Supported catalyst and method for producing ammonia

Abstract

To provide a supported catalyst having reduced generation of N2O as a by-product even at a low reaction temperature during the synthesis of ammonia from nitrogen oxides.SOLUTION: A supported catalyst includes a carrier and a platinum element. The carrier contains TiO2-x. The x is a real number greater than 0.0 and smaller than 2.0. The platinum element is supported on the TiO2-x.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a supported catalyst and a method for producing ammonia.

Background Art

[0002] From the viewpoint of environmental pollution prevention, methods for treating and detoxifying nitrogen oxides (NOx) such as nitrogen monoxide and nitrogen dioxide contained in exhaust gas have been studied. As a method for treating nitrogen oxides, reduction to nitrogen molecules using a reducing agent is known. However, it is difficult to effectively utilize the obtained nitrogen molecules. In recent years, due to the increasing interest in sustainable development goals (SDGs), it has been required to produce substances that can be effectively utilized from nitrogen oxides. Such substances include, for example, ammonia. As a supported catalyst for synthesizing ammonia (NH3) from nitrogen monoxide (NO), which is a nitrogen oxide, Patent Document 1 exemplifies a supported catalyst in which platinum (Pt) is supported on titanium oxide (TiO2). In Patent Document 1, using this supported catalyst, nitrogen monoxide is reduced with carbon monoxide (CO) and hydrogen (H2) to synthesize ammonia (NH3) (the following formula (1)). 2NO + 5H2 → 2NH3 + 2H2O (1)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as a result of investigations by the inventors, it was found that the supported catalyst in which Pt is supported on the above TiO2 produces nitrous oxide (N2O) as a by-product when the reaction temperature is lowered. The ability to produce ammonia at a low reaction temperature is desirable from the perspective of energy conservation. And since N2O is a strong greenhouse gas, it was recognized that there is a need for the emergence of a catalyst capable of synthesizing ammonia from nitrogen oxides while reducing the amount of by-produced N2O.

[0005] The present disclosure has been made in view of such circumstances, and provides a supported catalyst in which the amount of by-produced N2O is small even at a low reaction temperature when synthesizing ammonia from nitrogen oxides. Further, the present disclosure provides a method for producing ammonia using the nitrogen oxide reduction catalyst of the present disclosure.

Means for Solving the Problems

[0006] The present disclosure is a supported catalyst including a carrier and a platinum element, wherein the carrier contains TiO 2-x and x is a real number greater than 0.0 and less than 2.0, and the platinum element is supported on the TiO 2-x relates to a supported catalyst.

[0007] Also, the present disclosure is a method for producing ammonia, including a preparation step of preparing the supported catalyst of the present disclosure, a contact step A of bringing a gas containing nitrogen oxides into contact with the supported catalyst, and a contact step B of bringing a gas containing hydrogen into contact with the supported catalyst that has been brought into contact with the gas containing nitrogen oxides, relates to a method for producing ammonia having the above.

Effects of the Invention

[0008] According to the present disclosure, a supported catalyst in which the amount of by-produced N2O is small even at a low reaction temperature is provided when synthesizing ammonia from nitrogen oxides. Further, according to the present disclosure, a method for producing ammonia using the supported catalyst of the present disclosure is provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, the catalyst and the method for producing ammonia of the present disclosure will be described based on embodiments and examples. In addition, the description of "XX or more and YY or less" or "XX to YY" representing a numerical range means a numerical range including the lower limit and the upper limit which are endpoints unless otherwise specified. When the numerical ranges are described stepwise, the upper limit and the lower limit of each numerical range can be arbitrarily combined. Also, duplicate explanations will be omitted as appropriate.

