Shell-breaking spherical catalyst for hydrogen production through ammonia decomposition as well as preparation method and application of shell-breaking spherical catalyst

Abstract

The invention discloses a shell-breaking spherical catalyst for hydrogen production through ammonia decomposition and a preparation method and application thereof.The catalyst for hydrogen production through ammonia decomposition comprises a carrier and transition metal oxide nanoparticles, the transition metal oxide nanoparticles are evenly distributed on the surface of the carrier, and a heterostructure is formed by the transition metal oxide nanoparticles and the carrier; the carrier is shell-broken spherical molybdenum carbide, and the inner surface and the outer surface of a cavity of the carrier are each of a porous structure. The active component of the catalyst is the transition metal oxide nanoparticles, and the transition metal oxide nanoparticles are anchored on the surface of the carrier and form a stable heterostructure, so that the nanoparticles can be stabilized, and particle aggregation in the reaction process is avoided; the electronic structure of the catalyst can be optimized, and the energy conversion efficiency of ammonia decomposition is improved. The carrier loaded with the nanoparticles is shell-broken spherical molybdenum carbide, and the inside and the outside of a spherical cavity have porous structure characteristics, so that the catalyst has a high specific surface area and can adsorb a large number of ammonia molecules to catalytic sites, thereby improving the conversion efficiency of ammonia decomposition.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a shell-broken spherical ammonia decomposition hydrogen production catalyst and a preparation method and application thereof. Background Art

[0002] As a secondary energy source, hydrogen will play an important role as a bridge and link in the development of renewable energy and fossil energy, but its promotion and application are limited by factors such as high hydrogen storage cost and low transportation efficiency. Ammonia is used as a hydrogen storage carrier, which has high hydrogen storage density and mature transportation technology, and is convenient for distributed on-site hydrogen production and supply, avoiding the troubles caused by hydrogen storage and transportation. The key to the promotion and application of ammonia hydrogen technology lies in the development level of ammonia decomposition catalysts.

[0003] There are many types of hydrogen storage carriers currently under research, among which ammonia has high hydrogen storage density, easy liquefaction, mature transportation technology, low hydrogen production cost and no CO2 when decomposed. x It is considered to be one of the ideal hydrogen storage carriers due to its advantages such as high temperature and high temperature. However, in the field of hydrogen metallurgy research, the high-temperature conversion of ammonia into hydrogen requires a large amount of electricity. Although the currently commercialized nickel-iron-based catalyst can reduce the energy consumption of ammonia cracking, it still requires a temperature of more than 800°C to achieve an ammonia conversion rate of more than 99.5%.

[0004] Therefore, there is an urgent need to develop highly active, highly stable, and low-cost ammonia cracking catalysts to achieve low-temperature and efficient ammonia cracking to produce hydrogen. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a shell-broken spherical ammonia decomposition hydrogen production catalyst and a preparation method and application thereof, wherein the catalyst has high porosity and high specific surface area and high ammonia decomposition conversion efficiency.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides an ammonia decomposition hydrogen production catalyst, including a carrier and transition metal oxide nanoparticles, the transition metal oxide particles are uniformly distributed on the surface of the carrier and form a heterogeneous structure with the carrier; the carrier is a broken spherical molybdenum carbide, and the inner and outer surfaces of the cavity of the carrier have a porous structure.

[0007] Specifically, the active ingredient of the catalyst of the present invention is transition metal oxide nanoparticles, and the transition metal oxide particles are anchored on the surface of the carrier to form a stable heterogeneous structure, which is conducive to stabilizing the nanoparticles and avoiding particle agglomeration during the reaction; on the other hand, the heterogeneous structure can optimize the electronic structure of the catalyst, thereby regulating the adsorption capacity of the catalyst to ammonia molecules, promoting the dissociation of NH, and improving the energy conversion efficiency of ammonia decomposition. At the same time, the carrier that supports the nanoparticles is a broken spherical molybdenum carbide, and the inside and outside of the spherical cavity have porous structural characteristics, with the advantages of high porosity and high specific surface area, and can adsorb a large number of ammonia molecules to the catalytic site, thereby improving the conversion efficiency of ammonia decomposition.

[0008] In some embodiments of the present invention, the transition metal oxide is an oxide of at least one of iron, cobalt, vanadium, manganese, nickel, zirconium, strontium, lanthanum, cerium and ruthenium, and these metal oxides all have good catalytic activity.

