Method for producing hydrogen through ammonia decomposition

Abstract

The invention discloses a method for producing hydrogen through ammonia decomposition, which comprises the following steps: in a reactor, contacting and reacting an ammonia-containing raw material with a catalyst to obtain a hydrogen-containing product; the catalyst is a monatomic Ru / Mo2N catalyst, and the mass percentage content of Ru is 0.01-3%. The catalyst is prepared by a one-step temperature-programmed reduction nitriding method. The catalyst has the advantages of high reaction activity, simple preparation method and high stability, and has a wide application prospect in the field of hydrogen production by ammonia decomposition.

Description

Technical Field

[0001] The present application relates to a method for producing hydrogen by decomposing ammonia, and belongs to the field of chemistry and chemical engineering. Background Art

[0002] Hydrogen is an efficient and clean energy source. Due to the characteristics of hydrogen itself, the development of the hydrogen energy industry still faces major bottlenecks such as cross-regional, high safety, low cost, and large-scale storage and transportation of hydrogen. Using ammonia as a hydrogen storage carrier has the following advantages: 1) High energy density. The volume energy density of ammonia is about 13.6MJ / L, and the hydrogen content is 17.6wt%. 2) Low liquefaction storage and transportation costs (liquefaction pressure is 0.8MPa at 20°C); 3) Carbon-free energy storage can be achieved. Ammonia's mature technical system, standard specifications, and low-cost synthesis, storage, and transportation can achieve seasonal, long-distance, "carbon-free" "ammonia-hydrogen" energy storage. 4) High safety. Ammonia's fire hazard is only Class B, and its explosion limit (16% to 25%) is narrower than that of hydrogen (4% to 76%), so it is safer, and its pungent smell is a reliable alarm signal. After using renewable energy to generate electricity and electrolyze water to produce hydrogen, the storage and transportation of "green hydrogen" can be completed through the "hydrogen-ammonia-hydrogen" process, which can effectively solve the problems of high hydrogen storage and transportation costs and low safety. In order to achieve economical and safe hydrogen storage, it is particularly important to develop catalysts that can efficiently catalyze the decomposition reaction of ammonia.

[0003] The ammonia decomposition reaction to produce hydrogen is shown in formula (1). This reaction is an endothermic reaction with an increase in volume, so increasing the temperature and reducing the pressure are beneficial to the reaction.

[0004] 2NH3 = N2 + 3H2, ΔH = 92.5 kJ mol -1 (1)

[0005] At present, supported Ru-based catalysts are believed to have the highest catalytic ammonia decomposition activity, but Ru, as a precious metal, has a high cost, which limits its widespread application. Generally speaking, catalytic reactions usually occur at the surface / interface active sites of metals, and the atoms inside them are not used, resulting in waste. In addition, the catalysts prepared with granular Ru have uneven structures and properties of active components, resulting in low ammonia decomposition activity. By constructing efficient Ru-support interface sites, the catalytic reaction activity can be effectively improved. In order to reduce the cost of catalysts, it is necessary to improve the atomic utilization and intrinsic reaction activity of precious metals, so it is of great significance to prepare highly dispersed supported precious metal catalysts.

[0006] Single-atom catalysts are metal atoms dispersed on the surface of the carrier in the form of , with the highest dispersion and the highest atomic utilization efficiency. Traditional methods for preparing single-atom catalysts generally include impregnation, deposition precipitation, photochemical method, atomic layer deposition (ALD) method, etc. The traditional method for preparing single-atom Ru-based catalysts has complicated steps and requires the carrier to expose a specific crystal face. For example, Shik Chi Edman Tsang's team and others reported that single-atom Ru / MgO catalysts can only be prepared on MgO (111) carriers with exposed specific crystal faces, while Ru nanoparticles are obtained on the MgO (110) crystal face, rather than single Ru atoms. The single-atom Ru-based catalysts prepared by the above method are limited by the specific crystal face structure of the carrier, which limits the large-scale preparation of single-atom Ru-based catalysts and their application in ammonia decomposition reactions.

