A nickel silicate-derived spherical catalyst, its preparation method and application

Abstract

This invention relates to a nickel silicate-derived spherical catalyst, its preparation method, and its applications. The catalyst comprises a support and an active component; the support is nickel silicate-coated silica, and the active component is Ni, or Ni and Ru. In the preparation method, spherical silica is first obtained by hydrolysis of TEOS under alkaline conditions. Then, the surface of the silica spheres is etched using a hydrothermal method to form a nickel silicate derivative with a mesoporous structure. Finally, Ru doping is performed to obtain a spherical 1Ru-10Ni / SiO2 catalyst. This invention provides a green and simple method for preparing a highly efficient and stable ammonia decomposition catalyst. The reagents used are harmless to humans and do not generate environmental pollutants. This catalyst has advantages such as small particle size, good metal dispersion, and resistance to agglomeration at high temperatures.

Description

Technical Field

[0001] This invention relates to a nickel silicate-derived spherical catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen, as an environmentally friendly and sustainable resource, has attracted widespread attention worldwide. However, hydrogen has a low volumetric energy density, high hazard, and is inconvenient for long-distance transportation. Furthermore, safety and cost issues exist during storage and transportation. Therefore, attention has shifted to on-site hydrogen production using hydrogen storage materials. Compared to hydrogen storage materials such as metal hydrides and metal amine salts, ammonia has a higher volumetric energy density (10⁸ kg H₂ / m³). 3 Considering the hydrogen content (17.6 wt%), ammonia-to-hydrogen production has the lowest specific energy cost. The general activity order for metal catalysts used in ammonia decomposition is Ru > Ir > Rh > Co ~ Ni > Pt > Pd > Fe. Although Ru is expensive, Ru-based catalysts can recover 95% of Ru after the reaction, and the excellent ammonia decomposition performance of Ru-based catalysts is unmatched by non-precious metal catalysts; therefore, Ru remains an important ammonia decomposition catalyst. Ni-based catalysts, due to their low price and good ammonia decomposition performance, are commonly used non-precious metal catalysts. For example, patent CN117380198A prepared a monolithic nickel-based catalyst with a particle size of 3.4 nm using nickel foam as raw material and nickel silicate as an intermediate; however, this sample lacked a regular morphology, and its ammonia decomposition stability at 450℃ was only 5 h. Patent CN117983245A used graphite carbon as a support, precious metals as active components, and alkali metals as promoters; although the prepared series of catalysts achieved a space velocity of 30000 mL... NH3 (g cat *h) -1 At 500℃, the ammonia conversion rate is 72%-96%, but the metal content is large, with precious metals and alkali metals added at 2wt%-15wt%, and the calcination temperature is as high as 1000℃, resulting in high catalyst preparation cost, strict equipment requirements, and the catalyst activity decay rate is still as high as 5%-42% within 100h. Huang et al. reported a Ru / La2O3 catalyst prepared by co-precipitation method in "Ru / La2O3 catalyst for ammonia decomposition to hydrogen" (Applied Surface Science, 2019, 476:928-936.). This catalyst has better activity at a space velocity of 18000 mL. NH3 (g cat *h) -1 The ammonia conversion rate was 91% at 525℃, but its stability test lasted only 84 hours and still needs further improvement.

[0003] It is evident that the agglomeration of Ru and Ni particles at high temperatures remains a significant factor affecting the activity and stability of catalysts. There is an urgent need to find a new preparation method to produce a high-performance catalyst that can maintain good ammonia decomposition performance while reducing the amount of precious metals used, and can also suppress particle agglomeration at high temperatures to achieve excellent stability. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of current technologies by providing a nickel silicate-derived spherical catalyst, its preparation method, and its applications. The catalyst is spherical nickel silicate-coated silica, with Ru or Ru and Ni metal as the active components. In the preparation method, spherical silica is first obtained by hydrolysis of TEOS under alkaline conditions. Then, the surface of the silica spheres is etched using a hydrothermal method to form a nickel silicate derivative with a mesoporous structure. This nickel silicate derivative has a mesoporous structure but is not hollow, exhibiting good mechanical strength. The NH3·H2O added during the hydrothermal process both etches the silica spheres and participates in the formation of nickel silicate; the added CTAB promotes the formation of mesopores; Ru doping yields a spherical 1Ru-10Ni / SiO2 catalyst, which has more active sites and exhibits Ru-Ni metal-to-metal interactions. This invention prepares a highly efficient and stable ammonia decomposition catalyst using a green and simple method. The reagents used in the preparation process are harmless to humans and do not generate environmental pollutants. This catalyst has advantages such as small particle size, good metal dispersion, and resistance to agglomeration at high temperatures.

