An ammonia decomposition monolithic nickel-based catalyst, a preparation method thereof, a monolithic nickel-based catalyst precursor, and an ammonia decomposition hydrogen production reaction

Abstract

The application relates to an ammonia decomposition monolithic nickel-based catalyst, a preparation method, a monolithic nickel-based catalyst precursor, an ammonia decomposition hydrogen production reaction, and a preparation method of the monolithic nickel-based catalyst. The preparation method comprises the following steps: (1) cleaning foamed nickel with an inorganic acid solution to obtain acid-washed foamed nickel; (2) mixing the acid-washed foamed nickel with water to obtain a solid-liquid mixture; adding an ammonia water solution into the solid-liquid mixture to adjust the pH value to 8-12, and obtaining a solid-liquid mixture with an adjusted pH value; (3) heating the solid-liquid mixture with the adjusted pH value, then adding silicon sol into the mixture in multiple times until nickel silicate precipitates are generated, separating the solid phase, and obtaining a catalyst precursor; and (4) calcining and reducing the catalyst precursor in a reducing atmosphere to obtain a monolithic nickel-based catalyst for ammonia decomposition reaction. The monolithic nickel-based catalyst provided by the application has excellent ammonia decomposition reaction catalytic activity, can catalyze the complete conversion of ammonia at 500 DEG C, and has good stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ammonia decomposition hydrogen production, and particularly relates to a whole type nickel-based catalyst for ammonia decomposition, a preparation method thereof, a whole type nickel-based catalyst precursor and an ammonia decomposition hydrogen production reaction. BACKGROUND

[0002] Ammonia is a potential hydrogen carrier, which has high hydrogen density (about 17.7wt%), low price and CO x / NO x zero emission advantages. In addition, ammonia can be liquefied at room temperature and about 10 bar, which makes it easy to transport, store and separate, and can well make up for the storage and transportation problems of hydrogen. Since the ammonia molecule only contains nitrogen and hydrogen elements, the generation of carbon oxides (such as CO) can be avoided, so that it becomes an ideal choice for fuel cell hydrogen source.

[0003] Ammonia decomposition hydrogen production is widely concerned as a potential large-scale application of hydrogen production. However, at present, only noble metal (Ru) based catalysts have relatively satisfactory ammonia decomposition catalytic performance, and the high cost of which largely limits the real industrialization of ammonia decomposition hydrogen production reaction. Nickel-based catalysts also have high ammonia decomposition catalytic activity, but if these catalysts in the laboratory are really applied to large-scale, industrialized ammonia decomposition hydrogen production equipment, there will be various problems. For example, the stability problem of the catalyst, the forming problem, the heat transfer efficiency problem and the like. At present, a large number of researches expect to replace noble metal ruthenium with non-noble metal nickel to be applied to catalytic ammonia decomposition reaction, although significant progress has been made, but there are still some obvious shortcomings, for example: (1) the catalytic activity of nickel-based catalyst is not high enough, and a reaction temperature higher than 600 DEG C is usually required to achieve complete conversion of ammonia; (2) the stability of nickel-based catalyst needs to be strengthened, and the catalyst is easy to be deactivated; (3) the forming of the catalyst still has a big problem, and at present, the mechanical forming is mainly used, which not only makes a large amount of catalyst be embedded to reduce the catalytic activity, but also the poor heat conductivity of the formed catalyst will also cause the reduction of the catalytic performance.

[0004] Therefore, how to prepare a nickel-based catalyst with stable catalytic activity and high ammonia decomposition catalytic activity, and how to solve the forming and heat transfer problems encountered in the industrialization process of the catalyst are the technical problems to be solved at present. SUMMARY

[0005] The present application provides a whole type nickel-based catalyst for ammonia decomposition, a preparation method thereof, a whole type nickel-based catalyst precursor and an ammonia decomposition hydrogen production reaction, and aims to prepare a nickel-based catalyst with stable catalytic activity and high ammonia decomposition catalytic activity, so as to better catalyze the decomposition of ammonia to produce hydrogen.

[0006] In a first aspect, the present application relates to a preparation method of a monolithic nickel-based catalyst for ammonia decomposition reaction, comprising the following steps:

[0007] (1) washing the foamed nickel with an inorganic acid solution to obtain acid-washed foamed nickel;

[0008] (2) mixing the acid-washed foamed nickel with water to obtain a solid-liquid mixture; adding an aqueous ammonia solution to the solid-liquid mixture to adjust the pH value to 8-12 to obtain a solid-liquid mixture with adjusted pH value;

[0009] (3) heating the solid-liquid mixture with adjusted pH value, then adding silicon sol dropwise in multiple times until nickel silicate precipitates are formed, and separating the solid phase to obtain a catalyst precursor;

[0010] (4) calcining and reducing the catalyst precursor in a reducing atmosphere to obtain the monolithic nickel-based catalyst for ammonia decomposition reaction.

