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

Abstract

The present application belongs to the field of hydrogen production by ammonia decomposition catalysis, and relates to a Ru-based catalyst, a preparation method and application thereof in hydrogen production by ammonia decomposition, which is a Ru-based catalyst with TOF bimodal characteristics by regulating reduction conditions to realize Ru particle size regulation. The catalyst takes carbon powder as a carrier, takes ruthenium nitrosyl nitrate as a precursor, and the ruthenium loading is 2wt%-4wt%. The Ru / C catalyst with controllable particle size distribution is obtained by regulating reduction conditions such as reduction atmosphere and reduction temperature to regulate the particle size of ruthenium particles. The average particle size of Ru nanoparticles of the catalyst is controlled in the range of 2.18-3.90 nm, and the highest intrinsic activity is shown in the two particle size intervals of 2.25 nm and 3.70 nm, forming a TOF-particle size bimodal law. The catalyst of the present application can be used for hydrogen production by ammonia decomposition.

Description

Technical Field

[0001] This invention belongs to the field of ammonia decomposition hydrogen production catalysis technology, and relates to a Ru-based catalyst, its preparation method and its application in ammonia decomposition hydrogen production. It is a Ru-based catalyst with TOF bimodal characteristics that achieves ruthenium particle size control by regulating reduction conditions. Background Technology

[0002] Ammonia decomposition for hydrogen production, as a highly efficient and low-carbon hydrogen production technology, has attracted widespread attention in the field of hydrogen energy storage and conversion in recent years. Ammonia molecules have a high hydrogen content (17.7 wt%) and are easy to store and transport, making them considered one of the ideal hydrogen carriers. However, the ammonia decomposition reaction requires high temperatures and imposes stringent requirements on the activity and stability of the catalyst. Among numerous catalyst systems, ruthenium (Ru)-based catalysts are recognized as the most promising catalytic materials due to their excellent low-temperature activity, but their high cost and limited resource reserves restrict large-scale industrial applications. Therefore, how to improve the atom utilization efficiency and catalytic performance of Ru catalysts by reducing the loading and optimizing the microstructure of Ru catalysts has become a core scientific problem in current research.

[0003] The relationship between catalyst activity and metal particle size has long been a classic research topic in heterogeneous catalysis. Traditionally, it was believed that reducing the metal particle size could increase the number of active sites, thereby improving catalytic activity. However, increasing research indicates that the relationship between catalytic activity and particle size is not a simple linear one, but rather exhibits complex nonlinear characteristics. There is an optimal range for the effect of metal particle size on catalytic performance; excessively small or large particle sizes are detrimental to the catalytic reaction. In Ru-based catalyst systems, the particle size effect also exhibits significant structural sensitivity. It is widely accepted that the activity of ammonia decomposition depends on the number of B5 sites, which is related to the Ru crystallite size. Although numerous studies have been conducted to optimize the particle size and structure of Ru catalysts, the optimal particle size of Ru in the ammonia decomposition reaction remains controversial.

[0004] Furthermore, existing research remains significantly insufficient in systematically exploring the relationship between Ru particle size and intrinsic activity (TOF) in ammonia decomposition. Studies on whether a multimodal relationship exists between Ru particle size and TOF (e.g., the influence of other active sites) are almost entirely lacking. Clarifying this scientific question is crucial for guiding the rational design of Ru-based catalysts, providing greater design flexibility for catalyst optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a Ru-based catalyst, its preparation method, and its application in ammonia decomposition for hydrogen production. By adjusting the reduction conditions and Ru loading, the Ru particle size can be precisely controlled in the range of 2.18~3.90 nm. The invention also reveals the dual-volcano law of TOF-particle size and determines two optimal particle size ranges (2.25 nm and 3.70 nm).

[0006] The technical solution of this invention: A Ru-based catalyst is disclosed, wherein the support is carbon powder and the Ru loading is 2 wt% to 4 wt%. The average particle size of the support is 40–60 nm, and the BET specific surface area is 100–140 m². 2 / g.

