Preparation method and application of ammonia decomposition high-entropy alloy catalyst

Abstract

The invention provides a preparation method of a high-entropy alloy catalyst, which comprises the following steps: weighing at least five metal precursors such as iron, nickel, cobalt, magnesium, aluminum, niobium and tungsten according to a certain molar ratio, premixing solid powder by a mechanical ball milling method, filling the mixed powder into a crucible of an electric arc melting furnace, placing a reaction device in an inert atmosphere, and carrying out ball milling to obtain the high-entropy alloy catalyst. And material oxidation is prevented. Through arc discharge, the raw materials are melted in a rapid heating mode, and meanwhile in the melting process, electromagnetic stirring is used for ensuring that the materials are fully mixed and homogenized. And after smelting is completed, a melt is rapidly cooled and solidified under the action of a cooling system, after a sample is completely cooled, the crucible is taken out, thermal reduction is conducted in a reducing atmosphere, and the ammonia decomposition high-entropy alloy catalyst is obtained. The catalyst prepared by the invention has the characteristics of high activity, short preparation process time and high homogenization degree.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic hydrogen production by decomposition of ammonia, and in particular to a preparation method and application of a high-entropy alloy catalyst for decomposing ammonia. Background Art

[0002] Ammonia decomposition is a chemical reaction process that heats liquid ammonia to 800-850°C and decomposes it into hydrogen and nitrogen under the action of a nickel-based catalyst. The mixed gas produced in this process is about 75% hydrogen and 25% nitrogen. Ammonia decomposition is not only an effective method of hydrogen production, but also has environmental advantages and does not emit carbon dioxide.

[0003] Chinese patent application CN202211692623.0 A method for preparing a high entropy alloy catalyst comprises the following steps: using nickel salt, iron salt, aluminum salt, cobalt salt and copper salt as raw materials, dissolving the raw materials with citric acid, boric acid and L-type ascorbic acid in ionized water, and stirring well to obtain a clear solution; adding a nickel mesh or nickel foam to the obtained clear solution, mechanically stirring, and ultrasonically vibrating to make the metal salt evenly distributed on the nickel mesh or nickel foam; adding a reducing agent solution, and then reducing under a reducing gas to prepare a high entropy alloy catalyst. Compared with the present application, the existing preparation process is complicated, and the ammonia decomposition reaction activity of the currently known iron-based catalysts is generally low. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the iron-based catalyst preparation process in the prior art, such as complex process flow and low ammonia decomposition activity, thereby providing a method for preparing a high entropy alloy catalyst. The high entropy alloy catalyst prepared by the method provided by the present invention has the characteristics of high activity, short preparation process time and high degree of homogenization.

[0005] The present invention provides a method for preparing a high entropy alloy catalyst, comprising the following steps:

[0006] (1) Precursor solid powders of at least five metals selected from iron, nickel, cobalt, magnesium, aluminum, niobium and tungsten are subjected to mechanical ball milling to obtain a mixed metal powder;

[0007] Based on the mass of the high entropy alloy particles, the content of each metal is independently 10-50%;

[0008] (2) The mixed metal powder is loaded into a crucible of an arc melting furnace, and the metal powder is melted by rapid heating in an inert atmosphere by arc discharge; after the melt is rapidly cooled and solidified under the action of a cooling system, the crucible is taken out and thermally reduced in a reducing atmosphere to obtain an ammonia decomposition high entropy alloy catalyst.

[0009] The iron precursor is ferric nitrate, ferric chloride, and ferric oxalate;

[0010] The nickel precursor is one of nickel nitrate, nickel chloride or nickel acetate or a mixture of several thereof;

[0011] The cobalt precursor is one of cobalt nitrate, cobalt chloride or cobalt acetate or a mixture of several thereof;

[0012] The magnesium precursor is one of magnesium nitrate, magnesium chloride, and magnesium acetate, or a mixture of several thereof;

[0013] The aluminum precursor is aluminum nitrate and / or aluminum chloride;

[0014] The niobium precursor is niobium nitrate and / or niobium pentachloride;

[0015] The tungsten precursor is tungsten nitrate and / or ammonium tungstate.

[0016] The temperature of the arc melting furnace is 1800-2300°C and the heating time of the metal powder is 15-30 minutes.

[0017] The cooling system is as follows: cooling water is transported to the cooling pipe of the smelting furnace through a cooling water pump, flows through high-temperature parts such as electrodes, furnace walls and crucibles, absorbs heat from these parts, and achieves rapid cooling.

