A carrier size-regulated ammonia decomposition hydrogen production catalyst, a preparation method and application thereof

Abstract

The application relates to a carrier size-regulated ammonia decomposition hydrogen production catalyst and a preparation method and application thereof. The carrier size-regulated ammonia decomposition hydrogen production catalyst comprises an active component and a carrier; the active component is ruthenium, and the carrier is micron-grade magnesium oxide. By using micron-grade magnesium oxide as the carrier to load the active component ruthenium, the active component ruthenium can be highly dispersed and stabilized in an optimal size, the density of B5 type active sites is greatly improved, the Ru (10-11) crystal surface with higher activity can be preferentially exposed, the energy barrier of the ammonia decomposition rate-determining step is effectively reduced, and therefore the catalytic activity and catalytic stability of the catalyst are remarkably improved.

Description

Technical Field

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

[0002] Hydrogen is considered an ideal alternative to fossil fuels due to its pollution-free nature, renewability, and zero carbon emissions during combustion. However, hydrogen has a low energy density and is difficult to transport, necessitating the selection of a suitable hydrogen storage carrier. Among these, ammonia, with its high hydrogen content (17.6%), high energy density, and carbon-neutral properties, is considered a highly promising hydrogen storage and transportation option. Furthermore, the strong endothermic nature of ammonia decomposition makes improving the catalytic activity and stability of the catalyst in high-temperature, hydrogen-rich environments crucial for ammonia decomposition to produce hydrogen.

[0003] Currently, to simultaneously improve the catalytic activity and stability of catalysts in high-temperature hydrogen-rich environments, researchers are dedicated to developing advanced catalysts, including active metals, supports, and promoters. Among these, Ru-based catalysts exhibit excellent low-temperature activity (due to the strength of the Ru-N bond), and since ammonia decomposition is a structure-sensitive reaction, the B5-type active sites of Ru (composed of three atoms on the surface and two additional Ru atoms in the subsurface) are considered to be the active sites for ammonia decomposition. The concentration of B5-type active sites depends on the size and shape of the Ru particles.

[0004] CN113289620A discloses a single-atom ruthenium catalyst, its preparation method, and its application. By controlling the average pore size of the mesoporous rare earth oxide support, metallic ruthenium is anchored in the mesoporous mixed rare earth oxide in the form of single atoms, thus exhibiting excellent catalytic activity and stability. CN118384881A discloses an ammonia decomposition hydrogen production catalyst, its preparation method, its application, and a coating process. The ammonia decomposition hydrogen production catalyst prepared by the liquid-phase synthesis method has small and uniform active metal particles (1 nm to 3 nm).

[0005] Furthermore, the properties of the support are also a crucial factor affecting the catalytic activity and stability of ruthenium-based catalysts. MgO, as an alkaline metal oxide, possesses unique basicity and electronic properties that endow it with excellent electron-donating capabilities, thereby influencing the electronic properties of Ru particles. However, our understanding of the impact of MgO particle size variation and size effect on the active site mechanism is limited, indicating significant room for optimization in this area.

[0006] Therefore, how to control the support size to precisely design the electronic properties and adsorption configuration of the active center, and synthesize efficient and stable Ru-based catalysts for ammonia decomposition to hydrogen production, is an urgent problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a catalyst for ammonia decomposition and hydrogen production with support size control, its preparation method, and its application. This invention utilizes micron-sized magnesium oxide as a support to load the active component ruthenium, enabling the ruthenium to be highly dispersed and stabilized at its optimal size. This significantly increases the density of B5-type active sites and promotes the preferential exposure of the more active Ru(10-11) crystal facets, effectively lowering the energy barrier for the ammonia decomposition rate step, thereby significantly improving the catalytic activity and stability of the catalyst.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides an ammonia decomposition hydrogen production catalyst with support size control, the ammonia decomposition hydrogen production catalyst with support size control includes an active component and a support; the active component is ruthenium, and the support is micron-sized magnesium oxide.

[0010] This invention uses micron-sized magnesium oxide as a support to load the active component ruthenium, which can highly disperse and stabilize the active component ruthenium at its optimal size, significantly increasing the density of B5-type active sites. It can also promote the preferential exposure of the more active Ru(10-11) crystal facet, effectively reducing the energy barrier for the ammonia fractionation step, thereby significantly improving the catalytic activity and catalytic stability of the catalyst.

[0011] Preferably, the median particle size D50 of the micron-sized magnesium oxide is 1μm to 100μm, for example, it can be 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 50μm, 80μm or 100μm, and more preferably 15μm to 40μm.

[0012] This invention improves the catalytic activity of ammonia decomposition for hydrogen production by controlling the median particle size (D50) of micron-sized magnesium oxide, thereby balancing ruthenium species dispersibility, active site accessibility, and bed mass transfer performance. Specifically, when D50 is too small, the support particles are prone to agglomeration and accumulation, which may limit bed mass transfer channels and affect the uniform dispersion of ruthenium species on the support surface, reducing the number of effectively exposed active sites and thus decreasing catalytic activity. Conversely, when D50 is too large, the usable area on the outer surface of the support is relatively reduced, which is not conducive to the high dispersion of ruthenium species and may easily lead to local enrichment of ruthenium species. At the same time, larger particles may also increase the diffusion resistance of reactants and products, reducing the utilization efficiency of active components.

