A catalyst for hydrogen production from ammonia decomposition, its preparation method and application

Abstract

A catalyst for hydrogen production from ammonia decomposition, its preparation method, and its application are disclosed. The catalyst comprises a support and an active component. The support is a doped porous nanorod-shaped cerium dioxide; the active component is an alloy nanoparticle formed by ruthenium and other metals, with the ruthenium loading accounting for 0.8%–2% of the total catalyst mass. The catalyst preparation process involves first preparing the support and active component separately. The active component is then highly dispersed and anchored on the support through in-situ loading. A gradient reduction process with segmented heating is then used to achieve a strong synergistic catalytic effect between the active component and the support, exhibiting high activity and high stability at low temperatures. The catalyst performs well at ambient pressure (0.1 MPa), 450 °C, and a space velocity (24000 mL·g⁻¹). ‑1 ·h ‑1 Under the given reaction conditions, the ammonia decomposition conversion rate reached 99.5%, and it could operate stably for 1000 hours without significant deactivation.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a low-temperature, highly active, and highly stable ammonia decomposition hydrogen production catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy has garnered widespread attention due to its unique development potential and advantages. Ammonia (NH3) has a high energy density and is easy to store and transport, making it an excellent hydrogen storage material. Therefore, using ammonia for hydrogen storage and supply is one of the development trends in hydrogen energy, and developing high-performance ammonia decomposition catalysts for hydrogen production is a key aspect of this process. Currently, non-precious metal catalysts, such as nickel-based catalysts, are commercially available, but the reaction temperatures are generally above 800℃, and the reaction space velocity often does not exceed 1000 h⁻¹. -1 There is still considerable room for improvement in the thermal stability, energy conservation, emission reduction, and efficiency enhancement of catalysts. Ruthenium-based noble metal catalysts, for example, exhibit high activity at low temperatures, but the ruthenium loading has previously exceeded 5 wt%. Chinese patent CN117065765A discloses an ammonia decomposition hydrogen production catalyst with a maximum ruthenium loading of 10 wt%, achieving a reaction temperature of 600℃ and a firing rate of 60,000 h⁻¹. -1 The ammonia decomposition conversion rate reached 99.6% at a given space velocity; Chinese patent CN113289620A discloses a single-atom ruthenium catalyst with a maximum ruthenium loading of 6 wt%, which achieves a high ammonia decomposition reaction rate at 500℃ for 22000 h⁻¹. -1 Ammonia decomposition conversion rate of 99.8% was achieved at a specific space velocity; Chinese patent CN109529865A discloses a ruthenium-based ammonia decomposition hydrogen production catalyst with a maximum ruthenium loading of 6 wt%. In the ammonia decomposition reaction, an ammonia decomposition conversion rate of 99.2% can be achieved at 450℃, but the space velocity is only 5000 h⁻¹. -1 The advantages of ruthenium-based catalysts—high activity at low temperatures—have not been fully explored and utilized, and their high production costs have hindered their large-scale application. Therefore, developing low-temperature, efficient, highly stable, and low-cost catalysts is the main direction for the further development of ammonia decomposition for hydrogen production technology. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a low-temperature, high-activity, and high-stability ammonia decomposition hydrogen production catalyst, its preparation method, and its application.

[0004] Therefore, the first aspect of the present invention provides a low-temperature, highly active, and highly stable ammonia decomposition hydrogen production catalyst.

[0005] The catalyst includes a support and an active component. The support is a doped porous nanorod-shaped cerium dioxide, and the active component is an alloy nanoparticle formed by ruthenium and other metals.

[0006] Specifically, the carrier chosen in this invention is cerium dioxide (CeO2). As a rare earth oxide, CeO2 possesses unique geometric and electronic structural properties, such as Ce... 4+ With Ce 3+ The valence state transformation process generates abundant oxygen vacancies, which are positively charged. Their electrophilic nature allows them to serve as active sites for the adsorption and activation of many small molecules, thus effectively enhancing catalytic activity. Simultaneously, CeO2 can form strong interactions with the active components, helping to regulate their electronic structure and maintain their high dispersion, inhibiting sintering and agglomeration, and improving stability.

