Metallic cobalt-based catalysts, methods for their preparation and use
The cobalt-based catalyst prepared by a simple process solves the problems of complex preparation and pollution of cobalt-based catalysts, and realizes the preparation of highly active catalysts under mild conditions. It is suitable for ammonia synthesis reaction and has excellent catalytic performance and mechanical strength.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-12-24
- Publication Date
- 2026-06-26
AI Technical Summary
Existing cobalt-based catalysts are complex to prepare and have pollution problems, and their activity is insufficient under mild conditions, making it difficult to meet the requirements for efficient ammonia synthesis.
A simple process was used to prepare a cobalt-based catalyst without loading by reacting a solution of cobalt, barium, lead and/or silver sources with a precipitant. The particle size was controlled to be below 30 nm to ensure uniform mixing of the components and avoid premature precipitation. A reduction treatment was then performed to obtain a highly active catalyst.
The preparation of a highly active catalyst under mild conditions has been achieved. It exhibits excellent ammonia synthesis performance, is suitable for industrial production of conventional catalysts, and has high mechanical strength, making it suitable for ammonia synthesis reactions.
Smart Images
Figure CN122273530A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalysis technology, specifically relating to a cobalt-based metal catalyst, its preparation method, and its application in ammonia synthesis. Background Technology
[0002] Ammonia is one of the most important raw materials in modern industrial chemistry. Global ammonia production exceeds 140 million tons annually, with over 80% used in fertilizer production. Nitrogen activation is one of the most difficult reactions because the dissociation energy of the triple bond in the nitrogen molecule is as high as 945 kJ·mol⁻¹. -1 Moreover, it is the rate-determining step in the ammonia synthesis reaction. Currently, most ammonia is synthesized via the Haber-Bosch process, using hydrogen and nitrogen as feedstocks under high temperature (>400℃) and high pressure (>20MPa) conditions with an iron-based catalyst. However, the Haber-Bosch process is extremely energy-intensive, consuming approximately 2%–3% of the world's electricity supply. Furthermore, only 60% of the consumed energy is recovered and stored in the enthalpy of the ammonia molecule; the majority of the remaining energy is lost during hydrogen production, ammonia synthesis, and gas separation. In addition, the hydrogen used in the Haber-Bosch process is produced through steam reforming of coal or natural gas; therefore, this process emits a significant amount of carbon dioxide (1.9 tons of carbon dioxide per ton of ammonia), accounting for approximately 3% of global greenhouse gas emissions.
[0003] Recently, ammonia has received widespread attention as a candidate energy carrier for hydrogen production from renewable energy sources. Ammonia possesses a high energy density (12.8 GJ·m³). -3 Ammonia possesses high hydrogen storage capacity (17.6 wt%). At room temperature (20°C) and low pressure (0.8 MPa), ammonia is liquid, and its storage and transportation infrastructure is well-established. Furthermore, no carbon dioxide is released when ammonia is decomposed for hydrogen production or burned in turbines and internal combustion engines. Moreover, if ammonia could be produced from renewable energy sources such as solar, wind, and tidal power, this process could help alleviate global issues related to energy, global warming, and food production; however, renewable energy is widely distributed globally, with low energy concentration and fluctuating supply over time. Therefore, it is necessary to develop a process that uses highly active catalysts under mild conditions (≤400°C, ≤10 MPa) to synthesize ammonia, achieving a balance ammonia yield significantly higher than the 25% obtained by the Haber-Bosch process. Furthermore, for the catalysts to be practical, they should be easy to prepare and stable in air.
[0004] Currently, the main catalysts for ammonia synthesis under mild conditions are porous carbon-supported ruthenium catalysts, rare earth oxide-supported ruthenium catalysts, and non-precious metal catalysts.
[0005] Porous carbon-supported ruthenium catalysts and rare-earth oxide-supported ruthenium catalysts have limited applications due to the high cost of raw materials and the susceptibility of the active component, ruthenium, to hydrogen poisoning at high pressures. Non-precious metal catalysts, on the other hand, possess significant research value due to their inexpensive raw materials, diverse structural compositions, and reduced hydrogen poisoning observed in ruthenium-based catalysts. However, the preparation of highly active non-metallic catalysts remains a significant challenge.
