CN118527147A - Modified rare earth oxide supported cobalt-based catalyst for ammonia decomposition hydrogen production and preparation method thereof - Google Patents

Abstract

The present invention provides a modified rare earth oxide-supported cobalt-based catalyst for ammonia decomposition to produce hydrogen and a preparation method thereof. The cobalt-based modified rare earth oxide catalyst provided by the present invention is prepared by the following steps: (1) mixing a nitrate containing rare earth elements, transition elements, etc. with a surfactant solution, adding an organic amine for complexation, filtering, drying, and roasting to obtain a carrier; (2) loading cobalt onto the above-synthesized carrier by an impregnation method to obtain a modified rare earth oxide-supported cobalt-based catalyst. The catalyst prepared by the method of the present invention has a relatively simple preparation method and low preparation cost, and can better overcome the problem of low catalytic activity in the existing process, and can be used in the production of catalytic ammonia decomposition to produce hydrogen.

Description

A modified rare earth oxide-supported cobalt-based catalyst for hydrogen production by decomposing ammonia and its preparation method

Technical Field

The invention relates to the technical field of catalysts, and in particular to a modified rare earth oxide-supported cobalt-based catalyst for hydrogen production by decomposing ammonia and a preparation method thereof.

Background Art

Hydrogen is the simplest atom of all molecules and a material that has successfully completed many historical missions: it powers the engines of space rockets and plays a role in the steel industry and the electronics manufacturing industry. However, hydrogen often encounters problems with hydrogen storage during use: ① There is no infrastructure dedicated to transporting hydrogen energy; ② There are safety issues with vehicles or ships storing hydrogen; ③ There is no direct hydrogen energy source. Therefore, it is necessary to find a suitable hydrogen energy carrier that can generate high energy when used and has no safety issues. Since ammonia has a hydrogen storage capacity of 17.6wt%, a hydrogen storage capacity of 124g·L ^-1 , can be liquefied at room temperature and a medium pressure of about 8bar, and has an energy density of 4.25kWh·L ^-1 , ammonia is receiving more and more attention as a hydrogen storage energy carrier because it is easier to store and transport, and only emits water and nitrogen through complete combustion, without generating secondary pollution.

Ammonia decomposition to produce hydrogen generally requires catalysis, but existing catalysts have high synthesis costs, poor thermal stability, and average activity. CN112774676B discloses a method for preparing a rare earth oxide-supported ruthenium catalyst. Although the catalyst reported in the patent has strong catalytic activity for ammonia decomposition, its preparation method is complicated and uses a high content of precious metal ruthenium. The literature (Chen-Feng Cao, et al. Chemical Engineering Science 257 (2022 117719) reported that ruthenium (Ru) nanoparticles supported on LaAlO ₃ (a typical ABO ₃ perovskite oxide) were used as an effective catalyst for ammonia decomposition. The results showed that the Ru/La _0.8 Sr _0.2 AlO ₃ catalyst had a high hydrogen production rate and low activation energy. At GHSV = 30,000 mL g _cat ^-1 h ^-1 and 500 ° C, the hydrogen production rate was 941 mmol _{g Ru} ^-1 min ^-1 and the ammonia conversion rate was 71.6%. Although both patents and literature indicate the high activity of Ru-based catalysts, the high price and limited reserves of Ru limit its large-scale application in the future.

The literature (Hiroki Muroyama, et al. Applied Catalysis A: General 443–444 (2012) 119–124) prepared various nickel catalysts loaded with metal oxides and studied their catalytic activity for ammonia decomposition. When the nickel loading of the Ni/La ₂ O ₃ catalyst varied in the range of 10-70 wt%, the sample containing 40 wt% Ni showed the highest conversion rate of 78.9% at 550°C (GHSV = 6,000 mL g _cat ^-1 h ^-1 ), which shows that the disclosed non-precious metal catalysts have poor activity.

In summary, providing a low-temperature, high-activity, high-stability, low-cost non-precious metal catalyst is of great significance and is a problem that needs to be urgently solved by those skilled in the art.

