DE69930727T2 - Catalyst for exhaust gas purification - Google Patents

Description

BACKGROUND THE INVENTION

1. Technical area:

The present invention relates to a catalyst for effectively purifying the exhaust gas of an automotive internal combustion engine by removing nitrogen oxides (NO _x ), carbon monoxide (CO) and hydrocarbons (HC).

2. The description of the Prior art:

As is known, the exhaust gas of an internal combustion engine inevitably comprises harmful substances such as NO _x , CO and HC. Especially in recent years, the demands on exhaust gas purification have become increasingly strict from the viewpoint of environmental protection.

To remove the harmful substances described above, the so-called three-way catalyst has been used mostly. The three-way catalyst uses as an active substance a noble metal or metals such as Pt, Pd and / or Rh for reducing NO _x in N ₂ and for oxidizing CO and HC in CO ₂ and H ₂ O. The three-way catalyst acts as a catalyst for both Oxidation as well as for the reduction.

To improve the operation of the three-way catalyst, various studies have been carried out. One of the three-way catalysts resulting from such studies uses ceria (CeO ₂ ), which has an oxygen storage (OSC) capability; this means the ability to trap gaseous oxygen in the crystal structure and release the trapped oxygen from the crystal structure. More specifically, CeO _{2 is} added to a three-way catalyst to adjust the oxygen concentration in the gaseous atmosphere so that excess oxygen in the gaseous atmosphere is included in the crystal structure of CeO ₂ in an oxygen-rich state to remove the catalyst in the reduction of NO _x to N ₂ while the trapped oxygen in a CO and / or HC rich state is released into the gaseous atmosphere to assist the catalyst in the oxidation of CO and HC to CO ₂ and H ₂ O.

Japanese Patent Publication 5-47263 (which corresponds to the issued version of JP-A-63-156545) discloses a catalyst for purifying exhaust gas in which zirconia fine particles (ZrO ₂ ) carrying a noble metal (for example, Pt, Rh) are obtained a heat-resistant honeycomb carrier, together with particles of a heat-resistant inorganic oxide (for example, alumina) and oxygen-storing oxide particles of a rare earth element. In such a catalyst, the heat-resistant inorganic oxide and the rare earth element are sandwiched between the agglomerates of the zirconia particles to prevent the zirconia particles from growing due to agglomerate-to-agglomerate sintering in a high-temperature atmosphere, thereby decreasing the specific surface area that could lead to a deterioration of the catalytic activity.

Of the Prevented catalyst of the prior art described above although sintering of zirconia particle agglomerates, yet he can not prevent the Zirkonoxidpartikel itself, due particle-to-particle sintering to grow. Also, the catalyst may vary depending on its mounting position to be exposed to extremely high temperatures affecting grain growth promote the zirconia.

Namely, there is an increasing demand for shifting the mounting position of the catalyst from below the body floor to the exhaust manifold, which is located close to the engine, whereby the catalyst can be warmed up quickly after starting the engine. However, when the catalyst is placed close to the engine, it can often be exposed to high temperatures of not less than 900 ° C (or sometimes even higher than 1000 ° C), which causes grain growth of the ZrO ₂ due to particle-by-particle Can cause sintering. The result is that the specific surface area of the ZrO ₂ decreases and results in a decrease in the catalytic activity of the noble metal on the zirconia particles.

WO-A-98/13139 and WO-A-97/43035 disclose a catalyst comprising a zirconium complex oxide coated on a heat resistant support and further comprising a composition for storing oxygen in the form of a combination of Pt and Rh selected from Particles of, for example, alumina, titania, silica supported. However, the effectiveness of such catalysts is ver improvement capable.

EPIPHANY THE INVENTION

It It is therefore an object of the present invention to provide a Catalyst for purifying exhaust gas that does not cause excessive waste the catalytic activity of a noble metal or even metals under severe operating conditions above 900 ° C.

