JPH04141219A - Exhaust gas purifying apparatus of engine - Google Patents

Abstract

PURPOSE:To effectively reduce the concn. of NOX by alternately providing NOX adsorbing members adsorbing NOX at a predetermined temp. or less and reducing catalyst decomposing NOX in the vicinity of said temp. in this order from an upstream part as two or more sets. CONSTITUTION:An exhaust gas purifying apparatus S is equipped with the casing 2 integrally formed along with an exhaust pipe 1, the NOX adsorbing members 3 adsorbing NOX within a low temp. region of predetermined temp. or less provided in the casing 2 and the reducing catalysts 4 decomposing NOX within the high temp. region of the predetermined temp. or higher provided in the casing 2. The NOX adsorbing members 3 and the reducing catalysts 4 are alternately provided in this order in a laminar state in a close contact state from the upstream part in the casing 2. As the NOX adsorbing members 3, composite oxide represented by BaO-CuO is used and, as the reducing catalysts 4, it is proper to use zeolite ion-exchanged with a transition metal represented by a copper ion.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an engine exhaust gas purification device.

(Prior Art) Environmental issues have been attracting attention in recent years, and there are increasing signs that NOx, which causes acid rain, will be regulated. In that case, especially cars equipped with diesel engines,
Because they are operated in an oxygen-rich atmosphere, it is difficult to reduce and remove NOx, and stricter regulations on NOx are a big priority.

Under these circumstances, a copper ion exchange zeolite that directly decomposes NOx into N2, 02, etc. has been announced and is attracting a lot of attention. This copper ion-exchanged zeolite is made by supporting transition metals on zeolite through ion exchange and is used as a reduction catalyst to improve NOx decomposition performance. are arranged in order on the upstream side and the downstream side on the exhaust inflow side, and are used as an exhaust gas purifying device for an engine (see Japanese Patent Laid-Open No. 01-139'145).

(Problem to be Solved by the Invention) However, in the engine exhaust gas purification device as described above, the activation temperature at which NO is decomposed by the copper ion exchange zeolite (reduction catalyst) is 350°C, as shown in A in Fig. 4. ℃
Because the temperature is high, the purification ability (NOx decomposition ability) as a reduction catalyst is not demonstrated until this temperature is reached, and NOx is emitted without being purified (decomposed) at low temperatures (below 350 degrees Celsius), resulting in exhaust gas purification. The NOx concentration at the outlet of the device becomes high. In that case, although the copper ion exchange zeolite can activate its active purification ability itself, it is technically difficult to shift the activation temperature to a lower temperature side.

Therefore, as shown in FIG. 3, a known composite oxide BaO
Focusing on the fact that -CuO specifically adsorbs NOx up to a low temperature range of 350°C or less, we combined the NOx adsorption member having this BaO-CuO adsorbent with the above-mentioned copper ion exchange zeolite, that is, It is conceivable to effectively purify NO by configuring an exhaust gas purification device in which a NOx adsorption member and a reduction catalyst are arranged in order on the upstream side and the downstream side. Incidentally, FIG. 3 is a diagram showing the No removal state of the Cu-alkaline earth metal complex oxide.

However, within the exhaust gas purification device on the exhaust inlet side, there is a temperature difference between the upstream and downstream sides, so the NOx adsorption member on the upstream side changes from a low temperature range to a temperature range of 350°C or higher (high temperature range). Even if NOx reaches that point and starts to leave,
The copper ion exchange zeolite on the downstream side has not yet reached the temperature range of around 350°C, and its purification ability as a reduction catalyst is not demonstrated, making it impossible to effectively reduce the NOx concentration at the exhaust gas purification device outlet at low temperatures. .

The present invention has been made in view of these points, and its purpose is to improve and arrange the NOx adsorption member and the reduction catalyst so that the temperature path X at low temperatures becomes small in the exhaust gas purification device. However, the aim is to effectively reduce NOx by 8 degrees at the exhaust gas purification device outlet.

(Means for Solving the Problems and Their Effects) In order to achieve the above object, the solving means of the present invention uses an adsorbent that adsorbs NOx at a predetermined temperature or lower in the exhaust system of the engine as an engine exhaust gas purification device. A Noxe attachment member that performs
A plurality of sets of reduction catalysts, which are made by ion-exchange supporting a transition metal on zeolite and have NOx decomposition performance near the above-mentioned predetermined temperature, are provided alternately in the order of NOx adsorption members and reduction catalysts from the upstream side.

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

Further, as the reduction catalyst, it is appropriate to use zeolite (copper ion-exchanged zeolite) in which transition metals such as copper ions are ion-exchanged. The transition metals for this ion exchange include Cu, co, NE, Cr, Fe, and Mn.
, Pt, Pd, Rh.

Ru, Ir, etc. can also be used singly or in combination.

