KR19990084403A - Catalyst for purification of automobile exhaust - Google Patents

Abstract

The present invention relates to a catalyst for purifying automobile exhaust gas having high purification efficiency for particulate matter among exhaust gases generated in a diesel vehicle, and includes a carrier portion and a main catalyst component supported on the carrier portion, wherein the carrier portion is impregnated with iron. Modified zirconia dioxide, and the main catalyst component is platinum. The catalyst for automobile exhaust gas purification according to the present invention has the highest combustion activity in the operating temperature range (300-350 ° C.) of a general diesel vehicle and is excellent in stability at high temperatures. In addition, even if the amount of platinum supported is small, the desired catalytic activity can be obtained, thereby reducing the manufacturing cost.

Description

Catalyst for purification of automobile exhaust

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for automobile exhaust gas purification, and more particularly, to a catalyst for automobile exhaust gas purification having excellent particulate matter removal efficiency over an operating temperature range of a diesel engine by improving particulate matter oxidation activity and stability at high temperature. It is about.

In recent years, there has been a growing concern about environmental protection along with concerns about environmental destruction. Environmental pollution can be roughly classified into air pollution, water pollution, and soil pollution.

In particular, the phenomenon due to air pollution includes the destruction of the ozone layer due to the use of hydrogen fluoride (CFC), and the global greenhouse effect due to carbon dioxide generated when using fossil fuels. In addition, sulfur oxides, nitrogen oxides, hydrocarbons, and the like emitted from various pollutant discharge facilities cause various diseases to animals and plants.

Air pollution mainly comes from combustion bodies, and the severity of the damage is determined by the structure of the combustion facility, the method of operation, and external weather conditions. Representative combustion bodies include automobiles.

Unlike other air pollution emission facilities, cars emit pollutants while moving, and as the use of automobiles increases rapidly as living standards improve, the air pollution problem caused by cars becomes serious.

The composition and emissions of automobile emissions are related to the engine's temperature, pressure and proportion of air. That is, by properly adjusting the air / fuel ratio of the engine, it is possible to increase the exhaust gas purification efficiency. Exhaust gas components and emissions also depend largely on the type of fuel source and purification equipment used.

For automobiles driven by spark ignition engines using gasoline as a fuel source, many exhaust gas removal technologies such as three-way catalysts have been developed, and emissions of pollutants by gasoline vehicles have been significantly reduced.

On the other hand, diesel engines are not only inexpensive, but diesel engines using them as a fuel source have good thermal efficiency, so diesel engines are used in large vehicles such as trucks. However, despite these advantages, the technology for purifying the exhaust gas of diesel vehicles using diesel is very poor compared to gasoline vehicles, and thus, continuous research is required.

Diesel vehicles using diesel have slightly different pollutants due to the different characteristics of the fuel source and the engine engine's structural characteristics than those of gasoline vehicles. The emissions of carbon monoxide and hydrocarbons are lower than those of gasoline vehicles. Unlike gasoline cars, they emit large amounts of sulfur oxides (SO _x ) and particulate matter.

Particularly, particulate matter is solid and liquid substance containing carbon soot, soluble organic component, sulfates (SO ₃ and H ₂ SO ₄ ), not only carcinogenic, but also produced as a visible smoke. The development of the removal method is urgently required because of the discomfort.

In general, diesel exhaust after-treatment methods that are approaching practical use to date can be roughly classified into two types except for plasma discharge combustion methods that require more verification.

One of them is trapping particulate matter using a trap (filter) and then burning it with a diesel burner or electric heater, which aims to burn only the soot in the particulate matter and has a removal efficiency of more than 95%. Has the advantage of being adopted by some, but the structure is very complicated and requires a regeneration treatment device, high power consumption and extra fuel, especially in the regeneration of traps due to temperature variation, particulate matter There are various problems such as negative pressure generation due to overaccumulation of material, clogging of filter by combustion material, expensive manufacturing cost, and so on.

On the other hand, the other method is a flow-through type method using an open honeycomb, which, like a gasoline automobile catalyst, carries a noble metal and a transition metal on an oxide carrier so that particulate matter, hydrocarbons and As a method of oxidizing and purifying carbon monoxide gas, it is expected to be installed in a diesel engine in the near future in the near future because of all the drawbacks of the trap type exhaust gas purification method.

