KR19980077049A - Catalyst and method for producing the catalyst for decomposing nitrogen oxide emitted from diesel engine - Google Patents

Abstract

The present invention relates to a catalyst for decomposing nitrogen oxides discharged from a diesel engine, and a method for manufacturing the same, wherein La (NO 3) 3 .6H 2 O, in a molar ratio of 0.6: 0.4: 1-X: X (X is 0 to 1), M (NO3) 2, Co (NO3) 2 and Fe (NO3) 3.9H2O, wherein M is Sr or Ba, are mixed with nitric acid, dissolved in water to form a solution, and the base is added to adjust pH to weak acidity. And a lanthanoid-based perovskite catalyst of the general formula La0.6M0.4Co1-XFeXO3, wherein M is Sr or Ba and X is from 0 to 1, which is composed of drying and calcining.

Description

Catalyst and method for producing the catalyst for decomposing nitrogen oxide emitted from diesel engine

The present invention relates to a catalyst for decomposing nitrogen oxides discharged from a diesel engine and a method of manufacturing the same, and more particularly, to a lanthanoid-based perovskite catalyst having a large surface area for decomposing nitrogen oxides discharged from a diesel engine and a nitric acid. It relates to a method for producing these catalysts by the method.

Nitrogen oxides (NOx), known as air pollutants, cause serious environmental problems such as photochemical smog. And, the emission source of these nitrogen oxides is mainly exhaust gas of automobiles and the like. Therefore, efforts to reduce nitrogen oxides in automobile exhaust gas have been steadily progressed. Known methods of treating nitrogen oxides include fuel denitrification, which preliminarily removes nitrogen compounds contained in fuels that decompose nitrogen using catalysts, combustion modifications to reduce them during combustion, and post-treatment of exhaust gases. have. Among them, the most researched in the world is a method of decomposing nitrogen oxide using a catalyst in the post-treatment method. Catalysts used herein include zeolites, metal oxides, and the like. On the other hand, noble metal catalysts are used in the three-way catalytic device used to decompose nitrogen oxides in the exhaust gas in an actual gasoline automobile, but there are problems in that the reserves are limited, difficult to obtain, and expensive. In addition, heavy-duty diesel cars require high power and the ratio of fuel and air is different from gasoline cars, and therefore, precious metal catalysts currently developed and used for gasoline cars cannot be used.

Accordingly, an object of the present invention is to provide a catalyst for decomposing nitrogen oxides discharged from a diesel engine and a method of manufacturing the same.

Another object of the present invention is to provide a catalyst having a large surface area and excellent catalytic activity and conversion rate of nitrogen oxide in a nitrogen oxide decomposition reaction, and a method for producing the same.

The object of the present invention described above is M (NO 3) 2, Co (NO 3), wherein La (NO 3) 3 · 6H 2 O in a molar ratio of 0.6: 0.4: 1-X: X (X is 0 to 1), and M is Sr or Ba. Preparation of a lanthanoid-based perovskite catalyst consisting of 2 and Fe (NO3) 3.9H2O, mixed with nitric acid, dissolved in water to form a solution, and the addition of a base to adjust the pH to weak acidity, followed by drying and calcining. Is achieved by the method.

In addition, an object of the present invention is achieved by a lanthanoid-based perovskite catalyst of general formula La0.6M0.4Co1-XFeXO3, wherein M prepared by the above method is Sr or Ba and X is 0 to 1.

Conventional lanthanoid-based perovskite catalysts have been prepared by solid phase reaction or citric acid method. However, the lanthanoid-based perovskite catalyst prepared by this method has a low surface area, resulting in low conversion of nitrogen oxides during nitrogen decomposition. In the present invention, when the lanthanoid-based perovskite catalyst was prepared using the unggeum acid method, the surface area of the catalyst increased up to about 50 times compared with the case of the solid phase reaction method. Therefore, as the surface area of the catalyst increases, the activity of the catalyst in the decomposition reaction of the nitrogen oxide also increases.

Nitrate of each metal constituting the catalyst or its hydrate and nitric acid are mixed and dissolved in water, and then added to a base such as ammonia water to adjust the pH to weak acidity and dried sufficiently by drying in a dryer at high temperature to make porous. It is pulverized to make a powder and calcined while changing the temperature over three steps to prepare a lanthanoid-based perovskite catalyst.