Therefore, multiple sets of N are provided in the intake system of the engine.
The oxe attachment member and the reduction catalyst are the N.

The X adsorption member and the reduction catalyst are divided into layered bodies, and the thickness of each set of the NOx adsorption member and the reduction catalyst is thin. The exhaust gas temperature is sequentially and rapidly transmitted to the reduction catalyst via the NOx adsorption member.

Additionally, as shown in Figure 2, NOx located on the most upstream side
When the temperature of the adsorption member reaches 350°C, the NOx adsorbed by this NOx adsorption member starts to be released, and the NOx
The temperature of the reduction catalyst on the downstream side of the NOx adsorption member, which is divided into layers, immediately reaches 350°C, and the temperature of the reduction catalyst on the downstream side of the NOx adsorption member, which is divided into layered bodies, becomes 350°C, and the NOx is converted into N2 and 02. Disassemble. Moreover, due to the reduction catalyst downstream of the NOx adsorption member located on the most upstream side, N and 02
NOx that has not been completely decomposed into 350℃ is adsorbed by the NOx adsorption member on the downstream side, and when the temperature reaches 350℃, the reduction catalyst on the downstream side removes N2 and O,
It is repeatedly broken down into As a result, the NOx concentration on the exit side of the exhaust gas purification device took on the characteristics shown by β in the figure, and N2 and 02 were not completely decomposed due to the temperature difference between the NOx adsorption member and the reduction catalyst until they reached 350°C. The concentration of NOx becomes as small as possible.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an exhaust gas purification device S for a diesel engine according to an embodiment of the present invention.
It is provided in the middle of an exhaust pipe 1 that is the exhaust gas outflow side of an engine (not shown). The exhaust gas purification device S includes an exhaust pipe 1
a casing 2 integrally formed with the casing 2;
The NOx adsorption member 3 is installed inside the casing 2 and adsorbs NOx contained in the exhaust gas in a low temperature range of 350°C or lower. H-containing NOx is removed by N2 and 0
Reduction catalyst 4 that improves NOx decomposition performance
It is equipped with

As a method for manufacturing the NOx adsorption member 3, for example, 13
．． After mixing 6 g of CuO powder and, for example, 34.6 g of BaCO3 powder in a ball mill,
It is fired at 0°C (600°C to 1000°C) to crystallize it (form it into an oxide).

After that, it is crushed and binder (alumina slurry) is added to L.
og and baked at 850℃ for 5 hours to form NOx adsorbent 3a.
NOx with coloring material 3 is used.

In this case, the ratio of composite oxide CuO:BaO in one finished product is adjusted to 1:1.

On the other hand, as a method for producing the reduction catalyst 4, 60 parts of a mixture of silica sol and alumina sol mixed so that the Si/Al ratio was 40 was added with zeolite (Si/Al ratio was 40
) Add 100 parts of powder and 60 parts of water, stir thoroughly, adjust the pH to 3 to 6 with aluminum nitrate solution, and prepare a washcoat slurry as a binder. Then, the cordierite monolithic honeycomb carrier was immersed in water, the excess water was blown off, and then immersed in the above slurry for wash coating (binder), taken out, and the excess slurry was blown off with compressed air. It is dried at 600° C. for 20 minutes and then fired in an electric furnace at 600° C. for 1 hour.

The fired body thus obtained was immersed in a low concentration acetic acid aqueous solution of about 0.02 mol/1 for 24 hours, the ion exchange operation was repeated several times to support it, and then dried at 150°C for 2 hours to ionize it. A copper ion exchange zeolite (reduction catalyst 4) with an exchange rate of 143% is produced. In this case, as shown in Fig. 4, No. shown as A in the figure decomposed by the copper ion exchange zeolite with an ion exchange rate of 143% changes depending on the temperature change, N2 shown as B in the figure and C in the figure. It is decomposed into 02 shown in the figure and N20 shown in C in the figure. Furthermore, the purification rate can be increased by repeating the ion exchange operation several times. In addition, Figure 4 shows NO on a 143% exchanged Cu-Z catalyst.
FIG.

The NOx adsorption member 3 and the reduction catalyst 4 are each formed into a layered body so that the two members 3 and 4 form a pair. Further, three sets of the NOx adsorption member 3 and the reduction catalyst 4 are provided in close contact with each other in the order of the NOx adsorption member 3 and the reduction catalyst 4 from the upstream side.

The ratio of the NOx adsorption member 3 (NOx adsorbent 3a) to the reduction catalyst 4 is 1:1, and 50 cc of NOx @ 30 cc of the reduction catalyst 4 of the coloring material
A total of 100 cc is arranged in a layer of 2 cm to 4 cm.

In addition, the test conditions are SV (space velocity of test gas) -500~1000 (h-') Perform at NO-500 ppm.