[0007] At present, there is an urgent need to develop an efficient ammonia decomposition catalyst that can fully utilize Ru atoms and reduce the cost of the catalyst. Summary of the invention

[0008] The one-step programmed temperature reduction nitridation method utilizes the interaction between the substrate and the metal nanoparticles during the phase change process to achieve the redispersion of metal particles into single atoms. Specifically, in the preparation process of Ru / Mo2N catalyst, the Ru nanoparticles are redispersed into single atoms during the transformation of the MoO3 substrate into Mo2N in a high-temperature ammonia atmosphere. At the same time, the Ru atoms replace the Mo atoms on the outermost surface of Mo2N, thereby being firmly anchored on the Mo2N carrier, ensuring the high stability of the Ru single atom site. Therefore, the preparation of single-atom Ru / Mo2N catalysts can be achieved through a one-step programmed temperature reduction nitridation treatment. This method is simple and effective, and has no specific requirements for the exposed crystal surface of the carrier itself. It can realize the batch preparation of single-atom Ru-based catalysts and their application in the ammonia decomposition hydrogen production reaction.

[0009] According to one aspect of the present application, a method for producing hydrogen by decomposing ammonia is provided, comprising the following steps:

[0010] In a reactor, a raw material containing ammonia is contacted with a catalyst to react and obtain a product containing hydrogen;

[0011] The catalyst is a single-atom Ru / Mo2N catalyst, wherein the mass percentage of Ru is 0.01-3%. The catalyst is a supported metal catalyst, and Ru atoms are evenly dispersed in the form of single atoms on the carrier surface, and a high ammonia conversion rate can be obtained under low temperature and high space velocity conditions.

[0012] Using MoO3 as the substrate, Ru nanoparticles are loaded on the MoO3 substrate by an impregnation method. Using a programmed temperature reduction nitridation treatment in an ammonia atmosphere, the Ru nanoparticles are redispersed into single atoms during the phase change of the substrate. At the same time, Ru atoms replace the Mo atoms on the outermost surface of the Mo2N carrier, thereby being firmly anchored on the MO2N carrier, ensuring the high stability of the Ru single atom site, thereby obtaining a single-atom Ru1 / Mo2N catalyst.

[0013] Specifically, the catalyst is obtained by the following steps:

[0014] (1) calcining a molybdenum-based precursor to obtain a MoO3 substrate;

[0015] (2) immersing the MoO3 substrate in a solution containing a Ru source, drying, and calcining to obtain a Ru / MoO3 precursor;

[0016] (3) The Ru / MoO3 precursor is treated by a one-step programmed temperature reduction nitridation method to obtain the catalyst.

[0017] By using a one-step programmed temperature reduction nitridation method, the redispersion of Ru nanoparticles into single atoms during the transformation of MoO3 substrate into Mo2N in a high-temperature ammonia atmosphere is utilized to fully utilize the precious metal Ru.

[0018] The molybdenum-based precursor is selected from (NH4)2MoO4, (NH4)6Mo7O 24 At least one of;

[0019] The calcination temperature is 400-800°C;

[0020] The calcination time is 4 to 8 hours.

[0021] The Ru source is selected from at least one of Ru(NO)(NO3)3 and RuCl3;

[0022] The concentration of the solution containing the Ru source is 0.01 to 1 mol / L;

[0023] The mass ratio of the MoO3 substrate to the solution containing the Ru source is 2.5 to 25:1;

[0024] The immersion temperature is 25-30°C;

[0025] The immersion time is 12 to 48 hours;

[0026] The drying temperature is 80-120°C;

[0027] The drying time is 12 to 48 hours;

[0028] The calcination temperature is 300-500°C;

[0029] The calcination time is 4 to 12 hours.

[0030] The one-step programmed temperature reduction nitriding method comprises the following steps:

[0031] The Ru / MoO3 precursor was placed in a tube furnace and treated under an ammonia atmosphere.

[0032] The volume space velocity of the ammonia is 100-3600h -1 ;

[0033] The treatment temperature is 600-900°C;

[0034] The treatment time is 1 to 48 hours;

[0035] The heating rate of the treatment is 0.2-10°C / min;

[0036] The treatment pressure is normal pressure.

[0037] Optionally, the treatment temperature is 700-900°C;

[0038] Optionally, the heating rate of the treatment is 0.2-5°C / min.

[0039] The reaction temperature is 300-900°C.

[0040] Optionally, the reaction temperature is 400-500°C.

[0041] The reaction pressure is 0.1-1.0 MPa.

