JPH0568887A - Waste gas cleaning catalystic device - Google Patents

Abstract

PURPOSE:To clean enough hydrocarbon and CO in waste gas to improve NOx cleaning efficiency and to put a cleaning method to practical for an engine of a motor car in oxygen excess atmosphere, in a catalytic device for cleaning waste gas from a motor car. CONSTITUTION:A NOx cleaning catalyst 2 formed by supporting a transition metal on a zeolite upon ion-exchanged is attached to an exhausting path 1. A secondary catalyst 3 inhibiting ability of cleaning CO and cleaning hydrocarbon is attached to the exhausting path 1 at the upper course to the NOx cleaning catalyst 2. The secondary catalyst is formed, for example, by impregnating Pb to oxidation catalyst or catalytic converter rhodium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst device for purifying automobile exhaust gas.

[0002]

2. Description of the Related Art In recent years, the development of lean-burn engines with low fuel consumption has been underway. An automobile equipped with this lean combustion engine is operated with the engine combustion chamber placed in an excess oxygen atmosphere (lean), as in the case of a conventional diesel engine. At this time, a large amount of NOx, which is a toxic gas, is discharged from the engine, so this NOx must be removed to prevent its release into the atmosphere.

Conventionally, as a technique for removing NOx in exhaust gas, a method using a three-way catalyst such as Pt-Rh system, a selective reduction method with ammonia, urea, etc., and NOx with various adsorbents have been mainly used. There is a NOx absorption method of adsorbing. However, in the above-mentioned selective reduction method, there is a problem that the apparatus is large, and further, ammonia is discharged into the atmosphere and
There was a problem of causing next pollution. In addition, the above NOx
The absorption method has a problem that NOx adsorbed on the adsorbent must be post-treated by washing with water or the like. Moreover, the above-mentioned three conventional methods have a problem in that the effect cannot be exhibited in an oxygen excess atmosphere and NOx cannot be sufficiently removed.

Then, a copper ion-exchanged zeolite was invented, which directly decomposes NOx into N ₂ and O _2, etc., and was able to obtain a NOx purification rate of more than 90% in the laboratory stage. This copper ion-exchanged zeolite is prepared by carrying out copper ion-exchange support on zeolite and is
As a reduction catalyst that can purify Ox, it has attracted attention, and an exhaust gas purifying catalyst device in which this copper ion-exchanged zeolite is installed in the exhaust system of an engine is already known.

[0005]

However, the above exhaust gas purifying catalyst device has a problem that it cannot be put into practical use because it has not been applied yet in an excess oxygen atmosphere in a running automobile. The reason is that the copper ion-exchanged zeolite has a weak oxidizing ability of the catalyst, and therefore has insufficient purification performance for HC and CO.

That is, FIG. 1 shows the results of measuring the effect of the HC concentration in the exhaust gas on the NO purification rate of the copper ion-exchanged zeolite. In this measurement, NO was 2100 ppm,
O ₂ at 7.5%, CO at 0.18%, H ₂ at 650
Exhaust gas synthesized with ppm, CO ₂ of 9.4%, and N ₂ balance is flowed at a SV (space velocity) of 25,000 hr ⁻¹ to a copper ion-exchanged zeolite having a surface temperature of 400 ° C.
The concentration was changed. As a result, it was found that the copper ion-exchanged zeolite has an improved NO purification rate in proportion to the concentration of HC coexisting with NO in the exhaust gas in an oxygen excess atmosphere. Therefore, in order to increase the NO purification rate with respect to the exhaust gas in an oxygen-excess atmosphere, it is conceivable to flow the exhaust gas having a high HC concentration to the copper ion-exchanged zeolite.

However, when an experimental vehicle having a copper ion-exchanged zeolite arranged in the exhaust system was used and the vehicle was run in LA-IV mode, which is the exhaust gas regulation of USA, the NOx purification rate was 36%, which complied with the regulation. HC purification rate is 88%, C
The O purification rate was 38% and both could not pass the regulation. The test vehicle was equipped with a lean-burn engine with an air-fuel ratio of about 22 during steady running. Thus, the copper ion-exchanged zeolite has insufficient purification performance for HC and CO.

Therefore, it is conceivable to dispose a three-way catalyst having a high purification rate for HC and CO on the downstream side of the copper ion-exchanged zeolite. However, since the three-way catalyst has poor activity at low temperatures, there is a problem in that the temperature does not rise when it is provided on the downstream side, and the purification performance for HC and CO cannot be sufficiently exhibited.

On the other hand, an experimental vehicle equipped with a platinum / rhodium-based three-way catalyst on the upstream side of the copper ion-exchanged zeolite and equipped with the same lean combustion engine as above was used to run in the LA-IV mode. However, the HC purification rate is 98
%, CO purification rate is 94%, both of which meet the regulations, but NO
x The purification rate was 12%, which failed to clear the regulation. That is, in this case, since the three-way catalyst purifies HC, there arises a problem that the NOx purification rate of the copper ion-exchanged zeolite decreases.

