KR20090062338A - Catalyst for purifying automotive exhaust gas and method for manufacturing the same - Google Patents

Abstract

A catalyst for purifying automotive exhaust gas and a method for manufacturing the same are provided to remove a part to be lost due to the poising of engine oil and protect the activity of rear main catalyst simultaneously. A catalyst for purifying automotive exhaust gas comprises a conical auxiliary catalyst(11) in which ferric oxide is dipped in the front and noble metal is not contained; and three way catalyst(12) in which the noble metal is contained. An auxiliary catalyst constitutes ferric oxide(Fe2O3) of 30~60 weight% and silicate of 40~70 weight%. The silicate is dipped by 70~120 g/L with respect to entire carrier apparent volume. The auxiliary catalyst whose axial length is produced by 1 inch. The auxiliary catalyst and main catalyst are arranged at front and rear part to be in contact with each other.

Description

Catalyst for purifying automotive exhaust gas and method for manufacturing the same

The present invention relates to a catalyst for automobile exhaust gas purification and a method of manufacturing the same, more particularly, it is possible to remove the parts to be lost due to poisoning of the engine oil and at the same time protect the activity of the rear main catalyst to improve the overall catalyst durability, The present invention relates to a catalyst for automobile exhaust gas purification and a method of manufacturing the same which can improve catalyst performance as well as preparation for catalyst poisoning.

In general, automobile exhaust gas refers to a gas produced by the combustion of a mixer in an engine and released into the atmosphere through an exhaust pipe.

The exhaust gas contains a large amount of harmful substances such as carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC).

Accordingly, preventing air pollution due to automobile exhaust gas has emerged as a very important issue for environmental hygiene, and in ordinary automobiles, it is regulated to purify the exhaust gas before exhausting it.

The most commonly used device for purifying exhaust gas in automobiles is a catalytic converter using a three way catalyst, which is mounted in the middle of an exhaust pipe, and the specification of the catalyst is different because the exhaust gas emission varies depending on the vehicle.

The three-way catalyst generally used to remove contaminants such as nitrogen oxides refers to a catalyst that reacts with carbon monoxide, nitrogen oxides and hydrocarbon-based compounds, which are harmful components of exhaust gas, to remove these compounds, mainly Pt / Rh and Pd. Three-way catalysts of the / Rh or Pt / Pd / Rh system have been used.

Meanwhile, the three-way catalyst of an automobile deteriorates due to various factors during the vehicle driving period.

Sedimentation of engine oil in the degradation mode reduces the effective active surface area of the catalyst and adversely affects the NOx purification performance in particular.

The poisoning of the engine oil tends to increase as it is deposited from the inlet of the catalyst and becomes larger. As shown in FIG. 1, the deposition pattern of the poisoning component by the engine oil is measured from the catalyst inlet. It can be seen that the component is deposited.

The activity of the catalyst can deteriorate by approximately 5-20% due to engine oil poisoning, which is also a value that can determine whether the vehicle equipped with the catalyst meets the emission standards.

As such, catalysts contaminated with poisoning components such as engine oil are particularly detrimental to NOx performance deterioration, and preparations for poisoning are urgent in light of the recent trend of tightening NOx regulations.

Accordingly, the present invention has been invented in view of the above, and is an oxide-based co-catalyst that can exhibit minimal activity without supporting a precious metal at the inlet portion of the front inlet where deposition of engine oil may occur. By applying, it is possible to remove the parts to be lost due to poisoning of engine oil and at the same time protect the activity of the rear main catalyst to improve the overall catalyst durability and to improve the catalyst performance along with the preparation for catalyst poisoning. It is an object of the present invention to provide a catalyst for gas purification and a method of manufacturing the same.

In order to achieve the above object, the present invention is a catalyst for automobile exhaust gas purification, which is formed by arranging a cone-shaped auxiliary catalyst carrying iron oxide on the front and no noble metal, and a three-way catalyst containing noble metal on the rear side thereof. To provide.