According to the present invention as defined in the appended claim 1, there is provided a catalyst for purifying exhaust gas having the following features:
A heat-resistant carrier;
Particles of a zirconium complex oxide of the following formula Zr _{1- (x + y)} Ce _x R _y O _{2 -z} , wherein "R" represents at least one member selected from a group consisting of aluminum and rare earth metals other than Ce, "z" represents the degree of oxygen deficiency determined by the valence and content of the contained Al and / or rare earth element , 0.1 ≤ x + y ≤ 0.5, 0.1 ≤ x ≤ 0.5 and 0.1 ≤ y ≤ 0.2;
a combination of Pt and Rh carried together by the particles of zirconium complex oxide;
Particles of an oxygen-storing complex oxide of a rare earth element;
wherein the particles of the zirconium complex oxide are coated together with the particles of the oxygen-storing complex oxide as a coating on the heat-resistant support.

The present invention contemplates that a portion of the zirconia in the zirconia (ZrO ₂ ) is substituted by cerium (Ce), optionally by aluminum (Al) and / or a rare earth element or other elements other than cerium. Such substitution limits mass transfer of the zirconium at high temperature, thereby preventing the zirconia particles from overgrowth. As a result, Pt and Rh carried side by side by the zirconia particles can retain their catalytic activity above a predetermined level even at a high temperature.

Preferably For example, at least a portion of the zirconium complex oxide may be a solid solution. This feature is additional effective to arrest the mass transfer of Zr, causing the Durability of the catalyst is promoted at high temperature.

The Precious metals Pt and Rh are composed of the following together Particles of zirconium complex oxide worn. If Pt alone on the Zirconium complex oxide particles are applied, the Pt particles show due to the mass transfer of Pt at high temperature a growth tendency. In contrast, if Rh is present, it keeps the mass transfer of Pt and prevents grain growth (probably due to the formation of a rhodium oxide layer on the Pt particles containing the Mass transfer from Pt brakes).

In In the above formula, the relation "0.1 ≦ x + y ≦ 0.5" must be satisfied because if relationship the substitution of zirconium with cerium and other elements lower or higher As this range is difficult, the mass transfer of zircon is effectively prevent. If the substitution ratio is higher than this area is, can Pt and Rh coexistent on the zirconia complex, interact with each other adversely and the catalytic activity reduce. This is also true for "0.1 ≤ x ≤ 0.5" The value of "x + y" should preferably be in the range from 0.2 to 0.3 while the Value of "x" in the range of 0.1 should be set to 0.28. It is understood that the Zr content in which zirconium complex oxide may comprise 1 to 3% hafnium (Hf), which inevitably contained in zirconium ores.

Examples of rare earth elements "R" except Ce Y, Sc, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Of these examples, La and Nd are preferred. The reason for the partial Substitution of the Zr of zirconium complex oxide with a rare earth element except Ce is that such a substitution of the uniform fluorite structure zirconium complex oxide stabilized at room temperature while at the same time the mass transfer of Zr in cooperation with Ce Bremst.

alternative or additionally Part of the Zr may be in the zirconium complex oxide with Al alone or be substituted in combination with Y.

The value of "y" in the above formula is 0 to 0.2, and the value of "y" may be 0, so that the Zirconium complex oxide need not contain Al or a rare earth metal other than Ce, because Ce alone, when partially substituted for Zr in the zirconium complex oxide, can retain the grain growth of complex oxide particles to some extent. This is why the ranges for "x + y" and "x" coincide. However, since the inclusion of Al and / or a rare earth element other than Ce better restrain the growth of the zirconium complex oxide particles, the value of "y" should preferably be selected in the range of 0.02 to 0.2, a value of "y" above of 0.2 may result in the formation of by-products other than the desired zirconium complex oxide.

The Zirconium complex oxide particles can on the heat-resistant carrier together with the oxygen-storing complex oxide particles and Particles of a heat-resistant inorganic Oxids are preferably applied as a coating. In this Case, it is particularly advantageous if the combination of Pt and Rh selectively applied only to the zirconium complex oxide particles is.

The heat-resistant inorganic oxide may preferably be selected from a group of alumina, Silicon oxide, titanium oxide and magnesium oxide, all of which are commercially available available are. Especially useful is activated alumina.

The Oxygen-storing oxide of a rare earth metal may preferably Ceria or a Cerkomplexoxyd. Also, a precious metal like Pd selective only to the particles of oxygen-storing oxide in addition to The combination of Pt and Rh can be applied selectively only are present on the particles of Zirkonkomplexoxids.

