JP3300022B2 - Exhaust gas purification catalyst - Google Patents

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 In an exhaust system of an automobile engine, an exhaust gas purifying device for removing harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) in exhaust gas is provided. This apparatus is provided with a catalyst that promotes the oxidation reaction on carbon monoxide and hydrocarbons and the reduction reaction on nitrogen oxides, and includes platinum (Pt), rhodium (Rh), palladium ( Noble metals such as Pd) are generally used.

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

[0004]

However, the iridium volatilizes as a volatile oxide at 1000 ° C. or higher,
In addition, there is a problem with respect to heat resistance, such as alloying with another noble metal catalyst due to thermal deterioration to reduce the reaction promoting action of another noble metal catalyst.

Therefore, the present invention improves the heat resistance of a catalyst using iridium, stably obtains its excellent NOx purification performance over a long period of time, and also improves the purification performance of HC at a low temperature. That is the task.

[0006]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized in that it is configured as follows.

That is, the invention according to claim 1 of the present application (hereinafter referred to as the first invention) is an exhaust gas purification catalyst comprising a catalyst support layer containing a metal catalyst on the surface of a carrier. Iridium (Ir), barium (Ba), titanium (Ti), zirconium (Z
r), cobalt (Co), strontium (Sr), calcium (Ca), copper (Cu), neodymium (Nd) ,
Moth Doriniumu (Gd), characterized in that a lithium (Li), a composite oxide consisting of at least one of sodium (Na), was loaded with other noble metal catalyst.

The invention according to claim 2 (hereinafter referred to as second invention)
In the invention), as a catalyst support layer on the support surface
After forming a base coat layer and an overcoat layer,
(Ir), barium (Ba), titanium (Ti),
Zirconium (Zr), cobalt (Co), stront
(Sr), calcium (Ca), copper (Cu), neo
Indium (Nd), Lanthanum (La), Gadolinium (G
d), lithium (Li) and sodium (Na)
A base coat layer comprising at least one complex oxide
While supporting other noble metal catalysts on the base coat layer.
And one or both of the overcoat layers
And features.

Here, as the composite oxide, BaI
rO ₃ , BaIr _0.5 Co _0.5 O ₃ , BaIr
_{0.2 Co 0.8 O 2.80, BaIr 0.3} Co
_{0.7 O 2.83, Ba 0.67 Sr 0.33} IrO
_{3.0, Ca 2 IrO 4, CaIrO} 3, Ca 4 IrO
₆ , La ₂ CuIrO ₆ , Gd ₂ Ir ₂ O ₇ , LaLi
_0.5 Ir _0.5 O ₃ , Li ₂ IrO ₃ , Li ₈ IrO
₆ , Nd ₆ Ir ₂ O ₁₃ , Nd ₂ Ir ₂ O ₇ , Na ₂ I
rO ₃ , Na ₄ Ir ₃ O ₈ , Sr ₂ Ir ₃ O ₈ , Sr ₃
IrO ₅ , Sr ₂ IrO ₄ , Sr ₃ Ir ₂ O ₇ , Sr ₄
IrO ₆ , Sr ₄ Ir ₃ O ₁₀ , SrIrO ₃ , Zr ₆
Ir ₃ O or the like is used.

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

Here, the composite metallization according to the third aspect of the invention is described.
The compound is Al Ir , Al_ThreeIr , Al₉Ir_Two, C
aIr_Two, CeIr_Two, CeIr_Three, CeIr_Five, Cr_Three
Ir, Ir₁La, Ir_TwoLa, Ir_ThreeLa, Ir_FiveLa,
Ir₇La, Ir₁Li, Ir_ThreeLi, IrMg_Three, Mg₄₄
Ir₇, IrMn_Three, Mo_3.25Ir, Ir_TwoNd , Ir_ThreeN
d_Five, Ir_TwoSr, Ir Si_Three, Ir_TwoSi , Ir Si , I
r_ThreeSi , Ir Sm_Three, Ir Ti , Ir_ThreeTi , Ir T
i_Three, Ir_TwoY_Five, Ir Y_Three, Ir_TwoY , Zr_ThreeIr , Zr_Five
Ir_Three, Zr Ir_Three, Zr_TwoIr Etc. are used.

The invention according to claim 4 (hereinafter referred to as the fourth invention)
In the invention, a base coat layer and an overcoat layer are formed as a catalyst support layer on the carrier surface, and the iridium-containing composite metal compound of the third invention is supported on the base coat layer, and another noble metal catalyst is formed on the base coat layer. It is characterized by being carried on one or both of the overcoat layers.

[0013]

According to the above-mentioned structure, iridium, which is excellent in purifying NOx, is contained in the catalyst supporting layer in the form of a composite oxide or a composite metal compound. In this state, volatilization of the iridium is suppressed even at a high temperature, or alloying with another noble metal catalyst is prevented, so that heat resistance is improved. as a result,
A catalyst that can obtain excellent NOx purification performance even when used for a long time is realized.

