JP2011167631A - Osc material-containing catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas further improved in the exhaust gas cleaning performance, among various exhaust gas cleaning catalysts proposed containing a ceria/zirconia (CeO<SB>2</SB>-ZrO<SB>2</SB>) composite oxide as the OSC material. <P>SOLUTION: The catalyst for cleaning exhaust gas has the OSC material disposed in a preceding stage and a rear stage of the catalyst. The absorbing/discharging speed of the OSC material disposed in the preceding stage is faster than that of the OSC material disposed in the rear stage. A ratio Ra/Rb of the particle size (Ra) of the OSC material disposed in the preceding stage and the particle size (Rb) of the OSC material disposed in the rear stage is less than 1.0. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst including an OSC material (oxygen storage / release material) used in an exhaust gas purification catalyst for purifying exhaust gas from an internal combustion engine or the like.

Conventionally, a three-way catalyst that simultaneously performs oxidation of carbon monoxide (CO) and hydrocarbon (HC) and reduction of nitrogen oxides (NO _x ) has been used as an exhaust gas purification catalyst for automobiles. As such a catalyst, a catalyst in which a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported on a porous oxide carrier such as alumina (Al ₂ O ₃ ) is widely known. Yes. CO by the action of the three-way catalyst, for purifying simultaneously and efficiently three components of HC and NO _x, the air / fuel ratio to be supplied to the vehicle engine (air-fuel ratio A / F) the stoichiometric air-fuel ratio ( It is important to control in the vicinity.

  However, since the actual air-fuel ratio fluctuates to the rich (excess fuel atmosphere) side or lean (fuel lean atmosphere) side with the stoichiometric centering on the driving conditions of the automobile, etc., the exhaust gas atmosphere is also on the rich side or lean side as well. fluctuate. Therefore, it is not always possible to ensure high purification performance with only a three-way catalyst. Therefore, in order to absorb the fluctuation of the oxygen concentration in the exhaust gas and enhance the exhaust gas purification ability of the three-way catalyst, oxygen is stored when the oxygen concentration in the exhaust gas is high, and oxygen is released when the oxygen concentration in the exhaust gas is low. In other words, a material having a so-called oxygen absorption / release capacity is used in an exhaust gas purifying catalyst.

As such an OSC material (oxygen storage / release material), for example, a material based on ceria (CeO ₂ ) such as ceria (CeO ₂ ) or ceria-zirconia (CeO ₂ —ZrO ₂ ) composite oxide is known. Has been widely used. However, in order to achieve stable purification of exhaust gas, an oxygen storage / release material having a higher oxygen storage / release capacity is required and studied.

One of the problems of Patent Document 1 (Japanese Patent Laid-Open No. 2009-019537) is to efficiently absorb the fluctuation of the air-fuel ratio A / F of the exhaust gas and increase the exhaust gas purification rate. As means for solving this problem, “the upstream catalyst includes Rh / OSC in which Rh is supported on OSC material particles, and the downstream catalyst includes Rh / OSC in which Rh is supported on particles in OSC material, An exhaust gas purifying apparatus, characterized in that the upstream OSC particles have a better responsiveness to absorb and release oxygen in response to A / F fluctuations than that of the downstream OSC particles. It is disclosed. More specifically, the OSC material is made of a composite oxide containing Zr and Ce, _{ZrO 2} / CeO 2 weight ratio of the upstream OSC material than the _ZrO 2 / CeO ₂ weight ratio of the downstream OSC material It is characterized by being large. Patent Document 1 focuses on the ZrO ₂ / CeO ₂ mass ratio, but does not describe the particle size of the catalyst particles at all.

  The problem of Patent Document 2 (Japanese Patent Laid-Open No. 2008-68225) is that an exhaust gas discharged from an internal combustion engine of an automobile is brought into contact with a catalyst, and even when the hydrocarbon concentration fluctuates, an excellent purifying ability for nitrogen oxides is obtained. An object is to provide a catalyst system used in an exhaust gas purifying apparatus for automobiles, an exhaust gas purifying apparatus using the catalyst system, and an exhaust gas purifying method. As a means for solving this problem, “a catalyst system using two or more exhaust gas purification catalysts including a first catalyst supported on an inorganic structure carrier and a second catalyst different from the first catalyst, When the first catalyst is disposed in the exhaust gas passage, the first catalyst is carried on the portion of the inorganic structure carrier located on the upstream side, while the second catalyst is located on the downstream side when disposed in the exhaust gas passage. A cerium-zirconium based composite oxide (A) obtained by supporting an inorganic structure carrier to be supported and heating and melting the raw material mixture at a temperature equal to or higher than its melting point and then pulverizing the ingot formed by cooling. A catalyst system for use in an exhaust gas purification apparatus for automobiles, characterized in that it is contained. The average particle size of the cerium-zirconium-based composite oxide (A) is preferably 0.3 to 2.0 μm, particularly preferably 0.5 to 1.5 μm. That is, the particle size of the cerium-zirconium composite oxide crushed after being melted is in the submicron order.

