KR100332704B1 - Catalytic converter for cleaning exhaust gas - Google Patents

Abstract

The catalytic converter for purifying exhaust gas comprises a heat resistant support applied with zirconium complex oxide particles of the following _formula , Zr _{1- (x + y)} Ce _x R _y O _2-z , wherein 'R' Represents at least one element selected from the group consisting of rare earth elements other than Al and Ce, 'z' represents the degree of oxygen deficiency determined by the content and valence containing Al and / or rare earth, and 0.1 ≦ x + y <0.5, 0.1 <x <0.5, and 0 <y <0.2. The bonding of Pt and Rh is carried out in the coexistence on zirconium complex oxide particles. Moreover, the oxygen-storing complex oxide particles of the rare earth element are applied on the heat resistant support together with the zirconium complex oxide particles.

Description

Catalytic converter for exhaust gas purification {CATALYTIC CONVERTER FOR CLEANING EXHAUST GAS}

The present invention relates to nitrogen oxides (NO _x ), carbon monoxide in the exhaust gas of automobile internal combustion engines.

A catalytic converter for efficiently purifying by removing (CO) and hydrocarbons (HC).

As is known, exhaust gases of automotive internal combustion engines inevitably contain harmful substances such as NO _x , CO and HC. In recent years, in particular, restrictions on the purification of exhaust gases have become increasingly strict for environmental protection.

So-called three-way catalytic converters are most widely used to remove the above-mentioned harmful substances. Such three-way catalytic converters use, as active materials, precious metals or metals such as Pt, Pd and / or Rh to reduce NO _x to N ₂ and oxidize CO and HC to CO ₂ and H ₂ O. In this way, the three-way catalytic converter acts as a catalyst for both oxidation and reduction.

Various studies have been conducted to improve the performance of a three-way catalytic converter. One such three-way catalytic converter results in oxygen storage function (OSC), that is, cerium oxide (CeO ₂ ) which has the function of absorbing oxygen gas in the crystal structure and releasing oxygen absorbed from the crystal structure. I use it. In particular, CeO ₂ is added to the three-way catalytic converter to control the oxygen concentration in the gas atmosphere, so that excess oxygen in the gas atmosphere causes the CeO to be rich in oxygen to assist the catalytic converter in reducing NO _x to N ₂ . It is absorbed in the crystal structure of the _second hand to oxidize the CO and HC to CO ₂ and H ₂ O in order to assist in the catalytic converter releases the absorbed oxygen in the CO- and / or HC- rich state in gas atmosphere. Japanese Patent Publication No. 5-47263 (license number JP-A-63-156545) discloses a catalytic converter for purifying exhaust gas, wherein zirconium oxide (ZrO) containing noble metals (eg Pt, Rh) ₂ ) fine particles of ₂ ) are applied on heat resistant organic oxide (e.g. aluminum) particles and oxygen-storing oxide particles of rare earth elements. In such converters, heat-resistant inorganic oxides and rare earth elemental oxides are sandwiched between agglomerates of zirconium oxide particles so that agglomerates of zirconium oxide particles do not grow due to agglomerate-to-agglomerate sintering in a high temperature oxidizing atmosphere. Limit the reduction of certain surface areas that can slow activity. While the aforementioned prior art catalytic converter prevents sintering between zirconium oxide particle agglomerates, it does not prevent the growth of the zirconium particles themselves due to particle to particle sintering. Moreover, depending on its mounting position, the catalytic converter is subject to extreme high temperatures causing grain growth of zirconium oxide. In particular, the need to move the mounting position of the catalytic converter from the bottom of the body floor to the exhaust manifold near the engine increases, so that the catalyst can be heated rapidly after starting the engine. However, when a catalytic converter is placed near the engine, it may be exposed to a high temperature of at least 900 ° C. (or sometimes 100 ° C. or higher), which may cause grain growth of ZrO ₂ due to particle to particle sintering. As a result, certain surface areas of ZrO ₂ are reduced to reduce the catalytic activity of the noble metals performed on the zirconium oxide particles.

