Ru-based catalyst, preparation method thereof and application of Ru-based catalyst in ammonia decomposition hydrogen production reaction

Abstract

The invention relates to a Ru-based catalyst, a preparation method thereof and application of the Ru-based catalyst in ammonia decomposition hydrogen production reaction, and belongs to the technical field of catalyst preparation. According to the catalyst, defect-rich d-CeO2 is used as a carrier, Ru is used as an active component, and the mass percentage content of Ru is 0.01%-5.0%. According to the invention, Ru is deposited on a defect-rich d-CeO2 carrier by adopting an atomic layer deposition technology to prepare the Ru / d-CeO2 catalyst. According to the ammonia decomposition catalyst provided by the invention, the dispersity of Ru is close to 100%, and the precious metal Ru can be fully utilized. The catalyst disclosed by the invention has the advantages of low ammonia decomposition reaction temperature, high ammonia space velocity and high ammonia conversion rate, and shows relatively high catalytic activity and stability in ammonia decomposition reaction.

Description

Technical Field

[0001] The invention relates to a Ru-based catalyst and a preparation method thereof and application thereof in ammonia decomposition hydrogen production reaction, belonging to the technical field of catalyst preparation. Background Art

[0002] Hydrogen is considered to be one of the most ideal clean energy sources, but the high cost of hydrogen production, storage and transportation difficulties are the "bottlenecks" that restrict the development of the hydrogen energy industry. Ammonia is not only an important inorganic chemical product, but also has unique advantages as a hydrogen carrier. Specifically, it is manifested in the following aspects: 1) High energy density: the volume energy density of ammonia is about 13.6MJ / L, and the hydrogen content is 17.6wt%; 2) Low liquefaction storage and transportation costs: the liquefaction pressure is 0.8MPa at 20°C; 3) Carbon-free energy storage can be achieved: ammonia has a mature technical system, standard specifications, and low-cost synthesis, storage and transportation, which can achieve seasonal, long-distance, "carbon-free" "ammonia-hydrogen" energy storage; 4) High safety: ammonia has a fire hazard of only Class B, and its explosion limit (16% to 25%) is narrower than that of hydrogen (4% to 76%), so it is safer, and its pungent smell is a reliable alarm signal. Therefore, ammonia, as a hydrogen carrier, transforms the storage and transportation of hydrogen into the storage and transportation of ammonia, and the decomposition of ammonia to produce hydrogen has broad application prospects. In order to achieve economical and safe hydrogen storage and use, it is particularly important to develop catalysts that can efficiently catalyze the ammonia decomposition reaction.

[0003] The ammonia decomposition reaction to produce hydrogen is shown in formula (1). This reaction is an endothermic reaction with an increase in volume, so increasing the temperature and reducing the pressure are beneficial to the reaction. According to thermodynamic calculations, at normal pressure and a temperature of 400°C, the equilibrium conversion rate of ammonia decomposition can reach 99%. However, from a kinetic point of view, due to the very high activation energy of the reaction, the conversion rate of ammonia decomposition reaction is extremely low under normal pressure and without catalyst catalysis. At normal pressure and without any catalyst, the actual conversion rate of ammonia decomposition reaction at 700°C is less than 10%. Therefore, a highly active catalyst is required to achieve efficient decomposition of ammonia.

[0004] 2NH3 = N2 + 3H2, ΔH = 92.5 kJ mol -1 (1)

[0005] At present, supported Ru-based catalysts are recognized to have the highest catalytic ammonia decomposition activity, but Ru, as a precious metal, has a high cost. The use of high-content Ru increases the cost of the catalyst and limits its widespread application. It is generally believed that the active site of the Ru-based catalyst is the B5 site composed of two layers of atoms on Ru. In conventional Ru-based catalysts, metallic Ru mostly exists in the form of particles. Since the catalytic reaction usually occurs at the surface interface of the metal, the internal metal atoms cannot be effectively utilized. In addition, the Ru metal particle catalyst has an uneven structure and properties of the active components, resulting in low ammonia decomposition activity. In order to reduce the cost of the catalyst, it is necessary to improve the atomic utilization rate and intrinsic reaction activity of the precious metal. Therefore, it is of great significance to prepare efficient supported precious metal catalysts.

