Porous core-shell structure ammonia decomposition catalyst and its preparation method and application

Abstract

The present invention provides a porous core-shell structured ammonia decomposition catalyst, its preparation method and application. The preparation method includes the following steps: S100, preparing a supercritically in-situ doped cerium oxide support; S200, formulating a reaction solution B containing a precursor salt of an active component, a templating agent, the supercritically in-situ doped cerium oxide support, an inorganic base and water. The reaction solution B is subjected to a second heat treatment at 150-300 °C to obtain a second heat treatment product, which is washed, dried and calcined to obtain the porous core-shell structured ammonia decomposition catalyst. The catalyst of the present invention has low T90 and T100 temperatures, and the preparation method is simple and the equipment requirements are low.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen production by high-temperature thermal decomposition of green hydrogen-containing compounds, and particularly relates to a porous core-shell structure ammonia decomposition catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, energy is mainly obtained by burning fossil fuels, which has led to a common problem globally, namely the extremely serious environmental and climate problems caused by the overuse of fossil fuels. In particular, the combustion of fossil fuels generates carbon oxides and nitrogen oxides, which can cause disasters such as acid rain, haze, and the greenhouse effect. Among them, the harm caused by acid rain and haze to the human body is direct, and the greenhouse effect will cause the global temperature to rise, resulting in the melting of glaciers and the rise of sea levels. And these impacts will ultimately affect us humans. At the same time, energy is essential, and with the development of the times and the progress of technology, the demand for energy is increasing day by day. Therefore, it is necessary to study sustainable energy such as wind energy, solar energy, nuclear energy, tidal energy, etc., as well as hydrogen energy (hydrogen gas) that has attracted the attention of many scientists.

[0003] Hydrogen also has obvious disadvantages. For example, the density of hydrogen is low, and its density is only 0.084 g / L at 20 °C. For another example, hydrogen is not a relatively safe energy source, and the explosion limit of hydrogen is very wide, between 4% and 75.6%. Due to the above reasons, the transportation cost of hydrogen is also relatively high. Therefore, the hydrogen used is preferably stored in advance or prepared on-site.

[0004] Ammonia, as a hydrogen storage material, can be synthesized in large quantities by the Haber-Bosch method, and has great advantages in terms of production and physical and chemical properties. However, the reaction temperature for ammonia decomposition to produce hydrogen is relatively high, with high energy consumption, and it is necessary to study catalysts suitable for low-temperature reactions and with high conversion rates. Existing low-temperature catalysts are usually noble metal-based catalysts, which are costly.

[0005] Therefore, developing an ammonia decomposition catalyst with advantages such as low cost and low-temperature catalysis is the key to solving the above problems. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a porous core-shell structure ammonia decomposition catalyst, a preparation method thereof, and an application thereof, aiming at the disadvantages existing in the prior art.

[0007] The inventors of the present application found that by the coprecipitation method, nitrogen-doped cerium oxide was synthesized using an organic amine as the nitrogen source, and the cerium oxide support was further prepared by the supercritical in-situ doping method. Then, the active component transition metal oxides such as cobalt and nickel oxides were loaded onto the cerium oxide support through a template agent, and a porous core-shell structured ammonia decomposition catalyst was obtained. Such a catalyst has low T90 and T100 temperatures. In addition, the preparation method of the present invention is simple to operate and requires simple equipment.

[0008] The object of the present invention is achieved by the following technical solutions.

[0009] On the one hand, the present invention provides a preparation method of a porous core-shell structured ammonia decomposition catalyst, wherein the preparation method comprises the following steps:

[0010] S100. Prepare a supercritical in-situ doped cerium oxide support, including:

[0011] S110. Perform a first heat treatment on solution B containing a cerium salt, an organic amine, and an optional rare earth source other than the cerium source at 150 - 300 °C to obtain a first heat treatment product;

[0012] S120. Wash, dry, and calcine the first heat treatment product to obtain nitrogen-doped cerium oxide;

[0013] S130. React nitrogen-doped cerium oxide with liquid ammonia in a supercritical state to obtain a supercritical in-situ doped cerium oxide support;

[0014] S200. Prepare reaction solution B containing a precursor salt of the active component, a template agent, a supercritical in-situ doped cerium oxide support, an inorganic base, and water. The reaction solution B is subjected to a second heat treatment at 150 - 300 °C to obtain a second heat treatment product, and the second heat treatment product is washed, dried, and calcined to obtain a porous core-shell structured ammonia decomposition catalyst.

