KR100446599B1 - Catalyst for purifying exhaust gas of automobiles - Google Patents

Abstract

PURPOSE: To provide a catalyst for purifying exhaust gas from cars, which shows excellent activity of suppressing oxidation of sulfur dioxide. CONSTITUTION: The catalyst comprising at least one of a cocatalyst selected from the group consisting of a transition metal, an alkaline earth metal and oxides thereof and a noble metal supported on a metal is characterized in that the carrier is an oxidative carrier that is prepared by impregnating at least one metal oxide selected from the group consisting of a chromium oxide, a zinc oxide and a magnesium oxide with a porous medium selected from a titanium dioxide or a zirconium dioxide.

Description

Catalyst for purifying exhaust gas of automobiles

The present invention relates to a catalyst for automobile exhaust gas purification, and more particularly, to a catalyst for automobile exhaust gas purification that can exhibit oxidation inhibitory activity against sulfur oxides.

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), the global greenhouse due to carbon dioxide generated when using fossil fuel. 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 automotive exhaust gases are related to the engine's temperature, pressure and proportion of air. That is, the exhaust gas purification efficiency can be improved by appropriately adjusting the air / fuel ratio of the engine. 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 using diesel as a fuel source have good thermal efficiency, but emit large amounts of malignant pollutants. However, many diesel engines such as trucks are still equipped in many countries. Nevertheless, compared to gasoline cars, the technology for purifying the exhaust gas of diesel vehicles using diesel is very poor, and continuous research is required.

Diesel vehicles using diesel have slightly different pollutants than gasoline vehicles because the characteristics of the fuel source and engine engine are different from 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 (SOx) and particulate matter.

In particular, a sulfur component contained in a large amount in diesel oil is a problem, and the sulfur component reacts with oxygen to release sulfur dioxide.

However, currently widely used catalysts have excellent purification efficiency for various harmful components-unburned hydrocarbons, carbon monoxide, nitrogen oxides, soluble organic fractions (SOF), etc., but have a disadvantage of adsorbing large amounts of sulfur dioxide at low temperatures. The sulfur dioxide adsorbed in this way is desorbed in a high temperature atmosphere of 350 ° C. or higher and oxidized by the catalyst component or oxidized by itself and discharged as sulfur trioxide.

Sulfur trioxide released in this way causes sulfuric acid by combining with water vapor to cause acid rain, and itself provides a nucleus of crystal growth, thereby increasing the production of particulate matter. In addition, it acts as a poisoning factor to the catalyst to promote the deterioration of the performance of the catalyst aftertreatment device, as well as to be deposited on the aftertreatment device, causing a back pressure increase and the like.

Thus, the carrier and active component of the catalyst must be stable in a sulfur dioxide atmosphere and must not oxidize sulfur dioxide.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a catalyst for purifying automobile exhaust gas having excellent oxidation inhibitory activity against sulfur dioxide.

Technical problem of the present invention is a catalyst for automobile exhaust gas purification in which at least one promoter and a noble metal selected from the group consisting of transition metals, alkaline earth metals and oxides thereof are supported on a carrier, wherein the carrier is a zirconium oxide, chromium oxide, At least one metal oxide selected from aluminum oxide, zinc oxide, magnesium oxide and silicon oxide can be achieved by a catalyst for automobile exhaust purification, characterized in that it is an impregnated oxidative carrier.

In the catalyst for automobile exhaust gas purification according to the present invention, the porous body may include titanium dioxide or zirconium dioxide, and the content of the oxide is preferably 3-20% by weight based on the total amount of the porous body.

1 is a graph showing the results of a SO2 temperature programmed desorption (TPD) test for a conventional carrier and an oxidative carrier according to the present invention.

Sulfur dioxide gas is a gas having a very strong acidity, which is adsorbed on the surface of the carrier at low temperature and then oxidized when it is desorbed. However, when the surface of the carrier is strongly acidic, the amount of adsorption of sulfur dioxide at a low temperature is reduced, and as a result, desorption at high temperatures and oxidation to sulfur trioxide can be suppressed. Therefore, in the present invention using this principle, the oxidation activity of sulfur dioxide was suppressed by preparing an oxidizing carrier impregnated with a substance capable of strongly acidifying the surface of the carrier.

In the present invention, it is possible to improve the oxidation inhibitory activity on carbon dioxide by employing an oxidizing carrier that strongly oxidizes the surface of the porous titanium dioxide or zirconium dioxide with zirconium oxide, chromium oxide, aluminum oxide, zinc oxide, magnesium oxide, silicon oxide, and the like. Can be. The catalyst of the present invention thus obtained can prevent an increase in particulate matter, deterioration of the performance of the catalyst, induction of acid rain, and the like.

