Hollow nanocatalyst for hydrogen production by ammonia decomposition and preparation method and application thereof

Abstract

This invention discloses a hollow nanocatalyst for hydrogen production from ammonia decomposition, wherein ruthenium accounts for 0.1-2% of the total mass of the catalyst. The unique hollow structure of the catalyst provided by this invention helps to improve the conversion rate of ammonia decomposition reaction at low temperatures. At the same time, the sandwich shell structure of the hollow nanoreactor catalyst has a confinement effect, which can prevent the noble metal Ru from agglomerating at high temperatures and extend the service life of the catalyst, thereby solving the technical problems of high energy consumption and high cost in current ammonia decomposition processes.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a method for preparing and applying a hollow nanocatalyst for hydrogen production from ammonia decomposition. Background Technology

[0002] Against the backdrop of energy crisis and climate deterioration, countries are urgently seeking a clean energy source to replace fossil fuels. Hydrogen, as the most abundant element in the universe, produces only water as a byproduct of its combustion, which is harmless to the environment. It is considered one of the most promising new energy sources for the future.

[0003] However, the vast majority of commercial hydrogen on the market currently comes from the catalytic reforming of fossil fuels, which contradicts the clean and renewable nature of hydrogen energy. Furthermore, many key technologies regarding hydrogen storage and safety have yet to be mastered, temporarily hindering the development of hydrogen energy. Ammonia is an excellent carbon-free hydrogen storage medium with a hydrogen storage density as high as 17.8%, and it can be liquefied at -33℃ / 1 bar, potentially solving the challenges of hydrogen storage and transportation.

[0004] Current research on ammonia decomposition catalysts mainly focuses on metals such as ruthenium (Ru), iridium (Ir), nickel (Ni), cobalt (Co), and iron (Fe). Among these, Ru-based catalysts exhibit the highest activity, with catalytic performance at low temperatures far exceeding that of other non-noble metal-based catalysts. For example, patent document CN113019394A discloses a method for preparing a Ni-Pt / CeO2 bimetallic catalyst. After adding Pt, the catalyst's catalytic efficiency at 600℃ increased from 27.9% to 54.3%, but ammonia was only completely converted at 800℃, resulting in high energy consumption. Patent document CN113289693A discloses a Ru-based catalyst prepared using a one-pot method and ball milling. This catalyst achieves an ammonia conversion rate of 96.6% at 450℃ and a hydrogen production rate of 987.7 mmol·gRu. -1 ·h -1 This invention overcomes the drawbacks of existing technologies, such as the cumbersome and lengthy preparation process of MgO-supported Ru-based catalysts. To reduce the long-term operating costs of ammonia decomposition catalytic units, sufficiently low reaction temperatures must be designed. Under this premise, Ru-based catalysts possess significant advantages.

[0005] Currently, the Ru-based catalysts developed all maintain a high loading level. However, as Ru is a precious metal, a high loading will undoubtedly increase the cost of the catalyst. Therefore, how to improve the low-temperature activity of low Ru loading is a problem that needs to be solved in the field of ammonia decomposition. Summary of the Invention

[0006] In view of this, the present invention provides a hollow nanocatalyst for hydrogen production from ammonia decomposition, its preparation method and application, overcoming the low activity problem of Ru-based catalysts for ammonia decomposition under low loading in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition includes the following specific steps:

[0009] (1) Preparation of Ru nanoparticles: Ru nanoparticles / ethylene glycol dispersion system was prepared by liquid phase reduction method;

[0010] (2) Preparation of hollow SiO2 spheres: Sodium citrate solution is added dropwise to a dispersant to form micelles, tetraethyl orthosilicate is added to the micelles, and the precipitate is obtained by standing, which is H-SiO2;

[0011] (3) Modification of hollow SiO2 spheres: The H-SiO2 is dispersed in a mixed solution of ethanol and aminopropyltriethoxysilane, and the precipitate obtained after stirring is the amino-modified H-SiO2.