The heat-resistant support, which may consist of cordierite, mullite, α-alumina or a metal (for example, corrosion-resistant steel), should preferably have a honeycomb structure. In preparing the catalyst, 100 to 200 grams of the zirconia complex oxide having a specific surface area of 50 to 160 m ² / g should contain 30 to 150 g of the oxygen storage oxide having a specific surface area of 100 to 200 m ² / g and 0 to 200 g of the heat resistant inorganic oxide having a specific surface area of 150 to 200 m ² / g are applied together by the known wash-coating method on the honeycomb carrier per dm ³ (bulk volume).

The particles of zirconium complex oxide may preferably have an average particle size of 0.1 to 2 μm. With a typical example, 0.2 to 2 g of Pt and 0.04 to 1 g of Rh can be applied to a dm ³ (bulk volume) of the zirconium complex oxide of the honeycomb carrier.

The zirconium complex oxide according to the invention can be measured using known techniques such as the coprecipitation method or the alkoxide process getting produced.

The Coprecipitation method includes the steps of preparing a solution containing the respective salts of the zircon, the cer and if desired Aluminum and / or a rare earth element except cerium in a predetermined stoichiometric relationship contains. The saline solution becomes an aqueous Alkaline solution or an organic acid added so that the respective salts are brought together to fail. Thereafter, the resulting coprecipitate is heat treated for oxidation, to obtain a desired zirconium complex oxide.

Examples of zirconium salts include zirconium oxychloride, zirconium oxinitrate, zirconium oxysulfate and zikronoxiacetate. Examples of salt of cerium and other rare earth elements (and / or Al) include sulfates, nitrates, hydrochlorides, phosphates, Acetates and oxalates. Examples of aqueous alkali solutions include an aqueous solution of sodium carbonate, aqueous Ammonia and an aqueous solution of ammonium carbonate. Examples of organic acids include oxalic acid and Citric acid.

The heat treatment in the coprecipitation method comprises a drying section for drying the coprecipitate at about 50 to 200 ° C for 1 to 48 hours after filtration and a burning step for burning of the coprecipitate at about 350 to 1000 ° C (preferably about 400 to 700 ° C) for about 1 to 12 hours. While of burning should the firing conditions (the firing temperature and the burning time) depending on the composition of zirconium complex oxide selected be so that at least a part of the Zirkonkomplexoxids in the Form of a solid solution is present.

The alkoxide process comprises the steps of preparing a solution of a mixture of the alkoxides comprising zirconium, cerium and, if desired, Al and / or a rare earth element other than cerium in a predetermined stoichiometric ratio. Then, deionized water becomes the solution of the mixture of alkoxides to coprecipitate or hydrolyze zirconium, cerium and Al (and / or the rare earth element other than cerium). Finally, the resulting coprecipitate or hydrolyzate is heat treated to obtain a desired zirconium complex oxide.

Examples of alkoxides for the preparation of the solution The mixture of alkoxides include methoxides, ethoxides, propoxides and butoxides of zirconium, cerium and Al (and / or a rare earth element except Cerium). Instead, ethylene oxide addition salts are any of these Element used.

The heat treatment in the alkoxide process can be carried out in the same manner as in the coprecipitation process carried out become.

Pt and Rh can applied to the zirconium complex oxide using known techniques become. For example, first a solution a ent speaking salt (for example, 1 to 20 wt .-%) of Pt and Rh are prepared, whereupon the zirconium complex oxide with the saline solution waterproof becomes. Thereafter, the zirconium complex oxide is heat-treated. Examples of this Purpose of usable salts include nitrates, dinitrodiamine nitrate and Chlorides. The after impregnation and filtration performed heat treatment may be a drying of zirconium complex oxide by heating approximately 5 to 200 ° C for about 1 to 48 hours, after which the complex oxide at about 350 to 1000 ° C for about 1 to 12 Hours is burned.

Further Features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments with reference on the attached Drawing forth.

SHORT DESCRIPTION THE DRAWINGS

The drawing includes a single figure, which is called " 1 "and is a graph of the high temperature aging conditions used to evaluate various catalysts of the various embodiments of the present invention and the comparative examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will be described below together with comparative examples described. However, the invention is directed to these embodiments not limited. The term "oxides" used below also means that the zirconium complex oxide contains an appropriate amount of oxygen on one side the ratios the rest Elements is determined.

