JP2005224792A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a decrease in specific surface area and keep an OSC performance by suppressing a phase change (a phase transition) of Al<SB>2</SB>O<SB>3</SB>when a catalyst is exposed to a high-temperature exhaust gas while improving the exhaust gas cleaning performance with a part of the catalyst metal metallized by devising a composition of a support material in relation to the catalyst for cleaning the exhaust gas which is supported by the support material containing Al<SB>2</SB>O<SB>3</SB>, CeO<SB>2</SB>and ZrO<SB>2</SB>. <P>SOLUTION: In a three-way catalyst the support material of which based on a compound oxide containing Al, Ce, Zr, Y and La carries Pd, a ratio B/A for a total of Ce, Zr, Y and La atom molar number B against Al atom molar number A is more than 1/48 and less than 1/10, a part of Pd is metallized and the residual is oxided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purifying catalyst for automobiles.

A three-way catalyst that simultaneously purifies HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas of automobiles. Porous oxide (Al ₂ O ₃ ) and composite oxide (( _{al 2 O 3) a (CeO} 2) b (ZrO 2) 1-b (Y 2 O 3) c (La 2 O 3) d, where, to d are molar ratios, a = 0.4 to 2.5, a support material made of a mixed powder of b = 0.2 to 0.7, c = 0.01 to 0.2, d = 0.005 to 0.1) is washed on the honeycomb carrier together with a binder, and Pt and Rh are supported as catalyst noble metals on the coating layer Is known (see Patent Document 1). That is, this is intended to improve the durability of the catalyst by preventing the coating layer from peeling even under the harsh conditions of heating to a temperature of 1000 ° C. for about 10 to 20 hours.

Similarly, a three-way catalyst is known in which a honeycomb-shaped composite oxide is coated on a honeycomb carrier and Pt and Rh are supported on the coating layer (see Patent Document 2). In the composite oxide, for example, Al ₂ O ₃ and ZrO ₂ , Y ₂ O _3, or La ₂ O ₃ form a shell, and CeO ₂ fine particles are held in an island shape on Al ₂ O ₃ . . This is because the thermal stability of Al ₂ O ₃ is improved by ZrO ₂ , Y ₂ O ₃ or La ₂ O ₃ , and CeO ₂ fine particles are dispersed in the shape of islands in Al ₂ O ₃ and retained. This suppresses the grain growth when exposed to the exhaust gas, and maintains its performance (Oxygen Storage Component) as an OSC (Oxygen Storage Component).
JP 2000-271480 A JP 2002-248347 A

An object of the present invention relates to an exhaust gas purification catalyst in which a catalyst metal is supported on a support material containing Al ₂ O ₃ , CeO _2, and ZrO _2. While suppressing the phase change (phase transition) of Al ₂ O ₃ when this catalyst is exposed to high-temperature exhaust gas while preventing the reduction of specific surface area The purpose is to maintain the OSC ability.

  The present invention addresses such problems by forming a support material from a composite oxide containing Al, Ce, Zr, Y, and La, and the amount of Al, Ce, Zr, Y, and La in the support material. It adjusted so that it might become a predetermined atomic molar ratio.

That is, the present invention is an automobile exhaust gas purification catalyst having a honeycomb-shaped carrier and at least one catalyst layer formed on the carrier,
The catalyst layer includes a composite oxide-based support material containing Al, Ce, Zr, Y, and La, and a catalyst metal supported on the support material,
The ratio B / A of the total atomic mole number B of Ce, Zr, Y and La to the Al atomic mole number A in the support material is not less than 1/48 and not more than 1/10.
A part of the catalyst metal is in a metal state (simple substance), and the rest is in an oxide state.

  With such a configuration, even after the catalyst is exposed to high-temperature exhaust gas, the light-off performance relating to the purification of HC, CO, and NOx is high, and a high purification rate can be obtained even at a high temperature.

That is, in the support material, when Al, Ce, Zr, Y, and La are in an atomic molar ratio as described above, Al ₂ O ₃ constitutes matrix particles, and Ce, Zr, Y is formed on the surface and inside of the matrix particles. In addition, oxides of La and La and composite oxides in which two or more of these elements are combined are dispersed in a minute form, and Ce, Zr, and the like in a metallic state may be dispersed in a minute form.

For this reason, the phase change of Al ₂ O ₃ when the catalyst is exposed to high-temperature exhaust gas is suppressed, and the decrease in the specific surface area of the catalyst is reduced. Therefore, the catalyst metal is maintained in a highly dispersed state, and the exhaust gas comes into good contact with the catalyst metal, which is advantageous for purification. Further, CeO ₂ or a composite oxide of CeO ₂ and ZrO ₂ works as OSC, and when the air-fuel ratio of the automobile engine fluctuates from the stoichiometric air-fuel ratio to the lean side or the rich side, it stores or releases oxygen, A reduction in the purification performance of HC, CO and NOx is suppressed.

Thus, CeO ₂ acting as the OSC, or a complex oxide of CeO ₂ and ZrO ₂ is dispersed in a fine form in the matrix, so that sintering when exposed to high-temperature exhaust gas is prevented. This prevents the OSC ability from decreasing. As a result, excellent light-off performance and high-temperature purification performance are maintained, and the catalytic metal in the metal state and the catalytic metal in the oxide state are mixed, so that HC, CO and NOx can be purified. This is advantageous, particularly for NOx purification.

  Regarding the above support material, La is supported later on the composite oxide containing Al, Ce, Zr and Y as a component even when La forms a composite oxide together with Al, Ce, Zr and Y. It may be what was done.

  Preferably, the ratio of the atomic mole number of Ce and Zr in the total atomic mole number B of Ce, Zr, Y and La is 75% or more and 95% or less. That is, the Ce and Zr oxides act as OSCs useful for the three-way catalyst as described above, and increase the amount of Ce and Zr in order to improve this performance.

  It is preferable that the catalytic metal is Pd. This is advantageous in efficiently purifying HC, CO, and NOx since the exhaust gas temperature is relatively low, and is particularly advantageous in purifying NOx due to the mixture of Pd and PdO.