JP 2009-019537 A JP 2008-68225 A

As described above, various exhaust gas purification catalysts including ceria-zirconia (CeO ₂ —ZrO ₂ ) composite oxide as an OSC material have been proposed. However, further improvements in exhaust gas purification performance are required for exhaust gas purification catalysts.

  Accordingly, an object of the present invention is to provide an exhaust gas purification catalyst having further improved exhaust gas purification performance in view of the above situation.

  The present invention provides the following (1) to (2).

  (1) An exhaust gas purification catalyst in which an OSC material is disposed in the upstream and downstream stages of the catalyst, wherein the oxygen absorption / release rate of the OSC material disposed in the upstream stage is faster than the oxygen absorption / release rate of the OSC material disposed in the downstream stage. An exhaust gas purifying catalyst, wherein the ratio Ra / Rb of the particle size (Ra) of the OSC material disposed in the preceding stage and the particle size (Rb) of the OSC material disposed in the subsequent stage is less than 1.0. .

  (2) The exhaust gas purification catalyst according to (1), wherein 0 nm <Ra <9.2 nm and 15 nm <Rb <300 nm.

Represents the schematic structure of the catalyst of the present invention. Is a graph of the NOx purification rate with respect to Ra / Rb, where Ra is the primary particle size (nm) of the OSC material upstream of the catalyst, and Rb is the primary particle size (nm) of the OSC material downstream of the catalyst.

  The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst in which an OSC material is disposed in the upstream and downstream stages of the catalyst, and the oxygen absorption / release speed of the OSC material disposed in the subsequent stage is the oxygen absorption / release speed of the OSC material disposed in the preceding stage. And the ratio Ra / Rb between the particle size (Ra) of the OSC material disposed in the preceding stage and the particle size (Rb) of the OSC material disposed in the subsequent stage is less than 1.0. To do.

  In the present invention, the OSC material is disposed in the upstream and downstream of the catalyst. The OSC material can be supported on a monolithic structure type carrier (for example, a honeycomb structure) which is an inorganic structure carrier.

  The shape of the monolithic structure type carrier is not particularly limited and can be selected from known monolithic structure type carriers. However, in the case of a three-way catalyst for automobiles, it is preferable to use a flow-through type carrier. .

  Examples of the material of such an integral structure type carrier include metals and ceramics. In the case of metal, stainless steel is generally used, but the shape is generally honeycomb. Ceramic materials include cordierite, mullite, alumina, magnesia, spinel, silicon carbide, etc., but they are made of cordierite because they have good moldability for manufacturing honeycombs and are excellent in heat resistance and mechanical strength. It is preferable.

As the OSC material used in the present invention, a material based on CeO ₂ powder having a large oxygen storage and release ability can be preferably used. So far, many studies have been conducted on the improvement of oxygen storage capacity and release characteristics in CeO ₂ -based powders such as CeO ₂ -ZrO ₂ and exhaust gas purification catalysts using the same as an auxiliary catalyst. It has been shown to increase efficiency. They can be used as the OSC material of the present invention. Further, when a material other than a cerium element material and a zirconium element material is used as an optional additional component in the CeO ₂ —ZrO ₂ -based OSC material, it is within a range that does not impair the characteristics of the OSC material obtained by the present invention. Alkali, alkaline earth, metal components, etc. can be added. More specifically, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, lanthanum, yttrium, antimony, hafnium, tantalum, rhenium, bismuth, praseodymium, neodymium, samarium, gadolinium, holmium, thulium, ytterbium, germanium, Examples include selenium, cadmium, indium, scandium, titanium, niobium, chromium, iron, silver, rhodium, and platinum. Further, such an optional additional component may be contained from impurities in the cerium element material and the zirconium element material. However, it is needless to say that when such an optional additional component is subject to harmful regulation, it is desirable to reduce or eliminate the amount.

