KR100408503B1 - Catalyst for purifying exhaus gas of vehicle - Google Patents

Abstract

The present invention relates to a catalyst for automobile exhaust purification, characterized in that carrier materials, zeolite, platinum, rhodium and cobalt, are supported on a honeycomb. The catalyst according to the present invention restricts the content of platinum to inhibit the oxidation of hydrocarbons at low temperatures and improves the catalytic activity against nitrogen oxides at high temperatures by adding cobalt. Therefore, the highest activity at low temperature is slightly lower than the conventional catalyst, but the overall NOx purification rate is remarkably improved because the catalyst activity does not drop sharply even when the temperature is increased.

Description

Catalyst for Purifying Exhaust Gas of Vehicle

The present invention relates to a catalyst for automobile exhaust gas purification, and more particularly, to a catalyst having excellent purification ability against nitrogen oxides generated in automobiles even under a high temperature lean burn atmosphere.

Recently, due to the increasing interest in the environment, environmental pollution is being managed at the national level. Environmental pollution can be roughly classified into air pollution, water pollution, and soil pollution.

Of these, air pollutants that cause air pollution are usually emitted from combustion bodies. Therefore, air pollution is determined by the structure of the combustion facility, the operation method, and external weather conditions. A typical example of such a combustion body is an automobile.

Unlike other emission facilities, automobiles emit pollutants while moving, and the use of automobiles is increasing rapidly with the improvement of living standards, so the air pollution problem caused by the exhaust of automobiles is getting serious.

The main harmful components in automobile exhaust gases are hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ). Of these, nitrogen oxides, in particular, combine with oxygen in the air under the action of sunlight to produce ozone. When the ozone concentration on the ground becomes higher (0.12 ppm of ozone alarms), it causes respiratory diseases as well as degeneration of protein in the body. It causes biochemical reactions such as fat peroxidation.

Reduction of automobile exhaust gas is largely classified into fuel improvement, engine improvement, and exhaust gas treatment. In the case of the exhaust gas treatment method, it is most effective to use a catalyst.

Currently, ternary catalysts are the most representative catalysts for purifying automobile exhaust gas, in which γ-alumina coated on honeycomb is loaded with platinum, palladium, rhodium, and the like. These three-way catalysts exhibit high purification rates for hydrocarbons, carbon monoxide and nitrogen oxides, which are hazardous three-way gases, under ideal conditions with an air-fuel ratio (air / fuel ratio) of 14.7.

However, the three-way catalyst has a problem in that a conventional three-way catalyst cannot be used in the region where the air-fuel ratio is more than 14.7, that is, the purification ability for nitrogen oxide is lost in the lean combustion region using relatively excess air. In particular, lean combustion engines operating in an oxygen-rich region with an air-fuel ratio of 18 to 26 are used. Under these conditions, hydrocarbons and carbon monoxide are easily purified by oxidation, but reducing nitrogen oxides to harmless nitrogen (N ₂ ) it's difficult. Therefore, a catalyst for reducing nitrogen oxide generated in the lean burn region has been developed and used.

Nitrogen oxide reduction catalysts currently used have the disadvantage of showing good activity only in the low temperature region (400 ℃ or less). Examples thereof include those in which zeolite is supported by an active agent such as platinum, rhodium or palladium alone or in two or more components. In the catalyst, rhodium is excellent in reducing power of nitrogen oxides and excellent adsorptive power to nitrogen oxides, platinum serves to oxidize and remove carbon monoxide and hydrocarbons at low temperatures and to improve catalytic reactivity to nitrogen oxides.

However, since hydrocarbons promote catalytic activity for nitrogen oxides, when a large amount of platinum is present, a large amount of hydrocarbons are oxidized, and thus there is a problem in that catalytic activity for nitrogen oxides drops rapidly as temperature increases. That is, it exhibits the highest activity in the vicinity of about 250 ° C., but drops rapidly at a high temperature of 400 ° C. or higher. By the way, since the temperature of the engine is in the range of 200 to 600 ℃ while driving the vehicle there is a limit to purify the nitrogen oxide using such a conventional catalyst.

In addition, the catalyst is expensive because the production cost of the catalyst is increased because expensive precious metals are used as the activator, and in the manufacturing method, the catalyst is conventionally manufactured by a multi-step process in which ion, platinum, rhodium, and palladium are ion-exchanged sequentially. This is not only troublesome in the progress of the process, but also disadvantageous in terms of manufacturing cost.

Therefore, the development of a new catalyst that can overcome this limitation is required.

In addition, the development of a catalyst for reducing and purifying nitrogen oxides generated in industrial facilities such as boilers is also required.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a catalyst for purifying automobile exhaust gas, which has a very high purification rate and low cost for nitrogen oxide even in a high temperature lean burn atmosphere.

1 is a graph showing the nitrogen oxide purification rate with temperature change.

The technical problem of the present invention is to provide a catalyst for purification of automobile exhaust gas, characterized in that the zeolite carrier loaded with platinum, rhodium and cobalt is supported on a honeycomb.

In the catalyst of the present invention, the zeolite is preferably mordenite.

In addition, the catalyst according to the present invention preferably contains 0.5 to 10% by weight of platinum, 0.5 to 7% by weight of rhodium and 3 to 17% by weight of cobalt based on the zeolite.

The catalyst of the present invention further contains cobalt, which is a transition metal, in addition to platinum and rhodium, which are noble metals, as the activator, so that the catalyst is excellent in a high temperature lean-burn atmosphere. In addition, since the content of expensive platinum can be reduced, the production cost can be reduced.

