A ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, its preparation method and application

Abstract

The present invention relates to the technical field of ammonia synthesis catalysts, and particularly relates to a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, a preparation method thereof, and an application thereof. Mix dodecacarbonyltriruthenium and ruthenium-based cesium titanium composite oxide Cs 0.68 Ti 1.83 O4 in an organic solvent, and then remove the solvent to obtain a dry powder; calcine the dry powder, and then place the calcined powder in a hydrogen atmosphere for reduction to obtain the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst described in the present application. Using this catalyst in the ammonia synthesis reaction can reduce the reaction activation energy required for the ammonia synthesis process to Ea = 73 kJ / mol.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia synthesis catalysts, and particularly relates to a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Ammonia is not only an important raw material for the production of chemical nitrogen fertilizers and other ammonia-based chemical products, but also has a high hydrogen storage capacity (17.6 wt%) and is easily liquefied under mild conditions, and is expected to become a carrier of hydrogen. Therefore, under the combined action of various demands, the demand for ammonia is gradually increasing. However, the traditional iron-based ammonia synthesis catalyst-catalyzed Haber–Bosch process requires high temperature (400 - 500 °C) and high pressure (10 - 30 MPa) conditions to effectively dissociate the nitrogen-nitrogen triple bond (945 kJ), resulting in high energy consumption, and the Fe-based catalyst is prone to agglomeration during the reaction process, causing a decrease in catalyst activity. When a ruthenium-based catalyst is used in the ammonia synthesis process, the requirements for temperature and pressure are lower. In addition, since the support and promoter can significantly change the structure and electron distribution of the ruthenium active sites, thus greatly affecting the performance of the ruthenium-based ammonia synthesis catalyst, developing an ideal support for loading the ruthenium-based catalyst can effectively improve its catalytic activity and reduce the energy consumption in the ammonia synthesis process.

[0003] The perovskite-type composite oxide ABO3 is a new type of inorganic non-metallic material with unique physical and chemical properties. The A site is generally a rare earth or alkaline earth element ion, and the B site is a transition element ion. The perovskite composite oxide has a unique crystal structure. Compared with simple oxides, the perovskite structure can allow some elements to exist in abnormal valence states, have non-stoichiometric oxygen, or allow active metals to exist in mixed valence states, making the solid exhibit certain special properties. Since the properties of the solid are closely related to its catalytic activity, the particularity of the perovskite structure makes it widely used in catalysis.

[0004] Research has found that using the ABO3-type perovskite as a support to load the Ru-based catalyst has a certain effect on preventing the agglomeration of smaller nano-sized Ru particles, and the highly dispersed Ru particles can effectively alleviate the traditional hydrogen poisoning phenomenon. Based on this, it is urgent to develop different ruthenium-based / perovskite-type composite oxides for the ammonia synthesis process. Summary of the Invention

[0005] The purpose of the present invention is to provide a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, a preparation method thereof, and an application thereof.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] A preparation method of a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, comprising the following steps:

[0008] Step 1): Mix triruthenium dodecacarbonyl and Cs 0.68 Ti 1.83 O4 with an organic solvent to obtain a mixed solution;

[0009] Step 2): Remove the organic solvent from the mixed solution obtained in Step 1) to obtain a dry powder;

[0010] Step 3): Seal the dry powder obtained in Step 2) in a vacuum environment and calcine it at 280 - 500 °C for 2 - 5 h;

[0011] Step 4): Reduce the calcined powder in Step 3) in a hydrogen atmosphere to obtain the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4.

[0012] Optionally, in Step 1), the mass ratio of triruthenium dodecacarbonyl to Cs 0.68 Ti 1.83 O4 is 0.5 - 3:50;

[0013] The dosage ratio of the triruthenium dodecacarbonyl to the organic solvent is 1 mg:3 - 8 mL;

[0014] The organic solvent includes tetrahydrofuran.

[0015] Optionally, the removal of the organic solvent from the mixed solution prepared in Step 1) in Step 2) is specifically rotary evaporation for 3 - 5 h, and then rotary drying under the conditions of 30 - 50 °C and -0.1 - 0 Mpa.

[0016] Optionally, the reduction temperature in Step 4) is 300 - 500 °C, the reduction time is 1 - 4 h, and the flow rate of hydrogen during the reduction process is 80 - 120 mL / min.

[0017] The present invention provides the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared by the above preparation method.

