Nickel-based perovskite ammonia decomposition catalyst and preparation method thereof

Abstract

The invention relates to the technical field of thermocatalysis, and discloses a nickel-based perovskite ammonia decomposition catalyst and a preparation method thereof. The preparation method comprises the following steps: synthesizing a lanthanum-aluminum-nickel perovskite precursor by adopting a sol-gel method, and carrying out high-temperature roasting and high-temperature reduction to obtain the catalyst. The molar ratio of Ni to La in the catalyst is (0.2-1): 1, the Ni content is 5-25 wt%, the Ni metal dispersity is high, the sintering resistance is good, the catalyst shows good activity and stability to the ammonia decomposition reaction, the service life of the catalyst is greatly prolonged, and the catalytic efficiency of the catalyst in the ammonia decomposition reaction is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal catalysis, and specifically discloses a nickel-based perovskite ammonia decomposition catalyst and a preparation method thereof. Background Art

[0002] With the growing global demand for clean energy, hydrogen has attracted widespread attention as an ideal energy carrier with zero carbon emissions. Ammonia (NH3) has a high hydrogen storage density of up to 17.6wt% and mature transportation technology, making it a highly promising carbon-free hydrogen carrier. Among the many methods for producing hydrogen from ammonia decomposition, thermal catalytic ammonia decomposition is widely used due to its high efficiency and mature technology. However, this process is highly dependent on the performance of the catalyst. Therefore, the development of efficient and stable ammonia decomposition catalysts can significantly reduce the cost of hydrogen production and promote the application of hydrogen energy.

[0003] Currently, ammonia decomposition catalysts are primarily categorized as noble metal-based and non-noble metal-based. While Ru-based catalysts exhibit excellent ammonia decomposition activity at low temperatures, their high cost severely limits their large-scale industrial application. In contrast, Ni-based catalysts are relatively low-cost and second only to Ru-based catalysts in activity among non-noble metal catalysts, making them considered promising ammonia decomposition catalysts. However, Ni-based catalysts also present several challenges that need to be addressed. For example, when used alone, they exhibit low activity and poor stability in the ammonia decomposition reaction.

[0004] In the study of supported Ni-based catalysts, the support significantly influences their performance. Common supports include Al2O3, SiO2, MgO, carbon materials, and rare earth oxides. These supports influence the dispersion of Ni metal, particle size, and interactions with reactant molecules, thereby altering the activity and stability of the catalyst. For example, Al2O3, with its high surface area, provides an excellent dispersion environment for Ni particles, promoting ammonia decomposition. However, during high-temperature operation, there are challenges with the support reacting with Ni to form an inactive phase, and Ni particles sintering, leading to catalyst deactivation. While SiO2 as a support can improve Ni dispersion by regulating its pore structure, traditional preparation methods present difficulties in controlling particle size distribution and achieving ideal dispersion. Rare earth oxide supports, such as CeO2, can enhance catalytic activity and poisoning resistance through their unique redox properties and abundant oxygen vacancies, but more effective synthesis methods are needed to further optimize their performance. Furthermore, the addition of additives is an important means of enhancing the performance of Ni-based catalysts. For example, additives such as CeO2 and La2O3 can enhance the activity and stability of catalysts by modifying their surface properties and adjusting the size and dispersion of nickel metal particles. However, determining the optimal ratio of different additives in multi-component systems and ensuring their stability under high-temperature reaction conditions remain challenges in current research.

[0005] Perovskite oxides are a type of composite oxide with a unique crystal structure, often used as catalysts and catalyst supports. Perovskite has a cubic crystal structure and can be represented by the ABO3 molecular formula, where the A position is an alkaline earth metal element, located in the center of the cube, with a twelve-coordinate structure; the B position is a transition metal element, located at the eight vertices of the cube, and the transition metal ions form an octahedral coordination with the six oxygen ions. The types and proportions of metal cations at the A and B positions can be varied, resulting in a variety of physical and chemical properties. Perovskite oxides have been widely used in the field of photothermal and electrocatalysis due to their unique structural stability and excellent physical and chemical properties. Cao et al.'s research has shown that the use of Sr in LaAlO3 2+ Replace La 3+ The electronic properties of the support material can be adjusted and the electronic state of the Ru active site can be affected. Compared with the undoped Ru / LaAlO3 catalyst, the Ru / La 0.8 Sr 0.2 AlO3 catalyst showed higher catalytic activity and lower activation energy. The ammonia conversion rate at 500°C reached 71.6%, and the hydrogen generation rate was 941 mmol In addition, the catalyst has excellent durability, with no significant decrease in activity after 70 hours of continuous reaction testing. Doping with appropriate elements can optimize the electronic state of Ru, thereby increasing ammonia conversion and hydrogen production rate, while also improving the catalyst's heat resistance and resistance to poisoning.

