Preparation method of nickel-based catalyst and application thereof in hydrogen production by ammonia decomposition

Abstract

This invention provides a method for preparing a nickel-based catalyst and its application in ammonia decomposition for hydrogen production, wherein the nickel-based catalyst is Ni / CeO. x The catalytic system is an atomically dispersed Ni-O-Ce structure. The preparation steps are as follows: Nickel and Ce precursors are dispersed in ultrapure water and stirred to dissolve, yielding a nickel-cerium mixed salt solution A; sodium hydroxide and sodium carbonate are dissolved in ultrapure water and stirred to dissolve, forming a mixed alkaline solution B; after heating deionized water, solutions A and B are simultaneously added using a dropping funnel, followed by crystallization, precipitation, drying, and grinding to obtain the precursor; S4: The precursor is reduced under hydrogen to obtain the Ni / CeO catalyst constructed in this invention. x The catalytic system can be activated in 10 mL of ammonia per minute. ‑1 At a flow rate of 500℃, ammonia can be almost completely converted into hydrogen. At 550℃, the conversion rate has exceeded the equilibrium conversion rate. Even if the flow rate is increased by 3 times, the performance does not decrease and complete conversion is achieved. The hydrogen production rate can be increased without increasing the temperature, thus achieving efficient hydrogen production at low temperatures.

Description

Technical Field

[0001] This invention relates to the fields of catalyst preparation and heterogeneous catalysis, and more specifically, to a method for preparing a nickel-based catalyst and its application in ammonia decomposition for hydrogen production. Background Technology

[0002] With continuous societal progress, the hydrogen economy is booming. However, hydrogen gas is bulky and difficult to liquefy, making its storage and transportation a major challenge. (Ammonia decomposition reaction...) ΔH=91.2kJ mol -1 The release of hydrogen and nitrogen gases is environmentally friendly and pollution-free. Ammonia provides a clean molecular storage medium for hydrogen, making this reaction a research hotspot in recent years. However, the large-scale application of ammonia as a hydrogen carrier faces several bottlenecks. First, there is the issue of ammonia decomposition temperature. Ammonia decomposition is an endothermic reaction, requiring high temperatures for complete conversion, and because it is endothermic, a large energy input is needed to maintain the reaction conditions. Second, the toxicity of ammonia is a fundamental safety concern during operation. Therefore, it can be seen that the key strategy for large-scale utilization of NH3 as a hydrogen carrier is to design and construct highly efficient NH3 decomposition catalysts to reduce reaction temperature, lower energy costs, and improve process safety.

[0003] In recent years, a large number of research efforts have emerged to address this scientific problem, and numerous catalytic systems have been designed, such as Ru / MgO, Ru / CNTs, Ru / CeO2, Fe / MgO, Co / NC-600, and CuZn / Al2O3. Although Ru-based catalysts exhibit superior catalytic activity for ammonia decomposition, the high cost of their preparation is due to Ru's status as a precious metal and its limited reserves. Other non-precious metal catalysts show lower activity for ammonia decomposition and require higher temperatures, which hinders their industrial application. Nickel-based catalytic systems, due to their excellent catalytic performance for ammonia decomposition, have become a potentially powerful alternative to Ru-based catalysts. Therefore, an increasing number of researchers are turning their attention to Ni-based catalysts.

[0004] Nickel-based catalytic systems have been applied to the study of ammonia decomposition reaction, such as Ni / ZrO2, Ni / MgO, Ni / CeO2, Ni / CaNH, Ni / SiO2 and Ni / Al2O3. However, some problems still exist in many studies. For example, (1) the preparation process of some catalysts is relatively complicated and time-consuming, and the catalysts are not easy to prepare in large quantities, which is not conducive to industrial production; (2) nickel nanoparticles are prone to agglomeration during the reaction, which greatly affects the activity and stability of the catalyst; (3) the catalytic activity of nickel-based catalytic systems for ammonia decomposition is generally low at low temperatures (<450℃).