It is therefore an object of the present invention to provide a catalytic converter for purifying exhaust gases that does not cause excessive reduction of catalytic activity of precious metals or metals even under extreme operating conditions of 900 ° C or higher.

1 illustrates the high temperature aging state used to evaluate various catalytic converters in various embodiments and comparative examples of the present invention.

According to the present invention, there is provided a catalytic converter for purifying exhaust gas, the converter comprising: a heat resistant support; Zirconium complex oxide particles represented by Formula 1 below; A combination of Pt and Rh carried out in coexistence on zirconium complex oxide particles; And oxygen-storing complex oxide particles of rare earth elements; The zirconium complex oxide particles are applied on the heat resistant support together with the oxygen-storing complex oxide particles. [Formula 1] Zr _{1- (x + y)} Ce _x R _y O _2-z wherein 'R' is other than Al and Ce. At least one element selected from the group consisting of rare earth elements of 'z' indicates the amount of oxygen deficiency determined by the content of the rare earth elements other than Al and Ce and Ce in the complex and its valency, and , 0.1 ≦ x + y ≦ 0.5, 0.1 ≦ x ≦ 0.5, and 0 ≦ y ≦ 0.2.

The invention is characterized in that the zirconium moiety in zirconium oxide (ZrO ₂ ) is replaced by cerium (Ce) and optionally with aluminum (Al) and / or rare earth elements or elements other than cerium. Such substitution limits the mass transfer of zirconium at high temperatures, preventing the zirconium particles from growing inappropriately. As a result, Pt and Rh carried out coexisting on zirconium oxide particles can maintain their catalytic activity above a selected level even at high temperatures. Preferably, at least some of the zirconium complex oxides may be solid solutions. This property is additionally efficient in limiting the mass transport of Zr, thus increasing the durability of the catalytic converter at high temperatures. Precious metals Pt and Rh coexist on a zirconium complex oxide particle for the following reasons. If only one Pt is supported on the zirconium complex oxide particles, the Pt particles tend to grow due to mass transfer of Pt at high temperatures. In contrast, the coexistence of Rh limits the Pt mass transport to prevent particle growth (probably due to the formation of a rhodium oxide layer on the Pt particles which limits the mass transport of Pt).

In the above formula, the relation '0.1 ≦ x + y ≦ 0.5 needs to be satisfied because if the ratio of replacing zirconium with cerium and other elements is lower or higher than this range, it is difficult to effectively prevent zirconium mass transfer. . If the replacement ratio is higher than this range, Pt and Rh co-supported on the zirconium complex oxide may interact with each other in reverse to lower the catalytic activity. The same reason also applies to '0.1 ≦ x ≦ 0.5. Preferably, the value of 'x + y' should be in the range of 0.2 to 0.3, where the 'x' value should be set in the range of 0.1 to 0.28. It can be seen that the Zr content in the zirconium complex oxide may comprise 1 to 3% of hafnium (Hf) necessarily included in the Zr ore. Examples of rare earth elements 'R' other than Ce include Y, Sc, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu. In this example, La and Nd are preferred. The reason for the partial replacement of Zr of zirconium complex oxides with rare earth elements other than Ce is that such stabilization stabilizes the uniform fluorite structure of zirconium complex oxides at room temperature. Alternatively or in addition, some of the Zr in the zirconium complex oxide may be substituted alone or in combination with Y. In the above formula, the value of 'y' is 0 to 0.2. In this way, the value of 'y' becomes zero so that the zirconium complex oxide does not contain Al or rare earth other than Ce. This is because Ce alone, which partially replaces Zr of the zirconium complex oxide, can limit the particle growth of the complex oxide particles to some extent. This is because the ranges for 'x + y' and 'x' match. However, since inclusion of rare earth elements other than Al and / or Ce further restricts the growth of zirconium complex oxide particles, the 'y' value should be preferably set in the range of 0.02 to 0.2. A 'y' value of greater than 0.2 may rise to the side product rather than the desired zirconium complex oxide.

