Method for synthesizing ammonia and application

Abstract

The invention discloses a method for synthesizing ammonia, which is characterized in that nitrogen and hydrogen are used as reaction gases, and ammonia is synthesized under the normal pressure or low pressure condition under the action of a gaseous molecular accelerator and a catalyst, wherein the gaseous molecule accelerant is nitrogen oxide. Nitrogen oxide can react with hydrogen to generate ammonia, and active oxygen atoms generated by the reaction can activate nitrogen molecules, so that the ammonia synthesis reaction of nitrogen and hydrogen is greatly promoted, and efficient ammonia synthesis of nitrogen and hydrogen under normal pressure is realized. The synthesis ammonia reaction under the molecular accelerator can also be carried out at low pressure, and the synthesis ammonia rate and conversion rate can be improved by properly increasing the reaction pressure. Besides, a reaction system is optimized, such as reaction process parameters of a catalyst, air speed, composition, pressure, temperature and the like, so that the rate and the conversion rate of ammonia synthesis are also favorably improved, and the rate and the conversion rate of ammonia synthesis close to or exceeding those of traditional industrial Have-Bosch high-temperature and high-pressure ammonia synthesis are realized.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a method and application for synthesizing ammonia. Background Technology

[0002] Under the dual-carbon strategy, ammonia-hydrogen fusion has become a current development direction for green energy technologies. Besides being used as a basic chemical raw material in fertilizer production, ammonia (NH3) is also an excellent hydrogen storage carrier and zero-carbon fuel, with a hydrogen content as high as 17.7 wt% and an energy density as high as 3 kWh / kg. -1 This can achieve zero carbon emissions in the final energy source. Traditional industrial ammonia synthesis uses the Haber-Bosch process, which typically uses nitrogen (N2) and hydrogen (H2) as raw materials. The reaction is carried out under high temperature (300-500℃), high pressure (20-30MPa) and catalyst (such as iron catalyst) conditions to produce ammonia, as shown in formula (1).

[0003] (1) High temperatures are used to increase the rate of ammonia synthesis, but since this reaction is exothermic, high temperatures are detrimental to the forward reaction. Therefore, to balance this contradiction, industrial processes employ higher reaction temperatures and pressures to ensure a higher reaction rate and a certain ammonia synthesis rate. High pressure is crucial for increasing the ammonia synthesis rate because it involves a reduction in volume; pressure promotes the forward reaction. To increase the ammonia synthesis rate and conversion rate, pressures as high as 20-30 MPa are often required, with conversion rates typically between 10-20%. Therefore, traditional industrial Haber-Bosch ammonia synthesis is a high-energy-consuming and high-emission process.

[0004] Given that high-pressure processes are energy-intensive and place stringent requirements on production equipment to withstand high pressure, researchers are dedicated to exploring new ammonia synthesis technologies under milder conditions. These technologies reduce the pressure required for the ammonia synthesis reaction, thus saving energy and protecting the environment. However, existing ammonia synthesis technologies still require relatively high pressures (10-15 MPa) to ensure the ammonia synthesis rate and conversion rate required for industrialization. Summary of the Invention

[0005] This invention aims to reduce the high pressure problem in the Haber-Bosch process for ammonia synthesis and proposes a new method for ammonia synthesis. This method introduces a small amount of gaseous molecular promoter into the reaction system of nitrogen and hydrogen, and with the action of conventional catalysts, it can achieve efficient ammonia synthesis at high temperature (400-600℃) and normal pressure (0.1MPa).

