Cesium-modified cobalt-based vanadium nitride synthetic ammonia catalyst, and preparation method and application thereof

Abstract

The present application relates to the technical field of synthetic ammonia catalyst, in particular to a cesium-modified cobalt-based vanadium nitride synthetic ammonia catalyst, a preparation method and application thereof. When the cesium-modified cobalt-based vanadium nitride synthetic ammonia catalyst is prepared, cobalt acetylacetonate, vanadium nitride and an organic solvent are mixed, water and cesium nitrate are added, then the solvent of the above mixture is removed to obtain cesium ion promoted cobalt acetylacetonate / vanadium nitride, and the cesium ion promoted cobalt acetylacetonate / vanadium nitride is heat treated in a hydrogen atmosphere to obtain the cesium-modified cobalt-based vanadium nitride synthetic ammonia catalyst Cs-Co / VN. The cesium-modified cobalt-based vanadium nitride synthetic ammonia catalyst Cs-Co / VN prepared by the method can reduce the reaction activation energy required in the ammonia synthesis process to 48 kJ / mol.

Description

Technical Field

[0001] This invention relates to the field of ammonia synthesis catalyst technology, and in particular to a cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst, its preparation method, and its application. Background Technology

[0002] Currently, the challenge in ammonia synthesis lies in the significant energy barrier inherent in the process, namely the high activation energy required. Existing technologies primarily utilize industrial Fe-based catalysts to catalyze the ammonia synthesis reaction. However, iron-based catalysts offer limited reductions in energy barriers and activation energy, and the reaction conditions required for ammonia synthesis remain high when using them. Recently, many new ammonia synthesis catalysts have emerged, such as Ru-based catalysts, which can significantly lower the activation energy required for ammonia synthesis, enabling synthesis under lower reaction conditions. However, the high cost of precious metal catalysts remains a significant obstacle to their development.

[0003] Further reducing the activation energy required for ammonia synthesis, so that the ammonia synthesis reaction can be carried out under milder conditions, remains a goal pursued by those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to provide a cesium-modified cobalt-based vanadium nitride catalyst for ammonia synthesis, its preparation method, and its application, enabling the ammonia synthesis reaction to be carried out under milder conditions.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a cesium-modified cobalt-based vanadium nitride catalyst for ammonia synthesis includes the following steps:

[0007] Step 1): Mix cobalt acetylacetonate with vanadium nitride and an organic solvent, then add water and cesium nitrate;

[0008] Step 2): Remove the solvent from the mixture obtained in Step 1) to obtain cesium ion-promoted cobalt acetylacetonate / vanadium nitride;

[0009] Step 3): In a hydrogen atmosphere, the cesium ion-promoted cobalt acetylacetone / vanadium nitride obtained in step 2) is heat-treated to obtain the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN.

[0010] Optionally, in step 1), the mass ratio of cobalt acetylacetonate to vanadium nitride is 1:2 to 5, and the molar ratio of cesium nitrate to cobalt acetylacetonate is 0.8 to 1.5:1.

[0011] The organic solvent includes methanol;

[0012] Step 1) The mixing process of cobalt acetylacetone with vanadium nitride and organic solvent requires stirring at a rate of 40-60 r / min for 3-6 h. After adding water and cesium nitrate, the mixture is stirred at 25-60 r / min for 1-4 h.

[0013] Optionally, step 2) specifically involves removing the organic solvent by evaporation at -0.1 to 0 MPa and 30 to 50 °C.

[0014] Optionally, in step 3), the hydrogen flow rate is 70–120 mL / min, the heating temperature is 300–500 °C, and the heating time is 2–5 h.

[0015] Optionally, the vanadium nitride in step 1) is ball-milled vanadium nitride;

[0016] The ball milling process involves a rotation speed of 400–800 r / min and a milling time of 6–24 h.

[0017] The present invention also provides a cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN prepared by the aforementioned preparation method.

[0018] The present invention also provides the application of the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN in the catalytic synthesis of ammonia, wherein the ammonia synthesis process is carried out at a pressure of 3-7 MPa and a temperature of 450-550 °C, and hydrogen and nitrogen are mixed in a volume ratio of 1:2-4 to form a mixed gas with a flow rate of 50-75 r / min.

[0019] Optionally, when using the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN in the ammonia synthesis process, the amount of cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst used is 150–300 mg.

[0020] This application further adds a co-catalytic system to the transition metal supported on the surface of the catalyst, and uses cesium to further modify the catalyst, thereby promoting the ammonia synthesis process and further reducing the activation energy required for the ammonia synthesis process, making the synthesis of ammonia under mild conditions possible. Attached Figure Description

[0021] Figure 1 The reaction rate of ammonia synthesis catalyzed by the cesium-modified cobalt-based vanadium nitride catalyst Cs-Co / VN prepared in Example 1;

[0022] Figure 2 The activation energy is the reaction energy of the cesium-modified cobalt-based vanadium nitride catalyst Cs-Co / VN catalyzed ammonia synthesis process prepared in Example 1. Detailed Implementation

[0023] This invention provides a method for preparing a cesium-modified cobalt-based vanadium nitride catalyst for ammonia synthesis, comprising the following steps:

[0024] Step 1): Mix cobalt acetylacetonate with vanadium nitride and an organic solvent, then add water and cesium nitrate;

[0025] Step 2): Remove the solvent from the mixture obtained in Step 1) to obtain cesium ion-promoted cobalt acetylacetonate / vanadium nitride;

[0026] Step 3): In a hydrogen atmosphere, the cesium ion-promoted cobalt acetylacetone / vanadium nitride obtained in step 2) is heat-treated to obtain the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN.