[0042] In the raw material, the space velocity of ammonia is 200 to 60000 ml / g·h.

[0043] The beneficial effects of this application include:

[0044] 1) In the ammonia decomposition catalyst provided in the present application, the dispersion degree of Ru is 100%, and Ru is dispersed on the carrier in the form of single atoms, thereby achieving full utilization of the precious metal Ru.

[0045] 2) The ammonia decomposition catalyst provided in the present application can achieve efficient decomposition of ammonia at a relatively low temperature.

[0046] 3) The method for producing hydrogen by decomposing ammonia provided in the present application has the advantages of low ammonia decomposition reaction temperature and high ammonia conversion rate. The catalyst prepared according to the method provided in the present application exhibits high catalytic activity and stability in the ammonia decomposition reaction. DETAILED DESCRIPTION

[0047] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0048] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0049] Example 1

[0050] Take 5g (NH4)6Mo7O 24 ·4H2O, place it in a muffle furnace and roast it at 500℃ for 4h to obtain MoO3. Take 0.2g of RuCl3 aqueous solution with a concentration of 0.025mol / L and mix it with 4.8g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix it evenly. Then, immerse the mixture at room temperature for 12h and dry it at 120℃ for 12h. Then, transfer it to a muffle furnace and roast it at 300℃ for 4h to obtain a Ru / MoO3 precursor.

[0051] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0052] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0053] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia gas with a purity of >99.9% and a volumetric space velocity of 3600 h -1 The heating rate from room temperature to the treatment temperature is 0.2°C / min, the treatment temperature is 700°C, the pressure is normal pressure, and it is maintained at 700°C for 4 hours.

[0054] The obtained sample was taken out and marked as 0.01%Ru / Mo2N catalyst.

[0055] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0056] Example 2

[0057] Take 5g (NH4)6Mo7O 24·4H2O, place it in a muffle furnace and roast it at 600℃ for 6h to obtain MoO3. Take 0.2g of RuCl3 aqueous solution with a concentration of 0.25mol / L and mix it with 4.8g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix it evenly. Then, immerse the mixture at room temperature for 24h and dry it at 80℃ for 48h. Then, transfer it to a muffle furnace and roast it at 500℃ for 4h to obtain a Ru / MoO3 precursor.

[0058] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0059] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0060] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia gas with a purity of >99.9% and a volumetric space velocity of ammonia gas of 1000 h -1 The heating rate from room temperature to the treatment temperature is 1°C / min, the treatment temperature is 800°C, the pressure is normal pressure, and it is maintained at 800°C for 4 hours.

[0061] The obtained sample was taken out and marked as 0.1%Ru / Mo2N catalyst.

[0062] The reaction conditions for the catalyst decomposition with ammonia were: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocities of 200, 1000, 30000, and 60000 ml / g·h, respectively. The reaction results are shown in Table 1.

[0063] Example 3

[0064] Take 5g (NH4)2MoO4, place it in a muffle furnace and roast it at 400℃ for 8h to obtain MoO3. Take 2g of Ru(NO)(NO3)3 aqueous solution with a concentration of 0.074mol / L and mix it with 3g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix them evenly.

[0065] The mixture was then impregnated at room temperature for 48 h, dried at 100 °C for 24 h, and then transferred to a muffle furnace and calcined at 400 °C for 12 h to obtain a Ru / MoO3 precursor.

[0066] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0067] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0068] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia gas with a purity of >99.9% and a volumetric space velocity of ammonia gas of 100 h -1 The heating rate from room temperature to the treatment temperature is 5°C / min, the treatment temperature is 900°C, the pressure is normal pressure, and it is maintained at 900°C for 1h.

[0069] The obtained sample was taken out and marked as 0.3%Ru / Mo2N catalyst.

[0070] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0071] Example 4

[0072] Take 5g (NH4)6Mo7O 24 ·4H2O, place it in a muffle furnace and roast it at 800℃ for 8h to obtain MoO3. Take 2g of RuCl3 aqueous solution with a concentration of 0.124mol / L and mix it with 3g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix it evenly. Then, soak the mixture at room temperature for 12h and dry it at 80℃ for 24h. Then, transfer it to a muffle furnace and roast it at 500℃ for 12h to obtain a Ru / MoO3 precursor.

