CN117619390A - A kind of ammonia decomposition hydrogen production catalyst and its preparation method and application - Google Patents

Abstract

The invention belongs to the field of environmentally friendly hydrogen production technology, and specifically relates to an ammonia decomposition hydrogen production catalyst and its preparation method and application. The catalyst includes an active component, a cocatalyst and a carrier; the active component is a transition metal; the cocatalyst is an alkaline earth metal barium; the carrier is a rare earth metal oxide; based on 100 parts of the mass of the carrier rare earth metal oxide, the active component The loading amount of the catalyst is 25 to 35 parts, and the loading amount of the cocatalyst is 8 to 20 parts. By adding alkaline earth metal barium as cocatalyst, the electronic structure of the transition metal catalyst can be changed, promoting its electron donating ability, and improving the dispersion of metal active components, thereby improving the overall catalytic activity, and can decompose ammonia at lower temperatures. . Using rare earth metal oxides as carriers can strengthen the interaction between the metal and the carrier, promote the adsorption of ammonia molecules, increase the activity while lowering the reaction temperature, and also promote the stability of the catalyst.

Description

A kind of ammonia decomposition hydrogen production catalyst and its preparation method and application

Technical field

The invention belongs to the field of environmentally friendly hydrogen production technology, and specifically relates to an ammonia decomposition hydrogen production catalyst and its preparation method and application.

Background technique

With the continuous development of modern society, human beings' demand for energy is increasing day by day; however, since the industrial revolution, human beings' over-exploitation and use of traditional fossil resources has caused serious environmental pollution problems and emitted large amounts of _CO2 . Greenhouse gases cause global climate warming, seriously threatening the stability of the ecosystem and the survival and development of human society. Therefore, the development and utilization of environmentally friendly, green and pollution-free new energy sources have become the focus of attention. Among them, hydrogen energy is considered to be one of the new energy sources with the most practical application value in the future due to its many advantages such as zero pollution, high energy, rich resources, and wide range of uses. However, the low density, flammable and explosive characteristics of hydrogen itself make its transportation and storage very difficult, which seriously hinders the large-scale commercial application of hydrogen. At present, the most important hydrogen storage and transportation technology is high-pressure gas storage and transportation technology. Although it has been initially commercialized, it is currently only suitable for short-distance and small-scale storage, and cannot meet the demand for large-scale hydrogen use.

Using ammonia, methanol, calcium hydride and other hydrogen-containing compounds as hydrogen carriers to produce hydrogen online through chemical reactions can greatly improve the efficiency of hydrogen transportation and storage. Among them, ammonia has many advantages such as high hydrogen mass density (17.8wt%), easy liquefaction, decomposed by-products will not cause secondary pollution, low energy loss during the synthesis process, and is cheap and easy to obtain. It has become the current choice. One of the most valuable hydrogen storage compounds. However, the decomposition of ammonia to produce hydrogen is an endothermic reaction that requires high temperatures to produce high-purity hydrogen, which consumes a lot of energy. For this reason, it is crucial to develop efficient ammonia decomposition reaction catalysts with low-temperature activity.

At present, the catalysts for hydrogen production from ammonia decomposition are mainly precious metal (Ru, Ir, etc.) catalysts. However, precious metal catalysts are expensive and have small reserves, making it difficult to achieve commercial application. The catalytic activity of cheap and easily available transition metal catalysts at low temperatures is similar to that of There are obvious differences between noble metal catalysts, so how to improve the catalytic activity of transition metal catalysts for hydrogen production from ammonia decomposition at low temperatures is an urgent problem that needs to be solved.

Contents of the invention

In order to overcome the above problems, the present invention provides an ammonia decomposition hydrogen production catalyst and its preparation method and application. In the present invention, a supported transition metal-rare earth oxide-alkaline earth metal barium catalyst is prepared by a sedimentation method, using the transition metal as the active metal, the alkaline earth metal barium as the cocatalyst, and the rare earth oxide as the carrier. In the reaction of ammonia decomposition to produce hydrogen, the transition metal-based catalyst can realize efficient ammonia decomposition to produce hydrogen at low temperature.

In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

A first aspect of the present invention provides an ammonia decomposition hydrogen production catalyst, which includes an active component, a cocatalyst and a carrier;

The active component is a transition metal; the cocatalyst is alkaline earth metal barium; the carrier is a rare earth metal oxide;

Based on 100 parts of the mass of the carrier rare earth metal oxide, the loading amount of the active component is 25 to 35 parts, and the loading amount of the cocatalyst is 8 to 20 parts.