[Example 1]

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

(Preparation of zirconium complex oxide)

The zirconium complex oxide of the above composition was prepared by the so-called coprecipitation method. First, an aqueous mixture solution prepared by dissolving in 100 cm ³ deionized water of 0.080 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 mol of cerium nitrate (Ce (NO _{3) 3} · 6H ₂ O), 0.002 mol of lanthanum nitrate (La (NO _{3 3} x 6H ₂ O) and 0.002 mol of neodymium nitrate (Nd (NO ₃ ) ₃ .5H ₂ O).

Then, ³ of deionized water were prepared in 200 cm, a neutralizing coprecipitation solution by dissolving 25.0 g of sodium carbonate (Na ₂ CO _3). The previously prepared mixture solution was gradually dropped into the resulting coprecipitation solution to effect coprecipitation. After sufficient washing with water and filtration, the resulting coprecipitate was crushed for 24 hours in a commercially available ball mill with the addition of 100 cm ³ of isopropyl alcohol, which resulted in the formation of a paste containing the coprecipitate. The ball mill was made of zirconia (ZrO ₂ stabilized with 3 moles of Y ₂ O ₃ ).

After filtration, the resulting slurry was dried at 80 ° C under vacuum. After sufficient drying, the coprecipitate (which resulted after drying the slurry) was fired in air at 650 ° C for 3 hours to give a powder of zirconium complex oxide having the composition Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 Oxide in which Ce, La and Nd were obtained as a solid solution.

Two kilograms of the zirconium complex oxide powder obtained by repeating the above steps were added with 2 dm ^{3 of} isopropyl alcohol and then further crushed for 12 hours in a commercially available attrition mill with zirconia balls of 3 mm in average diameter, with isopropyl alcohol replenished as needed has been. Thereafter, the slurry containing the additional crushed powder of the zirconium complex oxide was filtered and dried at 80 ° C under vacuum. After sufficient drying, the zirconium complex oxide powder was ground in a mortar and then sieved through a 325 mesh sieve. The proportion of the zirconium complex oxide powder passing through the sieve had a mean particle size of 1.4 μm (determined by laser scattering).

(Preparation of the catalyst)

50 g of the sieved zirconium complex oxide powder was washed with an aqueous solution of dinitrodiammineplatinum nitrate (Pt content: 1.5 g) and an aqueous solution of rhodium nitrate (Rh content: 0.3 g). The so impregnated Powder was first at 110 ° C for 12 Dried hours and then fired at 500 ° C for 3 hours. To this As a result, the zirconium complex oxide carried 1.5 g Pt and 0.3 g Rh.

Then, the Pt- and Rh-bearing zirconium complex oxide was mixed with 130 g of a La-stabilized alumina powder (stabilized by La in solid solution and 75 g of a cerium complex oxide powder of composition Ce _0.6 Zr _0.3 Y _0.1 oxide in a ball mill and mixed The mixed slurry was then coated onto a monolithic cordierite honeycomb carrier having 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm The honeycomb carrier thus coated was dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours to obtain the aimed catalyst.

[Example 2]

In this example, a catalyst was again prepared using a zirconium complex oxide of composition Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 oxide. However, in preparing the zirconium complex oxide, at least two steps of crushing and sieving the zirconium complex oxide powder were omitted, unlike Example 1. Otherwise, Example 2 is exactly the same as Example 1.

[Example 3]

In this example, a catalyst was prepared using a zirconium complex oxide having the composition Zr _0.80 Ce _0.16 La _0.04 oxide.

(Preparation of zirconium complex oxide)

First, an aqueous mixture solution prepared by dissolving in 100 cm ³ deionized water of 0.080 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 mol of cerium nitrate (Ce (NO _{3) 3} · 6H ₂ O) and 0.004 mol of lanthanum nitrate (La (NO _{3 3} × 6H ₂ O).

Then, a neutralizing coprecipitation solution prepared in which 25.0 g of sodium carbonate (Na ₂ CO ₃₎ were dissolved in 200 cm ³ deionized water. The previously prepared mixture solution was gradually dripped into the resultant coprecipitation solution to effect coprecipitation. After sufficient washing with water and filtering, the resulting coprecipitate was dried at 80 ° C under vacuum. After sufficient drying, the coprecipitate was calcined in air at 650 ° C for 3 hours to form a powder of zirconium complex oxide of the aforementioned composition wherein Ce and La were contained as a solid solution. The mean grain size of the zirconium complex oxide powder was 6.1 μm (determined by laser scattering).

