JP5372410B2 - Exhaust gas purification catalyst, exhaust gas purification catalyst paint and diesel exhaust gas purification filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst which can be suitably used for oxidizes harmful gas components by burning the PM of diesel engine exhaust gas at low temperature and can reduce the content of an expensive noble metal element. <P>SOLUTION: In the exhaust gas clarifying catalyst, a composite oxide having a perovskite structure and a noble metal/oxide catalyst in which the noble metal is supported on an oxide are mixed mechanically in a prescribed ratio. The composite oxide is La<SB>x</SB>Ba<SB>1-x</SB>FeO<SB>3</SB>(0.6&le;x&le;0.9). and the noble metal/oxide catalyst is Pt/Al<SB>2</SB>O<SB>3</SB>. The mixing ratio between the composite oxide and the noble metal/oxide catalyst is 9:1-8:2. A coating for the exhaust gas clarifying catalyst contains the exhaust gas clarifying catalyst, a solvent, and an inorganic binder. A diesel exhaust gas clarifying filter has a porous filter and an exhaust gas clarifying catalyst layer containing the exhaust gas clarifying catalyst and the inorganic binder which is formed on the surface of the porous filter. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an exhaust gas purification catalyst composed of a composite oxide suitable for burning PM (particulate matter) discharged from a diesel engine such as an automobile, and a catalyst paint using the same and a paint on the substrate. The present invention relates to a filter for purifying diesel exhaust gas applied to a filter.

As a problem of diesel engine exhaust gas, harmful gases such as hydrocarbon compounds (HC), carbon monoxide (CO) nitrogen oxide (NO _x ) and fine particles mainly composed of carbon (hereinafter also referred to as “PM”) are exhaust gas. It is included inside and causes environmental pollution.

An exhaust gas purification catalyst in which noble metal particles having catalytic activity such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on a metal oxide support such as alumina (Al ₂ O ₃ ) is used to remove harmful gas components. It's being used.

  On the other hand, as a general method for removing PM, there is a method of collecting PM (trap) by installing a diesel particulate filter (DPF) made of porous ceramics in an exhaust gas passage. PM accumulates in the DPF, but the DPF can be regenerated to the state before PM collection by removing the PM by intermittently or continuously burning the collected PM.

In this DPF regeneration process, a method of burning PM by forced heating from the outside, such as an electric heater or a burner, an oxidation catalyst is installed on the engine side of the DPF, and NO contained in the exhaust gas is converted to NO ₂ by the oxidation catalyst. A method of burning PM by the oxidizing power of NO ₂ is generally used.

  However, in order to use an electric heater or a burner, it is necessary to install a power source outside, and since a mechanism for securing and operating them is required separately, the exhaust gas purification system itself becomes complicated. In addition, the oxidation catalyst has various problems such that the exhaust gas temperature is not so high that the catalytic activity is sufficiently exerted, and NO required for PM combustion is not contained in the exhaust gas unless it is under a certain operating condition. .

  Therefore, as a more preferable regeneration treatment method of DPF, a method is considered in which a catalyst is supported on DPF itself, and the PM combustion start temperature is lowered by the catalytic action, and then PM is combusted. And as the ultimate goal, the method of burning continuously at the exhaust gas temperature is most desirable.

  At present, various catalysts that lower the combustion start temperature of PM have been proposed. Patent Document 1 discloses a catalyst for PM combustion mainly composed of cerium oxide. Further, Patent Documents 2 to 4 disclose a mixture containing Ce and Bi or a transition metal element as an oxidation catalyst based on a ceria composite oxide not containing a noble metal element such as Pt. Patent Document 5 discloses a PM combustion catalyst having a perovskite structure.

  Now, in the exhaust gas system of a diesel engine, an exhaust gas purification part is provided in the middle of the exhaust pipe to remove gas harmful components and PM. However, since the method of removing gas harmful components and PM are different, it is necessary to devise the arrangement of the catalyst.

  Since PM is basically removed by a filter and the PM accumulated in the filter is burned at a low temperature using a catalyst, the PM combustion catalyst is preferably disposed on the wall of the filter on the engine side. This is because PM is accumulated in this portion.