[0011] In a second aspect, the present application relates to a monolithic nickel-based catalyst precursor for ammonia decomposition reaction, comprising foamed nickel and nickel silicate grown on the foamed nickel, and the mass ratio of the foamed nickel and the nickel silicate grown thereon is (5-15): 1.

[0012] Preferably, the preparation method of the monolithic nickel-based catalyst precursor comprises the following steps:

[0013] (1) washing the foamed nickel with an inorganic acid solution to obtain acid-washed foamed nickel;

[0014] (2) mixing the acid-washed foamed nickel with water to obtain a solid-liquid mixture; adding an aqueous ammonia solution to the solid-liquid mixture to adjust the pH value to 8-12 to obtain a solid-liquid mixture with adjusted pH value;

[0015] (3) heating the solid-liquid mixture with adjusted pH value, then adding silicon sol dropwise in multiple times until nickel silicate precipitates are formed, and separating the solid phase to obtain the monolithic nickel-based catalyst precursor.

[0016] In a third aspect, the present application relates to a monolithic nickel-based catalyst for ammonia decomposition reaction, which is prepared by calcining the monolithic nickel-based catalyst precursor of the second aspect in a reducing atmosphere to reduce part of the nickel silicate to metallic nickel and silicon dioxide.

[0017] Preferably, the monolithic nickel-based catalyst comprises foamed nickel and metallic nickel nanoparticles, silicon dioxide and residual nickel silicate grown on the foamed nickel; wherein the metallic nickel nanoparticles and silicon dioxide grown on the foamed nickel are obtained by partial calcination and reduction of the initial nickel silicate, and the mass ratio of the foamed nickel and the initial nickel silicate is (5-15): 1.

[0018] The metal nickel nanoparticles grown on the nickel foam have a particle size of 2-4.5 nm.

[0019] In a fourth aspect, the present application relates to a hydrogen production reaction by ammonia decomposition, which comprises contacting ammonia with the monolithic nickel-based catalyst for ammonia decomposition reaction prepared by the preparation method of the first aspect or the monolithic nickel-based catalyst of the third aspect to perform the ammonia decomposition reaction.

[0020] Advantages:

[0021] (1) The monolithic nickel-based catalyst of the present application exhibits excellent catalytic activity for ammonia decomposition reaction;

[0022] (2) The monolithic nickel-based catalyst of the present application can catalyze the complete conversion (about 98%) of ammonia at a relatively low temperature of 500℃;

[0023] (3) The monolithic nickel-based catalyst of the present application has excellent high-temperature catalytic stability: the activity of the monolithic nickel-based catalyst remains basically unchanged after the stability test at 450℃ for 300 min;

[0024] (4) The monolithic nickel-based catalyst of the present application has excellent high-temperature recyclability: the monolithic nickel-based catalyst does not show obvious deactivation after the low-temperature (200℃) to high-temperature (600℃) cycle test for 5 cycles;

[0025] (5) The monolithic nickel-based catalyst of the present application does not need to be subjected to a catalyst molding process, and can be directly placed in a reactor for reaction, which can effectively solve the problems of catalyst molding and heat transfer, and has great industrialization potential;

[0026] (6) The monolithic nickel-based catalyst precursor of the present application can be calcined and reduced in a reducing atmosphere to prepare the monolithic nickel-based catalyst with excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an SEM photograph of the raw material nickel foam used in Example 1;

[0028] Figure 2 and Figure 3 is an SEM photograph of the target catalyst prepared in Example 1;

[0029] Figure 4 is an XRD diffractogram of the nickel-based catalyst precursor and the target catalyst prepared in Example 1;

[0030] Figure 5 and Figure 6 is a TEM photograph of the nickel-based catalyst precursor and the target catalyst prepared in Example 1;

[0031] Figure 7 is a particle size histogram of the metal nickel nanoparticles in the target catalyst prepared in Example 1;

[0032] Figure 8 is an ammonia conversion-temperature graph of the target catalyst prepared in Example 1, the control samples prepared in Comparative Examples 1 to 4;

[0033] Figure 9 is a structural schematic diagram of a self-designed reactor used in Test Examples 4 to 6;

[0034] Figure 10 is an ammonia conversion-time graph of the target catalyst prepared in Example 1 at 450°C for 300 min;

[0035] Figure 11 is an ammonia conversion-temperature graph of the target catalyst prepared in Example 1 in a cyclic test at 200 to 600°C;

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] 1 hot plate, 2 graphite pad, 3 heating rod, 4 temperature control rod, 5 catalyst, 6 air hole. DETAILED DESCRIPTION

[0038] The present application will be further described by the accompanying drawings and examples. The features and advantages of the present application will become more apparent from the following description in conjunction with the accompanying drawings.