However, most of the flow-through type catalysts developed to date have a level of oxidative activity of about 20 to 30% for particulate matter and a slight purification rate for hydrocarbons, etc., and thus are still insufficient to be put into practical use. This is believed to be due to the characteristics of diesel exhaust gas itself and the limitation of inherent oxidation activity of the catalyst. In other words, since the exhaust gas emitted from diesel engines contains a large amount of carbon dioxide, excess oxygen, and H ₂ O generated by the sulfur content in the fuel as compared to general gasoline cars, they not only reduce the oxidation activity of the catalyst but also This is because the durability of the product for a long time reduces its lifespan.

As described above, the catalyst for purifying exhaust gases used in the flue-through type comprises an oxide carrier and a transition metal which is a noble metal and / or a promoter component as the main catalyst component.

Al ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO _2, etc. are commonly used as oxide carriers. Of these, when used in diesel engines, Al ₂ O ₃ adsorbs sulfur dioxide at low temperatures and oxidizes it to sulfur trioxide at high temperatures. In addition, the SiO ₂ carrier has the advantage of exhibiting strong endothelial toxicity to H ₂ O as well as sulfur dioxide, while the inherent oxidizing ability is low. Falls. On the other hand, TiO ₂ and ZrO ₂ can be used alone or as a mixture. The adsorption amount of sulfur dioxide is small and the amount of sulfate is generated, but the oxidation activity is lowered due to the sharp decrease of specific surface area at high temperature, and the activity of precious metal and transition metal. There is a problem that even lowers.

On the other hand, precious metals used as main catalysts include platinum and palladium. Platinum has excellent oxidation activity at low temperatures but is expensive, and thus, price is inferior in price competitiveness when used in large quantities. Although it is useful in that it exhibits oxidation activity to sulfur dioxide at about 450 ° C., there are disadvantages in that the oxidation activity at low temperature is low and the durability at high temperature is low for particulate matter.

Finally, transition metals and rare earth metals used as cocatalysts include oxides such as iron, cobalt, nickel, chromium, cesium, lanthanum, praseodymium, but they themselves have low initial activity as well as sulfur dioxide and H ₂ O. There is a disadvantage in that the long term activity is poor overall.

The technical problem to be achieved by the present invention is to provide a catalyst for automobile exhaust gas purification which is excellent in oxidation activity and stability at high temperature and excellent in removal efficiency for particulate matter.

Technical problem of the present invention is an automobile exhaust gas purification catalyst comprising a carrier part and a main catalyst component supported on the carrier part, wherein the carrier part is modified zirconia dioxide impregnated with iron and the main catalyst component is platinum. It can be achieved by a catalyst for gas purification.

1 is a graph illustrating the particulate matter oxidation activity of the catalyst according to the present invention.

In the present invention, the modified zirconia dioxide is 2.1 to 5% by weight of sulfuric acid (SO ₄ ^2- ) ions are added to the zirconia dioxide powder. If the addition amount is less than 2.1% by weight, the acidic properties of zirconia dioxide do not appear. On the contrary, if the addition amount is more than 5% by weight, the amount of the addition may be excessive to deteriorate the carrier.

Further, 1 to 10% by weight of iron is added based on the total amount of modified zirconia. If the addition amount is less than 1% by weight, the effect of addition is hardly exhibited. On the contrary, if the addition amount is more than 10% by weight, the excess amount of iron remains on the surface of the carrier, which does not help increase the activity at all. It only results in an increase.

Finally, the supported amount of platinum as the main catalyst component is preferably 0.05 to 0.5% by weight based on the total amount of the carrier portion. If the supported amount is less than 0.05% by weight, the combustion activity for the particulate matter is hardly exhibited. On the contrary, even if the amount is more than 0.5% by weight, there is no improvement in the amount of the combustion activity.

The principle of the present invention is as follows.

Zirconia dioxide powders originally have a low solid acid point but exhibit catalytic activity with the addition of metal oxides. However, as described above, not only the activity of the precious metal and the transition metal supported as the main catalyst component is lowered, but also the activity disappears with the decrease of the specific surface area at 600 ° C. or higher. In the present invention, by adding a predetermined amount of sulfate ions (SO ₄ ^2- ) on the lattice of the zirconia dioxide powder, not only can the specific surface area decrease at high temperatures, but also the high temperature activity of the carrier itself is improved.

In addition, by adding iron having high thermal stability and combustion power to the modified zirconia, the catalyst carrier itself is active, and the interaction between the carrier including the metal and the main catalyst metal is facilitated, thereby increasing the oxidation activity of the catalyst.