It is preferable that an atomic molar ratio Pd / La of Pd to La of the support material is 3/5 or more and 9/5 or less. That is, Pd is an oxide simply by being supported on Al ₂ O ₃ , but if La ₂ O ₃ is adjacent, it is easy to maintain a metallic state. Thus, when the Pd / La atomic molar ratio is set as described above, it is advantageous to appropriately mix Pd and PdO on the support material, and particularly for purification of HC, CO and NOx, This is advantageous for NOx purification.

In order to make Pd and La ₂ O ₃ adjacent to each other, it is preferable that a composite oxide containing Al, Ce, Zr, and Y is added to a Pd—La composite colloidal particle (Pd and La together to form a dispersant). It is impregnating and firing a colloidal solution in which colloidal particles surrounded) are dispersed.

That is, preferably, the support material is formed by impregnating a complex oxide containing Al, Ce, Zr, and Y with a solution containing La and firing, and the Al, Ce, Zr, and Y are contained in the support material. The composite oxide containing and La ₂ O ₃ are united,
The solution containing La is a colloid solution in which the Pd—La composite colloidal particles are dispersed,
The Pd is supported on the support material adjacent to the La ₂ O ₃ by the firing.

As a result, the Pd and the La ₂ O ₃ are surely adjacent to each other and the metal Pd and PdO are mixed.

Preferably, the atomic molar ratio Ce / Zr of Ce to Zr is from 1/9 to 9/1. That is, CeO ₂ has an excellent function as OSC, but it has low heat resistance. On the other hand, when a composite oxide of CeO ₂ and ZrO ₂ is used, the heat resistance is improved without significantly reducing the OSC ability. Thus, by setting the Ce / Zr atomic molar ratio within the above range, an OSC having high heat resistance is obtained. More preferably, the atomic molar ratio is made close to 1/1, for example, 1/2 or more. 2/1 or less.

It is preferable that at least Ce and Zr are dispersed in the Al ₂ O ₃ particles of the support material after being heated to a temperature of 1100 ° C. for 24 hours in an air atmosphere, and on the surface of the Al ₂ O ₃ particles, CeO ₂ , ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and a composite oxide containing two or more of these four types of oxides are dispersed and Pd metal and PdO are dispersed. It is appearing.

That is, Ce and Zr are dispersed in the Al ₂ O ₃ particles even after being heated to a temperature of 1100 ° C. for 24 hours in an air atmosphere, which means that the phase change of the Al ₂ O ₃ particles is suppressed. This means that the specific surface area is kept relatively large. Therefore, a large specific surface area is ensured even when exposed to a higher temperature exhaust gas, and a large decrease in exhaust gas purification performance is prevented.

In addition, CeO ₂ being dispersed on the surface of Al ₂ O ₃ particles means that the CeO ₂ is not very sintered even when exposed to high-temperature exhaust gas, and the OSC is not lowered. Further, by the Al ₂ O ₃ particles surface La ₂ O ₃ is present in a dispersed, exist Pd metal and Pd oxide in said Al ₂ O ₃ particles surface are dispersed, is exposed to high-temperature exhaust gas This means that three-way purification performance, particularly NOx purification performance, is ensured even after.

The above-mentioned “composite oxide containing two or more of the four oxides” is a composite oxide of CeO ₂ and ZrO ₂ or a composite oxide of CeO ₂ , ZrO ₂ and Y ₂ O ₃ . , A composite oxide of CeO ₂ , ZrO ₂ , Y ₂ O ₃ and La ₂ O ₃ .

Further, the present invention is an automobile exhaust gas purification catalyst having a honeycomb-shaped carrier, an inner catalyst layer formed on the carrier, and an outer catalyst layer formed on the inner catalyst layer,
The outer catalyst layer has active Al ₂ O ₃ on which a catalyst noble metal is supported, an oxygen storage material on which Rh is supported, and a ZrO ₂ coated Al ₂ O ₃ on which Rh is supported,
The inner catalyst layer includes a composite oxide-based support material containing Al, Ce, Zr, Y, and La, and a catalyst metal supported on the support material. The ratio B / A of the atomic mole number B of Ce, Zr, Y and La in total is 1/48 or more and 1/10 or less, part of the catalyst metal is in the metal state, and the rest is in the oxide state It is characterized by being.

That is, the inner catalyst layer has the same structure as the catalyst layer of the invention described above. Therefore, the phase change of Al ₂ O ₃ when the catalyst is exposed to high-temperature exhaust gas is suppressed, and the catalyst ratio is reduced. Reduced surface area and prevents sintering of CeO ₂ acting as OSC and complex oxides of CeO ₂ and ZrO _2, and mixed catalyst metal in metal state and catalyst metal in oxide state Therefore, even when used under severely thermal conditions, excellent light-off performance and high-temperature purification performance are maintained over a long period of time with respect to purification of HC, CO, and NOx.

On the other hand, in the outer catalyst layer, HC, CO, and R are supported by the noble metal supported on the active Al ₂ O ₃ having a large specific surface area and the Rh supported on the oxygen storage material and the ZrO ₂ coated Al ₂ O ₃ respectively. NOx is efficiently purified.

ZrO ₂ -coated Al ₂ O ₃ is obtained by fixing a large number of ZrO ₂ particles on the surface of Al ₂ O ₃ particles and covering the surface, and Rh is supported on the ZrO ₂ particles. Accordingly, since ZrO ₂ is interposed between the Rh and Al ₂ O _3, contact between the Rh and Al ₂ O ₃ is limited, even when exposed to high-temperature exhaust gas, Rh is Al ₂ O ₃ It is suppressed that it dissolves in the solution. Therefore, the exhaust gas purification performance is reduced less, that is, the exhaust gas purification performance is ensured without increasing the Rh carrying amount, and the cost can be reduced by reducing the Rh carrying amount.

Further, in a system in which Rh is supported on ZrO ₂ coated Al ₂ O ₃ , when moisture (H ₂ O) is present in the exhaust gas, steam (H ₂ ) is generated from this H ₂ O and HC. The forming reaction is promoted. The highly active hydrogen (H ₂ ) generated by this steam reforming reaction reduces the catalytic noble metal such as Rh, Pd, Pt and the like from the oxide state, so that the catalytic activity is increased and the catalyst temperature is increased. High purification performance can be obtained from a low level, and further reduction of NOx by the hydrogen (H ₂ ) occurs, which is advantageous for exhaust gas purification.

