JP2823251B2 - Exhaust gas purifying catalyst and method for producing exhaust gas purifying catalyst - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst having excellent heat resistance and a method for producing the exhaust gas purifying catalyst.

(Prior Art) Recently, it has been desired to improve the heat resistance of an exhaust gas purifying catalyst in order to increase the output of an engine, improve fuel, and improve emission.

Therefore, as shown in JP-B-62-14338, a slurry obtained by mixing activated alumina, cerium, zirconium, at least one of iron and nickel, and at least one of platinum, palladium and rhodium. There has been proposed an exhaust gas purifying catalyst obtained by wash-coating a liquid on the surface of a catalyst carrier.

On the other hand, as disclosed in JP-A-62-71536, platinum (P
a first coat layer made of an alumina layer containing t) and rhodium (Rh), and a second coat layer containing cerium oxide (CeO ₂ ) and palladium (Pd) provided on the first coat layer. Things are known.

(Problems to be Solved by the Invention) However, in the exhaust gas purifying catalyst, a noble metal catalyst component such as platinum (Pt) is supported on the alumina coat layer (wash coat layer), and the heat of the exhaust gas is reduced. Under such circumstances, the noble metal catalyst component tends to undergo sintering (coagulation and coarsening) and thermally deteriorate.

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent heat deterioration of a noble metal and improve heat resistance.

(Means and Actions for Solving the Problems) In order to achieve the above object, according to the first aspect of the present invention, there is provided an exhaust gas purification method in which an alumina layer containing a noble metal catalyst component is formed on a surface of a catalyst carrier. In the catalyst for use, the noble metal catalyst component of the alumina layer is lanthanum oxide,
The alumina layer is dispersed and contained in the alumina layer while being fixed to at least one of the barium oxide particles.

With the above configuration, the noble metal catalyst component of the alumina layer is
Lanthanum oxide, by being fixed to at least one of the barium oxide particles, the noble metal catalyst component and the particles of the lanthanum oxide and the like are in contact with each other, lanthanum oxide and the like as a heat stable component, the noble metal catalyst component The sintering is effectively suppressed, and the interaction between the noble metal catalyst component and the alumina of the alumina layer (particularly, the reaction at a high temperature) is also effectively suppressed. For this reason, heat deterioration of a noble metal can be suppressed and heat resistance can be improved.

In order to achieve the above object, according to the second aspect of the present invention, in the first aspect, the noble metal catalyst component is made of platinum.

According to the above configuration, even if the noble metal catalyst component is platinum, the same operation and effect as the above-described claim 1 are produced.

Furthermore, in order to achieve the above object, according to the third aspect of the present invention, in the second aspect, rhodium is fixed to alumina particles of the alumina layer.

With the above-described configuration, sintering between rhodiums and alloying of rhodium and platinum can be suppressed, and the purification performance of HC, NOx, and CO can be improved.

Furthermore, in order to achieve the above object, according to the invention of claim 4, a first coat layer made of an alumina layer containing a noble metal catalyst component is formed on the surface of the catalyst carrier, and the first coat layer is formed above the first coat layer. An exhaust gas purifying catalyst having a second coat layer formed of a noble metal catalyst component, cerium oxide and alumina, wherein the noble metal catalyst component of the first coat layer is fixed to at least one of lanthanum oxide and barium oxide particles. It is configured to be dispersed and contained in the first coat layer in the state of being performed.

With the configuration described above, the noble metal catalyst component of the first coat layer is fixed to at least one of lanthanum oxide and barium oxide particles, so that the noble metal catalyst component and the particles of the lanthanum oxide and the like are in contact with each other. And lanthanum oxide or the like as a heat stable component effectively suppresses sintering of the noble metal catalyst component, and also effectively interacts with the noble metal catalyst component and the alumina of the first coat layer (particularly, reaction at high temperature). Will be suppressed. For this reason, even if it has the first and second coat layers,
The heat deterioration can be improved by suppressing the thermal deterioration of the noble metal.

According to a fifth aspect of the present invention, there is provided a method for producing an exhaust gas purifying catalyst comprising forming an alumina layer containing a noble metal catalyst component on a surface of a catalyst carrier, comprising the steps of: Mixing at least one of the noble metal solution and the noble metal solution, and drying the mixture to produce a product in which the noble metal catalyst component is immobilized on at least one of barium oxide, and A second step of mixing the product of the first step with alumina and forming a coat layer on the surface of the catalyst carrier with the mixture.

