Catalyst for hydrogen production through ammonia decomposition as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for hydrogen production through ammonia decomposition and a preparation method and application thereof, and relates to the technical field of hydrogen production through ammonia decomposition, the catalyst for hydrogen production through ammonia decomposition is a metal fiber material, the average diameter of fibers in the metal fiber material is 0.03 mm, the metal fiber material is in a porous shape, and the average diameter of the fibers in the metal fiber material is 0.03 mm. The active component of the metal fiber material is a transition metal simple substance or an oxide thereof; according to the ammonia decomposition hydrogen production catalyst and the preparation method and application thereof, active sites on the surface of the ammonia decomposition hydrogen production catalyst, Fe atoms can react with N atoms in NH3, an Fe-N compound is formed while the active sites are provided, the surface property of the catalyst is reconstructed, adsorption of NH3 on the surface of the catalyst is enhanced, and reaction energy barriers are reduced; through deep oxidation and nitriding treatment, the surface structure of the catalyst is physically changed, a large number of holes are formed, adsorption and electron transfer of ammonia gas are facilitated, and the thermal cracking reaction of the ammonia gas is enhanced.

Description

Technical Field

[0001] The present invention relates to the technology of ammonia decomposition for hydrogen production, and particularly to an ammonia decomposition hydrogen production catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the green energy sources worldwide, hydrogen can achieve zero emissions during the consumption process, which has attracted wide attention worldwide. Ammonia is called "hydrogen energy 2.0". It has a high energy density (mass energy density of 22.5 MJ / kg and volume energy density of 13.6 MJ / L) and a hydrogen storage capacity (17.8 wt%), which are much higher than those of hydrogen storage materials such as methanol, formic acid, and hydrazine hydrate. The energy density of 1 L of liquid ammonia is equivalent to that of 4.5 L of high-pressure hydrogen (35.0 MPa) or 1200 L of normal-temperature and normal-pressure hydrogen. At the same time, NH 3 only needs a pressure of 1.0 MPa to be liquefied, with high safety, and has unique advantages in storage and transportation, and can achieve seasonal, long-distance, and carbon-free "ammonia-hydrogen" energy storage. Therefore, using NH 3 as a hydrogen storage medium is expected to solve the problems of traditional high-pressure hydrogen storage and transportation and achieve carbon-free utilization of hydrogen energy.

[0003] NH 3 The reaction enthalpy ΔH of the decomposition reaction 298K is 92 kJ·mol -1 , which is an endothermic reaction, and H dissociation from NH 3 needs to overcome a large energy barrier. Therefore, this reaction usually needs to be carried out at a certain high temperature. Although theoretically NH 3 can be completely converted at temperatures above 400 °C, the existence of severe thermodynamic and kinetic barriers limits the reaction rate. Taking the commercial Ni catalyst as an example, the conversion of NH 3 can only be achieved at temperatures above 700 °C. Therefore, it is necessary to develop a suitable catalyst to reduce the reaction energy barrier of the ammonia decomposition reaction to increase the reaction rate and conversion rate, and ultimately reduce the reaction temperature. Summary of the Invention

[0004] The purpose of the present invention is to provide an ammonia decomposition hydrogen production catalyst, a preparation method thereof, and an application thereof to solve the above deficiencies in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: An ammonia decomposition hydrogen production catalyst, wherein the ammonia decomposition hydrogen production catalyst is a metal fiber material, the average diameter of the fibers in the metal fiber material is 0.03 mm, the morphology of the metal fiber material is a porous morphology, and the active component of the metal fiber material is a transition metal element or its oxide.

[0006] Further, the transition metal is at least one of Fe, Co, and Ni.

[0007] A preparation method of a hydrogen production catalyst by ammonia decomposition, comprising the following steps:

[0008] S1. Put iron ore and coke into a blast furnace for smelting, then add a flux to prepare hot metal in the blast furnace; transfer the hot metal in the blast furnace into a converter, add alloying elements and blow in oxygen to prepare molten steel;

[0009] S2. Transfer the molten steel into a refining furnace, add a deoxidizer for reaction, and obtain refined molten steel after the reaction; pour the refined molten steel into a mold and form a steel billet after cooling;

[0010] S3. Process the steel billet through a hot rolling or cold rolling mill to obtain steel wires with a diameter of 2 - 8 mm; draw the steel wires in a wire drawing machine to obtain an average diameter of 0.03 mm, and anneal the drawn fine wires at a temperature of 600°C - 700°C to obtain steel wool;

[0011] S4. Pretreat the steel wool and load it into a quartz tube, then place it on a tubular furnace, and introduce oxygen for oxidation treatment to obtain oxidized steel wool;

[0012] S5. Load the oxidized steel wool into a quartz tube, then place it on a tubular furnace, and introduce ammonia for nitriding treatment to obtain a metal fiber material, that is, a hydrogen production catalyst by ammonia decomposition.

