KR101108819B1 - Catalyst for removal of nitrogen oxides, method of preparing the same and method of removal of nitrogen oxides using the same - Google Patents

Abstract

The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, a method for preparing the same, and a method for removing nitrogen oxides in exhaust gas using the same. More particularly, the catalyst is subjected to hydrothermal treatment of a ceramic fiber carrier before washcoating. The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, a method for preparing the same, and a method for removing nitrogen oxides in exhaust gas using the same.

The catalyst prepared according to the present invention has excellent hydrothermal stability, and the activity of the catalyst is maintained for a long time. Furthermore, by using such a catalyst to remove nitrogen oxides in the exhaust gas, the removal rate of nitrogen oxides is much improved.

Hydrothermal treatment, ceramic fiber carrier, washcoat, nitrogen oxides

Description

Catalyst for removing nitrogen oxide in exhaust gas, preparation method thereof and method for removing nitrogen oxide in exhaust gas using same {CATALYST FOR REMOVAL OF NITROGEN OXIDES

The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, a method for preparing the same, and a method for removing nitrogen oxides in exhaust gas using the same. More particularly, the catalyst is subjected to hydrothermal treatment of a ceramic fiber carrier before washcoating. The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, a method for preparing the same, and a method for removing nitrogen oxides in exhaust gas using the same.

In the case of diesel vehicles, sales are increasing due to energy efficiency and good output. However, diesel vehicles emit more particulate matter (PM) and nitrogen oxides (NOx) than gasoline vehicles, which contributes to metropolitan pollution. In particular, regulations on nitrogen oxides, which are the cause of diseases and environmental pollution, are being tightened, and much efforts are being made to develop their removal technologies.

Selective Catalytic Reduction (SCR) has been in the spotlight as the most effective method of removing nitrogen oxides, and various reducing agents and catalysts can be applied depending on various conditions such as the characteristics of the process applied, environmental aspects, and economics. have. Most effective in removing nitrogen oxides from stationary sources such as power plants and incinerators, and the commercially available selective catalytic reduction (NH ₃ / SCR) technology by ammonia has problems in storage / transportation and use of ammonia. In order to remove nitrogen oxides, urea is used to generate ammonia after decomposition. The method using such a factor as a reducing agent has recently been studied a lot as a post-treatment device for diesel vehicles, and is a technology that is commercially available in Europe and the like.

However, one of the important problems when applying this technique to automobiles is a carrier used in a catalytic converter capable of supporting a catalyst. Currently, ceramic cordierite carriers, developed by Corning in 1975, are used in more than 95% of the world's automotive catalytic converters. However, in light of fuel efficiency, the weight of cordierite carriers that are used as catalyst carriers may also be a problem as lighter bodies and components are needed. Therefore, research on the lighter material of the new concept is being made.

Korean Patent Laid-Open Publication Nos. 10-2007-0013206 and 10-2007-0012243 disclose a method of manufacturing a ceramic fiber filter for use as a diesel dust filter for removing particulate matter discharged from a diesel vehicle. The fiber filter is expected to be very useful because it has a high porosity (more than 80%), is resistant to heat and impact due to the inherent elasticity of the fiber, and can be molded into various structures. Accordingly, researches on whether technology development of a catalyst carrier using ceramic fibers can replace the existing cordierite catalyst carrier have become important.

In addition, not only the initial nitrogen oxide removal efficiency, but also the development of a catalyst and a carrier for removing nitrogen oxide with excellent stability capable of maintaining the initial activity even after long-term operation in a humid environment remains a problem.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide a catalyst for the removal of nitrogen oxides in the exhaust gas excellent in hydrothermal stability.

Another object of the present invention is to provide a method for producing a catalyst for removing nitrogen oxides in exhaust gas having excellent hydrothermal stability.

Another object of the present invention is to provide a method for removing nitrogen oxides in exhaust gas using a catalyst having excellent hydrothermal stability.

These and other objects of the present invention can be achieved by the present invention described below.

In order to achieve the above object,

Provided is a catalyst for removing nitrogen oxides in exhaust gas, wherein the hydrothermally treated ceramic carrier is coated with a washcoat including a vanadia / titania composite catalyst.

Also,

A first step of hydrothermally treating the ceramic fiber carrier;

A second step of preparing a washcoat aqueous solution by mixing the vanadia / titania composite catalyst slurry and a binder aqueous solution; And

A third step of manufacturing the washcoat ceramic fiber carrier by impregnating the hydrothermally treated ceramic fiber carrier into the prepared washcoat aqueous solution

It provides a method for producing a catalyst for removing nitrogen oxides in the exhaust gas comprising a.