[0006] Against this backdrop, developing a novel, highly efficient, and stable Ni-based ammonia decomposition catalyst is of great practical significance. This paper aims to prepare a nickel-based perovskite ammonia decomposition catalyst by doping LaAlO3 with the transition metal Ni at the B position. By regulating the Ni content, the catalyst's structure and performance are optimized, resulting in excellent activity and stability in the ammonia decomposition reaction. Summary of the Invention

[0007] In view of this, the present invention proposes a nickel-based perovskite ammonia decomposition catalyst and a preparation method thereof, aiming to prepare a nickel-based perovskite ammonia decomposition catalyst by doping transition metal Ni at the B position of LaAlO3, and optimizing the structure and performance of the catalyst by regulating the Ni content, so that it exhibits good activity and stability in the ammonia decomposition reaction.

[0008] On the one hand, the present invention provides a nickel-based perovskite ammonia decomposition catalyst, the chemical formula of the nickel-based perovskite ammonia decomposition catalyst is LaAl 1-x Ni x O3, where the value of x is 0.2-1.

[0009] Furthermore, the molar ratio of Ni to La in the nickel-based perovskite ammonia decomposition catalyst is (0.2-1):1, and the Ni content is 5-25 wt%.

[0010] On the other hand, the present invention also provides a method for preparing a nickel-based perovskite ammonia decomposition catalyst, comprising the following preparation steps:

[0011] Lanthanum nitrate, aluminum nitrate and nickel nitrate are dissolved in water to obtain a mixed solution, a complexing agent is added to the mixed solution, and after gelation, drying and coking, a precursor xerogel is obtained;

[0012] Grinding the precursor dry gel into fine powder, and calcining at high temperature to obtain a perovskite sample;

[0013] The perovskite sample is ground, tableted, and sieved, and a 30-60 mesh particle sample is taken and subjected to high-temperature reduction to obtain the nickel-based perovskite ammonia decomposition catalyst.

[0014] Furthermore, the molar ratio of the sum of the added aluminum nitrate and nickel nitrate to the added lanthanum nitrate is 1:1.

[0015] Furthermore, the high temperature calcination is specifically as follows:

[0016] The fine powder was heated to 750° C. at a rate of 3° C. / min in an air atmosphere and maintained at that temperature for 5 hours.

[0017] Furthermore, the high temperature reduction is specifically:

[0018] The screened perovskite sample was placed in a fixed bed reactor with ammonia as the raw gas, and the temperature was programmed to rise from room temperature to 600° C. at a rate of 10° C. / min for reduction for 0.5 hours.

[0019] Furthermore, the complexing agent is citric acid, and the molar ratio of the citric acid to the sum of the lanthanum ions, aluminum ions and nickel ions in the mixed solution is 1.1:1.

[0020] Furthermore, the total flow rate of the ammonia gas is 20 to 50 mL / min.

[0021] Furthermore, the gelation temperature is 80° C., and the gelation time is 12 hours; the coking temperature of the drying coking is 120° C., and the coking time is 24 hours.

[0022] On the other hand, the present invention also provides the use of the nickel-based perovskite ammonia decomposition catalyst in the ammonia decomposition hydrogen production reaction, including: the reaction conditions of the ammonia decomposition hydrogen production reaction are: normal pressure, temperature 400-700 ° C, catalyst loading amount 50 mg, ammonia flow rate 25 mL min -1 , space velocity 30000mL g cat-1 h -1 .

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. LaAl of the present invention 1-x Ni x O3 catalyst has good activity, stability and sintering resistance in the ammonia decomposition reaction. 1-x Ni x O3 catalyst can greatly improve the ammonia decomposition conversion rate;

[0025] 2. The present invention enables precise control of catalyst performance by adjusting the Ni doping level at the B site. Different Ni doping levels affect the catalyst's crystal structure, electronic properties, and distribution of surface active sites, thereby varying the catalyst's activity. This controllability enables optimized catalyst design based on varying reaction conditions and application requirements.

[0026] 3. The raw materials used in the present invention are cheap and widely available, the preparation process is simple, the cost is low, and it is easy to produce on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0028] Figure 1 This is the X-ray powder diffraction spectrum of the perovskite in Example 1 of the present invention.

[0029] Figure 2 This is the X-ray powder diffraction spectrum of the catalyst of Example 1 of the present invention.

[0030] Figure 3 This is the X-ray powder diffraction spectrum of the perovskite of Example 2 of the present invention.

[0031] Figure 4 This is the X-ray powder diffraction spectrum of the catalyst of Example 2 of the present invention.