The zirconium complex oxide particles may preferably be applied on the heat resistant support together with the oxygen-storing complex oxide particles and the particles of the heat resistant inorganic oxide. In this case, it is particularly advantageous if the combination of Pt and Rh is selectively transported only on zirconium complex oxide particles. Moreover, the heat resistant inorganic oxide may preferably be selected from the group consisting of all readily available alumina, silica, titania and magnesia. Especially useful are activated alumina. The oxygen storage oxide of the rare earth metal may preferably be cerium oxide or cerium complex oxide. Moreover, noble metals such as Pd may be selectively supported only on the particles of the oxygen storage oxide in addition to the Pt and Rh combinations which are selectively supported only on the particles of the zirconium complex oxide. The heat resistant support made of cordierite, mullite, α-alumina or metal (eg stainless steel) preferably has a honeycomb structure. In preparing a catalytic converter, 10 to 200 g of zirconium complex oxide having a specific surface area of 50 to 160 m ² / g, on a honeycomb support per dm ³ , by known wash-coating methods, 30 to 150 g of oxygen storage oxide having a specific surface area of 100 to 200 m ² / g and 0 to 200 g of a heat resistant inorganic oxide having a specific surface area of 150 to 200 m ² / g may be applied together.

Zirconium complex oxide particles preferably have an average particle size of 0.1 to 2 μm. In a typical example, 0.2 to 2 g of Pt and 0.04 to 1 g of Rh may be supported on particles of zirconium complex oxide per dm ³ (apparent volume) with honeycomb support.

Zirconium complex oxides according to the invention can be prepared using known techniques such as coprecipitation processes or alkoxide processes. This coprecipitation process prepares a solution comprising zirconium, cerium and, optionally, Al and / or each salt of a rare earth element other than cerium in a selected stoichiometric ratio, and then alkalis in the salt solution such that each salt is coprecipitated. A solution or organic acid is added and the resulting coprecipitation for oxidation is then heat treated to give the target zirconium oxide.

Examples of zirconium salts include zirconium oxychloride, zirconium oxynitrite, zirconium oxysulfite and zirconium oxyacetate. Examples of cerium salts and other rare earth elements (and / or Al) include sulfites, nitrites, hydrochlorides, phosphates, acetates and oxalates. Examples of aqueous alkaline solutions include aqueous sodium carbonate solutions, aqueous ammonia and aqueous ammonium carbonate solutions. Examples of organic acids include oxalic acid and citric acid. The heat treatment of the coprecipitation process comprises drying the coprecipitate at about 50 to 200 ° C. for about 1 to 48 hours after filtration and at about 350 to 1,000 ° C. (preferably about 400 to 700 ° C. for about 1 to 12 hours). Baking the co-precipitation at). During the baking step, the baking conditions (baking temperature and baking cycle) should be selected depending on the mixing of the zirconium complex oxide so that at least part of the zirconium complex oxide is in the form of a solid solution.

The alkoxide process prepares a solution of an alkoxide mixture comprising zirconium, cerium and optionally Al and / or rare earth elements other than cerium at a selected stoichiometric ratio, followed by zirconium, cerium and Al (and / or other than Ce). Adding deionized water to the alkoxide mixed solution to cause the rare earth element) to be co-precipitated or hydrolyzed, and then heat treating the final co-precipitation or hydrolysite to provide the target zirconium complex oxide. Examples of alkoxides used to prepare the alkoxide mixed solution include butoxides of methoxide, ethoxide and zirconium, cerium, and Al (and / or rare earth elements other than cerium), respectively. Instead, ethylene oxide addition salts of each of these elements may be used.

Heat treatment in the alkoxide process may be performed in the same manner as the coprecipitation process. Pt and Rh can be supported on zirconium complex oxides using known techniques. For example, a solution containing each salt of Pt and Rh (eg, 1-20% by weight) is prepared first, a solution containing a salt is injected into the zirconium complex oxide, and then the zirconium complex oxide is heat treated. Examples of salts used for this purpose include nitrite, dinitro diamine nitrite, and chloride. Heat treatments performed after injection and filtration include drying the zirconium complex oxide by heat treatment at about 50-200 ° C. for about 1-48 hours and then baking the complex oxide at about 350-1,000 ° C. for about 1-12 hours. .

