Cerium-based ammonia decomposition catalyst under low-temperature working condition as well as preparation method and application of cerium-based ammonia decomposition catalyst

Abstract

The invention discloses a cerium-based ammonia decomposition catalyst under a low-temperature working condition as well as a preparation method and application thereof, and belongs to the technical field of catalyst preparation and ammonia decomposition hydrogen production. The cerium-based ammonia decomposition catalyst comprises metal active components and a composite carrier, the metal active components comprise ruthenium, nickel and iron, and the composite carrier is cerium oxide doped aluminum oxide. The mass ratio of the active component Ru is 0.8 wt%, and Ru particles are uniformly distributed on the surface of the carrier by adopting an initial wetting impregnation method, a ball milling method, a hydrothermal method and the like. The catalyst has long stability of 5000 hours at least, has high ammonia decomposition conversion rate at low temperature with extremely low ruthenium content, and greatly reduces the energy consumption of hydrogen production through ammonia decomposition.

Description

Technical Field

[0001] The present invention belongs to the technical fields of catalyst preparation and ammonia decomposition for hydrogen production, and particularly relates to a cerium-based ammonia decomposition catalyst under low-temperature conditions, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] As a highly potential energy source, hydrogen has a broad application prospect in the future energy system and is an important part of the future national low-carbon energy system. However, the low volumetric energy density and high flammability of hydrogen pose great challenges to its storage and transportation. Compared with other hydrogen carriers (such as methanol, methane, and metal hydrides), liquid ammonia has attracted much attention due to its high hydrogen content (17.6 wt%) and no carbon emissions. Ammonia can be easily stored in liquid form at room temperature and low pressure (20 °C, 0.846 MPa), and its industrialization cost is also the lowest, which makes liquid ammonia an extremely attractive candidate material for hydrogen storage and transportation. Currently, among the ammonia decomposition for hydrogen production catalysts, the catalysts using noble metal ruthenium as the active center show relatively high catalytic activity, while the activity of non-noble metal catalysts is relatively poor.

[0004] The prior art discloses a Ru-based ammonia decomposition catalyst prepared by an electrostatic adsorption method using CeO2 / SiO2, and the content of ruthenium accounts for 0.5% - 1.5% of the catalyst mass. Although its stability is good, the process is complex. In the examples, the conversion rate of the catalyst with 1 wt% Ru loading is 89.5% at 500 °C. The prior art also discloses a preparation method of a Ru-based catalyst with a carrier of carbon layer-coated silica. The highest conversion rate of this catalyst is 61.8% at 500 °C and it can operate stably for 50 h, but it cannot meet the industrial requirements. Summary of the Invention

[0005] Aiming at the problems of high noble metal Ru loading, insufficient low-temperature activity, and low stability existing in the current ammonia decomposition for hydrogen production catalysts, the purpose of the present invention is to provide a cerium-based ammonia decomposition catalyst under low-temperature conditions, a preparation method thereof, and an application thereof. The catalyst includes a metal active component and an oxide carrier; the active component is an active metal ruthenium, nickel, iron-based heterogeneous component, and the carrier is a composite carrier of nano-ceria doped with alumina. The mass ratio of the active component Ru is 0.8 wt%. By using methods such as incipient wetness impregnation method, ball milling method, and hydrothermal method, Ru particles are evenly distributed on the surface of the carrier. This catalyst has a long stability of at least 5000 h, has a high ammonia decomposition conversion rate at low temperature with a very low ruthenium content, and greatly reduces the energy consumption of ammonia decomposition for hydrogen production.

[0006] To achieve the above object, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a cerium-based ammonia decomposition catalyst for low-temperature conditions. The cerium-based ammonia decomposition catalyst comprises a composite support and a metal active component supported on the composite support. The metal active component is ruthenium, nickel, and iron, and the composite support is cerium oxide doped with alumina.

[0007] In one or more embodiments, the mass percentage of the metal active component in the catalyst is 0.5 - 4.0 wt.%, preferably 0.8 - 3.0 wt.%, and more preferably 2.5 - 3 wt.%.