Here, the co-catalyst is prepared by supporting 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) and 40 to 70% by weight of silicate at 70 to 120 g / L relative to the total carrier apparent volume.

In addition, the present invention comprises the steps of preparing a cone-shaped auxiliary catalyst on which iron oxide is supported and does not contain precious metals; Preparing a three-way catalyst; And arranging the cocatalyst in front of the three-way catalyst to form a catalyst in which the co-catalyst and the three-way catalyst are combined before and after.

Here, the preparing of the cocatalyst may include obtaining iron oxide powder; Adding a silicate together with the obtained iron oxide powder to a mixed solution and then milling to prepare a slurry for the auxiliary catalyst; Coating the slurry for the cocatalyst on the surface of the carrier prepared in a cone shape, followed by drying and calcining to complete the cocatalyst supported with iron oxide.

In particular, in the step of obtaining the iron oxide powder, by adding ammonia water to the aqueous solution of iron precursor in the form of a metal salt to obtain a Fe (OH) ₂ precipitate, to obtain the iron oxide powder by washing the precipitate with distilled water, drying and calcining It features.

In addition, in the step of preparing the slurry, the slurry was prepared using 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) and 40 to 70% by weight of silicate 70 to 120 g / L relative to the total carrier apparent volume of the cocatalyst Characterized in that.

In the catalyst of the present invention as described above, poisoning of engine oil is achieved by applying an oxide-based co-catalyst that exhibits minimal activity without supporting a precious metal at the inlet portion of the front inlet where deposition of engine oil is lost. This can improve the overall catalyst durability by eliminating the parts to be lost, while protecting the activity of the rear main catalyst.

In particular, the front auxiliary catalyst serves to oxidize CO while the iron oxide coating layer serves to protect the main catalyst against the engine oil components, thereby providing the effect of improving the low temperature activity of the main catalyst during cold start.

In addition, by forming a front auxiliary catalyst in the shape of a cone containing no precious metal, it is possible to reduce the production cost of the catalyst, improve the exhaust gas distribution state throughout the catalyst carrier, thereby increasing the effective volume of the catalyst to utilize the catalyst There is an effect to increase the efficiency.

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

The present invention relates to a catalyst developed to prevent activity degradation by engine oil poisoning, and a method for manufacturing the same. The basic concept is that at least the inlet portion, which is not useful due to deposition of engine oil, is not supported and at least is not supported. By applying an oxide-based catalyst capable of exhibiting the activity of, to remove the parts to be lost due to poisoning of the engine oil while protecting the activity of the rear main catalyst to improve the overall catalyst durability.

In addition, it is intended to improve the overall purification performance by evenly distributing the exhaust gas flowing into the catalyst carrier through the shape change of the catalyst carrier.

FIG. 2 is a schematic view showing the configuration and shape of the catalyst according to the present invention. As shown in FIG. 2, an auxiliary catalyst 11 having iron oxide supported thereon and no precious metal is disposed thereon, and a noble metal contained behind it. The main catalyst 12 is arranged and configured.

At this time, the front auxiliary catalyst 11 disposed at the inlet side through which the exhaust gas is introduced and the main catalyst 12 disposed at the rear thereof are distinguished, and the front inlet side auxiliary catalyst 11 is formed in a cone shape. Then, the rear main catalyst 12 is formed in the same cylindrical shape as before.

The catalyst of the present invention is to prepare a catalyst for the auxiliary catalyst and the main catalyst, and then to coat each catalyst slurry on each carrier to prepare each catalyst by drying and sintering, and thus prepared two catalysts in front and rear It can comprise by combining and arrange | positioning.

At this time, the auxiliary catalyst 11 is formed in a cone shape, the main catalyst 12 is made of a conventional three-way catalyst shape, for example, a cylindrical shape, and the two catalysts (11, 12) abutted back and forth (butted type, The two catalysts 11 and 12 are spaced apart back and forth so as to have a form in which the two catalysts are in contact with each other, or spaced apart at intervals of 5 to 20 mm.

