Ru alloy monatomic catalyst, preparation method thereof and application of Ru alloy monatomic catalyst in hydrogen production through ammonia decomposition

Abstract

The invention discloses a Ru alloy monatomic catalyst, a preparation method thereof and application of the Ru alloy monatomic catalyst in hydrogen production through ammonia decomposition, and belongs to the technical field of catalyst preparation. According to the catalyst, Fe or Ni serves as main metal, Ru is anchored to the surface or near-surface sites of the Fe or Ni metal in a monatomic form by controlling intermetallic electron coupling and surface atomic coordination, and the conversion rate of the catalyst to ammonia decomposition at 450 DEG C can reach 90% or above. The catalyst can be prepared by combining an impregnation-surface replacement method with a low-temperature hydrogen reduction method, the process is simple, and large-scale production is easy to realize. A stable Ru-Fe (or Ru-Ni) coordinate bond is formed between Ru atoms and Fe or Ni, so that an N-H bond breakage energy barrier in ammonia decomposition can be effectively reduced, and the ammonia decomposition activity and the anti-sintering stability are remarkably improved. The method realizes high-efficiency ammonia decomposition hydrogen production under the condition of extremely low precious metal dosage, and has good cost advantage and industrial application prospect.

Description

TECHNICAL FIELD

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

[0002] Hydrogen is a high-efficiency and clean energy. Due to the characteristics of hydrogen itself, the development of hydrogen energy industry still faces major bottlenecks such as hydrogen cross-regional, high safety, low cost and large-scale storage and transportation difficulties. Ammonia (NH3) is considered to be a very potential hydrogen energy carrier due to its high hydrogen density, easy liquefaction and renewable preparation characteristics. In the distributed hydrogen production and fuel cell hydrogen supply system, ammonia decomposition hydrogen production is an important link to realize carbon-free hydrogen supply. The ammonia decomposition hydrogen production reaction is shown in formula (1), which is a strong endothermic reaction with volume increase, and usually requires a relatively high reaction temperature of 400-600 DEG C. The performance of the catalyst is a key factor to determine the ammonia decomposition efficiency and energy consumption.

[0003]

[0004] At present, Ru-based catalysts are considered to be the most active system in ammonia decomposition reaction. Ru / Al2O3, Ru / CNT, Ru / MgO and other catalysts exhibit excellent activity at medium-high temperature, but their high cost and easy agglomeration and sintering limit industrial application. Generally, catalytic reactions usually occur at the surface / interface active sites of metals, and the atoms inside are not used, which causes waste. On the other hand, inexpensive metals such as Fe, Ni and Co can also catalyze ammonia decomposition, but a higher temperature is required to achieve similar conversion rate, and the long-term running stability is poor. How to significantly reduce the amount of noble metal while maintaining high activity and improving the thermal stability of the catalyst is a key problem in current research and industrialization.

[0005] In recent years, the development of single-atom catalysis (SAC) concept provides a new idea for solving the problems of high cost and low utilization rate of noble metals. By constructing isolated atomic sites on the carrier or metal matrix, the atomic utilization rate of noble metals can be maximized, and the catalytic reaction path can be regulated through the coordination environment. However, in the ammonia decomposition reaction, the stable fixation of single-atom Ru and the anti-migration property at high temperature are still technical bottlenecks. In addition, the oxidizing environment on the surface of the carrier may cause the change of Ru valence state, affecting the activity.

[0006] At present, it is urgent to develop an efficient ammonia decomposition catalyst, which can realize the full utilization of Ru atoms and reduce the cost of the catalyst. SUMMARY

[0007] In order to solve the problems of low atomic utilization rate, high cost and easy change of valence state of monatomic Ru catalyst in the prior art of ammonia decomposition, a technical scheme for preparing a Ru alloy monatomic catalyst is provided, a new type of catalytic system in which Ru monatomic is anchored on a Fe or Ni alloy matrix is proposed, a Fe-based catalyst substrate is prepared by using a combination of surface limited replacement method and low temperature reduction method, and then Ru is anchored on the surface of Fe by using a combination of surface limited replacement method and low temperature reduction method, so as to prepare a catalyst with extremely low Ru content, realize full utilization of noble metal Ru, reduce the cost of the catalyst, and realize NH3 conversion rate higher than 90% at 450 ℃ when the catalyst is applied to ammonia decomposition.