[0008] The loading amount of ruthenium is 0.5 - 2%, preferably 0.5 - 1%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.

[0009] The loading amount of nickel is 1 - 3%, preferably 1 - 1.5%, such as 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%.

[0010] The loading amount of iron is 0.5 - 2%, preferably 0.8 - 1.2%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.

[0011] In one or more embodiments, the molar ratio of cerium oxide to alumina is 1 - 4:1, such as 1:1, 2:1, 3:1, 4:1, preferably 2 - 4:1.

[0012] The cerium oxide particle size is about 3 - 8 nm, the average particle size is 4 - 6 nm, and the ruthenium oxide particle size is 2 - 4 nm.

[0013] The specific surface area of the cerium-based ammonia decomposition catalyst is 100 - 150 m 2 ·g -1 , preferably 125 - 145 m 2 ·g -1 , more preferably 135 - 145 m 2 ·g -1 ; the pore volume is 0.1 - 0.5 cm 3 ·g-1 , preferably 0.1 - 0.3 cm 3 ·g -1 , more preferably 0.2 - 0.3 cm 3 ·g -1 ; the pore diameter is 5 - 10 nm, preferably 5 - 8 nm, more preferably 6 - 8 nm.

[0014] In a second aspect, the present invention provides a method for preparing the cerium-based ammonia decomposition catalyst under low-temperature conditions described in the first aspect, comprising the following steps: (1) Adding a basic precipitating agent to the metal salt precursor of cerium and the metal salt precursor of aluminum for hydrothermal treatment, washing, drying, and calcining to obtain a composite support; (2) Mixing the metal salt precursors of ruthenium, nickel, and iron with the composite support and then calcining to obtain the ammonia decomposition catalyst.

[0015] In one or more embodiments, the metal salt precursor of cerium is one or more of cerium nitrate and cerium acetate.

[0016] In one or more embodiments, the metal salt precursor of aluminum is one or more of aluminum nitrate and aluminum acetate.

[0017] In one or more embodiments, the metal salt precursor of ruthenium is one or more of ruthenium trichloride, ruthenium(III) nitrosyl nitrate, and ruthenium acetate.

[0018] In one or more embodiments, the metal salt precursor of nickel is one or more of nickel nitrate, nickel acetate, and nickel carbonate.

[0019] In one or more embodiments, the metal salt precursor of iron is one or more of iron nitrate, iron acetate, and iron carbonate.

[0020] In one or more embodiments, in step (1), the metal salt precursor of cerium and the metal salt precursor of aluminum are configured into a solution according to a certain molar ratio, continuously stirred, a basic precipitating agent is added thereto, and the mixed solution is subjected to hydrothermal treatment.

[0021] Further, the hydrothermal treatment conditions are to keep the temperature at 110 - 130 °C for 10 - 14 h, preferably to keep the temperature at 120 °C for 12 h.

[0022] Further, the basic precipitating agent is one or more of ammonia water, sodium hydroxide, and potassium hydroxide, so that the pH of the mixed solution is adjusted to 8 - 9.

[0023] Further, the mixed solution is continuously stirred for 5 - 8 h.

[0024] In one or more embodiments, in step (1), the suspension obtained after hydrothermal treatment is washed and filtered by suction multiple times, and the obtained precipitate is dried. After drying, it is calcined to obtain a composite support.

[0025] Furthermore, the drying temperature is 70 - 100 °C, and the drying time is 8 - 15 h.

[0026] Furthermore, the calcination temperature is 400 - 600 °C, with heat preservation for 2 - 5 h, preferably 500 °C with heat preservation for 4 h.

[0027] In one or more embodiments, in step (2), the mixing methods of the metal salt precursors of ruthenium, nickel, and iron and the composite support include incipient wetness impregnation method, ball milling method, hydrothermal method, etc., to uniformly distribute the metal particles on the surface of the composite support.

