A cobalt-modified hornesite catalyst, a preparation method and application thereof
The preparation of nanorod-shaped cobalt-modified manganese potassium ore catalysts by a one-step sol-gel method solves the problems of harsh reaction conditions and environmentally unfriendly preparation in the N2O decomposition process of existing technologies, and achieves efficient and low-cost catalytic decomposition effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANXI UNIV
- Filing Date
- 2024-02-05
- Publication Date
- 2026-05-19
AI Technical Summary
Existing transition metal oxide catalysts have problems in the catalytic decomposition of N2O, such as high reaction temperature, high pressure, long reaction time, easy change of crystal phase, and environmentally unfriendly preparation process. In particular, the catalytic activity is difficult to maintain under oxygen-containing and water vapor-containing conditions.
Cobalt-modified manganese potassium ore catalysts were prepared using a one-step sol-gel method at temperatures ranging from room temperature to 80 °C. Nanorod-shaped cobalt-modified manganese potassium ore catalysts were prepared by adding reducing organic acids and cobalt salts to potassium permanganate solution, thus avoiding the use of high-pressure reactors and strong acids.
The efficient catalytic decomposition of N2O was achieved under low temperature and oxygen- and water vapor-containing conditions, with significantly improved catalytic activity and enhanced resistance to impurity gases. The catalyst preparation is simple, environmentally friendly, and low-cost, making it suitable for industrial production.
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Figure CN118002141B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst and air pollution control technology, specifically relating to a cobalt-modified manganese potassium ore catalyst, its preparation method and application. Background Technology
[0002] Nitrous oxide (N2O), released in large quantities from industrial sources, is one of the six greenhouse gases defined in the Kyoto Protocol. Its global warming potential (GWP) is 310 times that of CO2 and 21 times that of CH4. N2O is also a major ozone layer depletor, with an atmospheric lifetime of up to 114 years, severely impacting the human environment. With rapid industrialization, particularly the significant increase in the production capacity of industries producing nitric acid and adipic acid, the concentration of N2O in the atmosphere has continued to rise, reaching unprecedented levels. Therefore, adopting appropriate technologies to effectively eliminate N2O emissions is of great significance and imperative. Direct catalytic decomposition technology, with its advantages of high catalytic efficiency and no secondary pollution, is considered one of the most economical and efficient N2O elimination technologies currently available.
[0003] To date, transition metal oxides have become a highly competitive class of catalysts for the direct catalytic decomposition of N2O due to their easily modulated composition and structure, unique redox properties, and excellent catalytic activity, coupled with advantages such as low cost and abundant resources. While spinel Co3O4, the most representative catalyst, exhibits excellent catalytic activity in the direct decomposition of N2O, both single Co3O4 and doped Co3O4 catalysts are prone to sintering during high-temperature calcination and use, leading to agglomeration of the active phase Co3O4 grains and a decrease in catalytic activity and stability. In particular, when the feed gas contains impurities such as O2, NO, and H2O, the catalytic activity is significantly inhibited, failing to meet the requirements for the catalytic removal of N2O from actual industrial exhaust gases.
[0004] Among transition metal oxides, besides cobalt-based oxides, manganese potassium oxide (K-OMS-2) also exhibits excellent catalytic performance in various reactions due to its wide availability, low cost, strong redox properties, abundant surface oxygen vacancies, active lattice oxygen, good hydrophobicity, and ease of ion modification.
[0005] The literature "The influence of silver on the properties of cryptomelane typemanganese oxides in N2O decomposition reaction, Catalysis Today, 2008, 137:397-402" describes the introduction of Ag into K-OMS-2 using both reflux and impregnation methods to prepare Ag-modified K-OMS-2 catalysts for N2O decomposition. Compared to pure K-OMS-2, Ag-modified K-OMS-2 has a relatively small, even negligible, effect on the catalytic decomposition performance of N2O. Both the reflux and impregnation methods produce Ag-modified K-OMS-2 with poor stability at high temperatures. Furthermore, the reflux method requires stringent reaction conditions, typically involving high reaction temperatures, long reaction times, and additional acetic acid consumption, while the impregnation method requires pre-preparation of the K-OMS-2 support, making the process relatively cumbersome.