[0011] The supported catalyst of the present disclosure includes a carrier and a platinum element, the carrier contains TiO 2-x and x is a real number greater than 0.0 and less than 2.0, and the platinum element is supported on TiO 2-x With such a configuration, when synthesizing ammonia from nitrogen oxides, it becomes a supported catalyst with a small amount of by-produced N2O even at a low reaction temperature. That is, the supported catalyst of the present disclosure can be used as a nitrogen oxide reduction catalyst for ammonia production. In the present disclosure, the "nitrogen oxide reduction catalyst" refers to a catalyst having the ability to reduce nitrogen oxides (NOx) such as nitric oxide and nitrogen dioxide. For example, a nitrogen oxide reduction catalyst for ammonia production can synthesize ammonia from nitrogen oxides and hydrogen. Nitrogen oxides (NO x) include NO, NO2, NO3, N2O3 (NO 1.5 ), N2O4 (NO2), N2O5 (NO 2.5 ), etc. These nitrogen oxides can be used alone or in combination of two or more kinds. When synthesizing ammonia from nitrogen oxides and hydrogen (H2), the chemical reaction is represented by the following formula (2). 2NO y +(2y + 3)H2 → 2NH3 + 2yH2O (2) (In formula (2), y represents a real number from 1 to 3.)

[0012] As described above, the supported catalyst contains TiO contained in the carrier 2-x and platinum element supported on TiO 2-x . x is a real number greater than 0.0 and less than 2.0. Although the reason for obtaining the effect of the present disclosure with such a configuration is not clear, the inventors speculate as follows.

[0013] TiO 2-x represents reduced titanium oxide. That is, it can also be said to be titanium oxide having oxygen deficiency. Titanium oxide having oxygen deficiency has a higher electron density than titanium oxide (TiO2) having no oxygen deficiency. When the electron density is high, atoms diffusing on the surface repel the surface with a high electron density and move quickly. As a result, it is considered that hydrogen spillover, which is a phenomenon in which the active hydrogen generated on the platinum element diffuses onto the TiO 2-x surface, occurs more easily and quickly. When hydrogen spillover occurs quickly, the rate of generating ammonia increases, and the amount of by-produced N2O can be suppressed. Alternatively, it is speculated that titanium oxide with oxygen deficiency has a strong ability to remove oxygen from compounds. Oxygen can be removed from the by-produced N2O and decomposed to suppress the by-production amount.

[0014] The value of x is preferably greater than 0.0 and less than or equal to 1.0, more preferably greater than 0.0 and less than or equal to 0.5, even more preferably greater than 0.0 and less than or equal to 0.2, and particularly preferably greater than 0.0 and less than or equal to 0.1. Also, it may be greater than or equal to 0.01 and less than 2.0, greater than or equal to 0.01 and less than or equal to 0.5, greater than or equal to 0.01 and less than or equal to 0.2, greater than or equal to 0.01 and less than or equal to 0.10. When within the above range, it becomes easier to accelerate hydrogen spillover. The value of x can be adjusted by changing the conditions when reducing titanium oxide. Specifically, when titanium oxide is exposed to high-temperature conditions in a hydrogen atmosphere for reduction, the value of x becomes smaller, and when the reduced titanium oxide is exposed to high-temperature conditions in an atmosphere containing air, water vapor, oxygen, etc. for oxidation, the value of x becomes larger. Also, TiO within the above range 2-x such as ENETIA (registered trademark) series TiO of Sakai Chemical Industry Co., Ltd. can be used. 2-δ

[0015] The carrier contains TiO 2-x and the value of x can be measured by X-ray photoelectron spectroscopy (XPS). Specifically, it is measured by the following method. Measure the 2p orbital of Ti by XPS. Obtain the area values of Ti 3+ and Ti 4+ from the peak of Ti. There is no oxygen deficiency in Ti 4+ , and assuming that there are two Ti 3+ with one oxygen deficiency, calculate the degree of oxygen deficiency from the area values of Ti 3+ and Ti 4+ and calculate the value of x.

[0016] The volume resistivity of TiO 2-x is preferably 10 -3 ~10 7 Ω·cm, more preferably 10 1 ~10 7 Ω·cm, even more preferably 10 3 ~10 7 Ω·cm, particularly preferably 10 5 ~10 7 Ω·cm.​6 ~10 7 It is particularly preferable that it is Ω·cm. When the volume resistivity is within the above range, hydrogen spillover is likely to occur quickly. The volume resistivity can be measured by a general conductivity meter. Specifically, it is measured by the following method. Using a press, apply a load to TiO 2-x to crush the voids and make it solid-like, and then contact the energizing electrode of the conductivity meter for measurement. With such a method, accurate measurement values can be obtained even if TiO 2-x is in powder form. To measure the volume resistivity more accurately, it is preferable to use a conductivity measuring instrument for semiconductors.

