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

Abstract

This invention belongs to the field of catalyst technology and discloses an ammonia decomposition hydrogen production catalyst, its preparation method, and its application. The preparation method of this ammonia decomposition hydrogen production catalyst includes the following steps: first, under an inert atmosphere, a carbon support is successively calcined and acid-treated to obtain an acid-treated graphitized carbon support; ruthenium precursor, rare earth element precursor, and alkali metal precursor are added to ethanol and mixed to obtain a mixed solution; then, the graphitized carbon support is added to the mixed solution and mixed; then, urea and a surfactant are added, and mixing continues, followed by standing to obtain a solid precipitate; finally, the solid precipitate is heat-treated under a reducing atmosphere to obtain the final product. This catalyst uses highly graphitized carbon material as a support and achieves low-temperature, high-activity ammonia decomposition hydrogen production and long-term stable operation through the synergistic regulation of a dual-agent system—alkaline environment provided by alkali metal doping and interface formation between rare earth metal oxides and Ru.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to an ammonia decomposition hydrogen production catalyst, its preparation method and application. Background Technology

[0002] Among secondary energy carriers, hydrogen is considered an ideal choice due to its abundant sources, high calorific value, and zero carbon emissions, and hydrogen energy has attracted significant attention from research institutions and enterprises. Currently, a hydrogen-based sustainable energy industry is being promoted by society. However, storage and transportation are among the key issues restricting its large-scale application. Ammonia is an ideal carrier for hydrogen storage and transportation. Ammonia has a high hydrogen content (17.6 wt%), high volumetric energy density, and is easily liquefied under low pressure (at normal pressure, ammonia liquefies at -33°C, while hydrogen liquefies at -253°C). Compared to hydrogen, ammonia requires smaller and lighter storage and transportation containers. Ammonia releases hydrogen through catalytic decomposition. The ammonia industry has a good safety record. Approximately 150 million tons of ammonia are produced globally each year and transported worldwide via existing maritime, road, rail, and pipeline networks. Ammonia decomposition for hydrogen production will greatly expand the scale of hydrogen energy market applications.

[0003] Catalysts can lower the activation barrier for ammonia decomposition. Before the 1990s, Fe-based catalysts were widely used in ammonia decomposition research; however, Fe catalysts have poor resistance to poisoning and are easily deactivated after high-temperature reactions. In the mid-1990s, Ru-based catalysts became the focus of ammonia catalytic decomposition research. JC Ganley et al. conducted experiments on 13 different metal catalysts, and the activity results showed Ru>Ni>Rh>Co>Ir>Fe>Pt>Cr>Pd>Cu>Te,Se,Pb. Yin et al. studied the effects of active components Ru, Rh, Pt, Pd, Ni, Fe and different supports on the catalytic decomposition of ammonia to produce CO-free products. x The influence of hydrogen: when CNTs are used as supports, the catalytic activity order for ammonia decomposition is Ru > Rh > Ni > Pt > Pd > Fe. Hendershot et al. studied the ammonolysis reactions of Ir, Ni, Cu, Pt, Ru, Pd, and Rh on different supports using FTIR, and found that their ammonolysis catalytic activity order was: Ru > Ni > Ir > Pt > Fe. It is evident that Ru has the highest activity among all pure elements, but its scarcity and high cost hinder its large-scale development, and its low-temperature conversion rate and stability still have room for improvement. For example, Chinese invention patent CN 116139859 A discloses a Ru-based catalyst with carbon-encapsulated silica SiO2@C support, at 600℃ and 30000 mL / (h·g) catThe conversion rate was 99.9% at 500℃, but the ammonia conversion efficiency was poor at low and medium temperatures, and the stability test only lasted 50 hours. Chinese invention patent CN 117983245 A discloses an ammonia decomposition hydrogen production catalyst and its preparation method, with a conversion rate of 99.9% at 500℃ and 30000 mL / (h·g) cat The conversion rate was 95% at the initial temperature, but the conversion rate was not high enough even though the temperature was not high. After 100 hours, the conversion rate decreased by 7%.