[0006] Current research on cobalt-based nonmetallic catalysts includes studies on catalyst products such as BaO@Co-MgO. However, these studies still have many drawbacks. For example, although BaO@Co-MgO catalysts have high performance in catalyzing ammonia synthesis under mild conditions, the preparation process is not only complex, but also has the problem of serious volatilization of the toxic gas tetrahydrofuran. Moreover, it must rely on the rearrangement effect that occurs when MgO is reduced at abnormally high temperatures.
[0007] In summary, further research is needed on cobalt-based catalysts to obtain a method for preparing highly active cobalt-based catalysts through a simple process. Summary of the Invention
[0008] To address the issues of complex preparation methods and pollution associated with existing cobalt-based catalysts, this invention presents a method for preparing highly active cobalt-based catalysts using a simple process. Furthermore, the obtained cobalt-based catalyst does not require a support and achieves excellent catalytic activity solely through the interaction of simple active components.
[0009] The present invention specifically adopts the following technical solution:
[0010] A method for preparing a cobalt-based metal catalyst, comprising the following steps:
[0011] S1. Fully disperse the cobalt source, barium source, lead source and / or silver source in the dispersion medium to obtain a mixed solution;
[0012] S2. A precipitate is prepared by dissolving at least one of the following as a precipitant: an alkali metal carbonate, an alkali metal hydroxide, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, an organic amine salt, or ammonia in water.
[0013] S3. The mixed solution and the precipitate are mixed under stirring, and a solid intermediate material is obtained by precipitation. The solid intermediate material is washed, filtered, dried and heat-treated to obtain the catalyst precursor.
[0014] S4. The catalyst precursor is reduced to obtain a cobalt-based catalyst.
[0015] In step S1, the cobalt source is selected from cobalt salts and / or cobalt oxide, and the cobalt salt is at least one of hydrated cobalt nitrate, cobalt chloride, cobalt acetate, cobalt carbonate, and hydrated cobalt sulfate; the barium source is selected from at least one of barium salts, barium oxide, and barium hydroxide, and the barium salt is at least one of barium chloride, barium nitrate, barium carbonate, and barium sulfate; the lead source is selected from lead salts and / or lead oxide, and the lead salt is at least one of lead nitrate, lead acetate, lead chloride, lead sulfate, and lead carbonate; the silver source is selected from silver salts and / or silver oxide, and the silver salt is at least one of silver nitrate and silver sulfate.
[0016] Generally, when the mixed solution contains hydroxide or chloride ions, separate solutions containing the corresponding anions are prepared to prevent the hydroxide or chloride ions from precipitating prematurely with other cations (such as silver or cobalt).
[0017] For example, when silver nitrate and cobalt chloride or barium chloride are selected, a mixture containing chloride ions and silver ions is prepared separately to avoid premature precipitation of the silver source; similarly, when barium hydroxide is selected as the barium source, its solution is prepared separately and then mixed with the mixed solvent and precipitate in step S3 to avoid premature formation of cobalt hydroxide precipitate.
[0018] Furthermore, the molar ratio of barium in the barium source to cobalt in the cobalt source is (0.01–0.70):1, the molar ratio of lead in the lead source to cobalt in the cobalt source is (0.01–0.26):1, and the molar ratio of silver in the silver source to cobalt in the cobalt source is (0.008–0.54):1.
[0019] Generally, the dispersion medium can be any of the following: gas, water, or organic solvent.
[0020] Generally, in step S2, the total molar concentration of the precipitant in the precipitate is controlled to be 0.01 mol / L to 4 mol / L, preferably 0.5 mol / L to 2.5 mol / L.
[0021] In step S3, the ratio of the total amount of metal in the mixed solution to the amount of precipitant in the precipitate is 1:(2-10).
[0022] Generally, heat treatment can be performed using non-equilibrium plasma treatment or heating treatment. When using non-equilibrium plasma treatment, the frequency of the two-stage application is generally 2kHz to 6kHz, the input power is 5W to 10W, and the time is 30min to 60min; when using heating treatment, the temperature is generally controlled at 400℃ to 900℃, and the time is 1h to 24h.