[0015] According to the preparation method provided by the present invention, the cerium salt is selected from cerium nitrate, cerium chloride, and their hydrates. For example, the cerium salt can be Ce(NO3)3·6H2O.

[0016] According to the preparation method provided by the present invention, examples of suitable organic amines include but are not limited to: ethylenediamine, 1,2-propanediamine, and 1,4-butanediamine.

[0017] According to the preparation method provided by the present invention, wherein the rare earth source other than the cerium source is selected from lanthanum source, praseodymium source, neodymium source, samarium source, gadolinium source and terbium source. The rare earth source other than the cerium source can be in the form of nitrate or its hydrate. In some embodiments, the rare earth source other than the cerium source is selected from La(NO3)3, Pr(NO3)3, Nd(NO3)3, Sm(NO3)3, Gd(NO3)3, Tb(NO3)3 and their hydrates. For example, the lanthanum source can be La(NO3)3·6H2O, the praseodymium source can be Pr(NO3)3·6H2O, the neodymium source can be Nd(NO3)3·6H2O, the samarium source can be Sm(NO3)3·6H2O, the gadolinium source can be Gd(NO3)3·6H2O, and the terbium source can be Tb(NO3)3·6H2O.

[0018] It is believed that introducing rare earth metal elements other than cerium into the cerium oxide carrier can increase carrier defects, stabilize nitrogen elements, and increase holes. At the same time, rare earth metal elements other than cerium can also improve activity and stability.

[0019] According to the preparation method provided by the present invention, wherein the solution B is prepared by the following method I or method II.

[0020] The method I includes:

[0021] S111. Under stirring conditions, an organic amine solution is added dropwise to an aqueous cerium salt solution until the pH value reaches 12.5 - 13.5 to obtain solution B.

[0022] The method II includes:

[0023] S111'. Under stirring conditions, an organic amine solution is added dropwise to an aqueous cerium salt solution until the pH value reaches 12.5 - 13.5 to obtain solution A;

[0024] S112'. The rare earth source other than the cerium source is dissolved in solution A, and stirred, preferably stirred at a temperature of 20 - 40 °C for 0.5 - 2 h to obtain solution B.

[0025] According to the preparation method provided by the present invention, wherein the concentration of the cerium salt in solution B is 1 - 10 wt%, preferably 5 - 10 wt%.

[0026] According to the preparation method provided by the present invention, wherein the mass ratio of the cerium salt to the rare earth source other than the cerium source in step S110 is 8:0 - 2, preferably 8:1 - 1.5.

[0027] According to the preparation method provided by the present invention, in step S110, the first heat treatment is carried out for 12 to 24 hours. In some embodiments, the conditions of the first heat treatment in step S110 include: the temperature is 180 - 220°C; the time is 20 - 24 hours.

[0028] According to the preparation method provided by the present invention, in step S120, the conditions of the calcination include: the temperature is 400 - 700°C, preferably 500 - 600°C; the time is 3 - 6 hours.

[0029] In the present invention, the calcination in step S120 is carried out in an oxygen atmosphere (such as air). In the present invention, an aerobic calcination method is adopted, which can remove the organic matter in the core layer and anions such as nitrate ions, so as to produce a porous structure in the remaining space; calcination at the above temperature can ensure that the particles are completely burned out. In addition, in order to prevent the porous structure from collapsing due to a sudden temperature rise, the present invention can further control the heating rate. For example, the heating rate can be 2 - 10°C / minute, preferably 4 - 6°C / minute.

[0030] According to the preparation method provided by the present invention, in step S130, the conditions of the reaction include: the supercritical state temperature is 190 - 210°C, such as 200°C; the supercritical state pressure is 14.5 - 16 MPa, such as 15 MPa; the reaction time is 4 - 8 hours.

[0031] In the present invention, the reaction of nitrogen-doped cerium oxide and liquid ammonia in step S130 is carried out in a closed reactor. The present invention has no special requirements for this closed container, and any known high-pressure resistant closed reactor in the art can be used, such as a high-pressure resistant closed reactor made of stainless steel.

