KR100408511B1 - Catalyst for purifying exhaust gas of automobile and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a catalyst for automobile exhaust gas purification and a method for producing the catalyst, characterized in that the support is supported on a noble metal and a transition metal. Not only is it excellent, it is also affordable.

Description

Catalyst for purifying exhaust gas of automobile and method for manufacturing the same

The present invention relates to a catalyst for automobile exhaust gas purification and a method for manufacturing the same, and more particularly, to a catalyst having excellent purification ability for nitrogen oxide at a high temperature and low cost.

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.

Since air pollution mainly comes from the combustion body, the magnitude 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 exhaust 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.

In contrast, diesel engines that use diesel as a fuel source have good thermal efficiency and emit large amounts of malignant pollutants. However, many diesel engines are still employed in large vehicles such as trucks in many countries. Nevertheless, there is a need for continuous research because it is a very poor condition for purifying exhaust gas of diesel vehicles using diesel compared to gasoline vehicles.

Exhaust gases of diesel vehicles include carbon monoxide, hydrocarbons, nitrogen oxides (NO _X ), sulfur oxides and particle matter. In particular, the particulate matter aggravates the photochemical smog phenomenon and the generation of suspended dust, which causes vision disturbances, and nitrogen oxides are combined with oxygen in the air under the action of sunlight to cause respiratory diseases, protein denaturation and fat in the body. Ozone is the cause of biochemical reactions such as peroxidation.

Therefore, it would be desirable if the particulate matter and the nitrogen oxide can be removed at the same time, but since the purification methods for them are mutually opposite to each other, it is impossible to remove them simultaneously with the current technology.

Some catalysts that can be used to remove nitrogen oxides have been disclosed. Examples include catalysts supporting palladium, platinum, or mixtures thereof on a carrier. There is a disadvantage that the economical efficiency is low because the price of the precious metal supported on the expensive. On the other hand, a catalyst supporting a transition metal instead of the noble metal has been disclosed, but this catalyst has a problem of low activity against nitrogen oxides. As a method for overcoming the problems described above, a catalyst using a noble metal and a transition metal together has been disclosed. However, it was true that this catalyst had no significant effect in terms of improving catalytic activity since the carrier supported by the noble metal was used as the main catalyst and the transition metal was used as the promoter for the main catalyst.

The technical problem to be achieved by the present invention is to provide a catalyst for purifying automobile exhaust gas which is excellent in activity against nitrogen oxides at a high temperature and low cost.

Another technical problem to be achieved by the present invention is to provide a method for producing a catalyst for purifying automobile exhaust gas which has excellent activity against nitrogen oxide at a high temperature and is low in cost.

1 is a graph showing the activity of the catalyst for automobile exhaust purification according to the present invention in comparison with conventional catalysts.

Technical problem of the present invention can be achieved by a catalyst for automobile exhaust gas purification, characterized in that the support is supported on the precious metal and transition metal.

In the catalyst for automobile exhaust gas purification according to the present invention, the carrier may be any of those commonly used in the field of the present invention, such as alumina, zirconia, titanium dioxide, zeolite and mordenite. In addition, a mixture of palladium and platinum may be used as the noble metal, and iron may be preferably used as the transition metal.

Preferably, the content of the noble metal is 1-1.5% by weight based on the total weight of the carrier, and the ratio of palladium and platinum in the noble metal is preferably 1: 1-3: 1. The content of the transition metal is 3-5% by weight based on the total weight of the carrier.

In addition, another technical problem of the present invention is to prepare a solution (1) by dissolving the platinum complex in a polyol; (b) dissolving the palladium-containing salt solution and the iron-containing salt in a polyol to prepare a solution (2); (c) incipient wetness of the solution (1) and the solution (2) on a carrier to prepare a catalyst carrying palladium, iron and platinum; (d) drying and pulverizing the catalyst to prepare a catalyst powder; (e) it can be achieved by a method for producing a catalyst for automobile exhaust gas purification comprising the step of heat-treating the powder.

In the method for producing a catalyst for automobile exhaust gas purification according to the present invention, the polyol is ethylene glycol or propylene glycol. Further, the palladium content in the palladium-containing salt solution, the iron content in the iron-containing salt and the platinum content in the platinum complex are 0.75-1 wt%, 3-5 wt% and 0.258-, respectively, based on the total weight of the carrier. It is preferably 0.5% by weight, and the step (e) is carried out at 400-600 ° C. for 2-5 hours.

