Preparation of rhenium-based dual-site catalyst and application thereof to synthesis of ammonia at low temperature and low pressure

Abstract

This invention provides a rhenium-based two-site catalyst for preparation and its application in low-temperature, low-pressure ammonia synthesis. The invention utilizes impregnation and calcination to prepare a KReO4 support, followed by impregnation with a transition metal and high-temperature calcination to obtain the rhenium-based two-site catalyst. KReO4 and the transition metal serve as active centers; KReO4 activates nitrogen, and the transition metal activates hydrogen, exhibiting good ammonia synthesis activity and stability under low-temperature, low-pressure conditions. Specifically, the 15% Co / KReO4 catalyst achieves an ammonia synthesis rate of 11.48 mmol g at 400℃ and 1 MPa. ‑1 h ‑1 The catalyst preparation method provided by this invention is simple, easy to mold, and has a much higher activity than previously reported rhenium-based ammonia synthesis catalysts, showing potential application prospects.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis catalyst material preparation, specifically relating to the preparation of a rhenium-based two-site catalyst and its application in low-temperature and low-pressure ammonia synthesis. Background Technology

[0002] Ammonia (NH3) is not only an important chemical raw material but also a crucial energy carrier for storing and transporting renewable energy, and one of the most widely produced chemical substances in human life. Currently, the main industrial source for ammonia synthesis is the Haber-Bosch process, which uses fossil resources as raw materials and employs iron-based or ruthenium-based catalysts to synthesize ammonia, achieving a net export value of 10-20%. However, the reaction requires high temperatures (400-500 °C) and high pressures (≥10 MPa), consuming approximately 2% of global energy and releasing about 1-2% of global carbon dioxide emissions.

[0003] With the development and utilization of renewable energy, converting it into electricity for hydrogen electrolysis and coupling it with ammonia synthesis is an important way to achieve green ammonia production. However, the output hydrogen pressure (≤5MPa) and temperature (≤400℃) of my country's pressure-type water electrolysis hydrogen production systems are far lower than the current ammonia synthesis reaction conditions. Therefore, it is necessary to develop ammonia synthesis technology that matches the reaction conditions of pressure-type water electrolysis hydrogen production. Developing efficient ammonia synthesis catalysts under mild conditions is key to solving this problem.

[0004] Compared to Fe-based catalysts, Ru-based ammonia synthesis catalysts exhibit superior activity under mild conditions. However, Ru is a precious metal with scarce reserves on Earth, which limits its large-scale application to some extent. Developing efficient non-precious metal low-temperature, low-pressure ammonia synthesis catalysts is of great significance. Rhenium metal dissociates N2 more readily than Fe and Ru, and related rhenium-based nitrides and supported rhenium-based ammonia synthesis catalysts have been reported, but efficient ammonia synthesis under mild conditions has not yet been achieved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a potassium perrhenate supported transition metal catalyst (TMs / KReO4), whose active components include TMs and KReO4.

[0006] According to an embodiment of the present invention, the TMs are selected from one or more of Fe, Co, Ni, and Mo, preferably Co.

[0007] According to an embodiment of the present invention, the loading of TMs in the catalyst is 5-30 wt.%, with examples being 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, and 30 wt.%.

[0008] In this invention, taking Co metal as an example, the loading amount refers to the weight of Co metal relative to KReO4.

[0009] Specifically, the present invention provides the following solution:

[0010] A method for preparing a rhenium-based two-site catalyst TMs / KReO4 includes the following steps:

[0011] (1) NH4ReO4 was calcined at high temperature in an NH3 atmosphere to obtain Re3N;

[0012] (2) Add an appropriate amount of KNO3 aqueous solution to the Re3N obtained in step (1) and dry it with an infrared lamp;

[0013] (3) The sample obtained in step (2) is calcined at high temperature in a reducing atmosphere for a certain time to obtain the target KReO4;

[0014] (4) Add an appropriate amount of transition metal precursor solution to the KReO4 obtained in step (3) and dry it. Then, calcine it at high temperature in a reducing atmosphere for a certain time to obtain the TMs / KReO4.