[0013] Further, the flux in S1 is limestone, and the alloying elements in S1 are at least one of manganese, silicon, chromium, and nickel.

[0014] Further, the mass ratio of the iron ore and coke added in S1 is 4:1, the mass of the flux added in S1 is 10% - 20% of the mass of the iron ore, and the mass of the alloying elements added in S1 is 0.06% - 0.8% of the mass of the hot metal in the blast furnace.

[0015] Further, the deoxidizer in S2 is at least one of aluminum and silicon, and the mass of the deoxidizer added in S2 is 0.1% - 0.15% of the mass of the molten steel.

[0016] Further, the pretreatment of the steel wool in S4 is as follows:

[0017] A1. Place the steel wool in a 3% NaOH solution, soak it at a temperature of 60 - 70°C for 5 - 10 minutes, and then rinse it with deionized water to obtain alkali-washed steel wool;

[0018] A2. Place the alkali-washed steel wool in a 5% dilute H 2 SO 4 solution, soak it for 2 - 5 minutes, and then rinse it with clean water to obtain acid-washed steel wool;

[0019] A3. Clean the pickled steel wool with alcohol with a concentration of 95%, then rinse it with deionized water. After the rinsing is completed, dry it at a temperature of 105°C for 12 hours to obtain the pretreated steel wool.

[0020] Furthermore, the space velocity of oxygen introduced in S4 is 1800 mL / g / h; the oxidation temperature of the oxidation treatment in S4 is 650 - 700°C, and the treatment time is 2 - 4 hours; the space velocity of ammonia introduced in S5 is 1800 - 7200 mL / g / h; the temperature of the nitridation treatment in S5 is 450 - 700°C, and the treatment time is 2 - 4 hours.

[0021] Application of an ammonia decomposition hydrogen production catalyst in the process of ammonia decomposition hydrogen production.

[0022] Application of an ammonia decomposition hydrogen production catalyst prepared by the described preparation method in the process of ammonia decomposition hydrogen production.

[0023] Compared with the prior art, for an ammonia decomposition hydrogen production catalyst, its preparation method and application provided by the present invention, the acidic active sites on the surface of the ammonia decomposition hydrogen production catalyst are beneficial to the chemisorption of ammonia, and the continuous dehydrogenation process promotes the reduction of part of the iron oxide, thereby exposing more empty active sites. The Fe atoms on the ammonia decomposition hydrogen production catalyst can react with the N atoms in NH 3 while providing active sites, forming Fe - N compounds, reconstructing the surface properties of the catalyst, and strengthening the adsorption of NH 3 on the catalyst surface and reducing the reaction energy barrier. Through deep oxidation and nitridation treatments, the surface structure of the catalyst has undergone physical changes, forming a large number of cavities, which is beneficial to the adsorption of ammonia and electron transfer, and strengthening the thermal cracking reaction of ammonia;

[0024] In terms of ammonia decomposition efficiency, the conversion rate of the ammonia decomposition hydrogen production catalyst is high and it has good stability; in addition, the iron - based material can also serve as a catalyst carrier to support a variety of transition metals, so as to be better applied to the process of ammonia decomposition hydrogen production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic diagram comparing the prices of common metals and the elements of global warming power provided by the embodiments of the present invention;

[0027] Figure 2 Schematic diagram of the conversion rate of ammonia decomposition by the ammonia decomposition hydrogen production catalyst provided by the embodiment of the present invention;

[0028] Figure 3 SEM image of the un-deeply oxidized steel wool provided by the embodiment of the present invention;

[0029] Figure 4 SEM image of the deeply oxidized steel wool provided by the embodiment of the present invention;