[0005] The technical solution adopted in this invention is:

[0006] A nickel silicate-derived spherical catalyst comprises a support and an active component; wherein the support is nickel silicate-coated silica, and the active component is Ni, or Ru and Ni; the active component accounts for 1-11% of the mass of the catalyst; when the active component consists of two elements, the ratio of Ru to Ni is 1:9-10.

[0007] The support is prepared by hydrothermal method from silicon dioxide (SiO2), hexadecyltrimethylammonium bromide (CTAB), Ni(NO3)2.6H2O, and NH3.H2O. Ru is loaded onto the support by equal volume impregnation method. The content of active component on the catalyst is about 1-11%, and the rest is the support.

[0008] The preparation method of the nickel silicate-derived spherical catalyst includes any one of the following two methods:

[0009] Method 1, for the preparation of nickel silicate-derived spherical catalysts with Ni as the active component, includes the following steps:

[0010] (1) Mix tetraethyl orthosilicate (TEOS) with anhydrous ethanol and deionized water, stir at room temperature for 10-20 min, then add ammonia dropwise into the mixture and continue stirring for 10-15 h to obtain suspension A;

[0011] For every 140-150 mL of anhydrous ethanol, add 13-14 g of tetraethyl orthosilicate (TEOS) and 10-12 mL of deionized water, and add 7-7.5 mL of ammonia solution with a concentration of 25-28 wt%.

[0012] (2) Centrifuge the suspension A obtained in step (1), wash the solid obtained with anhydrous ethanol and deionized water in sequence, and dry it at 60-120℃ for 6-24h to obtain SiO2.

[0013] (3) Mix the SiO2 obtained in step (2) with deionized water, CTAB, Ni(NO3)2.6H2O and NH3.H2O, and stir for 2-3 hours to obtain solution A;

[0014] The mass ratio of SiO2:deionized water:CTAB:Ni(NO3)2·6H2O:NH3·H2O is 1:40-50:0.8-1:0.54-0.56:5.8-6.2.

[0015] (4) Transfer the solution A obtained in step (3) to a high-pressure reactor and keep it at 140-200℃ for 10-36h; then centrifuge, wash the obtained solid twice with anhydrous ethanol and deionized water in turn, and dry it at 60-120℃ for 6-24h to obtain solid A.

[0016] (5) The solid A obtained in step (4) is calcined at 250-550℃ for 1-4 hours to obtain nickel silicate-derived spherical catalyst A with Ni as the active component.

[0017] Alternatively, Method 2 involves the preparation of nickel silicate-derived spherical catalysts with Ru and Ni as active components, comprising the following steps:

[0018] Steps (1)-(5) are the same as in Method 1;

[0019] (6) Dissolve RuCl3 in deionized water to obtain solution B; wherein, 0.02-0.06 g of RuCl3 is added to every 1.0-1.5 mL of deionized water;

[0020] (7) Add the nickel silicate-derived spherical catalyst A with Ni as the active component obtained in Method 1 to solution B, and stir until homogeneous to obtain a moist solid B; wherein, 0.9-1.1 g of catalyst A is added to every 1.2-1.5 mL of solution B;

[0021] (8) Place the solid B obtained in step (7) at room temperature for 12-24 hours, and then dry it in an oven at 40-80℃ for 3-6 hours to obtain solid C;

[0022] (9) The solid C obtained in step (8) is calcined at 400-600℃ for 1-4h under a hydrogen atmosphere to obtain Ru-doped nickel silicate-derived spherical catalyst B.

[0023] The aforementioned nickel silicate-derived spherical catalyst is used to catalyze the decomposition of ammonia to produce hydrogen and nitrogen. Specifically, it includes the following steps: NH3 and Ar (in a ratio of 3:1) are introduced into a fixed-bed reactor containing the nickel silicate-derived spherical catalyst at atmospheric pressure, and the reaction is carried out at 300–650°C to obtain hydrogen and nitrogen.