Summary of the invention

In order to solve the above problems, the first purpose of the present invention is to provide a method for preparing the above-mentioned yttrium oxide-loaded cobalt-based catalyst, wherein the yttrium oxide carrier is prepared by a surfactant template method, and cobalt is loaded on the yttrium oxide carrier by an impregnation method to prepare a yttrium oxide-loaded cobalt-based catalyst, which has the advantages of large catalyst specific surface area and high catalytic activity.

The second purpose of the present invention is to provide a method for preparing the above-mentioned other yttrium oxide-loaded nickel-based catalyst, wherein the yttrium oxide-metal oxide carrier is prepared by a surfactant template method, and cobalt is loaded on the yttrium oxide-metal oxide carrier by an impregnation method to prepare the catalyst. Since non-precious metals are used to synthesize the catalyst, the preparation cost is greatly reduced and it is expected to be applied on a large scale.

The third object of the present invention is to provide a catalyst prepared by the above method for use in ammonia decomposition to produce hydrogen, which has the advantages of high pure ammonia conversion rate and good stability, and overcomes the shortcomings of existing catalysts such as low ammonia conversion rate and poor thermal stability.

In order to achieve the above first purpose, the technical solution adopted by the present invention is: a rare earth oxide yttrium oxide supported cobalt-based catalyst, which comprises the following components by mass percentage:

1) Y ₂ O ₃ carrier 80-95%, the specific surface area of Y ₂ O ₃ carrier is 55m ² /g-80m ² /g,

2) Transition metal element cobalt 5-20%;

Alternatively, the following components are included in percentage by mass:

1) 70-95% of Y ₂ O ₃ -MyO _x carrier, M is other metal elements, _and the specific surface area of _the Y ₂ O ₃ -MyO _x carrier is 34m ² /g to 89m ² /g;

2) Transition metal element cobalt 5-30%.

It can be seen from the above technical solution that the specific surface area of the catalyst carrier provided by the present invention can reach up to 80 m ² /g at most.

In a further embodiment, M is one of the elements selected from the group consisting of magnesium, lanthanum, zinc, zirconium, aluminum, cerium, iron, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, lutetium, and scandium.

In order to achieve the above first purpose, the technical solution adopted by the present invention is: a method for preparing a rare earth oxide yttrium oxide supported cobalt-based catalyst, comprising the following steps:

1) dissolving one or more of a surfactant polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), coconut acid diethanolamide (6501), polyoxyethylene ether of isomeric decanol, and fatty alcohol polyoxyethylene ether (AEO-3) in deionized water, and then adding Y(NO ₃ ) ₃ .6H ₂ O under stirring to obtain a mixed solution A;

2) slowly adding an organic amine (one of diethylamine, triethylamine, triethanolamine, and tetrabutylammonium bromide) dropwise to the mixed solution A obtained in step 1), then continuing to stir, and aging in a water bath, and filtering while hot to obtain a white precipitate;

3) washing the white precipitate obtained in step 2) with deionized water until the filtrate is neutral, drying the white precipitate, and then calcining to obtain a Y ₂ O ₃ carrier;

4) dissolving a certain amount of Co(NO ₃ ) ₂ .6H ₂ O in an appropriate amount of organic solution containing hydroxyl or carbonyl groups, and then impregnating it on a Y ₂ O ₃ carrier. After drying, the dried product is calcined in an air atmosphere to obtain a catalyst precursor Co/Y ₂ O ₃ ;

It can be seen from the above technical scheme that the surfactant in step 1) has the function of reducing interfacial tension, facilitating emulsification, dispersion and stabilization of liquid particles, and may increase the specific surface area of the carrier; in step 2), organic amine is added to precipitate Y ³⁺ , and water bath aging can make the precipitation complete; in step 3), the precipitate is first washed to neutrality in order to remove OH ^-1 , and roasted to remove carbon and water in the carrier to obtain Y ₂ O ₃ carrier; in step 4), cobalt is impregnated on the carrier by impregnation. Experiments show that the specific surface area of the catalyst prepared by the present invention can be as high as 55m ² /g to 80m ² /g, and the catalytic activity of the catalyst is greatly enhanced.

