KR20050119225A - Multi function and multi layer catalyst for purifying automotive exhaust gas and method for manufacturing the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-functional multilayer catalyst for automobile exhaust gas purification and a method of manufacturing the same, wherein a hydrophilic water trap layer for adsorption / desorption of moisture in exhaust gas is formed on a surface of a carrier of a honeycomb structure. The present invention relates to a multilayer catalyst prepared by coating an HC trap layer, a three-way catalyst layer, and a NOx trap layer on top, and a method of manufacturing the same. According to the present invention, since the HC trap layer adsorbs HC in the exhaust gas and the NOx trap layer occludes and removes NOx before activation of the three-way catalyst layer at the initial startup, it is possible to greatly reduce the amount of harmful substances at the initial startup. In this case, HC trap, NOx trap and trapped HC, NOx can be purified by the function of each layer in one catalyst. There is an advantage in that the adsorption and desorption by this, and compactness of the catalyst system is possible.

Description

Multi function and multi layer catalyst for purifying automotive exhaust gas and method for manufacturing the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-functional multilayer catalyst for automobile exhaust gas purification and a method of manufacturing the same, wherein a hydrophilic water trap layer for adsorption / desorption of moisture in exhaust gas is formed on a surface of a carrier of a honeycomb structure. The present invention relates to a multilayer catalyst prepared by coating an HC trap layer, a three-way catalyst layer, and a NOx trap layer on top, and a method of manufacturing the same.

In general, automobile exhaust gas refers to a gas produced by the combustion of a mixer in an engine and released into the atmosphere through an exhaust pipe, and the exhaust gas contains a large amount of pollutants harmful to the human body.

Therefore, preventing air pollution due to automobile exhaust gas has emerged as an important issue for environmental hygiene, and automobiles are regulated to be cleaned before exhaust gas is discharged.

Among LA's legal driving modes, FTP mode requires the use of catalysts to reduce vehicle emissions.

In other words, the catalyst is used to purify the exhaust gas so that the amount of exhaust gas generated in the automobile does not exceed a predetermined amount.

Most of the exhaust gas generated when the gasoline supplied to an automobile engine is completely burned is carbon dioxide and water vapor, which is harmless to the human body. If incomplete combustion is caused for some reason, harmful pollutants are generated.

Most of the harmful substances generated in the engine are divided into carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). Among them, carbon monoxide and hydrocarbons are generated when gasoline is incompletely burned. Occurs when the temperature becomes 1500 ° C or higher.

Emission trends of carbon monoxide, hydrocarbons, and nitrogen oxides, which are harmful components in the exhaust gas, are opposite to each other.

In addition, when the actual air-fuel ratio is larger than the theoretical air-fuel ratio, the generation amount of nitrogen oxides is increased to become a peak, and when a thinner mixer is supplied, the amount of nitrogen oxides is decreased, but the amount of hydrocarbons is increased.

As such, the generation amounts of carbon monoxide, hydrocarbons, and nitrogen oxides are opposite to each other, so it is not easy to purify the harmful gases, and there are two methods to release the generated harmful gases into the atmosphere.

One is to reduce the generation of harmful gas itself in the engine itself, and the other is to harm the generated harmful gas before it is released into the atmosphere.

The method of detoxifying the generated harmful gas is to purify the harmful gas into harmless gas through oxidation or reduction reaction, carbon monoxide and hydrocarbon can be purified through oxidation reaction, and nitrogen oxide can be purified through reduction reaction. Can be.

Therefore, instead of using an oxidation catalyst or a reduction catalyst alone, a three way catalyst which simultaneously pursues an oxidation reaction and a reduction reaction is used.

The three-way catalyst is a very effective catalyst for purifying harmful gas generated from the engine.It has a disadvantage that it is activated only when it is above a certain temperature, and it takes time to be activated when the temperature of the catalyst material is low, such as during cold start. Since this takes a long time, there is a problem in that the emission of harmful exhaust gas is increased at the initial stage of cold start so that the FTP mode is not satisfied.