[0018] The present invention also provides the application of the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 in ammonia synthesis. In the ammonia synthesis process, the molar ratio of H2 to N2 is 2 - 4:1, the flow rate is 40 - 80 mL / min, the reaction temperature is 400 - 500 °C, the reaction pressure is 3 - 7 MPa, and the heating rate is 5 - 20 °C / min.

[0019] Optionally, during the ammonia synthesis process, the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti1.83 The dosage of O4 is 180 - 220 mg.

[0020] The activity of the catalyst is mainly determined by its structure. Catalysts prepared by different methods have different structures and significant differences in activity. In the present invention, the active component ruthenium is loaded on the carrier Cs 0.68 Ti 1.83 O4 by the impregnation method to obtain Ru / Cs 0.68 Ti 1.83 O4. Ruthenium particles can be highly dispersed on Ru / Cs 0.68 Ti 1.83 O4. Secondly, Cs, as a good promoter, directly exists in the oxide carrier, thus effectively alleviating the hydrogen poisoning phenomenon of the ruthenium-based ammonia synthesis catalyst. The catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared by this preparation method is used in the ammonia synthesis process, which can reduce the reaction energy barrier in the ammonia synthesis process and lower the activation energy required for the ammonia synthesis process. Description of the Drawings

[0021] Figure 1 It is a schematic diagram showing the change of ammonia synthesis rate with temperature during the ammonia synthesis reaction process catalyzed by the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared in Example 1;

[0022] Figure 2 It is a schematic diagram showing the change of ammonia synthesis rate with pressure during the ammonia synthesis reaction process catalyzed by the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared in Example 1;

[0023] Figure 3 The activation energy of the ammonia synthesis reaction process catalyzed by the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared in Example 1. Detailed Embodiments

[0024] The present invention provides a preparation method of a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst, which comprises the following steps:

[0025] Step 1): Mix dodecacarbonyltriruthenium and Cs 0.68 Ti 1.83 O4 with an organic solvent to obtain a mixed solution;

[0026] Step 2): Remove the organic solvent from the mixed solution obtained in Step 1) to obtain a dry powder;

[0027] Step 3): Seal the dry powder obtained in Step 2) in a vacuum environment and calcine it at 280 - 500 °C for 2 - 5 h;

[0028] Step 4): Reduce the calcined powder in Step 3) in a hydrogen atmosphere to obtain the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4.

[0029] In the present invention, the mass ratio of dodecacarbonyltriruthenium and Cs 0.68 Ti 1.83 O4 in Step 1) is 0.5 - 3:50, preferably 0.7 - 2.5:50, more preferably 0.9 - 2:50, and even more preferably 1 - 1.5:50;

[0030] The dosage ratio of the dodecacarbonyltriruthenium to the organic solvent is 1 mg:3 - 8 mL, preferably 1 mg:3.5 - 7.5 mL, more preferably 1 mg:4 - 7 mL, and even more preferably 1 mg:4.5 - 6 mL;

[0031] The organic solvent contains tetrahydrofuran.

[0032] In the present invention, specifically removing the organic solvent in the mixed solution prepared in Step 1) in Step 2) is to perform rotary evaporation for 3 - 5 h, preferably 3.5 - 4.5 h, more preferably 4 h; then rotary dry at 30 - 50 °C, preferably 35 - 45 °C, more preferably 40 °C, -0.1 - 0 Mpa, preferably -0.09 - -0.02 Mpa, more preferably -0.08 - -0.03 Mpa, and even more preferably -0.06 - -0.04 Mpa.

[0033] In the present invention, the calcination temperature in Step 3) is 280 - 500 °C, preferably 300 - 480 °C, more preferably 320 - 450 °C, and even more preferably 350 - 400 °C; the calcination time is 2 - 5 h, preferably 2.5 - 4.5 h, more preferably 3 - 4 h, and even more preferably 3.5 h.

[0034] In the present invention, the reduction temperature in Step 4) is 300 - 500 °C, preferably 320 - 480 °C, more preferably 350 - 450 °C, and even more preferably 360 - 420 °C; the reduction time is 1 - 4 h, preferably 1.25 - 3.5 h, more preferably 1.5 - 3 h, and even more preferably 1.75 - 2.5 h; the flow rate of hydrogen during the reduction process is 80 - 120 mL / min, preferably 85 - 115 mL / min, more preferably 90 - 110 mL / min, and even more preferably 95 - 100 mL / min.