A further scheme is that in step 1), the amount of surfactant is 5-10 mmol, the amount of Y(NO ₃ ) ₃ .6H ₂ O is 5-15 mmol, and the amount of deionized water is 100-200 mL; in step 2), organic amine is added to the mixed solution A and the stirring time is continued for 5-12 hours, the temperature of water bath heating is 50-100° C., and the aging time is 6-24 hours; in step 3), the drying temperature is 110-120° C., the drying time is 6-9 hours, and the calcination temperature range is 500° C.; in step 4), the organic solution containing hydroxyl or carbonyl groups is one of anhydrous ethanol, anhydrous methanol or anhydrous acetone, the drying temperature is 60-120° C., and the calcination temperature is 500-1000° C.

In order to achieve the above second object, the technical solution adopted by the present invention is: a method for preparing a modified yttrium oxide-supported cobalt-based catalyst, characterized in that it comprises the following steps:

1) dissolving one or more of a surfactant polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), coconut oil diethanolamide (6501), polyoxyethylene ether of isomeric decanol, and fatty alcohol polyoxyethylene ether (AEO-3) in deionized water, and then adding Y(NO ₃ ) ₃ .6H ₂ O and metal salt N under stirring to obtain a mixed solution B;

2) slowly adding an organic amine (one of diethylamine, triethylamine, triethanolamine, and tetrabutylammonium bromide) dropwise to the mixed solution B obtained in step 1), then continuing to stir, aging in a water bath, and filtering while hot to obtain a precipitate;

3) washing the precipitate obtained in step 2) with deionized water until the filtrate is neutral, drying the white precipitate, and then calcining to obtain a Y ₂ O _{3 -MyO x} carrier;

4) dissolving a certain amount of Co(NO ₃ ) ₂ .6H ₂ O in an appropriate amount of organic solution containing hydroxyl or carbonyl groups, and then impregnating the Y ₂ O _{3 -MyO x} carrier, and then transferring the mixture to a forced air drying oven for drying, and calcining the dried product in an air atmosphere to obtain the catalyst Co/Y ₂ O _{3 -MyO x} ;

A further scheme is that in step 1 ₎ , the amount of the surfactant _is 5 to 10 mmol, the amount of Y(NO ₃ ) ₃ .6H ₂ O is 3 to 9 mmol, _the molar ratio of the metal element in the metal salt N (N is one of magnesium nitrate pentahydrate, lanthanum nitrate hexahydrate, zinc acetate, zirconium nitrate hexahydrate, aluminum nitrate nonahydrate, iron nitrate nonahydrate, cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate, promethium nitrate hexahydrate, samarium nitrate hexahydrate, europium nitrate hexahydrate, gadolinium nitrate hexahydrate, terbium nitrate hexahydrate, erbium nitrate hexahydrate, thulium nitrate hexahydrate, ytterbium nitrate hexahydrate, lutetium nitrate hexahydrate, and scandium nitrate hexahydrate) is 1:1 to 1:9, and the amount of deionized water is 100 to 200 mL; step 2) adding an organic amine to the mixed solution A and continuing stirring for 5 to 12 hours, the water bath heating temperature is 60 to 120° C., and the aging time is 12 to 24 hours; in step 3), the drying temperature is 60 to 120° C., the drying time is 8 to 18 hours, and the calcination temperature is 300 to 900° C.; in step 4), the organic solution containing hydroxyl or carbonyl groups is one of anhydrous ethanol, anhydrous methanol or anhydrous acetone, the drying temperature is 60 to 180° C., and the catalyst is calcined in a muffle furnace at a temperature of 300 to 1000° C.

Experiments show that the specific surface area of the modified catalyst prepared by the present invention can reach up to 90 m ² /g.

