JPH05277369A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To improve the heat resistance of Ir supported on a catalyst carrier and to maintain satisfactory NOx removing performance and removing performance to HC, etc., at a low temp. over a long period of time by supporting a multiple oxide or a multiple metal compd. contg. Ir as well as other noble metal catalyst on a catalyst supporting layer formed on the surface of a carrier. CONSTITUTION:A catalyst supporting layer 11 contg. a metal catalyst is formed on the surface of a carrier 1 and the multiple oxide of Ir and at least one among Ba, Ti, Zr, Co, Sr, Ca, Cu, Nd, La, Gd, Li and Na as well as other noble metal catalyst is supported on the catalyst supporting layer 11. As a result, Ir excellent in NOx removing performance does not cause such thermal deterioration as vaporization at a high temp. or alloying with other metal catalysts and the satisfactory NOx removing performance is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for an exhaust emission control device provided in an automobile engine or the like.

[0002]

2. Description of the Related Art Exhaust gas purification systems for removing harmful components such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) in exhaust gas are used in the exhaust system of automobile engines. This device is provided with a catalyst that promotes the oxidation reaction for carbon monoxide and hydrocarbons and the reduction reaction for nitrogen oxides, and as the catalyst, platinum (Pt), rhodium (Rh), palladium ( Noble metals such as Pd) are commonly used.

Further, according to JP-A-63-116742, cerium (Ce) oxide and zirconium (Z
It has been suggested that, in addition to the above platinum, etc., a noble metal such as iridium (Ir), ruthenium (Ru), osmium (Os), etc. be supported as a catalyst on the support layer made of r) oxide or the like. Of these noble metal catalysts, iridium, in particular, is known to be excellent in NOx purification in an oxidizing atmosphere.

[0004]

However, the above-mentioned iridium becomes a volatile oxide and volatilizes at 1000 ° C or higher,
Further, there is a problem with respect to heat resistance, such as the fact that it is alloyed with other noble metal catalysts due to thermal deterioration to reduce the reaction promoting action of other noble metal catalysts.

Therefore, the present invention improves the heat resistance of the catalyst using iridium and stably obtains its excellent NOx purifying properties for a long period of time, and at the same time, improves the purifying properties of HC and the like at low temperatures. This is an issue.

[0006]

In order to solve the above problems, the present invention is characterized by having the following configuration.

That is, the invention according to claim 1 of the present application (hereinafter referred to as the first invention) is an exhaust gas purifying catalyst comprising a catalyst supporting layer containing a metal catalyst on the surface of a carrier, wherein Iridium (Ir), barium (Ba), titanium (Ti), zirconium (Z
r), cobalt (Co), strontium (Sr), calcium (Ca), copper (Cu), neodymium (Nd),
A composite oxide containing at least one of lanthanum (La), gadolinium (Gd), lithium (Li), and sodium (Na) is supported together with another noble metal catalyst.

Here, the complex oxide is BaI.
rO₃, BaIr_0.5Co_0.5O₃, BaIr_0.2Co_0.8O
_2.80, BaIr_0.3Co_0.7O_2.83, Ba_0.67Sr_0.33I
rO_3.0, Ca₂IrO_Four, Ca IrO₃, Ca_FourIrO₆,
La₂CuIrO₆, Gd₂Ir₂O₇, LaLi_0.5Ir
_0.5O₃, Li₂IrO₃, Li₈IrO₆, Nd₆Ir
₂O₁₃, Nd₂Ir₂O₇, Na₂Ir O₃, Na_FourIr
₃O₈, Sr₂Ir₃O₈, Sr₃Ir O_Five, Sr₂Ir O_Four,
Sr₃Ir₂O₇, Sr_FourIr O₆, Sr_FourIr₃O_Ten, Sr
Ir O₃, Zr₆Ir₃O or the like is used.

The invention according to claim 2 (hereinafter referred to as the second
In the present invention), a base coat layer and an overcoat layer are formed as a catalyst supporting layer on the surface of a carrier, the complex oxide containing iridium in the first invention is supported on the base coat layer, and another noble metal catalyst is added to the base coat layer. And one or both of the overcoat layer and the overcoat layer.

