A ru-based catalyst for ammonia decomposition to produce hydrogen, and a preparation method and application thereof

Abstract

The application provides a Ru-based catalyst for hydrogen production by ammonia decomposition, a preparation method and application thereof, and belongs to the technical field of hydrogen production by ammonia decomposition. The Ru-based catalyst comprises a carrier and active metal nanoparticles loaded on the carrier, the active metal nanoparticles comprise transition metal nanoparticles loaded on the carrier and a Ru atomic layer coated on the transition metal nanoparticles, and the mass fraction of the Ru atomic layer is 0.2-3wt% based on the total mass of the Ru-based catalyst being 100wt%. In the Ru-based catalyst, the Ru atomic layer is coated on the surface of the transition metal nanoparticles to form active metal nanoparticles, the utilization rate of Ru is improved, meanwhile, the inner transition metal nanoparticles have significant electron transfer capacity and strain effect on the surface Ru atomic layer, the adsorption energy of the catalyst for intermediate reaction products in hydrogen production by ammonia decomposition is optimized, and the catalytic activity is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen production by ammonia decomposition, and particularly relates to a Ru-based catalyst for hydrogen production by ammonia decomposition and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen is a green energy with high energy density, no pollution and wide sources, and is called "ultimate energy". However, as a gaseous fuel, hydrogen has the characteristics of low volumetric energy density, which makes it difficult to store and transport. Therefore, solving the problem of hydrogen storage and transportation is the premise of large-scale development of hydrogen energy in the future. Ammonia is a hydrogen-rich compound and is easy to be liquefied, stored and transported. In addition, ammonia has a mature technical system and standard specification in practical application. Therefore, ammonia as a hydrogen storage material is expected to solve the problem of hydrogen storage and transportation.

[0003] How to efficiently and low-cost release hydrogen in ammonia has become a key difficulty, and the thermal catalytic ammonia decomposition reaction is an effective way to solve this difficulty. At present, ammonia decomposition catalysts mainly include noble metal catalysts represented by Ru and non-noble metal catalysts represented by Fe and Ni. The traditional Ru-based supported catalyst has the problems of low Ru utilization rate and high cost, and the non-noble metal catalyst has the problems of large amount, low activity and high energy consumption, which are difficult to meet the actual application of ammonia decomposition for hydrogen production.

[0004] For example, patent application file CN201910537655.5 discloses a nickel and / or ruthenium ammonia decomposition catalyst and a preparation method and application thereof. The catalyst includes an active component and a carrier; the active component is one or both of nickel and ruthenium, the carrier includes graphitized activated carbon and an additive, the additive is one or several of oxides and carbonates of alkali metals, oxides and carbonates of alkaline earth metals, and rare earth oxides, the additive can modify the carrier and improve the activity of the catalyst; in addition, the activated carbon is treated by high-temperature graphitization, which improves the stability of the catalyst on the one hand, and the active component and the carbon of the carrier can form a strong interaction and electron transfer, which is beneficial to the desorption of reaction products N2 and H2, thereby further improving the low-temperature reaction activity and achieving good ammonia decomposition effect and improving the ammonia treatment efficiency. However, after the activated carbon is treated by high-temperature graphitization, the surface functional groups will be greatly reduced, and the surface functional groups play a role in dispersing active metal Ru atoms, so that the dispersion of Ru particles in the catalyst is poor, the particle size is large and the uniformity is poor, which affects the catalytic activity and stability.

[0005] For example, patent application file CN202310349366.9 discloses a Ru-based catalyst for ammonia decomposition to produce hydrogen and a preparation method thereof. The Ru-based catalyst includes Ru as an active component, an alkali metal, an alkaline earth metal, or a rare earth metal as an additive, and carbon-coated silicon dioxide SiO2@C as a carrier. The composite carrier SiO2@C has a large specific surface area porous structure, a uniform distribution of surface carbon layer doping, high stability, and good affinity for metals. The introduced metal additive can adjust the electronic properties of the Ru surface, enhance the basicity of the carrier surface, and enhance the strength of the synergistic effect between the metal and the carrier, thereby promoting the ammonia decomposition reaction and exhibiting excellent ammonia decomposition reaction catalytic performance. However, the preparation method of the Ru-based catalyst is to first synthesize the carrier, then introduce the additive, and finally load the Ru particles. The preparation process is complex and tedious, and the synthesized active sites are Ru particles, which cannot be effectively utilized, resulting in waste of Ru.

[0006] For example, patent application file CN202110478047.9 discloses an ammonia decomposition catalyst, a preparation method and application thereof. The preparation method of the ammonia decomposition catalyst includes the following steps: ball milling of ruthenium acetate, magnesium acetate and potassium acetate to obtain a metal salt mixture powder; calcining the metal salt mixture powder, and then reducing it with hydrogen to obtain an ammonia decomposition catalyst. The preparation method of the ammonia decomposition catalyst involves "one-pot" addition of specific raw materials ruthenium acetate, magnesium acetate and potassium acetate, and ball milling to obtain a metal salt mixture powder, which is then calcined and reduced with hydrogen to obtain an ammonia decomposition catalyst. The cooperation of the several steps can greatly reduce the particle size of ruthenium metal and improve the low-temperature activity of the catalyst. However, the one-pot method for preparing the Ru / MgO catalyst modified with alkali metal K cannot uniformly disperse the Ru salt, Mg salt and K salt by physical mixing, which may cause uneven dispersion of Ru and K on the catalyst and poor uniformity of particle size; and some Ru particles may enter the interior of the MgO, causing waste. SUMMARY