[0023] Generally, low frequency and low power combined with a longer heating time, or high frequency and high input power combined with a shorter heating time, can achieve comparable results. Similarly, lower heating temperature combined with a longer heating time, or higher heating temperature combined with a shorter heating time, can also achieve comparable results. Both methods aim to treat cobalt and barium into oxide form.
[0024] In step S4, the reduction process involves placing the catalyst precursor under a reducing atmosphere, which is selected from at least one of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide, or a mixture of the above reducing gases with nitrogen and / or an inert gas.
[0025] Furthermore, the reduction treatment is carried out at a temperature of 400℃ to 900℃ for a time of 1 hour to 40 hours.
[0026] The preparation method of the above-mentioned cobalt-based catalyst provided by the present invention selects conventional cobalt-containing, barium-containing, lead-containing, and / or silver-containing inorganic materials as cobalt source, barium source, lead source, and silver source, respectively. By fully mixing and adding a precipitant under stirring conditions, the effective components are first fully and uniformly mixed, and the premature formation of precipitates is avoided, which would lead to the problem of large particle size and poor uniformity (prematurely formed precipitates will grow into large-sized particles). Furthermore, under the action of lead and / or silver, the particle size of the final obtained particles is basically controlled to be no more than 30 nm, thereby exhibiting a large specific surface area and obtaining superior catalytic performance. Preferably, the component of the cobalt, barium, lead, and / or silver source that can react with other cations to form precipitates (a solution with hydroxide or chloride ions as anions) is prepared separately. When mixing with the mixed solution of other components, the mixture is rapidly added before the precipitate is added. This ensures that the obtained particles precipitate out later as the particles formed earlier gradually grow, thus avoiding the problem of poor particle uniformity caused by the premature formation of precipitates from the cobalt, barium, lead, and / or silver sources in the mixed state compared to the precipitate added later. The above preparation method, in a simple way, rationally controls the size of each particle in the obtained catalyst, resulting in a catalyst with extremely high ammonia synthesis catalytic activity.
[0027] Another object of the present invention is to provide a cobalt-based catalyst, which is uniformly mixed in particulate form with 30% to 92% metallic cobalt, 3% to 48% barium oxide, and 5% to 40% metallic lead and / or 1% to 26% metallic silver, all of which are mass percentages.
[0028] Among them, the particle size of the above-mentioned granular metallic cobalt, barium oxide, metallic lead and / or metallic silver does not exceed 30 nm.
[0029] The cobalt-based catalyst provided by this invention, firstly, based on the fundamental components of metallic cobalt and barium oxide, with barium providing electrons to cobalt, weakens the nitrogen-nitrogen triple bond energy when applied to the ammoniation reaction. Secondly, by controlling the specific amounts of metallic cobalt, barium oxide, metallic lead, and / or metallic silver, and ensuring their uniform mixing in the form of extremely fine particles, the specific surface area of the effective catalytic components is greatly increased. Ultimately, this results in excellent catalytic performance, guaranteeing superior ammonia synthesis activity when applied to the ammoniation reaction. Furthermore, due to its unique structure consisting entirely of metal and metal oxide particles, the cobalt-based catalyst possesses high mechanical strength.
[0030] The preparation method provided by this invention is simple and easy to operate, uses inexpensive and environmentally friendly raw materials, and can be applied to conventional catalyst industrial production equipment. The catalyst prepared by this method is easy to shape, has high mechanical strength and high catalytic activity, and therefore has a very strong prospect for industrial application.
[0031] Another object of the present invention is to provide an application of the above-mentioned cobalt-based catalyst in ammonia synthesis reaction. Attached Figure Description
[0032] Figure 1 This is a TEM image of the cobalt-based catalyst according to Example 1 of the present invention;
[0033] Figure 2 This is a TEM image of the third comparative cobalt-based catalyst in Comparative Example 3 according to the present invention. Detailed Implementation
[0034] To better understand the present invention, the following detailed description, in conjunction with specific embodiments, further illustrates the technical solution of the present invention. The embodiments presented below are intended to more clearly and explicitly explain the technical problems to be solved and the beneficial effects of the present invention. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available; the quantitative experiments in the following embodiments are all repeated experiments, and the results are averaged.
[0035] Example 1
[0036] This embodiment provides a cobalt-based catalyst, which is prepared by the following method:
[0037] First, weigh 25g of cobalt nitrate hexahydrate and 1.138g of lead nitrate to prepare a 350mL mixed solution. Then, weigh 2.3g of barium hydroxide octahydrate to prepare a 100mL individual solution.
[0038] Then, weigh out 24g of sodium carbonate and prepare 450mL of precipitate solution.
[0039] Next, while stirring, the individual solution was quickly poured into the mixed solution (within about 3 seconds), and then the precipitate was added dropwise while stirring continuously for 1 hour. The resulting precipitate was repeatedly washed with distilled water until the supernatant was neutral. After filtration, the precipitate was dried at 100°C for 4 hours, ground, and then heated in air at 500°C for 3 hours to obtain the catalyst precursor.
[0040] Finally, the catalyst precursor was reduced at 700°C for 1 hour in a slightly positive pressure, continuously flowing pure hydrogen atmosphere to obtain metallic cobalt (reduced zero-valent Co). 0 The content of lead (reduced zero-valent Pb) was 73.1 wt%, the content of barium oxide was 16.1 wt%, and the content of lead (reduced zero-valent Pb) was 16.1 wt%. 0 The Co-BaO-Pb catalyst has a content of 10.8 wt%.
[0041] The cobalt-based catalyst obtained above was subjected to transmission electron microscopy (TEM) analysis, and its TEM image is shown below. Figure 1 As shown. From Figure 1 As can be seen, the Co-BaO-Pb catalyst exhibits uniformly dispersed granular form, with particle sizes not exceeding 30 nm. Furthermore, these particles are formed from a single component and are fully dispersed and mixed, without any microstructures such as mutual coating or loading between components. Therefore, in this Co-BaO-Pb catalyst, metallic Co, BaO, and metallic Pb are uniformly dispersed as extremely small particles with particle sizes not exceeding 30 nm.
[0042] Example 2
[0043] This embodiment provides a cobalt-based catalyst, which is prepared by the following method:
[0044] First, weigh 25g of cobalt nitrate hexahydrate and 0.59g of silver nitrate to prepare a 350mL mixed solution, then weigh 1.5g of barium chloride to prepare a 100mL separate solution.
[0045] Then, weigh out 24g of sodium carbonate and prepare 450mL of precipitate solution.
[0046] Next, while stirring, the individual solution was quickly poured into the mixed solution, and then the precipitate was added dropwise, and stirring was continued for 1 hour. The resulting precipitate was repeatedly washed with distilled water until the supernatant was neutral. After filtration, the precipitate was dried at 100°C for 4 hours, ground, and then heated in air at 500°C for 3 hours to obtain the catalyst precursor.
[0047] Finally, under a slightly positive pressure and continuously flowing pure hydrogen atmosphere, the catalyst precursor was reduced at 700°C for 20 h to obtain metallic cobalt (reduced zero-valent Co). 0 The content of ) is 77.2 wt%, the content of barium oxide is 17.0 wt%, and the content of silver (reduced state, zero valence Ag) is 17.0 wt%.0 The catalyst has a content of 5.8 wt% Co-BaO-Ag.
[0048] In this Co-BaO-Ag catalyst, metallic Co, BaO, and metallic Ag are uniformly dispersed in the form of extremely small particles with a particle size not exceeding 30 nm.
[0049] Example 3
[0050] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 1, except that: the amount of sodium carbonate is adjusted to 102.4 g; the catalyst precursor is reduced at 600 °C for 30 h in a slightly positive pressure, continuously flowing pure hydrogen atmosphere; the rest is as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 73.4 wt%, a barium oxide content of 16.1 wt%, and a lead content of 10.5 wt% is obtained.
[0051] Example 4
[0052] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 1, except that 24g of sodium carbonate is replaced with 368.4g of tetrapropylammonium hydroxide (25wt% solution); the catalyst precursor is reduced at 400°C for 40h in a slightly positive pressure, continuously flowing pure hydrogen atmosphere; the rest is as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 73.0wt%, a barium oxide content of 16.2wt%, and a lead content of 10.8wt% is obtained.