[0005] Patent CN112337494B, in its specification, explicitly discloses a Ni / CeO2 ammonia decomposition hydrogen production catalyst in Comparative Example 1. The disclosed Ni / BN-CeO2 catalyst achieves an ammonia conversion rate of over 99.5% and a hydrogen production rate of 33.4 mmol / (gcat·min). However, this nickel-based catalytic system requires ammonia decomposition to hydrogen production in an NH3 atmosphere at 500–750°C. Patent CN117065765A discloses an ammonia decomposition hydrogen production catalyst, its preparation method, and its application. The Ni / BN-CeO2 ammonia decomposition hydrogen production catalyst prepared in Example 1 achieves a conversion efficiency of 99.6%, but requires ammonia decomposition to hydrogen production in an NH3 atmosphere at 650°C. CN115646500B provides an ammonia decomposition hydrogen production catalyst. Example 3 explicitly describes the preparation of a catalyst containing nickel and cerium, pre-reduced at 700°C for 1 h in a 50% H2 / N2 atmosphere (120 mL / min). After reduction, the reaction temperature was lowered to 550℃ under a 50% H2 / N2 atmosphere. After the temperature was lowered to 550℃, the reaction was switched to NH3 (molar ratio 1:1, GHSV = 6000 mL / g). cat •h) to carry out ammonia decomposition reaction. Journal article (Nano Research, Volume 11, pages 4412–4422, (2018)) discloses a simple synthesis of graphene-supported Ni-CeOx nanocomposite material as a highly efficient catalyst for the hydrolysis and dehydrogenation of borane. A nickel nanocatalyst (Ni-CeOx / graphene) doped with CeOx and supported on graphene was synthesized through a simple chemical reduction route and used as a strong catalyst for the hydrolysis of AB in aqueous solution at room temperature. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention innovatively employs a simple and efficient synthesis method to prepare an atomically dispersed catalyst. This catalyst can achieve complete ammonia decomposition under low-temperature conditions (<500℃), exhibiting excellent catalytic performance in the ammonia decomposition to hydrogen production reaction.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] On one hand, the present invention provides a nickel-based catalyst, wherein the nickel-based catalyst is Ni / CeO x The catalytic system (represented in this application as Ni / CeO) x (H450)), where 1≤x<2.

[0009] Furthermore, the catalytic system constructs an atomically dispersed Ni-O-Ce structure.

[0010] On the other hand, the present invention provides a method for preparing a nickel-based catalyst, the specific steps of which are as follows:

[0011] S1: Disperse the nickel precursor and Ce precursor in ultrapure water and stir to dissolve to obtain nickel-cerium mixed salt solution A;

[0012] S2: Dissolve sodium hydroxide and sodium carbonate in ultrapure water and stir to form a mixed alkaline solution B;

[0013] S3: After heating deionized water, solutions A and B are added simultaneously using a dropping funnel. After stirring, the solution crystallizes, and after centrifugation to wash the precipitate, it is dried and ground into powder to obtain the catalyst precursor.

[0014] S4: The precursor of the catalyst is reduced under a hydrogen atmosphere to obtain a nickel-based catalyst.

[0015] Furthermore, the nickel precursor is selected from soluble nickel salts such as nickel nitrate hexahydrate (Ni(NO3)2·6H2O), nickel chloride hexahydrate (NiCl2·6H2O), and nickel sulfate hexahydrate (NiSO4·6H2O).

[0016] Furthermore, the cerium precursor is selected from soluble cerium salts such as cerium nitrate hexahydrate (Ce(NO3)3·6H2O), cerium sulfate tetrahydrate (Ce(SO4)4·4H2O), and cerium ammonium nitrate ((NH4)2Ce(NO3)6).

[0017] Furthermore, the molar ratio of nickel to cerium in the nickel precursor and Ce precursor is 0.5–4. Changing the molar ratio of nickel to cerium in the nickel precursor and Ce precursor affects the number of Ni-Ce interfaces. Too low a molar ratio results in too few interfaces, weakening the electronic regulation of Ni and reducing the improvement in activity. Moreover, as an active metal, too low a Ni loading leads to poor activity. Conversely, if the molar ratio of nickel to cerium in the nickel precursor and Ce precursor is too high, the Ni content is too high and the Ce content is too low, weakening the interaction between Ni and Ce. This results in excessively large Ni particles during the reaction, making them prone to agglomeration and compromising stability, hindering long-term stable operation.