When the cone-shaped cocatalyst is applied as described above, since the axial length of the carrier becomes longer at the central part (catalyst cross-sectional reference center part), the flow of exhaust gas is suppressed, while from the central part toward the outside (radial direction) Since the axial length of the carrier is shortened, the exhaust gas flows smoothly while going out of the cone shape.

As a result, the exhaust gas is evenly distributed throughout the catalyst, thereby further improving the exhaust gas composition.

That is, in the related art, the flow of the exhaust gas is concentrated in the center, thereby reducing the catalyst utilization efficiency. However, in the catalyst shape of the present invention, the effective volume of the catalyst (exhaust gas treatment volume) is improved evenly with the distribution of the exhaust gas flowing into the catalyst. ) And the catalyst utilization efficiency is increased, thereby improving the purification performance.

This shape is particularly effective for WCC catalysts. The catalyst is prepared by placing a co-catalyst coated with an inexpensive iron catalyst (Fe ₂ O ₃ ) on a low cost, high temperature resistant alumina carrier, located at the inlet of the WCC catalyst. Configure.

On the other hand, the auxiliary catalyst formed in the cone shape as described above is a catalyst portion into which the exhaust gas flows, and serves as a sacrificial catalyst to improve the distribution of the exhaust gas, in particular iron oxide (Fe ₂ O ₃ ) and high heat resistance It is prepared by supporting silicate.

The main catalyst is a conventional three-way catalyst, that is, a conventional three-way catalyst in which a combination of Pt, Pd, Rh, ceria, and alumina is mixed and supported, and the function thereof is also the same as that of a conventional three-way catalyst.

However, in the catalyst of the present invention, the iron-based cone-type cocatalyst having the following functions in front of the conventional three-way catalyst improves the performance and durability of the three-way catalyst by the effect of the cocatalyst.

In the case of the co-catalyst, the engine oil poisoning component is absorbed in front of the main catalyst to suppress the engine oil poisoning component from flowing into the main catalyst, thereby protecting the main catalyst and increasing the durability of the main catalyst. To do that.

In addition, CO oxidation reaction by iron oxide (Fe ₂ O ₃ ) is induced during cold start to improve the low temperature activity of the main catalyst.

In addition, the auxiliary catalyst improves the low-temperature cold startability of the main catalyst through the water absorption during cold start, and also has the characteristic to distribute the exhaust gas evenly throughout the catalyst carrier due to the cone shape, as described above, Improve distribution.

The main catalyst is prepared by coating a conventional three-way catalyst slurry containing a noble metal on the surface of the carrier, followed by drying and calcining. The cocatalyst is prepared by coating a separate catalyst slurry containing no precious metal on the surface of the carrier, followed by drying and calcining. do.

Here, the cone-shaped cocatalyst and its manufacturing process will be described in more detail.

The cocatalyst is prepared by supporting 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) and 40 to 70% by weight of high heat resistant silicate (silicate) on a carrier, wherein the iron oxide and silicate have a specific surface area of 50 m 2 / g at the surface of the carrier. It is manufactured to be supported as above.

Here, the catalyst using iron oxide has oxidation characteristics, but the performance is inferior to precious metals, so in order to have an equivalent level of initial CO oxidation characteristics, iron oxides should be used at least five times the amount of precious metals used. Is limited to at least 30% by weight (lower limit).

However, since the specific surface area of iron oxide is 25 to 70 m 2 / g lower than that of silicate (variable according to the ammonia water addition rate, drying, firing temperature and time), the initial specific surface area when used in excess of 60% by weight Even when mixed with the silicate, it falls to 100 m 2 / g or less, which leads to a decrease in the gas contact area, thereby causing a problem of a lack of initial activity. Therefore, in this invention, the usage-amount of iron oxide is restrict | limited to 60 weight% (upper limit) or less.

