Alumina fiber supported cobalt catalyst for catalytic oxidation of methane

Abstract

The invention discloses an alumina fiber supported cobalt catalyst Co / Af for catalytic oxidation of methane, the catalyst takes alpha-alumina fiber as a carrier, the carrier has the characteristics of good thermal stability and formability, cobalt is supported by a hydrothermal method, the Co / Af catalyst is obtained through roasting, and the catalyst has the advantages of long service life, high temperature resistance, frequent heating and cooling start and the like. Therefore, the alumina fiber supported cobalt catalyst Co / Af is expected to become a substitute catalyst of a noble metal catalyst.

Description

Technical Field

[0001] The present invention relates to the preparation and application of an alumina fiber-supported cobalt catalyst for methane elimination, belonging to the technical field of environmental protection. Background Art

[0002] As an important carrier for the transformation of low-carbon energy, the methane component (volume ratio 85-95%) of natural gas has been applied in many fields. However, during the production, transportation and use of methane, methane waste gas will inevitably be generated. Engineering practice shows that about 12-18% of methane fails to be completely burned under unsteady conditions. These escaped methane, due to its global warming potential on the century scale far exceeding that of carbon dioxide, exacerbates the greenhouse effect. Therefore, methane purification and elimination are imminent. There are many methods for methane purification, such as physical separation and recovery, combustion. However, it is difficult to recover low-concentration methane, and below the combustion limit, conventional methods cannot purify and eliminate it. Catalytic oxidation to eliminate methane is an effective method to reduce methane waste gas, and the key is the research and development of catalysts.

[0003] After decades of development, a variety of methane oxidation catalysts have been developed. Currently, the catalysts used for catalytic oxidation of low-concentration methane are mainly of two types. One type is noble metal catalysts, such as palladium-based catalysts, rhodium-based catalysts, etc.; the other type is non-noble metal catalysts, such as cobalt-based catalysts, transition metal oxide catalysts, etc. Although noble metal catalysts have better low-temperature performance, usually below 450 °C (the temperature at which the methane conversion rate is 90%), their disadvantages of being easily poisoned and having poor activity at high space velocities, as well as their high prices, hinder their application. 90 Usually at (the temperature when the methane conversion rate is 90%) below 450 °C, their disadvantages of being easily poisoned and having poor activity at high space velocities, as well as their high prices, hinder their application.

[0004] The non-noble metal-catalyzed methane oxidation is a research hotspot in the fields of efficient utilization of natural gas and pollutant control. Research by Wei et al. (Nanomaterials, 13.13 (2023): 1917) shows that transition metal oxides can also effectively activate the C-H bond in CH4 at low temperatures. Currently, the mainstream catalysts mainly include transition metal oxides (such as Co, Mn, Fe-based), perovskite-type (ABO3), and spinel-type (AB2O4) materials. Among them, manganese oxides (such as MnO2) exhibit high activity in the low-temperature region (<400 °C). The abundant oxygen vacancies on their surface can promote methane activation, but they are prone to phase transformation at high temperatures, leading to deactivation. Research by Xiong et al. (International Journal of Hydrogen Energy, 105 (2025): 1153-1163) shows that although iron-based catalysts (such as Fe2O3) are low-cost, their redox ability is weak, and the active sites are easily covered by hydroxyl groups, resulting in a significantly lower methane conversion efficiency than the cobalt-based system. Research by Ling et al. (Separation and Purification Technology, 360 (2025): 131105) found that perovskite-type catalysts (such as LaMnO3) exhibit excellent thermal stability due to their stable crystal structure and adjustable B-site metals, but their low specific surface area and insufficient surface acidity limit the further improvement of activity.