[0015] According to an embodiment of the present invention, in steps (1), (3), and (4), the high-temperature calcination temperature is 300-500 °C, exemplarily 300 °C, 350 °C, 400 °C, 450 °C, and 500 °C. The high-temperature calcination time is 2-8 hours, exemplarily 2 hours, 4 hours, 6 hours, and 8 hours.

[0016] According to the embodiment of the present invention, in steps (2) and (4), the loading method is an impregnation method, which specifically includes: placing a certain amount of carrier under an infrared lamp, adding an appropriate amount of salt solution to the carrier, drying it, and continuing to add the solution until the carrier is completely impregnated.

[0017] According to an embodiment of the present invention, in steps (3) and (4), the reducing atmosphere is a mixture of hydrogen and argon. For example, the volume fraction of H2 in the mixture is 5-25%, exemplarily 10%.

[0018] According to an embodiment of the present invention, in step (4), the transition metal precursor is selected from one or more metal precursors of Fe, Co, Ni, and Mo, preferably a Co precursor.

[0019] According to an embodiment of the present invention, in step (4), the transition metal, taking Co as an example, may have a precursor that is one or more of metallic Co, cobalt nitrate, cobalt acetylacetonate, and cobalt phthalocyanine, with cobalt nitrate being an example.

[0020] The present invention also provides the application of the above-described catalyst in ammonia synthesis.

[0021] According to an embodiment of the present invention, it is specifically used in the field of low-temperature and low-pressure thermocatalytic ammonia synthesis, specifically, using nitrogen and hydrogen as raw materials, the ammonia synthesis temperature is 400 °C and the pressure is 1 MPa.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention synthesizes a KReO4-supported transition metal dual-site catalyst by impregnation method, wherein the transition metal and KReO4 serve as active sites for ammonia synthesis. KReO4 can activate nitrogen gas, and the transition metal can activate hydrogen gas, providing a new research idea for the development of efficient Re-based ammonia synthesis catalysts.

[0024] 2. The KReO4-supported transition metal dual-site catalyst of the present invention exhibits excellent ammonia synthesis performance and long-term catalytic stability under low temperature and low pressure conditions. Figure 3 Among them, the 15% Co / KReO4 catalyst achieved an ammonia synthesis rate of 11.48 mmol g at 400 ℃ and 1 MPa. -1 h -1 .

[0025] 3. The catalyst preparation method provided by this invention is relatively simple, and the catalyst is easy to shape, which helps to reduce the cost of industrial applications.

[0026] 4. In ammonia synthesis, a basic support is preferred, while rhenium dioxide, being an acidic support, is unsuitable. Furthermore, potassium perrhenate is easily oxidized and reacts with oxygen in the air to form potassium perrhenate. Therefore, potassium perrhenate, which is stable, is chosen as the support for loading other transition metals. There are few reports on Re-based ammonia synthesis. Ryoichi Kojima et al. (Kojima R, Aika K. Rhenium containing binary catalysts for ammonia synthesis[J]. Applied catalysis. A, General, 2001, 209(1):317-325.) reported that Co-Re4 synthesized ammonia at a rate of 492 μmol g / L under conditions of 0.1 MPa and 623 K. -1 h -1 The ammonia synthesis rate of Ni-Re4 under conditions of 0.1 MPa and 623 K is 143 μmol g. -1 h -1 None of these methods can achieve efficient ammonia synthesis under mild conditions. Attached Figure Description

[0027] Figure 1 The images show the XRD patterns of the catalysts obtained in Examples 1 and 2.

[0028] Figure 2 The graphs show the ammonia synthesis performance of Co / KReO4 catalysts with different Co loadings in Examples 1 and 2.

[0029] Figure 3 The graph shows the thermal stability of the catalyst obtained in Example 2 at 400 °C. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0031] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0032] Example 1

[0033] Preparation of KReO4 catalyst

[0034] (1) Place 2 g of NH4ReO4 in a tube furnace and heat at 350 °C for 2 h under NH3 gas flow conditions, with a heating rate of 2 °C / min. -1 A black sample, Re3N, was obtained.