[0039] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. Although various aspects of an implementation can be described in the drawings, it is not necessarily drawn to scale nor to precise proportions. In general, the drawings are intended to illustrate the aspects of an implementation, rather than to limit its scope.

[0040] Furthermore, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0041] In a first aspect, the present application relates to a preparation method of a bulk nickel-based catalyst for ammonia decomposition reaction, the preparation method comprising the following steps:

[0042] (1) washing a foamed nickel with an inorganic acid solution to obtain an acid-washed foamed nickel;

[0043] (2) mixing the acid-washed foamed nickel with water to obtain a solid-liquid mixture; adding an aqueous ammonia solution to the solid-liquid mixture to adjust the pH value to 8 to 12 to obtain a solid-liquid mixture after pH value adjustment;

[0044] (3) heating the solid-liquid mixture after pH value adjustment, then adding a silica sol dropwise in multiple times to generate nickel silicate precipitation, separating out the solid phase to obtain a catalyst precursor;

[0045] (4) calcining and reducing the catalyst precursor in a reducing atmosphere to obtain the monolithic nickel-based catalyst for ammonia decomposition reaction.

[0046] It is to be noted that the inventors of the present application have found in the process of years of research and development that foamed nickel has the advantages of light weight, good thermal conductivity and high mechanical strength. If a high-performance nickel-based catalyst system can be grown in situ on the surface of foamed nickel, not only the performance of the catalyst can be maintained, but also the problems of molding and heat transfer encountered in the industrialization of the catalyst can be further solved, which will play a certain role in promoting the large-scale industrialization of ammonia decomposition reaction and even the development and utilization of hydrogen energy. The preparation method of the present application uses foamed nickel as the nickel source to grow a nickel-based catalyst in situ. The nickel-based catalyst is firmly and uniformly grown. The nickel-based catalyst and the foamed nickel form a monolithic nickel-based catalyst which has been molded and can be directly placed in a reactor for hydrogen production reaction without further catalyst molding.

[0047] It is to be noted that in the preparation method of the present application, the foamed nickel after acid washing is subjected to the subsequent steps through the cleaning step of the inorganic acid solution in step (1), so that the nickel-based catalyst can be firmly grown; the pH value of the solid-liquid mixture is adjusted to 8-12 in step (2); in step (3), the silica sol is added dropwise to the solid-liquid mixture with adjusted pH value for multiple times until light green precipitate appears (i.e. until nickel silicate precipitate is formed), and the solid phase obtained by solid-liquid separation is the catalyst precursor; then the catalyst precursor is calcined and reduced in a reducing atmosphere in step (4) to obtain the target catalyst, i.e. the monolithic nickel-based catalyst. Through steps (1)-(3), the raw material foamed nickel is partially converted into nickel silicate and grown on the remaining foamed nickel. At this time, the catalyst precursor obtained includes the remaining foamed nickel and the nickel silicate grown thereon. Through the calcination and reduction in step (4), part of the nickel silicate is replaced by metallic nickel and silicon dioxide, which grows on the foamed nickel together with the remaining nickel silicate. At this time, the monolithic nickel-based catalyst obtained includes the remaining foamed nickel, metallic nickel nanoparticles, silicon dioxide and the remaining nickel silicate. In terms of structure, the metallic nickel forms the core in the inside, and the silicon dioxide and the remaining nickel silicate form the shell outside the metallic nickel nanoparticles. Therefore, in the monolithic nickel-based catalyst, the active part grown on the foamed nickel forms a core-shell structure.

[0048] The monolithic nickel-based catalyst prepared through the above steps (1)-(4) can exhibit high catalytic activity at a relatively low temperature (such as 500℃) when used for catalyzing the ammonia decomposition reaction for hydrogen production, and has excellent stability.

[0049] According to a specific embodiment of the preparation method according to the first aspect of the present application, in step (1),

[0050] The inorganic acid solution is a hydrochloric acid solution, and the molar concentration of the hydrochloric acid solution is 0.05-0.2M, preferably 0.10-0.15M; and / or,

[0051] The number of times of cleaning with the inorganic acid solution is 3-7 times.

[0052] It should be noted that the acid-washed foamed nickel obtained by cleaning with the hydrochloric acid solution having the above-mentioned concentration for 3-7 times is subjected to subsequent steps, so that the nickel-based catalyst can be more firmly and uniformly grown on the surface of the foamed nickel, and an integral nickel-based catalyst having better stability and ammonia decomposition catalytic activity is obtained.