[0018] Furthermore, in S1 and S2, the amount of ultrapure water used is 50-100 mL. The appropriate amount of ultrapure water is to ensure a certain ion concentration in the solution, enabling the formation of a uniform catalyst precursor. If too little water is used, the ion concentration will be too high, resulting in too rapid sedimentation and excessively large crystal particle size. If too much ultrapure water is used, the subsequent filtration and washing process will become overly complicated.

[0019] Furthermore, the molar amount of sodium hydroxide is 0.5 to 3 times the sum of the molar amounts of the nickel precursor and the Ce precursor. The molar amount of sodium hydroxide is used to ensure that the pH of the solution is within a suitable range, ensuring that the ions in the solution can precipitate and crystallize, without using excessive amounts of sodium hydroxide which would increase the cost of catalyst preparation.

[0020] Further, the molar amount of sodium carbonate is 1 to 4 times the sum of the molar amounts of the nickel precursor and the Ce precursor. Preferably, the sodium carbonate is anhydrous sodium carbonate. The molar amount of sodium carbonate is to ensure atomic-level dispersion between Ni and Ce. The catalyst preparation method is based on the preparation method of hydrotalcite, and the process involves CO3. 2- It will enter the intercalation to balance the charge.

[0021] Further, the crystallization temperature is 60–120°C, preferably 70–100°C. Further, the crystallization time is 1–6 hours, preferably 3 hours. Excessively high crystallization temperatures lead to larger grains, while excessively low temperatures make grain reconstruction difficult, preventing the formation of uniform grains. Longer crystallization times result in more uniform grains, but crystallization times exceeding the preferred duration of this application make catalyst preparation too time-consuming, while shorter crystallization times make it difficult to complete the crystallization process.

[0022] Furthermore, in S3, the deionized water needs to be heated to 70-100°C, preferably 80°C.

[0023] Furthermore, in step S3, solutions A and B are added simultaneously using a dropping funnel, and the mixture is stirred at 80°C for 2 hours until homogeneous. Afterward, crystallization is maintained at 80°C. Adding solutions A and B dropwise is to control the rapid increase in ion concentration and thus the sedimentation rate. Directly mixing solutions A and B and then heating would result in uneven sedimentation. Stirring is necessary during catalyst preparation to ensure a uniform distribution of ions in the solution.

[0024] Furthermore, the reduction temperature is 400–600°C, preferably 450°C, and the time is 1–4 hours, preferably 2 hours. The reduction time can be determined according to the amount of catalyst loaded. If the reduction time is too short, the catalyst cannot be completely reduced; if the reduction temperature is too low, the activity of the nickel-based catalyst will be weakened; if the reduction time is too long, the particle size of Ni will increase, and the pretreatment process will be too long.

[0025] On the other hand, the present invention provides an application of the nickel-based catalyst described herein in the field of ammonia decomposition for hydrogen production.

[0026] Beneficial effects:

[0027] This invention constructs Ni / CeO x In the catalytic system, the value of X ranges from 1 to 2. During catalyst preparation, a large number of Ni-O-Ce interfaces are constructed, and during reduction, a large amount of oxygen is removed, forming oxygen vacancies (such as...). Figure 2 As shown). Based on Ni / CeO x The atomic-level dispersion characteristic of the catalytic system, Ni and CeO xThe metals are in close contact, forming a strong metal-support interaction. This is achieved by constructing an atomically dispersed Ni-O-Ce structure to enhance the interaction between the metal supports. During the reduction process, a large amount of Ni-O is formed. V The -Ce structure regulates the electronic state of Ni, thereby inhibiting the aggregation of nickel nanoparticles and improving their catalytic activity at low temperatures. This enhances the stability and cyclicity of the catalytic system and has certain industrialization potential.

[0028] Traditional Ni-based catalysts (such as many catalysts mentioned in the background section) require 650–700 °C to achieve complete conversion. The Ni / CeO catalyst constructed in this invention… x The catalytic system can achieve complete conversion at 550℃ and maintain stable operation. After 5 cycles, the performance did not decline.