[0008] The technical scheme adopted by the application is as follows: According to the first aspect of the application, a preparation method of a Ru alloy monatomic catalyst is provided, comprising: S1, under stirring, a metal M salt solution is slowly added to a suspension of a carrier S, after continuous stirring, an ammonia solution is slowly added until the pH value of the suspension is 8-11, the suspension is left to stand, and the solid product obtained after filtration, washing and drying of the suspension is calcined and reduced I to obtain M-loaded S; Wherein, M is selected from Fe or Ni, and S is a metal oxide carrier; S2, a Ru source precursor is dissolved in an alcohol-water mixture to obtain a solution containing Ru ions; In a non-oxidizing atmosphere, the solution containing Ru ions is contacted with the M-loaded S, the solution containing Ru ions is uniformly wetted on the surface of the M / S sample, and then dried, the dried M / S sample is placed in a reducing atmosphere for reduction II, and then cooled in a non-active atmosphere to obtain the Ru alloy monatomic catalyst.

[0009] Optionally, the carrier S is selected from at least one of Al2O3, MgO and CeO2.

[0010] Optionally, the metal M salt is selected from at least one of FeCl3, Fe(NO3)3, Ni(NO3)2, NiCl2 and Ni(CH3COO)2.

[0011] Optionally, the Ru source is selected from at least one of Ru(NO)(NO3)3 and RuCl3.

[0012] Optionally, the concentration of the metal M salt solution is 0.1 mol / L-1 mol / L, calculated based on the molar amount of M element. Optionally, the mass content of element M in the M / S sample is 5-20 wt%; the amount of metal M salt solution added is calculated based on the content of element M in the M / S sample, and element M forms a precipitate under the action of ammonia and is uniformly deposited on the carrier S.

[0013] Optionally, the concentration of the ammonia solution is 5wt% to 15wt%.

[0014] Optionally, the concentration of the Ru source precursor is 0.5 wt% to 2 wt% based on the mass of Ru; the Ru source precursor is an aqueous solution of Ru source. Optionally, the ratio of the Ru source precursor to the alcohol-water mixture is 0.05~0.4g:1mL.

[0015] Optionally, the alcohol-water mixture is a mixture of water and ethanol in a volume ratio of 1:1.

[0016] Optionally, the continuous stirring time is 1 to 4 hours.

[0017] Optionally, the settling time is 1 to 3 hours.

[0018] Optionally, in step S1, the drying conditions include: a drying temperature of 80~120 ℃ and a drying time of 12~24 h.

[0019] Optionally, the calcination conditions include: a calcination temperature of 400~500 ℃, a calcination time of 2~4 h, and a heating rate of 1-5 ℃ / min.

[0020] Optionally, the conditions for reduction I include: a reduction temperature of 500~600 ℃, a reduction time of 1~3 h, a pressure of atmospheric pressure, and a heating rate of 1-5 ℃ / min.

[0021] Optionally, in step S1, the pH value is 9-10.

[0022] Optionally, the conditions for reduction II include: a reduction temperature of 400~500 ℃, a reduction time of 4~8 h, a pressure of atmospheric pressure, and a heating rate of 1-5 ℃ / min.

[0023] Optionally, in step S2, the drying conditions include: a drying temperature of 80~100 ℃ and a drying time of 2~4 h.

[0024] Optionally, the suspension of the carrier S is obtained by ultrasonically dispersing the carrier S in water.

[0025] Optionally, the slow addition is a dripping addition.

[0026] Optionally, the atmosphere of reduction I is pure hydrogen.

[0027] Optionally, the non-oxidizing atmosphere is a condition that does not come into contact with air or an atmosphere without oxidizing components.

[0028] Optionally, the reducing atmosphere is a mixture of hydrogen and inactive gases.

[0029] Optionally, the inactive atmosphere refers to inactive gas conditions, such as argon or nitrogen.

[0030] According to a second aspect of this application, a Ru alloy single-atom catalyst prepared by the above method is provided, comprising a support S loaded with metal M and Ru atoms dispersed in single-atom form; The Ru atoms are anchored to the surface of the carrier S, which is loaded with metal M.

[0031] Optionally, the Ru content in the Ru alloy single-atom catalyst is 0.01-0.5 wt% by mass. The mass content of metal M is 5-20 wt%.

[0032] According to a third aspect of this application, a Ru alloy single-atom catalyst prepared by the above method is provided, and the application of the above Ru alloy single-atom catalyst in ammonia decomposition for hydrogen production is provided.