[0028] Furthermore, when synthesizing by the incipient wetness impregnation method, the metal salt precursors of ruthenium, nickel, and iron are dissolved in water according to the loading ratio to prepare a metal salt precursor solution. The metal salt precursor solution is gradually added dropwise to the composite support, and after impregnation, it is calcined to obtain the final ammonia decomposition catalyst. Among them, the mass - volume ratio of the ruthenium metal salt precursor to water is 0.05 - 2 g:10 - 100 ml; the ratio of the metal salt precursor solution to the composite support is 5 - 20 mL:0.5 - 5 g; the calcination temperature is 400 - 600 °C, with heat preservation for 2 - 5 h, preferably 500 °C with heat preservation for 4 h.

[0029] Furthermore, when synthesizing by the hydrothermal method, the metal salt precursors of ruthenium, nickel, and iron are dissolved in water according to the loading ratio to prepare a metal salt precursor solution. The metal salt precursor solution is mixed with the composite support according to the loading ratio and placed in a hydrothermal autoclave for hydrothermal treatment. After hydrothermal treatment, it is filtered by suction and calcined to obtain the final ammonia decomposition catalyst. Among them, the mass - volume ratio of the ruthenium metal salt precursor to water is 0.05 - 2 g:10 - 100 ml. Among them, the hydrothermal method is carried out with 20 - 40 mL (preferably 30 mL) of the precursor solution and 3 - 8 g (preferably 5 g) of the composite support. The hydrothermal conditions are 150 - 170 °C, 10 - 14 h (preferably 160 °C, 12 h). The calcination temperature is 400 - 600 °C, with heat preservation for 2 - 5 h, preferably 500 °C with heat preservation for 4 h.

[0030] Furthermore, when synthesizing by ball milling, the metal salt precursors of ruthenium, nickel, and iron are mixed with the composite support according to the loading ratio and then subjected to ball milling treatment (such as being placed in a corundum ceramic pot). After mixing, calcination treatment is carried out to obtain the ammonia decomposition catalyst. Among them, the ball milling method rotates forward at 200 - 500 rpm for 20 - 40 s, rotates backward at 200 - 500 rpm for 20 - 40 s, with an interval of 5 - 15 s in the middle, and cycles 4 - 6 times. Preferably, the ball milling method rotates forward at 300 rpm for 30 s, rotates backward at 300 rpm for 30 s, with an interval of 10 s in the middle, and cycles 5 times. The calcination temperature is 400 - 600 °C, and the heat preservation is 2 - 5 h, preferably 500 °C, with a heat preservation of 4 h.

[0031] In a third aspect, the present invention provides the application of the above-mentioned cerium-based ammonia decomposition catalyst under low-temperature conditions in ammonia decomposition to produce hydrogen under low-temperature conditions.

[0032] In a fourth aspect, the present invention provides a method for ammonia decomposition to produce hydrogen under low-temperature conditions, including the following steps: Under a mixed atmosphere at 400 - 550 °C, the gas containing ammonia is reduced by using the above-mentioned cerium-based ammonia decomposition catalyst under low-temperature conditions.

[0033] Furthermore, the low temperature is 500 - 550 °C, and more preferably 525 - 550 °C.

[0034] Furthermore, the mixed atmosphere is a hydrogen-argon mixed gas.

[0035] Furthermore, the reaction space velocity is 14000 - 16000 mL g -1 h -1 , with a step size of 20 - 30 °C.

[0036] One or some of the above technical solutions have the following advantages or beneficial effects: The present invention uses a precipitation-hydrothermal method to prepare a cerium oxide-aluminum oxide composite support and uses the incipient wetness impregnation method to combine with the metal salt precursors of ruthenium, nickel, and iron to prepare an ammonia decomposition catalyst. The particle size of the cerium oxide support is about 3 - 8 nm, the average particle size is 5.1 nm, and the particle size of ruthenium oxide is 2 - 4 nm. The addition of aluminum oxide increases the specific surface area and pore volume of the support, promotes the dispersion degree of the active metal, and enhances the interaction strength between the support and the metal. The oxygen vacancies and redox potential of the cerium oxide support promote the enrichment of electrons on the surface of the active metal, promote the adsorption of ammonia and the abundance of nitrogen, and improve the ammonia decomposition reaction efficiency.