The catalyst for automobile exhaust gas purification according to the present invention may be prepared by a conventional method, for example, a) preparing a mixture by mixing diamine dichloroplatinum hydrate, rhodium nitrate solution, and cobalt nitrate hydrate with zeolite; b) heat treating the mixture to form a powder; c) mixing the powder with alumina and deionized water to form a slurry; d) supporting the slurry in honeycomb; e) it may be prepared according to a manufacturing method comprising the step of heat-treating the honeycomb carrier.

In the above-described method for producing a catalyst for automobile exhaust gas purification, in step a), the zeolite is preferably mordenite. Further, the amount of platinum added in the diaminedichloroplatinum hydrate, the amount of rhodium added in the rhodium nitrate solution, and the amount of cobalt added in the cobalt nitrate hydrate were 0.5 to 10% by weight, 0.5 to 7% by weight, respectively, based on the zeolite, and 3 to 17% by weight.

In step b), heat treatment is performed at 400 to 600 ° C. for 2 to 3 hours. In addition, in the step e), the heat treatment is carried out at 400 to 700 ℃ for 2 to 4 hours.

The catalyst thus prepared further includes cobalt, which is a transition metal, in addition to platinum and rhodium, thereby maintaining excellent catalytic activity against nitrogen oxides even at high temperatures, thereby improving overall nitrogen oxide purification efficiency. In addition, it is useful in terms of economics by limiting the amount of platinum added, and unlike the conventional manufacturing method, since the platinum, rhodium and cobalt are impregnated in the zeolite at the same time, the manufacturing process can be simplified.

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

Example 1

26.31 g of diaminedichloroplatinum hydrate [Pt (NH ₃ ) ₂ Cl ₂ xH ₂ O], 31.58 mL of rhodium nitrate [Rh (NO ₃ ) ₃ ] solution and 7.7953 g of cobalt nitrate hydrate [Co (NO ₃ ) 26H ₂ O 300 It was added to a beaker containing ㎖ distilled water and dissolved with stirring for 30 minutes. At this time, after confirming that there is no precipitation, 30 g of mordenite was added thereto. Then, after stirring for 2 hours, the beaker containing the reaction was placed on a hot plate and the moisture was dried under stirring at a temperature of 60 ° C. Next, a powder was prepared by heat treatment at 500 ° C. for 3 hours. 40 g of the powder was added together with 48 g of alumina sol (alumina content: 20%) and 100 g of deionized water into a ball mill reactor to react for 30 hours to prepare a slurry. The slurry was soaked in a honeycomb (40 × 40 × 100mm) to 20% by weight based on the weight of the honeycomb, and then heat-treated at 600 ° C. for 4 hours to provide 5% Pt / 5% Co / 5% as a catalyst. Rh / mordenite (a) was prepared.

Activity evaluation for the prepared catalyst was carried out under the following gas atmosphere and the results are shown in FIG. 1:

500 ppm NO, C ₃ H ₆ 800 ppm, O ₂ 8%, CO 0.2%, CO ₂ 14%, H ₂ O 10%,

Space velocity: 40,000 h ^-1 .

Examples 2 and 3

A catalyst 10% Pt / 5% Co / 5% Rh / mordenite (b) and a catalyst 15% Pt / 5% Co / 5% Rh / mordenite (c) were prepared in the same manner as in Example 1 Next, the catalyst activity was evaluated in the same manner as in Example 1, and the results are shown in FIG. 1.

Comparative Example 1

Catalyst 15% in the same manner as in Example 1 except that 55.55 g of diaminedichloroplatinum hydrate [Pt (NH ₃ ) ₂ Cl ₂ xH ₂ O] was added to a beaker containing 300 ml of distilled water and dissolved with stirring for 30 minutes. After preparing Pt / mordenite (d), the catalytic activity was evaluated in the same manner as in Example 1, and the results are shown in FIG. 1.

Comparative Example 2

88.24 g of diaminedichloroplatinum hydrate [Pt (NH ₃ ) ₂ Cl ₂ xH ₂ O] and 31.58 ml of rhodium nitrate [Rh (NO ₃ ) ₃ ] solution were placed in a beaker containing 300 ml of distilled water and dissolved for 30 minutes with stirring. Except for the preparation of the catalyst 15% Pt / mordenite (d) in the same manner as in Example 1, the catalyst activity was evaluated in the same manner as in Example 1 and the results are shown in FIG.

As can be seen from Fig. 1, the catalysts d and e for automobile exhaust gas purification in the prior art have excellent activity at low temperatures, but the catalyst activity drops rapidly from a predetermined temperature (about 250 DEG C) as the temperature rises.

That is, since platinum is contained, the activity at low temperatures is good, but the oxidation of hydrocarbons, which contributes to the catalytic activity to nitrogen oxides, results in a rapid decrease in catalytic activity at high temperatures.

On the other hand, in the catalyst for purification of automobile exhaust gas according to the present invention (catalysts a, b and c), the content of platinum is limited to inhibit the oxidation of hydrocarbons at low temperatures and the addition of cobalt improves catalytic activity against nitrogen oxides at high temperatures. Improved. Therefore, the catalytic activity at low temperature is slightly lower than the conventional catalyst, but the catalytic activity is not drastically reduced even when the temperature is raised, so that the overall nitrogen oxide purification rate is improved.

Claims (2)

A zeolite carrier carrying platinum, rhodium and cobalt is supported on honeycomb, Catalysts for purifying automobile exhaust gases, wherein the platinum, rhodium and cobalt contents are 0.5 to 10 wt%, 0.5 to 7 wt% and 3 to 17 wt%, respectively, based on the zeolite. The catalyst for automobile exhaust gas purification according to claim 1, wherein the zeolite is mordenite.