Further, the invention according to claim 3 (hereinafter, referred to as the third
In the same manner as the first invention, an exhaust gas purifying catalyst comprising a catalyst-supporting layer containing a metal catalyst on the surface of a carrier is the iridium (I).
r) and cerium (Ce), aluminum (Al), lanthanum (La), calcium (Ca), chromium (C)
r), lithium (Li), magnesium (Mg), manganese (Mn), molybdenum (Mo), neodymium (N
d), a strontium (Sr), silicon (Si), samarium (Sm), titanium (Ti), yttrium (Y), zirconium (Zr) composite metal compound and at least one of, together with other noble metal catalysts It is characterized by being carried.

Here, the composite metallization in the third invention
As a compound, Al Ir , Al₃Ir , Al₉Ir₂, C
aIr₂, CeIr₂, CeIr₃, CeIr_Five, Cr₃
Ir, Ir₁La, Ir₂La, Ir₃La, Ir_FiveLa,
Ir₇La, Ir₁Li, Ir₃Li, IrMg₃, Mg₄₄
Ir₇, IrMn₃, Mo_3.25Ir, Ir₂Nd , Ir₃N
d_Five, Ir₂Sr, Ir Si₃, Ir₂Si , Ir Si , I
r₃Si , Ir Sm₃, Ir Ti , Ir₃Ti , Ir T
i₃, Ir₂Y_Five, Ir Y₃, Ir₂Y , Zr₃Ir , Zr_Five
Ir₃, Zr Ir₃, Zr₂Ir Etc. are used.

The invention according to claim 4 (hereinafter, referred to as the fourth
According to the invention), a base coat layer and an overcoat layer are formed as a catalyst supporting layer on the surface of a carrier, the complex metal compound containing iridium in the third invention is supported on the base coat layer, and another precious metal catalyst is used as a base coat layer. It is characterized in that it is supported on one or both of the overcoat layers.

[0013]

According to the above structure, iridium, which is excellent in NOx purification, is contained in the catalyst supporting layer in a state of forming a complex oxide or a complex metal compound. In this state, volatilization of the iridium is suppressed or alloying with other noble metal catalyst is prevented even under high temperature, and heat resistance is improved. As a result, it is possible to realize a catalyst that is excellent in NOx purification even when used for a long period of time.

Further, by including the complex oxide or complex metal compound containing iridium, the purifying property at low temperature for HC and the like is maintained and promoted, and the emission amount increases when the engine is cold such as at the time of starting. HC will be effectively purified.

In particular, the one having one catalyst carrying layer according to the first and third inventions is excellent in the NOx purifying property, and the second and third inventions are excellent.
The two-layer structure of the catalyst supporting layer according to the fourth invention is H
It exhibits an excellent effect of purifying C etc. at a low temperature.

[0016]

EXAMPLES Examples of the present invention will be described below. Examples of the present invention include one using a complex oxide containing iridium and one using a complex metal compound containing iridium. Further, for each of them, one layer of catalyst is formed on the surface of the carrier. There are those in which a supporting layer is formed (single coat) and those in which two catalyst supporting layers are formed (double coat). Then, as a first embodiment, a single coat catalyst using a complex oxide of iridium will be described.

The catalyst according to the first embodiment is manufactured as follows.

First, iridium chloride (IrCl ₄ ) and barium oxide (BaO) are prepared, mixed, stirred, dried, calcined, and further powdered to form an iridium-barium composite oxide ( Forming a powder of BaIrO ₃ ). Then, γ-alumina (γ-
Al ₂ O ₃ ) powder 480 g, boehmite (hydrated alumina) 120 g, water 1000 cc, nitric acid (HNO ₃ ) 10
Add cc and stir them to make a first slurry.

Further, cerium oxide (CeO ₂ ) powder 5
40 g, boehmite 60 g, water 1000 cc, nitric acid 1
Add 0 cc and stir them to make a second slurry. Then, the first and second slurries are mixed to form a third slurry.

Next, the honeycomb-shaped carrier is immersed in the third slurry prepared as described above and pulled up. Then, the excess slurry is removed by air blow, and the carrier is heated at 250 ° C. for 2 hours.
Dry for an hour. Then, it is baked at 600 ° C. for 2 hours.