[0013] Preferably, the median particle size D50 of the active component is 1nm to 10nm, for example, it can be 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 8nm or 10nm, and is more preferably 2nm to 5nm.

[0014] The present invention preferably uses micron-sized magnesium oxide with a median particle size D50 of 15 μm to 40 μm to further promote the dispersion of the active component ruthenium and stabilize its median particle size D50 at 2 nm to 5 nm, thereby further increasing the density of B5 type active sites and significantly improving the catalytic activity and catalytic stability of the catalyst.

[0015] Preferably, the mass of the active component is 0.1wt% to 10wt% of the mass of the carrier, for example, it can be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 8wt% or 10wt%, etc., preferably 0.1wt% to 2wt%.

[0016] In this invention, the preferred mass of the active component is 0.1wt% to 2wt% of the support mass. If the loading of the active component is too low, the adsorption and activation capacity of the reactant molecules will be insufficient, resulting in a decrease in catalytic activity. If the loading of the active component is too high, the active component is prone to agglomeration, reducing its dispersion on the support surface and potentially causing pore blockage and limited mass transfer, which reduces the utilization rate of active sites and thus affects the reaction activity of the catalyst.

[0017] Preferably, the ammonia decomposition hydrogen production catalyst with carrier size control further includes an auxiliary agent.

[0018] Preferably, the additives include rare earth metal oxides.

[0019] Preferably, the rare earth metal oxide includes cerium dioxide.

[0020] This invention introduces the auxiliary agent cerium dioxide, whose unique Ce... 4+ / Ce 3+ Reversible valence state transitions and oxygen storage capacity can promote the generation of oxygen vacancy defects, enabling them to donate electrons to the active component ruthenium, thereby modulating the electronic state of ruthenium. This electronic modulation can increase the electron density on the Ru surface and optimize the interaction of Ru sites with NH3 and NH4+. x The adsorption strength of reactants and intermediates such as N makes NH3 more readily adsorbed and activated, and NH bond breaking more easily. Simultaneously, it avoids excessive adsorption of N species on the Ru surface, promoting the recombination of N atoms and the desorption of N2. Furthermore, the oxygen vacancies on the CeO2 surface can serve as anchoring sites for Ru species, enhancing the interaction between Ru and the support, inhibiting the migration, agglomeration, and sintering of Ru particles during high-temperature reactions, thereby improving the dispersibility and structural stability of the active components, ultimately further enhancing the catalytic activity and stability of the catalyst.

[0021] Preferably, the mass of the additive is 0.1wt% to 10wt% of the mass of the carrier, for example, it can be 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 8wt% or 10wt%, etc., preferably 0.5wt% to 3wt%.

[0022] In a second aspect, the present invention provides a method for preparing an ammonia decomposition hydrogen production catalyst with support size control as described in the first aspect, comprising the following steps: adding micron-sized magnesium oxide to a ruthenium salt solution, adding a precipitant to perform a deposition-precipitation reaction to obtain a precursor; and reducing the precursor to obtain the ammonia decomposition hydrogen production catalyst with support size control.

[0023] Preferably, the ruthenium salt in the ruthenium salt solution is any one or a combination of at least two of ruthenium trichloride, ruthenium oxynitrate, or ruthenium acetylacetonate. Typical but non-limiting combinations include combinations of ruthenium trichloride and ruthenium oxynitrate, combinations of ruthenium oxynitrate and ruthenium acetylacetonate, combinations of ruthenium trichloride and ruthenium acetylacetonate, and combinations of ruthenium trichloride, ruthenium oxynitrate, and ruthenium acetylacetonate.

[0024] It should be noted that the present invention does not limit the concentration of the ruthenium salt solution; it is sufficient to control the mass of the active component ruthenium within the range of 0.1wt% to 10wt% of the carrier mass.

[0025] Preferably, the solvent in the ruthenium salt solution includes water.

[0026] Preferably, the precipitant comprises urea.

[0027] Preferably, the molar ratio of ruthenium in the ruthenium salt to the precipitant is 1:(100~300), for example, it can be 1:100, 1:150, 1:200, 1:250 or 1:300, etc.

[0028] Preferably, the preparation method further includes preparing micron-sized magnesium oxide loaded with cerium dioxide, comprising the following steps: adding micron-sized magnesium oxide to a cerium salt aqueous solution, performing excess impregnation, and then calcining to obtain the micron-sized magnesium oxide loaded with cerium dioxide.