[0006] The inventive concept of this invention is as follows: Traditional industrial Haber-Bosch high-temperature, high-pressure ammonia synthesis uses nitrogen and hydrogen as reactant gases, without introducing nitrogen oxides. The main reasons for this are: First, nitrogen is an inert gas with stable molecules, readily available and inexpensive from the air; while nitrogen oxides are a major pollutant in automobile exhaust, with reactive and unstable molecules that are easily oxidized in the air. Second, nitrogen is non-toxic and harmless, while nitrogen oxides have certain corrosive and toxic properties. Third, the reaction of nitrogen and hydrogen only produces ammonia, while the reaction of nitrogen oxides with hydrogen produces both ammonia and water, which is detrimental to the performance and lifespan of the catalyst. This invention breaks with convention, proposing a method for synthesizing ammonia at high temperature and ambient pressure (or low pressure) with a molecular promoter. By introducing a small amount of nitrogen oxides as a molecular promoter into the hydrogen and nitrogen reaction system (the small amount of nitrogen oxides has low corrosiveness and toxicity), the nitrogen oxides can react with hydrogen to produce ammonia, and the reactive oxygen atoms generated in the reaction can activate nitrogen molecules, thereby greatly promoting the ammonia synthesis reaction between nitrogen and hydrogen, and thus achieving efficient ammonia synthesis from nitrogen and hydrogen at ambient pressure. Of course, the ammonia synthesis reaction under the molecular promoter of this invention can also be carried out at low pressure (0.2-5 MPa). Appropriately increasing the reaction pressure will improve the rate and conversion of ammonia synthesis. In addition, by optimizing the reaction system, such as the solid catalyst, system space velocity, system composition, reaction pressure, and reaction temperature, it is also beneficial to improve the rate and conversion of ammonia synthesis, achieving rates and conversions close to or exceeding those of traditional industrial Haber-Bosch high-temperature and high-pressure ammonia synthesis.

[0007] To solve the above-mentioned technical problems, the first aspect of the present invention provides a method for synthesizing ammonia, using nitrogen and hydrogen as reaction gases, and synthesizing ammonia under normal or low pressure conditions in the presence of a gaseous molecule promoter and a catalyst; wherein the gaseous molecule promoter is a nitrogen oxide.

[0008] In some embodiments of the present invention, the nitrogen oxide is selected from nitric oxide (NO) or nitrogen dioxide (NO2); preferably, the nitrogen oxide is NO. NO reacts with H2 to produce NH3, and the reactive oxygen atoms generated simultaneously activate N2, which can greatly promote the synthesis of ammonia from nitrogen and hydrogen under normal pressure.

[0009] In some embodiments of the present invention, the volume ratio of nitrogen to hydrogen is (0.2-2):1, that is, 2:1 to 1:5; such as 2:1, 1:1, 1:2, 1:3, 1:4 or 1:5, etc., including but not limited to the listed values. At the same time, other unlisted values ​​within the range are also applicable.

[0010] In some embodiments of the present invention, the amount of the gaseous molecule promoter introduced is 0.2-10 vol% of the reactant gas. Preferably, the amount of the gaseous molecule promoter introduced is 1-5 vol% of the reactant gas.

[0011] In some embodiments of the present invention, the low pressure is 0.2-5 MPa, and increasing the reaction pressure will increase the ammonia synthesis rate and conversion rate.

[0012] In some embodiments of the present invention, the synthesis temperature is 300-700°C; preferably, the synthesis temperature is 450-550°C.

[0013] In some embodiments of the present invention, the catalyst is selected from at least one of iron-based catalysts, ruthenium-based catalysts, cobalt-based catalysts, metal nitride catalysts, doped metal nitride catalysts, doped transition metal catalysts, and doped oxygen ion conductor oxide catalysts. The choice of catalyst affects the ammonia synthesis rate and conversion rate under the molecular promoter conditions of the present invention.

[0014] In some embodiments of the present invention, the ruthenium-based catalyst is a ruthenium-doped catalyst, such as a ruthenium-doped lanthanum ferrite catalyst, wherein the doping amount of ruthenium is 1-5 wt%.

[0015] In some embodiments of the present invention, the iron-based catalyst is an iron-containing catalyst, such as an iron catalyst, iron powder, porous foamed iron, etc. The porous foamed iron can be industrial or commercial porous foamed iron, or porous foamed iron impregnated with active substances such as metal oxides, metal nitrides, metals, or oxygen ion conductor oxides.

[0016] In some embodiments of the present invention, the method for synthesizing ammonia includes the following steps: The catalyst is placed in a reactor, heated, and treated with a reducing atmosphere. Then, a reaction gas and a gaseous molecular promoter are introduced to carry out the reaction. The gaseous products are collected to obtain the ammonia.

[0017] In some embodiments of the present invention, the space velocity of the reactant gas and the gaseous molecule promoter is 6000-60000 mL·h. -1 ·g cat -1 Preferably, the space velocity is 10000-30000 mL·h -1 ·g cat -1 More preferably, the space velocity is 10000-15000 mL·h -1 ·g cat -1 Changing the space velocity will also affect the ammonia synthesis rate and conversion rate under the molecular promoter conditions of this invention.

