JP3323233B2 - Method for producing exhaust gas purifying catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a catalyst for purifying exhaust gas.

[0002]

2. Description of the Related Art As an exhaust gas purifying catalyst for automobiles, C
O (carbon monoxide) and HC (hydrocarbon) oxidation and NO
Three-way catalysts that simultaneously perform reduction of x (nitrogen oxide) are generally known. The three-way catalyst is, for example, one in which Pt (platinum) and Rh (rhodium) are supported on γ-alumina, and the air-fuel ratio (A / F) of the engine is set at a stoichiometric air-fuel ratio of 1
When the control is performed at around 4.7, high purification efficiency is obtained.

[0003] On the other hand, in the field of automobiles, there is a demand for increasing the air-fuel ratio to reduce the fuel consumption of the engine. In this case, since the exhaust gas has a so-called lean atmosphere with excess oxygen, the three-way catalyst cannot oxidize and purify CO and HC, but cannot reduce and purify NOx.

[0004] In recent years, researches on zeolite catalysts in which a transition metal is supported by ion exchange have been advanced.
In the case of this zeolite catalyst, even in a lean atmosphere,
NOx directly or coexisting with a reducing agent (for example, C
O, HC, etc.) can be catalytically decomposed into N ₂ and O ₂ . The use of a cocatalyst for the purpose of improving the heat resistance and catalytic activity of the zeolite catalyst is also being studied.

For example, JP-A-3-202157 describes a catalyst in which Cu, an alkaline earth metal and a rare earth metal are supported on zeolite. In this case, an ion exchange method or an impregnation method is employed for supporting each of the metal active species.

That is, in the case of the ion exchange method, Cu,
The step of immersing zeolite in a mixed aqueous solution of each salt of an alkaline earth metal and a rare earth metal for 24 to 48 hours, a drying step, and a firing step are sequentially performed. The obtained catalyst material is slurried using water together with a binder, and wash-coated on a carrier. In the case of the impregnation method, a method is employed in which zeolite is immersed in a mixed aqueous solution of the above salt for 1 to 2 hours and then dried in the air.

[0007]

However, for example, Cu as a metal active species has a low melting point, the valence changes easily between Cu ⁺ and Cu ^2+, and at high temperatures, the vicinity of the ion exchange site is high. , The coagulation of Cu or the elimination of Al occur. Another problem is that Al is desorbed from the skeleton of the zeolite crystal due to hydrothermal treatment by H ₂ O vapor when the metal active species is subjected to ion exchange loading or when heated in the subsequent use as a catalyst. is there. If this desorbed Al is completely removed from the catalyst and its trace is replaced by Si, the Si / Al ratio increases and becomes stable, but otherwise, the desorbed A
When 1 exists as a cation in the ion exchange site, it acts as an impurity as a catalyst, and causes sintering of a metal active species such as Cu by heating, thereby reducing its activity.

[0008]

In order to solve the above-mentioned problems, the present invention does not directly carry out ion exchange loading of a main catalyst metal such as Cu on an aluminosilicate such as zeolite, but first stabilizes Al in the aluminosilicate. The ion-exchange loading is carried out after the loading of the promoter metal for enhancing the properties.

That is, a means for solving the above-mentioned problem is to provide an auxiliary contact at a position near an Al atom in aluminosilicate.
This is a method for producing an exhaust gas purifying catalyst, which comprises supporting Ga as a medium metal by an evaporation- drying method, and then supporting a main catalyst metal on the aluminosilicate by an ion exchange method.

-Regarding Catalyst Material-The above-mentioned aluminosilicate is a crystalline porous material having micropores, so-called zeolite, and is not limited, but hydrogen-type zeolite is preferable in terms of heat resistance. As this zeolite, A type, X type, Y type, ZSM-
5, various types such as ferrierite and mordenite can be used.

As the main catalyst metal, a transition metal is preferable. As the transition metal, Cu is preferable, but other Co, Cr, Ni, Fe, Mn, Zr, Mo, Zn,
Other transition metals such as Y, Ce, Tb, or noble metals can also be preferably used.

[0012] Ga is adopted as the above co-catalyst metal .
, The metal is for the detachment preventing of Al is an object of the present invention is effective especially <br/>.

-Supporting method of co-catalyst metal-For supporting the co-catalyst metal Ga , an evaporation to dryness method is adopted.
You . In this case, in the aluminosilicate, the ion exchangeable cation, for example, Na ion is bonded to the Al atom, so that the promoter metal Ga is adsorbed and supported at a position near the Al atom.

-Support of Main Catalyst Metal-The ion exchange method is used for supporting the main catalyst metal. That is, a method of sequentially carrying out a step of bringing the aluminosilicate into contact with an aqueous solution of the main catalyst metal salt while heating it to a predetermined temperature, a step of cooling, filtering, washing, a step of heating and drying, and a step of firing. However, in this ion exchange method, the main catalyst metal is not necessarily supported on the aluminosilicate by ion exchange, but is presumed to be partially supported by adsorption (by Van der Waals force). . Although the location of the carrier is not clear, it is assumed that most of the carrier is located near Al atoms in a form coexisting with the promoter metal Ga .

[0015]

As described above, in the present invention, the co-catalyst metal Ga is first placed near the Al atom in the aluminosilicate, and then the main catalyst metal is supported by the ion exchange method. In the case of
Is also prevented, and the subsequent heating in the presence of moisture also reduces the desorption of the Al, thereby preventing sintering of the main catalyst metal.