[0006] Single-atom catalysts are metals dispersed on the surface of the carrier in the form of single atoms, with the highest dispersion and the highest atomic utilization efficiency. However, the intrinsic activity of single-atom catalysts may be limited due to the lack of adjacent atoms. By increasing the number of active center atoms, sub-nano clusters are obtained, and the dispersion can still be kept close to 100%. Compared with single atoms, their electronic structure and geometric structure will change greatly, and there will be a synergistic effect between metal atoms, which helps sub-nano cluster catalysts to obtain high reactivity through new reaction mechanisms and break through the limitations of single-atom intrinsic activity. Gas-phase synthesis and size selection strategies are the main methods for preparing metal cluster-supported catalysts with precise atomic numbers. However, the yields of these methods are low and far from meeting the requirements of catalytic applications. With the advancement of preparation technology, some new strategies that can afford the synthesis of large-scale metal clusters have been applied, such as atomic layer deposition (ALD) technology.

[0007] ALD technology utilizes the steric hindrance between precursor molecules and the self-limiting reaction between precursor molecules and carriers, so that sub-nano clusters can be accurately prepared. The ALD technology can control the number of Ru atoms deposited, and it is expected to directly construct the B5 site of Ru on the carrier. The defect sites of the carrier are the key to the deposition of metal atoms. For metal oxide carriers, their own defect sites are limited, resulting in low metal loading. Constructing a carrier rich in defect sites can increase the metal loading while keeping the metal in a cluster state. Therefore, the preparation of catalyst carriers is very important for the precise construction of Ru sub-nano clusters using ALD technology. The precise construction of highly active Ru metal sub-nano cluster catalysts using ALD technology plays an important role in achieving efficient hydrogen production from ammonia decomposition.

[0008] At present, some patents have been applied for the preparation of ammonia decomposition catalysts. Chinese patent CN112774676A discloses a rare earth oxide supported ruthenium catalyst and its preparation method and use. Rare earth oxide is used as a carrier and ruthenium is used as an active component. A rare earth oxide supported ruthenium catalyst is prepared by a precipitation deposition method for ammonia decomposition reaction. However, the nanoparticle catalyst involved in the patent has uneven dispersion of ruthenium particles and low catalytic efficiency. Chinese patent CN114570361A discloses a Ru-based catalyst for ammonia decomposition and hydrogen production and its preparation method. Carbon layer modified SiO2 is introduced as a carrier of the ammonia decomposition catalyst, and the active component is metallic ruthenium. However, Ru exists in the form of particles, Ru atoms are not fully utilized, and the catalyst cost is high.

[0009] At present, there is an urgent need to develop an efficient ammonia decomposition catalyst and fully utilize Ru atoms to reduce the cost of the catalyst. Summary of the invention

[0010] The purpose of the present invention is to provide a Ru-based catalyst and a preparation method thereof and application in the ammonia decomposition hydrogen production reaction. By using atomic layer deposition technology, the dispersion of Ru can be effectively improved and the precious metal Ru can be fully utilized. The catalyst can obtain a high ammonia conversion rate under low temperature and high space velocity conditions.

[0011] In order to achieve the above object, the technical solution of the present invention is as follows:

[0012] On one hand, the present invention provides a Ru-based catalyst, wherein the catalyst is a defect-rich d-CeO2 carrier and Ru is an active component, wherein the mass percentage of Ru is 0.01% to 5.0%.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned Ru-based catalyst, the method comprising the following steps:

[0014] 1) The Ce source is dissolved in deionized water to obtain solution A, which is placed in a water bath at 60-80°C, and ammonia water is added dropwise thereto until the pH is 8-12, filtered, washed, dried, and then transferred to a muffle furnace and calcined at 400-600°C for 2-12h, and finally transferred to a tubular furnace and reduced at 400-800°C for 1-6h in a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0015] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol to obtain a suspension, evaporating the ethanol in the suspension, and drying;

[0016] 3) subjecting the defect-rich d-CeO2 carrier dried in step 2) to an atomic deposition treatment, wherein the parameters of the atomic deposition treatment are: using a liquid metal Ru source as a precursor, the pulse time of the Ru precursor is 1 to 20 seconds, the N2 gas purge time is 200 seconds, the NH3 gas pulse time is 1 to 20 seconds, the N2 gas purge time is 200 seconds, and the number of deposition cycles is 10 to 500 times;

[0017] 4) taking out the sample obtained in step 3) and performing reduction treatment to obtain the Ru-based catalyst.

[0018] In the above technical solution, further, in step 1), the concentration of the Ce source in the solution A is 0.01-2 mol / L;

[0019] The mass concentration of the ammonia water is 5 to 15 wt %;

[0020] The drying temperature is 60-120° C., and the drying time is 12 hours.

