CN114471553A - Preparation and application of a rare earth modified catalyst for hydrogen production by ammonia decomposition - Google Patents

Abstract

The invention relates to the technical field of hydrogen production, in particular to preparation and application of a rare earth modified catalyst for hydrogen production by ammonia decomposition. The invention takes yttrium and potassium as the auxiliary agent of the catalyst, and takes gamma-alumina as the carrier, and is matched with the yttrium and the potassium, thereby reducing the using amount of ruthenium and still ensuring the high conversion rate of ammonia gas at low temperature (430 ℃). Because of low decomposition temperature, the method effectively relieves the problem of high energy consumption of the prior ammonia decomposition, and in addition, because of the existence of rare earth element yttrium, H on ruthenium is effectively inhibited₂Poisoning and lowering the apparent activation energy. The preparation method is simple and feasible, the prepared catalyst has high catalytic activity and lower cost than other ruthenium-based catalysts, and the reaction temperature of ammonia decomposition can be reduced to 430 ℃. In conclusion, the catalyst is a novel ammonia decomposition catalyst and has good industrial application prospect.

Description

Preparation and application of a rare earth modified catalyst for hydrogen production by ammonia decomposition

technical field

The invention relates to the technical field of hydrogen production, in particular to the preparation and application of a rare earth modified catalyst for hydrogen production by ammonia decomposition.

Background technique

Hydrogen is the most abundant element on earth. Hydrogen comes from a wide range of sources. It can be obtained from various fossil fuels by reforming hydrogen or by ammonia cracking, or by electrolysis of water. Since the combustion product of hydrogen is water, it will not pollute the environment, so it is regarded as a clean energy with great application prospects. In addition to being directly combusted, hydrogen is also widely used in fuel cells to generate electricity to drive vehicles, and the process does not produce any CO _X and NO _X . Since hydrogen fuel cells can efficiently convert chemical energy into electrical energy, they are considered to be a promising next-generation energy supply system. Currently, hydrogen fuel cells are widely used in aerospace, automotive and other stationary or mobile energy supply systems.

At present, the main way of large-scale hydrogen production is fossil fuels, but the hydrogen obtained by this method is often accompanied by the production of CO _X , especially the CO in it will poison the fuel cell electrodes, so it needs to be purified after complicated post-processing. in order to meet the hydrogen standards for fuel cells. my country's ammonia production is large, the price is relatively low, and the hydrogen density is high and the energy density is high. At present, ammonia decomposition to hydrogen as a green technology is attracting more and more researchers' attention. This is because the decomposition of ammonia to produce hydrogen does not produce any carbon oxides, and the cost of hydrogen production is also low, which is one of the effective ways to produce hydrogen for fuel cells. In particular, ammonia can be liquefied and compressed under low pressure, which is convenient for storage and transportation.

Ammonia decomposition catalysts are currently studied more iron-based, ruthenium-based, nickel-based catalysts. Iron-based catalysts and nickel-based catalysts are rich in sources and low in cost, but their catalytic activity is low, so they need to react at higher temperatures (usually above 650 °C) to achieve higher conversion rates and higher energy consumption. Ruthenium-based catalysts are the most active catalysts found so far for ammonia decomposition, but they are expensive and limited in resources because they are precious metals, which limit their wide application.

Patent document CN112337494A discloses an ammonia decomposition catalyst for hydrogen production and its preparation method and application. The active component of the catalyst is non-precious metal Ni or Co with a mass fraction of 5-20 wt.%, and the carrier is a composite carrier of BN and CeO ₂ or Y ₂ O ₃ with a mass fraction of 80-95 wt. %. The catalyst has low preparation cost and good catalytic activity, but its corresponding reaction temperature is high.

Patent document CN1506299A discloses a nickel-based ammonia decomposition catalyst for hydrogen-nitrogen mixed gas production, the main active component is Ni, the carrier is SiO ₂ or Al ₂ O ₃ , and the auxiliary agent is IA, IIA, IIIB, VIII or rare earth elements such as Li One or more of , K, Y, Fe, Co; wherein the weight percentage of nickel is 1-40wt.%. The reaction temperature of the catalyst is ~650°C, which is about 150°C lower than the working temperature of the nickel-based catalyst used in industry. However, at this temperature, the catalytic activity is still low, and the ammonia decomposition effect is not good.

