KR20000008360A - Catalyst for purifying vehicle exhaust gas - Google Patents

Abstract

PURPOSE: A catalyst for purifying vehicle exhaust gas is provided to have excellent purification efficiency to nitrogen oxide among diesel vehicle exhaust gases. CONSTITUTION: The catalyst for purifying vehicle exhaust gas has: a carrier part that is made from degenerated zirconia dioxide impregnated one transferred metal oxide chosen from copper oxide and iron oxide; and a catalyst that is made from the other transferred metal oxide chosen from copper oxide and iron oxide. The degenerated zirconia dioxide dopes zirconia dioxide with sulfuric ion and the doping amount of the sulfuric ion is 0.01-10wt% of the whole amount of zirconia dioxide.

Description

Catalyst for purification of automobile exhaust

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 purification efficiency for nitrogen oxides in diesel vehicle exhaust gas.

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, air pollution is mainly generated from combustion bodies, and the magnitude of the damage is determined by the structure and operation method of the combustion facilities 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.

Therefore, in Korea, the regulation has begun to be strengthened, and in the case of lean burn cars using gasoline, the exhaust gas is almost completely purified by the three-way catalyst system.

However, the problem is different in diesel vehicles using diesel. Since diesel is cheaper and has higher thermal efficiency than gasoline, diesel vehicles using diesel as fuel are increasing. However, since diesel vehicles have different composition of exhaust gas from lean burn cars, there is a slight countermeasure even though a proper purification device is required.

Diesel cars, unlike lean burn cars, emit large amounts of harmful air pollutants such as nitrogen oxides, sulfur oxides, and particulate matter. Until now, diesel automobile exhaust gas purification devices have been mainly used to develop catalysts for removing particulate matter. Focus has been on. Particulate matter can be purified by a method of oxidation and removal.

On the other hand, nitrogen oxide, another major component of diesel vehicle exhaust gas, is produced during the combustion of fossil fuels and is known to cause acid rain and to generate ozone and photochemical smog by photochemical reactions with hydrocarbons. It is recognized. However, the nitrogen oxide may be purified by a method of reducing and removing the nitrogen oxide, unlike the method for purifying particulate matter. Therefore, in a large amount of oxygen and sulfur oxides (SO _x ), especially sulfur dioxide (SO ₂ ) atmosphere is a lot of difficulties in the purification.

Therefore, it is considered difficult to develop a diesel car purification catalyst that can effectively remove particulate matter and nitrogen oxide at the same time.

Typically, the two main components of the catalyst for automobile exhaust purification are the carrier and the main catalyst component.

Of these, the carrier is an important part of determining the overall characteristics of the catalyst while having a certain activity, alumina is a representative of the catalyst for automobile exhaust gas purification. However, when used in diesel engines, alumina has a fatal defect that it adsorbs sulfur dioxide at low temperature, oxidizes and releases sulfur trioxide at high temperature, increasing the amount of particulate matter generated and lowering catalyst activity and durability. In addition, titanium dioxide and zirconia dioxide may be used alone or as a composite, and they may not serve as carriers as well because they have a small amount of sulfur dioxide adsorption and a small amount of sulfate, but the specific surface area decreases rapidly at high temperatures. There is also a disadvantage in that the activity of the catalyst is lowered to promote deterioration of the catalyst. Another example is a silicon dioxide-based carrier, which has a problem of having a large amount of catalyst components because it has a high endothelial toxicity to H ₂ O as well as sulfur dioxide but has a low inherent activity.

In addition, a noble metal is used normally as a catalyst component. Precious metals represented by platinum and palladium are commonly used in three-way catalysts for gasoline automobiles, and have been shown to be highly effective catalytic agents for hydrocarbons, carbon monoxide, and nitrogen oxides. It is widely used.