[0005] In contrast, research by Song et al. (Applied Surface Science, 556 (2021): 149713) and Wang et al. (Applied Catalysis B: Environmental, 168 (2015): 42-50) found that Co3O4 metal can effectively catalyze the CH4 oxidation reaction. Although this gives it good application prospects, its thermal stability still cannot meet the actual use requirements, and further improvement of cobalt-based catalysts is still needed. Supported cobalt catalysts have been reported, and different carriers have been developed, but in terms of overall catalytic performance, they cannot meet the actual needs, and a more efficient cobalt-based catalytic system still needs to be developed. Summary of the Invention

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: Inventively, α-Al2O3 type alumina fiber is used as the carrier. This carrier has the advantages of good thermal stability and formability. Without forming, the alumina fiber-supported cobalt catalyst, abbreviated as Co / Af catalyst, is directly prepared by the hydrothermal method. This catalyst uses α-alumina fiber as the carrier and Co3O4 as the active component, rich in a relatively high concentration of Co 3+Moreover, it has the characteristics of small particle size, high surface oxygen, and high oxygen vacancy content, and shows excellent performance such as long life, high temperature resistance, and the ability to start frequently by heating and cooling in the methane catalytic oxidation reaction.

[0007] Using methane and air as raw materials, the air is provided by an air generator and enters the fixed-bed reactor according to a certain ratio and flow rate. The methane volume concentration is 1,000 - 30,000 ppm, the total flow rate is 10 - 200 mL / min, and air is used as the balance gas. 0.05 - 0.4 g of Co / Af catalyst is filled in the fixed-bed reactor, and the overall mass space velocity is 1,500 mL / g cat / h - 240,000 mL / g cat / h. The methane catalytic oxidation performance is tested by a programmed temperature rise method. The backend is directly connected to a gas chromatograph for on-line detection and analysis. The gas chromatograph is equipped with an FID detector, and the programmed temperature rise range is 200 - 1,000 °C.

[0008] The cobalt catalyst Co / Af supported on alumina fiber used in the present invention includes the following preparation steps: (1) Dissolve the cobalt source and sodium carbonate in a mixed solution of ethylene glycol and ammonia water. The molar ratio of the cobalt source, sodium carbonate, ethylene glycol, and ammonia water is 1:0.3:0.12:0.03, and stir evenly at room temperature; (2) Put the required mass of alumina fiber into the mixed solution and stir evenly by ultrasonic; (3) Transfer the mixed solution to a hydrothermal synthesis kettle, keep it at 160 - 190 °C for 15 - 19 h for hydrothermal crystallization, and then wash and dry the precipitate. After the hydrothermal reaction, wash the precipitate and dry it in an oven; (4) Calcinate the dried powder in an air atmosphere to obtain the cobalt catalyst Co / Af supported on alumina fiber.

[0009] In the above technical solution, further, in step (1), the cobalt source is one of Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, or CoCl2·6H2O.

[0010] In the above technical solution, further, in step (2), the mass ratio of the cobalt source to the alumina fiber is: 0.5:1, 0.6:1, 0.7:1, and 0.8:1.

[0011] In the above technical solution, further, in step (3), the calcination temperature is 500 - 900 °C, the time is 2 - 8 h, and the heating rate is 1 - 5 °C / min.

[0012] The present invention creatively designs a cobalt catalyst Co / Af supported on alumina fiber for methane catalytic oxidation. The catalyst uses α-alumina fiber as the carrier, which has the characteristics of good thermal stability and formability. Cobalt is loaded by the hydrothermal method and the Co / Af catalyst is obtained after calcination. This catalyst has excellent catalytic activity.

[0013] As Figure 1 and Figure 2 shown by the results of the methane oxidation catalyzed by the catalyst in Example 4, under the reaction conditions of a methane volume concentration of 20,000 ppm and a mass space velocity ≤ 120,000 mL / g cat / h, the temperature required to catalyze 50% of methane is 370 °C, and the temperature required to catalyze 90% of methane is 425 °C. CH4 can be completely converted into H2O and CO2; Figure 3 It verifies the excellent high-temperature tolerance of the catalyst in Example 4. In the catalytic methane test reaction, when the test temperature starts from 550 °C and then gradually increases to 850 °C, after experiencing the stepwise heating condition for 48 h, it still shows stable activity and the conversion rate is always 100%; Figure 4 and Figure 5 The results show that the catalyst in Example 4 can maintain good catalytic activity during frequent start-up at high (120,000 mL / g cat / h) or low (46,800 mL / g cat / h) mass space velocities. During the four heating and cooling cycles of repeated start-up, the performance of the second heating and cooling cycle decreases slightly, but remains consistent in subsequent tests without significant degradation; Figure 6 The results show that the methane conversion rate of the catalyst in Example 4 remains at about 92 - 96% during the 100 h continuous test, proving that this catalyst has excellent stability.