Also,

Mixing an exhaust gas containing nitrogen oxides with a reducing agent; And

Removing nitrogen oxides by a reduction reaction that takes place while passing the mixed components through a catalyst reactor to which a catalyst according to the invention is applied

It provides a method for removing nitrogen oxide in the exhaust gas comprising a.

The catalyst prepared according to the present invention has excellent hydrothermal stability, thereby suppressing the deactivation of the catalyst which may occur with long-term use in a humid environment, and maintaining the initial activity of the catalyst. In addition, by using such a long-lasting catalyst with excellent hydrothermal stability to remove nitrogen oxides in the exhaust gas, the removal rate of nitrogen oxides is much higher.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have made efforts to solve the above-mentioned problems. As a result, the present invention was able to induce a more stable carrier through the hydrothermal treatment process before coating the catalyst on the ceramic fiber carrier, and based on the hydrothermal stability of the wash-coated catalyst A method of promotion was developed. This allows the catalyst to be used stably for a long time.

That is, in the selective catalytic reduction process for removing nitrogen oxides in the exhaust gas, hydrothermal stability of the catalyst coated on the ceramic fiber carrier is improved by hydrothermally treating the ceramic fiber carrier before coating the catalyst on the ceramic fiber carrier.

The catalyst for removing nitrogen oxides in the exhaust gas according to the present invention is characterized in that a washcoat including a vanadia / titania composite catalyst is coated on a hydrothermally treated ceramic carrier.

The removal rate of nitrogen oxide using the catalyst according to the present invention is characterized in that the reaction temperature of 300 to 500 ℃ 80 to 95%.

Specifically, a method for producing a catalyst for removing nitrogen oxides in exhaust gas according to the present invention will be described.

The ceramic fiber carrier used in the present invention is preferentially hydrothermally treated before being impregnated with an aqueous solution of a washcoat including a catalyst. The fiber carriers are disclosed in Korean Patent Publication Nos. 10-2007-0013206 and 10-2007-0012243. It is prepared by the method disclosed in the call.

That is, (a) primary coating and drying the ceramic green paper prepared by using a slurry solution containing a ceramic fiber of 0.1 to 10 mm length with aluminum silicate solution and dried; (b) secondary coating and drying the dried ceramic green paper with an aluminum phosphate solution; And (c) calcining the secondary coated and dried ceramic green paper to prepare a ceramic fiber carrier.

The ceramic fiber should be made of a material that can withstand high temperatures of about 1200 ° C. or more, and may include one or more alumina or silica.

The ceramic green paper may be manufactured using a papermaking method commonly used in the art, and the slurry solution used may include organic fibers in addition to the ceramic fibers, and may further include a small amount of organic binder.

In addition, the aluminum silicate solution preferably contains C1 to C6 lower alcohols, aluminum nitrate, tetraalkyl orthosilicate and hydrochloric acid.

In addition, the aluminum phosphate solution preferably includes aluminum nitrate and phosphoric acid.

The process for coating the ceramic green paper with the aluminum silicate and aluminum phosphate solution is not particularly limited, and may be, for example, by impregnation or spraying.

Baking the ceramic green paper is preferably baked at a temperature of 400 to 1100 ℃ in a vacuum, inert gas or air.

In the hydrothermal treatment of the ceramic fiber carrier prepared as described above according to the invention, it is characterized in that it is carried out at a temperature of 300 to 900 ℃. If the temperature is less than 300 ℃, there is a problem that can not determine the effect of the hydrothermal treatment, if it exceeds 900 ℃ there is a problem of risk of damage, such as destruction of the structure of the ceramic carrier, but the actual temperature of the exhaust gas of the car up to 900 It does not rise.

In addition, the hydrothermal treatment is characterized in that it is carried out for 1 to 72 hours. If the treatment time is less than 1 hour, there is a problem that can not confirm the effect of sufficient hydrothermal treatment to the entire carrier due to too short treatment time, if it exceeds 72 hours to see the improvement of the improvement effect on the hydrothermal treatment time I can't.

In addition, the hydrothermal treatment is characterized in that it is carried out in an air atmosphere containing 0.1 to 50% water vapor. If the air contains less than 0.1% of the water vapor may cause problems of the hydrothermal treatment method due to insufficient water vapor, if it exceeds 50% there is a problem of weakening the adhesion of the ceramic carrier itself by high moisture However, the actual moisture content of the exhaust gases does not exceed 50%.

The hydrothermally treated ceramic fiber carrier as described above is dried at a temperature of from room temperature to 200 ℃, and then coated with a washcoat including a composite catalyst to be prepared.

