A yttrium trioxide modified cobalt-based porous material, a preparation method thereof and application thereof in catalyzing ammonia decomposition to produce hydrogen
By uniformly modifying the surface of ZIF-67(Co) with yttrium oxide, a cobalt-based porous material modified with yttrium oxide is formed, which solves the problem of easy deactivation of Co-based catalysts in ammonia decomposition reaction and achieves efficient and stable ammonia decomposition hydrogen production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUHAN UNIV OF TECH
- Filing Date
- 2023-12-26
- Publication Date
- 2026-06-05
Smart Images
Figure CN117816219B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology containing metals, metal oxides, or hydroxides, and specifically relates to a cobalt-based porous material modified with yttrium trioxide, its preparation method, and its application in catalytic ammonia decomposition for hydrogen production. Background Technology
[0002] Developing and utilizing green hydrogen energy with high energy density (143 MJ / kg) can effectively alleviate the energy crisis and environmental problems caused by the over-exploitation of fossil fuels. However, the difficulty in compressing hydrogen severely limits its widespread application due to storage and transportation issues. Considering that ammonia is easily liquefied at room temperature, has safe transportation, and possesses a high hydrogen content (17.6 wt%) and a large volumetric energy density (11.5 MJ / L), hydrogen production through ammonia decomposition is an efficient and feasible method to address the aforementioned challenges. However, ammonia decomposition is an endothermic reaction that requires high temperatures and consumes a large amount of energy. Studies have shown that adding a suitable catalyst can lower the activation energy of the reaction, thereby significantly reducing the energy consumption of the ammonia decomposition reaction. Among these, Ru-based catalysts are considered the best ammonia decomposition catalysts currently available, but their high price and scarcity hinder their commercial application. Therefore, it is essential to develop non-precious metal catalysts that are cost-effective and have excellent ammonia decomposition performance. Among numerous non-precious metal catalysts, Co-based catalysts have exhibited excellent ammonia decomposition activity and have great potential for achieving high economic efficiency in ammonia decomposition. However, the practical application of Co-based catalysts in ammonia decomposition is rarely mentioned, likely due to their tendency to deactivate at high temperatures and significant activity degradation at low temperatures. Therefore, developing a highly active and catalytically stable cobalt catalyst for hydrogen production from ammonia decomposition is of great significance. Summary of the Invention
[0003] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing a cobalt-based porous material modified with yttrium oxide, its preparation method and its application in catalytic ammonia decomposition for hydrogen production. The yttrium-modified cobalt-based porous material still has good catalytic ammonia decomposition activity at relatively low temperatures (around 550°C) and good catalytic stability.
[0004] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:
[0005] A cobalt-based porous material modified with yttrium oxide is provided, which is obtained by combining ZIF-67(Co) and yttrium oxide, wherein the yttrium oxide has a nanoscale size and is uniformly distributed on the surface of ZIF-67(Co).
[0006] According to the above scheme, the specific surface area of the yttrium trioxide-modified cobalt-based porous material is 140–270 m². 2 / g, the content of Co in the yttrium oxide-modified cobalt-based porous material is 28-31 wt%, and the content of Y2O3 is 2-8 wt%.
[0007] This invention also includes a method for preparing the above-mentioned yttrium trioxide-modified cobalt-based porous material, the specific steps of which are as follows:
[0008] 1) Preparation of ZIF-67(Co): 2-methylimidazole and cobalt salt were dissolved in water to obtain aqueous solutions containing 2-methylimidazole and Co salt respectively. Then, the aqueous solution containing 2-methylimidazole was slowly added to the aqueous solution containing Co salt under stirring. After stirring for 2 to 4 hours, a reaction solution containing ZIF-67(Co) was obtained.
[0009] 2) Preparation of Yttrium-modified cobalt-based porous materials: The reaction solution containing ZIF-67(Co) obtained in step 1) was mixed with yttrium salt and reacted under stirring. After the reaction was completed, the yttrium salt-doped ZIF-67(Co) was separated. Then, the obtained yttrium salt-doped ZIF-67(Co) was subjected to calcination and reduction reactions in sequence to obtain cobalt-based porous materials modified with yttrium oxide.
