KR20060096609A - Metal oxide catalyst for removing nox and method of preparing the same - Google Patents

Abstract

The present invention relates to a metal oxide catalyst having excellent nitric oxide (NOx) removal activity at a low temperature, and a method for preparing the same. More specifically, the metal oxide has a structure represented by the following Chemical Formula 1.

[Formula 1]

Cu _x Mn _y O _z

(Wherein 0 ≦ x ≦ 2, 0.01 ≦ y ≦ 3 and 2 ≦ z ≦ 8).

The metal oxide catalyst of the present invention is excellent in nitrogen oxide (NOx) removal activity at a low temperature of 50 to 250 ° C.

Catalyst, copper, manganese, composite oxide, low temperature activity, nitric oxide

Description

Metal oxide catalyst for removing nitric oxide and its manufacturing method {METAL OXIDE CATALYST FOR REMOVING NOx AND METHOD OF PREPARING THE SAME}

1 is a graph showing the NOx conversion efficiency according to the temperature of the metal oxide catalyst according to Examples 1, 4, 7, 8, 16 and 17 of the present invention.

2 is a graph showing the NOx conversion efficiency according to the temperature of the metal oxide catalyst according to Examples 22 to 26 and Example 28 of the present invention.

3 is a graph showing the NOx conversion efficiency with respect to the temperature of Pt / Al ₂ O ₃ of Comparative Example 1.

4 is a graph showing NOx conversion efficiency with respect to the temperature of CuO of Comparative Example 2. FIG.

FIG. 5 is a graph showing the NOx conversion efficiency with respect to the temperature of MnO ₂ of Comparative Example 3. FIG.

6 is a graph showing NOx conversion efficiency with respect to the temperature of Mn ₃ O ₄ / Al ₂ O ₃ of Comparative Example 4. FIG.

[Industrial use]

The present invention relates to a metal oxide catalyst for nitric oxide (NOx) removal and a method for producing the same, and more particularly, to a metal oxide catalyst having excellent nitric oxide removal activity at low temperatures and a method for producing the same.

[Prior art]

Nitrogen oxide (NOx), which is a representative air pollutant emitted from various combustion processes and pyrolysis processes according to industrialization with sulfur oxides, should be removed and discharged below a certain concentration due to the danger to the environment.

Selective Catalyst Reduction (SCR) is generally used as a method of removing such nitrogen oxides, and representative catalysts used are G. Ramis, J. Gatal., 157, 523 (1995) and G. Centi. , Appli. Catal. Metal oxide catalysts such as A, 132, 179 (1995), and the like. In addition, as reported by L. Pinoy, Catalyst Today, 17, 151 (1993) and G. Deo, J. Catal., 146, 334 (1994), the V ₂ O ₅ / TiO ₂ catalyst is reported to be particularly good. have. This method is a method of decomposing by reacting with a reducing agent such as ammonia at a high temperature of about 300 to 350 ℃ using a metal oxide catalyst, it is relatively efficient, but the reaction temperature is at least 300 ℃ high temperature as described above There are disadvantages.

I. Mochida, Japan Chemical Society, No. 6, 885 (1991) and I. Mochida, Japanese Chemical Society No. 6, p.694 (1993), etc., suggest a method for decomposing nitric oxide at temperatures as low as 100 ° C using activated carbon or activated carbon fibers. Doing. However, this method can lower the reaction temperature, but the disadvantage of low reaction efficiency.

In addition, in Korean Patent Application No. 2000-0080303, after dispersing the powder of V ₂ O ₅ / TiO _{2 in} the molten pitch and spinning it to produce a pitch fiber containing V ₂ O ₅ / TiO ₂ uniformly dispersed, A method of preparing an activated carbon fiber catalyst having excellent decomposition ability of nitric oxide by stabilizing, carbonizing and activating is proposed. This method suggests a method for producing a catalyst having better decomposition ability of nitrogen oxides compared to a method using general activated carbon or general activated carbon fibers such as I. Mochida, but reacts with a selective catalytic reduction method which reacts directly at a high temperature of 300 ° C. or higher. It has a downside in terms of conversion rate.

In order to solve the above problems, an object of the present invention is to provide a metal oxide catalyst having excellent nitric oxide removal activity in a low temperature section of 50 to 250 ℃.

The present invention also aims to provide a method for producing the metal oxide catalyst.