  The cerium raw material, zirconium raw material, and optional additional components are mixed at a predetermined ratio and charged into a melting apparatus. Next, the raw material mixture is melted in the apparatus. The melting method is not particularly limited as long as at least one of the raw material mixtures is melted, and examples thereof include an arc type and a high frequency thermal plasma type. Among them, a general electromelting method, that is, a melting method using an arc electric furnace can be preferably used. After the end of melting, the electric furnace is covered with carbon and slowly cooled for 20 to 30 hours to obtain a solid solution. The method for cooling the melt is not particularly limited, but it is usually taken out from the melting apparatus and allowed to cool in the atmosphere to 100 ° C. or lower, preferably 50 ° C. or lower. As a result, a solid solution of a cerium-zirconium composite oxide in which the cerium raw material and the zirconium raw material are uniform can be obtained.

  The solid solution is then pulverized. The pulverization of the solid solution is not particularly limited, but the ingot can be roughly pulverized by a pulverizer such as a jaw crusher or a roll crusher. The coarse powder obtained by the above method can be further finely pulverized. Although it does not specifically limit about fine pulverization, It can pulverize for 5 to 30 minutes with grinders, such as a planetary mill, a ball mill, or a jet mill. It is preferable that the average particle size of the cerium-zirconium-based composite oxide be set to the nanometer order by this fine pulverization. By finely pulverizing, the surface area of the composite oxide is increased, and an OSC material having a high oxygen absorption / release rate can be obtained.

  The OSC material thus produced can be used by supporting a catalytically active metal together with a porous inorganic oxide. Thereby, the catalytically active metal can be kept in a stable state with respect to heat and atmosphere, and the activity of the catalytically active metal can be increased.

  The catalytically active metal is not limited as long as it has activity for purification of exhaust gas, but it is desirable to contain one or more catalytically active metals selected from platinum, palladium, and rhodium. In addition, transition metals, rare earth metals and the like can be contained.

  As a base material on which a heat-resistant inorganic oxide, that is, a catalytically active metal is supported, a porous inorganic material having high heat resistance and a large specific surface area is preferable, active alumina such as γ-alumina and θ-alumina, zirconia, Cerium-zirconium composite oxide, ceria, titanium oxide, silica, various zeolites, and the like can be used. As such a porous inorganic base material, a material further improved in heat resistance by adding a rare earth such as lanthanum, cerium, barium, praseodymium, strontium or an alkaline earth metal may be used.

  An OSC material, a catalytically active metal, and a heat-resistant inorganic oxide are mixed with a water-size solvent to form a slurry, which is then coated on a monolithic structure type carrier, dried and fired to obtain the exhaust gas purification catalyst of the present invention. be able to.

  In the present invention, the particle size (Ra) of the OSC material disposed in the previous stage is different from the particle size (Rb) of the OSC material disposed in the subsequent stage. Here, the particle size is the primary particle size. The primary particle size is determined by spectroscopic methods such as XRD and observations such as SEM.

  The ratio Ra / Rb between the particle size (Ra) of the OSC material arranged in the preceding stage and the particle size (Rb) of the OSC material arranged in the latter stage is less than 1.0. That is, the particle size (Ra) of the OSC material arranged in the former stage is smaller than the particle size (Rb) of the OSC material arranged in the latter stage. About the specific surface area, the specific surface area of the OSC material arrange | positioned in the front | former stage is larger than the specific surface area of the OSC material arrange | positioned in the back | latter stage. When the specific surface area is large, the active area is also large, that is, the oxygen absorption / release rate is also fast. The rapid oxygen absorption / release rate of the OSC material arranged in the previous stage can quickly follow the A / F change of the exhaust gas introduced into the catalyst, maintain the stoichiometric state inside the catalyst, and obtain high NOx purification activity. .

  On the contrary, the specific surface area of the OSC material arranged in the latter stage is smaller than the specific surface area of the OSC material arranged in the former stage. When the specific surface area is small, the active area is also small, that is, the oxygen absorption / release rate is also slow (compared to the previous stage). Since the latter oxygen absorption / release rate is slower than the former oxygen absorption / release rate, the latter OSC material can absorb and release oxygen for a longer time than the former OSC material. Thereby, it is possible to cope with a gradual A / F change introduced into the catalyst and to obtain a high NOx purification activity.