That is, according to an experiment in which Cu and Ga are simultaneously supported on aluminosilicate by an ion exchange method, sintering of Cu is caused by hydrothermal treatment, and the catalytic activity is reduced. In the case of simultaneous loading, it is considered that Cu is arranged in the ion exchange seat in preference to Ga, and Ga is arranged around the Cu or in a portion where Cu does not exist. In such an arrangement, the decrease in catalytic activity, that is, the occurrence of Cu sintering is considered to be caused by the elimination of Al, but Ga sufficiently contributes to the stabilization of Al. Means not. On the contrary,
According to the method of the present invention, the decrease in catalytic activity due to hydrothermal treatment is small.

There are several possible reasons why the elimination of Al is prevented. One is that the co-catalyst metal Ga is preferentially arranged in the vicinity of Al of the aluminosilicate, and in some cases, is exchanged with the Na ion of the aluminosilicate, so that the Na ion in the catalyst becomes smaller than that of the conventional one. It is. Another reason is that the promoter metal G
Since a or its compound (oxide) is thermally stable,
That is, it acts as a steric hindrance to the migration aggregation of, for example, Cu as the main catalyst metal.

In this case, Ga has properties similar to Al in the lattice of the aluminosilicate, and tends to be a steric hindrance to the movement of the Al.

From the above, it can be seen that the promoter metal according to the present invention
When Ga is first placed on Al and the main catalyst metal is subsequently loaded, Al becomes stable by the co-catalyst metal Ga , and the main catalyst metal is placed near the Al. It is presumed that it is producing good results.

When each of the co-catalyst metals Ga is turned into an oxide, it does not become a strong acid as compared with other metals and has a reducing power. Therefore, the desorption of Al and the decomposition of NOx are promoted. Work to make it work.

[0021]

Therefore, according to the present invention, the promoter metal Ga is evaporated to dryness at a position near the Al atom of the aluminosilicate.
Since the main catalyst metal was supported on the aluminosilicate by an ion exchange method after supporting the main catalyst metal, the desorption of Al and the main catalyst metal during the support of the main catalyst metal and during the subsequent use of the catalyst were performed. The effect is obtained that sintering is prevented and the heat resistance of the catalyst is improved.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

-Preparation of Catalyst- < Reference Example > Na-type zeolite (ZSM-5, SiO ₂ / AlO ₃ = 3)
0) 20 g of powder and 1.52 g of gallium nitrate were sufficiently mixed in an ion exchange aqueous solution, and the mixture was heated to about 100 ° C. for about 2 hours, whereby Ga was supported on the zeolite.

Next, using an ion exchange aqueous solution obtained by adding 8.6 g of copper acetate to 375 ml of ion-exchanged water so that Cu: Ga = 1: 1, the zeolite supporting Ga was subjected to an ion exchange method. Cu was supported. The ion exchange rate is 100% or more (about 130%).

A slurry was prepared by adding 20% by weight of an alumina binder to the catalyst material thus obtained, and 25% by weight was prepared on a honeycomb carrier (Cordite, 400 cells / inch ² ).
Wash coat so that

< Example > The same Na-type zeolite powder as in the reference example was added to an aqueous gallium nitrate solution, mixed well, and evaporated to dryness to carry Ga on the zeolite. Next, Cu was supported on the zeolite by the same ion exchange method as in the reference example . In the case of this example, it was prepared so that Cu: Ga = 1: 0.5. Refer to the catalyst material obtained in this way.
The same honeycomb carrier was wash-coated under the same conditions as in the example.

[0027] After ion exchange carrying Cu using <Comparative Example> Reference Example and copper acetate aqueous solution in the same manner as Na-type zeolite powder, which was carried the Ga by addition to gallium nitrate aqueous ion exchange method, reference The same honeycomb carrier was wash-coated under the same conditions as in the example . The quantitative conditions of Cu and Ga were the same as in the reference example .

-Catalyst activity test and results-A / F for each catalyst of the above reference examples, examples and comparative examples
= 22, the initial activity (NOx purification rate in a fresh state) was examined. Then add one to each of these catalysts.
A heat treatment was performed at 600 ° C. for 8 hours in an atmosphere of 0% H ₂ O + 10% O ₂ (He balance), and then the activity after the heat treatment was examined under the same conditions as in the case of the initial activity.

The results are shown in FIG. In the case of the comparative example, although the initial activity is not bad, the activity after the heat treatment is bad, and the purification rate is reduced by about 40%. On the contrary,
In the case of the embodiment, the reduction amount of the purification rate after the heat treatment is at most about 20%. This indicates that it is effective to improve the heat resistance by supporting Ga first and then supporting Cu.

[Brief description of the drawings]

FIG. 1 is a graph showing NOx purification characteristics of a reference example, an example, and a comparative example.

[Explanation of symbols]

 None

Continued on the front page (72) Inventor Hideharu Iwakuni 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Takashi Takemoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP-A-5-305240 (JP, A) JP-A-4-215847 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37 / 36 B01D 53/86

Claims (1)

(57) [Claims] 1. A method in which Ga is supported as a co-catalyst metal at a position near an Al atom in an aluminosilicate by an evaporation- drying method, and then the main catalyst metal is supported on the aluminosilicate by an ion exchange method. A method for producing an exhaust gas purifying catalyst, comprising: