JP3327574B2 - Automotive 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 purifying automobile exhaust gas, which exhibits excellent catalytic performance by suppressing expansion of a metal foil as a base material of a metallic honeycomb carrier.

[0002]

2. Description of the Related Art Conventionally, many catalysts for purifying exhaust gas discharged from an internal combustion engine such as an automobile have been proposed.
At present, three-way catalysts for purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) at the same time have become mainstream.

[0003] The above three-way catalysts include alumina, alumina-
Platinum (P) is used for refractory inorganic oxide powders such as silica and silica.
t), a catalyst composition obtained by dispersing and supporting a catalyst component such as palladium (Pd) or rhodium (Rh) alone or in combination with a honeycomb carrier made of cordierite or metal, or the like. After coating a refractory inorganic oxide such as alumina, alumina-silica or silica on a honeycomb carrier such as cordierite or metal, the carrier is coated with platinum (Pt), palladium (Pd), rhodium (Rh). Such catalyst components are generally supported by immersing the catalyst components alone or in combination in an aqueous solution.

Further, in order to promote or stabilize the catalytic action of a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh) as a catalyst component, cerium (C) is used.
e), a rare earth compound such as lanthanum (La), a group VIII compound such as nickel (Ni) or iron (Fe), an alkali metal compound, an alkaline earth metal compound, or the like; It has been added to the composition.

[0005]

Among the above-mentioned conventional catalysts, the catalyst using a honeycomb carrier made of metal or the like is characterized by a difference in thermal expansion between the metal carrier and a refractory inorganic oxide such as alumina at a high temperature. In addition, there has been a problem that a coat layer on a metal foil which is a base material of a honeycomb carrier made of metal or the like is peeled off, and the catalytic performance is lowered.

[0006] The present invention solves such a conventional problem,
Oxidation of metal foil as base material of metal honeycomb carrier at high temperature
With excellent catalytic performance that can simultaneously purify hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) without suppressing the elongation of the coating layer on the metal foil and exfoliating the coating layer on the metal foil. It is intended to provide a source catalyst.

[0007]

Means for Solving the Problems The present invention has been made to achieve the above object, and a catalyst for purifying automobile exhaust gas according to the present invention is a metal honeycomb carrier catalyst which can be used at a high temperature in a metal honeycomb carrier. It is the part that is exposed
Only the exhaust gas outlet side portion and / or the central portion is made of an alkali metal and / or
Alternatively, an alumina layer containing an alkaline earth metal, or only this portion, the coating layer is a thick alumina layer containing the metal, and the carrier on which the coating layer is formed is further provided with platinum (Pt), palladium ( Pd), rhodium (R
h) coating an alumina layer containing at least one catalyst component selected from cerium (Ce), lanthanum (La), zirconium (Zr), nickel (Ni), iron (Fe) and barium (Ba). It is characterized by becoming.

In the exhaust gas purifying catalyst of the present invention, potassium (K) is used as the alkali metal contained in the first alumina coat layer or the thick alumina coat layer which comes into contact with the carrier substrate in the portion exposed to high temperatures. ) And the like, and as the alkaline earth metal, calcium (C
a), strontium (Sr), barium (Ba) and the like are preferable. Further, as the alumina layer, an activated alumina layer, an α-alumina layer or the like is used.

The portion of the catalyst of the present invention which is exposed to high temperature (high temperature portion) is the portion 2 of the metal honeycomb carrier 1 shown in FIG. 1 on the exhaust gas outlet side and / or the portion of the metal honeycomb carrier 1 shown in FIG. The central part 3. In FIGS. 1 and 2, reference numeral 4 denotes exhaust gas.

[0010]

In the present invention, although the mechanism by which the elongation of the metal foil is suppressed is not clear, only the portion of the metal honeycomb carrier exposed to high temperature is coated with the first coat layer in contact with the carrier substrate with an alkali metal. And / or forming an alumina layer containing an alkaline earth metal, or only this part of the coat layer as a thick alumina layer containing the metal, to elongate the metal foil as the carrier substrate. Can be suppressed. That is, as the exhaust gas passes through the catalyst, a temperature distribution occurs, and the degree of elongation of the metal foil differs between the high-temperature part and the low-temperature part, and the elongation in the high-temperature part is large. By forming the first coat layer in contact with the material as an alumina layer containing the metal or a thick alumina layer containing the metal and balancing the stretching force, the metal foil at a high temperature can be obtained. Elongation can be suppressed. Thus, in the catalyst of the present invention, an alumina layer containing the above-mentioned catalyst component is further coated on the carrier on which the above-mentioned coat layer has been formed, thereby imparting a function as a catalyst for purifying automobile exhaust gas. Let me.