[0053] According to another specific embodiment of the preparation method according to the first aspect of the present application, in step (2), the solid-liquid mass ratio when the acid-washed foamed nickel is mixed with water is (1-3):10; and / or,

[0054] The mass concentration of the ammonia water solution is 20%-40%, preferably 25%-28%.

[0055] It should be noted that the water mixed with the acid-washed foamed nickel can be ultrapure water, and the acid-washed foamed nickel is mixed with water according to the above-mentioned ratio, and such a dispersion system is subjected to subsequent steps, so that the nickel-based catalyst can be more uniformly grown on the surface of the foamed nickel. The pH value of the solid-liquid mixture is adjusted by using the ammonia water solution having the above-mentioned concentration, and then subsequent steps are performed, which is beneficial to further improve the performance of the catalyst.

[0056] According to one specific embodiment of the preparation method according to the first aspect of the present application, in step (2), the pH value of the solid-liquid mixture is adjusted to 9-10 by adding an ammonia water solution.

[0057] It should be noted that, as a preferred embodiment, the pH value of the solid-liquid mixture is adjusted to 9-10, and then the silica sol is added dropwise in multiple times, which is beneficial to further improve the stability of the prepared integral nickel-based catalyst and the catalytic activity of the ammonia decomposition reaction.

[0058] According to one specific embodiment of the preparation method according to the first aspect of the present application, the preparation method further comprises the following step between step (2) and step (3):

[0059] The solid-liquid mixture after the pH value is adjusted is subjected to ultrasonic immersion for 15min-1h.

[0060] It should be noted that, as a preferred embodiment, the solid-liquid mixture after adjusting the pH value is ultrasonically soaked for 15 min to 1 h, and then the heating and the multiple dropping of the silica sol in step (3) are performed, so that the silica sol is more firmly and uniformly grown on the surface of the foamed nickel as nickel silicate, and then the integral type nickel-based catalyst with uniform growth and firm connection is prepared through the roasting reduction in step (4), and the stability and the catalytic activity of the ammonia decomposition reaction are further improved.

[0061] According to a specific embodiment of the preparation method in the first aspect of the present application, in step (3), the solid-liquid mixture after adjusting the pH value is heated to a temperature of 50-90°C, preferably 60-80°C.

[0062] It should be noted that the heating can be performed by using a water bath or the like, and the silica sol is more uniformly and firmly grown on the surface of the foamed nickel by heating to the above-mentioned temperature and then dropping the silica sol in multiple times, so that the target catalyst with excellent performance is prepared.

[0063] According to a specific embodiment of the preparation method in the first aspect of the present application, in step (3), the silica sol is dropped in 2-5 times.

[0064] It should be noted that the uniform growth of the catalyst of the present application has an important influence on the catalytic activity and stability, and the present inventors have found through long-term research and development experiments that if the total amount of the silica sol is added at one time, the uniform growth of the nickel silicate on the surface of the foamed nickel is poor, and the stability and the ammonia decomposition reaction activity of the target catalyst obtained finally are adversely affected; therefore, the silica sol is dropped in multiple times in step (3), and preferably the total amount of the silica sol can be dropped in 3 times or 4 times, and the amount dropped each time can be equal, so that the nickel silicate is uniformly grown on the surface of the foamed nickel and is dense, and then the stability and the catalytic activity of the ammonia decomposition reaction of the integral type nickel-based catalyst obtained through the subsequent steps are more excellent.

[0065] According to a specific embodiment of the preparation method in the first aspect of the present application, in step (3),

[0066] The solid content of the silica sol is 30%-50%, and the particle size of the silicon dioxide contained in the silica sol is 10-30 nm; and / or,

[0067] The molar ratio of the foamed nickel to the silicon dioxide in the added silica sol is (5-20):1; and / or,

[0068] After the solid phase is separated, it is washed and dried to obtain the catalyst precursor.

[0069] It should be noted that, as a preferred embodiment, the silica sol with the above-mentioned solid content and particle size is selected, the connection between the nickel silicate grown through step (3) and the foamed nickel is stable, and after the roasting reduction of step (4), the formed monolithic nickel-based catalyst has uniform and firm connection between the nickel silicate, nickel nanoparticles, amorphous silicon dioxide and the foamed nickel, and has excellent catalytic activity and stability when used for catalyzing the ammonia decomposition reaction. When the silica sol is specifically Ludox HS-40, the amount can be 0.5-3 mL, preferably 0.5-1.5 mL. After the solid phase is separated, it can be washed with ultrapure water for 5 times and placed in a vacuum drying box for drying for 12 h, to obtain the catalyst precursor with the nickel silicate grown on the surface of the residual foamed nickel.