  On the other hand, since harmful gas components pass through the filter, the harmful gas component combustion catalyst is arranged on the open side of the atmosphere from the filter. This may be closer to the engine than the filter and closer to the atmosphere than the PM combustion catalyst. That is, a structure in which a gas harmful component combustion catalyst and a PM combustion catalyst are laminated in this order on the engine sidewall of the filter may be used.

JP 2007-245054 A Japanese Patent Laid-Open No. 6-211525 JP 2003-238159 A JP 2006-224032 A Japanese Patent Laid-Open No. 2007-237012

  The problem is that gas poisoning combustion catalysts are expensive because they use precious metals. However, as described above, since the mechanism for removing the gas harmful component and PM is different, the gas harmful component combustion catalyst needs to contain a noble metal necessary for removing the gas harmful component. That is, there has been a problem that the use of noble metals cannot be reduced in an exhaust gas purification system that removes PM and gas harmful components.

  As a result of intensive studies to achieve the above object, the present inventor has physically mixed a noble metal-containing catalyst with a composite oxide having a perovskite structure, so that even if the amount of noble metal element is small, the gas harmful component can be obtained. It has been found that an exhaust gas removal catalyst excellent in removal can be obtained, and the present invention has been completed.

That is, the exhaust gas purifying catalyst of the present invention includes La _x Ba _1-x FeO ₃ (0.6 ≦ x ≦ 0.9), which is a complex oxide having a perovskite structure, and an oxide support in which a noble metal is supported on an oxide. This is an exhaust gas purification catalyst in which only Pt / Al ₂ O ₃ which is a noble metal catalyst is mixed at a mixing ratio of 9: 1 to 8: 2.

  The present invention also provides a paint containing the exhaust gas purifying catalyst and a DPF in which the paint is applied to a porous filter.

  The exhaust gas purifying catalyst of the present invention is a mixture of a perovskite structure composite oxide and an oxide-supported noble metal catalyst in which a noble metal is supported on an oxide, so that even when the same noble metal-containing catalyst is used, removal of harmful gas components Ability improves. That is, if the removal ability of harmful components is the same, there is an effect that the amount of noble metal used can be reduced. Further, since the exhaust gas purifying catalyst of the present invention is in a state where a catalyst for PM and a harmful gas component is mixed, if this is used as a paint, the DPF with catalyst can be applied once to a porous filter substrate. The effect that can be produced is also produced.

The exhaust gas purifying catalyst of the present invention is a physical mixture of a composite oxide having a perovskite structure and an oxide-supported noble metal catalyst in which a noble metal is supported on an oxide. Perovskite is usually expressed in a composition formula AMO _3. Here, the A site is one or more rare earth elements and one or more alkaline earth metals, and the M site is one or more transition metal elements.

For example, the A site contains one or more elements such as La, Y, Dy, and Nd and one or more elements such as Sr, Ba, and Mg, and the M site contains one or more elements such as Mn, Fe, and Co. enter. More _{specifically, La x Sr 1-x FeO} 3 (x is 0.35 to _{0.9), La x Ba 1-} x FeO 3 (x is 0.35 to 0.9), and the like.

  The noble metal used in the present invention can be selected from Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, but is preferably at least one metal selected from Pt, Pd, and Rh. This is because these metals have high catalytic activity against noxious components among noble metals.

The oxide supporting the noble metal is particularly preferably a material such as SiO ₂ , Al ₂ O ₃ or ZrO ₂ . This is because these materials are highly resistant to fluctuations in the oxidation / reduction atmosphere as an exhaust gas purification catalyst, can maintain a high surface area, and are excellent in heat resistance. Among these, an alumina-supported platinum catalyst in which the noble metal element Pt is supported on Al ₂ O ₃ is preferable.

  The physical mixing (also simply referred to as “mixing”) of an oxide-supported noble metal catalyst in which a noble metal is supported on an oxide and a composite oxide having a perovskite structure refers to mechanical mixing. This is because the exhaust gas purifying catalyst of the present invention does not require chemical bonding between the composite oxide and the oxide-supported noble metal catalyst. Therefore, mixing can be performed while finely pulverizing each powder with a mortar or a pulverizer. Moreover, you may disperse | distribute and mix with media, such as a solvent and a binder.