[0004] Therefore, research on ammonia decomposition hydrogen production catalysts is increasingly focused on improving catalytic performance while reducing the amount of precious metals used. Developing ammonia decomposition hydrogen production catalysts with low loading, high performance and high stability has become a key strategy for improving catalytic economics. Summary of the Invention

[0005] This invention addresses the common technical problems of ammonia decomposition hydrogen production catalysts, such as high Ru content, limited low-temperature reaction kinetics, and insufficient NH3 conversion rates to meet industrial demands under current economic temperatures. It proposes an ammonia decomposition hydrogen production catalyst, its preparation method, and its applications. This catalyst uses highly graphitized carbon material as a support. Through the synergistic regulation of a dual-promoter mechanism—alkaline environment provided by alkali metal doping and interface formation between rare earth metal oxides and Ru—the electronic structure of the Ru active sites is significantly optimized, enhancing the adsorption and activation capacity for NH3. Simultaneously, utilizing the excellent thermal conductivity and chemical stability of highly graphitized carbon, low-temperature, highly active ammonia decomposition hydrogen production and long-term stable operation are achieved.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a method for preparing an ammonia decomposition hydrogen production catalyst, comprising the following steps:

[0007] Acid-treated graphitized carbon support was prepared by calcining and acid treatment of the carbon support in an inert atmosphere.

[0008] Ruthenium precursor, rare earth element precursor and alkali metal precursor are added to ethanol and mixed to prepare a mixed solution.

[0009] The graphitized carbon support is added to the mixed solution and mixed; then urea and surfactant are added, and mixing continues. After standing, the solid precipitate is separated.

[0010] The solid precipitate was heat-treated under a reducing atmosphere to obtain the ammonia decomposition hydrogen production catalyst.

[0011] Specifically, in the preparation process of the ammonia decomposition hydrogen production catalyst of the present invention, the carbon support is first subjected to high-temperature calcination and acid treatment to obtain a graphitized carbon support with high specific surface area and excellent electron transfer capability. The high specific surface area ensures the anchoring and dispersion of the support and active sites; high graphitization is beneficial to improving the catalyst's resistance to CH4 formation in a hydrogen-rich environment, thereby improving the catalyst's stability. Then, the ruthenium precursor, rare earth element precursor, alkali metal precursor, and graphitized carbon support are mixed and heat-treated under a reducing atmosphere. In the reducing atmosphere, Ru ions in the Ru precursor, due to the restriction of the graphitized support, form highly dispersed Ru nanoparticles. At high temperature, the rare earth element precursor generates rare earth metal oxides. During the co-precipitation process, the rare earth metal oxides are influenced by Ru and deposit near the Ru nanoparticles, improving the coordination environment on the Ru surface and forming a heterogeneous interface between Ru nanoparticles and rare earth metal oxides. Meanwhile, the alkali metal precursor solution etches the surface of carbon, causing significant changes to the surface of the carbon support; and during the heat treatment process, the alkali metal precursor undergoes an alkali activation reaction with the graphitized carbon support to generate alkali metal. The alkali metal is beneficial to improving the overall alkalinity and alkaline sites of the material and forming a carbon support doped with alkali metal single atoms.

[0012] In some embodiments of the present invention, the calcination temperature is not less than 2000°C, and the calcination time is 2-4 hours.

[0013] Specifically, calcination at ultra-high temperatures above 2000℃ is beneficial to improving the graphitization degree of the carbon support, thereby obtaining a graphitized carbon support with excellent conductivity and chemical stability, laying the foundation for achieving low-temperature, high-activity ammonia decomposition for hydrogen production and long-term stable operation.

[0014] In some embodiments of the present invention, the calcination temperature is 2000-3000℃, and the heating rate is 5-10℃ / min. Calcination temperatures that are too low or too high are detrimental to the catalytic activity and stability of the graphitized carbon support.

[0015] In some embodiments of the present invention, the intensity ratio of the Raman D peak and G peak of the graphitized carbon support, ID / IG, satisfies the following relationship: 0.4 ≤ ID / IG ≤ 0.89.