Further, the above-mentioned carrier is prepared by using dinitrodiamine platinum [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] and rhodium nitrate [Rh.
(NO ₃ ) ₃ ], and dinitrodiamine palladium [Pd
(NO ₂ ) ₂ (NO ₃ ) ₂ ] in each solution at 250 ° C.
It is soaked for 2 hours each in order to impregnate each noble metal catalyst component of platinum, rhodium and palladium with 600
Bake for 2 hours at ℃.

As a result, as shown in FIG. 1, a catalyst supporting layer 11 containing iridium-barium composite oxide and platinum, rhodium and palladium as catalyst components is formed on the surface of the carrier 1. Become.

In this case, the catalyst supporting layer is prepared so that the weight ratio thereof is 28% with respect to the carrier, and the amount of the iridium-barium composite oxide supported is 5% by weight with respect to the carrier layer. Adjusted to ~ 8%. Further, the loading amounts of platinum, rhodium and palladium in the loading layer are 1.33, 0.27 and 1 / liter, respectively, per liter of the carrier volume.
Prepared to 1.00 g.

Next, a method for producing a double-coated catalyst using the complex oxide containing iridium according to the second embodiment will be described.

Also in this embodiment, first, iridium chloride and barium oxide are used to form a powder of an iridium-barium composite oxide in the same manner as in the first embodiment, and then γ is added to the powder. 480 g of alumina powder,
120 g of boehmite, 1000 cc of water and 10 cc of nitric acid are added, and these are stirred to make a first slurry. This first slurry is the first slurry used in the first embodiment.
Is exactly the same as the slurry.

Next, in this example, after the carrier was immersed in the first slurry prepared as described above and pulled up,
Excess slurry is removed by air blow, 250 ℃
And dried at 600 ° C. for 2 hours.

Then, the carrier is immersed in each solution of dinitrodiamine platinum and rhodium nitrate at 250 ° C. for 2 hours to impregnate the noble metal catalyst components of platinum and rhodium, and calcined at 600 ° C. for 2 hours. To do.
Thereby, as shown in FIG. 2, first, on the surface of the carrier 1, a base coat layer 1 containing iridium-barium composite oxide as a catalyst component and platinum and rhodium.
2 will be formed.

Next, an aqueous dinitrodiaminepalladium solution was added to the cerium oxide powder, and the mixture was stirred, dried and fired, and crushed to form a cerium oxide powder containing palladium. 540 g of this powder was added to boehmite 60.
g, 1000 cc of water, and 10 cc of nitric acid are added, and these are stirred to form a second slurry.

Then, the carrier on which the base coat layer was formed as described above was dipped in this second slurry, and after pulling it up, excess slurry was removed and then 200 °
Dry at C for 2 hours and then bake at 600 ° C for 2 hours. As a result, the overcoat layer 13 containing palladium as a catalyst component on the base coat layer 12 is formed.
Will be formed.

In this case, in this double-coated catalyst, the base coat layer is 14% by weight with respect to the carrier.
The overcoat layer is prepared to be 28%. Further, as in the above-mentioned embodiment, iridium-
The supported amount of barium complex oxide is adjusted to 5 to 8% by weight ratio with respect to the catalyst supporting layer, and the supporting amounts of platinum, rhodium and palladium in the supporting layer are respectively per 1 liter of the carrier volume. 1.33, 0.27, 1.0
Prepared to 0 g.

As described above, single-coated and double-coated catalysts containing the iridium complex oxide are manufactured.

Next, the results of a test confirming the purifying properties of these catalysts against HC and NOx will be described.

Here, in the tests described below, in order to confirm the durability of the catalyst, a catalyst subjected to forced heat deterioration treatment by aging at 1000 ° C. for 50 hours was used, and exhaust gas was passed through it. At this time, the purification rate of HC and the purification rate of NOx were obtained using the exhaust gas temperature as a parameter.

In the HC purification rate confirmation test, the engine is operated with the air-fuel ratio set to a slightly rich (A / F = 14.5). In the NOx purification rate confirmation test, the air-fuel ratio is set to lean (A /F=16.0) was set for operation.

