Ruthenium atom cluster composite catalyst for hydrogen production through ammonia decomposition and preparation method of ruthenium atom cluster composite catalyst

Abstract

The invention provides a ruthenium cluster composite catalyst for hydrogen production through ammonia decomposition and a preparation method thereof, and the preparation method comprises the following steps: dispersing melamine, cyanuric acid and amino acid in a methanol aqueous solution, and stirring to form a mixed system; adding a rare earth metal precursor salt into the mixed system, continuously stirring, heating to evaporate the solvent, grinding the obtained white solid into powder, and transferring to a high temperature for pyrolysis to obtain a rare earth element modified nitrogen-rich carbon carrier; the preparation method comprises the following steps: dissolving precursor ruthenium salt and urea in deionized water to form an impregnation liquid, adding a rare earth element modified nitrogen-rich carbon carrier into the impregnation liquid, stirring and impregnating, filtering and collecting solids, and washing, drying and roasting the solids to obtain the catalyst, based on the high specific surface characteristic of the nitrogen-rich carbon carrier and modification of the rare earth element on the electron state of an active site ruthenium atom cluster, the use amount of ruthenium is reduced, the NH3 adsorption performance and the N-H bond breaking capacity are improved, and hydrogen production through ammonia decomposition is efficiently catalyzed and promoted under the low-temperature condition.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts and preparation, and particularly relates to a ruthenium atom cluster composite catalyst for ammonia decomposition to hydrogen and a preparation method thereof. Background Art

[0002] Energy is the key driving force for national development and the progress of human society. As a secondary energy source with rich sources, green and low-carbon, and wide applications, hydrogen energy not only helps to effectively consume renewable energy, but also enables the power grid to perform controllable peak shaving and cross-seasonal and cross-regional energy storage, and can also accelerate the low-carbon process in fields such as industry, construction, and transportation. Undoubtedly, it is the key force to promote the low-carbon transformation of energy. However, it must be mentioned that the extremely harsh conditions for its storage and transportation have greatly restricted the wider popularization and application of hydrogen energy, making the potential of hydrogen energy not fully released. There is an urgent need to achieve breakthrough innovations in storage and transportation technologies, so as to bring new opportunities and vitality to the transformation of the energy field.

[0003] Ammonia (NH3) is a relatively common chemical hydrogen storage material, with a hydrogen storage content as high as 17.7 wt.%, and ammonia can be easily stored in liquid form at room temperature and low pressure. The ammonia decomposition to hydrogen technology is a highly valuable, clean, and efficient in-situ green hydrogen production technology, which can effectively solve the problem of traditional high-pressure hydrogen storage. However, in reality, there are bottlenecks in ammonia decomposition to hydrogen. Usually, ammonia decomposition to hydrogen needs to be carried out at a high temperature of 600 - 800 °C, and this high-temperature environment will cause sintering inactivation of the catalyst and serious energy consumption.

[0004] At present, ruthenium-based catalysts are considered to be the most active ammonia decomposition catalysts at low temperatures. However, the ruthenium content in existing catalysts is high, resulting in high catalyst costs and inability to be put into commercial use. Moreover, ruthenium-based catalysts are prone to hydrogen poisoning, that is, a large amount of adsorbed hydrogen on the catalyst surface inhibits ammonia decomposition, greatly affecting the activity and stability of ruthenium-based catalysts. At the same time, the ammonia decomposition active temperature range is still very high (>450 °C), with high energy consumption.

[0005] Therefore, it is of great significance to develop a new type of low-ruthenium-loaded atom cluster composite catalyst to achieve efficient ammonia decomposition under mild conditions. Summary of the Invention

[0006] Aiming at the above problems existing in the prior art, the present invention provides a ruthenium atom cluster composite catalyst for ammonia decomposition to hydrogen and a preparation method thereof. The rare earth element is used to modify the nitrogen-rich carbon carrier and support the ruthenium atom cluster. The formed composite catalytic material has the advantage of low ruthenium loading, and can achieve efficient ammonia decomposition under mild conditions.

[0007] The specific content of the invention is as follows: In a first aspect, the present invention provides a method for preparing a ruthenium atomic cluster composite catalyst for ammonia decomposition to hydrogen, and the preparation method includes: Disperse melamine, cyanuric acid, and amino acid in an aqueous methanol solution, stir to form a mixed system, add a rare earth metal precursor salt to the mixed system, continuously stir for 2 - 6 hours, and then heat to evaporate the solvent to obtain a white solid; Grind the white solid into powder, transfer it to 700 - 850 °C for pyrolysis, and the obtained black powder is a rare earth element - modified nitrogen - rich carbon carrier, where the nitrogen content is between 10 - 20 wt.%; Dissolve a precursor ruthenium salt and urea in deionized water to form an impregnation solution, add the rare earth element - modified nitrogen - rich carbon carrier to the impregnation solution, carry out stirring impregnation, and the solid collected by filtration is washed, dried, and calcined to obtain the ruthenium atomic cluster composite catalyst.

[0008] Optionally, the concentration of the aqueous methanol solution is 20 - 50 wt.%, the molar ratio of melamine to cyanuric acid is 0.8 - 1.2, and the molar ratio of melamine to amino acid is 1.0 - 1.5.

[0009] Optionally, the amino acid is glycine, alanine, serine, or glutamic acid.

