Catalyst for synthesizing ammonia from nitrogen oxides

Abstract

To synthesize ammonia from nitrogen oxide by using a catalyst using a non-precious metal.SOLUTION: A catalyst includes cerium oxide and copper carried on cerium oxide. A mass of copper with respect to a sum of cerium oxide and copper is preferably 5-20%. A specific surface area of the cerium oxide is preferably 130-170 m2 / g. With this catalyst, ammonia can be efficiently synthesized from nitrogen oxide under environment of relatively low temperatures of 150-230°C.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to a method for synthesizing ammonia from nitrogen oxides using a catalyst that uses a non-noble metal. [Background technology]

[0002] Titania (TiO2) supported with platinum (Pt) is known as a catalyst for synthesizing ammonia (NH3) from nitric oxide (NO) (Non-Patent Document 1). However, when using a Pt / TiO2 catalyst to synthesize NH3 from NO, the reaction temperature is lowered and carbon monoxide, a reducing agent contained in the raw material gas, is strongly adsorbed to the Pt, inhibiting the conversion reaction. For this reason, the Pt / TiO2 catalyst was not efficient in synthesizing NH3 at relatively low temperatures. In addition, the Pt / TiO2 catalyst uses expensive precious metals. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Catal. Sci. Technol., 2019, 9, p.2898-2905 Summary of the Invention [Problem to be solved by the invention]

[0004] The present application has been made in view of the above circumstances, and has as its object to synthesize ammonia from nitrogen oxides using a catalyst that uses a non-noble metal. [Means for solving the problem]

[0005] The catalyst of one embodiment of the present application is a catalyst for preventing nitrogen oxides (NO x The catalyst for synthesizing ammonia from cerium oxide (CeO2) contains cerium oxide (CeO2) and copper (Cu) supported on the cerium oxide.

[0006] Another embodiment of the catalyst of the present application is a catalyst for synthesizing ammonia from nitrogen oxides, which comprises aluminum oxide and copper supported on aluminum oxide (Al2O3).

[0007] In the method for producing ammonia according to the present invention, nitrogen oxides, carbon monoxide (CO), and water (H2O) are reacted in the presence of the catalyst according to the present invention to synthesize ammonia. Effect of the Invention

[0008] The catalyst of the present application uses Cu. Therefore, the catalyst of the present application is less expensive than a catalyst using Pt. In addition, when the catalyst of the present application is used, NO is generated at a lower temperature than when a catalyst using Pt is used. x NH3 can be synthesized from [Brief description of the drawings]

[0009] [Figure 1] 1 is a graph showing the relationship between reaction temperature and NO conversion rate to NH3 when the catalysts of Example 1, Example 5, Comparative Example 1, and Comparative Example 2 are used, respectively. [Diagram 2] 1 is a graph showing the relationship between reaction temperature and conversion rate of NO to NH 3 when each of the catalysts of Examples 1 to 4 is used. [Diagram 3] 2 is a graph showing the relationship between reaction temperature and NO conversion rate to NH3 when the catalysts of Example 1 and Example 6 are used, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The catalyst and ammonia production method of the present application will be described below based on the embodiment and examples. In this application, when a range between two numerical values ​​is expressed using "~", these two numerical values ​​are also included in this range. In addition, duplicated explanations will be omitted as appropriate. The catalyst of the present application is a catalyst for synthesizing ammonia from nitrogen oxides. Examples of nitrogen oxides include NO, NO2, NO3, N2O3, N2O4, and N2O5. The chemical reaction when synthesizing ammonia from nitrogen oxides is expressed as follows. 2NO x+(2x+3)CO+3H2O→2NH3+(2x+3)CO2

[0011] The catalyst of the first embodiment of the present application comprises cerium oxide and copper. The copper is supported on the cerium oxide. The catalyst of the first embodiment can be produced by a normal method of supporting a metal on an inorganic compound support. For example, the catalyst of the first embodiment can be obtained by adding cerium oxide to an aqueous copper ion solution, leaving the solution to stand, evaporating the water, calcining the solution, and then reducing the solution with hydrogen. The catalyst of the first embodiment may contain a substance other than cerium oxide and copper as long as it does not interfere with the synthesis of ammonia from nitrogen oxides.

[0012] For example, the catalyst of the first embodiment may contain metals such as zinc, and metal oxides such as aluminum oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide. The mass of copper relative to the sum of the masses of cerium oxide and copper (mass of copper / (mass of cerium oxide+mass of copper)) is preferably 5 to 20%. This is because the conversion rate of NO to NH3 is high. The specific surface area of ​​cerium oxide is 130 to 170 m 2 / g is preferred because it provides a high conversion of NO to NH3.