The present invention has been made in view of the above points, and an object of the present invention is to sufficiently purify HC and CO in exhaust gas and also to increase the NOx purification rate in an oxygen excess atmosphere. The present invention aims to provide an exhaust gas purifying catalyst device that can be put to practical use in the automobile engine.

[0011]

In order to achieve the above-mentioned object, the invention according to claim 1 is provided in an exhaust passage of exhaust gas, and N is formed by carrying out ion exchange loading of transition metal on zeolite.
It is configured to include an Ox purification catalyst and a second catalyst that is disposed on the upstream side of the NOx purification catalyst and that suppresses the ability to purify CO and reduce HC.

According to a second aspect of the present invention, the second catalyst comprises an oxidation catalyst or a three-way catalyst impregnated with lead.

According to a third aspect of the present invention, the NOx purification catalyst is a zeolite in which cobalt or copper is ion-exchanged and supported, and the second catalyst is gold-supported ferrite.

[0014]

With the above construction, in the invention according to claim 1,
CO in the exhaust gas and a part of HC are the second on the upstream side of the exhaust passage.
It is purified by a catalyst and HC is discharged to the downstream side of the exhaust passage.
Since exhaust gas with high concentration flows, NOx and HC are
It is purified at a high purification rate by the Ox purification catalyst.

[0015]

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

FIG. 2 shows an exhaust gas purifying catalyst device according to a first embodiment of the present invention. This exhaust gas purification catalyst device includes a NOx purification catalyst 2 provided in an exhaust passage 1 for exhaust gas of a vehicle, and a second catalyst 3 arranged upstream of the NOx purification catalyst 2 in the exhaust passage 1. It has and.

The NOx purification catalyst 2 is made of copper ion-exchanged zeolite in which copper is ion-exchanged and supported on zeolite.

The second catalyst 3 is formed by impregnating lead with a platinum-rhodium ternary catalyst in which platinum and rhodium are supported on a monolith by ion exchange. The lead impregnation treatment and the post-treatment are performed as follows. That is, the above platinum-rhodium ternary catalyst was impregnated with an aqueous solution of lead acetate, allowed to stand in the atmosphere for about 3 hours, and then placed in an electric furnace for 4 hours.
Bake for 2 hours at 00 ° C.

Next, the operation of this embodiment will be described.
Since CO and a part of HC in the exhaust gas are purified by the second catalyst 3 on the upstream side of the exhaust passage 1, the exhaust gas having a high HC concentration flows to the downstream side of the exhaust passage 1, so that NOx and HC And are purified by the NOx purification catalyst 2 at a high purification rate. That is, since HC and CO in the exhaust gas can be sufficiently purified and the NOx purification rate can be improved, it can be put to practical use in an automobile engine under an oxygen excess atmosphere.

Further, since the exhaust gas purifying catalyst device of this embodiment has a simple structure in which the NOx purifying catalyst 2 and the second catalyst 3 are arranged in the exhaust passage 1, the entire device is miniaturized. It can be manufactured at low cost. Further, since the catalytic cracking action by the catalyst is used in purifying NOx, NOx does not remain in the exhaust passage, and the trouble of periodically taking out the catalyst and performing post-treatment for removing NOx is omitted. You can Moreover, NO
x Since no harmful substances are used for purification and no harmful substances are released into the atmosphere, secondary pollution will not occur.

When the purification performance of the second catalyst 3 against exhaust gas was measured, the results shown in FIG. 3 were obtained. As shown in the figure, by appropriately impregnating the platinum-rhodium three-way catalyst with lead, the purification rate of CO and NOx can be increased with respect to exhaust gas in an oxygen excess atmosphere (lean). It was possible to suppress only the purification rate of HC while maintaining it. Moreover, as shown in FIG. 3, the air-fuel ratio λ = 1
It was also possible to improve the CO and NOx purification rates during operation (acceleration region). Here, the reason why the purification rate of CO is improved is that the second catalyst 3 composed of a three-way catalyst is poor in activity at low temperatures.
Is disposed upstream of the NOx purification catalyst 2,
This is because there is no one that lowers the temperature of the exhaust gas further upstream thereof, so that the temperature easily rises, and it is advantageous in terms of temperature to exert the purification performance for CO.

Therefore, when the second catalyst 3 is arranged upstream of the NOx purification catalyst 2 in the exhaust passage and an experimental vehicle equipped with a lean combustion engine is used to run in the LA-IV mode, the Purification rate is 95%, CO purification rate is 98
%, The NOx purification rate was 42%, which all complied with the regulations.

