JP3106567B2 - Exhaust gas purification device - Google Patents

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 system provided with an exhaust gas purifying catalyst capable of reducing nitrogen oxides (hereinafter also referred to as NOx) in exhaust gas in an oxygen-excess atmosphere.
Relates apparatus, NOx in the exhaust gas of an automotive internal combustion engine
It is used for reduction and the like.

[0002]

2. Description of the Related Art Internal combustion engines for automobiles are required to have low fuel consumption in terms of performance, and in recent years, it has been desired to reduce CO ₂ emissions from the viewpoint of preventing global warming. As a solution that satisfies these requirements at once, a lean burn engine that burns on the air-fuel ratio lean side from stoichiometric air (stoichiometric air-fuel ratio) has been developed and partially put into practical use.

However, in a lean-burn engine, since the exhaust gas is in an oxygen-excess atmosphere, a three-way catalyst (which has an effect of purifying NOx, CO, and HC with respect to exhaust gas generated by stoichiometric combustion) is used. NOx cannot be reduced.

In order to solve this problem, Japanese Patent Laid-Open Publication No.
No. 145 proposes an exhaust purification device in which a catalyst in which Cu or Co is ion-exchanged and supported on zeolite is provided in an upstream portion of an exhaust system of an internal combustion engine, and a noble metal catalyst is provided in a downstream portion of the exhaust system. I have.

[0005]

However, a catalyst formed by supporting Co on alumina, zeolite or the like generates CoAl ₂ O ₄ at a high temperature (about 600 ° C. or higher), causing deterioration of the catalyst. Further, even if Cu or Ni is used,
And catalyst deterioration occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a NOx
It is an object of the present invention to provide an exhaust gas purifying apparatus provided with a catalyst for purifying exhaust gas, which has a resistance to high-temperature deterioration, which is a catalyst for reducing methane.

[0007]

In order to achieve the object of the present onset to achieve the above purpose
The light is as follows. Exhaust gas in the exhaust system of the internal combustion engine
Nitrogen oxides in an oxygen-excess atmosphere in the presence of hydrocarbons.
Ion exchange of transition metal with ZrO ₂ for reduction in presence
In this case, a supported catalyst is provided.
Pt / alumina catalyst with Pt supported on Mina
An exhaust gas purification device characterized by the following.

[0008]

In the exhaust gas purifying apparatus of the present invention, Co, C
Transition metals such as u do not react with ZrO ₂ even at high temperatures. Also, the heat resistance temperature of ZrO ₂ is very high, 900 °
C can withstand. As a result, the catalyst in which the transition metal is supported on ZrO ₂ has improved resistance to high-temperature deterioration as compared with the catalyst in which the transition metal is supported on zeolite or alumina. Also, Co exhibits excellent NOx purification activity at high temperatures. Therefore, C
By providing a catalyst carrying o and the like on ZrO ₂ in the exhaust system upstream of the internal combustion engine, which is a high temperature portion, NOx in exhaust gas from the internal combustion engine can be reduced at a high NOx purification rate,
In addition, an exhaust purification device having excellent durability can be obtained. Also,
A catalyst supporting Co or the like on ZrO ₂ is provided, and P
t / Alumina catalyst provided, so over a wide temperature range
A high NOx purification rate is obtained.

[0009]

FIG. 1 shows an exhaust gas purifying apparatus according to an embodiment of the present invention.
1 shows an exhaust gas purification catalyst 2 to be used . As shown in FIG. 1, a catalyst 2 comprises a cordierite monolith carrier 4 having a large number of independent flow paths, and a zirconia (ZrO ₂ ) layer 6 coated on the surface of the independent flow paths.
And a transition metal 8 carried on the zirconia layer 6 by ion exchange. As the transition metal 8, cobalt (C
o), copper (Cu), nickel (Ni)
x Suitable for use because of its excellent purification properties.