[0035] (2) Weigh 0.530 g of KNO3 and dissolve it in deionized water to obtain KNO3 aqueous solution. Weigh 1 g of the black sample obtained in step (1) and place it under an infrared lamp. Add the KNO3 aqueous solution dropwise to the black sample obtained in step (1). After drying, continue to add the solution until it is completely immersed in the black sample. Then place it in a 60 ℃ oven to dry for 12 h.

[0036] (3) Place the sample obtained in step (2) in a tube furnace and heat it at 400 °C for 2 h under a gas flow condition of 10% H2 / Ar by volume, with a heating rate of 2 °C / min. -1 KReO4 catalyst was obtained.

[0037] Example 2

[0038] Preparation of catalysts with different Co / KReO4 contents

[0039] The KReO4 prepared in Example 1 was combined with Co to prepare a Co / KReO4 catalyst using an initial impregnation method, as detailed below:

[0040] (1) Weigh out 0.2517 g, 0.5013 g, 0.7551 g, 1.0068 g, 1.2585 g, and 1.5102 g of Co(NO3)2·6H2O respectively and dissolve them in an appropriate amount of deionized water to obtain Co-containing solutions. Place 1 g of KReO4 catalyst under an infrared lamp and immerse it in different Co-containing solutions. Specifically, add the Co-containing solution dropwise to the KReO4 catalyst, dry it, and continue to add it dropwise until it is completely immersed on the support. Then place it in a 60 ℃ oven and dry it for 12 h to obtain the KReO4 catalyst supported on the Co precursor.

[0041] (2) The catalyst obtained in step (1) above was placed in a tube furnace and heated at 400 °C for 2 h under a gas flow condition of 10% H2 / Ar by volume, with a heating rate of 2 °C / min. -1 5%, 10%, 15%, 20%, 25%, and 30% Co / KReO4 catalysts were obtained.

[0042] Example 3

[0043] Preparation of 5% Fe / KReO4 catalyst

[0044] (1) Dissolve 0.3797 g Fe(NO3)3·9H2O in an appropriate amount of deionized water to obtain a Fe-containing solution. Place 1 g KReO4 catalyst under an infrared lamp and immerse it in the Fe-containing solution. Specifically, add the Fe-containing solution dropwise to the KReO4 catalyst, dry it, and continue to add it dropwise until it is completely immersed on the support. Then place it in a 60 ℃ oven to dry for 12 h to obtain a KReO4 catalyst supported on the Fe precursor.

[0045] (2) The catalyst obtained in step (1) above was placed in a tube furnace and heated at 400 °C for 2 h under a gas flow condition of 10% H2 / Ar by volume, with a heating rate of 2 °C / min. -1 A 5% Fe / KReO4 catalyst was obtained.

[0046] Example 4

[0047] Preparation of 5% Ni / KReO4 catalyst

[0048] (1) Dissolve 0.2596 g Ni(NO3)2·6H2O in an appropriate amount of deionized water to obtain a Ni-containing solution. Place 1 g KReO4 catalyst under an infrared lamp and immerse it in the Ni-containing solution. Specifically, add the Ni-containing solution dropwise to the KReO4 catalyst, dry it, and continue adding until the catalyst is completely immersed in the support. Then place it in a 60 ℃ oven to dry for 12 h to obtain a KReO4 catalyst supported on a Ni precursor.

[0049] (2) The catalyst obtained in step (1) above was placed in a tube furnace and heated at 400 °C for 2 h under a gas flow condition of 10% H2 / Ar by volume, with a heating rate of 2 °C / min. -1 A 5% Ni / KReO4 catalyst was obtained.