[0030] Figure 5 Result graph of the ammonia decomposition conversion rate of the un-deeply oxidized and deeply oxidized steel wool provided by the embodiment of the present invention;

[0031] Figure 6 XRD pattern of the ammonia decomposition hydrogen production catalyst provided by the embodiment of the present invention;

[0032] Figure 7 Overall schematic diagram of the ammonia decomposition hydrogen production catalyst provided by the embodiment of the present invention. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] Example 1:

[0035] Please refer to Figure 1 、 Figures 3 - 4 and Figures 6 - 7 , an ammonia decomposition hydrogen production catalyst, the ammonia decomposition hydrogen production catalyst is a metal fiber material, the average diameter of the fibers in the metal fiber material is 0.03 mm, the morphology of the metal fiber material is a porous morphology, and the active component of the metal fiber material is a transition metal element or its oxide.

[0036] The transition metal is at least one of Fe, Co, and Ni.

[0037] The specific implementation manner is that the ammonia decomposition hydrogen production catalyst can be further impregnated to load additives or active components subsequently.

[0038] An additive is an auxiliary substance, usually used to improve the performance of the catalyst. It can improve the stability, selectivity or anti-coking performance of the catalyst. Common additives include alkali metals (potassium, sodium), rare earth elements (lanthanum, cerium), etc.

[0039] The active component is the part directly participating in the catalytic reaction in the catalyst. The active component is a metal (nickel, cobalt, platinum) or its metal oxide; by loading the active component by the impregnation method, the activity or selectivity of the catalyst can be further improved.

[0040] The impregnation method is a commonly used catalyst preparation method for loading active components or promoters on a catalyst support. The substance to be loaded is dissolved in a suitable solvent to prepare an impregnation solution; the catalyst support is immersed in the impregnation solution so that the active components or promoters in the impregnation solution are evenly adsorbed on the surface or pores of the support; after impregnation, the support is taken out, the solvent is removed by drying, and then calcined at a high temperature to convert the loaded substance into an active component or promoter.

[0041] By loading additional active components, the active sites on the catalyst surface can be increased, thereby increasing the rate of the ammonia decomposition reaction; the promoter can adjust the surface properties of the catalyst to make it more conducive to the production of high-purity hydrogen while reducing the occurrence of side reactions; some promoters can improve the stability of the catalyst at high temperatures or during long-term reactions and extend the service life of the catalyst.

[0042] The acidic active sites on the surface of the metal fiber material are conducive to the chemisorption of ammonia, which is the first step of the reaction. The subsequent continuous dehydrogenation process promotes the reduction of some iron oxides. At about 346 °C, more empty active sites are exposed, and Fe-N compounds are formed, which is conducive to accelerating the desorption of surface nitrogen atoms. After ammonia dehydrogenation, hydrogen atoms and nitrogen atoms recombine on the surface active sites to form nitrogen and hydrogen.

[0043] The decomposition of ammonia is a process of stepwise dehydrogenation. Using a metal catalyst to catalyze the decomposition of ammonia to produce hydrogen, the rate-determining step is different for different metal catalysts. It is generally considered that when using noble metal (Ru, Ir, etc.) catalysts, the breaking of the N-H bond in ammonia is the rate-determining step, but for transition metals (Co, Fe, Ni, etc.), the desorption of nitrogen is the rate-determining step.

[0044] Example 2:

[0045] Based on Example 1, this example provides a technical solution: a preparation method of an ammonia decomposition hydrogen production catalyst, including the following steps:

[0046] S1. Put iron ore and coke into a blast furnace for smelting, then add a flux to prepare blast furnace hot metal; send the blast furnace hot metal into a converter, add alloying elements and blow in oxygen to prepare molten steel; the flux is limestone, and the alloying elements are at least one of manganese, silicon, chromium, and nickel; the mass ratio of iron ore and coke added is 4:1, the mass of the added flux is 10%-20% of the mass of the iron ore, and the mass of the added alloying elements is 0.06%-0.8% of the mass of the blast furnace hot metal;

[0047] The specific implementation method is to select high-quality iron ore, the main component of which is iron oxide (such as Fe 2 O 3 、Fe 3 O 4etc.), the iron content is usually above 50%; coke is the main reducing agent in blast furnace ironmaking, its main component is carbon, with a relatively high calorific value and good reduction performance; the flux is limestone (CaCO 3 ), and its function is to lower the melting point of the slag and help remove impurities (such as silicon, phosphorus, etc.) in the iron ore.