An embodiment in which the catalyst 2 is a Co / ZrO ₂ catalyst will be described. Wash coat slurry was produced by ball milling 100 parts of zirconia powder and 14 parts of a commercially available aqueous solution of aluminum nitrate together with water and nitric acid. The cross-sectional area 1in ² per about 4
A 0.65 liter cordierite integral carrier containing 00 channels was immersed in the washcoat slurry. Subsequently, the excess liquid in the cells of the integral carrier was blown off with compressed air, and the integral carrier was dried and baked at 700 ° C. for 1 hour to coat about 50 μm of zirconia on the integral carrier. Next, the integrated carrier was immersed in a 0.23 mol / l aqueous solution of cobalt nitrate, dried,
C. for 1 hour to carry 33 g / l of cobalt oxide. Thus, catalyst 2 was prepared.

Apart from the above-mentioned Co / ZrO ₂ catalyst, a catalyst 10 carrying Pt on alumina was prepared as a noble metal-based lean NOx catalyst as follows. Alumina was coated on the integral carrier in the same manner as described above using 1.3 liter of the cordierite integral carrier. Next, the above-mentioned integral carrier coated with alumina was immersed in an aqueous solution of cerium nitrate 2.5 mol / l, dried, and dried at 600 ° C. for 3 hours.
Calcium for 0.1 hour on the support
5 mol / l was loaded. Next, it is immersed in a 0.005 mol / l dinitrodiammineplatinum aqueous solution of nitric acid, dried and calcined at 200 ° C. for 1 hour to give 1.5 g / l.
Of platinum was supported. Thus, a Pt / alumina catalyst 10 was produced.

FIG. 2 shows Co / ZrO ₂ catalyst 2 and Pt
2 shows the mechanism of the NOx purification action of the alumina catalyst 10. Part of hydrocarbons (HC) contained in the exhaust gas is partially oxidized in the catalyst part to generate active species, and the remaining parts are completely oxidized to CO ₂ and H ₂ O. Some of the active species are catalyst 2,
React with NOx with the help of 10 to reduce NOx,
Purify with N ₂ , CO ₂ , H ₂ O. In addition, the remaining active species are oxidized to finally become CO ₂ . As is clear from the above mechanism, HC is required for NOx purification.

FIG. 3 schematically shows in which temperature range the Co / ZrO ₂ catalyst 2 and the Pt / alumina catalyst 10 exhibit a high NOx purification rate. Co is good NOx in high temperature range
Since the purification rate is shown, the peak of the NOx purification rate of the Co / ZrO ₂ catalyst 2 appears on the high temperature side as shown by the curve A. On the other hand, the peak of the NOx purification rate of the Pt-based lean NOx catalyst 10 appears on the relatively low temperature side as shown by the curve B.

FIG. 4 shows that the exhaust system 14 of the internal combustion engine 12 capable of lean combustion is ion-exchanged with a transition metal,
Catalyst 2 supported on O ₂ and Pt-based lean NOx catalyst 10
1 shows an exhaust gas purification system provided with. Co / Zr
The O ₂ catalyst 2 is disposed at a high temperature portion, that is, upstream of the exhaust system 14, and the Pt-based lean NOx catalyst 10 is disposed downstream of the exhaust system 14.

Various sensors for detecting operating conditions are provided, and include a throttle opening sensor 16, an intake pressure sensor 18, and a combustion pressure sensor 20. The sensor output is sent to an electronic control unit (ECU) 22. Further, the EGR valve 24 is controlled by an output signal of the ECU 22. When the EGR (exhaust gas recirculation) amount increases, combustion is slightly sacrificed, unburned hydrocarbons increase, and the amount of HC supplied to the catalysts 2, 10 increases.

The operation of the exhaust gas purification system shown in FIG. 4 is shown by a curve C in FIGS. 5 and 3. However, FIG. 5 shows a case where only the Pt / alumina catalyst is provided and the Co / ZrO ₂ catalyst is not provided as a comparative example. As can be seen from the curve C in FIG. 3, the Co / ZrO ₂ catalyst 2 effectively works to purify NOx in the operating region where the exhaust gas temperature is high, and the Pt / alumina catalyst 10 is effective in the operating region where the exhaust gas temperature is low. Working to purify NOx. Therefore, the temperature range in which a high NOx purification range can be shown is wider than curves A and B.

