the comparative example 3 at 450℃ is increased by 22.8% compared with the comparative example 1, and the traditional single doping makes the activity of the catalyst obviously improved. If Fe partially replaces LaMn 0.8Co 0.2 Co in O3, that is, Fe-Co synergistic doping modification perovskite, the catalytic temperature of examples 1, 2 and 3 is lower than that of the comparative example. The sample with the best catalytic performance is example 1, and the metal ratio of Mn, Fe and Co is 16:3:1. The T10, T50 and T90 of the catalyst are 365.8℃, 436.4℃ and 486.5℃, respectively, which is 121.9℃ lower than that of the comparative example 1. The catalytic performance is even comparable to some noble metal catalysts. 10 50 90 The T10, T50 and T90 of the catalyst are 365.8℃, 436.4℃ and 486.5℃, respectively, which is 121.9℃ lower than that of the comparative example 1. The catalytic performance is even comparable to some noble metal catalysts.

[0089] In addition to examples 1, 2 and 3, the patent mainly focuses on the perovskite B-site doping of Fe, Co, Ti, Cr, Al, Cu and other metal ions. The perovskite Mn has a good synergistic effect with Fe and Co, but Ti, Cr and Cu do not show good catalytic activity for methane. For example, the light-off temperature T10 of the perovskite catalyst doped with Ti and Cr is more than 500℃, which is much worse than that of the comparative example 1.

[0090] In the above description, many specific details are described in order to fully understand the present application, but the above description is only the preferred embodiment of the present application, and the present application can be implemented in many other ways different from the description. Therefore, the present application is not limited to the specific implementation disclosed above. Meanwhile, any person skilled in the art can make many possible changes and modifications to the technical solutions disclosed above, or modify them as equivalent embodiments, without departing from the scope of the technical solutions of the present application. Any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present application, without departing from the scope of the technical solutions of the present application, are still within the scope of protection of the technical solutions of the present application.​​

Claims

1. A method for preparing an Fe / Co synergistically doped perovskite catalyst, characterized in that, Its chemical formula is LaMn x Fe y Co 1-x-y O3, where 0.7≤x≤0.8, 0.05≤y≤0.15; The steps of the catalyst preparation method are as follows: Step 1: Based on LaMn x Fe y Co 1-x-y To determine the stoichiometric ratio of O3, weigh out lanthanum nitrate, manganese nitrate, ferric nitrate, cobalt nitrate, and a complexing agent, and dissolve them in deionized water to prepare a precursor solution. Step 2: Add ammonia or industrial strong alkali dropwise to the precursor solution, so that the pH of the solution is 1.5 to 3.0; Step 3: Place the solution in a room temperature water bath magnetic stirrer, add thickener, raise the water bath temperature to 80-95℃, add dispersant, and stir until viscous to obtain wet material; Step 4: Place the wet material in a muffle furnace for the first calcination to obtain precursor powder. The calcination temperature is 350-400℃. Step 5: The precursor powder is calcined in a muffle furnace at a temperature of 700-850℃. After cooling, Fe and Co doped perovskite powder catalyst material is obtained. Step 6: Weigh the powdered perovskite and aluminum sol or silica sol prepared in Step 5, dissolve them in deionized water, add a dispersant, stir until a slurry is formed, and then ball mill it. Step 7: Soak the cordierite matrix in a boiled oxalic acid solution, then dry it in a ventilated drying oven at 105°C for 1 hour, and then calcine it at high temperature in a muffle furnace. Step 8: Immerse the cordierite treated in Step 7 in deionized water for 30 seconds, then remove it and repeat 3 times. Then immerse the cordierite in the perovskite coating slurry in Step 6 to obtain a wet catalyst. Step 9: Place the wet catalyst obtained in Step 8 into a muffle furnace for calcination; The complexing agent mentioned in step 1 is a mixture of citric acid and glucose, with a molar ratio of citric acid to glucose of 8:2 and a molar ratio of complexing agent to total metal ions of 1.5:1 to 2:

1. In step 3, the thickener is hydroxymethyl cellulose, with a content of 0.1–0.3 wt.%; the dispersant is polyethylene glycol, with a content of 1–5 wt.%.

2. The method for preparing an Fe / Co synergistically doped perovskite catalyst according to claim 1, characterized in that, The total nitrate content in the precursor solution was 14–18 wt.%.

3. The method for preparing an Fe / Co synergistically doped perovskite catalyst according to claim 1, characterized in that, In steps 4 and 5, the heating and cooling rates of the muffle furnace are both 10℃ / min, and oxygen or air is continuously introduced during the calcination process at a flow rate of 30-60 ml / min. The calcination time in step 4 is 30-40 min, and the calcination time in step 5 is 1.5-2 h.

4. The method for preparing an Fe / Co synergistically doped perovskite catalyst according to claim 1, characterized in that, In step 7, the oxalic acid solution content is 30-50 wt.%, soaking for 1 hour, and calcination temperature and time are 450-550℃ and 1 hour, respectively.

5. The method for preparing an Fe / Co synergistically doped perovskite catalyst according to claim 1, characterized in that, In step 8, the perovskite loading on cordierite is 80–150 g / L.

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