A Ni / Al 1.8 Ce 0.2 O x Catalyst, method for preparing the same, and use thereof in hydrogen production by thermal catalytic ammonia decomposition

Abstract

The application discloses a Ni / Al 1.8 Ce 0.2 O x Catalyst, preparation method thereof and application of the catalyst in hydrogen production by thermal catalytic ammonia decomposition, soluble Ni salt, Al salt and Ce salt are uniformly dispersed in water to obtain a mixed solution, a complexing agent is added, a complex precursor is obtained through a sol-gel method, the complex precursor is pyrolyzed to obtain an oxide precursor, the oxide precursor is ultrasonically dispersed in water, lye is added to perform etching, an etched oxide precursor is obtained, and finally, the etched oxide precursor is calcined in a H2 / Ar atmosphere to obtain a Ni / Al 1.8 Ce 0.2 O x Catalyst, which is used for hydrogen production by thermal catalytic ammonia decomposition. The catalyst has the characteristics of structural stability and high dispersion of metal Ni, after being treated by alkali etching, the coating effect of the carrier on the metal Ni is effectively inhibited, the dissolved metal Ni has a pyramid shape, has more unsaturated coordination active sites, and the catalytic activity and stability of the catalyst are significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal catalytic materials, and specifically relates to a Ni / Al 1.8 Ce 0.2 O x Catalyst, preparation method thereof and application in thermal catalytic ammonia decomposition to produce hydrogen. Background Art

[0002] Currently, research on ammonia decomposition catalysts for hydrogen production focuses on optimizing the electronic state of the active metal through methods such as catalyst support properties and active metal alloying to control the M-N bond strength and promote the N-N recombination desorption step, thereby enhancing the ammonia decomposition reaction. However, little research has been conducted on the control of the active metal morphology in ammonia decomposition catalysts and its impact on the ammonia decomposition reaction. Summary of the Invention

[0003] The purpose of the present invention is to provide a Ni / Al 1.8 Ce 0.2 O x The invention relates to a catalyst, a preparation method thereof, and an application thereof in the thermal catalytic decomposition of ammonia to produce hydrogen. The catalyst has the characteristics of stable structure and highly dispersed metal Ni. After alkaline etching treatment, the coating effect of the carrier on the metal Ni is effectively inhibited. The dissolved metal Ni has a pyramid-shaped morphology and has more unsaturated coordinated active sites. The catalytic activity and stability of the catalyst are significantly improved, and it is easy to scale up production, with good industrial application prospects.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0005] A Ni / Al 1.8 Ce 0.2 O x The preparation method of the catalyst comprises the following steps:

[0006] (1) Dispersing soluble Ni salt, Al salt, and Ce salt uniformly in water to obtain a mixed solution, adding a complexing agent, and obtaining a complex precursor by a sol-gel method; the molar ratio of Ni to the sum of Al and Ce in the soluble Ni salt, Al salt, and Ce salt is 1:2;

[0007] (2) pyrolyzing the complex precursor to obtain an oxide precursor;

[0008] (3) ultrasonically dispersing the oxide precursor in water, and then adding alkaline solution for etching to obtain an etched oxide precursor;

[0009] (4) The etched oxide precursor is calcined in H2 / Ar atmosphere to obtain Ni / Al 1.8 Ce 0.2 O x catalyst.

[0010] Preferably, in step (1), the soluble Ni salt, Al salt and Ce salt are all nitrates of each.

[0011] Preferably, in step (1), the complexing agent is citric acid.

[0012] Preferably, in step (2), the pyrolysis temperature is 300-500 °C and the time is 3-5 h.

[0013] Preferably, in step (3), the alkali solution is a 30-35 wt% NaOH aqueous solution. The unetched catalyst has a nickel-aluminum spinel phase, the active metal Ni is in a granular form, and there is a coating layer on the surface. After alkali etching, the inventor unexpectedly found that the nickel-aluminum spinel phase in the catalyst disappears, and the metal Ni takes on a pyramidal shape, and the surface coating disappears, exposing more unsaturated coordinated active sites.

[0014] Preferably, in step (4), the volume ratio of H2 to Ar in the H2 / Ar atmosphere is 1:1; the calcination temperature is 550-650 °C, and the calcination time is 3-5 h.

[0015] The present invention also provides Ni / Al prepared by the above preparation method 1.8 Ce 0.2 O x catalyst.