On the other hand, as the regulation of exhaust gas becomes stricter, the performance of the catalyst at the initial start-up becomes more and more important.

In recent years, adsorption or occlusion catalysts have been introduced, which suppresses the emission of exhaust gas while the three-way catalyst is warmed up by adsorbing or occluding the exhaust gas component at the initial start of the vehicle.

For example, HC adsorption catalyst and NOx storage catalyst. Three-way catalyst takes some time to be activated, and it is installed to compensate for this. HC trap and NOx trap (NOx generated during initial start-up) account for about 70% of the total emissions: FTP mode (SULEV compatible), NOx generated during initial start-up Approximately 60% of all emissions: FTP mode (SULEV compatible)

1A and 1B are schematic views illustrating the purification characteristics of the HC adsorption catalyst and the NOx storage catalyst. The HC adsorption catalyst physically adsorbs HC at initial start-up, and then has a specific temperature (eg, 150 to 200 ° C.). When it reaches, the HC starts to be desorbed, and the NOx storage catalyst absorbs NOx when it reaches a certain temperature (eg, 150 ° C), and then the NOx stored in the exhaust gas is removed by the reducing agent component in the exhaust gas. do.

FIG. 2 shows a washcoat structure of the catalyst, in which a washcoat exhibiting catalytic properties is coated, and in particular, these components are supported on the cordierite carrier.

However, both the HC adsorption catalyst and the NOx storage catalyst require a considerable volume to perform their respective functions, and an engine or another condition is required to create conditions for adsorption / adsorption and discharge / desorption of each other. to be.

Nevertheless, in recent years, in view of the development of catalyst-related technology, the development of HC adsorption catalyst and NOx storage catalyst has been proceeded separately.

Therefore, temperature, exhaust gas composition, atmosphere, etc. must be adjusted separately for each system, and since the HC storage catalyst and the NOx storage catalyst occupy volume individually, the engine system becomes more compact in view of the engine system. The reality is that development is taking place.

In addition, the related arts are limited to the production of the HC adsorption catalyst and the production of the NOx storage catalyst, and require passive engine conditions, which are opposite conditions for reducing HC and NOx.

Therefore, there is a need for a catalyst technology that maximizes the efficiency of the HC trap and at the same time facilitates the operation of the NOx trap, and is capable of adsorbing / storing HC and NOx at initial startup and allowing the catalyst to operate normally. There is a need for a new catalyst system capable of releasing HC and NOx at temperatures.

Accordingly, the present invention has been invented to solve the above problems, a coating of a hydrophilic water trap layer for performing the adsorption / desorption of moisture in the exhaust gas on the surface of the carrier of the honeycomb structure, the upper portion of the water trap layer By coating the HC trap layer, the three-way catalyst layer and the NOx trap layer in turn, the HC trap layer adsorbs HC in the exhaust gas and the NOx trap layer occludes and removes NOx prior to activation of the three-way catalyst layer at initial startup. Hazardous emissions during initial start-up can be greatly reduced, and HC trap, NOx trap and trapped HC, NOx can be purified by the function of each layer in one catalyst. Cars have the advantage of being easy to adsorb and desorption due to the synergistic effect of the catalysts themselves and the compactness of the catalyst system. An object of the present invention is to provide a multifunctional multilayer catalyst for exhaust gas purification and a method of manufacturing the same.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Multifunctional multilayer catalyst for automobile exhaust gas purification according to the present invention,

A honeycomb carrier; A water trap layer containing a moisture adsorbent as the lowest layer coated on the surface of the carrier to perform adsorption / desorption of moisture in the exhaust gas; An HC trap layer coated on the water trap layer and containing an HC adsorbent to perform physical adsorption / desorption of HC in exhaust gas; A three-way catalyst layer coated on the HC trap layer and containing a noble metal catalyst to perform exhaust gas purification; And a NOx trap layer coated on the three-way catalyst layer and containing Pt and BaO to perform occlusion and decomposition removal of NOx.

In a preferred embodiment, the water trap layer is characterized by containing a hydrophilic zeolite acid catalyst or silica gel having a Si / Al ratio of 24 to 100.

