High-performance iron-based catalyst for solving ammonia slip problem and preparation method thereof

Abstract

The application provides a high-performance iron-based catalyst suitable for solving ammonia leakage problems and a preparation method thereof. The active component of the high-performance iron-based catalyst is FeO rich in iron vacancies. The preparation method of the catalyst is to modify common FeO by using a NaOH etching method, and the modified FeO catalyst is rich in iron vacancies, which is proved by HRTEM, ICP-OES, XPS, NH3-TPD and the like. The application utilizes iron vacancies to reduce the energy barrier of the starting step and important component of ammonia degradation, i.e. step-by-step dehydrogenation, so as to improve the efficiency of ammonia degradation, and can be applied to various ammonia leakage problems under low ammonia flow in a wide temperature range (300 DEG C to 900 DEG C). The catalyst shows extremely high catalytic activity in a wide temperature range, and no secondary harmful gases such as NO and NO2 are detected in the process, which is green and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to a high-performance iron-based catalyst suitable for solving the problem of ammonia leakage and a preparation method thereof, belonging to the technical field of safe utilization of ammonia. Background Art

[0002] Ammonia is not only an important chemical raw material but also a highly promising carbon-free alternative energy source and a potential high-quality hydrogen carrier. Ammonia synthesis is one of the most systematically and mature processes in the global chemical industry. The production, storage, and transportation systems for ammonia are already relatively well-established, and its future application is expected to become even more widespread. While ammonia is widely used, its use is often associated with issues such as ammonia leaks. Satellite data indicate that global atmospheric ammonia levels are already worthy of attention. Ammonia is also toxic. Its role in particulate matter formation can affect air quality, human health, and life expectancy. Excessive ammonia in the environment can also lead to ecosystem acidification and eutrophication, climate change, and adversely affect industrial processes. Therefore, addressing ammonia leaks in its industrial utilization and energy conversion is urgent.

[0003] The main methods for resolving ammonia leaks can be categorized as source sealing and plugging technology, and NH3 absorption and conversion treatment technology. Due to the specific nature of ammonia leaks, source sealing technology has a lower success rate. The plant absorption method within NH3 absorption and conversion technology is only suitable for improving indoor environments and is not suitable for large-scale ammonia leaks in industrial processes. The microbial absorption method, which addresses the reproduction, metabolism, and improvement of microorganisms, remains to be resolved. Physical and chemical adsorption methods have poor absorption effects and are only applicable to specific ammonia leaks. Low-temperature plasma ammonia leak treatment equipment is complex and requires operation under high-frequency and high-voltage conditions. This presents numerous safety hazards and carries the risk of secondary accidents such as fires and explosions following ammonia leaks.

[0004] Catalytic ammonia degradation offers a new solution to the problem of ammonia leakage during ammonia utilization. Its catalytic effect is stable and can achieve high ammonia conversion rates. This method has applications not only in the removal of ammonia from biomass gasification gas, coke oven gas, and petroleum refinery exhaust, as well as in the treatment of ammonia-nitrogen wastewater, but is also widely used to address ammonia leakage in various industries, including the chemical, steel, glass, and electronics industries. Currently, research on ammonia degradation catalysts primarily focuses on precious metal catalysts, such as ruthenium (Ru), and non-precious metal catalysts, such as nickel (Ni) and iron (Fe). While precious metals are relatively expensive, transition metals are relatively inexpensive and exhibit excellent catalytic activity, significantly reducing catalyst production costs. Consequently, research on transition metal catalysts has entered a period of intense activity. Iron (Fe) and its oxides exhibit excellent catalytic activity towards NH₃ and are readily available and inexpensive, making them of significant interest in the catalytic degradation of NH₃.

