Co / Li2O-La2O3 composite catalyst, preparation method thereof and application of Co / Li2O-La2O3 composite catalyst in hydrogen production through ammonia decomposition
The preparation of Co/Li2O-La2O3 composite catalysts by sol-gel method solves the problems of high cost of Ru-based catalysts and low Co-N bond energy, and achieves efficient ammonia decomposition and hydrogen production effect.
Patent Information
- Application Number
- CN202510309486.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-17
- Publication Date
- 2025-07-11
AI Technical Summary
The existing Ru-based catalysts have high cost in ammonia decomposition and low Co-N bond energy, resulting in insufficient catalytic activity and difficult to achieve efficient ammonia decomposition.
The Co/Li2O-La2O3 composite catalyst was prepared by sol-gel method. Through air atmosphere pyrolysis and reduction atmosphere reduction treatment, the metal Co was uniformly dispersed on Li2O-La2O3, and the 3d electron layout of Co was adjusted to form a moderate Co-N bond.
The catalyst is highly efficient thermal catalytic activity, the hydrogen production rate is improved, the catalytic activity center is uniform, and the moderate Co-N bond promotes the ammonia decomposition and hydrogen production reaction.
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Figure CN120286001A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of thermal catalytic materials, and particularly relates to a Co / Li2O-La2O3 composite catalyst, a preparation method thereof, and an application thereof in thermal catalytic ammonia decomposition for hydrogen production. Background Art
[0002] The decomposition kinetics of NH3 on a metal (denoted as M) depends on the strength of the M-N bond. A stronger M-N bond is beneficial to the dissociation of N-H in the NH3 molecule, but is not conducive to the desorption of N2 products on the catalyst surface; on the contrary, a weaker M-N bond is beneficial to the desorption of N2, but will hinder the dissociation of the N-H bond. An appropriate M-N bond strength is crucial for promoting ammonia decomposition. Ru-based catalysts are the best active metals for ammonia decomposition reported in the literature at present due to their moderate Ru-N bonds. However, their high cost is not conducive to large-scale applications. Co is one of the common non-precious metals in the ammonia decomposition reaction. However, the Co-N bond energy is low, and most current work mainly solves the Co-N bond strength problem by regulating the Co metal particle size, adding alkali metal promoters, and metal alloying. Summary of the Invention
[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a Co / Li2O-La2O3 composite catalyst, a preparation method thereof, and an application thereof in thermal catalytic ammonia decomposition for hydrogen production. The catalyst has a stable structure, and the active metal Co in the catalyst is uniformly dispersed. The active metal Co serves as an active site in the thermal catalytic reaction. La2O3 and Li2O jointly regulate the 3d electron arrangement of metal Co, making Co have a moderate Co-N bond, optimizing the H recombination desorption and N recombination desorption energy barriers, and having excellent thermal catalytic activity in thermal catalytic ammonia decomposition for hydrogen production.
[0004] In order to achieve the above technical purpose, the present invention adopts the following technical scheme:
[0005] A preparation method of a Co / Li2O-La2O3 composite catalyst, which comprises dissolving soluble Co salts, Li salts, La salts and citric acid in an ethylene glycol aqueous solution, synthesizing a perovskite precursor by a sol-gel method, and then thermally decomposing the perovskite precursor in an air atmosphere and reducing it in a reducing atmosphere to obtain the Co / Li2O-La2O3 composite catalyst.
[0006] Preferably, the soluble Co salts, Li salts, and La salts are all their nitrates, and the sum of the molar ratios of Li and La to Co is 1:1; the molar ratio of Li to La is 1:1 to 4; the molar ratio of the sum of Co, Li, and La to citric acid is 1:1.
[0007] Preferably, the temperature of the sol-gel reaction is 60-100 °C, and the time is 24-36 h.
[0008] Preferably, the pyrolysis temperature in the air atmosphere is 600 - 1000 °C, and the time is 4 - 10 h.
[0009] Preferably, the reducing atmosphere is 50% H2 / 50% Ar, that is, the volume ratio of H2 to Ar is 1:1; the reduction temperature is 400 - 800 °C, and the time is 2 - 5 h.
[0010] The present invention also provides a Co / Li2O-La2O3 composite catalyst prepared by the above preparation method.
[0011] The present invention also provides the application of the above Co / Li2O-La2O3 composite catalyst, which is used for thermocatalytic ammonia decomposition to produce hydrogen.