[0014] Figure 7 The analysis in the characterization results shows that the adsorbed oxygen / lattice oxygen value of Example 4 is 1.23, that of Comparative Example 1 is 0.59, and that of Comparative Example 3 is 0.56. This further proves that the catalyst in Example 4 has more oxygen vacancies. The ratio order of Co 3+ / Co 2+ is: Example 4 > Comparative Example 1 > Comparative Example 3. The Co 3+ / Co 2+ ratio of the catalyst in Example 4 is the highest, which means more Co 3+ exists, indicating that there are more active sites on the catalyst surface. At the same time, a small amount of Co 2+ can participate in the electron transfer process to help regenerate Co 3+ and maintain the catalytic cycle. From Figure 8The XRD characterization results were combined with the Scherrer formula to calculate that the catalyst particle sizes of Example 4, Comparative Example 1, and Comparative Example 2 were 26.1 nm, 28.7 nm, and 36.0 nm, respectively. The results show that the catalyst particle size of Example 4 is the smallest, which is the same as the trend of the activity results. The smaller the particle size, the better the catalytic methane oxidation activity.

[0015] Therefore, it has the advantages of small particle size, long life, high temperature resistance, and frequent heating and cooling startup. The synthesis method of the methane catalytic oxidation catalyst of the present invention is simple, the preparation cost is low, and the prepared Co / Af has rich oxygen vacancies and excellent activity in the methane catalytic oxidation reaction. At the same time, the high-valent Co 3+ species enriched on the catalyst surface act as the main active centers, which can significantly reduce the energy barrier for the activation of the methane C-H bond, thereby efficiently promoting its dissociation process. Co 3+ / Co 2+ The synergistic effect of the redox pair has a key impact on the catalytic performance - a higher Co 3+ proportion is beneficial to improving the intrinsic activity of methane oxidation, while the Co 2+ species can drive the dynamic regeneration of Co 3+ by participating in the electron transfer process of the metal-oxygen bond, forming a continuous cyclic redox path (Co 3+ ↔Co 2+ ). This dynamic equilibrium mechanism between valence states effectively maintains the stability of the active sites and the continuity of the reaction kinetics during the catalytic reaction process. Therefore, the cobalt catalyst Co / Af supported on alumina fiber is expected to become an alternative catalyst to noble metal catalysts. Description of the Drawings

[0016] Figure 1 is the CH4 conversion rate diagram of the catalysts of Examples 1-7 and Comparative Examples 1-3 varying with temperature.

[0017] Figure 2 is the CH4 conversion rate diagram of the catalysts of Example 4 and Comparative Examples 1 and 3 varying with space velocity.

[0018] Figure 3 is the high-temperature stability diagram of Example 4.

[0019] Figure 4 is the heating and cooling cycle stability diagram of Example 4 under the condition of a mass space velocity of 46,800 mL / g cat / h.

[0020] Figure 5 is the heating and cooling cycle stability diagram of Example 4 under the condition of a mass space velocity of 120,000 mL / g cat / h.

[0021] Figure 6It is the long-term stability curve graph of Example 4.

[0022] Figure 7 It is the XPS Co 2p and O 1s graphs of the catalysts of Example 4 and Comparative Examples 1 and 3.

[0023] Figure 8 It is the catalyst particle size graph obtained by calculating the XRD of the catalysts of Example 4 and Comparative Examples 1 and 3 using the Scherrer formula. Detailed implementation manners

[0024] The embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are only used to explain the present invention, and cannot be construed as a limitation to the present invention.