[0048] The mass ratio of the added iron ore to coke is 4:1; the mass of the flux is 10%-20% of the mass of the iron ore.

[0049] Load the iron ore, coke and flux into the blast furnace in proportion. The blast furnace is a huge vertical furnace, and the internal temperature can reach 1500°C to 1800°C; at high temperature, coke burns to produce carbon monoxide (CO), and carbon monoxide further reacts with iron oxides in the iron ore to generate iron and carbon dioxide (CO 2 ). Limestone decomposes at high temperature to produce calcium oxide (CaO), which reacts with impurities (such as SiO 2 , P 2 O 5 etc.) in the iron ore to form slag. The melting point of the slag is relatively low and can be discharged from the blast furnace smoothly.

[0050] The carbon content in the hot metal of the blast furnace is 3% to 4%. At this time, the temperature of the hot metal is about 1500°C and is in a liquid state. Send the blast furnace hot metal into the converter, and through blowing oxygen, an oxidation reaction is carried out to remove the excess carbon. Through the oxygen blowing operation, the carbon content in the hot metal is controlled between 0.05% - 0.25%. The specific control of the carbon content depends on the required steel grade.

[0051] Alloy element addition: According to the designed steel composition, appropriate alloy elements are added, such as manganese (Mn), silicon (Si), chromium (Cr), nickel (Ni), etc. The addition amount of alloy elements is 0.06% - 0.8% of the mass of the blast furnace hot metal. This invention mainly uses manganese metal. Manganese can improve the strength and toughness of the steel, and at the same time improve the hot working performance of the steel. The specific addition amount is adjusted according to the required steel grade and performance requirements.

[0052] After the above treatment, the carbon content and alloy element content in the molten steel reach the design requirements, and the required molten steel is prepared. The temperature of the molten steel is usually about 1600°C and is in a liquid state, and subsequent continuous casting or ingot casting and other processes can be carried out.

[0053] Through the processes of blast furnace ironmaking and converter steelmaking, the iron ore can be reduced to hot metal and further processed into molten steel. During the blast furnace ironmaking process, the iron ore and coke are added in a ratio of 4:1, and the addition amount of the flux is 10% - 20% of the mass of the iron ore. During the converter steelmaking process, the excess carbon is removed by blowing oxygen, and appropriate alloy elements (such as manganese, silicon, chromium, nickel, etc.) are added to make the molten steel reach the required chemical composition.

[0054] S2. Transfer the molten steel into a refining furnace, add a deoxidizer for reaction, and obtain refined molten steel after the reaction ends; pour the refined molten steel into a mold and form a steel billet after cooling; the deoxidizer is at least one of aluminum and silicon, and the added mass of the deoxidizer is 0.1%-0.15% of the mass of the molten steel.

[0055] Specifically, transfer the molten steel prepared in the converter into the refining furnace. The refining furnace is a device specifically used for refining molten steel, which can provide more precise temperature control and more sufficient reaction conditions.

[0056] The deoxidizer is a substance used to remove dissolved oxygen in the molten steel. Common deoxidizers include aluminum (Al) and silicon (Si). These deoxidizers can react with the oxygen in the molten steel to form stable oxides, thereby reducing the oxygen content in the molten steel; the added mass of the deoxidizer is 0.1%-0.15% of the mass of the molten steel. The deoxidizer reacts with the oxygen in the molten steel to form oxides and float to the surface of the molten steel to form slag and be discharged. The temperature in the refining furnace is between 1550°C and 1650°C to ensure that the deoxidation reaction proceeds fully, and the reaction time is 10-30 minutes.

[0057] Through deoxidation treatment, the oxygen content in the molten steel is significantly reduced, while ensuring the stability of the chemical composition of the molten steel. The refined molten steel has higher purity and better performance; during the refining process, the temperature in the refining furnace needs to be precisely controlled to ensure the smooth progress of the deoxidation reaction and the uniformity of the molten steel.

[0058] Pour the refined molten steel into a mold and form a steel billet after cooling. Before pouring, the mold needs to be preheated to 300°C - 500°C to prevent the molten steel from cooling too quickly during pouring and ensure that the molten steel can fill the mold evenly.