[0032] According to the preparation method provided by the present invention, the active component precursor salt is selected from iron salts, cobalt salts, nickel salts, and manganese salts. The active component precursor salt can be in the form of nitrates, chlorides, acetates, or their hydrates. In some embodiments, the active component precursor salts are selected from Fe(NO3)3, FeCl3, Ni(NO3)2, NiC4H6O4, Co(NO3)2, CoCl2, MnCl2, Mn(NO3)2, and their hydrates. For example, the iron salt can be Fe(NO3)3·9H2O, FeCl3·6H2O, the nickel salt can be Ni(NO3)2·6H2O, NiC4H6O4·4H2O, the cobalt salt can be Co(NO3)2·6H2O, CoCl2·6H2O, and the manganese salt can be MnCl2·4H2O, Mn(NO3)2·4H2O.

[0033] In some preferred embodiments, the active component precursor salt comprises or consists of a cobalt salt and a nickel salt, and the mass ratio of the cobalt salt to the nickel salt is 1:0.5 - 1.5, preferably 1:0.8 - 1.2. Using these two salts as the active component precursor salts, the T90 and T100 temperatures are further reduced.

[0034] According to the preparation method provided by the present invention, examples of the template agent include but are not limited to: cetyltrimethylammonium bromide (CTAB); polyether polyol; and sodium dodecylsulfonate. Examples of the polyether polyol suitable for use in the present invention include but are not limited to: F127, P123, F68, L62.

[0035] According to the preparation method provided by the present invention, the inorganic base is sodium hydroxide or potassium hydroxide.

[0036] According to the preparation method provided by the present invention, the mass ratio of the oxide corresponding to the active component precursor salt, the supercritically in-situ doped cerium oxide support, the template agent to the inorganic base in reaction solution B is (0.15 - 0.30):(2.40 - 2.85):(4 - 5):4, preferably (0.15 - 0.20):(2.50 - 2.65):(4 - 4.5):4.

[0037] According to the preparation method provided by the present invention, the preparation method of reaction solution B in step S200 includes:

[0038] S210. Adding the supercritically in-situ doped cerium oxide support to an aqueous solution comprising the active component precursor salt and the template agent, and stirring to obtain reaction solution A;

[0039] S220. Mixing reaction solution A with an aqueous solution of the inorganic base to obtain reaction solution B.

[0040] In some embodiments, the conditions for stirring in step S210 include: temperature of 20 - 40°C, time of 0.5 - 2 h, and in some other embodiments, the conditions for mixing in step S220 include: temperature of 20 - 40°C, time of 12 - 24 h.

[0041] In the present invention, the concentration of the aqueous solution of the inorganic base is 0.25 - 0.50 mol·L -1 .

[0042] According to the preparation method provided by the present invention, the present invention has no particular limitation on washing and drying, and any known method in the art can be used.

[0043] In some specific embodiments, the washing is hot water washing, and the number of washing times can be confirmed according to the washing effect. For example, the washing is performed 2 - 6 times.

[0044] In some specific embodiments, the drying conditions in step S120 include: a vacuum degree of -0.06 MPa to -0.09 MPa; a temperature of 90 - 120 °C; a time of 12 - 24 h; and in some other specific embodiments, the drying conditions in step S200 include: a vacuum degree of -0.06 MPa to -0.09 MPa; a temperature of 90 - 130 °C; a time of 4 - 8 h.

[0045] According to the preparation method provided by the present invention, wherein, the content of the cerium oxide support in the reaction solution B in step S200 is 0.1 wt% - 2 wt%, preferably 0.6 wt% - 1.2 wt%.

[0046] According to the preparation method provided by the present invention, wherein, the time of the second heat treatment in step S200 is 10 - 12 h.

[0047] According to the preparation method provided by the present invention, wherein, the calcination conditions in step S200 include: a temperature of 400 - 700 °C, preferably 500 - 600 °C; a time of 3 - 6 h.

[0048] In the present invention, the calcination in step S200 is carried out in an oxygen atmosphere (for example, air). In the present invention, an aerobic calcination method is adopted, which can remove the organic matter and nitrate in the shell layer, so as to produce a porous structure in the remaining space; calcination at the above temperature can ensure that the particles are completely burned out. In addition, in order to prevent the porous structure from collapsing due to a sudden temperature rise, the present invention can further control the heating rate. For example, the heating rate can be 2 - 10 °C / minute, preferably 4 - 6 °C / minute.