A second aspect of the present invention provides a method for preparing the above-mentioned ammonia decomposition hydrogen production catalyst, which includes the following steps:

(1) Dissolve rare earth metal nitrates in deionized water, then add NaOH solution drop by drop, place the mixed solution in an autoclave for hydrothermal reaction, and synthesize rare earth metal oxides;

(2) Disperse the metal oxide synthesized in step (1) in deionized water, add a mixed solution of transition metal nitrate and barium nitrate dropwise, and simultaneously add Na ₂ CO ₃ solution dropwise to control the pH value to be stable at 8 ~10, stir at room temperature and then age. The solid is suction filtered, dried, and calcined in a muffle furnace to obtain an ammonia decomposition hydrogen production catalyst.

A third aspect of the present invention provides the use of the above ammonia decomposition hydrogen production catalyst in an ammonia decomposition hydrogen production reaction.

The beneficial effects of the present invention are:

(1) The activity of cobalt-based transition metals in catalyzing hydrogen decomposition of ammonia is higher than that of other transition metal catalysts, but its catalytic activity at low temperatures is significantly different from that of noble metal catalysts. By adding cocatalyst alkaline earth metal barium, the electrons of the catalyst can be changed structure, promotes its electron-donating ability, and improves the dispersion of metal active components, thereby improving the overall catalytic activity, and can decompose ammonia at lower temperatures. Using rare earth metal oxides as carriers can strengthen the interaction between the metal and the carrier, promote the adsorption of ammonia molecules, increase the activity while lowering the reaction temperature, and also promote the stability of the catalyst.

(2) The addition of cocatalyst Ba in the present invention not only improves Co-based catalysts, but also all transition metal-based catalysts commonly used for ammonia decomposition, which illustrates that Ba as a promoter combined with rare earth oxides is effective for transition metal-based catalysts to catalyze ammonia. The universality of improved decomposition reaction activity.

(3) The decomposition of ammonia is a step-by-step dehydrogenation process. Metal catalysts are used to catalyze the decomposition of ammonia to produce hydrogen. Different metal catalysts have different rate-determining steps. It is generally believed that the use of precious metal (Ru, Ir, etc.) catalysts breaks the N-H bonds in ammonia. It is the rate-determining step, but for transition metals (Co, Fe, Ni, etc.), the analysis of nitrogen is the rate-determining step. Although alkaline earth metal barium as a cocatalyst can improve the activity of precious metal (Ru, Ir, etc.) catalysts, due to different catalysts The rate-determining step is different, and the mechanism of alkaline earth metal barium as a cocatalyst to improve the activity of different catalysts is different.

(4) The test results show that the ammonia decomposition hydrogen production catalyst provided by the present invention can achieve a high conversion rate of 87.5% when decomposing ammonia at 500°C, and the hydrogen production rate per gram of catalyst can reach 29.3mmol g _cat ^-1 min ^-1 , exceeding the existing transition metal-based ammonia decomposition hydrogen production catalysts, and even higher than some precious metal Ru-based catalysts.

Description of drawings

The description and drawings that constitute a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

Figure 1 is a graph showing the NH ₃ conversion rate of the catalyst prepared in Comparative Example 1, Comparative Example 4, Comparative Example 5 and Comparative Example 6 when used in ammonia decomposition reaction;

Figure 2 is a graph of the NH ₃ conversion rate of the catalyst prepared in Example 1, Example 4, Example 5, Comparative Example 1, Comparative Example 5 and Comparative Example 6 when used in ammonia decomposition reaction;

Figure 3 is a graph showing the NH ₃ conversion rate of the catalyst prepared in Example 1, Comparative Example 1, Comparative Example 4 and Comparative Example 7 when used in ammonia decomposition reaction;

Figure 4 is a graph of the NH ₃ conversion rate of the catalyst prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 when used in ammonia decomposition reaction;

Figure 5 shows the temperature-changing stability of the catalyst prepared in Example 1 and Comparative Example 1, where a is Comparative Example 1 and b is Example 1;

Figure 6 is an XRD image of the catalyst prepared in Example 1 and Comparative Example 1;

Figure 7 is a TEM image of the catalyst prepared in Example 1 and Comparative Example 1, where a is a TEM image of the catalyst prepared in Comparative Example 1, and b is a TEM image of the catalyst prepared in Example 1;

Figure 8 is a H ₂ yield curve diagram of catalysts with different cocatalyst contents used in ammonia decomposition reactions in Example 6;

Figure 9 is a graph showing the NH ₃ conversion rate of catalysts with different cobalt contents used in the ammonia decomposition reaction in Example 7.