[0012] Advantages of the present invention:
[0013] Through the sol-gel method, pyrolysis in the air atmosphere, and reduction treatment in the reducing atmosphere, the present invention realizes the loading of metallic Co on the mixed oxide Li2O-La2O3, and obtains a Co / Li2O-La2O3 composite catalyst. The composite catalyst has a flaky stacking structure, with uniform active centers and highly exposed active sites. La2O3 and Li2O jointly regulate the 3d electron arrangement of metallic Co, enabling Co to have a moderate Co-N bond and excellent thermocatalytic activity in thermocatalytic ammonia decomposition to produce hydrogen. Description of the Drawings
[0014] Figure 1 It is the SEM image of Co / Li2O-La2O3 prepared in Example 2;
[0015] As Figure 1 shown, Co / Li2O-La2O3 presents a flaky stacking structure.
[0016] Figure 2 It is the TEM image of Co / Li2O-La2O3 prepared in Example 2;
[0017] As Figure 2 shown, Co / Li2O-La2O3 has obvious La2O3 lattice fringes, and it can be seen that the amorphous region is in close contact with metallic Co, which can confirm that Li2O exists in an amorphous form.
[0018] Figure 3 It is the XRD pattern of Co / Li2O-La2O3 prepared in Example 2, Co / La2O3 prepared in Comparative Example 1, and Co / Li2O prepared in Comparative Example 2;
[0019] As Figure 3As shown, the XRD characterization has distinct characteristic peaks of metallic Co and La2O3. No obvious Li2O peak is seen in the Co / Li2O-La2O3 spectrum, which is consistent with the TEM results, confirming that Li2O exists in an amorphous form.
[0020] Figure 4 Figure of the temperature-dependent magnetic susceptibility (M-T) for Co / Li2O-La2O3 prepared in Example 2, Co / La2O3 prepared in Comparative Example 1, and Co / Li2O prepared in Comparative Example 2;
[0021] As Figure 4 shown, the M-T figure indicates that all three materials reach the paramagnetic state above 300 K. The magnetic moments of Co / La2O3, Co / Li2O-La2O3, and Co / Li2O at high temperatures can be calculated by the Curie-Weiss law as 1.39, 2.38, and 5.56 μB, respectively.
[0022] Figure 5 Figure of X -1 (Oe g emu -1 )×10 2 -K for Co / Li2O-La2O3 prepared in Example 2, Co / La2O3 prepared in Comparative Example 1, and Co / Li2O prepared in Comparative Example 2;
[0023] As Figure 5 shown, according to the Curie-Weiss law for calculating the magnetic moment in the paramagnetic state and its derived formula, the spin states of Co / La2O3, Co / Li2O-La2O3, and Co / Li2O are 92% LS + 8% HS, 73% LS + 27% HS, and 10% LS + 90% HS, respectively. The number of unpaired electrons in the 3d orbitals is 1.16, 1.54, and 2.80, respectively, proving that the composite catalyst Co / Li2O-La2O3 is in a medium spin state and has a moderate NH3 adsorption capacity.
[0024] Figure 6 Figure of NH3-TPD for Co / Li2O-La2O3 prepared in Example 2, Co / La2O3 prepared in Comparative Example 1, and Co / Li2O prepared in Comparative Example 2;
[0025] As Figure 6 shown, Co / Li2O-La2O3 has a moderate NH3 adsorption capacity, and the NH3 desorption peak is approximately at 410 °C, which is consistent with the above spin state characterization results.
[0026] Figure 7 Figure of DFT for Co / Li2O-La2O3 prepared in Example 2, Co / La2O3 prepared in Comparative Example 1, and Co / Li2O prepared in Comparative Example 2;
[0027] AsFigure 7 As shown, Co / Li2O-La2O3 has the best ammonia adsorption capacity, the lowest energy barrier in H-associative desorption, and a moderate N-associative desorption energy barrier. Specific Embodiments
[0028] The present invention will be further described in detail below in conjunction with embodiments, but the protection scope of the present invention is not limited to these embodiments.
[0029] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the reagents, materials, etc. used in the following examples can all be obtained from commercial sources.