[0009] In some embodiments of the present invention, the particle size of the transition metal oxide nanoparticles is less than 10 nm. Nanoscale particles are beneficial to further improve the activity of the catalyst and reduce the loading of the target metal particles.

[0010] In some embodiments of the present invention, the carrier is a spherical large particle composed of broken spherical small particles, and the particle size of the spherical large particle is 50-200nm. The large particle composed of small spherical particles is conducive to further increasing the specific surface area of ​​the catalyst, thereby improving the activity of the catalyst.

[0011] In some embodiments of the present invention, the mass ratio of the carrier to the transition metal oxide nanoparticles is 100:(0.1-10).

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned ammonia decomposition hydrogen production catalyst, comprising the following steps:

[0013] (1) After dispersing a molybdenum precursor in water, adding dopamine hydrochloride and ammonia water, adjusting the pH value of the solution, and stirring; centrifuging, washing, drying, and sintering under an inert atmosphere to obtain spherical molybdenum carbide;

[0014] (2) dispersing the spherical molybdenum carbide into an aqueous solution containing a surfactant and a soluble transition metal salt, centrifuging, washing, drying, and sintering under a reducing atmosphere to obtain the ammonia decomposition hydrogen production catalyst.

[0015] In some embodiments of the present invention, in step (1), the molybdenum precursor is selected from at least one of ammonium molybdate, potassium molybdate, sodium molybdate and hydrates of the above substances.

[0016] In some embodiments of the present invention, in step (1), the pH value is 7-12.

[0017] In some embodiments of the present invention, in step (2), the surfactant is selected from at least one of polyvinyl alcohol, F127 surfactant, hexadecyltrimethylammonium bromide, polyacrylamide, polyacrylate, polyether, polyethylene oxide-propylene oxide, water-soluble phenolic resin, and amino resin.

[0018] In some embodiments of the present invention, in step (2), the soluble transition metal salt is selected from the nitrate or chloride salt whose cation is any one of iron, cobalt, vanadium, manganese, nickel, zirconium, strontium, lanthanum, cerium and ruthenium.

[0019] In some embodiments of the present invention, in step (1), the sintering temperature regime is: first heating to 200-250°C and keeping warm for 30-60 min; then heating to 450-500°C and keeping warm for 60-90 min; then heating to 750-800°C and keeping warm for 90-120 min; the heating rate is 3-4°C / min.

[0020] In some embodiments of the present invention, in step (2), the sintering temperature regime is firstly to heat up to 100-150°C and keep it for 30-60 min; then to heat up to 400-500°C and keep it for 90-120 min; the heating rate is 3-4°C / min.

[0021] Specifically, the present invention adopts a gradient sintering process with segmented heating and heat preservation during the sintering process. The low-temperature stage is mainly used to fully dry the residual moisture in the sample, and the medium and high temperature stages can fully reduce the reaction, increase its specific surface area, void structure, and improve catalytic activity; at the same time, it is conducive to the preparation of transition metal nanoparticles, fully combining with the carrier, and evenly dispersing them on the surface of the carrier.

[0022] The third aspect of the present invention provides the use of the above-mentioned ammonia decomposition hydrogen production catalyst in the ammonia decomposition hydrogen production reaction.

[0023] Preferably, the reaction temperature is 550-650°C.

[0024] Preferably, the space velocity of the reaction is 50000-65000 mL / g / h.

[0025] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0026] (1) The active ingredient of the catalyst of the present invention is transition metal oxide nanoparticles, and the transition metal oxide particles are anchored on the surface of the carrier to form a stable heterostructure. On the one hand, this structure is conducive to stabilizing the nanoparticles and avoiding particle agglomeration during the reaction; on the other hand, the heterostructure can optimize the electronic structure of the catalyst, thereby regulating the adsorption capacity of the catalyst for ammonia molecules, promoting the dissociation of NH, and improving the energy conversion efficiency of ammonia decomposition.

[0027] (2) The carrier of the nanoparticles in the present invention is a spherical molybdenum carbide with a broken shell; and the inside and outside of the spherical cavity have porous structural characteristics, which has the advantages of high porosity and high specific surface area, and can adsorb a large number of ammonia molecules to the catalytic site, thereby improving the conversion efficiency of ammonia decomposition.