When the particle size (Ra) of the OSC material arranged in the former stage is 0 nm <Ra <9.2 nm and the particle size (Rb) of the OSC material arranged in the latter stage is 15 nm <Rb <300 nm, otherwise It has been confirmed by the present inventor that NOx purification activity that is significantly higher than the particle size of is obtained.
When Ra is 9.2 nm or more, the OSC material arranged in the previous stage is too slow to absorb and release oxygen, and cannot absorb A / F fluctuations when sudden A / F changes (acceleration, etc.). Emissions get worse.
When the Rb is 15 nm or less, the OSC material disposed in the latter stage has an oxygen absorption / release reaction that is too fast, and the A / F change cannot be absorbed for a long time under the ingress condition where the gas is rich or lean. Getting worse. In addition, when rich, a large amount of oxygen is released in a short time, so that the reduction of noble metals is inhibited and the emission deteriorates.
When Rb is 300 nm or more, as the OSC material disposed in the latter stage, the oxygen diffusion in the OSC material inner layer becomes rate-determining, and the oxygen absorption / release capacity of the particle core portion cannot be sufficiently used. Therefore, sufficient OSC capability cannot be obtained and the emission deteriorates. More preferably, Rb <250 nm, and still more preferably Rb <200 nm.

  Each of the front-stage OSC material and the rear-stage OSC material may include an OSC material in which the primary particle diameter Rc satisfies the relationship Ra <Rc <Rb. The OSC material having the primary particle diameter Rc may be contained up to a ratio of 1: 1 with respect to the OSC material having the primary particle diameter Ra and / or Rb.

In the present invention, a catalyst layer may be further coated as an upper layer of the former and latter OSC material coats. For a three-way catalyst for automobiles, it is preferable to coat the upper layer with a catalyst layer substantially free of Pt and Pd and containing Rh.
The reason why it is preferable to configure the monolithic catalyst in this way is considered as follows. That is, when Pt, Pd, and Rh are present in the same composition, Pd, Pt, and Rh react to cause sintering between noble metals, and the catalytic activity of Pt and Pd may be weakened. It is known that the exhaust gas purifying ability itself also decreases. Further, Pd has a problem of poisoning due to lead or sulfur in the exhaust gas, and it is known that the catalytic activity decreases when Pd is present on the surface of the structural catalyst. Although it is possible to take measures against this problem by increasing the amount of noble metal, it is not preferable that Pt, Pd and Rh exist in the same composition because there is a problem that the catalyst cost increases. (See paragraphs 0011 of JP-A-11-169712 and paragraph 0005 of JP-A-2005-021793).
Further, when Rh is disposed in the upper layer, NOx purification activity is activated at an early stage, particularly by disposing it in the surface layer of the monolithic catalyst. For this reason, it is preferable that the catalyst is an integral structure type catalyst in which Rh is disposed in the upper layer close to the exhaust gas and Pt, Pd, and OSC material are disposed in the lower layer.
Each component of the catalyst of the upper layer is 0 to 100 g / L for the OSC material, 0.01 to 1.0 g / L for the catalytically active metal, and 10 to 100 g / L for the heat-resistant inorganic oxide per unit volume of the honeycomb structure of the carrier. L is preferred.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

1. Production of Catalysts of Examples and Comparative Examples The catalysts of Examples 1 to 5 and Comparative Examples 1 to 5 were produced generally as follows. Ceria zirconia solid solutions (CZ-1) to (CZ-5) were prepared. Next, coating slurries (1) to (7) were prepared from these ceria zirconia solid solutions. Next, the honeycomb substrate was coated with the slurry. Details will be described below.

Preparation of zirconia solid solutions (CZ-1) to (CZ-5) (CZ-1): primary particle size = 15 nm, composition CeO ₂ / ZrO ₂ / La ₂ O ₃ / Y ₂ O ₃ = 60/30/5 / 5wt%
(CZ-2): primary particle size = 9.2 nm, composition CeO ₂ / ZrO ₂ / La ₂ O ₃ / Y ₂ O ₃ = 60/30/5/5 wt%, (CZ-1) was finely pulverized Material (CZ-3): primary particle size = 157 nm, composition CeO ₂ / ZrO ₂ = 58/42 wt%
(CZ-4): primary particle size = 22 nm, composition CeO ₂ / ZrO ₂ = 58/42 wt%, finely pulverized (CZ-3) (CZ-5): primary particle size = 5.7 nm, composition _{CeO 2 / ZrO 2 / La 2} O 3 / Y 2 O 3 = 30/60/5 / 5wt%

  Preparation of slurry for coating (1) to (7) from ceria zirconia solid solution (CZ-1) to (CZ-5)

Slurry (1)
Ceria zirconia solid solution (CZ-1) and alumina (manufactured by Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1, and then impregnated with 8% palladium nitrate aqueous solution. After supporting (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (1).