[0010] According to the above scheme, the cobalt salt in step 1) is one of cobalt nitrate hexahydrate, cobalt chloride, cobalt sulfate, and cobalt acetate tetrahydrate.
[0011] According to the above scheme, the molar ratio of cobalt salt to 2-methylimidazole in step 1) is 1:4 to 8.
[0012] According to the above scheme, the concentration of the aqueous solution containing 2-methylimidazole in step 1) is 0.2-0.4 mol / L.
[0013] According to the above scheme, in step 1), the concentration of the aqueous solution containing Co salt is 0.045–0.055 mol / L.
[0014] According to the above scheme, the yttrium salt in step 2) is one of yttrium nitrate hexahydrate, yttrium chloride, and yttrium sulfate, and the amount of yttrium salt is 0.1 to 1 times the amount of cobalt salt.
[0015] According to the above scheme, the reaction conditions for step 2) are: stirring at room temperature (15-35℃) for 2-4 hours.
[0016] According to the above scheme, the calcination process conditions in step 2) are as follows: under an inert atmosphere (Ar or N2), the temperature is increased from room temperature to 500–900°C at a rate of 1–5°C / min, and held for 1–6 hours. Calcination carbonizes the prepared ZIF-67(Co).
[0017] According to the above scheme, the reduction reaction conditions in step 2) are as follows: under an H2 / Ar mixed gas (where the H2 content is 3-8 vol%) or NH3 atmosphere, the temperature is increased from room temperature to 350-650℃ at a heating rate of 1-5℃ / min, and held at this temperature for 1-3 hours. The reduction reaction reduces Co to elemental form.
[0018] The present invention also provides an application of the above-mentioned yttrium trioxide-modified cobalt-based porous material in ammonia decomposition for hydrogen production.
[0019] The specific application method is as follows: Yttrium trioxide-modified cobalt-based porous material is placed in a fluidized bed reactor as a catalyst. Argon gas is purged for 30 minutes to remove impurities adhering to the catalyst. Then, the temperature is increased to 400–600°C at a rate of 5°C / min and held for 1 hour to activate the catalyst. After activation, pure ammonia gas is introduced at 400–600°C and a pure ammonia gas space velocity of 5000–40000 h⁻¹. -1 Catalytic decomposition of ammonia.
[0020] This invention provides a cobalt-based porous material modified with yttrium oxide (Y₂O₃). The coating effect of the CN (N-doped C) matrix generated by the pyrolysis of ZIF-67 significantly improves the dispersion of Co and increases the number of active sites for ammonia decomposition. Test results show that Y₂O₃ significantly increases the basicity of the catalyst surface through its electron-donating effect, increases the number of basic sites on the catalyst surface, and enhances the ability of N atoms to recombine and desorb from the catalyst surface, thereby improving the catalyst's ammonia decomposition activity at low temperatures. Simultaneously, Y₂O₃ can also anchor Co nanoparticles, inhibiting the sintering of Co nanoparticles during high-temperature reactions and improving the stability of the catalyst under high-temperature reaction conditions.
[0021] The beneficial effects of this invention are as follows: 1. The yttrium trioxide-modified cobalt-based porous material provided by this invention has a large specific surface area, many Co reactive sites, and high catalytic efficiency for ammonia decomposition, achieving high efficiency at 550℃ and a pure ammonia space velocity of 20000 h⁻¹. -1 The ammonia decomposition rate can reach up to 92.3%, and it exhibits good catalytic stability, showing promising application prospects in the field of catalytic ammonia decomposition for hydrogen production. 2. The preparation method of this invention is simple, low-cost, and easy to scale up for mass production. Attached Figure Description
[0022] Figure 1 This is a comparison chart of the ammonia decomposition activities of the samples prepared in Examples 1-4 and Comparative Example 1 of the present invention;
[0023] Figure 2 XRD patterns of samples prepared in Examples 1-4 and Comparative Example 1;
[0024] Figure 3N2-TPD diagrams of the samples prepared in Examples 1-4 and Comparative Example 1;
[0025] Figure 4 The figures show the catalytic stability test results of the samples prepared in Examples 1-4 and Comparative Example 1.