[0025] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained through commercial channels or prepared according to conventional methods well-known to those skilled in the art.

[0026] The cobalt catalyst Co / Af supported on alumina fiber prepared by the present invention is synthesized by a hydrothermal method. The specific operation details of synthesizing the catalyst and the catalytic performance of methane are as follows. Example

[0027] The preparation method thereof is as follows: Take reagents in an amount with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol and ammonia of 1:0.3:0.12:0.03, stir evenly at room temperature vigorously, add 0.40 g of Al2O3 fiber carrier, then transfer the mixed solution to a high-pressure reactor, keep it at 160 - 190 °C for 15 - 19 h, wash, filter and then dry in an oven, and then heat it to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere, and keep it for 2 - 8 h to obtain the catalyst, denoted as 50%Co / Af-N-600.

[0028] The method for catalytic oxidation of methane is as follows: Pack the catalyst prepared in Example 1 with a filling amount of 0.20 g in a fixed-bed reactor, introduce a mixed gas (the volume concentration of methane is 20,000 ppm, and the balance gas is air), adjust the mass space velocity to 46,800 mL / g cat / h; the heating rate is 10 °C / min, continuously heat from 200 °C to 600 °C, and keep it for 30 min every time it rises 50 °C. At each temperature point, use a gas chromatograph equipped with a flame ionization detector (FID) to detect the CH4 concentration in the fixed-bed tail gas twice. Example

[0029] The preparation method thereof is as follows: Take reagents in the molar ratio of Co(CH3COO)2·4H2O, sodium carbonate, ethylene glycol and ammonia water as 1:0.3:0.12:0.03, stir evenly at room temperature vigorously, add 0.40 g of Al2O3 fiber carrier, then transfer the mixed solution to a high-pressure reactor, keep it at 160 - 190 °C for 15 - 19 h, wash, filter and then dry in an oven, and then heat it to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere, keep it for 2 - 8 h to obtain a catalyst, denoted as 50%Co / Af-C-600.

[0030] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1. Example

[0031] Its preparation method is: Take reagents in the molar ratio of CoCl2·6H2O, sodium carbonate, ethylene glycol and ammonia water as 1:0.3:0.12:0.03, stir evenly at room temperature vigorously, add 0.40 g of Al2O3 fiber carrier, then transfer the mixed solution to a high-pressure reactor, keep it at 160 - 190 °C for 15 - 19 h, wash, filter and then dry in an oven, and then heat it to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere, keep it for 2 - 8 h to obtain a catalyst, denoted as 50%Co / Af-Cl-600.

[0032] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1. Example

[0033] Its preparation method is: Take reagents in the molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol and ammonia water as 1:0.3:0.12:0.03, stir evenly at room temperature vigorously, add 0.26 g of Al2O3 fiber carrier, then transfer the mixed solution to a high-pressure reactor, keep it at 160 - 190 °C for 15 - 19 h, wash, filter and then dry in an oven, and then heat it to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere, keep it for 2 - 8 h to obtain a catalyst, denoted as 60%Co / Af-N-600.

[0034] The method for catalytic oxidation of methane is: (1) The same as the method for catalytic oxidation of methane in Example 1.

[0035] (2) Pack the catalyst prepared in Example 1 with a filling amount of 0.33 g in a fixed-bed reactor, and other test conditions are the same as the method for catalytic oxidation of methane in Example 1.

[0036] (3) Tests at different space velocities: The catalyst prepared in Example 1 was filled into a fixed-bed reactor with a filling amount of 0.20 g, and a mixed gas (methane volume concentration was 20,000 ppm, and the balance gas was air) was introduced. The mass space velocity was adjusted to 46,800, 120,000, and 240,000 mL / g cat / h; The heating rate was 10 °C / min, and the temperature was continuously increased from 200 °C to 600 °C. At each temperature increase of 50 °C, it was maintained for 30 min. At each temperature point, the CH4 concentration in the fixed-bed tail gas was detected twice using a gas chromatograph equipped with a flame ionization detector (FID).