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

[0015] In particular, the catalyst support layer according to the first and third aspects of the present invention having a single catalyst support layer is excellent in NOx purifying property.
When the catalyst supporting layer according to the fourth invention has a two-layer structure,
It exhibits an excellent effect of purifying C at low temperatures at low temperatures.

[0016]

Embodiments of the present invention will be described below. Examples of the present invention include those using a composite oxide containing iridium and those using a composite metal compound containing iridium. Further, for each of them, one layer of catalyst is provided on the surface of the carrier. There is a type in which a support layer is formed (single coat) and a type in which two catalyst support layers are formed (double coat). Then, as a first embodiment, a single-coat catalyst using a composite 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 obtain a composite oxide of iridium-barium (BaO). (BaIrO ₃ ) powder is formed. Then, γ-alumina (γ-
480 g of powder of Al ₂ O ₃ ), 120 g of boehmite (hydrated alumina), 1000 cc of water, 10 nitric acid (HNO ₃ )
Add cc and stir them to make a first slurry.

In addition, 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, pulled up, and the excess slurry is removed by air blowing.
Let dry for hours. Then, firing is performed at 600 ° C. for 2 hours.

Further, the above-mentioned carrier was prepared by using dinitrodiamine platinum [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ], rhodium nitrate [Rh]
(NO ₃ ) ₃ ] and dinitrodiamine palladium [Pd
(NO ₂ ) ₂ (NO ₃ ) ₂ ] at 250 ° C.
For 2 hours to impregnate each of the noble metal catalyst components of platinum, rhodium and palladium,
Bake at 2 ° C for 2 hours.

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

In this case, the catalyst supporting layer is prepared so as to have a weight ratio of 28% with respect to the carrier, and the amount of the iridium-barium composite oxide to be supported is 5% by weight with respect to the supporting layer. Adjusted to ~ 8%. Further, the supported amounts of platinum, rhodium, and palladium in the support layer were 1.33, 0.27,
It is adjusted to 1.00 g.

Next, a method of manufacturing a double-coated catalyst using a composite oxide containing iridium according to the second embodiment will be described.

In this embodiment, first, a powder of a composite oxide of iridium-barium is formed using iridium chloride and barium oxide in the same manner as in the first embodiment. 480 g of alumina powder,
A first slurry is prepared by adding 120 g of boehmite, 1000 cc of water and 10 cc of nitric acid and stirring them. The first slurry is the first slurry used in the first embodiment.
It is exactly the same as the slurry.

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

The carrier is immersed in each of dinitrodiamineplatinum and rhodium nitrate solutions 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. I do.
Thereby, as shown in FIG. 2, first, on the surface of the support 1, a base coat layer 1 containing an iridium-barium composite oxide as a catalyst component, platinum and rhodium was contained.
2 will be formed.

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

Then, the carrier on which the base coat layer is formed as described above is immersed in the second slurry, pulled up, and after removing the excess slurry, the second slurry is dried at 200 ° C.
After drying at C for 2 hours, firing at 600 ° C. for 2 hours is performed. Thereby, the overcoat layer 13 containing palladium as a catalyst component on the base coat layer 12 is formed.
Is formed.

In this case, in this double-coated catalyst, the weight ratio of the base coat layer to the carrier is 14%.
The overcoat layer is prepared to be 28% so that Further, similarly to the above-described embodiment, iridium-
The supported amount of the barium composite oxide is adjusted to 5 to 8% by weight with respect to the catalyst supporting layer, and the supported amounts of platinum, rhodium and palladium in the supporting layer are each 1.33, 0.27, 1.0
It is adjusted to 0 g.

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

Next, the results of tests for confirming the purifying ability of these catalysts against HC and NOx will be described.

Here, in the test described below, in order to confirm the durability of the catalyst, a catalyst which had been subjected to forced thermal degradation treatment by aging at 1000 ° C. for 50 hours was used, and exhaust gas was passed through the catalyst. At this time, the purification rate of HC and the purification rate of NOx were determined using the exhaust gas temperature as a parameter.

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

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, iridium alone as a comparative example, and Purification rates were also confirmed for those containing no iridium. Among these test products, the content of each catalyst component of the product of this example and the product containing only iridium 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 is 1.6 in a mixture of Pt / Rh = 5/1, and Pd: 1.0. Here, the numerical value is the content (g / l) per liter of the carrier, and the content of 1.6 g / l of iridium in the product of the present example is the catalyst of the iridium-barium composite oxide (BaIrO ₃ ). This corresponds to 5% by weight of the carrier layer.

The results of the test under the above conditions are shown in FIG.
6 to FIG.

First, regarding the purifying property 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 composite oxide is as follows.
The same purification rate can be achieved at a low temperature as compared with those containing iridium alone and those not containing iridium. , And 50 hours of thermal degradation test. Among the comparative examples, the low-temperature purifying property of the product containing only iridium is lower than that of the non-containing product, because iridium contained alone alloys with other noble metal catalysts and adversely affects its purifying action. This is probably due to

FIG. 4 shows the purification performance of the single coat catalyst for NOx, which is the same as that of iridium.
x A remarkable effect on the purifying property was confirmed. In particular, the catalyst according to the example of the present invention containing the compound oxide as a composite oxide showed higher purifying property than the catalyst containing the catalyst alone.