[0026] Figure 5 The BET curves are for the samples prepared in Examples 1-4 and Comparative Example 1. Detailed Implementation
[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.
[0028] Example 1
[0029] The specific steps of the preparation method of a yttrium trioxide-modified cobalt-based porous material are as follows:
[0030] Dissolve 1.455 g of cobalt nitrate hexahydrate and 1.92 g of 2-methylimidazole in 100 mL of deionized water to obtain aqueous solutions containing Co salt and 2-methylimidazole, respectively. Under stirring at room temperature, slowly add the 2-methylimidazole aqueous solution to the Co salt solution. After stirring for 2 hours, add 0.327 g of yttrium nitrate hexahydrate to the reaction solution and continue stirring at room temperature for another 2 hours. After stirring, transfer the reaction solution to centrifuge tubes and centrifuge and wash with deionized water (centrifugation speed 10000 r / min). Repeat 5 times. After centrifugation and washing, the obtained product was dried in a 60℃ oven for 24 hours. Then, the dried sample was calcined in a tube furnace under an argon atmosphere. The temperature was increased to 600℃ at a rate of 3℃ / min at room temperature and calcined for 2 hours. Finally, the sample was reduced under a pure ammonia atmosphere. The temperature was increased to 600℃ at a rate of 3℃ / min at room temperature and held for 2 hours to obtain a yttrium-modified cobalt-based porous material with a Co content of 30.8 wt% and a Y2O3 content of 2 wt%.
[0031] 0.1 g of the yttrium trioxide-modified cobalt-based porous material prepared in this embodiment was placed in a fluidized bed reactor as a catalyst. Argon gas was purged for 30 minutes to remove impurity gases adhering to the catalyst. The temperature was then increased to 550°C at a rate of 5°C / min and held for 1 hour to activate the catalyst. After activation, once the temperature had cooled to room temperature, pure ammonia gas (99.9999 vol%) was introduced, and the reactor was heated at 550°C with a pure ammonia gas hourly space velocity (HHSV) of 20000 h⁻¹. -1 The reaction was carried out for 1 hour to catalyze the decomposition of ammonia. The ammonia decomposition rate was measured to be 84.7%, and the ammonia was converted into nitrogen and hydrogen.
[0032] Example 2
[0033] A cobalt-based porous material modified with yttrium oxide is prepared in a manner similar to that in Example 1, except that the amount of yttrium nitrate hexahydrate added is 0.654 g.
[0034] Using the same method as in Example 1, the ammonia decomposition rate of the yttrium oxide-modified cobalt-based porous material prepared in this example was measured to be 86.7% at 550°C.
[0035] Example 3
[0036] A cobalt-based porous material modified with yttrium oxide is prepared in a manner similar to that in Example 1, except that the amount of yttrium nitrate hexahydrate added is 0.981 g.
[0037] Using the same method as in Example 1, the ammonia decomposition rate of the yttrium oxide-modified cobalt-based porous material prepared in this example was measured to be 92.3% at 550°C.
[0038] Example 4
[0039] A cobalt-based porous material modified with yttrium oxide is prepared in a manner similar to that in Example 1, except that the amount of yttrium nitrate hexahydrate added is 1.308 g.
[0040] Using the same method as in Example 1, the ammonia decomposition rate of the yttrium oxide-modified cobalt-based porous material prepared in this example was measured to be 83.3% at 550°C.
[0041] Comparative Example 1
[0042] A cobalt-based porous material is prepared in a manner similar to that of Example 1, except that yttrium nitrate hexahydrate is not added.
[0043] Take 0.1g of the samples prepared in Examples 1-4 and Comparative Example 1 and place them in quartz tubes respectively. Introduce 99.9999% high-purity ammonia gas at a flow rate of 20000 h⁻¹. -1 The ammonia decomposition rate of each catalyst sample was tested at different temperatures (400℃, 450℃, 500℃, 550℃, 600℃) for 1 h. The test results are shown in Table 1.
