JPH054048A - Catalyst for treatment of exhaust gas and its production - Google Patents

Abstract

PURPOSE:To provide a catalyst for treatment of exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbon, and to provide the production method of this catalyst. CONSTITUTION:A metal carrier with varpor deposition of Al is worked into a corrugated form or honeycomb form, heated in a furnace to make the surface alloy, and further treated in an oxidizing atmosphere to produce an Al2O3 whisker. Then a crystalline silicate having molecular sieve structure containing copper and a binder is mixed in a wet state to obtain a slurry, which is then applied by wash coating on the metal honeycomb having the Al2O3 wisker above described. Thus, the catalyst for treatment of exhaust gas can be obtd. This catalyst for treatment of exhaust gas consists of a metal honeycomb coated with the crystalline silicate having molecular sieve containing copper.

Description

Detailed Description of the Invention

[0001]

The present invention relates to nitrogen oxides (hereinafter referred to as NO
abbreviated as x), carbon monoxide (CO), hydrocarbon (hereinafter, H
The present invention relates to a catalyst for treating exhaust gas containing abbreviated as c) and a method for producing the same.

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles and the like, it is common to purify NOx by using organic substances and CO in the exhaust gas. However, conventional Pt, Rh / Al ₂ O ₃ -based catalysts (this catalyst Is usually called a three-way catalyst), but NOx can be purified only in an extremely narrow range near the stoichiometric air-fuel ratio. In recent years, there has been a strong demand for low fuel consumption of automobiles, and a lean burn engine that burns at a ratio higher than the theoretical air-fuel ratio has been revived as a key technology. The lean burn engine emits a large amount of NOx, but recently, a catalyst having a molecular sieve structure containing copper has been developed as a practical catalyst capable of purifying NOx in the lean region.

However, when the conventional ceramic carrier is used, since the specific heat is large, the difference between the exhaust gas temperature at the catalyst inlet and the catalyst bed temperature is large, and it takes time to follow the temperature. Normal,
Although a large amount of NOx is generated in an instant lean region at the time of start-up acceleration, the catalyst having a molecular sieve structure could not exhibit sufficient denitration activity because of the low catalyst bed temperature.

[0004]

Generally, the catalyst bed temperature of the automobile exhaust gas purifying catalyst is higher than the catalyst inlet temperature by HC or C.
Due to the heat generated by the combustion of O, the temperature becomes high. However, the catalyst having a molecular sieve structure containing copper is conventional Pt, Rh / A
Since it has lower activity at low temperature for burning and removing HC and CO than the l ₂ O ₃ -based three-way catalyst, the catalyst bed temperature having a molecular sieve structure is lower than that of the three-way catalyst during start-up acceleration. Therefore, it is desired to support a catalyst having a molecular sieve structure on a honeycomb carrier having a small specific heat and a good thermal response.

When the influence of the coating thickness of the catalyst having the molecular sieve structure containing copper on the honeycomb substrate was examined, the larger the coating amount (thickness), the higher the denitration activity at low temperature, and the coating thickness was increased. It has been found that a catalyst layer having a thickness of 100 μm or more is preferable, but when a coat thickness of 100 μm is carried, a pressure loss in the vent hole becomes large in a 400-cell automobile honeycomb substrate, so a substrate having a thin honeycomb wall is used. The present situation is that it is preferable.

On the other hand, the conventional three-way catalyst has a coat thickness of 20 μm.
Since it has the same performance at m and above, pressure loss due to catalyst loading does not pose a problem.

In view of the above-mentioned state of the art, the present invention is to provide a catalyst having a molecular sieve structure containing copper capable of removing HC, CO and NOx, which is excellent in temperature responsiveness of a catalyst bed, and a method for producing the same. is there.

[0008]

[Means for Solving the Problems] The present inventors have proposed a catalyst which coats a catalyst having a molecular sieve structure containing copper on a metal honeycomb carrier to enhance the thermal response of the catalyst and further reduce the pressure loss of the honeycomb. I found it. Further, it has been found that a catalyst having a molecular sieve structure has a particle size of about several μm and thus it is difficult to coat it on the surface of a metal carrier, but the peeling resistance and the like can be improved by a specific method.

