JPH10354A - Catalyst for purification of exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst having a wide active temp. range for the reduction of NOx . SOLUTION: The catalyst is composed by deposing platinum group elements on a porous carrier composed of a ceramic material having higher thermal stability than alumina and having open voids. Preferably, the open voids rate is 1 to 40vol.%, and the ceramic material is one ore more kinds selected from zirconium oxide, zirconium carbide, silicon carbide, silicon nitride and titanium carbide. The catalyst is produced by adding carbon, an inorg. binder and water to a granular ceramic material, kneading the mixture, molding, drying and firing to volatilizing the carbon content to obtain a porous carrier, and then depositing platinum group elements. Otherwise, the platinum elements may be prepared in a slurry state and applied on the carrier. It is preferable to add 2 to 2 pts.wt. talc to 100 pts.wt. of the ceramic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst which has been particularly successful in the purification of exhaust gases containing nitrogen oxides (NO _x ) from diesel engines. More specifically, the present invention relates to a catalyst for purifying exhaust gas from a diesel engine that is effective over a wide temperature range.

[0002]

2. Description of the Related Art In order to reduce nitrogen oxides and hydrocarbons (HC) contained in exhaust gas from a diesel engine, a copper-zeolite (Cu-ZSM-5) catalyst or a platinum-alumina (Pt / Al ₂ ) is currently used. O ₃ ) catalysts are widely known.

[0003] However, copper-zeolite has a problem that it is easily degraded by coexisting water vapor and heat, and the platinum-alumina catalyst has a high catalytic activity in a narrow temperature range of 200 to 280 ° C, but has a high catalytic activity in a high temperature range. Disappears. For this reason, there is a demand for the development of a catalyst that is hardly deteriorated even with high-temperature exhaust gas and has a small decrease in catalytic activity.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a nitrogen oxide (NO) from a diesel engine which is resistant to coexisting steam and heat even in a high temperature range and has a small decrease in catalytic activity.
It is an object of the present invention to provide a catalyst which is particularly successful in purifying exhaust gas containing _X ) and a method for producing the same. Separately, the present invention provides
It is an object of the present invention to provide a catalyst applicable to a purification treatment of exhaust gas in a wide temperature range corresponding to a change of an engine from a low load range to a high load range, and a method of manufacturing the same.

[0005]

SUMMARY OF THE INVENTION As a result of diligent research, the present inventor has found that conventional platinum / alumina (Pt / Al ₂ O ₃ ) catalysts, as shown in FIG. While the supported platinum is finely dispersed in large numbers,
When (1) a ceramic having thermal stability exceeding alumina is used as a carrier, and (2) a porous carrier including open cavities is used, as shown in FIG.
Since the silicon carbide (SiC) is inactive and a large number of large cavities are present in the carrier, a large number of particles of the platinum group element can be supported, and as a result, the combustion activity of the hydrocarbon (HC) decreases. since then, combustion temperature nitrogen oxides by shifting to the high temperature side (NO _X) reducing the catalyst activation temperature region is shifted to the high temperature side, the catalyst,
It found that particularly successful for purification of exhaust gas containing nitrogen oxides from diesel engine (NO _X), thereby completing the exhaust gas purifying catalyst of the present invention.

That is, the exhaust gas purifying catalyst of the present invention is characterized in that a platinum group element is supported on a porous carrier comprising ceramics having higher thermal stability than alumina and including open cavities. Preferably, the open cavity ratio is 1 to 40 parts by volume. Preferably, the ceramic for the carrier is at least one selected from zirconium oxide, zirconium carbide, silicon carbide, silicon nitride and titanium carbide.

The exhaust gas purifying catalyst of the present invention is obtained by adding carbon, an inorganic binder, and water to granular ceramics having high thermal stability, kneading, molding, drying, and firing to volatilize the carbon component. It can be produced by forming a porous carrier containing open cavities and supporting a platinum group element on the porous carrier. When a substrate is used, carbon, an inorganic binder, and water are added to granular ceramics having higher thermal stability than alumina and kneaded to form a slurry. The slurry is applied to the substrate, dried, and further fired. By evaporating the carbon component to form a porous carrier containing open cavities, the carrier can be produced by supporting a platinum group element.

In producing the exhaust gas purifying catalyst of the present invention,
Preferably, 1 to 15 parts by weight of carbon is added to 100 parts by weight of the ceramic. In addition, preferably, 2 to 100 parts by weight of ceramics are used as a binder.
20 parts by weight of talc are added.

[0009]

Embodiments of the present invention will be described below in detail.