[0006] The literature "Co doped K-OMS-2 nanofiber: A novel and efficient water-tolerant catalyst for CO oxidation, ChemCatChem, 2017, 9: 1163-1167" reports a Co-doped K-OMS-2 catalyst for the CO reaction. The preparation method involves first mixing aqueous solutions of potassium permanganate, manganese sulfate, and cobalt nitrate, then adding concentrated sulfuric acid dropwise while stirring vigorously until the solution pH reaches 3–4. After stirring for 2 hours at room temperature, the solution is transferred to an autoclave and reacted at 120 °C for 24 hours. Finally, the reactants are washed and dried to obtain the target catalyst. This preparation method requires the additional consumption of concentrated sulfuric acid, which is prone to corrosion, and the preparation process is not environmentally friendly.
[0007] Patent CN 111644181B discloses a cobalt-doped manganese potassium ore catalyst resistant to water poisoning for the catalytic oxidation of VOCs. The preparation method involves sequentially adding cobalt salt, sulfuric acid, or nitric acid to a potassium permanganate solution, mixing thoroughly, and then adding manganese salt. The resulting mixture is reacted under sealed conditions at 50–100 °C for 6–24 h, followed by repeated washing and drying to obtain the target product. This method found that when the molar ratio of cobalt ions to manganese ions in the manganese potassium ore support is higher than 0.25, the final product is sodium manganese ore. That is, a cobalt-doped manganese potassium ore catalyst with high activity and resistance to water poisoning is obtained when the molar ratio of cobalt ions to potassium permanganate is in the range of (0.05–0.25):1. However, the concentration of the potassium permanganate solution in this method is relatively low, only 0.1–0.5 mmol / L.
[0008] In summary, existing methods for preparing transition metal oxide catalysts suffer from problems such as high reaction temperatures, high pressures, long reaction times, and the ease with which crystal phases can alter and maintain high activity. They also involve the additional consumption of strong acids, which can cause corrosion, and the preparation process is not environmentally friendly. Therefore, developing a transition metal oxide catalyst with mild reaction conditions, high efficiency, and high catalytic activity for the catalytic decomposition of N₂O is of paramount importance. Summary of the Invention
[0009] The purpose of this invention is to provide a cobalt-modified manganese potassium ore catalyst, its preparation method, and its applications. The catalyst provided by this invention has a wide range of applications, especially in the efficient catalytic decomposition of N2O under low-temperature and oxygen- and water-vapor-containing conditions. Furthermore, the catalyst preparation method is simple, low-cost, highly operable, and easy to industrialize.
[0010] To achieve the above objectives, the present invention adopts the following technical solution:
[0011] A method for preparing a cobalt-modified manganese potassium ore catalyst includes the following steps:
[0012] Step 1: Add reducing organic acid and cobalt salt to potassium permanganate solution, stir, and a redox reaction occurs to obtain sol-gel reaction solution;
[0013] Step 2: Filter the sol-gel reaction solution, wash, dry, and calcine the precipitate to obtain the cobalt-modified manganese potassium ore catalyst.
[0014] Preferably, the reducing organic acid in step 1 is one or more of fumaric acid, maleic acid, citric acid, oxalic acid, ascorbic acid, and itaconic acid, and the cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and cobalt oxalate.
[0015] Preferably, the molar ratio of potassium permanganate to reducing organic acid in step 1 does not exceed 5:1; more preferably, the molar ratio of potassium permanganate to reducing organic acid is (3-5):1.
[0016] Preferably, the molar concentration of the potassium permanganate solution in step 1 is 0.02~0.1 mol / L; more preferably, the molar concentration of the potassium permanganate solution is 0.05~0.1 mol / L.
[0017] Preferably, the Co / Mn molar ratio of metal ions in step 1 is 0.25 to 0.5.
