Catalyst for removing nitrous oxide and method for removing nitrous oxide

Abstract

This invention provides a catalyst for removing nitrous oxide and a method for removing nitrous oxide. [Solution] The catalyst for removing nitrous oxide comprises a metal oxide powder and an iron-copper compound. The iron-copper compound is attached to the surface of the metal oxide powder. The metal oxide powder comprises zinc oxide, magnesium oxide, aluminum oxide, or a combination thereof. The molar ratio of iron in the iron-copper compound to the metal in the metal oxide powder is 1:(1.3~4.0).

Description

[Technical Field]

[0001] The present invention relates to a catalyst for removing nitrous oxide and a method for removing nitrous oxide. [Background technology]

[0002] N2O decomposition catalysts have been studied for many years and are used in the treatment of industrial waste gases (such as semiconductor process exhaust gases containing N2O), as well as in the exhaust pipes of automobiles and motorcycles. However, since most of the active ingredients in the catalyst are precious metals, they are expensive and difficult to mass-produce, and they are susceptible to interference from water vapor and oxygen, which reduces catalytic activity.

[0003] Furthermore, conventional processing technologies have an efficiency of only about 60% for processing N2O, and there was a problem that processing N2O using high-temperature pyrolysis actually generated a large amount of NOx, an air pollutant. [Overview of the project] [Problems that the invention aims to solve]

[0004] This invention provides a low-cost catalyst for nitrous oxide removal that can improve the processing efficiency of N2O.

[0005] The present invention also provides a method for removing nitrous oxide that can efficiently decompose N2O without generating large amounts of the air pollutant NOx. [Means for solving the problem]

[0006] The nitrous oxide removal catalyst provided by the present invention comprises a metal oxide powder and an iron-copper compound, wherein the iron-copper compound is attached to the surface of the metal oxide powder. The metal oxide powder may contain zinc oxide, magnesium oxide, aluminum oxide, or a combination thereof. The molar ratio of iron in the iron-copper compound to metal in the metal oxide powder is 1:(1.3~4.0).

[0007] The present invention provides a method for removing nitrous oxide, which involves using the above-mentioned catalyst to decompose nitrous oxide into nitrogen (N2) and oxygen (O2). [Effects of the Invention]

[0008] The nitrous oxide decomposition catalyst of the present invention achieves a very high nitrous oxide removal rate by combining a low-cost transition metal and a metal oxide support, completely decomposing N2O into N2 and O2, and realizing zero pollution emissions.

[0009] To better understand the above-mentioned features of the present invention, the following embodiments will be described in detail with reference to the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1] These are the XRD spectra of the catalysts from Example 12, Comparative Example 3, and Example 1. [Figure 2] These are the XRD spectra of the catalysts from Example 16 and Example 1. [Figure 3] This is an overview of the equipment used to measure gas concentration and removal efficiency (DRE) in the experimental example. [Figure 4] This is a curve diagram showing the N2O removal rate and NO2 concentration for Example 7. [Figure 5] This is a curve diagram showing the N2O removal rate and NO2 concentration in Example 12. [Figure 6] This is the catalyst lifetime curve for Example 7. [Modes for carrying out the invention]

[0011] The following provides various embodiments for implementing various features of the present invention. However, these embodiments are merely illustrative and are not intended to limit the scope and application of the present invention.