[0049] In a second aspect, the present invention provides a porous core-shell structured ammonia decomposition catalyst prepared by the above preparation method.

[0050] According to the porous core-shell structured ammonia decomposition catalyst provided by the present invention, wherein, the porous core-shell structured ammonia decomposition catalyst includes a supercritically in-situ doped cerium oxide support as the core and an active component supported on the cerium oxide support as the shell.

[0051] According to the porous core-shell structured ammonia decomposition catalyst provided by the present invention, wherein, the core includes cerium oxide and optionally a rare earth metal oxide. In some embodiments, the porous core-shell structured ammonia decomposition catalyst includes 5 - 20 wt% of the active component, 0 - 20 wt% of the rare earth metal oxide, and the balance of cerium oxide; and in some embodiments, the porous core-shell structured ammonia decomposition catalyst includes 5 - 15 wt% of the active component, 0 - 15 wt%, preferably 5 - 15 wt% of the rare earth metal oxide, and the balance of cerium oxide.

[0052] The porous core-shell structured ammonia decomposition catalyst provided by the present invention, wherein the active component comprises one or more of iron oxide, cobalt oxide, nickel oxide, and manganese oxide.

[0053] In the present invention, the components of the porous core-shell structured ammonia decomposition catalyst are calculated as metal oxides. That is to say, the nitrogen element is not recorded in the percentage content of the above-mentioned porous core-shell structured ammonia decomposition catalyst.

[0054] In the third aspect, the present invention provides the application of the above-mentioned porous core-shell structured ammonia decomposition catalyst in ammonia decomposition for hydrogen production.

[0055] The present invention has the following advantages:

[0056] (1) By the coprecipitation method, nitrogen-doped cerium dioxide is synthesized using organic amine as the nitrogen source, and the cerium oxide support is further prepared by the supercritical in-situ doping method. Then, the active component transition metal oxides such as cobalt and nickel oxides are loaded on the cerium oxide support through a template agent, and a porous core-shell structured ammonia decomposition catalyst is prepared. Such a catalyst has low T90 and T100 temperatures

[0057] (2) The preparation method of the present invention is simple in operation and requires simple equipment, which is conducive to industrial promotion and application. Description of the Drawings

[0058] Figure 1 It is a schematic flow chart of an embodiment of the preparation method according to the present invention;

[0059] Figure 2 It is a TEM image of the porous core-shell structured ammonia decomposition catalyst prepared in Example 1 of the present invention;

[0060] Figure 3 It is a TEM image of the catalyst prepared in Comparative Example 4;

[0061] Figure 4 It is an adsorption curve graph of Example 1 and Comparative Example 5. Detailed Description of the Invention

[0062] The embodiments of the present invention will be described in detail below. Unless otherwise specified, the reagents used in the examples and comparative examples are of analytical grade.

[0063] Example 1

[0064] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0065] 1. Cerium Oxide Support

[0066] 1) 20.00 g of Ce(NO3)3·6H2O was added to 300 g of distilled water, stirred, and ethylenediamine was added dropwise until the pH value reached 13 to obtain solution A.

[0067] 2) Solution A was stirred at room temperature for 1 h, and then heat-treated in a reaction kettle at 200 °C for 24 h to obtain the first heat-treated product.

[0068] 3) The first heat-treated product was centrifuged to obtain a precipitate, which was washed 4 times with hot water and dried in a vacuum drying oven. The drying vacuum was -0.06 MPa, the temperature was 100 °C, and the time was 18 h. After drying, the material was calcined at 550 °C in an air atmosphere for 4 h with a heating rate of 5 °C / min. The obtained material was nitrogen-doped cerium dioxide.

[0069] 4) Nitrogen-doped cerium dioxide and liquid ammonia were added to a high-pressure resistant and airtight stainless steel reactor, and reacted at 200 °C and 15 MPa under the supercritical temperature and pressure of NH3 for 6 h to obtain a cerium oxide support, denoted as CeO2-N.

[0070] 2. Preparation of a porous core-shell structured ammonia decomposition catalyst from the cerium oxide support

[0071] 5) 3.89 g of Ni(NO3)2·6H2O and 14.67 g of cetyltrimethylammonium bromide (CTAB) were dissolved in 100 g of distilled water, 9 g of the cerium oxide support CeO2-N was added, and the mixture was stirred at room temperature for 1 h to obtain reaction solution A.