Further, since Rh is supported on the oxygen storage material, the NOx is higher at the time when the air-fuel ratio fluctuates than when Rh is directly supported on Al ₂ O ₃ , especially during engine acceleration (rich time). Purification performance can be obtained.

The mass ratio of the ZrO ₂ -coated Al ₂ O ₃ is preferably ZrO ₂ / Al ₂ O ₃ = 5/95 to 15/85, and the mass ratio is ZrO ₂ / Al ₂ O ₃ = 1 / 9 is preferred.

As described above, according to the present invention, the catalyst layer of the honeycomb-shaped carrier includes Al, Ce, Zr, Y, and La, and the atomic molar ratio of (Ce, Zr, Y, La total) / (Al) is Since the catalyst metal is partly in a metal state and the rest is in an oxide state and is supported on a composite oxide-based support material that is 1/48 or more and 1/10 or less, the catalyst is exhausted at a high temperature. The phase change of Al ₂ O ₃ when exposed to gas is suppressed, and sintering of CeO ₂ or the like that acts as OSC is prevented. HC, CO and NOx can be efficiently purified by the catalytic metal in the oxide state, and excellent light-off performance and high-temperature purification performance are maintained over a long period of time.

  When the catalyst metal is Pd, it is advantageous for improving the light-off performance of the catalyst, and particularly for NOx purification.

  When the Pd / La atomic molar ratio is 3/5 or more and 9/5 or less, the metal Pd and PdO can be appropriately mixed on the support material, thereby improving the light-off performance of the catalyst. This is advantageous, particularly for NOx purification.

Moreover, according to the one in which a composite oxide containing Al, Ce, Zr and Y is impregnated with a colloidal solution in which La—Pd composite colloidal particles are dispersed and baked, Pd and La ₂ O ₃ are reliably adjoined. In this state, the metals Pd and PdO can be mixed, which is advantageous for improving the light-off performance of the catalyst, and particularly for purifying NOx.

When a complex oxide of CeO ₂ and ZrO ₂ is formed with a Ce / Zr atomic molar ratio of 1/9 or more and 9/1 or less, heat resistance can be improved while ensuring OSC ability.

After heating to a temperature of 1100 ° C. for 24 hours in an air atmosphere, at least Ce and Zr are dispersed in the Al ₂ O ₃ particles of the support material, and CeO ₂ , ZrO is present on the surface of the Al ₂ O ₃ particles. ₂ , Y ₂ O ₃ , La ₂ O ₃ and a composite oxide containing two or more of these four oxides appear dispersed, and Pd metal and Pd oxide appear dispersed. As long as it is used, excellent light-off performance and high-temperature purification performance can be maintained over a long period of time for purification of HC, CO, and NOx even when used under severely thermal conditions.

Further, the inner catalyst layer of the honeycomb-shaped carrier contains Al, Ce, Zr, Y, and La, and the atomic molar ratio of (Ce, Zr, Y, La total) / (Al) is 1/48 or more and 1/10. The composite oxide-based support material described below has a structure in which the catalyst metal is supported in a metal state and an oxide state, and the outer catalyst layer includes active Al ₂ O ₃ on which the catalyst noble metal is supported, Rh According to the structure having the oxygen storage material supporting Rh and the ZrO ₂ coated Al ₂ O ₃ supporting Rh, the HC, CO, and NOx are efficiently used even under severe thermal conditions. It is possible to purify well, and it is suppressed that Rh is dissolved in Al ₂ O ₃ , and excellent light-off performance and high-temperature purification performance are maintained over a long period, and it is advantageous for cost reduction. Become.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a multi-cylinder engine 1 of an automobile. Each cylinder (only one cylinder is shown) 2 of the engine 1 has a combustion chamber 4 provided with a spark plug 5, and an intake passage 6 and an exhaust passage 7 are connected to the combustion chamber 4. . A three-way catalyst 8 as an exhaust gas purification catalyst is disposed in the exhaust passage 7.

  FIG. 2 shows a part of the three-way catalyst 8 according to the embodiment of the present invention. The three-way catalyst 8 includes a honeycomb carrier 11 made of cordierite and a catalyst layer 12 formed on the inner surface of the pores of the carrier 11. As shown in FIG. 3, the catalyst layer has a two-layer structure of an inner catalyst layer 12 formed on the inner surface of the pores of the honeycomb carrier 11 and an outer catalyst layer 13 formed on the inner catalyst layer 12. Or three or more layers.

The catalyst layer 12 includes a catalyst component (hereinafter referred to as Pd / CZLYA) in which Pd as a catalyst metal is supported on a composite oxide support material containing Al, Ce, Zr, Y, and La, and an OSC material. And CeO ₂ and CeO ₂ —ZrO ₂ —Nd ₂ O ₃ composite oxide as a binder, and ZrO ₂ as a binder. A ratio B / A of Ce, Zr, Y, and La total atomic mole number B to Al atomic mole number A in the support material of Pd / CZLYA is not less than 1/48 and not more than 1/10, and Pd is partly It is in a metal state (single), and the balance is oxide PdO.

In addition, the catalyst layer 12 can employ only one of CeO ₂ and CeO ₂ —ZrO ₂ —Nd ₂ O ₃ composite oxide as the OSC material, or Pd / CZLYA without providing the OSC material. And a binder.

FIG. 4 schematically shows the state of the Pd / CZLYA after the catalyst is heated to a temperature of 1100 ° C. for 24 hours in an air atmosphere. Since Al, Ce, Zr, Y, and La have the above atomic molar ratio, Al ₂ O ₃ constitutes matrix particles in the support material, and Ce, Zr is formed on the surface and inside of the Al ₂ O ₃ particles. Y and La are dispersed in the form of fine particles in a metallic state, in the form of an oxide, or in the form of a composite oxide in which two or more of these elements are combined.

That is, in the example of FIG. _{4, Al 2 O 3 Ce,} Zr and Y are dispersed within the particles, the Al ₂ O ₃ particles _{surface, CeO 2, ZrO 2, Y} 2 O 3, La 2 O 3 and their A composite oxide containing two or more of the four oxides appears in a dispersed manner, and Pd (metal) and PdO (oxide) appear in a dispersed manner. Further, large particles in the _{figure, CeO 2, ZrO 2, Y} 2 O 3, CeO 2 -ZrO 2 composite oxide, ZrO ₂ -Y ₂ O ₃ composite oxide, CeO ₂ -Y ₂ O ₃ composite oxide Or CeO ₂ —ZrO ₂ —Y ₂ O ₃ composite oxide. Pd adjacent to La ₂ O ₃ is in a metallic state, and the others are PdO.