[0018] In some embodiments of the present invention, the reactor is made of stainless steel or quartz glass. The ammonia synthesis reaction of the present invention can be effectively carried out in either stainless steel or quartz glass reactors.

[0019] Meanwhile, the ammonia synthesis reaction of this invention is carried out under normal or low pressure, thus eliminating the need for high-pressure equipment and processes (such as the six-stage compression section) found in traditional industrial Haber-Bosch systems. Only the addition of a molecular promoter generating device (such as a plasma generator) to the nitrogen production unit is required to achieve efficient and large-scale ammonia production. Compared to traditional industrial Haber-Bosch systems, this invention offers advantages such as a simpler process flow, lower energy consumption, easier operation, and higher safety, facilitating its industrial application.

[0020] A second aspect of the present invention provides the application of the above-described method for synthesizing ammonia in the conversion of renewable energy into liquid ammonia.

[0021] In some embodiments of the present invention, the renewable energy source includes wind energy, solar energy, marine energy, etc.

[0022] Due to the atmospheric or low-pressure characteristics of the ammonia synthesis reaction of this invention, its preparation process can be small-scale and modularized, which is conducive to the efficient conversion of renewable wind energy, solar energy, and offshore wind power into liquid ammonia, realizing green ammonia synthesis and efficient storage of renewable energy in remote areas and at sea, and has good application prospects.

[0023] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages: (1) This invention proposes a method for synthesizing ammonia under normal pressure. By introducing a small amount of nitrogen oxides as a molecular promoter into the reaction system of hydrogen and nitrogen, the nitrogen oxides can react with hydrogen to produce ammonia, and the reactive oxygen atoms generated in the reaction can activate nitrogen molecules, thereby greatly promoting the reaction of nitrogen and hydrogen to synthesize ammonia, thus achieving efficient ammonia synthesis from nitrogen and hydrogen under normal pressure. At a space velocity of 12000 mL·h -1 ·g cat -1 Under reaction temperatures of 450-550℃, the ammonia synthesis rate under the condition of introducing a molecular promoter is increased by 1-3 orders of magnitude compared with the condition of not introducing a molecular promoter; the ammonia conversion rate under the condition of introducing a molecular promoter can reach up to 7.1%, which is close to the conversion rate of industrial ammonia synthesis.

[0024] (2) The ammonia synthesis reaction of the present invention can also be carried out under low pressure (0.2-5 MPa). Appropriately increasing the reaction pressure will increase the ammonia synthesis rate and conversion rate. Furthermore, optimizing the reaction process parameters such as catalyst, space velocity, composition, pressure and temperature of the reaction system is also beneficial to improving the ammonia synthesis rate and conversion rate, achieving a rate and conversion rate close to or exceeding that of traditional industrial Haber-Bosch high-temperature and high-pressure ammonia synthesis.

[0025] (3) The method for synthesizing ammonia in this invention has a wide range of catalysts to choose from. It can be at least one of ruthenium-based catalysts, cobalt-based catalysts, metal nitride catalysts, doped metal nitride catalysts, doped transition metal catalysts, and doped oxygen ion conductor oxide catalysts. It can also be an industrial or commercial Haber-Bosch iron-based catalyst, such as iron catalyst, iron powder, porous foam iron, etc., to reduce the cost of catalysts.

[0026] (4) By introducing a molecular promoter, this invention has for the first time achieved efficient ammonia synthesis at high temperature and normal pressure or low pressure, effectively solving the high pressure problem of nitrogen and hydrogen ammonia synthesis reaction, greatly reducing the energy consumption of ammonia synthesis process, and the ammonia synthesis rate and conversion rate have reached the level of existing industrial Haber-Bosch ammonia synthesis application. Due to its characteristics of ammonia synthesis at normal pressure or low pressure, it can realize small-scale and modular process flow, effectively converting renewable energy such as wind energy, solar energy and offshore wind power into liquid ammonia, realizing green ammonia synthesis and efficient storage of renewable energy in remote areas and at sea, and has good application prospects. Attached Figure Description

[0027] Figure 1 The images show a physical diagram of the fixed-bed reactor used in the ammonia synthesis process of this invention, along with a schematic diagram of the reaction flow. Figure 2 The ammonia synthesis rate graphs for Example 1 and Comparative Example 1 are shown. Figure 3 This is a graph showing the ammonia synthesis rate of Comparative Example 2; Figure 4 The ammonia synthesis rate graphs for Example 2 and Comparative Example 3 are shown. Figure 5 The ammonia synthesis rate graph is shown for Comparative Example 4. Figure 6 The ammonia synthesis rate graphs are for Example 3 and Comparative Examples 5-6; Figure 7 This is a comparison diagram of the apparent activation energies of ammonia synthesis in Example 1 and Comparative Example 2; Figure 8 This is a comparison diagram of the apparent activation energies of ammonia synthesis in Example 2 and Comparative Example 4. Detailed Implementation

[0028] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0029] The fixed-bed reactor (a) and reaction flow diagram (b) used in the following examples and comparative examples for ammonia synthesis are shown below. Figure 1 As shown.