In order to achieve the above object, the present invention provides a metal oxide catalyst excellent in nitric oxide removal activity at low temperatures.

The present invention also provides a step of adjusting the pH by adding a precipitant to a) a solution containing a manganese raw material or a mixed solution of a copper raw material and a solution containing a manganese raw material, b) obtained by filtering the pH-controlled solution It provides a method for producing a metal oxide catalyst comprising the step of washing the filtrate and c) drying and then calcining the washed filtrate.

Hereinafter, the present invention will be described in more detail.

The metal oxide catalyst of the present invention has excellent nitric oxide removal activity at low temperature, and preferably has a structure represented by the following formula (1).

[Formula 1]

Cu _x Mn _y O _z

(Wherein 0 ≦ x ≦ 2, 0.01 ≦ y ≦ 3 and 2 ≦ z ≦ 8).

In the above formula, MnO ₂ having x = 0, y = 1, and z = 2 has an amorphous form in which XRD peaks hardly appear, unlike conventional MnO ₂ . Therefore, there is a characteristic that the surface area is very high than in the case of the amorphous form when the activity is also increased. In fact, the MnO ₂ of the present invention exhibited a surface area of almost 10 times that of the conventional MnO ₂ .

The metal oxide catalyst of the present invention may further include at least one metal selected from the group consisting of cesium, iron, cobalt, nickel and zirconium.

The metal oxide catalyst of the present invention is prepared by coprecipitation using a precipitant.

More specifically, a) adjusting the pH by adding a precipitant to a solution containing a manganese raw material or a mixed solution of a copper raw material and a solution containing manganese raw material, b) filtering the solution by adjusting the pH Washing the obtained filtrate and c) drying and calcining the washed filtrate to obtain a metal oxide catalyst.

The concentration of the manganese raw material in the manganese raw material containing solution in step a) is preferably 0.01 M to 0.5 M, more preferably 0.25 to 0.5 M. If the concentration of the manganese raw material is less than 0.01 M, it is difficult to control the pH of the solution, the amount of precipitate produced is very small, and the size of the particles becomes large during precipitation, which is undesirable. It is difficult, and when the temperature is lowered to 25 ° C., precipitation occurs, which is not preferable. Manganese nitrate, manganese sulfate, manganese chloride, or manganese acetate may be used as the manganese raw material, and more preferably, manganese nitrate is used.

In addition, the concentration of the copper raw material in the solution containing the copper raw material is preferably 0.01 to 0.5 M, more preferably 0.25 to 0.5 M. If the concentration of the copper raw material is less than 0.01 M, it is difficult to control the pH of the solution, the amount of precipitate produced is very small and the size of the particles becomes large during precipitation, which is undesirable. It is difficult, and when the temperature is lowered to 25 ° C., precipitation occurs, which is not preferable. As the copper raw material, copper nitrate, copper sulfate, copper chloride, copper acetate, or the like may be used. More preferably, copper nitrate is used.

In addition, the copper source material-containing solution and the manganese source material-containing solution is preferably mixed so that the molar ratio of copper and manganese is 0.01 to 1: 0.01 to 1, more preferably 0.25 to 0.5: 0.25 to 0.5. If the molar ratio of copper and manganese is out of the above range, the oxidation activity at low temperature is drastically reduced, or the activity is drastically decreased at 200 ° C. or higher, which is not preferable.

In this case, water, ethanol, propanol or butanol may be used as the solvent, and more preferably water is used.

 In step a), before adding the precipitant, one or more metal raw materials selected from the group consisting of cesium, iron, cobalt, nickel, and zirconium may be further added. In addition, they dissolve a desired amount of metal raw material in a solvent and then add it in solution. As a solvent which can be used, water, ethanol, propanol, butanol, etc. can be used, More preferably, water is used. In this case, the concentration of the metal raw material in the solution containing the metal raw material is preferably 0.01M to 0.5M.

In step a), the precipitant is composed of sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), ammonia water (NH ₄ OH), and ammonium carbonate At least one compound selected from the group may be used, and more preferably sodium carbonate (Na ₂ CO ₃ ) is used. The precipitant is preferably added until the pH of the mixed solution is 8 to 10, preferably 8 to 8.5. If the pH is less than 8, manganese hardly penetrates, and only copper in the solution precipitates, which is undesirable, and even if a stronger salt is used, the pH cannot exceed 10. In addition, sodium carbonate (Na ₂ CO ₃ ) among the precipitants used above is most preferred, and when the final metal oxide catalyst is used, nitric oxide removal activity at low temperatures is much better than that of other salts.