[0012] In one embodiment of the present invention, the catalyst for removing nitrous oxide comprises a metal oxide powder and an iron-copper compound. The metal oxide powder may include zinc oxide, magnesium oxide, aluminum oxide, or a combination thereof. The iron and copper in the iron-copper compound exist, for example, in the form of iron oxide, copper oxide, or a combination thereof, respectively. The iron-copper compound may be a binary iron-copper (Fe-Cu) compound. The iron-copper compound may consist of copper oxide and iron oxide. The iron-copper compound may further be doped with other elements to improve the properties of the catalyst. For example, the iron-copper compound may be doped with an aluminum compound and may be called an aluminum-doped iron-copper compound. It mainly consists of copper oxide and iron oxide and contains a small amount of aluminum oxide to improve the mechanical properties of the catalyst. The molar ratio of iron in the iron-copper compound to the metal in the metal oxide powder may be 1:(1.3~4.0). For example, the metal oxide powder is zinc oxide, and the molar ratio of iron in the iron-copper compound to zinc in the zinc oxide powder is 1:(1.4~4.0). The metal oxide powder is magnesium oxide, and the molar ratio of iron in the iron-copper compound to magnesium in the magnesium oxide powder is 1:(1.4~4.0). The metal oxide powder is aluminum oxide, and the molar ratio of iron in the iron-copper compound to aluminum in the aluminum oxide powder is 1:(1.3~3.6).

[0013] In one embodiment, the metal oxide powder is zinc oxide, and the molar ratio of iron to copper in the iron-copper compound is 1:(1.8~6.2). In some embodiments, the metal oxide powder is magnesium oxide, and the molar ratio of iron to copper in the iron-copper compound is 1:(1.5~6.0). In some embodiments, the metal oxide powder is aluminum oxide, and the molar ratio of iron to copper in the iron-copper compound is 1:(0.2~2.7). When the molar ratio of iron to copper is within the above range, an excellent nitrous oxide removal efficiency (DRE) can be obtained.

[0014] Also, by X-ray diffraction analysis (XRD), it was found that when the metal oxide powder is zinc oxide or magnesium oxide, the formed catalyst shows an obvious Fe3O4 diffraction peak. Therefore, it is inferred that the catalyst may further contain an Fe3O4 crystal structure.

[0015] In one embodiment, the catalyst for nitrous oxide removal may further contain a small amount of aluminum. For example, the molar ratio of iron in the iron-copper compound to the small amount of aluminum is 1:(0.1 - 0.5), and the aluminum exists on the surface of the metal oxide powder in the form of, for example, aluminum oxide.

[0016] In one embodiment, the specific surface area of the catalyst for nitrous oxide removal is 20 m 2 g -1 ~200 m 2 g -1 is.

[0017] In one embodiment, the particle size of the catalyst for nitrous oxide removal may be 100 μm or more, for example, about 200 μm - 5 mm, and also for example, about 1 mm - 5 mm.

[0018] In one embodiment, the porosity of the catalyst for nitrous oxide removal is 60% - 90%.

[0019] In one embodiment, when the catalyst particles are relatively large (for example, 1 mm or more), the mechanical strength of the catalyst for nitrous oxide removal is 0.5 kgw - 3.0 kgw, which contributes to preventing breakage during use that affects the nitrous oxide treatment process.

[0020] In one embodiment, the nitrous oxide removal catalyst may be manufactured by attaching an iron-copper compound to the surface of a metal oxide powder through a granulation and firing process.

[0021] In another embodiment of the present invention, the method for removing nitrous oxide involves using the above catalyst to decompose nitrous oxide into nitrogen (N2) and oxygen (O2). Furthermore, the flow rate of nitrous oxide is 400 sccm to 1350 sccm, NO X It can achieve a 99% nitrous oxide removal rate (DRE) without generating harmful by-products such as [list of by-products].

[0022] The above-mentioned nitrous oxide removal catalyst of the present invention can be used to treat semiconductor process exhaust gases containing N2O, waste gases generated during the production of nitric acid and adipic acid (e.g., 2HNO3 → N2O + H2O + O2), medical anesthetic waste gases, and can also be used to treat exhaust gases containing flammable gases such as CH4 and H2.

[0023] The nitrous oxide decomposition catalyst of the present invention achieves a very high nitrous oxide removal rate by combining a low-cost transition metal and a metal oxide support. For example, it can completely decompose N2O into N2 and O2, replacing the high-temperature pyrolysis method commonly used for treating N2O exhaust gas in semiconductor processes, thereby achieving zero pollution emissions.