Patent document CN109954493A discloses a rare earth metal oxide supported ruthenium catalyst for hydrogen production by ammonia decomposition. The catalyst uses ruthenium as an active component and a rare earth metal oxide as a carrier. The content of ruthenium (the mass of ruthenium accounts for the mass of the rare earth metal oxide) is about 1-10 wt.%, and the catalyst is mainly prepared by a precipitation method. For the decomposition of pure ammonia, it can completely convert ammonia into nitrogen and hydrogen at 500°C under the condition of gas space velocity of 36000ml·g ^-1 ·h ^-1 . However, the cost of the catalyst is still high due to the high ruthenium loading.

Recently, patent document CN110339840A discloses a preparation method for preparing Ni and/or Ru-based ammonia decomposition catalyst by using hydrotalcite-like. In the method, hydrotalcite-like is used as the precursor of the catalyst, and then the catalyst is prepared by a co-precipitation method. Since this type of hydrotalcite precursor can be calcined to obtain a composite metal oxide with high specific surface area, and then the active metal Ni can be reduced, Ru or Ru-Ni can be highly dispersed in the carrier, which can improve the activity and stability of the catalyst. sex. However, the decomposition temperature of the catalyst corresponding to higher ammonia conversion rate generally needs to be 650-700 °C, and the best is 550 °C, and there is still room for further improvement.

Patent document CN 111215063 A, discloses the application of a metal catalyst supported by rare earth carbonate as a carrier precursor in ammonia decomposition reaction. Embodiment 6 of the technical solution discloses that under the condition of temperature of 450°C, the ammonia conversion rate is 97.5%, but the load of ruthenium is 5%, and the content of yttrium is more than about 30%, and the cost of the catalyst is relatively high; and the catalyst needs to use cerium carbonate as the precursor of the carrier, and the obtained catalyst is a cerium oxide-supported ruthenium catalyst . In short, its preparation process is complicated, the process has uncontrollable factors, and the preparation process also involves a certain amount of carbon emissions, which may not meet the requirements of existing environmental policies, and there are certain restrictions on its use; in addition, the price (cost) of cerium oxide is relatively high. High, which is 3-5 times that of alumina, resulting in higher catalyst cost, and the porosity and high temperature stability of ceria are not as good as alumina (with certain limitations).

To sum up, there is currently no real low-cost catalyst with high activity and high stability that can decompose ammonia into hydrogen more completely at lower temperature. Therefore, it is necessary to seek and develop new ammonia decomposition catalysts. It is of great significance to promote the development of ammonia decomposition hydrogen production technology, especially the promotion of fuel cell technology.

SUMMARY OF THE INVENTION

In order to solve the problems mentioned in the above background technology, in one embodiment of the present invention, a rare earth modified catalyst for hydrogen production by ammonia decomposition is provided, which uses γ-alumina as a carrier, the catalyst active component is ruthenium, and further comprises: Yttrium and potassium are used as auxiliaries.

In the technical aspect of the above technical solution, in a preferred embodiment, the content of ruthenium is 1% to 4% of the catalyst mass; the content of yttrium is 1% to 4% of the catalyst mass; the potassium content is 8% of the catalyst mass %～12%.

In the technical aspect of the above technical solution, in a preferred embodiment, the ratio of ruthenium, yttrium and potassium is (1-4):(1-4):(8-12) in terms of mass units.

In the technical aspect of the above technical solution, in a preferred embodiment, the yttrium and potassium are respectively added with yttrium chloride and potassium acetate as precursors.

The present invention also provides an embodiment of a method for preparing a rare earth modified catalyst for hydrogen production by ammonia decomposition, comprising the following preparation steps:

Step a: drying the γ-alumina carrier;

Step b: after mixing ruthenium, yttrium and potassium as (1-4):(1-4):(8-12) according to mass ratio, they are dissolved in deionized water to obtain an impregnation solution;

Step c: Impregnating the γ-alumina carrier: under the condition of constant stirring of the impregnation solution, immerse the dried γ-alumina carrier into the impregnation solution until the γ-alumina carrier is fully impregnated;

Step d: drying treatment: the impregnated γ-alumina carrier is taken out from the solution and placed in an oven for drying treatment;

The γ-alumina carrier in step c and step d is repeated to carry out the impregnation treatment step and the drying treatment step, until the increase in the weight of the γ-alumina carrier reaches a predetermined value;

In step e, the γ-alumina carrier obtained above is ground, heated, and calcined in the air to obtain the rare earth modified catalyst for hydrogen production by ammonia decomposition.

