A cobalt-based vanadium nitride ammonia synthesis catalyst and its preparation method and application

Abstract

The present invention relates to the technical field of ammonia synthesis catalysts, and in particular to a cobalt-based vanadium nitride ammonia synthesis catalyst, its preparation method, and application. The vanadium nitride is ball-milled and mixed with cobalt acetylacetonate in an organic solvent. After stirring for a period of time, the organic solvent is removed to obtain the cobalt acetylacetonate / vanadium nitride. The cobalt acetylacetonate / vanadium nitride is heated in a hydrogen atmosphere to obtain the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN. The catalyst Co / VN prepared by this method can effectively reduce the activation energy required for the ammonia synthesis process and lower the reaction energy barrier.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia synthesis catalysts, and in particular to a cobalt-based vanadium nitride ammonia synthesis catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Ammonia synthesis primarily relies on the energy-intensive industrial Haber-Bosch process, which operates at high temperature and pressure and exhibits highly reversible reactions. Currently, the N2 dissociation-adsorption process is generally considered the rate-determining step in the overall ammonia synthesis kinetics. As the most stable diatomic molecule, N2 has a bond energy of up to 945 kJ / mol. The primary task of an ammonia synthesis catalyst is to minimize the energy required to activate N2. The traditional industrial Haber-Bosch process utilizes Fe-based catalysts, which reduce the activation energy of the entire ammonia synthesis reaction to approximately 140 kJ / mol.

[0003] The preparation of a catalyst that can further reduce the activation energy required for the ammonia synthesis process and make ammonia synthesis simpler remains a continuous goal in the field of ammonia synthesis catalysts. Summary of the Invention

[0004] The purpose of the present invention is to provide a cobalt-based vanadium nitride ammonia synthesis catalyst and its preparation method and application. The cobalt-based vanadium nitride ammonia synthesis catalyst prepared by the method can greatly reduce the reaction energy barrier of the ammonia synthesis process.

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

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

[0007] Step 1): ball milling vanadium nitride;

[0008] Step 2): mixing the cobalt acetylacetonate with the vanadium nitride ball-milled in step 1) and an organic solvent;

[0009] Step 3): removing the organic solvent from the mixture obtained in step 2) to obtain cobalt acetylacetonate / vanadium nitride;

[0010] Step 4): heat-treating the cobalt acetylacetonate / vanadium nitride obtained in step 3) in a hydrogen atmosphere to obtain a cobalt-based vanadium nitride ammonia synthesis catalyst.

[0011] Optionally, in step 2), the mass ratio of cobalt acetylacetonate to vanadium nitride is 1:30-60;

[0012] The organic solvent comprises methanol;

[0013] Step 2) The mixing process is carried out at a stirring rate of 40 to 60 r / min for 2 to 6 hours.

[0014] Optionally, the rotation speed of the ball milling process in step 1) is 400-800 r / min, and the ball milling time is 12-36 h.

[0015] Optionally, the removing of the organic solvent in step 3) is specifically performed by evaporating the solvent at 0-0.1 MPa and 35-55°C.

[0016] Optionally, in step 4), the hydrogen flow rate during the heat treatment process is 70-120 mL / min, the heating temperature is 300-500° C., and the heating time is 2-5 h.

[0017] The invention provides a cobalt-based vanadium nitride ammonia synthesis catalyst prepared by the preparation method.

[0018] The present invention also provides an application of the cobalt-based vanadium nitride ammonia synthesis catalyst in catalytic ammonia synthesis. The pressure of the ammonia synthesis process is 3 to 7 MPa, the temperature is 450 to 550°C, the volume ratio of hydrogen to nitrogen is 2 to 4:1, and the flow rate of the mixed gas composed of hydrogen and nitrogen is 40 to 80 mL / min.

[0019] Optionally, the amount of the cobalt-based vanadium nitride ammonia synthesis catalyst used in the ammonia synthesis process is 150 to 300 mg.

[0020] The activity of a catalyst is mainly determined by its structure. Catalysts prepared by different methods have different structures and their activities vary greatly.

[0021] The present invention produces Co / VN by loading the active component cobalt onto a carrier VN through an impregnation method. Specifically, cobalt acetylacetonate containing the active component cobalt is mixed with the catalyst carrier VN in the organic solvent methanol. The cobalt acetylacetonate diffuses in the methanol and is gradually adsorbed by the carrier VN. After removing the solvent, the cobalt acetylacetonate / vanadium nitride is obtained. This is then calcined and reduced to yield Co / VN. In this process, the amount of solvent used does not affect the structure of the cobalt acetylacetonate / vanadium nitride. In the Co / VN ammonia synthesis catalyst, both cobalt and VN are catalytically active centers. Compared to VN or cobalt, which each have a single catalytic center, Co / VN has two catalytic centers, significantly reducing the reaction activation energy.