[0016] Specifically, in Raman spectroscopy, the D peak and G peak represent two characteristic peaks of carbon materials. The D peak characterizes structural defects or disorder in carbon materials, while the G peak characterizes the degree of graphitization and structural order. The ID / IG ratio represents the intensity ratio of the D and G peaks, and its magnitude reflects the relative degree of graphitization and disorder in the carbon material. A larger ratio indicates more structural defects or disorder in the material; conversely, a smaller ratio indicates a higher degree of graphitization and lower disorder. This invention controls the range of the ID / IG ratio of the graphitized carbon support to ensure the degree of graphitization of the carbon material.

[0017] In some embodiments of the present invention, the acid treatment uses a mixed solution of nitric acid and hydrogen peroxide.

[0018] In some embodiments of the present invention, the concentration of nitric acid is 65-75%, the concentration of hydrogen peroxide is 25-35%, and the volume ratio of nitric acid to hydrogen peroxide is 1:(0.5-1.5).

[0019] In some embodiments of the present invention, the inert atmosphere is a nitrogen or argon atmosphere, and the gas flow rate is 50-100 mL / min.

[0020] In some embodiments of the present invention, the ruthenium precursor is selected from at least one of ruthenium nitrite and ruthenium chloride.

[0021] In some embodiments of the present invention, the rare earth element precursor is selected from at least one of rare earth element nitrates and their hydrates. For example, yttrium nitrate hexahydrate, lanthanum nitrate hexahydrate, praseodymium nitrate hexahydrate, cerium nitrate hexahydrate, etc.

[0022] In some embodiments of the present invention, the alkali metal precursor is selected from at least one of alkali metal nitrates and alkali metal carbonates. For example, potassium nitrate, potassium carbonate, etc.

[0023] In some embodiments of the present invention, the mass ratio of the graphitized carbon support to the ruthenium precursor, the rare earth element precursor and the alkali metal precursor is 100:(1-10):(1-10):(1-10); the preferred mass ratio is 100:(4-6):(4-6):(4-6).

[0024] In some embodiments of the present invention, the surfactant comprises hexadecyltrimethylammonium bromide (CTAB).

[0025] In some embodiments of the present invention, the carbon support can be a commonly used carbon support in the art, such as XC-72, EC300J, ECP600JD, etc.

[0026] In some embodiments of the present invention, the molar ratio of urea to ruthenium precursor is (15-30):1; the preferred molar ratio is (15-25):1.

[0027] In some embodiments of the present invention, the mass ratio of the surfactant to the graphitized carbon support is (10-30):100; the preferred mass ratio is (10-20):100.

[0028] Specifically, urea has the characteristic of slow decomposition upon heating, and surfactants (such as CTAB) have a regulatory effect on the ion concentration and local environment in the solution, so that the prepared composite precursor can dissociate at a slower rate, thereby ensuring the mildness of the reaction and the uniformity of precipitation.

[0029] In some embodiments of the present invention, the temperature of the heat treatment is 450-800°C, and the time of the heat treatment is 1-3 hours.

[0030] In some embodiments of the present invention, the heating rate of the heat treatment is 3-10°C / min.

[0031] In some embodiments of the present invention, the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume percentage of hydrogen is not less than 5%, and the gas flow rate is 50-200 mL / min.

[0032] A second aspect of the present invention provides an ammonia decomposition hydrogen production catalyst, prepared by the above-described preparation method, comprising a support and an active component, wherein the active component is uniformly distributed on the surface of the support; the support is graphitized carbon doped with alkali metal single atoms, and the active component comprises ruthenium metal nanoparticles and rare earth metal oxides, wherein the ruthenium metal nanoparticles and rare earth metal oxides form a heterojunction interface.

[0033] Specifically, the ammonia decomposition hydrogen production catalyst of the present invention significantly optimizes the mass transfer process through dual doping via the alkaline environment provided by alkali metals and the interface effect formed by rare earth metal oxides and ruthenium metal nanoparticles. At the same time, by improving the microstructure and surface properties of the catalyst, the diffusion and transport efficiency of ammonia, hydrogen and nitrogen are significantly improved, thereby accelerating the reaction rate and enhancing the overall performance of the catalyst.

[0034] 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.