[0070] According to a specific embodiment of the preparation method of the first aspect of the present application, in step (4), the reducing atmosphere comprises hydrogen and inert gas, and the proportion of hydrogen in the total volume of the reducing atmosphere is 5%-40%;

[0071] Preferably, the inert gas is selected from argon and / or nitrogen.

[0072] It should be noted that, under the above-mentioned reducing atmosphere, the roasting reduction can convert part of the nickel silicate in the catalyst precursor into nickel, and the obtained target catalyst has a suitable amount of nickel silicate and nickel, and has better catalytic activity and stability when used for catalyzing the ammonia decomposition reaction to produce hydrogen.

[0073] According to a specific embodiment of the preparation method of the first aspect of the present application, in step (4), the temperature of the roasting reduction is 300-600℃, the time is 1-4 h, and the temperature rising speed is 5-20℃·min -1 ; preferably, the temperature is 400-500℃, the time is 2-3 h, and the temperature rising speed is 7-13℃·min -1 .

[0074] It should be noted that, under the above-mentioned temperature, time and temperature rising speed, the nickel silicate in the catalyst precursor is converted into nickel at a suitable ratio, and the prepared target catalyst has further improved catalytic activity and stability when used for catalyzing the ammonia decomposition reaction to produce hydrogen.

[0075] Secondly, the present application relates to a monolithic nickel-based catalyst precursor for ammonia decomposition reaction, which comprises foamed nickel and nickel silicate grown on the foamed nickel, and the mass ratio of the foamed nickel and the nickel silicate grown thereon is (5-15):1.

[0076] Preferably, the preparation method of the monolithic nickel-based catalyst precursor comprises the following steps:

[0077] (1) washing the foamed nickel with an inorganic acid solution to obtain acid-washed foamed nickel;

[0078] (2) mixing the acid-washed foamed nickel with water to obtain a solid-liquid mixture; adding an aqueous ammonia solution to the solid-liquid mixture to adjust the pH value to 8-12 to obtain a solid-liquid mixture with adjusted pH value;

[0079] (3) heating the solid-liquid mixture with adjusted pH value, then adding silicon sol dropwise in multiple times until nickel silicate precipitates are formed, and separating the solid phase to obtain the monolithic nickel-based catalyst precursor.

[0080] In a third aspect, a monolithic nickel-based catalyst for ammonia decomposition reaction is prepared by calcining the monolithic nickel-based catalyst precursor of the second aspect in a reducing atmosphere to reduce part of the nickel silicate to metallic nickel and silicon dioxide.

[0081] Preferably, the monolithic nickel-based catalyst comprises foamed nickel and metallic nickel nanoparticles, silicon dioxide and residual nickel silicate grown on the foamed nickel; wherein the metallic nickel nanoparticles and silicon dioxide grown on the foamed nickel are obtained by partial calcination and reduction of the initial nickel silicate, the mass ratio of the foamed nickel to the initial nickel silicate is (5-15):1, and the particle size of the metallic nickel nanoparticles grown on the foamed nickel is 2-4.5 nm.

[0082] In a fourth aspect, the present application relates to a hydrogen production reaction by ammonia decomposition, which comprises contacting ammonia with the monolithic nickel-based catalyst for ammonia decomposition reaction prepared by the preparation method of the first aspect or the monolithic nickel-based catalyst of the third aspect.

[0083] It should be noted that the monolithic nickel-based catalyst for ammonia decomposition reaction prepared by the preparation method of the first aspect or the monolithic nickel-based catalyst of the third aspect exhibits excellent catalytic activity, stability and high and low temperature recyclability in the catalytic decomposition reaction of ammonia to produce hydrogen.

[0084] It should be noted that in the preparation method of the monolithic nickel-based catalyst for ammonia decomposition reaction, the monolithic nickel-based catalyst precursor for ammonia decomposition reaction or the monolithic nickel-based catalyst for ammonia decomposition reaction, the chemical formula of the nickel silicate can be represented as Ni3Si2O5(OH)4.

[0085] It should be noted that the monolithic nickel-based catalyst of the third aspect can be prepared by the preparation method of the monolithic nickel-based catalyst for ammonia decomposition reaction of the first aspect. In the preparation method of the monolithic nickel-based catalyst for ammonia decomposition reaction of the first aspect, the materials, reaction conditions and the like for preparing the catalyst precursor are applicable to the preparation process of the monolithic nickel-based catalyst precursor for ammonia decomposition reaction of the second aspect.

[0086] The present application is further illustrated in detail by the following examples, but is not limited to the present application. In the following examples, the experimental instruments and raw materials involved are commercially available products, unless otherwise specified. The silica sol Ludox HS-40 used in the following examples was purchased from Shanghai Shuanglun Industry Co., Ltd., with a solid content of 40%, a density of 1.3 g / mL, and a particle size of 12 nm of the contained silicon dioxide. The foamed nickel was purchased from Tianjin Aivixin Chemical Technology Co., Ltd., with a surface density of 350 g·m -3 , a size of 0.5 mm*200 mm*250 mm, a pore size of 0.1 mm, and a porosity of 97.2%.