[0007] Using metal-doped cerium dioxide with a porous nanorod structure can provide more defect sites and synergistically regulate the electronic structure of the active component, making the dissociation of NH bonds in the reactants and the desorption of products from the surface of the active component more efficient, thus improving catalyst performance. On the other hand, the porous nanorod structure of cerium dioxide with a high specific surface area provides more attachment sites for ruthenium alloy nanoparticles. This not only promotes a more uniform distribution of ruthenium alloy nanoparticles on or near the surface of the nanoparticles, improving the utilization rate of ruthenium, but also enables a larger amount of ammonia molecules to be adsorbed onto the catalytic sites, thereby improving the conversion rate of ammonia decomposition.

[0008] The doping element is at least one of magnesium, aluminum, calcium, manganese, yttrium, zirconium, and lanthanum.

[0009] The molar ratio of the dopant element to cerium dioxide is (0.05~0.5):1.

[0010] Porous nanorod-shaped cerium dioxide particles have a length of 50–200 nm, a diameter of 10–50 nm, and a specific surface area of ​​100–300 m². 2 / g, pore volume 0.10~0.30cm 3 / g, average pore size 5-10nm.

[0011] Specifically, the active component of this invention is ruthenium forming alloy nanoparticles with other metals. Compared with unmodified ruthenium, the added metals not only have an alloying effect, improving the dispersion of ruthenium and avoiding the aggregation of ruthenium metal during the reaction, but also optimize the electronic structure of ruthenium, thereby reducing the NH bond cleavage barrier on the surface of the active component, improving the adsorption of N atoms and the recombination and desorption of NN atoms, further reducing the reaction temperature and improving the ammonia decomposition conversion rate.

[0012] The other metal is at least one of iron, cobalt, nickel, copper, zinc, rhodium, and iridium.

[0013] The molar ratio of ruthenium to other metals is 1:(0.01 to 0.1).

[0014] The ruthenium alloy nanoparticles have a size of 0.5–5.0 nm, and the ruthenium accounts for 0.8%–2% of the total mass of the catalyst.

[0015] The second aspect of the present invention provides a method for preparing the above-mentioned ammonia decomposition hydrogen production catalyst.

[0016] The catalyst preparation process includes three parts: support synthesis, active component synthesis, and in-situ loading of the active component onto the support.

[0017] Specifically, the following steps are included:

[0018] 1. Carrier Synthesis

[0019] (1) Weigh out a certain proportion of cerium precursor salt, dopant salt, pore expander, and pure water and mix and dissolve them. The cerium precursor salt is selected from one of nitrates, sulfates, chlorides, or organic ligand salts, preferably including cerium nitrate hexahydrate, cerium sulfate tetrahydrate, cerium chloride heptahydrate, cerium chloride trihydrate, cerium acetate pentahydrate, cerium bromide monohydrate, and cerium acetylacetone; the dopant salt is selected from one of nitrates or chlorides of magnesium, aluminum, calcium, manganese, yttrium, zirconium, and lanthanum, preferably including magnesium nitrate, aluminum nitrate, calcium nitrate, manganese nitrate, yttrium nitrate, zirconium nitrate, and lanthanum nitrate; the pore expander is selected from one of dimethylformamide, urea, and hexamethylenetetramine, and the molar ratio of the pore expander to cerium is (1-10):1, and the molar ratio of pure water to cerium is (50-200):1.

[0020] (2) At room temperature, the above mixture is slowly dropped into a 10-15 mol / L NaOH solution. After stirring for 2-20 h at room temperature, it is transferred to a reaction vessel for crystallization reaction.

[0021] Preferably, the molar ratio of NaOH to cerium is (50–200):1; the crystallization temperature is 100–120℃; and the crystallization time is 24–48 h.

[0022] (3) After the crystallization reaction, the product is cooled and allowed to stand to separate into layers. The upper clear liquid is replaced with pure water multiple times until the conductivity of the upper clear liquid is ≤50μS / cm. After centrifugation and drying, it is ground to obtain powder, and then calcined in air at 600℃ for 2 hours at a heating rate of 5℃ / min to obtain the carrier.