[0029] This invention first loads cerium dioxide onto micron-sized magnesium oxide using an excess impregnation method, and then loads ruthenium onto the cerium-loaded micron-sized magnesium oxide using a deposition-precipitation method. This allows the cerium dioxide additive to be uniformly dispersed and anchored on the magnesium oxide support surface beforehand, forming a stable CeO2-MgO composite interface and abundant oxygen vacancy defect sites. This structure neither disrupts the original alkaline environment and structural stability of the micron-sized magnesium oxide support, nor significantly covers or buries the subsequently formed Ru active sites; on the contrary, the pre-introduced CeO2 can serve as an anchoring point for Ru species, promoting high dispersion of Ru on the support surface and inhibiting the migration, agglomeration, and sintering of Ru particles during reduction treatment and ammonia decomposition reactions. Simultaneously, CeO2 possesses Ce... 4+ / Ce 3+ The reversible transformation capability and good oxygen storage and release characteristics can regulate the electronic structure of Ru through Ru-CeO2-MgO interface interaction, improve the adaptability of Ru sites to NH3 activation, NH bond breaking and N2 desorption processes, thereby further enhancing the ammonia decomposition activity and stability of the catalyst.

[0030] Preferably, the cerium salt in the cerium salt aqueous solution includes cerium nitrate and / or cerium trichloride.

[0031] It should be noted that the present invention does not limit the concentration of the cerium salt solution; it is only necessary to control the mass of the auxiliary agent cerium dioxide within the range of 0.1wt% to 10wt% of the carrier mass.

[0032] Preferably, the excessive soaking time is 3h to 8h, for example, it can be 3h, 4h, 5h, 6h, 7h or 8h.

[0033] Preferably, after the excessive impregnation, the process before roasting further includes segmented drying.

[0034] Preferably, the segmented drying includes drying in an 80°C oven for 1 to 24 hours, followed by drying in a 120°C oven for more than 4 hours.

[0035] For example, the drying time in an 80°C oven can be 1h, 2h, 4h, 8h, 10h, 12h, 15h, 18h, 20h, or 24h, etc.; the drying time in a 120°C oven can be 4h, 8h, 10h, 12h, 15h, 18h, 20h, or 24h, etc.

[0036] Preferably, the roasting is carried out in a muffle furnace.

[0037] Preferably, the roasting temperature is 400℃~600℃, for example, it can be 400℃, 450℃, 500℃, 550℃ or 600℃.

[0038] Preferably, the heating rate of the calcination is 1℃ / min to 5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc.

[0039] Preferably, the roasting time is 1 hour to 5 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.

[0040] Preferably, the temperature of the deposition-precipitation reaction is 60℃~90℃, for example, it can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃.

[0041] Preferably, the deposition-precipitation reaction time is 6h to 15h, for example, it can be 6h, 7h, 8h, 9h, 10h, 12h or 15h, preferably 7h to 9h.

[0042] Preferably, the deposition-precipitation reaction is carried out under stirring conditions.

[0043] Preferably, the stirring speed is 300 rpm to 600 rpm, for example, it can be 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm.

[0044] Preferably, after the deposition-precipitation reaction and before the reduction treatment, the process further includes segmented drying.

[0045] Preferably, the segmented drying includes drying in an 80°C oven for 1 to 24 hours, followed by drying in a 120°C oven for more than 4 hours.

[0046] For example, the drying time in an 80°C oven can be 1h, 2h, 4h, 8h, 12h, 15h, 18h, 20h or 24h, etc.; the drying time in a 120°C oven can be 4h, 8h, 10h, 12h, 15h, 18h, 20h or 24h, etc.

[0047] Preferably, the reduction process is carried out in a tube furnace.

[0048] Preferably, the atmosphere for the reduction treatment is a mixture of hydrogen and nitrogen.

[0049] Preferably, in the mixed atmosphere of hydrogen and nitrogen, the volume fraction of hydrogen is 5 vol% to 20 vol%, for example, it can be 5 vol%, 10 vol%, 15 vol%, or 20 vol%.

[0050] Preferably, the volume hourly space velocity (VHSV) of the hydrogen and nitrogen mixture is 200 h⁻¹. -1 ~5000h -1For example, it could be 200h -1 300h -1 500h -1 1000h -1 1500h -1 1800h -1 2000h -1 2500h -1 3000h -1 4000h -1 or 5000h -1 etc., preferably 300h -1 ~1800h -1 .

[0051] Preferably, the temperature of the reduction treatment is 400℃~800℃, for example, it can be 400℃, 500℃, 600℃, 700℃ or 800℃, etc., preferably 500℃~600℃.

[0052] Preferably, the heating rate of the reduction treatment is 0.1℃ / min to 25℃ / min, for example, it can be 0.1℃ / min, 0.5℃ / min, 1℃ / min, 2℃ / min, 5℃ / min, 10℃ / min, 15℃ / min, 20℃ / min or 25℃ / min, etc., preferably 1℃ / min to 15℃ / min.

[0053] Preferably, the reduction treatment time is 0.5h to 24h, for example, it can be 0.5h, 1h, 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h or 24h, etc., preferably 1h to 12h.