In the technical aspect of the above technical solution, in a preferred embodiment, in step a, the ruthenium and yttrium are respectively RuCl ₃ and anhydrous yttrium chloride as precursors;

The potassium was added and mixed as _KCH3COO .

In the technical aspect of the above technical solution, in a preferred embodiment, the mass ratio of the ruthenium, yttrium and potassium is (1-4):(1-4):(8-12).

In the technical aspect of the above technical solution, in a preferred embodiment, in step a, the temperature of the drying treatment of the γ-alumina carrier is 105-125° C., and the duration is 2-4 hours;

In step d, the temperature of the drying treatment of the γ-alumina carrier is 120-140° C., and the duration is 30-45 min.

In the technical aspect of the above technical solution, in a preferred embodiment, in step e, the γ-alumina carrier is ground and heated at a temperature of 200°C for 2-5 hours;

In step e, the calcination temperature in air is 550-650° C., and the duration is 3-5 hours.

The present invention also provides a rare earth modified catalyst for hydrogen production by ammonia decomposition as described in any of the above and the catalyst prepared by the preparation method of a rare earth modified catalyst for hydrogen production by ammonia decomposition as described in any of the above. Applications.

In the embodiment technical scheme provided by the invention, with yttrium and potassium as the auxiliary agent of the catalyst, by taking γ-alumina as the carrier, and cooperating with yttrium and potassium, the usage amount of ruthenium has been reduced, and still can be used at low temperature ( 430 °C) can still ensure the high conversion rate of ammonia gas, which effectively alleviates the problem of high energy consumption for ammonia decomposition. In addition, due to the presence of rare earth element yttrium, _H2 poisoning on ruthenium can be suppressed while reducing the apparent activation energy.

Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the description, claims and drawings.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are the present invention. Some examples, but not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1 (430°C)

In the rare earth modified catalyst for hydrogen production by ammonia decomposition provided in this embodiment, the mass fraction of ruthenium is 1%, the mass fraction of yttrium is 3%, and the mass fraction of potassium is 12%.

According to the definition of the above catalyst, those skilled in the art can obtain it by some other methods. And the catalyst of the present embodiment can also be prepared by the following method:

Step a. Dry the carrier γ-Al ₂ O ₃ at 110° C. for 2 hours, and then use it for later use;

Step b. Mix an appropriate amount of RuCl ₃ , anhydrous chloride salt and KCH ₃ COO, wherein the ratio of the three metals Ru:Y:K is 1:3:12, and dissolve them in deionized water to prepare an impregnating solution ;

Step c, immersing the dried carrier in the above solution under magnetic stirring to achieve preliminary immersion;

Step d, drying the impregnated carrier at 130° C. for 30 minutes; repeating the above process continuously until the weight increase on the carrier reaches the expected value;

Step e. Finally, the impregnated catalyst is ground and heated at 200°C for 2 hours, and then calcined in air at 600°C for 3 hours;

The catalyst prepared above was subjected to ammonia cracking hydrogen production reaction in a laboratory small-scale device, reaction conditions: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar, and the temperature of ammonia decomposition was 430°C.

As a result, the hydrogen content in the mixed gas was about 73.2%, the nitrogen content was about 24.4%, and the conversion rate of ammonia was about 95.4%.

Example 2 (400°C)

The present embodiment provides a rare earth modified catalyst for hydrogen production by decomposition of ammonia, the mass fraction of ruthenium is 2%, the mass fraction of yttrium is 2%, and the mass fraction of potassium is 12%.

According to the definition of the above catalyst, those skilled in the art can obtain it by some other methods. And the catalyst of the present embodiment can also be prepared by the following method:

Step a. Dry the carrier γ-Al ₂ O ₃ at 110° C. for 2 hours, and then use it for later use;

Step b. Mix an appropriate amount of RuCl ₃ , anhydrous chloride salt and KCH ₃ COO, wherein the ratio of the three metals Ru:Y:K is 2:2:12, and dissolve them in deionized water to prepare an impregnating solution ;

Step c, immersing the dried carrier in the above solution under magnetic stirring to achieve preliminary immersion;

Step d, drying the impregnated carrier at 120° C. for 40 min, and repeating the above process continuously until the weight on the carrier is increased to the expected value;

Step e. Finally, the impregnated catalyst is ground and heated at 200° C. for 3 hours, and then calcined in air at 600° C. for 3 hours.

