LaBO3 type perovskite ammonia synthesis catalyst and preparation method and application thereof

Abstract

The invention belongs to the technical field of synthesis ammonia catalysts, and provides a LaBO3 type perovskite synthesis ammonia catalyst and a preparation method and application thereof, and the method comprises the following steps: mixing a fourth period metal salt, lanthanum nitrate, citric acid and water, and sequentially heating and calcining to obtain the LaBO3 type perovskite synthesis ammonia catalyst, the fourth period metal salt is nickel nitrate, ferric nitrate or cobalt nitrate. According to the catalyst provided by the invention, in ammonia synthesis, nano-particles are separated out on the surface of the catalyst through reduction of hydrogen, a B / La2O3 nano-particle catalyst for metal dissolution is formed in situ, the uniform nano-particle catalyst with catalytic activity can improve ammonia synthesis catalytic performance, and the problems of sintering agglomeration and performance reduction of the catalyst are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia synthesis catalysts, and in particular to a LaBO3 type perovskite ammonia synthesis catalyst and a preparation method and application thereof. Background Art

[0002] There are many methods for preparing supported metal nanoparticle catalysts, including physical mixing, physical or chemical vapor deposition, deposition precipitation and wet chemical impregnation. However, the above methods may cause problems such as catalyst agglomeration and poisoning, which leads to a decrease in catalytic efficiency and a limited rate of ammonia synthesis.

[0003] In order to further solve the common problems of catalyst agglomeration and poisoning, the development of new in-situ intelligent catalysts so that the central metal of the synthetic ammonia catalyst can be dissolved faster and evenly distributed on the carrier surface, thereby accelerating the ammonia synthesis rate has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a LaBO3 type perovskite ammonia synthesis catalyst and a preparation method and application thereof.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a LaBO3-type perovskite ammonia synthesis catalyst, comprising the following steps:

[0007] The fourth period metal salt, lanthanum nitrate, citric acid and water are mixed and then heated and calcined in sequence to obtain the LaBO3 type perovskite ammonia synthesis catalyst;

[0008] The fourth period metal salt is nickel nitrate, iron nitrate or cobalt nitrate.

[0009] Preferably, when the fourth period metal salt is nickel nitrate, the mass ratio of lanthanum nitrate, nickel nitrate and citric acid is 0.5-1.5:0.5-1.5:2.7-3.3;

[0010] The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

[0011] Preferably, when the fourth period metal salt is ferric nitrate, the mass ratio of lanthanum nitrate, ferric nitrate and citric acid is 0.5-1.5:0.5-1.5:3.5-4.5;

[0012] The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

[0013] Preferably, when the fourth period metal salt is cobalt nitrate, the mass ratio of lanthanum nitrate, cobalt nitrate and citric acid is 0.5-1.5:0.5-1.5:0.5-1.5;

[0014] The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

[0015] Preferably, the heating temperature is 80-90°C and the heating time is 2-3h;

[0016] The heating rate of the calcination is 8-10°C / min, and the calcination time is 5-12h.

[0017] Preferably, when the fourth period metal salt is nickel nitrate, the calcination temperature is 700-800°C.

[0018] Preferably, when the fourth period metal salt is ferric nitrate, the first calcination temperature is 450-550°C; the second calcination temperature is 600-800°C.

[0019] Preferably, when the fourth period metal salt is cobalt nitrate, the calcination temperature is 650-750°C.

[0020] The present invention also provides a LaBO3 type perovskite ammonia synthesis catalyst prepared by the preparation method.

[0021] The present invention also provides application of the LaBO3 type perovskite ammonia synthesis catalyst in ammonia synthesis.

