JP3046051B2 - Engine exhaust gas purifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purifying apparatus for an engine.

(Prior Art) In recent years, environmental issues have been highlighted, and there are increasing signs that NOx causing acid rain is being regulated. In that case, especially the car with diesel engine,
Since it is operated in an oxygen-excess atmosphere, it is difficult to reduce and remove NOx, and this stricter regulation of NOx is given as a major proposition.

And under such circumstances, NOx is directly converted to N ₂ and O ₂
Copper ion-exchanged zeolites that decompose into such have been announced and have attracted much attention. This copper ion-exchanged zeolite is obtained by carrying a transition metal on a zeolite by ion-exchange.
x Used as a reduction catalyst having decomposition performance, this reduction catalyst and an oxidation catalyst or a three-way catalyst in which a catalyst component is supported on alumina are sequentially arranged on the exhaust inflow side on the upstream side and the downstream side, and the exhaust gas of the engine is It is used as a purification device (see JP-A-01-139145).

(Problems to be Solved by the Invention) However, in the exhaust gas purifying apparatus for an engine as described above, the activation temperature at which NO is decomposed by the copper ion-exchanged zeolite (reduction catalyst) is set to 350, as shown in FIG. ° C, the purification capacity (NOx decomposition ability) as a reduction catalyst is not exhibited until this temperature is reached.
(Less than or equal to ° C.), the NOx is discharged without being purified (decomposed), and the NOx concentration at the outlet of the exhaust gas purification device becomes high. In that case, the copper ion-exchanged zeolite can activate the activity purifying ability itself, but it is technically difficult to shift the activation temperature to a lower temperature side.

Therefore, as shown in FIG.
-Focusing on the fact that CuO specifically adsorbs NOx up to a low temperature side of 350 ° C or lower, the NOx adsorbing member having this BaO-CuO adsorbent and the above-mentioned copper ion-exchanged zeolite are used in combination. In other words, the exhaust gas purifying apparatus in which the NOx adsorbing member and the reduction catalyst are arranged on the upstream
Can be effectively purified. FIG. 3 shows Cu
FIG. 3 is a view showing an embodiment of removing NO from an alkaline earth metal-based composite oxide.

However, in the exhaust gas purification device on the exhaust inflow side, there is a temperature difference between the upstream side and the downstream side, so the upstream NOx adsorbing member moves from a low temperature range to a temperature range of 350 ° C or more (high temperature range). Even if NOx begins to desorb, the downstream copper ion-exchanged zeolite still does not reach the temperature range around 350 ° C and does not exhibit the purification ability as a reduction catalyst, and the NOx concentration at the exhaust gas purifier outlet at low temperatures Cannot be effectively reduced.

The present invention has been made in view of such points, and an object of the present invention is to improve and arrange a NOx adsorbing member and a reducing catalyst in the exhaust gas purifying apparatus so that a temperature difference at a low temperature is reduced. Another object of the present invention is to effectively reduce the NOx concentration at the exhaust gas purifier outlet.

(Means for Solving the Problems and Their Functions) In order to achieve the above object, a solution for the invention according to claim 1 is as an exhaust gas purifying device for an engine, wherein NOx is adsorbed to an exhaust system of the engine at a predetermined temperature or lower. N with adsorbent
The Ox adsorbing member and the reducing catalyst having NOx decomposing performance around the predetermined temperature, such that the reducing catalyst has a temperature at which the NOx adsorbing member can decompose NOx at a temperature at which the NOx adsorbing member starts to desorb the adsorbed NOx. In this configuration, the NOx adsorption member and the reduction catalyst are provided in this order from the upstream side.

Here, in the invention according to claim 2, the reduction catalyst according to claim 1 has a zeolite supporting a transition metal. In the invention of claim 3, the NOx adsorbing member of claim 1 is made of BaO-CuO. Further, in the invention of claim 4, in the above-mentioned claim 1, NO
It is assumed that a plurality of sets of the x adsorption member and the reduction catalyst are provided alternately in the order of the NOx adsorption member and the reduction catalyst from the upstream side.

In this case, the adsorbent (NOx adsorbing member) is BaO
It is appropriate to use a composite oxide represented by -CuO.

As the reduction catalyst, zeolite obtained by ion-exchange of a transition metal represented by copper ions (copper ion-exchanged zeolite) is suitably used. The transition metals for this ion exchange include Cu, Co, Ni, Cr, Fe, Mn, Pt, Pd, Rh,
Ru, Ir, etc. can also be used in a single or composite form.

Therefore, the NOx adsorbing member and the reducing catalyst provided in the intake system of the engine are divided into a layered body, the thickness of the NOx adsorbing member and the reducing catalyst is reduced, and the NOx adsorbing member and the reducing catalyst are arranged in order from the upstream side. The NOx adsorbing material adsorbs N
The temperature of the exhaust gas is sequentially and quickly transmitted to the reduction catalyst via the NOx adsorbing member so that the temperature of the reduction catalyst becomes a temperature at which NOx can be decomposed at the temperature at which Ox is released.