[0035] The ammonia decomposition hydrogen production catalyst of the present invention can achieve a conversion rate of 99.0-99.8% when the reaction temperature in ammonia decomposition hydrogen production is 500℃ and the reaction space velocity is 30000mL / g / h.

[0036] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0037] (1) A good support should have strong conductivity to transfer electrons, and a high specific surface area to ensure anchoring and dispersion with active sites. This invention prepares a graphitized carbon support with high specific surface area and excellent electron transfer capability by subjecting the carbon support to ultra-high temperature calcination and acid treatment, which exhibits excellent performance in ammonia decomposition. Simultaneously, this invention further optimizes the performance of ammonia decomposition by alkali doping the graphitized support, providing sufficient electron density. Furthermore, a highly graphitized support can improve the catalyst's resistance to CH4 formation in a hydrogen-rich environment, thereby improving material stability. Therefore, the graphitized support of this invention significantly optimizes the mass transfer process of reactants and products by improving the catalyst's microstructure and surface properties, providing an important guarantee for efficient ammonia decomposition. Improving environmental alkalinity accelerates electron conduction, accelerating NH3 adsorption and N2 and H2 desorption processes, thereby accelerating the ammonia decomposition reaction and improving ammonia conversion performance.

[0038] (2) This invention mixes ruthenium precursor, rare earth element precursor, alkali metal precursor and graphitized carbon support, and performs heat treatment under a reducing atmosphere to bring Ru nanoparticles and rare earth metal oxides into close proximity. The rare earth metal oxides improve the coordination environment of the Ru surface, forming a heterogeneous interface between Ru nanoparticles and rare earth metal oxides. The interface effect not only accelerates mass transport and increases the reaction rate, thereby effectively enhancing the catalytic effect, but also affects the preferential orientation of Ru nanoparticles. The rare earth metal oxides, as an effective promoter to prevent high-temperature sintering of Ru nanoparticles, work together with Ru nanoparticles to enhance the structural stability of the catalyst, while reducing the deactivation of active sites and the occurrence of side reactions by optimizing surface properties and mass transfer processes.

[0039] (3) The ammonia decomposition hydrogen production catalyst prepared in this invention has good low-temperature high-efficiency catalytic activity and stability, achieving a space velocity of 30000 mL / hg at 500℃. -1 Under the given reaction conditions, the ammonia decomposition conversion rate can reach 99.0-99.8%; at a temperature of 773.15K, the decay rate is less than 2% after 300 hours. Attached Figure Description

[0040] Figure 1 This is a TEM image of the ammonia decomposition hydrogen production catalyst prepared in Example 1 of the present invention;

[0041] Figure 2 The graph shows the ammonia decomposition conversion performance distribution of the ammonia decomposition hydrogen production catalysts prepared in Examples 1-4 and Comparative Examples 1-3 of this invention.

[0042] Figure 3 This is a stability performance distribution diagram of the ammonia decomposition hydrogen production catalysts prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0043] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0044] Example 1

[0045] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0046] (1) XC-72 carbon support was placed in a high-temperature furnace, and argon gas was introduced at a rate of 4 L / min. The temperature was increased to 2000℃ at a rate of 10℃ / min and held for 3 h. The ID / IG ratio of the obtained graphitized carbon support was 0.89. Then, 70% nitric acid and 30% hydrogen peroxide were mixed at a volume ratio of 1:1 to obtain a mixed solution. 300 mL of the mixed solution and 10 g of graphitized carbon support were placed in a flask and connected to a reflux condenser and a conical flask for recovering impurity gas products. The mixture was heated to 80℃ and held for 4 h. After cooling to room temperature, it was centrifuged and filtered once (solid-liquid separation). Then, deionized water was added to wash and the mixture was filtered. The mixture was placed in a vacuum oven at 60℃ and dried for 12 h. The mixture was then ground in a mortar to obtain acid-treated graphitized XC-72 carbon support. The BET test of the graphitized XC-72 carbon support showed a specific surface area of ​​956 m². 2 / g.