[0033] Optionally, the reaction conditions for ammonia decomposition include: a reaction temperature of 400~500 ℃ and a reaction space velocity of 1000~50000 ml / g·h.

[0034] Optionally, the Ru alloy single-atom catalyst has a conversion rate of NH3 ≥90% at 450 °C.

[0035] The beneficial effects of this application include: (1) The ammonia decomposition catalyst provided in this application disperses Ru in the form of single atoms on the Fe or Ni substrate, thereby making full use of the precious metal Ru and reducing the Ru content to less than 1 / 10 of that of traditional catalysts while still maintaining high activity.

[0036] (2) The ammonia decomposition catalyst provided in this application forms a strong intermetallic coordination bond between Ru and the Fe or Ni alloy matrix, which effectively inhibits agglomeration and migration at high temperature and achieves long-term stable operation of the ammonia decomposition reaction.

[0037] (3) The preparation process is simple and scalable. The entire process adopts wet chemical method and low-temperature hydrogen reduction method, which does not require complicated equipment and is suitable for industrial production. Attached Figure Description

[0038] Figure 1The results show the reaction stability test results of ammonia decomposition on the 0.1Ru-10Fe / Al2O3 catalyst of this application. Detailed Implementation

[0039] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0040] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0041] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0042] Among existing ammonia decomposition catalysts for hydrogen production, Ru-based systems exhibit excellent low-temperature activity, but suffer from high noble metal content, easy agglomeration and deactivation, and difficulty in large-scale preparation. While non-noble metal catalysts such as Fe and Ni are inexpensive, they suffer from high reaction temperatures, difficulty in activation, and short lifespans. Furthermore, in traditional supported catalysts such as Ru / Al2O3 and Ru / MgO, Ru particles are prone to migration or sintering at high temperatures, leading to a reduction in active sites. Although single-atom Ru can improve atom utilization, it is prone to agglomeration and deactivation in the absence of a stable coordination environment under reducing atmospheres. To address these issues, this application proposes a novel catalytic system in which Ru single atoms are anchored to an Fe or Ni alloy matrix. Specifically, in the preparation process of the Ru1Fe / Al2O3 catalyst, an Fe / Al2O3 catalyst is first prepared, and then Ru atoms are preferentially deposited on high-energy sites on the Fe surface using a surface-confined substitution method, forming an atomic-level dispersion. After processing, the Ru1Fe / Al2O3 catalyst is obtained. By designing a metal-metal synergistic interface and utilizing the electronic regulation of Ru by the Fe or Ni matrix, single-atom Ru can stably exist on the alloy surface, while significantly enhancing the NH3 dissociation rate and N2 desorption rate. Therefore, a surface-confined substitution method can be used to prepare alloy single-atom Ru1Fe or Ru1Ni-based catalysts. This system combines the high activity and structural stability of Ru, fundamentally improving the high cost and sintering problems of traditional Ru catalysts, and providing a new technical route for efficient ammonia decomposition to hydrogen production with low noble metal usage.

[0043] The technical objective of this application is: 1. By constructing a stable synergistic interface between Ru single atoms and Fe or Ni alloy matrix, the thermal stability anchoring of single-atom Ru is achieved, and the interaction between Ru and Ni or Fe is used to promote NH bond breaking, reduce the NH3 dissociation energy barrier, and enhance the ammonia decomposition reaction activity. 2. Achieving a NH3 conversion rate of over 90% with extremely low Ru loading (≤0.5wt%), significantly reducing the cost of precious metals; 3. A simple, controllable, and scalable catalyst preparation method is provided, which is convenient for industrialization.

[0044] To address the problem of catalysts for hydrogen production from ammonia decomposition, a catalyst with extremely low Ru content is provided, which can fully utilize Ru atoms, reduce catalyst costs, and achieve an NH3 conversion rate of over 90% at 450 °C.

[0045] According to one embodiment of this application, a Ru-based alloy single-atom catalyst comprises Ru atoms dispersed in single-atom form, the Ru atoms being anchored to the surface of a metal matrix primarily composed of Fe or Ni; the catalyst contains 0.01-0.5 wt% Ru, 5-20 wt% Fe or Ni, and the remainder is a support with a support content of 79.5-94.95 wt%. At 450 °C, the conversion rate of NH3 is ≥90%.