(Preparation of the catalyst)

Under Use of 50 g of zirconium complex oxide powder thus obtained was a catalyst prepared in Example 1 in the same manner.

[Example 4]

In this example, a catalyst was prepared using a zirconium complex oxide having the composition Zr _0.70 Ce _0.16 Al _0.06 Y _0.08 oxide.

(Preparation of zirconium complex oxide)

A zirconium complex oxide powder having the above composition was prepared in the same manner as in Example 3 except that 0.070 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.016 mol of cerium nitrate (Ce (NO ₃ ) ₃ · 6H ₂ O), 0.006 mol of aluminum nitrate (Al (NO _{3) 3} · 9H ₂ O) and 0.008 mol of yttrium nitrate (Y (NO _{3) 3} · 6H ₂ O) were used as the starting material. The zirconium complex oxide powder had a mean grain size of 7.0 μm (determined by laser scattering).

(Preparation of the catalyst)

Under Use of 50 g of zirconium complex oxide powder thus obtained was a catalyst prepared in the same manner as in Example 1.

[Example 5]

In this example, a catalyst was prepared using a zirconium complex oxide of composition Zr _0.70 Ce _0.10 Al _0.20 Oxide.

(Preparation of zirconium complex oxide)

A zirconium complex oxide powder of the above composition was prepared in the same manner as in Example 3 except that 0.70 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O), 0.010 mol of cerium nitrate (Ce (NO ₃ ) ₃ · 6H ₂ O) and 0.020 Mol of aluminum nitrate AL (NO ₃ ) ₃ .9H ₂ O) were used as the starting material. The zirconium complex oxide powder had a mean grain size of 7.3 μm determined by laser scattering).

(Preparation of the catalyst)

Under Use of 50 g of the zirconium complex oxide powder thus prepared For example, a catalyst was prepared in the same manner as in Example 1.

[Example 6]

In this example, a catalyst was prepared using a zirconium _complex oxide of composition Zr _0.80 Ce _0.20 Oxide.

(Preparation of zirconium complex oxide)

The zirconium complex oxide powder of the above composition was prepared in the same manner as in Example 3 except that 0.080 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O) and 0.020 mol of cerium nitrate (Ce (NO ₃ ) ₃ · 6H ₂ O) were used as the starting material. The zirconium complex oxide powder had a mean grain size of 6.3 μm (determined by laser scattering).

(Preparation of the catalyst)

Under Use of 50 g of the zirconium complex powder thus obtained became Catalyst in the same manner as in Example 1 produces.

[Example 7]

In this example, a catalyst was prepared using a zirconium complex oxide of composition Zr _0.09 Ce _0.10 oxide.

(Preparation of zirconium complex oxide)

Zirconium complex oxide powder of the above composition was prepared in the same manner as in Example Produced 3 except that 0.090 mol of zirconium oxychloride (ZrOCl ₂ · 8H ₂ O) and 0.010 mol of cerium nitrate (Ce (NO _{3) 3} · 6H ₂ O) were used as starting materials. The zirconium complex oxide powder had an average grain size of 7.8 μm (determined by laser scattering).

(Preparation of the catalyst)

Under Use of 50 g of zirconium complex oxide powder thus obtained was a catalyst in the same manner as in Example 1 submitted.

[Example 8]

In this example, the same zirconium complex oxide powder (composition: Zr _0.80 Ce _0.16 La _0.02 Nd _0.2 oxide, average grain size: 5.2 μm) was used as in Example 2 to prepare a slightly different catalyst, such as described below.

(Preparation of the catalyst)

50 z of the zirconium complex oxide powder (average particle size: 5.2 μm) were mixed with an aqueous Solution of Dinitrodiaminplatinnitrat (Pt content: 0.8 g) and an aqueous solution of rhodium nitrate (Rh content: 0.3 g). The so impregnated Powder was first 110 ° C for 12 hours dried and then at 500 ° C for 3 hours burned. As a result, the zirconium complex oxide carried 0.8 g of Pt and 0.3 Rh.

