Co-based amine decomposition catalyst, method for preparing the same, and use thereof

Abstract

The application belongs to the technical field of hydrogen production by ammonia decomposition, and particularly relates to a Co-based catalyst for hydrogen production by ammonia decomposition and a preparation method and application thereof. x The composite oxide and the alkaline earth or rare earth metal oxide; the calcium-iron structure metal oxide has an octahedral lattice, the active metal elements are uniformly distributed in the calcium-iron structure, the active species separated out after reduction is uniformly dispersed, is favorable for the exposure of active sites and the generation of a structure stable carrier, effectively avoids the covering of the active sites in the reaction process, makes the ammonia gas fully contact with the active component, and thus improves the ammonia decomposition efficiency; the introduction of the alkaline earth or rare earth oxide additive can adjust the electronic properties of the Co species, and at the same time, enhances the alkalinity of the catalyst surface, promotes the ammonia decomposition reaction to proceed; meanwhile, the in-situ treatment with ammonia gas is favorable for the formation of Co particles with small size and good dispersion, and thus the excellent ammonia decomposition reaction catalytic performance is exhibited.

Description

Technical Field

[0001] This invention belongs to the field of ammonia decomposition for hydrogen production technology, specifically relating to a Co-based catalyst for ammonia decomposition for hydrogen production, its preparation method, and its application. Background Technology

[0002] Hydrogen energy boasts advantages such as high heat of combustion, wide availability, and zero emissions, making it an ideal emerging energy source. However, its application suffers from issues like poor safety and high storage and transportation costs. Currently, researchers are conducting in-depth studies on on-demand hydrogen production and exploring various in-situ hydrogen production technologies, such as water electrolysis and reforming. While water electrolysis is pollution-free, it suffers from high energy consumption and cost; reforming methanol, ethanol, and other alcohols to produce hydrogen involves CO2. x The formation of chemical compounds can easily lead to fuel cell poisoning. Compared to the hydrogen production methods mentioned above, ammonia decomposition for hydrogen production (2NH3→N2+3H2) produces hydrogen and nitrogen as decomposition products, without CO. x Since ammonia is less polluting, using it as a hydrogen storage carrier is inherently greener, safer, and more economical.

[0003] Currently, catalysts for ammonia decomposition to hydrogen production mainly include noble metal catalysts, represented by Ru-based catalysts, and non-noble metal catalysts, represented by Co and Ni-based catalysts. The supports used are mostly metal oxides and carbon materials. Noble metal-based catalysts exhibit significantly better catalytic performance than non-noble metal catalysts; however, their application cost is high, making research on non-noble metal catalysts essential. Compared to carbon supports, metal oxide supports have a smaller specific surface area. Supported catalysts prepared using traditional impregnation, co-precipitation, and deposition-precipitation methods are prone to having their active sites covered by metal oxides, resulting in poor activity. However, carbon material supports have poor stability and are prone to methanation at high temperatures, severely affecting ammonia decomposition performance. Therefore, there is an urgent need to find catalysts with relatively stable support structures that can expose more active sites. Perovskite materials, due to their relatively regular crystal lattice arrangement, allow active metal elements to be uniformly distributed within the precursor. Reduction can then precipitate active metal species in situ, meeting the requirements for exposed active sites and a stable support. Common methods for preparing perovskite include combustion, coprecipitation, hydrothermal, and sol-gel methods. However, combustion methods generate nitrogen oxides, polluting the environment; coprecipitation can lead to particle agglomeration due to uneven precipitation; and hydrothermal methods require high control parameters, have poor controllability, and have long preparation cycles. Therefore, this invention proposes to use the sol-gel method to introduce active metal Co into the structure of perovskite oxide, ensuring its uniform distribution, and then obtain a Co-based catalyst through additive modification and in-situ reduction treatment, thereby providing a highly efficient Co-based ammonia decomposition catalyst and its preparation method. Summary of the Invention