[0018] In step (2), the reducing atmosphere is a mixture of hydrogen (40%-100%) and an inert gas, or a mixture of hydrogen (60%-100%) and an inert gas; the reducing temperature is 300-600° C., and the reducing time is 2-4 hours.

[0019] A method for producing hydrogen by decomposing ammonia comprises the following steps:

[0020] (1) The ammonia decomposition high entropy alloy catalyst is loaded into a fixed bed reaction;

[0021] (2) Filling the reactor with ammonia gas at a space velocity of 1000 to 10000 h -1 Under the conditions of , the reaction temperature is 500-600°C, the reaction pressure is 0.1-0.5MPa, and ammonia is decomposed into hydrogen and nitrogen.

[0022] The present invention provides a method for preparing a high entropy alloy catalyst, which comprises weighing at least five metal precursors of iron, nickel, cobalt, magnesium, aluminum, niobium, tungsten and the like in a certain molar ratio, premixing the solid powder by mechanical ball milling, loading the mixed powder into a crucible of an arc melting furnace, and placing the reaction device in an inert atmosphere to prevent oxidation of the material. The raw materials are melted by arc discharge to achieve rapid temperature rise, and electromagnetic stirring is used to ensure that the materials are fully mixed and homogenized during the melting process. After the smelting is completed, the melt is rapidly cooled and solidified under the action of a cooling system, and after the sample is completely cooled, the crucible is taken out, and a high entropy alloy catalyst for ammonia decomposition is obtained by thermal reduction under a reducing atmosphere. The catalyst prepared by the present invention has the characteristics of high activity, short preparation process time and high homogenization degree.

[0023] The high entropy alloy catalyst prepared by adding additives to iron-based metals in the present application has significantly improved ammonia decomposition reaction activity, and has the characteristics of high activity, short preparation process time and high degree of particle size uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is a SEM electron microscope image of the catalyst prepared in Example 1 of the present invention; DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The chemical reagents used in the following exemplary embodiments that are not specifically described can all be purchased on the market.

[0028] The present invention provides a method for preparing a high entropy alloy catalyst, comprising the following steps:

[0029] (1) Premixing solid powders of at least five metal precursors, including iron, nickel, cobalt, magnesium, aluminum, niobium, and tungsten, in a certain molar ratio by mechanical ball milling.

[0030] (2) The mixed powder is loaded into the crucible of the arc melting furnace, and the reaction device is placed in an inert atmosphere to prevent oxidation of the material. The raw materials are melted by rapid heating through arc discharge, and electromagnetic stirring is used during the melting process to ensure that the materials are fully mixed and homogenized. After the melting is completed, the melt is rapidly cooled and solidified under the action of the cooling system. After the sample is completely cooled, the crucible is taken out and thermally reduced in a reducing atmosphere to obtain an ammonia decomposition high entropy alloy catalyst;

[0031] As an example, in step (1), the content of each metal in at least five solid powders in the high entropy alloy catalyst is independently 10-50% based on the mass of the high entropy alloy particles;

[0032] As an example, in step (2), the arc current and voltage are adjusted so that the temperature of the arc melting furnace can reach above 1800°C.

[0033] As an example, in step (2), the arc melting furnace is heated at 1800° C. for 15 minutes.

[0034] As an example, in step (2), the cooling system is as follows: cooling water is transported to the cooling pipe of the smelting furnace through a cooling water pump, flows through high-temperature parts such as electrodes, furnace walls and crucibles, absorbs heat from these parts, and achieves rapid cooling.

[0035] As an example, in step (2), the reduction temperature is 300-600° C. and the reduction time is 2-4 h.

[0036] The present invention also provides an ammonia decomposition high entropy alloy catalyst obtained according to the preparation method of the ammonia decomposition high entropy alloy catalyst described in any one of the above items.

[0037] The present invention further provides the use of the nickel-based methanogenic catalyst, that is, the catalyst is subjected to a reaction at a reaction temperature of 500 to 600°C, a reaction pressure of 0.1 to 0.5 MPa, and a space velocity of 1000 to 10000 h -1 Under the conditions of , ammonia decomposes to produce hydrogen and nitrogen.