Nitrogen degradability and conversion test of the catalyst was carried out under the same conditions as the actual diesel exhaust gas. In other words, when applied to the actual diesel engine, it was tested by adopting all possible ranges of temperature, nitrogen oxide concentration, hydrocarbon concentration as reducing agent, and water vapor concentration, and the space velocity was tested according to the actual exhaust gas conditions.

Nitrogen monoxide (NO) gas was used as the nitrogen oxide for the test of the present invention. In the present specification, the conversion rate of NO gas represents the ratio of the amount converted by the reaction among the total amount of NO gas introduced into the reactor.

Specifically, the conditions used for the test of the present invention, the pressure of the atmospheric pressure and the temperature range of 200-500 ℃ 100-2000ppm concentration of nitrogen oxides, the concentration of hydrocarbons as reducing agent 10-2000ppm, the concentration of oxygen is 0-20 %, Water concentration was 0-20%, space velocity was 10,000-100,000hr-1. As the reducing agent, ethane, propane, ethylene and propylene were used.

In order to be used as a decomposition catalyst of nitrogen oxides in the off-gas, a stable state must be maintained for a long time. In other words, since the activity must be maintained even when traveling over 20,000 km, the catalyst was tested for a long time in the present invention.

The present invention will be described in more detail with reference to the following Examples.

Example 1

13.39g La (NO3) 3.6H2O, 4.36g Sr (NO3) 2, 12g Co (NO3) 2, 4.04g Fe (NO3) 3.9H2O and 6.7g 1N nitric acid were dissolved in 100cc of ultrapure water to make a solution. Ammonia water diluted to 10% was slowly added dropwise, and the whole solution was stirred sufficiently to adjust the pH to 4.0. It was dried to a temperature of 150 ℃ in a dryer to make a porous. It was pulverized well and then calcined in an electric furnace for 30 minutes at 200 ℃, 30 minutes at 350 ℃, 12 hours at 600 ℃ to prepare a catalyst powder. The surface area of this catalyst was 20.0 m 3 / g.

Each of these catalysts was placed in a reactor of a fixed bed reactor, and the reaction product was subjected to atmospheric pressure under the conditions of a reaction temperature of 200-400 ° C., a concentration of NO of 1000 ppm, a concentration of propane of 1000 ppm, a concentration of 4% of oxygen, and a space velocity of 30,000hr-1. Analyzed with an oxide analyzer. The analysis results are shown in Table 1.

In addition, in order to test the stability of the catalyst over a long period of time, the conversion rate of nitrogen monoxide after 48 hours was measured at a reaction temperature of 325 ° C., a space velocity of 30,000 hr −1, a concentration of NO of 1000 ppm, of a concentration of 1000 ppm of oxygen, and a concentration of 4% of oxygen. The result was 87.3%.

Comparative Example 1

3.2582g of La2O, 2.908g of Sr (NO3) 2, 8g of Co (NO3) 2 · 6H2O and 2.6935g of Fe (NO3) 3 · 9H2O were sufficiently dried in a dryer at 120 ° C, and then ground again to a fine powder using a grinder. It was calcined for 12 hours in an electric furnace at 1150 ℃. The surface area of this catalyst was 0.7 m 3 / g.

Each of these catalysts was placed in a reactor of a fixed bed reactor, and the reaction product was subjected to atmospheric pressure under the conditions of a reaction temperature of 200-400 ° C., a concentration of NO of 1000 ppm, a concentration of propane of 1000 ppm, a concentration of 4% of oxygen, and a space velocity of 30,000hr-1. Analyzed with an oxide analyzer. The analysis results are shown in Table 1.

[Table 1] Comparison of Activity of La0.6M0.4Co0.8Fe0.2O3 Catalysts Prepared by Solid State Reaction Method and Tungumum Acid Method

La0.6M0.4Co0.8Fe0 of the present invention of Example 1 prepared by the tungstic acid method compared to the La0.6M0.4Co0.8Fe0.2O3 catalyst of Comparative Example 1 prepared by the solid phase reaction method as shown in Table 1. It can be seen that the 2O 3 catalyst shows a high NO conversion under the same conditions.