[0022] The present invention provides a method for preparing a LaBO3 type perovskite ammonia synthesis catalyst, comprising the following steps: mixing a fourth period metal salt, lanthanum nitrate, citric acid and water, and then heating and calcining in sequence to obtain the LaBO3 type perovskite ammonia synthesis catalyst; the fourth period metal salt is nickel nitrate, iron nitrate or cobalt nitrate. The catalyst provided by the present invention, in the synthesis of ammonia, precipitates nanoparticles on the catalyst surface through hydrogen reduction, and forms a metal-dissolved B / La2O3 nanoparticle catalyst in situ. These uniform and catalytically active nanoparticle catalysts can improve the catalytic performance of ammonia synthesis, and avoid the problem of catalyst sintering and agglomeration, and performance degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The X-ray diffraction diagram of the catalyst in Example 1 before and after the reaction;

[0024] Figure 2 The X-ray diffraction diagram of the catalyst in Example 2 before and after the reaction;

[0025] Figure 3 The X-ray diffraction diagram of the catalyst in Example 3 before and after the reaction;

[0026] Figure 4 is a graph of ammonia synthesis rate of the catalysts of Examples 1 to 3;

[0027] Figure 5 The graphs are of the ammonia synthesis rate of the catalysts of Examples 1 to 3 at different temperatures. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a LaBO3-type perovskite ammonia synthesis catalyst, comprising the following steps:

[0029] The fourth period metal salt, lanthanum nitrate, citric acid and water are mixed and then heated and calcined in sequence to obtain the LaBO3 type perovskite ammonia synthesis catalyst;

[0030] The fourth period metal salt is nickel nitrate, iron nitrate or cobalt nitrate.

[0031] In the present invention, when the fourth period metal salt is nickel nitrate, the mass ratio of lanthanum nitrate, nickel nitrate and citric acid is preferably 0.5-1.5:0.5-1.5:2.7-3.3, more preferably 0.6-1.4:0.6-1.4:2.8-3.2, and more preferably 0.8-1.2:0.8-1.2:2.9-3.1.

[0032] In the present invention, when the fourth period metal salt is nickel nitrate, the mass volume ratio of the lanthanum nitrate and water is preferably 1-3 g:30-50 mL, more preferably 1.5-2.5 g:35-45 mL, and more preferably 1.8-2.2 g:38-42 mL.

[0033] In the present invention, when the fourth period metal salt is ferric nitrate, the mass ratio of lanthanum nitrate, ferric nitrate and citric acid is preferably 0.5-1.5:0.5-1.5:3.5-4.5, more preferably 0.6-1.4:0.6-1.4:3.6-4.4, and more preferably 0.8-1.2:0.8-1.2:3.8-4.2.

[0034] In the present invention, when the fourth period metal salt is ferric nitrate, the mass volume ratio of the lanthanum nitrate and water is preferably 1-3 g: 30-50 mL, more preferably 1.5-2.5 g: 35-45 mL, and more preferably 1.8-2.2 g: 38-42 mL.

[0035] In the present invention, when the fourth period metal salt is cobalt nitrate, the mass ratio of lanthanum nitrate, cobalt nitrate and citric acid is preferably 0.5-1.5:0.5-1.5:0.5-1.5, more preferably 0.6-1.4:0.6-1.4:0.6-1.4, and more preferably 0.8-1.2:0.8-1.2:0.8-1.2.

[0036] In the present invention, when the fourth period metal salt is cobalt nitrate, the mass volume ratio of the lanthanum nitrate and water is preferably 1-3 g:30-50 mL, more preferably 1.5-2.5 g:35-45 mL, and more preferably 1.8-2.2 g:38-42 mL.

[0037] In the present invention, the heating temperature is preferably 80-90°C, more preferably 82-88°C, more preferably 84-86°C; the heating time is preferably 2-3h, more preferably 2.2-2.8h, more preferably 2.4-2.6h; the stirring rate is preferably 800-1200rpm, more preferably 850-1150rpm, more preferably 900-1100rpm.

[0038] In the present invention, the purpose of heating is to form a gel.

[0039] In the present invention, the obtained gel is dried to remove moisture to obtain a powder block; the drying temperature is preferably 70 to 80°C, more preferably 72 to 78°C, and more preferably 74 to 76°C.

[0040] In the present invention, the obtained powder mass is calcined.

[0041] In the present invention, the heating rate of the calcination is preferably 8-10°C / min, more preferably 8.5-9.5°C / min, more preferably 8.8-9.2°C / min; the calcination time is preferably 5-12h, more preferably 6-11h, more preferably 8-10h.

[0042] In the present invention, when the fourth period metal salt is nickel nitrate, the calcination temperature is preferably 700-800°C, more preferably 720-780°C, and even more preferably 740-760°C.