[0004] To address the problem that active sites in metal oxide-supported ammonia decomposition hydrogen production catalysts are easily covered, the present invention aims to provide a highly efficient Co-based catalyst for ammonia decomposition hydrogen production and its preparation method. The catalyst uses perovskite subtype calcium iron oxide as a precursor, modifies it by introducing an additive, and prepares the Co-based catalyst by in-situ ammonia reduction, thereby developing and designing a highly efficient ammonia decomposition hydrogen production catalyst.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A Co-based catalyst using perovskite-structured oxides as precursors comprises an active component, a support, and an auxiliary agent; the active component is Co, and the support is SrO and SrCoO. x The composite oxide, wherein the auxiliary agent is an alkaline earth metal or rare earth metal oxide; by mass percentage, Co accounts for 25-35% and the auxiliary agent accounts for 1-20%.

[0007] The preparation method of the Co-based catalyst includes the following steps:

[0008] (1) Dissolve strontium salt, cobalt salt and auxiliary metal salt in solvent, then add complexing agent and stir to dissolve;

[0009] (2) Continue stirring the solution obtained in step (1) in an oil bath until it becomes gel-like, and dry the resulting gel sample in an oven at 120°C for 48 hours;

[0010] (3) The dried product obtained in step (2) is ground into powder, and then calcined in a muffle furnace to obtain the calcium iron oxide, labeled as Sr. 1-x A x CoO 2.5 .

[0011] (4) The calcium iron oxide obtained in step (3) is reduced in situ to 400°C in an ammonia atmosphere at a heating rate of 5°C / min to obtain the Co-based catalyst.

[0012] Further, the cobalt salt mentioned in step (1) is at least one of cobalt nitrate, cobalt carbonate, and cobalt acetylacetonate.

[0013] Further, the strontium salt in step (1) is at least one of strontium nitrate, strontium carbonate, and strontium hydroxide.

[0014] Furthermore, the molar ratio of strontium salt to cobalt salt in step (1) is 0.5 to 1.2:1.

[0015] Further, the molar ratio of the auxiliary metal salt to the cobalt salt in step (1) is 0.05 to 0.50:1.

[0016] Furthermore, the doped metal salt is at least one of magnesium nitrate, calcium nitrate, barium nitrate, lanthanum nitrate, cerium nitrate, and samarium nitrate.

[0017] Further, the molar ratio of the metal salt to the complexing agent in step (1) is 0.75 to 2:1.

[0018] Furthermore, the complexing agent is at least one of citric acid, polyvinylpyrrolidone, and ethylenediaminetetraacetic acid.

[0019] Further, the solvent mentioned in step (1) is at least one of water, ethanol, and acetone.

[0020] Furthermore, the temperature of the oil bath in step (2) is 90-130℃.

[0021] Furthermore, the roasting temperature in step (3) is 600-1000℃ and the time is 3-8h.

[0022] The Co-based catalyst prepared above, with calcium iron oxide as a precursor, can be used for hydrogen production from ammonia decomposition.

[0023] The technical solution of the present invention has the following advantages:

[0024] (1) This invention provides a Co-based ammonia decomposition catalyst, in which the nitrogen dissociation and desorption energy on the surface of the active component Co is low, which is beneficial to the ammonia decomposition reaction. The calciferite structure is a subtype of the perovskite structure, which has BO6 octahedra similar to the perovskite lattice structure and ordered oxygen vacancies. The active metal elements are uniformly distributed in the calciferite, and the active species precipitated after reduction are uniformly dispersed, which is beneficial to the exposure of active sites and the generation of structurally stable supports. This effectively avoids the active sites being covered during the reaction, allowing ammonia to fully contact the active components, thereby improving the ammonia decomposition efficiency.

[0025] (2) The sol-gel method is employed, which offers simple and easily controllable preparation conditions. Metal species and complex groups are bonded to the overall structure of the complexing agent. After calcination, the active metal is uniformly dispersed in the precursor, facilitating the effective in-situ precipitation of Co during the reaction. Furthermore, the complexing agent can be screened and controlled according to the desired structure to obtain catalysts with specific dispersions or structures. This invention uses citric acid as the complexing agent. Its tricarboxylic acid can bond with metal ions, exhibiting strong complexing ability and resulting in a more uniform precursor oxide.

[0026] (3) Additive doping affects the precipitation of Co particles in the precursor and interacts with oxygen vacancies in the system to improve the electronic conduction performance of the support, thereby regulating the electronic state of Co to promote the recombination and desorption of nitrogen in the rate-determining step, regulating the size of Co particles on the catalyst, promoting the dispersion of active components, and facilitating electron transfer between active components and the support; at the same time, the doping of additives can increase the number of strong basic sites on the catalyst surface, which is beneficial to electron transfer between active metal and support, and promotes the association and desorption of N on the catalyst surface.

[0027] (4) The present invention introduces the additive and active component Co into the calcium iron oxide precursor and obtains the Co-based catalyst by in-situ atmosphere treatment. The preparation process is simple and easy to operate. The obtained catalyst has good ammonia decomposition performance at high space velocity. Attached Figure Description

[0028] Figure 1 The XRD patterns are of the catalyst samples obtained in Examples 1-6.

[0029] Figure 2 The images show the XRD patterns of the catalyst samples after reaction in Examples 1, 2, 5 and Comparative Examples 1 and 2.

[0030] Figure 3 This is a comparison chart showing the ammonia decomposition activity results of the catalyst samples obtained in Example 2, Comparative Example 1, and Comparative Example 2.

[0031] Figure 4 The above are the SEM test results of the catalyst sample obtained in Example 1.

[0032] Figure 5 The results are the Co-mapping test results of the catalyst sample obtained in Example 1. Detailed Implementation

[0033] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0034] Example 1

[0035] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, and 5.7536g of citric acid into a beaker, add 100mL of deionized water, and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Dry the beaker in a 120℃ oven for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress the sample into tablets and sieve to obtain SrCoO. 2.5 Catalyst sample.

[0036] Example 2

[0037] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, 0.2564g of magnesium nitrate, and 5.7536g of citric acid into a beaker, add 100mL of deionized water, and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Place the beaker in a 120℃ oven and dry for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress and sieve the sample to obtain Sr. 1- x Mg x CoO 2.5 Catalyst sample.

[0038] Example 3

[0039] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, 0.2613g of barium nitrate, and 5.7536g of citric acid into a beaker, add 100mL of deionized water, and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Dry the beaker in a 120℃ oven for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress and sieve the sample to obtain Sr. 1- x Ba x CoO 2.5 Catalyst sample.

[0040] Example 4

[0041] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, 0.4330g of lanthanum nitrate, and 5.7536g of citric acid into a beaker, add 100mL of deionized water, and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Place the beaker in a 120℃ oven and dry for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress and sieve the sample to obtain Sr. 1- x La x CoO 2.5 Catalyst sample.

[0042] Example 5

[0043] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, 0.4342g of cerium nitrate, and 5.7536g of citric acid into a beaker, add 100mL of deionized water, and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Dry the beaker in a 120℃ oven for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress the sample into tablets and sieve to obtain Sr. 1- x Ce x CoO 2.5 Catalyst sample.

[0044] Example 6

[0045] Weigh 2.1163g of strontium nitrate, 2.9103g of cobalt nitrate, 0.4445g of samarium nitrate, and 5.7536g of citric acid into a beaker. Add 100mL of deionized water to the beaker and stir overnight. Place the resulting mixture in a 120℃ oil bath and stir for 2-3 hours until a gel forms in the beaker. Place the beaker in a 120℃ oven and dry for 48 hours to allow the gel to fully foam and caramelize. Grind and crush the resulting sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000℃ for 6 hours. Then, compress and sieve the sample to obtain Sr. 1- x Sm x CoO 2.5 Catalyst sample.

[0046] Comparative Example 1

[0047] Weigh 4.2362 g of strontium nitrate and 5.7536 g of citric acid into a beaker, add 100 mL of deionized water to the beaker, and stir overnight. Place the resulting mixed solution in an oil bath at 120 °C and stir for 2-3 h until a gel-like state appears in the beaker. Place the beaker in an oven at 120 °C and dry for 48 h to allow the gel to fully foam and caramelize. Grind and crush the obtained sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000 °C for 6 h to obtain SrO.