[0007] The present application is based on the discovery and realization of the inventors on the following facts and problems: The Ru-based catalyst for ammonia decomposition to produce hydrogen in the related art is usually a traditional supported Ru particle catalyst or a Ru alloy catalyst, and these two catalysts have certain problems in the application process. For the traditional supported Ru particle catalyst, there are problems such as high Ru dosage and low utilization rate, for example, the traditional carbon-supported Ru particle and the transition metal oxide-supported Ru particle, due to the inertness of the carrier, the activity of the Ru particle is often not modified, thereby resulting in low activity, and the catalytic reaction only occurs on the surface of the Ru particle, and the internal Ru atoms cannot be effectively utilized and are wasted. For the Ru alloy catalyst, there is a problem that the heteroatoms occupy a certain number of surface Ru atom sites, resulting in a decrease in the number of exposed Ru atoms, so although the single Ru atom active site is significantly improved, the overall activity is reduced due to the decrease in the number of exposed Ru atoms. At the same time, like the traditional supported Ru particle catalyst, a large number of Ru atoms are preserved inside and cannot be effectively utilized.

[0008] The present application aims to at least solve one of the technical problems in the related art to some extent. To this end, an embodiment of the present application proposes a Ru-based catalyst for ammonia decomposition to produce hydrogen and a preparation method and application thereof.

[0009] The Ru-based catalyst for ammonia decomposition to produce hydrogen according to an embodiment of the present application comprises a carrier and active metal nanoparticles supported on the carrier, the active metal nanoparticles comprise transition metal nanoparticles supported on the carrier and a Ru atom layer coated on the transition metal nanoparticles, and the mass fraction of the Ru atom layer is 0.2-3wt% based on 100wt% of the total mass of the Ru-based catalyst.

[0010] The Ru-based catalyst according to an embodiment of the present application has the following advantages and technical effects:

[0011] 1. In the Ru-based catalyst according to an embodiment of the present application, the Ru atom layer is coated on the surface of the transition metal nanoparticles to form active metal nanoparticles, and compared with the Ru-based catalyst in the related art, the Ru-based catalyst according to an embodiment of the present application has low Ru loading and high utilization rate, and can significantly reduce the cost of the catalyst;

[0012] 2. In the Ru-based catalyst according to an embodiment of the present application, there is a significant difference in electronegativity between the transition metal nanoparticles and the Ru atom layer, which is conducive to the electron transfer effect, effectively regulates the electronic structure of the Ru atom layer, optimizes the adsorption strength between the Ru sites and the intermediate reaction products in the ammonia decomposition to produce hydrogen, and improves the catalytic activity;

[0013] 3. In the Ru-based catalyst of the present invention, due to the difference in lattice spacing between the transition metal nanoparticles and the Ru atomic layer, the Ru atomic layer undergoes lattice strain, thereby adjusting the adsorption strength between the Ru sites and the intermediate reaction products of ammonolysis to hydrogen production, which is beneficial to improving catalytic activity.

[0014] In some embodiments, the number of Ru atomic layers is 1-2, and / or the lattice compressive stress of the Ru atomic layers is 0.2-2.5%.

[0015] In some embodiments, the number of Ru atomic layers is 1, and / or the lattice compressive stress of the Ru atomic layers is 0.2-2%.

[0016] In some embodiments, the mass fraction of the Ru atomic layer is 0.5-2 wt%.

[0017] In some embodiments, the average particle size of the active metal nanoparticles is 1-5 nm.

[0018] In some embodiments, the transition metal nanoparticles are at least one of Fe, Cu, Co, and Ni nanoparticles; and / or, the mass fraction of the transition metal nanoparticles is 5-30 wt%.

[0019] In some embodiments, the Ru-based catalyst further includes an auxiliary agent, which is at least one selected from alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates, and rare earth metal oxides.

[0020] In addition, this invention also provides a method for preparing a Ru-based catalyst for hydrogen production by ammonolysis, comprising the following steps:

[0021] (1) The carrier, transition metal salt and first dispersant are mixed evenly and dried to obtain a mixed powder;

[0022] (2) The mixed powder is subjected to a first sintering treatment at 300-1000°C in a mixed atmosphere of hydrogen and inert gas to obtain a first sintered product;

[0023] (3) The first sintered product, Ru salt and the second dispersant are mixed evenly and stirred. After filtration, washing and drying, catalyst powder is obtained.

[0024] (4) The catalyst powder is subjected to a second sintering treatment to obtain the Ru-based catalyst.

[0025] The advantages and technical effects of the Ru-based catalyst preparation method of this invention are as follows:

[0026] 1. The Ru-based catalyst preparation method of the embodiment of the present application adopts a two-step method to synthesize the Ru-based catalyst, first, the transition metal particles are uniformly loaded on the carrier, and then the Ru atoms are used to replace the surface atoms of the transition metal nanoparticles by ion exchange method through the difference in redox potential between the Ru atoms and the transition metal atoms, to form a Ru atomic layer, the synthesis process is relatively simple and easy to mass production.

[0027] 2. Compared with the Ru-based catalyst in the related art, the Ru atoms are uniformly loaded on the surface layer in the embodiment of the present application, the utilization of each Ru atom is fully utilized, the utilization rate of Ru is improved, and at the same time, the inner transition metal atoms and the surface Ru atoms can realize effective electron transfer and lattice stress regulation due to the difference in electronegativity and the difference in lattice spacing, so as to optimize the adsorption energy of the Ru site to the intermediate product in the ammonia decomposition hydrogen production reaction, and greatly improve the catalytic activity.

[0028] 3. Compared with the Ru-based catalyst in the related art, the Ru dosage in the embodiment of the present application is less, and the cost is lower.