Other features and advantages of the invention will be apparent from the detailed description of the preferred embodiments with reference to the accompanying drawings. Preferred embodiments of the invention are described below in conjunction with comparative examples. However, it will be appreciated that the present invention is not limited to these examples. Moreover, the term 'oxide' as used below means that the zirconium complex oxide contains a suitable proportion of oxygen which is determined solely by the ratio of the other elements.

Example 1

In this example, the catalytic converter was prepared using a zirconium complex oxide having a composition of Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90 .

(Preparation of zirconium complex oxide)

Zirconium complex oxides having the above compositions were prepared by a so-called coprecipitation process. First, a mixed aqueous solution was prepared, in a deionized water of 100 cm ³ , 0.080 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 mol of cerium nitrite (Ce (NO ₃ ) ₃ · 6H ₂ O), lanthanum nitrite It was prepared by dissolving 0.002 mol of (La (NO ₃ ) ₃ .6H ₂ O) and 0.002 mol of neodymium nitrite (Nd (NO ₃ ) ₃ .5H ₂ O).

Thereafter, a neutralized coprecipitation solution was prepared by dissolving 25.0 g of sodium carbonite (Na ₂ CO ₃ ) in 200 cm ³ of deionized water, and the preprepared mixed solution as described above was gradually added to the final coprecipitation solution to cause coprecipitation. Falls into. After sufficient washing with water and filtering, the final coprecipitation was ground for 24 hours in a ball mill readily obtainable by addition of 100 cm ³ of isopropyl alcohol, resulting in a slurry comprising the coprecipitation. This ball mill was made of zirconium oxide (ZrO ₂ stabilized with 3 moles of Y ₂ O ₃ ).

After filtration, the slurry so obtained was dried at 80 ° C. in a vacuum. After sufficient drying, the coprecipitation (as a result of drying this slurry) was baked in air at 650 ° C. for 3 hours to provide a powder of zirconium complex oxide having a composition of Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90 . Ce, La and Nd are included here as solid solutions.

Isopropyl alcohol 2 dm ³ was supplied to 2 kg of zirconium complex oxide powder obtained by repeating the above-described steps, and then pulverized in a characteristic mill easily obtainable using a zirconia ball having an average diameter of 3 mm for 12 hours, and isopropyl Alcohol is supplemented as required. Thereafter, the slurry comprising additionally ground powder of zirconium complex oxide is filtered and dried at 80 ° C. under vacuum. Fully dried, the zirconium complex oxide powder is loosened in mortar and then filled with a 325-mesh screen. As a result, the zirconium complex oxide portion passing through the screen has an average particle size of 1.4 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

50 g of zirconium complex oxide powder was injected with an aqueous solution of dinitrodiaminepallatinum nitrite (Pt content: 0.3 g) and an aqueous solution of rhodium nitrite (Rh content: 0.3 g). The powder so injected was first dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. As a result, zirconium complex oxides were prepared to support or support 1.5 g of Pt and 0.3 g of Rh.

The Pt- and Rh-supporting zirconium complex oxides were then prepared with 130 g La-stabilized alumina powder (stabilized by La in solid solution) and 75 g cerium complex oxide having a composition of Ce _0.6 Zr _0.3 Y _0.1 O _1.65 in a ball mill. Mixed into powder. The mixed slurry was then applied onto a monolithic cordierite honeycomb support of 400 cells / in ² (62 cells / cm ² ), 105.7 mm in diameter and 100 mm in length. The honeycomb support thus applied was dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. The target catalytic converter was thus obtained.

Example 2

In this example, again, the catalytic converter was prepared using a zirconium complex oxide having a composition of Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90 . In preparing the zirconium complex oxide in this example, it was made in exactly the same manner as in Example 1 except that the last two steps of grinding and filling were omitted so that the average particle size of the complex oxide powder was 5.2 μm.

Example 3

In this example, the catalytic converter was prepared using a zirconium complex oxide having a composition of Zr _0.80 Ce _0.16 La _0.04 O _1.90 .