FIG. 5 shows vehicle speed and NO in the system of FIG.
x Shows relationship with purification rate. When the vehicle speed is high, the exhaust gas temperature becomes high, but the Co / ZrO ₂ catalyst 2 works effectively to purify NOx, so that a high NOx purification rate is shown. Further, although the exhaust gas temperature becomes low in the low speed range, the Pt / alumina catalyst 10 works effectively to purify NOx, so that
It shows a high NOx purification rate. Therefore, a high NOx purification rate can be exhibited regardless of whether the speed is low or high. On the other hand, in the comparative example, the temperature becomes high at a high speed, and the NOx purification rate of the Pt-based lean NOx catalyst 10 decreases, so that the NOx purification rate of the system also decreases.

Further, since Co is supported on ZrO ₂ , when Co is supported on alumina or zeolite, CoAl ₂ O ₄ generated in a high temperature range is not generated, and Co is not generated.
The / ZrO ₂ catalyst 2 also solves the problem of high temperature degradation of conventional catalysts.

In a high temperature range, the complete oxidation of HC in the exhaust gas by the catalyst is promoted, and the amount of active species generated decreases, and
Since there is a possibility that the Ox purification rate may decrease, in order to prevent this, signals from various operation sensors are input to the ECU 22, and the ECU 22 determines whether or not the operating region is at a high exhaust gas temperature, and the high exhaust gas temperature is reached. EGR when operating
The EGR amount is increased by increasing the opening of the valve 24 so that HC generated from the unburned fuel is supplied to the Co / ZrO ₂ catalyst 2. In the above embodiment, the transition metal of the catalyst 2 is C
Although o is taken as an example, Cu, Ni or the like may be used.

[0020]

According to the present invention, the exhaust system of an internal combustion engine
Nitrogen oxides in exhaust gas are carbonized in an oxygen-rich atmosphere.
Transition metal to ZrO ₂ for reduction in the presence of hydrogen
Provide a catalyst supported by ion exchange, and
Pt / alumina catalyst with Pt supported on alumina on the side
Since there is provided, taking as an example such as Co as the transition metal (as also Cu or Ni), (b) Co is good NOx purification rate is obtained at a high temperature by showing excellent NOx purification performance In the high-temperature (B) CoAl ₂ O ₄ as in the case where alumina or zeolite is used for the carrier because ZrO ₂ is used for the carrier.
There is prevented the high temperature deterioration of the catalyst by not generated, the (c) excellent high-temperature durability by having the ZrO ₂ excellent heat resistance resulting et al is, (d) a higher temperature range the NOx purification rate is obtained Hiroga
You.

[Brief description of the drawings]

FIG. 1 is a side view showing a cross section of a part of an exhaust gas purifying catalyst according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a NOx purification mechanism of the catalyst of FIG.

FIG. 3 is a graph showing the relationship between the NOx purification rate and temperature of various catalysts or combinations of catalysts.

FIG. 4 is a system diagram of an exhaust gas purification device for an internal combustion engine equipped with the catalyst of FIG. 1;

FIG. 5 is a relationship diagram between the NOx purification rate and the vehicle speed of the system of FIG. 4 and the system of the comparative example.

[Explanation of symbols]

2 Catalyst (Co / ZrO ₂ catalyst) 4 Cordierite monolith support 6 Zirconia (ZrO ₂ ) layer 8 Transition metal (for example, Co) 10 Pt / alumina catalyst

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86-53/96 CA (STN)

Claims (1)

(57) [Claims] To 1. A exhaust system of an internal combustion engine, the nitrogen oxides in the exhaust gas, in an oxygen-rich atmosphere, the order to reduced in the presence of hydrocarbons, a transition metal is ion-exchanged to the ZrO ₂ carrier And a catalyst is provided on the downstream side of the catalyst.
An exhaust gas purification device comprising a Pt / alumina catalyst supporting t .