[0024] space velocity is 6000-120000 mL NH3 (g cat *h) -1 .

[0025] The nickel silicate-derived spherical catalyst is characterized in that most of the Ni exists in the form of nickel silicate, the metal particles are small and well dispersed, there are interactions between metals and between metal and support, and it is not easy to agglomerate at high temperatures.

[0026] The method for preparing the nickel silicate-derived spherical catalyst is characterized in that: Ni(NO3)2.6H2O and SiO2 are first reacted by a hydrothermal method to form nickel silicate Ni3Si4O. 10 (OH)2.5H2O, at this point Ni is evenly distributed in the catalyst, the specific surface area of ​​the support increases, and then Ru is impregnated by equal volume, so that Ru particles are also evenly distributed.

[0027] The essential features of this invention are:

[0028] Catalysts available for ammonia decomposition to hydrogen production include noble metals, non-noble metals, transition metals, bimetals, metal nitrides, metal carbides, and imine catalysts. The deactivation of Ru-based catalysts is mainly due to the sintering and agglomeration of metal particles or hydrogen poisoning; metal agglomeration also occurs on Ni-based catalysts. In catalyst preparation methods for ammonia decomposition to hydrogen production systems, current technologies mostly employ conventional impregnation methods to prepare supported non-noble metal catalysts, such as Ni, Fe, and Mo. However, the particle size of catalysts prepared by this method is difficult to control, and the particles are prone to agglomeration at high temperatures, resulting in poor stability. Furthermore, non-noble metals cannot achieve the ammonia decomposition performance of noble metal Ru, leading to high metal loading, high resource consumption, and low energy utilization.

[0029] This invention develops a highly efficient and stable nickel silicate-derived spherical catalyst. This catalyst is produced using a hydrothermal method, where Ni first reacts with SiO2 to form a stable nickel silicate, Ni3Si4O.10 The catalyst is prepared by impregnating a small amount of Ru with (OH)₂·5H₂O using an equal-volume method, resulting in a strong interaction between Ru and Ni, achieving small particle size and high dispersion. Compared with supported catalysts prepared by traditional impregnation methods, the catalyst prepared in this invention has smaller particle size, higher dispersion, and is less prone to agglomeration at high temperatures. Therefore, it can achieve high activity and excellent stability in the ammonia decomposition to hydrogen production reaction.

[0030] In this invention, Ni species mostly exist in the form of recalcitrant nickel silicates. An interaction force exists between Ni and Si, resulting in a uniform Ni distribution and preventing agglomeration at high temperatures. Under a strong reducing atmosphere during the reaction, Ni species in the nickel silicates can be further reduced to Ni. 0 The addition of Ru provides more active sites for ammonia decomposition. Ru not only increases the number of active sites, but also enhances the interaction forces between Ru and Ni, and between Ni and Si. The synergistic effect of these interactions further enhances the ammonia decomposition performance of the catalyst, and the catalyst can maintain a complete spherical morphology throughout the process, exhibiting a certain degree of structural stability.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention prepares a nickel silicate-derived spherical catalyst. First, silica is obtained by hydrolysis of TEOS under alkaline conditions. Then, nickel silicate is coated onto the silica surface via a hydrothermal method, forming a nickel silicate-derived catalyst with a mesoporous structure. Furthermore, the catalyst is doped with Ru to form a Ru-Ni dual-active component nickel silicate-derived catalyst. This catalyst possesses a large specific surface area, good dispersibility, strong metal-support interaction, and suitable particle size. Results show that the Ru-doped nickel silicate-derived spherical catalyst 1Ru-10Ni / SiO2 can achieve a high space velocity (30000 mL / day). NH3 (g cat *h) -1 At 650℃, the ammonia conversion rate reached 98%. In the stability test, the ammonia conversion rate of the comparative example 1Ru / SiO2-IW decreased rapidly with the extension of reaction time, indicating rapid catalyst deactivation. However, the 1Ru-10Ni / SiO2 catalyst operated stably at 600℃ for 165 hours with almost no decrease in ammonia conversion rate, indicating that the catalyst did not deactivate within 165 hours and exhibited excellent stability. The application of ammonia decomposition catalysts is largely limited by catalyst stability. The nickel silicate-derived spherical catalyst prepared in this invention possesses both good ammonia decomposition performance and excellent stability, making it worthy of further research. Attached Figure Description

[0033] Figure 1The images show the XRD patterns of the nickel silicate-derived spherical catalysts and the comparative catalysts obtained in Examples 1 and 2.