On the other hand, 75 g of cerium complex oxide powder of the composition Ce _0.6 Zr _0.3 Y _0.1 oxide was impregnated with an aqueous solution of dinitrodiammineplatinum nitrate (Pt content: 0.7 g). The impregnated cerium complex oxide powder was first dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours. As a result, the cerium complex oxide carried 0.7 g of Pt.

Subsequently, the two types of complex oxide powder were mixed with 130 g of a La-stabilized alumina powder (stabilized with La in a ball mill) and wet-crushed for 12 hours to give an aqueous mixture slurry. The mixture slurry was then coated with a monolithic cordierite honeycomb carrier having 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm. The thus coated honeycomb carrier was dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours. The desired catalyst was thus obtained.

[Example 9]

This example is the same as Example 7 with respect to the use of zirconium complex oxide of composition Zr _0.90 Ce _0.10 oxide, however, differs in that the amount of zirconium complex oxide was increased to 180 ° C to the alumina powder at the time to save the coating of the monolithic cordierite honeycomb carrier.

Comparative Example 1

To the Comparative was a catalyst using commercially available Zirconia powder with an average particle size of 7.6 μm (determined by laser scattering) instead of the zirconium complex oxide powder according to the invention produced according to the invention.

(Preparation of the catalyst)

50 zirconia powder was treated with an aqueous solution of dinitrodiamine platinum nitrate (Pt: 1.5 g) and an aqueous solution of rhodium nitrate (Rh content: 0.3 g). The impregnated Zirconia powder was initially at 110 ° C for 12 Dried hours and then fired at 500 ° C for 3 hours. As a result The zirconia powder carried 1.5 g of Pt and 0.3 g of Rh.

Then, the Pt and Rh supporting zirconia powder was mixed with 130 g of load-stabilized aluminum powder (stabilized by La in solid solution) and 75 g of cerium complex oxide powder, the composition Ce _0.6 Zr _0.3 Y _0.1 oxide in a ball mill, and blended for 12 Wet crushed hours, so that an aqueous mixture slurry resulted. The mixture slurry was then coated with a cordierite monolithic honeycomb carrier having 400 cells / in ² (62 cells / cm 2), a diameter of 105.7 mm and a length of 100 mm tet. The thus coated honeycomb carrier was dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours. In this way the desired catalyst was obtained.

Comparative Example 2

In Comparative Example 2, the same zirconium complex oxide powder (composition: Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 oxide, average grain size: 5.2 μm) was used as in Example 2, but Pt and Rh were obtained Alumina powder instead of zirconium complex oxide powder, as described below.

(Preparation of the catalyst)

130 g of a commercially available La-stabilized alumina powder (stabilized by La in solid solution) were with an aqueous solution of dinitrodiammineplatinum nitrate (Pt content: 1.5 g) and an aqueous solution of rhodium nitrate (Rh content: 0.3 g). The impregnated Alumina powder was first at 110 ° C for 12 Dried hours and then fired at 500 ° C for 3 hours. As a result The alumina powder carried 1.5 g of Pt and 0.3 g of Rh.

The Pt and Rh supporting alumina powder was then mixed with 50 g of the zirconium complex oxide powder (average particle size 5.2 μm) and 75 g of cerium complex oxide powder having a composition Ce _0.6 Zr _0.3 Y _0.1 Oxide in a ball mill and incubated for 12 Wet crushed hours, so that an aqueous mixture slurry was formed. The mixture slurry was then coated with a monolithic cordierite honeycomb carrier having 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm. The thus-coated honeycomb carrier was dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours. Thus, the aimed catalyst was obtained.

Comparative Example 3

In Comparative Example 3, the catalyst was prepared in the same manner as in Comparative Example 1 except that (1) the amount of the zirconia powder was reduced to 8 g, (2) 75 g of the cerium complex oxypowder was replaced by 40 g of a commercially available pure ceria powder (CeO ₂ ), (3) the applied amount of Rh was reduced to 0.15 g, and (4) the applied amount of Pt was reduced to 0.75 g.

Comparative Example 4

The Comparative Example 4 was consistent with Comparative Example 3 in terms coincide with the use of zirconium oxide powder with an average particle size of 7.6 μm, however, differed in the coating material Zirconia powder and the carrier material, on which Pt was applied as described below.