[0012] (4) The Ru nanoparticle / ethylene glycol dispersion system was added to the amino-modified H-SiO2 solution. After ultrasonic treatment, the product was washed and then added to an ethanol solution containing deionized water and concentrated ammonia. Tetraethyl orthosilicate was added dropwise. After stirring and reacting, the precipitate was washed and dried to obtain a hollow nanocatalyst for ammonia decomposition to produce hydrogen.

[0013] The catalyst of this invention uses sodium citrate as a soft template agent. Due to the poor solubility of sodium citrate in alcohol solvents, it can form uniform spherical micelles. In the system, tetraethyl orthosilicate is gradually hydrolyzed and coated on the surface of the micelles under the action of ammonia. After multiple washings, the sodium citrate template is removed, and regular and uniform H-SiO2 particles are synthesized. At the same time, by modifying the surface of H-SiO2, Ru nanoparticles obtained by liquid-phase reduction are successfully adsorbed onto the surface. After hydrolysis of tetraethyl orthosilicate, a layer of SiO2 is deposited on the outer layer, so that the Ru nanoparticles are confined in the middle region, forming a hollow nanoreactor catalyst H-SiO2@Ru@SiO2 with a sandwich shell structure.

[0014] In traditional ammonia decomposition catalyst structures, the active centers are typically exposed on the support surface to obtain a larger reaction contact area. However, at high temperatures, hydrogen gas can cause the active centers to migrate and aggregate, resulting in an irreversible decrease in catalyst activity. Simultaneously, nitrogen molecules generated by nitrogen atom recombination are difficult to desorb from the catalyst surface, significantly limiting the ammonia decomposition reaction rate. In contrast, the catalyst of this invention, on the one hand, confines the active center Ru between two SiO2 shells, making it less prone to aggregation at high temperatures, maintaining good thermal stability, and reducing the amount of precious metals used. On the other hand, the catalyst has an inner diameter of several hundred nanometers, allowing it to function as a nanoreactor system. External ammonia molecules enter the shell through surface pores, where the NH bonds rapidly break under the action of the active components, transforming into adsorbed hydrogen and nitrogen atoms. Due to the drastic reduction in space, the gas flow rate increases rapidly, leading to the desorption of the adsorbed components. When the gas reaches the internal cavity of the nanoreactor, the sudden increase in space from the narrow pores causes a sharp decrease in instantaneous pressure, which facilitates the forward movement of the ammonia decomposition reaction, thereby improving the low-temperature activity of the catalyst.

[0015] Preferably, the specific steps of the liquid phase reduction method in step (1) are as follows: dissolve the Ru precursor salt and sodium hydroxide in ethylene glycol, introduce an inert atmosphere, and heat to 80-90℃ and maintain for 5-30 min to remove water from the system; then raise the temperature to 150-180℃ and maintain for 2-5 h, and obtain the Ru nanoparticle / ethylene glycol dispersion system after the solution cools down.

[0016] Preferably, the mass ratio of the Ru precursor salt to the sodium hydroxide is 1:1.6-3; more preferably 1:2.

[0017] The Ru precursor salt is any one of ruthenium trichloride hydrate, ruthenium acetylacetonate, and ruthenium acetate;

[0018] The inert atmosphere flow rate is 10-50 mL / min, preferably 20-30 mL / min; the inert atmosphere is argon or nitrogen.

[0019] Preferably, the sodium citrate solution in step (2) is prepared by dissolving sodium citrate dihydrate in deionized water containing concentrated ammonia; the concentration of the sodium citrate solution is 0.05-1 mol / mL; preferably, the concentration is 0.066-0.07 mol / mL.

[0020] Preferably, the volume ratio of the deionized water, the concentrated ammonia, and the dispersant in step (2) is 3.2-3.9:1:60-100:0.078-0.39;

[0021] The dispersant is any one of methanol, ethanol, and isopropanol; preferably ethanol.

[0022] The sodium citrate solution is added to the dispersant at a uniform rate using a peristaltic pump with a rotation speed of 10-150 r / min, corresponding to a flow rate of 38-570 mL / min; preferably 120-150 r / min.

[0023] The amount of tetraethyl orthosilicate added is 0.5-2.5 mL, and the standing time is 6-12 h.