[0032] Figure 5 This is the X-ray powder diffraction spectrum of the perovskite of Example 3 of the present invention.

[0033] Figure 6 This is the X-ray powder diffraction spectrum of the catalyst of Example 3 of the present invention.

[0034] Figure 7This is the X-ray powder diffraction spectrum of the perovskite of Example 4 of the present invention.

[0035] Figure 8 This is the X-ray powder diffraction spectrum of the catalyst of Example 4 of the present invention.

[0036] Figure 9 This is the X-ray powder diffraction spectrum of the perovskite of Example 5 of the present invention.

[0037] Figure 10 This is the X-ray powder diffraction spectrum of the catalyst of Example 5 of the present invention.

[0038] Figure 11 This is a high-angle annular dark-field scanning transmission electron microscope image of the catalyst in Example 5 of the present invention.

[0039] Figure 12 This is the X-ray powder diffraction spectrum of the perovskite in Comparative Example 1 of the present invention.

[0040] Figure 13 This is the X-ray powder diffraction spectrum of the catalyst of Comparative Example 1 of the present invention.

[0041] Figure 14 The results are for testing the ammonia decomposition activity of the catalyst of Example 5 of the present invention.

[0042] Figure 15 These are the long-term stability test results of the catalyst for ammonia decomposition according to Example 5 of the present invention.

[0043] Figure 16 This is the X-ray powder diffraction spectrum of the catalyst of Example 5 of the present invention after long-term stability test of ammonia decomposition.

[0044] Figure 17 This is a high-angle annular dark-field scanning transmission electron microscopy image of the catalyst of Example 5 of the present invention after long-term stability testing of ammonia decomposition.

[0045] Figure 18 The figure is a flow chart of the preparation method of the nickel-based perovskite ammonia decomposition catalyst in the embodiment of the present invention. DETAILED DESCRIPTION

[0046] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0047] Reference Figure 1-17 As shown, in some embodiments of the present application, a nickel-based perovskite ammonia decomposition catalyst, wherein the chemical formula of the nickel-based perovskite ammonia decomposition catalyst is LaAl 1-x Ni x O3, wherein the value of x is 0.2-1; the molar ratio of Ni and La in the nickel-based perovskite ammonia decomposition catalyst is (0.2-1):1, and the Ni content is 5-25wt%.

[0048] The value of x is preferably 0.2, 0.4, 0.6, 0.8 and 1;

[0049] The value of x is more preferably 1.

[0050] It is understood that the present invention can achieve precise control of catalyst performance by adjusting the Ni doping level at the B site. Different Ni doping levels affect the catalyst's crystal structure, electronic properties, and distribution of surface active sites, thereby changing the catalyst's activity. This controllability enables the catalyst to be optimized according to different reaction conditions and application requirements.

[0051] It is understood that the LaAl 1-x Ni x O3 catalyst has good activity, stability and sintering resistance in the ammonia decomposition reaction. 1-x Ni x O3 catalyst can greatly improve the ammonia decomposition conversion rate;

[0052] Reference Figure 18 As shown, in some embodiments of the present application, a method for preparing the nickel-based perovskite ammonia decomposition catalyst includes the following preparation steps:

[0053] Lanthanum nitrate, aluminum nitrate and nickel nitrate are dissolved in water to obtain a mixed solution, a complexing agent is added to the mixed solution, and after gelation, drying and coking, a precursor xerogel is obtained;

[0054] Grinding the precursor dry gel into fine powder, and calcining at high temperature to obtain a perovskite sample;

[0055] The perovskite sample is ground, tableted, and sieved, and a 30-60 mesh particle sample is taken and subjected to high-temperature reduction to obtain the nickel-based perovskite ammonia decomposition catalyst.

[0056] Specifically, the water is preferably deionized water.

[0057] like Figure 18 As shown, in some embodiments of the present application, the molar ratio of the sum of the added aluminum nitrate and nickel nitrate to lanthanum nitrate is 1:1.

[0058] like Figure 18 As shown, in some embodiments of the present application, the high temperature calcination is specifically:

[0059] The fine powder was heated to 750° C. at a rate of 3° C. / min in an air atmosphere and maintained at that temperature for 5 hours.

[0060] Specifically, during high-temperature calcination, the fine powder is first placed in a crucible, and then the crucible is placed in a muffle furnace for calcination.

[0061] It is understood that slowly increasing the temperature to 750°C and maintaining it for a period of time is beneficial for the formation and improvement of the perovskite crystal structure. Under these temperature and time conditions, salts such as lanthanum nitrate, aluminum nitrate, and nickel nitrate undergo decomposition and reaction processes, more fully forming a stable perovskite structure, enabling good crystal growth and improved crystallinity, thus obtaining a perovskite sample with excellent catalytic performance.

