A Ni / LaAlO x Composite catalysts, their preparation methods, and their application in thermocatalytic ammonia decomposition for hydrogen production.

Abstract

The application discloses a kind of Ni / LaAlO x Composite catalyst and its preparation method and application in thermal catalytic ammonia decomposition hydrogen production, soluble Ni salt, Al salt, La salt and urea are dissolved in ethylene glycol, then LDHs precursor is synthesized by solvothermal method, then LDHs precursor is pyrolyzed under reducing atmosphere to obtain Ni / LaAlO x Composite catalyst. The application realizes that metal Ni is loaded on mixed oxide LaAlO x By solvothermal method and reducing atmosphere pyrolysis treatment, Ni / LaAlO x , the composite material is sheet-shaped accumulation structure, has larger active surface area, and active center is uniform, active site is highly exposed, simultaneously, the introduction of La increases carrier vacancy concentration, enhances active metal and carrier interaction, promotes the progress of oxidation-reduction reaction, and has excellent thermal catalytic ammonia decomposition hydrogen production performance.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalytic materials technology, specifically relating to a Ni / LaAlO material. x Composite catalysts, their preparation methods, and their application in thermocatalytic ammonia decomposition for hydrogen production. Background Technology

[0002] Layered hydrogen hydroxides (LDHs) have become a research hotspot for adsorbents and heterogeneous catalysts due to their controllable structure and good hydrothermal stability. Typically, catalysts prepared by impregnation methods rapidly deactivate due to the sintering and / or aggregation of metal nanoparticles. In contrast, LDH-derived catalysts exhibit good stability due to the anchoring effect of their supports and are less prone to sintering and / or aggregation of active materials. This method can prepare supported metal nanoparticle catalysts with specific morphologies and good stability. However, in certain catalytic reactions, LDH-derived single-oxide-supported active metal catalysts still suffer from relatively low catalytic performance. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a Ni / LaAlO x The composite catalyst, its preparation method, and its application in thermocatalytic ammonia decomposition for hydrogen production are described. The catalyst has a stable structure and the active metal is uniformly dispersed in the catalyst. The active metal serves as the active site in the thermocatalytic reaction and exhibits excellent thermocatalytic activity in thermocatalytic ammonia decomposition for hydrogen production.

[0004] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0005] A Ni / LaAlO x The method for preparing the composite catalyst involves dissolving soluble Ni, Al, and La salts and urea in ethylene glycol, then synthesizing LDH precursors via a solvothermal method, and finally pyrolyzing the LDH precursors at high temperature under a reducing atmosphere to obtain Ni / LaAlO₂. x Composite catalyst.

[0006] Preferably, the soluble Ni salt is an acetate of metallic Ni, and the soluble Al salt and La salt are both their nitrates. The molar ratio of the soluble Ni salt, soluble Al salt, soluble La salt and urea is 6:1.5-2.5:0.5-1.5:10.

[0007] Preferably, the solvothermal temperature is 180-240℃ and the time is 12-36h.

[0008] Preferably, the reducing atmosphere is 50% H2 / Ar, that is, the volume ratio of H2 to Ar is 1:1.

[0009] Preferably, the high-temperature pyrolysis temperature is 550-650℃ and the time is 2-4h.

[0010] The invention also provides Ni / LaAlO prepared by the above method. x Composite catalyst.

[0011] The invention also provides the above-mentioned Ni / LaAlO x The composite catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen.

[0012] Advantages of this invention:

[0013] This invention achieves the loading of metallic Ni onto the mixed oxide LaAlO through solvothermal method and high-temperature pyrolysis in a reducing atmosphere. x Ni / LaAlO was prepared. x The composite material has a sheet-like stacked structure with a large active surface area, uniform active centers, and highly exposed active sites. At the same time, the introduction of La increases the vacancy concentration of the support, enhances the interaction between the active metal and the support, promotes the redox reaction, and has excellent thermocatalytic performance for hydrogen production from ammonia decomposition. Attached Figure Description

[0014] Figure 1 SEM images of LDH precursors obtained in the example;

[0015] like Figure 1 The image shows a SEM image of the LDH precursor, which has a morphology of nanosheet-like stacked structure.