Detailed ways

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, the singular forms are also intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, it will be understood that when the terms "comprises" and/or "includes" are used in this specification, they indicate There are features, steps, operations, means, components and/or combinations thereof.

A first typical embodiment of the present invention provides an ammonia decomposition hydrogen production catalyst, which includes an active component, a cocatalyst and a carrier;

The active component is a transition metal; the cocatalyst is alkaline earth metal barium; the carrier is a rare earth metal oxide;

Based on 100 parts of the mass of the carrier rare earth metal oxide, the loading amount of the active component is 25 to 35 parts, and the loading amount of the cocatalyst is 8 to 20 parts.

In one or more embodiments, the transition metal includes Co, Fe and Ni, preferably Co.

In one or more embodiments, the rare earth metal oxide includes Y ₂ O ₃ , Sm ₂ O ₃ and CeO ₂ , preferably Y ₂ O ₃ .

In one or more embodiments, the loading amount of the active component is 30 parts, and the loading amount of the cocatalyst is 10 parts.

A second typical embodiment of the present invention provides a method for preparing the above-mentioned ammonia decomposition hydrogen production catalyst, which includes the following steps:

(1) Dissolve rare earth metal nitrates in deionized water, then add NaOH solution drop by drop, place the mixed solution in an autoclave for hydrothermal reaction, and synthesize rare earth metal oxides;

(2) Disperse the metal oxide synthesized in step (1) in deionized water, add a mixed solution of transition metal nitrate and barium nitrate dropwise, and simultaneously add Na ₂ CO ₃ solution dropwise to control the pH value to be stable at 8 ~10, stir at room temperature and then age. The solid is suction filtered, dried, and calcined in a muffle furnace to obtain an ammonia decomposition hydrogen production catalyst.

In one or more embodiments, the temperature of the hydrothermal reaction in step (1) is 95-105°C, preferably 100°C; the reaction time is 10-30 hours.

In one or more embodiments, in step (2), the pH value is controlled to be stable at 9.

In one or more embodiments, in step (2), the stirring time at room temperature is 20 to 40 minutes, preferably 30 minutes.

In one or more embodiments, in step (2), the aging time is 0.5 to 1.5 h, preferably 1 h.

In one or more embodiments, in the step (2), the calcination temperature is 550-650°C, preferably 600°C; the calcination time is 3-5h, preferably 4h.

The third typical embodiment of the present invention provides the use of the above ammonia decomposition hydrogen production catalyst in an ammonia decomposition hydrogen production reaction.

In order to enable those skilled in the art to understand the technical solution of the present invention more clearly, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

Solution configuration:

Cobalt nitrate solution: Weigh 2.91g of cobalt nitrate hexahydrate and dissolve it in 100mL of high-purity water;

Ferric nitrate solution: Weigh 4.04g of ferric nitrate nonahydrate and dissolve it in 100mL of high-purity water;

Nickel nitrate solution: Weigh 2.91g of nickel nitrate hexahydrate and dissolve it in 100mL of high-purity water.

Preparation of vector:

Preparation of Y ₂ O ₃ nanosheet carrier: Weigh 6.9g yttrium nitrate hexahydrate and dissolve it in 360mL deionized water, then add 10wt% NaOH solution dropwise (5g NaOH dissolved in 50mL deionized water), and control the pH value of the solution Stable at 12. Finally, the obtained mixed solution was transferred to a polytetrafluoroethylene liner, and the liner was placed in a stainless steel reactor. The temperature in the oven was set to 100°C and the reaction was carried out for 12 hours. After hydrothermal treatment, the obtained product was centrifugally washed, 4 times with deionized water and 1 time with absolute ethanol. After the cleaning was completed, the precipitate was dried in an oven at a temperature of 80°C for 4 hours. After drying, it was ground with agate. The powder is ground into fine powder in a bowl to obtain a Y ₂ O ₃ nanosheet carrier.