[0016] It should be noted that, in the present invention, x It means that the catalyst is rich in oxygen vacancies. It is a commonly used expression and will not be repeated here.

[0017] The present invention also provides the above-mentioned Ni / Al 1.8 Ce 0.2 O x The catalyst is used for thermal catalytic decomposition of ammonia to produce hydrogen.

[0018] Beneficial effects of the present invention:

[0019] (1) Ni / Al of the present invention 1.8 Ce 0.2 O x The catalyst has the characteristics of stable structure and highly dispersed metal Ni. After alkaline etching treatment, the coating effect of the carrier on the active metal Ni is effectively inhibited. The dissolved metal Ni has a pyramid-shaped morphology and has more unsaturated coordinated active sites. The catalytic activity and stability of the catalyst are significantly improved.

[0020] (2) Ni / Al of the present invention 1.8 Ce 0.2 O xThe catalyst has excellent catalytic activity in the thermal catalytic decomposition of ammonia to produce hydrogen, achieving full conversion of NH3 at 470°C, and the performance of the catalyst did not show a significant decline in the stability test lasting up to 1000 h.

[0021] (3) Ni / Al of the present invention 1.8 Ce 0.2 O x The catalyst exhibits excellent activity and stability in ammonia decomposition to produce hydrogen, and kilogram-level preparation of the catalyst can be achieved in a single batch, which has good potential for large-scale production and industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The SEM images of the catalysts prepared in Example 1 (right) and Comparative Example 3 (left);

[0023] like Figure 1 As shown, obvious holes appear in the catalyst after etching.

[0024] Figure 2 The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-4 are shown;

[0025] like Figure 2 As shown in the figure, the catalyst samples in all the examples and comparative examples have the characteristic peak of Ni, and no characteristic peak of Al2O3 appears, indicating that Al2O3 is amorphous; the unetched catalyst has a nickel aluminum spinel phase, and after alkali etching, Ni / Al2O x The nickel aluminum spinel phase in the catalyst disappears.

[0026] Figure 3 TEM image of the catalyst prepared in Comparative Example 3;

[0027] like Figure 3 As shown, the active metal Ni in the unetched catalyst is in granular form and has a coating layer on the surface.

[0028] Figure 4 TEM image of the catalyst prepared in Example 1;

[0029] like Figure 4 As shown in Figure 3, the active metal Ni in the catalyst after etching is pyramid-shaped, and its surface coating disappears, exposing more unsaturated coordinated active sites.

[0030] Figure 5 H2-TPR diagrams of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3;

[0031] like Figure 5 As shown, Example 1 has the lowest reduction temperature, indicating that Ce doping and alkali etching can weaken the interaction between metal and support.

[0032] Figure 6 The SSNMR diagrams of the catalysts prepared in Example 1 and Comparative Example 3 are shown;

[0033] like Figure 6 As shown in the figure, after alkaline etching, the content of pentacoordinated Al in the catalyst is significantly reduced. The decrease in the content of pentacoordinated Al can weaken the metal-support interaction and promote the formation of pyramid-shaped Ni particles.

[0034] Figure 7 The catalytic activity of the catalyst prepared in Example 1 at different temperatures (space velocity 900 mlg cat -1 ·h -1 );

[0035] like Figure 7 As shown in Figure 3, the catalyst achieved full conversion at 470 °C.

[0036] Figure 8 The catalyst prepared in Example 1 (space velocity: 900 mlg cat -1 ·h -1 , temperature: 420 ℃) ​​stability test diagram;

[0037] like Figure 8 As shown in the figure, the performance of the catalyst did not decrease during the stability test lasting up to 1000 h.

[0038] Figure 9 This is a physical picture of the catalyst prepared in Example 2;

[0039] like Figure 9 As shown, kilogram-scale preparation of the catalyst can be achieved in a single batch, indicating that the catalyst is easy to produce on a large scale.

[0040] Figure 10 This is a performance comparison chart of the catalyst prepared by enlarging Example 2 and the catalyst prepared by Example 1;

[0041] like Figure 10 As shown in the figure, the performance of the scaled-up catalyst is basically consistent with the bench-scale test results. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0044] Thermal catalytic ammonia decomposition to produce hydrogen:

[0045] 200 mg of catalyst was weighed and placed in a quartz reaction tube, and 10% NH3 / Ar was introduced. The tail gas composition was detected by gas chromatography, and the ammonia decomposition reaction conversion rate was measured.