[0034] Figure 2 The ammonia decomposition conversion curves are shown for the nickel silicate-derived spherical catalysts and comparative catalysts obtained in Examples 1 and 2.

[0035] Figure 3 The results show the stability test results of the nickel silicate-derived spherical catalysts and comparative catalysts obtained in Examples 1 and 2.

[0036] Figure 4 Figure 1 shows TEM images of the nickel silicate-derived spherical catalysts obtained in Examples 1 and 2. Figure 4 (a) is a TEM image of the Ru-doped nickel silicate-derived spherical catalyst obtained in Example 2. Figure 4 (b) is a TEM image of the nickel silicate-derived spherical catalyst obtained in Example 1; Figure 4 (c) is a TEM image of the nickel silicate-derived catalyst obtained in Example 1. Detailed Implementation

[0037] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified.

[0038] The following detailed description of the nickel silicate-derived spherical catalyst, preparation method, and application provided by the present invention, with reference to specific examples, should not be construed as limiting the scope of protection of the present invention.

[0039] The application of the nickel silicate-derived spherical catalyst in the ammonia decomposition hydrogen production system includes the following steps:

[0040] The ammonia decomposition reaction was carried out in a fixed-bed reactor connected to an online gas chromatograph. First, 60 mg of a 40-60 mesh catalyst was weighed and packed into a quartz tube. Then, H2 was introduced at a rate of 20 mL / min. The bed temperature was increased to 550 °C (for nickel silicate-derived spherical catalysts) or 450 °C (for comparative catalysts) at a rate of 5 °C / min and held for 1 h for in-situ reduction. Subsequently, NH3 at a rate of 30 mL / min and Ar at a rate of 10 mL / min were introduced, and the ammonia decomposition reaction was carried out at 300-650 °C with a heating rate of 5 °C / min and a temperature gradient of 50 °C. Each temperature point was held for 1 h, and the space velocity was 30,000 mL / min. NH3 (g cat *h) -1 .

[0041] Stability tests were conducted at 600 °C with 30 mL / min NH3 and 10 mL / min Ar, a heating rate of 5 °C / min, and a space velocity of 30,000 mL / min. NH3 (g cat *h) -1 .

[0042] In this invention, the nickel silicate is Ni3Si4O 10 (OH)2.5H2O.

[0043] Example 1

[0044] 10Ni / SiO2

[0045] 14 g of tetraethyl orthosilicate (TEOS) was mixed thoroughly with 150 mL of anhydrous ethanol and 10 mL of deionized water, and stirred for 20 min. Then, 7.5 mL of 25-28 wt% NH3·H2O was added dropwise to the solution, and stirring was continued for 12 h. The resulting suspension was centrifuged, and the solid was washed twice with anhydrous ethanol and deionized water, respectively, and dried at 120 °C for 24 h to obtain silica. 1 g of SiO2, 1 g of CTAB, 0.55 g of Ni(NO3)2·6H2O, 6 g of NH3·H2O (25-28 wt%), and 45 g of deionized water were mixed and stirred for 2 h. The mixture was then transferred to a high-pressure reactor, sealed, and placed in an oven at 180 °C for 24 h. The solid obtained by centrifugation was washed twice, successively with anhydrous ethanol and deionized water, dried at 120°C for 24 h, and then calcined at 550°C for 4 h to obtain the nickel silicate-derived spherical catalyst 10Ni / SiO2. (The theoretical Ni content is 10 wt%)

[0046] The catalyst 10Ni / SiO2 was used for the ammonia decomposition reaction, and the results are as follows: Figure 2 At 30 mL / min NH3 and 10 mL / min Ar, the space velocity was 30000 mL. NH3 (g cat *h) -1 At 650℃, the conversion rate of ammonia is 98%; for example... Figure 3 In the 165h stability test, the conversion rate of ammonia corresponding to 10Ni / SiO2 decreased from 68% to 61%.