In order to achieve the above-mentioned third purpose, the technical solution adopted by the present invention is: the yttrium oxide-supported cobalt-based catalyst of the present invention is used in the decomposition of ammonia to produce hydrogen, with pure ammonia as the raw material, and the reaction temperature is 300-600°C, the reaction pressure is atmospheric pressure (±0.01MPa), and the weight space velocity is 6000-30000mLh ^-1 _gcat ^-1. Under the conditions of contact with the catalyst bed (in the reactor, the catalyst needs to be reduced with hydrogen before contacting with ammonia, and the hydrogen reduction temperature is in the range of 500-700°C), and the reaction generates a product containing hydrogen.

The catalyst prepared by the preparation method of the present invention is used in the field of hydrogen production by decomposing ammonia, which reduces the preparation cost and improves the raw material conversion rate.

DETAILED DESCRIPTION

[Example 1]

Yttrium oxide supported cobalt-based catalyst preparation method:

1. Dissolve 4 g of surfactant in a beaker filled with 150 mL of deionized water, add a clean magnetic stir bar to the beaker, place the beaker on a magnetic stirrer, and add 4.2319 g of Y(NO ₃ ) ₃ ·6H ₂ O under constant stirring to obtain a mixed solution A.

2. Three hours later, organic amine was slowly added to the mixed solution A obtained in step 1, and stirring was continued until the pH of the solution reached 10. Stirring was then continued for 4 hours, and the mixture was aged in a 90° C. water bath for 3 hours. The mixture was filtered while hot to obtain a white precipitate.

3. Filter and wash the white precipitate obtained in step 2 with deionized water until the filtrate is neutral, then put the white precipitate into a 70°C oven and dry it for 12 hours. Then put the dried precipitate into a muffle furnace, control the muffle furnace to heat up to 400°C at a heating rate of 5°C/min, and then calcine for 2 hours to obtain _{a Y2O3} carrier.

4. Use an electronic analytical balance to weigh 0.8000g _of the above-mentioned _Y2O3 carrier and 0.4390g of Co( _NO3 ) ₂ · _6H2O respectively, add Co( _NO3 ) ₂ · _6H2O and 15mL of deionized water into a beaker (capacity 100mL), stir until Co( _NO3 ) ₂ · _6H2O is dissolved, put a clean magnetic stirring bar and _the weighed _Y2O3 carrier into the beaker, place the beaker on a magnetic stirrer and stir for 3h, then put it into a 60℃ forced drying oven and dry it for 12h, then put the dried product into a muffle furnace, and calcine it at 600℃ at a heating rate of 5℃/min in an air atmosphere for 2h to obtain the _catalyst Co/ _Y2O3 .

[Example 2-5]

Y(NO ₃ ) ₃ .6H ₂ O, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and triethylamine (TEA) are prepared according to the conditions in Table 1 and the steps in Example 1 to obtain the Co/Y ₂ O ₃ catalysts of Examples 2-5.

Table 1

[Examples 6-10] Cobalt-based catalysts are used to decompose ammonia to produce hydrogen.

Using ammonia as a raw material and the Co/Y ₂ O ₃ catalyst obtained in Example 1-5, the catalyst performance was evaluated according to the reaction conditions in Table 2.

Table 2

Conclusion: It can be seen from Tables 1 and 2 that when the space velocity is 6000mLg _cat ^-1 h ^-1 , the catalyst obtained in Example 1 has the largest specific surface area and the best catalytic performance. When the reaction temperature is 300-600°C and the reaction is under normal pressure, the ammonia decomposition conversion rate can reach 95%.

[Example 11]

Preparation method of modified Co/Y ₂ O ₃ catalyst:

1. Dissolve 4 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) in a beaker filled with 200 mL of deionized water, add a clean magnetic stir bar to the beaker, place the beaker on a magnetic stirrer, and add 1.9652 g of Y(NO ₃ ) ₃ ·6H ₂ O and 2.1648 g of La(NO ₃ ) ₃ ·6H ₂ O under continuous stirring to obtain a mixed solution B;

2. After one hour, triethylamine (TEA) was slowly added to the mixed solution B obtained in step 1, and the mixture was stirred continuously until the pH value of the solution reached 10. The mixture was then stirred for 4 hours, and aged in a water bath at 90° C. for 3 hours. The mixture was filtered while hot to obtain a white precipitate.