[0017] TiO 2-x The crystal structure of is not particularly limited and can be rutile type, anatase type, or brookite type. Among them, the rutile type is preferable.

[0018] The aspect in which the supported catalyst contains a platinum element is not particularly limited, and examples include aspects such as nanoparticles, sub-nanoparticles, nanorods, single atoms, bulk crystals, and elements derived from precursors remaining and being compounded.

[0019] The content of the platinum element in the supported catalyst is not particularly limited, but it is preferably 0.2 to 2.0% by mass, more preferably 0.5 to 1.5% by mass, and even more preferably 0.7 to 1.3% by mass. When it is within the above range, the catalytic activity is likely to be suitable. The content of the platinum element in the supported catalyst can be measured by inductively coupled plasma mass spectrometry.

[0020] The content of the carrier in the supported catalyst is not particularly limited, but it is preferably 98.0 to 99.8% by mass, more preferably 98.5 to 99.5% by mass, and even more preferably 98.7 to 99.3% by mass. TiO in the carrier 2-x The content of is not particularly limited, but it is preferably 90.0 to 100.0% by mass, more preferably 92.5 to 100.0% by mass with respect to the carrier <,> It is more preferably 95.0 to 100.0% by mass.

[0021] The supported catalyst may contain inevitable impurities as long as it does not prevent the synthesis of ammonia from nitrogen oxides. Inevitable impurities are impurities that cannot be avoided during production. The content of inevitable impurities in the supported catalyst is 1% by mass or less. That is, the supported catalyst preferably consists essentially of only a carrier and a platinum element. Further, it is more preferable that the carrier consists of only TiO 2-x alone. Here, "consisting essentially of only" means that, in addition to the carrier and the platinum element, a small amount of other impurities (for example, 1% by mass or less based on the supported catalyst) is allowed to be mixed in.

[0022] The method for producing the supported catalyst is not particularly limited, and the supported catalyst can be produced by a known method of supporting a metal on an inorganic compound carrier. For example, TiO 2-x is added to an aqueous platinum solution and allowed to stand to obtain a slurry, and then the water is evaporated. Then, after firing the obtained solid content, the supported catalyst is obtained by hydrogen reduction. That is, the method for producing the supported catalyst preferably includes a step of preparing an aqueous platinum solution. Further, it preferably includes a slurry preparation step of adding TiO 2-x to the aqueous platinum solution. Furthermore, it preferably includes a drying step of drying the slurry obtained in the slurry preparation step to obtain a solid. Furthermore, it preferably includes a firing step of firing the solid obtained in the drying step to obtain a fired product. In addition, it preferably includes a reduction step of reducing the fired product obtained in the firing step. It is more preferable to have the above steps in this order.

[0023] The step of preparing the aqueous platinum solution is, for example, a step of dissolving a platinum source such as hexachloroplatinate(IV) acid in ion-exchanged water. Stirring may be performed if necessary. The content of platinum in the aqueous platinum solution is not particularly limited, but is preferably 0.2 to 2.0% by mass, more preferably 0.5 to 1.5% by mass, and even more preferably 0.7 to 1.3% by mass.

[0024] The slurry preparation step is a step of adding TiO 2-x to an aqueous solution of platinum. At this time, ion-exchanged water may be further added to prepare a slurry. The drying step is a step of drying the slurry to obtain a solid. The drying method is not particularly limited, and examples include heating the slurry to volatilize ion-exchanged water. The heating conditions are not particularly limited, and examples include 80 to 120°C for 6 to 18 hours. The firing step is a step of firing the solid obtained in the drying step to obtain a fired product. The firing conditions are not particularly limited, and examples include 450 to 550°C for 3 to 5 hours in an air atmosphere.

[0025] The reduction step is a step of reducing the fired product obtained in the firing step. By reducing the fired product, the supported catalyst of the present disclosure is easily obtained. The reduction conditions are not particularly limited, but for example, it is preferably 350 to 450°C for 0.5 to 2 hours. The reduction atmosphere is not particularly limited as long as it is a reducing gas, but an H2 gas atmosphere is preferred. For example, a mixed gas of H2 and N2 may be used. The reducing gas is preferably under flow conditions.