According to the configuration described above, in the first step, the noble metal catalyst component can be selectively impregnated and fixed to at least one of lanthanum oxide and barium oxide, and such a product and alumina are mixed in the second step. By using this, it is possible to produce the exhaust gas purifying catalyst according to claim 1 having improved heat resistance.

Furthermore, in order to achieve the above object, according to the invention of claim 6, in mixing at least one of lanthanum oxide and barium oxide with a noble metal solution,
At least one of barium oxides is used in a powder state.

According to the above configuration, even if at least one of lanthanum oxide and barium oxide is in a powder state, in the first step, the noble metal catalyst component is selectively added to at least one of lanthanum oxide and barium oxide. Can be impregnated and fixed, and also in this case, the exhaust gas purifying catalyst according to claim 1 with improved heat resistance can be manufactured.

Furthermore, in order to achieve the above object, according to the invention of claim 7, the method according to claim 5, wherein at least one of lanthanum oxide and barium oxide is mixed with the noble metal solution,
At least one of barium oxides is used in a solution state.

With the above configuration, even if at least one of lanthanum oxide and barium oxide is in a solution state, in the first step, the noble metal catalyst component is selectively added to at least one of lanthanum oxide and barium oxide. In this case, the catalyst can be impregnated and fixed, and also in this case, the exhaust gas purifying catalyst according to claim 1 having improved heat resistance can be manufactured.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 to 4, reference numeral 1 denotes an exhaust gas purifying catalyst according to an embodiment of the present invention. The catalyst 1 has a structure as shown in the specific example 1 of FIG. 3 and the specific example 2 of FIG. They have a structure in which a first coat layer 3 as an alumina coat layer and a second coat layer 4 containing cerium oxide as a main component are sequentially provided on a catalyst carrier 2.

The catalyst carrier 2 is formed in a honeycomb structure in both the specific examples 1 and 2, and the catalyst carrier 2 is made of a ceramic such as cordierite. In place of this ceramic, a heat-resistant metal, a heat-resistant inorganic fiber, or the like may be used.

The first coat layer 3 contains activated alumina as a main component,
The active alumina contains a noble metal catalyst component. Activated alumina, in the specific example 1,
Rhodium (Rh) is immobilized on the surface of each particle, and in Example 2, Rh is simply dispersed in the alumina layer. For example, Pt is used as the noble metal component. The Pt is lanthanum oxide (La ₂ O _3), is fixed with at least one in the dispersion state of the barium oxide (BaO) particles, the La ₂ O
_The Pt is dispersed in the first coat layer 3 via _three particles or the like.

The second coat layer 4 is configured to contain cerium oxide (CeO ₂ ), a noble metal catalyst component, and alumina.
In specific example 1, zirconium (Zr) is immobilized on CeO ₂ , and as a noble metal catalyst component, for example, palladium (Pd)
In the specific example 2, Pd as a noble metal catalyst component is fixed on the surface of each particle of CeO ₂ .

Such a catalyst 1 (specific examples 1 and 2) is manufactured as follows.

(Specific Example 1) First, a solution of rhodium nitrate was added to 100 g of γ-Al ₂ O ₃ as active alumina and 100 g of boehmite and mixed, and the mixture was dried to obtain a solid mass, which was pulverized to obtain powder A. obtain.

On the other hand, a solution of gintrodiamine platinum [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] is added to BaO particles and La ₂ O ₃ particles and mixed, and the mixture is dried to form a solid mass, which is pulverized. To obtain powder B.

Next, a slurry liquid is prepared by mixing powders A and B, 240 cc of water and 1.0 cc of nitric acid, and a catalyst carrier having a honeycomb structure is immersed in the slurry liquid, and then pulled up to remove excess slurry liquid by air blowing. . Then, the catalyst carrier 2 to which the slurry liquid has adhered is dried at a temperature of 130 ° C. for 1 hour, and then fired at a temperature of 550 ° C. for 1.5 hours to form a first coat layer 3. In this case, the alumina amount (wash coat amount) is 7% by weight based on the catalyst carrier 2, and the total noble metal amount is 1.6 g.
/ (However, Pt: Rh = 5: 1).

Next, a solution of zirconium nitrate [Zr (NO ₃ ) ₂ ] is added to 120 g of CeO ₂ and 50 g of boehmite and mixed, and the mixture is dried to obtain a solid mass, which is pulverized to obtain powder C.

Next, a solution of palladium chloride and 240 cc of water are added to the powder C to form a slurry solution, and the catalyst carrier 2 on which the first coat layer 3 is formed is immersed in the slurry solution, and then pulled up to remove excess The slurry liquid is removed by air blow.
Then, the catalyst carrier 2 to which the slurry liquid has adhered is heated to 130 ° C.
At 550 ° C for 1.5 hours.
By firing for a time, the second coat layer 4 is formed on the first coat layer 3.