[0037] (4) High-temperature stability test: The catalyst prepared in Example 1 was filled into a fixed-bed reactor with a filling amount of 0.20 g, and a mixed gas (methane volume concentration was 20,000 ppm, and the balance gas was air) was introduced. The mass space velocity was adjusted to 46,800 mL / g cat / h; The heating rate was 10 °C / min. First stage: The temperature was directly increased from 200 °C to 550 °C and maintained for 12 h; Second stage: The temperature was increased from 550 °C to 650 °C and maintained for 12 h; Third stage: The temperature was increased from 650 °C to 750 °C and maintained for 12 h; Second stage: The temperature was increased from 750 °C to 850 °C and maintained for 12 h. At each temperature point, the CH4 concentration in the fixed-bed tail gas was detected once every 30 min using a gas chromatograph equipped with a flame ionization detector (FID).

[0038] (5) Heating and cooling cycle stability test: The catalyst prepared in Example 1 was filled into a fixed-bed reactor with a filling amount of 0.20 g, and a mixed gas (methane volume concentration was 20,000 ppm, and the balance gas was air) was introduced. The mass space velocity was adjusted to 46,800 mL / g cat / h and 120,000 mL / g cat / h; The heating rate was 10 °C / min, and the temperature was continuously increased from 200 °C to 600 °C. At each temperature increase of 50 °C, it was maintained for 30 min. At each temperature point, the CH4 concentration in the fixed-bed tail gas was detected twice using a gas chromatograph equipped with a flame ionization detector (FID). After the temperature was increased to 600 °C, it was naturally cooled. The CH4 concentration was detected at each temperature decrease of 50 °C.

[0039] (6) Stability test: The catalyst prepared in Example 1 was filled into a fixed-bed reactor with a filling amount of 0.20 g, and a mixed gas (methane volume concentration was 20,000 ppm, and the balance gas was air) was introduced. The mass space velocity was adjusted to 46,800 mL / g cat / h; The heating rate was 10 °C / min, directly heated from 200 °C to 450 °C, and maintained for 100 h. At each temperature point, the CH4 concentration in the fixed-bed tail gas was detected every 30 min using a gas chromatograph equipped with a flame ionization detector (FID). Example

[0040] The preparation method thereof is as follows: Take reagents in an amount with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03, stir vigorously at room temperature until homogeneous, add 0.17 g of Al2O3 fiber carrier, then transfer the mixture to a high-pressure reaction kettle, maintain at 160 - 190 °C for 15 - 19 h, wash, filter, and dry in an oven, and then heat to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintain for 2 - 8 h to obtain a catalyst, denoted as 70%Co / Af-N-600.

[0041] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1. Example

[0042] The preparation method thereof is as follows: Take reagents in an amount with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03, stir vigorously at room temperature until homogeneous, add 0.26 g of Al2O3 fiber carrier, then transfer the mixture to a high-pressure reaction kettle, maintain at 160 - 190 °C for 15 - 19 h, wash, filter, and dry in an oven, and then heat to 800 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintain for 2 - 8 h to obtain a catalyst, denoted as 60%Co / Af-N-800.

[0043] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1. Example

[0044] The preparation method thereof is as follows: Take reagents in an amount with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03, stir vigorously at room temperature until homogeneous, add 0.26 g of Al2O3 fiber carrier, then transfer the mixture to a high-pressure reaction kettle, maintain at 160 - 190 °C for 15 - 19 h, wash, filter, and dry in an oven, and then heat to 900 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintain for 2 - 8 h to obtain a catalyst, denoted as 60%Co / Af-N-900.

[0045] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1.

[0046] The comparative examples of the present invention are described in detail below. The following nasal drop examples are illustrative and are only used to explain the present invention and should not be construed as limiting the present invention.