[0024] Preferably, the mass ratio of H-SiO2 in step (3) to aminopropyltriethoxysilane in the mixed solution is 2:1;

[0025] The volume ratio of the ethanol to the aminopropyltriethoxysilane is 26.7-40:1; the preferred ratio is 40:1.

[0026] The stirring time is 12-13 hours.

[0027] Preferably, in step (4), the mass ratio of Ru nanoparticles to amino-modified H-SiO2 is 1:50-1000; and the mass ratio of amino-modified H-SiO2 to ethanol in the amino-modified H-SiO2 solution is 5-100:20-40.

[0028] The mass ratio of the Ru nanoparticles to the tetraethyl orthosilicate is 1:20-450;

[0029] The volume ratio of the ethanol, the deionized water, the concentrated ammonia, and the tetraethyl orthosilicate is 20:3:1:0.04-0.1, and the stirring reaction time is 3-4 hours.

[0030] The drying conditions are 70-80℃ for 8-12 hours.

[0031] Hollow nanocatalysts prepared by the preparation method described above.

[0032] Preferably, ruthenium accounts for 0.1-2% of the total mass of the catalyst.

[0033] Application of hollow nanocatalysts prepared by the method described above in ammonia decomposition for hydrogen production.

[0034] The hollow nanoreactor catalyst prepared in this invention exhibits a high hydrogen production rate. Test results show that 150-H-SiO2@Ru@SiO2 achieves a hydrogen production rate at a space velocity of 12000 mL·g⁻¹. cat -1 ·h -1 At 450℃, the ammonia conversion rate was 59.6%, and the hydrogen production rate was 1462 mmol·g. Ru -1 ·min -1It is superior to most current ammonia decomposition catalysts, and the ammonia conversion rate can reach 99.9% at 600℃.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a catalyst with a unique hollow structure that helps to improve the conversion rate of ammonia decomposition reaction at low temperatures. At the same time, the sandwich shell structure of the hollow nanoreactor catalyst has a confinement effect, which can prevent the noble metal Ru from agglomerating at high temperatures and extend the service life of the catalyst, so as to solve the technical problems of high energy consumption and high cost in the current ammonia decomposition process. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 XRD patterns of the catalysts in Examples 3, 4, Comparative Example 1, and Comparative Example 2;

[0039] Figure 2 This is a TEM image of 150-H-SiO2 in Example 3 of the present invention;

[0040] Figure 3 This is a TEM image of catalyst 150-H-SiO2@Ru in Example 3 of the present invention;

[0041] Figure 4 This is a TEM image of the nanoreactor catalyst 150-H-SiO2@Ru@SiO2 in Example 4 of the present invention;

[0042] Figure 5 This is a SEM image of solid SiO2 in Comparative Example 1 of the present invention;

[0043] Figure 6 The figure shows the long-term stability test results of the nanoreactor catalyst 150-H-SiO2@Ru@SiO2 in the ammonia decomposition reaction in Example 4 of this invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used as the inert atmosphere. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a Ru nanoparticle / ethylene glycol dispersion system was obtained.

[0047] (2) Dissolve 0.4706 g of sodium citrate dihydrate and 6.4 mL of concentrated ammonia in 24 mL of deionized water, and add it dropwise to 100 mL of methanol using a peristaltic pump at a speed of 120 r / min (corresponding flow rate of 456 mL / min). Then add 0.7 mL of tetraethyl orthosilicate dropwise, let stand for 10 h, centrifuge the white suspension after standing, wash the precipitate twice with deionized water to obtain 120-H-SiO2, and disperse it in 5 mL of ethanol for storage.

[0048] (3) 120-H-SiO2 stored in the ethanol phase was added to a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane, stirred for 12 h and then centrifuged and washed to obtain amino-modified 120-H-SiO2; 120-H-SiO2 was dispersed in 5 mL ethanol to obtain a 120-H-SiO2 / ethanol dispersion system.