[0062] It is understood that appropriate heat treatment temperature and duration can affect the catalyst's specific surface area, pore size distribution, and active site formation. Maintaining the catalyst at 750°C for 5 hours can create a suitable pore structure and a larger specific surface area, which facilitates the adsorption and diffusion of reactant molecules, increases the exposure of active sites, and thus improves the catalyst's activity and selectivity.

[0063] like Figure 18 As shown, in some embodiments of the present application, the high temperature reduction is specifically:

[0064] The screened perovskite sample was placed in a fixed bed reactor with ammonia as the raw gas, and the temperature was programmed to rise from room temperature to 600° C. at a rate of 10° C. / min for reduction for 0.5 hours.

[0065] It is understandable that under reducing conditions of 600°C, ammonia can undergo a reduction reaction with certain components in the catalyst, reducing the metal ions to a suitable valence state to form catalytically active species, thereby precisely regulating the active sites on the catalyst surface and improving the catalytic activity of the catalyst for specific reactions.

[0066] It is understood that during the reduction process, the effect of ammonia helps form a specific pore structure and surface morphology within the catalyst. The synergistic effect of the heating rate, reduction temperature, and time results in a catalyst with a suitable pore size distribution and a high specific surface area, which facilitates the diffusion of reactants and products and improves the efficiency of the catalytic reaction.

[0067] like Figure 18 As shown, in some embodiments of the present application, the complexing agent is citric acid, and the molar ratio of the citric acid to the sum of the lanthanum ions, aluminum ions and nickel ions in the mixed solution is 1.1:1.

[0068] It is understood that citric acid can form stable complexes with metal ions such as lanthanum nitrate, aluminum nitrate, and nickel nitrate. These complexes can be evenly dispersed in solution, allowing the various metal ions to mix uniformly at the atomic level, which facilitates the subsequent formation of a uniform perovskite structure and avoids the variability in catalyst performance caused by uneven distribution of metal ions.

[0069] It is understood that the complex formed by citric acid affects the gel network structure during the gelation process. It makes the gel structure more fluffy and porous, increasing the specific surface area and porosity. This fluffy and porous structure facilitates gas escape and diffusion during subsequent heat treatment, helping to form perovskite samples with a well-defined pore structure and high specific surface area, thereby improving catalyst performance.

[0070] like Figure 18 As shown, in some embodiments of the present application, the total flow rate of the ammonia gas is 20 to 50 mL / min.

[0071] It is understood that an appropriate ammonia flow rate can provide a sufficient reducing atmosphere, allowing the relevant components in the catalyst to fully contact the ammonia and undergo a reduction reaction. A flow rate that is too low, resulting in insufficient ammonia supply, may lead to incomplete reduction reactions, affecting the formation of active sites and catalyst performance. A flow rate that is too high, while still ensuring the reduction reaction, may result in ammonia waste and may also place excessive pressure on the reaction system, affecting reaction stability.

[0072] like Figure 18 As shown, in some embodiments of the present application, the gelation temperature is 80° C. and the gelation time is 12 hours; the coking temperature of the drying coking is 120° C. and the coking time is 24 hours.

[0073] Reference Figure 14-17 As shown, in some embodiments of the present application, the nickel-based perovskite ammonia decomposition catalyst is used at normal pressure, temperature 400-700 ° C, catalyst loading amount 50 mg, ammonia flow rate 25 mL min -1 , space velocity 30000mL g cat -1 h -1 The catalytic ammonia decomposition reaction to produce hydrogen under the reaction conditions.

[0074] Example 1

[0075] S1. Weigh 5.8987 g of lanthanum nitrate (La(NO3)3·6H2O), 0.7923 g of nickel nitrate (Ni(NO3)2·6H2O), and 4.0882 g of aluminum nitrate (Al(NO3)3·9H2O), dissolve them in 100 mL of deionized water, and mix to form a uniform mixed metal salt solution.

[0076] S2. Weigh 6.0879 g of citric acid monohydrate (C6H8O7·H2O) and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved. The molar amount of citric acid monohydrate is 1.1 times the total molar amount of lanthanum ions, aluminum ions, and nickel ions. Add citric acid as a complexing agent to the mixed metal salt solution and stir thoroughly to mix the solution evenly.

