Preparation method and application of a supported molybdenum nitride catalyst suitable for high-temperature reverse water gas shift reaction

Abstract

This invention discloses a method for preparing a supported molybdenum nitride catalyst suitable for high-temperature countercurrent water gas shift reactions. The invention innovatively employs a bottom-up synthesis strategy, first highly dispersing the molybdenum salt precursor on the support surface, and then directly performing amination treatment in an ammonia atmosphere without oxidation. This achieves the controllable synthesis of small-sized molybdenum nitride, yielding highly dispersed molybdenum nitride material. The highly dispersed molybdenum nitride catalyst prepared by this method exhibits high activity, high CO selectivity, and good stability in countercurrent water gas shift reactions, remaining active even after repeated cycling for extended periods, and shows broad application prospects in the field of high-temperature countercurrent water gas.

Description

(I) Technical Field

[0001] This invention relates to a method for preparing and applying a highly active and stable supported molybdenum nitride catalyst suitable for high-temperature countercurrent water gas reaction. (II) Background Technology

[0002] CO2 catalytic conversion is an effective means of mitigating global climate change and ocean threats. Among these, the conversion of CO2 into platform small molecule CO (CO can be synthesized into high-value-added chemicals through the mature Fischer-Tropsch process) has important industrial applications (Applied Catalysis B: Environmental, 2021, 284). Noble metals are considered very effective catalysts (Advanced Energy Materials, 2023, 13(12): 2203806), but their disadvantages are scarcity, high price, and poor high-temperature selectivity and stability (Applied Catalysis B: Environmental, 2021, 291: 120101). However, from the perspective of thermodynamic chemical equilibrium, high temperature is more conducive to the reverse water-gas shift reaction, and its equilibrium conversion rate will be further improved. Therefore, the development of high-temperature reverse water-gas shift reaction has greater industrial potential. The most crucial aspect of this is the development of highly efficient catalysts.

[0003] Molybdenum carbide catalysts (Physical Chemistry Chemical Physics, 2022, 24(27): 16556-16565.) possess noble metal-like catalytic properties and have been used in reverse water-gas shift reactions, but they suffer from complex preparation methods and low CO selectivity. Besides molybdenum carbide catalysts, nitride materials recently discovered by Lin et al. (Chinese Journal of Chemical Engineering, 2022, 43: 248-254.), such as molybdenum nitride, also exhibit high CO selectivity in reverse water-gas shift reactions. However, due to their bulk structure, they have small specific surface areas and limited exposed active sites, resulting in low catalytic activity. Therefore, the development of highly dispersed molybdenum nitride catalysts with fully exposed active sites is urgently needed. (III) Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a highly active and stable supported molybdenum nitride catalyst suitable for high-temperature countercurrent gas reactions. The preparation method is simple, low-cost, safe and efficient. When this type of catalyst is applied to the CO2 hydrogenation to CO reaction, it exhibits high catalytic activity, good stability and high CO selectivity at high temperatures. It has promising industrial application prospects in the field of high-temperature countercurrent gas and solves the problems of high cost, poor stability and low CO selectivity in existing technologies.

[0005] The technical solution adopted in this invention is:

[0006] This invention provides a method for preparing a highly active and stable supported molybdenum nitride catalyst suitable for high-temperature countercurrent water-gas reactions, the method comprising the following steps:

[0007] (1) Dissolve molybdic acid or molybdate thoroughly in water to obtain solution A;

[0008] (2) The solution A obtained in step (1) is uniformly impregnated on the carrier to form precursor B;

[0009] (3) In step (2), precursor B is dried thoroughly at 60-120℃ for 10-15h to obtain solid powder;

[0010] (4) The solid powder in step (3) is calcined at 500-800℃ for 1-6h in an ammonia atmosphere to obtain a highly dispersed supported molybdenum nitride catalyst.

[0011] Furthermore, in step (1), the molybdate is selected from one or more of ammonium molybdate tetrahydrate, ammonium molybdate, and sodium molybdate; the volume of water used is 1-15 mL / g (preferably 6-9 mL / g) based on the mass of molybdic acid or molybdate.