[0035] The present invention provides a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 prepared by the above preparation method.

[0036] The present invention also provides the application of the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 in ammonia synthesis. During the ammonia synthesis process, the volume ratio of H2 to N2 is 2-4:1, preferably 2.2-3.8:1, more preferably 2.5-3.5:1, and even more preferably 2.7-3.2:1;

[0037] During the ammonia synthesis process, the flow rate of the hydrogen-nitrogen mixed gas is 40-80 mL / min, preferably 45-75 mL / min, more preferably 50-70 mL / min, and even more preferably 55-65 mL / min;

[0038] During the ammonia synthesis process, the reaction temperature is 400-500 °C, preferably 420-490 °C, more preferably 440-480 °C, and even more preferably 450-470 °C;

[0039] During the ammonia synthesis process, the reaction pressure is 3-7 MPa, preferably 3.5-6.5 MPa, more preferably 4-6 MPa, and even more preferably 4.5-5.5 MPa;

[0040] During the ammonia synthesis process, the heating rate is 5-20 °C / min, preferably 7-18 °C / min, more preferably 9-15 °C / min, and even more preferably 10-12 °C / min.

[0041] In the present invention, during the ammonia synthesis process, the dosage of the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4 is 180-220 mg, preferably 185-215 mg, more preferably 190-210 mg, and even more preferably 195-205 mg.

[0042] 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.

[0043] Example 1

[0044] 1) 0.0432 g of dodecacarbonyltriruthenium and 1 g of Cs 0.68 Ti 1.83O4 was dissolved in 200 mL of tetrahydrofuran. The rotary evaporator was turned on, and the rotation speed was adjusted to 110 r / min. It was rotated at room temperature for 4 h.

[0045] 2) Then, the solvent was removed by vacuum rotary evaporation at 40 °C and -0.1 Mpa to obtain dry powder.

[0046] 3) The obtained powder was sealed in a vacuum tube and calcined at 390 °C for 3 h.

[0047] 4) The calcined powder was placed under a hydrogen atmosphere with a flow rate of 90 - 100 mL / min and heated to 400 °C at a heating rate of 5 °C / min. After reduction for 2 h, it was naturally cooled to room temperature to obtain the Ru / Cs 0.68 Ti 1.83 O4 ammonia synthesis catalyst.

[0048] Example 2

[0049] (1) In a glove box, 0.0864 g of dodecacarbonyltriruthenium and 2 g of Cs 0.68 Ti 1.83 O4 were added to a rotary bottle with a specification of 500 mL. Then, the rotary bottle was sealed with a sealing film. The rotary bottle was transferred to room temperature conditions, 400 mL of tetrahydrofuran was quickly added, and then the solution was soaked for 2 h to obtain dodecacarbonyltriruthenium / Cs 0.68 Ti 1.83 O4;

[0050] (2) The dodecacarbonyltriruthenium / Cs 0.68 Ti 1.83 O4 obtained in step (1) was separated. The rotary evaporator was turned on, the rotation speed was set to 90 r / min, and it was rotated at room temperature for 6 h. Then, the temperature was set to 40 °C and the pressure was set to -0.1 MPa. After removing the solvent, the solid was collected and then ground in an agate mortar for 10 min and collected for standby to obtain RuOx / Cs 0.68 Ti 1.83 O4;

[0051] (3) By hydrogen reduction method, 200 mg of RuOx / Cs 0.68 Ti 1.83 O4 was put into a stainless steel catalyst reaction bed. Then, it was heated in hydrogen with a flow rate of 100 mL / min at 400 °C for 2 h, and the heating rate was 5 °C / min. The cooling process was natural cooling. After cooling to room temperature, the Ru / Cs 0.68 Ti 1.83 O4 ammonia synthesis catalyst was obtained.