[0047] like Figure 1 As shown, Ni3Si4O is present in 10Ni / SiO2. 10The diffraction peaks of (OH)₂·5H₂O indicate that nickel silicate has been successfully formed. Meanwhile, the intensity of the diffraction peaks in 10Ni / SiO₂ is significantly weaker than that of the catalyst obtained in the comparative example, indicating that the Ni particles in the catalyst are small in size and well-dispersed. Figure 4 (b) Figure 4 As can be seen in (c), 10Ni / SiO2 still maintains a spherical morphology, and metal particles can be seen on the surface.

[0048] Table 1

[0049]

[0050] Table 1 shows the specific surface area, average pore size, average particle size, metal dispersion, and Ni content of the nickel silicate-derived spherical catalyst and the comparative catalyst before and after the ammonia decomposition reaction. 0 with Ni 2+ Content ratio data. The catalyst after the reaction is suffixed with "-used". For example, if the catalyst of Example 1 is loaded into a reaction tube and subjected to an ammonia decomposition reaction at 300-650°C, the catalyst after the reaction is 10Ni / SiO2-used. Other catalysts are similarly derivable.

[0051] Table 1 shows that the average particle size of 10Ni / SiO2 is 2.73 nm, which is much smaller than that of the comparative 10Ni / SiO2-IW (with an average particle size of 17.54 nm). Furthermore, the dispersion of 10Ni / SiO2 is higher at 29.97%, compared to 7.83% for 10Ni / SiO2-IW, consistent with the XRD results. Table 1 also shows that the specific surface area of ​​10Ni / SiO2 is 129.34 m². 2 / g, which is much larger than that of the 10Ni / SiO2-IW obtained in the comparative example (whose specific surface area is 10.52m²). 2 The presence of Ni / g indicates that 10Ni / SiO2 has a higher proportion of mesoporous structures (average pore size greater than 2 nm, less than 50 nm is considered mesoporous). This provides more space for the ammonia decomposition reaction, and the larger specific surface area also contributes to improved metal dispersion, thereby enhancing the catalyst's catalytic activity. Table 1 also shows that Ni in 10Ni / SiO2... 0 / Ni 2+ The value is less than 1Ru-10Ni / SiO2-IW, indicating the existence of interaction forces between Ni and the support, making Ni species difficult to reduce; and the Ni content in 10Ni / SiO2 before the reaction is less than 1Ru-10Ni / SiO2. 0 / Ni 2+ The value was 0.53 initially, but increased to 0.58 after the reaction, indicating that the Ni species in nickel silicates could be further reduced to Ni during the reaction. 0 This leads to Ni 0 With increased content, Ni 0 / Ni 2+ The particle size of the catalyst obtained in the comparative example increased after the reaction, while the particle size of 10Ni / SiO2 only increased by 0.22 nm. This is because the strong interaction between the metal and the support inhibited the agglomeration of Ni particles at high temperatures, thereby enhancing the stability of the catalyst.

[0052] Example 2

[0053] 1Ru-10Ni / SiO2

[0054] 0.04 g RuCl3 was dissolved in 1.2 mL of deionized water, and 1 g of 10Ni / SiO2 obtained in Example 1 was added to the above solution. The mixture was left to stand at room temperature for 12 h. Subsequently, it was dried in an oven at 50 °C for 6 h, and the resulting solid was calcined at 500 °C for 2 h under a hydrogen atmosphere to obtain the Ru-doped nickel silicate-derived spherical catalyst 1Ru-10Ni / SiO2.

[0055] The catalyst 1Ru-10Ni / SiO2 was used for the ammonia decomposition reaction, and the results are as follows: Figure 2 At 30 mL / min NH3 and 10 mL / min Ar, the space velocity was 30000 mL. NH3 (g cat *h) -1 At 650℃, the conversion rate of ammonia is 98%; for example... Figure 3 In the 165h stability test, the conversion rate of ammonia corresponding to 1Ru-10Ni / SiO2 hardly decreased.