[0012] Further, the support in step (2) comprises silica, alumina, cerium oxide, or a mesoporous molecular sieve, preferably silica or mesoporous molecular sieve MCM-41. The volume of solution A is 1-5 mL / g (preferably 2.5 mL / g) based on the mass of the support. The loading of molybdenum nitride is 20-30% based on the mass of the catalyst.

[0013] Further, step (3) involves drying at 80°C for 12 hours.

[0014] Furthermore, in step (4), the ammonia atmosphere is pure ammonia (NH3) or a mixture containing ammonia. The mixture is calcined at 700-800℃ for 4-6 hours.

[0015] This invention also provides an application of the supported molybdenum nitride catalyst prepared by the method described above in a high-temperature countercurrent water gas reaction. The method of application is as follows: the supported molybdenum nitride catalyst is added to a fixed bed, and a mixture of CO2 and H2 gas (CO2 to H2 volume ratio of 1:7-7:10) is introduced to complete the process of CO2 hydrogenation to CO. The reaction temperature is 200-600℃, and the reaction space velocity is 20000-60000 ml / g. cat / h, reaction pressure is atmospheric pressure.

[0016] Furthermore, the volume ratio of CO2 to H2 is 1:3. The reaction temperature is 500-550℃, and the reaction space velocity is 36000-50000 ml / g. cat / h.

[0017] Furthermore, the gas mixture is introduced at a rate of 70-100 mL / min, preferably 83 mL / min.

[0018] Furthermore, the catalyst addition amount is 2-4 mg / cm³ based on the effective volume of the fixed bed. 3 .

[0019] Furthermore, the fixed bed is a quartz tube, preferably with an inner diameter of 8 mm, an outer diameter of 11 mm, and a length of 59 cm.

[0020] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0021] This invention innovatively employs a bottom-up synthesis strategy, first highly dispersing the molybdenum salt precursor on the support surface, and then directly ammonifying it in an ammonia atmosphere without oxidation treatment. This achieves the controllable synthesis of small-sized molybdenum nitride, yielding highly dispersed molybdenum nitride materials. Compared to existing methods that first oxidize the molybdenum salt to form molybdenum oxide and then perform programmed ammoniation to form a bulk molybdenum nitride catalyst, this invention not only has a simpler preparation process, eliminates the need for oxidation treatment, but also produces a highly dispersed and highly active molybdenum nitride catalyst with excellent hydrogenation performance and catalytic stability.

[0022] The catalytic performance of the molybdenum nitride catalyst prepared by the method of this invention is as follows: with a flow rate of 83 mL / min for a mixture of CO2 and H2 (CO2 to H2 volume ratio of 1:3), a reaction temperature of 550 °C, and a reaction space velocity of 50000 mL / g. cat The reaction was carried out at atmospheric pressure for 6 hours, with a CO2 conversion rate of over 50% and a CO selectivity of over 99.9%.

[0023] The molybdenum nitride catalyst prepared by this invention exhibits good high-temperature stability. When a mixture of CO2 and H2 (CO2 to H2 volume ratio of 1:3) is introduced at a flow rate of 83 mL / min, the reaction temperature is 550 °C, and the reaction space velocity is 50000 mL / g. cat The reaction was carried out at atmospheric pressure for nearly 250 hours. The CO2 conversion rate remained at 50%, the CO selectivity was over 99%, and there was almost no loss of CO. It also showed good high-temperature stability.

[0024] The highly dispersed molybdenum nitride catalyst prepared by the method of this invention exhibits high activity, high CO selectivity, and good stability in the reverse water gas shift reaction. It does not deactivate even after repeated cycles for a long time and has broad application prospects in the field of high-temperature reverse water gas. (iv) Description of the attached drawings

[0025] Figure 1 XRD pattern (a) and XPS pattern (b) of molybdenum nitride prepared in Example 1.

[0026] Figure 2 Scanning electron microscope mapping image of molybdenum nitride prepared in Example 1.

[0027] Figure 3 CO2 conversion and CO selectivity histogram of molybdenum nitride prepared in Example 1.