In addition, the HC trap layer is characterized by containing a zeolite having a Si / Al ratio of 500 to 1000, the number of oxygen atoms forming a pore inlet 10 to 12, the pore inlet diameter is 5 ~ 8Å.

On the other hand, the method for producing a multifunctional multilayer catalyst for automobile exhaust gas purification according to the present invention,

Preparing a slurry containing a moisture adsorbent and then coating the slurry on the surface of the honeycomb structural carrier and then drying to form a water trap layer; Preparing a slurry containing a hydrocarbon adsorbent and then coating the slurry on top of the water trap layer to dry to form an HC trap layer; Preparing a slurry for a three-way catalyst containing a noble metal catalyst and then coating the slurry on the HC trap layer and drying to form a three-way catalyst layer; And preparing a slurry for NOx occlusion containing Pt and BaO, and then coating the slurry on top of the three-way catalyst layer to dry to form a NOx trap layer.

In a preferred embodiment, in the forming of the water trap layer, the slurry is prepared by mixing hydrophilic zeolite acid catalyst or silica gel having a Si / Al ratio of 24 to 100 with colloidal silica as a binder and then wet milling. It is done.

In the step of forming the HC trap layer, the slurry is a binder containing a zeolite having a Si / Al ratio of 500 to 1000, the number of oxygen atoms forming a pore inlet 10 to 12, the pore inlet diameter of 5 ~ 8Å It is characterized in that it is prepared by mixing with wet colloidal silica and then wet milling.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-functional multilayer catalyst for exhaust gas purification of automobiles and a method of manufacturing the same, wherein several layers of functional washcoats are coated on a carrier to purify HC traps, NO x traps, and trapped HC and NO x by the function of each layer. The present invention relates to a multifunctional multilayer catalyst capable of maximizing the efficiency of the HC trap and at the same time allowing the NOx trap to occur smoothly and a method of manufacturing the same.

The catalyst of the present invention can effectively adsorb / purify exhaust gas generated during initial startup, and by forming a multilayer in one catalyst, adsorption and desorption are easy due to mutual synergy of the catalysts themselves, and the layout can be compact. There is an advantage to being terminated.

Hereinafter, the configuration of the multilayer catalyst according to the present invention will be described.

3 is a cross-sectional view illustrating a washcoat structure of a multilayer catalyst according to the present invention, and reference numeral 6 denotes an exhaust gas passage in the carrier.

As shown here, the washcoat coated on the surface of the carrier 1 is composed of a total of four multilayers. As the lowest layer directly on the surface of the carrier 1, a water trap layer 2 is provided. The upper layer has a structure in which the HC trap layer 3 is coated, and the upper layer has the ternary catalyst layer 4 and the NOx trap layer 5 coated in this order.

First, the water trap layer 2 is a hydrophilic water adsorption layer, which collects water vapor contained in the exhaust gas at the initial start-up. When the water trap layer 2 collects water vapor, the upper layer is formed as a whole. The rise in the temperature of the phosphorus HC trap layer 3 can be suppressed, thereby making it possible to lower the temperature of the HC trap layer 3 relatively than when there is no water trap layer 2.

That is, the water trap layer 2 serves to lower the temperature of the HC trap layer 3, and when the temperature of the HC trap layer 3 is lowered by the water trap layer 2, the temperature is lowered. Since the time for trapping HC at initial start-up becomes longer, the HC trap effect can be exerted for a relatively long time.

Generally, the water trap layer 2 may use an absorbent such as zeolite or silica gel, and although the bonds of the atoms in the crystal structure are loose, the skeleton remains intact even when the water that fills therein is released at a high temperature. It can adsorb.

The water trap layer 2 can be implemented with a coating layer of silica gel or a hydrophilic zeolite acid catalyst having a Si / Al ratio of 100 or less, and includes fluorite (FAU), lanthanum (La), cerium (Ce), and the like. (LTA) and the like can be used for moisture adsorption.