[0026] The method for producing ammonia includes a preparation step of preparing the supported catalyst of the present disclosure, a contact step A of bringing a gas containing nitrogen oxides into contact with the supported catalyst, and a contact step B of bringing a gas containing hydrogen into contact with the supported catalyst that has been brought into contact with the gas containing nitrogen oxides. By using the supported catalyst of the present disclosure, ammonia can be suitably produced.

[0027] As the step of preparing the supported catalyst, the method for producing the supported catalyst described above can be used.

[0028] In the contact step A, a gas containing nitrogen oxides such as nitrogen monoxide and nitrogen dioxide is brought into contact with the supported catalyst. The nitrogen oxides to be used are not particularly limited, but can be directly obtained from the atmosphere or exhaust gas The recovered nitrogen oxides can also be used. The exhaust gas is not particularly limited as long as it contains nitrogen oxides, and for example, exhaust gas generated by incineration of waste can be used, regardless of its source or contained components.

[0029] The concentration of nitrogen oxides in the gas is not particularly limited, and for example, it may be 100 to 100,000 volume ppm, may be 500 to 50,000 volume ppm, or may be 500 to 10,000 volume ppm. The gas preferably contains little oxygen. For example, the concentration of oxygen in the raw material gas is preferably 0.5 mass% or less. Specifically, it is preferably 0.0 to 0.5 mass%. Within the above range, the reduction reaction of nitrogen oxides tends to proceed, and the generated ammonia is less likely to be oxidized.

[0030] The temperature in the contacting step A is not particularly limited, but is preferably 100 to 600 °C, more preferably 200 to 550 °C, and even more preferably 300 to 550 °C. Also, it is preferably 100 to 300 °C or 100 to 200 °C.

[0031] In the contacting step B, a gas containing hydrogen is brought into contact with the supported catalyst that has been contacted with the gas containing nitrogen oxides to obtain ammonia. Hydrogen acts as a reducing agent. The method for bringing the gas into contact with the supported catalyst is not particularly limited, and known methods can be used. Also, the contacting step A and the contacting step B may be carried out simultaneously. For example, a gas containing nitrogen oxides and hydrogen may be brought into contact with the supported catalyst. This makes it easier for the amount of by-produced N2O to be less.

[0032] The concentration of hydrogen in the gas is not particularly limited, and for example, it may be 300 to 100,000 volume ppm, may be 500 to 50,000 volume ppm, or may be 1000 to 10,000 volume ppm. The temperature in the contact step B is not particularly limited, but is preferably 100 to 500°C, more preferably 100 to 300°C, and even more preferably 100 to 200°C. By being within the above range, ammonia can be synthesized more efficiently.

Example

[0033] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

[0034] <Example 1> (Preparation of 1 mass% Pt / TiO 2-x catalyst) TiO 2-x As TiO 2-δ (manufactured by Sakai Chemical Industry Co., Ltd., conductive titanium oxide ENETIA (registered trademark) series TiO 2-δ , volume resistivity 10 6 ~10 7 Ω·cm) was used. The value of δ exceeds 0.0 and is 0.1 or less. Hexachloroplatinic(IV) acid (manufactured by Fujifilm Wako Pure Chemical Corporation, reagent special grade) was dissolved in ion-exchanged water to obtain a 1 mass% Pt aqueous solution. To 1.314 mL of this aqueous solution, 2.0 g of TiO 2-δ was added, and further 17.87 mL of ion-exchanged water was added to obtain a slurry. This slurry was dried at 100°C for 10 hours to obtain a solid.

[0035] The obtained solid 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 1 mass% Pt / TiO 2-δ catalyst (the value of mass of Pt element / (mass of Pt element + mass of TiO 2-δ ) × 100 is 1, and the Pt element is supported on TiO2. The same applies hereinafter). In addition, the "1 mass% Pt / TiO 2-δ catalyst" may be simply described as "1Pt / TiO 2-δ ". The same applies to the catalysts of Comparative Examples 1 to 2.