In addition, the catalyst of the present invention exhibits improved heat resistance compared to conventional catalysts employing conventional carriers, and thus can stably exhibit catalytic activity even at high temperatures.

The catalyst for purifying automobile exhaust gas of the present invention may be prepared according to a conventional method as follows.

First, at least one nitrate hydrate of zirconium, chromium, aluminum, zinc, magnesium and silicon is dissolved in a predetermined amount of distilled water. Into this solution, a porous body was heated to a temperature of 60-80 ° C. under stirring to obtain a porous powder impregnated with at least one metal oxide of zirconium oxide, chromium oxide, aluminum oxide, zinc oxide, magnesium oxide and silicon oxide in the pores of the porous body. Manufacture. The powder is dried in an oven and then calcined at 500-600 ° C. for 2-5 hours to obtain an oxidizing carrier.

Next, the oxidizing carrier is supported with transition metals, alkaline earth metals and oxides thereof and at least one precious metal to obtain a final product catalyst.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

Preparation of Carrier

36.7937 g of aluminum nitrate hydrate (Al (NO 3) 3 .9H 2 O) was placed in a beaker, and 30 g of deionized water was added thereto to prepare an aqueous aluminum nitrate solution. 100 g of TiO2 was added to the solution and heated to 70 ° C under stirring. Subsequently, the resultant was dried at 120 ° C. for 12 hours and then calcined at 600 ° C. for 5 hours to prepare Al-TiO 2, which is an oxidizing carrier.

SO2 Temporary Programmed Desorption (TPD) Test on Prepared Carrier

After putting 1 g of the carrier prepared as described above into the reaction tube, He gas was injected into the reaction tube for 1 hour. Subsequently, SO2 gas was injected into the reaction tube at a rate of 100 ml / min for 30 minutes, and then the temperature was raised to 550 ° C. at a rate of 5 ° C./min while He gas was supplied for 1 hour. At this time, the adsorption and desorption of the SO 2 gas was measured using an SO 2 analyzer. The result is shown in FIG. 1 as curve (a).

Example 2

An oxidative carrier Mg-TiO 2 was prepared in the same manner as in Example 1 except for using 63.5947 g of magnesium nitrate hydrate (Mg (NO 3) 2 .6H 2 O) instead of aluminum nitrate hydrate. The carrier was subjected to the SO2 TPD test in the same manner as in Example 1, and the results are shown as curves (b) in FIG.

Example 3

An oxidative carrier Zn-TiO 2 was prepared in the same manner as in Example 1 except that 36.5535 g of zinc nitrate hydrate (Zn (NO 3) .6H 2 O) was used instead of the aluminum nitrate hydrate. This carrier was subjected to the SO2 TPD test in the same manner as in Example 1, and the results are shown as a curve (c) in FIG.

Example 4

An oxidative carrier Cr-TiO 2 was prepared in the same manner as in Example 1 except that 26.3218 g of magnesium nitrate hydrate (Cr (NO 3) 3 .9H 2 O) was used instead of the aluminum nitrate hydrate. The carrier was subjected to the SO2 TPD test in the same manner as in Example 1, and the results are shown as curves (d) in FIG.

Comparative example

The SO 2 TPD test was performed on TiO 2 in the same manner as in Example 1, and the result is shown as a curve (e) in FIG. 1.

As can be seen from the result of FIG. 1, in the case of TiO 2 (comparative example), a peak is shown at around 350 ° C. FIG. On the other hand, when Al, Mg, Zn, and Cr were added to TiO2, respectively (Example 1-4), it turns out that there is no big change in the desorption amount of SO2 gas even if temperature rises. That is, the oxidative carrier according to the present invention has been shown to have excellent oxidation inhibitory activity against sulfur dioxide, compared to the conventional TiO2 carrier.

The catalyst according to the present invention has excellent oxidation inhibitory activity against sulfur dioxide. Therefore, there is an advantage that it is possible to prevent various adverse effects accompanying the oxidation of sulfur dioxide, for example, causing acid rain, increase in particulate contaminants, and the like.

Claims (2)

In the catalyst for automobile exhaust gas purification in which at least one promoter and a precious metal selected from the group consisting of transition metals, alkaline earth metals and oxides thereof are supported on a carrier, A catalyst for purifying automobile exhaust gas, wherein the carrier is an oxidative carrier impregnated with at least one metal oxide selected from chromium oxide, zinc oxide and magnesium oxide in a porous body selected from titanium dioxide or zirconium dioxide. The catalyst for purifying automobile exhaust gas according to claim 1, wherein the content of the oxide is 3-20% by weight based on the total amount of the porous body.

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