[0053] Example 5
[0054] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 1, except that 24g of sodium carbonate is replaced with a mixture of 12.68g of sodium bicarbonate, 11.932g of ammonium bicarbonate and 14.5g of ammonium carbonate; the rest is the same as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 72.7wt%, a barium oxide content of 16.8wt%, and a lead content of 10.5wt% is obtained.
[0055] Example 6
[0056] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 1, except that in the third step, the heat treatment method of the dried precipitate is adjusted to apply an AC voltage with a frequency of 5 kHz and an input power of 8 W to the two poles of the non-equilibrium plasma reactor for non-equilibrium plasma treatment for 30 min; the rest is as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 72.9 wt%, a barium oxide content of 16.0 wt%, and a lead content of 11.1 wt% is obtained.
[0057] Example 7
[0058] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 1, except that in the last step, the catalyst is reduced at 400°C for 12 hours in a slightly positive pressure, continuously flowing hydrogen-nitrogen mixed atmosphere (hydrogen gas fraction of 20%); the rest is as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 73.0 wt%, a barium oxide content of 16.3 wt%, and a lead content of 10.7 wt% is obtained.
[0059] Example 8
[0060] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the cobalt-based catalyst in Example 7, except that in the last step, the reduction at 400°C for 12 hours is changed to reduction at 900°C for 1 hour; the rest is the same as described in Example 7, and a Co-BaO-Pb catalyst with a cobalt content of 73.1 wt%, a barium oxide content of 16.1 wt%, and a lead content of 10.8 wt% is obtained.
[0061] Example 9
[0062] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 31.46 g, the amount of lead nitrate is adjusted to 0.53 g, and the amount of barium hydroxide octahydrate is adjusted to 0.43 g; the rest is the same as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 92.0 wt%, a barium oxide content of 3.0 wt%, and a lead content of 5.0 wt% is obtained.
[0063] Example 10
[0064] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 18.16 g, the amount of lead nitrate is adjusted to 1.98 g, and the amount of barium hydroxide octahydrate is adjusted to 4.01 g; the rest is the same as described in Example 1, and a Co-BaO-Pb catalyst with a cobalt content of 53.1 wt%, a barium oxide content of 28.1 wt%, and a lead content of 18.8 wt% is obtained.
[0065] Example 11
[0066] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 10.26 g, the amount of lead nitrate is adjusted to 2.32 g, and the amount of barium hydroxide octahydrate is adjusted to 6.86 g. A Co-BaO-Pb catalyst with a cobalt content of 30.0 wt%, a barium oxide content of 48.0 wt%, and a lead content of 22.0 wt% is obtained.
[0067] Example 12
[0068] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 15.05 g, the amount of lead nitrate is adjusted to 4.21 g, and the amount of barium hydroxide octahydrate is adjusted to 2.29 g. A Co-BaO-Pb catalyst with a cobalt content of 44.0 wt%, a barium oxide content of 16.0 wt%, and a lead content of 40.0 wt% is obtained.
[0069] Example 13
[0070] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 31.46 g, the amount of silver nitrate is adjusted to 0.51 g, and the amount of barium hydroxide octahydrate is adjusted to 0.43 g. A Co-BaO-Ag catalyst with a cobalt content of 92.0 wt%, a barium oxide content of 3.0 wt%, and a silver content of 5.0 wt% is obtained.
[0071] Example 14
[0072] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 17.82 g, the amount of silver nitrate is adjusted to 2.02 g, and the amount of barium hydroxide octahydrate is adjusted to 4.02 g. A Co-BaO-Ag catalyst with a cobalt content of 52.1 wt%, a barium oxide content of 28.1 wt%, and a silver content of 19.8 wt% is obtained.
[0073] Example 15
[0074] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 8.93 g, the amount of silver nitrate is adjusted to 2.64 g, and the amount of barium hydroxide octahydrate is adjusted to 6.84 g. A Co-BaO-Ag catalyst with a cobalt content of 26.1 wt%, a barium oxide content of 47.9 wt%, and a silver content of 26.0 wt% is obtained.
[0075] Example 16
[0076] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that of the catalyst in Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 27.73 g, the amount of silver nitrate is adjusted to 0.10 g, and the amount of barium hydroxide octahydrate is adjusted to 2.56 g. A Co-BaO-Ag catalyst with a cobalt content of 81.1 wt%, a barium oxide content of 17.9 wt%, and a silver content of 1.0 wt% is obtained.