[0072] 6) Reaction solution A was mixed with 700 ml of a sodium hydroxide aqueous solution with a concentration of 0.5 mol·L -1 and stirred at room temperature for 12 h to obtain reaction solution B.

[0073] 7) Reaction solution B was heat-treated in a reaction kettle at 200 °C for 18 h to obtain the second heat-treated product, filtered, washed 4 times with hot water, and then dried in a vacuum drying oven. The drying vacuum was -0.06 MPa, the temperature was 110 °C, and the time was 6 h. Then it was calcined at 550 °C in an air atmosphere for 4 h with a heating rate of 5 °C / min to obtain a porous core-shell structured ammonia decomposition catalyst.

[0074] Example 2

[0075] This example is used to illustrate a porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0076] Refer to Figure 1 , the conditions and operations were basically the same as those in Example 1, except that 2.66 g of La(NO3)3·6H2O was added as a rare earth source to solution A and stirred in step 2).

[0077] Example 3

[0078] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0079] The conditions and operations are basically the same as those in Example 1, with the only difference being that in step 5), adding 3.89 g of Ni(NO3)2·6H2O is changed to adding a mixture of 1.95 g of Ni(NO3)2·6H2O and 1.95 g of Co(NO3)2·6H2O.

[0080] Example 4

[0081] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0082] The conditions and operations are basically the same as those in Example 1, with the only difference being that in step 1), 16.33 g of CeCl3·6H2O with an equimolar amount is used instead of Ce(NO3)3·6H2O.

[0083] Example 5

[0084] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0085] The conditions and operations are basically the same as those in Example 1, with the only difference being that in step 5), 3.89 g of Co(NO3)2·6H2O with an equimolar amount is used instead of Ni(NO3)2·6H2O.

[0086] Example 6

[0087] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0088] The conditions and operations are basically the same as those in Example 1, with the only difference being that in step 5), 3.18 g of CoCl2·6H2O with an equimolar amount is used instead of Co(NO3)2·6H2O.

[0089] Example 7

[0090] This example is used to illustrate the porous core-shell structured ammonia decomposition catalyst and its preparation method.

[0091] The conditions and operations are basically the same as those in Example 1, with the only differences being: (1) In step 2), 2.66 g of La(NO3)3·6H2O is added as a rare earth source and dissolved in solution A followed by stirring; (2) In step 5), adding 3.89 g of Ni(NO3)2·6H2O is changed to adding a mixture of 1.95 g of Ni(NO3)2·6H2O and 1.95 g of Co(NO3)2·6H2O.

[0092] Comparative Example 1

[0093] The conditions and operations are basically the same as those in Example 1, except that in step 1), ethylenediamine is not added dropwise as the nitrogen source for the first-step nitrogen doping.

[0094] Comparative Example 2

[0095] The conditions and operations are basically the same as those in Example 1, except that in step 4), supercritical in-situ nitrogen doping is no longer carried out.

[0096] Comparative Example 3

[0097] The conditions and operations are basically the same as those in Example 1, except that in step 5), the template agent CTAB is not added.

[0098] Comparative Example 4

[0099] The conditions and operations are basically the same as those in Example 1, except that in step 1), ethylenediamine is no longer added dropwise as the nitrogen source for the first-step nitrogen doping. And in step 4), supercritical in-situ nitrogen doping is no longer carried out.

[0100] Comparative Example 5

[0101] 1) Take 20.00 g of Ce(NO3)3·6H2O and add it to 300 g of distilled water. While stirring, add ethylenediamine dropwise until the pH value reaches 13 to obtain solution A.

[0102] 2) Dissolve 2.66 g of La(NO3)3·6H2O in solution A and stir at room temperature for 1 h, then heat-treat in a reaction kettle at 200 °C for 24 h.

[0103] 3) After the reaction is completed, centrifuge the product to obtain a precipitate. Wash the precipitate with hot water 4 times and dry it in a vacuum drying oven. The drying vacuum degree is -0.06 MPa, the temperature is 100 °C, and the time is 18 h. After drying, the material is calcined in an air atmosphere at 550 °C for 4 h, and the heating rate is 5 °C / min. The obtained material is cerium dioxide doped with nitrogen element.