The heat resistance of the cocatalyst is such that the specific surface area is satisfied within 10% of the initial specific surface area after deterioration at 950 ° C. for 10 hours, and the coaxial catalyst is prepared to have an axial length of approximately 1 inch.

In order to prepare the cocatalyst as described above, it is necessary to first obtain iron oxide (Fe ₂ O ₃ ) powder to be used for preparing the catalyst slurry, and the process of obtaining the iron oxide powder is as shown in FIG. 3.

Iron oxide powder (iron oxide powder) is prepared by a precipitation process using an iron precursor (nitrate, sulfate, hydrochloride, etc.) in the form of a metal salt.

As an example, first, ammonia water of 2 to 10% concentration is added to an aqueous solution of 0.2 to 2 moles of Fe nitrate or hydrochloride, and ammonia water is added so that the pH of the mixed solution is 10 or less.

As described above, after obtaining the Fe (OH) ₂ precipitate by adding ammonia water, the precipitate was washed with secondary distilled water, but washed until the pH of the distilled water after the washing process dropped to 8 or less.

Thereafter, after over night drying at 80 ° C. for more than 12 hours, the product is calcined in air at 500 ° C. for 2 hours. Through such a firing process, iron oxide having a specific surface area of 25 to 70 m 2 / g (Fe ₂ O ₃ ) The powder is finally obtained.

When iron oxide (Fe ₂ O ₃ ) powder is obtained through the above process, using iron oxide and silicate as a wash coat of the cone-type carrier to prepare a cone-type co-catalyst carrying iron oxide and silicate, iron oxide (Fe ₂ O ₃ ) The process for preparing the washcoating cocatalyst is as shown in FIG.

First, 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) having a specific surface area of 25 to 70 m 2 / g and 40 to 70% by weight of silicate having a specific surface area of 100 to 150 m 2 / g are added to the mixed solution. Milling produces a catalyst slurry.

At this time, the iron oxide and the silicate are mixed at the above-mentioned use ratio, but the amount of the mixture is used so that 70 ~ 120 g / L (Dry Gain basis) relative to the total volume of the cone-shaped carrier.

Distilled water (secondary or more) may be used as the mixed solution. After adding iron oxide and silicate to distilled water, the pH is adjusted to 7-9 using acetic acid or hydroxyl.

At the time of milling, milling while controlling the particle size by the method of a ball mill, and finely powdered particles having a particle size of 2 μm or less to 90 vol% or more of the total particles. A catalyst slurry of 7-9 is obtained.

After the catalyst slurry is prepared as described above, it is coated on an alumina cone carrier. After coating, it is dried for 20 minutes with hot air at 150 ° C., and then calcined for 2 hours in air at 500 ° C. to form a final Fe ₂ O ₃ based co-catalyst. You are done.

As the carrier of the co-catalyst, alumina having a high temperature durability or a material equivalent thereto is used.

When the cone-type cocatalyst is completed as described above, the finished cocatalyst is placed in front of a conventional three-way catalyst to form a catalyst for automobiles.

On the other hand, the present inventors confirmed the improvement effect of the catalyst according to the application of the cone-type co-catalyst using iron oxide as described above, the improvement effect (improving the distribution, latent heat utilization by CO oxidation, water vapor adsorption and TWC ( Three Way Catalyst) is the result of the combination of improvement effect of LOT deterioration by water vapor).

a) deterioration criteria

: Electric furnace deterioration, test after deterioration for 100 hours at 1100 ℃

b) Existing catalyst (three-way catalyst)

: 7 Pd / Rh (weight ratio Pd: Ph = 7: 1) was used at 2.0 g / L based on the apparent volume of the carrier, 1.0 L total catalyst volume, and 25 g / L ceria content relative to the apparent volume of the carrier.

c) the catalyst of the present invention (iron-based co-catalyst + conventional catalyst (three-way catalyst))

: Iron Cone Cocatalyst-35% by weight Fe ₂ O ₃ + 65% by weight silicate at 47g / L based on the carrier apparent volume, 0.2L total catalyst, no ceria and precious metals

: Existing catalyst-7Pd / Rh (weight ratio Pd: Ph = 7: 1) was used as 2.0g / L for the carrier apparent volume, 0.7L total catalyst volume, 25g / L ceria content for the carrier apparent volume

Table 1 shows the improvement effect of the catalyst according to the application of the iron-based cone-type cocatalyst as a test result.