[0023] 2. Synthesis of active components

[0024] A certain proportion of ruthenium precursor salt, other metal salts, NaOH, and reducing agent are weighed and mixed. The mixture is stirred and refluxed vigorously at 100–200°C for 10–50 h. The product obtained after cooling is the active component. The ruthenium precursor salt is selected from one of the nitrate, chloride, and organic ligand salts of ruthenium, preferably including ruthenium trichloride hydrate, anhydrous ruthenium chloride, ruthenium acetate, ruthenium oxalate, ruthenium acetylacetone, triphenylphosphine ruthenium chloride, and carbonyl ruthenium chloride. The other metal salts are selected from one of the nitrate, sulfate, and chloride salts of iron, cobalt, nickel, copper, zinc, rhodium, and iridium, preferably including cobalt nitrate, ferric nitrate, nickel nitrate, copper acetate, zinc nitrate, rhodium chloride, and iridium chloride. The reducing agent is one of ethylene glycol, isopropanol, and glycerol. The molar ratio of ruthenium, NaOH, and reducing agent is 1:(2–10):(500–2000).

[0025] 3. Active components are loaded in situ onto the carrier.

[0026] The pure water, cerium, and ruthenium elements are mixed in a molar ratio of (2000-10000):(20-60):1. The mixture is stirred at 40-100℃ for 1-5 hours, then a complexing agent is added. The mixture is stirred for another 1-5 hours, followed by sonication for 1-3 hours. The mixture is then allowed to stand for 5-20 hours to complete the in-situ loading of the active components onto the carrier.

[0027] The complexing agent is one of citric acid, tartaric acid, or oxalic acid, and the molar ratio of the complexing agent to ruthenium is (20-100):1.

[0028] The product after settling was centrifuged and washed until the conductivity was ≤50μS / cm, then vacuum dried at 80℃ for 10-24h, and then heated from room temperature to 200℃ at 5℃ / min and held for 2h under a 10% hydrogen + argon atmosphere, then heated to 400℃ at 3℃ / min and held for 2h, and then heated to 600℃ at 3℃ / min and held for 2h, to obtain the above ammonia decomposition hydrogen production catalyst.

[0029] During the reduction process, the catalyst undergoes a gradient reduction process with segmented heating. In the low-temperature stage, residual moisture in the sample is removed, while in the medium- and high-temperature stages, pore expanders and complexing agents are fully decomposed to form a pore structure on the support, increasing its specific surface area and enhancing catalytic active sites. At the same time, the active components are fully reduced, forming ultra-small ruthenium nanoparticles that are uniformly dispersed on or near the surface of the support, allowing them to fully combine with the support to form a strong synergistic catalytic effect.

[0030] A third aspect of the present invention provides the application of the above-described ammonia decomposition hydrogen production catalyst in the ammonia decomposition hydrogen production reaction.

[0031] Preferably, the reaction takes place in a high-purity NH3 atmosphere at a temperature of 300–500 °C and a space velocity of 24,000 mL·g. -1 ·h -1The reaction pressure is 0.1 MPa at atmospheric pressure.

[0032] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0033] (1) The active component of the ammonia decomposition hydrogen production catalyst of the present invention is an alloy nanoparticle formed by ruthenium and other metals. The added other metals can not only improve the dispersion of ruthenium metal, but also synergistically regulate the electronic structure of the catalyst, which helps to improve the activity and stability of the catalyst.

[0034] (2) In this invention, ruthenium metal accounts for only 0.8% to 2% of the total weight of the catalyst, which is lower than the technical level reported in the prior art, and has an advantage in catalyst manufacturing cost.

[0035] (3) The support of the ammonia decomposition hydrogen production catalyst of the present invention is a doped porous nanorod-shaped cerium dioxide. The addition of doped metal further enriches the defect sites on the surface of cerium dioxide and promotes the improvement of catalyst activity. During the preparation process, the addition of pore expander enriches the pore structure of the support, increases the specific surface area of ​​the support, and promotes the uniform distribution of ruthenium alloy nanoparticles to its surface or near the surface, so that the synergistic catalytic advantages of active sites and support can be fully utilized, thereby improving the ammonia decomposition conversion rate and its stability.

[0036] (4) During the preparation of the ammonia decomposition hydrogen production catalyst of the present invention, the active component is loaded in situ onto the support, and the added complexing agent helps ruthenium to anchor on or near the surface of the support, thereby improving the dispersion of ruthenium; in the later stage, the catalyst is subjected to a gradient reduction process of segmented heating to form an alloy nanoparticle catalyst with moderate size and stable structure.