[0005] The main drawbacks of existing ammonia degradation catalysts are their narrow application window (effective activity only at specific temperatures) and the lack of catalysts that address ammonia leakage, a problem encountered at extremely low ammonia flow rates. Furthermore, previous catalyst research has primarily focused on pure metals and their oxides. Even research on vacancies has primarily focused on oxygen vacancies, with little research on metal cation vacancies. Summary of the Invention

[0006] The present invention aims to provide a high-performance iron-based catalyst suitable for addressing ammonia leakage at low ammonia flow rates over a wide temperature range, and a method for its preparation. This method utilizes the abundant iron vacancies in the catalyst to enhance the efficiency of the gradual dehydrogenation of ammonia, thereby increasing the ammonia conversion rate during ammonia degradation. This method utilizes readily available, inexpensive raw materials, achieves high conversion rates, and utilizes a simple, corrosion-free, mechanically strong, and inexpensive catalyst preparation method. It can effectively and cleanly treat leaked ammonia while avoiding the generation of secondary pollutants such as NO and NO2.

[0007] The technical solutions provided to achieve the purpose of the present invention are as follows:

[0008] The high-performance iron-based catalyst has ferrous oxide as its main active component and is prepared by a NaOH etching method.

[0009] The preparation method is as follows:

[0010] Dissolving NaOH solid (1) in deionized water (3) to form a homogeneous solution equivalent to a 2 mol / L NaOH solution, and transferring the solution to a container as an alkaline etchant (4);

[0011] After sieving the FeO solid, weigh no more than 50% of the mass of the NaOH solid (1) and transfer the FeO solid (2) into the alkaline etchant (4). Stir the solution at room temperature of 25°C using a magnetic stirrer (5).

[0012] The etching reaction was continued for 1 hour, and then vacuum filtration was performed to obtain a solid mixture;

[0013] The obtained uniform mixture is placed in a drying oven (6) for heating and drying;

[0014] The solid obtained after drying is crushed, ground and sieved to a required particle size range to obtain a high-performance iron-based oxide catalyst solid powder.

[0015] Compared with the prior art, the present invention has significant advantages:

[0016] 1. Ammonia catalytic degradation does not require the introduction of other gases, the process is simple, energy consumption is reduced, the applicable temperature range is wide, and the application range is wide. It can be well applied to various ammonia leakage problems with extremely low ammonia flow;

[0017] 2. The use of high-performance iron-based catalysts to catalyze the degradation of ammonia can be applied to the clean and safe utilization of ammonia without producing secondary pollutants such as NO and NO2;

[0018] 3. The catalyst is prepared by NaOH etching method, which improves the catalytic activity: at 300℃, 500℃, 700℃ and 900℃

[0019] The ammonia conversion rates can reach 94.25%, 95.74%, 96.86% and 97.98% respectively;

[0020] 4. The catalyst raw materials are cheap and readily available, the preparation is simple, the operability is strong, and it is simple and convenient;

[0021] 5. The prepared catalyst has a wide range of particle size distribution and is suitable for fixed bed or fluidized bed processes and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a process flow chart for the preparation of a high-performance ammonia degradation catalyst.

[0023] Among them, there are (1) NaOH solid; (2) FeO solid; (3) deionized water; (4) alkaline etchant; (5) magnetic stirrer; (6) drying oven.

[0024] Figure 2-5 The catalytic activities of the catalysts in Example 1 and Comparative Examples 1-3.

[0025] in, Figure 2The NH3 conversion rates of three iron-based catalysts modified by NaOH etching method in catalytic NH3 degradation experiments under the same conditions (temperature 300℃, 500℃, 700℃, 900℃, NH3 flow rate of 1mL / min, Ar flow rate of 299mL / min). Figure 3 The NH3 conversion rates of three iron-based catalysts modified by NaOH etching method in catalytic NH3 degradation experiments under the same conditions (temperature 300℃, 500℃, 700℃, 900℃, NH3 flow rate of 1mL / min, Ar flow rate of 299mL / min). Figure 4 It is the NH3 conversion rate of NH3 degradation experiment catalyzed by three common iron-based catalysts under the same conditions (temperature 300℃, 500℃, 700℃, 900℃, NH3 flow rate of 1mL / min, Ar flow rate of 299mL / min). Figure 5 Three common iron-based oxides catalyze the degradation of ammonia to produce NO at different temperatures. x The graph of changes over time (the heating rate is 10℃ / min and other reaction conditions are NH3 flow rate: 1mL / min, Ar flow rate: 299mL / min).