[0077] To verify the necessity of each component and operation in the above-mentioned cobalt-based catalyst and its preparation method of the present invention, several comparative experiments were conducted.
[0078] Comparative Example 1
[0079] The comparative catalyst of this example is prepared in the same way as the cobalt-based catalyst of Example 1, except that the amount of cobalt nitrate hexahydrate is adjusted to 12.5g, the amount of barium hydroxide octahydrate is adjusted to 12.2g, and lead nitrate is not added; the rest is the same as described in Example 1, and the first comparative cobalt-based catalyst is prepared.
[0080] The first comparative cobalt-based catalyst is specifically a Co-BaO catalyst with a cobalt content of 30.0 wt% and a barium oxide content of 70.0 wt%.
[0081] Comparative Example 2
[0082] The comparative catalyst of this example is prepared in a manner that is basically the same as that of the cobalt-based catalyst in Example 1, except that the amount of barium hydroxide octahydrate is adjusted to 0.32 g and lead nitrate is not added; the rest is as described in Example 1, and the second comparative cobalt-based catalyst is prepared.
[0083] The second comparative cobalt-based catalyst is specifically a Co-BaO catalyst with a cobalt metal content of 97.0 wt% and a barium oxide content of 3 wt%.
[0084] Comparative Example 3
[0085] The comparative catalyst of this example is prepared in the same way as the cobalt-based catalyst of Example 1, except that lead nitrate is not added; otherwise, the preparation method is the same as described in Example 1, and the third comparative cobalt-based catalyst is obtained.
[0086] The third comparative cobalt-based catalyst is specifically a Co-BaO catalyst with a cobalt metal content of 81.9 wt% and a barium oxide content of 18.1 wt%.
[0087] The third comparative cobalt-based catalyst obtained above was subjected to transmission electron microscopy (TEM) analysis, and its TEM image is shown below. Figure 2 As shown. From Figure 2 As can be seen, compared with the Co-BaO-Pb catalyst in Example 1, this Co-BaO catalyst exhibits obvious particle stacking and extremely poor dispersibility; moreover, the particle size is also significantly larger, showing at least 30 nm or more, and generally in the range of 40 nm to 50 nm.
[0088] Comparative Example 4
[0089] The comparative catalyst of this example is prepared in the same way as the cobalt-based catalyst of Example 1, except that barium hydroxide is not added; otherwise, the preparation method is the same as described in Example 1, and a fourth comparative cobalt-based catalyst is obtained.
[0090] The fourth comparative cobalt-based catalyst is specifically a Co-Pb catalyst with a cobalt content of 87.6 wt% and a lead content of 12.4 wt%.
[0091] Comparative Example 5
[0092] The comparative catalyst of this example is prepared in the same way as the cobalt-based catalyst of Example 2, except that barium hydroxide is not added; otherwise, the fifth comparative cobalt-based catalyst is prepared as described in Example 2.
[0093] The fifth comparative cobalt-based catalyst is specifically a Co-Ag catalyst with a cobalt content of 93.1 wt% and a silver content of 6.9 wt%.
[0094] Comparative Example 6
[0095] The comparative catalyst in this example is prepared in a method that is basically the same as that of the cobalt-based catalyst in Example 1. The only difference is that the final reduction treatment was not performed, and the catalyst precursor obtained in the third step was used as the sixth comparative cobalt-based catalyst.
[0096] The sixth comparative cobalt-based catalyst is specifically a CoO-BaO-PbO catalyst with a cobalt oxide content of 77.0 wt%, a barium oxide content of 13.4%, and a lead oxide content of 9.6 wt%.
[0097] Comparative Example 7
[0098] The comparative catalyst of this example is prepared in a manner that is basically the same as that of the cobalt-based catalyst in Example 1, except that: in the first step, barium hydroxide solution is not prepared separately, but is dissolved together with cobalt nitrate and lead nitrate to form a 450 mL mixed solution; the rest is as shown in Example 1, and the seventh comparative cobalt-based catalyst is obtained.
[0099] The seventh comparative cobalt-based catalyst is specifically a CoO-BaO-Pb catalyst with a cobalt oxide content of 73.3 wt%, a barium oxide content of 15.8%, and a lead content of 10.9 wt%.