Outer catalytic layer 13, a Pt / active Al ₂ O ₃ component Pt is supported on the active Al ₂ O ₃ is a precious metal, Rh is supported on CeO ₂ -ZrO ₂ -Nd ₂ O ₃ composite oxide and _{Rh / CeO 2 -ZrO 2 -Nd 2} O 3 composite oxide component comprising, a Rh / ZrO ₂ coated Al ₂ O ₃ component comprising Rh is loaded on the ZrO ₂ coated Al ₂ O _3, ZrO as a binder material ₂ and contains. Here, in the Rh / CeO ₂ —ZrO ₂ —Nd ₂ O ₃ composite oxide component, the mass ratio is CeO ₂ / ZrO ₂ / Nd ₂ O ₃ = 20 to 25/65 to 70/5 to 15, preferably Is 23/67/10. In the Rh / ZrO ₂ -coated Al ₂ O ₃ component, the mass ratio is ZrO ₂ / Al ₂ O ₃ = 5/95 to 15/85.

<Method for producing the three-way catalyst shown in FIG. 2>
Pd / CZLYA of the catalyst layer 12 can be prepared by a hydrothermal synthesis method or a coprecipitation method.

-Hydrothermal synthesis method-
A slurry is prepared by mixing aluminum hydroxide powder with a solution of Ce, Zr, Y, and La acetates and Pd nitrate. This slurry is transferred to an autoclave and kept under pressure (0.98-1.37 MPa) at a temperature of 200 ° C. or higher and 220 ° C. or lower for 6 hours or longer and 48 hours or shorter (preferably held at a temperature of 200 ° C. for 24 hours). Hydrothermal treatment is performed to obtain slurry-like boehmite carrying Pd, Ce, Zr, Y and La. The metal-supported boehmite is washed with water and dried at a temperature of 150 ° C. to form a powder. This powder is heated and slowly heated over a period of 8 hours until it reaches a temperature of 200 ° C. to about 600 ° C., firing is performed at that temperature for 1 hour, and then pulverized to obtain Pd / CZLYA.

  As a solvent for the mixed solution of the acetate and Pd nitrate, a mixed solvent of water and butanediol or ethylene glycol may be used, and the ratio of the amount of butanediol or ethylene glycol may be 20% by volume or more and 40% by volume or less. preferable.

-Coprecipitation method-
The nitrates of Al, Ce, Zr, La and Y are mixed, water is added, and the mixture is stirred at room temperature for about 1 hour. The neutralization process which mixes this mixed solution and alkaline solution (preferably 28% ammonia water) is performed. This neutralization treatment is performed at room temperature or by heating to a temperature of about 80 ° C. When using a disperser for mixing at the time of neutralization, the rotational speed should be about 4000 rpm to 6000 rpm, the addition rate of the nitrate mixed solution should be about 53 mL / min, for example, and the addition rate of the alkaline solution should be about 3 mL / min, for example. Is preferred. The solution clouded by this neutralization is left for a whole day and night, and the resulting cake is centrifuged and washed thoroughly with water. The cake washed with water is dried at a temperature of about 150 ° C., and then fired and ground under the condition that it is held at a temperature of about 600 ° C. for about 5 hours and then held at a temperature of about 500 ° C. for 2 hours.

  Thereafter, a solution of palladium nitrate is added to the obtained powder and evaporated to dryness. The obtained dried product is pulverized and fired to obtain Pd / CZLYA.

  In the above coprecipitation method, a composite oxide containing Al, Ce, Zr, La and Y was obtained by coprecipitation, and then Pd was supported thereon, but Al, Ce, Zr and Y were contained. After the composite oxide (containing no La) is obtained by coprecipitation, La may be post-supported together with Pd. Further, the post-loading is not limited to the above evaporation / drying method, and an impregnation method may be adopted.

-Formation of catalyst layer 12-
The Pd / CZLYA, CeO ₂ , CeO ₂ —ZrO ₂ —Nd ₂ O ₃ composite oxide and zirconyl nitrate are mixed, water and nitric acid are added thereto, and the mixture is stirred with a disperser to obtain a slurry.

  The carrier 11 is coated on the carrier 11 by repeating the operation of immersing the carrier 11 in this slurry and pulling it up and removing excess slurry by air blow.

  Thereafter, the support 11 is heated at a constant heating rate from room temperature to 450 ° C. over 1.5 hours, and held at that temperature for 2 hours (drying / firing). The original catalyst is obtained.

<Method for producing the three-way catalyst shown in FIG. 3>
The three-way catalyst shown in FIG. 3 can be obtained by forming the catalyst layer 12 of the three-way catalyst shown in FIG. 2 as an inner catalyst layer and further forming an outer catalyst layer 13 thereon.

That is, a Pt / active Al ₂ O ₃ catalyst powder is obtained by adding a dinitrodiamine platinum nitrate aqueous solution dropwise to active Al ₂ O ₃ powder to which 5% by mass of La has been added, and drying and baking at 450 ° C.

Furthermore, nitric acid was added dropwise an aqueous solution of rhodium to CeO ₂ -ZrO ₂ -Nd ₂ O ₃ composite oxide, the _{Rh / CeO 2 -ZrO 2 -Nd 2} O 3 composite oxide catalyst powder by drying and baking at 450 ° C. obtain.

Further, a rhodium nitrate aqueous solution is dropped onto Al ₂ O ₃ on which Zr is supported, and dried and fired at 450 ° C. to obtain Rh / ZrO ₂ -coated Al ₂ O ₃ catalyst powder.

Then, a the Pt / active Al ₂ O ₃ catalyst powder, and _{Rh / CeO 2 -ZrO 2 -Nd 2} O 3 composite oxide catalyst powder, and Rh / ZrO ₂ coated Al ₂ O ₃ catalyst powder, and zirconyl nitrate Mix, add water and nitric acid to this, and mix and stir with a disperser to obtain a slurry.

  A predetermined amount of slurry is coated on the inner catalyst layer by immersing the carrier 11 on which the inner catalyst layer 12 is formed in this slurry and pulling it up and removing excess slurry by air blowing.