By adding platinum having excellent oxidation activity at low temperatures as a main catalyst component to the carrier thus made, the particulate matter can be burned even at low temperatures.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example

<Production of Catalyst>

A solution prepared by dissolving 2.170 g of Fe (NO ₃ ) ₂ in distilled water was mixed with 10 g of modified zirconia powder added with sulfate ions, and then dried and calcined at 500 ° C. for 3 hours to support iron in modified zirconia. A carrier powder (Fe-MZrO ₂ where MZrO ₂ means modified zirconia) was prepared.

Subsequently, a solution in which Pt (NH ₃ ) ₄ Cl ₂ H ₂ O (platinum content is 0.1% by weight relative to the total amount of carrier powder) was dissolved in the ethylene glycol solution was impregnated into the carrier powder to support 0.1 Pt / of platinum. Fe-MZrO ₂ was obtained.

<Measurement of Catalyst Activity>

The prepared catalyst was mixed with the particulate matter taken from the bus (mixture weight ratio of catalyst: particulate matter = 20: 1), and then pelletized. Only pellets having a particle size of 1 to 2 mm were selected using a sieve, placed in a reactor, reacted under the following conditions, and the carbon dioxide concentration was measured using a CO ₂ analyzer. The oxidative activity of particulate matter is proportional to the concentration of carbon dioxide, with the temperature representing the highest carbon dioxide concentration being the highest active site temperature:

Diesel exhaust composition: NO 500ppm, C ₃ H ₆ 800ppm, O ₂ 8%, CO 2000ppm ,, SO ₂ 200ppm, H ₂ O 10%, He remainder

Reaction temperature 200-600 degreeC

Space Speed: 40,000h ^-1

The measurement results of the catalytic activity are shown in FIG. 1.

Comparative Example 1

A catalyst was prepared in the same manner as in Example 1, except that zirconia dioxide was used as the carrier, and the activity thereof was measured and shown in FIG. 1.

Comparative Example 2

A catalyst was prepared in the same manner as in Example 1 except that iron was not supported, and the activity thereof was measured and shown in FIG. 1.

Comparative Example 3

A catalyst was prepared in the same manner as in Example 1, except that the supported amount of platinum was 1% by weight based on the total amount of the carrier powder, and the activity thereof was measured and shown in FIG. 1.

As can be seen from Figure 1, if the amount of platinum supported is the same (Examples 1, 1 and 2), the catalyst using Fe-MZrO ₂ carrier (Example 1) shows a carbon dioxide concentration of 5500 ppm at 300 ℃ In the case of the catalyst using the Fe-ZrO ₂ carrier (Comparative Example 1), 5000 ppm at 420 ° C and the catalyst using the MZrO ₂ carrier (Comparative Example 2) are 5100 ppm at 400 ° C. That is, the catalyst of the present invention shows the highest carbon dioxide concentration at the lowest temperature, which shows that the particulate matter removal efficiency at low temperature is superior to other catalysts (Comparative Examples 1 and 2).

On the other hand, as a result of evaluating the catalytic activity by varying the amount of platinum supported (Example 1 and Comparative Example 3), even if the amount of platinum supported was 10 times higher, there was almost no difference in carbon dioxide concentration or maximum active site temperature. That is, as in the catalyst of Example 1, excellent catalytic activity can be obtained with only a small amount of platinum.

The catalyst for automobile exhaust gas purification according to the present invention has the highest combustion activity in the operating temperature range (300-350 ° C.) of a general diesel vehicle and is excellent in stability at high temperatures. In addition, even if the amount of platinum supported is small, the desired catalytic activity can be obtained, thereby significantly reducing the cost of producing the catalyst.

Claims (4)

A catalyst for automobile exhaust gas purification comprising a carrier portion and a main catalyst component supported on the carrier portion, A catalyst for purification of automobile exhaust gas, wherein the carrier portion is modified zirconia dioxide impregnated with iron, and the main catalyst component is platinum. The catalyst for purifying automobile exhaust gas according to claim 1, wherein the modified zirconia dioxide is added with 2.1 to 5% by weight of sulfuric acid (SO ₄ ^2- ) ions to the zirconia dioxide powder. The catalyst for purifying automobile exhaust gas according to claim 1, wherein the amount of iron added is 1 to 10% by weight based on the total amount of modified zirconia dioxide. The catalyst for automobile exhaust gas purification according to claim 1, wherein the supported amount of platinum is 0.05 to 0.5% by weight based on the total amount of the carrier part.