[0036] <Comparative Example 1> (Preparation of 1 mass% Pt / TiO₂ catalyst) TiO 2-x 1Pt / TiO₂ was obtained in the same manner as in Example 1, except that TiO₂ (manufactured by Sakai Chemical Industry Co., Ltd., rutile type titanium oxide) was used instead of TiO.

[0037] <Reference Example 1> (Preparation of 1 mass% Pt / Ti₄O₇ catalyst) TiO 2-x 1Pt / Ti₄O₇ was obtained in the same manner as in Example 1, except that Ti₄O₇ (manufactured by Sakai Chemical Industry Co., Ltd., conductive titanium oxide ENETIA (registered trademark) series Ti₄O₇, volume resistivity 10 -3 ~10 1 Ω·cm) was used instead of TiO.

[0038] <Catalyst activity evaluation> For the catalysts of Example 1, Comparative Example 1, and Reference Example 1, the activities of producing ammonia from nitrogen monoxide and hydrogen were evaluated respectively. As the raw material gas, a mixed gas composed of 1000 volume ppm of NO, 3000 volume ppm of H₂, and the balance being argon was used. The chemical reaction when synthesizing ammonia by reacting nitrogen monoxide and hydrogen is represented by the following formula (1). 2NO + 5H₂ → 2NH₃ + 2H₂O (1)

[0039] 0.15 g of the catalyst sandwiched vertically with quartz glass wool was placed at the central part inside the reaction tube of a 360 - mm - long quartz reaction tube in which a 10 - mm - inner - diameter × 180 - mm - long part and an 8 - mm - inner - diameter × 180 - mm - long part were connected. This reaction tube was placed inside the electric furnace with the openings at both ends facing up and down, and the above - mentioned raw material gas was supplied into the reaction tube at 250 mL per minute from the upper opening, and the raw material gas was brought into contact with the catalyst. The temperature at this time was 500°C. Further, the temperature inside the reaction tube was maintained at 500°C, and the post - contact gas, that is, the post - reaction gas, 30 minutes after the start of the supply of the raw material gas was collected from the lower opening and analyzed. Among them, the results in the range of reaction temperature from 100 to 300°C are shown in Figures 1 to 3. The analysis was performed using a Fourier transform infrared spectrometer (ThermoFischer, Nicolet is50) equipped with a multiple reflection gas cell and a gas chromatograph (Agilent, 490 MicroGC). After collecting the post-reaction gas as described above, the temperature in the reaction tube was decreased from 500 °C, and in the same manner as when it was at 500 °C, the post-reaction gas at any temperature during the temperature decrease was analyzed.

[0040] The concentrations of NO, NH3, and N2O in the post-reaction gas were measured at 1875 cm -1 and 1195 cm -1 and 2241 cm -1 from the area values, respectively. Also, the conversion rate of NO, the yield of NH3 (conversion rate of NO to NH3), and the yield of N2O (conversion rate of NO to N2O) were calculated respectively by the following calculation formulas based on the amount of nitrogen in the raw material gas. Conversion rate of NO (%) = (NO concentration in raw material gas - NO concentration in post-reaction gas) / NO concentration in raw material gas × 100 Yield of NH3 (%) = NH3 concentration in post-reaction gas / NO concentration in raw material gas × 100 Yield of N2O (%) = (N2O concentration in post-reaction gas × 2) / NO concentration in raw material gas × 100

[0041] Figure 1 shows the relationship between the reaction temperature and the conversion rate of NO in Example 1, Comparative Example 1, and Reference Example 1. As shown in Figure 1, NO was consumed even at around 100 °C which is a relatively low temperature. Figure 2 shows the relationship between the reaction temperature and the yield of NH3 in Example 1, Comparative Example 1, and Reference Example 1. As shown in Figure 2, NH3 was synthesized even at around 100 °C which is a relatively low temperature.

[0042] Figure 3 shows the relationship between the reaction temperature and the yield of N2O in Example 1, Comparative Example 1, and Reference Example 1. As shown in Figure 3, 1Pt / TiO 2-δ hardly produced N2O in almost all temperature regions where NH3 was synthesized.