3. The white precipitate obtained in step 2 was filtered and washed with deionized water until the filtrate was neutral, and then the white precipitate was placed in a 70°C oven for drying for 12 hours, and then the dried precipitate was placed in a muffle furnace, and the muffle furnace was controlled to heat up to 500°C at a heating rate of 5°C/min and then calcined for 2 hours to obtain _{a Y2O3 -La2O3 carrier} , which was recorded as Y-La;

4. Use an electronic balance to weigh 0.8000g of the above carrier and 0.9878g of Co(NO ₃ ) ₂ ·6H ₂ O respectively, add the weighed Co(NO ₃ ) ₂ ·6H ₂ O and 15mL of deionized water into a beaker (capacity 100mL), stir until Co(NO ₃ ) ₂ ·6H ₂ O is dissolved, put a clean magnetic stirring bar and the weighed Y ₂ O ₃ -La ₂ O ₃ carrier into the beaker, place the beaker on a magnetic stirrer and stir for 3h, then put it into a 60℃ forced drying oven and dry it for 12h, then put the dried product into a muffle furnace, and calcine at 600℃ in an air atmosphere at a heating rate of 5℃/min for 2h to obtain the catalyst Co/Y-La.

The obtained catalyst contains 80% Y-La mixed oxide carrier, the content of metal cobalt as an active component in the catalyst is 20% by weight, and the specific surface area of the catalyst is 44 ^m2 /g.

[Examples 12-19]

Y(NO ₃ ) ₃ ·6H ₂ O, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), triethylamine (TEA) and nitrate compound raw materials containing the elements magnesium, lanthanum, zinc, zirconium, aluminum, cerium, iron, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, lutetium and scandium are prepared according to the preparation conditions in Table 3 and the steps in Example 11 to obtain the modified catalysts of Examples 12-19.

Table 3

Conclusion: A series of carriers can be obtained according to the conditions in the table. These carriers are modified by adding different metal nitrates. A series of magnesium-modified yttrium oxide carriers with different molar ratios of yttrium and lanthanum are also prepared. Subsequent catalytic activity tests show that the lanthanum-modified yttrium oxide carrier has a significant improvement in catalytic activity, among which the carrier with a molar ratio of lanthanum to yttrium metal equal to 1 is the best.

[Examples 20-28] Using modified catalysts to produce hydrogen by decomposing ammonia

Using ammonia as raw material and the modified catalysts obtained in Examples 11-19, the catalyst performance was evaluated according to the reaction conditions in Table 4.

Table 4

Conclusion: It can be seen from the table that when the space velocity is 12,000mLg _at ^-1 h ^-1 and the reaction temperature is in the range of 300-600℃, among a series of metal-modified Co/Y ₂ O _{3 -MyO x} catalysts, the lanthanum-modified catalyst achieves good ammonia decomposition conversion rate, among which the catalyst with a molar ratio of yttrium to lanthanum of 1:1 has the best ammonia decomposition conversion rate at 600℃.

[Example 29]

Preparation method of modified Co/Y ₂ O ₃ catalyst:

1. Dissolve 4 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) in a beaker filled with 200 mL of deionized water, add a clean magnetic stir bar to the beaker, place the beaker on a magnetic stirrer, and add 1.9652 g of Y(NO ₃ ) ₃ ·6H ₂ O and 1.8757 g of Al(NO ₃ ) ₃ ·9H ₂ O under continuous stirring to obtain a mixed solution C;

2. After one hour, triethylamine (TEA) was slowly added to the mixed solution C obtained in step 1, and the mixture was stirred continuously until the pH value of the solution was 10. The mixture was then stirred for 4 hours, and aged in a water bath at 90° C. for 3 hours. The mixture was filtered while hot to obtain a white precipitate.

