KR20030038035A - A system for the three way catalytic aftertreatment of gasoline automotive emissions - Google Patents

Abstract

PURPOSE: A three way catalyst system is provided to significantly reduce environmental contamination by efficiently purifying NOx of exhaust gas of gasoline vehicle. CONSTITUTION: A three way catalyst system comprises two catalyst systems constituted by different components. The first catalyst system disposed at the exhaust gas inlet unit is formed by adding palladium to an alumina support, without adding ceria. The second catalyst system disposed at the exhaust gas outlet unit is formed by adding palladium, rhodium and ceria to an alumina support. The vehicle exhaust gas purifying system has improved efficiency in that the first catalyst converter removes hydro-carbon, and the second catalyst converter removes carbon monoxide and NOx.

Description

A system for the three way catalytic aftertreatment of gasoline automotive emissions}

The present invention relates to a three-way catalyst system for automobile exhaust gas purification, and more particularly, two catalyst systems composed of different components constitute a converter in a form arranged before and after, but the first catalyst system located at the exhaust gas introduction portion is formed on an alumina support. Supporting palladium and not ceria, the second catalyst system located in the exhaust gas outlet supports palladium, rhodium and ceria on an alumina support, so that hydrocarbons are removed in the first converter and carbon monoxide and nitrogen oxides in the second converter. The present invention relates to a new three-way catalyst system for improving the purification characteristics of gaseous vehicle exhaust gas, especially nitrogen oxides by establishing an efficient purification system.

In the early twentieth century, automobiles, which began mass production at Ford Corp. in the United States, exploded and became an indispensable vehicle for now. As the utilization of such vehicles increases, traffic congestion, damage caused by various traffic accidents and vibrations, and serious air pollution due to exhaust gas are becoming serious and important social problems.

Gases emitted from automobiles are divided into exhaust gas, blow-by gas and evaporative gas. Among the exhaust gas is a gas fuel is dedicated to act by expansion after the combustion in the cylinder as a gas at a high temperature and high pressure discharged into the atmosphere from an exhaust pipe, which accounts for most of the exhaust gas water vapor and carbon dioxide (CO ₂₎ And other harmful substances such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). Among the components in the exhaust gas, carbon monoxide, hydrocarbons, and nitrogen oxides, which are called three-way gas, cause very serious environmental pollution, and studies are being actively conducted to reduce such substances. In other words, studies are being conducted to develop automobiles in which exhaust gas is not generated at all, but there are still considerable difficulties in commercializing many improvements in efficiency.

On the other hand, the research to reduce the generation of harmful exhaust gas by improving the shape, operating conditions and operating conditions of each engine in the conventional automobile is continuing.

In addition, research has been conducted to reduce the emission of these harmful components by decomposing exhaust gas into a catalyst, and this effort has been applied to various vehicles at present.

Catalysts are usefully applied in many fields, including exhaust gas treatment of internal combustion engines such as engines of automobiles and other gasoline fuels. Emission standards for these pollutants are set by the government, and new vehicles must meet these standards. In order to meet these standards, a so-called three way catalytic converter containing a suitable noble metal catalyst is installed in the exhaust gas pipe of the internal combustion engine to promote the decomposition of hydrocarbons, oxidation of carbon monoxide and reduction of nitrogen oxides.

Catalytic converters are largely classified into functional catalytic converters and three-way catalytic converters.

Presently, the noble metal three-way catalyst used for exhaust gas purification of gasoline cars is manufactured by adding ceria, which is an oxide of cerium, as an oxygen storage material for absorption or release of oxygen under oxidizing or reducing conditions, as shown in the accompanying drawings.

Various studies have been conducted to improve the activity of three-way catalysts. For example, attention has been paid to the function of absorbing and storing oxygen in the gas phase of ceria, which is an oxide of cerium, or releasing it from the crystal. That is, the ceria is added to the three-way catalyst to control the oxygen concentration in the gaseous atmosphere. In the oxygen-rich state, the excess oxygen is absorbed and stored in the crystal of ceria in the gaseous atmosphere to reduce the nitrogen oxides by the three-way catalyst. On the other hand, in a state rich in carbon monoxide and hydrocarbons, oxygen insufficient in the gas phase atmosphere is released from the crystal, and the three-way catalyst is intended to improve the oxidation reaction efficiency.

However, the ceria promotes a water gas reaction in which carbon monoxide and water are reacted to generate carbon dioxide and hydrogen gas, as shown in Scheme 1 below.