[0028] Figure 4 High-temperature stability diagram of molybdenum nitride prepared in Example 1 at 550°C.

[0029] Figure 5 Comparison of CO2 conversion and CO selectivity bar charts for molybdenum nitride and Pt-based catalysts prepared in Example 1.

[0030] Figure 6 Comparison of CO2 conversion rates at 550°C between the catalyst prepared using conventional synthesis methods and the catalyst prepared in Example 1.

[0031] Figure 7 XRD pattern of molybdenum nitride prepared in Example 2.

[0032] Figure 8 Scanning electron microscope mapping image of molybdenum nitride prepared in Example 2.

[0033] Figure 9 CO2 conversion rate and CO selectivity of molybdenum nitride prepared in Example 2: bar graph.

[0034] Figure 10 XRD pattern of molybdenum nitride prepared in Example 3.

[0035] Figure 11Example 3: CO2 conversion rate and CO selectivity of molybdenum nitride prepared in Example 3.

[0036] Figure 12 XRD pattern of molybdenum nitride prepared in Example 4.

[0037] Figure 13 Example 4: CO2 conversion rate and CO selectivity histogram of molybdenum nitride prepared in Example 4. (V) Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0039] Example 1: Preparation and Performance Testing of Supported Molybdenum Nitride Catalyst

[0040] 1. Preparation of supported molybdenum nitride catalysts

[0041] (1) Dissolve 300.52 mg of molybdic acid in 2.5 mL of water to obtain 2.5 mL of solution A;

[0042] (2) 2.5 mL of solution A obtained in step (1) is uniformly impregnated onto 1 g of silica to form precursor B;

[0043] (3) The precursor B obtained in step (2) is dried at 80°C for 12 hours to obtain a solid powder;

[0044] (4) Add all the solid powder obtained in step (3) to a tube furnace and calcine at 750°C for 6 hours under an ammonia atmosphere to obtain 1.5g of highly dispersed supported molybdenum nitride catalyst, denoted as Mo2N / SiO2, with a particle size of about 10nm and a molybdenum nitride mass loading of 20%.

[0045] XRD patterns of Mo2N / SiO2, Mo2N, and SiO2 are shown below. Figure 1 As shown in figure a, Mo2N was successfully loaded onto the surface of SiO2; the XPS plot of Mo2N / SiO2 is shown in figure a. Figure 1 Figure b demonstrates that the prepared Mo2N / SiO2 contains Mo-N bonds; the scanning electron microscope mapping image of Mo2N / SiO2 is shown below. Figure 2 In summary, it can be seen that a highly dispersed molybdenum nitride catalyst has been successfully prepared.

[0046] 2. Performance Testing

[0047] (1) Effect of different calcination temperatures on catalyst performance

[0048] 0.1 g of the supported molybdenum nitride catalyst prepared in step 1 was packed into a quartz tube (model ICES5F2H, Xiamen Baidewo Intelligent Technology Co., Ltd., quartz reaction tube inner diameter 8 mm, outer diameter 11 mm, length 59 cm) in a catalytic evaluation device. The catalyst dosage was 3 mg / cm³ based on the effective volume of the fixed bed. 3 A mixture of CO2 and H2 gas (CO2 to H2 volume ratio of 1:3) was introduced at a flow rate of 83 mL / min. The reaction temperatures were 300, 350, 400, 450, 500, and 550 °C, and the reaction space velocity was 50,000 mL / g. cat The reaction was carried out at atmospheric pressure for 6 hours, completing the process of CO2 hydrogenation to CO. Results of CO2 conversion and CO selectivity are shown below. Figure 3 As shown in Table 1, it can be seen that the CO2 conversion rate of the supported molybdenum nitride catalyst prepared in step 1 increases with increasing temperature, and the CO selectivity gradually increases and stabilizes.

[0049] (2) High-temperature stability of the catalyst

[0050] Change the temperature in step (1) to 550℃, keeping other conditions unchanged. The results for CO2 conversion rate and CO selectivity are shown below. Figure 4 As shown, after nearly 250 hours of reaction, the CO2 conversion rate remained at 50%, the CO selectivity was over 99%, with almost no loss, and the high-temperature stability was good.