[0047] Comparative Example 1 Its preparation method is as follows: A solution with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03 was vigorously stirred evenly at room temperature. Then the mixture was transferred to a high-pressure reactor and maintained at 160 - 190 °C for 15 - 19 h. After washing, filtering, and drying in an oven, it was then heated to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintained for 2 - 8 h to obtain a catalyst, denoted as Co3O4.

[0048] The method for catalytic oxidation of methane is as follows: (1) The same as the method for catalytic oxidation of methane in Example 1 (1).

[0049] (2) Testing at different space velocities: The same as the method for catalytic oxidation of methane in Example 4 (3).

[0050] Comparative Example 2 Its preparation method is as follows: A solution with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03 was vigorously stirred evenly at room temperature. 0.26 g of commercial α-Al2O3 powder carrier was added. Then the mixture was transferred to a high-pressure reactor and maintained at 160 - 190 °C for 15 - 19 h. After washing, filtering, and drying in an oven, it was then heated to 600 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintained for 2 - 8 h to obtain a catalyst, denoted as 60%Co / α-Al2O3.

[0051] The method for catalytic oxidation of methane is: the same as the method for catalytic oxidation of methane in Example 1 (1).

[0052] Comparative Example 3 Its preparation method is as follows: A solution with a molar ratio of Co(NO3)2·6H2O, sodium carbonate, ethylene glycol, and ammonia of 1:0.3:0.12:0.03 was vigorously stirred evenly at room temperature. 0.26 g of commercial γ-Al2O3 powder carrier was added. Then the mixture was transferred to a high-pressure reactor and maintained at 160 - 190 °C for 15 - 19 h. After washing, filtering, and drying in an oven, it was then heated to 500 - 800 °C at a rate of 1 - 5 °C / min in an air atmosphere and maintained for 2 - 8 h to obtain a catalyst, denoted as 60%Co / γ-Al2O3.

[0053] The method for catalytic oxidation of methane is as follows: (1) The same catalytic oxidation method of methane as in Example 1.

[0054] (2) Tests at different space velocities: The same catalytic oxidation method of methane as in Example 4 (3).

[0055] Figure 1 The results show that the catalytic activity of complete oxidation of methane in Example 4 is the best. When the catalyst dosage is 0.20 g, the temperature required to catalyze 50% of methane is 370 °C, and the temperature required to catalyze 90% of methane is 425 °C; when the catalyst dosage is 0.33 g, the temperature required to catalyze 50% of methane is 340 °C, and the temperature required to catalyze 90% of methane is 390 °C.

[0056] Figure 2 The results show that at a mass space velocity lower than 120,00 mL / g cat / h, the catalytic activity of Example 4 remains almost unchanged. When the mass space velocity doubles to 240,000 mL / g cat / h, the T 10 、T 50 and T 90 decrease by 41, 32 and 65 °C respectively. Although there is a decrease, the decrease amplitude is not serious, and good catalytic performance for methane oxidation is still maintained. In contrast, Comparative Example 1 and Comparative Example 3 show a significant decrease in methane catalytic activity at higher space velocities. This indicates that Example 4 can maintain high catalytic activity in a wider space velocity range.

[0057] Figure 3 The results show that when the reaction starts at 550 °C and then gradually increases to 850 °C, after 48 h of stepwise temperature increase conditions, the catalyst in Example 1 still shows stable activity, and the conversion rate is always 100%, verifying the excellent temperature tolerance of the catalyst in Example 1.

[0058] Figure 4 and Figure 5 The results show the cycle cooling performance of Example 4 at low (46,800 mL / g cat / h) and high (120,000 mL / g cat / h) mass space velocities. In four heating and cooling cycles of repeated startup, the performance of the second heating and cooling cycle decreases slightly, but remains consistent in subsequent tests without significant degradation. This indicates that the catalyst in Example 4 can maintain good catalytic activity at high or low mass space velocities, providing ideas for the design of catalysts facing complex working conditions.

[0059] Figure 6 The results show that the methane conversion rate of Example 4 still remains at about 92 - 96% under a 100 - h continuous test, proving that the catalyst has excellent stability.