[0028] (3) The ammonia decomposition catalyst prepared by the present invention has good catalytic performance at 500°C and a space velocity of 60000 mL / hg -1 Under the reaction conditions, the ammonia decomposition conversion efficiency can reach more than 96%, and the highest can reach 98.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The XRD pattern of the ammonia decomposition hydrogen production catalyst prepared in Example 1;

[0030] Figure 2 This is a SEM image of the ammonia decomposition hydrogen production catalyst prepared in Example 1;

[0031] Figure 3 This is the SEM image of the ammonia decomposition hydrogen production catalyst prepared in Comparative Example 1. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the examples, so that the technical personnel of the relevant technical field can understand the present invention. It is necessary to point out here that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The non-essential improvements and adjustments made to the present invention by the skilled person in the relevant field according to the above invention content should still belong to the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0033] Example 1

[0034] A method for preparing a catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

[0035] (1) 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water under stirring at room temperature for 5 min, and 300 mg of dopamine hydrochloride was added. After stirring for 30 min, a wine-red solution was obtained; then, 150 mL of anhydrous ethanol was added to the wine-red solution, and the solution turned orange and turbid. After stirring for 10 min, 0.4 mL of 25-28% ammonia water was added dropwise to the solution and continued to stir for 2 hours; the solution was washed with deionized water and ethanol for 3 times respectively to remove unreacted substances; finally, the solid product was collected by centrifugation and dried at 70° C. for 12 hours to obtain an orange-red powder;

[0036] (2) subjecting the powder obtained in step (1) to gradient sintering in a nitrogen atmosphere, wherein the temperature regime of the gradient sintering is: firstly heating to 200°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 450°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 800°C at a heating rate of 3°C / min and keeping the temperature for 120 min; and obtaining a spherical molybdenum carbide carrier;

[0037] (3) adding the support prepared in step (2) to 500 mL of an aqueous solution containing 0.1 g of hexadecyltrimethylammonium bromide, 0.2 mol of cobalt nitrate, 0.2 mol of nickel nitrate, 0.2 mol of lanthanum nitrate and 0.2 mol of ruthenium chloride, stirring for 2 hours, centrifuging, collecting the solid product, and drying at 70° C. for 12 hours;

[0038] (4) Sintering the powder obtained in step (3) in an environment of hydrogen and argon (volume ratio of 3:2), wherein the sintering temperature regime is: first heating to 150° C. at a heating rate of 4° C. / min and keeping warm for 60 min; then heating to 450° C. at a heating rate of 4° C. / min and keeping warm for 90 min, thereby obtaining the ammonia decomposition hydrogen production catalyst of this embodiment.

[0039] Example 2

[0040] A method for preparing a catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

[0041] (1) 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water under stirring at room temperature for 5 min, and 400 mg of dopamine hydrochloride was added. After stirring for 30 min, a wine-red solution was obtained; then, 150 mL of anhydrous ethanol was added to the wine-red solution, and the solution turned orange and turbid. After stirring for 10 min, 0.4 mL of 25-28% ammonia water was added dropwise to the solution and continued to stir for 2 hours; the solution was washed with deionized water and ethanol for 3 times respectively to remove unreacted substances; finally, the solid product was collected by centrifugation and dried at 70° C. for 12 hours to obtain an orange-red powder;

[0042] (2) subjecting the powder obtained in step (1) to gradient sintering in a nitrogen atmosphere, wherein the temperature regime of the gradient sintering is: firstly heating to 200°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 450°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 800°C at a heating rate of 3°C / min and keeping the temperature for 120 min; and obtaining a spherical molybdenum carbide carrier;

[0043] (3) adding the support prepared in step (2) to 500 mL of an aqueous solution containing 0.1 g of polyvinyl alcohol, 0.2 mol of cobalt nitrate, 0.2 mol of nickel nitrate, 0.2 mol of lanthanum nitrate and 0.2 mol of ruthenium chloride, stirring for 2 hours, centrifuging, collecting the solid product, and drying at 70° C. for 12 hours;

[0044] (4) Sintering the powder obtained in step (3) in an environment of hydrogen and argon (volume ratio of 3:2), wherein the sintering temperature regime is: first heating to 150° C. at a heating rate of 4° C. / min and keeping warm for 60 min; then heating to 450° C. at a heating rate of 4° C. / min and keeping warm for 90 min, thereby obtaining the ammonia decomposition hydrogen production catalyst of this embodiment.