[0056] like Figure 1 As shown, Ni3Si4O appeared in 1Ru-10Ni / SiO2. 10 The diffraction peaks of (OH)₂·5H₂O indicate that nickel silicate has been successfully formed. Meanwhile, no Ru species diffraction peaks were observed in 1Ru-10Ni / SiO₂, and the intensity of the Ni species diffraction peaks was significantly weaker than that of the catalyst obtained in the comparative example, indicating that the average size of Ru and Ni particles in the catalyst is small and their dispersion is good. Figure 4 As can be seen, 1Ru-10Ni / SiO2 still maintains a spherical morphology. Table 1 shows that the average particle size of 1Ru-10Ni / SiO2 is 2.88 nm, much smaller than that of the comparative examples 1Ru-10Ni / SiO2-IW and 1Ru / SiO2-IW (with average particle sizes of 15.87 and 11.03 nm, respectively); and 1Ru-10Ni / SiO2 has the highest dispersion at 31.58%, while 1Ru-10Ni / SiO2-IW has 8.77% and 1Ru / SiO2-IW has 14.27%. Table 1 also shows that the specific surface area of ​​1Ru-10Ni / SiO2 is 124.57 m². 2 / g, which is much larger than that of 1Ru-10Ni / SiO2-IW and 1Ru / SiO2-IW obtained in the comparative example (whose specific surface areas are 11.25 and 13.47 m², respectively). 2 The presence of Ni (g) indicates that 1Ru-10Ni / SiO2 has a higher proportion of mesoporous structures. Table 1 also shows that Ni in 1Ru-10Ni / SiO2... 0 / Ni 2+ The value was 0.56, less than the 2.83 of 1Ru-10Ni / SiO2-IW, indicating that there is an interaction force between Ni and the support in 1Ru-10Ni / SiO2, making Ni species difficult to reduce. The Ni content in 1Ru-10Ni / SiO2 after the reaction was... 0 / Ni 2+ The value increased to 1.02, indicating that the Ni species in nickel silicate can be further reduced to Ni during the reaction. 0 This leads to Ni 0 With increased content, Ni 0 / Ni 2+ The particle size of 1Ru-10Ni / SiO2 increased almost completely after the reaction. This is because the strong interaction between the metal and the support inhibited the agglomeration of Ru and Ni particles at high temperatures, thereby enhancing the stability of the catalyst.

[0057] Comparative Example 1

[0058] 1Ru / SiO2-IW

[0059] 0.04 g RuCl3 was dissolved in 0.8 mL of deionized water, and 1 g of the silica obtained in Example 1 was added to the above solution. The solution was left to stand at room temperature for 12 h. Then it was dried in an oven at 50 °C for 6 h, and the resulting solid was calcined at 500 °C for 2 h to obtain 1Ru / SiO2-IW.

[0060] The catalyst 1Ru / SiO2-IW was used for the ammonia decomposition reaction, and the results are as follows: Figure 2 At 30 mL / min NH3 and 10 mL / min Ar, the space velocity was 30000 mL. NH3 (g cat *h) -1 The ammonia conversion rate at 650℃ is 99%; stability test results are as follows. Figure 3 During the 115-hour stability test, the ammonia conversion rate continued to decrease, dropping from 97% to 55%.

[0061] Comparative Example 2

[0062] 10Ni / SiO2-IW

[0063] 0.55 g of Ni(NO3)2·6H2O was dissolved in 0.8 mL of deionized water. 1 g of the silicon dioxide obtained in Example 1 was added to the above solution and left to stand at room temperature for 12 h. Subsequently, it was dried in an oven at 50 °C for 6 h, and the resulting solid was calcined at 500 °C for 2 h to obtain 10Ni / SiO2-IW.

[0064] The catalyst 10Ni / SiO2-IW was used for the ammonia decomposition reaction, and the results are as follows: Figure 2 At 30 mL / min NH3 and 10 mL / min Ar, the space velocity was 30000 mL. NH3 (g cat *h) -1 The conversion rate of ammonia at 650℃ is 88%.

[0065] Comparative Example 3

[0066] 1Ru-10Ni / SiO2-IW

[0067] 0.04 g RuCl3 was dissolved in 0.8 mL of deionized water. 1 g of 10Ni / SiO2-IW obtained from Comparative Example 2 was added to the above solution and left to stand at room temperature for 12 h. Subsequently, it was dried in an oven at 50 °C for 6 h, and the resulting solid was calcined at 500 °C for 2 h to obtain 1Ru-10Ni / SiO2-IW.