[0054] Thirdly, the present invention provides an application of the support size-controlled ammonia decomposition hydrogen production catalyst as described in the first aspect, wherein the support size-controlled ammonia decomposition hydrogen production catalyst is used to catalyze the ammonia decomposition reaction.

[0055] Preferably, the ammonia decomposition reaction is carried out in a fixed-bed reactor.

[0056] Preferably, the raw material for the ammonia decomposition reaction is pure ammonia gas (>99.999% purity).

[0057] Preferably, the volume hourly space velocity (VHSV) of the feedstock for the ammonia decomposition reaction is 3000 h⁻¹. -1 ~40000h -1 For example, it could be 3000h -1 6000h -1 9000h -1 12000h -1 15000h -1 30000h-1 36000h -1 or 40000h -1 wait.

[0058] Preferably, the temperature of the ammonia decomposition reaction is 300℃~500℃, for example, it can be 300℃, 350℃, 400℃, 450℃ or 500℃.

[0059] Preferably, in the ammonia decomposition reaction, the amount of the ammonia decomposition hydrogen production catalyst with support size control is 0.05g to 100g, for example, it can be 0.05g, 0.1g, 1g, 2g, 5g, 10g, 20g, 50g or 100g, etc.

[0060] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] This invention uses micron-sized magnesium oxide as a support to load the active component ruthenium, which can highly disperse and stabilize the active component ruthenium at its optimal size, significantly increasing the density of B5-type active sites. It can also promote the preferential exposure of the more active Ru(10-11) crystal facet, effectively reducing the energy barrier for the ammonia fractionation step, thereby significantly improving the catalytic activity and catalytic stability of the catalyst. Attached Figure Description

[0063] Figure 1 These are TEM and HRTEM images of the ammonia decomposition hydrogen production catalyst with support size control provided in Example 1 of this invention.

[0064] Figure 2 These are TEM and HRTEM images of the ammonia decomposition hydrogen production catalyst with support size control provided in Comparative Example 1 of this invention.

[0065] Among them, a-TEM image and b-HRTEM image.

[0066] Figure 3 The ammonia conversion rate curves are provided by the support size-controlled ammonia decomposition hydrogen production catalysts in Example 1 and Comparative Example 1 of this invention when catalyzing the ammonia decomposition reaction at 500°C for 100 h. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0068] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0069] Unless otherwise specified, the term "at least two combinations" in this invention refers to a quantity greater than or equal to 2. For example, "any one or at least two combinations" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention.

[0070] In this invention, unless otherwise specified, the feature or solution corresponding to "and / or" covers any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a set consisting of A, B, and combinations of A and B. "Including A and / or B" can be understood, depending on the context of the statement, as including A, including B, or simultaneously including both A and B. In this invention, "optional" means that the corresponding feature, component, step, or solution is not essential, i.e., selected from either "present" or "absent" parallel solutions. If multiple "optional" limitations appear in a technical solution, unless otherwise specified and without technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0071] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A may consist only of a1, a2, and a3, or it may include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements."

[0072] All embodiments and optional embodiments of the present invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of the present invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment or implementation of the present invention. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this invention can be combined with other embodiments without technical conflict.

[0073] In this invention, the ordinal numbers “first,” “second,” “third,” and “fourth” used in expressions such as “first aspect,” “second aspect,” “third aspect,” and “fourth aspect” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0074] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0075] Example 1

[0076] This embodiment provides a catalyst for hydrogen production from ammonia via support size control, comprising an active component and a support; the active component is ruthenium, and the support is micron-sized magnesium oxide. The median particle size D50 of the micron-sized magnesium oxide is 27 μm, the median particle size D50 of the ruthenium is 2.2 nm, and the mass of the ruthenium is 1 wt% of the mass of the micron-sized magnesium oxide.

[0077] The preparation method of the ammonia decomposition hydrogen production catalyst with support size control provided in this embodiment includes the following steps:

[0078] (1) Add 0.021g RuCl3 to 180mL of water, stir evenly, then add 1g of micron-sized magnesium oxide and 1.2g of urea. Under the stirring conditions of 80℃ and 500rpm, carry out the deposition-precipitation reaction for 8h. Then transfer to Buchner funnel, wash three times with deionized water, dry in an oven at 80℃ for 8h, and then dry in an oven at 120℃ for 4h to obtain the precursor.

[0079] (2) Place the precursor obtained in step (1) in a tube furnace, introduce a mixture of hydrogen and nitrogen (hydrogen volume fraction of 10 vol%) and control the volume hourly space velocity to 1800 h⁻¹. -1 A temperature-programmed heating method was used, with the heating rate controlled at 5℃ / min. The temperature was increased to 600℃ and then reduced for 3 hours to obtain an ammonia decomposition hydrogen production catalyst with a support size regulated, denoted as 1Ru / MgO-μm.

[0080] Example 2

[0081] This embodiment provides a catalyst for hydrogen production from ammonia via support size control, comprising an active component and a support; the active component is ruthenium, and the support is micron-sized magnesium oxide. The median particle size D50 of the micron-sized magnesium oxide is 10 μm, the median particle size D50 of ruthenium is 3.5 nm, and the mass of ruthenium is 0.1 wt% of the mass of the micron-sized magnesium oxide.