[0073] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0074] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0075] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia gas with a purity of >99.9% and a volumetric space velocity of 2000 h -1 The heating rate from room temperature to the treatment temperature is 2°C / min, the treatment temperature is 700°C, the pressure is normal pressure, and it is maintained at 700°C for 48 hours.

[0076] The obtained sample was taken out and marked as 0.5%Ru / Mo2N catalyst.

[0077] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0078] Example 5

[0079] Take 5g (NH4)6Mo7O 24 ·4H2O, place it in a muffle furnace and roast it at 500℃ for 6h to obtain MoO3. Take 2g of RuCl3 aqueous solution with a concentration of 0.249mol / L and mix it with 3g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix it evenly. Then, immerse the mixture at room temperature for 12h and dry it at 80℃ for 24h. Then, transfer it to a muffle furnace and roast it at 500℃ for 6h to obtain a Ru / MoO3 precursor.

[0080] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0081] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0082] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia, purity> 99.9%, and the volumetric space velocity of ammonia is 3000h -1 The heating rate from room temperature to the treatment temperature is 3°C / min, the treatment temperature is 800°C, the pressure is normal pressure, and it is maintained at 800°C for 6 hours.

[0083] The obtained sample was taken out and marked as 1%Ru / Mo2N catalyst.

[0084] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0085] Example 6

[0086] Take 5g (NH4)6Mo7O 24·4H2O, place it in a muffle furnace and roast it at 500℃ for 6h to obtain MoO3. Take 2g of RuCl3 aqueous solution with a concentration of 0.76mol / L and mix it with 3g of deionized water, then add it dropwise to 5g of the above MoO3 substrate precursor and mix it evenly. Then, soak the mixture at room temperature for 12h and dry it at 80℃ for 24h. Then, transfer it to a muffle furnace and roast it at 500℃ for 6h to obtain a Ru / MoO3 precursor.

[0087] The Ru / MoO3 precursor prepared above was used to prepare the single-atom Ru / Mo2N catalyst by a one-step temperature-programmed reduction nitridation method. The specific steps are:

[0088] An appropriate amount of Ru / MoO3 precursor is placed in a tubular furnace, a certain amount of ammonia is introduced, and the furnace temperature is raised from room temperature to the reduction nitridation temperature in a programmed temperature manner.

[0089] The parameters for the one-step programmed temperature reduction nitriding are set as follows: the reduction nitriding process is ammonia gas with a purity of >99.9% and a volumetric space velocity of 3600 h -1 The heating rate from room temperature to the treatment temperature is 4°C / min, the treatment temperature is 800°C, the pressure is normal pressure, and it is maintained at 800°C for 6 hours.

[0090] The obtained sample was taken out and marked as 3%Ru / Mo2N catalyst.

[0091] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 0.1 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0092] Comparative Example 1

[0093] Take 5g (NH4)6Mo7O 24 ·4H2O, placed it in a muffle furnace and calcined at 600℃ for 6h to obtain MoO3.

[0094] Take 5 g of the MoO3 carrier prepared above to prepare Ru / MoO3 catalyst by impregnation method.

[0095] The specific steps are:

[0096] Measure 5 ml of Ru to obtain a concentration of 10 mg mL -1 The RuCl3 solution was added dropwise to the MoO3 carrier, impregnated at room temperature for 12 hours, and dried in an oven at 80°C for 6 hours to obtain a Ru / MoO3 sample. Then, it was reduced with hydrogen at a temperature of 400°C, a heating rate of 5°C / min from room temperature to the reduction temperature, and a hydrogen volume space velocity of 2000h / min. -1, the pressure was normal pressure, and the reduction time was 4 h. The catalyst was obtained and recorded as 0.1%Ru / MoO3-IWI.

[0097] The reaction conditions for the catalyst decomposition with ammonia are: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, reaction pressure of 1.0 MPa, and space velocity of 30000 ml / g·h. The reaction results are shown in Table 1.