  The oxide-supported noble metal catalyst of the present invention can be prepared by an impregnation method in which an oxide serving as a support is immersed in an aqueous solution of a noble metal salt, dried and calcined. Moreover, you may prepare by the conventional incipient wetness method. In this method, a noble metal solution is dropped onto an oxide serving as a support to obtain a noble metal-oxide-supported noble metal catalyst.

The exhaust gas purification catalyst of the present invention may be a paint together with a solvent and a binder.
As the solvent, either a polar solvent or a nonpolar solvent may be used. A solvent having a low boiling point is preferable in order to dry quickly after coating on the filter, but an aqueous solvent may be used in consideration of ease of handling. Specifically, isopropyl alcohol, terpineol, 2-octanol, butyl carbitol acetate and the like can be suitably used.

As the inorganic binder, powders such as Al ₂ O ₃ , TiO ₂ , and SiO ₂ are preferably used. This is because the PM combustion catalyst is exposed to a high temperature, and therefore a material exhibiting stable characteristics even at a high temperature is preferable. These materials are applied to the surface of a porous filter to be a DPF after adjusting the viscosity to be easy to handle by application or spray.

  The structure of the DPF using the composite oxide of the present invention is not particularly limited. For example, FIG. 8 shows an example of the structure of the DPF. The DPF 1 has a cylindrical shape with a honeycomb structure as viewed from the entrance side 10 and is made of porous ceramic. The entrance side 10 and the exit side 11 do not have direct through holes, and porous ceramics are used as a filter. Specifically, ceramics, cordierite, silicon carbide, aluminum titanate, and the like are preferably used for the porous ceramic. Further, the shape may be a foam, a mesh, or a plate shape in addition to the structure shown in FIG.

  The exhaust gas purifying catalyst of the present invention is preferably formed on the engine side wall surface 12 of the DPF (30). This is because a PM (combustion) catalyst is included, and therefore, the PM combustion temperature cannot be lowered unless the engine accumulates PM. Since the exhaust gas purifying catalyst of the present invention includes a noble metal that becomes a catalyst for oxidizing a gas such as hydrocarbon or carbon monoxide, the exhaust gas purifying catalyst may be formed on the wall 14 on the open side of the atmosphere (40). Moreover, you may form the catalyst layer with respect to gas harmful components other than the exhaust gas purification catalyst of this invention in the wall surface 14 by the side of open | release to the atmosphere.

Examples will be described in detail below.
<Production of composite oxide>
The composite oxide of each example and comparative example was produced as follows.
Lanthanum nitrate, barium nitrate, and iron nitrate so that the molar ratio of lanthanum element, barium element, and iron element is x: 1-x: 1 (where x = 0.6, 0.8, 0.9). Mixed. Water was added to the mixture so that the total molar concentration of lanthanum element, barium element, and iron element was 0.2 mol / L to obtain a raw material solution (hereinafter referred to as “raw material 1”).

<La _0.6 Ba _0.4 FeO ₃ >
The temperature of the solution is adjusted to 15 ° C. while stirring the raw material 1 (x = 0.6), and when the temperature reaches 15 ° C., the pH is adjusted to 7 to 8 while adding an ammonium carbonate solution as a precipitant. did. Thereafter, stirring was continued for 1 hour while maintaining the reaction temperature at 15 ° C., whereby the formation of precipitates was sufficiently advanced. The resulting precipitate was collected by filtration, washed with water, and dried at 145 ° C. overnight. The obtained powder was calcined at 800 ° C. for 2 hours in the air atmosphere, pulverized with a crusher (sample mill), and then aggregated using a vibrating sieve (200 mesh).

_<La 0.8 _Ba 0.2 _FeO 3>
While stirring the raw material 1 (x = 0.8), the temperature of the solution was adjusted to 30 ° C., and when the temperature reached 30 ° C., an ammonium solution was added as a precipitant, and then carbon dioxide was blown into the solution. Urged the formation of a precipitate. Thereafter, the stirring was continued for 0.5 hours while maintaining the reaction temperature at 30 ° C., thereby sufficiently causing the precipitation. The resulting precipitate was collected by filtration, washed with water, and dried at 250 ° C. for 1.5 hours. The obtained powder was calcined at 800 ° C. for 2 hours in the air atmosphere, pulverized, and adjusted to a predetermined particle size by wet grinding.