(Zirconium Complex Oxide Preparation)

First, the mixed aqueous solution is 0.008 moles of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 moles of cerium nitrite (Ce (NO ₃ ) ₃ .6H ₂ O), and 0.004 moles of lanthanum in 100 cm ³ of deionized water. Prepared by dissolving nitrite (La (NO ₃ ) ₃ .6H ₂ 0). The neutralized coprecipitation solution was then prepared by dissolving 25.0 g of sodium carbonite (Na ₂ CO ₃ ) in 200 cm ³ of deionized water, and the previously prepared mixed solution gradually dropped into the final coprecipitation solution to cause coprecipitation as described above. lost. After sufficient washing with water and filtration, the final coprecipitation was dried at 80 ° C. under vacuum. After sufficient drying, this coprecipitation was baked in the prior art at 650 ° C. for 3 hours to provide a zirconium complex oxide powder having the above-mentioned composition, where Ce and La were included as a solid solution. The average particle size of the zirconium complex oxide powder was 6.1 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

Using 50 g of the zirconium complex oxide powder thus obtained, the catalytic converter was assembled in the same manner as in Example 1.

Example 4

In this example, the catalytic converter was prepared using a zirconium complex oxide having a composition of Zr _0.70 Ce _0.16 Al _0.06 Y _0.08 0 _1.85 .

(Preparation of zirconium complex oxide)

A powder of zirconium complex oxide having the above-described composition was prepared in the same manner as in Example 3, with the exception of 0.070 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 mol of cerium nitrite (Ce (NO ₃₎ ) ₃ · 6H ₂ O), 0.006 mol of aluminum nitrite (Al (NO ₃ ) ₃ · 9H ₂ O), and 0.008 mol of yttrium nitrite (Y (NO ₃ ) ₃ · 6H ₂ O) are used as starting materials It is. Zirconium complex oxide powders have an average particle size of 7.0 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

Using 50 g of the zirconium complex oxide powder thus obtained, the catalytic converter was assembled in the same manner as in Example 1.

Example 5

In this example, the catalytic converter was prepared using a zirconium complex oxide having a composition of Zr _0.70 Ce _0.10 Al _0.20 O _1.85 .

(Preparation of zirconium complex oxide)

Zirconium complex oxide powder having the above-described composition was prepared in the same manner as in Example 3, with the exception of 0.070 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.010 mol of cerium nitrite (Ce (NO ₃ ) ₃ 6H ₂ O), 0.020 mol of aluminum nitrite (Al (NO ₃ ) ₃ .9H ₂ O) was used as starting material. Zirconium complex oxide powders have an average particle size of 7.3 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

Using 50 g of the zirconium complex oxide powder thus obtained, the catalytic converter was assembled in the same manner as in Example 1.

Example 6

In this example, the catalytic converter was made using a zirconium complex oxide having a composition of Zr _0.80 Ce _0.20 O _1.90 .

(Preparation of zirconium complex oxide)

Zirconium complex oxide powder having the above-described composition was prepared in the same manner as in Example 3, with the exception of 0.080 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.020 mol of cerium nitrite (Ce (NO ₃ ) ₃ 6H ₂ O) was used as starting material. Zirconium complex oxide powders have an average particle size of 6.3 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

Using 50 g of the zirconium complex oxide powder thus obtained, the catalytic converter was assembled in the same manner as in Example 1.

Example 7

In this example, the catalytic converter was made using a zirconium complex oxide having a composition of Zr _0.90 Ce _0.10 O _1.95 .

(Preparation of zirconium complex oxide)

Zirconium complex oxide powder having the above-described composition was prepared in the same manner as in Example 3, with the exception of 0.090 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.010 mol of cerium nitrite (Ce (NO ₃ ) ₃ 6H ₂ O) was used as starting material. Zirconium complex oxide powders have an average particle size of 7.8 μm (as determined by laser diffraction scattering).

(Assembly of the catalytic converter)

Using 50 g of the zirconium complex oxide powder thus obtained, the catalytic converter was assembled in the same manner as in Example 1.

Example 8

In this example, the catalytic converter is a zirconium complex oxide powder (composition: Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90 ; average particle size, as used in Example 2 to produce slightly different catalytic converters, as described below). : 5.2 μm).