In this case, the alumina amount (wash coat amount) is 14% by weight with respect to the catalyst carrier 2, and the Pd amount is 1.0 g /.

In the catalyst 1 according to the specific example 1, La ₂ O
_{3. The} amount of BaO added is 5% by weight for 100% by weight of the wash coat, and the amount of CeO ₂ is 14% by weight for 100% by weight of the wash coat.

(Specific Example 2) BaO, La ₂ O ₃ and gintrodiamine platinum [Pt (NO ₂ ) (N
H ₃ ) ₂ ], and the mixture is dried to a solid mass, which is ground to obtain powder A.

Next, the powder A, 100 g of activated alumina, 100 g of boehmite, 240 cc of water, and 1.0 cc of nitric acid were mixed to prepare a slurry, and the catalyst carrier 2 was immersed in the slurry, and then pulled up. The excess slurry liquid is removed by air blow. Then, the catalyst carrier is dried at a temperature of 130 ° C. for 1 hour, and calcined at a temperature of 550 ° C. for 1.5 hours to form a coat layer. Next, the coating layer of the catalyst carrier 2 was impregnated with a rhodium nitrate solution, and the solution was heated at 130 ° C. for 1 hour.
The first coat layer 3 is formed by drying for 1.5 hours and firing at a temperature of 550 ° C. for 1.5 hours. In this case, the alumina amount (wash coat amount) is 7% by weight based on the catalyst carrier 2, and the total noble metal amount is 1.6 g / (Pt: Rh = 5: 1).

Next, palladium chloride is added to 120 g of CeO ₂ and 50 g of boehmite and mixed and dried to obtain a solid mass, which is pulverized to obtain a powder. 240 cc of water is added to the powder to form a slurry liquid, the catalyst carrier on which the first coat layer 3 is formed is immersed in the slurry liquid, and then it is pulled up to remove excess slurry liquid by air blowing. And 130
At 550 ℃ for 1 hour, then at 550 ℃
Baking for 1.5 hours, the second coat layer 4 on the first coat layer 3
To form In this case, the alumina amount (wash coat amount) is 14% by weight with respect to the catalyst carrier 2, and the Pd amount is 1.0 g /.

In the catalyst 1 according to the specific example 2, La ₂ O
_3, the added amount of BaO is, each 5% by weight with respect to the washcoat amount 100% by weight, the addition amount of CeO ₂ is 14% by weight relative to the washcoat.

Therefore, in the catalyst 1 according to the specific example 1, Pt as the noble metal catalyst component of the first coat layer 3 is La.
Because it is dispersed in immobilized state ₂ O _3, BaO particles, a state in which the Pt is in contact with each other in the particles such as the _{La 2 O 3, La 2 O} 3 and the like, as a heat stabilizer component, In addition to effectively suppressing the sintering of Pt, the interaction between Pt and activated alumina (particularly, the reaction at a high temperature) is also effectively suppressed. For this reason, heat deterioration of Pt can be suppressed and heat resistance can be improved.

Further, in the catalyst 1 according to the specific example 1, Zr is fixed to the CeO ₂ particles. Therefore, Zr is that it is possible to suppress the crystallization enlargement of CeO _2, so that it is possible to suppress the thermal degradation of CeO _2. This makes it possible to utilize the oxygen storage effect of CeO ₂ for a long time.

Furthermore, in the catalyst 1 according to the specific example 1, Rh is fixed to activated alumina particles having a large surface area. For this reason, the purification performance of HC, NOx, and CO can be improved.

On the other hand, in the catalyst 1 according to the specific example 2, Pt is La.
_Since it is dispersed in a state of being fixed to the ₂ O ₃ and BaO particles, the heat deterioration of Pt can be suppressed and the heat resistance can be improved as in the case of the specific example 1.

Next, in order to confirm the heat resistance of the catalysts of the specific examples 1 and 2 according to the above-described example, a test was performed under certain test conditions while comparing with the following comparative examples 1 and 2 which are conventional exhaust gas purifying catalysts. Was done.

Comparative Example 1 First, 240 g of water was added to 100 g of γ-Al ₂ O ₃ and 100 g of boehmite.
c, 1 cc of nitric acid is added and mixed to form a slurry liquid, and the slurry liquid has a total wash coat amount of 21% by weight with respect to the catalyst carrier (honeycomb structure) and a wash coat amount of 100% by weight. 5% by weight of Zr, 5% of La
% By weight and 5% by weight of Ba are added and stirred to obtain an alumina slurry liquid.