[0038] Example 1

[0039] Cobalt nitrate, nickel nitrate, iron nitrate, aluminum nitrate, and niobium oxalate were pre-mixed into solid powders by mechanical ball milling, and the mixed powders were loaded into the crucible of the arc melting furnace, and the reaction device was placed in an argon atmosphere to prevent material oxidation. The arc current and voltage were adjusted to make the temperature of the arc melting furnace reach 1800°C and maintained for 20 minutes. Cooling water was transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 1800°C to room temperature in 20 minutes. The catalyst precursor was loaded into the reactor and reduced under the atmosphere of hydrogen and argon mixed gas. The reduction temperature was 500°C and the reduction time was 2 hours. It was recorded as CoNiFeAlNb high entropy alloy catalyst, and its SEM electron microscope image is as follows Figure 1 As shown, the particle size of the high entropy alloy particles on the catalyst is about 6.2 nm.

[0040] Example 2

[0041] Cobalt nitrate, nickel nitrate, iron nitrate, aluminum nitrate, and niobium oxalate are pre-mixed into solid powders by mechanical ball milling, and the mixed powders are loaded into a crucible of an arc melting furnace, and the reaction device is placed in an argon atmosphere to prevent oxidation of the materials, and the arc current and voltage are adjusted to make the temperature of the arc melting furnace reach 2000°C and maintained for 15 minutes. Cooling water is transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 2000°C to room temperature in 25 minutes. The catalyst precursor is loaded into a reactor and reduced under the atmosphere of a hydrogen-argon mixed gas, the reduction temperature is 550°C, the reduction time is 2 hours, and it is recorded as a CoNiFeAlNb high entropy alloy catalyst, and the particle size of the high entropy alloy particles on the catalyst is about 7.2nm.

[0042] Example 3

[0043] Cobalt nitrate, nickel chloride, ferric chloride, aluminum nitrate, and niobium oxalate are pre-mixed into solid powders by mechanical ball milling, and the mixed powders are loaded into a crucible of an arc melting furnace, and the reaction device is placed in an argon atmosphere to prevent oxidation of the materials, and the arc current and voltage are adjusted to make the temperature of the arc melting furnace reach 1800°C and maintained for 20 minutes. Cooling water is transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 1800°C to room temperature in 20 minutes. The catalyst precursor is loaded into a reactor and reduced under the atmosphere of a hydrogen-argon mixed gas, the reduction temperature is 500°C, the reduction time is 2 hours, and it is recorded as a CoNiFeAlNb high entropy alloy catalyst, and the particle size of the high entropy alloy particles on the catalyst is about 7.5nm.

[0044] Example 4

[0045] Cobalt nitrate, nickel chloride, ferric chloride, aluminum nitrate, and niobium oxalate are pre-mixed into solid powders by mechanical ball milling, and the mixed powders are loaded into a crucible of an arc melting furnace, and the reaction device is placed in an argon atmosphere to prevent oxidation of the materials, and the arc current and voltage are adjusted to make the temperature of the arc melting furnace reach 1800°C and maintained for 20 minutes. Cooling water is transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 1800°C to room temperature in 20 minutes. The catalyst precursor is loaded into a reactor and reduced under the atmosphere of a hydrogen-argon mixed gas, the reduction temperature is 500°C, the reduction time is 2 hours, and it is recorded as a CoNiFeAlNb high entropy alloy catalyst, and the particle size of the high entropy alloy particles on the catalyst is about 8.3nm.

[0046] Example 5

[0047] Cobalt nitrate, nickel nitrate, iron nitrate, aluminum nitrate and magnesium nitrate are pre-mixed into solid powders by mechanical ball milling, and the mixed powders are loaded into the crucible of the arc melting furnace, and the reaction device is placed in an argon atmosphere to prevent oxidation of the materials, and the arc current and voltage are adjusted to make the temperature of the arc melting furnace reach 1800°C and maintained for 15 minutes. Cooling water is transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 1800°C to room temperature in 20 minutes. The catalyst precursor is loaded into the reactor and reduced under the atmosphere of hydrogen and argon mixed gas, the reduction temperature is 500°C, the reduction time is 2 hours, and it is recorded as CoNiFeAlMg high entropy alloy catalyst, and the particle size of the high entropy alloy particles on the catalyst is about 4.8nm.