[0077] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor xerogel;

[0078] S4. Grind the precursor dry gel into fine powder, put it into a crucible and place it in a muffle furnace for calcination. Raise the temperature to 750°C at 5°C / min in an air atmosphere and keep it for 5 hours to fully decompose organic matter such as citric acid. Press the calcined product into tablets, crush it, and sieve it. Take a 30-60 mesh sample to obtain LaAl 0.8 Ni 0.2 O3 perovskite sample;

[0079] S5. The perovskite sample was placed in a fixed bed reactor, and ammonia (25 mL / min) was introduced at 600° C. for half an hour to obtain the nickel-based perovskite ammonia decomposition catalyst, which was recorded as LaAl 0.8 Ni 0.2 O3-NR.

[0080] Example 2

[0081] S1. Weigh 5.7336 g of lanthanum nitrate (La(NO3)3·6H2O), 1.5402 g of nickel nitrate (Ni(NO3)2·6H2O), and 2.9803 g of aluminum nitrate (Al(NO3)3·9H2O), dissolve them in 100 mL of deionized water, and mix to form a uniform mixed metal salt solution.

[0082] S2. Weigh 5.7135 g of citric acid monohydrate (C6H8O7·H2O) and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved. The molar amount of citric acid monohydrate is 1.1 times the total molar amount of lanthanum ions, aluminum ions, and nickel ions. Add citric acid as a complexing agent to the mixed metal salt solution and stir thoroughly to mix the solution evenly.

[0083] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor xerogel;

[0084] S4. Grind the dry gel into fine powder, put it into a crucible and place it in a muffle furnace for calcination. Raise the temperature to 750°C at 5°C / min in an air atmosphere and keep it for 5 hours to fully decompose organic matter such as citric acid. Press the calcined product into tablets, crush it, and sieve it. Take a 30-60 mesh sample to obtain LaAl 0.6 Ni 0.4 O3 perovskite sample;

[0085] S5. The perovskite sample was placed in a fixed bed reactor, and ammonia (25 mL / min) was introduced at 600° C. for half an hour to obtain the nickel-based perovskite ammonia decomposition catalyst, which was recorded as LaAl 0.6 Ni 0.4 O3-NR.

[0086] Example 3

[0087] S1. Weigh 5.5775 g of lanthanum nitrate (La(NO3)3·6H2O), 2.2474 g of nickel nitrate (Ni(NO3)2·6H2O), and 1.9328 g of aluminum nitrate (Al(NO3)3·9H2O), dissolve them in 100 mL of deionized water, and mix to form a uniform mixed metal salt solution;

[0088] S2. Weigh 5.3594 g of citric acid monohydrate (C6H8O7·H2O) and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved. The molar amount of citric acid monohydrate is 1.1 times the total molar amount of lanthanum ions, aluminum ions, and nickel ions. Add citric acid as a complexing agent to the mixed metal salt solution and stir thoroughly to mix the solution evenly.

[0089] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor xerogel;

[0090] S4. Grind the precursor dry gel into fine powder, put it into a crucible and place it in a muffle furnace for calcination. Raise the temperature to 750°C at 5°C / min in an air atmosphere and keep it for 5 hours to fully decompose organic matter such as citric acid. Press the calcined product into tablets, crush it, and sieve it. Take a 30-60 mesh sample to obtain LaAl 0.4 Ni 0.6 O3 perovskite sample;

[0091] S5. The perovskite sample was placed in a fixed bed reactor, and ammonia (25 mL / min) was introduced at 600° C. for half an hour to obtain the nickel-based perovskite ammonia decomposition catalyst, which was recorded as LaAl 0.4 Ni 0.6 O3-NR.

[0092] Example 4

[0093] S1. Weigh 5.4296 g of lanthanum nitrate (La(NO3)3·6H2O), 2.9170 g of nickel nitrate (Ni(NO3)2·6H2O), and 0.9408 g of aluminum nitrate (Al(NO3)3·9H2O), dissolve them in 100 mL of deionized water, and mix to form a uniform mixed metal salt solution;

[0094] S2. Then, 5.0241 g of citric acid monohydrate (C6H8O7·H2O) was weighed and dissolved in 100 mL of deionized water, and magnetic stirring was applied until completely dissolved. The molar amount of citric acid monohydrate was 1.1 times the total molar amount of lanthanum ions, aluminum ions, and nickel ions. Citric acid was added to the mixed metal salt solution as a complexing agent, and the solution was stirred thoroughly to mix uniformly.

[0095] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor xerogel;

[0096] S4. Grind the precursor dry gel into fine powder, put it into a crucible and place it in a muffle furnace for calcination. Raise the temperature to 750°C at 5°C / min in an air atmosphere and keep it for 5 hours to fully decompose organic matter such as citric acid. Press the calcined product into tablets, crush it, and sieve it. Take a 30-60 mesh sample to obtain LaAl 0.2 Ni 0.8 O3 perovskite sample;

[0097] S5. The perovskite sample was placed in a fixed bed reactor, and ammonia (25 mL / min) was introduced at 600° C. for half an hour to obtain the nickel-based perovskite ammonia decomposition catalyst, which was recorded as LaAl 0.2 Ni 0.8 O3-NR.