[0018] Preferably, the reaction temperature in step 1 is room temperature to 80 ℃, and the reaction time is 0.5 to 10 h.
[0019] Preferably, the drying temperature in step 2 is 100~120 ℃ and the drying time is 1~5 h.
[0020] Preferably, the roasting temperature in step 2 is 400~550 ℃ and the roasting time is 2~5 h.
[0021] A cobalt-modified manganese potassium ore catalyst prepared by the preparation method described above, wherein the catalyst has a nanorod structure of manganese potassium ore and the molar ratio of metal ions Co / Mn in the catalyst is 0.25 to 0.5.
[0022] Application of a cobalt-modified manganese potassium ore catalyst prepared by the method described above in the N2O catalytic decomposition reaction.
[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0024] (1) When the cobalt-modified manganese potassium ore catalyst of the present invention is used for the catalytic decomposition of N2O, the space velocity is 10000 h⁻¹. -1 At a reaction temperature of 420 °C, the conversion rate of N2O can reach 100%. Under the same conditions, its catalytic activity is much higher than that of the unmodified K-OMS-2 catalyst and can be compared with the classic Co3O4 catalyst.
[0025] (2) The catalyst of the present invention greatly improves the catalyst’s resistance to impurity gases by introducing a small amount of cobalt into hard manganese potassium ore, which to some extent solves the problem that metal oxide catalysts are difficult to apply in practice due to easy deactivation under water vapor conditions, and can provide support for the actual industrial promotion of N2O catalytic decomposition technology.
[0026] (3) The present invention employs a mild one-step sol-gel method to prepare Co-modified manganese potassium ore catalyst at a lower synthesis temperature and a shorter reaction time. The preparation process is simple, does not require a high-pressure reactor, additional preparation of a support, or the addition of strong acid, and is convenient to operate, has high reaction efficiency, low cost, and is environmentally friendly. Attached Figure Description
[0027] Figure 1 The XRD patterns of the catalysts prepared in this invention are shown below: (a) pure manganese potassium ore, (b) Co / Mn molar ratio of 0.25, and (c) Co / Mn molar ratio of 0.5.
[0028] Figure 2 TEM images of the catalysts prepared in this invention: (a) pure manganese potassium ore, (b) Co / Mn molar ratio of 0.25, (c) Co / Mn molar ratio of 0.3, (d) Co / Mn molar ratio of 0.5;
[0029] Figure 3 Figure 1 shows the test results of the catalytic decomposition performance of cobalt-modified manganese potassium ore and Co3O4 catalyst under anhydrous conditions;
[0030] Figure 4 Figure 1 shows the test results of the cobalt-modified manganese potassium ore catalyst for catalytic decomposition of N2O under four cycles of water vapor conditions.
[0031] Figure 5 The graph shows the test results of the Co3O4 catalyst in four cycles of catalytic decomposition of N2O under water vapor conditions. Detailed Implementation
[0032] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.
[0033] In the following examples, N2O conversion rate = (Amount of N2O in feed gas - Amount of N2O in tail gas) / Amount of N2O in feed gas × 100%. Example 1
[0034] Preparation of cobalt-modified manganese potassium ore catalysts
[0035] (1) Weigh out 3.16 g, 0.02 mol of potassium permanganate and dissolve it in 200 mL of distilled water. Stir in a 30 °C water bath for 20 min to obtain a potassium permanganate solution.
[0036] (2) Add solid fumaric acid (0.78 g, 0.0067 mol) and cobalt nitrate hexahydrate (1.45 g, 0.005 mol) to potassium permanganate solution, stir and react for 30 min at the same temperature, and then let stand at room temperature for 1 h.
[0037] (3) A black solid product was obtained by vacuum filtration, washed with 100 mL of distilled water, dried at 120 °C for 5 h, and calcined at 450 °C for 2 h to obtain a cobalt-modified manganese potassium ore catalyst. The Co / Mn molar ratio in the catalyst was 0.25.
