Nitrogen dioxide decomposition catalyst

Abstract

To provide a catalyst capable of decomposing (de-toxifying) N2O in relatively low temperature conditions such as combustion furnace exhaust heat, a decomposition method, and a method of producing the catalyst.SOLUTION: A nitrous oxide decomposition catalyst containing a compound represented by the formula (1) in the figure, where x represents 0.00 to 1.00, is used to decompose and de-toxify N2O contained in combustion furnace exhaust into nitrogen and oxygen.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a nitrous oxide decomposition catalyst.

Background Art

[0002] The N2O emission amount is approximately 12.2 kt-N2O per year. If this is priced compared to carbon pricing, the economic scale in the Japanese market will be up to 51 billion yen per year, and the size of the assumed market scale is remarkable. Enterprises having local emission facilities are expected to work on N2O emission reduction on the market scale of the "carbon pricing price accumulated every year" in order to avoid the above burden. Nitrous oxide (N2O) is a greenhouse gas about 300 times that of carbon dioxide (CO2), and the emission sources are mainly the energy industry (combustion furnace) and agricultural land. In particular, the emission from the combustion furnace is at a high concentration. If this exhaust heat can be used for N2O decomposition, more energy-saving N2O decomposition will be possible. Regarding the decomposition method of nitrous oxide, in Non-Patent Document 1, the decomposition activity of N2O using a catalyst of Ni x Co 1-x Co2O4 is described, but even when the evaluation test under these conditions was carried out, the N2O decomposition ability under the temperature conditions corresponding to the exhaust heat of the incinerator was inferior. Thus, in the conventional technology, there is no report on a catalyst capable of decomposing (detoxifying) N2O discharged in a relatively low-temperature state such as the exhaust heat of a combustion furnace.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a catalyst capable of decomposing (detoxifying) N2O under relatively low temperature conditions such as the exhaust heat of a combustion furnace.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have developed a high-performance Ni x Cu 1-x Co2O4 catalyst that can decompose N2O contained in the exhaust gas of a combustion furnace into nitrogen (N2) and oxygen (O2) at low temperatures. That is, the present invention includes the following aspects: In one aspect of the present invention, 〔1〕A dinitrogen monoxide decomposition catalyst containing a compound represented by the following formula (1).

Chemical formula

Advantages of the Invention

[0006] The catalyst according to the present invention does not contain noble metals, is composed of inexpensive elements, and the production method is also mass-producible. The N2O decomposition performance of the catalyst of the present invention is comparable to or higher than that of general noble metal catalysts such as Pt and Ir / ZrO2, and it can be used even under relatively low temperature conditions such as the exhaust heat of a combustion furnace, so it is energy-saving. In the future, as the pricing of greenhouse gases (carbon pricing) also progresses, it can contribute to solving the N2O emission problem.

Brief Description of the Drawings

[0007]

Figure 1

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Mode for Carrying Out the Invention

[0008] One aspect of the present invention provides a dinitrogen monoxide decomposition catalyst containing a compound represented by the following formula (1).

Chemical formula

[0009] In a preferred embodiment, x in formula (1) is 0.00 < x < 1.00. More preferably, x is 0.50 or more and less than 1.00, and still more preferably, x is in the range of 0.60 or more and 0.90 or less. As the most preferred embodiment, x is 0.75, and the compound represented by formula (1) is Ni 0.75 Cu 0.25 Co2O4.

[0010] The nitrous oxide catalyst according to the present invention has the ability to decompose nitrous oxide under relatively low temperature conditions as compared with conventional nitrous oxide catalysts. Here, the low temperature conditions refer to 400 ° C or lower (for example, 350 ° C or lower, 300 ° C or lower, 250 ° C or lower, 240 ° C or lower, 230 ° C or lower, or 220 ° C or lower), preferably 210 ° C or lower.

[0011] Another aspect of the present invention is a method for producing a compound represented by the following formula (1), which includes a step of adding a coprecipitant to an aqueous solution prepared by mixing a nickel salt, a cobalt salt, and a copper salt to coprecipitate a precipitate containing the compound. A manufacturing method is provided.