[0037] (5) The ammonia decomposition catalyst prepared in this invention has good catalytic performance at a Ru loading of 1 wt.%, atmospheric pressure of 0.1 MPa, 450 °C, and space velocity of 24000 mL·g. -1 ·h -1 Under the given reaction conditions, the ammonia decomposition conversion rate reached 99.5%, and it could operate stably for 1000 hours without significant deactivation. Attached Figure Description

[0038] Figure 1 The X-ray diffraction pattern of the catalyst in Example 1 is shown below.

[0039] Figure 2 The accompanying figures show the low-temperature nitrogen adsorption-desorption of the catalysts in Example 1 and Comparative Example 4;

[0040] Figure 3 Here is a scanning electron microscope image of the catalyst from Example 1;

[0041] Figure 4 The energy dispersive X-ray spectrum of the catalyst in Example 1 is shown below.

[0042] Figure 5 This is a lifetime graph showing the ammonia decomposition activity of the catalyst in Example 1 after 1000 hours.

[0043] Figure 6 The catalyst of Example 1 was tested at a space velocity of 30,000 mL·g -1 ·h -1 Activity testing;

[0044] Figure 7 This is a transmission electron microscope (TEM) image of the catalyst from Example 1. Detailed Implementation

[0045] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] Example 1

[0047] A method for preparing and applying an ammonia decomposition hydrogen production catalyst includes the following steps:

[0048] (1) Carrier synthesis: Weigh 3.65g of cerium nitrate hexahydrate, 0.92g of zirconium nitrate pentahydrate, 4.94g of dimethylformamide, and 21.6g of pure water and mix and dissolve them; at room temperature, slowly drop the above mixture into a NaOH solution prepared from 45g of sodium hydroxide and 150g of pure water; after stirring at room temperature for 2h, transfer it to a 500mL reactor for static crystallization reaction at 120℃ for 48h; allow the reaction product to stand and separate into layers, and replace the upper liquid with pure water multiple times until the conductivity of the upper clear liquid is ≤50μS / cm. After centrifugation and drying, grind to obtain powder, and then calcine at 600℃ in air atmosphere for 2h to obtain the carrier.

[0049] (2) Synthesis of active components: Weigh 0.0471 g of ruthenium trichloride hydrate, 0.003 g of cobalt nitrate hexahydrate, 0.058 g of sodium hydroxide and 21.11 g of ethylene glycol and mix them in a 50 mL round-bottom flask. Stir vigorously and reflux at 160 °C for 48 h. The product obtained after cooling is the active component.

[0050] (3) In-situ loading of active components onto the carrier: The carrier and active components prepared above are mixed with 26g of pure water, stirred at 50℃ for 2h, 3.07g of citric acid is added, stirred for another 2h, sonicated for 1h, and then allowed to stand for 20h to complete the in-situ loading of active components onto the carrier.

[0051] (4) The product after settling was centrifuged and washed until the conductivity of the supernatant was ≤50 μS / cm. After vacuum drying at 80℃ for 24 h, the catalyst was pressed into tablets, crushed, and sieved into 40-80 mesh particles to obtain a RuCo / CeO2-ZrO2 catalyst with a 1% ruthenium loading. 0.1 g of the catalyst was weighed and mixed with twice the volume of quartz sand of the same particle size, and packed into a stainless steel fixed-bed reactor with an inner diameter of 8 mm. A gradient reduction process with segmented heating was adopted, specifically, an air velocity of 10000 mL·g⁻¹ was introduced. -1 ·h -1 The catalyst was reduced with 10% H₂ + Ar reducing gas, and the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature was increased to 400℃ at a rate of 3℃ / min and held for 12 hours, followed by an increase to 600℃ at a rate of 3℃ / min and held for 2 hours. After the catalyst reduction treatment, the temperature was naturally cooled to 450℃ and held for 2 hours. Then, high-purity ammonia gas preheated at 450℃ was introduced to begin testing the catalyst activity. The catalyst evaluation conditions were: reaction temperature 450℃, atmospheric pressure 0.1 MPa, and 24000 mL·g⁻¹. -1 ·h -1 The ammonia decomposition conversion rate data after 48 hours of catalytic reaction are shown in Table 1.