[0010] Optionally, the rare earth metal precursor salt is lanthanum nitrate, lanthanum acetate, cerium nitrate, or cerium acetate, and the addition amount of the rare earth metal precursor salt accounts for 1.0 - 5.0 wt.% of the total mass of melamine, cyanuric acid, and amino acid.

[0011] Optionally, the pyrolysis is carried out in an argon or nitrogen atmosphere, and the heating rate is 2 - 5 °C / min.

[0012] Optionally, the temperature of the impregnation solution is 70 - 90 °C; The time of the stirring impregnation is 6 - 12 hours.

[0013] Optionally, the precursor ruthenium salt is ruthenium trichloride or ruthenium nitrosyl nitrate; The concentration of ruthenium in the impregnation solution is 0.5 - 5.0 mg Ru / mL, and the concentration of urea in the impregnation solution is 20 - 100 mg / mL; The mass ratio of ruthenium in the impregnation solution to the mass of the rare earth element - modified nitrogen - rich carbon carrier is 0.5 - 2.0 wt.%.

[0014] Optionally, the solid collected by filtration is washed, dried, and calcined, including: washing 2 - 3 times with ethanol and deionized water respectively, carrying out vacuum drying at 60 - 90 °C for 2 - 12 hours, and then carrying out reduction at 200 - 300 °C for 1 - 3 hours.

[0015] In a second aspect, the present invention provides a ruthenium atom cluster composite catalyst obtained by the preparation method described in the first aspect above.

[0016] Optionally, when the ruthenium atom cluster composite catalyst is used to catalyze ammonia for ammonia decomposition to produce hydrogen, the reaction space velocity of the ammonia is 5000 - 50000 mL·g -1 ·h -1 , the reaction temperature is 200 - 500 °C, and the reaction pressure is 0.1 - 5.0 MPa.

[0017] Compared with the prior art, the present invention has the following advantages: The present invention provides a preparation method for a ruthenium atom cluster composite catalyst for ammonia decomposition to produce hydrogen. The preparation method includes: dispersing melamine, cyanuric acid, and amino acid in an aqueous methanol solution and stirring to form a mixed system; adding a rare earth metal precursor salt to the mixed system, continuously stirring for 2 - 6 hours, then heating to evaporate the solvent to obtain a white solid; grinding the white solid into powder, transferring it to pyrolyze at 700 - 850 °C, and the obtained black powder is a rare earth element-modified nitrogen-rich carbon support; dissolving a precursor ruthenium salt and urea in deionized water to form an impregnation solution, adding the rare earth element-modified nitrogen-rich carbon support to the impregnation solution, stirring for impregnation, and the collected solid after filtration is washed, dried, and calcined to obtain the ruthenium atom cluster composite catalyst.

[0018] The ruthenium atom cluster composite catalyst obtained by the preparation method provided by the present invention, based on the high specific surface characteristics of the nitrogen-rich carbon support and the modification of the electronic state of the active site ruthenium atom cluster by rare earth elements, can greatly reduce the usage amount of precious metals, effectively improve the NH3 adsorption performance and N - H bond-breaking ability, and realize efficient catalytic promotion of ammonia decomposition to produce hydrogen under low-temperature conditions. This catalyst has high catalytic activity, and the ammonia decomposition conversion rate can reach 93.7% under the reaction conditions of 375 °C and 0.1 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 Shows a flowchart of the preparation method of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention; Figure 2 Shows a transmission electron microscope image of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention; Figure 3 Shows the EDS energy spectrum elemental analysis diagram of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention; Figure 4 Shows the ammonia conversion rate of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention; Figure 5 Shows the comparison of the ammonia decomposition performance of the ruthenium atom cluster composite catalysts provided by the embodiments and comparative examples of the present invention; Figure 6 Shows the influence of the reaction temperature of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention on the ammonia decomposition performance; Figure 7 Shows the influence of the reaction pressure of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention on the ammonia decomposition performance; Figure 8 Shows the influence of the space velocity of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention on the ammonia decomposition performance; Figure 9 Shows the long-term ammonia decomposition performance diagram of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention. Detailed implementation manners

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with the features of other existing technologies that is the same as or similar to the present invention falls within the protection scope of the present invention. In addition, all other embodiments obtained by those of ordinary skill in the art without creative efforts also belong to the protection scope of the present invention.

[0022] For the specific experimental steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the existing technologies in the field can be followed. For the reagents and other instruments not specified for the manufacturers, they are all conventional reagent products that can be obtained through commercial purchases. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus their repeated descriptions will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0023] Technologies, methods, and devices that are known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices shall be regarded as part of the specification of the present invention.

[0024] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of differentiating the corresponding components. Without further statement, the above terms have no special meaning, and thus should not be construed as limiting the protection scope of the present invention.

[0025] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] In a first aspect, the present invention provides a method for preparing a ruthenium atom cluster composite catalyst for ammonia decomposition to produce hydrogen. Figure 1 The flowchart of the method for preparing the ruthenium atom cluster composite catalyst provided by the present invention is shown. As Figure 1 shown, the preparation method includes: S1. Dissolve melamine, cyanuric acid, and amino acid in an aqueous methanol solution, stir to form a mixed system, add a rare earth metal precursor salt to the mixed system, continuously stir for 2 - 6 hours, and then heat to evaporate the solvent to obtain a white solid. In the specific implementation of this step, melamine, cyanuric acid, and amino acid are used as the carbon source and nitrogen source. Melamine (C3H6N6) and cyanuric acid (C3H3N3O3) form a supramolecular network structure (similar to the melamine - cyanuric acid complex, MCA) in the methanol - aqueous solution, providing a nitrogen source and a carbon skeleton for the subsequent nitrogen - rich carbon carrier. Amino acids (such as lysine, glutamic acid, etc.) contain -NH2 and -COOH groups, can form peptide bonds (-CO - NH -) with melamine or cyanuric acid, and are partially embedded in the MCA structure, providing additional nitrogen or carbon sources during the subsequent pyrolysis process and affecting the pore structure of the nitrogen - rich carbon carrier.