Next, the HC trap layer 3 is a hydrophobic hydrocarbon adsorption layer, which physically adsorbs HC having a carbon number of 3 or more to the zeolite sheave as a zeolite component, and thus adsorbs HC when the catalyst has no purification ability at the initial startup. So that it does not discharge.

When the temperature of the HC trap layer 3 rises (about 150-200 ° C.), the movement of gas molecules becomes active, leaving the zeolite sieve and desorbing HC.

The HC trap layer 3 includes a zeolite having a Si / Al ratio of 500 to 1000 or silicalite containing almost no aluminum.

Next, in the three-way catalyst layer 4, HC exiting from the HC trap layer 3 reacts, and the HC becomes water and carbon dioxide. At this time, the temperature of the three-way catalyst layer 4 increases because HC undergoes an oxidative exothermic reaction. .

The three-way catalyst layer 4 is formed by coating a slurry carrying at least one precious metal selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof on the HC trap layer 3.

On the other hand, the NOx trap layer 5 is a general Pt / BaO catalyst, and when the temperature is above a certain temperature, the NOx begins to occlude, and then the NOx occluded is separated into CO ₂ and N ₂ in a high-temperature reducing atmosphere (650 ° C. or higher). .

The NOx trap layer 5 starts to store NOx at 150 ° C. or higher. Therefore, the faster the temperature of the NOx trap layer 5 rises and the faster the storage, the greater the amount of NOx that can be reduced. In 4), when the heat of oxidative heating reaction is generated during HC purification, the heat of oxidation reaction is transferred to the upper layer so that the temperature of the NOx trap layer 5 is raised. As a result, the NOx trap layer 5 can store NOx within a short time. To reach a certain temperature.

FIG. 4 is a schematic diagram showing the role of each layer in the washcoat described above, and FIG. 5 is a schematic diagram showing the NOx occlusion and NOx removal mechanism of the NOx trap layer.

During initial cold start, water and hydrocarbon are adsorbed to the hydrophilic water trap layer 2 while passing through the catalyst of the present invention, and hydrocarbon is adsorbed to the hydrophobic HC trap layer 3.

Gradually, when the temperature of the exhaust gas rises (more than 100 ° C.), the three-way catalyst layer 4 starts to be activated, and the water trap layer 2 starts to desorb water while the three-way catalyst layer 4 is heated. As a result, the HC trap layer 3 is cooled, so that HC desorption is delayed.

At the time when HC of the HC trap layer 3 starts to desorb, the three-way catalyst layer 4 is sufficiently heated and activated, and the desorbed HC is effectively oxidized and removed in the three-way catalyst layer 4.

At this time, since it generates heat while being oxidized, heat is transferred to the uppermost NOx trap layer 5 to help the NOx trap layer be activated.

The NOx trap layer 5 occludes NOx at initial start-up, but as shown in FIG. 5, if the temperature is above a certain temperature (eg, 150 ° C.), Pt oxidizes NO to NO ₂ , and NO ₂ to BaO to BaO. After occluding in the form of (NO ₃ ) ₂ , Ba (NO ₃ ) ₂ is decomposed into N ₂ and CO ₂ to remove the occluded NO x by creating a high-temperature reducing atmosphere.

In the structure of the present invention, the heat of oxidation of HC desorbed from the HC trap layer 3 is transferred from the three-way catalyst layer 4 to the NOx trap layer 5, which is the upper layer, and the temperature of the NOx trap layer 5 is increased. As a result, it is possible to make the occlusion condition of the NOx trap layer 5 in a short time by using the amount of oxidation calorific value with the existing exhaust gas heat transfer.

On the other hand, the process for producing a multilayer catalyst of the above-described structure is as follows.

First, a water trap layer 2 serving as a moisture adsorption layer is formed on the surface of the ceramic carrier 1 having a honeycomb structure.

In order to form the water trap layer 2, first, a hydrophilic zeolite acid catalyst or silica gel having a Si / Al ratio of 24 to 100 is mixed with a binder, and then wet milled to prepare a slurry.

Then, the slurry prepared as described above is first coated on the surface of the carrier and then dried at 150 ° C. for 3 hours.