[0052] Example 2

[0053] A method for preparing and applying an ammonia decomposition hydrogen production catalyst includes the following steps:

[0054] (1) Carrier synthesis: Weigh 3.65g of cerium nitrate hexahydrate, 0.56g of lanthanum nitrate hexahydrate, 4.06g of urea, and 21.6g of pure water and mix and dissolve them. At room temperature, slowly drop the above mixture into a NaOH solution prepared from 45g of sodium hydroxide and 150g of pure water. After stirring at room temperature for 2 hours, transfer it to a 500mL reactor for static crystallization reaction at 120℃ for 48 hours. The reaction product was allowed to stand and separate into layers. The upper liquid was replaced with pure water several times until the conductivity of the upper clear liquid was ≤50μS / cm. After centrifugation and drying, the powder was ground and then calcined at 600℃ in air for 2 hours to obtain the carrier.

[0055] (2) Synthesis of active components: Weigh 0.0471 g of ruthenium trichloride hydrate, 0.003 g of iridium trichloride hydrate, 0.058 g of sodium hydroxide and 31.33 g of glycerol and mix them in a 50 mL round bottom flask. Stir vigorously and reflux at 160 °C for 48 h. The product obtained after cooling is the active component.

[0056] (3) In-situ loading of active components onto the carrier: The carrier and active components prepared above are mixed with 26g of pure water, stirred at 50℃ for 2h, 1.44g of oxalic acid is added, stirred for another 2h, sonicated for 1h, and then allowed to stand for 20h to complete the in-situ loading of active components onto the carrier.

[0057] (4) The product after settling was centrifuged and washed until the conductivity of the supernatant was ≤50 μS / cm. After vacuum drying at 80℃ for 24 h, the catalyst was pressed into tablets, crushed, and sieved into 40-80 mesh particles to obtain a RuIr / CeO2-La2O3 catalyst with a 1% ruthenium loading. 0.1 g of the catalyst was weighed and mixed with twice the volume of quartz sand of the same particle size, and packed into a stainless steel fixed-bed reactor with an inner diameter of 8 mm. A gradient reduction process with segmented heating was used, specifically, an air velocity of 10000 mL·g⁻¹ was introduced. -1 ·h -1 The catalyst was reduced with 10% H₂ + Ar reducing gas, and the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature was increased to 400℃ at a rate of 3℃ / min and held for 12 hours, followed by an increase to 600℃ at a rate of 3℃ / min and held for 2 hours. After the catalyst reduction treatment, the temperature was naturally cooled to 450℃ and held for 2 hours. Then, high-purity ammonia gas preheated at 450℃ was introduced to begin testing the catalyst activity. The catalyst evaluation conditions were: reaction temperature 450℃, atmospheric pressure 0.1 MPa, and 24000 mL·g⁻¹. -1 ·h -1 The ammonia decomposition conversion rate data after 48 hours of catalytic reaction are shown in Table 1.

[0058] Example 3

[0059] A method for preparing and applying an ammonia decomposition hydrogen production catalyst includes the following steps:

[0060] (1) Carrier synthesis: Weigh 3.85g of cerium nitrate hexahydrate, 1.22g of magnesium nitrate hexahydrate, 9.47g of hexamethylenetetramine, and 21.6g of pure water and mix and dissolve them. At room temperature, slowly drop the above mixture into a NaOH solution prepared from 45g of sodium hydroxide and 150g of pure water. After stirring at room temperature for 2 hours, transfer it to a 500mL reactor for static crystallization reaction at 120℃ for 48 hours. The reaction product was allowed to stand and separate into layers. The upper liquid was replaced with pure water several times until the conductivity of the upper clear liquid was ≤50μS / cm. After centrifugation and drying, the powder was ground and then calcined at 600℃ in air atmosphere for 2 hours to obtain the carrier.

[0061] (2) Synthesis of active components: Weigh 0.0471 g of ruthenium trichloride hydrate, 0.004 g of nickel nitrate hexahydrate, 0.058 g of sodium hydroxide and 20.45 g of isopropanol and mix them in a 50 mL round-bottom flask. Stir vigorously and reflux at 160 °C for 48 h. The product obtained after cooling is the active component.