[0007] The preparation method of the above Ru-based catalyst includes the following steps: S1. Carrier pretreatment: The carrier carbon powder is treated at a constant temperature to remove adsorbed moisture, dust and other impurities. After treatment, it is naturally cooled to room temperature for later use.

[0008] S2. Impregnation and loading: Ru(NO)(NO3)x(OH)y, x+y=3 is used as a precursor and dissolved in deionized water to obtain a precursor solution; the carbon powder pretreated in step S1 is added to the precursor solution and placed in a water bath environment with continuous stirring to ensure that the precursor solution uniformly impregnates the support; then it is aged at room temperature to allow the precursor to be fully adsorbed on the surface of the carbon powder, and then dried overnight to obtain the Ru-based catalyst precursor.

[0009] S3. Reduction Control: The Ru-based catalyst precursor is placed in a tube furnace and reduced using a programmed temperature rise method. The ruthenium particle size is precisely controlled by adjusting the reduction atmosphere and reduction temperature. After reduction, the product is naturally cooled to room temperature and then ground into a uniform powder to obtain the Ru-based catalyst.

[0010] Preferably, in step S1, the treatment is carried out at a constant temperature of 200~300℃ in a rare gas atmosphere for 2~4 hours.

[0011] Preferably, in step S2, the water bath temperature is 60℃~80℃; the room temperature aging time is 12~24 h; and the overnight drying temperature is 90~110℃ for 8~12 h.

[0012] Preferably, in step S3, the heating rate is controlled at 5~10℃ / min, and the reduction time is 2~4h.

[0013] Preferably, in step S3, the reducing atmosphere is a volume ratio of H2 to Ar of 1:9 or a volume ratio of H2 to Ar of 1:1 or a pure H2 atmosphere, and the total gas velocity is 100 mL / min; the reducing temperature is 300-700℃.

[0014] The Ru-based catalyst prepared by this invention has an average Ru nanoparticle size of 2.18–3.90 nm. Preferably, it exhibits the highest intrinsic ammonia decomposition activity at average particle sizes of 2.25 nm and 3.70 nm.

[0015] The Ru-based catalyst prepared by the above method is used for hydrogen production from ammonia decomposition. Specifically, the feed gas is pure NH3, and the NH3 flow rate is 800~1200 mL / g per gram of catalyst. -1 min -1 The reaction temperature is 400~500℃.

[0016] The beneficial effects of this invention are: (1) By adjusting the reducing atmosphere and reducing temperature, the present invention achieves the control of ruthenium particle size (2.18nm~3.90nm) of Ru-based catalyst (Ru / C catalyst). The preparation method has clear parameters, simple steps and no need for complicated equipment. At the same time, the TEM characterization (statistical analysis of about 200 particles) is clearly used to determine the ruthenium particle size, which improves the accuracy of catalyst performance evaluation.

[0017] (2) The Ru / C catalyst of the present invention exhibits a unique double volcano curve in the ammonia decomposition reaction (450℃). The ruthenium particle size and TOF value show a double peak characteristic. The two optimal particle sizes (double volcano curve inflection points) are 2.25nm and 3.70nm, which breaks the limitation of the existing technology that "single particle size corresponds to high activity" and provides a new idea for the design of ruthenium-based catalysts. Attached Figure Description

[0018] Figure 1 This is a TEM image of the 2.25 nm Ru / C catalyst in Example 2.

[0019] Figure 2 This is a Ru particle size distribution diagram of the 2.25 nm Ru / C catalyst in Example 2.

[0020] Figure 3 This is a TEM image of the 3.70 nm Ru / C catalyst in Example 7.

[0021] Figure 4 This is a Ru particle size distribution diagram of the 3.70 nm Ru / C catalyst in Example 7.

[0022] Figure 5 The figures show the XRD patterns of the Ru / C catalysts in Examples 1-8. The figures are arranged from bottom to top as 2wt% Ru / C catalyst and 4wt% Ru / C catalyst, and are plotted according to the particle size from smallest to largest at their respective loadings.