In the obtained catalyst, the mass fraction of ruthenium is 2%, the mass fraction of yttrium is 2%, and the mass fraction of potassium is 12%.

As a result, the hydrogen content in the mixed gas is about 72.4%, and the nitrogen content is about 24.1%. The reaction conditions are: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar, the temperature of ammonia decomposition is 400 ℃, and the conversion rate of ammonia is about 93.3 %.

Example 3 (430°C)

The present embodiment provides a rare earth modified catalyst for hydrogen production by decomposition of ammonia, the mass fraction of ruthenium is 2%, the mass fraction of yttrium is 2%, and the mass fraction of potassium is 12%.

According to the definition of the above catalyst, those skilled in the art can obtain it by some other methods. And the catalyst of the present embodiment can also be prepared by the following method:

Step a. Dry the carrier γ-Al ₂ O ₃ at 125° C. for 2 hours, and then use it for later use;

Step b. Mix an appropriate amount of RuCl ₃ , anhydrous chloride salt and KCH ₃ COO, wherein the ratio of the three metals Ru:Y:K is 2:2:12, and dissolve them in deionized water to prepare an impregnating solution ;

Step c, immersing the dried carrier in the above solution under magnetic stirring to achieve preliminary immersion.

Step d, drying the impregnated carrier at 125°C for 30 min, and repeating the above process continuously until the weight increase on the carrier reaches the expected value;

Step e. Finally, the impregnated catalyst is first ground and heated at 200°C for 2 hours, and then calcined in air at 500°C for 3 hours;

The catalyst obtained above was subjected to ammonia cracking and hydrogen production reaction in a laboratory small-scale device, reaction conditions: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar, and the temperature of ammonia decomposition was 430 ° C; as a result, a mixed gas was obtained. The hydrogen content is about ~74.5%, the nitrogen content is about 24.8%, and the conversion rate of ammonia is about 98.7%.

Comparative Example 1 (400°C)

This comparative example provides a rare earth modified catalyst for hydrogen production by ammonia decomposition, which is specifically prepared by the following method:

Step a. Dry the carrier γ-Al ₂ O ₃ at 110° C. for 2 hours, and then use it for later use;

Step b. Mix an appropriate amount of RuCl ₃ and KCH ₃ COO, wherein the ratio of Ru:K two metals (without yttrium) is 4:12, and dissolve in deionized water to prepare an impregnating liquid;

Step c, immersing the dried carrier in the above solution under magnetic stirring to achieve preliminary immersion;

Step d, drying the impregnated carrier at 120° C. for 40 min, and repeating the above process continuously, until the weight increase on the carrier reaches the expected value;

Step e. Finally, the impregnated catalyst is ground and heated at 200° C. for 3 hours, and then calcined in air at 600° C. for 3 hours.

In the obtained catalyst, the mass fraction of ruthenium is 4%, no yttrium is added, and the mass fraction of potassium is 12%.

The catalyst obtained above was subjected to ammonia cracking and hydrogen production reaction in a laboratory small-scale device, reaction conditions: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar, and the temperature of ammonia decomposition was 400 ° C;

As a result, the hydrogen content in the mixed gas was about 69.7%, the nitrogen content was about 23.2%, and the conversion rate of ammonia was about 86.7%.

Comparative Example 2 (400°C)

This comparative example provides a rare earth modified catalyst for hydrogen production by ammonia decomposition, which is specifically prepared by the following method:

Step a. Dry the carrier γ-Al ₂ O ₃ at 110° C. for 2 hours, and then use it for later use;

Step b, mixing an appropriate amount of RuCl ₃ and anhydrous chloride salt, wherein the ratio of Ru:Y (without K) two metals is 2:2, and dissolving in deionized water to prepare an impregnating liquid;

Step c, immersing the dried carrier in the above solution under magnetic stirring to achieve preliminary immersion;

Step d, drying the impregnated carrier at 120° C. for 40 min, and repeating the above process continuously, until the weight increase on the carrier reaches the expected value;

Step e. Finally, the impregnated catalyst is ground and heated at 200° C. for 3 hours, and then calcined in air at 600° C. for 3 hours.

In the obtained catalyst, the mass fraction of ruthenium is 2%, the mass fraction of yttrium is 2%, and K is not added.