In step c), the firing temperature is preferably 300 to 600 ° C, more preferably 350 to 400 ° C. If the firing temperature is less than 300 ° C, the nitric acid of copper and manganese raw materials may not be removed, which is not preferable.

The metal oxide catalyst of the present invention prepared as described above is excellent in nitric oxide removal catalytic activity at low temperatures, and exhibits a better nitric oxide removal effect than the noble metal platinum-based catalyst known to be excellent in conventional nitric oxide removal activity.

The present invention also provides a method for removing nitrogen oxide using the metal oxide catalyst.

The selective reduction method of nitrogen oxide using ammonia as a reducing agent in the low temperature region follows the following reaction.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following examples are provided only to more easily understand the present invention, and the present invention is not limited to the following examples.

Example 1

500 ml of 0.5 M copper nitrate aqueous solution and 500 ml of 0.5 M manganese nitrate aqueous solution were mixed, dissolved in distilled water at 80 ° C. for 1 hour, and stirred using a magnetic stirrer until the temperature reached room temperature. After reaching room temperature, the solution was slowly titrated until pH reached 8 using sodium carbonate (Na ₂ CO ₃ ), and then stirred for 1 hour. The mixture was filtered using a vacuum filter and washed three times with distilled water. After drying for 4 hours at a temperature of 100 ℃ and calcined for 4 hours at a temperature of 350 ℃ and air atmosphere to prepare a metal oxide catalyst for removing nitrogen oxides.

[Examples 2 to 27]

A metal oxide catalyst for removing nitric oxide was prepared in the same manner as in Example 1 except for varying the number of moles and firing temperature of copper and manganese as shown in Table 1 below.

Copper (mol) Manganese (mol) Firing temperature (℃) Example 2 0.010 0.010 450 Example 3 0.010 0.010 550 Example 4 0.010 0.250 350 Example 5 0.010 0.250 450 Example 6 0.010 0.250 550 Example 7 0.010 0.500 350 Example 8 0.010 0.500 450 Example 9 0.010 0.500 550 Example 10 0.250 0.010 350 Example 11 0.250 0.010 450 Example 12 0.250 0.010 550 Example 13 0.250 0.250 350 Example 14 0.250 0.250 450 Example 15 0.250 0.250 550 Example 16 0.250 0.500 350 Example 17 0.250 0.500 450 Example 18 0.250 0.500 550 Example 19 0.500 0.010 350 Example 20 0.500 0.010 450 Example 21 0.500 0.010 550 Example 22 0.500 0.250 350 Example 23 0.500 0.250 450 Example 24 0.500 0.250 550 Example 25 0.500 0.500 350 Example 26 0.500 0.500 450 Example 27 0.500 0.500 550

Example 28

1,000 ml of 0.5 M manganese nitrate aqueous solution was mixed, dissolved in distilled water at 80 ° C. for 1 hour, and stirred using a magnetic stirrer until it reached room temperature. After reaching room temperature, the solution was slowly titrated until pH reached 8 using sodium carbonate (Na ₂ CO ₃ ), and then stirred for 1 hour. The mixture was filtered using a vacuum filter and washed three times with distilled water. After drying for 4 hours at a temperature of 100 ℃ and calcined for 4 hours at a temperature of 350 ℃ and air atmosphere to prepare a metal oxide catalyst for removing nitrogen oxides.

Example 29

450 ml of 0.5 M copper nitrate aqueous solution and 450 ml 0.5 M manganese nitrate aqueous solution were further added to the mixed solution, 50 ml of 0.5 M cobalt nitrate aqueous solution was dissolved in distilled water at 80 ° C. for 1 hour, and the magnetic stirrer was allowed to reach room temperature. And stirred. After reaching room temperature, the solution was slowly titrated until pH reached 8 using sodium carbonate (Na ₂ CO ₃ ), and then stirred for 1 hour. The mixture was filtered using a vacuum filter and washed three times with distilled water. After drying for 4 hours at a temperature of 100 ℃ and calcined for 4 hours at a temperature of 350 ℃ and air atmosphere to prepare a metal oxide catalyst for removing nitrogen oxides.