[0027] In specific implementation, first disperse melamine and cyanuric acid in an aqueous methanol solution, and magnetically stir at room temperature for 2 - 6 h. During this process, melamine (C3H6N6) and cyanuric acid (C3H3N3O3) form a supramolecular network structure (similar to the melamine - cyanuric acid complex, MCA) in the methanol - aqueous solution. Then add a specific type of amino acid to the above suspension containing melamine and cyanuric acid, and magnetically stir at room temperature for 2 - 6 h. During this process, the carboxyl group of the amino acid combines with the amino group of melamine, and the amino group of the amino acid combines with the carboxyl group of cyanuric acid, and is partially embedded in the MCA structure, so that the exposed amino acid side chains (such as hydrophobic chains or polar groups) play a role in regulating the pore structure and surface chemical properties of the complex.

[0028] Furthermore, after melamine, cyanuric acid and amino acid are combined to form a complex, they are further mixed with a rare earth metal precursor salt. During this process, after the rare earth metal precursor salt is dissolved, rare earth ions are released and coordinate with the organic components. The coordination makes the rare earth ions uniformly dispersed in the organic framework, thereby forming a networked organic supramolecular-rare earth complex. Finally, the temperature of the mixed system is raised to evaporate the solvent, and a white solid, the networked organic supramolecular-rare earth complex, is obtained. During this process, the temperature for heating to evaporate the solvent is not higher than 100 °C. The effective fixation between the rare earth metal and the networked organic supramolecule through coordination bonds avoids agglomeration during subsequent pyrolysis, thereby obtaining a nitrogen-rich carbon support with rare earth metals uniformly dispersed in the organic framework.

[0029] In some embodiments, in the mixed system, the concentration of the methanol aqueous solution is 20 - 50 wt.%, the molar ratio of melamine to cyanuric acid is between 0.8 - 1.2, and the molar ratio of melamine to amino acid is between 1.0 - 1.5.

[0030] In some embodiments, the amino acid is selected from glycine, alanine, serine or glutamic acid.

[0031] In some embodiments, the rare earth metal precursor salt is lanthanum nitrate, lanthanum acetate, cerium nitrate or cerium acetate, and the addition amount of the rare earth metal precursor salt accounts for 1.0 - 5.0 wt.% of the total mass of melamine, cyanuric acid and amino acid.

[0032] S2. Grind the white solid into powder, transfer it to pyrolyze at 700 - 850 °C, and the obtained black powder is a rare earth element-modified nitrogen-rich carbon support; When this step is specifically implemented, grind the white solid obtained in the above step S1 into powder, perform vacuum drying at 25 - 90 °C for 2 - 12 hours, place the obtained solid powder in a porcelain boat, transfer it into a tube furnace, and pyrolyze at 700 - 850 °C for 2 - 5 hours. The atmosphere used for pyrolysis is an argon or nitrogen atmosphere, and the heating rate is 2 - 5 °C / min. The obtained black powder is a nitrogen-rich carbon support modified with rare earth elements, and the nitrogen content in the nitrogen-rich carbon support is between 10 - 20 wt.%.

[0033] During the pyrolysis process, the melamine-cyanuric acid complex polycondenses to form graphitic carbon nitride (g-C3N4), and further decomposes into nitrogen-doped graphite carbon. The gases (such as CO2, NH3, etc.) generated by the decomposition of organic substances during the pyrolysis process escape, leaving a porous structure. The decomposition behavior of the amino acid further regulates the pore size distribution of the support, which makes the formed rare earth element-modified nitrogen-rich carbon support have a high specific surface area and porosity, so that the rare earth single atoms coordinated to the support are fully exposed.

[0034] S3. Dissolve the precursor ruthenium salt and urea in deionized water to form an impregnation solution. Add the rare earth element-modified nitrogen-rich carbon support to the impregnation solution, stir and impregnate, and the collected solid after filtration is subjected to washing, drying, and calcination treatments to obtain the ruthenium atom cluster composite catalyst.

[0035] In the specific implementation of this step, the impregnation solution is formed by dissolving the precursor ruthenium salt and urea in a certain amount of deionized water. Among them, the precursor ruthenium salt is ruthenium trichloride or ruthenium nitrosyl nitrate; the concentration of ruthenium in the impregnation solution is 0.5 - 5.0 mg Ru / mL, and the concentration of urea in the impregnation solution is 20 - 100 mg / mL.

[0036] In the specific implementation, the temperature of the impregnation solution used for impregnation is 70 - 90 °C, and the stirring impregnation time is 6 - 12 hours; the presence of urea in the impregnation solution can slowly decompose ammonium ions, making the impregnation solution weakly alkaline, promoting the gradual transformation of Ru³⁺ in the impregnation solution to form ruthenium atom clusters and being loaded on the rare earth element-modified nitrogen-rich carbon support; the mass ratio of ruthenium in the impregnation solution to the mass of the rare earth element-modified nitrogen-rich carbon support is 0.5 - 2.0 wt.%.