  Thereafter, the carrier 11 on which the coating has been performed is heated at a constant heating rate over 1.5 hours from normal temperature to 450 ° C., and held at that temperature for 2 hours (drying and firing). The outer catalyst layer 13 is formed.

<Effect of Al / (Ce + Zr + Y + La) atomic molar ratio>
Regarding Pd / CZLYA, each catalyst powder in which the atomic molar ratios of Al, Ce, Zr, Y and La constituting the support material were set as shown in Table 1 was prepared by the hydrothermal synthesis method. The amount of Pd was 1% by mass (mass% in Pd / CZLYA powder). For each catalyst powder, a slurry is prepared by mixing with a predetermined amount of zirconyl nitrate and water. A cordierite honeycomb carrier is dipped in the slurry and pulled up, and excess slurry is blown off, followed by firing at 500 ° C. for 2 hours. As a result, test catalysts A to F were obtained. The carrier has a diameter of 25.4 mm, a length of 50 mm, 400 cells per square inch (about 6.54 cm ² ), and a wall thickness of 6 mils (about 0.15 mm) separating adjacent cells. Therefore, the size of the carrier is about 25 mL. The supported amount of catalyst powder per liter of support is 100 g / L, and thus the supported amount of Pd is 1 g / L.

そうして、各供試触媒Ａ〜Ｆについて、大気雰囲気において１１００℃で２４時間保持する熱エージングを行なった後のライトオフ性能及び高温浄化性能を調べた（リグテスト）。

Thus, for each of the test catalysts A to F, the light-off performance and the high-temperature purification performance after thermal aging that was maintained at 1100 ° C. for 24 hours in an air atmosphere were examined (rig test).

The simulated exhaust gas is similar to the exhaust gas when the engine is operated at an air-fuel ratio A / F = 14.7 ± 0.9. Specifically, the main stream gas corresponding to the air-fuel ratio A / F = 14.7 is constantly flowed, and a predetermined amount of fluctuation gas is added in a pulse form at 1 Hz so that the A / F is ± 0. It was forcibly vibrated with an amplitude of 9. The composition of the main stream gas is as follows: CO ₂ : 13.9%, O ₂ : 0.6%, CO: 0.6%, H ₂ : 0.2%, C ₃ H ₆ : 0.056%, NO: 0.1%, H ₂ O: 10%, and the remaining N ₂ . The flow rate of the simulated exhaust gas into the three-way catalyst was 25 L / min (SV = 60000 h ⁻¹ ). Furthermore, as a gas for fluctuation, when A / F is swung to the lean side (A / F = 15.6), O ₂ is used, and when swung to the rich side (A / F = 13.9). Used H ₂ and CO.

  And T50 and C500 regarding purification | cleaning of HC, CO, and NOx were calculated | required about test catalyst AF. T50 gradually increases the simulated exhaust gas temperature from 100 ° C. to 500 ° C. at a rate of temperature increase of 30 ° C./min, and the concentration of the component (HC, CO or NOx) of the gas detected downstream of the test catalyst This is the catalyst inlet gas temperature (light-off temperature) at the time when the component concentration of the gas flowing into the test catalyst becomes half (when the purification rate becomes 50%). C500 is the purification rate of each component when the simulated exhaust gas temperature at the catalyst inlet is 500 ° C. The result of the light-off temperature T50 is shown in FIG. 5, and the result of the high temperature purification rate C500 is shown in FIG.

  Looking at the light-off temperature T50, the test catalysts B to E having an atomic molar ratio of Al / (Ce + Zr + La + Y) = 12 to 48 are low for any of HC, CO, and NOx. When the test catalyst A (the atomic molar ratio 4.8) is changed to the test catalyst B (the atomic molar ratio 12), the light-off temperature is relatively abruptly decreased, and the atomic molar ratio is 10. However, it is considered that a low light-off temperature is exhibited.

  Looking at the high temperature purification rate C500, there is no significant difference between the test catalysts A to F with respect to HC (both have a high purification rate of 98% or more), but with respect to CO and NOx, the atomic molar ratio Al / (Ce + Zr + La + Y) = 12 to 48 Each of the test catalysts B to E shows a relatively high purification rate. In particular, regarding NOx, between test catalyst A (the atomic molar ratio 4.8) and test catalyst B (the atomic molar ratio 12), test catalyst E (the atomic molar ratio 48) and the test catalyst. There is a clear difference between each of them with F (atomic molar ratio of 60).

  From the above, it can be said that when the atomic molar ratio Al / (Ce + Zr + La + Y) of Pd / CZLYA is set to 10 to 48, excellent light-off performance and high-temperature purification performance can be obtained.

<Effect of La atomic molar ratio>
In the test catalyst B, T50 and C500 after thermal aging when the La atom mole number per 120 Al atom moles was changed to 0, 0.8 and 1.6 are the above <Al / (Ce + Zr + Y + La) The measurement was performed in the same manner as in the section “Effect of atomic molar ratio> The size of the carrier is about 25 mL, the amount of catalyst powder supported per liter of carrier is 100 g / L, and the amount of Pd supported is 1 g / L. The result of T50 is shown in FIG. 7, and the result of C500 is shown in FIG. The horizontal axis “La (mol)” in FIGS. 7 and 8 represents the number of La atomic moles per 120 Al atomic moles.

  Looking at the light-off temperature T50, the La atomic molar ratio of 0.8 is the lowest for any of HC, CO, and NOx. Looking at the high temperature purification rate C500, there is no influence of the change in the La atomic molar ratio with respect to HC, but the purification rate tends to decrease as the La atomic molar ratio increases with respect to CO, and La atoms with respect to NOx. The highest is when the number of moles is 0.8.

When the La atomic mole number is 0.8, this is 1.7% by mass when converted to the La ₂ O ₃ amount, while the Pd amount is 1% by mass, so the mass number of La ₂ O ₃ is Assuming that the atomic weight of 326 and Pd is 106, the molar ratio of Pd / La atoms in this case is about 9/10. According to FIGS. 6 and 7, relatively good results are obtained at a La atom mole number of 0.4 to 1.2 (La ₂ O ₃ content = 0.85 to 2.54 mass%). When the Pd / La atomic molar ratio is about 6/10 or more and 18/10 or less, it can be seen that good results can be obtained with respect to light-off performance and high-temperature purification performance.