[0022] The catalyst Co / VN prepared by this preparation method is used in the ammonia synthesis process, which can reduce the reaction energy barrier of the ammonia synthesis process and reduce the activation energy required for the ammonia synthesis process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The reaction rate of ammonia synthesis catalyzed by the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN prepared in Example 1;

[0024] Figure 2 is the reaction activation energy of the ammonia synthesis process catalyzed by the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing a cobalt-based vanadium nitride catalyst for ammonia synthesis, comprising the following steps:

[0026] Step 1): ball milling vanadium nitride;

[0027] Step 2): mixing the cobalt acetylacetonate with the vanadium nitride ball-milled in step 1) and an organic solvent;

[0028] Step 3): removing the organic solvent from the mixture obtained in step 2) to obtain cobalt acetylacetonate / vanadium nitride;

[0029] Step 4): heat-treating the cobalt acetylacetonate / vanadium nitride obtained in step 3) in a hydrogen atmosphere to obtain a cobalt-based vanadium nitride ammonia synthesis catalyst.

[0030] In the present invention, the rotation speed of the ball milling process in step 1) is 400-800 r / min, preferably 450-750 r / min, more preferably 500-700 r / min, and further preferably 550-650 r / min; the ball milling time is 12-36 h, preferably 15-32 h, more preferably 18-30 h, and further preferably 21-28 h.

[0031] In the present invention, the mass ratio of cobalt acetylacetonate to vanadium nitride in step 2) is 1:30-60, preferably 1:35-55, more preferably 1:40-50, and even more preferably 1:42-46;

[0032] The organic solvent comprises methanol;

[0033] Step 2) The mixing process is carried out at a stirring rate of 40 to 60 r / min, preferably 42 to 58 r / min, more preferably 45 to 55 r / min for 2 to 6 hours, preferably 2.5 to 5.5 hours, more preferably 3 to 5 hours, and even more preferably 2.5 to 4.5 hours.

[0034] In the present invention, the removal of the organic solvent in step 3) is specifically carried out by evaporating the solvent at 0 to -0.1 MPa, preferably -0.01 to -0.08 MPa, more preferably -0.03 to -0.06 MPa, and even more preferably -0.04 to -0.06 MPa; 35 to 55°C, preferably 38 to 52°C, more preferably 40 to 50°C, and even more preferably 42 to 48°C.

[0035] In the present invention, in step 4), the hydrogen flow rate during the heat treatment process is 70 to 120 mL / min, preferably 75 to 110 mL / min, more preferably 80 to 105 mL / min, and more preferably 85 to 100 mL / min; the heating temperature is 300 to 500°C, preferably 320 to 480°C, more preferably 360 to 470°C, and more preferably 380 to 420°C; the heating time is 2 to 5 h, preferably 2.5 to 4.5 h, more preferably 3 to 4 h, and more preferably 3.5 h.

[0036] In the present invention, step 4) is followed by natural cooling after the heat treatment.

[0037] The invention provides a cobalt-based vanadium nitride ammonia synthesis catalyst prepared by the preparation method.

[0038] The present invention also provides the use of the cobalt-based vanadium nitride ammonia synthesis catalyst in catalytic ammonia synthesis. The pressure of the ammonia synthesis process is 3-7 MPa, preferably 4-6 MPa, and more preferably 5 MPa; the temperature is 450-550°C, preferably 460-530°C, more preferably 480-520°C, and more preferably 500°C; the volume ratio of hydrogen to nitrogen is 2-4:1, preferably 2.2-3.8:1, more preferably 2.4-3.5:1, and more preferably 2.8-3.2:1; and the flow rate of the mixed gas composed of hydrogen and nitrogen is 40-80 mL / min, preferably 45-75 mL / min, more preferably 50-70 mL / min, and more preferably 55-65 mL / min.

[0039] In the present invention, the amount of the cobalt-based vanadium nitride ammonia synthesis catalyst used in the catalytic synthesis of ammonia is 150 to 300 mg, preferably 175 to 280 mg, more preferably 190 to 255 mg, and even more preferably 200 to 230 mg.

[0040] The technical solutions provided by the present invention are 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.

[0041] Example 1

[0042] 1) Mechanically mill VN in a planetary ball mill at a speed of 600 r / min for 24 h.

[0043] 2) In a glove box, place cobalt acetylacetonate and ball-milled VN in a 500 ml spinner flask, add 300 ml of methanol, and stir at room temperature for 4 h at a stirring rate of 50 rpm. The amount of cobalt acetylacetonate used is 318 mg, and the amount of ball-milled VN used is 12.738 g.

[0044] 3) The solvent was evaporated at -0.1 MPa and 45° C. to obtain cobalt acetylacetonate / VN.