[0029] In some embodiments, the temperature of the stirring treatment is 30-90℃, and the time is 2-24h.

[0030] In some embodiments, the temperature of the stirring treatment is 40-90℃, and the time is 3-24h.

[0031] In some embodiments, in step (4), the catalyst powder is mixed with an auxiliary precursor salt and a third dispersant, and after drying, the second sintering treatment is performed to obtain the Ru-based catalyst.

[0032] In addition, the Ru-based catalyst of the embodiment of the present application or the Ru-based catalyst obtained by the preparation method of the embodiment of the present application can be applied to the ammonia decomposition hydrogen production reaction.

[0033] The application of the embodiment of the present application has the following advantages and technical effects:

[0034] The Ru-based catalyst of the embodiment of the present application or the Ru-based catalyst obtained by the preparation method of the embodiment of the present application can greatly improve the efficiency of the ammonia decomposition hydrogen production reaction. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The structure schematic diagram of the Ru-based catalyst for ammonia decomposition hydrogen production of the present application is shown;

[0036] Figure 2 The ammonia conversion rate curve of the Ru-based catalyst for ammonia decomposition hydrogen production of the present application at 500℃ of ammonia decomposition hydrogen production is shown. DETAILED DESCRIPTION

[0037] Embodiments of the present application are described below in detail with examples shown in the accompanying drawings. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0038] The Ru-based catalyst for ammonia decomposition to produce hydrogen provided by the embodiments of the present application comprises a carrier and active metal nanoparticles supported on the carrier, the active metal nanoparticles comprise transition metal nanoparticles supported on the carrier and a Ru atomic layer coated on the transition metal nanoparticles, and the mass fraction of the Ru atomic layer is 0.2-3wt% based on the total mass of the Ru-based catalyst as 100wt%.

[0039] Working principle: the structural model of the Ru-based catalyst of the embodiments of the present application is shown in Figure 1 . Among them, the transition metal nanoparticles are coated with a Ru atomic layer, and each Ru atom in the outer layer is exposed on the surface and can be fully utilized, and the Ru loading in the catalyst is low, which significantly reduces the cost of the catalyst; there is an electronegativity difference between the Ru atoms and the transition metal atoms, which makes the electrons easily transfer from the transition metal nanoparticles to the Ru atomic layer, which can weaken the adsorption energy between the Ru active sites and NH3 molecules and their derived intermediate reaction products (*NH2, *NH, *N), thereby facilitating the improvement of catalytic activity; at the same time, since the radius of the transition metal atom is smaller than the radius of the Ru atom, the interatomic distance of the transition metal nanoparticles is smaller than the interatomic distance of the Ru atomic layer, therefore, the transition metal nanoparticles with smaller internal interatomic distance will produce a certain compression stress on the Ru atomic layer, causing the adsorption energy between the Ru active sites and NH3 molecules and their derived intermediate reaction products to be weakened, thereby facilitating the improvement of catalytic activity.

[0040] The number of layers of the Ru atomic layer is mainly determined by the content of the transition metal nanoparticles and the content of the Ru atomic layer. Preferably, in some embodiments, the number of layers of the Ru atomic layer is 1-2 layers. When the Ru atomic layer is 1-2 layers, it helps to improve the catalytic activity of the Ru-based catalyst. When there are more than 2 layers of Ru atomic layer, the Ru atoms on the surface layer are weakened by the effects of electron transfer and compression stress from the internal transition metal nanoparticles, which affects the optimization of the adsorption energy of the intermediate reaction products, thereby not conducive to improving the catalytic activity. More preferably, in some embodiments, the number of layers of the Ru atomic layer is 1 layer. When the Ru atomic layer is a single layer, each Ru atom is exposed on the surface and can be fully utilized, i.e. the utilization rate is 100%, and the Ru loading in the catalyst is the lowest, which significantly reduces the cost of the catalyst.

[0041] Preferably, in some embodiments, the lattice compressive stress of the Ru atomic layer is 0.2-2.5%, such as 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, etc. More preferably, in some embodiments, the lattice compressive stress of the Ru atomic layer is 0.2-2%. When the lattice compressive stress of the Ru atomic layer is too small, the Ru active sites cannot effectively adjust the adsorption capacity of the intermediate reaction products, and when the lattice compressive stress of the Ru atomic layer is too large, the Ru active sites will cause the adsorption capacity of the intermediate reaction products to be too strong, which will cause the ammonia decomposition products to be unable to be effectively desorbed, and is not conducive to improving the catalytic activity.

[0042] In the Ru-based catalyst of the embodiments of the present application, the mass fraction of the Ru atomic layer is 0.2-3wt%, such as 0.2wt%, 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, 3wt%, etc. When the mass fraction of the Ru atomic layer is less than 0.2wt%, the Ru cannot fully coat the surface of the transition metal nanoparticles, and the Ru content is extremely low, which will significantly reduce the catalytic activity. When the mass fraction of the Ru atomic layer is greater than 3wt%, the surface of the transition metal nanoparticles has been basically covered by Ru atoms, which causes too many Ru ions to be unable to be loaded on the catalyst by ion exchange method, so that the excess Ru ions remain in the first dispersant, causing waste of Ru.

[0043] Preferably, in some embodiments, the mass fraction of the Ru atomic layer is 0.5-2wt%, such as 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, etc. The mass fraction of the Ru atomic layer in the above range is helpful to further improve the catalytic activity.