[0104] 4) Add the cerium dioxide doped with nitrogen element and liquid ammonia into a stainless-steel high-pressure resistant closed reactor, and react at the supercritical state temperature and pressure of NH3 at 200 °C and 15 MPa for 6 h to obtain a cerium oxide support, denoted as CeO2-N.

[0105] 5) Add 3.89 g of Ni(NO3)2·6H2O to 9 g of the supercritical in-situ doped cerium oxide support and stir and mix at room temperature for 1 h.

[0106] 6) After the stirring and mixing are completed, vacuum drying is carried out at 75 °C using a rotary evaporator. Then, it is calcined at 550 °C for 4 h in an air atmosphere, and the heating rate is 5 °C / min. The obtained material is denoted as NiO / CeO2-N.

[0107] Comparative Example 6

[0108] 1) Take 20.00 g of Ce(NO3)3·6H2O and 3.89 g of Ni(NO3)2·6H2O and add them to 100 g of distilled water. While stirring, gradually add ethylenediamine dropwise until the pH value reaches 13.

[0109] 2) Dissolve 2.66 g of La(NO3)3·6H2O in the solution and stir at room temperature for 1 h, then heat-treat in a reaction kettle at 200 °C for 24 h.

[0110] 3) After the reaction is completed, centrifuge the product to obtain a precipitate. Wash the precipitate with hot water 4 times and dry it in a vacuum drying oven. The drying vacuum degree is -0.06 MPa, the temperature is 100 °C, and the time is 18 h. The dried material is calcined at 550 °C for 4 h in an air atmosphere, and the heating rate is 5 °C / min. The obtained material is (NiO-CeO2)-N.

[0111] Catalyst Characterization

[0112] The catalysts prepared in each example and comparative example were characterized by TEM. Among them, Figure 2 shows the TEM image of the porous core-shell structured ammonia decomposition catalyst prepared in Example 1, Figure 3 shows the TEM image of the catalyst prepared in Comparative Example 4. It can be seen from Figure 2-3 that the catalyst prepared in Example 1 has a regular shape, N is uniformly doped in the core, and Ni is dispersed on the surface in a porous form; while the catalyst prepared in Comparative Example 4 has an irregular shape and Ni is closely distributed.

[0113] The TEM of the catalysts in Examples 2-7 of the present invention is Figure 2 similar, indicating that the catalysts prepared by the preparation method of the present invention have a regular shape, N is uniformly doped in the core, and Ni and / or Co are dispersed on the surface in a porous form.

[0114] Using nitrogen as the adsorption gas, the isothermal adsorption curves of Examples 1-7 and Comparative Examples 1-8 were plotted. Among them, Figure 4 shows the adsorption curves of Example 1 and Comparative Example 5. It can be seen from Figure 4 that the catalysts of Example 1 and Comparative Example 5 of the present invention are porous structures.

[0115] Similarly, the results show that the catalysts of Examples 2-7 also have porous structures.

[0116] Determination of catalyst composition

[0117] The composition of the catalyst was characterized by XRF (nitrogen element was not determined). Table 1 shows the results of the examples and comparative examples.

[0118] Table 1 Metal oxide composition of the catalyst

[0119]

[0120]

[0121] Application example

[0122] The materials obtained from the above examples and comparative examples were used as catalysts for ammonia decomposition experiments. The experimental conditions were as follows: the ammonia flow rate was controlled by a mass flowmeter, the flow rate was 20 mL / min, the catalyst dosage was 4.00 g, and compared with T 90％ With T 100％ , and the results are shown in Table 2 below.