[0098] Example 5

[0099] S1. Weigh 5.2894 g of lanthanum nitrate (La(NO3)3·6H2O) and 3.5521 g of nickel nitrate (Ni(NO3)2·6H2O), dissolve them in 100 mL of deionized water, and mix them to form a uniform mixed metal salt solution;

[0100] S2. Weigh 4.7061 g of citric acid monohydrate (C6H8O7·H2O) and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved. The molar amount of citric acid monohydrate is 1.1 times the total molar amount of lanthanum ions and nickel ions. Add citric acid as a complexing agent to the mixed metal salt solution and stir thoroughly to mix the solution evenly.

[0101] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor dry gel.

[0102] S4. Precursor: Grind the dry gel into a fine powder, place it in a crucible, and calcine it in a muffle furnace. In an air atmosphere, heat it up to 750°C at a rate of 5°C / min and hold it for 5 hours to fully decompose organic matter such as citric acid. The calcined product is tableted, crushed, and sieved. A 30-60 mesh sample is taken to obtain a LaNiO3 perovskite sample.

[0103] S5. The perovskite sample was placed in a fixed bed reactor, and ammonia gas (25 mL / min) was introduced at 600° C. for reduction for half an hour to obtain the nickel-based perovskite ammonia decomposition catalyst, which was recorded as LaNiO 3 -NR.

[0104] Comparative Example

[0105] S1. Weigh 6.0736 g of lanthanum nitrate (La(NO3)3·6H2O) and 5.2618 g of aluminum nitrate (Al(NO3)3·9H2O), dissolve them in 100 mL of deionized water, and mix to form a uniform mixed metal salt solution.

[0106] S2. Then, 6.6846 g of citric acid monohydrate (C6H8O7·H2O) was weighed and dissolved in 100 mL of deionized water, and magnetic stirring was applied until completely dissolved. The molar amount of citric acid monohydrate was 1.1 times the total molar amount of lanthanum ions and aluminum ions. Citric acid was added to the mixed metal salt solution as a complexing agent, and the solution was stirred thoroughly to mix uniformly.

[0107] S3. Transfer the mixed solution to a constant temperature drying oven and dry it at 80°C for 12 hours until the solution gradually evaporates to form a viscous gel; then adjust the drying oven to 120°C and continue drying for 24 hours to remove residual moisture and volatiles to obtain a fluffy and porous precursor xerogel;

[0108] S4. Grind the precursor dry gel into a fine powder, place it in a crucible, and calcine it in a muffle furnace. Raise the temperature to 750°C at a rate of 5°C / min in an air atmosphere and hold for 5 hours to fully decompose organic matter such as citric acid. Press the calcined product into tablets, crush it, and sieve it. Take a 30-60 mesh sample to obtain a LaAlO3 perovskite sample.

[0109] S5. The perovskite sample was placed in a fixed bed reactor and reduced by introducing ammonia (25 mL / min) at 600° C. for half an hour to obtain a catalyst, which was recorded as LaAlO 3 -NR.

[0110] Effect test

[0111] (1) X-ray diffraction analysis was performed on the perovskite samples and catalyst powders prepared in Examples 1-5 and the comparative example. The results are as follows:

[0112] Figure 1 The LaAl prepared in Example 1 0.8 Ni 0.2 The X-ray powder diffraction spectrum of the O3 perovskite sample shows diffraction peaks at 2θ=27.21°, 38.87°, 48.05°, 56.11°, 63.52°, 70.37°, 83.54°, 89.75° and 96.18°, which belong to perovskite. Compared with the LaAlO3 standard card (JCPDS 01-085-1071), all diffraction peaks are shifted to lower angles, and no diffraction peaks of nickel oxide are seen, indicating that nickel species have entered the perovskite structure. Figure 2 It is LaAl 0.8 Ni 0.2 The X-ray powder diffraction spectrum of the O3-NR catalyst shows that the characteristic diffraction peaks of perovskite do not change significantly, indicating that the perovskite structure remains stable under ammonia reduction conditions.