[0087] Example 1: Preparation of a monolithic nickel-based catalytic system

[0088] (1) The foamed nickel was cleaned with 0.1 M hydrochloric acid solution for 5 times;

[0089] (2) 10 g of the cleaned foamed nickel was placed in a beaker containing 50 mL of ultrapure water, and an appropriate amount of 25%-28% ammonia water (Guoyao ammonia water 25%-28%) was added to adjust the pH to about 10, and then ultrasonic immersion was performed for 30 min;

[0090] (3) The beaker was placed in a water bath at 80°C, and an appropriate amount of silica sol Ludox HS-40 was added dropwise in three times (0.5 mL each time), until a light green precipitate appeared in the solution (nickel silicate precipitate was formed);

[0091] (4) The foamed nickel (solid phase) was taken out and cleaned with ultrapure water for 5 times, and then placed in a vacuum drying oven for drying for 12 h, to obtain a monolithic structure with a nickel-based catalyst precursor grown thereon (catalyst precursor);

[0092] (5) The catalyst precursor was placed in a H2 / Ar (v / v=1 / 3) atmosphere for reduction (reduction conditions: 10°C min -1 , 450°C, 2 h), to obtain the target catalyst Ni@SiO2(H450) / Ni foam.

[0093] Comparative Example 1: Preparation of Control Sample 1

[0094] Only the hydrochloric acid cleaning step in Example 1 was removed, and the others remained unchanged.

[0095] Comparative Example 2: Preparation of Control Sample 2

[0096] Only the three-time addition of silica sol Ludox HS-40 in Example 1 was replaced by one-time addition of 1.5 mL of Ludox HS-40, and the others remained unchanged.

[0097] Comparative Example 3: Preparation of Control Sample 3

[0098] Only the treatment atmosphere of the catalytic precursor in Example 1 is changed from H2 / Ar (v / v = 1 / 3) to air, and the others remain unchanged.

[0099] Preparation of Comparative Example 4: Control Sample (IV)

[0100] Only the foamed nickel in Example 1 is replaced by ordinary nickel sheet, and the others remain unchanged.

[0101] Test Example 1

[0102] The raw material foamed nickel used in Example 1 and the final target catalyst prepared are respectively subjected to scanning electron microscope (SEM) analysis. The SEM photo of the raw material foamed nickel is shown in Figure 1 , and the SEM photo of the target catalyst is shown in Figure 2 and Figure 3 . By comparing Figure 1 and Figures 2-3 , it can be seen that the foamed nickel surface indeed grows a very uniform and dense layer of catalyst structure.

[0103] Test Example 2

[0104] In order to further determine the structure of the substance grown on the foamed nickel, the part grown on the foamed nickel in the nickel-based catalyst precursor (before reduction) prepared in step (4) of Example 1 is scraped off from the foamed nickel for X-ray diffraction (XRD) analysis, and the part grown on the foamed nickel in the target catalyst (after reduction) prepared in step (5) is scraped off from the foamed nickel for X-ray diffraction (XRD) analysis. The obtained XRD diffraction patterns are shown in Figure 4 .

[0105] As can be seen from Figure 4 , the substance before reduction is a nickel silicate crystal phase (only the diffraction peak of nickel silicate before reduction), and after reduction, it is a crystal phase coexisting with metal nickel and nickel silicate (after reduction, there are diffraction peaks of nickel and nickel silicate). It is proved that after reduction, a nickel-based catalytic system is indeed formed. In addition, part of the nickel silicate is reduced to metal nickel at the same time to generate amorphous silicon dioxide. Therefore, the final catalyst prepared after reduction includes the remaining foamed nickel, metal nickel nanoparticles grown on the foamed nickel, amorphous silicon dioxide and remaining nickel silicate. The metal nickel nanoparticles form the core inside, and the silicon dioxide and the remaining nickel silicate form the shell outside the metal nickel, thereby forming a core-shell structure.