[0037] In the metal active components of the present invention, ruthenium, nickel, and iron are used simultaneously. Compared with the use of only ruthenium or the combination of other metal components, the ammonia decomposition catalyst obtained by the combination of ruthenium, nickel, and iron provided by the present invention has the technical effects of high specific surface area, high pore volume, and large pore diameter, and also has better technical effects during low-temperature catalysis.

[0038] The catalyst prepared by the present invention has excellent stability and conversion rate. At the same time, the preparation method is simple, the metal loading is low, and the cost is lower.

[0039] The ammonia conversion rate of the catalyst prepared by the present invention is close to 100% at 550 °C, and basically complete conversion is achieved. And after a long-term durability test of 48 h, the efficiency remains unchanged all the time, and the catalyst has excellent stability.

[0040] The catalyst prepared by the present invention has a long stability of at least 5000 h, and has a high ammonia decomposition conversion rate at low temperature with a very low ruthenium content (the mass ratio of the active component Ru is 0.8 wt.%), which greatly reduces the energy consumption of ammonia decomposition for hydrogen production. Description of the Drawings

[0041] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0042] Figure 1 Ru obtained in Example 3 of the present invention 0.8 Ni 1.2 TEM images of the Fe1 / 3Ce-Al catalyst sample obtained in Example 3 of the present invention at different magnifications; Figure 2 Ammonia conversion rate diagrams of the catalysts obtained in the examples and comparative examples of the present invention; Figure 3 Stability test diagrams of the catalysts in the examples and comparative examples of the present invention. Detailed Description of the Invention

[0043] In order to enable those skilled in the art to more clearly understand the technical solutions of the present invention, the technical solutions of the present invention will be described in detail below in combination with specific examples.

[0044] If no specific experimental steps or conditions are indicated in the examples, the operations or conditions of the conventional experimental steps described in the art can be followed. For the reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0045] Example 1: Measure 200 mL of deionized water, 5.428 g of cerium nitrate, and 4.689 g of aluminum nitrate and add them to a beaker. Stir continuously to dissolve them. Then, use a dropper to slowly add ammonia water to the beaker drop by drop. Use pH test paper to measure the pH value of the solution. When the pH of the solution reaches 8 - 9, stop adding ammonia water. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reactor for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in a drying oven at 80 °C for 12 h, and then calcine it in a muffle furnace at 500 °C for 4 h to obtain a support with a molar ratio of cerium oxide to aluminum oxide of 1:1.

[0046] Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Conduct a calcination treatment on the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / 1Ce - Al catalyst.

[0047] Example 2: Measure 200 mL of deionized water, 5.428 g of cerium nitrate, and 2.345 g of aluminum nitrate and add them to a beaker. Stir continuously to dissolve them. Then, use a dropper to slowly add ammonia water to the beaker drop by drop. Use pH test paper to measure the pH value of the solution. When the pH of the solution reaches 8 - 9, stop adding ammonia water. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reactor for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in a drying oven at 80 °C for 12 h, and then calcine it in a muffle furnace at 500 °C for 4 h to obtain a support with a molar ratio of cerium oxide to aluminum oxide of 2:1.

[0048] Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Conduct a calcination treatment on the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / 2Ce - Al catalyst.

[0049] Example 3: Measure 200 mL of deionized water, 10.856 g of cerium nitrate, and 3.126 g of aluminum nitrate and add them to a beaker. Stir continuously to dissolve them. Then, use a dropper to slowly add ammonia water to the beaker, and test the pH value of the solution with pH test paper. Stop adding ammonia water when the pH of the solution reaches 8 - 9. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reactor for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in a drying oven at 80 °C for 12 h, and then calcine it in a muffle furnace at 500 °C for 4 h to obtain a support with a molar ratio of cerium oxide to aluminum oxide of 3:1.

[0050] Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Calcinate the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / 3Ce - Al catalyst.