[0048] Weigh 2.9103g of cobalt nitrate and add it to 10mL of deionized water. Impregnate 1.0362g of SrO support 3-5 times evenly. The resulting sample is then dried at 80℃ for 6-8h, and then calcined in a muffle furnace at 500℃ for 6h. After pressing and sieving, the Co / SrO catalyst sample is obtained.

[0049] Comparative Example 2

[0050] Weigh 4.2362 g of strontium nitrate and 5.7536 g of citric acid into a beaker, add 100 mL of deionized water to the beaker, and stir overnight. Place the resulting mixed solution in an oil bath at 120 °C and stir for 2-3 h until a gel-like state appears in the beaker. Place the beaker in an oven at 120 °C and dry for 48 h to allow the gel to fully foam and caramelize. Grind and crush the obtained sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000 °C for 6 h to obtain SrO.

[0051] Weigh 5.8206 g of cobalt nitrate and 5.7536 g of citric acid into a beaker, add 100 mL of deionized water to the beaker, and stir overnight; place the resulting mixed solution in an oil bath at 120 °C and stir for 2-3 h until a gel-like state appears in the beaker; place the beaker in an oven at 120 °C and dry for 48 h to allow the gel to fully foam and caramelize; grind and crush the obtained sample, place it in a porcelain boat, and calcine it in a muffle furnace at 1000 °C for 6 h to obtain Co3O4.

[0052] Weigh 1.0363g SrO and 0.8029g Co3O4 into a ball mill jar, balance the mixture, and place it in a planetary ball mill. Mill the mixture at 250 rpm for 6 hours. Remove the sample, press it into a tablet, and sieve it to obtain the Co3O4-SrO catalyst sample.

[0053] X-ray powder diffraction analysis was performed on an X'pert Pro diffractometer from Panalytic, Netherlands, using an X'Celerator detector, Co-Kα (λ = 0.1789 nm) target radiation, tube voltage 40 kV, tube current 40 mA, scan step size 0.0167°, each step 10.16 s, and scan range 2θ = 10-100°.

[0054] Scanning electron microscopy (SEM) experiments were performed on a ZEISS GeminiSEM 300 from Germany, operating at 15 kV. Samples were ground and demagnetized before testing. Morphology was measured using secondary electron mode, and energy dispersive spectroscopy (EDS) data were collected to obtain mapping results.

[0055] Activity testing conditions: The feed gas was pure ammonia, and the catalyst was heated to the test temperature in an ammonia atmosphere at a heating rate of 5℃ / min before the test began. The test space velocity was 30000 mL·g. -1 h -1 The test temperature range was 400–750℃. The catalyst activity was expressed as NH3 conversion rate, calculated as: Ammonia conversion rate = (Initial ammonia content - Ammonia content after treatment) / Initial ammonia content × 100%. The activity evaluation results of the examples and comparative examples are shown in the table below:

[0056] Table 1. Activity evaluation results (%) of the examples and comparative examples

[0057]

[0058] Table 2. Grain sizes (nm) of the examples and comparative examples.

[0059]

[0060] As shown in Table 1, the catalysts prepared in Examples 1-6 exhibit good performance at high space velocities (30000 mL·g⁻¹). -1 h -1 The catalysts obtained in Examples 1-6 exhibit high ammonia decomposition performance. Table 2 shows that the crystallite size on the (111) crystal plane of the catalysts obtained in Examples 1-6 is smaller than that of Comparative Examples 1-2. Example 2 achieved a 97.5% ammonia conversion rate and a smaller crystallite size at 600℃. This is because the present invention successfully prepared an alkaline earth metal magnesium-modified calcium iron stone structure catalyst via the sol-gel method. After ammonia treatment, the active metal precipitates in situ on the catalyst surface, which helps reduce the phenomenon of active sites being covered, allowing more active metal to be uniformly dispersed and exposed in the reaction medium, thus facilitating the ammonia decomposition reaction. By introducing alkaline earth metal magnesium to regulate the electronic properties between vacancies and Co species in the system, and to regulate the interaction strength between Co and ammonia molecules, the surface alkalinity of the support is enhanced. The synergistic effect of electronic properties and surface alkalinity promotes the ammonia decomposition reaction, thus exhibiting superior ammonia decomposition performance.