[0030] The industrial iron catalyst used in the following examples and comparative examples for ammonia synthesis was type A110, purchased from Qizhong Chemical (Zhengzhou) Co., Ltd.; the reduced iron powder was analytical grade from Shanghai Experimental Chemical Co., Ltd., purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] Example 1 A method for synthesizing ammonia using N2 / H2 / NO includes the following steps: Take 0.2 g of ruthenium-doped lanthanum ferrite (LFRu, ruthenium doping amount of 2 wt.%) catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 8.3 mL·min. -1 N2, 29.7 mL·min -1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0032] Comparative Example 1 A method for synthesizing ammonia using Ar / H2 / NO includes the following steps: Take 0.2 g of ruthenium-doped lanthanum ferrite (LFRu, ruthenium doping amount of 2 wt.%) catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 8.3 mL·min. -1 Ar, 29.7 mL·min -1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0033] The reaction tail gases of Example 1 and Comparative Example 1 were respectively passed through 200 mL of a solution containing 0.05 mol·L⁻¹ -1 The ammonia synthesis performance was tested using a dilute sulfuric acid solution after 2 hours of absorption, and the results were obtained by combining Nessler's reagent method with an Agilent Cary 60 UV-Vis spectrophotometer. Figure 2 As shown. The test conditions were: LFRu at atmospheric pressure, N2 / H2 / NO = 8.3 / 29.7 / 2 or Ar / H2 / NO = 8.3 / 29.7 / 2, and a space velocity of 12000 mL·h. -1 ·g cat -1 .

[0034] Depend on Figure 2 It can be seen that the ammonia synthesis rate of LFRu under normal pressure and at 400-600℃, with Ar / H2 / NO = 8.3 / 29.7 / 2, is 5.1-9.7 mmol. NH3 ·h -1 ·g cat -1 The optimal ammonia rate was measured at 550°C and was 9.7 mmol / L. NH3 ·h -1 ·g cat -1 The corresponding NO-to-ammonia conversion rate was 36.3%. Under normal pressure and at 400-600℃, with N2 / H2 / NO = 8.3 / 29.7 / 2, the ammonia synthesis rate was 7.7-17.8 mmol / L. NH3 ·h -1 ·g cat -1 The optimal ammonia rate was measured at 550°C and was 17.8 mmol / L. NH3 ·h -1 ·g cat -1 The total nitrogen conversion rate for ammonia synthesis was 7.1%, which is close to the conversion rate of industrial ammonia synthesis.

[0035] Comparative Example 2 A method for synthesizing ammonia from N2 / H2 includes the following steps: Take 0.2 g of ruthenium-doped lanthanum ferrite (LFRu, ruthenium doping content of 2 wt%) catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 10 mL·min. -1 N2 and 30 mL·min -1 H2 is reacted to produce ammonia.

[0036] The reaction tail gas of Comparative Example 2 was passed through 200 mL of a solution with a concentration of 0.05 mol·L⁻¹. -1 The ammonia synthesis performance was tested using a dilute sulfuric acid solution after 2 hours of absorption, and the results were obtained by combining Nessler's reagent method with an Agilent Cary 60 UV-Vis spectrophotometer. Figure 3 As shown. The test conditions were: LFRu at atmospheric pressure, N2 / H2 = 1 / 3, and space velocity of 12000 mL·h. -1 ·g cat -1 .

[0037] like Figure 3 As shown, the ammonia synthesis rate of LFRu under normal pressure and at 400-600℃ with N2 / H2=1 / 3 is 12.8-99.5 μmol. NH3 ·h -1 ·g cat -1 The highest ammonia rate was measured at 550°C, at 0.0995 mmol / L. NH3 ·h -1 ·g cat -1 The corresponding ammonia conversion rate was 0.037%, which is far lower than the ammonia synthesis performance of NO introduced in Example 1.