[0082] The preparation method of the ammonia decomposition hydrogen production catalyst with support size control provided in this embodiment includes the following steps:

[0083] (1) Add 0.002g RuCl3 to 60mL of water, stir evenly, then add 1g of micron-sized magnesium oxide and 0.18g of urea. Under the stirring conditions of 60℃ and 300rpm, carry out the deposition-precipitation reaction for 15h. Then transfer to Buchner funnel, wash three times with deionized water, dry in an oven at 80℃ for 24h, and then dry in an oven at 120℃ for 6h to obtain the precursor.

[0084] (2) Place the precursor obtained in step (1) in a tube furnace, introduce a mixture of hydrogen and nitrogen (hydrogen volume fraction of 5 vol%) and control the volume hourly space velocity to 200 h⁻¹. -1A temperature-programmed heating method was used, with the heating rate controlled at 15℃ / min. The temperature was increased to 800℃ and then reduced for 1 hour to obtain an ammonia decomposition hydrogen production catalyst with a support size regulated, denoted as 0.1Ru / MgO-μm.

[0085] Example 3

[0086] This embodiment provides a catalyst for hydrogen production from ammonia via support size control, comprising an active component and a support; the active component is ruthenium, and the support is micron-sized magnesium oxide. The median particle size D50 of the micron-sized magnesium oxide is 20 μm, the median particle size D50 of ruthenium is 4.8 nm, and the mass of ruthenium is 6 wt% of the mass of the micron-sized magnesium oxide.

[0087] The preparation method of the ammonia decomposition hydrogen production catalyst with support size control provided in this embodiment includes the following steps:

[0088] (1) Add 0.13g RuCl3 to 45mL of water, stir evenly, then add 1g of micron-sized magnesium oxide and 3.8g of urea. Under the stirring conditions of 90℃ and 600rpm, carry out the deposition-precipitation reaction for 6h. Then transfer to Buchner funnel, wash three times with deionized water, dry in 80℃ oven for 1h, and then dry in 120℃ oven for 24h to obtain the precursor.

[0089] (2) Place the precursor obtained in step (1) in a tube furnace, introduce a mixture of hydrogen and nitrogen (hydrogen volume fraction of 20 vol%) and control the volume hourly space velocity to 5000 h⁻¹. -1 By using programmed heating and controlling the heating rate at 1℃ / min, the temperature was raised to 400℃ and then subjected to reduction treatment for 12h to obtain an ammonia decomposition hydrogen production catalyst with support size control, denoted as 6Ru / MgO-μm.

[0090] Example 4

[0091] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the addition of cerium dioxide as an auxiliary agent, the mass of which is 1 wt% of the mass of micron-sized magnesium oxide, everything else is the same as in Example 1.

[0092] The preparation method of the ammonia decomposition hydrogen production catalyst with carrier size control provided in this embodiment is the same as that in Example 1, except that the 1g of micron-sized magnesium oxide added in step (1) is replaced with micron-sized magnesium oxide loaded with cerium dioxide prepared from 1g of micron-sized magnesium oxide.

[0093] The method for preparing micron-sized magnesium oxide supported on cerium dioxide includes the following steps:

[0094] 0.031 g Ce(NO3)3·6H2O was added to 10 mL of water and stirred evenly. Then 1 g of micron-sized magnesium oxide was added and impregnated in excess for 6 h. After drying in an oven at 80 °C for 8 h, it was dried in an oven at 120 °C for 4 h. Then it was transferred to a muffle furnace and heated to 500 °C at a heating rate of 1 °C / min and calcined for 2 h to obtain micron-sized magnesium oxide loaded with cerium dioxide.

[0095] Example 5

[0096] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the addition of cerium dioxide as an auxiliary agent, the mass of which is 1 wt% of the mass of micron-sized magnesium oxide, everything else is the same as in Example 1.

[0097] The preparation method of the ammonia decomposition hydrogen production catalyst with carrier size control provided in this embodiment is the same as that in Example 1, except that in step (1) 0.021g RuCl3 and 0.031g Ce(NO3)3·6H2O are added to 180mL of water.

[0098] Example 6

[0099] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the median particle size D50 of micron-sized magnesium oxide being 0.5 μm and the median particle size D50 of ruthenium being 0.35 nm, everything else is the same as in Example 1.

[0100] Example 7

[0101] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the median particle size D50 of micron-sized magnesium oxide being 5 μm and the median particle size D50 of ruthenium being 1 nm, all other aspects are the same as in Example 1.

[0102] Example 8

[0103] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the median particle size D50 of 100 μm for micron-sized magnesium oxide and 10 nm for ruthenium, everything else is the same as in Example 1.

[0104] Example 9

[0105] This embodiment provides an ammonia decomposition hydrogen production catalyst with adjustable support size. Except for the median particle size D50 of 150 μm for micron-sized magnesium oxide and 14 nm for ruthenium, everything else is the same as in Example 1.