The present invention has been completed based on the above findings, and (1) An exhaust gas treatment catalyst comprising a metal honeycomb coated with a crystalline silicate having a molecular sieve structure containing copper.

(2) The metal carrier on which Al is vapor-deposited is subjected to corrugation processing or honeycomb processing, the surface is alloyed by heating in an atmosphere furnace, and further Al ₂ O ₃ whiskers are formed in an oxidizing atmosphere, and then copper is contained. A method for producing an exhaust gas treatment catalyst, characterized in that a binder obtained by adding a binder to the crystalline silicate having a molecular sieve structure and wet-mixing the resulting slurry is wash-coated on the Al ₂ O ₃ whisker-formed metal honeycomb. . Is.

The crystalline silicate having a molecular sieve structure as referred to in the present invention means Y type zeolite, mordenite and a dehydrated form in which the molar ratio of oxides is (1 ± 0.8) R ₂ O. [aM ₂ O ₃ .. bAl ₂ O ₃ ] .ySiO _{2 In the} above formula, R: an ion or hydrogen ion of an alkali metal ion and / or an organic nitrogen-containing compound, M: a Group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, gallium, antimony , Ions of one or more elements from the group consisting of tantalum, a + b = 1, a ≧ 20, b ≧ 0, y ≧ 11, and the X-ray diffractogram shows the reflections particularly shown in Table 1. Those are preferable.

[Table 1]

As a method of incorporating copper into a crystalline silicate having a molecular sieve structure, a method of carrying it by an ion exchange method or an impregnation method using an aqueous solution of copper nitrate, copper acetate, copper chloride or copper sulfate metal copper salt is used. Is preferred.

As a material for a metal carrier which supports a crystalline silicate having a molecular sieve structure containing copper, it is excellent in high temperature oxidation resistance even at a high temperature such as 800 ° C., and is easily heated to 50 μm or less by hot rolling or cold rolling. A low alloy steel containing 5% or more of Cr or a ferritic stainless steel is preferable because it can be processed into a foil.

A method of coating a crystalline silicate having a molecular sieve structure containing copper on a metal carrier will be described below. A foil of low alloy steel or ferritic stainless steel containing 5% or more of Cr is used as a material for the metal carrier, and after corroding Al, corrugation processing or honeycomb processing is performed. In the case of Al vapor deposition, a preferable means is to perform Ar sputtering as a pretreatment to clean the surface, and heat vapor deposit Al by electron beam under a pressure of 10 ⁻⁵ to 10 ⁻⁴ Torr. Al
The film thickness of 1 to 8 μm, particularly 2 to 6 μm is preferable from the viewpoint of operability and peeling stability.

Next, after processing the Al vapor deposition foils, they are laminated and heated in an atmosphere furnace to diffuse Al in the vicinity of the foil surface to alloy the surface. That is, the product obtained in the above process is metal A
Since the 1-layer exists only on the surface of the metal foil, it is heat-treated at a temperature of 700 to 1200 ° C. to form an alloy layer of the base metal and Al on the surface of the metal base. By this heat treatment, for example, Fe (Ni) Al ₃ , Fe (N
i) An alloy layer such as ₂ Al ₅ is formed.

After that, oxidation treatment is performed in an oxidizing atmosphere to form an Al ₂ O ₃ oxide film or Al ₂ O ₃ whiskers on the surface. Oxidation conditions are preferably 900 to 1000 ° C. and 5 to 15 hours.

Finally, a crystalline silicate (catalyst) having a molecular sieve structure containing copper and silica sol or alumina sol as a binder are wet mixed to obtain a slurry, and the slurry is wash-coated on the metal carrier produced by the above method. , A predetermined catalyst is supported on a metal carrier. At this time, with respect to 100 parts by weight of the catalyst, 3 to 30 parts by weight of silica sol,
It is preferable to produce the slurry at a ratio of 0.3 to 10 parts by weight of the alumina sol. If the proportion of the binder (silica sol and alumina sol) is large, the catalytic activity is lowered, and if the proportion is small, there is a problem in the peelability of the catalyst. In addition, silica sol /
Alumina sol ratio in the range of 2 to 100 gives relatively preferable results.