[0059] Through the deoxidation treatment in the refining furnace, the oxygen content in the molten steel can be significantly reduced, improving the purity and performance of the steel. The addition amount of the deoxidizer (aluminum, silicon) is 0.1%-0.15% of the mass of the molten steel to ensure that the deoxidation reaction proceeds fully. The refined molten steel is poured into the preheated mold and forms a steel billet after cooling for the next processing.

[0060] S3. Process the steel billet through a hot rolling or cold rolling mill to obtain steel wires with a diameter of 2-8 mm; draw the steel wires in a wire drawing machine to obtain an average diameter of 0.03 mm, and anneal the drawn fine wires under the temperature condition of 600°C - 700°C to obtain steel wool.

[0061] Specifically, clean the surface of the cooled steel billet to remove the scale and impurities on the surface to ensure the smooth progress of the rolling process.

[0062] The steel billet is processed through a hot rolling or cold rolling mill, and the processing steps are as follows: For hot rolling, the steel billet is heated to 1000°C to 1200°C to make it have good plasticity and fluidity, and then rolled through a hot rolling mill. During the hot rolling process, the steel billet is gradually compressed at high temperature to form a steel bar with a diameter of 2 - 8 mm; Cold rolling is carried out at room temperature, and through multiple rollings, the steel billet is gradually compressed into a steel wire with a diameter of 2 - 8 mm.

[0063] There may be slight scale and burrs on the surface of the rolled steel bar or steel wire, and surface treatment such as pickling or sandblasting is required to ensure the smooth progress of the subsequent drawing process.

[0064] The steel bar with a diameter of 2 - 8 mm is passed through multiple drawing dies to gradually draw it to the required diameter. The aperture of each drawing die gradually decreases, and usually the reduction rate of each drawing is between 10% - 20%. During the drawing process, the steel wire will experience cold hardening, that is, the hardness of the steel wire increases and the ductility decreases. This may lead to fractures and surface defects during the subsequent drawing process, so annealing treatment is required. The diameter of the drawn steel wire is usually 0.03 mm to 0.3 mm, and the drawn steel wire is annealed at a temperature of 600°C - 700°C to obtain steel wool.

[0065] The drawn steel wire is neatly placed in an annealing furnace, ensuring there is enough space between the steel wires for uniform heat transfer.

[0066] Annealing process: Heat the annealing furnace to 600°C - 700°C at a heating rate of 10°C / min - 20°C / min; Keep it at a temperature of 600°C - 700°C for 10 - 30 minutes to ensure the steel wire is fully annealed; After the holding ends, slowly cool the annealing furnace at a cooling rate of 5°C / min - 10°C / min to ensure that no new internal stress is generated in the steel wire during the cooling process.

[0067] After annealing, the hardness of the steel wire decreases, the ductility is restored, the surface is smooth, and there is no internal stress, making it suitable for subsequent processing into steel wool; Annealing treatment can eliminate the internal stress generated during the drawing process, restore the ductility and toughness of the steel wire, and ensure that the steel wool has good performance during use.

[0068] The steel billet is processed into a steel bar or steel wire with a diameter of 2 - 8 mm through hot rolling or cold rolling, and then undergoes multiple drawings in a drawing machine to draw the steel wire to 0.03 mm to 0.3 mm. The drawn steel wire is annealed at a temperature of 600°C - 700°C to eliminate internal stress and restore ductility, finally obtaining steel wool with excellent performance. This process not only improves the processing accuracy and surface quality of the steel wire, but also ensures the reliability and safety of the steel wire during use.

[0069] S4. Pretreat the steel wool and load it into a quartz tube, then place it on a tube furnace, introduce oxygen for oxidation treatment to obtain oxidized steel wool; the space velocity of the introduced oxygen is 1800 mL / g / h; the oxidation temperature for the oxidation treatment is 650 - 700 °C, and the treatment time is 2 - 4 hours.

[0070] The pretreatment steps are as follows:

[0071] A1. Place the steel wool in a 3% NaOH solution, soak it at a temperature of 60 - 70 °C for 5 - 10 minutes, and then rinse it with deionized water to obtain alkali-washed steel wool.

[0072] A2. Place the alkali-washed steel wool in a 5% dilute H 2 SO 4 solution, soak it for 2 - 5 minutes, and then rinse it with clean water to obtain acid-washed steel wool.