Therefore, in the plurality of sets of NOx@g members 3 and reduction catalysts 4 in the open air gas purification device S provided in the middle of the intake pipe 1, the NOx adsorption member 3 and the reduction catalyst 4 are divided into layered bodies. The thickness of the NOx adsorption member 3 and reduction catalyst 3 per set is thin, about 2 cll to 4 cm, and three sets of NOx adsorption members 3 are arranged alternately from the upstream side.
The exhaust gas temperature is sequentially and rapidly transmitted to the reduction catalyst 4 via the NOx adsorption member 3.

As a result, NOx@? j
The temperature difference between the member 3 and the reduction catalyst 4 can be made as small as possible.

Moreover, as explained in FIG. 2, when the temperature of the NOx adsorption member 3 located on the most upstream side, that is, the first coarse upstream side, reaches 350°C, the NOx adsorbed on this NOx adsorption member 3
begins to separate, and the N after the first coarse NOx adsorption member 3
At 711 degrees Ox, the characteristics are as shown by α in the figure, but the temperature of the first set of reduction catalysts 4 on the downstream side of the NOx adsorption member 3 divided into layered bodies immediately reaches 350 degrees Celsius, and the NOx is reduced to N.

02 and N! Decomposes into O. Moreover, the first set of reduction catalysts 4 allows N! , 0! The NOx that has not been completely decomposed into N20 is adsorbed up to 350°C by the second set of NOx adsorption members 3 on the downstream side, and when the temperature reaches 350°C, the second set of reducing catalysts 4 on the downstream side absorbs N,... The decomposition into O, N, and 0 is repeated until the third set. As a result, the NOx concentration on the exit side of the exhaust gas purification device S is reduced to β in the figure.
The characteristics are as shown by , and due to the temperature difference between NOx @ colored member coloring material 3 and catalyst 4 reaching 350°C, N,,0
．． Also, the concentration of NOx that has not been completely decomposed into N and O becomes as small as possible, so that the purification performance of the exhaust gas purification device S can be improved.

It should be noted that the present invention is not limited to the above embodiments, but includes various other modifications.

For example, in the above embodiment, the NOx adsorption member 3 and the reduction catalyst 4 are provided in the casing 2 of the exhaust gas purification device S, but the exhaust gas can be purified by providing the NOx absorption member and the reduction catalyst in the exhaust system of the engine. The device may be configured.

Further, in the above embodiment, the exhaust pipe 1 of the diesel engine
Although the exhaust gas purification device S is provided in the above, it is of course possible to apply the exhaust gas purification device to the exhaust system of a gasoline engine.

(Effects of the Invention) As described above, according to the engine exhaust gas purification device of the present invention, multiple sets of NOx @ attachment members and reduction catalysts are divided into layered bodies to reduce the amount of N per set.

The thickness of the X adsorption member and the reduction catalyst are made thin, and the exhaust gas temperature is sequentially and quickly transmitted to the reduction catalyst through multiple sets of NOx absorbing members arranged alternately from the upstream side, resulting in exhaust gas purification. The temperature difference between the NOx adsorption member and the reduction catalyst within the device can be made as small as possible. Moreover, the N that was not completely decomposed into N2 and 02 by the reduction catalyst downstream of the NOx adsorption member located on the most upstream side
By repeating the adsorption of Ox by the NOx adsorption member on the downstream side and decomposition into N2 and 02 by the reduction catalyst, the concentration of NOx due to the temperature difference between the NOx adsorption member and the reduction catalyst is reduced as much as possible. becomes a small value,
Therefore, the purification performance of the exhaust gas purification device can be improved.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view of an exhaust gas purification device in the middle of an exhaust pipe, showing an embodiment of the present invention. Also, Figures 2 to 4
The figure shows a modified example, and FIG. 2 is N. N when the X adsorbent and reduction catalyst reach a predetermined temperature. An explanatory diagram showing X concentration characteristics, FIG. 3 is an adsorption characteristic diagram of BaO-CuO with respect to temperature, and FIG. 4 is a diagram of decomposition characteristics of No with respect to temperature. 3...NOx adsorption member 3a...NOx adsorption material 4...Reduction catalyst S...of the exhaust gas purification device) Fig. Humidity (''C) Fig. 3...NOx adsorption member 3a...・-NOx adsorbent 4...Reduction catalyst S...Exhaust gas purification device 350℃ Fig.

Claims (1)

[Claims] (1) In the exhaust system of the engine, a NOx adsorption member having an adsorbent that adsorbs NOx at a temperature below a predetermined temperature, and a reduction catalyst made by ion-exchange supporting a transition metal on zeolite and having NOx decomposition performance near the predetermined temperature. is NOx from the upstream side
An exhaust gas purification device for an engine, characterized in that a plurality of sets of adsorption members and reduction catalysts are provided alternately in this order.