[0046] This application utilizes a combination of surface-confined substitution and low-temperature reduction methods to first prepare an Fe-based catalyst substrate, and then uses the same method to anchor Ru onto the Fe surface, thereby preparing a Ru-based alloy single-atom catalyst and achieving full utilization of the noble metal Ru.

[0047] According to one embodiment of this application, the preparation steps of the Ru-based alloy single-atom catalyst include: (1) Preparation of M / S samples A certain amount of carrier S was weighed and ultrasonically dispersed in deionized water to obtain a suspension of carrier S. A certain amount of Fe or Ni precursor was weighed and dissolved in deionized water to obtain a metal M salt solution. While stirring, the metal M salt solution was slowly added to the carrier S suspension, and stirring continued for a period of time after the addition was complete. Subsequently, ammonia was added dropwise to the above mixed suspension to adjust the pH to 8-11, allowing the metal M precipitate to be uniformly deposited on the carrier. After standing, the sample was filtered, washed, and then dried in an oven. Finally, it was calcined in a muffle furnace, and the calcined sample was reduced for a period of time in a pure hydrogen atmosphere to obtain the M / S sample.

[0048] (2) Preparation of Ru1M / S catalyst The reduced M / S sample was transferred to a glove box without air contact. A certain amount of Ru precursor solution was dissolved in water-ethanol (1:1 volume ratio). The Ru solution was slowly added dropwise to the M / S sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum drying oven. The dried sample was then placed in a tube furnace and reduced under 5% H₂ / Ar conditions, finally cooled to room temperature in nitrogen to obtain the sample, denoted as Ru₁M / S.

[0049] In one embodiment, the carrier S mentioned in step 1) is any one of Al2O3, MgO, and CeO2.

[0050] In one embodiment, the precursor of Fe in step 1) is any one of FeCl3 and Fe(NO3)3; the precursor of Ni is any one of Ni(NO3)2, NiCl2, and Ni(CH3COO)2.

[0051] In one embodiment, the Ru source mentioned in step 2) is either Ru(NO)(NO3)3 or RuCl3.

[0052] In one embodiment, in step 1), the concentration of the metal M precursor salt solution is 0.1 mol / L to 1 mol / L; and the concentration of the ammonia solution is 5 wt% to 15 wt%.

[0053] In one embodiment, in step 2), the concentration of the Ru precursor salt solution is 0.5wt% to 2wt%.

[0054] In one embodiment, in step 1), the pH is 9-10.

[0055] In one embodiment, in step 1), the stirring time is 1-4 h; the settling time is 1-3 h.

[0056] In one embodiment, in step 1), the drying temperature is 80~120 ℃ and the drying time is 12~24 h.

[0057] In one embodiment, in step 1), the calcination temperature is 400~500 ℃, the calcination time is 2~4 h, and the heating rate from room temperature to reduction temperature is 1-5 ℃ / min.

[0058] In one embodiment, in step 1), the reduction temperature is 500~600 ℃, the reduction time is 1~3 h, the pressure is atmospheric pressure, and the heating rate from room temperature to the reduction temperature is 1-5 ℃ / min.

[0059] In one embodiment, in step 2), the temperature of the vacuum drying is 80~100 ℃, and the drying time is 2~4 h.

[0060] In one embodiment, in step 2), the reduction temperature is 400~500 ℃, the reduction time is 4~8 h, the pressure is atmospheric pressure, and the heating rate from room temperature to the reduction temperature is 1-5 ℃ / min.

[0061] In one embodiment, a Ru-based alloy single-atom catalyst is heated to the reaction temperature of ammonia decomposition and then ammonia gas is introduced to obtain the products hydrogen and nitrogen.

[0062] According to one embodiment of this application, the aforementioned Ru-based alloy single-atom catalyst is applied to ammonia decomposition.

[0063] In one embodiment, the reaction temperature for ammonia decomposition is 400-500 °C.

[0064] In one embodiment, the space velocity of the ammonia decomposition is 1000~50000 ml / g·h.

[0065] Example 1 1) Preparation of Fe / Al2O3 Weigh 2.0 g of γ-Al₂O₃ and ultrasonically disperse it in 50 mL of deionized water for 15 min. Weigh 1.606 g of Fe(NO₃)₃·9H₂O and dissolve it in 10 mL of deionized water. While the Al₂O₃ suspension is continuously stirred, the Fe salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 2 h after the addition is complete. Subsequently, 10 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 9, so that the Fe(OH)₃ precipitate is uniformly deposited on the support. After standing for 2 h, the sample is filtered, washed, and then dried in an oven at 120 ℃ for 12 h. Subsequently, it is calcined in a muffle furnace at 400 ℃ for 3 h with a heating rate of 3 ℃ / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 600 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain the Fe / Al₂O₃ sample.