Next, the catalyst carrier is immersed in this alumina slurry liquid,
Thereafter, the slurry is pulled up and excess slurry liquid is removed by air blow.

Next, the catalyst carrier to which the alumina slurry was
At 550 ℃ for 1 hour, then at 550 ℃
Firing for 1.5 hours to form a coat layer on the surface of the catalyst carrier.

Next, the catalyst carrier on which the coat layer was formed was immersed in a solution of Pt, Rh, and Pd at a predetermined concentration, and the same amount of P as in this example was used.
Impregnate t, Rh and Pd. Then, this catalyst carrier is
C. for 1 hour and then calcined at a temperature of 600.degree. C. for 2 hours to obtain a catalyst according to Comparative Example 1.

Comparative Example 2 First, 100 g of γ-Al ₂ O ₃ and 100 g of boehmite were mixed with 240 c of water.
c, 1 cc of nitric acid is added and mixed to form a slurry liquid, and a catalyst carrier having a honeycomb structure is immersed in the slurry liquid, and then pulled up to remove excess slurry liquid by air blowing. Then, it is dried at a temperature of 130 ° C. for 1 hour, and then calcined at a temperature of 550 ° C. for 1.5 hours to form a coat layer on the surface of the catalyst carrier.

Next, the coat layer of the catalyst carrier is impregnated with platinum chloride and rhodium chloride, respectively, dried at a temperature of 200 ° C. for 1 hour, and calcined at 600 ° C. for 2 hours to form a first coat layer on the catalyst carrier. I do. In this case, the alumina amount (wash coat amount) of the first coat layer is 7% by weight with respect to the catalyst carrier, and the total noble metal amount is 1.6 g / (Pt: Rh = 5: 1).

Next, palladium chloride is added to 50 g of CeO ₂ and boehmite and mixed and dried to obtain a solid mass, which is pulverized to obtain a powder. 240 cc of water is added to the powder to form a slurry liquid, and the catalyst carrier on which the first coat layer is formed is immersed in the slurry liquid, and then it is pulled up to remove excess slurry liquid by air blowing. Then, it is dried at a temperature of 130 ° C. for 1 hour, and then baked at a temperature of 550 ° C. for 1.5 hours to form a second coat layer on the first coat layer. In this case, the alumina amount (wash coat amount) of the second coat layer is 14% by weight based on the catalyst carrier, and the Pd amount is 1.0 g /.

Test conditions The catalyst capacity is 24 ml for each case.

Before the test, aging is performed by heating at 900 ° C for 50 hours.

Under the air-fuel ratio A / F of 14.7, the space velocity is set at 60,000H- ¹ , and the HC purification rate is examined by changing the exhaust gas temperature at the catalyst inlet.

Test Results As a result of such a test, the contents shown in FIG. 5 were obtained. According to this content, specific examples 1 and 2 of the present embodiment are comparative examples 1 and 2.
It can be understood that the purification performance is exhibited from the exhaust temperature lower than that of the exhaust gas of Example 2, and the heat deterioration is suppressed and the heat resistance is improved.

Next, the addition amounts of Zr, La ₂ O ₃ , BaO, and CeO ₂ in the coat layer were examined.

The addition amount of Zr La ₂ O _3, BaO, respectively 1 wt%, in the case of CeO ₂ 14 wt%, La ₂
When O ₃ and BaO are each 5% by weight and CeO _{2 is} 14% by weight, La ₂ O ₃ and B
400 ° C for each case of 10% by weight of aO and 14% by weight of CeO ₂
HC purification performance (A / F:
14.7).

As a result, the contents shown in FIG. 6 were obtained. According to this content, in each case, when the amount of Zr added was less than 1% by weight or more than 10% by weight, the purification performance was reduced. It is considered that the reason why the purification performance deteriorates when the added amount of Zr exceeds 10% by weight is that the amount of Zr is too large and the function of other components is suppressed. Therefore, the addition of Zr is preferably 1 to 10% by weight.

Addition amount of La ₂ O ₃ 1% by weight of Zr, 14% by weight of CeO ₂ , 5% by weight of Zr, CeO
_In the case of ₂ 14% by weight, Zr 10% by weight, and CeO ₂ 14% by weight, the amount of La ₂ O ₃ was changed at a temperature of 400 ° C. for each case.
The purification performance of HC (H / F: 14.7) was examined.

As a result, the content shown in FIG. 7 was obtained. According to this content, in each case, when the added amount of La ₂ O ₃ was less than 1% by weight or more than 10% by weight, the purification performance was reduced. Therefore, the addition amount of La ₂ O ₃ is preferably 1 to 10% by weight.