Next, the HC trap layer 3 is coated on the water trap layer 2.

In order to form the HC trap layer 3, a zeolite or silicalite having a Si / Al ratio of 500 to 1000 as a hydrocarbon adsorbent is mixed with a binder (e.g., 60 to 80 wt% of the zeolite 20 to colloidal silica as a binder). Mixed with 40 wt%), and wet milled to prepare a slurry.

The zeolite used as described above has a moderately strong hydrocarbon adsorption strength and excellent thermal safety, so that the hydrocarbon is effectively adsorbed and stored at a low temperature, desorbed and purified at an appropriate high temperature, and maintains stable activity in the long term.

Although the structure and type of zeolite reaches several hundred species, as an example of the structure meeting the object of the present invention, MFI, mordenite and beta may be used.

The zeolite is characterized in that the number of oxygen atoms constituting the pore inlet range from 10 to 12, the pore inlet diameter is 5 ~ 8Å, this structure is very suitable as a hydrocarbon adsorbent.

In addition, since these are synthetic zeolites, it is relatively free to control the ratio of Si / Al through adjustment of the composition of the synthesis mixture.

The ratio of Si / Al is indirectly able to know the adsorption capacity of the hydrocarbon, in the present invention, the ratio of Si / Al is 500 to 1000. If the ratio is less than 500, the thermal stability of the catalyst is low and the hydrocarbon is long-term. If the adsorption capacity cannot be maintained, and it is larger than 1000, the strength of adsorbing the hydrocarbon is lowered, which causes undesirable problems in that the adsorbed hydrocarbon is released before the three-way catalyst layer is activated.

After the slurry for the HC trap layer 3 is prepared as described above, the slurry for the HC trap layer is coated on the water trap layer 2 by dipping the carrier in the slurry, and then dried at 150 ° C. for 3 hours.

Next, the three-way catalyst layer 4 is coated on the HC trap layer 3.

At this time, the slurry was prepared by wet milling together alumina (Al ₂ O ₃ ), cerium oxide (CeO ₂ ), and a noble metal catalyst (Pt, Pd, Rh, etc.), and then coating the slurry on the HC trap layer. Dry at 150 ° C. for 3 hours.

Next, the NOx trap layer 5 is coated on the three-way catalyst layer 4.

At this time, the slurry was prepared by wet milling alumina (Al ₂ O ₃ ), barium oxide (BaO), and platinum (Pt) together, and then coating the slurry on the three-way catalyst layer 4 and then at 150 ° C. for 3 hours. To dry.

Next, through the calcination process after drying as described above it is possible to obtain a finished catalyst as a ratio.

This calcination process is already known in the art along with wet milling, for example, is carried out for 10 hours in an electric furnace of 450 ~ 550 ℃ temperature.

In addition, the wet milling may adopt a method commonly used in the art, and the present invention does not limit the method.

Thus, the multifunctional multilayer catalyst of the present invention comprises a carrier 1 having a honeycomb structure, a water trap layer 2 composed of a water adsorbent such as zeolite or silica gel and laminated on the carrier 1, HC trap layer 3 composed of zeolite stacked on top of water trap layer 2, ternary catalyst layer 4 stacked on HC trap layer 3, and NOx laminated on this ternary catalyst layer 4 It consists of the trap layer 5.

On the other hand, to determine the exhaust gas reduction effect of the multilayer catalyst according to the present invention prepared as described above, the evaluation was carried out in the FTP mode with respect to the existing system and the system applied with the multilayer catalyst of the present invention, the results are attached to Figure 6 Same as

The same result as in FIG. 6 was obtained in the cold startup Bag 1, but CO was almost the same, but THC showed about 70% reduction and NOx showed about 45% reduction.

However, in the multilayer catalyst according to the present invention, a lean start should be performed during cold start, and NOx is occluded in the NOx trap layer by the lean start, and when the catalyst is warmed up, it is richly controlled (rich control) naturally. NOx stored in the NOx trap layer is decomposed into CO ₂ and N ₂ .