[0066] 2) Preparation of Ru1Fe / Al2O3 catalyst The reduced Fe / Al₂O₃ sample was transferred to a glove box without air contact. 0.2 g of a 1 wt% RuCl₃ aqueous solution was dissolved in 3 ml of water-ethanol (1:1 volume ratio). The Ru solution was slowly added dropwise to the Fe / Al₂O₃ sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum oven at 100 °C for 2 h. The dried sample was then placed in a tube furnace and reduced at 450 °C at a rate of 2 °C / min under 5% H₂ / Ar for 4 h. Finally, it was cooled to room temperature under nitrogen to obtain the sample, designated as the 0.1Ru-10Fe / Al₂O₃ catalyst.

[0067] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocities of 1000, 30000, and 50000 ml / g·h. The reaction results are shown in Table 1.

[0068] In addition, stability tests were conducted on the 0.1Ru-10Fe / Al2O3 catalyst at a reaction temperature of 450 °C, a reaction pressure of 0.1 MPa, and a space velocity of 30,000 ml / g·h. The reaction results are shown below. Figure 1 .

[0069] Example 2 1) Preparation of Ni / Al2O3 Weigh 2.0 g of γ-Al₂O₃ and disperse it ultrasonically in 50 mL of deionized water for 15 min. Weigh 1.099 g of Ni(NO₃)₂·6H₂O and dissolve it in 5 mL of deionized water. While the Al₂O₃ suspension is continuously stirred, the Ni salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 1 h after the addition is complete. Subsequently, 5 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 9, so that Ni(OH)₂ precipitate is uniformly deposited on the support. After standing for 1 h, the sample is filtered, washed, and then dried in an oven at 80 °C for 24 h. Subsequently, it is calcined in a muffle furnace at 400 °C for 2 h with a heating rate of 1 °C / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 500 °C for 1 h with a heating rate of 1 °C / min to obtain the Ni / Al₂O₃ sample.

[0070] 2) Preparation of Ru1Ni / Al2O3 catalyst The reduced Ni / Al2O3 sample was transferred to a glove box without contact with air. 0.4 g of a 0.5 wt% Ru(NO)(NO3)3 aqueous solution was dissolved in 3 ml of water-ethanol (volume ratio 1:1). The Ru solution was slowly added dropwise to the Ni / Al2O3 sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum oven at 80 °C for 4 h. The dried sample was then placed in a tube furnace and reduced to 400 °C at a rate of 1 °C / min under 5% H2 / Ar for 8 h. Finally, it was cooled to room temperature under nitrogen to obtain the sample, designated as the 0.1Ru-10Ni / Al2O3 catalyst.

[0071] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0072] Example 3 1) Preparation of Fe / Al2O3 Weigh 2.0 g of γ-Al₂O₃ and ultrasonically disperse it in 50 mL of deionized water for 15 min. Weigh 0.7617 g of FeCl₃·9H₂O and dissolve it in 10 mL of deionized water. While the Al₂O₃ suspension is continuously stirred, the Fe salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 3 h after the addition is complete. Subsequently, 15 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 10, so that Fe(OH)₃ precipitate is uniformly deposited on the support. After standing for 3 h, the sample is filtered, washed, and then dried in an oven at 100 ℃ for 16 h. Subsequently, it is calcined in a muffle furnace at 500 ℃ for 4 h with a heating rate of 5 ℃ / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 550 ℃ for 2 h with a heating rate of 3 ℃ / min to obtain the Fe / Al₂O₃ sample.

[0073] 2) Preparation of Ru1Fe / Al2O3 catalyst The reduced Fe / Al₂O₃ sample was transferred to a glove box without contact with air. 0.11 g of a 2wt% RuCl₃ aqueous solution was dissolved in 3 ml of water-ethanol (1:1 volume ratio). The Ru solution was slowly added dropwise to the Fe / Al₂O₃ sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum oven at 90 °C for 3 h. The dried sample was then placed in a tube furnace and reduced at 500 °C for 4 h under 5% H₂ / Ar conditions with a heating rate of 5 °C / min. The sample was then cooled to room temperature under nitrogen to obtain the 0.1Ru-5Fe / Al₂O₃ catalyst.