[0047] (2) Add ruthenium nitrite, yttrium hexahydrate and potassium nitrate to ethanol, mix to prepare a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support to the mixed solution, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60°C; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 800°C at a rate of 3°C / min, and keep at the temperature for 2 h to obtain the Ru / C ammonia decomposition hydrogen production catalyst with dual K and Y2O3 regulation in this embodiment.

[0048] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate, yttrium hexahydrate, and potassium nitrate is 100:5:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L; the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 20:100.

[0049] Figure 1 The image shows the TEM morphology of the ammonia decomposition hydrogen production catalyst prepared in this embodiment. Figure 1 The lattice fringes of Y₂O₃ and Ru can be clearly seen. Measurements show that the spacing between Y₂O₃ on the (222) crystal plane is 0.306 nm, and the spacing between Ru on the (101) crystal plane is 0.205 nm. Furthermore, the rare earth metal oxides Y₂O₃ and Ru form a clear heterogeneous interface. The formation of the heterogeneous interface is beneficial for accelerating product desorption and improving catalyst activity.

[0050] Example 2

[0051] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0052] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0053] (2) Add ruthenium nitrite, lanthanum nitrate hexahydrate and potassium nitrate to ethanol, mix to obtain a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60°C; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 800°C at a rate of 3°C / min, and keep at the temperature for 2 h to obtain the Ru / C ammonia decomposition hydrogen production catalyst with dual K and La2O3 regulation in this embodiment.

[0054] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate, lanthanum nitrate hexahydrate, and potassium nitrate is 100:5:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L; the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 20:100.

[0055] Example 3

[0056] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0057] (1) Following the preparation method of Example 1, only the calcination temperature was changed to 3000℃, and the resulting graphitized carbon support ID / IG ratio was 0.4.

[0058] (2) Add ruthenium nitrite nitrate, praseodymium nitrate hexahydrate and potassium nitrate to ethanol, mix to obtain a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly, and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60℃; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 800℃ at a rate of 3℃ / min, and hold for 2 h to obtain K and Pr6O in this example. 11 A dual-regulated Ru / C ammonia decomposition hydrogen production catalyst.

[0059] The mass ratio of graphitized XC-72 carbon support to ruthenium nitrite nitrate, praseodymium nitrate hexahydrate, and potassium nitrate is 100:5:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L; the molar ratio of urea to ruthenium nitrite nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 20:100.

[0060] Example 4

[0061] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0062] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0063] (2) Add ruthenium nitrite, cerium nitrate hexahydrate and potassium nitrate to ethanol, mix to obtain a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60°C; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 800°C at a rate of 3°C / min, and keep at the temperature for 2 h to obtain the Ru / C ammonia decomposition hydrogen production catalyst with dual K and CeO2 regulation in this embodiment.

[0064] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate, cerium nitrate hexahydrate, and potassium nitrate is 100:5:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L; the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 20:100.

[0065] Comparative Example 1

[0066] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0067] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0068] (2) Add ruthenium nitrite to ethanol, mix, and prepare ruthenium nitrite solution. Stir for 5 min. Then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min. Then add urea and CTAB, stir evenly and let stand. Then filter the precipitate, wash with deionized water, and dry in an oven at 60°C. Place the dried precipitate in a tube furnace under H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 450°C at a rate of 3°C / min, and keep warm for 2 h to obtain the Ru / C ammonia decomposition hydrogen production catalyst of this comparative example.

[0069] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate is 100:5, the mass-volume ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate solution is 35g:1L, the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1, and the mass ratio of CTAB to graphitized XC-72 carbon support is 10:100.

[0070] The difference between Comparative Example 1 and Example 1 is that yttrium hexahydrate and potassium nitrate were not added during the preparation process.

[0071] Comparative Example 2

[0072] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0073] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0074] (2) Add ruthenium nitrite and yttrium hexahydrate to ethanol, mix to obtain a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly, and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60℃; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 600℃ at a rate of 3℃ / min, and keep warm for 2 h to obtain the comparative example of Y2O3-regulated Ru / C ammonia decomposition hydrogen production catalyst.

[0075] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate and yttrium nitrate hexahydrate is 100:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L; the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 10:100.

[0076] The difference between Comparative Example 2 and Example 1 is that potassium nitrate was not added during the preparation process.