Slurry (2)
Ceria zirconia solid solution (CZ-2) and alumina (Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1, and then impregnated with 8% palladium nitrate aqueous solution. After supporting (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (2).

Slurry (3)
After impregnating and supporting 2.8% aqueous Rh nitrate solution on a commercially available ZrO ₂ powder (manufactured by Daiichi Rare Element Chemical Co., Ltd., ZrO ₂ 80 wt%, Y ₂ O ₃ 8 wt%, Nd ₂ O ₃ 12%) (impregnation condition 1 Time, 80 ° C.), drying and firing (firing conditions 1 hour, 500 ° C.) to obtain Rh-supported powder. The Rh-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (3).

Slurry (4)
Ceria zirconia solid solution (CZ-4) and alumina (Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1, and then impregnated with 8% palladium nitrate aqueous solution. After supporting (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (4).

Slurry (5)
Ceria zirconia solid solution (CZ-3) and alumina (manufactured by Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1, and then impregnated with 8% palladium nitrate aqueous solution. After supporting (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a slurry for coating (5).

Slurry (6)
Ceria zirconia solid solution (CZ-5) and alumina (Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1, and then impregnated with 8% palladium nitrate aqueous solution. After supporting (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare slurry for coating (6).

Slurry (7)
Ceria zirconia solid solution (CZ-1), (CZ-2) and alumina (Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1: 2, and then Then, after impregnating and supporting an 8% aqueous palladium nitrate solution (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and an alumina binder (DISPAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (7).

Slurry (8)
Ceria zirconia solid solution (CZ-1), (CZ-4) and alumina (Sasol (La ₂ O ₃ 4 wt%, Al ₂ O ₃ 96 wt%)) were mixed at a mass ratio of 1: 1: 2, and then Then, after impregnating and supporting an 8% aqueous palladium nitrate solution (impregnation condition 1 hour, 80 ° C.), drying and firing (firing condition 1 hour, 500 ° C.), a Pd-supported powder was obtained. This Pd-supported powder and alumina binder (DISAL manufactured by Sasol) were mixed at a mass ratio of 20: 1, and 200 ml of distilled water was added to prepare a coating slurry (8).

  Preparation of catalysts of Examples and Comparative Examples from coating slurries (1) to (8)

Catalyst preparation of Example 1 Slurry (2) is introduced from an upper opening of a honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate is sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, the honeycomb substrate was dried (250 ° C., 6 hours, in the air (electric furnace)) and fired (500 ° C., 1 hour, in the air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (2) is not charged is set upward, and the slurry (1) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (1). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, slurry (3) was coated on the slurry (2) and (1), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (2) was 75 g / L, the coating amount of the slurry (1) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Example 2 The slurry (2) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (2) is not charged is set upward, and the slurry (4) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coats of the slurries (2) and (4), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (2) was 75 g / L, the coating amount of the slurry (4) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Example 3 Slurry (2) is introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate is sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (2) is not charged is set upward, and the slurry (5) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (5). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coats of the slurries (2) and (5), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (2) was 75 g / L, the coating amount of the slurry (5) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Example 4 Slurry (6) is introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate is sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the amount of slurry charged, the solid content, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (6). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (6) is not charged is set upward, and the slurry (4) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coats of the slurries (6) and (4), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (6) was 75 g / L, the coating amount of the slurry (4) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Preparation of catalyst of Example 5 The slurry (7) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (7). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (7) is not charged is set upward, and the slurry (8) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (8). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, slurry (3) was coated on the slurry (7) and (8), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (7) was 75 g / L, the coating amount of the slurry (8) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Comparative Example 1 The slurry (2) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (2) is not charged is set upward, and the slurry (2) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, slurry (3) was coated on the slurry (2) and (2), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (2) was 75 g / L, the coating amount of the slurry (2) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Comparative Example 2 The slurry (2) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (2) is not charged is set upward, and the slurry (6) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the amount of slurry charged, the solid content, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (6). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coats of the slurries (2) and (6), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (2) was 75 g / L, the coating amount of the slurry (6) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Comparative Example 3 The slurry (4) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (4) is not charged is set upward, and the slurry (6) is charged from there, and the lower opening of the honeycomb substrate is formed. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the amount of slurry charged, the solid content, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (6). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, slurry (3) was coated on the slurry (4) and (6), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (4) was 75 g / L, the coating amount of the slurry (6) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Comparative Example 4 The slurry (4) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, the opening on the side where the slurry (4) is not charged is set upward, and the slurry (2) is charged from there, and the lower opening of the honeycomb substrate is set. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (2). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coating of the slurry (4) and (2), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (4) was 75 g / L, the coating amount of the slurry (2) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