[0013] In the method for producing ammonia according to the first embodiment of the present application, nitrogen oxide, carbon monoxide, and water are reacted in the presence of the catalyst according to the first embodiment to synthesize ammonia. The temperature at which nitrogen oxide, carbon monoxide, and water are reacted is preferably 130 to 300°C. Although the conversion rate of NO to NH3 increases when the reaction is performed at a temperature of 130°C or higher, the conversion rate of NO to NH3 does not improve much compared to when the reaction is performed at a temperature of 200 to 300°C. Since the conversion rate of NO to NH3 is high, the reaction temperature is more preferably 150 to 230°C. Note that when the reaction is performed at a temperature of 150 to 200°C, the conversion rate of NO to NH3 is about 80% to 90% or more.

[0014] The catalyst of the second embodiment of the present application includes aluminum oxide and copper. The copper is supported on the aluminum oxide. As with the catalyst of the first embodiment, the catalyst of the second embodiment may contain a substance other than aluminum oxide and copper as long as it does not interfere with the synthesis of ammonia from nitrogen oxide. In the method for producing ammonia of the second embodiment of the present application, ammonia is synthesized by reacting nitrogen oxide, carbon monoxide, and water in the presence of the catalyst of the second embodiment. The temperature at which nitrogen oxide, carbon monoxide, and water are reacted is preferably 180 to 300°C. This is because the conversion rate of NO to NH3 is 60% or more. EXAMPLES

[0015] Example 1: Preparation of 5% Cu / CeO2 catalyst 0.60 g of copper nitrate trihydrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 5 mL of ion-exchanged water. CeO2 (Daiichi Kigenso Kagaku Kogyo Co., Ltd., Type A, specific surface area 170 m 2 3 g of Cu / g was added and left to stand for 30 minutes to obtain a mixed liquid. This mixed liquid was dried at 100°C for 16 hours to obtain a solid content. This solid content was calcined in air at 500°C for 4 hours, and then reduced at 400°C for 1 hour under a mixed gas flow of 90 vol% nitrogen and 10 vol% hydrogen to obtain a 5%Cu / CeO2 catalyst (a catalyst in which Cu mass / (CeO2 mass+Cu mass) is 5% and Cu is supported on CeO2; the same applies below).

[0016] Example 2: Preparation of 10% Cu / CeO2 catalyst A 10% Cu / CeO2 catalyst was obtained in the same manner as in Example 1, except that 1.20 g of copper nitrate trihydrate was used.

[0017] Example 3: Preparation of 20% Cu / CeO2 catalyst A 20% Cu / CeO2 catalyst was obtained in the same manner as in Example 1, except that 2.40 g of copper nitrate trihydrate was used.

[0018] Example 4: Preparation of 1% Cu / CeO2 catalyst A 1% Cu / CeO2 catalyst was obtained in the same manner as in Example 1, except that 0.12 g of copper nitrate trihydrate was used.

[0019] Example 5: Preparation of 5% Cu / CeO2 catalyst 2 CeO2 (Daiichi Kigenso Kagaku Kogyo Co., Ltd., Type B, specific surface area 130m 2 A 5% Cu / CeO2 catalyst was obtained in the same manner as in Example 1, except that Cu / CeO2 was used.

[0020] Example 6: Preparation of 5% Cu / Al2O3 catalyst A 5% Cu / Al2O3 catalyst was obtained in the same manner as in Example 1, except that Al2O3 (Kojundo Chemical Laboratory Co., Ltd., 29424D) was used instead of CeO2.

[0021] Comparative Example 1: Preparation of 5% Cu / ZrO2 catalyst A 5% Cu / ZrO2 catalyst was obtained in the same manner as in Example 1, except that ZrO2 (Daiichi Kigenso Kagaku Kogyo Co., Ltd., RSC-H) was used instead of CeO2.

[0022] Comparative Example 2: Preparation of 5% Cu / SiO2 catalyst A 5% Cu / SiO2 catalyst was obtained in the same manner as in Example 1, except that SiO2 (Fuji Silysia Ltd., Q-15) was used instead of CeO2.

[0023] Catalytic activity evaluation The catalysts of Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated for their activity in converting nitrogen monoxide to ammonia. A mixed gas consisting of 1000 ppm NO, 3000 ppm CO, 10000 ppm H2O, and argon as the balance gas was used as the raw material gas. The chemical reaction when ammonia is synthesized by reacting nitrogen oxides, carbon monoxide, and water is represented as follows. 2NO+5CO+3H2O→2NH3+5CO2

[0024] 0.15 g of each substance was placed in the center of a quartz reaction tube with an inner diameter of 10 mm and a length of 360 mm, sandwiched between quartz glass wool. The reaction tube was placed so that the openings at both ends were on the top and bottom, and the raw material gas was supplied into the reaction tube from the upper opening at 250 mL per minute to contact each substance. The temperature inside the reaction tube was maintained at 500°C, and the contact gas, i.e., the reaction gas, was collected from the upper opening 30 minutes after the start of the raw material gas supply and analyzed. The analysis was performed using a Fourier transform infrared spectrometer (ThermoFischer, Nicolet is50) equipped with a multi-reflection gas cell and a gas chromatograph (Inficon, 3000 MicroGC). The temperature inside the reaction tube was lowered from 500°C, and the reaction gas was analyzed 60 minutes after the start of the raw material gas supply in the same manner at a specified temperature.