[0010] The exhaust gas purifying catalyst of the present invention is characterized in that the carrier is made of ceramics having higher thermal stability than alumina. That is, various ceramics are known, but in the present invention, ceramics having higher thermal stability than alumina are used. Here, high thermal stability specifically means that the surface is still chemically inert even when the temperature is increased (specifically, even at about the firing temperature). The degree of activity can be evaluated by measuring the change in specific surface area during firing. Zirconium oxide, zirconium carbide, silicon carbide, silicon nitride, titanium carbide, and titanium nitride can be used. These can be used alone or in combination. Further, the carrier of the exhaust gas purifying catalyst of the present invention is characterized in that it is a porous body including an open cavity, that is, an open cavity. As a result, the particles of the large active ingredient in the cavity can be supported. Preferably, the open porosity of the carrier of the present invention is 1 to
40% by volume. Note that the upper limit was set in terms of mechanical strength.

[0011] Typical of the platinum group elements which are active ingredients are platinum, palladium, rhodium, ruthenium and iridium. In addition, rare earth elements such as lanthanum, yttrium, cerium, samarium, and preseodymium, and transition metal elements such as cobalt, nickel, and iron, and alkaline earth elements such as magnesium, barium, sodium, and strontium are also used as cocatalysts in an amount of 100% by weight of the active ingredient. Up to 20 parts by weight per part may be included. Preferably, the loading of the active ingredient is between 0.1 and 20% by weight. The upper limit is significantly higher than before. This is because the particles of the platinum group element, which is the active ingredient, became large. It should be noted that the upper limit is merely provided because if it exceeds that, it is not possible to expect an increase in the catalytic function corresponding to the increase in the active component. Further, the platinum group element may be supported in any form of oxide, ion and element.

The exhaust gas purifying catalyst of the present invention is obtained by adding carbon, an inorganic binder, and water to granular ceramics having high thermal stability, kneading, molding, drying, and further firing to volatilize carbon. It can be produced by forming a porous carrier containing open cavities and supporting a platinum group element on the porous carrier.

As described above, the ceramic raw material can be appropriately selected from ceramics having higher thermal stability than alumina, such as zirconium oxide, zirconium carbide, silicon carbide, silicon nitride, and titanium carbide. Preferably, the particle size is between 1 and 100 microns and the specific surface area is between 1 and 50 m ²
/ G. As the carbon raw material, carbon black, Ketchin black, channel black, furnace black, graphite (graphite), coke, and the like can be used, but carbon black is preferable. In addition, carbon can also be added as an organic binder. Preferably, 5 parts of carbon are added to 100 parts by weight of ceramics.
Add ~ 15 parts by weight.

As the inorganic binder, talc (Mg ₃
Si ₄ O ₁₀ (OH) ₂ ), silica sol, aluminum nitrate, alumina sol and the like can be used, but talc is preferred. Preferably, 2 to 20 parts by weight of a binder is added to 100 parts by weight of the ceramic.

Carbon, an inorganic binder and water are added to the granular ceramic and kneaded to form a clay, which is formed into an appropriate shape, for example, by extrusion. Although various shapes such as a spherical shape and a pellet shape are known as the shape of the catalyst, a honeycomb shape is preferable in consideration of mechanical strength. The honeycomb-shaped catalyst structure may include a conventional molding aid, a reinforcing body, and the like. Further, the porosity of the honeycomb is preferably 60 to 95%. In addition,
As for water, it is preferable to use ion-exchanged water in order to prevent contamination of impurities. The molded body is preferably cured at 90 to 110 ° C. for 5 minutes.
Dry for ~ 10 hours. Furthermore, preferably 7
Firing at 00-1100 ° C. for 3-4 hours in an oxidizing atmosphere, typically air, to remove carbon.
The resulting fired body is a porous support containing open cavities.

[0016] Separately, carbon, an inorganic binder and water are added to the granular ceramics and kneaded to form a slurry.
The porous carrier including the open cavities can be formed by applying the composition to a substrate having an appropriate shape, and then drying and calcining to evaporate the carbon content in the same manner as described above. As the structure of the substrate, a honeycomb-like structure is preferable in consideration of mechanical strength. A typical substrate is
Cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2)
It is. To apply the slurry, a method of dipping the substrate in the slurry and pulling up, or brushing or spraying the substrate on the substrate can be used.

In order to support the platinum group element as an active ingredient on the carrier, when the impregnation method is used, the carrier is immersed in an aqueous solution containing the platinum group element, pulled up, dried, and further calcined to be supported. it can. In this case, a compound containing a platinum group element capable of forming an aqueous solution (that is, an inorganic salt, an organic salt, a metal acid or a salt thereof (including a double salt)) is dissolved in water to form an aqueous solution. Preferred compounds are: chloroplatinic acid H ₂ PtCl ₆ .nH ₂ O dinitrodiammine platinum Pt (NH ₃ (NO ₂ ) ₂ ) palladium nitrate Pd (NO ₃ ) ₂ rhodium nitrate Rh (NO ₃ ) ₃ chloride Ruthenium RuCl ₃ Iridium chloride H ₂ IrCl ₆ .nH ₂ O A surfactant, preferably a polyoxyethylene-based nonionic surfactant may be added in order to promote the coating on the carrier.