[0113] Figure 3 The LaAl prepared in Example 2 0.6 Ni 0.4 The X-ray powder diffraction spectrum of the O3 perovskite sample shows that the diffraction peaks at 2θ=27.16°, 38.72°, 47.91°, 55.95°, 63.34°, 70.11°, 83.09°, 89.46° and 95.92° belong to the characteristic diffraction peaks of perovskite. Compared with the LaAlO3 standard card (JCPDS 01-085-1071), all diffraction peaks are shifted to lower angles, and no diffraction peaks of nickel oxide are seen, indicating that nickel species have entered the perovskite structure. Figure 4 It is LaAl 0.6 Ni 0.4 The X-ray powder diffraction spectrum of the O3-NR catalyst shows that the characteristic diffraction peaks of perovskite do not change significantly, indicating that the perovskite structure remains stable under ammonia reduction conditions.

[0114] Figure 5 The LaAl prepared in Example 3 0.4 Ni 0.6The X-ray powder diffraction spectrum of the O3 perovskite sample shows that the diffraction peaks at 2θ=27.0°, 38.56°, 47.84°, 55.75°, 63.24°, 69.79°, 82.68°, 89.19° and 95.32° belong to the characteristic diffraction peaks of perovskite. Compared with the LaAlO3 standard card (JCPDS 01-085-1071), all diffraction peaks are shifted to lower angles, and no diffraction peaks of nickel oxide are seen, indicating that nickel species have entered the perovskite structure. Figure 6 It is LaAl 0.4 Ni 0.6 The X-ray powder diffraction spectrum of the O3-NR catalyst shows that the characteristic diffraction peaks of perovskite do not change significantly, indicating that the perovskite structure remains stable under ammonia reduction conditions.

[0115] Figure 7 The LaAl prepared in Example 4 0.2 Ni 0.8 The X-ray powder diffraction spectrum of the O3 perovskite sample shows that the diffraction peaks at 2θ=26.95°, 38.38°, 47.64°, 55.48°, 62.94°, 69.55°, 82.12°, 88.78° and 94.93° belong to the characteristic diffraction peaks of perovskite. Compared with the LaAlO3 standard card (JCPDS 01-085-1071), all diffraction peaks are shifted to lower angles, and no diffraction peaks of nickel oxide are seen, indicating that nickel species have entered the perovskite structure. Figure 8 It is LaAl 0.2 Ni 0.8 The X-ray powder diffraction spectrum of the O3-NR catalyst shows that the characteristic diffraction peaks of perovskite do not change significantly, indicating that the perovskite structure remains stable under ammonia reduction conditions.

[0116] Figure 9 This is the X-ray powder diffraction spectrum of the prepared LaNiO3 perovskite sample. The diffraction peaks at 2θ=26.88°, 38.26°, 47.45°, 55.36°, 62.52°, 69.30°, 81.83°, 88.73° and 94.61° belong to perovskite. Compared with the LaAlO3 standard card (JCPDS 01-085-1071), all diffraction peaks shift to low angles, and no diffraction peaks of nickel oxide are seen, indicating that nickel species enter the perovskite structure. Figure 10The X-ray powder diffraction spectrum of LaNiO3-NR catalyst shows that the characteristic diffraction peaks of perovskite disappear. The diffraction peaks at 2θ=52.18°, 61.02° and 91.76° correspond to the (111), (200) and (220) crystal planes of nickel (JCPDS 00-004-0850). The diffraction peaks at 2θ=34.41°, 34.94°, 46.24°, 54.07°, 61.36°, 63.29°, 65.39°, 66.02°, 71.45°, 73.79°, 86.21°, 90.37°, 95.44° and 97.70° correspond to lanthanum oxide La2O3 (JCPDS 00-005-0602), indicating that LaNiO3 perovskite is transformed into Ni metal and La2O3 after ammonia reduction treatment. Figure 11 This is a high-angle annular dark-field scanning transmission electron microscope of the LaNiO3-NR catalyst. The nickel metal particles are mainly concentrated in the range of 6-12nm, with an average particle size of 9.3nm.

[0117] Figure 12 This is the X-ray powder diffraction spectrum of the prepared LaAlO3 perovskite sample. The diffraction peaks at 2θ = 27.30°, 38.96°, 48.22°, 56.32°, 63.74°, 70.72°, 83.81°, 90.46° and 96.58° are attributed to LaAlO3 (JCPDS 01-085-1071), indicating the formation of a perovskite structure. Figure 13 This is the X-ray powder diffraction spectrum of the LaAlO3-NR catalyst. The diffraction peak of the perovskite has not changed significantly, indicating that the perovskite structure remains stable under ammonia reduction conditions.