[0016] Figure 2 Ni / LaAlO prepared for the example x SEM image;

[0017] like Figure 2 As shown, Ni / LaAlO x The SEM images show that the nanosheet-like stacked structure of the LDH precursor maintains good structural stability.

[0018] Figure 3 TEM image of the LDHs precursor obtained in Example 1;

[0019] like Figure 3 As shown in the TEM image of the LDH precursor, no aggregation of nanoparticles was observed.

[0020] Figure 4 The Ni / LaAlO prepared in Example 1 x TEM image;

[0021] like Figure 4 As shown, Ni / LaAlOx The TEM image shows a large number of dispersed metal nanoparticles.

[0022] Figure 5 The XRD patterns of the LDH precursors obtained in Examples 1-3 are shown below.

[0023] like Figure 5 As shown, the XRD characterization shows characteristic peaks of LDHs such as (003), (006), and (009), indicating the successful preparation of LDHs precursors.

[0024] Figure 6 The Ni / LaAlO prepared in Examples 1-3 x XRD patterns;

[0025] like Figure 6 As shown, XRD characterization indicates that Ni / LaAlO x Successful preparation. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0027] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents and materials used in the following examples are commercially available unless otherwise specified.

[0028] Thermocatalytic ammonia decomposition to produce hydrogen:

[0029] Weigh 100 mg of catalyst (40-60 mesh) and add it to a quartz reaction tube. Pass pure ammonia (99.999%) through the tube. In the range of 450℃-650℃, with a temperature gradient of 50℃, test for 40 min at each temperature point. Detect the ammonia conversion rate by gas chromatography.

[0030] Example 1

[0031] Ni / Al2LaO x

[0032] (1) 6 mmol nickel acetate, 2 mmol aluminum nitrate, 1 mmol lanthanum nitrate, and 10 mmol urea were added to 40 ml ethylene glycol and mixed evenly. After stirring for 60 minutes, the mixture was placed in a crystallization reactor and treated at 200 °C for 24 h. After cooling to room temperature, the mixture was washed several times with ethanol and then dried under vacuum at 60 °C to obtain the LDH precursor.

[0033] (2) The obtained LDH precursor powder was heat-treated at 600℃ and 50% H2 / Ar for 3h to obtain a sample denoted as Ni / Al2LaO. x ;

[0034] Prepared Ni / Al2LaO x The catalyst was used for the thermocatalytic decomposition of ammonia to produce hydrogen. Under conditions of 600℃ and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 30.47 mmol / g. (cat) -1 ·min -1 .

[0035] Example 2

[0036] Ni / Al 2.5 La 0.5 O x

[0037] (1) 6 mmol nickel acetate, 2.5 mmol aluminum nitrate, 0.5 mmol lanthanum nitrate, and 10 mmol urea were added to 40 ml ethylene glycol and mixed evenly. After stirring for 60 minutes, the mixture was placed in a crystallization reactor and treated at 200 °C for 24 h. After cooling to room temperature, the mixture was washed several times with ethanol and then dried under vacuum at 60 °C to obtain the LDH precursor.

[0038] (2) The obtained LDHs precursor powder was heat-treated at 600℃ and 50% H2 / Ar for 3 hours. The resulting sample was denoted as Ni / Al. 2.5 La 0.5 O x ;

[0039] Prepared Ni / Al 2.5 La 0.5 O x The catalyst was used for the thermocatalytic decomposition of ammonia to produce hydrogen. Under conditions of 600℃ and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 28.79 mmol / g. (cat) -1 ·min -1 .