[0123] Table 2 Catalyst performance

[0124] catalyst <![CDATA[T 90％ > <![CDATA[T 100％ > Example 1 480℃ 603℃ Example 2 468℃ 597℃ Example 3 456℃ 588℃ Example 4 483℃ 599℃ Example 5 503℃ 639℃ Example 6 484℃ 610℃ Example 7 447℃ 573℃ Comparative Example 1 625℃ 672℃ Comparative Example 2 604℃ 658℃ Comparative Example 3 603℃ 642℃ Comparative Example 4 648℃ 689℃ Comparative Example 5 534℃ 657℃ Comparative Example 6 554℃ 653℃

[0125] It can be found from the data in Table 2 that in the present invention, the core-shell structure ammonia decomposition catalyst of double transition metal oxides forming a porous structure coating coprecipitation method and supercritical in-situ method with two nitrogen dopings of cerium dioxide is the preferred scheme. The porous core-shell structure ammonia decomposition catalyst prepared by supercritical in-situ doping in the present invention can achieve excellent low-temperature activity for ammonia decomposition to hydrogen, and the temperatures at which the ammonia decomposition conversion rate is 90% and 100% are both relatively low; moreover, the preparation process of the porous core-shell structure ammonia decomposition catalyst of the present invention is simple, the raw materials are cheap and easily available, and it is very suitable for situations where hydrogen is not easy to store and requires low-temperature decomposition, such as on-site hydrogen production and hydrogenation in hydrogen refueling stations, etc.

Claims

1. Preparation method of porous core-shell structure ammonia decomposition catalyst, wherein, The preparation method includes the following steps: S100. Prepare a supercritical in-situ doped cerium oxide support, including: S110. Perform a first heat treatment on solution B containing a cerium salt, an organic amine, and an optional rare earth source other than the cerium source at 150 - 300 °C to obtain a first heat treatment product; the organic amine is selected from ethylenediamine, 1,2 - propylenediamine, and 1,4 - butanediamine; S120. Wash, dry, and calcine the first heat treatment product to obtain nitrogen-doped cerium oxide; S130. React the nitrogen-doped cerium oxide with liquid ammonia in a supercritical state to obtain a supercritical in-situ doped cerium oxide support; S200. Prepare reaction solution B containing a precursor salt of the active component, a template agent, a supercritical in-situ doped cerium oxide support, an inorganic base, and water. React solution B at 150 - 300 °C for a second heat treatment to obtain a second heat treatment product. Wash, dry, and calcine the second heat treatment product to obtain a porous core-shell structure ammonia decomposition catalyst.

2. The preparation method according to claim 1, wherein, The cerium salt is selected from cerium nitrate, cerium chloride, and their hydrates; and / or, the rare earth source other than the cerium source is selected from lanthanum source, praseodymium source, neodymium source, samarium source, gadolinium source, and terbium source.

3. The preparation method according to claim 2, wherein, The lanthanum source, praseodymium source, neodymium source, samarium source, gadolinium source, and terbium source are nitrates or their hydrates.

4. The preparation method according to claim 1, wherein, Solution B is prepared by the following method: Method I, including: S111. Under stirring conditions, dropwise add an organic amine solution to an aqueous cerium salt solution until the pH value is 12.5 - 13.5 to obtain solution B; Or, Method II, including: S111’. Under stirring conditions, dropwise add an organic amine solution to an aqueous cerium salt solution until the pH value is 12.5 - 13.5 to obtain solution A; S112’. Dissolve the rare earth source other than the cerium source in solution A and stir to obtain solution B.

5. The preparation method according to claim 4, wherein, In step S112’, the stirring is carried out at a temperature of 20 - 40 °C for 0.5 - 2 h.

6. The preparation method according to claim 1, wherein, The concentration of the cerium salt in solution B is 1 - 10 wt%; and / or, the mass ratio of the cerium salt to the rare earth source other than the cerium source in step S110 is 8:0 - 2.

7. The preparation method according to claim 6, wherein, The concentration of the cerium salt in solution B is 5 - 10 wt%.

8. The preparation method according to claim 6, wherein, In step S110, the mass ratio of the cerium salt to the rare earth source other than the cerium source is 8:1 - 1.

5.

9. The preparation method according to claim 1, wherein, In step S110, the first heat treatment is carried out for 12 - 24 h; and / or, the calcination conditions in step S120 include: carried out in an oxygen atmosphere, at a temperature of 400 - 700 °C; for a time of 3 - 6 h; and / or the heating rate is 2 - 10 °C / minute; and / or, the reaction conditions in step S130 include: the supercritical state temperature is 190 - 210 °C; the supercritical state pressure is 14.5 - 16 MPa; the reaction time is 4 - 8 h.

10. The preparation method according to claim 9, wherein, In step S120, the heating rate is 4 - 6 °C / minute; in step S130, the supercritical state temperature is 200 °C, and the supercritical state pressure is 15 MPa.