In addition, as shown in FIG.
When the temperature of the adsorption member reaches 350 ° C., desorption of the NOx adsorbed by the NOx adsorption member starts, and
Although the NOx concentration has the characteristic indicated by α in the figure, the temperature of the reduction catalyst downstream of the NOx adsorbing member divided into the layered body immediately becomes 350 ° C., and the NOx is decomposed into N ₂ and O ₂ . In addition, NOx that has not been completely decomposed into N ₂ and O ₂ by the reduction catalyst on the downstream side of the NOx adsorbing member located on the most upstream side is adsorbed to 350 ° C. by the NOx adsorbing member on the downstream side, and similarly 350 ° C. When it becomes, it is repeatedly decomposed into N ₂ and O _{2 by} the reduction catalyst on the downstream side. This allows
The NOx concentration at the exhaust gas purifier outlet side has the characteristic indicated by β in the figure, and the NOx adsorbing member and the reduction catalyst could not be completely decomposed into N ₂ and O ₂ due to the temperature difference until reaching 350 ° C. The NOx concentration is as small as possible.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an exhaust gas purifying apparatus S for a diesel engine according to an embodiment of the present invention.
Is provided in the middle of the exhaust pipe 1 on the exhaust outlet side of the engine (not shown). The exhaust gas purifying apparatus S includes a casing 2 integrally formed with an exhaust pipe 1 and a NOx provided in the casing 2 and adsorbing NOx contained in exhaust gas at a low temperature range of 350 ° C. or less. An adsorbing member 3 and a reduction catalyst 4 provided in the casing 2 and having NOx decomposing performance for decomposing NOx contained in exhaust gas into N ₂ and O _{2 in} a high temperature region around 350 ° C. Be prepared.

As a method of manufacturing the NOx adsorbing member 3, for example, 13.6 g
After mixing the weighed CuO powder and, for example, 34.6 g of weighed BaCO ₃ powder in a ball mill, 1000 ° C. (600 ° C. to 1000 ° C.)
For crystallization (to form an oxide). afterwards,
Grind and add 10g of binder (alumina slurry) to 8
By firing at 50 ° C. for 5 hours, the NOx adsorbing member 3 having the NOx adsorbing material 3a is produced. In this case, the finished composite oxide CuO: BaO
Is adjusted to be 1: 1.

On the other hand, the production method of the reduction catalyst 4 is as follows.
60 parts of zeolite (Si / Al ratio: 40) powder and 60 parts of water are added to 60 parts of a mixture of silica sol and alumina sol mixed so that the mixture is sufficiently stirred, and then mixed with an aluminum nitrate solution.
The pH is adjusted to 3 to 6, and the slurry for wash coating is adjusted as a binder. Then, the cordierite monolithic honeycomb carrier is immersed in water, excess water is blown off, and then immersed in the wash coat slurry (binder). After drying at 20 ° C for 20 minutes, it is fired in an electric furnace at 600 ° C for 1 hour. The fired body thus obtained was immersed in an aqueous solution of copper acetate having a low concentration of about 0.02 mol / for 24 hours, ion-exchange operation was repeated several times, and then dried at 150 ° C. for 2 hours to obtain an ion exchange rate of 143%. Is produced (reduction catalyst 4). In this case, as shown in FIG. 4, NO shown in A in the figure decomposed by the copper ion-exchanged zeolite having an ion exchange rate of 143% is changed to N ₂ shown in B in FIG. are disassembled into N ₂ O indicated by O ₂ and D in the figure indicated by. Further, the purification rate is increased by repeating the ion exchange operation several times.
FIG. 4 is a diagram showing catalytic decomposition of NO on a 143% exchanged Cu-Z catalyst.

The NOx adsorbing member 3 and the reduction catalyst 4 are separately formed in a layered body such that the two 3, 4 constitute one pair. The NOx adsorbing member 3 and the reducing catalyst 4 are provided in three sets alternately in close contact with the NOx adsorbing member 3 and the reducing catalyst 4 in this order from the upstream side.

The ratio between the NOx adsorbing member 3 (NOx adsorbing material 3a) and the reducing catalyst 4 is set to 1: 1. A total of 50cc NOx adsorbing member 3 and 50cc reducing catalyst 4 is 1
00cc is arranged in a layer of 2 cm to 4 cm.

The test conditions are as follows: SV (space velocity of test gas) = 500 to 1000 (h ^-1 ) NO = 500 ppm.

Therefore, a plurality of sets of the NOx adsorbing member 3 and the reducing catalyst 4 in the exhaust gas purifying device S provided in the exhaust pipe 1 are provided.
Is that the NOx adsorbing member 3 and the reducing catalyst 4 are divided into a layered body, and the thickness of the NOx adsorbing member 3 and the reducing catalyst 3 per pair is as thin as about 2 cm to 4 cm, and the NOx adsorbing member 3 and the reducing catalyst 3 are alternately arranged from the upstream side. NOx adsorbing member 3 and reducing catalyst 4
The temperature of the exhaust gas is sequentially and quickly transmitted to the reduction catalyst 4 via the NOx adsorption member 3 so that the reduction catalyst 4 becomes a temperature at which the reduction catalyst 4 can decompose NOx at the temperature at which the adsorption member 3 starts to release the adsorbed NOx. You. As a result, the temperature difference between the NOx adsorption member 3 and the reduction catalyst 4 in the exhaust gas purification device S can be reduced as much as possible.