[0044] Preferably, in some embodiments, the average particle size of the active metal nanoparticles is 0.8-10 nm, such as 0.8 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, etc. More preferably, in some embodiments, the average particle size of the active metal nanoparticles is 1-5 nm, such as 1 nm, 1.3 nm, 1.6 nm, 1.8 nm, 2 nm, 2.3 nm, 2.6 nm, 2.8 nm, 3 nm, 3.3 nm, 3.6 nm, 3.8 nm, 4 nm, 4.3 nm, 4.6 nm, 4.8 nm, 5 nm, etc. When the average particle size of the active metal nanoparticles is too small, the Ru-based catalyst will be prone to severe agglomeration during high-temperature reaction. When the average particle size of the active metal nanoparticles is too large, the coordination unsaturation of surface Ru atoms in the active metal nanoparticles will be significantly reduced, which is not conducive to improving the catalytic activity.

[0045] The Ru-based catalyst of the embodiments of the present application is not particularly limited in the type of transition metal nanoparticles, as long as it is a transition metal. Preferably, in some embodiments, the transition metal nanoparticles are at least one of Fe, Cu, Co, and Ni nanoparticles. These transition metals can form metal-state nanoparticles, and there is a certain redox potential difference between the transition metal atoms and the Ru atoms, so that the Ru atoms can replace the surface layer of transition metal atoms by ion exchange under relatively mild reaction conditions, forming transition metal nanoparticles coated with a layer of Ru atoms.

[0046] Preferably, in some embodiments, the mass fraction of the transition metal nanoparticles is 5-30 wt%, such as 5 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, etc. When the mass fraction of the transition metal nanoparticles is too small, the transition metal nanoparticles are prone to agglomeration during the reaction in step (2) of the preparation method, because the particle size of the transition metal nanoparticles is too small. When the mass fraction of the transition metal nanoparticles is too large, the particle size of the transition metal nanoparticles is too large, which is not conducive to improving the catalytic activity.

[0047] Preferably, in some embodiments, the Ru-based catalyst further comprises an additive, which is at least one of alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates and rare earth metal oxides. The above-mentioned additives are easy to lose electrons due to their low electronegativity, which causes the electrons to transfer from the additive to the active metal nanoparticles and finally to the Ru active sites, thereby optimizing the adsorption energy of the active sites and the intermediate products in the ammonia decomposition reaction and improving the catalytic activity. At the same time, the presence of the above-mentioned additives is conducive to inhibiting the agglomeration of the active metal nanoparticles and improving the stability of the reaction in step (4) of the preparation method.

[0048] The Ru-based catalyst of the embodiments of the present application is not particularly limited in terms of the type of carrier and any carrier in the related art can be used. For example, the carrier can be a carbon material and / or a metal oxide, the carbon material can be at least one of carbon black, activated carbon, graphene and carbon nanotubes, and the metal oxide can be at least one of MgO, CeO2, SiO2, TiO2, Cr2O3, La2O3 and Al2O3.

[0049] In addition, the embodiments of the present application also provide a preparation method of a Ru-based catalyst for ammonia decomposition to produce hydrogen, which comprises the following steps:

[0050] (1) mixing the carrier, the transition metal salt and the first dispersant uniformly, and drying to obtain a mixed powder;

[0051] (2) performing first sintering treatment on the mixed powder in a mixed atmosphere of hydrogen and inert gas at 300-1000℃ to obtain a first sintered product;

[0052] (3) mixing the first sintered product, the Ru salt and the second dispersant uniformly, and performing stirring treatment, and then performing filtration, washing and drying to obtain a catalyst powder;

[0053] (4) performing second sintering treatment on the catalyst powder to obtain the Ru-based catalyst.

[0054] Working principle: the preparation method of the embodiments of the present application mainly comprises loading of transition metal nanoparticles and formation of a Ru atomic layer. The loading of transition metal nanoparticles is completed through steps (1) and (2), and transition metal nanoparticles are obtained by reducing transition metal ions attached to the surface of the carrier. The formation of the Ru atomic layer is completed through steps (3) and (4), and the Ru ions replace the transition metal atoms on the surface layer of the transition metal nanoparticles by ion exchange method due to the difference in redox potential between Ru atoms and transition metal atoms, thereby forming the Ru atomic layer.

[0055] Preferably, in some embodiments, in step (1), the transition metal salt is at least one of Fe salt, Cu salt, Ni salt and Co salt.

[0056] The preparation method of the embodiments of the present application does not have a particular limitation on the type of the first dispersant in step (1) as long as it can be used to uniformly disperse the carrier and the transition metal salt. Preferably, in some embodiments, the first dispersant can be at least one of water, methanol, isopropyl alcohol and ethanol. The above types of first dispersants are non-toxic and have a relatively low boiling point, and are easy to evaporate during the drying process.

[0057] Preferably, in some embodiments, in step (2), the volume fraction of hydrogen in the mixed atmosphere is 3-50%, such as 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% and the like. When the volume fraction of hydrogen in the mixed atmosphere is too low, it is not conducive to the full reduction of the transition metal salt to form transition metal nanoparticles. When the volume fraction of hydrogen in the mixed atmosphere is too high, it is relatively dangerous. As for the inert gas, it can be at least one of N2, He and Ar.