[0106] Comparative Example 1

[0107] This comparative example provides a support-size-controlled ammonia decomposition hydrogen production catalyst. Except that the support is nano-sized magnesium oxide with a median particle size D50 of 50 nm and the ruthenium median particle size D50 is 1.8 nm, all other aspects are the same as in Example 1. The obtained support-size-controlled ammonia decomposition hydrogen production catalyst is denoted as 1Ru / MgO-nm.

[0108] Figure 1 TEM and HRTEM images of the ammonia decomposition hydrogen production catalyst with support size control provided in Example 1 are shown. TEM results indicate that the median particle size D50 of ruthenium in 1Ru / MgO-μm is approximately 2.2 nm, which falls within the 2 nm to 3 nm median particle size range favorable for the formation of high-density B5 sites. Further HRTEM results show that the ruthenium nanoparticles in 1Ru / MgO-μm have an interplanar spacing of approximately 0.21 nm, corresponding to the Ru(10-11) crystal plane.

[0109] Figure 2 TEM and HRTEM images of the ammonia decomposition hydrogen production catalyst with size-controlled support provided for Comparative Example 1 are shown. TEM results indicate that in 1Ru / MgO-nm, the median particle size D50 of ruthenium is approximately 1.8 nm, and ruthenium mainly exists in highly dispersed clusters. Further HRTEM results show that in 1Ru / MgO-nm, the ruthenium nanoparticles have a crystal plane spacing of approximately 0.24 nm, corresponding to the Ru(10-10) crystal plane.

[0110] This demonstrates that micron-sized magnesium oxide can not only regulate the particle size of Ru, but also promote the preferential exposure of the Ru(10-11) crystal facet. This Ru(10-11) crystal facet has more abundant step sites and B5-type active sites, which helps to lower the energy barrier of key steps in the ammonia decomposition reaction, promoting NH3 activation, NH bond breaking, N atom recombination, and N2 desorption processes, thereby enhancing the ammonia decomposition activity and stability of the catalyst.

[0111] Comparative Example 2

[0112] This comparative example provides a support-size-controlled ammonia decomposition hydrogen production catalyst. Except that the support is nanoscale silica, and the median particle size D50 of the nanoscale silica is 50 nm, all other aspects are the same as in Example 1. The obtained support-size-controlled ammonia decomposition hydrogen production catalyst is denoted as 1Ru / SiO2-nm.

[0113] Comparative Example 3

[0114] This comparative example provides a support-size-controlled ammonia decomposition hydrogen production catalyst. Except that the support is nano-sized alumina, and the median particle size D50 of the nano-sized alumina is 50 nm, all other aspects are the same as in Example 1. The obtained support-size-controlled ammonia decomposition hydrogen production catalyst is denoted as 1Ru / Al2O3-nm.

[0115] 50 mg of the ammonia decomposition hydrogen production catalyst with carrier size control provided in Examples 1-9 and Comparative Examples 1-3, and 400 mg of quartz sand were weighed and placed in a fixed-bed reactor. Pure ammonia gas (>99.999% purity) was introduced and its volume hourly space velocity was controlled at 36000 h⁻¹. -1 The ammonia decomposition reaction was catalyzed at 400℃, 450℃ and 500℃ respectively.

[0116] The ammonia conversion rates at different temperatures are shown in Table 1.

[0117]

[0118] As can be seen from Table 1, the ammonia decomposition hydrogen production catalysts with support size control provided in Examples 1 to 3 all exhibit high ammonia conversion rates at different temperatures when used to catalyze the ammonia decomposition reaction.

[0119] Compared to Example 1, Examples 4 and 5, due to the further introduction of the auxiliary agent cerium dioxide, have a unique Ce... 4+ / Ce 3+ Reversible valence state transitions and oxygen storage capacity can promote the generation of oxygen vacancy defects, enabling them to donate electrons to the active component ruthenium, thereby modulating the electronic state of ruthenium. This electronic modulation can increase the electron density on the Ru surface and optimize the interaction of Ru sites with NH3 and NH4+. x The adsorption strength of N and other reactants and intermediates makes it easier for NH3 to undergo adsorption activation and NH bond breaking, while avoiding excessive adsorption of N species on the Ru surface, promoting the recombination of N atoms on the surface and the desorption of N2, thereby promoting the enhancement of the catalyst's ammonia decomposition activity and further improving the ammonia conversion rate.

[0120] Furthermore, loading cerium dioxide onto micron-sized magnesium oxide first, and then loading ruthenium onto the cerium dioxide-loaded micron-sized magnesium oxide, allows the cerium dioxide promoter to be pre-dispersed and anchored on the magnesium oxide support surface, forming a stable CeO2-MgO composite interface and abundant oxygen vacancy defect sites. This structure neither significantly affects the original alkaline environment and structural stability of the micron-sized magnesium oxide support, nor does it significantly cover or bury the subsequently formed Ru active sites; on the contrary, the pre-introduced cerium dioxide can serve as an anchoring point for Ru species, promoting high dispersion of Ru on the support surface, enhancing the interaction between Ru and the support, and inhibiting the migration, agglomeration, and sintering of Ru particles during reduction treatment and ammonia decomposition reactions, thereby improving the structural stability and long-term operational stability of the catalyst.