Catalyst preparation of Comparative Example 5 The slurry (4) was introduced from the upper opening of the honeycomb substrate (600 cells, wall thickness 3 mm, inner diameter 103 mm × length 105 mm), and the lower opening of the honeycomb substrate was sucked. The coating was applied up to the center in the longitudinal direction inside the honeycomb substrate. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the honeycomb substrate is turned upside down in the longitudinal direction, and the opening on the side where the slurry (4) is not charged is set to the upper side. Then, the slurry (4) is charged from there, and the lower opening of the honeycomb substrate is set. By suctioning, the honeycomb substrate was coated up to the center in the longitudinal direction. At this time, the slurry input amount, the solid content amount, and the suction conditions were adjusted so that the center of the honeycomb base material in the longitudinal direction was coated with the slurry (4). Next, this honeycomb substrate was dried (250 ° C., 6 hours in air) and fired (500 ° C., 1 hour in air).
Next, the slurry (3) was coated on the coats of the slurries (4) and (4), dried and fired. The total coating amount was adjusted so that the mass after firing was 200 g / L. The coating amount of the slurry (4) was 75 g / L, the coating amount of the slurry (4) was 75 g / L, and the coating amount of the slurry (3) was 50 g / L. The supported amounts of Pd and Rh were adjusted to 0.6 [g / L] and 0.1 [g / L], respectively.

2. Catalyst durability test In order to confirm whether or not the catalyst activity of the example and comparative example produced in Example 1 was maintained after a certain amount of running, an accelerated deterioration test (endurance test) was performed using an actual engine and its exhaust gas. Details will be described below.

  1. Ceramic mats (thickness: 12 mm) were wound around the honeycomb catalysts of Examples and Comparative Examples manufactured in the above. Next, the honeycomb catalyst was canned in the exhaust pipe. Next, a thermocouple was inserted in the center of the honeycomb. Next, the exhaust pipe was connected to the engine. Next, the engine speed / torque etc. were adjusted so that the temperature of the thermocouple in the honeycomb was 950 ± 20 ° C. At this time, the air-fuel ratio A / F of the exhaust gas continued for 50 hours (endurance test time) under the condition of vibrating 14 and 15 at 1 Hz.

3. 1. Catalyst evaluation method The honeycomb catalysts of the examples and comparative examples that were subjected to the durability test were canned in the exhaust pipe. Next, the exhaust pipe was connected to the engine. The same mounting flange was used in the durability test and the catalyst evaluation. The engine speed / torque was adjusted so that the exhaust gas temperature in the pipe 10 mm before the catalyst inlet was 600 ° C. After adjusting the exhaust gas air-fuel ratio A / F to be 14.6, the exhaust gas air-fuel ratio A / F was changed within a range of 14.2 to 15.0 at regular intervals (1 second) at intervals of 1 second. The NOx purification rate by this catalyst was calculated | required from the NOx amount in exhaust gas of a catalyst inlet_port | entrance and an exit at this time.
NOx purification rate (%) = (catalyst inlet NOx amount−catalyst outlet NOx amount) / catalyst inlet NOx amount × 100

4). 1. Catalyst evaluation results 2. Using the catalysts of Examples and Comparative Examples subjected to the catalyst durability test, Table 4 shows the NOx purification rate obtained by the catalyst evaluation method. Table 4 also lists Ra: primary particle size (nm) of the OSC material before the catalyst, Rb: primary particle size (nm) of the OSC material after the catalyst, and Ra / Rb. FIG. 1 shows a graph of the NOx purification rate with respect to Ra / Rb. As shown in FIG. 1, the NOx purification rate is remarkably improved in the range of Ra / Rb <1.0, which is the range of the present invention.

Claims (2)

  An exhaust gas purification catalyst in which an OSC material is disposed in the upstream and downstream stages of the catalyst, wherein the oxygen absorption / release rate of the OSC material disposed in the upstream stage is faster than the oxygen absorption / release rate of the OSC material disposed in the downstream stage, An exhaust gas purifying catalyst, wherein a ratio Ra / Rb between a particle size (Ra) of the OSC material arranged in the above and a particle size (Rb) of the OSC material arranged in the latter stage is less than 1.0.   2. The exhaust gas purification catalyst according to claim 1, wherein 0 nm <Ra <9.2 nm and 15 nm <Rb <300 nm.

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