[0044] Table 1
[0045] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 400℃ 5.6％ 8.5％ 5.4％ 4.8％ 2.7％ 450℃ 19.0％ 23.7％ 20.4％ 17.3％ 9.0％ 500℃ 50.6％ 56.0％ 52.3％ 48.3％ 29.5％ 550℃ 84.7％ 92.3％ 86.7％ 83.3％ 72.3％ 600℃ 99.7％ 99.9％ 98.8％ 98.4％ 85.1％
[0046] The samples prepared in Examples 1-4 and Comparative Example 1, based on the data in Table 1, were tested at an ammonia space velocity of 20000 h⁻¹. -1 The comparison chart of ammonia decomposition activity under different temperatures (400℃, 450℃, 500℃, 550℃, 600℃) is shown below. Figure 1As shown, the ammonia decomposition performance of the catalysts in Examples 1-4 at different temperatures is significantly higher than that of the catalyst in Comparative Example 1, indicating that the modification of Y2O3 can significantly improve the ammonia decomposition activity of the cobalt catalyst.
[0047] Figure 2 The XRD patterns of the samples prepared in Examples 1-4 and Comparative Example 1 show the diffraction peaks of Co in all samples, while the diffraction peaks of Y2O3 are not present, indicating that Y2O3 is very uniformly dispersed and the particles are small (nanoscale).
[0048] The samples prepared in Examples 1-4 and Comparative Example 1 were subjected to N2 temperature-programmed adsorption-desorption (N2-TPD) experiments. The measured N2-TPD diagrams are shown below. Figure 3 As shown in the figure, the Y2O3-modified catalysts all exhibited a relatively obvious N2 desorption peak at high temperature, while the undoped Y2O3 catalysts did not show an N2 desorption peak. This indicates that the modification of Y2O3 significantly improved the N atom recombination and desorption ability of the catalysts, thereby improving the ammonia decomposition activity of the catalysts.
[0049] The catalytic stability of the samples prepared in Examples 1-4 and Comparative Example 1 was tested by subjecting them to a test at 550°C and an ammonia space velocity of 20000 h⁻¹. -1 The reaction was carried out under the conditions for 72 hours, and the comparison of ammonia decomposition rates is shown in the figure below. Figure 4 As shown in the figure, the catalysts prepared in Examples 1-4 all exhibited excellent stability during the 72-hour reaction. After the reaction, the ammonia decomposition activity of the catalysts did not decrease. However, the ammonia decomposition activity of the catalyst prepared in Comparative Example 1 decreased significantly during the 72-hour reaction, indicating that the modification of Y2O3 significantly improved the stability of the catalyst.
[0050] Figure 5 The figures show the BET curves of the samples prepared in Examples 1-4 and Comparative Example 1. It can be seen from the figures that all samples exhibit hysteresis loops at both low and high pressures in their BET curves, indicating a high specific surface area and mesoporous structure. The specific surface areas of Examples 1-4 and Comparative Example 1 are 213.4 m², respectively. 2 / g, 265.1m 2 / g, 237.1m 2 / g, 146.1m 2 / g and 126.1m 2 / g.
Claims
1. A cobalt-based porous material modified with yttrium trioxide, characterized in that, It is obtained by combining ZIF-67 (Co) and yttrium oxide, wherein the yttrium oxide has a nanoscale size and is uniformly distributed on the surface of ZIF-67 (Co), and the specific surface area of the cobalt-based porous material modified with yttrium oxide is 140~270 m². 2 / g, the content of Co in the yttrium oxide-modified cobalt-based porous material is 28~31wt%, and the content of Y2O3 is 2~8wt%; The specific steps of its preparation method are as follows: 1) Preparation of ZIF-67 (Co): 2-methylimidazole and cobalt salt were dissolved in water to obtain aqueous solutions containing 2-methylimidazole and Co salt respectively. Then, the aqueous solution containing 2-methylimidazole was slowly added to the aqueous solution containing Co salt under stirring. After stirring for 2-4 hours, a reaction solution containing ZIF-67 (Co) was obtained. 2) Preparation of cobalt-based porous materials modified with yttrium oxide: The reaction solution containing ZIF-67 (Co) obtained in step 1) is mixed with yttrium salt and reacted under stirring. After the reaction is completed, yttrium salt-doped ZIF-67 (Co) is separated. Then, the obtained yttrium salt-doped ZIF-67 (Co) is subjected to calcination and reduction reactions in sequence to obtain cobalt-based porous materials modified with yttrium oxide.