[0118] (2) The catalyst prepared above was tested for ammonia decomposition activity:

[0119] The activity of the catalyst for ammonia decomposition reaction was evaluated in a fixed-bed reactor at atmospheric pressure. The reaction conditions were: 50 mg of catalyst, pure ammonia as feed gas, flow rate of 25 mL / min, and space velocity of 30000 mL / (g cat h), the reaction pressure is normal pressure, and the reaction temperature is 300-700°C. Figure 14The ammonia decomposition conversion rate of the catalyst of Example 5 changes with the reaction temperature. As the reaction temperature increases, the ammonia decomposition conversion rate gradually increases, and the conversion rate at 700°C is 98.5%, which is close to complete conversion. Table 1 shows the ammonia decomposition activity test results of the catalysts of Examples 1-5 and Comparative Example 1. It can be seen that the nickel content has a significant effect on the ammonia decomposition activity of the catalyst. In the absence of active metal Ni, the ammonia decomposition activity of the LaAlO3 catalyst is almost zero. As the nickel content increases, the ammonia decomposition activity gradually increases, and the LaNiO3 catalyst shows the best activity. According to the X-ray powder diffraction spectrum and high-angle annular dark field scanning transmission electron microscopy image of the LaNiO3 catalyst, nickel metal nanoparticles are precipitated after LaNiO3 is reduced by ammonia. These nickel metals serve as active sites for the ammonia decomposition reaction, which significantly improves the ammonia decomposition activity.

[0120] Table 1 Test results of nickel-doped perovskite catalyst for ammonia decomposition reaction

[0121]

[0122] Figure 15 The results of the long-term stability test of the catalyst in Example 5 for the ammonia decomposition reaction at 600° C. are shown. The initial ammonia conversion rate was 86%, and after 100 hours of reaction, the ammonia conversion rate remained above 80%, demonstrating good long-term stability. Figure 16 This is the X-ray powder diffraction spectrum of the catalyst of Example 5 after stability testing. There is no obvious change in the phase structure before and after the reaction. Figure 17 This is a high-angle annular dark-field scanning transmission electron microscope of the catalyst of Example 5 after stability testing. It can be seen that the nickel metal particles are mainly concentrated in the range of 6-14 nm, with an average particle size of 10.4 nm, indicating that the catalyst prepared by the present invention has good sintering resistance.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A nickel-based perovskite ammonia decomposition catalyst, characterized in that The chemical formula of the nickel-based perovskite ammonia decomposition catalyst is LaAl 1-x Ni x O3, where the value of x is 0.2-1.

2. The nickel-based perovskite ammonia decomposition catalyst according to claim 2, characterized in that The molar ratio of Ni to La in the nickel-based perovskite ammonia decomposition catalyst is (0.2-1):1, and the Ni content is 5-25 wt%.

3. A method for preparing the nickel-based perovskite ammonia decomposition catalyst according to any one of claims 1 to 2, characterized in that: The method comprises the following preparation steps: Lanthanum nitrate, aluminum nitrate and nickel nitrate are dissolved in water to obtain a mixed solution, a complexing agent is added to the mixed solution, and after gelation, drying and coking, a precursor xerogel is obtained; Grinding the precursor dry gel into fine powder, and calcining at high temperature to obtain a perovskite sample; The perovskite sample is ground, tableted, and sieved, and a 30-60 mesh particle sample is taken and subjected to high-temperature reduction to obtain the nickel-based perovskite ammonia decomposition catalyst.

4. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 3, wherein: The molar ratio of the sum of the added aluminum nitrate and nickel nitrate to the added lanthanum nitrate is 1:

1.

5. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 3, characterized in that: The high temperature roasting is specifically: The fine powder was heated to 750° C. at a rate of 3° C. / min in an air atmosphere and maintained at that temperature for 5 hours.

6. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 3, wherein: The high temperature reduction is specifically: The screened perovskite sample was placed in a fixed bed reactor with ammonia as the raw gas, and the temperature was programmed to rise from room temperature to 600° C. at a rate of 10° C. / min for reduction for 0.5 hours.

7. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 3, characterized in that: The complexing agent is citric acid, and the molar ratio of the citric acid to the sum of the lanthanum ions, aluminum ions and nickel ions in the mixed solution is 1.1:

1.

8. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 6, characterized in that: The total flow rate of the ammonia gas is 20-50 mL / min.

9. The method for preparing the nickel-based perovskite ammonia decomposition catalyst according to claim 3, characterized in that: The gelation temperature is 80° C., and the gelation time is 12 hours; the coking temperature of the drying and coking is 120° C., and the coking time is 24 hours.

10. Use of the nickel-based perovskite ammonia decomposition catalyst according to any one of claims 1 to 2 in ammonia decomposition hydrogen production reaction, characterized in that: The reaction conditions of the ammonia decomposition hydrogen production reaction are: atmospheric pressure, temperature 400-700°C, catalyst loading 50 mg, ammonia flow rate 25 mL min -1 , space velocity 30000mL g cat -1 h -1 .

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