Example 2

8.39g La (NO3) 3.6H2O, 3.54g Ba (NO3) 2, 5g Co (NO3) 2, 6.73g Fe (NO3) 3.9H2O and 1N nitric acid were dissolved in 100cc of ultrapure water to make a solution. The ammonia water diluted with was slowly added dropwise, and the whole solution was sufficiently stirred to adjust the pH to 4.0. It was dried to a temperature of 150 ℃ in a dryer to make a porous. It was pulverized well and then calcined in an electric furnace for 30 minutes at 200 ℃, 30 minutes at 350 ℃, 12 hours at 600 ℃ to prepare a catalyst powder. The surface area of this catalyst was 12.2m 3 / g.

Each of these catalysts was placed in a reactor of a fixed bed reactor, and the reaction product was subjected to atmospheric pressure under the conditions of a reaction temperature of 200-400 ° C., a concentration of NO of 1000 ppm, a concentration of propane of 1000 ppm, a concentration of 4% of oxygen, and a space velocity of 30,000hr-1. Analyzed with an oxide analyzer. The analysis results are shown in Table 2.

In order to test the stability of the catalyst for a long time, the conversion rate of nitrogen monoxide after 48 hours was measured at a reaction temperature of 350 ° C., a space velocity of 30,000 hr −1, a concentration of NO of 1000 ppm, a concentration of propane of 1000 ppm, and a concentration of 4% of oxygen. 82.3 Was%.

Comparative Example 2

3.2582g of La2O, 3.5381g of Ba (NO3) 2, 5g of Co (NO3) 2 · 6H2O and 6.737 of Fe (NO3) 3 · 9H2O were sufficiently dried in a dryer at 120 ° C and then pulverized again to a fine powder using a grinder 1150 It was calcined for 12 hours in an electric furnace at ℃.

Each of these catalysts was placed in a reactor of a fixed bed reactor, and the reaction product was subjected to atmospheric pressure under the conditions of a reaction temperature of 200-400 ° C., a concentration of NO of 1000 ppm, a concentration of propane of 1000 ppm, a concentration of 4% of oxygen, and a space velocity of 30,000hr-1. Analyzed with an oxide analyzer. The analysis results are shown in Table 2.

[Table 2] Comparison of Activities of La0.6M0.4Co0.5Fe0.5O3 Catalysts Prepared by Solid State Reaction Method and Tungumum Acid Method

a: reaction temperature 370 ° C.

La0.6M0.4Co0.5Fe0 of the present invention of Example 2 prepared by tungstic acid method compared to La0.6M0.4Co0.5Fe0.5O3 catalyst of Comparative Example 2 prepared by the solid-phase reaction method as shown in Table 2. It can be seen that the 5O 3 catalyst shows a high NO conversion under the same conditions. In addition, the La 0.6 M 0.4 Co 0.5 Fe 0.5 O 3 catalyst of Example 2 exhibited high activity at a wide range of reaction temperatures. Such a catalyst is an excellent catalyst that can be easily applied even when the temperature of the exhaust gas varies depending on the operating conditions of the engine.

As can be seen above, the lanthanoid-based perovskite catalyst of the general formula La0.6M0.4Co1-XFeXO3 prepared by the method of the present invention has a large surface area and has excellent activity and thus nitrogen oxides in the exhaust gas emitted from the diesel engine. It is an excellent catalyst that can effectively remove and maintain the stability of the catalyst for a long time.

Claims (2)

La (NO 3) 3 .6H 2 O in a molar ratio of 0.6: 0.4: 1-X: X (X is 0 to 1), M (NO 3) 2, Co (NO 3) 2 and Fe (NO 3) 3, wherein M is Sr or Ba. A method for producing a lanthanoid-based perovskite catalyst comprising mixing 9H2O with nitric acid to dissolve in water to form a solution, adding a base to adjust pH to weak acidity, and then drying and calcining. Lanthanoid-based perovskite catalyst of the general formula La0.6M0.4Co1-XFeXO3 wherein M prepared by the method of claim 1 is Sr or Ba and X is 0-1.