Preparation of Sm ₂ O ₃ nanorods and CeO ₂ nanorods: Dissolve 14.4g NaOH in 40 mL deionized water, and then add 3 mmol of nitrate (Sm(NO ₃ ) ₃ ·6H ₂ O or Ce(NO ₃ ) ₃ · The aqueous solution of 6H ₂ O) was added to the NaOH solution, and stirred for 30 min to disperse the solution evenly. After hydrothermal reaction at 100°C for 24 hours, the resulting mixed solution was transferred to a polytetrafluoroethylene liner, and the liner was placed in a stainless steel reactor. The temperature was set to 100°C in the oven and the reaction was carried out for 24 hours. After the hydrothermal treatment, the obtained product was centrifuged and washed, 4 times with deionized water and 1 time with absolute ethanol. After the cleaning was completed, the precipitate was placed in an oven and dried at 60°C for 24 hours. After drying, Sm ₂ O was obtained. ₃ nanorods and CeO ₂ nanorods.

Example 1

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution A. Remove 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir thoroughly and ultrasonicate until the two are evenly mixed, record it as solution B. Add solution B dropwise to solution A, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst 30Co-Y ₂ O ₃ -10Ba is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co is 30 parts, and the loading of the cocatalyst Ba is 10 parts) .

Example 2

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution C. Remove 26.8 mL of 0.1 M Fe(NO ₃ ) ₃ 9H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir thoroughly and ultrasonicate until the two are evenly mixed, record it as solution D. Add solution D dropwise to solution C, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst 30Fe-Y ₂ O ₃ -10Ba is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Fe is 30 parts, and the loading of the cocatalyst Ba is 10 parts) .

Example 3

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution E. Remove 25.5 mL of 0.1 M Ni(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir thoroughly and ultrasonicate until the two are evenly mixed, record it as solution F. Add solution F dropwise to solution E, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst 30Ni-Y ₂ O ₃ -10Ba is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Ni is 30 parts, and the loading of the cocatalyst Ba is 10 parts) .

Example 4

Disperse 0.5g Sm ₂ O ₃ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed. Record it as solution H. Remove 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir thoroughly and ultrasonicate until the two are evenly mixed, and record it as solution I. Add solution I dropwise to solution H, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst 30Co-Sm ₂ O ₃ -10Ba is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co is 30 parts, and the loading of the cocatalyst Ba is 10 parts) .

Example 5

Disperse 0.5g of CeO ₂ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution G. Pipette 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953 g. of Ba(NO ₃ ) ₂ , stir and ultrasonic fully to mix the two evenly, record it as solution K, add solution K dropwise to solution G, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise, and control the pH value to stabilize at 9. Then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h to obtain Ammonia decomposition hydrogen production catalyst 30Co-CeO ₂ -10Ba (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co is 30 parts, and the loading of the cocatalyst Ba is 10 parts).

Example 6

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution L. Remove 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution and add For different masses of Ba(NO ₃ ) ₂ , stir and ultrasonicate thoroughly until the two are evenly mixed, record it as solution M. Add solution M dropwise to solution L, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst 30Co-Y ₂ O ₃ -XBa is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co is 30 parts, and the loading of the cocatalyst Ba is X parts) .

Example 7

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Record it as solution P. Remove different volumes of 0.1M Co(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir and ultrasonic thoroughly to mix the two evenly, record it as solution Q. Add solution Q dropwise to solution P, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value. Stable at 9, then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h Finally, an ammonia decomposition hydrogen production catalyst YCo-Y ₂ O ₃ -10Ba is obtained (based on the mass of the carrier rare earth metal oxide being 100 parts, the loading amount of the active component Co is Y parts, and the loading amount of the cocatalyst Ba is 10 parts) .

Comparative example 1

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed. Add 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution dropwise into the solution, and simultaneously Add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value to stabilize at 9, then stir at room temperature for 0.5h and age for 1h. Filter the solid, then dry it at 70°C for 10h, and place it in a muffle furnace at 2°C/min. The heating rate was raised from room temperature to 600°C. After calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Co-Y ₂ O ₃ was obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co was 30 parts ).