[0026] Figure 6 HRTEM analysis of the catalysts in Example 1 and Comparative Example 3. (a) is an HRTEM image of FeO, (b) is an HRTEM image of the modified FeO after NaOH etching, and (c) is an enlarged HRTEM image of the modified FeO after NaOH etching.

[0027] Figure 7 NH3-TPD analysis of the catalysts in Example 1 and Comparative Example 3.

[0028] Figure 8 The O1s XPS spectra of the catalysts in Example 1 and Comparative Example 3 are shown. (a) is the O1s XPS spectrum of standard FeO, (b) is the O1s XPS spectrum of standard Fe2O3, and (c) is the O1s XPS spectrum of standard Fe3O4. (d) is the O1s XPS spectrum of the modified FeO treated with NaOH. (e) is the O1s XPS spectrum of the modified FeO treated with NaOH after the 900°C experiment. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the examples and drawings. It should be understood that the following examples are only intended to illustrate and should not be regarded as limiting the scope of the present invention.

[0030] The present invention provides a high-performance iron-based catalyst suitable for resolving ammonia leakage problems and a method for preparing the same. The high-performance iron-based catalyst, whose main active component is ferrous oxide, is prepared using a NaOH etching method. The catalyst preparation comprises the following steps:

[0031] Step 1: dissolving NaOH solid (1) in deionized water (3) to form a homogeneous solution equivalent to a 2 mol / L NaOH solution, and transferring the solution into a container as an alkaline etchant (4);

[0032] Step 2: After sieving the FeO solid, weigh no more than 50% of the mass of the NaOH solid (1) and transfer the FeO solid (2) into the alkaline etchant (4). Stir the solution at room temperature of 25° C. using a magnetic stirrer (5). The etching reaction lasts for 1 hour, and then vacuum filtration is performed to obtain a solid mixture.

[0033] Step 3: placing the obtained uniform mixture in a drying oven (6) for heating and drying;

[0034] Step 4: The solid obtained after drying is crushed, ground and sieved to a required particle size range to obtain a high-performance iron-based oxide catalyst solid powder.

[0035] Example 1

[0036] Dissolve 40g of NaOH in 500ml of deionized water to form a homogeneous solution (equivalent to a 2mol / L NaOH solution) and transfer it to a beaker as an alkaline etchant. After sieving the FeO solid, weigh 20g of the FeO solid and transfer it to the alkaline etchant. Stir the solution with a magnetic stirrer at room temperature of 25°C. The etching reaction continues for 1 hour, followed by vacuum filtration to obtain a solid mixture. The resulting homogeneous mixture is placed in a drying oven at 120°C and heated to dry for 6 hours. After the temperature drops to room temperature, remove the catalyst particles that have been ground and sieved to the desired particle size. This catalyst is called a modified FeO catalyst and is represented as NaOH-FeO in the figure.

[0037] The catalyst prepared in Example 1 is a high-performance modified FeO catalyst with high catalytic activity and produces NO x Situation Figure 2-3 shown.

[0038] Comparative Example 1

[0039] Dissolve 40g of NaOH in 500ml of deionized water to form a homogeneous solution (equivalent to a 2mol / L NaOH solution) and transfer it to a beaker as an alkaline etchant. After sieving the FeO solid, weigh 20g of Fe2O3 solid and transfer it to the alkaline etchant. Stir the solution with a magnetic stirrer at room temperature (25°C) for 1 hour, then vacuum filter to obtain a solid mixture. The resulting homogeneous mixture is placed in a drying oven at 120°C and dried for 6 hours. After the temperature drops to room temperature, remove the catalyst particles, which have been ground and sieved to the desired particle size. This catalyst is called a modified Fe2O3 catalyst and is represented in the figure as NaOH-Fe2O3.

[0040] The catalyst prepared in Comparative Example 1 is a high-performance modified Fe2O3 catalyst with high catalytic activity and produces NO x Situation Figure 2-3 shown.