<La _0.9 Ba _0.1 FeO ₃ >
While stirring the raw material 1 (x = 0.9), the temperature of the solution was adjusted to 15 ° C., and when the temperature reached 15 ° C., an ammonium solution was added as a precipitant, and then carbon dioxide was blown further. Urged the formation of a precipitate. Thereafter, the stirring was continued for 0.5 hours while maintaining the reaction temperature at 15 ° C., thereby sufficiently causing the precipitation. The resulting precipitate was collected by filtration, washed with water, and dried at 125 ° C. overnight. The obtained powder was calcined at 800 ° C. for 2 hours in the air atmosphere, pulverized with a crusher (sample mill), and then aggregated using a vibrating sieve (200 mesh).

Table 1 shows the mass% and molar ratio of La, Ba, and Fe elements of the samples obtained. The sum of mass% does not become 100%, but the rest is oxygen. Hereinafter, each perovskite sample is referred to as La and its molar ratio. For example, La _0.6 Ba _0.4 FeO ₃ is called La0.6.

<< Preparation of oxide-supported noble metal catalyst >>
Next, Pt / Al ₂ O ₃ was prepared as an oxide-supported noble metal catalyst. 180 ml of pure water was added to 3.57 g of Pt (NH ₃ ) ₂ (NO ₂ ) ₂ solution (Pt concentration: 8.486%) to prepare a metal salt solution. While stirring this solution with a magnetic stirrer, 30 g of Al ₂ O ₃ was added thereto, followed by stirring for 1 hour. The obtained solution was transferred to an evaporator, and the solvent was removed at a temperature of 80 ° C. and a rotation speed of 25 rpm to obtain a powder. This powder was dried at 130 ° C. overnight and then calcined in air at 500 ° C. for 2 hours (heating rate 5 ° C./min) to obtain Pt (1%) / Al ₂ O ₃ powder.

<Production of sample>
Examples 1 to 5 and Comparative Examples 1 to 5 (however, Comparative Example 2 is a missing number), which are exhaust gas purifying catalysts of the present invention, were prepared as follows.
Example 1
La0.8 and an oxide-supported noble metal catalyst (Pt / Al ₂ O ₃ ) were weighed at a mass ratio of 9: 1, respectively, and mixed in an automatic mortar for 30 minutes to obtain an exhaust gas purification catalyst of Example 1. When measuring the gas oxidation activity, the sample stage placed in the reaction tube was filled with a 1.84 g sample. Specifically, it is a mixture of 1.656 g of La0.8 and 0.184 g of Pt / Al ₂ O ₃ .

(Example 2)
La0.8 and oxide-supported noble metal catalyst (Pt / Al ₂ O ₃ ) were weighed at a mass ratio of 8: 2, respectively, and mixed in an automatic mortar for 30 minutes to obtain an exhaust gas purification catalyst of Example 2. When measuring the gas oxidation activity, the sample stage placed in the reaction tube was filled with a 1.84 g sample. Specifically, it is a mixture of 1.472 g of La0.8 and 0.368 g of Pt / Al ₂ O ₃ .

( Reference example )
La0.8 and oxide-supported noble metal catalyst (Pt / Al ₂ O ₃ ) were weighed at a mass ratio of 5: 5, respectively, and mixed in an automatic mortar for 30 minutes to obtain an exhaust gas purification catalyst of Reference Example . When measuring the gas oxidation activity, the sample stage placed in the reaction tube was filled with a 1.84 g sample. Specifically, it is a mixture of 0.92 g of La0.8 and 0.92 g of Pt / Al ₂ O ₃ .

Example 4
La0.9 and the oxide-supported noble metal catalyst (Pt / Al ₂ O ₃ ) were weighed at a mass ratio of 9: 1, respectively, and mixed in an automatic mortar for 30 minutes to obtain an exhaust gas purification catalyst of Example 4. When measuring the gas oxidation activity, the sample stage placed in the reaction tube was filled with a 1.84 g sample. Specifically, it is a mixture of 1.656 g of La0.9 and 0.184 g of Pt / Al ₂ O ₃ .

(Example 5)
La0.6 and oxide-supported noble metal catalyst (Pt / Al ₂ O ₃ ) were weighed at a mass ratio of 9: 1, respectively, and mixed in an automatic mortar for 30 minutes to obtain an exhaust gas purification catalyst of Example 5. When measuring the gas oxidation activity, the sample stage placed in the reaction tube was filled with a 1.84 g sample. Specifically, it is a mixture of 1.656 g of La0.6 and 0.184 g of Pt / Al ₂ O ₃ .