[0058] In the preparation method of the embodiments of the present application, the temperature of the first sintering treatment in step (2) is 300-1000℃, such as 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃ and the like. When the temperature of the first sintering treatment is lower than 300℃, the transition metal ions cannot be fully reduced, which will cause the particle size of the transition metal nanoparticles loaded on the carrier to be significantly small, and at the same time, will cause the loss of the transition metal ions that are not reduced, so that the overall content of the loaded transition metal is reduced, and finally the loadable Ru content is reduced. When the temperature of the first sintering treatment is higher than 1000℃, the transition metal nanoparticles loaded on the carrier will be severely agglomerated, the particle size will be significantly large, the catalytic activity will be reduced, and at the same time, the exposed surface area will be reduced, resulting in a reduction in the loadable Ru content. Preferably, in some embodiments, the temperature of the first sintering treatment in step (2) is 300-900℃. When the temperature of the first sintering treatment is too high, it is not conducive to reducing the agglomeration of the transition metal nanoparticles, and thus is not conducive to improving the catalytic activity.

[0059] As for the time of the first sintering treatment in step (2), it is generally 1-8h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h and the like, which needs to be set according to the temperature of the first sintering treatment, for example, when the temperature of the first sintering treatment is relatively high, the time can be set a little shorter, and when the temperature of the first sintering treatment is relatively low, the time can be set a little longer accordingly.

[0060] Preferably, in some embodiments, in step (3), the Ru salt can be at least one of ruthenium trichloride, ruthenium acetylacetonate, ruthenium nitrosyl nitrate, and ruthenium acetate, etc.

[0061] The stirring treatment in step (3) of the preparation method of the embodiments of the present application is to enable the Ru ions to fully replace the transition metal atoms, so as to improve the Ru loading. Preferably, in some embodiments, the stirring treatment is at a temperature of 30-90℃, such as 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., and the stirring treatment is for a time of 2-24h, such as 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc. More preferably, in some embodiments, the stirring treatment is at a temperature of 40-90℃, and the stirring treatment is for a time of 3-24h. When the temperature of the stirring treatment is too low or the time of the stirring treatment is too short, it is not conducive to the Ru ions fully replacing the transition metal atoms, so as to not be conducive to improving the Ru loading. When the temperature of the stirring treatment is too high or the time of the stirring treatment is too long, the replacement effect will not be further significantly improved, and it is not conducive to improving the production efficiency.

[0062] The preparation method of the embodiments of the present application does not have special limitations on the type of the second dispersant in step (3), as long as it can be used to uniformly disperse the first sintered product and the Ru salt. Preferably, in some embodiments, the second dispersant can be at least one of water, methanol, isopropanol, and ethanol, etc. The above types of second dispersants are non-toxic and have a relatively low boiling point, and are easy to evaporate during the drying process.

[0063] Step (4) of the preparation method of the embodiments of the present application is to improve the structural stability of the Ru atomic layer. High-temperature sintering converts the Ru atomic layer with unstable structure obtained after step (3) into a Ru atomic layer with stable structure, so as to improve the durability of the catalyst. The preparation method of the embodiments of the present application does not have special limitations on the sintering atmosphere of the second sintering treatment, which can be at least one of N2, He, Ar, Air (air), and O2, or a mixed gas atmosphere of H2 and the above several gases, but it should be noted that, in order to ensure safety, the volume fraction of H2 cannot exceed 50%.

[0064] Preferably, in some embodiments, in step (4), the second sintering treatment is at a temperature of 300-600℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, etc., and the second sintering treatment is for a time of 1-5h, such as 1h, 2h, 3h, 4h, 5h, etc. When the temperature of the second sintering treatment is too low or the time of the second sintering treatment is too short, it is not conducive to improving the structural stability of the Ru atomic layer and it is difficult to fully convert the promoter salt into the promoter oxide. When the temperature of the second sintering treatment is too high or the time of the second sintering treatment is too long, it is easy to cause the Ru to agglomerate on the surface of the transition metal.

[0065] Preferably, in some embodiments, in step (4), the catalyst powder is mixed with the assistant precursor salt and a third dispersant uniformly, and after drying, the second sintering treatment is performed to obtain the Ru-based catalyst. The above steps serve to introduce the assistant into the Ru-based catalyst, and the assistant is loaded on the surface of the carrier and connected with the active metal nanoparticles, which can further improve the catalytic activity of the catalyst.

[0066] Preferably, in some embodiments, in step (4), the assistant precursor salt is at least one of an alkali metal salt, an alkaline earth metal salt, and a rare earth metal salt. More preferably, in some embodiments, in step (4), the assistant precursor salt is an alkali metal salt, which can be at least one of a Li salt, a Na salt, a K salt, an Rb salt, and a Cs salt.

[0067] The preparation method of the embodiments of the present application does not have a particular limitation on the type of the third dispersant in step (4) as long as it can be used to uniformly disperse the catalyst powder and the assistant precursor salt. Preferably, in some embodiments, the third dispersant can be at least one of water, methanol, isopropanol, and ethanol. The above types of third dispersants are non-toxic and have a relatively low boiling point, and are easy to evaporate during the drying process.

[0068] In addition, the Ru-based catalyst of the embodiments of the present application or the Ru-based catalyst obtained by the preparation method of the embodiments of the present application can be applied to an ammonia decomposition reaction.

[0069] The Ru-based catalyst of the embodiments of the present application or the Ru-based catalyst obtained by the preparation method of the embodiments of the present application can greatly improve the efficiency of the ammonia decomposition reaction.

[0070] The present application will be described in detail below with reference to the embodiments and the accompanying drawings.