[0041] Comparative Example 2

[0042] Dissolve 40g of NaOH in 500ml of deionized water to form a homogeneous solution (equivalent to a 2mol / L NaOH solution) and transfer it to a beaker as an alkaline etchant. After sieving the FeO solid, weigh 20g of Fe3O4 solid and transfer it to the alkaline etchant. Stir the solution with a magnetic stirrer at room temperature (25°C) for 1 hour, then vacuum filter to obtain a solid mixture. The resulting homogeneous mixture is placed in a drying oven at 120°C and dried for 6 hours. After the temperature drops to room temperature, remove the catalyst particles, which have been ground and sieved to the desired particle size. This catalyst is called a modified Fe3O4 catalyst and is represented in the figure as NaOH-Fe3O4.

[0043] The catalyst prepared in Comparative Example 2 is a high-performance modified Fe3O4 catalyst with high catalytic activity and produces NO x Situation Figure 2-3 shown.

[0044] Comparative Example 3

[0045] Ordinary FeO, Fe2O3, and Fe3O4 that have not been modified by the NaOH etching method are represented in the figure as FeO, Fe2O3, and Fe3O4, respectively. The catalytic activity produces NO x Situation Figure 4-5 shown.

[0046] Table 1 shows the ICP-OES elemental analysis of the catalysts in Example 1 and Comparative Example 3. Sample 1 is standard FeO, while Samples 2 and 3 are modified FeO catalysts containing iron vacancies, prepared using the NaOH etching method at two different times. As shown in Table 1, the mass fraction of iron in the FeO catalysts modified by NaOH etching, Samples 2 and 3, is significantly lower than that in the standard FeO catalyst samples, demonstrating that the modified FeO catalysts contain more iron vacancies, based on their elemental content.

[0047] Table 1

[0048]

[0049] Depend on Figure 6 It can be seen that the lattice defects are clearly visible in the magnified HRTEM image of the modified FeO after NaOH treatment, which is attributed to the fact that the modified FeO after NaOH treatment has more iron vacancies. Figure 6 Comparison between (a) and (b) shows that the modified FeO catalyst after NaOH treatment has significant lattice distortion compared with ordinary FeO, which may be due to the strain effect caused by the increased iron vacancies, indirectly proving that the modified FeO catalyst after NaOH treatment contains more iron vacancies.

[0050] Depend on Figure 7 As can be seen, compared to the standard FeO catalyst, the modified FeO catalyst treated with NaOH exhibits a more pronounced desorption peak at 620°C, indicating that the modified FeO catalyst has one more acid site than the standard FeO catalyst. This is likely due to the increased iron vacancies, which lead to more exposed metal cations, attracting more electron pairs and manifesting as an increase in acidic sites. Therefore, from the perspective of acidic sites, the modified FeO catalyst has more acidic sites than the standard FeO catalyst, indirectly suggesting that the modified FeO catalyst may contain more iron vacancies.

[0051] Table 2 shows the ratios of the three types of oxygen in the catalysts of Example 1 and Comparative Example 3 obtained through XPS analysis. (a) is the O1s XPS spectrum of FeO, (b) is the O1s XPS spectrum of Fe2O3, (c) is the O1s XPS spectrum of Fe3O4, (d) is the O1s XPS spectrum of the modified FeO catalyst after treatment with NaOH etching, and (e) is the O1s XPS spectrum of the modified FeO catalyst after treatment with NaOH etching at 900°C.

[0052] Table 2

[0053]

[0054] Depend on Figure 8 As can be seen from Table 2, the figure shows the2- The three sub-peaks of oxygen ions (O I ), oxygen ions with unsaturated bonds (O II ) and surface-adsorbed oxygen ions (O III The second type of oxygen (O) in FeO of the three common iron-based oxides II ) accounts for the largest proportion, considering the oxygen ions with unsaturated bonds (O II If it refers to oxygen vacancies in metal oxides, then it should promote the oxidation reaction to produce NO or NO2. However, in the experiments on the catalytic degradation of ammonia by three iron-based oxides, no NO and NO2 were detected when FeO catalyzed the degradation of ammonia. Therefore, the large number of oxygen ions with unsaturated bonds in FeO may indicate that the content of iron vacancies in FeO is relatively rich. Compared with ordinary FeO, the second type of oxygen (O II ) was significantly increased, indicating that the iron vacancies in the modified FeO catalyst increased after NaOH treatment, and the second type of oxygen (O II ) decreased compared with that before the experiment, but was still slightly higher than that of ordinary FeO catalysts, which indicated that the iron vacancies might be consumed in the ammonia degradation experiment and might be covered by other atoms.