CO + H ₂ O → CO ₂ + H ₂

As described above, carbon monoxide consumed in the water gas reaction is highly utilized as a reducing agent of nitrogen oxides, and since carbon monoxide is mostly consumed by the water gas reaction as described above, there is no room for use as a reducing agent in the reduction reaction of nitrogen oxides. In the removal reaction of the oxide is quite disadvantageous, there is a problem that the purification of the seriously harmful nitrogen oxide is not made properly.

Therefore, there is an urgent need to develop a method that can solve the problem that the carbon monoxide is consumed and the nitrogen oxide removal efficiency is lowered in the vehicle exhaust gas purification.

Therefore, the inventor of the present invention comprises a converter of the catalyst for purifying automobile exhaust gas composed of two catalyst systems, but without adding ceria to the first catalyst system located at the part where the exhaust gas is introduced, the second catalyst system located at the part where the exhaust gas is discharged. Only when ceria is added to the composition, the water gas generation reaction can be suppressed, thereby completing the present invention.

Therefore, the present invention is to improve the purification performance of the nitrogen oxide by greatly improving the purification performance of the nitrogen oxides by making the catalytic converter system consisting of two catalyst systems in the three-component catalyst system for the exhaust gas purification of gasoline cars by different components of each catalyst system The purpose is to provide a three-way catalyst system.

1 is a simplified illustration of the components of a conventional three-way catalyst system,

2 is a view showing the configuration of the three-way catalyst system for automobile exhaust gas purification and the components of each converter according to the present invention.

According to the present invention, in the three-way catalyst system for automobile exhaust gas purification, the catalytic converter is composed of two catalyst systems having different component configurations, but the first catalyst system of the exhaust gas introduction portion is composed of a catalyst in which palladium is supported on an alumina support without addition of ceria. The second catalyst system of the exhaust gas outlet is characterized by a three-way catalyst system consisting of a catalyst carrying palladium, rhodium and ceria on an alumina support.

Hereinafter, the present invention will be described in detail.

The present invention constitutes a three-way catalytic converter consisting of two catalyst systems in a three-way catalyst system, but does not support ceria in the first catalyst system located at the exhaust gas introduction, and supports ceria in an alumina carrier at the second catalyst system located in the exhaust gas discharge. It is a new three-way catalyst system that improves the purification characteristics of nitrogen oxide so that the purification effect is achieved by effectively using carbon monoxide in the exhaust gas of gasoline cars by constructing a converter which is a component composition.

Looking at the two catalyst systems with different components constituting the catalytic converter of the three-way catalyst system according to the present invention in detail as follows.

First, the first catalyst system located at the portion of the vehicle exhaust gas flows is formed by supporting palladium on the alumina support. The alumina carrier impregnated with palladium is prepared by wet milling into a slurry, coated on a carrier of a honeycomb structure, and then dried and calcined.

In this case, it is a feature of the present invention that no ceria is added. In the first catalyst system, hydrocarbons are mainly removed by an oxidation reaction, and carbon monoxide is positioned in an exhaust gas discharge part without being completely removed, and then transferred to the second catalyst system.

The second catalyst system located in the exhaust gas outlet is loaded with a palladium solution and a rhodium solution on the porous support to which the ceria, which is a feature of the present invention, is added together with the alumina support. The porous support on which palladium and rhodium are supported is prepared as a slurry by wet milling, coated on a honeycomb carrier, and then dried and calcined. In this case, the amount of ceria added is 10 to 50 parts by weight based on 100 parts by weight of the porous carrier.

Ceria, an oxide of the lanthanide element cerium, has been found in a number of studies aimed at improving the activity of three-way catalysts.It has the ability to absorb, store, or release oxygen in the gas phase in the crystal of oxide. It is a substance.

In other words, by adding the ceria to the three-way catalyst, the oxygen concentration in the gaseous atmosphere can be controlled. The mechanism is as follows. When oxygen is abundant in the gas phase, excess oxygen is stored in the crystal of ceria to reduce nitrogen oxides by the three-way catalyst. The reaction is accelerated, and in a state rich in carbon monoxide and hydrocarbons, oxygen released in the gas phase atmosphere is released from the crystal, and the oxidation reaction by the three-way catalyst is promoted.

The chemical formula of ceria is typically represented by CeO ₂ , but a compound having zirconium, yttrium, niobium, or the like added to ceria used in an automobile catalyst is improved in heat resistance. Therefore, it is apparent that the ceria referred to in the present specification includes a compound having improved heat resistance.

At this time, if the amount of ceria added is less than 10 parts by weight, the storage capacity of oxygen is insufficient, and if it exceeds 50 parts by weight, it is disadvantageous to secure an active specific surface area.