[0073] A3. Wash the acid-washed steel wool with 95% alcohol, then rinse it with deionized water. After rinsing, dry it at a temperature of 105 °C for 12 hours to obtain the pretreated steel wool.

[0074] The specific implementation method is that the purpose of pretreating the steel wool is to remove the oil, oxides, and other impurities on the surface of the steel wool to ensure the uniformity and effect of the subsequent oxidation treatment. The specific steps are as follows:

[0075] Prepare a 3% NaOH solution, completely immerse the steel wool in the NaOH solution, control the temperature at 60 - 70 °C, and soak it for 5 - 10 minutes. The purpose of this step is to remove the oil and organic pollutants on the surface of the steel wool. After soaking, thoroughly rinse the steel wool with deionized water to ensure that all NaOH solution and oil are removed. It can be rinsed multiple times until there is no slippery feeling on the surface of the steel wool.

[0076] Prepare a 5% dilute H 2 SO 4 solution, completely immerse the alkali-washed steel wool in the dilute H 2 SO 4 solution, soak it for 2 - 5 minutes to remove the oxides and other inorganic substances on the surface of the steel wool. After soaking, thoroughly rinse the steel wool with clean water to ensure that all H 2 SO 4 solution and impurities are removed. It can be rinsed multiple times until there is no sour taste on the surface of the steel wool.

[0077] Use alcohol with a concentration of 95%. Immerse the pickled steel wool completely in 95% alcohol for cleaning. The purpose of this step is to remove possible organic pollutants and ensure the cleanliness of the steel wool surface. After cleaning, thoroughly rinse the steel wool with deionized water to ensure the removal of all alcohol. Rinsing can be done multiple times until there is no alcohol smell on the steel wool surface.

[0078] Place the cleaned steel wool in a drying oven. Set the drying temperature to 105°C and the drying time to 12 hours. The purpose of this step is to thoroughly remove the bound water and surface moisture in the steel wool and ensure the uniformity of subsequent oxidation treatment. After drying, check the dryness of the steel wool to ensure there is no moisture on the surface.

[0079] The purpose of oxidation treatment is to form a uniform oxide layer on the steel wool surface to improve its corrosion resistance and other properties. Evenly load the pretreated steel wool into a quartz tube, ensuring sufficient gaps between the steel wool so that oxygen can fully contact. Place the quartz tube in a tube furnace to ensure uniform temperature inside the furnace and precise control of the oxidation temperature and time. Introduce high-purity oxygen and control the space velocity to 1800 mL / g / h. The space velocity refers to the gas volume passing through the unit mass of steel wool per unit time, ensuring that oxygen can fully react with the steel wool.

[0080] Heat the tube furnace to 650 - 700°C and hold for 2 - 4 hours. After the oxidation treatment, slowly cool the tube furnace. The cooling rate is usually 5°C / min - 10°C / min to ensure that no new internal stress is generated in the steel wool during the cooling process.

[0081] After cooling is completed, take out the oxidized steel wool and store the oxidized steel wool properly to avoid moisture and contamination and ensure its stable performance.

[0082] Through pretreatment (alkali washing, pickling, alcohol cleaning, and drying) and oxidation treatment (introducing high-purity oxygen and controlling temperature and time), oxidized steel wool with excellent performance can be prepared. The pretreatment steps ensure the cleanliness and impurity-free surface of the steel wool, and the oxidation treatment forms a uniform oxide layer on the steel wool surface, improving its corrosion resistance and other properties. This process not only improves the surface quality of the steel wool but also ensures its reliability and safety in subsequent applications.

[0083] S5. Load the oxidized steel wool into a quartz tube, then place it on a tube furnace, introduce ammonia for nitridation treatment to obtain a metal fiber material, namely an ammonia decomposition hydrogen production catalyst. The space velocity of introducing ammonia is 1800 - 7200 mL / g / h. The nitridation treatment temperature is 450 - 700°C, and the treatment time is 2 - 4 hours.