[0100] Comparative Example 8
[0101] The comparative catalyst of this example is prepared in a manner that is basically the same as that of the cobalt-based catalyst in Example 1, except that in the third step, 100 mL of barium hydroxide solution is added dropwise to a mixed solution of cobalt nitrate and lead nitrate under stirring (the whole process takes about 4 min to 5 min), and then the precipitate is added dropwise; the rest is as shown in Example 1, and the eighth comparative cobalt-based catalyst is obtained.
[0102] The eighth comparative cobalt-based catalyst is specifically a CoO-BaO-Pb catalyst with a cobalt oxide content of 73.0 wt%, a barium oxide content of 16.2%, and a lead content of 11.8 wt%.
[0103] The ammoniation rates of the cobalt-based catalysts provided in the above embodiments and comparative examples were tested to evaluate the ammoniation activity of each catalyst.
[0104] Take 0.20 g of each catalyst, with a mass hourly space velocity (WHSV) of 60000 mL·g. -1 ·h -1 The ammonia synthesis rate was determined on an ammonia synthesis catalyst performance evaluation device. The change in NH3 concentration in the outlet tail gas was determined by ion chromatography (Thermo Scientific, DIONEX, ICS-600). The reaction gas composition was 25 vol% N2 + 75 vol% H2, and the ammonia synthesis rate of the catalyst was determined under the conditions of 400℃ and 5 MPa.
[0105] The ammonia synthesis rates of the cobalt-based catalysts provided in each embodiment and comparative example are shown in Table 1 below.
[0106] Table 1. Ammonia synthesis rates of the cobalt-based catalysts provided in each embodiment and comparative example.
[0107]
[0108] As can be seen from the experimental results in Table 1 above, by comparing Examples 1 to 16, it can be seen that when the content of metallic Co in the Co-BaO-Pb catalyst is controlled in the range of 30% to 92%, the content of BaO is controlled in the range of 3% to 48%, the content of metallic Pb is controlled in the range of 5% to 40%, and / or the content of metallic silver is controlled in the range of 1% to 26%, the catalyst can achieve excellent catalytic activity.
[0109] Specifically, by comparing Example 1 and Example 2, it can be seen that, under the premise of similar content, both Pb and Ag exhibit excellent and similar active site modification effects, which are very beneficial to the catalyst's ammonia synthesis activity.
[0110] By comparing Examples 1 and 3-5, it can be seen that changing the type and amount of precipitant also affects the performance of the catalyst in ammonia synthesis. Appropriately reducing the amount of precipitant and preferably using sodium carbonate as the precipitant is beneficial for preparing high-performance ammonia synthesis catalysts.
[0111] By comparing Examples 1 and 6, it can be seen that plasma treatment is more conducive to the preparation of high-performance catalysts than traditional air roasting heat treatment.
[0112] By comparing Examples 1, 7, and 8, it can be seen that for the final reduction process, a higher processing temperature is more effective in improving catalyst performance than a lower processing temperature.
[0113] By comparing Example 1 and Comparative Examples 1-3, it can be seen that the addition of Pb can modify the cobalt active sites, thereby significantly improving the ammonia synthesis activity of the catalyst. Without the modification effect of Pb, even adjusting the content of metallic cobalt or barium oxide to extremely high levels cannot compensate for the decrease in ammonia synthesis activity caused by Pb modification. Meanwhile, by comparing Example 2 and Comparative Example 3, it can be seen that the addition of Ag can also modify the cobalt active sites. When the BaO content remains similar, even replacing Ag with a comparable amount of metallic Co, which plays a major active role, still results in a significant deterioration in the ammonia synthesis activity.
[0114] By comparing Example 1 and Comparative Example 4, and Comparative Example 2 and Comparative Example 5, it can be seen that the introduction of barium has a more significant effect on the catalyst’s performance in catalytic ammonia synthesis than the effects of Pb and Ag. Even when BaO is replaced with an equivalent amount of Co, which plays a major active role, while keeping the contents of Pb and Ag similar, there is still a significant deterioration in the ammonia synthesis activity.