[0021] In the above technical solution, further, in step 1), the Ce source is any one of Ce(NO3)3 and CeCl3.

[0022] The calcination temperature is 500-550°C and the calcination time is 4-8h;

[0023] The reduction temperature is 500-600°C.

[0024] In the above technical scheme, further, in step 3), the liquid metal Ru source is any one of RuCp2, Ru(EtCp)2, Ru(od)2 and Ru(thd)3, wherein Cp represents cyclopentadienyl, Et represents ethyl, od represents octanedione, and thd represents 2,2,6,6-tetramethyl-3,5-heptanedione.

[0025] In the above technical solution, further, in step 4), the atmosphere of the reduction treatment is hydrogen, the purity of the hydrogen is >99.9%, and the volume space velocity of the hydrogen is 100 to 3600h -1 The heating rate from room temperature to the reduction treatment temperature is 1 to 10°C / min, the reduction treatment temperature is 200 to 400°C, the pressure is normal pressure, and the reduction time is 1 to 48h.

[0026] The present invention also provides an application of a Ru-based catalyst prepared by the above preparation method, wherein the catalyst is used for ammonia decomposition hydrogen production reaction.

[0027] In the above technical solution, further, the reaction space velocity of the ammonia decomposition is 200-60000 ml / g·h, and the reaction pressure is 0.1 MPa.

[0028] In the above technical solution, further, the reaction temperature of the ammonia decomposition is 350-800°C, preferably 400-500°C.

[0029] The beneficial effects of the present invention are:

[0030] 1) The ammonia decomposition catalyst provided by the present invention has a dispersion degree of Ru close to 100%, which can fully utilize the precious metal Ru.

[0031] 2) The catalyst of the present invention has the advantages of low ammonia decomposition reaction temperature, high ammonia space velocity, and high ammonia conversion rate. The catalyst prepared according to the method provided by the present invention exhibits high catalytic activity and stability in the ammonia decomposition reaction. For 0.1% Ru / d-CeO2 catalyst, an ammonia conversion rate of >99% can be achieved at 500°C. For 0.01% Ru / d-CeO2 catalyst, based on the mass of Ru, the space-time yield of H2 per unit mass of Ru reaches 16091 mol H2 / g Ru / h. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the electron microscope mapping image of 0.1% Ru / d-CeO2 prepared in Example 2. DETAILED DESCRIPTION

[0033] The technical details of the present invention are described in detail by the following examples. It should be noted that the examples are only used to further illustrate the technical features of the present invention, rather than to limit the present invention.

[0034] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained through commercial channels or prepared according to conventional methods well known to those skilled in the art.

[0035] Example 1

[0036] 1) 10.30 g of CeCl3·6H2O was dissolved in 50 ml of deionized water to prepare a solution, which was placed in a 60° C. water bath, and 5 wt% ammonia water was added dropwise until the pH value was 10. The obtained turbid liquid was then filtered and washed, and the obtained solid was dried at 60° C. for 12 h. The obtained solid was then transferred to a muffle furnace and calcined at 400° C. for 12 h. Finally, it was transferred to a tubular furnace and reduced at 400° C. for 6 h in a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0037] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0038] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source Ru(EtCp)2 (Et represents ethyl, Cp represents cyclopentadienyl) as a precursor, the pulse time of the Ru precursor is 1 s, the N2 gas purge time is 200 s, the NH3 gas pulse time is 1 s and the N2 gas purge time is 200 s, and the number of deposition cycles is set to 10 times;

[0039] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 100h -1 , the heating rate was 1°C / min, the reduction temperature was 200°C, the pressure was normal pressure, the reduction time was 1h, and a Ru / d-CeO2 catalyst with a Ru content of 0.01wt% was obtained, recorded as 0.01%Ru / d-CeO2.

[0040] The catalyst prepared in Example 1 was used for the reaction conditions of ammonia decomposition: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400-500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0041] Example 2

[0042] 1) 12.62 g of Ce(NO3)3·6H2O was dissolved in 100 ml of deionized water to prepare a solution, which was placed in a 70°C water bath, and 10 wt% ammonia water was added dropwise until the pH was 11, and then the obtained turbid liquid was filtered and washed, and the obtained solid was dried at 80°C for 12 h, and then the obtained solid was transferred to a muffle furnace and calcined at 500°C for 4 h, and finally transferred to a tubular furnace and reduced at 600°C for 4 h under a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0043] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0044] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source RuCp2 (Cp represents a cyclopentadienyl group) as a precursor, the pulse time of the Ru precursor is 10 s, the N2 gas purge time is 200 s, the NH3 gas pulse time is 10 s and the N2 gas purge time is 200 s, and the deposition cycle number is set to 50 times;

[0045] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 2000h -1 , the heating rate was 5°C / min, the reduction temperature was 300°C, the pressure was normal pressure, the reduction time was 2h, and a Ru / d-CeO2 catalyst with a Ru content of 0.1wt% was obtained, recorded as 0.1%Ru / d-CeO2.