In the tests of the first and second examples, in addition to the catalyst containing the iridium-barium composite oxide produced by the above-described method, as a comparative example, one containing iridium alone, and The purification rate was also confirmed for those that did not contain iridium. Among these test products, the content of each catalyst component of the product of this example and the product containing iridium alone was Pt: 1.33, Rh: 0.27, Pd: 1.0, I
r: 1.6, and the content of each catalyst component in the iridium-free product was: Pt / Rh = 5/1 mixture: 1.6, Pd: 1.0. Here, the numerical value is the content (g / l) per liter of the carrier, and the content of iridium of 1.6 g / l in the product of this example is the catalyst of iridium-barium composite oxide (BaIrO ₃ ). This corresponds to 5% by weight with respect to the carrier layer.

The result of the test under the above conditions is shown in FIG.
~ As shown in Fig. 6.

First, regarding the purification performance of the single coat catalyst for HC, as shown in FIG. 3, the catalyst according to the embodiment of the present invention containing iridium as a complex oxide is
It is possible to achieve the same purification rate at a low temperature as compared with those containing iridium alone and those not containing iridium, and the catalyst according to the present example has a low-temperature purifying property for HC of 1000 ° C. It was confirmed that it was maintained even after a 50-hour heat deterioration test. Incidentally, among the comparative examples, the iridium alone-containing product has lower low-temperature purifying properties than the non-containing product, because the iridium contained alone alloys with other noble metal catalysts and adversely affects its purifying action. It is thought to be due to the fact.

The purifying property of the single coat catalyst for NOx is as shown in FIG.
x A remarkable effect on the purifying property was confirmed, and in particular, the catalyst according to the example of the present invention containing this as a complex oxide exhibits a higher purifying property as compared with the catalyst containing it alone.

Further, the purification performance of the double-coated catalyst for HC is as shown in FIG. 5, and as in the case of the single coat shown in FIG. 3, the catalyst according to the embodiment of the present invention containing iridium as a complex oxide. It was confirmed that the low-temperature purifying property of is superior to that of iridium alone and that of iridium alone.

As is clear from the comparison of the result of FIG. 5 with the result of FIG. 3, the double coat provides a higher HC purifying property at a lower temperature than the single coat.

Further, the purification performance of the double-coated catalyst for NOx is as shown in FIG. 6, and the iridium NO
x The effect on purifying property is shown, but the effect is
It is not as noticeable as in the case of the single coat shown in FIG. This is because the NOx purification action of iridium is activated in the oxygen atmosphere, but in the case of the double coat,
It is considered that oxygen is deficient in the base coat layer supporting iridium as a result of oxygen being taken into the overcoat layer.

In the above examples, iridium chloride and barium oxide were used as the material of the first slurry containing the complex oxide containing iridium, but oxides can also be used as the compound of iridium. There are compounds that form a complex with this, such as barium, titanium, zirconium, cobalt, strontium, calcium,
Copper, neodymium, lanthanum, gadolinium, lithium,
It is possible to use sodium oxide, chloride, nitric oxide, hydroxide and carbonate.

Next, as the third and fourth embodiments of the present invention,
A single-coated catalyst and a double-coated catalyst using a composite metal compound containing iridium will be described.

First, the single-coated catalyst according to the third embodiment is manufactured as follows, in substantially the same manner as the catalyst of the first embodiment.

That is, in this embodiment, first, iridium and lanthanum as metals are prepared, mixed, stirred, dried, fired, and further pulverized to obtain an iridium-lanthanum composite metal. Compound (Ir ₂ L
Form the powder of a). Then, 480 g of γ-alumina powder, 120 g of boehmite, and 1000 c of water were added to this powder.
c, nitric acid 10 cc are added, and they are stirred to make a first slurry.

To 540 g of cerium oxide powder, 60 g of boehmite, 1000 cc of water, and 10 cc of nitric acid were added, and these were stirred to form a second slurry. And
The first and second slurries are mixed to form a third slurry.