[0051] Example 4: Measure 200 mL of deionized water, 10.856 g of cerium nitrate, and 2.345 g of aluminum nitrate and add them to a beaker. Stir continuously to dissolve them. Then, use a dropper to slowly add ammonia water to the beaker, and test the pH value of the solution with pH test paper. Stop adding ammonia water when the pH of the solution reaches 8 - 9. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reactor for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in a drying oven at 80 °C for 12 h, and then calcine it in a muffle furnace at 500 °C for 4 h to obtain a support with a molar ratio of cerium oxide to aluminum oxide of 4:1.

[0052] Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Calcinate the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / 4Ce - Al catalyst.

[0053] Comparative Example 1: Measure 200 mL of deionized water and add 15 g of cerium nitrate into a beaker. Stir continuously to dissolve it. Then, use a dropper to add ammonia water drop by drop into the beaker. Test the pH value of the solution with pH test paper. When the pH of the solution reaches 8 - 9, stop adding ammonia water. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reaction kettle for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in an oven at 80 °C and dry it for 12 h. Then, place it in a muffle furnace and calcine it at 500 °C for 4 h to obtain a pure cerium oxide support. Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Calcinate the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / CeO2 catalyst.

[0054] Comparative Example 2: Measure 200 mL of deionized water and add 15 g of aluminum nitrate into a beaker. Stir continuously to dissolve it. Then, use a dropper to add ammonia water drop by drop into the beaker. Test the pH value of the solution with pH test paper. When the pH of the solution reaches 8 - 9, stop adding ammonia water. Stir the mixed solution continuously for 6 h. After stirring, place the solution in a hydrothermal reaction kettle for hydrothermal treatment at 120 °C for 12 h. After hydrothermal treatment, wash and filter the solution multiple times to make the pH of the solution neutral. Place the obtained precipitate in an oven at 80 °C and dry it for 12 h. Then, place it in a muffle furnace and calcine it at 500 °C for 4 h to obtain a pure alumina support. Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Fe at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Calcinate the impregnated sample to obtain Ru 0.8 Ni 1.2 Fe1 / Al2O3 catalyst.

[0055] Comparative Example 3: Prepare a support with a molar ratio of cerium oxide to alumina of 3:1 according to the method of Example 3. Weigh 1 g of the composite support. According to the loading of Ru at 0.8 wt%, Ni at 1.2 wt%, and Mn at 1 wt%, weigh a certain mass of metal salts and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. Use the incipient wetness impregnation method to drop the metal solution into the composite support in small amounts and multiple times. Calcinate the impregnated sample to obtain Ru 0.8 Ni 1.2 Mn1 / 3Ce - Al catalyst.

[0056] Comparative Example 4: Prepare a support with a cerium oxide to alumina molar ratio of 3:1 according to the method of Example 3. Weigh 1 g of the composite support. Weigh a certain mass of metal salts according to 0.8 wt% Ru loading, 1.2 wt% Ni loading, and 1 wt% Co loading and dissolve them in 10 mL of deionized water to obtain a mixed metal salt solution. The metal solution was added dropwise to the composite support in small portions and multiple times using the incipient wetness impregnation method. The impregnated sample was calcined to obtain Ru 0.8 Ni 1.2 Co1 / 3Ce-Al catalyst.

[0057] Comparative Example 5: Prepare a support with a cerium oxide to alumina molar ratio of 3:1 according to the method of Example 3. Weigh 1 g of the composite support. Weigh a certain mass of metal salt according to 0.8 wt% Ru loading and dissolve it in 10 mL of deionized water to obtain a mixed metal salt solution. The metal solution was added dropwise to the composite support in small portions and multiple times using the incipient wetness impregnation method. The impregnated sample was calcined to obtain Ru 0.8 / 3Ce-Al catalyst.

[0058] Table 1 Sample preparation parameters of examples and comparative examples

[0059] Table 2 Structural parameters of examples and comparative examples

[0060] Catalyst efficiency test conditions: The test gas is pure ammonia. The catalyst is reduced with a hydrogen-argon mixture at 500 °C for 1 h, and the reaction space velocity is 15000 mLg -1 h -1 , and the test temperature range is 400 - 550 °C with a step size of 25 °C. The activity of the catalyst is expressed by ammonia conversion rate. The activity evaluation results of examples and comparative examples are as follows Figure 2 shown.