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

<Example 1>

Pd (NO ₃ ) ₃ solution (containing 0.15 g of palladium) and Fe (NO ₃ ) ₂ .9H ₂ O (containing 0.9 g of iron) were dissolved in 6 ml of ethylene glycol to prepare an ethylene glycol solution of palladium and iron. Then, Pt (NH ₃ ) ₄ Cl ₂ .H ₂ O (containing 0.05 g of platinum) was dissolved in 2 ml of ethylene glycol to prepare an ethylene glycol solution of platinum. Subsequently, 0.75Pd0.25Pt4.5Fe / ZrO ₂ loaded with palladium, platinum, and iron was prepared by gradually adding ethylene glycol solution of platinum and ethylene glycol solution of palladium and iron to 20 g of zirconia (ZrO ₂ ) as a carrier. The product was put into an oven at 80 ° C. and dried, then ground in a mortar and put into an electric furnace to be powdered by heat treatment at 500 ° C. for 2 hours. The powder was made into pellets, and then only those with a size of about 1-2 mm were selected using a sieve. 2 ml of the catalyst in the form of pellets prepared as described above was placed in a reactor, and catalytic activity of nitrogen oxide was measured. The exhaust gas composition and reaction conditions in the measurement are as follows:

NO: 500 ppm, C ₃ H ₆ : 800 ppm, O ₂ : 8%, CO ₂ : 14%, CO: 0.2%, SO ₂ : 200 ppm

Reaction temperature: 200-600 ℃

Space Speed: 40,000h ^-1 .

The catalytic activity measurement results are shown in the graph of FIG. 1 (a).

Comparative Example 1

Pd (NO ₃ ) ₃ solution (containing 0.15 g of palladium) was dissolved in 6 ml of ethylene glycol to prepare an ethylene glycol solution of palladium and iron, followed by Pt (NH ₃ ) ₄ Cl ₂ H ₂ O (0.05 g Of platinum) was dissolved in 2 ml of ethylene glycol to prepare an ethylene glycol solution of platinum. Subsequently, 0.75Pd0.25Pt / ZrO ₂ loaded with platinum and palladium was prepared by gradually adding platinum ethylene glycol solution and palladium ethylene glycol solution to 20 g of zirconia (ZrO ₂ ) as a carrier. This product was subjected to the same drying, grinding and heat treatment processes as in Example 1 to form a powder, which was then pelletized again. Catalytic activity for this pellet type catalyst was carried out under the same exhaust gas composition and reaction conditions as those in Example 1. The results are shown in Figure 1 (b).

Comparative Example 2

10 g of 0.75 Pd 0.25 Pt / ZrO ₂ and 3 g of Fe ₂ O ₃ prepared in the same manner as in Comparative Example 1 were mixed and ground in a mortar, and then placed in an electric furnace for heat treatment at 400 ° C. for 2 hours to give 0.75 Pd0.25 Pt / A mixed powder of ZrO ₂ + Fe ₂ O ₃ was prepared. The catalyst in powder form was then pelletized and its catalytic activity was carried out under the same exhaust gas composition and reaction conditions as in Example 1. The results are shown in Figure 1 (c).

As can be seen from the results in FIG. 1, the conventional catalyst (b) having only a noble metal has a low maximum activity value and a rapid decrease in nitrogen oxide conversion at a temperature of 300 ° C or higher. On the other hand, the conventional catalyst (c) using a transition metal as a promoter does not drastically lower the conversion rate of nitrogen oxides even at a high temperature exceeding 300 ° C., but not only the maximum activity value of the catalyst is low but also in almost all diesel engine operating temperature ranges. It shows low catalytic activity. On the contrary, the catalyst (a) of the present invention had a significantly higher maximum activity value of the catalyst, and especially at a high temperature of 300 ° C. or higher, the activity was generally higher than that of the conventional catalyst.

The catalyst for purifying automobile exhaust gas prepared according to the method of the present invention is not only cheaper than the conventional catalyst in which only the precious metal is supported on the carrier, but also greatly improves the maximum activity value of the catalyst. There is an advantage.

Claims (10)

(a) dissolving the platinum complex in a polyol to prepare a solution (1); (b) dissolving the palladium-containing salt solution and the iron-containing salt in a polyol to prepare a solution (2); (c) incipient wetness of the solutions (1) and (2) on a carrier to prepare a catalyst supporting palladium, iron and platinum; (d) drying and pulverizing the catalyst to prepare a catalyst powder; (e) a method of manufacturing a catalyst for automobile exhaust gas purification, comprising the step of heat treating the powder. The method of claim 1, wherein the polyol is ethylene glycol or propylene glycol. The method of claim 1, wherein the carrier is alumina, zirconia, titanium dioxide, zeolite or mordenite. The method of claim 1, wherein the palladium content in the palladium-containing salt solution is 0.75-1% by weight based on the total weight of the carrier. The method of claim 1, wherein the iron content in the iron-containing salt is 3-5% by weight based on the total weight of the carrier. The method of claim 1, wherein the platinum content in the platinum complex is 0.25-0.5% by weight based on the total weight of the carrier. The method of claim 1, wherein the step (e) is carried out at 400-600 ° C for 2-5 hours. It is prepared by the manufacturing method according to any one of claims 1 to 7, A catalyst for purifying automobile exhaust gas, which is a 1: 1 to 3: 1 mixture of palladium and platinum selected from alumina, zirconia, titanium dioxide, zeolite or mordenite and iron. The catalyst for purifying automobile exhaust gas according to claim 8, wherein the mixture of palladium and platinum is 1 to 1.5% by weight based on the total weight of the carrier. 10. The catalyst for purifying automobile exhaust gas according to claim 9, wherein the iron content is 3 to 5% by weight based on the total weight of the carrier.