[0043] In the present invention, when the fourth period metal salt is ferric nitrate, the first calcination temperature is preferably 450-550°C, more preferably 460-540°C, and more preferably 480-520°C; the second temperature is preferably 600-800°C, more preferably 650-750°C, and more preferably 680-720°C; when ferric nitrate is used, the heating rate from room temperature to the first calcination temperature and the heating rate from the first calcination temperature to the second calcination temperature are both the calcination heating rate, i.e. 8-10°C / min; the calcination time at the first calcination temperature and the calcination time at the second calcination temperature are equal, and the sum of the two times is the calcination time, i.e. 5-12h.

[0044] In the present invention, when the fourth period metal salt is cobalt nitrate, the calcination temperature is preferably 650-750°C, more preferably 660-740°C, and even more preferably 680-720°C.

[0045] The present invention also provides a LaBO3 type perovskite ammonia synthesis catalyst prepared by the preparation method.

[0046] The present invention also provides application of the LaBO3 type perovskite ammonia synthesis catalyst in ammonia synthesis.

[0047] The present invention also provides a method for synthesizing ammonia, wherein the LaBO3 type perovskite ammonia synthesis catalyst is placed in a mixed gas of nitrogen and hydrogen to form a B / La2O3 perovskite catalyst, and then ammonia is synthesized.

[0048] In the present invention, the molar ratio of nitrogen to hydrogen is preferably 1:2-4, more preferably 1:2.5-3.5, and more preferably 1:2.8-3.2; the flow rate of the mixed gas is preferably 50-75 r / min, more preferably 55-70 r / min, and more preferably 60-65 r / min.

[0049] In the present invention, the usage of the LaBO3 type perovskite ammonia synthesis catalyst is preferably 80 to 100 mg, more preferably 85 to 95 mg, and even more preferably 88 to 92 mg.

[0050] In the present invention, the synthesis temperature is preferably 400-500°C, more preferably 420-480°C, more preferably 440-460°C; the pressure is preferably 3-6 MPa, more preferably 4-5 MPa, more preferably 4.4-4.6 MPa.

[0051] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0052] Example 1

[0053] 1 g of nickel nitrate, 1 g of lanthanum nitrate and 3 g of citric acid were dissolved in 40 mL of water to obtain a mixed solution, which was then stirred at 80°C and 1000 rpm for 3 h to obtain a gel. The gel was dried at 80°C to remove moisture to obtain a powder block, which was heated to 750°C at a rate of 9°C / min and then calcined for 12 h to obtain a LaNiO3 perovskite catalyst.

[0054] Example 2

[0055] 1 g of ferric nitrate, 1 g of lanthanum nitrate and 4 g of citric acid were dissolved in 30 mL of water to obtain a mixed solution, which was then stirred at 80°C and 1100 rpm for 2.5 h to obtain a gel. The gel was dried at 70°C to remove moisture to obtain a powder block, the powder block was heated to 500°C at a rate of 10°C / min, and then calcined for 3 h; then the temperature was raised to 700°C at a rate of 8°C / min, and then calcined for 3 h to obtain a LaFeO3 perovskite catalyst.

[0056] Example 3

[0057] 1 g of cobalt nitrate, 1 g of lanthanum nitrate and 1 g of citric acid were dissolved in 50 mL of water to obtain a mixed solution, which was then stirred at 80 °C and 900 rpm for 2.5 h to obtain a gel. The gel was dried at 75 °C to remove moisture to obtain a powder block. The powder block was heated to 650 °C at a rate of 8 °C / min and then calcined for 6 h to obtain a LaCoO3 perovskite catalyst.

[0058] Performance Testing

[0059] The catalysts prepared in Examples 1 to 3 were tested under the following conditions: the reaction pressure was 5 MPa, the hydrogen and nitrogen were mixed in a molar ratio of 3:1, and the mixed gas flow rate was 60 r / min to catalyze the synthesis of ammonia (reaction at 500°C for 80 h); the X-ray diffraction pattern of the catalyst in Example 1 before and after the reaction was as follows: Figure 1 As shown, the X-ray diffraction pattern of the catalyst in Example 2 before and after the reaction is as shown Figure 2 As shown, the X-ray diffraction patterns of the catalyst in Example 3 before and after the reaction are as follows Figure 3 As shown, from Figure 1 , Figure 2 and Figure 3 It can be seen that after the ammonia synthesis reaction, the characteristic peaks of metal elements can be clearly observed in the B-site nickel and cobalt, that is, the B-site metal in LaBO3 gradually dissolves and precipitates during the ammonia reaction, forming a reaction active center. LaFeO3 still maintains a relatively good structure after 12 hours of reaction. The change in XRD means that the lattice gradually shrinks, which requires further valence and structural environment tests to verify this change. This shows that as iron may continue to precipitate from the perovskite, it leads to the collapse of the perovskite structure.