Comparative example 2

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed. Add 26.8 mL of 0.1 M Fe(NO ₃ ) ₃ 9H ₂ O solution dropwise into the solution, and simultaneously Add 0.5M Na ₂ CO ₃ solution dropwise, control the pH value to stabilize at 9, then stir at room temperature for 0.5h and age for 1h, filter the solid, then dry it at 70°C for 10h, and place it in a muffle furnace at 2°C/min. The heating rate was raised from room temperature to 600°C, and after calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Fe-Y ₂ O ₃ was obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Fe was 30 parts) .

Comparative example 3

Disperse 0.5g Y ₂ O ₃ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed. Add 25.5 mL of 0.1 M Ni(NO ₃ ) ₂ 6H ₂ O solution dropwise into the solution, and simultaneously Add 0.5M Na ₂ CO ₃ solution dropwise, control the pH value to stabilize at 9, then stir at room temperature for 0.5h and age for 1h, filter the solid, then dry it at 70°C for 10h, and place it in a muffle furnace at 2°C/min. The heating rate is raised from room temperature to 600°C, and after calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Ni-Y ₂ O ₃ is obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Ni is 30 parts) .

Comparative example 4

Disperse 0.5g SiO ₂ nanosheet carrier in 25 mL of high-purity water and stir at room temperature until completely dispersed. Add 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution dropwise into the solution while adding dropwise 0.5M Na ₂ CO ₃ solution, control the pH value to be stable at 9, then stir at room temperature for 0.5h and age for 1h, filter the solid, and then dry it at 70°C for 10h, and place it in a muffle furnace with a temperature rise of 2°C/min. The rate was increased from room temperature to 600°C, and after calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Co-SiO ₂ was obtained (based on 100 parts of SiO ₂ mass, the loading of the active component Co was 30 parts).

Comparative example 5

Disperse 0.5g Sm ₂ O ₃ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed. Add 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution dropwise into the solution, and simultaneously Add 0.5M Na ₂ CO ₃ solution dropwise to control the pH value to stabilize at 9, then stir at room temperature for 0.5h and age for 1h. Filter the solid, then dry it at 70°C for 10h, and place it in a muffle furnace at 2°C/min. The heating rate was raised from room temperature to 600°C. After calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Co-Sm ₂ O ₃ was obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co was 30 parts ).

Comparative example 6

Disperse 0.5g of _CeO2 nanosheet carrier in 25mL of high _- purity water and stir at room temperature until completely dispersed. Add 25.5mL of 0.1M Co( _NO3 ) _26H2O solution dropwise into the solution while adding dropwise 0.5M Na ₂ CO ₃ solution, control the pH value to be stable at 9, then stir at room temperature for 0.5h and age for 1h, filter the solid, and then dry it at 70°C for 10h, and place it in a muffle furnace with a temperature rise of 2°C/min. The rate was raised from room temperature to 600°C, and after calcination for 4 hours, an ammonia decomposition hydrogen production catalyst 30Co-CeO ₂ was obtained (based on 100 parts of the mass of the carrier rare earth metal oxide, the loading of the active component Co was 30 parts).

Comparative example 7

Disperse 0.5g SiO ₂ nanosheet carrier in 25 mL of high-purity water, and stir at room temperature until completely dispersed, recorded as dissolved N. Pipette 25.5 mL of 0.1 M Co(NO ₃ ) ₂ 6H ₂ O solution and add 0.0953g of Ba(NO ₃ ) ₂ , stir and ultrasonic fully to mix the two evenly, record it as solution O, add solution O dropwise into solution N, and at the same time, add 0.5M Na ₂ CO ₃ solution dropwise, and control the pH value to stabilize at 9. Then stirred at room temperature for 0.5h and aged for 1h, filtered the solid, dried at 70℃ for 10h, placed in a muffle furnace from room temperature to 600℃ at a heating rate of 2℃/min, and calcined for 4h to obtain Ammonia decomposition hydrogen production catalyst 30Co-SiO ₂ -10Ba (based on 100 parts of SiO ₂ mass, the loading of active component Co is 30 parts, and the loading of cocatalyst Ba is 10 parts).