(Preparation of the catalyst)

6 g of the zirconium oxide powder were mixed with an aqueous solution of rhodium nitrate (Rh content: 0.15 g). The impregnated Zirconia powder was at 110 ° C first for 12 Dried hours and then fired at 500 ° C for 3 hours. As a result The zirconia powder carried 0.15 g of Rh.

77 g commercially available La-stabilized alumina powder (La stabilized in solid solution) with an aqueous solution of dinitrodiammineplatinum nitrate (Pt content: 0.75 g). The impregnated Alumina powder was first at 110 ° C for 12 Dried hours and then fired at 500 ° C for 3 hours. In the result the alumina powder carried 0.75 g of Pt.

The Rh-bearing zirconia powder and the Pt-carrying alumina powder were mixed with 40 g of commercially available pure ceria powder (CeO ₂ ) in a ball mill and wet-crushed for 12 hours to give an aqueous mixture slurry. The mixture slurry was then coated with a monolithic cordierite honeycomb carrier having 400 cells / in ² (62 cells / cm ² ), a diameter of 105.7 mm and a length of 100 mm. The thus coated honeycomb carrier was dried at 110 ° C for 12 hours and then fired at 500 ° C for 3 hours. Thus, the aimed catalyst was obtained.

[Assessment of the operation the catalysts]

The each according to Examples 1 to 9 and Comparative Examples 1 to 4 manufactured catalysts were in terms of their operation tested in the purification of exhaust gas.

(Aging conditions)

For the purpose of aging, each of the catalysts was mounted on a bench (4 cylinder) of a 4 liter V8 engine installed in a car and the engine exhaust gas was fed into the catalyst. Specifically, the in 1 cycle that lasted 60 seconds, repeats 3000 times for a total of 50 hours.

As in 1 As shown, the cycle included a stoichiometric section (0-40 sec.) with the engine set to run under feedback control with the supply of a stoichiometric air-fuel mixture (A / F = 14.6), so that the internal temperature of the catalyst was maintained at about 850 ° C. The stoichiometric section was followed by a fuel-rich section (40-44 seconds), with the engine running with fuel excess (A / F = 11.7) fed with feedback control off. The fuel-rich section was then followed by a temperature ramp-up section (44-56 sec.), With the engine continuing to supply excess fuel while the feedback control was continuously interrupted, but secondary air was introduced into the catalyst from outside the engine, with the excess of fuel flowing into it Catalyst should react, causing a temperature rise to a maximum of 1050 ° C was caused. The air-fuel mixture supplied to the motor / catalyst combination in this temperature rise section was slightly fuel lean (A / F = 14.8). The temperature rise section is followed by a fuel lean section (56-60 sec.) With the feedback control re-operating with respect to the engine, with the catalyst under continued supply of secondary air in a fuel lean condition (A / F = 18.0). remains.

The Temperature in the catalyst was monitored by a thermocouple, which in the honeycomb carrier added was.

(Method of evaluation)

To execution the above-described aging was the procedure for cleaning of the exhaust gas in each of the catalysts is evaluated in the following manner.

The engine was run with an air-fuel mixture continuously changing from a fuel-rich state to a fuel-lean state, and the resulting exhaust gas was introduced into the catalyst for removing harmful gases such as CO and NO _x . The CO or NO _x removal factors were measured to determine the CO NO _x removal cross point at which the CO removal rate coincides with the NO _x removal rate. The CO-NO _x removal crosspoint thus determined was used as an evaluation of the operation of the catalyst.

at In this test to evaluate the operation, the engine was without Mounting on a vehicle used and it was the temperature of the exhaust gas introduced in the catalyst 450 ° C. The air-fuel mixture was engine with a space velocity of 90,000 / h with a A / F fluctuation of ± 1.0 fed.