[0077] Comparative Example 3

[0078] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0079] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0080] (2) Add ruthenium nitrite and potassium nitrate to ethanol, mix to obtain a mixed solution, and stir for 5 min; then add graphitized XC-72 carbon support, sonicate for 5 min and stir for 5 min; then add urea and CTAB, stir evenly, and let stand; then filter the precipitate, wash with deionized water, and dry in an oven at 60℃; place the dried precipitate in a tube furnace under an H2 / Ar (H2 volume percentage is 5%) atmosphere, heat to 800℃ at a rate of 3℃ / min, and keep warm for 2 h to obtain the K-controlled Ru / C ammonia decomposition hydrogen production catalyst of this comparative example.

[0081] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate and potassium nitrate is 100:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35g:1L; the molar ratio of urea to nitrosyl ruthenium nitrate is 20:1; and the mass ratio of CTAB to graphitized XC-72 carbon support is 10:100.

[0082] The difference between Comparative Example 3 and Example 1 is that yttrium nitrate hexahydrate was not added during the preparation process.

[0083] Comparative Example 4

[0084] The only difference between Comparative Example 4 and Example 1 is that the calcination temperature of the XC-72 carbon support is 1000°C, and the resulting graphitized carbon support has an ID / IG ratio of 0.98.

[0085] Comparative Example 5

[0086] A method for preparing an ammonia decomposition hydrogen production catalyst includes the following steps:

[0087] (1) Acid-treated graphitized XC-72 carbon support was prepared using the same method as in Example 1.

[0088] (2) Ruthenium nitrite nitrate, yttrium hexahydrate and potassium nitrate were added to ethanol and mixed to obtain a mixed solution. The mixture was stirred for 5 min. Then, graphitized XC-72 carbon support was added, and the mixture was sonicated for 5 min and stirred for 5 min. Then, rotary evaporation was performed until the solvent evaporated at a temperature of 40℃ and a rotation speed of 100 r / min. The precipitate was then dried in an oven at 60℃. The dried precipitate was placed in a tube furnace under an H2 / Ar atmosphere (H2 volume percentage of 5%) and heated to 450℃ at a rate of 3℃ / min. The temperature was maintained for 2 h to obtain the ammonia decomposition hydrogen production catalyst of this comparative example.

[0089] The mass ratio of graphitized XC-72 carbon support to nitrosyl ruthenium nitrate, yttrium nitrate hexahydrate, and potassium nitrate is 100:5:5:5; the mass-volume ratio of graphitized XC-72 carbon support to the mixed solution is 35 g:1 L.

[0090] The only difference between Comparative Example 5 and Example 1 is that the solvent evaporation method is used instead of the coprecipitation method in Example 1.

[0091] Performance testing

[0092] The ammonia decomposition hydrogen production catalysts prepared in Examples 1-4 and Comparative Examples 1-5 were tested for their ammonia decomposition reaction performance. The tests were conducted in a fixed-bed reaction system, where the reaction tube was a quartz tube with an inner diameter of 8 mm, and the catalyst loading was 0.1 g. The heat required for the reaction was provided by a vertical tube furnace. Pure NH3 was introduced at a rate of 50 mL / min within a temperature range of 300-550 °C to evaluate the catalytic performance. The temperature was maintained for 1 hour per test to ensure stability. The hydrogen emission concentration was analyzed online using a gas chromatograph equipped with a thermal conductivity detector. A stability test was conducted at 773.15 K for 300 hours, and the corresponding data were continuously collected.

[0093] The ammonia decomposition and conversion performance of Examples 1-4 and Comparative Examples 1-3 are as follows: Figure 2 As shown, by Figure 2 It can be seen that the dual-regulated catalysts prepared in Examples 1-4 exhibit significantly higher performance than the catalysts prepared in Comparative Examples 1-5. This indicates that the catalysts in Examples 1-4 demonstrate improved basicity sites and interfacial effects, promoting the desorption of hydrogen and nitrogen, thereby enhancing the catalyst activity. Specifically, the ammonia decomposition hydrogen production catalyst prepared in Example 1, at a relatively low temperature of 450°C, has a space velocity of 30000 mL / hg. -1 Under the given reaction conditions, the ammonia decomposition conversion rate can still reach 99.2%.