Subsequently, in order to prepare a washcoat aqueous solution, which is a catalytically active component, a varadia / titania composite catalyst slurry and a binder aqueous solution are mixed.

The Vanadia / Titania composite catalyst is a catalyst that shows an efficient activity in the selective reduction of nitrogen oxides by ammonia in a fixed source and can be applied as a mobile source. Most preferably, vananium, the active material in the catalyst, contains 1 to 3% by weight. It is difficult to expect high activity at 1 wt% or less, and at 3 wt% or more, there is a problem in that the selective reduction reaction activity decreases due to ammonia oxidation at high temperature.

The method for producing the catalyst uses a commercially available impregnation method. Ammonium-Vanadate, calculated to carry vanadium, was dissolved in distilled water at 60 ~ 70 ^o C, adjusted to pH 2.5 ~ 3.0 with Oxalic Acid (COOH) ₂ , mixed with TiO ₂ , impregnated, and dried. Then, it bakes at 500 ^degreeC for 5 hours. In the same manner as above to adjust the weight percent of vanadium to prepare a catalyst.

The vanadia / titania composite catalyst slurry and the binder aqueous solution is characterized in that the mixture in a weight ratio of 1: 1 ~ 7. If the weight ratio is less than 1: 1, there is a problem of adhesion when the slurry is coated, and if it exceeds 1: 7, there is a problem in that the content of the binder increases when coating decreases the catalyst active point.

At this time, the vanadia / titania composite catalyst slurry is characterized in that the composite catalyst and distilled water is produced by mixing in a weight ratio of 1: 1 ~ 7. If the weight ratio is less than 1: 1, there is a problem of blocking the cells of the carrier due to the large amount of coating at once to produce a composite catalyst slurry having a high viscosity due to too much catalyst amount. If it exceeds 1: 7, there is a problem that the concentration of the complex catalyst in the slurry is lowered due to the small amount of catalyst.

In addition, the binder aqueous solution is characterized in that the binder and distilled water is prepared by mixing in a weight ratio of 1: 5 ~ 10. When the weight ratio is less than 1: 5, the viscosity of the binder aqueous solution is increased due to the large amount of binder, so that a large amount is coated at a time. When the weight ratio is greater than 1:10, the viscosity of the binder aqueous solution is lowered, so that coating is easy when coating the composite catalyst. There is a problem that does not work.

The aqueous binder solution used in the present invention is characterized in that it is prepared using an alumina sol.

Thereafter, the prepared washcoat aqueous solution is impregnated with the hydrothermally treated ceramic fiber carrier to prepare a washcoat ceramic fiber carrier. This step is to immerse the ceramic fiber carrier in the washcoat aqueous solution and then use an air gun to coat the cells of the monolithic ceramic carrier without clogging.

The washcoat ceramic fiber carrier is characterized in that it comprises 1 to 40% by weight of the supported washcoat. The inclusion of 40% or more by weight of washcoat results in narrowing and clogging of the carrier cells.

By firing the washcoat ceramic fiber carrier at 400 to 600 ° C. for 1 to 24 hours in an air atmosphere, the preparation of the catalyst for removing nitrogen oxides in the exhaust gas according to the present invention is completed.

The present invention also provides a method for removing nitrogen oxides in exhaust gas using the catalyst prepared according to the present invention.

That is, mixing the exhaust gas containing nitrogen oxides with a reducing agent; And removing the nitrogen oxides by a reduction reaction occurring while passing the mixed components through the catalyst reactor to which the catalyst prepared according to the present invention is applied.

At this time, the reducing agent is used ammonia or urea, the amount of ammonia or urea can be appropriately adjusted according to the amount and concentration of nitrogen oxide to be removed.

Designed and installed in a continuous fixed bed catalytic reactor, the exhaust gas containing nitrogen oxides is diffused into the coated catalyst while passing through each cell of the catalytic reactor to remove the nitrogen oxides through a reduction reaction on the catalyst surface.

First, when ammonia is used as a reducing agent, the reaction formula is as follows.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)

In addition, when using urea as a reducing agent, the reaction formula is as follows.

2NH ₂ -CO-NH ₂ + 4NO + O ₂ → 4N ₂ + 4H ₂ O + 2CO ₂ (2)

Through the above main reaction, nitrogen oxides are converted into harmless nitrogen by reacting with ammonia or urea, which is a reducing agent.