[0046] Example 1

[0047] Ni / Al 1.8 Ce 0.2 O x -etched:

[0048] (1) Dissolve 4.80 mmol Ni(NO3)2·6H2O, 8.64 mmol Al(NO3)3·9H2O, and 0.96 mmol Ce(NO3)3·6H2O in 15 mL of deionized water. Stir thoroughly and add 6.31 g of citric acid. Continue stirring until completely dissolved. Then, heat the solution to 90°C and stir at this temperature for 18 h to obtain a dry complex precursor.

[0049] (2) Place the complex precursor in a muffle furnace and heat at 5 °C·min -1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0050] (3) Weigh 500 mg of the above oxide precursor, disperse it in 10 mL of deionized water, and ultrasonicate it for 10 min. Then, add 10 mL of a 32.4% NaOH aqueous solution and stir at room temperature for 1 h for alkaline etching. After the reaction is complete, centrifuge, wash with water, and finally dry in a vacuum drying oven at 60 °C to obtain the etched oxide precursor.

[0051] (4) Place the etched oxide precursor in a tube furnace and heat it at 5°C·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al 1.8 Ce 0.2 O x -etched.

[0052] The catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen, and the conversion rate of ammonia decomposition reaction was 99.99% (470 ℃, 900 ml g cat -1 ·h -1 ), achieving full conversion of NH3.

[0053] Example 2

[0054] Kilogram-scale scale-up preparation of Ni / Al 1.8 Ce0.2 O x -etched:

[0055] (1) Dissolve 4.80 mol Ni(NO3)2·6H2O, 8.64 mol Al(NO3)3·9H2O, and 0.96 mol Ce(NO3)3·6H2O in 15 L of deionized water. Stir thoroughly and add 6.31 kg of citric acid. Continue stirring until completely dissolved. Then, heat the solution to 90°C and react at this temperature for 18 h to obtain a dry complex precursor.

[0056] (2) Place the complex precursor in batches in a muffle furnace and heat at 5 °C·min -1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0057] (3) 150 g of the above oxide precursor was weighed in batches, dispersed in 50 mL of deionized water, and ultrasonically treated for 10 min. 50 mL of a 32.4% NaOH aqueous solution was then added and stirred at room temperature for 1 h for alkaline etching. After the reaction was completed, the oxide precursor was obtained by centrifugation, washing with water, and finally drying in a vacuum drying oven at 60 °C.

[0058] (4) Place the etched oxide precursor in batches in a tube furnace and heat it at 5 ℃·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al 1.8 Ce 0.2 O x -etched (enlarged).

[0059] The catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen, and the conversion rate of ammonia decomposition reaction was 99.99% (470 ℃, 900 ml g cat -1 ·h -1 ), achieving full conversion of NH3.

[0060] Comparative Example 1

[0061] Ni / Al 1.5 Ce 0.5 O x -etched:

[0062] (1) Dissolve 4.80 mmol Ni(NO3)2·6H2O, 7.20 mmol Al(NO3)3·9H2O, and 2.40 mmol Ce(NO3)3·6H2O in 15 mL of deionized water. Stir thoroughly and add 6.31 g of citric acid. Continue stirring until completely dissolved. Then, heat the solution to 90°C and stir at this temperature for 18 h to obtain a dry complex precursor.

[0063] (2) Place the complex precursor in a muffle furnace and heat at 5 °C·min -1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0064] (3) Weigh 500 mg of the above oxide precursor, disperse it in 10 mL of deionized water, and ultrasonicate it for 10 min. Then, add 10 mL of a 32.4% NaOH aqueous solution and stir at room temperature for 1 h for alkaline etching. After the reaction is complete, centrifuge, wash with water, and finally dry in a vacuum drying oven at 60 °C to obtain the etched oxide precursor.

[0065] (4) Place the etched oxide precursor in a tube furnace and heat it at 5°C·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al 1.5 Ce 0.5 O x -etched.

[0066] The catalyst was used for the thermal catalytic ammonia decomposition reaction to produce hydrogen, and the ammonia decomposition reaction conversion rate was 90.55% (470 ℃, 900 ml g cat -1 ·h -1 ).

[0067] Comparative Example 2

[0068] Ni / Al2O x -etched:

[0069] (1) Dissolve 4.80 mmol Ni(NO3)2·6H2O and 9.60 mmol Al(NO3)3·9H2O in 15 mL deionized water, stir thoroughly, add 6.31 g citric acid, and continue stirring until completely dissolved. Then, heat the solution to 90°C and stir at this temperature for 18 h to obtain a dry complex precursor.