[0040] Example 3

[0041] Ni / Al 1.5 La 1.5 O x

[0042] (1) 6 mmol nickel acetate, 1.5 mmol aluminum nitrate, 1.5 mmol lanthanum nitrate, and 10 mmol urea were added to 40 ml ethylene glycol and mixed evenly. After stirring for 60 minutes, the mixture was placed in a crystallization reactor and treated at 200 °C for 24 h. After cooling to room temperature, the mixture was washed several times with ethanol and then dried under vacuum at 60 °C to obtain the LDH precursor.

[0043] (2) The obtained LDHs precursor powder was heat-treated at 600℃ and 50% H2 / Ar for 3 hours. The resulting sample was denoted as Ni / Al. 1.5 La 1.5 O x ;

[0044] Prepared Ni / Al 1.5 La 1.5 The Ox catalyst was used in the thermocatalytic decomposition of ammonia to produce hydrogen. Under conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 29.46 mmol / g. (cat) -1 ·min -1 .

[0045] Comparative Example 1

[0046] Ni / La-Al2O3

[0047] (1) A La-modified Ni / Al2O3 catalyst was prepared by impregnation. Nickel acetate, lanthanum nitrate, and alumina were used as the nickel source, lanthanum source, and support, respectively, according to a Ni:Al:La ratio of 6:2:1. The alumina support was added to an aqueous solution of nitrates containing nickel and lanthanum. The mixture was maintained in a steam bath at 80°C until the solution evaporated. The resulting powder was calcined in air at 600°C for 5 hours, and then reduced at 600°C for 2 hours under a 50% H2 / Ar atmosphere to obtain the Ni / La-Al2O3 catalyst.

[0048] (2) The prepared Ni / La-Al2O3 catalyst was used for the thermocatalytic decomposition of ammonia to produce hydrogen. Under the conditions of 600℃ and pure NH3 (99.999%), the hydrogen production rate of the catalyst was 12.05 mmol g. (cat) -1 ·min -1 .

[0049] Comparative Example 2

[0050] Ni / MgAl2O x

[0051] (1) 6 mmol nickel acetate, 2 mmol aluminum nitrate, 1 mmol magnesium nitrate, and 10 mmol urea were added to 40 ml ethylene glycol and mixed evenly. After stirring for 60 minutes, the mixture was placed in a crystallization reactor and treated at 200°C for 24 hours. After cooling to room temperature, the mixture was washed several times with ethanol and then dried under vacuum at 60°C to obtain the LDH precursor.

[0052] (2) The obtained LDH precursor powder was heat-treated at 600℃ and 50% H2 / Ar for 3h to obtain a sample denoted as Ni / MgAl2O. x ;

[0053] Prepared Ni / MgAl2O x The catalyst was used for the thermocatalytic decomposition of ammonia to produce hydrogen. Under conditions of 600℃ and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 20.96 mmol / g. (cat) -1 ·min -1 .

Claims

1. A Ni / LaAlO x The application of composite catalysts in thermocatalytic ammonia decomposition for hydrogen production is characterized by, The Ni / LaAlO x The composite catalyst is prepared by dissolving soluble Ni salt, Al salt, La salt, and urea in ethylene glycol, then synthesizing LDH precursors via a solvothermal method, and finally pyrolyzing the LDH precursors at high temperature under a reducing atmosphere to obtain Ni / LaAlO. x Composite catalyst.

2. The application according to claim 1, characterized in that: The soluble Ni salt is an acetate of metallic Ni, and the soluble Al salt and La salt are both its nitrates. The molar ratio of the soluble Ni salt, soluble Al salt, soluble La salt and urea is 6:1.5-2.5:0.5-1.5:

10.

3. The application according to claim 1, characterized in that: The solvothermal temperature is 180-240°C, and the time is 12-36h.

4. The application according to claim 1, characterized in that: The reducing atmosphere is 50% H2 / Ar.

5. The application according to claim 1, characterized in that: The high-temperature pyrolysis is performed at a temperature of 550-650°C for 2-4 hours.

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