Experimental Example  One

Green line MK2 (manufactured by Eurotron) was used to measure the NOx conversion according to the temperature of the metal oxide catalysts prepared in Examples 1, 4, 7, 8, 16, 17, 22 to 26 and 28.

At this time, the temperature of the reactor was changed to 50 to 300 ℃, the concentration of supplied NO was 500ppm, NH ₃ was adjusted to 500ppm. In addition, the oxygen concentration was maintained at 5% and the space velocity was maintained at 25,000 ~ 50,000 h ^-1 . In order to exclude the effects of moisture and oxidation value adsorbed on the catalyst before the reaction, it was maintained at 300 ° C. in an oxygen atmosphere for 1 hour, and then cooled to the reaction temperature, and then the activity experiment was conducted while the temperature was raised. For comparison of NOx conversion effects, 1% Pt / Al ₂ O ₃ used as a catalyst for removing nitric oxide (Comparative Example 1), CuO (Comparative Example 2), MnO ₂ (Comparative Example 3) and Mn ₃ O ₄ / Al ₂ O ₃ (Comparative Example 4) were used. Experimental results are shown in FIGS. 1 to 5.

As a result of the experiment, as shown in Figures 1 and 2, the copper-manganese composite oxide catalyst prepared in Examples 1, 4, 7, 8, 16, 17 and 22 to 28 showed excellent activity in the low temperature region of 50 to 250 ℃ Could know. In contrast, as shown in FIGS. 3 to 6, all of the catalysts of Comparative Examples 1 to 4 had lower catalytic activity in the low temperature region than the metal oxide catalysts of Examples 1 to 28.

As described above, the metal oxide catalyst according to the present invention has excellent removal activity of nitrogen oxide in a low temperature section of 50 to 250 ℃.

Claims (15)

Metal oxide catalyst for removing nitric oxide having excellent NOx removal activity at low temperature. The metal oxide catalyst of claim 1, wherein the metal oxide catalyst has a structure represented by the following Chemical Formula 1. [Formula 1] Cu _x Mn _y O _z (Wherein 0 ≦ x ≦ 2, 0.01 ≦ y ≦ 3 and 2 ≦ z ≦ 8). The metal oxide catalyst of claim 1, wherein the metal oxide catalyst further comprises at least one metal selected from the group consisting of cesium, iron, cobalt, nickel, and zirconium. The metal oxide catalyst of claim 1, wherein the metal oxide catalyst is prepared by coprecipitation using a precipitating agent. The method of claim 1, wherein the precipitant is sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), ammonia water (NH ₄ OH), sodium carbonate ( Na ₂ CO ₃ ) metal oxide catalyst selected from the group consisting of. a) adjusting the pH by adding a precipitant to a solution containing a manganese raw material or a mixed solution of a copper raw material containing solution and a manganese raw material containing solution; b) washing the filtrate obtained by filtering the pH adjusted solution; And c) a method of preparing a metal oxide catalyst for removing nitric oxide, comprising the step of obtaining a metal oxide catalyst by drying and washing the washed filtrate. The method for preparing a metal oxide catalyst according to claim 6, wherein the concentration of the copper raw material in the solution containing the copper raw material in step a) is 0.01 to 0.5 M. The method of claim 6, wherein the copper raw material in step a) is selected from the group consisting of copper nitrate, copper sulfate, copper chloride, and copper acetate. The method of claim 6, wherein the concentration of the manganese raw material in the manganese raw material containing solution in step a) is 0.01 to 0.5 M. The method of claim 6, wherein the manganese raw material in step a) is selected from the group consisting of manganese nitrate, manganese sulfate, manganese chloride, and manganese acetate. The method of claim 6, wherein the mixed solution of the copper raw material-containing solution and the manganese raw material-containing solution in step a) has a mixing molar ratio of copper and nitrogen of 0.01 to 1: 0.01 to 1. The method of claim 6, further comprising adding a solution containing at least one metal raw material selected from the group consisting of cesium, iron, cobalt, nickel and zirconium before adding the precipitant in step a). The method of claim 6, wherein the precipitant in step a) is sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), ammonia water (NH ₄ OH), carbonic acid Method for producing a metal oxide catalyst selected from the group consisting of sodium (Na ₂ CO ₃ ). The method of claim 6, wherein the precipitant in step a) is added in an amount such that the pH of the mixed solution is 8 to 10. The method of claim 6, wherein the firing in step c) is carried out at a temperature of 300 to 600 ℃.

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