[0049] (4) Under ultrasonic conditions, with a loading of 0.5wt%, the Ru nanoparticle / ethylene glycol dispersion system was added dropwise to the 120-H-SiO2 / ethanol dispersion system. The ultrasonic time was maintained for 25 min. The product after ultrasonication was washed twice with ethanol and dried under vacuum at 70℃ for 12 h to obtain the catalyst 120-H-SiO2@Ru.

[0050] Example 2

[0051] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used as the inert atmosphere. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a Ru nanoparticle / ethylene glycol dispersion system was obtained.

[0052] (2) Dissolve 0.4706 g of sodium citrate dihydrate and 6.4 mL of concentrated ammonia in 24 mL of deionized water, and add it dropwise to 100 mL of methanol using a peristaltic pump at a speed of 120 r / min. Then add 0.7 mL of tetraethyl orthosilicate dropwise, let stand for 10 h, centrifuge the white suspension after standing, wash the precipitate twice with deionized water to obtain 120-H-SiO2, and disperse it in 5 mL of ethanol for storage.

[0053] (3) 120-H-SiO2 stored in the ethanol phase was added to a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane, stirred for 12 h and then centrifuged and washed to obtain amino-modified 120-H-SiO2, which was then redispersed in 5 mL ethanol to obtain a 120-H-SiO2 / ethanol dispersion system.

[0054] (4) Under ultrasonic conditions, with a loading of 0.5 wt%, the Ru nanoparticle / ethylene glycol dispersion system was added dropwise to the 120-H-SiO2 / ethanol dispersion system. The ultrasonic time was maintained for 25 min. After ultrasonication, the product was washed and added to a mixed solution of 12 mL deionized water, 4 mL concentrated ammonia and 80 mL ethanol, and 0.3 mL tetraethyl orthosilicate was added dropwise. The mixture was stirred for 3 h. The precipitate was washed twice with deionized water and ethanol, and then vacuum dried at 70 °C for 12 h to obtain the hollow nanoreactor catalyst 120-H-SiO2@Ru@SiO2.

[0055] Example 3

[0056] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used as the inert atmosphere. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a Ru nanoparticle / ethylene glycol dispersion system was obtained.

[0057] (2) Dissolve 0.4706 g of sodium citrate dihydrate and 6.4 mL of concentrated ammonia in 24 mL of deionized water, and add the solution dropwise to 100 mL of isopropanone using a peristaltic pump at a speed of 150 r / min (corresponding flow rate of 570 mL / min). Then add 0.7 mL of tetraethyl orthosilicate dropwise to the solution, let it stand for 10 h, centrifuge the white suspension after standing, wash the precipitate twice with deionized water to obtain 150-H-SiO2, and disperse it in 5 mL of ethanol for storage.

[0058] (3) 150-H-SiO2 stored in the ethanol phase was added to a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane, stirred for 12 h and then centrifuged and washed to obtain amino-modified 150-H-SiO2, which was then redispersed in 5 mL ethanol to obtain a 150-H-SiO2 / ethanol dispersion system.

[0059] (4) Under ultrasonic conditions, with a loading of 0.5 wt%, the Ru nanoparticle / ethylene glycol dispersion system was added dropwise to the 120-H-SiO2 / ethanol dispersion system. The ultrasonic time was maintained for 25 min. The product after ultrasonication was washed twice with ethanol to obtain the catalyst 150-H-SiO2@Ru.

[0060] Example 4

[0061] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a mixture of Ru nanoparticles and ethylene glycol was obtained.

[0062] (2) Dissolve 0.4706 g of sodium citrate dihydrate and 6.4 mL of concentrated ammonia in 24 mL of deionized water, and add it dropwise to 100 mL of ethanol at a constant speed of 150 r / min using a peristaltic pump. Then add 0.7 mL of tetraethyl orthosilicate dropwise, let stand for 10 h, centrifuge the white suspension after standing, wash the precipitate twice with deionized water to obtain 150-H-SiO2, disperse it in 5 mL of ethanol and store it.

[0063] (3) 150-H-SiO2 stored in the ethanol phase was added to a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane, stirred for 12 h and then centrifuged and washed to obtain amino-modified 150-H-SiO2, which was then redispersed in 5 mL ethanol to obtain a 150-H-SiO2 / ethanol dispersion system.