[0030] Thermocatalytic ammonia decomposition for hydrogen production reaction:
[0031] Weigh 100 mg of the catalyst (40 - 60 mesh) and add it to a quartz reaction tube. Then, introduce pure ammonia (99.999%) and, within the range of 450°C - 650°C, with a temperature interval gradient of 50°C, test for 40 min at each temperature point, and detect the ammonia conversion rate through gas chromatography.
[0032] Example 1
[0033] (1) Add 10 mmol of cobalt nitrate, 5 mmol of lanthanum nitrate, 5 mmol of lithium nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol to 400 ml of ultrapure water and mix evenly. After stirring for 10 minutes, place it in an oil bath and treat it at 80°C for 24 h. After cooling to room temperature, dry it at 80°C to obtain the ABO3 precursor;
[0034] (2) First, heat-treat the ABO3 precursor at 800°C under air conditions for 6 h; then heat-treat it at 700°C under 50% H2 / Ar conditions for 2 h to obtain the Co / Li2O-La2O3 composite catalyst.
[0035] The Co / Li2O-La2O3 composite catalyst prepared in Example 1 was used for the thermocatalytic ammonia decomposition for hydrogen production reaction. Under the conditions of 600°C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 26.08 mmol g (cat) -1 ·min -1 .
[0036] Example 2
[0037] (1) Add 10 mmol of cobalt nitrate, 7 mmol of lanthanum nitrate, 3 mmol of lithium nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol to 400 ml of ultrapure water and mix evenly. After stirring for 10 minutes, place it in an oil bath and treat it at 80°C for 24 h. After cooling to room temperature, dry it at 80°C to obtain the ABO3 precursor;
[0038] (2) The ABO3 precursor was first heat-treated at 800 °C under air conditions for 6 h; then it was heat-treated at 700 °C under 50% H2 / Ar conditions for 2 h to obtain the Co / Li2O-La2O3 composite catalyst.
[0039] The Co / Li2O-La2O3 catalyst prepared in Example 2 was used for the thermal catalytic ammonia decomposition to produce hydrogen reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 27.29 mmol g (cat) -1 ·min -1 。
[0040] Example 3
[0041] (1) 10 mmol of cobalt nitrate, 8 mmol of lanthanum nitrate, 2 mmol of lithium nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed evenly. After stirring for 10 minutes, it was placed in an oil bath and treated at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0042] (2) The ABO3 precursor was first heat-treated at 800 °C under air conditions for 6 h; then it was heat-treated at 700 °C under 50% H2 / Ar conditions for 2 h to obtain the Co / Li2O-La2O3 composite catalyst.
[0043] The Co / Li2O-La2O3 catalyst prepared in Example 3 was used for the thermal catalytic ammonia decomposition to produce hydrogen reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 26.01 mmol g (cat) -1 ·min -1 。
[0044] Comparative Example 1
[0045] (1) 10 mmol of cobalt nitrate, 10 mmol of lanthanum nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed evenly. After stirring for 10 minutes, it was placed in an oil bath and treated at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0046] (2) The ABO3 precursor was first heat-treated at 800 °C under air conditions for 6 h; then it was heat-treated at 700 °C under 50% H2 / Ar conditions for 2 h to obtain the Co / La2O3 catalyst.
[0047] The Co / La2O3 catalyst prepared in Comparative Example 1 was used in the thermal catalytic ammonia decomposition for hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 21.22 mmol g (cat) -1 ·min -1 。
[0048] Comparative Example 2
[0049] (1) 10 mmol of cobalt nitrate, 10 mmol of lithium nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed uniformly. After stirring for 10 minutes, it was placed in an oil bath at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0050] (2) The ABO3 precursor was first heat-treated at 800 °C in air for 6 h; then it was heat-treated at 700 °C in 50% H2 / Ar for 2 h to obtain the Co / Li2O catalyst.
[0051] The Co / Li2O catalyst prepared in Comparative Example 2 was used in the thermal catalytic ammonia decomposition for hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 19.65 mmol g (cat) -1 ·min -1 。
[0052] Comparative Example 3
[0053] (1) A Li-modified Co / La2O3 catalyst was prepared by the impregnation method. According to Co:La:Li = 10:7:3, cobalt nitrate, lithium nitrate, and lanthanum oxide were used as the cobalt source, lithium source, and carrier, respectively. The lanthanum oxide carrier was added to the aqueous nitrate solution containing cobalt and lithium. The mixture was kept in an oil bath at 80 °C until the solution evaporated. The obtained powder was calcined in air at 800 °C for 6 hours, and then reduced in a 50% H2 / Ar atmosphere at 700 °C for 2 h to obtain the Co / Li2O-La2O3 catalyst.