Chemical formula

[0012] Examples of the nickel salt that can be used in the production method of the present invention include inorganic metal salts of nickel. Examples of the inorganic metal salt of nickel include, but are not limited to, nickel nitrate, nickel sulfate, nickel chloride, and the like. Examples of the cobalt salt that can be used in the production method of the present invention include inorganic metal salts of cobalt. Examples of the inorganic metal salt of cobalt include, but are not limited to, cobalt nitrate, cobalt sulfate, cobalt chloride, and the like. Examples of the copper salt that can be used in the production method of the present invention include inorganic metal salts of copper. Examples of the inorganic metal salt of copper include, but are not limited to, copper nitrate, copper sulfate, copper chloride, and the like. As the solvent for mixing the above nickel salt, cobalt salt, and copper salt, ion-exchanged water or ultrapure water can be used. The nickel salt added to the solvent can be added, for example, to a concentration of 0.01 mol / L or higher, preferably 0.1 mol / L or higher, and can also be added, for example, to a concentration of 10 mol / L or lower, preferably 1 mol / L or lower. The cobalt salt added to the solvent can be added, for example, at a concentration of 0.02 mol / L or more, preferably 0.2 mol / L or more, and can also be added, for example, at a concentration of 20 mol / L or less, preferably 2 mol / L or less. The copper salt added to the solvent can be added, for example, at a concentration of 0.01 mol / L or more, preferably 0.1 mol / L or more, and can also be added, for example, at a concentration of 10 mol / L or less, preferably 1 mol / L or less. In addition, the molar ratios of the nickel salt, cobalt salt, and copper salt added to the solvent may be adjusted so that the desired composition ratio is obtained in the compound of formula (1), and then added.

[0013] After preparing a mixed solution of nickel salt, cobalt salt, and copper salt, a coprecipitant is added, and a precipitate containing the compound represented by formula (1) is coprecipitated in the mixed solution. As the coprecipitant, an alkaline liquid or solid can be used. Specifically, although not limited to the following, examples include K2CO3, aqueous NH3, NaOH, and the like. The coprecipitant may be added to the extent that a precipitate is formed in the mixed solution. For example, it may be added dropwise until the pH of the mixed solution reaches 9. The addition of the coprecipitant can be carried out at room temperature.

[0014] The obtained precipitate is collected using an aspirator or the like. The collected precipitate is preferably washed with ion-exchanged water. The collected precipitate can be made into a dry powder by a drying process such as evaporation to dryness. The drying method is not limited, and any known method can be adopted as long as a dry powder can be obtained from the precipitate. As the drying conditions, the drying temperature is, for example, 70°C or higher, preferably 90°C or higher, and, for example, 120°C or lower. Also, the drying time is, for example, 6 hours or longer, and, for example, 100 hours or shorter, preferably 50 hours or shorter, more preferably 12 hours or shorter.

[0015] Furthermore, by firing the obtained dry powder, a catalyst composed of the compound represented by formula (1) can be obtained. The method of firing the dry powder is not limited as long as the desired catalyst can be obtained, and a known firing method can be adopted. As the firing conditions, the firing temperature is, for example, 400 °C or higher, preferably 500 °C or higher, and, for example, 800 °C or lower, preferably 700 °C. Also, the firing time is, for example, 0.5 hours or longer, preferably 1 hour or longer, and, for example, 12 hours or shorter, preferably 6 hours or shorter, more preferably 4 hours or shorter, and even more preferably 3 hours or shorter.