2. A method for preparing the yttrium trioxide-modified cobalt-based porous material according to claim 1, characterized in that, The specific steps are as follows: 1) Preparation of ZIF-67 (Co): 2-methylimidazole and cobalt salt were dissolved in water to obtain aqueous solutions containing 2-methylimidazole and Co salt respectively. Then, the aqueous solution containing 2-methylimidazole was slowly added to the aqueous solution containing Co salt under stirring. After stirring for 2-4 hours, a reaction solution containing ZIF-67 (Co) was obtained. 2) Preparation of cobalt-based porous materials modified with yttrium oxide: The reaction solution containing ZIF-67 (Co) obtained in step 1) is mixed with yttrium salt and reacted under stirring. After the reaction is completed, yttrium salt-doped ZIF-67 (Co) is separated. Then, the obtained yttrium salt-doped ZIF-67 (Co) is subjected to calcination and reduction reactions in sequence to obtain cobalt-based porous materials modified with yttrium oxide.
3. The method for preparing yttrium trioxide-modified cobalt-based porous materials according to claim 2, characterized in that, The cobalt salt in step 1) is one of cobalt nitrate hexahydrate, cobalt chloride, cobalt sulfate, and cobalt acetate tetrahydrate; the molar ratio of the cobalt salt to 2-methylimidazolium in step 1) is 1:4~8.
4. The method for preparing yttrium trioxide-modified cobalt-based porous materials according to claim 2, characterized in that, The concentration of the aqueous solution containing 2-methylimidazole in step 1) is 0.2~0.4 mol / L; the concentration of the aqueous solution containing Co salt in step 1) is 0.045~0.055 mol / L.
5. The method for preparing yttrium trioxide-modified cobalt-based porous materials according to claim 2, characterized in that, Step 2) The yttrium salt is one of yttrium nitrate hexahydrate, yttrium chloride, and yttrium sulfate. The amount of yttrium salt is 0.1 to 1 times the amount of cobalt salt. The reaction conditions for step 2) are: stirring at room temperature for 2 to 4 hours.
6. The method for preparing yttrium trioxide-modified cobalt-based porous materials according to claim 2, characterized in that, Step 2) The calcination process conditions are as follows: under an inert atmosphere, the temperature is increased from room temperature to 500-900℃ at a rate of 1-5℃ / min, and held for 1-6 hours.
7. The method for preparing yttrium trioxide-modified cobalt-based porous materials according to claim 2, characterized in that, Step 2) The reduction reaction conditions are as follows: under a H2 / Ar mixed gas or NH3 atmosphere, the temperature is increased from room temperature to 350~650℃ at a heating rate of 1~5℃ / min, and held for 1~3h.
8. The application of the yttrium trioxide-modified cobalt-based porous material according to claim 1 in ammonia decomposition for hydrogen production.
9. The application of the yttrium trioxide-modified cobalt-based porous material according to claim 8 in ammonia decomposition for hydrogen production, characterized in that, The specific application method is as follows: Yttrium trioxide-modified cobalt-based porous material is placed in a fluidized bed reactor as a catalyst. Argon gas is purged for 30 minutes to remove impurities adhering to the catalyst. Then, the temperature is increased to 400-600℃ at a rate of 5℃ / min, and held for 1 hour to activate the catalyst. After activation, pure ammonia gas is introduced at 400-600℃ and a pure ammonia gas space velocity of 5000-40000 h⁻¹. -1 Catalytic decomposition of ammonia.