Addition amount of BaO 1% by weight of Zr, 14% by weight of CeO ₂ , 5% by weight of Zr, CeO
_The purification performance (A / F: 14.7) was examined at a temperature of 400 ° C. for the case of ₂ 14% by weight, Zr 10% by weight, and CeO ₂ 14% by weight while changing the amount of BaO added.

As a result, the contents shown in FIG. 8 were obtained. According to this content, in each case, when the added amount of BaO was less than 1% by weight or more than 10% by weight, the purification performance was reduced. 10% by weight of BaO added
The purification performance is reduced when the pressure exceeds the same as in the case of Zr. Therefore, the addition amount of BaO is also preferably 1 to 10% by weight.

Addition amount of CeO ₂ La ₂ O ₃ , 1% by weight of BaO, Zr 1% by weight, La ₂ O
₃ , 5% by weight of BaO and 5% by weight of Zr, 400 ° C for each case of 1% by weight of La ₂ O ₃ and BaO and 10% by weight of Zr
Purification performance (A / F: 1) by changing the amount of CeO ₂
4.7) was examined.

As a result, the contents shown in FIG. 9 were obtained. According to the contents, in each case, when the added amount of CeO ₂ was less than 5% by weight or more than 30% by weight, the purification performance was reduced. Therefore, the addition amount of CeO ₂ is preferably 5 to 30% by weight.

(Effects of the Invention) As described above, the present invention can prevent heat deterioration of a noble metal and improve heat resistance. Thereby, the low-temperature activity can be stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an exhaust gas purifying catalyst according to an embodiment of the present invention, FIG. 2 is a partially enlarged sectional view showing an exhaust gas purifying catalyst according to an embodiment of the present invention, and FIG. FIG. 4 is a diagram conceptually illustrating a catalyst according to a specific example i of the invention, FIG. 4 is a diagram conceptually illustrating a catalyst according to a specific example 2 of the present invention, and FIG. 5 is an HC purification rate-exhaust gas at a catalyst inlet. FIG. 6 is a characteristic diagram showing the relationship between the addition amount of zirconium and the HC purification rate, and FIG. 7 is a characteristic line diagram showing the relationship between the addition amount of lanthanum oxide and the HC purification ratio. FIG. 8 is a characteristic diagram showing the relationship between the added amount of barium oxide and the HC purification rate, and FIG. 9 is a characteristic diagram showing the relationship between the added amount of cerium oxide and the HC purification ratio. 1: Catalyst 2: Catalyst carrier 3: First coat layer 4: Second coat layer

Claims (7)

(57) [Claims] 1. An exhaust gas purifying catalyst in which an alumina layer containing a noble metal catalyst component is formed on the surface of a catalyst carrier, wherein the noble metal catalyst component of the alumina layer is at least one of lanthanum oxide and barium oxide particles. An exhaust gas purifying catalyst, which is dispersed and contained in the alumina layer in a fixed state. 2. The exhaust gas purifying catalyst according to claim 1, wherein the noble metal catalyst component is platinum. 3. The exhaust gas purifying catalyst according to claim 2, wherein rhodium is fixed to the alumina particles of the alumina layer. 4. A first coat layer comprising an alumina layer containing a noble metal catalyst component is formed on the surface of a catalyst carrier, and a second coat layer comprising a noble metal catalyst component, cerium oxide and alumina is formed above the first coat layer. Wherein the noble metal catalyst component of the first coat layer is lanthanum oxide,
An exhaust gas purifying catalyst, which is dispersed and contained in the first coat layer while being fixed to at least one of barium oxide particles. 5. A method for producing an exhaust gas purifying catalyst wherein an alumina layer containing a noble metal catalyst component is formed on the surface of a catalyst carrier, comprising mixing at least one of lanthanum oxide and barium oxide with a noble metal solution. Drying the mixture, a first step of producing a product in which the noble metal catalyst component is immobilized on at least one of lanthanum oxide and barium oxide; mixing the product of the first step with alumina; A second step of forming a coating layer on the surface of the catalyst carrier using the mixture. 2. A method for producing an exhaust gas purifying catalyst, comprising: 6. The method according to claim 5, wherein at least one of lanthanum oxide and barium oxide is mixed with the noble metal solution, at least one of the lanthanum oxide and barium oxide is used in a powder state. A method for producing an exhaust gas purifying catalyst. 7. The method according to claim 5, wherein when mixing at least one of lanthanum oxide and barium oxide with the noble metal solution, at least one of the lanthanum oxide and barium oxide is used as a solution. Of producing exhaust gas purifying catalyst.