Regardless of the atmosphere, the HC trap layer naturally desorbs HC that has been physically adsorbed when the temperature is raised.

As described above, according to the multi-functional multilayer catalyst for automobile exhaust gas purification according to the present invention and a method for manufacturing the same, the HC trap layer adsorbs HC in the exhaust gas before the activation of the three-way catalyst layer at initial startup, and the NOx trap layer is NOx. As a result, it is possible to significantly reduce the emission of harmful substances at the initial start-up, and to purify HC traps, NOx traps, and trapped HC and NOx by the function of each layer in one catalyst. By constructing a multi-layered laminated structure having a function of, the adsorption and desorption by the synergistic effect of the catalysts themselves and the compactness of the catalyst system are possible.

1a and 1b schematically show the purification characteristics of the conventional HC adsorption catalyst and NOx storage catalyst,

2 is a schematic cross-sectional view showing a washcoat structure of a general catalyst,

3 is a cross-sectional view showing a washcoat structure of a multilayer catalyst according to the present invention;

4 is a schematic view showing the role of each layer in the washcoat in the multilayer catalyst according to the present invention,

5 is a schematic diagram showing the NOx occlusion and NOx removal mechanism of the NOx trap layer;

Figure 6 is a result of the evaluation in the FTP mode for the existing system and a system to which the multilayer catalyst of the present invention is applied.

<Explanation of symbols for the main parts of the drawings>

1 carrier 2 water trap layer

3: HC trap layer 4: three-way catalyst layer

5: NOx trap layer

Claims (6)

A honeycomb carrier; A water trap layer containing a moisture adsorbent as the lowest layer coated on the surface of the carrier to perform adsorption / desorption of moisture in the exhaust gas; An HC trap layer coated on the water trap layer and containing an HC adsorbent to perform physical adsorption / desorption of HC in exhaust gas; A three-way catalyst layer coated on the HC trap layer and containing a noble metal catalyst to perform exhaust gas purification; A NOx trap layer coated on the three-way catalyst layer and containing Pt and BaO to occlude and decompose and remove NOx; Multifunctional multilayer catalyst for automobile exhaust gas purification comprising a. The method according to claim 1, The water trap layer, Multifunctional multilayer catalyst for automobile exhaust gas purification, characterized in that a hydrophilic zeolite acid catalyst having a Si / Al ratio of 24 to 100 or silica gel is contained. The method according to claim 1, The HC trap layer, A multi-functional multilayer catalyst for automobile exhaust gas purification, comprising a zeolite having a Si / Al ratio of 500 to 1000, a pore inlet number of 10 to 12 oxygen atoms, and a pore inlet diameter of 5 to 8 kPa. Preparing a slurry containing a moisture adsorbent and then coating the slurry on the surface of the honeycomb structural carrier and then drying to form a water trap layer; Preparing a slurry containing a hydrocarbon adsorbent and then coating the slurry on top of the water trap layer to dry to form an HC trap layer; Preparing a slurry for a three-way catalyst containing a noble metal catalyst and then coating the slurry on the HC trap layer and drying to form a three-way catalyst layer; Preparing a slurry for occluding NOx containing Pt and BaO and then coating the slurry on top of the three-way catalyst layer and drying to form a NOx trap layer; Method for producing a multifunctional multilayer catalyst for automobile exhaust gas purification comprising a. The method according to claim 4, In the forming of the water trap layer, The slurry is a method for producing a multi-functional multilayer catalyst for automobile exhaust gas purification, characterized in that the hydrophilic zeolite acid catalyst having a Si / Al ratio of 24 to 100 or silica gel is mixed with colloidal silica as a binder and then wet milled. The method according to claim 4, In the step of forming the HC trap layer, The slurry is prepared by mixing a zeolite having a Si / Al ratio of 500 to 1000 and a pore inlet of 10 to 12 oxygen atoms and a pore inlet diameter of 5 to 8 kPa with colloidal silica as a binder and then wet milling. Method for producing a multi-functional multilayer catalyst for automobile exhaust gas purification, characterized in that.