[0061] Combined with Figure 1 it can be clearly observed that the Ru 0.8 Ni 1.2 Fe1 / 3Ce-Al catalyst sample obtained in Example 3 has a transmission electron microscope image at different magnifications, and various crystals are marked. It can be seen that the particles are arranged neatly and the morphology is uniform.

[0062] Combined with Figure 2It can be seen that the catalysts prepared in the examples and comparative examples have high ammonia decomposition performance at high space velocity. Among them, compared with the comparative examples, the catalysts provided in the examples of the present invention have an ammonia conversion rate greater than 80% at 550 °C, and further all are above 98%. In particular, the ammonia conversion rate of Example 3 at 550 °C is as high as 99.9%, basically achieving complete conversion.

[0063] Combined with Figure 3 It can be seen that: The catalyst prepared in Example 3 was subjected to a long-term durability test for 48 hours, and the efficiency remained unchanged all the time, and the catalyst has excellent stability.

[0064] The cerium oxide-based composite support catalyst prepared by the present invention using the precipitation hydrothermal method has the characteristics of high specific surface area, uniform particle dispersion, and small size. The addition of alumina improves the strong interaction between the support and the metal, makes the acidic sites on the support surface more abundant, and cerium oxide provides rich oxygen vacancies and efficient electron transfer for Ru, making Ru in a rich electron state, which is beneficial to the adsorption of ammonia, enhances the adsorption and desorption of nitrogen, and is beneficial to the improvement of reaction efficiency.

[0065] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cerium-based ammonia decomposition catalyst for low-temperature conditions, characterized in that, The cerium-based ammonia decomposition catalyst includes a composite support and metal active components supported on the composite support. The metal active components are ruthenium, nickel, and iron, and the composite support is cerium oxide doped alumina.

2. The cerium-based ammonia decomposition catalyst according to claim 1, wherein The mass percentage of the metal active components in the catalyst is 0.5-4.0 wt.%, preferably 0.8-3.0 wt.%, and more preferably 2.5-3 wt.%. Preferably, the loading amount of ruthenium is 0.5-2 wt.%, preferably 0.5-1 wt.%. Preferably, the loading amount of nickel is 1-3 wt.%, preferably 1-1.5 wt.%. Preferably, the loading amount of iron is 0.5-2 wt.%, preferably 0.8-1.2 wt.%. Preferably, the molar ratio of cerium oxide to alumina is 1-4:1, preferably 2-4:

1. Preferably, the specific surface area of the cerium-based ammonia decomposition catalyst is 100-150 m 2 ·g -1 , preferably 125-145 m 2 ·g -1 ; the pore volume is 0.1-0.5 cm 3 ·g -1 , preferably 0.1-0.3 cm 3 ·g -1 ; the pore diameter is 5-10 nm, preferably 5-8 nm.

3. A preparation method of the cerium-based ammonia decomposition catalyst under low-temperature conditions according to claim 1 or 2, characterized in that, It includes the following steps: (1) Adding an alkaline precipitating agent to the metal salt precursors of cerium and aluminum for hydrothermal treatment, washing, drying, and calcining to obtain a composite support. (2) Mixing the metal salt precursors of ruthenium, nickel, and iron with the composite support and then calcining to obtain the ammonia decomposition catalyst.

4. The preparation method according to claim 3, wherein The metal salt precursor of cerium is one or more of cerium nitrate and cerium acetate. Preferably, the metal salt precursor of aluminum is one or more of aluminum nitrate and aluminum acetate. Preferably, the metal salt precursor of ruthenium is one or more of ruthenium trichloride, ruthenium(III) nitrosyl nitrate, and ruthenium acetate. Preferably, the metal salt precursor of nickel is one or more of nickel nitrate, nickel acetate, and nickel carbonate. Preferably, the metal salt precursor of iron is one or more of iron nitrate, iron acetate, and iron carbonate.