[0050] Example 5

[0051] Preparation of 5% Mo / KReO4 catalyst

[0052] (1) Take 0.6774 g of (NH4)2Mo4O 13 Dissolve the KReO4 catalyst in an appropriate amount of deionized water to obtain a Mo-containing solution. Place 1 g of KReO4 catalyst under an infrared lamp and immerse it in the Mo-containing solution. Specifically, add the Mo-containing solution dropwise to the KReO4 catalyst, dry it, and continue adding it dropwise until the entire support is immersed. Then place it in a 60 °C oven to dry for 12 h to obtain a KReO4 catalyst supported on a Mo precursor.

[0053] (2) The catalyst obtained in step (1) above was placed in a tube furnace and heated at 400 °C for 2 h under a gas flow condition of 10% H2 / Ar by volume, with a heating rate of 2 °C / min. -1 A 5% Mo / KReO4 catalyst was obtained.

[0054] Test Example 1

[0055] Ammonia synthesis catalyst performance evaluation

[0056] Weigh 0.20 g of the catalyst from the above examples; the gas hourly space velocity (GHSV) of the reaction is 60,000 mL g. -1 h -1 The ammonia synthesis rate was determined using an ammonia synthesis catalyst performance evaluation device. The change in NH3 concentration in the outlet tail gas was determined by ion chromatography (Thermo Scientific, DIONEX, ICS-600). The composition of the reaction gas was 25 vol % N2 + 75 vol % H2. The ammonia synthesis rate of the catalyst was determined at 400 ℃ and 1 MPa.

[0057] Table 1 shows the ammonia synthesis performance of the catalysts obtained in Examples 1-5.

[0058] Table 1

[0059]

[0060] The exemplary embodiments of the present invention have been described above. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a rhenium-based two-site catalyst for catalytic ammonia synthesis, characterized in that, The active components of the rhenium-based dual-site catalyst are a transition metal and KReO4; KReO4 serves as both the support and the active component in the catalyst; the transition metal is selected from one or more of Fe, Co, Ni, and Mo; the loading of the transition metal in the catalyst is 5-20 wt%; and the KReO4 precursor is ammonium perrhenate. The carrier preparation method includes the following steps: (1) NH4ReO4 was calcined at high temperature under a specific atmosphere to obtain Re3N; (2) Dissolve an appropriate amount of KNO3 in deionized water; (3) Add the KNO3 aqueous solution from step (2) dropwise to the Re3N obtained in step (1) and dry it; (4) The product obtained in step (3) is calcined at high temperature under a reducing atmosphere to obtain KReO4 support; an appropriate amount of transition metal precursor solution is added dropwise to the KReO4 obtained in step (4) and dried, and then calcined at high temperature in a reducing atmosphere for a certain time to obtain the rhenium-based dual-site catalyst. The specific atmosphere mentioned in step (1) is NH3 gas, the calcination temperature is 350 ℃, and the high-temperature calcination time is 2-3 h; The reducing atmosphere in step (4) is selected from a mixture of hydrogen and argon, the calcination temperature is 400 ℃, and the high-temperature calcination time is 2h.

2. The production method according to claim 1, characterized by, The preparation method involves loading a transition metal onto a KReO4 support via impregnation, and includes the following steps: 1) Dissolve an appropriate amount of transition metal precursor in deionized water; 2) Add the aqueous solution of the transition metal precursor from step 1) dropwise onto the KReO4 support and dry it; 3) The product obtained in step 2) is calcined at high temperature for a certain time under a reducing atmosphere to obtain the rhenium-based two-site catalyst.

3. The preparation method according to claim 2, characterized in that, The transition metal precursor is a transition metal nitrate.

4. The production method according to claim 2, characterized by, The reducing atmosphere in step 3) is selected from a mixture of hydrogen and argon, the calcination temperature is 400 ℃, and the high-temperature calcination time is 2-3 h.

5. A rhenium-based two-site catalyst prepared by the method according to any one of claims 1-4.

6. The application of the rhenium-based dual-site catalyst according to claim 5 in the field of thermocatalytic ammonia synthesis.

7. Use according to claim 6, characterized in that, The temperature for ammonia synthesis is 400℃ and the pressure is 1 MPa.

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