[0121] When ruthenium and cerium dioxide are simultaneously loaded onto micron-sized magnesium oxide, the ruthenium and cerium species may compete for deposition during deposition, nucleation and growth. This can easily lead to cerium dioxide covering some Ru active sites, or make it difficult for Ru to form an effective interface synergy with CeO2 and MgO, thereby affecting the dispersion state and electronic structure regulation effect of Ru.

[0122] Therefore, compared with simultaneous loading, stepwise loading of cerium dioxide and ruthenium is more conducive to leveraging the electronic regulation, oxygen vacancy anchoring and structural stabilization effects of CeO2 promoters, thereby enabling the catalyst to exhibit higher ammonia decomposition activity and stability.

[0123] Compared with Example 1, Examples 6-9 investigated the effects of the size of the micron-sized magnesium oxide support on the dispersibility of the active component ruthenium and the catalyst's ammonia decomposition activity. It can be seen that when the median particle size D50 of the micron-sized magnesium oxide is too small or too large, the ammonia conversion rate decreases significantly. This indicates that there is an optimal range for the support size. By controlling the median particle size D50 of the micron-sized magnesium oxide, it is helpful to balance the dispersibility of ruthenium species, the accessibility of active sites, and bed mass transfer performance, thereby improving the catalytic activity for hydrogen production from ammonia decomposition. Specifically, when D50 is too small, the support particles are prone to agglomeration and accumulation, which may lead to limited bed mass transfer channels and affect the uniform dispersion of ruthenium species on the support surface, reducing the effectively exposed active sites and thus decreasing catalytic activity. When D50 is too large, the usable area on the outer surface of the support is relatively reduced, which is not conducive to the high dispersion of ruthenium species and easily leads to local enrichment of ruthenium species. At the same time, larger particles may also increase the diffusion resistance of reactants and products, reducing the utilization efficiency of the active component.

[0124] Compared with Example 1, Comparative Example 1 uses nano-sized magnesium oxide as a support, which is less effective in promoting the high dispersion and stability of the active component ruthenium at its optimal size. The density of B5 type active sites is significantly reduced, and it cannot promote the preferential exposure of the more active Ru(10-11) crystal facet. The energy barrier for the ammonia fractionation step is high, which leads to a significant decrease in the catalytic activity of the catalyst and a substantial decrease in the ammonia conversion rate.

[0125] Compared to Example 1, Comparative Examples 2 and 3, which used nano-sized silica and nano-sized alumina as supports respectively, showed significantly reduced ammonia decomposition activity in their catalysts. This is because the micron-sized magnesium oxide support possesses unique surface alkalinity and electron-donating capabilities, enabling it to modulate the electronic structure of Ru particles through metal-support interactions. This maintains a high electron density on the Ru surface, thereby optimizing the Ru sites' response to NH3 and NH4+. x The adsorption strength of N and other reactants and intermediates promotes the adsorption activation of NH3, the breaking of NH bonds, the recombination of N atoms on the surface, and the desorption process of N2.

[0126] In contrast, the surface of nanoscale silica is relatively inert, lacking effective alkaline sites and electron-donating capabilities, making it difficult to exert a significant electronic regulation effect on Ru particles; the surface of nanoscale alumina mainly exhibits Lewis acidity, and although it can interact with Ru to some extent, its electron-donating capability is insufficient, which may lead to a decrease in the electron enrichment of the Ru surface, resulting in excessive adsorption of nitrogen-containing intermediates, especially N species, by Ru sites, which is not conducive to the generation and desorption of N2.

[0127] Therefore, when using nano-sized silica and nano-sized alumina as supports, it is difficult to effectively control the electronic properties of Ru and the adsorption behavior of reaction intermediates as effectively as micron-sized magnesium oxide supports, which leads to a significant decrease in the catalytic activity of the catalyst and a substantial decrease in ammonia conversion rate.

[0128] The ammonia decomposition hydrogen production catalyst with carrier size control provided in Example 1 and Comparative Example 1, along with 400 mg of quartz sand, were placed in a fixed-bed reactor. Pure ammonia gas (>99.999% purity) was introduced, and its volume hourly space velocity was controlled at 36000 h⁻¹. -1 The catalytic stability of the ammonia decomposition reaction was verified by catalyzing the reaction at 500℃ for 100 h.