[0045] 4) In a glove box, cobalt acetylacetonate / VN was loaded into a stainless steel reactor and heated in a hydrogen atmosphere at a hydrogen flow rate of 90 ml / min, a heating temperature of 400°C, and a heating time of 3 h. After natural cooling, a cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN was obtained.

[0046] Example 2

[0047] 1) Mechanically mill VN in a planetary ball mill at a speed of 600 r / min for 24 h.

[0048] 2) In a glove box, place 200 mg of cobalt acetylacetonate and 8.14 g of ball-milled VN in a 500 ml round-bottom flask. Add 400 ml of methanol and stir at room temperature for 4 h at a stirring rate of 50 rpm.

[0049] 3) The solvent was evaporated at -0.1 MPa and 40° C. to obtain cobalt acetylacetonate / VN.

[0050] 4) In a glove box, cobalt acetylacetonate / VN was loaded into a stainless steel reactor and heated in a hydrogen atmosphere at a hydrogen flow rate of 95 ml / min, a heating temperature of 410°C, and a heating time of 3 h. After natural cooling, the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN was prepared.

[0051] Catalyst synthesis ammonia performance test

[0052] The catalyst Co / VN prepared in Example 1 was used to catalyze the ammonia synthesis reaction process. The pressure of the ammonia synthesis process was 5 MPa, the volume ratio of hydrogen to nitrogen was 3:1, the flow rate of the hydrogen and nitrogen mixed gas was 60 mL / min, the amount of catalyst was 200 mg, and the temperatures were 400°C, 425°C, 450°C, and 475°C, respectively. The results are as follows: Figure 1 .

[0053] pass Figure 1 It can be found that at 500°C, the ammonia synthesis activity is as high as approximately 250 μmol / g / h. Furthermore, the ammonia synthesis rate continues to increase with increasing temperature, showing no downward trend, indicating that the reaction process does not exhibit the common reversible reaction of ammonia synthesis.

[0054] The activation energy required for the ammonia synthesis process is calculated using the Arrhenius equation, such as Figure 2 As shown by Figure 2As can be seen, the activation energy required for ammonia synthesis using the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN prepared in Example 1 of the present invention is only 70 kJ / mol. This indicates that the catalyst provided by the present invention significantly reduces the reaction energy barrier for ammonia synthesis, making the reaction more likely to occur.

[0055] It can be seen that the cobalt-based vanadium nitride ammonia synthesis catalyst Co / VN prepared in the present invention can effectively reduce the activation energy required for the ammonia synthesis process, greatly reduce the reaction energy barrier, and enable the ammonia synthesis reaction to be carried out under milder conditions.

[0056] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-based vanadium nitride catalyst for ammonia synthesis, characterized in that: The following steps are involved: Step 1): ball milling vanadium nitride; Step 2): mixing the cobalt acetylacetonate with the vanadium nitride ball-milled in step 1) and an organic solvent; Step 3): removing the organic solvent from the mixture obtained in step 2) to obtain cobalt acetylacetonate / vanadium nitride; Step 4): heat-treating the cobalt acetylacetonate / vanadium nitride obtained in step 3) in a hydrogen atmosphere to obtain a cobalt-based vanadium nitride ammonia synthesis catalyst; The mass ratio of cobalt acetylacetonate to vanadium nitride in step 2) is 1:30-60; Step 4) The hydrogen flow rate of the heat treatment is 70-120 mL / min, the heating temperature is 300-500° C., and the heating time is 2-5 h.

2. The preparation method according to claim 1, characterized in that The organic solvent comprises methanol; Step 2) The mixing is performed by stirring at a rate of 40-60 r / min for 2-6 hours.

3. The preparation method according to claim 1 or 2, characterized in that Step 1) The ball milling speed is 400-800 r / min, and the ball milling time is 12-36 h.

4. The preparation method according to claim 1 or 2, characterized in that Step 3) removing the organic solvent from the mixture obtained in step 2) is specifically performed by evaporating the solvent at 0-0.1 MPa and 35-55°C.

5. A cobalt-based vanadium nitride catalyst for ammonia synthesis obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the cobalt-based vanadium nitride ammonia synthesis catalyst according to claim 5 in catalytic ammonia synthesis, characterized in that: The pressure of the ammonia synthesis process is 3~7MPa, the temperature is 450~550℃, the volume ratio of hydrogen to nitrogen is 2~4:1, and the flow rate of the mixed gas composed of hydrogen and nitrogen is 40~80mL / min.

7. Use of the cobalt-based vanadium nitride ammonia synthesis catalyst according to claim 6 in catalytic ammonia synthesis, characterized in that: The usage of cobalt-based vanadium nitride ammonia synthesis catalyst in the ammonia synthesis process is 150~300mg.

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