Of these, platinum has the advantage of showing a relatively good nitrogen oxide purification activity even in diesel engines operated in an excessive oxidizing atmosphere, whereas at 300 ° C or higher, sulfur dioxide is extremely oxidized to provide nuclei of particulate matter. There is a problem that results in increasing the amount of production. In order to overcome this problem, a method of suppressing the oxidation power of sulfur dioxide has been proposed by adding vanadium oxide, but vanadium oxide not only reduces the oxidation power of sulfur dioxide, but also the oxidation activity of particulate matter, hydrocarbons, carbon monoxide gas, etc. Decrease.

On the other hand, palladium is useful in that it exhibits an oxidation activity against sulfur dioxide when it is about 450 ° C., but has a disadvantage of low oxidation activity at low temperatures and low durability at high temperatures.

In addition, precious metals are not only expensive in common, but also considering the limited reserves, it is urgent to develop new alternative catalysts. However, since no satisfactory main catalyst components have been found to replace them completely, instead of reducing the use of precious metals, it is possible to add a cocatalyst component of transition metals, rare earth metals and their oxides to assist them. I am satisfied.

However, there is a problem that the promoter component has a low initial activity and is poisoned by sulfur dioxide and moisture in a diesel car, thereby deteriorating overall long-term activity.

The technical problem to be achieved by the present invention is to provide a catalyst for purifying nitrogen oxides, in particular, a catalyst for purifying nitrogen oxides which can be selectively reduced to purify nitrogen oxides even in a large amount of oxygen and sulfur oxide atmospheres.

Technical problem of the present invention is a catalyst for automobile exhaust gas purification comprising a carrier part and a catalyst component supported on the carrier part, wherein the carrier part is modified zirconia dioxide impregnated with one transition metal oxide selected from copper oxide or iron oxide, The catalyst component may be made by a catalyst for automobile exhaust purification, characterized in that the other transition metal oxide selected from copper oxide or iron oxide.

1 is a view for explaining the partial oxidation activity and the oxidation activity of sulfur dioxide for the hydrocarbon of the carrier Fe-Z4 according to the present invention.

2 is a view for explaining the nitrogen oxide reduction activity of the carrier Cu-Z4 according to the present invention.

3 to 8 are views for explaining the nitrogen oxide reduction activity of the catalyst according to the present invention.

The modified zirconia dioxide according to the present invention is added with 0.01 to 10% by weight of sulfuric acid (SO ₄ ^2- ) ions based on the total amount of zirconia dioxide powder. If the amount is less than 0.01% by weight, the acidic properties of zirconia dioxide do not appear, on the contrary, if the amount is more than 10% by weight, the amount of the additive may be excessive to deteriorate the characteristics of the carrier.

In addition, the impregnation amount of the transition metal oxide in the carrier portion is preferably 0.1 to 15% by weight based on the total amount of modified zirconia dioxide.

In addition, the specific surface area of the carrier portion is preferably 80 to 120 m 2 / g, but the decrease in specific surface area hardly occurs even after heat treatment at a high temperature of 600 ° C.

On the other hand, the supported amount of the transition metal oxide used as the catalyst component is 0.1 to 15% by weight, preferably 2 to 4% by weight, based on the total amount of the carrier portion.

In addition, the catalyst for automobile exhaust purification according to the present invention may further include lanthanide metal oxides such as cerium oxide or praseodymium oxide, and / or precious metals such as platinum, palladium or rhodium as cocatalyst components. At this time, the supported amount of the lanthanide metal oxide and the noble metal is preferably 1 to 5% by weight and less than 0.5% by weight based on the total amount of the carrier portion.

In addition, the catalyst of the present invention may further include at least one selected from barium oxide, nickel oxide or molybdenum oxide as a promoter component, the content of which is from 0.1 to 50% by weight of the catalyst component including the carrier portion and the promoter desirable.

The method for producing an automobile exhaust gas catalyst according to the present invention can be used without limitation as long as it can be used in the field of the present invention, for example, impregnation, coprecipitation and incipient wetness methods can be used. Can be.

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 to penetrate the sulfate ions (SO ₄ ^2- ) on the lattice of the zirconia dioxide powder, it is possible not only to prevent the reduction of specific surface area at high temperatures but also to improve the high temperature activity of the carrier itself. Let's do it.