(Comparative Example 1)
In Comparative Example 1, the same perovskite and Pt / Al ₂ O ₃ as in Example 1 are laminated. Specifically, 1.656 g of La0.8 was deposited on the sample stage placed in the reaction tube so that 0.184 g of Pt / Al ₂ O ₃ was on the upstream side. Here, the upstream and the downstream are referred to as the upstream when the inspection gas is flowed closer to the outflow source.

(Comparative Example 3)
Comparative Example 3 has the same perovskite and Pt / Al ₂ O ₃ layered structure as in the reference example . Specifically, the sample stage was placed in the reaction tube, the downstream side La0.8 of 0.92g, Pt / _Al 2 _{O 3} of 0.92g were deposited such that the upstream side.

(Comparative Example 4)
In Comparative Example 4, the same perovskite and Pt / Al ₂ O ₃ as in Example 4 are laminated. Specifically, 1.656 g of La0.9 was deposited on the sample stage disposed in the reaction tube so that 0.184 g of Pt / Al ₂ O ₃ was on the upstream side.

(Comparative Example 5)
In Comparative Example 5, the same perovskite and Pt / Al ₂ O ₃ as in Example 5 are laminated. Specifically, 1.656 g of La0.6 was deposited on the sample stage disposed in the reaction tube so that 0.184 g of Pt / Al ₂ O ₃ was on the upstream side.

As described above, Comparative Example 1 is a sample having the same composition as Example 1 and a layer structure. Similarly, Comparative Examples 3 , 4 , and 5 are samples corresponding to Reference Examples and Examples 4 and 5. In addition, since the layer structure sample of the same composition as Example 2 was not prepared, the comparative example 2 was a missing number.

<< Measurement of CB combustion temperature >>
A sample to be measured for the CB combustion temperature was prepared. Moreover, commercially available CB (carbon black: manufactured by Mitsubishi Chemical Corporation) or an equivalent of this material was prepared.

  Then, weigh the sample to be measured and carbon black so that the weight ratio is 6: 1 and mix for 20 minutes with an automatic mortar machine (AGA type manufactured by Ishikawa Factory) or an equivalent of this device. A mixed powder was obtained.

  20 mg of this mixed powder was placed in a thermogravimetric / differential calorimetry (TG / DTA) apparatus, and the temperature was raised from 50 ° C. to 700 ° C. in the air at a temperature rising rate of 10 ° C./min, and the weight was measured. . The thermogravimetric and differential thermal measurement (TG / DTA) apparatus is TG / DTA (6300 type) manufactured by Seiko Instruments Inc. or an equivalent of this apparatus, and the carbon has a maximum DTA peak intensity. The black combustion temperature was used. If the combustion temperature of carbon black is low, it is a guideline that can be judged useful as a catalyst for PM combustion.

Table 2 shows the CB combustion temperatures of La 0.6, La 0.8, La 0.9, Pt / Al ₂ O ₃ and Examples 1 to 2 and Reference Example . Further, in FIG. 7, La0.8, shows a graph of Examples 1 to 2 and Reference Example and Pt / _Al 2 _{O 3} the CB combustion temperature in relation to the mixing amount of Pt / _Al 2 _{O 3.}

<Measurement of particle size distribution>
For the particle size distribution, D ₅₀ diameter (or simply D ₅₀ ) was measured by particle size distribution measurement by laser diffraction method. D ₅₀ is the particle diameter (μm) of the intermediate particles of the total number of particles when arranged in order from the smallest particle diameter. Table 2 shows D ₅₀ of La 0.6, La 0.8, and La 0.9.

<< Measurement of BET specific surface area >>
The sample to be measured was pulverized with an agate mortar to form a powder, and then the specific surface area (S _BET : m ² / g) was determined by the BET method. The measurement was carried out using 4 Saab US made by Your Sonics. Table 2 shows S _BET of La 0.6, La 0.8, La 0.9, and Pt / Al ₂ O ₃ .

<Measurement of gas oxidation activity>
The oxidation activity of CO and C ₃ H ₆ was measured as follows.
The exhaust gas purifying catalyst of the present invention of Examples 1 , 4 , 5 , and Reference Example was charged with 1.84 g of a sample made into a 1 to 2 mm pellet in a fixed bed flow system reactor.