Experimental example 1

Test the performance of the catalysts prepared in Examples 1 to 5 and Comparative Examples 1 to 7: Mix 50 mg of catalyst (20 to 40 mesh) and 500 mg of quartz sand (20 to 40 mesh), and put them into a reaction tube with an inner diameter of 8 mm. middle. Before the catalytic test, the catalyst was first activated in a pure _NH atmosphere at 600°C for 1 h, and then the conversion rate test was performed between 450 and 600°C. One point was collected at a reactor temperature interval of 50°C (GHSV = 30,000 cm ³ ·g _cat ^-1 ·h ^-1 ). The outlet gas is analyzed by an online gas chromatograph, and then real-time N ₂ and NH ₃ contents are obtained. The conversion rate of NH ₃ is calculated by the following formula.

1.1 Selection of catalyst carrier

The catalysts prepared in Comparative Example 1, Comparative Example 4, Comparative Example 5 and Comparative Example 6 without supporting alkaline earth metal barium were used to conduct performance tests on the catalytic decomposition of ammonia. The results are shown in Figure 1. Rare earth oxide (Y ₂ O ₃ , Sm ₂ O ₃ , CeO ₂ ) as the carrier, the ammonia decomposition conversion rate of the catalyst is significantly better than that of the 30Co-SiO ₂ catalyst with SiO ₂ as the carrier, and the catalytic activity is the best with the 30Co-Y ₂ O ₃ catalyst. A conversion rate of 51% can be achieved at 500°C. This shows that rare earth oxides represented by Y ₂ O ₃ can improve activity when used as a carrier for ammonia decomposition reaction catalysts to support transition metals.

The catalysts prepared in Example 1, Example 4, Example 5, Comparative Example 1, Comparative Example 5 and Comparative Example 6 were respectively used to perform performance tests on the catalytic decomposition of ammonia. The results are shown in Figure 2. The catalytic promoter is alkaline earth metal barium. The addition of Ba significantly improved the activity of the catalyst, especially the 30Co-Y ₂ O ₃ catalyst prepared in Comparative Example 1. The ammonia decomposition conversion rate of the catalyst after adding Ba (30Co-Y ₂ O ₃ -10Ba in Example 1) was 500℃ increased by nearly 40% (from 51% to 88%). The resulting 30Co-Y ₂ O ₃ -10Ba catalyst can achieve a hydrogen production rate of 29.3mmol g _cat ^-1 per gram of catalyst at 500℃. min ^-1 ; exceeds the existing transition metal-based ammonia decomposition hydrogen production catalysts, and is even higher than some precious metal Ru-based catalysts.

In order to further verify whether rare earth oxides have unique advantages as carriers in ammonia decomposition reactions, the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 4 and Comparative Example 7 were used to conduct ammonia catalytic decomposition performance tests. The results are as follows As shown in Figure 3, the activity of the 30Co-SiO ₂ catalyst after adding Ba has not been improved, and even decreased slightly. It can be concluded that the transition metal-rare earth oxide-based catalyst not only has higher activity itself, but also further combines with the cocatalyst After Ba, the activity of the catalyst is improved, which also shows that rare earth oxides have unique advantages when combining transition metal and alkaline earth metal Ba promoters.

1.2 The cocatalyst Ba has universal applicability in improving the catalytic activity of transition metals.

Using Y ₂ O ₃ as a carrier, select other transition metals (Fe, Ni) to load and then conduct ammonia decomposition activity testing, namely Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3. The ammonia decomposition activity of the catalyst prepared in was tested. The results are shown in Figure 4. The addition of cocatalyst Ba not only improves Co-based catalysts, but also all transition metal-based catalysts commonly used for ammonia decomposition. This shows that Ba serves as a promoter. The universality of combining rare earth oxides to improve the activity of transition metal-based catalysts in catalytic ammonia decomposition reactions.

1.3 Catalyst stability evaluation

The catalysts prepared in Example 1 and Comparative Example 1 were evaluated. The evaluation method was: temperature rise and fall stability test, at 550°C and 500°C (GHSV=60,000cm ³ ·g _cat ^-1 ·h ^-1 ) A total of 200h was carried out. The results are shown in Figure 5. During the 200h temperature change test, the NH ₃ conversion rate of the catalyst after adding Ba only decreased by 3% (GHSV=60,000cm ³ ·g _cat ^-1 ·h ^-1 ), and the catalyst showed excellent Stability; this also reflects the advantages of rare earth oxide-supported transition metal catalysts in ammonia decomposition reactions.

1.4

The catalytic activity of the catalysts prepared in Example 1, Example 4, Example 5, Comparative Example 1, Comparative Example 2, Comparative Example 5, Comparative Example 6 and Comparative Example 7 is summarized after ammonia decomposition activity test. The results are as shown in Table 1 Show.