[0025] The concentrations of NO and NH3 were measured using an infrared spectrometer at 1934 cm -1 and 1122cm -1 The conversion rate of NO to NH3 was calculated using the following formula: Conversion rate of NO to NH3 (%) = NH3 concentration in gas after reaction / NO concentration in raw gas × 100

[0026] FIG. 1 shows the relationship between the reaction temperature and the conversion rate of NO to NH3 when the catalysts of Example 1, Example 5, Comparative Example 1, and Comparative Example 2 are used. FIG. 2 shows the relationship between the reaction temperature and the conversion rate of NO to NH3 when the catalysts of Example 1 to Example 4 are used. FIG. 3 shows the relationship between the reaction temperature and the conversion rate of NO to NH3 when the catalysts of Example 1 and Example 6 are used. As shown in FIG. 1, with the 5% Cu / CeO2 catalyst, 42 to 92% of NO could be converted to NH3 at a reaction temperature of 130 to 300°C, and even at a relatively low reaction temperature of 150 to 230°C, 78 to 92% of NO could be converted to NH3. Also, with the 5% Cu / Al2O3 catalyst, 62 to 70% of NO could be converted to NH3 at a reaction temperature of 180 to 300°C.

[0027] In contrast, the 5%Cu / ZrO2 catalyst was only able to convert a maximum of 37% of NO to NH3 at reaction temperatures below 300°C. With the 5%Cu / ZrO2 catalyst, the conversion rate of NO to NH3 reached 42% or more when the reaction temperature exceeded 330°C. With the Cu / SiO2 catalyst, the conversion rate of NO to NH3 increased as the reaction temperature increased, but even when the reaction temperature exceeded 500°C, the conversion rate of NO to NH3 was only 36%. From the above, it was found that Cu / CeO2 (a material in which Cu is supported on CeO2; the same applies below) and Cu / Al2O3 have superior NO to NH3 conversion performance compared to Cu / ZrO2 and Cu / SiO2.

[0028] As shown in Figure 2, when the Cu loading in the Cu / CeO2 catalyst was 5-20 mass%, 79-95% of NO was converted to NH3 even at a relatively low reaction temperature of 150-230°C. The 1%Cu / CeO2 catalyst had slightly lower NO to NH3 conversion performance than the 5%Cu / CeO2, 10%Cu / CeO2, and 20%Cu / CeO2 catalysts. However, the 1%Cu / CeO2 catalyst was able to convert 71% of NO to NH3 even at a relatively low reaction temperature of 200°C, and was found to function sufficiently as a catalyst for synthesizing ammonia from nitrogen oxides.

[0029] In addition, as shown in Figure 3, it was found that the larger the specific surface area of ​​CeO2, the better the conversion performance of NO to NH3 in the Cu / CeO2 catalyst. However, when the specific surface area of ​​CeO2 is 130m 2 / g, and the catalyst of Example 1 with a specific surface area of ​​CeO2 of 170 m 2 It was found that the catalyst of Example 6, which had a catalytic activity of 0.1% to 1.0% by weight, was capable of converting 53 to 92% of NO to NH3 even at a relatively low reaction temperature of 200°C, and thus functioned satisfactorily as a catalyst for synthesizing ammonia from nitrogen oxides.

Claims

1. A method for producing ammonia, comprising reacting nitrogen oxides with carbon monoxide and water at a temperature of 130 to 300°C in the presence of a catalyst for synthesizing ammonia from nitrogen oxides, the catalyst comprising cerium oxide and copper supported on the cerium oxide, to synthesize ammonia.

2. In claim 1, The method for producing ammonia, wherein the mass of the copper is 5 to 20% relative to the sum of the masses of the cerium oxide and the copper.

3. In claim 1 or 2, The specific surface area of ​​the cerium oxide is 130 to 170 m ２ / g of ammonia.

4. In any one of claims 1 to 3, A method for producing ammonia by reacting nitrogen oxides, carbon monoxide and water at temperatures between 150 and 230°C.

5. A method for producing ammonia, comprising reacting nitrogen oxides with carbon monoxide and water at a temperature of 180 to 300°C in the presence of a catalyst for synthesizing ammonia from nitrogen oxides, the catalyst comprising aluminum oxide and copper supported on the aluminum oxide, to synthesize ammonia.

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