[0038] Preparation of pure manganese potassium ore catalyst
[0039] (1) Weigh out 3.16 g, 0.02 mol of potassium permanganate and dissolve it in 200 mL of distilled water. Stir in a 30 ℃ water bath for 20 min to obtain potassium permanganate solution.
[0040] (2) Add solid fumaric acid (0.78 g, 0.0067 mol) to potassium permanganate solution, continue stirring the reaction for 30 min at the same temperature, and then let it stand at room temperature for 1 h.
[0041] (3) The black solid product was obtained by vacuum filtration, washed with 100 mL of distilled water, dried at 120 °C for 5 h, and calcined at 450 °C for 2 h to obtain pure manganese potassium ore catalyst. Example 2
[0042] In Example 1, cobalt nitrate hexahydrate (1.45 g, 0.005 mol) was replaced with cobalt nitrate hexahydrate (1.75 g, 0.006 mol), and the stirring reaction time was changed from 30 min to 1 h. A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.3. Example 3
[0043] In Example 1, cobalt nitrate hexahydrate (1.45 g, 0.005 mol) was replaced with cobalt nitrate hexahydrate (2.91 g, 0.01 mol), and the stirring reaction time was changed from 30 min to 1 h. A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.5. Example 4
[0044] In Example 1, solid fumaric acid (0.78 g, 0.0067 mol) was replaced with solid anhydrous citric acid (1.28 g, 0.0067 mol). A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.25. Example 5
[0045] In Example 1, solid fumaric acid (0.78 g, 0.0067 mol) was replaced with oxalic acid (0.60 g, 0.0067 mol). A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.25. Example 6
[0046] In Example 1, solid fumaric acid (0.78 g, 0.0067 mol) was replaced with ascorbic acid (1.18 g, 0.0067 mol). A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.25. Example 7
[0047] In Example 1, cobalt nitrate hexahydrate (1.45 g, 0.005 mol) was replaced with cobalt oxalate dihydrate (0.91 g, 0.005 mol). A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.25. Example 8
[0048] In Example 1, cobalt nitrate hexahydrate (1.45 g, 0.005 mol) was replaced with cobalt acetate tetrahydrate (1.25 g, 0.005 mol). A cobalt-modified manganese potassium ore catalyst was prepared using the same method, with a Co / Mn molar ratio of 0.25.
[0049] Comparative Example
[0050] The classic Co3O4 catalyst was prepared by precipitation method, specifically as follows:
[0051] Weigh 4.0500 g of cobalt nitrate hexahydrate and dissolve it in 30 mL of distilled water. Then, slowly add 1 mol L⁻¹ water dropwise while stirring magnetically. -1 Adjust the pH to 9 with Na₂CO₃ solution. Continue stirring for 1 h, allow to stand for 3 h, then filter and wash with distilled water until the filtrate is neutral. Dry the precipitate at 120 °C for 12 h, and finally heat in a muffle furnace at 2 °C for 1 min. -1 The classic Co3O4 catalyst was obtained by calcining at 450 °C for 3 h.
[0052] Structural characterization
[0053] The catalysts obtained in Examples 1 and 3 were characterized by XRD, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the catalysts of the present invention all retain the structure of manganese potassium ore.
[0054] The catalysts prepared in Examples 1-3 were characterized by TEM, and the results are as follows: Figure 2 As shown. By Figure 2 It is known that the catalyst of the present invention has a nanorod structure.
[0055] Catalytic activity evaluation
[0056] The catalysts prepared in Examples 1-4 and the comparative example were subjected to N2O catalytic decomposition reaction under the following conditions: catalyst loading of 300 mg, feed gas composition of 1000 ppm N2O / Ar, and space velocity of 10000 h⁻¹. -1 See reaction results. Figure 3 .Depend on Figure 3 It can be seen that the catalysts prepared in Examples 1, 2, and 4 exhibited catalytic activity comparable to that of the classical Co3O4 catalyst in the catalytic decomposition of N2O. The catalyst prepared in Example 1 achieved 100% N2O conversion at a reaction temperature of 420 °C. The catalyst prepared in Example 2 achieved 100% N2O conversion at a reaction temperature of 440 °C. The catalyst prepared in Example 4 achieved 100% N2O conversion at a reaction temperature of 440 °C. The catalyst prepared in Example 3 achieved 90% N2O conversion at a reaction temperature of 520 °C.