(Assembly of the catalytic converter)

50 g of zirconium complex oxide powder (average particle size: 5.2 μm) was injected with an aqueous solution of dinitro diamineplatinum nitrite (Pt content: 0.8 g) and an aqueous solution of rhodium nitrite (Rh content: 9.3 g). The powder so injected was first dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. As a result, zirconium complex oxides were prepared to support or carry 0.8 g of Pt and 0.3 g of Rh. Meanwhile, an aqueous solution of dinitrodiamineplatinum nitrite (Pt content: 0.7 g) was injected into 75 g of cerium complex oxide powder having a composition of Ce _0.6 Zr _0.3 Y _0.1 O _1.65 . The implanted cerium complex oxide powder was first dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. As a result, cerium complex oxides were prepared to support or carry 0.7 g of Pt.

Then, two kinds of complex oxide powders were mixed in a ball mill (130 g stabilized by La in a solid solution) of La-stabilized alumina powder and wet milled for 12 hours to provide an aqueous mixed slurry. The mixed slurry was then applied on a single cordierite honeycomb support of 400 cells / in ² (62 cells / cm ² ), 105.7 mm in diameter and 100 mm in length. The honeycomb support thus applied was dried at 110 ° C. for 12 hours and baked at 500 ° C. for 3 hours. The target catalytic converter was thus obtained.

Example 9

This example is the same as Example 7 for the use of a zirconium complex oxide having a composition of Zr _0.90 Ce _0.10 O _1.95 , but of the zirconium complex oxide to exempt alumina powder at the time of coating onto the monolithic cordierite honeycomb support. The difference is that the amount is increased to 180g.

Comparative Example 1

For comparison, catalytic converters were prepared using easily obtainable zirconium powder having an average particle size of 7.6 μm (as determined by laser diffraction scattering) instead of using the zirconium complex oxide powder according to the present invention.

[Assembly of the catalytic converter]

50 g of zirconium powder was injected with an aqueous solution of dinitro diamine platinum nitrite (Pt content: 1.5 g) and an rhodium nitrite (Rh content: 0.3 g) solution. The zirconia powder so injected was first dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. As a result, zirconia powder was prepared to support or carry 1.5 g of Pt and 0.3 g of Rh.

The Pt- and Rh-supporting zirconia powders were then 130 g La-stabilized alumina powder (stabilized by La in solid solution) and 75 g cerium complex oxide powder having a composition of Ce _0.6 Zr _0.3 Y _0.1 O _1.65 in a ball mill. And wet milled for 12 hours to provide an aqueous mixed slurry. The mixed slurry was then applied onto a monolithic cordierite honeycomb support of 400 cells / in ² (62 cells / cm ² ), 105.7 mm in diameter and 100 mm in length. The honeycomb support thus applied was dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. The target catalytic converter was thus obtained.

Comparative Example 2

In Comparative Example 2, a zirconium complex oxide powder (composition: Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90 ; average particle size: 5.2 μm) as used in Example 2 was used, but Pt and Rh are described below. It was supported on alumina powder instead of zirconium complex oxide powder.

[Assembly of the catalytic converter]

130 g of easily obtainable La-stabilized alumina powder (stabilized by La in a solid solution) contains an aqueous solution of dinitro diamineplatinum nitrite (Pt content: 1.5 g) and an rhodium nitrite (Rh content: 0.3 g) Was injected. The injected alumina powder was first dried at 110 ° C. for 12 hours and baked at 500 ° C. for 3 hours. As a result, alumina powder was prepared to support or carry 1.5 g of Pt and 0.3 g of Rh. The Pt- and Rh-supporting alumina powders were then mixed with 50 g of zirconium complex oxide powder (average particle size: 5.2 μm) and 75 g of cerium complex oxide powder having a composition of Ce _0.6 Zr _0.3 Y _0.1 O _1.65 in a ball mill, Wet grinding for 12 hours to provide an aqueous mixed slurry. The mixed slurry was then applied onto a single cordierite honeycomb support of 400 cells / in ² (62 cells / cm ² ), 105.7 mm in diameter and 100 mm in length. The honeycomb support thus applied was dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. The target catalytic converter was thus obtained.