[0046] The catalyst prepared in Example 2 was used for the reaction conditions of ammonia decomposition: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400-500°C, reaction pressure of 0.1 MPa, and space velocities of 200, 1000, 30000 and 60000 ml / g·h, respectively. The reaction results are shown in Tables 1 and 2.

[0047] Depend on Figure 1 It can be seen that the metal Ru is very evenly dispersed on the surface of the carrier CeO2, and the dispersion of Ru is close to 100%, which can achieve full utilization of the precious metal Ru.

[0048] Example 3

[0049] 1) Take 12.62g Ce(NO3)3·6H2O and dissolve it in 200ml deionized water to prepare a solution. Place it in a water bath at 80℃, add 15wt% ammonia water until the pH is 8, then filter and wash the obtained turbid liquid, and dry the obtained solid at 120℃ for 12h, then transfer the obtained solid to a muffle furnace, calcine it at 600℃ for 2h, and finally transfer it to a tubular furnace, reduce it at 400℃ for 6h under a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0050] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0051] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source Ru(thd)3 (thd represents 2,2,6,6-tetramethyl-3,5-heptanedione) as a precursor, the pulse time of the Ru precursor is 10s, the N2 gas purge time is 200s, the NH3 gas pulse time is 10s and the N2 gas purge time is 200s, and the deposition cycle number is set to 100 times;

[0052] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 3600h -1 , the heating rate is 10℃ / min, the reduction temperature is 200℃, the pressure is normal pressure, the reduction time is 48h, and a Ru / d-CeO2 catalyst with a Ru content of 0.5wt% is obtained, recorded as 0.5%Ru / d-CeO2.

[0053] The catalyst prepared in Example 3 was used for the reaction conditions of ammonia decomposition: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0054] Example 4

[0055] 1) Take 12.62g Ce(NO3)3·6H2O and dissolve it in 100ml deionized water to prepare a solution. Place it in a 70℃ water bath, add 10wt% ammonia water until the pH is 12, then filter and wash the obtained turbid liquid, and dry the obtained solid at 80℃ for 12h, then transfer the obtained solid to a muffle furnace, calcine it at 500℃ for 4h, and finally transfer it to a tubular furnace, reduce it at 800℃ for 1h under a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0056] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0057] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source Ru(od)2 (od represents octanedione) as a precursor, the pulse time of the Ru precursor is 20s, the N2 gas purge time is 200s, the NH3 gas pulse time is 20s and the N2 gas purge time is 200s, and the deposition cycle number is set to 100 times;

[0058] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 2000h -1 , the heating rate is 10℃ / min, the reduction temperature is 300℃, the pressure is normal pressure, the reduction time is 12h, and a Ru / d-CeO2 catalyst with a Ru content of 1wt% is obtained, recorded as 1%Ru / d-CeO2.

[0059] The catalyst prepared in Example 4 was used for the reaction conditions of ammonia decomposition: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0060] Example 5

[0061] 1) Take 12.62g Ce(NO3)3·6H2O and dissolve it in 100ml deionized water to prepare a solution. Place it in a 70℃ water bath, add 10wt% ammonia water until the pH is 12, then filter and wash the obtained turbid liquid, and dry the obtained solid at 80℃ for 12h, then transfer the obtained solid to a muffle furnace, calcine it at 500℃ for 4h, and finally transfer it to a tubular furnace, reduce it at 800℃ for 1h under a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0062] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0063] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source Ru(od)2 (od represents octanedione) as a precursor, the pulse time of the Ru precursor is 20s, the N2 gas purge time is 200s, the NH3 gas pulse time is 20s and the N2 gas purge time is 200s, and the deposition cycle number is set to 300 times;

[0064] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 2000h -1 , the heating rate was 10℃ / min, the reduction temperature was 300℃, the pressure was normal pressure, the reduction time was 12h, and a Ru / d-CeO2 catalyst with a Ru content of 3wt% was obtained, recorded as 3%Ru / d-CeO2.