[0038] At 550℃, the ammonia synthesis rate promoted by the molecular promoter can be calculated by subtracting the ammonia synthesis rate generated by the reaction of NO and H2 (measured under the condition of Ar / H2 / NO=8.3 / 29.7 / 2) from the total ammonia synthesis rate (measured under the condition of N2 / H2 / NO=8.3 / 29.7 / 2); as shown in equation (2).

[0039] (2) in: For the overall ammonia synthesis rate, The ammonia synthesis rate from NO is calculated under the conditions of 550℃, atmospheric pressure, and LFRu catalyst. It was 8.1 mmol. NH3 ·h -1 ·g cat -1 This is far higher than the ammonia synthesis rate under the condition of N2 / H2=1 / 3 (0.0995 mmol). NH3 ·h -1 ·g cat -1 ).therefore, This represents the ammonia synthesis rate accelerated by a molecular promoter. The molecular promoter directly reacts with hydrogen on the LFRu catalyst to produce ammonia, while simultaneously generating reactive oxygen atoms to activate nitrogen molecules, thus promoting the reaction of nitrogen and hydrogen on the LFRu catalyst to produce ammonia. The amount of ammonia produced by the molecular promoter is 8.0 mmol. NH3 ·h -1 ·g cat -1 It accounts for 45% of the total ammonia synthesis rate, which greatly improves the total ammonia synthesis rate of LFRu catalyst under normal pressure.

[0040] Example 2 A method for synthesizing ammonia using N2 / H2 / NO includes the following steps: Take 0.2 g of industrial-grade iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 40 mL / min at 480 °C. -1 After H2 reduction for 4 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 8.3 mL·min. -1 N2, 29.7 mL·min -1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0041] Comparative Example 3 A method for synthesizing ammonia using Ar / H2 / NO includes the following steps: Take 0.2 g of industrial-grade iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 40 mL / min at 480 °C. -1 After H2 reduction for 4 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 8.3 mL·min. -1 Ar, 29.7 mL·min -1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0042] The reaction tail gases from Examples 2 and 3 were respectively passed through 200 mL of a solution containing 0.05 mol·L⁻¹. -1 The ammonia synthesis performance was tested using a dilute sulfuric acid solution after 2 hours of absorption, and the results were obtained by combining Nessler's reagent method with an Agilent Cary 60 UV-Vis spectrophotometer. Figure 4 As shown. The test conditions were: LFRu at atmospheric pressure, N2 / H2 / NO = 8.3 / 29.7 / 2 or Ar / H2 / NO = 8.3 / 29.7 / 2, and a space velocity of 12000 mL·h. -1 ·g cat -1 .

[0043] Depend on Figure 4 It can be seen that the ammonia synthesis rate of industrial iron catalysts under normal pressure and at 400-600℃, with Ar / H2 / NO = 8.3 / 29.7 / 2, is 3.4-12.8 mmol / L. NH3 ·h -1 ·g cat -1 The ammonia synthesis rate at 450℃ was 8.0 mmol / L. NH3 ·h -1 ·g cat -1 The corresponding NO-to-ammonia conversion rate was 30%. Under normal pressure and at 400-600℃, with an N2 / H2 / NO ratio of 8.3 / 29.7 / 2, the ammonia synthesis rate was 6.5-15.2 mmol / L. NH3 ·h -1 ·g cat -1 The ammonia synthesis rate at 450℃ was 14.6 mmol / L. NH3 ·h -1 ·g cat -1 The total nitrogen conversion rate for ammonia synthesis was 6.0%, which is close to the conversion rate of industrial ammonia synthesis.

[0044] Comparative Example 4 A method for synthesizing ammonia from N2 / H2 includes the following steps: Take 0.2 g of industrial-grade iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 40 mL / min at 480 °C. -1 After H2 reduction for 4 hours, the temperature was lowered to 400 / 450 / 500 / 550 / 600℃, and the reaction gas composition was switched to 10 mL·min. -1 N2 and 30 mL·min -1 H2 is reacted to produce ammonia.