Comparative Example 3

In Comparative Example 3, the catalytic converter was prepared in the same manner as in Comparative Example 1, with the exception of (1) the amount of zirconia powder was reduced to 8 g, and (2) 75 g of cerium complex oxide powder was obtained with 40 g of pure, easily obtainable It was replaced with ceria powder (CeO ₂ ), (3) the amount of Rh supported was reduced to 0.15g, and (4) the amount of Pt supported was reduced to 0.75g.

[Comparative Example 4]

Comparative Example 4 is the same as Comparative Example 3 in using zirconia powder having an average particle size of 7.6 µm, but differs in the application amount of the zirconia powder and the carrier material supported by Pt, which will be described later.

[Assembly of the catalytic converter]

6 g of zirconia powder was injected with an aqueous solution of rhodium nitrite (Rh content: 0.15 g). The injected zirconia powder was first dried at 110 ° C. for 12 hours and baked at 500 ° C. for 3 hours. As a result, zirconia powder was prepared to support 0.15 g of Rh.

77 g of easily obtainable La-stabilized alumina powder (stabilized by La in a solid solution) was injected with an aqueous solution of dinitro diamineplatinum nitrite (Pt content: 0.75 g). The injected alumina powder was first dried at 110 ° C. for 12 hours and baked at 500 ° C. for 3 hours. As a result, alumina powder was produced to support 0.75 g of Pt.

The Rh-supporting zirconia powder and Pt-supporting alumina powder were then mixed with 40 g of pure ceria powder (CeO ₂ ) readily available in a ball mill and wet milled for 12 hours to provide an aqueous mixed slurry. The mixed slurry was then applied onto a monolithic cordierite honeycomb support of 400 cells / in ² (62 cells / cm ² ), 105.7 mm in diameter and 100 mm in length. The honeycomb support thus applied was dried at 110 ° C. for 12 hours and then baked at 500 ° C. for 3 hours. The target catalytic converter was thus obtained.

[Evaluation of Catalyst Converters]

Each catalytic converter assembled according to Examples 1-9 and Comparative Examples 1-4 was tested for its performance in purifying exhaust gas.

[Aging]

In aging, each catalytic converter was actually mounted on a bank (four cylinders) of a four liter V8 engine installed in a vehicle, and engine exhaust gas was introduced into the converter. In particular, the cycle shown in FIG. 1 and lasting 60 seconds was repeated 3,000 times for a total period of 50 hours.

As shown in FIG. 1, the cycle included a stoichiometric driving cycle (0-40 seconds), where the engine ran under the feedback control with a supply of stoichiometric air-fuel mixture (A / F = 14.6). The internal temperature of the converter is maintained at about 850 ° C. The stoichiometric driving period is followed by a fuel-rich period (40-44 seconds), where the engine is set to run with the supply of excess fuel (A / F = 11.7) under the interruption of feedback control. The fuel-rich cycle is followed by a temperature-rise cycle (44-56 seconds), where the engine continues to run with excessive fuel supply under a continuous interruption of feedback control, but in order to react excess fuel to secondary air in the converter. Secondary air is introduced into the catalytic converter outside the engine, causing the temperature to rise to a maximum of 1,050 ° C. The air-fuel mixture supplied to the assembly of the engine and catalytic converter in this temperature ramp cycle is slightly short of fuel under continuous supply of secondary air (A / F = 14.8). It can be seen here that the temperature in the catalytic converter was detected for thermal bonds inserted in the honeycomb support.

[Assessment Methods]

After performing the aging described above, the exhaust gas purification performance of each catalytic converter was evaluated in the following manner.

The engine ran with a continuously fluctuating air-fuel mixture from fuel rich to fuel scarce, and the final exhaust gas entered the catalytic converter to remove harmful gases such as CO and NO _x . Removal ratio of CO and NO _x is a CO- remove NO _x ratio - was measured to determine the C0-NO _x removal cross point matching the removal rate. The CO-NO _x removal crossover point thus determined was used to evaluate the performance of the catalytic converter. In this performance test, the engine was used without stopping the vehicle, and the temperature of the exhaust gas introduced into the catalyst was 450 ° C. Moreover, air-fuel mixture was fed to the engine at a space speed of 90,000 / h with A / F fluctuations of ± 1.0.