[0106] In addition, the mass of the initial foamed nickel in Example 1 and the mass of the catalyst before reduction (i.e. the catalyst precursor obtained from step (4)) are respectively measured, which are m1 and m2 (m2 > m1) respectively;

[0107] The relative molecular weight of Si2O5(OH)4in the nickel silicate Ni3Si2O5(OH)4is M1, and the number of moles of Si2O5(OH)4is n=(m2-m1)÷M1;

[0108] The relative molecular weight of Ni3Si2O5(OH)4is M2, and the mass of the nickel silicate Ni3Si2O5(OH)4in the catalyst precursor before reduction is m3=n×M2;

[0109] The mass of the nickel foam in the catalyst precursor before reduction is m2-m3;

[0110] The mass of the nickel foam in the catalyst after reduction is equal to the mass of the nickel foam in the catalyst precursor before reduction, both of which are m2-m3, and the ratio of the mass of the nickel foam in the catalyst after reduction (m2-m3) to the mass of the nickel silicate Ni3Si2O5(OH)4in the catalyst precursor before reduction (m3) in Example 1 is 10:1, i.e., the ratio of the mass of the nickel foam in the catalyst precursor (m2-m3) to the mass of the nickel silicate Ni3Si2O5(OH)4in the catalyst precursor before reduction in Example 1 is 10:1.

[0111] Test Example 3

[0112] The part of the nickel-based catalyst precursor (before reduction) prepared in step (4) of Example 1 grown on the nickel foam was scraped off the nickel foam for transmission electron microscope (TEM) analysis, and the part of the target catalyst (after reduction) prepared in step (5) grown on the nickel foam was scraped off the nickel foam for transmission electron microscope (TEM) analysis. Specifically, the part of the nickel-based catalyst precursor (before reduction) and the part of the target catalyst (after reduction) grown on the nickel foam were respectively dispersed in an ethanol solution and ultrasonically dispersed for about 30 min, and finally a small amount of the ethanol solution of the sample was dropped on the surface of an ultrathin carbon film for transmission electron microscope (TEM) analysis. The TEM photos of the part of the nickel-based catalyst precursor (before reduction) and the part of the target catalyst (after reduction) grown on the nickel foam are respectively shown in Figure 5 and Figure 6 The particle size statistical diagram of the metal nickel nanoparticles grown on the nickel foam in the target catalyst (after reduction) is shown in Figure 7 .

[0113] It can be seen from Figure 5 and Figure 6 that the catalyst precursor is a flaky layered structure, and it can be seen from Figure 7 that a large number of small-sized (about 3.4 nm) and uniform-sized nickel nanoparticles are produced after the reduction atmosphere treatment and are embedded in the catalyst substrate, and the whole catalyst is recorded as Ni@SiO2(H450) / Ni foam.

[0114] Test Example 4

[0115] The target catalyst Ni@SiO2(H450) / Ni foam prepared in Example 1 and the control samples ①, ②, ③ and ④ prepared in Comparative Examples 1-4 were respectively placed in a self-designed reactor as shown in Figure 9 , and the catalytic activity of ammonia decomposition reaction was tested in the range of 200-600℃, to produce an ammonia decomposition reaction activity evaluation graph with ammonia conversion rate as the vertical coordinate and temperature as the horizontal coordinate, as shown in Figure 8 .

[0116] As can be seen from the ammonia decomposition reaction activity evaluation graph Figure 8 , the monolithic catalyst prepared in Example 1 has excellent ammonia decomposition reaction catalytic performance, and can achieve complete conversion of ammonia (about 98%) at 500℃.

[0117] The structure of the self-designed reactor is shown in Figure 9 , and the prepared monolithic catalyst can be directly placed in the reactor for hydrogen production by ammonia decomposition test, and the conversion of ammonia is achieved by heating. As shown in Figure 9 , the reactor includes a heating plate 1, a graphite pad 2, a heating rod 3, a temperature control rod 4 and a catalyst 5. The graphite pad 2 is placed between two adjacent heating plates 1, and the heating plates 1 on the upper and lower sides of the graphite pad 2 are provided with a plurality of air holes 6, and the catalyst 5 is placed in the middle empty position of the reactor.

[0118] Test Example 5

[0119] The monolithic catalyst prepared in Example 1 was directly placed in a self-designed reactor as shown in Figure 9 , and a catalyst stability evaluation experiment was carried out at 450℃ for 300min, and the obtained ammonia conversion rate-temperature graph at 450℃ is shown in Figure 10 .

[0120] As can be seen from Figure 10 , the target catalyst prepared in Example 1 has undergone a stability test at 450℃ for 300min, and the activity of the catalyst has not decreased obviously, indicating that the monolithic catalyst structure has excellent stability.

[0121] Test Example 6

[0122] The monolithic catalyst prepared in Example 1 was directly placed in a self-designed reactor as shown in Figure 9 , and a recyclable evaluation experiment was carried out for five times in succession in the range of 200-600℃, and the obtained ammonia conversion rate-temperature graph for 1-5 cycles is shown in Figure 11 .

[0123] After five cycles of low temperature (200℃) to high temperature (600℃), the activity of the catalyst did not decrease obviously, indicating that the catalyst has excellent recyclability.