Further, Comparative Examples 1, 3, 4, and 5 have a laminated structure in which perovskite is filled on the same sample stage and Pt / Al ₂ O ₃ is filled thereon. Perovskite and Pt / Al ₂ O ₃ used the mass of the above ratio. In all comparative examples, the catalyst was charged in a total of 1.84 g. The measurement gas was flowed so that Pt / Al ₂ O ₃ was on the upstream side and perovskite was on the downstream side.

Next, a simulated mixed gas of diesel exhaust gas having the composition shown in Table 3 was circulated at room temperature at a total gas flow rate of 8 L / min. At the outlet side of the fixed bed flow system reactor, the CO concentration was measured by an infrared analyzer (VIA-510 manufactured by Horiba), and the C ₃ H ₆ concentration was measured by a hydrogen ionization analyzer (FIA-510 manufactured by Horiba). Respectively. The temperature of the catalyst packed bed is raised from room temperature to 500 ° C., and the CO conversion rate (%) and C ₃ H ₆ conversion rate (%) are calculated from the CO concentration and C ₃ H ₆ concentration at the measurement temperature by the following formula (1): And (2). The values in Table 3 were used for the inlet CO concentration and the inlet C ₃ H ₆ concentration in the equations (1) and (2).

CO conversion rate (%) = (inlet CO concentration−outlet CO concentration) × 100 / inlet CO concentration
(1)
C ₃ H ₆ conversion (%) = (inlet C ₃ H ₆ concentration−outlet C ₃ H ₆ concentration) × 100 / inlet C ₃ H ₆ concentration
(2)

With reference to FIG. 1 and FIG. 2, the oxidation activity with respect to CO of Example 1 and the reference example will be described. In both FIG. 1 and FIG. 2, the vertical axis represents the CO conversion (%), and the horizontal axis represents the catalyst temperature (° C.). Referring to FIG. 1, Example 1 in which La0.8 and Pt / Al ₂ O ₃ were mixed had an earlier rise in oxidation activity characteristics than Comparative Example 1 in which each was independently formed into a laminated structure. That is, for example, the CO conversion rate of Example 1 was higher than that of Comparative Example 1 at an arbitrary temperature up to 200 ° C., for example. This means that more CO can be oxidized if the temperature is the same. In other words, CO emissions can be reduced.

The reason why Example 1 in which La0.8 and Pt / Al ₂ O ₃ are mixed in this way has higher oxidation activity than Comparative Example 1 having a laminated structure is not clear. However, since La0.8 and Pt / Al ₂ O ₃ are mixed, it is presumed that the oxygen storage / release ability of La0.8 and the oxidizing action of Pt / Al ₂ O ₃ work synergistically.

In Example 1, La0.8 and Pt / Al ₂ O ₃ are 9: 1 in mass ratio. Considering the total mass of Pt, gas oxidation activity is obtained with much less Pt than Comparative Example 1. Will be.

On the other hand, referring to FIG. 2, in the reference example in which Pt / Al ₂ O ₃ having the same mass as La0.8 and Pt / Al ₂ O ₃ mixed together and Laminate each, La0.8 has slightly higher oxidation activity. The mixed structure and the laminated structure showed almost the same characteristics. This indicates that as Pt increases, there is not much difference in oxidation activity between mixing and stacking.

In other words, when La0.8 and a small amount of Pt / Al ₂ O ₃ are mixed, the oxidation activity is improved as compared with the case where each is used as an independent formation layer.

FIG. 7 shows measurement results of La0.8 itself, Examples 1 to 2, Reference Example, and CB combustion temperature of Pt / Al ₂ O ₃ alone. The vertical axis represents the CB combustion temperature (° C.), and the horizontal axis represents the mixing amount (% by mass) of Pt / Al ₂ O ₃ . Since the La0.8 perovskite is a catalyst having CB combustion activity, the CB combustion temperature was low at 367 ° C. when La0.8 alone (the horizontal axis corresponds to zero). Then, as the amount of Pt / Al ₂ O ₃ mixture increased, the CB combustion temperature increased.