[0062] (3) In-situ loading of active components onto the carrier: The carrier and active components prepared above are mixed with 26g of pure water, stirred at 50℃ for 2h, 2.4g of tartaric acid is added, stirred for another 2h, sonicated for 1h, and then allowed to stand for 20h to complete the in-situ loading of active components onto the carrier.

[0063] (4) The product after settling was centrifuged and washed until the conductivity of the supernatant was ≤50 μS / cm. After vacuum drying at 80℃ for 24 h, the catalyst was pressed into tablets, crushed, and sieved into 40-80 mesh particles to obtain a RuNi / CeO2-MgO catalyst with a 1% ruthenium loading. 0.1 g of the catalyst was weighed and mixed with twice the volume of quartz sand of the same particle size, and packed into a stainless steel fixed-bed reactor with an inner diameter of 8 mm. A gradient reduction process with segmented heating was adopted, specifically, an air velocity of 10000 mL·g⁻¹ was introduced. -1 ·h -1 The catalyst was reduced with 10% H₂ + Ar reducing gas, and the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature was increased to 400℃ at a rate of 3℃ / min and held for 12 hours, followed by an increase to 600℃ at a rate of 3℃ / min and held for 2 hours. After the catalyst reduction treatment, the temperature was naturally cooled to 450℃ and held for 2 hours. Then, high-purity ammonia gas preheated at 450℃ was introduced to begin testing the catalyst activity. The catalyst evaluation conditions were: reaction temperature 450℃, atmospheric pressure 0.1 MPa, and 24000 mL·g⁻¹. -1 ·h -1 The ammonia decomposition conversion rate data after 48 hours of catalytic reaction are shown in Table 1.

[0064] Comparative Example 1

[0065] The only difference between Comparative Example 1 and Example 1 is that zirconium nitrate pentahydrate was not added during the carrier synthesis process in step (1).

[0066] Comparative Example 2

[0067] The only difference between Comparative Example 2 and Example 1 is that cobalt nitrate hexahydrate was not added during the synthesis of the active component in step (2).

[0068] Comparative Example 3

[0069] The only difference between Comparative Example 3 and Example 1 is that citric acid was not added in step (3), that is, the carrier and active component were not loaded in situ, but the active component was simply impregnated on the carrier.

[0070] Comparative Example 4

[0071] The only difference between Comparative Example 4 and Example 1 is that dimethylformamide was not added during the carrier synthesis process in step (1).

[0072] Comparative Example 5

[0073] The only difference between Comparative Example 5 and Example 1 is that Comparative Example 5 was not subjected to the gradient reduction process with segmented heating, but was directly treated at 600°C for 2 hours under the same reducing atmosphere by heating at 5°C / min.

[0074] Table 1

[0075] sample Ammonia decomposition conversion rate (%) Example 1 99.5 Example 2 99.1 Example 3 99.4 Comparative Example 1 93.2 Comparative Example 2 91.8 Comparative Example 3 80.6 Comparative Example 4 89.1 Comparative Example 5 93.6

[0076] As shown in Table 1, the ammonia decomposition hydrogen production catalyst prepared in Example 1, under the conditions of a reaction temperature of 450℃, atmospheric pressure of 0.1MPa, and reaction space velocity of 24000mL·g, showed good performance. -1 ·h -1 The conversion rate reached 99.5% after a reaction time of 48 hours, demonstrating excellent ammonia decomposition catalytic performance.

[0077] Figure 1 The X-ray diffraction pattern of Example 1 shows that only the characteristic diffraction peaks of CeO2 appeared in the sample, and no diffraction signals of Zr species or RuCo alloy were observed. This is because Zr is embedded in the CeO2 lattice and the RuCo alloy nanoparticles formed are highly dispersed, with very small particle size and low content.

[0078] Figure 2 The attached figures show the low-temperature nitrogen adsorption-desorption catalysts of Example 1 and Comparative Example 4. As can be seen from the figures, Example 1, with the addition of the pore-expanding agent dimethylformamide, has a larger specific surface area and pore volume, both reaching 200.6 m². 2 / g and 0.30cm 3 / g, the isothermal adsorption-desorption curve is type IV, indicating a mesoporous structure with an average pore size of 9.1 nm. Comparative Example 4, without the addition of dimethylformamide, has a specific surface area of ​​167.6 m². 2 / g, pore volume 0.27cm 3 / g, average pore size 8.2nm.