[0023] Figure 6This is a TEM image of the Ru / C catalyst in Comparative Example 1.

[0024] Figure 7 This is a TEM image of the Ru / C catalyst in Comparative Example 2.

[0025] Figure 8 This is a bivolcano trend diagram of the TOF value and Ru particle size of the catalysts obtained in Examples 1-8 at 450°C. The particles are arranged from left to right in order of increasing particle size. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0027] Example 1 Prepare a 2wt% Ru / C catalyst (average particle size 2.18 nm) Step (1) Carrier pretreatment: 50nm, BET 120m 2 / g of charcoal powder is placed in a tube furnace and treated at 250℃ for 3 hours, then cooled to room temperature for later use.

[0028] Step (2) Impregnation loading: Take 0.193g of Aladdin reagent ruthenium nitrite as the precursor, add 5.4g of deionized water to prepare a precursor solution with a ruthenium loading of 2wt%, add 3g of pretreated carbon powder, stir at 70℃, age at room temperature for 12h, and dry at 100℃ for 12h to obtain Ru / C precursor.

[0029] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce a mixed atmosphere of H2:Ar=50:50 (volume ratio) (total flow rate 100mL / min), and reduce at a constant temperature of 300℃ for 3h.

[0030] Catalyst 1 was prepared, and the average particle size of ruthenium particles in catalyst 1 was 2.18 nm.

[0031] Performance testing: 0.3g of catalyst 1 was packed into a fixed-bed reactor, and the reaction was carried out at a temperature of 450℃, with pure ammonia as the feed gas and a space velocity of 1000 mLg. -1 min -1 The ammonia decomposition reaction was tested under the specified conditions to investigate its conversion rate. The test results showed that the ammonia decomposition conversion rate was 3.01%, and the TOF value was 0.1980 s⁻¹. -1 .

[0032] Example 2 Prepare a 2wt% Ru / C catalyst (average particle size 2.25 nm) Steps (1)-(2) are the same as in Example 1.

[0033] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce a mixed atmosphere of H2:Ar=10:90 (total flow rate 100mL / min), and reduce at a constant temperature of 300℃ for 3h.

[0034] Catalyst 2 was prepared; TEM results are shown in […]. Figure 1 Ru particle size distribution is shown in Figure 2 The average particle size of ruthenium particles in catalyst 2 is 2.25 nm.

[0035] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 4.45%, and the TOF value was 0.2576 s. -1 .

[0036] Example 3 Prepare a 2wt% Ru / C catalyst (average particle size 3.42 nm) Steps (1)-(2) are the same as in Example 1.

[0037] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, first introduce Ar and heat treat at 500℃ for 3h, then introduce H2 (flow rate 100mL / min) and reduce at 500℃ for 3h.

[0038] Catalyst 3 was prepared; the average particle size of ruthenium particles in catalyst 3 was 3.42 nm.

[0039] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 1.96%, and the TOF value was 0.1955 s. -1 .

[0040] Example 4 Prepare a 2wt% Ru / C catalyst (average particle size 2.57 nm) Steps (1)-(2) are the same as in Example 1.

[0041] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce H2 (flow rate 100mL / min), and reduce at a constant temperature of 500℃ for 3h.

[0042] Catalyst 4 was prepared; the average particle size of ruthenium particles in catalyst 4 was 2.57 nm.

[0043] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 2.34%, and the TOF value was 0.1644 s. -1 .

[0044] Example 5 Prepare a 2wt% Ru / C catalyst (average particle size 2.87 nm) Steps (1)-(2) are the same as in Example 1.

[0045] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce H2 (flow rate 100mL / min), and reduce at a constant temperature of 600℃ for 3h.

[0046] Catalyst 5 was prepared; the average particle size of ruthenium particles in catalyst 5 was 2.87 nm.

[0047] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 0.82%, and the TOF value was 0.0643 s. -1 .

[0048] Example 6 Prepare a 2wt% Ru / C catalyst (average particle size 3.81 nm) Steps (1)-(2) are the same as in Example 1.