[0060] Perform XPS characterization on Example 4 and Comparative Examples 1 and 3: Figure 7 From the characterization results, it is analyzed that the adsorbed oxygen / lattice oxygen value of Example 4 is 1.23, the adsorbed oxygen / lattice oxygen value of Comparative Example 1 is 0.59, and the adsorbed oxygen / lattice oxygen value of Comparative Example 3 is 0.56. This further proves that the catalyst of Example 4 has more oxygen vacancies.

[0061] Co 3+ / Co 2+ The proportion order is: Example 4 > Comparative Example 1 > Comparative Example 3. Co 3+ As an active site, it may be easier to promote the cleavage of the C-H bond of methane. And Co 3+ / Co 2+ A high ratio means the presence of more Co 3+ There may be more active sites formed. At the same time, the presence of Co 2+ may participate in the electron transfer process to help regenerate Co 3+ and maintain the catalytic cycle.

[0062] Figure 8 The following is the catalyst particle size diagram of Example 4 and Comparative Examples 1 and 2 calculated by combining the XRD characterization results with the Scherrer formula. The diagram shows that the catalyst particle sizes of Example 4, Comparative Example 1, and Comparative Example 2 are 26.1 nm, 28.7 nm, and 36.0 nm respectively. The catalyst particle size of Example 4 is the smallest. Combining with the activity results trend, it shows that the smaller the particle size, the better the catalytic activity for methane oxidation.

[0063] The above content is a further detailed description of the present invention in combination with specific embodiments. It cannot be considered that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, simple modifications and substitutions made should be regarded as belonging to the protection scope of the present invention.

Claims

1. Application and preparation method of cobalt catalyst Co / Af supported on alumina fiber for methane catalytic oxidation, and its methane catalytic oxidation is characterized in that: (1) The dosage of Co / Af catalyst is 0.05 - 0.4 g; (2) The volume concentration of methane is 1,000 - 30,000 ppm; (3) The total flow rate is 10 - 200 mL / min, and the balance gas is air; (4) The mass space velocity is 1,500 mL / g cat / h - 240,000 mL / g cat / h; (5) Program temperature rise test, the reaction temperature is 200 - 1,000 °C.

2. The Co / Af catalyst according to claim 1 is a cobalt catalyst supported on alumina fibers, characterized in that: α-aluminum oxide fiber as the carrier, Co3O4 as the active component, rich in a relatively high concentration of Co 3+ , and having a relatively high surface oxygen and a high oxygen vacancy content.

3. The catalyst Co / Af according to claim 2, and its preparation method is: (1) Dissolve cobalt source and sodium carbonate in a mixed solution of ethylene glycol and ammonia water, and the molar ratio of cobalt source, sodium carbonate, ethylene glycol, and ammonia water is 1:0.3:0.12:0.03, and stir evenly at room temperature; (2) Put the required mass of alumina fiber into the mixed solution and stir evenly by ultrasonic; (3) Transfer the mixed solution to a hydrothermal synthesis kettle, keep it at a specific temperature for a period of time for hydrothermal crystallization, wash the precipitate after hydrothermal treatment, and dry it in an oven; (4) Calcinate the dried powder in an air atmosphere to obtain the cobalt catalyst Co / Af supported on alumina fiber.

4. The preparation method according to claim 3, wherein In step (1), the cobalt source is one or a mixture of Co(NO3)2·6H2O, Co(CH3COO)2·4H2O or CoCl2·6H2O.

5. The preparation method according to claim 3, characterized in that: In step (2), the mass ratio of the cobalt source to the alumina fiber is: 0.5:1, 0.6:1, 0.7:1 and 0.8:

1.

6. The preparation method according to claim 3, characterized in that: In step (3), the temperature is 160 - 190 °C, and the time is 15 - 19 h.

7. The preparation method according to claim 4, characterized in that: In step (5), the calcination temperature is 500 - 900 °C, the time is 2 - 8 h, and the heating rate is 1 - 5 °C / min.

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