[0011]

【Example】

Example 1 First, an activated alumina slurry containing Ca was coated uniformly on a metal honeycomb carrier (1 shown in FIGS. 1 and 2) having a diameter of 80 mm and a length of 105 mm, and fired at 300 ° C. (Coat amount: 30 g). Further, the slurry was applied to the exhaust gas outlet side portion (portion 2 shown in FIG. 1) of the carrier by 30 mm.
The thickness of the first coat layer in contact with the carrier substrate in this portion was increased and calcined at 300 ° C. (total coat amount: 40 g).

The carrier on which the above-mentioned coating layer is formed has C
e, activated alumina slurry containing La, Zr
And baked at 600 ° C. (total coat weight 240 g). Further, Pt, Pd, and Rh are respectively 0.2,
Catalyst A was prepared by supporting 0.4 and 0.1 g.

Embodiment 2 A central portion of a metal honeycomb carrier similar to that of Embodiment 1 [FIG.
The active alumina slurry containing Ca is coated only on the portion 3 (diameter 50 mm) shown in (1), and the first coat layer in contact with the carrier substrate in this portion is replaced with the alumina layer containing Ca. And calcined at 300 ° C. (coat amount 15
g). Thereafter, in the same manner as in Example 1, Ce and L were added to the carrier.
After the activated alumina containing a and Zr was coated, it was calcined (total coating amount: 200 g), and further added with Pt and Pt.
Catalyst B was prepared by supporting d and Rh.

Example 3 An active alumina slurry containing Ca was uniformly coated on the entire metallic honeycomb carrier as in Example 1 and fired at 300 ° C. (coat amount: 30 g). Next, in the same manner as in Example 1, the slurry was coated on the exhaust gas outlet side portion of the carrier with a width of 30 mm and fired (total coating amount: 40 g). Further, in the same manner as in Example 2, the same slurry was coated on the center portion of the carrier and calcined (total coating amount: 55 g).

The carrier on which the coating layer has been formed is described below.
In the same manner as in Example 1, an activated alumina slurry containing Ce, La, and Zr was coated and calcined (total coat amount 1).
55g), which further carries Pt, Pd, Rh,
Catalyst C was prepared.

Comparative Example 1 A metallic honeycomb carrier similar to that of Example 1 was prepared by adding Ce, La,
Activated alumina slurry containing Zr is coated at 600 ° C.
(Coat amount 100 g). In addition, P
t, Pd, and Rh were supported in the same manner as in Example 1, and the catalyst D
Was prepared.

The catalysts A to D prepared in Examples 1 to 3 and Comparative Example 1 were attached to an engine having a displacement of 4000 cc, A / F = 14.6 (stoichiometric air-fuel ratio, ie, stoichiometric), an inlet gas temperature of 900 ° C., A 50-hour endurance test was performed under the following conditions.

The purification performance of each of the catalysts after the endurance was evaluated. Evaluation is A / F with 2000cc engine
= 14.6 (stoichiometric), and the input gas temperature was 460 ° C. Table 1 below shows the evaluation results of the catalysts A to D.

[0019]

[Table 1]

[0020]

According to the catalyst for purifying automobile exhaust gas of the present invention, the elongation of the metal foil, which is the base material of the metal honeycomb carrier, is suppressed at a high temperature. Does not decrease. Therefore, as shown in Table 1 above, the catalysts of the present invention (catalysts A to C) are superior in catalytic performance to the conventional catalyst (catalyst D).

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an exhaust gas outlet side portion of a metal honeycomb carrier which is a portion exposed to a high temperature in a catalyst of the present invention.

FIG. 2 is an explanatory view showing a central portion of a metal honeycomb carrier which is a portion exposed to a high temperature in the catalyst of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal honeycomb support, 2 ... Exhaust gas outlet side part (high temperature part), 3 ... Central part of carrier (high temperature part), 4 ...
Exhaust gas.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akimasa Hirai 7800 Chihama, Oto-cho, Ogasa-gun, Shizuoka Prefecture Inside Cataler Industry Co., Ltd. (72) Inventor Toshihiro Takada 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor (56) References JP-A-2-194842 (JP, A) JP-A-3-38250 (JP, A) JP-A-4-265155 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86

Claims (1)

(57) [Claims] 1. A metal honeycomb carrier catalyst, which is a part of the metal honeycomb carrier that is exposed to a high temperature.
Only the gas outlet side part and / or the central part , the first coat layer in contact with the carrier substrate is an alumina layer containing an alkali metal and / or an alkaline earth metal,
Only in this portion, the coating layer is a thick alumina layer containing the metal, and the carrier on which the coating layer is formed is further selected from platinum, palladium, rhodium, cerium, lanthanum, zirconium, nickel, iron and barium. An automotive exhaust gas purifying catalyst comprising an alumina layer containing at least one catalyst component.