5. The preparation method according to claim 3, characterized in that, In step (1), the metal salt precursors of cerium and aluminum are configured into a solution according to a certain molar ratio, continuously stirred, an alkaline precipitating agent is added thereto, and the mixed solution is subjected to hydrothermal treatment. The suspension obtained after hydrothermal treatment is subjected to multiple water washes and suction filtrations, the obtained precipitate is dried, and after drying, it is calcined to obtain the composite support.

6. The preparation method according to claim 5, characterized in that, The hydrothermal treatment conditions are to keep the temperature at 110-130 °C for 10-14 h. Preferably, the alkaline precipitating agent is one or more of ammonia water, sodium hydroxide, and potassium hydroxide. Preferably, the mixed solution is continuously stirred for 5-8 h. Preferably, the drying temperature is 70-100 °C, and the drying time is 8-15 h. Preferably, the calcination temperature is 400-600 °C, and the heat preservation time is 2-5 h.

7. The preparation method according to claim 3, wherein In step (2), the mixing methods of the metal salt precursors of ruthenium, nickel, and iron and the composite support include the incipient wetness impregnation method, the ball milling method, and the hydrothermal method. Preferably, when synthesized by the incipient wetness impregnation method, the metal salt precursors of ruthenium, nickel, and iron are dissolved in water according to the loading ratio to prepare a metal salt precursor solution. The metal salt precursor solution is gradually added dropwise to the composite support. After impregnation, it is calcined to obtain the final ammonia decomposition catalyst. Further preferably, the mass-volume ratio of the ruthenium metal salt precursor to water is 0.05-2 g:10-100 ml; the ratio of the metal salt precursor solution to the composite support is 5-20 mL:0.5-5 g; the calcination temperature is 400-600 °C, and the heat preservation time is 2-5 h. Preferably, when synthesized by the hydrothermal method, metal salt precursors of ruthenium, nickel, and iron are dissolved in water according to the loading ratio to prepare a metal salt precursor solution. The metal salt precursor solution is mixed with the composite support according to the loading ratio and then placed in a hydrothermal autoclave for hydrothermal treatment. After hydrothermal treatment, filtration and calcination are carried out to obtain the final ammonia decomposition catalyst. Further preferably, the mass-volume ratio of the ruthenium metal salt precursor to water is 0.05 - 2 g:10 - 100 ml; the ratio of the metal salt precursor solution to the composite support is 20 - 40 mL:3 - 8 g, and the hydrothermal conditions are 150 - 170 °C for 10 - 14 h. Preferably, when synthesized by the ball milling method, metal salt precursors of ruthenium, nickel, and iron are mixed with the composite support according to the loading ratio and then subjected to ball milling treatment. After mixing, calcination treatment is carried out to obtain the ammonia decomposition catalyst. Further preferably, the ball milling method rotates forward at 200 - 500 rpm for 20 - 40 s, rotates backward at 200 - 500 rpm for 20 - 40 s, with an interval of 5 - 15 s in the middle, and cycles 4 - 6 times; the calcination temperature is 400 - 600 °C, and the heat preservation is 2 - 5 h.

8. Application of the cerium-based ammonia decomposition catalyst under low-temperature conditions as described in claim 1 or 2 or the cerium-based ammonia decomposition catalyst under low-temperature conditions obtained by the preparation method described in any one of claims 3 - 7 in hydrogen production by ammonia decomposition under low-temperature conditions.

9. A method for hydrogen production by ammonia decomposition under low-temperature conditions, characterized in that, Using the cerium-based ammonia decomposition catalyst under low-temperature conditions as described in claim 1 or 2 or the cerium-based ammonia decomposition catalyst under low-temperature conditions obtained by the preparation method described in any one of claims 3 - 7, the following steps are included: under a mixed atmosphere at 400 - 550 °C, the cerium-based ammonia decomposition catalyst under low-temperature conditions is used to reduce the ammonia-containing gas.

10. The method according to claim 9, characterized in that, The low temperature is 500 - 550 °C, and further preferably 525 - 550 °C; Preferably, the mixed atmosphere is a hydrogen-argon mixture; Preferably, the reaction space velocity is 14,000 - 16,000 mL g -1 h -1 , and the step size is 20 - 30 °C.

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