[0124] In summary, the monolithic catalyst prepared by the method of the present application has excellent catalytic ammonia decomposition activity, stability and recyclability, and the monolithic catalyst does not need to be further shaped and can be directly placed in a reactor for ammonia decomposition hydrogen production reaction, having great industrialization potential.

[0125] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "back", "left", "right" and the like indicate the orientation or positional relationship based on the working state of the present application, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0126] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0127] The above describes the present application in combination with the preferred embodiments, but these embodiments are only exemplary and serve only to illustrate. On this basis, various substitutions and improvements can be made to the present application, which all fall within the scope of protection of the present application.

Claims

1. A method for producing a monolithic nickel-based catalyst for ammonia decomposition reaction, characterized by, The preparation method comprises the following steps: (1) cleaning the foamed nickel with an inorganic acid solution to obtain acid-cleaned foamed nickel; (2) mixing the acid-cleaned foamed nickel with water to obtain a solid-liquid mixture; adding an ammonia solution to the solid-liquid mixture to adjust the pH value to 8-12 to obtain a solid-liquid mixture with adjusted pH value; (3) heating the solid-liquid mixture with adjusted pH value, then adding silicon sol dropwise in multiple times until nickel silicate precipitates are formed, separating out the solid phase to obtain a catalyst precursor; (4) calcining and reducing the catalyst precursor in a reducing atmosphere, part of the nickel silicate is converted into metallic nickel and silicon dioxide, which grows on the foamed nickel together with the remaining nickel silicate to obtain the monolithic nickel-based catalyst for ammonia decomposition reaction.

2. The production method according to claim 1, characterized by, In step (1), the inorganic acid solution is a hydrochloric acid solution, and the molar concentration of the hydrochloric acid solution is 0.05-0.2 M; and / or, the number of times of cleaning with the inorganic acid solution is 3-7 times.

3. The production method according to claim 1, characterized by, In step (2), the solid-liquid mass ratio when the acid-cleaned foamed nickel is mixed with water is (1-3):10; and / or, the mass concentration of the ammonia solution is 20%-40%.

4. The production method according to claim 1 or 3, characterized by, In step (2), the pH value of the solid-liquid mixture is adjusted to 9-10 by adding the ammonia solution.

5. The preparation method according to claim 1, characterized in that, The preparation method further comprises the following step between step (2) and step (3): ultrasonic immersion of the solid-liquid mixture with adjusted pH value for 15 min-1 h.

6. The method of claim 1, wherein, In step (3), the solid-liquid mixture with adjusted pH value is heated to a temperature of 50-90°C.

7. The preparation method according to claim 1, characterized in that, In step (3), the silicon sol is added dropwise in 2-5 times.

8. The production method according to claim 1 or 7, characterized by, In step (3), the solid content of the silicon sol is 30%-50%, and the particle size of the silicon dioxide contained in the silicon sol is 10-30 nm; and / or, the molar ratio of the foamed nickel to the silicon dioxide in the added silicon sol is (5-20):1; and / or, after the solid phase is separated out, the catalyst precursor is obtained by cleaning and drying.

9. The method of claim 1, wherein, In step (4), the reducing atmosphere comprises hydrogen and an inert gas, and the proportion of hydrogen in the total volume of the reducing atmosphere is 5%-40%; wherein the inert gas is selected from argon and / or nitrogen.

10. The production method according to claim 1 or 9, characterized by, In step (4), the temperature of the roasting reduction is 300-600°C, the time is 1-4 h, and the temperature rising speed is 5-20°C·min -1 .

11. The method of claim 2, wherein, The molar concentration of the hydrochloric acid solution is 0.10-0.15 M.

12. The method of claim 3, wherein, The mass concentration of the ammonia solution is 25%-28%.

13. The preparation method according to claim 6, characterized in that, The solid-liquid mixture with adjusted pH value is heated to a temperature of 60-80°C.

14. The production method according to claim 1 or 9, characterized by, In step (4), the temperature of the roasting reduction is 400-500°C, the time is 2-3 h, and the temperature rising speed is 7-13°C·min -1 .

15. A monolithic nickel-based catalyst for ammonia decomposition reaction, characterized by, The monolithic nickel-based catalyst is obtained by the preparation method of any one of claims 1-14; wherein the monolithic nickel-based catalyst comprises foamed nickel and metallic nickel nanoparticles, silicon dioxide and residual nickel silicate grown on the foamed nickel; the particle size of the metallic nickel nanoparticles grown on the foamed nickel is 2-4.5 nm.

16. An ammonia decomposition reaction for hydrogen production, characterized by, The ammonia decomposition reaction is carried out by contacting ammonia with the monolithic nickel-based catalyst of claim 15.

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