[0074] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0075] Example 4 1) Preparation of Ni / Al2O3 Weigh 2.0 g of γ-Al₂O₃ and ultrasonically disperse it in 50 mL of deionized water for 15 min. Weigh 2.025 g of NiCl₂·6H₂O and dissolve it in 10 mL of deionized water. While the Al₂O₃ suspension is continuously stirred, the Ni salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 2 h after the addition is complete. Subsequently, 10 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 10, so that Ni(OH)₂ precipitate is uniformly deposited on the support. After standing for 2 h, the sample is filtered, washed, and then dried in an oven at 120 ℃ for 16 h. Subsequently, it is calcined in a muffle furnace at 450 ℃ for 3 h with a heating rate of 3 ℃ / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 500 ℃ for 3 h with a heating rate of 3 ℃ / min to obtain the Ni / Al₂O₃ sample.

[0076] 2) Preparation of Ru1Ni / Al2O3 catalyst The reduced Ni / Al₂O₃ sample was transferred to a glove box without contact with air. 0.44 g of a 1 wt% RuCl₃ aqueous solution was dissolved in 3 ml of water-ethanol (volume ratio 1:1). The Ru solution was slowly added dropwise to the Ni / Al₂O₃ sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum oven at 80 °C for 3 h. The dried sample was then placed in a tube furnace and reduced at 450 °C at a rate of 5 °C / min under 5% H₂ / Ar for 6 h. Finally, it was cooled to room temperature under nitrogen to obtain the sample, designated as the 0.2Ru-20Ni / Al₂O₃ catalyst.

[0077] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0078] Example 5 1) Preparation of Ni / MgO Weigh 2.0 g MgO and ultrasonically disperse it in 50 mL deionized water for 15 min. Weigh 0.9413 g Ni(CH3COO)2·4H2O and dissolve it in 15 mL deionized water. While the MgO suspension is continuously stirred, the Ni salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 2 h after the addition is complete. Subsequently, 10 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 9, so that Ni(OH)2 precipitate is uniformly deposited on the support. After standing for 2 h, the sample is filtered, washed, and then dried in an oven at 100 ℃ for 16 h. Subsequently, it is calcined in a muffle furnace at 450 ℃ for 3 h with a heating rate of 3 ℃ / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 500 ℃ for 2 h with a heating rate of 3 ℃ / min to obtain the Ni / MgO sample.

[0079] 2) Preparation of Ru1Ni / MgO catalyst The reduced Ni / MgO sample was transferred to a glove box without contact with air. 0.044 g of a 0.5 wt% Ru(NO)(NO3)3 aqueous solution was dissolved in 3 ml of water-ethanol (volume ratio 1:1). The Ru solution was slowly added dropwise to the Ni / MgO sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum drying oven at 80 °C for 4 h. The dried sample was then placed in a tube furnace and reduced to 400 °C at a rate of 1 °C / min under 5% H2 / Ar for 8 h. Finally, it was cooled to room temperature under nitrogen to obtain the sample, designated as the 0.01Ru-10Ni / MgO catalyst.

[0080] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocities of 1000, 30000, and 50000 ml / g·h. The reaction results are shown in Table 1.

[0081] Example 6 1) Preparation of Fe / CeO2 Weigh 2.0 g of CeO2 and disperse it ultrasonically in 50 mL of deionized water for 15 min. Weigh 1.606 g of Fe(NO3)3·9H2O and dissolve it in 10 mL of deionized water. While the CeO2 suspension is continuously stirred, the Fe salt solution is slowly added at a rate of 0.5 mL / min, and stirring is continued for 2 h after the addition is complete. Subsequently, 10 wt% ammonia solution is added dropwise to the above mixed suspension to adjust the pH to 9, so that Fe(OH)3 precipitate is uniformly deposited on the support. After standing for 2 h, the sample is filtered, washed, and then dried in an oven at 120 ℃ for 12 h. Subsequently, it is calcined in a muffle furnace at 400 ℃ for 3 h with a heating rate of 3 ℃ / min. The calcined sample is then reduced in a pure hydrogen atmosphere at 600 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain the Fe / CeO2 sample.