In addition, the reduction reaction is characterized in that it is carried out at a space velocity of 100 to 100,000 h ^-1 at a temperature of 150 to 600 ℃. It is most preferable in terms of the efficiency of nitrogen oxide removal to be performed under the above conditions. As a result of the reduction reaction, the nitrogen oxides in the exhaust gas are removed by reduction with nitrogen and water.

According to the present invention, the removal rate of nitrogen oxide in the exhaust gas is characterized in that 80 to 95% at a reduction reaction temperature of 300 to 500 ℃.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

Example  One

<Method for producing catalyst for removing nitrogen oxides in exhaust gas>

Ceramic fiber carrier of 200 CPSI cell size (manufactured by LG Chem) was hydrothermally treated at 700 ^° C. under an air atmosphere containing 10% water vapor for 24 hours and then dried at 110 ^° C. for 5 hours.

In addition, as a catalyst for making a washcoat, a vanadium / titania composite catalyst containing about 2% by weight of vanadium was prepared to a size of 200 mesh or less. The washcoat was prepared by mixing a composite catalyst slurry (slurry) and a binder aqueous solution in a weight ratio of 1: 4 and stirring for 12 hours. At this time, the composite catalyst slurry was prepared by mixing the catalyst and distilled water in a weight ratio of 3: 7, and the binder aqueous solution was mixed with the binder and distilled water in a weight ratio of 1: 9. The binder used an alumina sol.

The prepared washcoat was coated on the hydrothermally treated ceramic fiber carrier. The coating method is to immerse the ceramic fiber carrier in the washcoat solution by dipping, then use an air gun to coat the monolith cell without clogging and to dry it. This process is repeated 4 to 6 times. The washcoated ceramic fiber carrier was calcined in an air atmosphere at 500 ^° C. for 5 hours to produce a monolith catalytic reactor coated with 20 wt% (1.1 g) of the washcoat based on the weight of the carrier.

<Method of removing nitrogen oxide in exhaust gas>

(1) Fresh to show initial activity of catalyst

A gas composition mixed with 500 ppm of nitrogen monoxide (NO), 500 ppm of ammonia (NH ₃ ), 5% of oxygen (O ₂ ) and 10% of water (H ₂ O) was passed over the prepared catalytic reactor. At this time, inside the reactor, a reduction reaction was performed at a space velocity of 10,000 h ⁻¹ in a temperature range of 150 to 500 ^° C. As a result, the removal rate (%) of nitrogen oxide according to the reaction temperature of the catalyst is shown in FIG. 1 (Fresh).

(2) Experiment to show the activity of the catalyst with long term operation

Aging)

In addition, in order to measure the hydrothermal stability of the catalyst, the prepared catalytic reactor was hydrothermally treated at 700 ^o C for 24 hours in an air atmosphere containing 10% water vapor, and then the nitrogen oxide removal rate (%) was measured again according to the reaction temperature. The results are shown in FIG. 1 (After Aging).

Comparative example  One

<Method for producing catalyst for removing nitrogen oxides in exhaust gas>

In the same manner as in Example 1 except that the ceramic fiber carrier was not hydrothermally treated before wash coating in Example 1, a catalyst reactor coated with a wash coat of about 1.1 g was prepared.

<Method of removing nitrogen oxide in exhaust gas>

Nitrogen oxide removal efficiency and hydrothermal stability of the prepared catalytic reactor were carried out in the same manner as in Example 1 and the results are shown in FIG.

1 is a graph showing the removal rate (%) of nitrogen monoxide according to the reaction temperature according to Example 1 and Comparative Example 1 of the present invention.

In Figure 1, ○ represents the initial activity (Fresh) of the catalytic reactor wash-coated to the hydrothermally treated ceramic fiber carrier according to Example 1, △ is wash-coated to the ceramic fiber carrier without hydrothermal treatment according to Comparative Example 1 Indicates initial activity of the catalytic reactor. In addition, ● represents the hydrothermal stability of the catalytic reactor wash-coated to the hydrothermally treated ceramic fiber carrier according to Example 1, that is, the activity (After Aging) of the catalyst due to long-term operation, ▲ is the hydrothermal treatment according to Comparative Example 1 The hydrothermal stability of the catalytic reactor, which is washcoated on the ceramic fiber carrier, that is, the activity (After Aging) of the catalyst due to long-term operation, and the removal rate (%) of nitrogen monoxide (NO) according to the reaction temperature.

As shown in FIG. 1, Example 1 (After Aging) corresponding to the wash-coated catalytic reactor after hydrothermal treatment of the ceramic fiber carrier at 700 ^° C. for 24 hours in the presence of 10% moisture is not hydrothermally treated. It was found that hydrothermal stability was superior to Comparative Example 1 (After Aging) corresponding to the catalytic reactor wash-coated on the ceramic fiber carrier.