[0045] Example 3

[0046] A method for preparing a catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

[0047] (1) 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water under stirring at room temperature for 5 min, and 300 mg of dopamine hydrochloride was added. After stirring for 30 min, a wine-red solution was obtained; then, 150 mL of anhydrous ethanol was added to the wine-red solution, and the solution turned orange and turbid. After stirring for 10 min, 0.4 mL of 25-28% ammonia water was added dropwise to the solution and continued to stir for 2 hours; the solution was washed with deionized water and ethanol for 3 times respectively to remove unreacted substances; finally, the solid product was collected by centrifugation and dried at 70° C. for 12 hours to obtain an orange-red powder;

[0048] (2) subjecting the powder obtained in step (1) to gradient sintering in a nitrogen atmosphere, wherein the temperature regime of the gradient sintering is: firstly heating to 200°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 450°C at a heating rate of 3°C / min and keeping the temperature for 60 min; then heating to 800°C at a heating rate of 3°C / min and keeping the temperature for 120 min; and obtaining a spherical molybdenum carbide carrier;

[0049] (3) adding the carrier prepared in step (2) to 500 mL of an aqueous solution containing 0.5 g of F127 surfactant, 0.2 mol of cobalt nitrate, 0.2 mol of nickel nitrate, 0.2 mol of lanthanum nitrate and 0.2 mol of ruthenium chloride, stirring for 2 hours, centrifuging, collecting the solid product, and drying at 70° C. for 12 hours;

[0050] (4) Sintering the powder obtained in step (3) in an environment of hydrogen and argon (volume ratio of 3:2), wherein the sintering temperature regime is: first heating to 150° C. at a heating rate of 4° C. / min and keeping warm for 60 min; then heating to 450° C. at a heating rate of 4° C. / min and keeping warm for 90 min, thereby obtaining the ammonia decomposition hydrogen production catalyst of this embodiment.

[0051] Comparative Example 1

[0052] The only difference between Comparative Example 1 and Example 1 is that dopamine hydrochloride is not added in step (1).

[0053] Comparative Example 2

[0054] The only difference between Comparative Example 2 and Example 1 is that hexadecyltrimethylammonium bromide is not added in step (3).

[0055] Comparative Example 3

[0056] The only difference between Comparative Example 3 and Example 1 is that in step (4), Comparative Example 3 does not adopt a gradient sintering temperature system, that is, heating to 450° C. at a heating rate of 4° C. / min and keeping the temperature for 90 min.

[0057] Characterization and performance testing

[0058] 1. Composition analysis and microstructure

[0059] Figure 1 The XRD pattern of the ammonia decomposition hydrogen production catalyst prepared in Example 1 is as follows: Figure 1 The horizontal axis 2θ in is the diffraction angle, and the vertical axis Intensity represents the intensity of the diffraction peak. Figure 1 It can be seen that the ammonia decomposition hydrogen production catalyst contains molybdenum carbide crystal phase, proving that the carrier is molybdenum carbide.

[0060] Figure 2 This is a SEM image of the ammonia decomposition hydrogen production catalyst prepared in Example 1. Figure 2 It can be seen that the carrier of the catalyst is a large spherical particle composed of small spherical particles with broken shells, the particle size of the large spherical particle is about 50-200nm, and the inner and outer surfaces of the broken shell spherical cavity have a porous structure.

[0061] Figure 3 This is a SEM image of the ammonia decomposition hydrogen production catalyst prepared in Comparative Example 1. Figure 3 It can be seen that the catalyst carrier is a complete spherical particle with no broken shell and no porous structure.

[0062] 2. Ammonia decomposition performance test

[0063] Activity test conditions: the raw gas is pure ammonia, the test space velocity is 60000 mL / g / h, the test temperature is 500°C, and the ammonia decomposition conversion efficiency is shown in Table 1.

[0064] Table 1: Comparison of ammonia decomposition conversion efficiency prepared in Examples 1-3 and Comparative Examples 1-3

[0065] Example Ammonia conversion efficiency (%) Example 1 98.6 Example 2 97.1 Example 3 96.7 Comparative Example 1 88.7 Comparative Example 2 89.3 Comparative Example 3 88.1

[0066] As shown in Table 1, the ammonia decomposition hydrogen production catalyst prepared in Example 1 exhibits the best ammonia decomposition performance at a test space velocity of 60000 mL / g / h and a test temperature of 500° C., and its conversion efficiency reaches 98.6%.