[0024] To verify the effectiveness of the present invention, several experiments are described below, but these experiments and their results do not limit the scope of application of the present invention.

[0025] <Preparation Example 1> Catalyst containing zinc oxide powder and an iron-copper compound

[0026] Examples 1 to 4 were obtained by preparing the following according to the usage amounts shown in Table 1 below.

[0027] First, zinc oxide powder (DIAMONCHEM INTERNATIONAL CO., LTD., model number AZO-900) was dispersed in water to prepare colloidal solution 1. Iron nitrate was dissolved in water to prepare solution 2. Solution 2 and a 2.0 M sodium hydroxide (pH adjuster) solution were added together to colloidal solution 1, and then the mixture was reacted at room temperature (25°C) for 1.5 hours to form colloidal solution 3.

[0028] After precipitation, colloidal solution 3 was filtered and dried to obtain a precipitate. The precipitate was dispersed in water, and then 4 wt% of a biopolymer solution was added as a chelating agent and mixed into a homogeneous colloidal solution 4. Examples of biopolymers include, but are not limited to, alginic acid, cellulose, chitin, chitosan, carrageenan, and gelatin. Subsequently, colloidal solution 4 was added to a copper nitrate solution (copper ion concentration 15,000 ppm) to produce granules. The granules were heat-treated at a calcination temperature of 500°C to obtain an Fe / Cu / ZnO catalyst.

[0029] [Table 1]

[0030] <Preparation Example 2> Catalyst containing zinc oxide powder and an iron-copper compound

[0031] Examples 5 to 8 were prepared using the following method.

[0032] Similar to Preparation Example 1, first, 33.78 g of zinc oxide powder was dispersed in water to prepare colloidal solution 1. 83.8 g of iron nitrate was dissolved in water to prepare solution 2. Solution 2 was then added to colloidal solution 1, and the mixture was stirred at room temperature for 1 hour to prepare colloidal solution 3. Subsequently, 2.0 M potassium carbonate (pH adjuster) was added to colloidal solution 3, and the mixture was stirred at room temperature for another 1 hour to prepare colloidal solution 4.

[0033] After precipitation, colloidal solution 4 was filtered and dried to obtain a precipitate. The precipitate was dispersed in water, and then 4 wt% of biopolymer solution was mixed into the homogeneous colloidal solution 5 as a chelating agent. Subsequently, colloidal solution 5 was added to copper nitrate solution (copper ion concentration 15,000 ppm), and allowed to stand (3, 8, 24, and 24 hours in Examples 5-8, respectively) to produce granules. Finally, the granules were heat-treated (the calcination temperature for Examples 5-7 was approximately 500°C, and for Example 8 it was approximately 400°C) to obtain an Fe / Cu / ZnO catalyst.

[0034] <Preparation Example 3> Catalyst containing zinc oxide powder and an iron-copper compound

[0035] The following preparations were made using the same method as in Example 8 of Preparation Example 2, according to the amounts used in Table 2 below. Here, only Example 9 was fired at a temperature of 300°C, while the firing temperature for the other examples was 500°C, yielding Examples 9 to 11.

[0036] [Table 2]

[0037] <Comparative Preparation Example 1> Catalyst containing zinc oxide powder and an iron or copper compound

[0038] The catalyst was prepared using the same method as in Example 7 of Preparation Example 1, but instead of using copper nitrate solution, a 15,000 ppm zinc nitrate solution was used to obtain Comparative Example 1.

[0039] The catalyst was prepared using the same method as in Example 7 of Preparation Example 1, but iron nitrate was replaced with 83.7 g of copper nitrate to obtain Comparative Example 2.

[0040] <Comparative Preparation Example 2> Catalyst containing titanium dioxide powder and an iron-copper compound

[0041] The catalyst was prepared using the same method as in Example 1 of Preparation Example 1, but the zinc oxide powder was replaced with titanium dioxide (Emperor Chemical Co., Ltd, product number 20130227123, average particle size 30 nm) to obtain Comparative Example 3.