3. The white precipitate obtained in step 2 was filtered and washed with deionized water until the filtrate was neutral, and then the white precipitate was placed in a 70°C oven for drying for 12 hours, and then the dried precipitate was placed in a muffle furnace, and the muffle furnace was controlled to heat up to 500°C at a heating rate of 5°C/min and then calcined for 2 hours to obtain _{a Y2O3-Al2O3 carrier , which} was recorded as Y-Al;

4. Use an electronic balance to weigh 0.8000g of the above carrier and 0.9878g of Co(NO ₃ ) ₂ ·6H ₂ O respectively, add the weighed Co(NO ₃ ) ₂ ·6H ₂ O and 15mL of deionized water into a beaker (capacity 100mL), stir until Co(NO ₃ ) ₂ ·6H ₂ O is dissolved, put a clean magnetic stirring bar and the weighed Y-Al carrier into the beaker, place the beaker on a magnetic stirrer and stir for 3h, then put it into a 60℃ forced drying oven and dry it for 12h, then put the dried product into a muffle furnace, and calcine it at 600℃ in an air atmosphere at a heating rate of 5℃/min for 2h to obtain the catalyst Co/Y-Al.

The obtained catalyst contains 80% Y-Al mixed oxide carrier, the content of metal cobalt as an active component in the catalyst is 20% by weight, and the specific surface area of the catalyst is 65 ^m2 /g.

[Examples 30-35]

Y(NO ₃ ) ₃ ·6H ₂ O, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), triethylamine (TEA) and nitrate compound raw materials containing the elements magnesium, lanthanum, zinc, zirconium, aluminum, cerium, iron, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, lutetium and scandium are prepared according to the preparation conditions in Table 4 and the steps in Example 29 to obtain the modified catalysts of Examples 30-35.

Table 5

[Examples 36-42] Using modified catalysts to produce hydrogen by decomposing ammonia

Using ammonia as raw material and the modified catalysts obtained in Examples 29-35, the catalyst performance was evaluated according to the reaction conditions in Table 6.

Table 6

Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims (4)