[0084] The specific implementation method is as follows: evenly load the pre-treated oxidized steel wool into a quartz tube, place the quartz tube in a tube furnace, first purge the air in the tube furnace with nitrogen for 30 minutes to ensure the purity of the furnace atmosphere; then introduce high-purity ammonia gas, control the space velocity to 1800 mL / g / h, heat the tube furnace to 600 - 700 °C, and keep it warm for 2 - 3 hours. The heating rate can be controlled at 5 °C / min - 10 °C / min to ensure uniform temperature increase.

[0085] After the nitriding treatment, slowly cool the tube furnace. The cooling rate is usually 5 °C / min - 10 °C / min. Under the ammonia gas atmosphere, cool it down to room temperature. First, close the main ammonia valve, and then close the pressure reducing valve to ensure that all ammonia gas is completely discharged.

[0086] Passivate it with nitrogen containing 1% oxygen for 12 hours to prevent the nitrided steel wool from oxidizing in the air. After cooling is completed, take out the nitrided steel wool to obtain a metal fiber material, that is, a hydrogen production catalyst by ammonia decomposition;

[0087] Through high-temperature nitriding treatment, load the oxidized steel wool into a quartz tube, place it on a tube furnace, introduce ammonia gas for high-temperature nitriding at a space velocity of 1800 mL / g / h, the temperature range is 600 - 700 °C, and the treatment time is 2 - 3 hours to achieve nitriding and form Fe - N compounds. This process not only improves the surface quality of the steel wool but also ensures its reliability and safety in subsequent applications.

[0088] Example three:

[0089] Please refer to Figure 2 and Figure 5 This example provides a technical solution based on Example one: conduct an activity test on the hydrogen production catalyst by ammonia decomposition.

[0090] Evaluate the ammonia decomposition catalytic characteristics on a quartz fixed-bed reactor (inner diameter 8 mm, outer diameter 24 mm). Heat it with a 3 kW muffle furnace, load 500 mg of the catalyst on the middle reactor, then heat it to 450 °C to 700 °C (at intervals of 50 °C), with a heating rate of 15 °C / min, and use 15 mL / min of nitrogen as the purge gas.

[0091] When the set temperature is reached, inject pure ammonia at a flow rate of 15 - 60 ml / min. The inlet gas flow rate is controlled by a flow controller (Alicat, accuracy ±0.4%, reading is +0.2% of the full scale, control range 0 - 100 mL / min), and the outlet gas flow rate is read and recorded by a flow controller (Alicat, accuracy ±0.6%, control range 0 - 200 mL / min).

[0092] The reaction time for the activity test was set to 8 h and 18 h for the catalyst stability test. The ammonia conversion reaction is a reaction in which the product volume doubles.

[0093] 1. Based on the inlet gas flow rate and the outlet gas flow rate, the ammonia conversion rate can be obtained by the following formula:

[0094] NH 3 convers i on(%)=F outlet / 2F inlet ×100%;

[0095] where F outlet represents the inlet ammonia gas flow rate, and F inlet represents the gas flow rate of the outlet gas after absorbing the remaining ammonia.

[0096] 2. The apparent reaction rate of ammonia cracking can be obtained by the following formula:

[0097]

[0098] where V 1 is the ammonia inlet gas flow rate, X NH3 is the ammonia conversion rate, and W is the catalyst weight.

[0099] 3. The apparent activation energy of ammonia cracking can be obtained by the following formula:

[0100] l nr=-E a / RT+n

[0101] where r is the apparent reaction rate of ammonia cracking, T is the reaction temperature at which r is generated, R is the gas constant of 9.314 J / (mol*K), and E a can be obtained from the slope of the graph of T -1 and l nr.

[0102] Please refer to Figure 2 (B). As can be seen in Figure 2 (B), at reaction temperatures of 450, 550, and 650 °C respectively, four different flow rates of NH 3 were introduced, with flow rates of 1800 mL / g / h, 3600 mL / g / h, 5400 mL / g / h, and 7200 mL / g / h respectively. As the NH 3 flow rate increased, its conversion rate also increased.

[0103] Please refer to Figure 5 , in Figure 5It can be seen that for the deeply oxidized steel wool, within the lower temperature range of 500 - 600 °C, the conversion rate of ammonia decomposition is much greater than that of the steel wool without deep oxidation treatment. For the deeply oxidized steel wool, the ammonia decomposition conversion rate is 20.7% at 500 °C, 55.4% at 550 °C, and 87.8% at 600 °C.