[0042] <Preparation Example 4> Catalyst containing aluminum oxide powder and an iron-copper compound

[0043] Examples 12 to 15 were obtained by preparing the following according to the usage amounts shown in Table 3 below.

[0044] First, aluminum oxide powder was dispersed in water to form colloidal solution 1. Here, the aluminum oxide was material number A000WL purchased from EIKME INTERNATIONAL LTD. The boehmite was material number AC-G2 purchased from Zibo Honghe Chemical Co., Ltd. 80.9 g of iron nitrate and 12.1 g of copper nitrate were dissolved in water to form solution 2. Solution 2 and a 2.0 M sodium hydroxide solution were added together to colloidal solution 1, and then the mixture was reacted at room temperature for 1.5 hours to form colloidal solution 3.

[0045] After precipitation, colloidal solution 3 was filtered and dried to obtain a precipitate. The precipitate was dispersed in water, and then 4 wt% of biopolymer solution was mixed into the homogeneous colloidal solution 4 as a chelating agent. Subsequently, colloidal solution 4 was added to copper nitrate solution (copper ion concentration 15,000 ppm) to prepare granules. The granules were heat-treated at a calcination temperature of 500°C to obtain an Fe / Cu / Al2O3 catalyst.

[0046] [Table 3]

[0047] <Comparative Preparation Example 3> Catalyst containing aluminum oxide powder but no copper compounds

[0048] Comparative Examples 4-6 were obtained by preparing the following according to the usage amounts shown in Table 4 below.

[0049] The catalyst was prepared using the same method as in Example 14 of Preparation Example 4.

[0050] [Table 4]

[0051] <Preparation Example 5> Catalyst containing magnesium oxide powder and an iron-copper compound

[0052] First, 40.4 g of magnesium oxide powder (Nippon Kamishima Chemical Industry Co., Ltd., material number #50) and 83.8 g of iron nitrate were dispersed in water to prepare colloidal solution 1. Then, 2.0 M potassium carbonate was added to colloidal solution 1, and the mixture was stirred at room temperature for another hour to prepare colloidal solution 2. After precipitation, colloidal solution 2 was filtered and dried to obtain the precipitate.

[0053] After dispersing the above precipitate in water, 4 wt% biopolymer solution was added and mixed into a homogeneous colloidal solution 3. Subsequently, colloidal solution 3 was added to copper nitrate solution (copper ion concentration 15,000 ppm) to produce granules. The granules were heat-treated at a calcination temperature of 500°C to obtain the Fe / Cu / MgO catalyst of Example 16.

[0054] <Analysis of physical properties>

[0055] 1. XRD analysis

[0056] Using an XRD instrument, the catalysts of Example 12, Comparative Example 3, and Example 1 were analyzed, and the XRD spectra shown in Figure 1 were obtained. As can be seen from Figure 1, the catalyst supported by zinc oxide (ZnO) powder has a clear Fe3O4 diffraction peak, so it can be inferred that this type of catalyst has an Fe3O4 crystal structure.

[0057] Using an XRD instrument, the XRD analysis results of the catalyst in Example 16 were compared with the XRD spectrum of Example 1, and Figure 2 was obtained. Here, since the catalyst supported by magnesium oxide (MgO) powder also has a clear Fe3O4 diffraction peak (marked with an asterisk), it can be inferred that this type of catalyst also has an Fe3O4 crystal structure.

[0058] 2. Molar Ratio: The content of specific elements in the catalyst and their relative content were obtained using an energy-dispersive X-ray (EDX) spectrometer (Hitachi S-4800). In addition, EDX mapping was performed using a scanning electron microscope (Hitachi SU8010) with a fixed operating voltage of 10-15kV for element detection and localization.

[0059] The molar ratios of iron to metal (in the metal oxide powder) in each example and comparative example, measured according to the method described above, are shown in Tables 5 to 7 below.