[0082] 2) Preparation of Ru1Fe / CeO2 catalyst The reduced Fe / CeO2 sample was transferred to a glove box without air contact. 1.1 g of a 1 wt% RuCl3 aqueous solution was dissolved in 3 ml of water-ethanol (1:1 volume ratio). The Ru solution was slowly added dropwise to the Fe / CeO2 sample in the glove box, and the reaction was allowed to proceed for 30 min to allow the Ru precursor to uniformly wet the surface and undergo rapid adsorption and displacement, avoiding exposure to an oxidizing atmosphere. The sample was then filtered to dryness and subsequently dried in a vacuum drying oven at 100 °C for 2 h. The dried sample was then placed in a tube furnace and reduced at 450 °C for 4 h under 5% H2 / Ar conditions at a rate of 2 °C / min. The sample was then cooled to room temperature under nitrogen to obtain the 0.5Ru-10Fe / CeO2 catalyst.

[0083] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0084] Comparative Example 1 2.0 g of Al2O3 support was weighed, and a Ru / Al2O3 catalyst was prepared by impregnation. The specific steps were as follows: 0.2 g of Ru (1 wt%) in a RuCl3 aqueous solution was dissolved in 3 ml of water-ethanol (volume ratio 1:1). The Ru solution was then slowly added dropwise to the Al2O3 sample. Impregnation was carried out at room temperature for 12 h, followed by drying in an oven at 80 ℃ for 6 h to obtain the Ru / Al2O3 sample. Then, the sample was subjected to hydrogen reduction at 450 ℃, with a heating rate of 3 ℃ / min from room temperature to the reduction temperature and a hydrogen volume hourly space velocity of 2000 h⁻¹. -1 The pressure was at atmospheric pressure, and the reduction time was 4 h. The resulting catalyst was denoted as 0.1Ru / Al2O3-IWI.

[0085] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0086] Comparative Example 2 Weigh 1.0 g of Al₂O₃ support and 0.3113 g of NiNO₃, dissolve them in 2 g of deionized water to prepare a mixed solution with a Ni mass concentration of 1.2 wt%. Pour the Al₂O₃ support directly into the NiNO₃ solution. Impregnate at room temperature for 12 h, dry at 80 ℃ for 12 h, and calcine at 600 ℃ in air for 4 h, with a Ni mass content of 10%. Then, reduce it with hydrogen at 600 ℃ at a heating rate of 5 ℃ / min from room temperature to the reduction temperature, with a hydrogen volume hourly space velocity of 2000 h⁻¹. -1 The pressure was at atmospheric pressure, and the reduction time was 3 h. The resulting catalyst was denoted as 10Ni / Al2O3.

[0087] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0088] Comparative Example 3 2.0 g of Al2O3 support was weighed, and a Ru-Fe / Al2O3 catalyst was prepared using a co-impregnation method. The specific steps were as follows: 0.22 g of Ru (1 wt%) in a RuCl3 aqueous solution and 1.606 g of Fe(NO3)3·9H2O were dissolved in 10 ml of water-ethanol (volume ratio 1:1). The Ru and Fe mixed solution was then slowly added dropwise to the Al2O3 sample. Impregnation was carried out at room temperature for 12 h, followed by drying in an 80 ℃ oven for 6 h to obtain the Ru-Fe / Al2O3 sample. Then, it was subjected to hydrogen reduction at 500 ℃, with a heating rate of 3 ℃ / min from room temperature to the reduction temperature and a hydrogen volume hourly space velocity of 2000 h⁻¹. -1 The pressure was at atmospheric pressure, and the reduction time was 4 h. The resulting catalyst was denoted as 0.1Ru-10Fe / Al2O3-IWI.

[0089] The prepared catalyst was used for ammonia decomposition performance testing. The reaction conditions were: ammonia concentration of 99.9%, fixed-bed reactor, reaction temperature of 400 ℃~500 ℃, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0090] Table 1 Reaction performance of ammonia decomposition on different catalysts

[0091] Results analysis: Table 1 shows that the Ru-based alloy single-atom catalysts prepared by the impregnation-surface replacement method combined with the low-temperature hydrogen reduction method exhibit excellent ammonia decomposition reaction performance. Among them, the 0.1Ru-10Fe / Al2O3 catalyst shows significantly higher activity in the ammonia decomposition hydrogen production reaction than the 0.1Ru-10Fe / Al2O3-IWI catalyst prepared by the co-impregnation method. These experimental results indicate that the impregnation-surface replacement method combined with the low-temperature hydrogen reduction method has significant advantages, is simple to prepare, and effectively improves the reaction performance of the catalyst.