Further, as described in FIG. 2, the temperature of the NOx adsorbing member 3 located at the most upstream side, that is, the first set of the upstream side NOx adsorbing members 3 is 350 ° C.
Then, the desorption of NOx adsorbed by the NOx adsorbing member 3 starts, and the NOx concentration after the first set of NOx adsorbing members 3 has a characteristic indicated by α in the figure, but is divided into layered bodies. Was
The temperature of the first set of reduction catalysts 4 on the downstream side of the NOx adsorbing member 3 immediately becomes 350 ° C. and decomposes NOx into N ₂ , O ₂ and N ₂ O. In addition, N ₂ , O ₂ and N ₂
NOx not completely decomposed into O is adsorbed to 350 ° C. by the second set of NOx adsorbing members 3 on the downstream side, and similarly,
When the temperature reaches 350 ° C., N ₂ , O ₂
And the decomposition into N ₂ O up to the third set. As a result, the NOx concentration on the outlet side of the exhaust gas purifying device S has a characteristic indicated by β in the figure, and N ₂ , O ₂ and N _{2 are determined} by the temperature difference until the NOx adsorbing member 3 and the reduction catalyst 4 reach 350 ° C. _Two
The concentration of NOx that has not been completely decomposed into O becomes a value as small as possible, so that the purification performance of the exhaust gas purification device S can be improved.

The present invention is not limited to the above embodiment,
Other various modifications are included. For example, in the above embodiment, the casing 2 of the exhaust gas purifying device S
Although the NOx adsorbing member 3 and the reducing catalyst 4 are provided, the exhaust gas purifying device may be configured by providing the NOx adsorbing member and the reducing catalyst in the exhaust system of the engine.

In the above embodiment, the exhaust gas purifier S is provided in the exhaust pipe 1 of the diesel engine. However, the exhaust gas purifier may be applied to the exhaust system of the gasoline engine.

(Effect of the Invention) As described above, according to the exhaust gas purifying apparatus for an engine of the present invention, the NOx adsorbing member and the reducing catalyst are divided into a layered body to reduce the thickness of the NOx adsorbing member and the reducing catalyst. When the temperature at which the adsorbing member starts to release the adsorbed NOx is arranged in order from the upstream side so that the reducing catalyst becomes a temperature at which the NOx can be decomposed, the transmission of the exhaust gas temperature to the reducing catalyst via the NOx adsorbing member is performed. The temperature difference between the NOx adsorbing member and the reduction catalyst in the exhaust gas purification device can be reduced as quickly as possible. Moreover, NOx that did fully decomposed such as N ₂ and O ₂ by the NOx adsorption member downstream of the reduction catalyst located at the most upstream side, and the adsorption by the NOx adsorption member at the downstream side, with a reducing catalytic N ₂ and O _Two
By repeating the decomposition, the concentration of NOx due to the temperature difference between the NOx adsorbing member and the reduction catalyst becomes as small as possible, so that the purification performance of the exhaust gas purification device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional side view of an exhaust gas purifying device in an exhaust pipe, showing an embodiment of the present invention. 2 to 4
FIG. 2 shows a modified example, FIG. 2 is an explanatory diagram showing NOx concentration characteristics of the NOx adsorbent and the reduction catalyst when a predetermined temperature is reached, FIG. 3 is an adsorption characteristic diagram with respect to temperature of BaO—CuO, and FIG. FIG. 4 is a decomposition characteristic diagram with respect to temperature of FIG. 3 NOx adsorbing member 3a NOx adsorbent 4 reduction catalyst S exhaust gas purification device

Continuation of the front page (51) Int.Cl. ⁷ identification code FI F01N 3/24 B01D 53/34 129A 3/28 301 (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 53/94 B01D 53 / 86 B01J 21/00-38/74 F01N 3/28 F01N 3/24

Claims (4)

(57) [Claims] An exhaust system for an engine is provided with NOx at a predetermined temperature or lower.
The NOx adsorbing member having an adsorbent for adsorbing NOx and the reducing catalyst having NOx decomposing performance near the predetermined temperature are decomposed by the reducing catalyst at the temperature at which the NOx adsorbing member starts to desorb the adsorbed NOx. An exhaust gas purifying apparatus for an engine, wherein a NOx adsorbing member and a reducing catalyst are provided in this order from the upstream side so as to reach a possible temperature. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the reduction catalyst is formed by supporting a transition metal on zeolite. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the NOx adsorbing member is made of BaO—CuO. 4. The NOx adsorbing member and the reduction catalyst are connected to the NOx adsorber from the upstream side.
2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein a plurality of sets are provided alternately in the order of the adsorbing member and the reducing catalyst.