As a result, the hydrogen content in the mixed gas is about 60.6%, and the nitrogen content is about 20.2%. The reaction conditions are: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar, the temperature of ammonia decomposition is 400 ℃, and the conversion rate of ammonia is about 67.8 %.

The catalysts of the embodiment of the present invention and the catalyst of the comparative example were tested at different temperatures and the rest of the environments were the same (reaction conditions: 100% NH ₃ , 5400 mL/hr/gcat, P=1.01 bar.), as shown in Table 1:

Table 1

index temperature Ammonia conversion rate (%) Example 1 430℃ 95.4 Example 2 400℃ 93.3 Example 3 430℃ 98.7 Comparative Example 1 400℃ 86.7 Comparative Example 2 400℃ 67.8

Among them, the thermodynamic basis for the hydrogen production reaction of ammonia decomposition can be carried out at about 430 ° C as shown in Figure 1.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (10)

1. A rare earth modified catalyst for ammonia decomposition hydrogen production is characterized in that: the gamma-alumina is used as a carrier, the active component of the catalyst is ruthenium, and yttrium and potassium are also used as auxiliary agents.

2. The rare earth-modified catalyst for ammonia decomposition hydrogen production according to claim 1, characterized in that: the content of the ruthenium accounts for 1-4% of the mass of the catalyst; the content of yttrium is 1-4% of the mass of the catalyst; the content of potassium accounts for 8-12% of the mass of the catalyst.

3. The rare earth-modified catalyst for ammonia decomposition hydrogen production according to claim 1, characterized in that: the ratio of the ruthenium, the yttrium and the potassium is (1-4) to (8-12) calculated by mass unit.

4. The rare earth-modified catalyst for ammonia decomposition hydrogen production according to claim 1, characterized in that: the yttrium and the potassium are respectively added by taking yttrium chloride and potassium acetate as precursors.

5. A preparation method of a rare earth modified catalyst for ammonia decomposition hydrogen production is characterized by comprising the following preparation steps:

step a: drying the gamma-alumina carrier;

step b: mixing ruthenium, yttrium and potassium according to the mass ratio of (1-4) to (8-12), and dissolving in deionized water to obtain an impregnation solution;

step c: carrying out impregnation treatment on the gamma-alumina carrier: under the condition of continuously stirring the impregnation liquid, immersing the dried gamma-alumina carrier into the impregnation liquid until the gamma-alumina carrier is fully impregnated;

step d: and (3) drying treatment: taking the impregnated gamma-alumina carrier out of the solution, and placing the impregnated gamma-alumina carrier in an oven for drying treatment;

repeating the steps of dipping and drying the gamma-alumina carrier in the steps c and d until the weight increase of the gamma-alumina carrier reaches a preset value;

and e, grinding the obtained gamma-alumina carrier, heating, and calcining in air to obtain the rare earth modified catalyst for preparing hydrogen by decomposing ammonia.

6. The method for preparing a rare earth modified catalyst for ammonia decomposition hydrogen production according to claim 1, characterized in that: in step a, the ruthenium and the yttrium are respectively expressed by RuCl₃Anhydrous yttrium chloride is used as a precursor;

the potassium is KCH₃COO is added and mixed.

7. The method for preparing a rare earth modified catalyst for ammonia decomposition hydrogen production according to claim 5, characterized in that: the mass ratio of the ruthenium to the yttrium to the potassium is (1-4) to (8-12).

8. The method for preparing a rare earth modified catalyst for ammonia decomposition hydrogen production according to claim 5, characterized in that: in the step a, the drying treatment temperature of the gamma-alumina carrier is 105-125 ℃, and the time duration is 2-4 hours;

in the step d, the drying treatment temperature of the gamma-alumina carrier is 120-140 ℃, and the time duration is 30-45 min.

9. The method for preparing a rare earth modified catalyst for ammonia decomposition hydrogen production according to claim 5, characterized in that:

in the step e, the gamma-alumina carrier is ground and heated at the temperature of 200 ℃ for 2-5 hours;

in step e, the calcination temperature in air is 550-650 ℃ for 3-5 hours.

10. The use of the rare earth modified catalyst for ammonia decomposition hydrogen production according to any of claims 1 to 4 and the catalyst prepared by the method for preparing the rare earth modified catalyst for ammonia decomposition hydrogen production according to any of claims 5 to 9 in the preparation of hydrogen by ammonia decomposition.

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