1. A method for preparing a rare earth yttrium oxide supported cobalt-based catalyst, characterized in that it comprises the following steps: 1) dissolving the surfactant in deionized water, and then adding Y(NO ₃ ) ₃ .6H ₂ O under stirring to obtain a mixed solution A; 2) slowly adding the organic amine solution dropwise to the mixed solution A obtained in step 1), then continuously stirring for a period of time under water bath heating, taking out and aging for a period of time, and then filtering to obtain a white precipitate; 3) washing the white precipitate obtained in step 2) with deionized water until the filtrate is neutral, drying the white precipitate, and then calcining to obtain a Y ₂ O ₃ carrier; Step 2) the calcination temperature is in the range of 300-1000°C; 4) dissolving a certain amount of Co(NO ₃ ) ₂ .6H ₂ O in a proper amount of a mixed solution containing deionized water, hydroxyl or carbonyl, and then impregnating it on the Y ₂ O ₃ carrier, drying and calcining the dried product in an air atmosphere to obtain a catalyst Co/Y ₂ O ₃ ; The yttrium oxide-supported cobalt-based catalyst comprises the following components in percentage by mass: a) 80-95% of Y ₂ O ₃ carrier, the specific surface area of the Y ₂ O ₃ carrier ^is 55-80 m ² /g, b) Transition metal element cobalt 5-20%. 2. The preparation method according to claim 1, characterized in that: In step 1), the surfactant is one or more of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), coconut acid diethanolamide (6501), polyoxyethylene ether of isomeric decanol, and fatty alcohol polyoxyethylene ether (AEO-3), the amount of the surfactant is 5-10 mmol, the amount of Y(NO ₃ ) ₃ .6H ₂ O is 5-15 mmol, and the amount of deionized water is 100-200 mL; In step 2), the organic amine is one of diethylamine, triethylamine, triethanolamine and tetrabutylammonium bromide; the organic amine is added to the mixed solution A and the stirring time is continued for 5 to 12 hours, the water bath heating temperature is 50 to 100° C., and the aging time is 6 to 24 hours; In step 3), the drying temperature is 60 to 120° C. and the drying time is 8 to 24 hours; The mixed solution in step 4) is a combination of one or more of deionized water, anhydrous ethanol, anhydrous methanol or anhydrous acetone, the drying temperature is 60-120°C, and the calcination temperature is 400-1000°C. 3. A method for preparing a modified yttrium oxide-supported cobalt-based catalyst, characterized in that it comprises the following steps: 1) dissolving the surfactant in deionized water, and then adding Y(NO ₃ ) ₃ .6H ₂ O and metal salt N under stirring to obtain a mixed solution B; 2) slowly adding an organic amine dropwise to the mixed solution B obtained in step 1), then continuing to stir, aging in a water bath, and filtering while hot to obtain a precipitate; 3) washing the precipitate obtained in step 2) with deionized water until the filtrate is neutral, drying the white precipitate, and then calcining to obtain a Y ₂ O _{3 -MyO x} carrier; 4) dissolving a certain amount of Co(NO ₃ ) ₂ .6H ₂ O in a proper amount of mixed solution containing deionized water, hydroxyl or carbonyl, and then impregnating it into the above Y ₂ O _{3 -MyO x} carrier, drying and calcining the dried product in an air atmosphere to obtain the catalyst Co/Y ₂ O _{3 -MyO x;} The catalyst comprises the following components in percentage by mass: c) 70-95% of _{a Y2O3} - _{MyOx carrier} , wherein M is one of magnesium, lanthanum, zinc, zirconium, aluminum, cerium, iron, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, lutetium and scandium, and the specific surface area of the _Y2O3 - _{MyOx carrier} is _30m2 ^/ g to ^90m2 /g, d) 5-30% of transition metal element cobalt; The cobalt-based catalyst is used in the decomposition of ammonia to produce hydrogen. Ammonia is used as the raw material. The reaction temperature is 300-600°C, the reaction pressure is normal pressure (±0.01MPa), and the weight space velocity is 6000-30000mLh ^- _1gcat ^-1 . The catalyst is reduced with hydrogen before contacting with ammonia in the reaction furnace. The hydrogen reduction temperature is in the range of 500-700°C. The reaction generates nitrogen and hydrogen products. 4. The preparation method according to claim 3, characterized in that: In step 1), the surfactant is one or more of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), coconut acid diethanolamide (6501), polyoxyethylene ether of isomeric decanol, and fatty alcohol polyoxyethylene ether (AEO-3), the amount of the surfactant is 5-10 mmol, the amount of Y(NO ₃ ) ₃ .6H ₂ O is 3-9 mmol, and the amount of Y(NO ₃ ) ₃ .6H ₂ The molar ratio of O to the metal salt N is 1:1 to 1:9, and the amount of deionized water is 100 to 200 mL; the metal salt N is one or more of magnesium nitrate pentahydrate, lanthanum nitrate hexahydrate, zinc acetate, zirconium nitrate hexahydrate, aluminum nitrate nonahydrate, iron nitrate nonahydrate, cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate, promethium nitrate hexahydrate, samarium nitrate hexahydrate, europium nitrate hexahydrate, gadolinium nitrate hexahydrate, terbium nitrate hexahydrate, erbium nitrate hexahydrate, thulium nitrate hexahydrate, ytterbium nitrate hexahydrate, lutetium nitrate hexahydrate, and scandium nitrate hexahydrate; In step 2), the organic amine is one of diethylamine, triethylamine, triethanolamine and tetrabutylammonium bromide; the organic amine is added to the mixed solution B and the stirring time is continued for 5 to 12 hours, the water bath heating temperature is 60 to 120° C., and the aging time is 12 to 24 hours; In step 3), the drying temperature is 60-120°C, the drying time is 8-18h, and the calcination temperature is 300-1000°C; The mixed solution in step 4) is a combination of one or more of deionized water, anhydrous ethanol, anhydrous methanol or anhydrous acetone, the drying temperature is 60-180° C., and the catalyst is calcined in a muffle furnace at a temperature of 300-900° C.