FIG. 4 shows an exhaust gas purifying catalyst device according to a second embodiment of the present invention. This exhaust gas purification catalyst device is provided in the exhaust passage 1 for exhaust gas of a vehicle and is provided with NOx purification catalyst 4 made of cobalt ion-exchanged zeolite and in the exhaust passage 1 upstream of the NOx purification catalyst 4. And a second catalyst 5 made of gold-supported ferrite.

The cobalt ion-exchanged zeolite is a catalyst in which cobalt is ion-exchanged and supported on zeolite, and the gold-supported ferrite is a catalyst in which gold is supported on ferrite.

Next, the operation of this embodiment will be described.
Since CO and a part of HC in the exhaust gas are purified by the second catalyst 5 on the upstream side of the exhaust passage 1, and the exhaust gas having a high HC concentration flows to the downstream side of the exhaust passage 1, NOx and HC And are purified by the NOx purification catalyst 4 at a high purification rate. That is, since HC and CO in the exhaust gas can be sufficiently purified and the NOx purification rate can be improved, it can be put to practical use in an automobile engine under an oxygen excess atmosphere.

As with the first embodiment, the exhaust gas purifying catalyst device of the present embodiment can be downsized and can be manufactured at low cost. Further, it is possible to save the trouble of performing the post-treatment for removing NOx. Moreover, secondary pollution does not occur.

Therefore, when the second catalyst 5 is arranged on the upstream side of the exhaust passage of the NOx purifying catalyst 4 and an experimental vehicle equipped with a lean combustion engine is used to run in the LA-IV mode, the Purification rate 93%, CO purification rate 96
%, The NOx purification rate was 39%, all of which complied with regulations.

As described above, the exhaust gas purifying catalyst device of this embodiment uses HC, CO and NOx in the exhaust gas.
The reasons for being able to comply with all of the regulations are as follows.

That is, the gold-supported ferrite (the second catalyst 5) preferentially causes the CO-NO reaction to selectively oxidize and desorb CO, and as shown in FIG. However, the purification rate is low for HC. Further, the cobalt ion exchanged zeolite (catalyst for NOx purification 4), since the _{HC-NO-O 2} reaction selectively causing, when a large amount of HC is flowing, as shown in FIG. 6, with respect to HC and NO It shows a high purification rate. In addition,
In FIGS. 5 and 6, the temperature of the exhaust gas was measured at the entrance of each catalyst.

The NOx purifying catalyst is not limited to those of the first and second embodiments, but may be a catalyst in which a transition metal other than copper or cobalt is ion-exchanged and supported on zeolite. ..

In the first embodiment, the second catalyst 3
Was a platinum-rhodium three-way catalyst impregnated with lead, but is not limited to this.Three-way catalysts other than the above are impregnated with lead, and the oxidation catalyst contains lead. It may be impregnated.

[0032]

As described above, according to the exhaust gas purifying catalyst device of the present invention, the second catalyst on the upstream side of the exhaust passage purifies CO and a part of HC in the exhaust gas, and also downstream. Since exhaust gas having a high HC concentration flows to the side, the NOx purification catalyst purifies NOx and HC at a high purification rate. That is, since HC and CO in the exhaust gas can be sufficiently purified and the NOx purification rate can be improved, it can be put to practical use in an automobile engine under an oxygen excess atmosphere.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of HC concentration in exhaust gas on the NO purification rate of copper ion-exchanged zeolite.

FIG. 2 is a configuration diagram of an exhaust gas purifying catalyst device showing a first embodiment of the present invention.

FIG. 3 is a graph showing a purification rate of exhaust gas of a second catalyst in the first embodiment.

FIG. 4 is a view, corresponding to FIG. 2, showing a second embodiment of the present invention.

FIG. 5 is a graph showing a purification rate of exhaust gas of a second catalyst in the second embodiment.

FIG. 6 is a graph showing the purification rate of the NOx purification catalyst for exhaust gas in the second embodiment.

[Explanation of symbols]

 1 Exhaust passage 2,4 NOx purification catalyst 3,5 Second catalyst

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Kyogoku 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd.

Claims (3)

[Claims] 1. A NOx purification catalyst, which is provided in an exhaust gas exhaust passage and has a zeolite carrying a transition metal by ion exchange, and a NOx purification catalyst disposed upstream of the NOx purification catalyst.
An exhaust gas purifying catalyst device, comprising: a second catalyst having an ability to purify HC and suppress HC. 2. The exhaust gas purifying catalyst device according to claim 1, wherein the second catalyst is an oxidation catalyst or a three-way catalyst impregnated with lead. 3. The exhaust gas purifying catalyst device according to claim 1, wherein the NOx purifying catalyst is a zeolite in which cobalt or copper is ion-exchanged and supported, and the second catalyst is gold-supporting ferrite.