As shown in Table 1, it can be seen that according to the cocatalyst, the purification efficiency of THC and NOx is comparable but the purification efficiency of CO can be significantly improved.

1 is a view showing the result of measuring the deposition pattern of the poisoning component by the engine oil from the catalyst inlet in a conventional catalyst,

Figure 2 is a schematic diagram showing the configuration and the shape of the catalyst according to the present invention,

3 is a process chart for preparing iron oxide powder for the preparation of the cocatalyst according to the present invention;

 4 is a process chart for preparing a cocatalyst according to the present invention.

<Explanation of symbols for the main parts of the drawings>

11: cocatalyst 12: main catalyst

Claims (10)

A catalyst for automobile exhaust gas purification, comprising a conical auxiliary catalyst in the form of a cone supported on iron oxide and free of precious metals, and a three-way catalyst containing noble metals disposed behind. The method according to claim 1, The cocatalyst is an automobile exhaust gas purification catalyst prepared by supporting 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) and 40 to 70% by weight of silicate at 70 to 120 g / L based on the total carrier apparent volume. . The method according to claim 1, The catalyst for the exhaust gas purification of the automobile, characterized in that the coaxial catalyst is made of 1 inch in the axial length. The method according to claim 1, The catalyst for automobile exhaust gas purification, characterized in that the auxiliary catalyst and the main catalyst are arranged before and after contact with each other. The method according to claim 1, The auxiliary catalyst and the main catalyst is a catalyst for automobile exhaust gas purification, characterized in that arranged in front and rear spaced at intervals of 5 ~ 20 mm. Preparing a cone-shaped cocatalyst supported on iron oxide and free of precious metals; Preparing a three-way catalyst; Arranging the cocatalyst in front of the three-way catalyst to form a catalyst in which the co-catalyst and the three-way catalyst are combined before and after; Method for producing a catalyst for automobile exhaust gas purification comprising a. The method according to claim 6, Preparing the cocatalyst, Obtaining iron oxide powder; Adding a silicate together with the obtained iron oxide powder to a mixed solution and then milling to prepare a slurry for the auxiliary catalyst; Coating the slurry for the cocatalyst on the surface of the carrier prepared in a cone shape, followed by drying and calcining to complete the cocatalyst supported with iron oxide; Method for producing a catalyst for automobile exhaust gas purification, characterized in that comprising a. The method according to claim 7, In the step of obtaining the iron oxide powder, by adding ammonia water to the aqueous solution of iron precursor in the form of a metal salt to obtain a Fe (OH) ₂ precipitate, the precipitate is washed with distilled water, dried and calcined to obtain iron oxide powder Method for producing a catalyst for purification of automobile exhaust gas. The method according to claim 8, Add 2 to 10% aqueous ammonia to an aqueous solution of 0.2 to 2 molar concentrations of Fe nitrate or hydrochloride, add ammonia water to bring the pH of the mixed solution to 10 or less, and obtain a Fe (OH) ₂ precipitate. Method of producing a catalyst for automobile exhaust gas purification, characterized in that to obtain iron oxide powder by washing with dry and calcined after washing with. The method according to claim 7, In the step of preparing the slurry, using a 30 to 60% by weight of iron oxide (Fe ₂ O ₃ ) and 40 to 70% by weight of silicate to 70 to 120 g / L with respect to the total carrier apparent volume of the cocatalyst to prepare a slurry Method for producing a catalyst for automobile exhaust gas purification, characterized in that.

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