[0049] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce H2 (flow rate 100mL / min), and reduce at a constant temperature of 700℃ for 3h.

[0050] Catalyst 6 was prepared; the average particle size of ruthenium particles in catalyst 6 was 3.81 nm.

[0051] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 1.12%, and the TOF value was 0.1244 s. -1 .

[0052] Example 7 Prepare a 4wt% Ru / C catalyst (average particle size 3.70 nm) Step (1) is the same as in Example 1.

[0053] Step (2) Impregnation loading: Take 0.393g of Aladdin reagent ruthenium nitrite as the precursor, add 5.4g of deionized water to prepare a precursor solution with a ruthenium loading of 4wt%, add 3g of pretreated carbon powder, stir at 70℃, age at room temperature for 12h, and dry at 100℃ for 12h to obtain Ru / C precursor.

[0054] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce a mixed atmosphere of H2:Ar=50:50 (volume ratio) (total flow rate 100mL / min), and reduce at a constant temperature of 700℃ for 3h.

[0055] Catalyst 7 was prepared; TEM results are shown in […]. Figure 3 The particle size distribution results of Ru particles are shown in the figure. Figure 4 The average particle size of ruthenium particles in catalyst 7 is 3.70 nm.

[0056] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was found to be 6.05%, and the TOF value was 0.3264 s. -1 .

[0057] Example 8 Prepare a 4wt% Ru / C catalyst (average particle size 3.90 nm) Steps (1)-(2) are the same as in Example 7.

[0058] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce H2 (flow rate 100mL / min), and reduce at a constant temperature of 700℃ for 3h.

[0059] Catalyst 8 was prepared; the average particle size of ruthenium particles in catalyst 8 was 3.90 nm. XRD results of samples from Examples 1-8 are shown below. Figure 5 .

[0060] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 1.28%, and the TOF value was 0.0728 s. -1 .

[0061] Comparative Example 1 Following the preparation method of this invention, the ruthenium loading was adjusted to prepare a 0.5 wt% Ru / C catalyst (average particle size 1.35 nm). Steps (1) and (3) are the same as in Example 1. In step (2), 0.047g of Aladdin reagent ruthenium nitrite nitrate was used as a precursor, and 5.4g of deionized water was added to prepare a 0.5wt% ruthenium precursor solution. The rest was repeated in step (2) of Example 1.

[0062] Finished product: After cooling to room temperature, grind evenly to obtain the catalyst; TEM results are shown below. Figure 6 The average particle size of the ruthenium particles in the catalyst is 1.35 nm.

[0063] Performance testing: 0.3 g of catalyst was loaded into a fixed-bed reactor, and an ammonia decomposition reaction was tested at a reaction temperature of 450℃ and an ammonia gas flow rate of 300 mL / min to examine its conversion rate. The tested ammonia decomposition conversion rate was 0.46%, and the TOF value was 0.0749 s⁻¹. -1 .

[0064] The difference between Comparative Example 1 and Example 1 is the amount of ruthenium loading.

[0065] The TEM morphology results show that the average ruthenium particle size is significantly reduced with a ruthenium loading of 0.5 wt%, resulting in a low conversion rate under the same reaction conditions. The TOF value is significantly smaller than that of the Ru / C catalysts with particle sizes of 2.18 nm and 2.25 nm.

[0066] Comparative Example 2 Following the preparation method of this invention, the reduction temperature was adjusted to prepare a 4wt% catalyst (average particle size of 3.98 nm). Steps (1)-(2) are the same as in Example 7.

[0067] Step (3) Reduction control: Place the Ru / C precursor into a tube furnace, heat at a rate of 10℃ / min, introduce a mixed atmosphere of H2:Ar=50:50 (volume ratio) (total flow rate 100mL / min), and reduce at 800℃ for 3h.

[0068] Finished product: After cooling to room temperature, grind evenly to obtain the catalyst; TEM results are shown below. Figure 7 The average particle size of the ruthenium particles in the catalyst is 3.98 nm.