[0065] The catalyst prepared in Example 5 was used for the reaction conditions of ammonia decomposition: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0066] Example 6

[0067] 1) Take 12.62g Ce(NO3)3·6H2O and dissolve it in 100ml deionized water to prepare a solution, place it in a water bath at 80℃, add 15wt% ammonia water until the pH is 8, then filter and wash the obtained turbid liquid, and dry the obtained solid at 80℃ for 12h, then transfer the obtained solid to a muffle furnace and calcine it at 550℃ for 4h. Finally, transfer it to a tubular furnace and reduce it at 550℃ for 4h under a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier;

[0068] 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol, dispersing the obtained particles into a suspension by stirring or ultrasonic treatment, and then gradually evaporating the ethanol in the suspension and drying;

[0069] 3) transferring the defect-rich d-CeO2 carrier dried in step 2) to an atomic layer deposition sample chamber for atomic deposition treatment, purging the sample chamber and pipelines of the atomic layer deposition equipment with nitrogen, and setting the parameters of the atomic deposition treatment as follows: using a room temperature liquid source RuCp2 (Cp represents cyclopentadienyl) as a precursor, the pulse time of the Ru precursor is 20s, the N2 gas purge time is 200s, the NH3 gas pulse time is 20s and the N2 gas purge time is 200s, and the deposition cycle number is set to 500 times;

[0070] 4) Take out the sample obtained in step 3) and perform reduction treatment. The reducing gas is pure H2 with a purity of >99.9% and a space velocity of 2000h -1 , the heating rate was 10℃ / min, the reduction temperature was 300℃, the pressure was normal pressure, the reduction time was 4h, and a Ru / d-CeO2 catalyst with a Ru content of 5wt% was obtained, recorded as 5%Ru / d-CeO2.

[0071] The reaction conditions for the decomposition of the catalyst prepared in Example 6 with ammonia were: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0072] Comparative Example 1

[0073] 1) 12.62 g of Ce(NO3)3·6H2O was dissolved in 100 ml of deionized water to prepare a solution, which was placed in a 70°C water bath, and 10 wt% ammonia water was added dropwise until the pH value reached 11. The obtained turbid liquid was then filtered and washed, and the obtained solid was dried at 80°C for 12 h. The obtained solid was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain a CeO2 carrier;

[0074] 2) Take 5 g of the CeO2 carrier prepared above and prepare Ru / CeO2 catalyst by impregnation method. The specific steps are as follows:

[0075] Measure 5 ml of Ru to obtain a concentration of 10 mg mL -1 The RuCl3 solution was added dropwise to the CeO2 carrier, impregnated at room temperature for 12 h, and dried in an oven at 80 °C for 6 h to obtain a Ru / CeO2 sample, which was then reduced with hydrogen at 400 °C. The heating rate from room temperature to the reduction temperature was 5 °C / min, and the volume space velocity of hydrogen was 2000 h -1 , the pressure was normal pressure, the reduction time was 4 h, and the obtained catalyst was recorded as 0.1% Ru / CeO2-IWI.

[0076] The catalyst prepared in Comparative Example 1 was used for ammonia decomposition under the following reaction conditions: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0077] Comparative Example 2

[0078] Weigh 1.0g Al2O3 carrier, weigh 0.5369g Ni(NO3)2 and dissolve it in 2g deionized water to prepare a mixed solution, the mass concentration of Ni is 1.8wt%, add it dropwise to the Al2O3 carrier and mix it evenly, soak it at room temperature for 12h, dry it at 120℃ for 4h, and calcine it at 500℃ in air atmosphere for 6h, wherein the mass content of Ni is 15%, then, reduce it with hydrogen at a temperature of 700℃, the heating rate from room temperature to the reduction temperature is 10℃ / min, and the volume space velocity of hydrogen is 1000h -1 , the pressure was normal pressure, the reduction time was 4 h, and the obtained catalyst was recorded as 15% Ni / Al2O3.

[0079] The catalyst prepared in Comparative Example 2 was used for ammonia decomposition under the following reaction conditions: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400-500°C, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0080] Result analysis:

[0081] As can be seen from Table 1, the activity of the 0.1% Ru / d-CeO2 catalyst prepared by atomic layer deposition in the ammonia decomposition hydrogen production reaction is significantly higher than that of the 0.1% Ru / d-CeO2-IWI catalyst prepared by the impregnation method. The above experimental results show that the atomic layer deposition method has advantages and improves the reaction performance of the catalyst.