Fe is also a metal with very good partial oxidation to hydrocarbons. Therefore, as can be seen in Figure 1, the carrier prepared by impregnating iron oxide in modified zirconia can exhibit excellent partial oxidation ability against hydrocarbons to generate carbon monoxide gas, thereby exhibiting excellent reducing activity against nitrogen oxides. In the region of 500 ° C, the oxidation power against sulfur dioxide is relatively low over the entire temperature range, although it shows excellent reducing activity against nitrogen oxides.

On the other hand, copper is a metal exhibiting a high reduction activity of nitrogen oxide, and as shown in FIG. 2, a carrier prepared by impregnating copper oxide in modified zirconia has a reduction reaction of nitrogen oxide consistent with a region where carbon monoxide is consumed. Appeared.

Therefore, if a predetermined amount of copper, which shows high reducing power with respect to iron and nitrogen oxides that oxidize hydrocarbons to generate carbon monoxide, is added in an appropriate ratio, high reducing power can be obtained with respect to nitrogen oxides even in an oxidizing atmosphere. Therefore, when iron is impregnated into the carrier, copper is supported as the main catalyst component. On the contrary, when copper is impregnated into the carrier, iron is preferably supported by the main catalyst component and combined.

In addition, in the present invention, the noble metal and / or lanthanide metal oxide may be added as a cocatalyst component to increase the purification efficiency of the nitrogen oxide and further enhance the catalytic activity by further including a promoter component.

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to this.

Example 1

<Production of Catalyst>

A modified zirconia dioxide carrier (specific surface area: 80 to 130 m 2 / g) added with 4% by weight of sulfate ions was mixed with an aqueous solution of Fe (NO ₃ ) ₂ , dried, calcined at 500 ° C. for 3 hours, and weighed 5%. A carrier powder (hereinafter referred to as Fe-Z4) to which% Fe ₂ O ₃ was added was prepared.

Subsequently, after dissolving 3.8 g of Cu (NO ₃ ) ₂ .3H ₂ O in 40 ml of distilled water, the solution was mixed well by adding little to 100 g of Fe-Z4 powder, and then dried at 120 ° C. for 2 hours. And calcined at 500 ℃ for 2 hours to prepare a catalyst 1Cu / Fe-Z4.

<Measurement of Catalyst Activity>

The prepared catalyst powder was pressed into 0.5 kgf / cm 2, pelletized, and then sieved through only sieves of 1 to 2 mm in size. 2 ml of the filtered particles were taken into the reactor and the nitrogen oxide purifying activity was measured under the following conditions, and the results are shown in FIG.

Gas composition: NO 500ppm, C ₃ H ₆ 800ppm, O ₂ 8%, CO ₂ 14%, CO 2000ppm, SO ₂ : 200pp, H ₂ O 10%, He remaining amount

Reaction temperature: 200-600 degreeC

Space speed: 40,000 / h

Example 2

<Production of Catalyst>

Carrier powder to which 2.9% by weight of CuO was added (hereinafter referred to as Cu-Z4) was carried out in the same manner as in Example 1, except that Cu (NO ₃ ) ₂ aqueous solution was used instead of Fe (NO ₃ ) ₂ aqueous solution. Is called).

Subsequently, 7.25 g of Fe (NO ₃ ) ₂ .9H ₂ O was dissolved in 40 ml of distilled water, and the solution was mixed well by adding little to 100 g of Cu-Z4 powder, followed by drying at 120 ° C. for 2 hours. And calcining at 500 ° C. for 2 hours to prepare 1Fe / Cu-Z4 as a catalyst.

<Measurement of Catalyst Activity>

Measurements were made under the same conditions and methods as in Example 1, and the results are shown in FIG. 4.

Example 3

A catalyst 3Cu / Fe-Z4 was prepared in the same manner as in Example 1 except that 11.4 g of Cu (NO ₃ ) ₂ .3H ₂ O was dissolved in 40 ml of distilled water.