[0115] By comparing Example 1 and Comparative Example 6, it can be seen that the reduction treatment after heat treatment, which reduces the generated CoO to metallic cobalt, is very important for the activity of the ammonia synthesis catalytic reaction. The extremely low ammonia synthesis rate maintained in Comparative Example 6 may be due to the partial generation of metallic cobalt in situ during the catalytic reaction of hydrogen and nitrogen mixed gas.
[0116] By comparing Examples 1, 7, and 8, it can be seen that when mixing metal solutions, preparing solutions that would generate precipitates separately and mixing them rapidly during the mixing process is beneficial for preparing highly active catalysts, as it avoids the premature formation of too much precipitate before the addition of the precipitate solution. This may be because, during the mixing of the catalyst components, maximizing the mixing of each component in solution or small particle state helps to fully increase the contact area or degree of mixing between the fine precipitates of each component, thereby ensuring the final product with extremely small particles, which is conducive to improving catalytic activity.
[0117] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art to which this invention pertains can make various modifications and refinements without departing from the spirit and scope of the invention.
Claims
1. A method for preparing a cobalt-based metal catalyst, characterized in that, Includes the following steps: S1. A mixed solution is obtained by fully dispersing a cobalt source, a barium source, and a lead source and / or a silver source in a dispersion medium; wherein the molar ratio of barium in the barium source to cobalt in the cobalt source is 0.01:1 to 0.70:1, the molar ratio of lead in the lead source to cobalt in the cobalt source is 0.01:1 to 0.26:1, and the molar ratio of silver in the silver source to cobalt in the cobalt source is 0.01:1 to 0.54:
1. S2. A precipitate is prepared by dissolving at least one of the following as a precipitant: an alkali metal carbonate, an alkali metal hydroxide, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, an organic amine salt, or ammonia in water. S3. The mixed solution and the precipitate are mixed under stirring to obtain a solid intermediate material by precipitation. The solid intermediate material is washed, filtered, dried and heat-treated to obtain a catalyst precursor containing cobalt oxide and barium oxide. S4. The catalyst precursor is reduced to obtain the cobalt-based catalyst.
2. The preparation method according to claim 1, characterized in that, In step S1, the cobalt source is selected from cobalt salts and / or cobalt oxide; the barium source is selected from at least one of barium salts, barium oxide, and barium hydroxide; the lead source is selected from lead salts and / or lead oxide; and the silver source is selected from silver salts and / or silver oxide.
3. The preparation method according to claim 2, characterized in that, In step S1, the cobalt salt is at least one of hydrated cobalt nitrate, cobalt chloride, cobalt acetate, cobalt carbonate, and hydrated cobalt sulfate; the barium salt is at least one of barium chloride, barium nitrate, barium carbonate, and barium sulfate; the lead salt is at least one of lead nitrate, lead acetate, lead chloride, lead sulfate, and lead carbonate; and the silver salt is at least one of silver nitrate and silver sulfate.
4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S3, the ratio of the total amount of metal ions in the mixed solution to the amount of precipitant in the precipitate is 1:2 to 1:
10.
5. The preparation method according to claim 4, characterized in that, In step S3, the heat treatment is either non-equilibrium plasma treatment or heating treatment.
6. The preparation method according to claim 5, characterized in that, In step S3, when non-equilibrium plasma treatment is used, the frequency applied to the two electrodes is 2kHz to 6kHz, the input power is 5W to 10W, and the time is 30min to 60min; when heat treatment is used, the temperature is 400℃ to 900℃, and the time is 1h to 24h.
7. The preparation method according to any one of claims 1 to 3, characterized in that, In step S4, the reduction treatment is carried out by placing the catalyst precursor under a reducing atmosphere, which is selected from at least one reducing gas selected from hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide, or a mixture of the reducing gas and nitrogen and / or an inert gas; and / or, the temperature of the reduction treatment is 400℃~900℃, and the time is 1h~40h.
8. A cobalt-based catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It is a uniformly mixed granular form of 30%–92% metallic cobalt, 3%–48% barium oxide, 5%–40% metallic lead and / or 1%–26% metallic silver, all of which are mass percentages; wherein the particle size does not exceed 30 nm.
9. The application of the cobalt-based catalyst as described in claim 8 in the ammoniation reaction.