[0048] Example 6

[0049] Cobalt nitrate, nickel nitrate, iron nitrate, aluminum nitrate and magnesium nitrate are pre-mixed into solid powder by mechanical ball milling, and the mixed powder is loaded into the crucible of the arc melting furnace, and the reaction device is placed in an argon atmosphere to prevent oxidation of the material, and the arc current and voltage are adjusted to make the temperature of the arc melting furnace reach 2000°C and maintained for 15 minutes. Cooling water is transported to the cooling pipe of the melting furnace through a cooling water pump, and cooled from 2000°C to room temperature in 25 minutes. The catalyst precursor is loaded into the reactor and reduced under the atmosphere of hydrogen and argon mixed gas, the reduction temperature is 550°C, the reduction time is 2 hours, and it is recorded as CoNiFeAlMg high entropy alloy catalyst, and the particle size of the high entropy alloy particles on the catalyst is about 5.2nm.

[0050] Evaluation Examples

[0051] A method for producing hydrogen by decomposing ammonia using the high entropy alloy particles prepared in Examples 1-6, wherein: (1) the ammonia decomposition high entropy alloy catalyst according to any one of Claims 1-4 is loaded on a fixed bed reactor;

[0052] (2) Filling ammonia into the fixed bed reactor, the ammonia space velocity is 1000-10000h -1 Under the conditions of , the reaction temperature is 500-600°C, the reaction pressure is 0-0.5MPa, and ammonia is decomposed into hydrogen and nitrogen.

[0053] Evaluation conditions: catalyst loading 5 ml, reaction ammonia space velocity 5000 h -1 , ammonia gas flow rate is 416 ml / min, reaction temperature is 550°C, and reaction pressure is 0.1 MPa.

[0054] Example 1 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 99.1%

[0055] Example 2 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 98.5%

[0056] Example 3 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 98.7%

[0057] Example 4 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 97.8%

[0058] Example 5 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 99.5%

[0059] Example 6 Ammonia decomposition conversion rate Ammonia decomposition conversion rate 99.3%

[0060] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing a high entropy alloy catalyst for ammonia decomposition, characterized in that: The steps include: (1) Precursor solid powders of at least five metals selected from iron, nickel, cobalt, magnesium, aluminum, niobium and tungsten are subjected to mechanical ball milling to obtain a mixed metal powder; Based on the mass of the high entropy alloy particles, the content of each metal is independently 10-50%; (2) The mixed metal powder is loaded into a crucible of an arc melting furnace, and the metal powder is melted by rapid heating in an inert atmosphere by arc discharge; after the melt is rapidly cooled and solidified under the action of a cooling system, the crucible is taken out and thermally reduced in a reducing atmosphere to obtain an ammonia decomposition high entropy alloy catalyst.

2. The method for preparing ammonia decomposition high entropy alloy catalyst according to claim 1, characterized in that: The iron precursor is ferric nitrate, ferric chloride, and ferric oxalate; The nickel precursor is one of nickel nitrate, nickel chloride or nickel acetate or a mixture of several thereof; The cobalt precursor is one of cobalt nitrate, cobalt chloride or cobalt acetate or a mixture of several thereof; The magnesium precursor is one of magnesium nitrate, magnesium chloride, and magnesium acetate, or a mixture of several thereof; The aluminum precursor is aluminum nitrate and / or aluminum chloride; The niobium precursor is niobium nitrate and / or niobium pentachloride; The tungsten precursor is tungsten nitrate and / or ammonium tungstate.

3. The method for preparing ammonia decomposition high entropy alloy catalyst according to claim 1, characterized in that: The temperature of the arc melting furnace is 1800-2300°C, and the heating time of the metal powder is 15-30 minutes.

4. The method for preparing ammonia decomposition high entropy alloy catalyst according to claim 1, characterized in that: The cooling system is as follows: cooling water is transported to the cooling pipe of the smelting furnace through a cooling water pump, flows through high-temperature parts such as electrodes, furnace walls and crucibles, absorbs heat from these parts, and achieves rapid cooling.

5. The method for preparing ammonia decomposition high entropy alloy catalyst according to claim 1, characterized in that: In step (2), the reducing atmosphere is a mixture of hydrogen (40%-100%) and an inert gas, or a mixture of hydrogen (60%-100%) and an inert gas; the reducing temperature is 300-600° C., and the reducing time is 2-4 hours.

6. A method for producing hydrogen by decomposing ammonia, characterized in that: The steps include: (1) The ammonia decomposition high entropy alloy catalyst according to any one of claims 1 to 5 is loaded into a fixed bed reaction; (2) Filling the reactor with ammonia gas at a space velocity of 1000 to 10000 h -1 Under the conditions of , the reaction temperature is 500-600°C, the reaction pressure is 0.1-0.5MPa, and ammonia is decomposed into hydrogen and nitrogen.

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