[0029] The Ni / CeO constructed in this invention x The catalytic system can be activated in 10 mL of ammonia gas per minute. -1 At a flow rate of [value missing], ammonia gas can be almost completely converted into hydrogen gas at 500℃. The conversion rate exceeds the equilibrium conversion rate at 550℃. Even with a three-fold increase in flow rate, performance remains unchanged, achieving complete conversion. This allows for increased hydrogen production rate without raising the temperature, enabling efficient hydrogen production at low temperatures. Compared to traditional Ni-based catalysts, the temperature for complete conversion is reduced by over 100℃, significantly lowering the material requirements for hydrogen production equipment. Furthermore, the lower temperature leads to a substantial reduction in energy consumption, contributing to energy conservation. Additionally, the catalyst preparation method is simple, easily repeatable, and inexpensive, facilitating industrialization. Attached Figure Description

[0030] Figure 1 For the catalyst sample Ni / CeO x Activity evaluation of (H450) and control samples Ni / CeO2-IM and Ni / Al2O3

[0031] Figure 2 For the catalyst sample Ni / CeO x (H450) Magnified Test Image

[0032] Figure 3 For the catalyst sample Ni / CeO x (H450) Cyclicity evaluation curve

[0033] Figure 4 For the catalyst sample Ni / CeO x Stability evaluation of (H450)

[0034] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Detailed Implementation

[0035] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0036] Example 1 Ni / CeO x Preparation of (H450)

[0037] (1) Add 0.1 mol of nickel precursor Ni(NO3)2·6H2O and 0.05 mol of Ce precursor Ce(NO3)3·6H2O to 50 mL of ultrapure water and stir for 20 min to form a homogeneous nickel-cerium mixed salt solution A.

[0038] (2) Add 0.3 mol of Na2CO3 and NaOH to 50 mL of ultrapure water and stir for 20 min to form a homogeneous mixed alkaline solution B;

[0039] (3) Add 10 mL of deionized water to a beaker and heat to 80 °C. Then, add solutions A and B to the beaker simultaneously using a dropping funnel and stir at 80 °C for 2 hours.

[0040] (4) Then stop stirring, crystallize at 80°C for 3 hours, wash the precipitate with deionized water by centrifugation, and wash by centrifugation several times until the supernatant is neutral, and then dry at 90°C for 12 hours; after it is fully dried, grind it into powder to obtain the catalyst precursor.

[0041] (5) The precursor was reduced at 450°C in a hydrogen atmosphere for 2 hours at a heating rate of 5°C / min to obtain the catalyst system of the present invention, represented as: Ni / CeO x (H450).

[0042] Example 2

[0043] The difference from Example 1 is that the nickel precursor is replaced with NiCl2·6H2O, the molar ratio of nickel to cerium precursor is 0.5, the amount of ultrapure water is 100 mL, and the amount of anhydrous sodium carbonate is 4 times the sum of the molar amounts of nickel and cerium precursors; the crystallization temperature is 100℃, the crystallization time is 6 h, and the hydrogen reduction temperature is 400℃ for 4 h.

[0044] Example 3

[0045] The difference from Example 1 is as follows: the nickel precursor is replaced with NiSO4·6H2O, the molar ratio of nickel to cerium precursor is 4, the amount of ultrapure water is 100 mL, the amount of sodium hydroxide is 0.5 times the sum of the molar amounts of nickel and cerium precursors, and the amount of anhydrous sodium carbonate is 1 times the sum of the molar amounts of nickel and cerium precursors; the crystallization temperature is 70°C, the crystallization time is 1 h, and the hydrogen reduction temperature is 600°C for 2 h.

[0046] Example 4

[0047] The difference from Example 1 is that: the Ce precursor is replaced with Ce(SO4)4·4H2O, the molar ratio of nickel to cerium precursor is 1, the amount of sodium hydroxide is 1 times the sum of the molar amounts of nickel and cerium precursors, and the amount of anhydrous sodium carbonate is 4 times the sum of the molar amounts of nickel and cerium precursors; the crystallization temperature is 90°C, the crystallization time is 2 hours, and the hydrogen reduction temperature is 500°C for 3 hours.