[0068] The catalyst 1Ru-10Ni / SiO2-IW was used for the ammonia decomposition reaction, and the results are as follows: Figure 2 At 30 mL / min NH3 and 10 mL / min Ar, the space velocity was 30000 mL. NH3 (g cat *h) -1 The conversion rate of ammonia at 650℃ is 88%.

[0069] The carriers in Comparative Examples 1-3 were non-porous spherical silica with a specific surface area of ​​less than 15 m². 2 / g, its surface has fewer functional groups that can anchor Ru and Ni, and the metal nanoparticles on the catalysts obtained in Comparative Examples 1-3 have a diameter greater than 10nm, while the dispersion of the catalysts is also relatively small. Therefore, the ammonia decomposition activity of the catalysts obtained in Comparative Examples 2 and 3 is poor. Since Ru is the best ammonia decomposition catalyst, the ammonia conversion rate corresponding to 1Ru / SiO2-IW of the catalyst obtained in Comparative Example 1 is still relatively high. The particle size on the catalysts obtained in Comparative Examples 1-3 continues to increase after one ammonia decomposition reaction. The agglomeration of particles at high temperatures will inhibit the ammonia decomposition reaction, such as Figure 3As shown, the ammonia conversion rate of the catalyst 1Ru / SiO2-IW obtained in Comparative Example 1 decreased rapidly with the extension of reaction time. For the catalysts obtained in Examples 1 and 2, the surface of the spherical SiO2 was etched during the hydrothermal process, forming a porous structure and increasing the specific surface area of ​​the catalyst; nickel silicate was successfully generated on the SiO2 surface, and a strong interaction was formed between Ni and Si, improving the metal dispersion; Ru doping increased the number of active sites on the one hand, and also formed an interaction force between Ru and Ni on the other hand, resulting in metal particles with a particle size of less than 3 nm. The larger specific surface area, metal dispersion, suitable metal particle size, and the synergistic effect of the two interaction forces suppressed particle agglomeration at high temperature, improved the ammonia decomposition performance of the catalysts obtained in Examples 1 and 2, and made the ammonia conversion rate of the catalyst basically stable during the 165h ammonia decomposition test.

[0070] Example 3

[0071] First, SiO2 was prepared, with other steps the same as in Example 1, except that the TEOS hydrolysis time was changed from 12h to 10h. After obtaining SiO2, it was mixed with CTAB, Ni(NO3)2·6H2O, NH3·H2O, and deionized water for hydrothermal treatment, with other steps the same as in Example 1, except that the hydrothermal treatment time was changed from 24h to 36h. The catalyst of Example 3 was obtained through these steps. The performance of the obtained catalyst was similar to that of Example 1.

[0072] Example 4

[0073] The other steps are the same as in Example 2, except that the amount of RuCl3 is replaced from 0.04 g to 0.06 g, thus obtaining the catalyst of Example 4. The obtained material was used for ammonia decomposition reaction at 30 mL / min NH3 and 10 mL / min Ar, with a space velocity of 30000 mL. NH3 (g cat *h) -1 The conversion rate of ammonia at 650℃ is 97%.

[0074] Example 5

[0075] The other steps are the same as in Example 2, except that the amount of RuCl3 is replaced from 0.04 g to 0.02 g, thus obtaining the catalyst of Example 5. The obtained material was used for ammonia decomposition reaction at 30 mL / min NH3 and 10 mL / min Ar, with a space velocity of 30000 mL. NH3 (g cat *h) -1 The conversion rate of ammonia at 650℃ is 97%.

[0076] Example 6

[0077] The other steps are the same as in Example 2, except that the treatment temperature in hydrogen is changed from 500°C to 450°C, thus obtaining the catalyst of Example 6. The obtained material was used for ammonia decomposition reaction at 30 mL / min NH3 and 10 mL / min Ar, with a space velocity of 30000 mL / min. NH3 (g cat *h) -1 The conversion rate of ammonia is 99% at 650℃.