[0064] (4) Under ultrasonic conditions, with a loading of 0.5 wt%, the Ru nanoparticle / ethylene glycol dispersion system was added dropwise to the 150-H-SiO2 / ethanol dispersion system. The ultrasonic time was maintained for 25 min. After ultrasonication, the product was washed and added to a mixed solution of 12 mL deionized water, 4 mL concentrated ammonia and 80 mL ethanol. 0.3 mL tetraethyl orthosilicate was added dropwise. The mixture was stirred for 3 h. The precipitate was washed twice with deionized water and ethanol, and then vacuum dried at 70 °C for 12 h to obtain the hollow nanoreactor catalyst 150-H-SiO2@Ru@SiO2.

[0065] Comparative Example 1

[0066] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used as the inert atmosphere. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a Ru nanoparticle / ethylene glycol dispersion system was obtained.

[0067] (2) Add 52.6 mL of anhydrous ethanol, 7.7 mL of ammonia and 2.7 mL of deionized water to a beaker, stir for 30 min in a 30°C water bath until they are mixed evenly, then add 11.5 mL of tetraethyl orthosilicate dropwise, continue stirring and reacting for 16 h, centrifuge the final turbid liquid at 6000 r / min for 10 min, centrifuge and wash the separated white microspheres four times under the same conditions, and vacuum dry at 70°C for 24 h to obtain solid SiO2 spheres;

[0068] (3) Solid SiO2 spheres were dispersed in a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane. After stirring for 12 h, the mixture was centrifuged and washed to obtain solid SiO2 spheres with amino-modified surface. Under ultrasonic conditions, Ru nanoparticles / ethylene glycol dispersion system was added dropwise to the above mixture with a loading of 0.5 wt%. The ultrasonic time was maintained for 25 min. The product after ultrasonication was washed twice with ethanol to obtain the catalyst SiO2@Ru.

[0069] Comparative Example 2

[0070] (1) Under stirring conditions, 0.1 g of ruthenium trichloride hydrate and 0.2 g of flake sodium hydroxide were dissolved in 50 mL of ethylene glycol. An inert atmosphere was introduced with a flow rate of 20 mL / min and argon gas was used as the inert atmosphere. The mixture was heated to 80 °C and maintained for 30 min. The temperature was then raised to 160 °C and maintained for 3 h. After cooling, a Ru nanoparticle / ethylene glycol dispersion system was obtained.

[0071] (2) Add 52.6 mL of anhydrous ethanol, 7.7 mL of ammonia and 2.7 mL of deionized water to a beaker, stir for 30 min in a 30°C water bath until they are mixed evenly, then add 11.5 mL of tetraethyl orthosilicate dropwise, and continue stirring for 16 h. Centrifuge the final turbid liquid at 6000 r / min for 10 min, centrifuge and wash the separated white microspheres four times under the same conditions, and vacuum dry at 70°C for 24 h to obtain solid SiO2 spheres.

[0072] (3) Disperse solid SiO2 spheres in a mixed solution of 40 mL ethanol and 1 mL aminopropyltriethoxysilane, stir for 12 h, centrifuge and wash to obtain solid SiO2 spheres with amino-modified surface, and then add 5 mL ethanol to obtain SiO2 / ethanol dispersion system.

[0073] (4) Under ultrasonic conditions, with a loading of 0.5 wt%, the Ru nanoparticle / ethylene glycol dispersion system was added dropwise to the above SiO2 / ethanol dispersion system. The ultrasonic time was maintained for 25 min. After ultrasonication, the product was washed and added to a mixed solution of 12 mL deionized water, 4 mL concentrated ammonia and 80 mL ethanol, and 0.3 mL tetraethyl orthosilicate was added dropwise. The mixture was stirred for 3 h. The precipitate was washed twice with deionized water and ethanol, and then vacuum dried at 70 °C for 12 h to obtain the catalyst SiO2@Ru@SiO2.