Therefore, in the second catalyst system, the reduction reaction of the nitrogen oxides can be promoted by carbon monoxide not removed from the first catalyst system, so that the nitrogen oxides in the vehicle exhaust gas can be efficiently purified.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example

10 parts by weight of a palladium solution was loaded onto 90 parts by weight of an alumina carrier based on 100 parts by weight of the first catalyst system, and then wet milled to prepare a slurry. The slurry was coated on a carrier of a honeycomb structure, dried, calcined, and exhausted. The first catalyst system of the three-way catalyst system located in the section was prepared.

7 parts by weight of palladium solution and 3 parts by weight of rhodium solution were loaded on 30 parts by weight of ceria and 60 parts by weight of alumina carrier to prepare a slurry by wet milling, and then the slurry was prepared on a carrier having a honeycomb structure. After coating, drying and firing to prepare a second catalyst system of the three-way catalyst system located in the exhaust gas inlet.

Comparative Example 1:

10 parts by weight of a palladium solution was loaded on 30 parts by weight of ceria and 60 parts by weight of an alumina carrier, followed by wet milling to prepare a slurry. The slurry was coated on a carrier of a honeycomb structure, and then dried. The first catalyst system of the three-way catalyst system was prepared by firing and placed in the exhaust gas inlet.

The second catalyst system was immersed in 7 parts by weight of palladium solution and 3 parts by weight of rhodium solution to 30 parts by weight of ceria and 60 parts by weight of alumina carrier to prepare a slurry by wet milling and then coated the slurry on the carrier of the honeycomb structure After drying and firing to prepare a second catalyst system of the three-way catalyst system located in the exhaust gas inlet.

Comparative Example 2:

10 parts by weight of a palladium solution was loaded on 30 parts by weight of ceria and 60 parts by weight of an alumina carrier, followed by wet milling to prepare a slurry. The slurry was coated on a carrier of a honeycomb structure, and then dried. The first catalyst system of the three-way catalyst system was prepared by firing and placed in the exhaust gas inlet.

10 parts by weight of a palladium solution was loaded on 30 parts by weight of ceria and 60 parts by weight of an alumina carrier, followed by wet milling to prepare a slurry. The slurry was coated on a carrier of a honeycomb structure, dried, and then fired. To prepare a second catalyst system of a three-way catalyst system located at the exhaust gas inlet.

Test Example

50% purification rate of nitrogen oxide while allowing the exhaust gas of the engine to pass through the three-way catalyst system of the present invention prepared in the above embodiment and the three-way catalyst system prepared in Comparative Examples 1 and 2 at time = 0 at room temperature. To measure the time it takes to reach, and the concentration of the nitrogen oxide emitted as a result of operating in the domestic authorized evaluation mode equipped with a three-way catalytic converter manufactured in the above Examples and Comparative Examples shown in Table 1 below.

As shown in Table 1, the time required for purifying nitrogen oxide 50% in the engine evaluation is 53 seconds in the embodiment of the present invention, purifying the nitrogen oxides compared to Comparative Example 1 represented by 175 seconds and Comparative Example 2 represented by 175 seconds It can be seen that the time required was greatly reduced by three to four times.

Exhaust gas exhaust time of the vehicle is extremely short, as shown in Table 1, the short time required to remove 50% of the nitrogen oxides means that the purification efficiency is high.

On the other hand, the concentration of nitrogen oxides discharged per unit kilometer in the vehicle test evaluation is a result indicating the degree of purification of nitrogen oxides when the vehicle equipped with the three-way catalyst system is directly operated, compared to the conventional comparative example is 0.05 or 0.06 As shown in the example of 0.04, this also means that the purification efficiency of the three-way catalyst system according to the present invention is high.

As described above, according to the three-way catalyst system according to the present invention, it is possible to purify nitrogen oxides in the exhaust gas of a gasoline automobile more efficiently, thereby reducing the environmental pollution.

Claims (2)

In the three-way catalyst system for automobile exhaust gas purification, the catalytic converter is composed of two catalyst systems having different component configurations, but the first catalyst system of the exhaust gas introduction portion is composed of a catalyst in which palladium is supported on an alumina support without addition of ceria. The second catalyst system of the gas discharge portion is a three-way catalyst system, characterized in that consisting of a catalyst supporting the palladium, rhodium on a support consisting of alumina support and ceria. The three-way catalyst system according to claim 1, wherein the ceria is added in an amount of 10 to 50 parts by weight based on 100 parts by weight of the porous support.