[0071] Embodiment 1

[0072] (1) 10 g of carbon black, 18 g of iron nitrate, and 500 g of water were mixed uniformly, and after drying, a mixed powder was obtained;

[0073] (2) The obtained mixed powder was subjected to a first high-temperature sintering treatment, and the sintering atmosphere was a mixed gas of H2 and N2, wherein the volume fraction of H2 was 20%, the sintering temperature was 600°C, and the sintering time was 5 h, to obtain a sintered product;

[0074] (3) The sintered product, 0.23 g of ruthenium trichloride, and 500 g of water were mixed uniformly, and stirring treatment was performed, the stirring temperature was 60°C, the stirring time was 12 h, and then suction filtration, washing, and drying were performed to obtain a catalyst powder;

[0075] (4) mixing the catalyst powder, 3 g of sodium nitrate and 500 g of water uniformly, drying and then performing a second high-temperature sintering treatment, the sintering atmosphere being a mixture of H2 and N2, wherein the volume fraction of H2 accounts for 10%, the sintering temperature being 400°C, and the sintering time being 4 h, to obtain an ammonia decomposition hydrogen production Ru-based catalyst, denoted as Na-Ru@Fe / C.

[0076] The catalyst parameters and performance prepared in this example are shown in Table 1, and the ammonia decomposition hydrogen production activity curve is shown in Figure 2 The catalyst has one layer of Ru monatomic layers.

[0077] Example 2

[0078] (1) mixing 10 g of carbon nanotubes, 2.5 g of cobalt nitrate and 500 g of water uniformly, and drying to obtain a mixed powder;

[0079] (2) performing a first high-temperature sintering treatment on the obtained mixed powder, the sintering atmosphere being a mixture of H2 and Ar, wherein the volume fraction of H2 accounts for 3%, the sintering temperature being 900°C, and the sintering time being 1 h, to obtain a sintered product;

[0080] (3) mixing the sintered product, 0.125 g of ruthenium trichloride and 500 g of water uniformly, and performing stirring treatment, the stirring temperature being 90°C, the stirring time being 3 h, and then performing suction filtration, washing and drying to obtain a catalyst powder;

[0081] (4) mixing the catalyst powder, 1.3 g of potassium nitrate and 300 g of water uniformly, drying and then performing a second high-temperature sintering treatment, the sintering atmosphere being a mixture of H2 and Ar, wherein the volume fraction of H2 accounts for 5%, the sintering temperature being 600°C, and the sintering time being 1 h, to obtain an ammonia decomposition hydrogen production Ru-based catalyst, denoted as K-Ru@Co / CNTs.

[0082] The catalyst parameters and performance prepared in this example are shown in Table 1, and the ammonia decomposition hydrogen production activity curve is shown in Figure 2 The catalyst has one layer of Ru monatomic layers.

[0083] Example 3

[0084] (1) mixing 10 g of MgO, 22 g of iron nitrate and 500 g of ethanol uniformly, and drying to obtain a mixed powder;

[0085] (2) performing a first high-temperature sintering treatment on the obtained mixed powder, the sintering atmosphere being a mixture of H2 and N2, wherein the volume fraction of H2 accounts for 50%, the sintering temperature being 300°C, and the sintering time being 8 h, to obtain a sintered product;

[0086] (3) The sintered product, 1.6 g of ruthenium acetate, and 500 g of ethanol were uniformly mixed and subjected to stirring treatment at a stirring temperature of 40°C for 24 h, followed by suction filtration, washing, and drying, to obtain a catalyst powder;

[0087] (4) The catalyst powder, 1.5 g of cesium nitrate, and 300 g of water were uniformly mixed, dried, and then subjected to second high-temperature sintering treatment in a mixed gas of O2 and Ar, in which the volume fraction of O2 was 20%, at a sintering temperature of 300°C for 5 h, to obtain an ammonia decomposition hydrogen production Ru-based catalyst, which was denoted as Cs-Ru@Fe / MgO.

[0088] The catalyst parameters and performance obtained in this example are shown in Table 1, and the ammonia decomposition hydrogen production activity curve is shown in FIG. 1. Figure 2 The number of layers of Ru monomers in the catalyst was 1 layer.

[0089] Example 4

[0090] (1) 10 g of Al2O3, 5 g of nickel nitrate, and 500 g of methanol were uniformly mixed to obtain a mixed powder;

[0091] (2) The mixed powder obtained was subjected to first high-temperature sintering treatment in a mixed gas of H2 and He, in which the volume fraction of H2 was 10%, at a sintering temperature of 700°C for 6 h, to obtain a sintered product;

[0092] (3) The sintered product, 0.25 g of ruthenium acetylacetonate, and 500 g of methanol were uniformly mixed and subjected to stirring treatment at a stirring temperature of 80°C for 6 h, followed by suction filtration, washing, and drying, to obtain a catalyst powder;

[0093] (4) The catalyst powder, 1.1 g of rubidium nitrate, and 300 g of water were uniformly mixed, dried, and then subjected to second high-temperature sintering treatment in a mixed gas of Air and He, in which the volume fraction of Air was 30%, at a sintering temperature of 500°C for 3 h, to obtain an ammonia decomposition hydrogen production Ru-based catalyst, which was denoted as Rb-Ru@Ni / Al2O3.

[0094] The catalyst parameters and performance obtained in this example are shown in Table 1, and the ammonia decomposition hydrogen production activity curve is shown in FIG. 1. Figure 2 The number of layers of Ru monomers in the catalyst was 1 layer.

[0095] Example 5

[0096] The same method as in Example 1 was used, except that the amount of ruthenium trichloride was doubled to 0.46 g. The number of layers of Ru monomers in the catalyst was 2 layers. The catalyst parameters and performance obtained in this example 5 are shown in Table 1.

[0097] Example 6

[0098] The same method as Example 1 was used, except that the first sintering temperature was changed to 1000°C.

[0099] The parameters and properties of the catalyst prepared in Example 6 are shown in Table 1.

[0100] Example 7

[0101] The same method as Example 1 was used, except that sodium nitrate was not added.