[0129] Figure 3 These are the ammonia conversion curves of the ammonia decomposition hydrogen production catalysts with support size control provided in Example 1 and Comparative Example 1 during the ammonia decomposition reaction at 500°C for 100 hours. Figure 3As can be seen, the ammonia decomposition hydrogen production catalyst with support size control provided in Example 1 exhibits excellent stability during the test period, with the ammonia conversion rate curve remaining stable and showing no significant decrease. In contrast, the ammonia decomposition hydrogen production catalyst with support size control provided in Comparative Example 1 shows that the ammonia conversion rate decreases by more than 20% within the initial 10 hours of reaction. This indicates that the support-scale engineering strategy is beneficial for exposing more B5-type active sites and accelerating the association and desorption of adsorbed nitrogen species, avoiding N poisoning on the catalyst surface and promoting the regeneration of active sites, thereby enabling the ammonia decomposition hydrogen production catalyst with support size control to exhibit excellent catalytic stability.

[0130] In summary, by using micron-sized magnesium oxide as a support to load the active component ruthenium, the present invention can highly disperse and stabilize the active component ruthenium at its optimal size, significantly increasing the density of B5-type active sites. It can also promote the preferential exposure of the more active Ru(10-11) crystal facets, effectively reducing the energy barrier for the ammonia fractionation step, thereby significantly improving the catalytic activity and catalytic stability of the catalyst.

[0131] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A carrier size-regulated ammonia decomposition hydrogen production catalyst, characterized by, The ammonia decomposition hydrogen production catalyst with support size control includes an active component and a support. The active component is ruthenium, and the carrier is micron-sized magnesium oxide.

2. The ammonia decomposition hydrogen production catalyst with support size control according to claim 1, characterized in that, The median particle size D50 of the micron-sized magnesium oxide is 1μm~100μm, preferably 15μm~40μm; Preferably, the median particle size D50 of the active component is 1 nm to 10 nm, and more preferably 2 nm to 5 nm.

3. The ammonia decomposition hydrogen production catalyst with support size control according to claim 1 or 2, characterized in that, The mass of the active component is 0.1wt% to 10wt% of the mass of the carrier, preferably 0.1wt% to 2wt%.

4. The ammonia decomposition hydrogen production catalyst with support size control according to any one of claims 1 to 3, characterized in that, The ammonia decomposition hydrogen production catalyst with carrier size control also includes an auxiliary agent. Preferably, the additives include rare earth metal oxides; Preferably, the rare earth metal oxide includes cerium dioxide; Preferably, the mass of the additive is 0.1wt% to 10wt% of the mass of the carrier, and more preferably 0.5wt% to 3wt%.

5. A method for preparing an ammonia decomposition hydrogen production catalyst with support size control as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Micron-sized magnesium oxide was added to a ruthenium salt solution, and a precipitant was added to carry out a deposition-precipitation reaction to obtain the precursor; The precursor is reduced to obtain the ammonia decomposition hydrogen production catalyst with the support size controlled.

6. The preparation method according to claim 5, characterized in that, The ruthenium salt in the ruthenium salt solution is any one or a combination of at least two of ruthenium trichloride, ruthenium oxynitrate, or ruthenium acetylacetonate. Preferably, the solvent in the ruthenium salt solution includes water; Preferably, the precipitant comprises urea; Preferably, the molar ratio of ruthenium in the ruthenium salt to the precipitant is 1:(100~300).

7. The preparation method according to claim 5 or 6, characterized in that, The preparation method further includes preparing micron-sized magnesium oxide loaded with cerium dioxide, comprising the following steps: Micron-sized magnesium oxide was added to a cerium salt aqueous solution, subjected to excess impregnation, and then calcined to obtain the micron-sized magnesium oxide loaded with cerium dioxide. Preferably, the cerium salt in the cerium salt aqueous solution includes cerium nitrate and / or cerium trichloride; Preferably, the excessive soaking time is 3h to 8h; Preferably, the calcination temperature is 400℃~600℃; Preferably, the heating rate of the calcination is 1℃ / min to 5℃ / min; Preferably, the roasting time is 1 hour to 5 hours.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The temperature for the deposition-precipitation reaction is 60℃~90℃; Preferably, the deposition-precipitation reaction takes 6 to 15 hours, more preferably 7 to 9 hours; Preferably, the deposition-precipitation reaction is carried out under stirring conditions; Preferably, the stirring speed is 300 rpm to 600 rpm.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The atmosphere for the reduction treatment is a mixture of hydrogen and nitrogen. Preferably, in the mixed atmosphere of hydrogen and nitrogen, the volume fraction of hydrogen is 5 vol% to 20 vol%. Preferably, the volume hourly space velocity of the mixed atmosphere of hydrogen and nitrogen is 200 h -1 ~5000h -1 , preferably 300 h -1 ~1800h -1 ; Preferably, the temperature of the reduction treatment is 400℃~800℃, more preferably 500℃~600℃; Preferably, the heating rate of the reduction treatment is 0.1℃ / min to 25℃ / min, more preferably 1℃ / min to 15℃ / min; Preferably, the reduction treatment time is 0.5h to 24h, and more preferably 1h to 12h.

10. The application of an ammonia decomposition hydrogen production catalyst with support size control as described in any one of claims 1 to 4, characterized in that, The carrier-sized controlled ammonia decomposition hydrogen production catalyst is used to catalyze the ammonia decomposition reaction.

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