[0048] Example 5

[0049] The difference from Example 1 is that: the Ce precursor is replaced with (NH4)2Ce(NO3)6, the molar ratio of nickel and cerium precursor is 1, the amount of sodium hydroxide is 3 times the sum of the molar amounts of nickel and cerium precursors, and the amount of anhydrous sodium carbonate is 1 times the sum of the molar amounts of nickel and cerium precursors; the crystallization temperature is 75°C, the crystallization time is 5 hours, and the hydrogen reduction temperature is 600°C for 1 hour.

[0050] Preparation of Control Sample 1 in Comparative Example 1

[0051] The difference from Example 1 is that the Ce precursor is replaced with Al(NO3)3·9H2O, represented as Ni / Al2O3(H450).

[0052] Comparative Example 2

[0053] Weigh 0.1 mol of commercial CeO2 and disperse it in 50 mL of ultrapure water. Sonicate the dispersion for 20 min. Weigh 0.1 mol of Ni(NO3)2·6H2O and add it to the above solution. After evaporating to dryness at 90 °C, reduce the solution at 450 °C in a hydrogen atmosphere for 2 h with a heating rate of 5 °C / min to obtain Ni / CeO2-IM.

[0054] Testing 1Ni / CeO x Application of catalytic systems in ammonia decomposition reaction

[0055] (1) Weigh approximately 90 mg of the catalyst sample Ni / CeO prepared in Example 1. x The catalyst activity of (H450) and control samples Ni / CeO2-IM and Ni / Al2O3 was evaluated in the range of 250℃ to 650℃, with 10 mL of ammonia gas per minute. -1The flow rate; such as Figure 1 As shown.

[0056] As can be seen from the figure, the catalyst sample Ni / CeO prepared in Example 1... x (H450) exhibited excellent activity enhancement, with its activity increasing twofold compared to Ni / Al2O3 at 450℃, demonstrating that the strategy of improving the catalyst activity for ammonia decomposition to hydrogen production by controlling the electronic state is feasible. Compared to Ni / CeO2-IM prepared by the impregnation method (Comparative Example 2), the catalyst sample Ni / CeO2 prepared in Example 1 showed significantly improved activity. x The (H450) activity was more than doubled, demonstrating the superior performance of the atomically dispersed catalyst obtained by this method in the ammonia decomposition to hydrogen production reaction. Furthermore, compared to existing catalysts, traditional Ni-based catalysts require temperatures above 700°C to achieve complete conversion; the catalyst sample Ni / CeO prepared in Example 1... x (H450) almost completely transforms at 500℃.

[0057] (2) Weigh approximately 90 mg of the catalyst sample Ni / CeO prepared in Example 1. x (H450) Catalyst cycleability evaluation experiments were conducted. During each cycle, the temperature was raised to 650℃ for testing, then lowered to 150℃, and then raised to 650℃ again for a second test. Figures 2-3 As shown.

[0058] from Figure 3 As can be seen from the results, the catalyst prepared in Example 1 was subjected to a scale-up test. The test results show that complete conversion was achieved at 500℃, and the conversion rate reached as high as 93% at 450℃.

[0059] The catalyst needs to reach a temperature between 500-550℃ to achieve complete conversion. Figure 3 As can be seen, after five cycles of low temperature (250℃) to high temperature (650℃), the activity did not show a significant decrease, indicating that the catalyst prepared in Example 1 has excellent recyclability and has the potential for industrialization.

[0060] Experiments show that the catalyst prepared in Example 1 has excellent catalytic activity for ammonia decomposition: it can almost completely convert ammonia at 500℃, and the reaction rate is at the highest level of nickel-based catalysts to date. The catalyst prepared in Example 1 has excellent stability and recyclability: after a stability test at 500℃ for 65 hours, the activity of this catalytic system did not show a significant decrease; in addition, after five cycles of heating (250℃) and cooling (650℃), the activity did not show a significant decrease.