[0016] One aspect of the present invention provides a method for decomposing nitrous oxide, including a step of decomposing nitrous oxide using the nitrous oxide decomposition catalyst according to the present invention. The step of decomposing nitrous oxide using the nitrous oxide catalyst according to the present invention involves bringing the nitrous oxide decomposition catalyst according to the present invention into contact with nitrous oxide, and the contact method is not limited as long as the nitrous oxide can be decomposed. Here, the nitrous oxide that can be decomposed by the method for decomposing nitrous oxide of the present invention is not limited to the following, but examples include nitrous oxide contained in exhaust gases such as incinerators, boiler exhaust gases, and automobile exhaust gases. Therefore, one embodiment of the method for decomposing nitrous oxide of the present invention can include a step of bringing a gas containing nitrous oxide, such as exhaust gas from an incinerator, into contact with the nitrous oxide decomposition catalyst of the present invention. Also, in a preferred embodiment of the method for decomposing nitrous oxide of the present invention, the step of decomposing nitrous oxide is carried out under low-temperature conditions. The low-temperature conditions are those under which the nitrous oxide decomposition catalyst of the present invention can exhibit its decomposition catalytic ability and are the same as the low-temperature conditions defined above. Also, in a preferred embodiment of the decomposition method of the present invention, the waste heat of the incinerator is utilized. More preferably, it is a form in which only the waste heat of the incinerator is utilized to decompose nitrous oxide. Thereby, the step of further heating the exhaust gas can be omitted for decomposing nitrous oxide, which is preferable.

[0017] Hereinafter, embodiments of the present invention will be described in more detail using examples, but the present invention is not limited to the following embodiments.

Examples

[0018] <Example 1. Catalyst Synthesis> Ni 1-x Cu x Co2O4 catalysts (x = 0.00, 0.25, 0.50, 0.75, 1.00) were synthesized by the coprecipitation method. Ni(NO3)2·6H2O (FUJIFILM Wako Pure Chemical Corporation), Cu(NO3)2·3H2O (FUJIFILM Wako Pure Chemical Corporation), and Co(NO3)2·6H2O (FUJIFILM Wako Pure Chemical Corporation) were weighed to achieve the aforementioned molar ratios and mixed and dissolved in 50 mL of H2O. A 5 wt% aqueous solution of K2CO3 (FUJIFILM Wako Pure Chemical Corporation) was added dropwise at room temperature until the pH of the mixed solution reached 9 to form a mixed precipitate. The mixed precipitate was washed with ion-exchanged water using an aspirator, collected, and stored in a dryer set at 100 °C for 5 h to evaporate to dryness. The recovered powders were placed in crucibles and calcined in air at 400 °C for 3 h to obtain Ni 1-x Cu x Co2O4 catalysts.

[0019] <Example 2. Catalyst Analysis> Each Ni obtained in Example 1 1-x Cu x Co2O4 catalyst was identified for its composition using a desktop fluorescent X-ray elemental analyzer (MESA-500W, HORIBA). The identification results are shown in the following table.

Table 1

[0020] Next, each Ni 1-x Cu xFor Co2O4 catalysts (x = 0.00, 0.25, 0.50, 0.75, 1.00), XRD patterns were measured using MiniFlex600 (Rigaku, 40 kV, 15 mA). The results are shown in Figure 1. As shown in Figure 1, all catalysts showed diffraction lines due to cubic close-packed (spinel)-type, and Ni 0.25 Cu 0.75 In Co2O4 and CuCo2O4, diffraction lines due to CuO were also observed. Ni 0.75 Cu 0.25 Since only cubic close-packed (spinel)-type was attributed to Co2O4, it is suggested that a uniform spinel was obtained. Figure 2 shows the details of the diffraction peaks of the (311) plane of each Ni 1-x Cu x Co2O4 catalyst (x = 0.00, 0.25, 0.50, 0.75, 1.00). As the molar ratio of Cu increases from NiCo2O4, it shifts closer to the diffraction peak of the (311) plane of CuCo2O4, suggesting that the Ni 1-x Cu x Co2O4 catalyst forms a solid solution.