Here, in Example 2 (symbol 71) in which the mixing amount of Pt / Al ₂ O ₃ was 20% by mass, the CB combustion temperature was 411 ° C. This is a temperature that is sufficiently practical for use as a PM combustion catalyst. That is, if the mixed amount of Pt / Al ₂ O ₃ is 20% by mass or less, it is practically used as a PM combustion catalyst. In consideration of the results of FIGS. 1 and 2, the gas oxidation active catalyst can be used as a PM combustion catalyst as long as the amount of Pt / Al ₂ O ₃ is at least in the range of 10% by mass to 20% by mass. It can be said that it showed excellent characteristics.

FIG. 3 shows the relationship between the CO oxidation activity of Example 4 and Comparative Example 4 and the catalyst temperature, and FIG. 4 shows the oxidation activity of C ₃ H ₆ of Example 4 and Comparative Example 4. In each graph, the vertical axis represents the oxidation activity, and the horizontal axis represents the catalyst temperature. In any case, the case of mixing showed higher oxidation activity than the case of lamination. That is, there is an effect that the total amount of Pt for obtaining the same oxidation activity may be small.

5 and 6 show the gas oxidation activity for CO and C ₃ H _{6 in} Example 5 and Comparative Example 5. FIG. The horizontal and vertical axes are the same as those in FIGS. Again, the mixing had higher oxidation activity than the stack. That is, as in Example 4, the effect is that the total amount of Pt for obtaining the same oxidation activity may be small.

  Examples 4 and 5 are cases where La is 0.9 and 0.6. Referring to Table 2, the CB combustion temperatures of La 0.6 and La 0.9 were 365 ° C. and 392 ° C., respectively. Since the CB combustion temperature of La0.8 was 367 ° C., the CB combustion temperature increases as the La content increases.

Referring to FIG. 7 again, in the mixing of perovskite and Pt / Al ₂ O ₃ , the CB combustion temperature increased almost in proportion to the amount of Pt / Al ₂ O ₃ mixed. Therefore, when La0.9 is plotted on the graph (reference numeral 72), the dependency on the mixing amount of Pt / Al ₂ O ₃ when the line 70 is La0.9 is shown. Reference numeral 73 indicates that Pt / Al ₂ O ₃ is assumed to be 20 mass%. The CB combustion temperature at point 73 is approximately 447 ° C.

Also in this assumed Pt / Al ₂ O ₃ mixing amount dependency, a CB combustion temperature of 450 ° C. or less can be expected when the Pt / Al ₂ O ₃ content is 10% by mass to 20% by mass. That is, when the La content in the perovskite is in the range of 0.6 to 0.9, the mixed catalyst of the composite oxide and the oxide-supported noble metal catalyst of the present invention has good characteristics as a PM combustion catalyst and a gas oxidation active catalyst. Have

  The present invention can be suitably used for an exhaust gas filter (DPF) of a diesel engine.

4 is a graph showing CO oxidation activity of Example 1 and Comparative Example 1. 5 is a graph showing CO oxidation activity of Reference Example and Comparative Example 3. 4 is a graph showing CO oxidation activity of Example 4 and Comparative Example 4. ₆ is a graph showing C ₃ H ₆ oxidation activity of Example 4 and Comparative Example 4. 5 is a graph showing CO oxidation activity of Example 5 and Comparative Example 5. ₆ is a graph showing C ₃ H ₆ oxidation activity of Example 5 and Comparative Example 5. It is a graph showing the relationship between the mixing ratio and CB combustion temperature of perovskite and Pt / _Al 2 _{O 3.} It is a figure which shows the structure of DPF using the exhaust gas purification catalyst of this invention.

Claims (3)

La _x Ba _1-x FeO ₃ (0.6 ≦ x ≦ 0.9) which is a complex oxide having a perovskite structure and Pt / Al ₂ O ₃ which is an oxide-supported noble metal catalyst in which a noble metal is supported on an oxide. Diesel exhaust gas purification catalyst in which only these were mixed at a mass ratio of 9: 1 to 8: 2, respectively. An exhaust gas purifying catalyst according to claim 1;
Paint for exhaust gas purification catalyst containing solvent and inorganic binder. A porous filter;
Formed on the surface of the porous filter,
An exhaust gas purifying catalyst according to claim 1;
A diesel exhaust gas purification filter having an exhaust gas purification catalyst layer containing an inorganic binder.