Next, the carrier is dipped in the third slurry and pulled up, and then the excess slurry is removed by air blow and dried at 250 ° C. for 2 hours, and then 600 ° C.
Bake for 2 hours.

Further, the above carrier is immersed in each solution of dinitrodiamine platinum, rhodium nitrate and dinitrodiamine palladium at 250 ° C. for 2 hours for impregnation with each noble metal catalyst component of platinum, rhodium and palladium. This is baked at 600 ° C. for 2 hours.

As a result, as shown in FIG. 7, on the surface of the carrier 1, a catalyst supporting layer 21 containing an iridium-lanthanum complex metal compound and platinum, rhodium and palladium as catalyst components is formed. Become.

Here, the catalyst-supporting layer was prepared so that the weight ratio to the carrier was 28%, and the amount of the iridium-lanthanum composite metal compound supported was 5 to the carrier layer in the weight ratio. Adjusted to 8%. Further, the loading amounts of platinum, rhodium and palladium in the loading layer are 1.33, 0.27 and 1 / liter, respectively, per liter of the carrier volume.
Prepared to 1.00 g.

Next, a method for producing a double-coated catalyst using the complex metal compound containing iridium according to the second embodiment will be described.

Also in this embodiment, iridium and lanthanum as metals are used, and the iridium-lanthanum composite metal compound (Ir ₂ L) is used in the same manner as in the third embodiment.
a) powder is formed, and then 480 g of γ-alumina powder, 120 g of boehmite, and 1000 c of water are added to this powder.
c and nitric acid (10 cc) are added, and these are stirred to make a first slurry. This first slurry is the third
It is exactly the same as the first slurry used in the examples.

Next, the carrier is dipped in the first slurry, pulled up to remove excess slurry, dried at 250 ° C. for 2 hours, and then calcined at 600 ° C. for 2 hours.

Then, this carrier was immersed in each solution of dinitrodiamine platinum and rhodium nitrate at 250 ° C. for 2 hours to impregnate the noble metal catalyst components of platinum and rhodium and calcined at 600 ° C. for 2 hours. To do.
As a result, as shown in FIG. 8, first, the base coat layer 22 containing iridium-lanthanum mixed metal compound as a catalyst component and platinum and rhodium is formed on the surface of the carrier 1.

Next, to the cerium oxide powder, an aqueous solution of cynitrodiamine palladium was added, and the mixture was stirred, dried and fired, and crushed to form a cerium oxide powder containing palladium. 540 g of this powder was added to boehmite. 60
g, 1000 cc of water, and 10 cc of nitric acid are added, and these are stirred to form a second slurry.

Then, the carrier having the base coat layer 22 formed thereon is dipped in the second slurry, pulled up, and then the excess slurry is removed, followed by drying at 200 ° C. for 2 hours and further at 600 ° C. Bake for 2 hours. As a result, the overcoat layer 23 containing palladium as a catalyst component is formed on the base coat layer 22.

In this case, in this double-coated catalyst, the base coat layer is 14% by weight with respect to the carrier.
The overcoat layer is prepared to be 28%. Further, as in the third embodiment, the supported amount of the iridium-lanthanum mixed metal compound was adjusted to 5 to 8% by weight ratio with respect to the catalyst supporting layer, and further platinum, rhodium and palladium in the supporting layer were adjusted. The supported amounts are 1.33 and 0.2, respectively, per liter of the carrier volume.
7. Prepared to 1.00 g.

As described above, as the third and fourth examples, single-coated and double-coated catalysts containing the complex metal compound of iridium are manufactured.

Next, the results of the purifying ability confirmation test for HC and NOx of these catalysts will be described.

Here, in the tests on these examples, as in the case of the first and second examples, 10
Using a catalyst that has been subjected to forced heat deterioration treatment by aging at 00 ° C for 50 hours, and in the HC purification rate confirmation test, the engine was set at a slightly rich air-fuel ratio (A / F = 14.5). In the test for confirming the NOx purification rate, the engine was operated with the air-fuel ratio set to lean (A / F = 16.0).

In addition to the catalysts containing the iridium-lanthanum composite metal compounds according to the third and fourth examples, as comparative examples, those containing iridium alone and those not containing iridium were also tested. Further, the content of each catalyst component in these samples is the same as in the above-mentioned first and second embodiments.