[0021] Also, for the Ni 0.75 Cu 0.25 Co2O4 catalyst, high-magnification and low-magnification TEM images and EDX mapping images were obtained using a JEM-ARM200CF microscope (Jeol). The obtained images are shown in Figure 3. The high-magnification TEM image (Figure 3(b)) shows the area of the dashed square in the low-magnification TEM image (Figure 3(a)). The formation of secondary particles formed by the aggregation of particles of several nm was confirmed from the TEM image. Also, the fluorescence lines of each of the EDX mapping images (Co-K, Ni-K, Cu-K) were almost the same shape as the high-magnification TEM image. In addition, when line analysis was performed in the direction of the yellow dotted arrow, as shown in Figure 4, the count numbers of the fluorescence lines of each of the same (Co-K, Ni-K, Cu-K) also showed a similar profile with respect to the distance. That is, it is suggested that each element is uniformly solid-dissolved in the catalyst.

[0022] <Example 3. Reaction Test> Each Ni synthesized in Example 1 1-x Cu x The N2O decomposition activity of the Co2O4 catalyst was measured. The N2O decomposition activity was evaluated using a fixed-bed flow reactor at atmospheric pressure. Ni 1-x Cu x The powder catalyst of Co2O4 was press-molded into granules with a size of 10-20 mesh and a thickness of <0.3 mm, and 50 mg of the granular catalyst was weighed. The weighed granular catalyst was placed in a quartz reaction tube (outer diameter 6 mm, inner diameter 4 mm), and both ends of the catalyst were fixed with quartz wool. The gas composition was assumed to be the exhaust gas from a combustion furnace, 200 ppm of N2O, 10% O2 and N2 balance at 100 m 3 ·min -1 (W / F = 5.0×10 -4 g·min·cm -3 ), 1 atm, and the quartz reaction tube filled with the catalyst was heated from room temperature to 600 °C at a constant rate of 10 °C·min -1 to evaluate the decomposition activity. The N2O and NO concentrations in the outlet gas were quantified using an infrared spectrometer (VA-3011, Horiba). In the control group, instead of the Ni 1-x Cu x Co2O4 catalyst, a noble metal catalyst, 5 wt% Ir / ZrO2, was used. 5 wt% Ir / ZrO2 was prepared by impregnating ZrO2 (manufactured by Ube Industries) with IrCl3 corresponding to 5 wt% Ru and then calcining it in air at 600 °C for 3 h.

[0023] The comparison data of various catalysts are shown in FIGS. 1 and 2. As shown in FIG. 1, it was revealed that by changing the composition ratio of Ni x Cu 1-x Co2O4, the N2O conversion temperature changed significantly. The higher the ratio of Ni to Cu, the higher the catalytic activity, and it was found that the Ni 0.75 Cu 0.25 Co2O4 catalyst showed the highest activity. As shown in FIG. 2, it was also found that it showed comparable performance compared to 5 wt% Ir / ZrO2, a noble metal catalyst reported as an active catalyst.

Claims

1. A dinitrogen monoxide decomposition catalyst comprising a compound represented by the following formula (1). 【Chemical Formula 1】 (In formula (1), x represents 0.25 to 0.75.)

2. The nitrous oxide decomposition catalyst according to claim 1, wherein the compound is Ni ０．７５ Cu ０．２５ Co ２ O ４ The nitrous oxide decomposition catalyst is as follows.

3. A method for decomposing dinitrogen monoxide, comprising a step of decomposing dinitrogen monoxide using the dinitrogen monoxide decomposition catalyst according to Claim 1 or 2.

4. The method for decomposing dinitrogen monoxide according to Claim 3, wherein the step of decomposing dinitrogen monoxide is a step of decomposing dinitrogen monoxide under a temperature condition of 400 °C or lower.

5. The method for decomposing dinitrogen monoxide according to Claim 4, wherein the step of decomposing dinitrogen monoxide utilizes the exhaust heat of an incinerator.

6. A method for producing the dinitrogen monoxide decomposition catalyst according to Claim 1 or 2, comprising a step of adding a coprecipitant to an aqueous solution prepared by mixing a nickel salt, a cobalt salt, and a copper salt to coprecipitate a precipitate containing the compound.

7. The method for producing the dinitrogen monoxide decomposition catalyst according to Claim 6, further comprising a step of obtaining a dry powder of the precipitate and firing the powder.

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