The purification performance of the double coat 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 composite oxide. It was confirmed that the low-temperature purifying property was superior to those containing iridium alone and those not containing iridium.

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

Further, the purifying property of the double coat catalyst for NOx is as shown in FIG.
xEffects on purification are shown, but the effects are:
It is not noticeable as in the case of the single coat shown in FIG. This is because iridium's NOx purification action is activated in an oxygen atmosphere.
It is considered that as a result of oxygen being taken into the overcoat layer, the base coat layer supporting iridium is insufficient in oxygen.

In the above embodiment, iridium chloride and barium oxide are used as the material of the first slurry containing the composite oxide containing iridium, but an oxide can be used as the iridium compound. Yes, and as a compound to be compounded with this, barium, titanium, zirconium, cobalt, strontium, calcium,
Copper, neodymium, lanthanum, gadolinium, lithium,
Sodium oxides, chlorides, nitrates, hydroxides, carbonates and the like can be used.

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

First, the single-coated catalyst according to the third embodiment is manufactured in the following manner, 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 powdered to obtain a composite metal of iridium-lanthanum. Compound (Ir ₂ L
Form the powder of a). Then, 480 g of gamma alumina powder, 120 g of boehmite, and 1000 c of water were added to this powder.
c, 10 cc of nitric acid is added, and these are stirred to form a first slurry.

Further, 60 g of boehmite, 1000 cc of water and 10 cc of nitric acid are added to 540 g of cerium oxide powder, and these are stirred to form a second slurry. And
The third slurry is prepared by mixing the first and second slurries.

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

Further, the carrier is immersed in a solution of dinitrodiamine platinum, rhodium nitrate, and dinitrodiamine palladium for 2 hours at 250 ° C. for 2 hours to impregnate the noble metal catalyst components of platinum, rhodium and palladium. This is baked at 600 ° C. for 2 hours.

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

The catalyst supporting layer is prepared so as to have a weight ratio of 28% with respect to the carrier, and the supporting amount of the iridium-lanthanum composite metal compound is 5 to 5% by weight with respect to the supporting layer. It is adjusted to 8%. Further, the supported amounts of platinum, rhodium, and palladium in the support layer were 1.33, 0.27,
It is adjusted to 1.00 g.

Next, a method for manufacturing a double-coated catalyst using a composite metal compound containing iridium according to the fourth embodiment will be described.

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

Next, the carrier is immersed in the first slurry, pulled up, removed of excess slurry, dried at 250 ° C. for 2 hours, and then fired at 600 ° C. for 2 hours.

The carrier was immersed in a solution of dinitrodiamine platinum and rhodium nitrate for 2 hours 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. I do.
As a result, as shown in FIG. 8, first, the base coat layer 22 containing the iridium-lanthanum composite metal compound, platinum, and rhodium as the catalyst components is formed on the surface of the carrier 1.

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

Then, the carrier on which the base coat layer 22 is formed is immersed in the second slurry, pulled up, removed of excess slurry, dried at 200 ° C. for 2 hours, and further dried at 600 ° C. For 2 hours. Thus, 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% so that Similarly to the third embodiment, the loading amount of the iridium-lanthanum composite metal compound is adjusted to 5 to 8% by weight with respect to the catalyst supporting layer, and the platinum, rhodium and palladium in the supporting layer are further adjusted. The loading amount was 1.33 and 0.2, respectively, per liter of the volume of the carrier.
7, adjusted to 1.00 g.

As described above, as the third and fourth embodiments, single-coated and double-coated catalysts containing an iridium composite metal compound are produced.

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

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

Further, in addition to the catalyst containing the iridium-lanthanum composite metal compound according to the third and fourth examples, tests were carried out for those containing iridium alone and those not containing iridium as comparative examples. The content of each catalyst component in these test samples is the same as in the first and second embodiments described above.

Test results for the third and fourth embodiments are as shown in FIGS. As is clear from these figures, even when the iridium-lanthanum composite metal compound is supported, the same result as that obtained when the iridium-barium composite oxide is supported is obtained. Thus, it was confirmed that the low-temperature purifying property of HC and HC was maintained even in a heat deterioration test at 1000 ° C. for 50 hours.

[0063]

As described above, according to the exhaust gas catalyst of the present invention, iridium, which is excellent in NOx purifying property, is heated at a high temperature by volatilization or alloying with other metal catalysts. Good NOx without degradation
Purification will be maintained. In addition, low-temperature purifying properties of HC, which emits a large amount of gas when the engine is cold, such as at the time of starting, are improved and maintained. A catalyst whose purifying property is maintained for a long period of time is realized.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating a configuration 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 embodiment.

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

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

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

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

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

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carrier 11,21 Catalyst carrying layer 12,22 Catalyst carrying layer (base coat layer) 13,23 Catalyst carrying layer (overcoat layer)

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86 F01N 3/28

Claims (4)

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