[0082] For 0.1% Ru / d-CeO2 catalyst, ammonia conversion rate > 99% can be achieved at 500°C. For 0.01% Ru / d-CeO2 catalyst, based on Ru mass, the space-time yield of H2 per unit mass of Ru reaches 16091.5 mol H2 / g Ru / h. The Ru-based catalyst prepared by atomic layer deposition can achieve efficient decomposition of ammonia under high space velocity and low temperature conditions.

[0083] Table 2 shows the ammonia decomposition reaction performance of 0.1% Ru / d-CeO2 at different temperatures and different space velocities in Example 2. The performance at different space velocities is that the ammonia conversion rate gradually increases with the increase of temperature. At 400°C, as the space velocity gradually increases from 200ml / g·h to 60000ml / g·h, the ammonia conversion rate gradually decreases from 69.5% to 48.6%. However, when the reaction temperature is 500°C, although the space velocity gradually increases from 200ml / g·h to 60000ml / g·h, the ammonia conversion rate only decreases slightly, from 99.7% to 92.2%. It shows that the catalyst has excellent ammonia decomposition performance, can adapt to the efficient conversion of ammonia at different space velocities, and provides a larger operating window for the practical application of the catalyst.

[0084] Table 1 Reaction performance of ammonia decomposition on different catalysts

[0085]

[0086] Table 2 Reaction performance of ammonia decomposition under different space velocity conditions

[0087]

[0088] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A Ru-based catalyst, characterized in that: The catalyst uses defect-rich d-CeO2 as a carrier and Ru as an active component, wherein the mass percentage of Ru is 0.01%-5.0%.

2. A method for preparing the Ru-based catalyst according to claim 1, characterized in that: The method comprises the following steps: 1) The Ce source is dissolved in deionized water to obtain solution A, which is placed in a water bath at 60-80°C, and ammonia water is added dropwise thereto until the pH is 8-12, filtered, washed, dried, and then transferred to a muffle furnace and calcined at 400-600°C for 2-12h, and finally transferred to a tubular furnace and reduced at 400-800°C for 1-6h in a hydrogen atmosphere to obtain a defect-rich d-CeO2 carrier; 2) dispersing the defect-rich d-CeO2 carrier obtained in step 1) in anhydrous ethanol to obtain a suspension, evaporating the ethanol in the suspension, and drying; 3) subjecting the defect-rich d-CeO2 carrier dried in step 2) to an atomic deposition treatment, wherein the parameters of the atomic deposition treatment are: using a liquid metal Ru source as a precursor, the pulse time of the Ru precursor is 1 to 20 seconds, the N2 gas purge time is 200 seconds, the NH3 gas pulse time is 1 to 20 seconds, the N2 gas purge time is 200 seconds, and the number of deposition cycles is 10 to 500 times; 4) taking out the sample obtained in step 3) and performing reduction treatment to obtain the Ru-based catalyst.

3. The preparation method according to claim 2, characterized in that: In step 1), the concentration of Ce source in solution A is 0.01-2 mol / L; The mass concentration of the ammonia water is 5 to 15 wt %; The drying temperature is 60-120° C., and the drying time is 12 hours.

4. The preparation method according to claim 2, characterized in that: In step 1), the Ce source is any one of Ce(NO3)3 and CeCl3. The calcination temperature is 500-550°C and the calcination time is 4-8h; The reduction temperature is 500-600°C.

5. The preparation method according to claim 2, characterized in that: In step 3), the liquid metal Ru source is any one of RuCp2, Ru(EtCp)2, Ru(od)2 and Ru(thd)3, wherein Cp represents cyclopentadienyl, Et represents ethyl, od represents octanedione, and thd represents 2,2,6,6-tetramethyl-3,5-heptanedione.

6. The preparation method according to claim 2, characterized in that: In step 4), the atmosphere of the reduction treatment is hydrogen, the purity of the hydrogen is >99.9%, and the volume space velocity of the hydrogen is 100 to 3600 h -1 The heating rate from room temperature to the reduction treatment temperature is 1 to 10°C / min, the reduction treatment temperature is 200 to 400°C, the pressure is normal pressure, and the reduction time is 1 to 48h.

7. Use of the Ru-based catalyst according to claim 1 or the Ru-based catalyst prepared by the preparation method according to any one of claims 2 to 6 in ammonia decomposition hydrogen production reaction.

8. The use according to claim 7, characterized in that: The reaction space velocity of the ammonia decomposition is 200-60000 ml / g·h, and the reaction pressure is 0.1 MPa.

9. The use according to claim 7, characterized in that: The reaction temperature of the ammonia decomposition is 350-800°C.

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