[0037] Furthermore, after the stirring impregnation is completed, the obtained suspension is filtered, washed 2 - 3 times with ethanol and deionized water respectively, vacuum dried at 60 - 90 °C for 2 - 12 hours, the obtained solid powder is placed in a porcelain boat and transferred to a tubular furnace, and reduced at 200 - 300 °C for 1 - 3 hours. The atmosphere used is argon or nitrogen, and the heating rate is 2 - 5 °C / min.

[0038] In the second aspect, the present invention provides a ruthenium atom cluster composite catalyst obtained by the preparation method described in the first aspect above. The ruthenium atom cluster composite catalyst provided by the present invention is formed by a rare earth element modifying a nitrogen-rich carbon support and supporting ruthenium atom clusters; among them, the rare earth element is combined with the nitrogen-rich carbon support in a coordination form, and metallic ruthenium is uniformly loaded on the rare earth element-modified nitrogen-rich carbon support in the form of atom clusters.

[0039] The ruthenium atom cluster composite catalyst provided by the present invention can be expressed as Ru x / [RE y -NC]; where Ru x represents ruthenium atom clusters with a mass fraction of x % in the ruthenium atom cluster composite catalyst, and x ranges from 0.2 to 2.5; RE y represents rare earth elements (cerium or lanthanum) with a mass fraction of y % in the ruthenium atom cluster composite catalyst, and y ranges from 5 to 25. That is, the ruthenium atom cluster composite catalyst provided in the embodiment of the present invention (Ru x / [RE y-NC], the mass fraction of the ruthenium atomic cluster is 0.2 - 2.5%, and the mass fraction of the rare earth element cerium is 5 - 25%; for example, in the Ru2 / [Ce 15 -NC] provided in the embodiment of the present invention, it means that in the ruthenium atomic cluster composite catalyst, the mass fraction of the ruthenium atomic cluster is 2%, and the mass fraction of the rare earth element cerium is 15%.

[0040] Since in the ruthenium atomic cluster composite catalyst provided by the present invention, the rare earth element is combined with the nitrogen-rich carbon support in a coordinated form, and metallic ruthenium is loaded on the rare earth element-modified nitrogen-rich carbon support in atomic form, based on the high specific surface characteristics of the nitrogen-rich carbon support and the modification of the electronic state of the active site ruthenium atomic cluster by the rare earth element, the amount of precious metal can be greatly reduced, the NH3 adsorption performance and the N-H bond-breaking ability can be effectively improved, and efficient catalytic promotion of ammonia decomposition to hydrogen can be achieved under low-temperature conditions.

[0041] Optionally, when the ruthenium atomic cluster composite catalyst is used to catalyze ammonia for ammonia decomposition to hydrogen reaction, the reaction space velocity of the ammonia is 5000 - 50000 mL·g -1 ·h -1 , the reaction temperature is 200 - 500 °C, and the reaction pressure is 0.1 - 5.0 MPa.

[0042] Specifically in implementation, under the reaction conditions of 375 °C and 0.1 MPa, the ammonia decomposition conversion rate of the ruthenium atomic cluster composite catalyst provided by the present invention can reach 93.7%.

[0043] To make those skilled in the art understand the present invention more clearly, the following examples are now used to elaborate in detail on a ruthenium atomic cluster composite catalyst for ammonia decomposition to hydrogen and its preparation method described in the present invention.

[0044] Example 1 Weigh 3.78 g (0.03 mol) of melamine and 3.87 g (0.03 mol) of cyanuric acid respectively, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and stir magnetically at room temperature for 2 hours. Weigh 2.67 g (0.03 mol) of alanine and add it to the above mixed system, and continue to stir at room temperature for 2 hours. Weigh 0.30 g of cerium nitrate and add it to the above mixed system, and continue to stir at room temperature for 2 hours. Heat up to 100 °C to evaporate the solvent to obtain a white solid.

[0045] The obtained white solid is ground into powder, vacuum-dried at 80 °C for 6 hours, and the obtained solid powder is placed in a porcelain boat; pyrolyzed at 800 °C in a tube furnace for 3 hours, the atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a rare earth element-modified nitrogen-rich carbon support [Ce 15 -NC].

[0046] Weigh 0.041 g of ruthenium trichloride and 1.0 g of urea separately, dissolve them in 30 mL of deionized water to form an impregnation solution (the concentration of ruthenium in the impregnation solution is 0.67 mg Ru / mL, and the mass of ruthenium in the impregnation solution is 20 mg). Add 1.0 g of [Ce 15 -NC] to the solution, and carry out magnetic stirring impregnation at 80 °C for 12 hours; filter the obtained suspension, wash it three times with ethanol and deionized water respectively, then carry out vacuum drying at 80 °C for 6 hours, and place the obtained solid powder in a porcelain boat; carry out reduction at 250 °C in a tube furnace for 2 hours, the atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a composite catalytic material Ru2 / [Ce 15 -NC] supported by a rare earth element modified nitrogen-rich carbon carrier with ruthenium atom clusters.