[0074] like Figure 1 The XRD patterns of the catalysts obtained in Examples 3-4 and Comparative Examples 1-2 are shown in the figure. As can be seen from the figure, apart from the characteristic peak of SiO2, no extra diffraction peaks appeared in the samples, indicating that the Ru content was low and no impurities were introduced.

[0075] like Figure 2 The image shows a TEM image of 150-H-SiO2 in Example 3 of this invention. As can be seen from the image, using sodium citrate as a template, the synthesized H-SiO2 is a regular sphere with a smooth surface and uniform thickness. When the dropping speed is 150 r / min, the diameter of the hollow silicon spheres is about 360 nm and the wall thickness is about 30 nm.

[0076] like Figure 3 The image shows a TEM image of catalyst 150-H-SiO2@Ru in Example 3 of this invention. As can be seen from the image, the synthesized Ru nanoparticles are only distributed on the outer surface of the spheres and do not enter the inner cavity of the hollow silicon spheres, and the particle size distribution is uniform.

[0077] like Figure 4 The image shows a TEM image of the nanoreactor catalyst 150-H-SiO2@Ru@SiO2 in Example 4 of this invention. As can be seen from the image, the roughness of the outer surface of the catalyst is significantly reduced compared to 150-H-SiO2@Ru, indicating that after being coated with SiO2, the Ru nanoparticles are effectively confined within the silicon layer.

[0078] like Figure 5 The image shows an SEM image of solid SiO2 in Comparative Example 1 of this invention. As can be seen from the image, the synthesized solid SiO2 has high sphericity, good dispersibility, uniform particle size, and a particle size similar to that of 150-H-SiO2, approximately 350 nm.

[0079] Test Example 1

[0080] The activity test of the above catalyst was conducted on a gas chromatograph in an ammonia decomposition hydrogen production reactor. 100 mg of catalyst was packed into a quartz tube and activated with high-purity ammonia gas at 450 °C for 2 h before the catalytic reaction, with a flow rate of 20 mL / min. After activation, the temperature was lowered to the reaction temperature at the start of the test. Reaction conditions: high-purity ammonia gas as feed gas, flow rate 20 mL / min. -1 The space velocity is 12000 mL·g cat -1 ·h -1 The reaction pressure was 1 bar, and the reaction temperatures were 350℃, 400℃, 450℃, 500℃, 550℃, and 600℃. The ammonia conversion rate was calculated using the formula: ammonia conversion rate = (initial ammonia molar amount - post-reaction ammonia molar amount) / initial ammonia molar amount × 100%. The test results are shown in Table 1.

[0081] Table 1 shows the test results of the ammonia decomposition performance of the above catalysts in the temperature range of 350–600℃.

[0082]

[0083] As can be seen from the data in Table 1, the ammonia conversion rates of the ammonia decomposition catalysts prepared in Comparative Example 4, Comparative Example 1 and Comparative Example 2 show that the catalyst with the hollow sphere structure has a much higher activity than the ordinary solid SiO2-based catalyst, and has a relatively high conversion rate at 350℃, with an ammonia decomposition conversion rate of over 90% at 500℃.

[0084] Further comparison of the ammonia conversion rates of the ammonia decomposition catalysts prepared in Examples 1 and 3 shows that the rotation speed of the peristaltic pump during the H-SiO2 synthesis process affects the activity of the catalyst, and the activity of catalyst 150-H-SiO2@Ru is higher than that of 120-H-SiO2@Ru.

[0085] Further comparison of the activities of the ammonia decomposition catalysts prepared in Examples 1, 2, 3 and 4 shows that Example 4, i.e., the hollow nanoreactor catalyst with a sandwich structure and a dropping rate of 150 r / min, was selected as the optimal sample.

[0086] Test Example 2

[0087] The long-term stability of the hollow nanoreactor catalyst prepared in Example 4 was tested in the ammonia decomposition reaction at 450℃. The stability test of the ammonia decomposition reaction was carried out in a fixed-bed reactor at atmospheric pressure. The reaction conditions were: 0.1 g catalyst, high-purity ammonia (99.999%) as feed gas, and a flow rate of 20 mL / min. -1 The space velocity is 12000 mL·g cat -1 ·h -1The reaction pressure was 0.1 bar; the test was conducted in 20-hour cycles, first raising the temperature to 450℃, then continuing to raise it to 500℃, and finally lowering it back to 450℃. Three measurements were taken every 2 hours, and the average value was used to complete the stability test. The test results are as follows: Figure 6 As shown, after 60 h of reaction, the catalyst in the hollow nanoreactor remained stable at 450 °C without a significant decrease in activity, indicating that it has excellent catalytic stability.