As described above, the best mode is the test catalyst B, and the number of La atoms in Table 1 in this best mode is preferably 0.4 to 1.2, and the number of Y atoms is preferably 0.2 to 0.4. In addition, when Al, Ce, Zr, La and Y constituting CZLYA of the best mode (test catalyst B) are expressed by mass% of their oxides, Al ₂ O ₃ = 80.3%, CeO ₂ = 10 0.4%, ZrO ₂ = 7.3%, La ₂ O ₃ = 1.7%, and Y ₂ O ₃ = 0.3%.

<Effect of Ce / Zr atomic molar ratio>
With respect to Pd / CZA containing no La and Y (a catalyst in which Pd as a catalyst metal is supported on a composite oxide-based support material containing Al, Ce and Zr), the Ce / Zr atomic molar ratio was changed. A test catalyst was prepared by the hydrothermal synthesis method described above, and T50 and C500 after thermal aging were measured by the same method as in the above <Effect of Al / (Ce + Zr + Y + La) atomic molar ratio>. The size of the carrier is about 25 mL, the amount of catalyst powder supported per liter of carrier is 100 g / L, and the amount of Pd supported is 1 g / L. The result of T50 is shown in FIG. 9, and the result of C500 is shown in FIG. The horizontal axis “Zr amount X (mol)” in FIGS. 9 and 10 represents the number of moles of atoms per 120 moles of Al atoms.

  The light-off temperature T50 is low when the Zr amount X is 1 to 9, and is particularly low when X = 5. Looking at the high-temperature purification rate C500, there is almost no effect of changes in the amount of X on HC, but for CO and NO, there is a peak near X = 5, and either X decreases or increases There is also a tendency for C500 to decrease.

  Therefore, good light-off performance and high-temperature purification performance can be obtained when the atomic molar ratio Ce / Zr of Ce to Zr is 1/9 or more and 9/1 or less, and particularly good results when Ce / Zr = 3-7. Can be obtained.

<XRD result of Pd / CZLYA>
FIG. 11 shows the result of structural analysis by XRD (X-ray diffraction) after subjecting the test catalyst B to the thermal aging. Three “◎” are CeO ₂ —ZrO ₂ composite oxides, two large “◯” are CeO ₂ and ZrO ₂ attached next to each, and three small thick lines “○”. Are both θ-Al ₂ O ₃ , two small thin lines “◯” are δ-Al ₂ O ₃ , “「 ”is Pd, and“ Δ ”is La ₂ O ₃ .

According to this, CeO ₂ , ZrO ₂ , La ₂ O ₃ and CeO ₂ —ZrO ₂ composite oxide, and Pd are present, and Al ₂ O ₃ stays in the phase change up to the θ phase, that is, It can be seen that the α phase having a small specific surface area does not change, and that a relatively large specific surface area is secured in spite of severe thermal aging. Note that the Y component is not shown in the diffraction result because it is a very small amount.

<Results of XAFS structural analysis of Pd / CZLYA>
Next, the results of structural analysis by XAFS (X-ray absorption fine structure) regarding the above Pd / CZLYA will be described.

  FIG. 12 shows a radial structure function around the Pd atom obtained by Fourier transforming the EXAFS signal. In the example of the figure, the test catalyst B (Pd / CZLYA) is subjected to the above thermal aging, and in the comparative example, Pd is supported on a heat stabilized alumina to which La is added.

The highest peak in the example represents a Pd atom (the Pd atom is adjacent to the Pd atom), and it can be seen that Pd is in a metal state (single element). On the other hand, in the comparative example, a peak indicating that Pd is in a metal state does not appear, and an O atom constituting PdO or a Pd atom of another PdO only appears as an adjacent atom. In the examples, it is considered that Pd is in a metal state due to the influence of La ₂ O ₃ .

FIG. 13 shows a “precursor” obtained by hydrothermal synthesis of the test catalyst B (Pd / CZLYA), “fresh” after drying / calcination (not subjected to thermal aging), and after thermal aging “ The radial structure function around Ce atoms analyzed by XAFS is shown for “after aging” and “CeO ₂ ” (standard sample).

“Precursor” and “fresh” have a generally flat distribution in which no peak appears clearly. This indicates that Ce atoms exist in an amorphous state (atoms and molecules), that is, no other element component exists around Ce atoms. On the other hand, in “after aging”, as in the standard sample “CeO ₂ ”, peaks indicating that Ce atoms and O atoms are adjacent atoms appear, and some Ce atoms are changed to oxides. You can see that

  FIG. 14 shows the radial structure function around the Zr atom analyzed by XAFS for “precursor”, “fresh” and “after aging”.

  In any of these three types of material states, a peak indicating that the adjacent atom is an O atom appears, indicating that Zr exists as an oxide. In all the material states, a peak appears in the vicinity of 3 mm, which is considered to be derived from the presence of Al atoms as adjacent atoms. However, as a result of measuring the same material by XRD, the peak of the Al—Zr—O solid solution does not appear (see FIG. 11), and the peak in the vicinity of 3Å simply has many Al atoms around the Zr atom. It can be estimated that this is shown. Thus, in “after aging”, the peak is large in the vicinity of 3 mm, and it can be said that new Zr—Al bonds are generated by thermal aging.

<Influence of Y addition>
FIG. 15 shows the test catalyst B (shown as “Y0.2 mol added” in FIG. 15) and Pd / CZLA synthesized in the same manner as the test catalyst B except that Y was not added ( FIG. 15 shows the result of structural analysis by XRD after performing the above thermal aging. In the case where Y is added, the ZrO ₂ peak is shifted, indicating that a complex oxide of Zr—Y is formed.

  From the above XAFS and XRD results (FIGS. 11 to 15), it can be said that the sample catalyst B has a form schematically shown in FIG.