Then, the same conditions and methods as in Example 1 were measured, and the results are shown in FIG. 5.

Example 4

A catalyst 6Cu / Fe-Z4 was prepared in the same manner as in Example 1 except that 22.8 g of Cu (NO ₃ ) ₂ .3H ₂ O was dissolved in 40 ml of distilled water.

Subsequently, measurement was carried out under the same conditions and methods as in Example 1, and the results are shown in FIG. 6.

Example 5

The same manner as in Example 1 except for dissolving 11.4g of _{Cu (NO 3) 2 · 3H} 2 O and 0.045g of _{[Pt (NH 3)] 4} Cl 2 · H 2 O in distilled water at 40㎖ Was carried out to prepare 0.025 Pt 3 Cu / Fe-Z 4 as a catalyst.

Then, the same conditions and methods as in Example 1 were measured, and the results are shown in FIG. 7.

Example 6

6 g of BaO was mixed with 94 g of the catalyst 3Cu / Fe-Z4 obtained in Example 3 to prepare 3Cu / Fe-Z4 + 6BaO as a catalyst.

Subsequently, the same conditions and methods as in Example 1 were measured and the results are shown in FIG. 8.

Comparing FIGS. 3 and 4, it can be seen that the catalyst supporting Cu on the Fe-Z4 carrier is better in terms of nitrogen oxide activity than when Fe is supported on the Cu-Z4 carrier.

3, 5, and 6, it can be seen that the most excellent nitrogen oxide purification rate when the amount of Cu supported is about 3% by weight relative to the total amount of the carrier.

In addition, when comparing Figs. 7 and 8 with Fig. 5, it can be seen that when the noble metal is further supported as a promoter component or when a promoter component is further mixed, it shows better nitrogen oxide purification rate.

The catalyst for purifying automobile exhaust gas according to the present invention exhibits a high purification rate for nitrogen oxides while maintaining a low oxidation rate for sulfur dioxide even under an atmosphere of peroxygen.

Claims (11)

A catalyst for automobile exhaust gas purification comprising a carrier part and a catalyst component supported on the carrier part, The carrier portion is a modified zirconia dioxide impregnated with one transition metal oxide selected from copper oxide or iron oxide, A catalyst for automobile exhaust gas purification, characterized in that the catalyst component is another transition metal oxide selected from copper oxide or iron oxide. The catalyst for purification of automobile exhaust gas according to claim 1, wherein the modified zirconia dioxide is doped with sulfate ions (SO ₄ ^2- ) in zirconia dioxide. 3. The catalyst for automobile exhaust gas purification according to claim 2, wherein the doping amount of sulfate ions is 0.01 to 10% by weight based on the total amount of zirconia dioxide. The catalyst for purifying automobile exhaust gas according to claim 1, wherein the impregnation amount of the transition metal oxide in the carrier is 0.1 to 15% by weight based on the total amount of the modified zirconia dioxide. The catalyst for automobile exhaust gas purification according to claim 1, wherein the specific surface area of the carrier portion is 80 to 120 m 2 / g. The catalyst for automobile exhaust gas purification according to claim 1, wherein the supported amount of the transition metal oxide used as the catalyst component is 0.1 to 15% by weight based on the total amount of the carrier portion. The catalyst for purifying automobile exhaust gas according to claim 1, further comprising 1 to 5% by weight of lanthanide metal oxide or less than 5% by weight of a noble metal with respect to the total amount of the carrier portion as a promoter component. 8. The catalyst for automobile exhaust purification according to claim 7, wherein the lanthanide metal oxide is cerium oxide or praseodymium oxide. 8. The catalyst for automobile exhaust purification according to claim 7, wherein the precious metal is platinum, palladium or rhodium. 2. The catalyst for automobile exhaust purification according to claim 1, comprising at least one selected from barium oxide, nickel oxide or molybdenum oxide as a promoter component. 11. The catalyst for automobile exhaust gas purification according to claim 10, wherein the content of the promoter component is 0.1 to 50% by weight based on the total amount of the carrier portion and the catalyst component.