[0060] The molar ratios of iron and copper in the catalysts of different metal oxide powders are as follows:

[0061] In the examples / comparative examples where the metal oxide powder is zinc oxide (ZnO), the molar ratio of iron to copper in Example 1 is 1:4.2, in Example 2 it is 1:6.0, in Example 3 it is 1:4.4, in Example 4 it is 1:5.3, in Example 5 it is 1:2.0, in Example 6 it is 1:3.2, in Example 7 it is 1:3.4, in Example 8 it is 1:3.4, in Example 9 it is 1:3.4, in Example 10 it is 1:5.7, in Example 11 it is 1:7.2, in Comparative Example 1 it is 1:0, and in Comparative Example 2 it is 0:1.

[0062] In Comparative Example 3, where the metal oxide powder is titanium dioxide (TiO2), the molar ratio of iron to copper is 1:1.3.

[0063] In the examples where the metal oxide powder is aluminum oxide (Al2O3), the molar ratio of iron to copper in Example 12 is 1:0.7, in Example 13 it is 1:1.3, in Example 14 it is 1:0.5, and in Example 15 it is 1:2.5.

[0064] In Example 16, where the metal oxide powder is magnesium oxide (MgO), the molar ratio of iron to copper is 1:2.8.

[0065] 3. Specific surface area and porosity: The specific surface area was measured using a nitrogen gas isothermal adsorption / desorption apparatus (Micromeritics TriStar II). Nitrogen gas isothermal adsorption / desorption tests were conducted under controlled temperature conditions of 77K to measure the specific surface area of ​​the material. Porosity was measured using a graduated cylinder and defined as (weight of catalyst-filled water / weight of unfilled water) × 100% in a given volume.

[0066] The specific surface area and porosity of each example and comparative example, measured according to the above method, are similarly shown in Tables 5 to 7 below.

[0067] <Evaluation Method>

[0068] 1. Removal Rate (DRE) and NO X Concentration: Measured using the equipment shown in Figure 3. This includes providing a heating reactor. The catalysts of each example and comparative example were placed in the heating reactor, and the inlet and outlet of the heating reactor each had corresponding FTIR detectors used to measure the concentration of a specific gas before and after (after catalytic treatment) in the heating reactor and its change (i.e., removal rate). Here, the catalyst volume was 20 mL, and the temperature of the heating reactor was maintained at 500°C. Simultaneously, nitrous oxide (N2O) and nitrogen (N2) were introduced into the inlet by a mass flow controller (MFC). Here, the volume concentration of nitrous oxide was 1%, and the flow rate was controlled to introduce it into the heating reactor at 400 sccm to 1350 sccm.

[0069] Figure 4 shows the N2O removal rate and NO2 concentration curve for the catalyst of Example 7. Figure 5 shows the N2O removal rate and NO2 concentration curve for the catalyst of Example 12. From Figures 4 and 5, it can be seen that the catalyst of the present invention achieves a DRE of 99% or more at 500°C, and the spatial flow rate is 3300 h. -1 The following shows that NO2 is hardly produced.

[0070] According to the above method, the DRE and NO at 450 °C and 500 °C of each example and comparative example measured under the condition that the flow rate is 623.3 sccm X The by-product concentrations are similarly shown in Tables 5 to 7 below.

[0071]

Table 5

[0072]

Table 6

[0073]

Table 7

[0074] Also, similarly, using the equipment in Fig. 3, a catalyst life test was conducted on the catalyst of Example 7. Here, the total gas flow rate was 623.3 sccm, the catalyst volume was 20 mL, and the space flow rate was 1870 h -1 is. The results are shown in Fig. 6.

[0075] As can be seen from Fig. 6, the catalyst of Example 7 can be continuously operated for 430 hours or more under the above conditions, and the nitrous oxide DRE at 500 °C was maintained at 99% or more. Therefore, the catalyst of the present invention has the effects of high stability and high efficiency.

[0076] Also, when only the calcination temperature was changed to 800 °C using the catalyst preparation method of Example 13, according to the above test, the nitrous oxide DRE of all of them exceeded 99%, and NO X It was verified that the by-product concentration was about 1000 ppm.