[0047] Figure 2 The transmission electron microscope image of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention is shown. As Figure 2 shown, the morphology of this catalyst presents a porous sheet structure with a high specific surface area. The supported ruthenium atom clusters show a highly dispersed state, and their size is between 0.5 - 1.0 nm; Figure 3 The EDS energy spectrum elemental analysis diagram of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention is shown. As Figure 3 shown, the carbon content of this catalyst is 62.04 wt.%, the nitrogen content is 15.26 wt.%, the oxygen content is 6.19 wt.%, the ruthenium content is 1.92 wt.%, and the cerium content is 14.59 wt.%.

[0048] Example 2 Weigh 3.78 g (0.03 mol) of melamine and 3.87 g (0.03 mol) of cyanuric acid separately, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and carry out magnetic stirring at room temperature for 2 hours. Weigh 2.25 g (0.03 mol) of glycine and add it to the above mixed system, and continue to stir at room temperature for 2 hours. Weigh 0.30 g of lanthanum nitrate and add it to the above mixed system, and continue to stir at room temperature for 2 hours. Heat up to 100 °C to evaporate the solvent to dryness to obtain a white solid.

[0049] Grind the obtained white solid into powder, carry out vacuum drying at 80 °C for 6 hours, and place the obtained solid powder in a porcelain boat; carry out pyrolysis at 800 °C in a tube furnace for 3 hours, the atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a rare earth element modified nitrogen-rich carbon carrier [La 15 -NC].

[0050] Weigh 0.041 g of ruthenium(III) chloride and 1.0 g of urea separately, dissolve them in 30 mL of deionized water to form an impregnation solution (the concentration of ruthenium in the impregnation solution is 0.67 mg Ru / mL, and the mass of ruthenium in the impregnation solution is 20 mg). Add 1.0 g of [La 15 -NC] to the solution and carry out magnetic stirring impregnation at 80 °C for 12 hours. Filter the obtained suspension, wash it three times with ethanol and deionized water respectively, and then carry out vacuum drying at 80 °C for 6 hours. Place the obtained solid powder in a porcelain boat; carry out reduction at 250 °C in a tubular furnace for 2 hours, with the atmosphere being argon and the heating rate being 5 °C / min. The obtained black powder is a rare earth element-modified nitrogen-rich carbon support-supported ruthenium atom cluster composite catalytic material Ru2 / [La 15 -NC].

[0051] The EDS energy spectrum elemental analysis results of Ru2 / [La 15 -NC] are as follows: The carbon content of this catalyst is 61.77 wt.%, the nitrogen content is 14.65 wt.%, the oxygen content is 6.76 wt.%, the ruthenium content is 1.89 wt.%, and the lanthanum content is 14.93 wt.%.

[0052] Example 3 Weigh 3.78 g (0.03 mol) of melamine and 3.87 g (0.03 mol) of cyanuric acid separately, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and carry out magnetic stirring at room temperature for 2 hours. Weigh 2.67 g (0.03 mol) of alanine and add it to the above mixed solution, and continue stirring at room temperature for 2 hours. Weigh 0.30 g of cerium nitrate and add it to the above mixed solution, continue stirring at room temperature for 2 hours, and heat up to 100 °C to evaporate the solvent to obtain a white solid.

[0053] Grind the obtained white solid into powder, carry out vacuum drying at 80 °C for 6 hours, and place the obtained solid powder in a porcelain boat; carry out pyrolysis at 800 °C in a tubular furnace for 3 hours, with the atmosphere being argon and the heating rate being 5 °C / min. The obtained black powder is a rare earth element-modified nitrogen-rich carbon support [Ce 15 -NC].

[0054] Weigh 0.021 g of ruthenium(III) chloride and 1.0 g of urea separately, dissolve them in 20 mL of deionized water to form an impregnation solution (the concentration of ruthenium in the impregnation solution is 0.5 mg Ru / mL, and the mass of ruthenium in the impregnation solution is 10 mg). Add 1.0 g of [Ce 15-NC], impregnate it under magnetic stirring at 80 °C for 12 hours. Filter the resulting suspension, wash it three times with ethanol and deionized water respectively, and then conduct vacuum drying at 80 °C for 6 hours. Place the obtained solid powder in a porcelain boat; conduct reduction at 250 °C in a tubular furnace for 2 hours. The atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a composite catalytic material of ruthenium atom clusters supported on a rare earth element-modified nitrogen-rich carbon support, Ru1 / [Ce 15 -NC].

[0055] Ru1 / [Ce 15 -NC] has the following EDS energy spectrum elemental analysis results: The carbon content of this catalyst is 62.37 wt.%, the nitrogen content is 15.56 wt.%, the oxygen content is 6.25 wt.%, the ruthenium content is 1.05 wt.%, and the cerium content is 14.77 wt.%.

[0056] Example 4 Weigh 3.78 g (0.03 mol) of melamine and 3.87 g (0.03 mol) of cyanuric acid respectively, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and stir magnetically at room temperature for 2 hours. Weigh 2.67 g (0.03 mol) of alanine and add it to the above mixed system, then continue to stir at room temperature for 2 hours. Weigh 0.20 g of cerium nitrate and add it to the above mixed system, continue to stir at room temperature for 2 hours, and heat up to 100 °C to evaporate the solvent to obtain a white solid.