In addition, it can be seen that the catalytic reactor in the case of hydrothermal treatment of the ceramic fiber carrier maintains the initial nitrogen oxide removal activity, thereby improving hydrothermal stability.

Although described in detail above with reference to the specific embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and such modifications and modifications belong to the appended claims. It is also natural.

1 is a graph showing the removal rate (%) of nitrogen monoxide according to the reaction temperature according to Example 1 and Comparative Example 1 of the present invention.

Claims (22)

A catalyst for removing nitrogen oxides in exhaust gas, characterized in that a washcoat comprising a vanadia / titania composite catalyst is coated on a hydrothermally treated ceramic carrier. The method of claim 1, The vanadium / titania composite catalyst comprises 1 to 3% by weight of vanadium catalyst for the removal of nitrogen oxides in the exhaust gas. The method of claim 1, The hydrothermal treatment is a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that carried out at a temperature of 300 to 900 ℃. The method of claim 1, The hydrothermal treatment is a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that performed for 1 to 72 hours. The method of claim 1, The hydrothermal treatment is a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that carried out in an air atmosphere containing 0.1 to 50% water vapor. The method of claim 1, The ceramic fiber carrier coated with the washcoat includes 1 to 40% by weight of a supported washcoat, the catalyst for removing nitrogen oxides in the exhaust gas. The method of claim 1, The removal rate of the nitrogen oxides using the catalyst for removing nitrogen oxides in the exhaust gas is 80 to 95% at a reaction temperature of 300 to 500 ℃ catalyst for removing nitrogen oxides in the exhaust gas. A first step of hydrothermally treating the ceramic fiber carrier; A second step of preparing a washcoat aqueous solution by mixing the vanadia / titania composite catalyst slurry and a binder aqueous solution; And A third step of manufacturing the washcoat ceramic fiber carrier by impregnating the hydrothermally treated ceramic fiber carrier into the prepared washcoat aqueous solution Method for producing a catalyst for removing nitrogen oxides in the exhaust gas comprising a. The method of claim 8, The hydrothermal treatment is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that carried out at a temperature of 300 to 900 ℃. The method of claim 8, The hydrothermal treatment is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that performed for 1 to 72 hours. The method of claim 8, The hydrothermal treatment is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that carried out in an air atmosphere containing 0.1 to 50% water vapor. The method of claim 8, The ceramic fiber carrier comprises the steps of: (a) first coating and drying ceramic green paper prepared using a slurry solution containing ceramic fibers of 0.1 to 10 mm length with an aluminum silicate solution; (b) secondary coating and drying the dried ceramic green paper with an aluminum phosphate solution; And (c) calcining the secondary coated and dried ceramic green paper. The method of claim 8, The vanadium / titania composite catalyst comprises 1 to 3% by weight of vanadium catalyst for the removal of nitrogen oxides in the exhaust gas. The method of claim 8, The method of producing a catalyst for removing nitrogen oxides in exhaust gas is characterized in that the vanadia / titania composite catalyst slurry and the binder aqueous solution is mixed in a weight ratio of 1: 1-7. The method of claim 8, The Vanadia / Titania composite catalyst slurry is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that the catalyst and distilled water is mixed in a weight ratio of 1: 1 to 7. The method of claim 8, The binder aqueous solution is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that the binder and distilled water is mixed in a weight ratio of 1: 5 to 10. The method of claim 8, The binder is a method for producing a catalyst for removing nitrogen oxides in the exhaust gas, characterized in that the alumina sol. The method of claim 8, The washcoat ceramic fiber carrier comprises 1 to 40% by weight of a supported washcoat manufacturing method of the catalyst for removing nitrogen oxides in the exhaust gas. Mixing an exhaust gas containing nitrogen oxides with a reducing agent; And Removing nitrogen oxides by a reduction reaction which takes place while passing the mixed components through the catalyst reactor to which the catalyst according to claim 1 is applied. Method of removing nitrogen oxides in the exhaust gas comprising a. The method of claim 19, And the reducing agent is ammonia or urea. The method of claim 19, The reduction reaction is nitrogen oxide in the exhaust gas, characterized in that carried out at a space velocity of 100 to 100,000 h ^-1 at a temperature of 150 to 600 ℃. The method of claim 19, The removal rate of nitrogen oxides in the exhaust gas is nitrogen oxide in the exhaust gas, characterized in that 80 to 95% at a reduction reaction temperature of 300 to 500 ℃.

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