[0018]

【Example】

(Example 1) 1. Method for supporting catalyst having molecular sieve structure containing copper supported on metal carrier

(1) The thin metal plate used is 5 wt% of Cr.
% Low alloy steel with a thickness of 50 μm was used.

(2) The Al coating was applied by a vacuum vapor deposition method in order to obtain a thin coating weight and obtain a uniform film thickness. A schematic diagram of the vapor deposition apparatus used will be described with reference to FIG. Metal thin plate (50 μm thick 5 wt% Cr-containing low alloy steel thin plate) 1
Is sent out from the coil, sent into the vacuum atmosphere through the differential pressure roll 5, and is first discharged from the substrate pretreatment high-frequency sputtering electrode 2 in the Ar atmosphere in the pretreatment chamber.
Sputtering with r ions cleans the surface.
(The degree of vacuum is about 5 × 10 ⁻⁴ Torr) Next, the thin metal plate is sent to the vapor deposition chamber, and the Al vapor evaporated from the electron beam evaporation source 3 for Al vapor deposition (crucible temperature around 1400 ° C.) 3 is vapor deposited. (The degree of vacuum in the deposition chamber is about 3 × 10 ^-4 Torr)
The metal thin plate after Al vapor deposition passes through the differential pressure roll 5 and is wound up by the winding roll 4. At this time, the thickness of the Al vapor deposition film should be 4
μm.

(3) Next, the low alloy steel thin plate on which Al is vapor-deposited is introduced into an oxidation furnace and treated at 930 ° C. for 8 hours to form an Al ₂ O ₃ oxide film and an Al ₂ O ₃ whisker on the surface. It was

(4) The low alloy steel thin plate was corrugated, molded into an oval honeycomb, wash-coated with a slurry having the following composition, dried and then repeatedly wash-coated to coat the catalyst to a thickness of 60 μm. .
This catalyst is designated as catalyst A. Slurry composition Crystalline silicate having a molecular sieve structure containing copper: 100 parts by weight Water: 200 parts by weight Silica sol (containing 20% of SiO ₂ ): 50 parts by weight Alumina sol (containing 20% of Al ₂ O ₃ ): 20 parts by weight

It has a molecular sieve structure containing the above copper
The crystalline silicate produced by
is there. In the dehydrated form, the oxide molar ratio is Na₂O
[0.4Fe₂O₃・ 0.1Co ₂O₃・ 0.5Al₂
O₃] ・ 30SiO₂Has a chemical composition represented by
X-ray diffractogram is a crystalline matrix showing the reflection shown in Table 1 above.
The silicate was stored in an aqueous solution containing 0.04 molar copper oxide
Perform ion exchange operation for 12 hours at a temperature four times and wash.
After being purified and filtered, it is dried at 100 ° C for 12 hours.
And the molar ratio of oxides in the dehydrated form is 1.2 Cu
O ・ [0.4Fe₂O₃・ 0.1Co₂O₃・ 0.5A
l₂O₃] ・ 30SiO₂Is represented by.

2. Peeling test In order to confirm the peeling state of the catalyst on the thin metal plate prepared by the above method, a catalyst peeling test was carried out by the following method. The peeling test was performed by applying a washcoat of about 60 μm thickness, heating for 5 seconds with a propane / air burner with a flame temperature of 1100 ° C., and then blowing compressed air for 25 seconds automatically.
When the peelability of the washcoat was observed repeatedly over time, it was confirmed that the catalyst was hardly peeled.