[0060] The ammonia synthesis rate of the catalysts of Examples 1 to 3 is shown in FIG. Figure 4 As shown, from Figure 4 It can be seen that as the dissolution time increases, more and more metals are dissolved, more active sites are formed, and the rate of ammonia synthesis is also getting higher and higher.

[0061] The catalysts prepared in Examples 1 to 3 were tested under the following conditions: the reaction pressure was 5 MPa, the hydrogen and nitrogen were mixed in a molar ratio of 3:1, and the mixed gas flow rate was 60 r / min to catalyze the synthesis of ammonia. The ammonia synthesis rates of the ammonia synthesis catalysts at reaction temperatures of 400°C, 425°C, 450°C, 475°C, and 500°C were compared. The results are as follows: Figure 5 As shown in the figure, it can be seen that in the temperature range of 400-500°C, its ammonia synthesis activity gradually increases, and the ammonia synthesis rate reaches the mmol level, which also provides application prospects for practical industrial applications.

[0062] As can be seen from the above embodiments, the present invention provides a method for preparing a LaBO3 type perovskite ammonia synthesis catalyst, comprising the following steps: mixing a fourth period metal salt, lanthanum nitrate, citric acid and water, and then heating and calcining in sequence to obtain the LaBO3 type perovskite ammonia synthesis catalyst; the fourth period metal salt is nickel nitrate, iron nitrate or cobalt nitrate. The catalyst provided by the present invention, in the synthesis of ammonia, precipitates nanoparticles on the catalyst surface through hydrogen reduction, and forms a metal-dissolved B / La2O3 nanoparticle catalyst in situ. These uniform and catalytically active nanoparticle catalysts can improve the catalytic performance of ammonia synthesis, avoid the problem of catalyst sintering and agglomeration, and performance degradation.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a LaBO3 type perovskite ammonia synthesis catalyst, characterized in that: It includes the following steps: The fourth period metal salt, lanthanum nitrate, citric acid and water are mixed and then heated and calcined in sequence to obtain the LaBO3 type perovskite ammonia synthesis catalyst; The fourth period metal salt is nickel nitrate, iron nitrate or cobalt nitrate.

2. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 1, characterized in that: When the fourth period metal salt is nickel nitrate, the mass ratio of lanthanum nitrate, nickel nitrate and citric acid is 0.5-1.5:0.5-1.5:2.7-3.3; The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

3. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 1, characterized in that: When the fourth period metal salt is ferric nitrate, the mass ratio of lanthanum nitrate, ferric nitrate and citric acid is 0.5-1.5:0.5-1.5:3.5-4.5; The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

4. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 1, characterized in that: When the fourth period metal salt is cobalt nitrate, the mass ratio of lanthanum nitrate, cobalt nitrate and citric acid is 0.5-1.5:0.5-1.5:0.5-1.5; The mass volume ratio of the lanthanum nitrate and water is 1-3 g:30-50 mL.

5. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to any one of claims 1 to 4, characterized in that: The heating temperature is 80-90°C and the heating time is 2-3h; The heating rate of the calcination is 8-10°C / min, and the calcination time is 5-12h.

6. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 5, characterized in that: When the fourth period metal salt is nickel nitrate, the calcination temperature is 700-800°C.

7. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 5, characterized in that: When the fourth period metal salt is ferric nitrate, the first calcination temperature is 450-550°C; the second calcination temperature is 600-800°C.

8. The method for preparing the LaBO3 type perovskite ammonia synthesis catalyst according to claim 5, characterized in that: When the fourth period metal salt is cobalt nitrate, the calcination temperature is 650-750°C.

9. The LaBO3 type perovskite ammonia synthesis catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the LaBO3 type perovskite ammonia synthesis catalyst according to claim 9 in ammonia synthesis.

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