[0102] The parameters and properties of the catalyst prepared in Example 7 are shown in Table 1.

[0103] Example 8

[0104] The same method as Example 1 was used, except that the temperature of the stirring treatment was changed to 30°C.

[0105] The parameters and properties of the catalyst prepared in Example 8 are shown in Table 1.

[0106] Example 9

[0107] The same method as Example 1 was used, except that the amount of iron nitrate added was changed to 30 g, so that the Fe loading in the catalyst was 15 wt%.

[0108] The parameters and properties of the catalyst prepared in Example 9 are shown in Table 1.

[0109] Example 10

[0110] The same method as Example 1 was used, except that the amount of iron nitrate added was changed to 2 g, so that the Fe loading in the catalyst was 3 wt%.

[0111] The parameters and properties of the catalyst prepared in Example 10 are shown in Table 1.

[0112] Example 11

[0113] The same method as Example 2 was used, except that the stirring treatment time was changed to 2 h.

[0114] The parameters and properties of the catalyst prepared in Example 11 are shown in Table 1.

[0115] Comparative Example 1

[0116] The same method as Example 1 was used, except that the first sintering atmosphere was changed to pure N2.

[0117] The parameters and properties of the catalyst prepared in Comparative Example 1 are shown in Table 1.

[0118] Comparative Example 2

[0119] The same method as in Example 1, except that the first sintering temperature was changed to 250°C.

[0120] The parameters and properties of the catalyst prepared in Comparative Example 2 are shown in Table 1.

[0121] Comparative Example 3

[0122] The same method as in Example 1, except that no iron nitrate was added.

[0123] The parameters and properties of the catalyst prepared in Comparative Example 3 are shown in Table 1.

[0124] Comparative Example 4

[0125] The same method as in Example 1, except that no ruthenium trichloride was added.

[0126] The parameters and properties of the catalyst prepared in Comparative Example 4 are shown in Table 1.

[0127] Comparative Example 5

[0128] The same method as in Example 1, except that no iron nitrate was added, and the filtration process in step (3) was replaced by rotary evaporation to prepare carbon-supported Ru nanoparticles, and then the same steps were used to load alkali metal Na to prepare Na-Ru NPs / C.

[0129] The parameters and properties of the catalyst prepared in Comparative Example 5 are shown in Table 1.

[0130] Comparative Example 6

[0131] Comparative Example 6 used a commercial catalyst Ru / C, with a Ru loading of 5wt%.

[0132] The parameters, the conversion of ammonia at 500°C for the production of hydrogen by ammonia decomposition of the Ru-based catalysts of Examples 1-11 and Comparative Examples 1-6 are shown in Table 1. Among them, the average particle size of the active metal nanoparticles was obtained by TEM analysis. The lattice compression stress of Ru atoms was obtained by spherical aberration electron microscopy analysis, which was done by measuring the distance between two Ru atoms (d1), and the difference between the distance between two Ru atoms on the traditional Ru particles (d2) and the distance between two Ru atoms on the traditional Ru particles (d2) (d2-d1) divided by the distance between two Ru atoms on the traditional Ru particles (d2), i.e. (d2-d1) / d2, was the lattice compression stress. The conversion of ammonia at 500°C for the production of hydrogen by ammonia decomposition was obtained by fixed bed reactor performance evaluation, with a space velocity of 30000 mL / (h·g cat ).

[0133] Table 1. Parameters, conversion of ammonia at 500°C for the production of hydrogen by ammonia decomposition of the Ru-based catalysts of Examples 1-11 and Comparative Examples 1-6

[0134]

[0135] As can be seen from Table 1:

[0136] (1) Compared with the commercial catalyst of Comparative Example 6, the Ru-based catalysts of Examples 1-11 have a low Ru loading and a low catalyst cost, in addition, the catalysts of Examples 1-11 are a structure in which transition metal nanoparticles are coated with a Ru atomic layer, the transition metal nanoparticles in the inner layer have an effective electronic and stress regulation effect on the Ru atomic layer in the surface layer, the adsorption energy of the Ru active sites and the intermediate reaction products in the ammonia decomposition reaction is adjusted, and the catalytic activity is optimized. In particular, the Ru-based catalysts of Examples 1-4 are a structure in which transition metal nanoparticles are coated with a single-layer Ru atomic layer, and the catalytic activity is more excellent.

[0137] (4) Example 6 is to change the first sintering temperature in Example 1 to 1000°C, and the higher sintering temperature than that in Example 1 causes the loaded Fe nanoparticles to agglomerate, the average particle size of the active metal nanoparticles increases significantly, resulting in a decrease in the catalytic activity of Example 6 compared with Example 1, and at the same time, the exposed surface area of the Fe nanoparticles decreases, resulting in a decrease in the loadable amount of Ru, which is not conducive to improving the catalytic activity.

[0138] (7) Example 7 is to cancel the addition of sodium nitrate in Example 1, and the lack of the addition of an alkali metal additive causes the electronic structure of the Ru atoms to not be fully optimized, so that it has a stronger adsorption energy for the intermediate products in the ammonia decomposition reaction than the catalyst obtained in Example 1, resulting in a decrease in the catalytic activity.

[0139] (8) Example 8 is to change the stirring treatment temperature in Example 1 to 30°C, and the lower stirring treatment temperature than that in Example 1 is not conducive to the replacement process of the ion exchange of Ru ions with Fe atomic ions, resulting in a decrease in the loading amount of Ru, which is not conducive to improving the catalytic activity.