[0092] The 0.1Ru-10Fe / Al2O3 catalyst can achieve an ammonia conversion rate >90% at 450 °C. It also exhibits excellent stability. Figure 1 The data show that the ammonia conversion rate is above 90% within 600 h. This indicates that the Ru-based alloy single-atom catalyst prepared by the impregnation-surface replacement method combined with the low-temperature hydrogen reduction method has high activity and anti-sintering stability.

[0093] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a Ru alloy single-atom catalyst, characterized in that, include: S1. Under stirring, a metal M salt solution is slowly added to the suspension of the carrier S. After continuous stirring, an ammonia solution is slowly added until the pH of the suspension is 8-11. After standing, the suspension is filtered, washed and dried. The solid product is then calcined and reduced to obtain S loaded with M. Where M is selected from Fe or Ni, and S is a metal oxide support; S2. Dissolve the Ru source precursor in an alcohol-water mixture to obtain a solution containing Ru ions; In a non-oxidizing atmosphere, a solution containing Ru ions is brought into contact with S loaded with M, so that the solution containing Ru ions uniformly wets the surface of the M / S sample and then it is dried. The dried M / S sample is then placed in a reducing atmosphere for reduction II, and then cooled in an inactive atmosphere to obtain the Ru alloy single-atom catalyst.

2. The preparation method according to claim 1, characterized in that, The carrier S is selected from at least one of Al2O3, MgO, and CeO2; Preferably, the metal M salt is selected from at least one of FeCl3, Fe(NO3)3, Ni(NO3)2, NiCl2, and Ni(CH3COO)2; Preferably, the Ru source is selected from at least one of Ru(NO)(NO3)3 and RuCl3.

3. The preparation method according to claim 1, characterized in that, The concentration of the metal M salt solution is 0.1 mol / L to 1 mol / L, based on the molar amount of element M. Preferably, the mass content of element M in the M / S sample is 5-20 wt%; Preferably, the concentration of the ammonia solution is 5wt% to 15wt%.

4. The preparation method according to claim 1, characterized in that, The concentration of the Ru precursor, based on the mass of Ru, is 0.5 wt% to 2 wt%. Preferably, the ratio of the Ru source precursor to the alcohol-water mixture is 0.05~0.4g:1mL; Preferably, the alcohol-water mixture is a mixture of water and ethanol in a volume ratio of 1:

1.

5. The preparation method according to claim 1, characterized in that, The continuous stirring time is 1-4 hours; Preferably, the settling time is 1 to 3 hours; Preferably, in step S1, the drying conditions include: a drying temperature of 80~120 ℃ and a drying time of 12~24 h; Preferably, the calcination conditions include: a calcination temperature of 400~500 ℃, a calcination time of 2~4 h, and a heating rate of 1-5 ℃ / min; Preferably, the conditions for reduction I include: a reduction temperature of 500~600 ℃, a reduction time of 1~3 h, a pressure of atmospheric pressure, and a heating rate of 1-5 ℃ / min; Preferably, in step S1, the pH value is 9-10.

6. The preparation method according to claim 1, characterized in that, The conditions for reduction II include: a reduction temperature of 400~500 ℃, a reduction time of 4~8 h, a pressure of atmospheric pressure, and a heating rate of 1-5 ℃ / min; Preferably, in step S2, the drying conditions include: a drying temperature of 80~100 ℃ and a drying time of 2~4 h.

7. The Ru alloy single-atom catalyst obtained by the preparation method according to any one of claims 1 to 6, characterized in that, It includes a support S carrying metal M and Ru atoms dispersed in single-atom form; The Ru atoms are anchored to the surface of the carrier S, which is loaded with metal M.

8. The Ru alloy single-atom catalyst according to claim 7, characterized in that, In the Ru alloy single-atom catalyst, the mass content of Ru is 0.01-0.5 wt%. The mass content of metal M is 5-20 wt%.

9. The application of the Ru alloy single-atom catalyst obtained by the preparation method according to any one of claims 1 to 6, or the Ru alloy single-atom catalyst according to claim 7 or 8, in ammonia decomposition for hydrogen production.

10. The application according to claim 9, characterized in that, The reaction conditions for ammonia decomposition include: a reaction temperature of 400~500 ℃ and a reaction space velocity of 1000~50000 ml / g·h; Preferably, the Ru alloy single-atom catalyst has a conversion rate of NH3 ≥ 90% at 450 °C.

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