[0027] In this invention, the mass ratio of cobalt acetylacetonate to vanadium nitride in step 1) is 1:2 to 5, preferably 1:2.4 to 4.5, more preferably 1:2.7 to 4, and even more preferably 1:3 to 3.5; the molar ratio of cesium nitrate to cobalt acetylacetonate is 0.8 to 1.5:1, preferably 0.85 to 1.4:1, more preferably 0.9 to 1.25:1, and even more preferably 1 to 1.1:1.

[0028] The organic solvent contains methanol; the amount of organic solvent used will not affect the structure of cobalt acetylacetonate / vanadium nitride and cesium ion-promoted cobalt acetylacetonate / vanadium nitride.

[0029] In this invention, the mixing process of cobalt acetylacetone, vanadium nitride, and organic solvent in step 1) requires stirring at a rate of 40-60 r / min, preferably 45-55 r / min, more preferably 50 r / min for 3-6 h, preferably 3.5-5.5 h, more preferably 4-5 h, and even more preferably 4-4.5 h; after adding water and cesium nitrate, stirring is carried out at 25-60 r / min, preferably 30-55 r / min, more preferably 35-50 r / min, and even more preferably 40-45 r / min for 1-4 h, preferably 1.5-3.5 h, more preferably 2-3 h, and even more preferably 2-2.5 h.

[0030] In this invention, the cesium nitrate is anhydrous cesium nitrate solid. The purpose of adding deionized water is to dissolve the cesium nitrate, and the amount added is sufficient to dissolve all the required cesium nitrate.

[0031] In this invention, the vanadium nitride in step 1) is ball-milled vanadium nitride;

[0032] The ball milling process is carried out at a rotation speed of 400-800 r / min, preferably 450-750 r / min, more preferably 500-700 r / min, and even more preferably 550-650 r / min; the ball milling time is 6-24 h, preferably 8-20 h, more preferably 10-18 h, and even more preferably 12-15 h.

[0033] In this invention, the removal of organic solvent in step 2) specifically involves evaporating and removing the solvent at -0.1 to 0 MPa, preferably -0.09 to -0.02 MPa, more preferably -0.07 to -0.04 MPa; 30 to 50°C, preferably 32 to 48°C, more preferably 35 to 45°C, and even more preferably 38 to 42°C.

[0034] In this invention, the hydrogen flow rate in the heat treatment process of step 3) is 70-120 mL / min, preferably 75-115 mL / min, more preferably 80-110 mL / min, and even more preferably 85-100 mL / min; the heating temperature is 300-500℃, preferably 320-470℃, more preferably 350-450℃, and even more preferably 380-420℃; the heating time is 2-5 h, preferably 2.5-4.5 h, more preferably 3-4 h, and even more preferably 3-3.5 h.

[0035] In this invention, step 3) involves natural cooling after heat treatment.

[0036] The present invention also provides a cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN prepared by the aforementioned preparation method.

[0037] The present invention also provides the application of the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN in the catalytic synthesis of ammonia. The pressure of the ammonia synthesis process is 3-7 MPa, preferably 3.5-6.5 MPa, more preferably 4-6 MPa, and even more preferably 4.5-5.4 MPa; the temperature is 450-550℃, preferably 460-540℃, more preferably 475-525℃, and even more preferably 490-510℃; hydrogen and nitrogen are mixed in a volume ratio of 1:2-4, preferably 1:2.4-3.8, more preferably 1:2.6-3.5, and even more preferably 1:2.8-3.2 to form a mixed gas, and the flow rate of the mixed gas is 50-75 r / min, preferably 55-70 r / min, and even more preferably 60-65 r / min.

[0038] In this invention, when using the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN in the ammonia synthesis process, the amount of cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst used is 150-300 mg, preferably 180-270 mg, more preferably 200-250 mg, and even more preferably 210-240 mg.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] 1) Place VN in a glove box and mechanically ball mill it at 400 r / min for 12 hours. Collect the solid for later use.

[0042] 2) In a glove box, place 318 mg of cobalt acetylacetonate and 1000 mg of ball-milled VN into a 300 ml rotary flask, add 150 ml of methanol solution, and stir at room temperature for 4 h at a stirring rate of 50 r / min.

[0043] 3) Add 50 mL of deionized water and 232 mg of anhydrous CsNO3 solid, stir at 40 r / min for 2 h, remove the solvent under -0.1 MPa and 50 °C, and collect the solid in a glove box for later use.