[0088] The various embodiments are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between the various embodiments can be referred to each other.

[0089] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition, characterized in that, The specific steps include the following: (1) Preparation of Ru nanoparticles: Ru nanoparticles / ethylene glycol dispersion system was prepared by liquid phase reduction method; (2) Preparation of hollow SiO2 spheres: Sodium citrate solution is added dropwise to a dispersant to form micelles, tetraethyl orthosilicate is added to the micelles, and the precipitate is obtained by standing, which is H-SiO2; (3) Modification of hollow SiO2 spheres: The H-SiO2 is dispersed in a mixed solution of ethanol and aminopropyltriethoxysilane, and the precipitate obtained after stirring is the amino-modified H-SiO2. (4) The Ru nanoparticle / ethylene glycol dispersion system is added to the amino-modified H-SiO2 solution. After ultrasonic treatment, the product is washed and then added to an ethanol solution containing deionized water and concentrated ammonia. Tetraethyl orthosilicate is added dropwise. After stirring and reacting, the precipitate is washed and dried to obtain a hollow nanocatalyst for ammonia decomposition to produce hydrogen.

2. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 1, characterized in that, The specific steps of the liquid phase reduction method described in step (1) are as follows: dissolve the Ru precursor salt and sodium hydroxide in ethylene glycol, introduce an inert atmosphere, and heat to 80-90℃ and maintain for 5-30 min to remove water from the system; then raise the temperature to 150-180℃ and maintain for 2-5 h, and obtain the Ru nanoparticle / ethylene glycol dispersion system after the solution cools down.

3. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 2, characterized in that, The mass ratio of the Ru precursor salt to the sodium hydroxide is 1:1.6-3; The Ru precursor salt is any one of ruthenium trichloride hydrate, ruthenium acetylacetonate, and ruthenium acetate; The inert atmosphere flow rate is 10-50 mL / min; the inert atmosphere is argon or nitrogen.

4. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 1, characterized in that, The method for preparing sodium citrate solution in step (2) is as follows: sodium citrate dihydrate is dissolved in deionized water containing concentrated ammonia. The concentration of the sodium citrate solution is 0.05-1 mol / mL.

5. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 4, characterized in that, The volume ratio of the deionized water, the concentrated ammonia, the dispersant, and the tetraethyl orthosilicate in step (2) is 3.2-3.9:1:60-100:0.078-0.39; The dispersant is any one of methanol, ethanol, and isopropanol; The sodium citrate solution was added to the dispersant at a constant rate using a peristaltic pump with a rotation speed of 10-150 r / min and a corresponding flow rate of 38-570 mL / min. The settling time is 6-12 hours.

6. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 1, characterized in that, In step (3), the mass ratio of H-SiO2 to aminopropyltriethoxysilane in the mixed solution is 2:1; The volume ratio of the ethanol to the aminopropyltriethoxysilane is 26.7-40:1; The stirring time is 12-13 hours.

7. The method for preparing a hollow nanocatalyst for hydrogen production from ammonia decomposition according to claim 1, characterized in that, The mass ratio of Ru nanoparticles to amino-modified H-SiO2 in step (4) is 1:50-1000; The mass ratio of the Ru nanoparticles to the tetraethyl orthosilicate is 1:20-450.

8. Hollow nanocatalyst prepared by the preparation method according to any one of claims 1-7.

9. The hollow nanocatalyst according to claim 8, characterized in that, Ruthenium accounts for 0.1-2% of the total mass of the catalyst.

10. The application of the hollow nanocatalyst prepared by the preparation method according to any one of claims 1-7 in the ammonia decomposition to hydrogen production reaction.

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