Table 1 Catalytic activity summary

1.5 Cocatalyst alkaline earth metal barium improves the dispersion of metal active components

The catalysts prepared in Example 1 and Comparative Example 1 were characterized. The XRD image is shown in Figure 6 and the TEM image is shown in Figure 7. As can be seen from Figure 6, Co exists in the form of Co ₃ O ₄ on the catalyst before and after Ba doping. The addition of Ba promotes the dispersion of Co species before the reaction. At the same time, there is a diffraction peak corresponding to BaCO ₃ on the 30Co-Y ₂ O ₃ -10Ba catalyst, indicating that Ba exists in the form of BaCO ₃ before the reaction. In addition, in the TEM image of the catalyst before the reaction, it can be clearly seen that the size of the Co species after adding Ba is significantly smaller than that of the 30Co-Y ₂ O ₃ catalyst without adding Ba promoter, which is also consistent with the XRD results.

Experimental Example 2 Determination of the Adding Amount of Active Metal Cobalt and Cocatalyst Barium

The performance of the catalyst prepared in Example 6 was tested, and the results are shown in Figure 8. It was found that the Ba content and catalytic activity showed a volcanic trend. At 500°C, 10% Ba additive content is optimal. Further increasing the Ba content will gradually reduce the catalyst activity. When 50% Ba content is added, the promoting effect of Ba on the activity completely disappears.

Experimental Example 3 Determination of Cobalt Adding Amount

The performance of the catalyst prepared in Example 7 was tested, and the results are shown in Figure 9. It was found that 30% Co content of cobalt was optimal, and excessive Co content (50%) would lead to a decrease in activity.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A catalyst for producing hydrogen by decomposing ammonia, which is characterized by comprising an active component, a cocatalyst and a carrier;

the active component is transition metal; the promoter is alkaline earth barium; the carrier is rare earth metal oxide;

the loading amount of the active component is 25-35 parts and the loading amount of the cocatalyst is 8-20 parts based on 100 parts of the mass of the carrier rare earth metal oxide.

2. The ammonia destruction hydrogen production catalyst of claim 1, wherein the transition metal comprises Co, fe, and Ni, preferably Co.

3. The ammonia destruction hydrogen production catalyst of claim 1, wherein the rare earth metal oxide comprises Y ₂ O ₃ 、Sm ₂ O ₃ And CeO ₂ Preferably Y ₂ O ₃ 。

4. The ammonia destruction hydrogen production catalyst of claim 1 wherein the loading of the active component is 30 and the loading of the promoter is 10.

5. The method for producing an ammonia decomposition hydrogen production catalyst according to any one of claims 1 to 4, comprising the steps of:

(1) Dissolving rare earth metal nitrate in deionized water, dropwise adding NaOH solution, and placing the mixed solution in an autoclave for hydrothermal reaction to synthesize rare earth metal oxide;

(2) Dispersing the metal oxide synthesized in the step (1) in deionized water, dropwise adding a mixed solution of transition metal nitrate and barium nitrate, and simultaneously dropwise adding Na ₂ CO ₃ The pH value of the solution is controlled to be stabilized between 8 and 10, the solution is stirred at room temperature and then aged, the solid is filtered by suction, then dried and calcined in a muffle furnace to obtain the catalystTo obtain the catalyst for producing hydrogen by decomposing ammonia.

6. The process according to claim 5, wherein the hydrothermal reaction in step (1) is carried out at a temperature of 95 to 105 ℃, preferably 100 ℃; the reaction time is 10-30 h.

7. The method according to claim 5, wherein in the step (2), the pH is controlled to be stabilized at 9.

8. The process according to claim 5, wherein in step (2), the stirring time at room temperature is 20 to 40min, preferably 30min;

or, in the step (2), the aging time is 0.5-1.5 h, preferably 1h.

9. The process according to claim 5, wherein in step (2), the calcination temperature is 550 to 650 ℃, preferably 600 ℃; the calcination time is 3 to 5 hours, preferably 4 hours.

10. Use of the catalyst for producing hydrogen by ammonia decomposition according to any one of claims 1 to 4 or the catalyst for producing hydrogen by ammonia decomposition prepared by the preparation method according to any one of claims 5 to 9 in a reaction for producing hydrogen by ammonia decomposition.