[0051] (3) The effect of catalyst type on CO2 conversion

[0052] The reaction temperature in step (1) was changed to 450, 500, 550, and 600℃ respectively, while other operations remained unchanged. Pt / CeO2 (preparation method referred to in Journal of Environmental Chemical Engineering, 2020, 8(5):104236. optimal conditions) was used as a control. The results are shown in […]. Figure 5 .

[0053] Figure 5 This indicates that the CO selectivity of highly dispersed molybdenum nitride catalysts does not decrease compared to noble metal Pt-based catalysts, while the CO selectivity of noble metal Pt-based catalysts decreases with increasing reaction temperature. Therefore, highly dispersed molybdenum nitride catalysts are superior to Pt-based catalysts.

[0054] Comparative Example 1: Supported molybdenum nitride catalyst synthesized by conventional methods

[0055] A supported molybdenum nitride catalyst was prepared using the traditional temperature-programmed ammoniation method (prepared under optimal conditions according to the literature, Wu Zili. Infrared Spectroscopic Study on Simple Molecular Adsorption and Activation on Supported Molybdenum Nitride Catalysts [D]. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 2001.). The catalyst was tested using the method of Example 1, and its performance was far inferior to the highly dispersed molybdenum nitride catalyst prepared in Example 1, as shown in Figure 6.

[0056] Example 2: Preparation and Performance Testing of Supported Molybdenum Nitride Catalyst

[0057] 1. Preparation of supported molybdenum nitride catalysts

[0058] (1) Dissolve 300.52 mg of ammonium molybdate in 2.5 mL of water to obtain 2.5 mL of solution A;

[0059] (2) 2.5 mL of solution A obtained in step (1) is uniformly impregnated onto 1 g of silica to form precursor B;

[0060] (3) The precursor B obtained in step (2) is dried at 80°C for 12 hours to obtain a solid powder;

[0061] (4) Add all the solid powder obtained in step (3) to a tube furnace and calcine at a constant temperature of 750°C for 6 hours under an ammonia atmosphere to obtain 1.5g of highly dispersed supported molybdenum nitride catalyst with a molybdenum nitride mass loading of 20%.

[0062] See XRD diagram Figure 7 XRD analysis confirms the successful preparation of the molybdenum nitride catalyst. Scanning electron microscopy mapping analysis shows that the prepared molybdenum nitride catalyst is highly dispersed, as shown in the image. Figure 8 As shown.

[0063] 2. Performance Testing

[0064] The supported molybdenum nitride catalyst prepared in step 1 was tested under the same conditions as in step 2(1) of Example 1. The CO2 conversion rate and CO selectivity results are shown in [reference needed]. Figure 9 As shown in Table 1.

[0065] Example 3: Preparation and performance testing of supported molybdenum nitride catalysts

[0066] 1. Preparation of supported molybdenum nitride catalysts

[0067] (1) Dissolve 300.52 mg of molybdic acid in 1.5 mL of water to obtain 1.5 mL of solution A;

[0068] (2) 1.5 mL of solution A obtained in step (1) is uniformly impregnated onto 1 g of silicon dioxide to form precursor B;

[0069] (3) The precursor B obtained in step (2) is dried at 80°C for 12 hours to obtain a solid powder;

[0070] (4) Add all the solid powder obtained in step (3) to a tube furnace and calcine at 800°C for 4 hours under an ammonia atmosphere to obtain 1.4 g of highly dispersed supported molybdenum nitride catalyst with a molybdenum nitride mass loading of 20%.

[0071] See XRD diagram Figure 10 XRD results show that the molybdenum nitride catalyst was successfully prepared.

[0072] 2. Performance Testing

[0073] The supported molybdenum nitride catalyst prepared in step 1 was tested under the same conditions as in step 2(1) of Example 1. The CO2 conversion rate and CO selectivity results are shown in [reference needed]. Figure 11 As shown in Table 1.