[0079] Figure 3 The image shows a scanning electron microscope (SEM) image of the catalyst in Example 1. As can be seen, the catalyst exhibits a distinct nanorod structure, which facilitates the anchoring of the active component to the surface or near-surface of the support, forming strong interactions. The scale bar in the lower left corner of the image is 20 nm. In comparison, the porous nanorod-shaped cerium dioxide particles have a length distribution of 50–200 nm, with an average length of 150 nm, and a diameter distribution of 10–50 nm, with an average diameter of 18 nm.

[0080] Figure 4 The image shows the energy dispersive X-ray spectrum of the catalyst in Example 1. As can be seen from the image, the RuCo nano-alloy particles formed by the catalyst are distributed on the surface of the CeO2 support, which can inhibit the sintering and agglomeration of ruthenium.

[0081] Figure 5The graph shows the ammonia decomposition activity lifetime of the catalyst in Example 1 after 1000 hours. As can be seen from the graph, the catalyst exhibits the following activity at ambient pressure (0.1 MPa), 450 °C, and a space velocity (24000 mL·g⁻¹). -1 ·h -1 Under the given reaction conditions, the ammonia decomposition conversion rate reaches 99.5%, and it can operate stably for 1000 hours without significant deactivation, demonstrating extremely excellent thermocatalytic ammonia decomposition performance.

[0082] Change the reaction conditions, increasing the space velocity from 24000 mL·g -1 ·h -1 Adjust to 30000 mL·g -1 ·h -1 See Figure 6 The ammonia decomposition conversion rate reaches 93.1%, and it can operate stably for 100 hours without significant deactivation. Even at higher space velocities, its performance remains excellent.

[0083] Figure 7 The image shows a transmission electron microscope (TEM) image of the catalyst in Example 1. As can be seen from the image, the size of the formed RuCo nanoalloy particles is around 3.0 nm.

[0084] As can be seen from the reaction data of Example 1 and Comparative Example 1, the catalytic performance of Comparative Example 1 was reduced because zirconium nitrate pentahydrate was not added during the synthesis of the support, which resulted in the failure to further enrich the defect sites on the surface of the support and optimize the electronic structure of the active components.

[0085] As can be seen from the reaction data of Example 1 and Comparative Example 2, since cobalt nitrate hexahydrate was not added in Comparative Example 2, it was unable to form alloy nanoparticles with ruthenium, resulting in partial agglomeration of ruthenium during the long reaction process and a decrease in dispersion, which led to a significant decrease in catalytic performance.

[0086] As can be seen from the reaction data of Example 1 and Comparative Example 3, in Comparative Example 3, due to the absence of the complexing agent citric acid, the active component was unevenly distributed on the support, resulting in larger ruthenium-cobalt alloy nanoparticles after reduction, which led to a significant decrease in conversion rate. In contrast, in Example 1, which included the complexing agent, the support and active metal were in a highly dispersed slurry state. This allowed the in-situ loaded active component to better bind to the surface or near-surface of the support, forming highly dispersed, small-sized ruthenium-cobalt alloy nanoparticles. Therefore, the activity of the prepared catalyst could be effectively improved.

[0087] As can be seen from the reaction data of Example 1 and Comparative Example 4, in Comparative Example 4, because the pore-expanding agent dimethylformamide was not added during the synthesis of the support, the support failed to effectively form a porous structure and a high specific surface area, which affected the loading of the active component and led to a decrease in catalyst activity.

[0088] As can be seen from the reaction data of Example 1 and Comparative Example 5, the catalyst without the staged heating gradient reduction process may exhibit high-temperature sintering and agglomeration of ruthenium, which is not conducive to the formation of a metal-oxide structure of moderate size and stable structure, resulting in catalytic activity that is not as good as that of Example 1.