[0140] (9) Example 9 is to change the amount of iron nitrate added in Example 1 to 11 g, and the introduction of more Fe atoms causes the particle size of the Fe nanoparticles to increase significantly, so that the exposed surface area decreases, resulting in a decrease in the ion exchange amount of Ru, and at the same time, the large-size active metal nanoparticles reduce the catalytic activity.

[0141] (10) Example 10 is to change the amount of iron nitrate added in Example 1 to 2 g, and the introduction of less Fe atoms causes the particle size of the Fe nanoparticles to decrease significantly, which is easy to agglomerate, and at the same time, the loading amount of Ru decreases due to the decrease in the ion exchange amount, which is not conducive to improving the catalytic activity.

[0142] (11) Example 11 is to change the stirring treatment time in Example 2 to 2h, shorter stirring treatment time than Example 2 makes the Ru ion replacement for Fe atom not enough, resulting in Ru loading significantly reduced, making the lattice compression of Fe nanoparticles to Ru atomic layer larger, resulting in its adsorption of ammonia decomposition hydrogen intermediate reaction products too weak, in turn leading to the catalytic activity of Example 11 relative to Example 2 is reduced.

[0143] (2) Comparative Example 1 is to change the first sintering atmosphere in Example 1 to pure N2, lack of introduction of reducing atmosphere, resulting in adsorbed ferric nitrate decomposing to form iron oxide at high temperature, making the subsequent Ru ion exchange impossible, causing Ru atoms cannot be loaded.

[0144] (3) Comparative Example 2 is to change the first sintering temperature in Example 1 to 250℃, lower than the sintering temperature defined in the application, neither can reduce Fe ions sufficiently, causing the particle size of loaded Fe nanoparticles significantly smaller, nor can play a role in the reduction of Fe ions, causing the problem of Ru atom loading difficulty.

[0145] (5) Comparative Example 3 is to cancel the addition of ferric nitrate in Example 1, the addition of no ferric nitrate will cause no Fe nanoparticles, therefore, Ru ions cannot be ion exchanged to achieve loading, resulting in Ru loading of 0.

[0146] (6) Comparative Example 4 is to cancel the addition of ruthenium trichloride in Example 1, lack of introduction of active site Ru atoms, resulting in the catalyst almost deactivated, only showing the extremely low ammonia decomposition activity of Fe nanoparticles.

[0147] (12) Comparative Example 5 is to synthesize a catalyst system of carrier-aid-Ru nanoparticles, namely Na-Ru NPs / C, which does not exist Ru lattice compression stress and does not exist the effective electron transfer effect of transition metal to Ru, resulting in the activity significantly lower than the Ru-based catalyst of the application, in addition, the Ru atoms inside the Ru nanoparticles of Comparative Example 5 cannot be effectively utilized, resulting in the waste of noble metal Ru.

[0148] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present disclosure. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terminology "comprising" is used in the disclosure as comprising but not limited to, that is, it is open-ended and does not exclude the presence of additional features, structures, materials, or characteristics.

[0149] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above-described embodiments are exemplary, and are not to be interpreted as limiting the present disclosure, and the ordinary skilled in the art can make changes, modifications, replacements, and variations to the above-described embodiments within the scope of the present disclosure.

Claims

1. A Ru-based catalyst for ammonia decomposition for hydrogen production, characterized by, The Ru-based catalyst comprises a carrier and active metal nanoparticles supported on the carrier, the active metal nanoparticles comprise transition metal nanoparticles supported on the carrier and a Ru atomic layer coated on the transition metal nanoparticles, the mass fraction of the Ru atomic layer is 0.2-3wt% based on the total mass of the Ru-based catalyst, the number of layers of the Ru atomic layer is 1 layer, the lattice compressive stress of the Ru atomic layer is 0.2-2%, and the transition metal nanoparticles are at least one of Fe, Cu and Co nanoparticles.

2. The Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 1, characterized in that, The mass fraction of the Ru atomic layer is 0.5-2wt%.

3. The Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 1, wherein, The average particle size of the active metal nanoparticles is 1-5nm.

4. The Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 1, wherein, The mass fraction of the transition metal nanoparticles is 5-30wt%.

5. The Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 1, wherein, The assistant is at least one of alkali metal oxides, alkali metal carbonates, alkaline earth metal oxides, alkaline earth metal carbonates and rare earth metal oxides.

6. The process for the preparation of a Ru-based catalyst for the hydrogen production by ammonia decomposition according to any one of claims 1-5, characterized by the fact that, The method comprises the following steps: (1) uniformly mixing the carrier, a transition metal salt and a first dispersant, and drying to obtain a mixed powder; (2) performing first sintering treatment on the mixed powder in a mixed atmosphere of hydrogen and inert gas at 300-1000℃ to obtain a first sintering product; (3) uniformly mixing the first sintering product, a Ru salt and a second dispersant, and performing stirring treatment, and then performing filtration, washing and drying to obtain a catalyst powder; (4) performing second sintering treatment on the catalyst powder to obtain the Ru-based catalyst.

7. The method for preparing a Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 6, characterized by, The temperature of the stirring treatment is 30-90℃, and the time is 2-24h.

8. The method for preparing a Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 7, characterized by, The temperature of the stirring treatment is 40-90℃, and the time is 3-24h.

9. The method for preparing a Ru-based catalyst for ammonia decomposition to produce hydrogen according to claim 6 or 7, characterized in that, In step (4), the catalyst powder is uniformly mixed with an assistant precursor salt and a third dispersant, and then dried and subjected to the second sintering treatment to obtain the Ru-based catalyst.

10. Application of the Ru-based catalyst according to any one of claims 1-5 or the Ru-based catalyst obtained by the preparation method in any one of claims 6-9 in an ammonia decomposition reaction.

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