[0061] (3) Take approximately 90 mg of the catalyst sample Ni / CeO prepared in Example 1. x (H450), a catalyst stability evaluation experiment was conducted at 500℃ for 65 h; such as Figure 4 As shown.

[0062] from Figure 4 As can be seen, after a stability test at 500℃ for 65 hours, the activity of the catalytic system prepared in Example 1 did not show a significant decrease, indicating that the catalyst exhibits excellent recyclability and stability, making the catalytic system a potential industrial product.

[0063] The experimental results of Test 1 show that the catalytic system prepared in this application embodiment is atomically dispersed, with the metal in close contact with the support. Compared with the ordinary impregnation method, the nickel nanoparticles form a strong interaction with CeO2, effectively regulating the geometry and electronic structure of metallic nickel. This significantly promotes the rate-determining step in ammonia decomposition and enhances its catalytic performance at low temperatures, enabling complete ammonia conversion at 500℃. The strong interaction formed by the atomically dispersed nickel nanoparticles and CeO2 effectively inhibits the aggregation of nickel nanoparticles, enhancing the stability and cyclicity of the catalytic system.

[0064] In summary, the atomically dispersed catalyst obtained by this method improves the dispersion between Ni and Ce, enhances the interaction between the metal supports, and modulates the electronic structure of nickel by constructing a Ni-O-Ce interface, resulting in the formation of a large amount of Ni-O during the reduction process. V The -Ce interface increases the electron density on Ni, promotes N association and desorption, and achieves high activity at low temperature (500℃). By utilizing the metal support interaction between Ni and CeO2, the aggregation of nickel nanoparticles is suppressed, thereby enhancing the stability of the catalytic system and giving it certain industrial application potential.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-based catalyst, characterized in that, The specific steps are as follows: S1: Disperse the nickel precursor and cerium precursor in ultrapure water and stir to dissolve to obtain nickel-cerium mixed salt solution A; S2: Dissolve sodium hydroxide and sodium carbonate in ultrapure water and stir to form a mixed alkaline solution B; S3: After heating deionized water, solutions A and B are added simultaneously using a dropping funnel. After stirring, the solution crystallizes, and after centrifugation to wash the precipitate, it is dried and ground into powder to obtain the catalyst precursor. S4: The precursor of the catalyst is reduced under a hydrogen atmosphere to obtain a nickel-based catalyst; The molar ratio of nickel to cerium in the nickel precursor and cerium precursor is 0.5 to 4; the molar amount of sodium hydroxide is 0.5 to 3 times the sum of the molar amounts of the nickel precursor and cerium precursor; and the molar amount of sodium carbonate is 1 to 4 times the sum of the molar amounts of the nickel precursor and cerium precursor. In step S3, the deionized water needs to be heated to 70~100 ℃. After adding solution A and solution B simultaneously using a dropping funnel, the mixture is stirred at 80 ℃ for 2 hours. After mixing evenly, the mixture is maintained at 80 ℃ for crystallization. The crystallization time is 1~6 hours. The reduction temperature is 400~600℃, and the time is 1~4 h.

2. The preparation method according to claim 1, characterized in that, The nickel precursor is selected from at least one of nickel nitrate hexahydrate, nickel chloride hexahydrate, and nickel sulfate hexahydrate.

3. The preparation method according to claim 1, characterized in that, The cerium precursor is selected from at least one of cerium nitrate hexahydrate, cerium sulfate tetrahydrate, and cerium ammonium nitrate.

4. The preparation method according to claim 1, characterized in that, In S1 and S2, the amount of ultrapure water used is 50~100mL.

5. The preparation method according to claim 1, characterized in that, The crystallization time is 3 hours.

6. The preparation method according to claim 1, characterized in that, The reduction temperature was 450℃ and the time was 2 hours.

7. A nickel-based catalyst prepared by the method according to any one of claims 1 to 6, characterized in that, The nickel-based catalyst is Ni / CeO. x Catalytic system, wherein 1 ≤ x < 2; The catalytic system constructs an atomically dispersed Ni-O-Ce structure.

8. The application of the nickel-based catalyst of claim 7 in the field of ammonia decomposition for hydrogen production.

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