The results of the tests on the third and fourth examples are shown in FIGS. As is clear from these figures, even when the iridium-lanthanum complex metal compound was supported, the same results as when the complex oxide of iridium-barium was supported were obtained, and iridium had good purification performance against NOx. It was confirmed that the low temperature detergency against HC and HC was maintained by a heat deterioration test at 1000 ° C. for 50 hours.

[0063]

As described above, according to the exhaust gas catalyst of the present invention, the heat of iridium, which is excellent in the ability to purify NOx, is volatilized at high temperatures or alloyed with other metal catalysts. Good NOx without deterioration
Cleanability will be maintained. In addition, the purification performance at low temperatures for HC, which emits a large amount when the engine is cold, such as at the time of starting, is improved and maintained, and as a result, a good exhaust gas is obtained especially as a catalyst for an engine for automobiles. A catalyst whose purifying property is maintained for a long period of time will be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a catalyst according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of a catalyst according to a second embodiment of the present invention.

FIG. 3 is a graph showing the HC purification performance of the catalyst according to the first example.

FIG. 4 is a graph showing the NOx purification performance of the catalyst according to the first example.

FIG. 5 is a graph showing the HC purification performance of the catalyst according to the second example.

FIG. 6 is a graph showing the NOx purification performance of the catalyst according to the second example.

FIG. 7 is a sectional view showing the structure of a catalyst according to a third embodiment of the present invention.

FIG. 8 is a sectional view showing a structure of a catalyst according to a fourth embodiment of the present invention.

FIG. 9 is a graph showing the HC purification performance of the catalyst according to the third example.

FIG. 10 is a graph showing the NOx purification performance of the catalyst according to the third example.

FIG. 11 is a graph showing the HC purification performance of the catalyst according to the fourth example.

FIG. 12 is a graph showing the NOx purification performance of the catalyst according to the fourth example.

[Explanation of symbols]

 1 Carrier 11,21 Catalyst Support Layer 12,22 Catalyst Support Layer (Base Coat Layer) 13,23 Catalyst Support Layer (Overcoat Layer)

Claims (4)

[Claims] 1. A catalyst for exhaust gas purification, comprising a catalyst supporting layer containing a metal catalyst on the surface of a carrier, wherein iridium, barium, titanium, zirconium, cobalt and strontium are contained in the catalyst supporting layer. calcium,
Copper, neodymium, lanthanum, gadolinium, lithium,
An exhaust gas purifying catalyst comprising a complex oxide containing at least one of sodium and other precious metal catalysts. 2. An exhaust gas purifying catalyst comprising a catalyst-supporting layer containing a metal catalyst on the surface of a carrier, wherein the catalyst-supporting layer comprises a base coat layer and an overcoat layer. , Iridium and at least one of barium, titanium, zirconium, cobalt, strontium, calcium, copper, neodymium, lanthanum, gadolinium, lithium, and sodium are supported, and another noble metal catalyst is used as the base coat. An exhaust gas purifying catalyst, which is supported on one or both of a layer and an overcoat layer. 3. An exhaust gas purifying catalyst comprising a catalyst-supporting layer containing a metal catalyst on the surface of a carrier, wherein iridium, cerium, aluminum, lanthanum, calcium and chromium are contained in the catalyst-supporting layer. Lithium, magnesium, manganese, molybdenum, neodymium, strontium, silicon, samarium, titanium, yttrium,
An exhaust gas purifying catalyst comprising a composite metal compound containing at least one of zirconium and another noble metal catalyst. 4. An exhaust gas purifying catalyst comprising a catalyst-supporting layer containing a metal catalyst on the surface of a carrier, wherein the catalyst-supporting layer comprises a base coat layer and an overcoat layer. , Iridium and at least one of cerium, aluminum, lanthanum, calcium, chromium, lithium, magnesium, manganese, molybdenum, neodymium, strontium, silicon, samarium, titanium, yttrium, and zirconium are supported together with An exhaust gas purifying catalyst, wherein the other noble metal catalyst is supported on one or both of the base coat layer and the overcoat layer.