[0098] Comparative Example 2

[0099] Weigh 1.0g Al2O3 carrier, weigh 0.3113g NiNO3 and dissolve it in 2g deionized water to prepare a mixed solution, the mass concentration of Ni is 1.2wt%. Pour the above Al2O3 carrier directly into the above NiNO3 solution. Soak at room temperature for 12h, dry at 80℃ for 12h, and calcine at 600℃ in air atmosphere for 4h, wherein the mass content of Ni is 10%. Then, it is reduced with hydrogen at a temperature of 700℃, a heating rate from room temperature to the reduction temperature of 5℃ / min, and a volume space velocity of hydrogen of 2000h -1 , the pressure was normal pressure, and the reduction time was 6 h. The catalyst was obtained and was recorded as 10% Ni / Al2O3.

[0100] The reaction conditions for the catalyst decomposition with ammonia were: ammonia concentration of 99.9%, fixed bed reactor, reaction temperature of 400°C to 500°C, and space velocity of 30,000 ml / g·h. The reaction results are shown in Table 1.

[0101] Example result analysis:

[0102] As shown in Table 1, the single-atom Ru-based catalyst prepared by the one-step reduction nitridation method has excellent ammonia decomposition reaction performance. Among them, the activity of the 0.1% Ru / Mo2N catalyst in the ammonia decomposition hydrogen production reaction is significantly higher than that of the 0.1% Ru / MoO3-IWI catalyst prepared by the impregnation method. The above experimental results show that the one-step reduction nitridation method has obvious advantages, the preparation method is simple, and the reaction performance of the catalyst is effectively improved.

[0103] For 0.1% Ru / Mo2N catalyst, ammonia conversion rate > 99% can be achieved at 500°C. Based on Ru mass, the space-time yield of H2 per unit mass of Ru reaches 2008 mol H2 / g Ru / h. The Ru-based catalyst prepared by a one-step reduction nitridation method can achieve efficient decomposition of ammonia under high space velocity and low temperature conditions.

[0104] Table 1 Reaction performance of ammonia decomposition on different catalysts

[0105]

[0106]

[0107] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for producing hydrogen by decomposing ammonia, characterized in that: The following steps are involved: In a reactor, a raw material containing ammonia is contacted with a catalyst to react and obtain a product containing hydrogen; The catalyst is a single-atom Ru / Mo2N catalyst, wherein the mass percentage of Ru is 0.01-3%.

2. The method according to claim 1, characterized in that The catalyst is obtained by the following steps: (1) calcining a molybdenum-based precursor to obtain a MoO3 substrate; (2) immersing the MoO3 substrate in a solution containing a Ru source, drying, and calcining to obtain a Ru / MoO3 precursor; (3) The Ru / MoO3 precursor is treated by a one-step programmed temperature reduction nitridation method to obtain the catalyst.

3. The method according to claim 2, characterized in that The molybdenum-based precursor is selected from (NH4)2MoO4, (NH4)6Mo7O 24 At least one of; The calcination temperature is 400-800°C; The calcination time is 4 to 8 hours.

4. The method according to claim 2, characterized in that: The Ru source is selected from at least one of Ru(NO)(NO3)3 and RuCl3; The concentration of the solution containing the Ru source is 0.01 to 1 mol / L; The mass ratio of the MoO3 substrate to the solution containing the Ru source is 2.5 to 25:1; The immersion temperature is 25-30°C; The immersion time is 12 to 48 hours; The drying temperature is 80-120°C; The drying time is 12 to 48 hours; The calcination temperature is 300-500°C; The calcination time is 4 to 12 hours.

5. The method according to claim 2, characterized in that: The one-step programmed temperature reduction nitriding method comprises the following steps: The Ru / MoO3 precursor was placed in a tube furnace and treated under an ammonia atmosphere.

6. The method according to claim 5, characterized in that The volume space velocity of the ammonia is 100-3600h -1 ; The treatment temperature is 600-900°C; The treatment time is 1 to 48 hours; The heating rate of the treatment is 0.2-10°C / min; The treatment pressure is normal pressure.

7. The method according to claim 5, characterized in that The treatment temperature is 700-900°C; The heating rate of the treatment is 0.2-5°C / min.

8. The method according to claim 1, characterized in that The reaction temperature is 300-900°C; Preferably, the reaction temperature is 400-500°C.

9. The method according to claim 1, characterized in that: The reaction pressure is 0.1-1.0 MPa.

10. The method according to claim 1, characterized in that In the raw material, the space velocity of ammonia is 200 to 60000 ml / g·h.

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