[0054] (2) The prepared Co / Li2O-La2O3 catalyst was used in the thermal catalytic ammonia decomposition for hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 11.18 mmol g (cat) -1 ·min -1 。
[0055] Comparative Example 4
[0056] (1) 10 mmol of cobalt nitrate, 3 mmol of sodium nitrate, 7 mmol of lanthanum nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed uniformly. After stirring for 10 minutes, it was placed in an oil bath and treated at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0057] (2) The ABO3 precursor was first heat-treated at 800 °C in air for 6 h; then it was heat-treated at 700 °C in 50% H2 / Ar for 2 h to obtain the Co / Na2O-La2O3 composite catalyst.
[0058] The Co / Na2O-La2O3 catalyst prepared in Comparative Example 4 was used for the thermal catalytic ammonia decomposition hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 18.90 mmol g (cat) -1 ·min -1 。
[0059] Comparative Example 5
[0060] (1) 10 mmol of cobalt nitrate, 3 mmol of magnesium nitrate, 7 mmol of lanthanum nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed uniformly. After stirring for 10 minutes, it was placed in an oil bath and treated at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0061] (2) The ABO3 precursor was first heat-treated at 800 °C in air for 6 h; then it was heat-treated at 700 °C in 50% H2 / Ar for 2 h to obtain the Co / MgO-La2O3 composite catalyst.
[0062] The Co / MgO-La2O3 catalyst prepared in Comparative Example 5 was used for the thermal catalytic ammonia decomposition hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst was 20.84 mmol g (cat) -1 ·min -1 。
[0063] Comparative Example 6
[0064] (1) 10 mmol of cobalt nitrate, 3 mmol of barium nitrate, 7 mmol of lanthanum nitrate, 20 mmol of citric acid, and 1.12 ml of ethylene glycol were added to 400 ml of ultrapure water and mixed uniformly. After stirring for 10 minutes, it was placed in an oil bath and treated at 80 °C for 24 h. After cooling to room temperature, it was dried at 80 °C to obtain the ABO3 precursor;
[0065] (2) Heat-treat the ABO3 precursor at 800 °C in air for 6 h first; then heat-treat it at 700 °C under 50% H2 / Ar for 2 h to obtain the Co / BaO-La2O3 composite catalyst.
[0066] Use the Co / BaO-La2O3 catalyst prepared in Comparative Example 6 for the thermal catalytic ammonia decomposition hydrogen production reaction. Under the conditions of 600 °C and pure NH3 (99.999%), the hydrogen production rate of this catalyst is 17.65 mmol g (cat) -1 ·min -1 .
Claims
1. A preparation method of Co / Li2O-La2O3 composite catalyst, characterized in that: Dissolve soluble Co salt, Li salt, La salt and citric acid in an ethylene glycol aqueous solution, synthesize a perovskite precursor by the sol-gel method, and then pyrolyze the perovskite precursor in an air atmosphere and reduce it in a reducing atmosphere to obtain a Co / Li2O-La2O3 composite catalyst.
2. The preparation method according to claim 1, characterized in that: The soluble Co salt, Li salt and La salt are all their nitrates, and the molar ratio of the sum of Li and La to Co is 1:1; the molar ratio of Li to La is 1:1 - 4; the molar ratio of the sum of Co, Li and La to citric acid is 1:
1.
3. The preparation method according to claim 1, wherein: The temperature of the sol-gel reaction is 60 - 100 °C, and the time is 24 - 36 h.
4. The preparation method according to claim 1, characterized in that: The pyrolysis temperature in the air atmosphere is 600 - 1000 °C, and the time is 4 - 10 h.
5. The preparation method according to claim 1, characterized in that: The reducing atmosphere is 50% H2 / 50% Ar, the reducing temperature is 400 - 800 °C, and the time is 2 - 5 h.
6. The Co / Li2O-La2O3 composite catalyst prepared by the preparation method according to any one of claims 1 - 5.
7. Use of the Co / Li2O-La2O3 composite catalyst according to claim 6, characterized in that: Use it for thermocatalytic ammonia decomposition to produce hydrogen.