Comparative Example 1 For comparison, a conventional method for preparing a catalyst having a molecular sieve structure in a ceramic honeycomb will be described below. A cordierite ceramic honeycomb was wash-coated in a slurry solution having the same composition as in Example 1, air-purged sufficiently to prevent clogging, and then dried, and wash-coated repeatedly to coat a catalyst to a thickness of 60 μm. This catalyst is referred to as catalyst B. In addition, Example 1
Both the corrugated metal honeycomb carrier and the cordierite carrier shown in 1) have an outer surface area of 2.7 m ² / l liter volume.

3. Activity evaluation test The 1 liter honeycomb catalysts of catalysts A and B shown in Example 1 and Comparative Example 1 were mounted in the exhaust system of a 1.6 liter engine to start the operation, and the change in catalyst activity with time was examined. A
/ F = 18 (around lean state), rotation speed 2000 rp
Fig. 2 (catalyst A), Fig. 2 (catalyst A), showing the changes over time in inlet exhaust gas temperature, catalyst bed temperature and purification efficiency of exhaust gas (hydrocarbons, carbon monoxide, nitrogen oxides) when operation was started at m, manifold negative pressure of 350 mmHg 3 (catalyst B). 2 and 3, it can be seen that the catalyst A of the present invention has good temperature responsiveness and thus has instant exhaust gas purification activity.

(Example 2) Two kinds of honeycomb substrates (wall thickness: metal 0) having the same shape but different wall thickness were used for the catalyst having the molecular sieve structure containing copper (the same catalyst as in Example 1). ．
2 μm, cordierite 0.4 mm) was coated to have the same porosity. As a result, 200μ for the metal honeycomb
It was possible to support the catalyst with a coat thickness of 100 μm on m 2 and cordierite. These honeycomb catalysts are referred to as catalysts C and D, and schematic views of the coated state are shown in FIGS.
Shown in.

Using both catalysts, a catalyst activity evaluation test in a steady state was carried out under the following reaction conditions. Reaction conditions SV: 30000h ⁻¹ Exhaust gas composition NO: 400ppm, C ₃ H ₆ : 340p
pm, C ₂ H ₄ : 1000 ppm, O ₂ : 8%, C
O ₂ : 10%, CO: 1000 ppm The results of the denitration rate at each reaction temperature are shown in FIG. From this result, it can be seen that the denitration activity at a low temperature is larger when the metal honeycomb substrate that can coat a large amount of the catalyst is used.

[0029]

As shown in FIGS. 2 and 3, the catalyst of the present invention has a good temperature responsiveness of the catalyst bed at the initial stage of operation, so that it is possible to remove hydrocarbons, CO and NO instantaneously. Further, compared with the conventional cordierite honeycomb, the metal honeycomb can coat a large amount of the catalyst having the molecular sieve structure with the same pressure loss, and thus the low temperature activity of the catalyst can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view of a vacuum deposition method of Al when manufacturing a metal honeycomb according to an embodiment of the present invention.

FIG. 2 is a chart showing changes with time in catalyst bed temperature and exhaust gas purification rate when a catalyst according to an embodiment of the present invention is used.

FIG. 3 is a chart showing changes with time in catalyst bed temperature and exhaust gas purification rate when a comparative catalyst is used.

FIG. 4 is a schematic view of a metal honeycomb coated with a molecular sieve catalyst.

FIG. 5 is a schematic view of a cordierite honeycomb coated with a molecular sieve catalyst.

FIG. 6 is a chart showing the denitration activity test results of the catalyst of the present invention and the comparative catalyst.

Claims (2)

[Claims] 1. An exhaust gas treatment catalyst comprising a metal honeycomb coated with a crystalline silicate having a molecular sieve structure containing copper. 2. A metal carrier on which Al is vapor-deposited is subjected to corrugation processing or honeycomb processing, the surface is alloyed by heating in an atmosphere furnace, and further Al ₂ O ₃ whiskers are formed in an oxidizing atmosphere, and then copper is contained. A method for producing an exhaust gas treatment catalyst, characterized in that a binder obtained by adding a binder to crystalline silicate having a molecular sieve structure and wet-mixing the resulting slurry is wash-coated on a metal honeycomb having Al ₂ O ₃ whiskers formed thereon.