[0044] 4) Cs-modified cobalt acetylacetonate / VN was loaded into a stainless steel reactor in a glove box and heated in a hydrogen atmosphere at a flow rate of 90 ml / min and a temperature of 400 °C for 3 h. After natural cooling, the Cs-Co / VN ammonia synthesis catalyst was obtained.

[0045] Example 2

[0046] 1) Place VN in a glove box and mechanically ball mill it at 450 r / min for 10 h, then collect the solid for later use;

[0047] 2) In a glove box, place 300 mg of cobalt acetylacetonate and 945 mg of ball-milled VN into a 300 ml rotary flask, add 150 ml of methanol solution, and stir at room temperature for 4 h at a stirring rate of 50 r / min.

[0048] 3) Add 30 mL of deionized water and 180 mg of anhydrous CsNO3 solid, stir at 40 r / min for 2 h, remove the solvent under -0.1 MPa and 50 °C, and collect the solid in a glove box for later use.

[0049] 4) Cs-modified cobalt acetylacetonate / VN was loaded into a stainless steel reactor in a glove box and heated in a hydrogen atmosphere at a flow rate of 90 ml / min and a temperature of 400 °C for 3 h. After natural cooling, the Cs-Co / VN ammonia synthesis catalyst was obtained.

[0050] Ammonia synthesis process performance testing

[0051] The ammonia synthesis reaction was catalyzed using Co / VN and the ammonia synthesis catalyst Cs-Co / VN prepared in Example 1 at a reaction pressure of 5 MPa, a hydrogen-nitrogen mixture at a volume ratio of 1:3, and a mixed gas flow rate of 60 mL / min. The ammonia synthesis rates of the two catalysts at reaction temperatures of 400℃, 425℃, 450℃, 475℃, and 500℃ were compared. The results are as follows: Figure 1 .

[0052] like Figure 1 As shown, the Cs-Co / VN ammonia synthesis catalyst obtained by modifying Co / VN with Cs exhibits a significantly improved ammonia synthesis activity compared to Co / VN. At 500℃, the ammonia synthesis activity of Cs-Co / VN reaches approximately 1700 μmol / g / h. The ammonia synthesis activity of Cs-Co / VN is approximately 6.8 times that of Co / VN.

[0053] The activation energy required for the synthesis of ammonia using the Co / VN ratio and the catalyst Cs-Co / VN in Example 1 was calculated using the Arrhenius equation. Figure 2 As shown, by Figure 2 It is evident that, compared to Co / VN, the addition of the promoter Cs ions further reduces the activation energy of the reaction to 48 kJ / mol. This indicates that the reaction becomes easier to proceed after the addition of Cs, which provides promising prospects for industrial applications. Therefore, the catalyst provided by this invention can further reduce the reaction intensity in the ammonia synthesis process, making the reaction more readily occurring.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a cesium-modified cobalt-based vanadium nitride catalyst for ammonia synthesis, characterized in that, Includes the following steps: Step 1): Mix cobalt acetylacetonate with vanadium nitride and an organic solvent, then add water and cesium nitrate; Step 2): Remove the solvent from the mixture obtained in Step 1) to obtain cesium ion-promoted cobalt acetylacetonate / vanadium nitride; Step 3): In a hydrogen atmosphere, the cesium ion-promoted cobalt acetylacetone / vanadium nitride obtained in step 2) is heat-treated to obtain the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN. In step 3), the hydrogen flow rate during the heat treatment process is 70-120 mL / min, the heating temperature is 300-500℃, and the heating time is 2-5 h.

2. The preparation method according to claim 1, characterized in that, In step 1), the mass ratio of cobalt acetylacetonate to vanadium nitride is 1:2~5, and the molar ratio of cesium nitrate to cobalt acetylacetonate is 0.8~1.5:

1. The organic solvent includes methanol; Step 1) The mixing process of cobalt acetylacetone with vanadium nitride and organic solvent needs to be stirred at a rate of 40~60 r / min for 3~6 h. After adding water and cesium nitrate, it should be stirred at 25~60 r / min for 1~4 h.

3. The preparation method according to claim 1 or 2, characterized in that, Step 2) The solvent removal from the mixture obtained in step 1) is specifically achieved by evaporation at -0.1~0 MPa and 30~50℃.

4. The preparation method according to claim 1 or 2, characterized in that, Step 1) The vanadium nitride mentioned is ball-milled vanadium nitride; The ball milling process involves a rotation speed of 400-800 r / min and a milling time of 6-24 h.

5. The cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN as described in claim 5 in the catalytic synthesis of ammonia, characterized in that, The ammonia synthesis process is carried out at a pressure of 3-7 MPa and a temperature of 450-550°C. Hydrogen and nitrogen are mixed in a volume ratio of 1:2-4, and the flow rate of the mixed gas is 50-75 r / min.

7. The application of the cesium-modified cobalt-based vanadium nitride ammonia synthesis catalyst Cs-Co / VN according to claim 6 in the catalytic synthesis of ammonia, characterized in that, The amount of cobalt-based vanadium nitride catalyst used in the ammonia synthesis process is 150~300mg.

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