[0067] Compared with Example 1, since no dopamine hydrochloride is added to form a complete spherical catalyst in Comparative Example 1, the inner surface of the cavity cannot be fully utilized, the number of catalytic sites is reduced, and the residence time of ammonia molecules on the inner and outer surfaces of the catalyst cannot be retained, resulting in a decrease in ammonia decomposition efficiency.

[0068] Compared with Example 1, since the surfactant hexadecyltrimethylammonium bromide was not added in Comparative Example 2, porous and ultra-small transition metal oxide nanoparticles could not be prepared, and the catalytic activity was also reduced.

[0069] Compared with Example 1, since Comparative Example 3 does not adopt gradient sintering, the powder shrinks rapidly during the sintering process, the porosity between particles decreases, and the nanoparticles are partially agglomerated, resulting in a reduction in exposed active sites, a decrease in catalytic activity, and thus a decrease in ammonia decomposition efficiency.

[0070] For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, without having to go through creative labor. Therefore, simple improvements made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the protection scope of the present invention. The above embodiments are preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made should belong to the protection scope of the present invention.

Claims

1. A catalyst for hydrogen production by decomposing ammonia, characterized in that: It comprises a carrier and transition metal oxide nanoparticles, wherein the transition metal oxide particles are evenly distributed on the surface of the carrier and form a heterogeneous structure with the carrier; the carrier is a broken spherical molybdenum carbide, and both the inner and outer surfaces of the cavity of the carrier have a porous structure.

2. The catalyst for hydrogen production from ammonia decomposition according to claim 1, characterized in that: The transition metal oxide is an oxide of at least one of iron, cobalt, vanadium, manganese, nickel, zirconium, strontium, lanthanum, cerium and ruthenium.

3. The catalyst for hydrogen production by decomposing ammonia according to claim 1, characterized in that: The carrier is a spherical large particle composed of broken spherical small particles, and the particle size of the spherical large particle is 50-200nm.

4. The catalyst for hydrogen production by decomposing ammonia according to claim 1, characterized in that: The mass ratio of the carrier to the transition metal oxide nanoparticles is 100:(0.1-10).

5. A method for preparing the catalyst for hydrogen production by decomposing ammonia according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) After dispersing the molybdenum precursor in water, adding dopamine hydrochloride and ammonia water, adjusting the pH value of the solution, and stirring; After centrifugation, washing, drying and sintering in an inert atmosphere, spherical molybdenum carbide is obtained; (2) dispersing the spherical molybdenum carbide into an aqueous solution containing a surfactant and a soluble transition metal salt, centrifuging, washing, drying, and sintering under a reducing atmosphere to obtain the ammonia decomposition hydrogen production catalyst.

6. The method for preparing ammonia decomposition hydrogen production catalyst according to claim 5, characterized in that: In step (1), the molybdenum precursor is selected from at least one of ammonium molybdate, potassium molybdate, sodium molybdate and hydrates of the above substances; and / or the pH value is 7-12.

7. The method for preparing ammonia decomposition hydrogen production catalyst according to claim 5, characterized in that: In step (2), the surfactant is selected from at least one of polyvinyl alcohol, F127 surfactant, hexadecyltrimethylammonium bromide, polyacrylamide, polyacrylate, polyether, polyethylene oxide-propylene oxide, water-soluble phenolic resin, and amino resin.

8. The method for preparing ammonia decomposition hydrogen production catalyst according to claim 5, characterized in that: In step (2), the soluble transition metal salt is selected from nitrates or chlorides whose cations are any one of iron, cobalt, vanadium, manganese, nickel, zirconium, strontium, lanthanum, cerium and ruthenium.

9. The method for preparing ammonia decomposition hydrogen production catalyst according to claim 5, characterized in that: In step (1), the sintering temperature regime is: firstly heating to 200-250°C and keeping warm for 30-60min; then heating to 450-500°C and keeping warm for 60-90min; then heating to 750-800°C and keeping warm for 90-120min; the heating rate is 3-4°C / min; And / or, in step (2), the sintering temperature regime is: first, heating to 100-150°C and keeping warm for 30-60 min; then heating to 400-500°C and keeping warm for 90-120 min; the heating rate is 3-4°C / min.

10. Use of the catalyst for producing hydrogen by decomposing ammonia according to any one of claims 1 to 4 in a reaction for producing hydrogen by decomposing ammonia.

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