(Results of the evaluation)

C.P.:

Kreuzungspunkt

Emb.:

Beispiel

C.E.:

Vergleichsbeispiel

ZCLN;

Zr_0,80Ce_0,16La_0,02Nd_0,02Oxid

ZCL:

Zr_0,80Ce_0,16La_0,04Oxid

ZCAY:

Zr_0,70Ce_0,06Al_0,06Y_0,08Oxid

ZCA:

Zr_0,80Ce_0,16La_0,02Nd_0,02Oxid

Z8C:

Zr_0,80Ce_0,20Oxid

Z9C:

Zr_0,90Ce_0,10Oxid

CZY:

Ce_0,6Zr_0,3Y_0,1Oxid

Table 1 shows the CO-NO _x removal crosspoint thus determined for each of the catalysts. The following abbreviations are used in the table:

CP:

intersection

Emb .:

example

CE:

Comparative example

ZCLN;

Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 oxide

ZCL:

Zr _0.80 Ce _0.16 La _0.04 oxide

ZCAY:

Zr _0.70 Ce _0.06 Al _0.06 Y _0.08 oxide

ZCA:

Zr _0.80 Ce _0.16 La _0.02 Nd _0.02 oxide

Z8C:

Zr _0.80 Ce _0.20 Oxide

Z9C:

Zr _0.90 Ce _0.10 oxide

CZY:

Ce _0.6 Zr _0.3 Y _0.1 oxide

Table 1

[Conclusion]

As can be seen from Table 1, the zirconium complex oxide in any one of Examples 1 to 9 exhibits a higher CO-NO _x removal crosspoint (determined after high-temperature aging) than those in Comparative Examples 1 to 4. That is, the zirconium complex oxide of the present invention While the selective coexistence of Pt and Rh on the particles of zirconium complex oxides slows grain growth of Pt at high temperature.

Farther lets in Comparison of Example 1 (wherein the average grain size of the zirconium complex oxide powder not more than 2 μm was) with Example 2 (wherein the average grain size is higher than 2 μm), recognize that the effectiveness of cleaning the exhaust with a Decrease of the mean grain size of the zirconium complex oxide powder increases. After all Examples 2 to 6 show that the substitution of Zr by Al and / or a rare earth element (for example La, Y, Nd) in solid solution also an improvement in the mode of action for cleaning the Gets exhaust.

It follows that an inventive catalyst with advantage in the range of an outlet Krümmers can be accommodated and provides a good catalytic activity even at high temperatures.

Claims (10)

A catalyst for exhaust gas purification comprising: a heat-resistant carrier; Particles of a zirconium complex oxide of the following formula Zr _{1- (x + y)} Ce _x R _y O _{2 -z} , wherein "R" represents at least one element selected from a group consisting of Al and rare earth elements other than Ce, "z" represents the degree of oxygen deficiency determined by the valence and content of the contained Al and / or rare earth element , 0.1 ≤ x + y ≤ 0.5, 0.1 ≤ x ≤ 0.5 and 0 ≤ y ≤ 0.2; a combination of Pt and Rh and particles of an oxygen-storing complex oxide of a rare earth element, which are different from the zirconium complex oxide particles; wherein the zirconium complex oxide particles are coated on the heat-resistant support together with the oxygen-storing complex oxide particles, characterized in that the combination of Pt and Rh is carried on the zirconium complex oxide particles. Catalyst according to claim 1, wherein the zirconium complex oxide particles on the heat-resistant carrier together with the oxygen-storing complex oxide particles and particles a heat-resistant inorganic Oxyds applied to the heat-resistant support are, where the combination of Pt and Rh optionally only on the Zirconium complex oxide particles is carried. Catalyst according to claim 1 or 2, wherein the zirconium complex oxide the conditions 0.2 ≤ x + y ≤ 0.3, 0.1 ≤ x ≤ 0.28 and 0.02 ≤ y ≤ 0.2 in the Formula fulfilled. A catalyst according to any one of claims 1 to 3, wherein R in the Formula either La alone, Al alone, a combination of La and Nd or a combination of Al and Y is. Catalyst according to one of claims 1 to 4, wherein at least a part of the zirconium complex oxide is a solid solution. A catalyst according to any one of claims 1 to 5, wherein the particles of zirconium complex oxide has an average grain size of 0.1 to about 2 microns exhibit. A catalyst according to any one of claims 1 to 6, wherein the oxygen storing oxide of rare-earth metal, cerium oxide or a cerium complex oxide is. A catalyst according to any one of claims 1 to 7, wherein the particles of the oxygen-storing oxide Pd. A catalyst according to any one of claims 2 to 8, wherein the heat-resistant inorganic Oxyd selected from a group is made of aluminum oxide, silica, titanium dioxide and magnesium oxide consists. A catalyst according to any one of claims 1 to 9, wherein the heat-resistant support is a Honeycomb structure has.