[0104] The test results show that the catalyst can achieve ammonia conversion rates of 63% and 100% at 600 °C and 700 °C respectively. The catalyst still has good stability after 18 hours of continuous ammonia decomposition reaction under the conditions of 450 - 700 °C, and there is no obvious decrease in activity during the second cycle.

[0105] Only some exemplary embodiments of the present invention have been described by way of illustration above. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A catalyst for hydrogen production by decomposing ammonia, characterized in that: The ammonia decomposition hydrogen production catalyst is a metal fiber material, the average diameter of the fibers in the metal fiber material is 0.03 mm, the morphology of the metal fiber material is porous, and the active component of the metal fiber material is a transition metal element or its oxide.

2. The catalyst for hydrogen production by decomposing ammonia according to claim 1, characterized in that: The transition metal is at least one of Fe, Co and Ni.

3. A method for preparing a catalyst for hydrogen production by decomposing ammonia, characterized in that: The steps include: S1. Put iron ore and coke into a blast furnace for smelting, then add flux to prepare blast furnace molten iron; send the blast furnace molten iron into a converter, add alloy elements and blow in oxygen to prepare molten steel; S2, transferring the molten steel into a refining furnace, and adding a deoxidizer to react, and obtaining refined molten steel after the reaction is completed; pouring the refined molten steel into a casting mold, and forming a steel billet after cooling; S3, processing the steel billet through a hot rolling or cold rolling mill to obtain a steel wire with a diameter of 2-8 mm; drawing the steel wire in a wire drawing machine to obtain an average diameter of 0.03 mm, and annealing the drawn filaments at a temperature of 600° C. to 700° C. to obtain steel wool; S4, pre-treating the steel wool and loading it into a quartz tube, then placing it on a tube furnace, introducing oxygen for oxidation treatment, and obtaining oxidized steel wool; S5. Load the oxidized steel wool into a quartz tube, then place it on a tube furnace, introduce ammonia gas to perform nitridation treatment, and obtain a metal fiber material, i.e., ammonia decomposition hydrogen production catalyst.

4. The method for preparing a catalyst for hydrogen production by decomposing ammonia according to claim 3, characterized in that: The flux described in S1 is limestone, and the alloy element described in S1 is at least one of manganese, silicon, chromium and nickel.

5. The method for preparing a catalyst for hydrogen production by decomposing ammonia according to claim 3, characterized in that: The mass ratio of iron ore and coke added in S1 is 4:1, the mass of flux added in S1 is 10%-20% of the mass of iron ore, and the mass of alloy elements added in S1 is 0.06%-0.8% of the mass of blast furnace molten iron.

6. The method for preparing a catalyst for hydrogen production by decomposing ammonia according to claim 3, characterized in that: The deoxidizer in S2 is at least one of aluminum and silicon, and the mass of the deoxidizer added in S2 is 0.1%-0.15% of the mass of the molten steel.

7. The method for preparing a catalyst for hydrogen production by decomposing ammonia according to claim 3, characterized in that: S4 pre-treats the steel wool, and the pre-treating steps are: A1. Place steel wool in a 3% NaOH solution at 60-70°C for 5-10 minutes, then rinse with deionized water to obtain alkali-washed steel wool; A2. Alkali-washed steel wool is placed in a 5% dilute H2SO4 solution for 2-5 minutes, and then rinsed with clean water to obtain acid-washed steel wool; A3. Clean the pickled steel wool with 95% alcohol, then rinse with deionized water, and dry it at 105° C. for 12 hours to obtain pretreated steel wool.

8. The method for preparing a catalyst for hydrogen production by decomposing ammonia according to claim 3, characterized in that: The space velocity of oxygen introduced in S4 is 1800mL / g / h; the oxidation temperature of oxidation treatment in S4 is 650-700℃, and the treatment time is 2-4 hours; the space velocity of ammonia introduced in S5 is 1800-7200mL / g / h; the temperature of nitriding treatment in S5 is 450-700℃, and the treatment time is 2-4 hours.

9. Use of the catalyst for producing hydrogen by decomposing ammonia according to any one of claims 1 to 2 in a process for producing hydrogen by decomposing ammonia.

10. Use of the ammonia decomposition hydrogen production catalyst prepared by the preparation method according to any one of claims 3 to 8 in ammonia decomposition hydrogen production process.

Images