[0057] Grind the obtained white solid into powder, conduct vacuum drying at 80 °C for 6 hours, place the obtained solid powder in a porcelain boat; conduct pyrolysis at 800 °C in a tubular furnace for 3 hours. The atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a rare earth element-modified nitrogen-rich carbon support [Ce 10 -NC].[[]END]]

[0058] Weigh 0.041 g of ruthenium trichloride and 1.0 g of urea respectively, dissolve them in 30 mL of deionized water to form an impregnation solution (the concentration of ruthenium in the impregnation solution is 0.67 mg Ru / mL, and the mass of ruthenium in the impregnation solution is 20 mg). Add 1.0 g of [Ce 10 -NC] to the solution, impregnate it under magnetic stirring at 80 °C for 12 hours. Filter the resulting suspension, wash it three times with ethanol and deionized water respectively, and then conduct vacuum drying at 80 °C for 6 hours. Place the obtained solid powder in a porcelain boat; conduct reduction at 250 °C in a tubular furnace for 2 hours. The atmosphere used is argon, and the heating rate is 5 °C / min. The obtained black powder is a composite catalytic material of ruthenium atom clusters supported on a rare earth element-modified nitrogen-rich carbon support, Ru2 / [Ce 10-NC].

[0059] Ru2 / [Ce 10 The EDS energy spectrum elemental analysis results of [Ru2 / [Ce The carbon content of this catalyst is 64.21 wt.%, the nitrogen content is 16.45 wt.%, the oxygen content is 7.14 wt.%, the ruthenium content is 1.87 wt.%, and the cerium content is 10.33 wt.%.

[0060] Comparative Example 1 Weigh 3.78 g (0.03 mol) of melamine and 3.87 g (0.03 mol) of cyanuric acid respectively, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and stir magnetically at room temperature for 2 hours. Weigh 2.67 g (0.03 mol) of alanine and add it to the above mixed solution, and continue to stir at room temperature for 2 hours. Heat up to 100 °C to evaporate the solvent to dryness to obtain a white solid.

[0061] The obtained white solid is ground into powder, vacuum dried at 80 °C for 6 hours, and the obtained solid powder is placed in a porcelain boat; pyrolyzed at 800 °C in a tube furnace for 3 hours, with argon as the atmosphere and a heating rate of 5 °C / min, and the obtained black powder is a nitrogen-rich carbon support [NC]; Weigh 0.041 g of ruthenium trichloride and 1.0 g of urea respectively, dissolve them in 30 mL of deionized water to form an impregnation solution (the concentration of ruthenium in the impregnation solution is 0.67 mg Ru / mL, and the mass of ruthenium in the impregnation solution is 20 mg). Add 1.0 g of [NC] to the solution, and stir magnetically at 80 °C for impregnation for 12 hours. Filter the obtained suspension, wash it three times with ethanol and deionized water respectively, and then vacuum dry at 80 °C for 6 hours. The obtained solid powder is placed in a porcelain boat; reduce it at 250 °C in a tube furnace for 2 hours, with argon as the atmosphere and a heating rate of 5 °C / min, and the obtained black powder is a nitrogen-rich carbon support supported ruthenium cluster catalyst material Ru2 / [NC].

[0062] Comparative Example 2 Weigh 3.78 g of melamine and 3.87 g of cyanuric acid respectively, disperse them in 100 mL of 45 wt.% methanol aqueous solution, and stir magnetically at room temperature for 2 hours. Weigh 2.67 g of alanine and add it to the above mixed solution, and continue to stir at room temperature for 2 hours. Weigh 0.30 g of cerium nitrate and add it to the above mixed solution, and continue to stir at room temperature for 2 hours. Heat up to 100 °C to evaporate the solvent to dryness to obtain a white solid.

[0063] The obtained white solid was ground into powder and vacuum-dried at 80 °C for 6 hours. The obtained solid powder was placed in a porcelain boat. Pyrolysis was carried out at 800 °C for 3 hours in a tubular furnace with argon as the atmosphere and a heating rate of 5 °C / min. The obtained black powder was a rare earth element-modified nitrogen-rich carbon support [Ce 15 -NC].

[0064] Performance test The ammonia conversion rates of the ruthenium atom cluster composite catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were tested The ruthenium atom cluster composite catalyst was loaded in a fixed-bed tubular reactor. Nitrogen was introduced at a flow rate of 50 mL / min at room temperature and heated to 500 °C at a rate of 5 °C / min. After stabilizing at 500 °C for 1 hour, the reaction gas was introduced to test the ammonia decomposition performance. After the ammonia in the product gas was absorbed by dilute sulfuric acid, it was detected by ion chromatography

[0065] Figure 4 The ammonia conversion rates of the ruthenium atom cluster composite catalysts provided in the examples of the present invention are shown (reaction conditions: reaction temperature is 375 °C, reaction pressure is 0.1 MPa, ammonia concentration is 10 vol.%, reaction space velocity is 30000 mL·g -1 ·h -1 ), as Figure 4 shown, at a reaction temperature of 375 °C, a reaction pressure of 0.1 MPa, an ammonia concentration of 10 vol.%, and a reaction space velocity of 30000 mL·g -1 ·h -1 conditions, the ammonia conversion rates of the ruthenium atom cluster composite catalysts provided in Examples 1-4 are not less than 95%.

[0066] Figure 5 The comparison of the ammonia decomposition performances of the ruthenium atom cluster composite catalysts provided in the examples and comparative examples of the present invention is shown (reaction conditions: reaction temperature is 250 - 500 °C, reaction pressure is 0.1 MPa, ammonia concentration is 10 vol.%, reaction space velocity is 30000 mL·g -1 ·h -1 ), as Figure 5 shown. By comparing Example 1 and Comparative Example 1, it can be seen that the modification of the ruthenium atom cluster composite catalyst by rare earth metals can effectively improve the ammonia decomposition activity. This is mainly because, by virtue of the high specific surface characteristics of the nitrogen-rich carbon support and the rare earth element electronic promoter, the catalyst has higher NH3 adsorption performance and N-H bond-breaking ability. From the comparison between Example 1 and Comparative Example 2, it can be seen that the ruthenium atom cluster in the catalyst is also essential in the ammonia decomposition reaction. The combination of the rare earth element-modified high specific surface nitrogen-rich carbon support and the ruthenium atom cluster can achieve efficient catalytic promotion of ammonia decomposition to hydrogen under low-temperature conditions

[0067] The ruthenium atom cluster composite catalyst provided in Example 1 was selected for performance testing below. (1) Influence of reaction temperature on ammonia decomposition performance In a fixed-bed tubular reactor, Ru2 / [Ce 15 -NC] catalyst was loaded for the hydrogen production reaction by ammonia decomposition. Nitrogen was introduced at a flow rate of 50 mL / min at room temperature and heated to 500 °C at a rate of 5 °C / min. After stabilizing at 500 °C for 1 hour, the reaction gas was introduced for the performance test of ammonia decomposition. After the ammonia in the product gas was absorbed by dilute sulfuric acid, it was detected by ion chromatography. Reaction conditions: reaction space velocity was 30000 mL·g -1 ·h -1 , the reaction temperature range was 375 - 500 °C, the reaction pressure was 0.1 MPa, and the ammonia concentration was 10 vol.%.

[0068] Figure 6 The influence of the reaction temperature of the ruthenium atom cluster composite catalyst provided in the examples of the present invention on the ammonia decomposition performance is shown (reaction conditions: reaction temperatures were 375, 400, 425, 450, 475, 500 °C, the reaction pressure was 0.1 MPa, the ammonia concentration was 10 vol.%, and the reaction space velocity was 30000 mL·g -1 ·h -1 ), as Figure 6 shown, when the ammonia decomposition reaction temperatures were 375, 400, 425, 450, 475, 500 °C, the corresponding ammonia conversion rates were: 93.7, 99.7, 99.8, 99.9, 99.9, 99.8 %; the corresponding hydrogen production rates were: 284.6, 302.9, 303.4, 303.5, 303.6, 303.4 mmol g -1 ·h -1 .

[0069] (2) Influence of reaction pressure on ammonia decomposition performance In a fixed-bed tubular reactor, Ru2 / [Ce 15 -NC] catalyst was loaded for the hydrogen production reaction by ammonia decomposition. Nitrogen was introduced at a flow rate of 50 mL / min at room temperature and heated to 500 °C at a rate of 5 °C / min. After stabilizing at 500 °C for 1 hour, the reaction gas was introduced for the performance test of ammonia decomposition. After the ammonia in the product gas was absorbed by dilute sulfuric acid, it was detected by ion chromatography. Reaction conditions: reaction space velocity was 30000 mL·g -1 ·h -1 , the reaction temperature was 400 °C, the reaction pressure range was 0.1 - 1 MPa, and the ammonia concentration was 10 vol.%.

[0070] Figure 7Shows the influence of the reaction pressure of the ruthenium atom cluster composite catalyst provided by the embodiments of the present invention on the ammonia decomposition performance (reaction conditions: reaction temperature is 400 °C, reaction pressures are 0.1, 0.3, 0.6, 1.0 MPa, ammonia concentration is 10 vol.%, reaction space velocity is 30000 mL·g -1 ·h -1 ), as Figure 7 shown, when the ammonia decomposition reaction pressures are 0.1, 0.3, 0.6, 1.0 MPa, the corresponding ammonia conversion rates are respectively: 99.7, 95.9, 91.8, 90.1%; the corresponding hydrogen production rates are respectively: 302.9, 291.5, 278.9, 273.7 mmol g -1 ·h -1 .

[0071] (3) Influence of space velocity on ammonia decomposition performance Load the Ru2 / [Ce 15 -NC] catalyst in a fixed-bed tubular reactor for ammonia decomposition to produce hydrogen. Introduce nitrogen at 50 mL / min at room temperature and heat it to 500 °C at a rate of 5 °C / min. After stabilizing at 500 °C for 1 hour, introduce the reaction gas to test the ammonia decomposition performance. After the ammonia in the product gas is absorbed by dilute sulfuric acid, it is detected by ion chromatography. Reaction conditions: reaction space velocity is 30000 mL·g -1 ·h -1 , reaction temperature is 400 °C, reaction pressure is 0.1 - 1 MPa, ammonia concentration is 10 vol.%.

[0072] Figure 8 Shows the influence of the space velocity of the ruthenium atom cluster composite catalyst provided by the embodiments of the present invention on the ammonia decomposition performance (reaction conditions: reaction temperature is 400 °C, reaction pressure is 0.1 MPa, ammonia concentration is 10 vol.%, reaction space velocities are 12000, 18000, 30000, 48000 mL·mL·g -1 ·h -1 ), as Figure 8 shown, when the ammonia decomposition reaction space velocities are 12000, 18000, 30000, 48000 mL·g -1 ·h -1 , the corresponding ammonia conversion rates are respectively: 99.9, 99.8, 99.7, 96.8 %; the corresponding hydrogen production rates are respectively: 303.6, 303.4, 302.9, 294.3 mmol g -1 ·h -1 .

[0073] (4) Long-term ammonia decomposition performance Load the Ru2 / [Ce15 The [Ru2 / [Ce - NC] catalyst was used for the ammonia decomposition to produce hydrogen. Nitrogen was introduced at a flow rate of 50 mL / min at room temperature, and the temperature was raised to 500 °C at a rate of 5 °C / min. After stabilizing at 500 °C for 1 hour, the reaction gas was introduced to test the ammonia decomposition performance. After the ammonia in the product gas was absorbed by dilute sulfuric acid, it was detected by ion chromatography. Reaction conditions: the reaction space velocity was 30000 mL·g -1 ·h -1 , the reaction temperature was 400 °C, the reaction pressure was 0.1 MPa, and the ammonia concentration was 10 vol.%.

[0074] Figure 9 The long - term ammonia decomposition performance diagram of the ruthenium atom cluster composite catalyst provided by the embodiment of the present invention is shown (reaction conditions: the reaction temperature is 400 °C, the reaction pressure is 0.1 MPa, the ammonia concentration is 10 vol.%, and the reaction space velocity is 30000 mL·g -1 ·h -1 ). As Figure 9 shown, in the 100 - hour long - term ammonia decomposition performance test, the ammonia conversion rate of Ru2 / [Ce 15 -NC] was 99.4%; the corresponding hydrogen production rate was 302.1 mmol g -1 ·h -1 .

[0075] In summary, the ruthenium atom cluster composite catalyst provided by the present invention, with a rare - earth - element - modified carbon - supported low - content ruthenium atom cluster composite catalytic material Ru x / [RE y -NC], has good ammonia decomposition activity. It can achieve an ammonia decomposition conversion rate of not less than 92% at a temperature of 375 - 500 °C and a pressure of 0.1 - 1 MPa, showing broad practical application prospects.

[0076] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above - mentioned terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0077] For the method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should be aware that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0078] The above has introduced in detail a ruthenium atom cluster composite catalyst for ammonia decomposition to hydrogen and its preparation method provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A preparation method of a ruthenium atomic cluster composite catalyst for ammonia decomposition to hydrogen, characterized in that, The preparation method includes the following steps: Melamine, cyanuric acid, and amino acid are dispersed in an aqueous methanol solution, and stirred to form a mixed system. A rare earth metal precursor salt is added to the mixed system. After continuously stirring for 2 - 6 hours, the solvent is evaporated by heating to obtain a white solid; The white solid is ground into powder and transferred to pyrolyze at 700 - 850 °C. The obtained black powder is a nitrogen-rich carbon support modified with rare earth elements; A precursor ruthenium salt and urea are dissolved in deionized water to form an impregnation solution. The nitrogen-rich carbon support modified with rare earth elements is added to the impregnation solution, and stirred for impregnation. The solid collected by filtration is washed, dried, and calcined to obtain the ruthenium atom cluster composite catalyst.

2. The preparation method according to claim 1, wherein In the mixed system, the concentration of the aqueous methanol solution is 20 - 50 wt.%, the molar ratio of melamine to cyanuric acid is 0.8 - 1.2, and the molar ratio of melamine to amino acid is 1.0 - 1.

5.

3. The preparation method according to claim 1, characterized in that, The amino acid is glycine, alanine, serine, or glutamic acid.

4. The preparation method according to claim 1, characterized in that, The rare earth metal precursor salt is lanthanum nitrate, lanthanum acetate, cerium nitrate, or cerium acetate. The addition amount of the rare earth metal precursor salt accounts for 1.0 - 5.0 wt.% of the total mass of melamine, cyanuric acid, and amino acid.

5. The preparation method according to claim 1, characterized in that, The pyrolysis is carried out in an argon or nitrogen atmosphere, and the heating rate is 2 - 5 °C / min.

6. The preparation method according to claim 1, wherein, The temperature of the impregnation solution is 70 - 90 °C; The time of the stirring impregnation is 6 - 12 hours.

7. The preparation method according to claim 1, wherein The precursor ruthenium salt is ruthenium trichloride or ruthenium nitrosyl nitrate; The concentration of ruthenium in the impregnation solution is 0.5 - 5.0 mg Ru / mL, and the concentration of urea in the impregnation solution is 20 - 100 mg / mL; The mass ratio of ruthenium in the impregnation solution to the mass of the nitrogen-rich carbon support modified with rare earth elements is 0.5 - 2.0 wt.%.

8. The preparation method according to claim 1, wherein The solid collected by filtration is washed, dried, and calcined, including: washing 2 - 3 times with ethanol and deionized water respectively, drying in vacuum at 60 - 90 °C for 2 - 12 hours, and then reducing at 200 - 300 °C for 1 - 3 hours.

9. A ruthenium atom cluster composite catalyst obtained by the preparation method according to any one of claims 1 - 8 above.

10. The ruthenium atom cluster composite catalyst according to claim 9, characterized in that, When the ruthenium atom cluster composite catalyst is used to catalyze ammonia for ammonia decomposition to produce hydrogen, the reaction space velocity of the ammonia is 5000 - 50000 mL·g -1 ·h -1 , the reaction temperature is 200 - 500 °C, and the reaction pressure is 0.1 - 5.0 MPa.

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