[0052] Ammonia synthesis performance test

[0053] Using the Ru / Cs prepared in Example 10.68 Ti 1.83 Using Ti 1.83 O4 as the catalyst, in the ammonia synthesis process, a mixed gas with a molar ratio of H2 / N2 = 3 was introduced into the reaction at a flow rate of 60 mL / min. The reaction pressure was 5 MPa, and the heating rate was 10 °C / min. The ammonia synthesis rates were detected at reaction temperatures of 400 °C, 425 °C, 450 °C, 475 °C, and 500 °C, and the results were obtained as follows; Figure 1 ;

[0054] Using the Ru / Cs 0.68 Ti 1.83 O4 prepared in Example 1 as the catalyst, in the ammonia synthesis process, a mixed gas with a molar ratio of H2 / N2 = 3 was introduced into the reaction at a flow rate of 60 mL / min. The reaction temperature was 500 °C, and the heating rate was 10 °C / min. The ammonia synthesis rates were detected at reaction pressures of 1 MPa, 2 MPa, 3 MPa, 4 MPa, and 5 MPa, and the results were obtained as follows; Figure 2 ;

[0055] It can be found that by using Ru / Cs Figure 1 Ti 0.68 Ti 1.83 O4 prepared in the present invention as the catalyst for the ammonia synthesis reaction, as the reaction temperature rises, the ammonia synthesis rate continuously increases;

[0056] It can be seen that by using Ru / Cs Figure 2 Ti 0.68 Ti 1.83 O4 prepared in the present invention as the catalyst for the ammonia synthesis reaction, as the reaction pressure increases, the ammonia synthesis rate increases, which is contrary to the effect shown by traditional Ru-based catalysts (if there is a hydrogen poisoning phenomenon, as the pressure increases, more H2 will adsorb on the active sites, resulting in no active sites for N2 molecules to adsorb, thus showing a decrease in the reaction rate as the pressure increases), indicating that the hydrogen poisoning phenomenon has been alleviated to a certain extent.

[0057] Using the Ru / Cs 0.68 Ti 1.83 O4 prepared in Example 1 as the catalyst, in the ammonia synthesis process, a mixed gas with a molar ratio of H2 / N2 = 3 was introduced into the reaction at a flow rate of 60 mL / min. When the reaction temperature was 500 °C and the reaction pressure was 5 MPa, the activation energy required for the ammonia synthesis process was calculated by the Arrhenius equation, as shown in; Figure 3 shown;

[0058] It can be found that by using Ru / Cs Figure 3 Ti 0.68 Ti 1.83When the O4 catalyst is used for the catalytic synthesis of ammonia, the required reaction activation energy Ea = 73 kJ / mol. It can be seen that the reaction energy barrier of the catalyst provided by the present invention in the process of ammonia synthesis is greatly reduced, and the reaction is more likely to occur.

[0059] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of a ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst in ammonia synthesis, characterized in that, The preparation method of the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst comprises the following steps: Step 1): Mix dodecacarbonyltriruthenium and Cs 0.68 Ti 1.83 O4 with an organic solvent to obtain a mixed solution; Step 2): Remove the organic solvent from the mixed solution obtained in Step 1) to obtain a dry powder; Step 3): Seal the dry powder obtained in Step 2) in a vacuum environment and calcine it at 280-500 °C for 2-5 h; Step 4): Reduce the calcined powder in step 3) in a hydrogen atmosphere to obtain the ruthenium-based cesium titanium composite oxide ammonia synthesis catalyst Ru / Cs 0.68 Ti 1.83 O4; In step 1), the mass ratio of dodecacarbonyltriruthenium and Cs 0.68 Ti 1.83 O4 is 0.5 to 3:50; The reaction temperature for ammonia synthesis is 400-500 °C, and the reaction pressure is 3-7 MPa.

2. The application according to claim 1, wherein The dosage ratio of the dodecacarbonyltriruthenium to the organic solvent is 1 mg: 3-8 mL; The organic solvent comprises tetrahydrofuran.

3. The application according to claim 1 or 2, characterized in that, The removal of the organic solvent from the mixed solution prepared in Step 1) in Step 2) specifically means rotary evaporation for 3-5 h, and then rotary drying at 30-50 °C and -0.1 to 0 Mpa.

4. The application according to claim 1 or 2, characterized in that, The reduction temperature in Step 4) is 300-500 °C, the reduction time is 1-4 h, and the flow rate of hydrogen during the reduction process is 80-120 mL / min.

5. The application according to claim 1, characterized in that, In the ammonia synthesis process, the molar ratio of H2 to N2 is 2-4:1, the flow rate is 40-80 mL / min, and the heating rate is 5-20 °C / min.

6. The application according to claim 5, wherein Ru / Cs composite oxide ammonia synthesis catalyst for ammonia synthesis process 0.68 Ti 1.83 The dosage of O4 is 180 - 220 mg.

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