[0055] Table 3 shows the energy barriers for the gradual dehydrogenation of ammonia on the FeO(100) surface containing iron vacancies and on the ordinary FeO(100) surface, calculated using Materials Studio software. As can be seen from Table 3, the third-step dehydrogenation barrier of ammonia above the iron vacancies on the FeO(100) surface containing iron vacancies, 1.396 eV, is significantly lower than the energy barrier of ammonia dehydrogenation on the ordinary FeO(100) surface, 3.451 eV. At the same time, the third-step dehydrogenation barrier of ammonia above the non-iron vacancies on the FeO(100) surface containing iron vacancies was also calculated to be 3.319 eV, which is also significantly higher than the energy barrier of dehydrogenation above the iron vacancies. This proves that iron vacancies improve the ammonia degradation efficiency by reducing the energy barriers for the gradual dehydrogenation of ammonia, especially the third-step dehydrogenation barrier.

[0056] Table 3

[0057]

[0058] Depend on Figure 2-5The iron-vacancy-rich modified FeO catalyst prepared by the NaOH etching method exhibits the highest catalytic activity at 300°C, 500°C, 700°C, and 900°C, compared to modified Fe2O3 and Fe3O4 catalysts, as well as unmodified conventional FeO, Fe2O3, and Fe3O4 catalysts. Ammonia conversion rates of 94.25%, 95.74%, 96.86%, and 97.98%, respectively, are achieved, with no detectable production of NO or NO2. This catalyst exhibits excellent catalytic activity over a wide temperature range at low ammonia concentrations and produces no secondary pollution, suggesting broad application prospects.

Claims

1. A method for preparing a high-performance iron-based catalyst suitable for solving the problem of ammonia leakage, characterized in that: The catalyst preparation method is NaOH etching method, the steps are as follows: Step 1, dissolving NaOH solid (1) in deionized water (3) to form a homogeneous solution equivalent to a 2 mol / L NaOH solution, and transferring it to a container as an alkaline etchant (4); Step 2: After sieving the FeO solid (2), weigh no more than 50% of the mass of the NaOH solid (1) and transfer the FeO solid (2) into an alkaline etchant (4); stir the solution at room temperature of 25° C. using a magnetic stirrer (5); and continue the etching reaction for 1 hour, followed by vacuum filtration to obtain a solid mixture; Step 3, placing the obtained uniform solid mixture in a drying oven (6) for heating and drying; Step 4: crushing, grinding and screening the solid obtained after drying to a required particle size range to obtain a high-performance iron-based oxide catalyst solid powder.

2. The method for preparing a high-performance iron-based catalyst suitable for solving ammonia leakage problems according to claim 1, characterized in that: In step 1, the NaOH solid (1) used is white granular uniform particles with a purity greater than 98%.

3. The method for preparing a high-performance iron-based catalyst suitable for solving ammonia leakage problems according to claim 1, characterized in that: In step 2, the FeO solid (2) used is black granular uniform particles, the mesh number of the sieve is 80 mesh, and the purity is greater than 98%.

4. The method for preparing a high-performance iron-based catalyst suitable for solving ammonia leakage problems according to claim 1, characterized in that: In step 2, the vacuum filtration rate is 3.6m 3 / h, vacuum degree is 5Pa.

5. The method for preparing a high-performance iron-based catalyst suitable for solving ammonia leakage problems according to claim 1, characterized in that: In step 3, the drying temperature in the drying oven is not less than 120° C., and the drying time is not less than 6 hours.

6. An iron-based catalyst obtained by the preparation method of a high-performance iron-based catalyst suitable for solving ammonia leakage problems according to any one of claims 1 to 5, characterized in that: The active component of the iron-based catalyst is FeO solid powder rich in iron vacancies.

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