[0069] Performance testing: Under the same reaction conditions as in Example 1, the ammonia decomposition conversion rate was 0.66%, and the TOF value was 0.0766 s. -1 .

[0070] The difference between Comparative Example 2 and Example 7 lies in the reduction temperature.

[0071] The particle size results of Ru particles in the Ru / C catalysts of the examples and comparative examples, as well as the ammonia decomposition conversion rate and TOF value at 450℃, are shown in Table 1.

[0072] Table 1. Ammonia conversion and TOF value of Ru / C catalysts with different particle sizes at 450℃

[0073] Through Table 1 and Figure 8 It can be observed that at a reaction temperature of 450℃, the TOF value and Ru particle size exhibit a bivolcanic trend within the range of 2.18~3.90 nm, with the highest values ​​appearing at 2.25 nm and 3.70 nm. This invention achieves the control of ruthenium particle size by adjusting conditions such as the reducing atmosphere and reduction temperature. Figure 1 It can be observed that the Ru particles prepared by this method have a relatively uniform size distribution.

Claims

1. A Ru-based catalyst, characterized in that, In the Ru-based catalyst, the support is carbon powder, and the Ru loading is 2 wt%~4 wt%; the average particle size of the support is 40~60 nm, and the BET specific surface area is 100~140 m². 2 / g.

2. The method for preparing the Ru-based catalyst according to claim 1, characterized in that, The steps are as follows: S1. Carrier pretreatment: The carrier carbon powder is treated at a constant temperature to remove adsorbed moisture, dust and other impurities. After treatment, it is naturally cooled to room temperature for later use. S2, Impregnation and Loading: Ruthenium nitrite nitrate was used as a precursor and dissolved in deionized water to obtain a precursor solution; the carbon powder pretreated in step S1 was added to the precursor solution and placed in a water bath environment with continuous stirring to ensure that the precursor solution uniformly impregnates the support; then it was aged at room temperature to allow the precursor to be fully adsorbed on the surface of the carbon powder, and then dried overnight to obtain the Ru-based catalyst precursor. S3. Reduction Control: The Ru-based catalyst precursor is placed in a tube furnace and reduced by programmed temperature rise. Precise control of ruthenium particle size can be achieved by adjusting the reducing atmosphere and reducing temperature. After reduction, the product was naturally cooled to room temperature and then ground into a uniform powder to obtain the Ru-based catalyst.

3. The method for preparing the Ru-based catalyst according to claim 2, characterized in that, In step S1, the sample is treated at a constant temperature of 200-300℃ in a rare gas atmosphere for 2-4 hours.

4. The method for preparing the Ru-based catalyst according to claim 2, characterized in that, In step S2, the water bath temperature is 60℃~80℃; the room temperature aging time is 12~24 h; and the overnight drying temperature is 90~110℃ for 8~12 h.

5. The method for preparing the Ru-based catalyst according to claim 2, characterized in that, In step S3, the heating rate is controlled at 5~10℃ / min, and the reduction time is 2~4h.

6. The method for preparing the Ru-based catalyst according to claim 2, characterized in that, In step S3, the reducing atmosphere is a volume ratio of H2 to Ar of 1:9 or a volume ratio of H2 to Ar of 1:1 or a pure H2 atmosphere, and the total gas velocity is 100 mL / min.

7. The method for preparing the Ru-based catalyst according to claim 2, characterized in that, In step S3, the reduction temperature is 300-700℃.

8. The method for preparing the Ru-based catalyst according to any one of claims 2-7, characterized in that, The average particle size of Ru nanoparticles is 2.18~3.90 nm.

9. A Ru-based catalyst prepared by any one of claims 1-7, used for hydrogen production from ammonia decomposition.

10. The application according to claim 9, characterized in that, During the ammonia decomposition to produce hydrogen, the feed gas is pure NH3, and the NH3 flow rate is 800~1200 mL / g per gram of catalyst. -1 min -1 The reaction temperature is 400~500℃.

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