[0074] Example 4: Preparation and performance testing of supported molybdenum nitride catalyst

[0075] 1. Preparation of supported molybdenum nitride catalysts

[0076] (1) Dissolve 300.52 mg of molybdic acid in 2 mL of water to obtain 2 mL of solution A;

[0077] (2) 2 mL of solution A obtained in step (1) is uniformly impregnated onto 1 g of mesoporous molecular sieve MCM-41 to form precursor B;

[0078] (3) The precursor B obtained in step (2) is dried at 80°C for 12 hours to obtain a solid powder;

[0079] (4) Add all the solid powder obtained in step (3) to a tube furnace and calcine at 700°C for 5 hours under an ammonia atmosphere to obtain 1.2g of highly dispersed supported molybdenum nitride catalyst with a molybdenum nitride mass loading of 20%.

[0080] See XRD diagram Figure 12 XRD results show that the molybdenum nitride catalyst was successfully prepared.

[0081] 2. Performance Testing

[0082] The supported molybdenum nitride catalyst prepared in step 1 was tested under the same conditions as in step 2(1) of Example 1. The CO2 conversion rate and CO selectivity results are shown in [reference needed]. Figure 13 As shown in Table 1.

[0083] Table 1. Conversion rate and CO selectivity of highly dispersed molybdenum nitride synthesized under different conditions.

[0084]

[0085] a. Test conditions: CO2:H2 = 1:3, reaction temperature 550℃, reaction space velocity 50000 ml / g cat / h, the reaction pressure is atmospheric pressure, and the control catalyst is prepared by impregnation method (Journal of Environmental Chemical Engineering, 2020, 8(5): 104236.).

[0086] b. Test conditions: CO2:H2 = 1:3, reaction temperature 450℃, reaction space velocity 36000 ml / g cat The reaction pressure was atmospheric pressure, and the control catalyst was prepared by impregnation method (Research on Chemical Intermediates, 2019, 45: 5125-5141.).

Claims

1. A method for preparing a supported molybdenum nitride catalyst suitable for high-temperature countercurrent water-gas reaction, characterized in that, The method includes the following steps: (1) Dissolve molybdic acid or molybdate thoroughly in water to obtain solution A; (2) The solution A obtained in step (1) is uniformly impregnated on the carrier to form precursor B; (3) In step (2), precursor B is dried thoroughly at 60-120℃ for 10-15h to obtain solid powder; (4) The solid powder in step (3) is calcined at 500-800℃ for 1-6h in an ammonia atmosphere to obtain a highly dispersed supported molybdenum nitride catalyst.

2. The method as described in claim 1, characterized in that, In step (1), the molybdate is selected from one or more of ammonium molybdate tetrahydrate, ammonium molybdate, and sodium molybdate.

3. The method as described in claim 1, characterized in that, The volumetric amount of water used is 1-15 mL / g, calculated by mass of molybdic acid or molybdate.

4. The method as described in claim 1, characterized in that, The carrier in step (2) includes silica, alumina, cerium oxide or mesoporous molecular sieve.

5. The method as described in claim 1, characterized in that, The volume of solution A used in step (2) is 1-5 mL / g based on the mass of the carrier.

6. The method as described in claim 1, characterized in that, Step (3) Dry at 80℃ for 12 hours.

7. The method as described in claim 1, characterized in that, Step (4) The ammonia atmosphere is pure ammonia or a mixture containing ammonia.

8. The method as described in claim 1, characterized in that, Step (4) calcination at 700-800℃ for 4-6 hours.

9. The application of a supported molybdenum nitride catalyst prepared by the method of claim 1 in a high-temperature countercurrent water gas reaction.

10. The application as described in claim 9, characterized in that, The application method is as follows: the supported molybdenum nitride catalyst is added to a fixed bed, and a mixture of CO2 and H2 gas is introduced to complete the process of CO2 hydrogenation to CO. The reaction temperature is 200-600℃, and the reaction space velocity is 20000-60000 ml / g. cat The reaction pressure is atmospheric pressure; the volume ratio of CO2 to H2 is 1:7-7:10; the gas flow rate is 70-100 mL / min.

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