[0043] Figure 4 shows the N2O yields at 150 °C in the long-term reaction according to Example 1 and Comparative Example 1. Specifically, the evaluation was performed according to the following procedure. At the center of the reaction tube of a 360-mm-long quartz reaction tube, where a 10-mm-inner-diameter × 180-mm-long part and an 8-mm-inner-diameter × 180-mm-long part were connected, 0.15 g of the catalyst sandwiched vertically with quartz glass wool was installed. This reaction tube was installed inside the electric furnace with the openings at both ends facing up and down, and the above raw material gas was supplied into the reaction tube from the upper opening at 250 mL per minute, bringing the raw material gas into contact with the catalyst. The temperature at this time was 500 °C. Further, the temperature inside the reaction tube was maintained at 500 °C. After 30 minutes had elapsed since the start of the supply of the raw material gas, the temperature inside the reaction tube was lowered from 500 °C and maintained at 150 °C, and analysis was performed approximately every hour using the Fourier transform infrared spectrometer equipped with the above multiple reflection gas cell and the above gas chromatograph. A flow reaction of approximately 10 hours per day was performed, and after the measurement, the temperature was lowered to room temperature. The next day, the measurement was repeated from heating to 500 °C again with the same procedure. As a result, for 1Pt / TiO 2-δ almost no N2O was generated even after 65 hours had elapsed.

[0044] Illustrating the invention understood from the above disclosure is as follows. [1] A supported catalyst containing a carrier and a platinum element, wherein the carrier contains TiO 2-x and x is a real number greater than 0.0 and less than 2.0, and the platinum element is supported on the TiO 2-x ; a supported catalyst. [2] The supported catalyst according to [1], wherein the volume resistivity of the TiO 2-x is 10 -3 to 10 7 Ω·cm. [3] The supported catalyst according to [1] or [2], wherein the volume resistivity of the TiO 2-x is 10 6 to 10 7 Ω·cm. [4] The supported catalyst according to any one of [1] to [3], wherein the content of the platinum element in the supported catalyst is 0.2 to 2.0% by mass. [5] The supported catalyst according to any one of [1] to [4], wherein the supported catalyst is a nitrogen oxide reduction catalyst for ammonia production. [6] A method for producing ammonia, comprising: a preparation step of preparing the supported catalyst according to any one of [1] to [5]; a contact step A of bringing a gas containing nitrogen oxides into contact with the supported catalyst; a contact step B of bringing a gas containing hydrogen into contact with the supported catalyst that has been brought into contact with the gas containing nitrogen oxides; and a method for producing ammonia having the above steps. [7] The method for producing ammonia according to [6], wherein the temperature in the contact step B is 100°C to 300°C. [8] The method for producing ammonia according to [6] or [7], wherein the contact step A and the contact step B are performed simultaneously. [9] The method for producing ammonia according to any one of [6] to [8], wherein the nitrogen oxide is nitric oxide.

Claims

1. A supported catalyst comprising a carrier and a platinum element, The carrier contains TiO ２－ｘ and wherein x is a real number greater than 0.0 and less than 2.0, The platinum element is supported on the TiO ２－ｘ to form a supported catalyst.

2. The TiO ２－ｘ has a volume resistivity of 10 －３ to 10 ７ Ω·cm, and the supported catalyst according to claim 1.

3. The volume resistivity of the TiO ２－ｘ is 10 ６ to 10 ７ Ω·cm, and the supported catalyst according to claim 1.

4. The supported catalyst according to claim 1, wherein the content of the platinum element in the supported catalyst is 0.2 to 2.0% by mass.

5. The supported catalyst according to claim 1, wherein the supported catalyst is a nitrogen oxide reduction catalyst for ammonia production.

6. A method for producing ammonia, comprising: a preparation step of preparing the supported catalyst according to any one of claims 1 to 5; a contact step A of bringing a gas containing nitrogen oxides into contact with the supported catalyst; a contact step B of bringing a gas containing hydrogen into contact with the supported catalyst that has been brought into contact with the gas containing nitrogen oxides; and a method for producing ammonia having the above steps.

7. The method for producing ammonia according to claim 6, wherein the temperature in the contact step B is 100°C to 300°C.

8. The method for producing ammonia according to claim 6, wherein the contact step A and the contact step B are carried out simultaneously.

9. The method for producing ammonia according to claim 6, wherein the nitrogen oxide is nitric oxide.

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