(Evaluation results)

Table 1 shows the CO-NO _x removal intersections determined for each catalytic converter. In Table 1, the following abbreviations are used.

C.P. : Crossing point Emb. Example

CE: Comparative Example ZCLN: Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 O _1.90

ZCL: Zr _0.80 Ce _0.16 La _0.04 O _1.90 ZCAY: Zr _0.70 Ce _0.16 Al _0.06 Y _0.08 O _1.85

ZCA: Zr _0.70 Ce _0.10 Al _0.20 O _1.85 Z8C: Zr _0.80 Ce _0.20 O _1.90

Z9C: Zr _0.90 Ce _0.10 O _1.95 CZY: Ce _0.6 Zr _0.3 Y _0.1 O _1.80

The practice of the present invention can provide a catalytic converter for purifying exhaust gases that does not cause excessive reduction of catalytic activity of precious metals or metals even under extreme operating conditions of 900 ° C or higher.

[conclusion]

As can be seen from the table, the zirconium complex oxide of any of Examples 1-9 indicates a higher CO-NO _x removal crossover point (as determined after high temperature aging) than in Comparative Examples 1-4. This means that the zirconium complex oxide of the present invention effectively limits grain growth at high temperatures while the selective coexistence of Pt and Rh on the particles of zirconium complex oxide prevents grain growth of Pt at high temperatures. Furthermore, comparing Example 1 (where the average particle size of the zirconium complex oxide powder is 2 μm or less) to Example 2 (where the average particle size is 2 μm or more), the exhaust gas purification performance is reduced in the average particle size of the zirconium complex oxide powder. Shows an improvement. Furthermore, Examples 2-6 show that replacing Zr with Al and / or rare earth elements (eg, Y, Nd) in a solid solution provides an improvement in exhaust gas purification performance. Therefore, in conclusion, the catalytic converter according to the present invention can be advantageously employed in the internal manifold to provide good catalysis even at high temperatures.

Claims (10)

A catalytic converter for purifying exhaust gas, the converter comprising: a heat resistant support; Zirconium complex oxide particles represented by Formula 1 below; Bonding of Pt and Rh carried out in coexistence on zirconium complex oxide particles; And oxygen-storing complex particles of rare earth elements; And the zirconium complex oxide particles are applied on a heat resistant support together with the oxygen-storing complex oxide particles. Zr _{1- (x + y)} Ce _x R _y O _2-z In the above formula, 'R' represents at least one element selected from the group consisting of rare earth elements other than Al and Ce, and 'z' represents the content and valency of rare earth elements other than Al and Ce and the Ce complex oxide The degree of oxygen deficiency determined by is represented by 0.1 ≦ x + y ≦ 0.5, 0.1 ≦ x ≦ 0.5, and 0 ≦ y ≦ 0.2. The catalytic converter according to claim 1, wherein the zirconium complex oxide particles are applied on the heat resistant support together with the oxygen storage complex oxide particles and the heat treated inorganic oxide particles, and the combination of Pt and Rh is selectively supported only on the zirconium complex oxide particles. The catalytic converter of claim 1, wherein the zirconium complex oxide satisfies the relationship 0.2 ≦ x + y ≦ 0.3, 0.1 ≦ x ≦ 0.28, and 0.02 ≦ y ≦ 0.2. The catalytic converter according to claim 1, wherein R in formula is La alone, Al alone, a combination of La and Nd, or a combination of Al and Y. The catalytic converter of claim 1, wherein at least a portion of the zirconium complex oxide is a solid solution. The catalytic converter of claim 1, wherein the particles of zirconium complex oxide have an average particle size of 0.1 to 2 μm. The catalytic converter of claim 1, wherein the oxygen-storing oxide of the rare earth metal is cerium oxide or cerium complex oxide. The catalytic converter according to claim 1, wherein the particles of the oxygen-storing oxide carry Pd. The catalytic converter of claim 2 wherein the heat resistant inorganic oxide is selected from the group consisting of alumina, silica, titania and magnesia. The catalytic converter according to claim 1, wherein the heat resistant support has a honeycomb structure.