[0077] 2. Mechanical strength: Using a TH-1 digital tablet hardness tester manufactured by HSIANG TAI MACHINERY INDUSTRY CO., LTD., the compression strength of the catalyst was measured in kilogram-force (officially called kilogram-force, kgw).

[0078] The mechanical strength measured according to the above method is as follows:

[0079] In the example where the metal oxide powder is zinc oxide (ZnO), the mechanical strength is approximately 0.05 kgw to 0.45 kgw.

[0080] In the example where the metal oxide powder is aluminum oxide (Al2O3), the mechanical strength is approximately 0.20 kgw to 1.60 kgw.

[0081] In the example where the metal oxide powder is magnesium oxide (MgO), the mechanical strength is approximately 0.15 kgw to 0.75 kgw.

[0082] Furthermore, experiments have shown that adding a small amount of aluminum during the preparation process, for example, by adding an even smaller amount of aluminum nitrate to solution 2, improves the mechanical strength of the resulting catalyst, which is beneficial in extending the catalyst's lifespan and thereby improving the overall durability of the nitrous oxide removal system.

[0083] Although the present invention is disclosed by the embodiments described above, the present invention is not limited to those embodiments, and those skilled in the art can make changes and modifications without departing from the spirit and scope of the invention. Accordingly, the scope of protection of this disclosure shall be determined by the scope of the appended patent application. [Industrial applicability]

[0084] The nitrous oxide removal catalyst of the present invention can be used to treat semiconductor process exhaust gases containing N2O, waste gases generated during the production of nitric acid and adipic acid, medical anesthesia waste gases, and can also be used to treat exhaust gases containing flammable gases, etc.

Claims

1. Metal oxide powders containing zinc oxide, magnesium oxide, aluminum oxide, or combinations thereof, The metal oxide powder contains an iron-copper compound attached to its surface, The molar ratio of iron in the iron-copper compound to metal in the metal oxide powder is 1:(1.3 to 4.0). A catalyst for removing nitrous oxide.

2. The metal oxide powder is zinc oxide or magnesium oxide, and the catalyst is Fe ３ O ４ Further including the crystal structure, The catalyst for removing nitrous oxide according to claim 1.

3. The metal oxide powder is zinc oxide, the molar ratio of iron to copper in the iron-copper compound is 1:(1.8 to 6.2), and the molar ratio of iron in the iron-copper compound to metal in the metal oxide powder is 1:(1.4 to 4.0). The catalyst for removing nitrous oxide according to claim 1.

4. The compound further contains aluminum, and the molar ratio of iron to aluminum in the iron-copper compound is 1:(0.1 to 0.5). The catalyst for removing nitrous oxide according to claim 3.

5. The metal oxide powder is magnesium oxide, the molar ratio of iron to copper in the iron-copper compound is 1:(1.5 to 6.0), and the molar ratio of iron in the iron-copper compound to metal in the metal oxide powder is 1:(1.4 to 4.0). The catalyst for removing nitrous oxide according to claim 1.

6. The metal oxide powder is aluminum oxide, the molar ratio of iron to copper in the iron-copper compound is 1:(0.2 to 2.7), and the molar ratio of iron in the iron-copper compound to metal in the metal oxide powder is 1:(1.3 to 3.6). The catalyst for removing nitrous oxide according to claim 1.

7. The specific surface area of ​​the catalyst is 20 m². ２ g －１ ~200m ２ g －１ The porosity of the catalyst is 60% to 90%. The catalyst for removing nitrous oxide according to claim 1.

8. The mechanical strength of the catalyst is 0.5 kgw to 3.0 kgw. The catalyst for removing nitrous oxide according to claim 1.

9. Using the catalyst according to any one of claims 1 to 8, nitrous oxide is converted to nitrogen (N ２ ) and oxygen (O ２ This includes breaking it down into, Methods for removing nitrous oxide.

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