<Effect of Y addition>
-T50, C500-
In the test catalyst B, T50 after thermal aging (maintained at a temperature of 1100 ° C. for 24 hours in an air atmosphere) when the number of moles of Y atoms per 120 moles of Al atoms is changed in the range of 0 to 1.6. And C500 were measured by the same method as in the above section <Effect of Al / (Ce + Zr + Y + La) atomic molar ratio>. The size of the carrier is about 25 mL, the amount of catalyst powder supported per liter of carrier is 100 g / L, and the amount of Pd supported is 1 g / L. The result of T50 is shown in FIG. 16, and the result of C500 is shown in FIG. Note that “mol” in the Y addition amount column of both figures represents the number of moles of Y atoms per 120 moles of Al atoms. Moreover, the data of FIG.16 and FIG.17 were obtained using another measuring apparatus similar to the measuring apparatus used for data preparation of FIG.5, FIG.6 etc., and there is no consistency with those data. .

  Looking at the light-off temperature T50, except that the T50 of CO when Y = 0 mol is low, T50 tends to decrease as the Y atomic molar ratio increases for any of HC, CO, and NOx. It can be seen. However, regarding NOx, there is no decrease in T50 when the number of moles of Y atoms increases to 0.8 and 1.6. On the other hand, looking at the high temperature purification rate C500, there is no influence of the change in the Y atom molar ratio with respect to HC. Regarding CO, the purification rate tends to increase as the Y atom molar ratio increases. The same tendency is observed with respect to NOx, but when the number of moles of Y atoms is 0.8 and 1.6, C500 is lower than when the number of moles of Y atoms is 0.3 and 0.4.

  From the above, when the number of moles of Y atoms per 120 moles of Al atoms is about 0.2 to 1.6, it is advantageous in improving the light-off performance of HC, CO, and NOx as a whole. It can be seen that a value of about 2 to 0.4 is advantageous in increasing the high temperature purification rate of NOx.

<Performance comparison between examples and comparative examples by coprecipitation method>
-Rigtest-
Example 1 Pd / CZLYA corresponding to the test catalyst B was prepared by the coprecipitation method described above (where Pd and La were post-supported). That is, a composite oxide containing Al, Ce, Zr and Y is produced by a coprecipitation method, a solution of palladium nitrate and lanthanum nitrate is added to the powder of this composite oxide, evaporated to dryness, and then the obtained dry oxide is obtained. Pd / CZLYA according to Example 1 was obtained by pulverizing and firing the solid matter.

  Example 2 Pd / CZLYA corresponding to the above test catalyst B was prepared by the coprecipitation method described above (however, only Pd was post-supported). That is, a composite oxide containing Al, Ce, Zr, La and Y is produced by a coprecipitation method, a palladium nitrate solution is added to the powder of this composite oxide, and evaporated to dryness. Was pulverized and heated and fired to obtain Pd / CZLYA according to Example 2.

  Example 3: Pd colloidal solution containing Al, Ce, Zr, La and Y similar to Example 2 was impregnated with Pd colloid solution, dried and fired to obtain Pd according to Example 3. / CZLYA was obtained. The Pd colloid solution will be described later.

  Example 4: The same composite oxide powder containing Al, Ce, Zr, and Y as in Example 1 was impregnated with a Pd—La composite colloid solution, followed by drying and firing. Pd / CZLYA was obtained.

  The Pd-La complex colloid solution was prepared by the procedure shown in FIG. That is, a solution in which 5.8 g of a metal Pd nitric acid solution (Pd concentration: 4.332% by mass) and 0.91 g of lanthanum nitrate were dissolved in 10 g of ion-exchanged water was prepared. 100 g of solution A was prepared. The atomic molar ratio Pd / La in this A liquid is 2.4 / 2.7. Moreover, 1.86g of polyvinylpyrrolidone as a dispersing agent was weighed, and the B liquid which added ion-exchange water to this and made the whole quantity to 100g was prepared.

  The A liquid and B liquid were mixed, 50 g of ethanol was added thereto, and the mixture was stirred at room temperature for 30 minutes. After stirring, the mixed solution was refluxed at 90 ° C. for 3 hours, heated to a temperature of 100 ° C. or higher, and concentrated to a total amount of 20 g to obtain the Pd—La composite colloid solution.

  FIG. 19 shows Pd—La composite colloidal particles of the obtained colloid solution. Pd and La are surrounded by a dispersant to form micelles.

  The Pd colloidal solution was also prepared in the same manner as the Pd-La composite colloidal solution except that the solution A was a solution containing only palladium nitrate.

  T50 and C500 after thermal aging (maintained at a temperature of 1100 ° C. for 24 hours in air) for Examples 1 to 4 and Comparative Example (Pd supported on heat-stabilized alumina to which La was added) Was measured by the same method as in the above section <Effect of Al / (Ce + Zr + Y + La) atomic molar ratio>. In each of Examples 1 to 4 and the comparative example, the size of the carrier is about 25 mL, the amount of catalyst powder supported per liter of carrier is 100 g / L, and the amount of Pd supported is 1 g / L. The result of T50 is shown in FIG. 20, and the result of C500 is shown in FIG.

  Looking at the light-off temperature T50 in FIG. 20, Examples 1 and 2 are not much different except that T50 of Example 2 is slightly higher with respect to CO, but T50 is higher than that of the comparative example with respect to HC and NOx. It is low. Next, looking at Examples 3 and 4 using a colloidal solution, T50 is lower than Examples 1 and 2 and the comparative example for any of HC, CO and NOx.

  Looking at the high temperature purification rate C500 in FIG. 21, there is no significant difference between the example and the comparative example with respect to HC, but with respect to CO and NOx, the example has a higher purification rate than the comparative example. The purification rates of Examples 3 and 4 using the colloidal solution are high.

As described above, the examples show better results than the comparative examples because of suppression of phase change of Al ₂ O ₃ , suppression of sintering of OSC material, and metallization of Pd by La ₂ O ₃ This is considered to be due to the effect of.

  Example 3 using a Pd colloid solution shows better results than Example 2 using a palladium nitrate solution because Pd became colloidal particles, and thus its dispersibility was improved. This is thought to be due to the high dispersion of Pd in the support material. In addition, Example 4 using the Pd-La composite colloid solution shows a better result than Example 3 in the state where Pd is adjacent to La in addition to the effect of high dispersion of Pd. This is considered to be because the Pd was easily supported in a metal state by being supported by the support material.