11. According to the preparation method described in claim 1, wherein, The precursor salt of the active component is selected from iron salts, cobalt salts, nickel salts, and manganese salts; and / or, the template agent is selected from cetyltrimethylammonium bromide, polyether polyol, and sodium dodecylsulfonate; and / or, the inorganic base is sodium hydroxide or potassium hydroxide; And / or, the mass ratio of the oxide corresponding to the active component precursor salt, the supercritically in-situ doped cerium oxide support, the templating agent and the inorganic base in the reaction solution B is (0.15~0.30):(2.40~2.85):(4 - 5):

4.

12. The preparation method according to claim 11, wherein, The iron salt, cobalt salt, nickel salt and manganese salt are selected from Fe(NO3)3, FeCl3, Ni(NO3)2, NiC4H6O4, Co(NO3)2, CoCl2, MnCl2, Mn(NO3)2 and their hydrates.

13. The preparation method according to claim 11, wherein The active component precursor salt is composed of a cobalt salt and a nickel salt, and the mass ratio of the cobalt salt to the nickel salt is 1:0.5 - 1.

5.

14. The preparation method according to claim 11, wherein, The active component precursor salt is composed of a cobalt salt and a nickel salt, and the mass ratio of the cobalt salt to the nickel salt is 1:0.8 - 1.

2.

15. The preparation method according to claim 11, wherein, The mass ratio of the oxide corresponding to the active component precursor salt, the supercritically in-situ doped cerium oxide support, the templating agent and the inorganic base in the reaction solution B is (0.15~0.20):(2.50~2.65):(4~4.5):

4.

16. According to the preparation method described in claim 1, wherein, The preparation method of the reaction solution B in step S200 includes: S210. Adding the supercritically in-situ doped cerium oxide support into an aqueous solution including the active component precursor salt and the templating agent, and stirring to obtain a reaction solution A; S220. Mixing the reaction solution A with an aqueous solution of an inorganic base to obtain a reaction solution B.

17. The preparation method according to claim 16, wherein, The conditions for stirring in step S210 include: temperature of 20 - 40°C and time of 0.5 - 2 h; the conditions for mixing in step S220 include: temperature of 20 - 40°C and time of 12 - 24 h.

18. The preparation method according to claim 16, wherein, The concentration of the inorganic base aqueous solution is 0.25 - 0.50 mol·L -1 .

19. The preparation method according to claim 1, wherein The drying conditions in step S120 include: vacuum degree of -0.06 MPa to -0.09 MPa; temperature of 90 - 120°C; time of 12 - 24 h; And / or, the drying conditions in step S200 include: vacuum degree of -0.06 MPa to -0.09 MPa; temperature of 90 - 130°C; time of 4~8 h; And / or, the time for the second heat treatment in step S200 is 10~12 h; And / or, the conditions for calcination in step S200 include: carried out in an oxygen atmosphere, temperature of 400~700°C; time of 3~6 h; and / or heating rate of 2 - 10°C / minute.

20. The preparation method according to claim 19, wherein In step S200, the heating rate is 4 - 6°C / minute.

21. The porous core-shell structured ammonia decomposition catalyst prepared by the preparation method according to claim 1, wherein the porous core-shell structured ammonia decomposition catalyst comprises a supercritically in-situ doped cerium oxide support as the core and an active component supported on the cerium oxide support as the shell; the core comprises cerium oxide and optionally rare earth metal oxides other than cerium; based on the metal oxides in the porous core-shell structured ammonia decomposition catalyst, the porous core-shell structured ammonia decomposition catalyst comprises 5~20 wt% of the active component, 0~20 wt% of rare earth metal oxides other than cerium and the balance of cerium oxide.

22. The porous core-shell structured ammonia decomposition catalyst according to claim 21, wherein, The porous core-shell structured ammonia decomposition catalyst comprises 5~15 wt% of the active component, 5~15 wt% of rare earth metal oxides other than cerium and the balance of cerium oxide.

23. The porous core-shell structured ammonia decomposition catalyst according to claim 21, wherein, The active component includes one or more of iron oxide, cobalt oxide, nickel oxide and manganese oxide.

24. Application of the porous core-shell structured ammonia decomposition catalyst according to any one of claims 21-23 in ammonia decomposition for hydrogen production.

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