[0070] (2) Place the complex precursor in a muffle furnace and heat at 5 °C·min-1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0071] (3) Weigh 500 mg of the above oxide precursor, disperse it in 10 mL of deionized water, and ultrasonicate it for 10 min. Then, add 10 mL of a 32.4% NaOH aqueous solution and stir at room temperature for 1 h for alkaline etching. After the reaction is complete, centrifuge, wash with water, and finally dry in a vacuum drying oven at 60 °C to obtain the etched oxide precursor.

[0072] (4) Place the etched oxide precursor in a tube furnace and heat it at 5°C·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al2O x -etched.

[0073] The catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen, and the conversion rate of ammonia decomposition reaction was 86.08% (470 ℃, 900 ml g cat -1 ·h -1 ).

[0074] Comparative Example 3

[0075] Ni / Al 1.8 Ce 0.2 O x -unetched:

[0076] (1) Dissolve 4.80 mmol Ni(NO3)2·6H2O, 8.64 mmol Al(NO3)3·9H2O, and 0.96 mmol Ce(NO3)3·6H2O in 15 mL of deionized water. Stir thoroughly and add 6.31 g of citric acid. Continue stirring until completely dissolved. Then, heat the solution to 90°C and stir at this temperature for 18 h to obtain a dry complex precursor.

[0077] (2) Place the complex precursor in a muffle furnace and heat at 5 °C·min -1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0078] (3) The oxide precursor was placed in a tube furnace and heated at 5°C·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al 1.8 Ce 0.2 Ox -unetched.

[0079] The catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen, and the conversion rate of ammonia decomposition reaction was 83.55% (470 ℃, 900 ml g cat -1 ·h -1 ).

[0080] Comparative Example 4

[0081] Ni / Al2O x -unetched:

[0082] (1) Dissolve 4.80 mmol Ni(NO3)2·6H2O and 9.60 mmol Al(NO3)3·9H2O in 15 mL deionized water, stir thoroughly, add 6.31 g citric acid, and continue stirring until completely dissolved. Then, heat the solution to 90°C and stir at this temperature for 18 h to obtain a dry complex precursor.

[0083] (2) Place the complex precursor in a muffle furnace and heat at 5 °C·min -1 The temperature was raised to 400 °C, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain an oxide precursor.

[0084] (3) The oxide precursor was placed in a tube furnace and heated at 5°C·min in a 50% H2 / Ar mixed atmosphere. -1 The temperature was raised to 600 °C at a rate of 1000 ℃, kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain the target catalyst Ni / Al2O x -unetched.

[0085] The catalyst was used for the thermal catalytic ammonia decomposition reaction to produce hydrogen, and the ammonia decomposition reaction conversion rate was 77.86% (470 ℃, 900 ml g cat -1 ·h -1 ).

Claims

1. A Ni / Al 1.8 Ce 0.2 O x The use of a catalyst is characterized in that It is used for the thermal catalytic decomposition of ammonia to produce hydrogen; The specific preparation process includes the following steps: (1) Dispersing soluble Ni salt, Al salt, and Ce salt uniformly in water to obtain a mixed solution, adding a complexing agent, and obtaining a complex precursor by a sol-gel method; the molar ratio of Ni to the sum of Al and Ce in the soluble Ni salt, Al salt, and Ce salt is 1:2; (2) pyrolyzing the complex precursor to obtain an oxide precursor; (3) ultrasonically dispersing the oxide precursor in water, and then adding alkaline solution for etching to obtain an etched oxide precursor; (4) The etched oxide precursor is calcined in H2 / Ar atmosphere to obtain Ni / Al 1.8 Ce 0.2 O x catalyst.

2. The use according to claim 1, characterized in that In step (1), the soluble Ni salt, Al salt and Ce salt are all nitrates of each.

3. The use according to claim 1, characterized in that In step (1), the complexing agent is citric acid.

4. The use according to claim 1, characterized in that In step (2), the pyrolysis temperature is 300-500°C and the time is 3-5 h.

5. The use according to claim 1, characterized in that In step (3), the alkali solution is a NaOH aqueous solution with a mass fraction of 30-35wt%.

6. The use according to claim 1, characterized in that In step (4), the volume ratio of H2 to Ar in the H2 / Ar atmosphere is 1:1; the calcination temperature is 550-650°C, and the calcination time is 3-5 h.

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