[0045] The reaction tail gas of Comparative Example 4 was passed through 200 mL of a solution with a concentration of 0.05 mol·L⁻¹. -1 The ammonia synthesis performance was tested using a dilute sulfuric acid solution after 2 hours of absorption, and the results were obtained by combining Nessler's reagent method with an Agilent Cary 60 UV-Vis spectrophotometer. Figure 5 As shown. The test conditions were: industrial iron catalyst at atmospheric pressure, N2 / H2 = 1 / 3, and space velocity of 12000 mL·h. -1 ·g cat -1 .

[0046] Depend on Figure 5It can be seen that the ammonia synthesis rate of industrial iron catalysts under normal pressure, 400-600℃, and N2 / H2=1 / 3 conditions is 33.1-325 μmol / L. NH3 ·h -1 ·g cat -1 The ammonia synthesis rate at 450℃ was 0.23 mmol / L. NH3 ·h -1 ·g cat -1 The iron catalyst, under normal pressure and at 450°C, achieved a corresponding ammonia synthesis conversion rate of 0.09%, which is far lower than the ammonia synthesis performance of the method using NO introduced in Example 2.

[0047] The ammonia synthesis acceleration rate under the action of molecular promoters at 450℃, normal pressure, and with industrial iron catalyst. It was 6.6 mmol. NH3 ·h -1 ·g cat -1 This is far higher than the ammonia synthesis rate (0.23 mmol) under the condition of N2 / H2=1 / 3. NH3 ·h -1 ·g cat -1 The role of the molecular promoter is to directly react with hydrogen on the iron catalyst to produce ammonia. Simultaneously, it generates reactive oxygen atoms on-site to activate nitrogen molecules, thus promoting the reaction of nitrogen and hydrogen on the iron catalyst to produce ammonia. The amount of ammonia produced by the molecular promoter is 6.37 mmol. NH3 ·h -1 ·g cat -1 It accounts for 44% of the total ammonia synthesis rate, which greatly improves the total ammonia synthesis rate of iron catalysts under normal pressure.

[0048] Example 3 A method for synthesizing ammonia using N2 / H2 / NO includes the following steps: Take 0.2 g of iron powder catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 550℃, and the reaction gas composition was changed to 8.3 mL·min. -1 N2, 29.7 mL·min - 1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0049] Comparative Example 5 A method for synthesizing ammonia using Ar / H2 / NO includes the following steps: Take 0.2 g of iron powder catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 550℃, and the reaction gas composition was changed to 8.3 mL·min. -1 Ar, 29.7 mL·min -1 H2 and 2 mL·min -1 NO reacts to produce ammonia.

[0050] Comparative Example 6 A method for synthesizing ammonia from N2 / H2 includes the following steps: Take 0.2 g of iron powder catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8 mm. React at 700 °C using 40 mL / min. -1 After H2 reduction for 5 hours, the temperature was lowered to 550℃, and the reaction gas composition was changed to 10 mL·min. -1 N2 and 30 mL·min - 1 H2 is reacted to produce ammonia.

[0051] The reaction tail gases from Examples 3 and Comparative Examples 5-6 were passed through 200 mL of a solution containing 0.05 mol·L⁻¹. -1 The ammonia synthesis performance was tested using a dilute sulfuric acid solution after 2 hours of absorption, and the results were obtained by combining Nessler's reagent method with an Agilent Cary 60 UV-Vis spectrophotometer. Figure 6 As shown. The test conditions were: iron powder catalyst, at atmospheric pressure, N2 / H2 / NO = 8.3 / 29.7 / 2, Ar / H2 / NO = 8.3 / 29.7 / 2 or N2 / H2 = 1 / 3, and a space velocity of 12000 mL·h. -1 ·g cat -1 .

[0052] Depend on Figure 6 It can be seen that the ammonia synthesis rate of iron powder catalyst under the conditions of atmospheric pressure, 550℃, and Ar / H2 / NO = 8.3 / 29.7 / 2 is 7.3 mmol. NH3 ·h -1 ·g cat -1 The corresponding NO-to-ammonia conversion rate was 27.3%. The ammonia synthesis rate using iron powder catalyst under atmospheric pressure, 550℃, and N2 / H2 / NO ratios of 8.3 / 29.7 / 2 was 12.9 mmol / L. NH3 ·h -1 ·g cat -1The total nitrogen conversion rate for ammonia synthesis was 5.2%, close to the conversion rate of industrial ammonia synthesis. The ammonia synthesis rate using iron powder catalyst under atmospheric pressure, 550℃, and N2 / H2 = 1 / 3 conditions was 0.107 mmol / L. NH3 ·h -1 ·g cat -1 The corresponding ammonia conversion rate was 0.04%, which is far lower than the ammonia synthesis performance of NO introduced in Example 3.