[0094] The stability performance of Example 1 and Comparative Example 1 is as follows: Figure 3 As shown, by Figure 3It can be seen that the dual-regulated catalyst prepared in Example 1 has better stability than the catalyst prepared in Comparative Example 1, with a degradation of less than 2% after 300 h. The high stability is due to the synergistic effect of alkali metal and rare earth metal oxides, which not only enhances the structural stability of the catalyst, but also reduces the deactivation of active sites and the occurrence of side reactions by optimizing surface properties and mass transfer processes.

[0095] The ammonia decomposition hydrogen production catalysts prepared in Examples 1-4 and Comparative Examples 1-5 were tested at 500°C and a space velocity of 30000 mL / hg. -1 Under the reaction conditions, the ammonia decomposition conversion rate is shown in Table 1.

[0096] Table 1:

[0097]

[0098] As shown in Table 1, the ammonia decomposition hydrogen production catalysts prepared in Examples 1-4 all exhibited excellent ammonia decomposition performance under the conditions of a test space velocity of 30000 mL / g / h and a test temperature of 500℃, with ammonia decomposition conversion rates exceeding 99.0%, and Example 1 even reaching 99.8%. Compared to Example 1, Comparative Examples 1-5 all showed varying degrees of decrease in ammonia decomposition conversion rates due to differences in the active components, supports, or preparation processes used in preparing the ammonia decomposition hydrogen production catalysts.

[0099] In summary, the combined use of different carbon-supported Ru with alkali metals and rare earth metal oxides in catalysts has a significant positive effect on catalyst performance. This synergistic effect is not only reflected in the individual performance enhancements of each component, but also in the significant performance gains resulting from their combined action. Meanwhile, the preparation process also has a considerable impact on the catalytic performance of the catalyst.

[0100] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for producing an ammonia decomposition hydrogen production catalyst, characterized by, The method comprises the following steps: The carbon carrier is calcined and acid treated successively under an inert atmosphere to obtain an acid-treated graphitized carbon carrier; the calcination temperature is not less than 2000 ℃, and the calcination time is 2-4 hours; the intensity ratio ID / IG of the Raman D peak and G peak of the graphitized carbon carrier satisfies the relationship 0.4≤ID / IG≤0.89; the acid treatment uses a mixed solution of nitric acid and hydrogen peroxide; A ruthenium precursor, a rare earth element precursor and an alkali metal precursor are added into ethanol, mixed to obtain a mixed solution; the ruthenium precursor is selected from at least one of ruthenium nitrosyl nitrate and ruthenium chloride; the rare earth element precursor is selected from at least one of a nitrate and a hydrate of a rare earth element; the alkali metal precursor is selected from at least one of a nitrate and a carbonate of an alkali metal; The graphitized carbon carrier is added into the mixed solution and mixed; then urea and a surfactant are added and continuously mixed, and the solid precipitate is separated after standing; the mass ratio of the graphitized carbon carrier to the ruthenium precursor, the rare earth element precursor and the alkali metal precursor is 100:(1-10):(1-10):(1-10); the molar ratio of the urea to the ruthenium precursor is (15-30):1; and the mass ratio of the surfactant to the graphitized carbon carrier is (10-20):100; The solid precipitate is heat treated under a reducing atmosphere, the heat treatment temperature is 450-800 ℃, and the heat treatment time is 1-3 hours to obtain the ammonia decomposition hydrogen production catalyst.

2. An ammonia decomposition hydrogen production catalyst characterized by, The ammonia decomposition hydrogen production catalyst is prepared by the method of claim 1, and comprises a carrier and active ingredients, wherein the active ingredients are uniformly distributed on the surface of the carrier; the carrier is alkali metal single atom-doped graphitized carbon, and the active ingredients include ruthenium metal nanoparticles and rare earth metal oxides, and the ruthenium metal nanoparticles and the rare earth metal oxides form a heterojunction interface.

3. The ammonia decomposition hydrogen production catalyst of claim 2 is applied in an ammonia decomposition hydrogen production reaction.

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