[0057] The catalytic activity of the catalysts prepared in Examples 5-8 was evaluated under the above-described catalytic activity evaluation conditions. The results are as follows: The catalyst prepared in Example 5 achieved a 100% N2O conversion rate at a reaction temperature of 440 °C. The catalyst prepared in Example 6 achieved a 100% N2O conversion rate at a reaction temperature of 400 °C. The catalyst prepared in Example 7 achieved a 100% N2O conversion rate at a reaction temperature of 440 °C. The catalyst prepared in Example 8 achieved a 100% N2O conversion rate at a reaction temperature of 420 °C.
[0058] Under the above-mentioned catalytic activity evaluation conditions, 3.3 vol.% H2O was introduced, and the catalysts prepared in Example 1 and the comparative example were tested for their N2O decomposition performance under four cycles of water vapor conditions. The test results are shown in [reference needed]. Figure 4 , Figure 5 .Depend on Figure 4 , Figure 5 It can be seen that, compared with the case where there is no water vapor in the feed gas, when using the catalyst of the present invention, the complete conversion temperature of N2O only decreases by 20 ℃ (420 ℃ vs 440 ℃), and its catalytic performance remains almost unchanged in 4 cycles; when using the Co3O4 catalyst, the Co3O4 catalyst undergoes different degrees of deactivation process, and the complete conversion temperature of N2O increases significantly with the increase of the number of reactions.
[0059] In summary, this invention employs a mild one-step sol-gel method to obtain a cobalt-modified manganese potassium ore catalyst with high catalytic activity and resistance to impurity gases at a relatively low synthesis temperature, wherein the molar ratio of Co / Mn ions in the catalyst is 0.25–0.5. This method does not alter the crystal structure and rod-like morphology of the manganese potassium ore, and the process is simple, requires no high-pressure reactor or additional support preparation, is convenient to operate, has high reaction efficiency, and low cost.
[0060] The above description is only for better explaining the embodiments of the present invention and is not intended to limit them. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention shall fall within the scope of the present invention.
Claims
1. An application of a cobalt-modified manganese potassium ore catalyst, characterized in that, In the application of N2O catalytic decomposition reaction, the catalyst has a manganese potassium ore nanorod structure, and the molar ratio of metal ions Co / Mn in the catalyst is 0.25 to 0.
5. The preparation method of the cobalt-modified manganese potash catalyst is as follows: Step 1: Add reducing organic acid and cobalt salt to potassium permanganate solution, stir, and a redox reaction occurs to obtain sol-gel reaction solution; Step 2: Filter the sol-gel reaction solution, wash, dry, and calcine the precipitate to obtain the cobalt-modified manganese potassium ore catalyst; The reducing organic acid in step 1 is one or more of fumaric acid, maleic acid, citric acid, oxalic acid, ascorbic acid, and itaconic acid. In step 1, the molar ratio of potassium permanganate to reducing organic acid does not exceed 5:
1.
2. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, In step 1, the cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and cobalt oxalate.
3. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, The molar concentration of the potassium permanganate solution in step 1 is 0.02~0.1 mol / L.
4. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, In step 1, the Co / Mn molar ratio of metal ions is 0.25 to 0.
5.
5. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, In step 1, the reaction temperature is room temperature to 80 ℃, and the reaction time is 0.5 to 10 h.
6. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, In step 2, the drying temperature is 100~120 ℃ and the drying time is 1~5 h.
7. The application of the cobalt-modified manganese potassium ore catalyst according to claim 1, characterized in that, In step 2, the roasting temperature is 400~550 ℃ and the roasting time is 2~5 h.