[0078] Example 7

[0079] The other steps are the same as in Example 2, except that the treatment temperature in hydrogen is changed from 500°C to 550°C, thus obtaining the catalyst of Example 7. The obtained material was used for ammonia decomposition reaction at 30 mL / min NH3 and 10 mL / min Ar, with a space velocity of 30000 mL / min. NH3 (g cat *h) -1 The conversion rate of ammonia at 650℃ is 98%.

[0080] The present invention has been described in detail above with specific embodiments. Obviously, the described examples are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0081] Matters not covered in this invention are common knowledge.

Claims

1. An application of a Ru-doped nickel silicate-derived spherical catalyst for the catalytic decomposition of ammonia to produce hydrogen and nitrogen, characterized in that Ru... The doped nickel silicate-derived spherical catalyst consists of two parts: a support and an active component. Its support is nickel silicate coated silica, and the active components are Ru and Ni, with the active components accounting for 1-11% of the catalyst by mass; the ratio of Ru to Ni is 1:9-10. The preparation method of the Ru-doped nickel silicate-derived spherical catalyst includes the following steps: (1) Tetraethyl orthosilicate (TEOS) is mixed with anhydrous ethanol and deionized water and stirred at room temperature for 10-20 min. Then, ammonia water is added dropwise to the mixture and stirred continuously for 10-15 h to obtain suspension A; For every 140-150 mL of anhydrous ethanol, add 13-14 g of tetraethyl orthosilicate (TEOS) and 10-12 mL of deionized water, and add 7-7.5 mL of ammonia water dropwise. (2) Centrifuge the suspension A obtained in step (1), wash the solid obtained with anhydrous ethanol and deionized water in sequence, and then dry it to obtain silicon dioxide (SiO2). (3) Mix the SiO2 obtained in step (2) with deionized water, CTAB, Ni(NO3)2.6H2O and ammonia water, and stir for 2-3 h to obtain solution A; The mass ratio of SiO2:deionized water:CTAB:Ni(NO3)2·6H2O:NH3·H2O is 1:40-50:0.8-1:0.54-0.56:5.8-6.

2. (4) Transfer the solution A obtained in step (3) to a high-pressure reactor and keep it at 140-200 °C for 10-36 h; then centrifuge, and wash the obtained solid twice with anhydrous ethanol and deionized water, and then dry it to obtain solid A; (5) The solid A obtained in step (4) is calcined at 250-550 °C for 1-4 h to obtain nickel silicate-derived spherical catalyst A with Ni as the active component; (6) Dissolve RuCl3 in deionized water to obtain solution B; add 0.02-0.06 g of RuCl3 to every 1.0-1.5 mL of deionized water; (7) Add the nickel silicate-derived spherical catalyst A with Ni as the active component obtained in step (5) to solution B, and stir until homogeneous to obtain a moist solid B; wherein, 0.9-1.1 g of catalyst A is added to every 1.2-1.5 mL of solution B; (8) Place the solid B obtained in step (7) at room temperature for 12-24 h, and then dry it in an oven at 40-80 ℃ for 3-6 h to obtain solid C; (9) The solid C obtained in step (8) is treated in a hydrogen atmosphere at 400-600 °C for 1-4 h to obtain Ru-doped nickel silicate-derived spherical catalyst B.

2. The application of the Ru-doped nickel silicate-derived spherical catalyst as described in claim 1 for the catalytic decomposition of ammonia to produce hydrogen and nitrogen, characterized in that, In steps (1) and (3), the concentration of ammonia is 25-28 wt%.

3. The application of the Ru-doped nickel silicate-derived spherical catalyst as described in claim 1 for the catalytic decomposition of ammonia to produce hydrogen and nitrogen, characterized in that, The drying in steps (2) and (4) is to dry at 60-120 °C for 6-24 h.

4. The application of the Ru-doped nickel silicate-derived spherical catalyst as described in claim 1 for the catalytic decomposition of ammonia to produce hydrogen and nitrogen, characterized in that, The process includes the following steps: NH3 and Ar are introduced into a fixed-bed reactor containing a Ru-doped nickel silicate-derived spherical catalyst, and the reaction is carried out at atmospheric pressure and 300-650 °C to produce hydrogen and nitrogen; the space velocity is 6000-120000 mL / min. NH3 (g) cat *h) -1 .

Images