[0061] Figure 1 The figures show the XRD patterns of the catalyst samples obtained in Examples 1-6. It is clearly visible in the figures that Examples 1-3 all exhibit SrCoO₂. 2.5 The characteristic diffraction peaks indicate that the hedonic iron oxide structure was successfully synthesized; the XRD patterns of Examples 4-6 show SrCoO 2.5 The structure and characteristic diffraction peaks of SrCoO3 indicate that the doping of rare earth elements promotes the transformation of the hematite structure to the perovskite structure.

[0062] Figure 2 The XRD patterns of the catalyst samples from Examples 1, 2, and 5 and Comparative Examples 1 and 2 after reaction are shown. The peak at approximately 51.6° is attributed to the characteristic diffraction peak of the (111) crystal plane of Co. It can be clearly seen in the figure that the peak of the (111) crystal plane in the examples is significantly broadened compared to the peak in the comparative examples, indicating that the formation of the calc-iron mineral structure is conducive to the formation of smaller active metal grains in the reaction.

[0063] Figure 3 This is a comparison chart of the ammonia decomposition activity results of the catalyst samples obtained in Example 2, Comparative Example 1, and Comparative Example 2. As can be seen from the chart, Example 2 exhibits the best ammonia decomposition conversion rate.

[0064] Figure 4The figure shows the SEM test results of the catalyst sample obtained in Example 1. As can be seen from the figure, the catalyst sample obtained in Example 1 forms relatively uniformly dispersed active metal particles after the reaction.

[0065] Figure 5 The figure shows the Co-mapping test results of the catalyst sample obtained in Example 1. As can be seen from the figure, after the reaction, uniformly dispersed active metal particles were precipitated on the surface of the catalyst sample obtained in Example 1.

[0066] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of a Co-based catalyst using perovskite-structured oxides as precursors in ammonia decomposition for hydrogen production, characterized in that, The Co-based catalyst comprises an active component, a support, and an auxiliary agent; the active component is Co, and the support is SrO and SrCoO. x The composite oxide, wherein the auxiliary agent is an alkaline earth metal or rare earth metal oxide; by mass percentage, Co accounts for 25-35%, and the auxiliary agent accounts for 1-20%; the perovskite-structured oxide is Sr 1-x A x CoO 2.5 ; The preparation method of the Co-based catalyst includes the following steps: (1) Dissolve strontium salt, cobalt salt and auxiliary metal salt in solvent, and then add complexing agent and stir to dissolve; (2) Continue stirring the solution obtained in step (1) in an oil bath until it becomes gel-like, and dry the resulting gel-like sample in an oven at 120°C for 48 h; (3) Grind the dried product obtained in step (2) into powder, and calcine it in a muffle furnace to obtain the calcium iron oxide structure; (4) The calcium iron oxide obtained in step (3) is reduced in situ by ammonia to obtain the Co-based catalyst; The molar ratio of the auxiliary metal salt to the complexing agent in step (1) is 0.75 to 2:1, and the complexing agent is citric acid; The roasting temperature in step (3) is 1000 ℃ and the time is 6 h.

2. The application according to claim 1, characterized in that, The cobalt salt mentioned in step (1) is at least one of cobalt nitrate, cobalt carbonate, and cobalt acetylacetonate.

3. The application according to claim 1, characterized in that, The molar ratio of strontium salt to cobalt salt in step (1) is 0.5~1.2:1; the strontium salt is at least one of strontium nitrate, strontium carbonate, and strontium hydroxide.

4. The application according to claim 1, characterized in that, The molar ratio of the auxiliary metal salt to the cobalt salt in step (1) is 0.05~0.50:1; the auxiliary metal salt is at least one of magnesium nitrate, calcium nitrate, barium nitrate, lanthanum nitrate, cerium nitrate, and samarium nitrate.

5. The application according to claim 1, characterized in that, The solvent mentioned in step (1) is at least one of water, ethanol, and acetone.

6. The application according to claim 1, characterized in that, The oil bath temperature in step (2) is 90-130 ℃.

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