-Engine bench test-
Pd / CZLYA corresponding to the test catalyst B was prepared by the coprecipitation method of Example 1 described above (Pd and La are post-supported), and this Pd / CZLYA was used to form a two-layer coat shown in FIG. A three way catalyst was formed. That is, the three-way catalyst in this embodiment, Pd / CZLYA inner catalyst layer is constituted by _{CeO 2, CeO 2 -ZrO 2 -Nd} 2 O 3 composite oxide and a binder (ZrO _2), an outer catalyst layer Pt / Active Al ₂ O ₃ , Rh / CeO ₂ —ZrO ₂ —Nd ₂ O ₃ composite oxide, Rh / ZrO ₂ coated Al ₂ O ₃ and binder (ZrO ₂ ).

  Further, as a comparative example, instead of Pd / CZLYA in the above example, a heat-stabilized alumina to which La was added was supported by Pd, and the rest of the three-layer coating was the same as in the example. The original catalyst was formed.

  About the said Example and a comparative example, after performing acceleration / deceleration endurance driving | operation (catalyst temperature of 980 degreeC) for 100 hours by engine bench test, it is per 1 mile (1.6093km) in FTP (US exhaust measurement driving mode) total. HC, CO and NOx emissions were measured.

  The result is shown in FIG. Regarding HC, there is no great difference between the example and the comparative example, but regarding the CO and NOx, the example has a smaller emission amount.

  Therefore, according to the present invention, it can be seen that the heat resistance of the catalyst is improved and good light-off performance and high-temperature purification performance can be maintained even after the catalyst has been exposed to high-temperature exhaust gas for a long time. .

It is a figure which shows the structure of the engine of a motor vehicle. It is sectional drawing which shows a part of catalyst for exhaust gas purification. It is sectional drawing which shows a part of other example regarding the catalyst for exhaust gas purification | cleaning. It is a figure which shows typically the state after the heat aging of the catalyst which concerns on this invention. It is a graph which shows the influence which Al / (Ce + Zr + La + Y) atomic molar ratio of the Example catalyst by a hydrothermal synthesis method has on T50. It is a graph which shows the influence which Al / (Ce + Zr + La + Y) atomic molar ratio of the catalyst has on C500. It is a graph which shows the influence which La amount of the catalyst has on T50. It is a graph which shows the influence which La amount of the catalyst has on C500. It is a graph which shows the influence which the amount of Zr has on T50 in the catalyst which carry | supported Pd on the Al-Ce-Zr complex oxide. It is a graph which shows the influence which the amount of Zr has on C500 in the catalyst which carry | supported Pd on the Al-Ce-Zr complex oxide. It is a figure which shows the XRD analysis result of an Example catalyst. It is a figure which shows the radial structure function around Pd atom by XAFS of an example catalyst and a comparative example catalyst. It is a figure which shows the radial structure function around the Ce atom by XAFS of each of the precursor of an Example catalyst, fresh and after thermal aging, and CeO ₂ (standard sample). It is a figure which shows the radial structure function around the Zr atom by the XAFS of each of the precursor of an Example catalyst, fresh and after thermal aging. It is a figure which shows the XRD analysis result of Zr-Y complex oxide and Zr oxide. It is a graph which shows the influence which Y amount of an Example catalyst has on T50. It is a graph which shows the influence which Y amount of the catalyst has on C500. It is process drawing which shows the preparation method of Pd-La composite colloidal particle. It is a figure which shows typically a Pd-La composite colloid particle. It is a graph which shows the T50 measurement result of an Example catalyst and a comparative example catalyst. It is a graph which shows the C500 measurement result of an Example catalyst and a comparative example catalyst. It is a graph which shows the total discharge | emission amount in the FTP mode of the Example catalyst of a 2 layer coat, and a comparative example catalyst.

Explanation of symbols

1 Engine 8 Three-way catalyst 11 Support 12 Catalyst layer (inner catalyst layer)
13 Outer catalyst layer

Claims (6)

An automobile exhaust gas purification catalyst having a honeycomb-shaped carrier and at least one catalyst layer formed on the carrier,
The catalyst layer includes a composite oxide-based support material containing Al, Ce, Zr, Y, and La, and a catalyst metal supported on the support material,
The ratio B / A of the total atomic mole number B of Ce, Zr, Y and La to the Al atomic mole number A in the support material is not less than 1/48 and not more than 1/10.
An exhaust gas purifying catalyst characterized in that a part of the catalyst metal is in a metal state and the rest is in an oxide state. In claim 1,
An exhaust gas purifying catalyst, wherein the catalyst metal is Pd, and an atomic molar ratio Pd / La of Pd to La of the support material is 3/5 or more and 9/5 or less. In claim 2,
The support material is formed by impregnating a complex oxide containing Al, Ce, Zr, and Y with a solution containing La and firing.
The solution containing La is a colloidal solution in which colloidal particles in which Pd and La are combined and surrounded by a dispersing agent are dispersed,
The exhaust gas purifying catalyst, wherein the Pd is supported on the support material adjacent to the La by the firing. In any one of Claims 1 to 3,
An exhaust gas purifying catalyst, wherein an atomic molar ratio Ce / Zr of Ce to Zr is 1/9 or more and 9/1 or less. In any one of Claims 1 thru | or 4,
When heated to a temperature of 1100 ° C. for 24 hours in an air atmosphere, at least Ce and Zr are dispersed in the Al ₂ O ₃ particles of the support material, and CeO ₂ , ZrO ₂ is present on the surface of the Al ₂ O ₃ particles. , Y ₂ O ₃ , La ₂ O ₃ and a composite oxide containing two or more of these four oxides appear dispersed, and Pd metal and Pd oxide appear dispersed. An exhaust gas purifying catalyst characterized by that. An automobile exhaust gas purification catalyst having a honeycomb-shaped carrier, an inner catalyst layer formed on the carrier, and an outer catalyst layer formed on the inner catalyst layer,
The outer catalyst layer has active Al ₂ O ₃ on which a catalyst noble metal is supported, an oxygen storage material on which Rh is supported, and a ZrO ₂ coated Al ₂ O ₃ on which Rh is supported,
The inner catalyst layer includes a composite oxide-based support material containing Al, Ce, Zr, Y, and La, and a catalyst metal supported on the support material. The ratio B / A of the atomic mole number B of Ce, Zr, Y and La in total is 1/48 or more and 1/10 or less, part of the catalyst metal is in the metal state, and the rest is in the oxide state An exhaust gas purifying catalyst, characterized in that it exists.

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