[0053] The ammonia synthesis acceleration rate under the action of molecular promoters at 550℃, atmospheric pressure, and with iron powder catalyst. It was 5.6 mmol. NH3 ·h -1 ·g cat -1 This is far higher than the ammonia synthesis rate under the condition of N2 / H2=1 / 3 (0.107 mmol). NH3 ·h -1 ·g cat -1 The role of the molecular promoter is to directly react with hydrogen on the iron catalyst to produce ammonia. Simultaneously, it generates reactive oxygen atoms on-site to activate nitrogen molecules, thus promoting the reaction of nitrogen and hydrogen on the iron catalyst to produce ammonia. The amount of ammonia produced by the molecular promoter is 5.6 mmol. NH3 ·h -1 ·g cat -1 It accounts for 43% of the total ammonia synthesis rate, which greatly improves the total ammonia synthesis rate of iron catalysts under normal pressure.

[0054] According to the Arrhenius equation ,in, r NH3 Represents the rate of ammonia synthesis, measured in mmol. NH3 ·h -1 ·g cat -1 E a It is the apparent activation energy, with units of J·mol. -1 R is the molar gas constant, with units of J·mol. -1 ·K -1 T is the reaction temperature, in K; A refers to the pre-factor, its unit is K. r NH3 same.

[0055] From the above equations, we can see that and The linear relationship is shown in the graphs plotted on the series of experimental data for ammonia synthesis in Examples 1 and 2, and Examples 2 and 4, respectively. The x-axis is... Using the ordinate as the vertical axis, the results are as follows: Figure 7 and Figure 8 As shown in the figure, the apparent activation energy of each catalyst under the reaction conditions can be calculated from the slope of the straight line in the figure.

[0056] Depend on Figure 7 It can be seen that the apparent activation energy for introducing NO into the LFRu catalyst in Example 1 is 31.7 kJ·mol⁻¹. -1 It is lower than the apparent activation energy (65.1 kJ·mol⁻¹) under NO-free conditions in Comparative Example 1. -1 ).Depend on Figure 8 It can be seen that the apparent activation energy for introducing NO into the industrial iron catalyst in Example 2 is 67.8 kJ·mol⁻¹. -1 This is lower than the apparent activation energy (145.9 kJ·mol⁻¹) under NO-free conditions in Comparative Example 2. -1 It is evident that the introduction of NO significantly lowers the energy barrier for the ammonia synthesis reaction between N2 and H2 on the catalyst, thereby greatly increasing the ammonia synthesis rate under normal pressure.

[0057] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method of synthesizing ammonia, characterized by, The ammonia is synthesized under normal pressure or low pressure conditions by using nitrogen and hydrogen as reaction gas, under the action of gaseous molecular promoter and catalyst; the gaseous molecular promoter is nitrogen oxide.

2. The method of claim 1, wherein, The nitrogen oxide is selected from nitric oxide or nitrogen dioxide.

3. The method of claim 1, wherein, The volume ratio of the nitrogen and hydrogen is (0.2-2):1, and the introduced amount of the gaseous molecular promoter is 0.2-10 vol% of the reaction gas.

4. The method of claim 1 wherein, The low pressure is 0.2-5 MPa.

5. The method of claim 1 wherein, The synthesis temperature is 300-700℃.

6. The method of claim 1 wherein, The catalyst is selected from at least one of iron-based catalyst, ruthenium-based catalyst, cobalt-based catalyst, metal nitride catalyst, doped metal nitride catalyst, doped transition metal catalyst, and doped oxygen ion conductor oxide catalyst.

7. The process for the synthesis of ammonia according to any one of claims 1-6, characterized in that, The method comprises the following steps: The catalyst is placed in a reactor, heated, treated by reduction atmosphere, and then the reaction gas and gaseous molecular promoter are introduced to carry out the reaction, and the gaseous product is collected to obtain the ammonia.

8. The method of claim 7, wherein, The space velocity of the reaction gas and gaseous molecular promoter is 6000-60000 mL·h -1 ·g cat -1 .

9. The method of claim 7, wherein, The material of the reactor is stainless steel or quartz glass.

10. Use of the method for synthesizing ammonia according to any one of claims 1-9 in the conversion of renewable energy into liquid ammonia.

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