Claims

1. A method for preparing a catalyst for hydrogen production from ammonia decomposition, characterized in that, Includes the following steps: 1) Support synthesis: Cerium precursor salt, doped salt, pore expander and water are mixed and dissolved and then dropped into NaOH solution. After stirring, the mixture is transferred to a hydrothermal reactor for constant temperature crystallization. The crystallized product is washed with water and alcohol until a certain conductivity is reached, then centrifuged, dried and calcined at high temperature to obtain the support. 2) Synthesis of active components: Ruthenium precursor salt, other metal salts, NaOH, reducing agent and water are mixed and dissolved, stirred and refluxed at a constant temperature, and the product obtained after cooling is the active component; 3) In-situ loading of active components onto the carrier: After mixing and stirring water, carrier and active components, a complexing agent is added, followed by sonication, stirring and settling to complete the in-situ loading of active components onto the carrier; 4) Gradient reduction by staged heating: The product is centrifuged, washed, vacuum dried, and reduced by staged heating to obtain the ammonia decomposition hydrogen production catalyst; In step 1), the doped salt is selected from one of the nitrates or chlorides of magnesium, aluminum, calcium, manganese, yttrium, zirconium, and lanthanum; the pore-expanding agent is selected from one of dimethylformamide, urea, and hexamethylenetetramine; the molar ratio of the pore-expanding agent to the cerium precursor salt is (1~10):1; the crystallization temperature is 100~120℃, the crystallization time is 24~48h; the high-temperature calcination temperature is 500~800℃, and the calcination time is 2~6h. In step 2), the other metal salt is selected from the nitrate, sulfate, and chloride salts of iron, cobalt, nickel, copper, zinc, rhodium, and iridium; the reducing agent is selected from the ethylene glycol, isopropanol, and glycerol; the molar ratio of the reducing agent to the ruthenium precursor salt is (500~2000):1; the stirring and reflux temperature is 100~200℃, and the time is 10~50h; In step 3), the complexing agent is one of citric acid, tartaric acid, and oxalic acid, and the molar ratio of the complexing agent to the active component is (20~100):1; the molar ratio of the carrier to the active component is (20~60):

1. In step 4), the segmented heating and reduction process involves raising the temperature from room temperature to 100-200℃ and holding it for 1-5 hours, then raising it to 300-400℃ and holding it for 1-5 hours, and then raising it to 500-600℃ and holding it for 1-5 hours.

2. The method for preparing an ammonia decomposition hydrogen production catalyst as described in claim 1, characterized in that: In step 1), the cerium precursor salt is selected from one of nitrates, sulfates, chlorides or organic ligand salts.

3. The method for preparing an ammonia decomposition hydrogen production catalyst as described in claim 1, characterized in that: In step 2), the ruthenium precursor salt is selected from one of the ruthenium nitrate, chloride, and organic ligand salts.

4. The method for preparing an ammonia decomposition hydrogen production catalyst as described in claim 1, characterized in that: In step 4), the reducing atmosphere for heating is one of hydrogen, a mixture of hydrogen and argon, or a mixture of hydrogen and helium.

5. A catalyst for hydrogen production from ammonia decomposition, characterized in that: Prepared by any one of the preparation methods of claims 1 to 4.

6. The ammonia decomposition hydrogen production catalyst as described in claim 5, characterized in that: The catalyst comprises a support and an active component. The support is a doped porous nanorod-shaped cerium dioxide with a molar ratio of dopant element to cerium dioxide of (0.05~0.5):

1. The active component is an alloy nanoparticle formed by ruthenium and other metals, with ruthenium accounting for 0.8%~2% of the total mass of the catalyst and a molar ratio of ruthenium to other metals of 1:(0.01~0.1).

7. The ammonia decomposition hydrogen production catalyst as described in claim 6, characterized in that: The porous nanorod-shaped cerium dioxide has a length of 50–200 nm and a diameter of 10–50 nm, and the catalyst has a specific surface area of ​​100–300 m². 2 / g, pore volume 0.10~0.30 cm³ 3 / g, with an average pore size of 5~10 nm and the size of the alloy nanoparticles is 0.5~5.0 nm.

8. The application of the catalyst prepared by any one of the preparation methods of claims 1 to 4 or the catalyst according to any one of claims 5 to 7, characterized in that: It is used in the thermocatalytic decomposition of ammonia to produce hydrogen.

9. The application as described in claim 8, characterized in that, The reaction parameters are as follows: reaction temperature 300~500℃ in an NH3 atmosphere, and reaction space velocity 10000~50000 mL·g. -1 ·h -1 The reaction pressure is 0.1 MPa at atmospheric pressure.

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