Drying is carried out in the air, preferably 100 to 1
Performed at 50 ° C. for 8-12 hours. Firing is performed in an oxidizing atmosphere, for example, in the air, or in a reducing atmosphere, for example,
400-700 ° C in a reducing flame or a hydrogen-containing nitrogen gas stream
For 3 to 10 hours.

The loading is not limited to the impregnation method, and other known methods such as a deposition method and an ion exchange method may be used, or a combination thereof may be used.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to only the following Examples.

(Preparation of Catalyst of Examples)
m of silicon carbide powder and 100 parts by weight of the powder
0 parts by weight of powdered carbon (carbon black), 5 parts by weight of talc binder and 100 parts by weight of the powder are further mixed and kneaded to obtain a viscosity, extruded into a honeycomb shape, and extruded. It was dried in air at 100 ° C. for 8 hours, and further calcined in air at 1000 ° C. for 3 hours and the carbon was burned to form an open cavity in the carrier. The open cavity ratio was 12% by volume. The obtained fired body is immersed in an aqueous solution of chloroplatinic acid, pulled up, dried in air at 100 ° C. for 10 hours, and further dried in air.
Firing at 00 ° C. for 4 hours. Platinum loading rate is 3
% By weight.

[0022] To evaluate the catalyst (Catalyst Evaluation of Performance) Example, the NO _X reduction performance of the platinum / alumina catalyst which is commonly conventionally as a comparative example (loading of platinum was the same as Example) For this purpose, a gas with the following composition (weight ratio), which is assumed to be exhaust gas from a diesel engine, is flowed at the following space velocity (SV), and the nitrogen oxide reduction rate is measured. No: 1000 ppm C ₃ H ₆ : 1360 ppm O ₂ : 10% SO ₂ : 20 ppm H ₂ O: 4% N ₂ : balance SV: 20,000 hr ^-1 The results are shown in FIG. The upper limit of the nitrogen oxide reduction rate is
The catalysts of the example and the comparative example were almost the same, but the active temperature range of the catalyst was 200 to 380 ° C.
And the temperature of the catalyst of the comparative example is significantly shifted to a higher temperature side than 200 to 280 ° C., and the catalyst of the example has a wider active temperature range.

[0023]

According to the catalyst of the present invention, the active temperature range for reducing nitrogen oxides is shifted to a higher temperature side and wider than that of the conventional one. Therefore, it can be successfully used for purification treatment of exhaust gas from a diesel engine.

[Brief description of the drawings]

FIG. 1a is a diagram schematically showing the state of loading of a platinum / alumina catalyst of the prior art with platinum. FIG. 1b is a view schematically showing a platinum-supported state of the platinum / silicon carbide catalyst of the present invention.

FIG. 2 shows the reduction rates of nitrogen oxides of the catalysts of Examples and Comparative Examples.

Continued on the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location B01J 27/224 B01J 37/00 K 27/24 37/02 301B 37/00 B01D 53/36 ZAB 37/02 301 102A 102H

Claims (7)

[Claims] 1. An exhaust gas purifying catalyst comprising a ceramic having higher thermal stability than alumina and a platinum carrier supported on a porous carrier including an open cavity. 2. The exhaust gas purifying catalyst according to claim 1, wherein the open porosity is 1 to 40% by volume. 3. The exhaust gas purifying catalyst according to claim 1, wherein the ceramic is at least one selected from zirconium oxide, zirconium carbide, silicon carbide, silicon nitride, and titanium carbide. 4. An open cavity is obtained by adding carbon, an inorganic binder, and water to granular ceramics having higher thermal stability than alumina, kneading, molding, drying, and further firing to volatilize carbon. The method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein a porous carrier containing the catalyst is formed, and a platinum group element is supported on the porous carrier. 5. A granular ceramic having a higher thermal stability than alumina, to which carbon, an inorganic binder and water are added and kneaded to form a slurry, which is applied to a substrate, dried, and
The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein a porous carrier including an open cavity is formed by calcining to remove a carbon component, and a platinum group element is supported on the porous carrier. Manufacturing method. 6. The method according to claim 4, wherein 1 to 15 parts by weight of carbon is added to 100 parts by weight of the ceramic.
Or the method for producing an exhaust gas purifying catalyst according to 5. 7. The method for producing an exhaust gas purifying catalyst according to claim 4, wherein 2 to 20 parts by weight of talc is added as a binder to 100 parts by weight of the ceramic. .