JP2004204700A - Exhaust gas purification device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying device surely preventing clogging when adopting a high temperature active type HC selective reduction NOX catalyst. <P>SOLUTION: This exhaust gas purifying device is equipped with a high temperature active type HC selective reduction NOx catalyst 10 composed of base metal oxidation catalyst with improved reaction selectivity so as to selectively react NOx with HC even under coexistence of oxygen in the midway of an exhaust gas pipe 9. Low temperature active type HC oxidation catalyst 12 composed of noble metal oxidation catalyst is carried by replacing for the high temperature active type HC selective reduction NOx catalyst 10 only in a prescribed range from a front end face to a rear part of a carrier carrying the HC selective reduction NOx catalyst. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust purification device applied to an internal combustion engine such as a diesel engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a diesel engine, an HC having an enhanced reaction selectivity so that NOx (nitrogen oxide) can be selectively reacted with HC (hydrocarbon) even in the presence of oxygen in an exhaust pipe through which exhaust gas flows. Equipped with a selective reduction type NOx catalyst, a necessary amount of HC is added upstream of the HC selective reduction type NOx catalyst, and the HC is reduced and reacted with NOx in exhaust gas on the HC selective reduction type NOx catalyst. There is an apparatus which can reduce the emission concentration of NOx by using such a method (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP 2001-317346 A
As this type of HC selective reduction type NOx catalyst, noble metal-based oxidation catalysts such as platinum and palladium and base metal-based oxidation catalysts such as copper / zeolite and iron / zeolite are already known as having the above-mentioned properties. However, as shown by the curve A in FIG. 3, the HC selective reduction type NOx catalyst composed of the noble metal-based oxidation catalyst shows high activity in a low temperature range, and as shown by the curve B in FIG. The HC selective reduction type NOx catalyst composed of an oxidation catalyst exhibits high activity in a high temperature range.
[0005]
In vehicles such as domestic route buses that mainly drive at low speeds, an HC selective reduction NOx catalyst composed of a noble metal-based oxidation catalyst is adopted to increase the NOx reduction rate in a low temperature range of exhaust gas. In vehicles such as long-distance transport trucks used mainly for traveling abroad, an HC selective reduction NOx catalyst composed of a base metal-based oxidation catalyst is employed so as to increase the NOx reduction rate in a high temperature range of exhaust gas.
[0006]
[Problems to be solved by the invention]
However, in a vehicle employing a high-temperature activated HC selective reduction NOx catalyst composed of a base metal-based oxidation catalyst, low-speed running with low exhaust gas temperature continued, HC was excessively added, and a large amount of soot was generated. In this case, unprocessable HC accumulates on the front end face of the HC selective reduction type NOx catalyst having a low catalytic activity, whereby the front end face of the HC selective reduction type NOx catalyst becomes sticky and wet, and soot is reduced. There is a risk that the soot component will continue to accumulate without being oxidized, and the HC selective reduction type NOx catalyst will be clogged.
[0007]
That is, as shown by the curve A in FIG. 4, the low-temperature activated HC selective reduction type NOx catalyst composed of a noble metal-based oxidation catalyst shows a high HC combustion rate from a relatively low temperature range, whereas the curve A in FIG. As shown by B, the high-temperature activated HC selective reduction NOx catalyst composed of a base metal-based oxidation catalyst does not increase the HC combustion rate unless it reaches a certain high temperature range. Therefore, the low-temperature activated HC composed of a noble metal-based oxidation catalyst is used. The problem of clogging, which hardly occurs with the selective reduction type NOx catalyst, could occur.
[0008]
The present invention has been made in view of the above-described circumstances, and provides an exhaust gas purification apparatus that can reliably prevent clogging when a high-temperature active HC selective reduction type NOx catalyst is employed. It is aimed at.
[0009]
[Means for Solving the Problems]
The present invention relates to a high-temperature activated HC selective reduction type comprising a base metal-based oxidation catalyst having an enhanced reaction selectivity so that NOx can be selectively reacted with HC in the middle of an exhaust pipe through which exhaust gas flows, even in the presence of oxygen. A low-temperature activated HC oxidation catalyst composed of a noble metal-based oxidation catalyst is provided with the NOx catalyst, and only in a required range from the front end face to the rear of the carrier carrying the HC selective reduction type NOx catalyst, The present invention relates to an exhaust gas purifying apparatus characterized in that it is carried by replacing the HC selective reduction type NOx catalyst.
[0010]
Thus, when the vehicle is running at a low speed with a low exhaust gas temperature, when HC is excessively added, or when a large amount of soot is generated, the HC selective reduction type NOx catalyst is supported. Even if HC adheres to the front end face of the carrier, a low-temperature activated HC oxidation catalyst composed of a noble metal-based oxidation catalyst is carried here, so that the adhered HC is oxidized well, so that the carrier The front end face is kept in a dry state, so that adhesion of soot hardly occurs, and a problem that soot continues to accumulate on the front end face of the carrier without being oxidized and causes clogging does not occur.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
1 and 2 show an example of an embodiment of the present invention. In the drawings, reference numeral 1 denotes an engine (internal combustion engine) which is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The air 4 guided from the air cleaner 3 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 for cooling. The air 4 is guided from the intercooler 6 to an intake manifold (not shown) and introduced into each cylinder of the engine 1.
[0013]
Exhaust gas 7 discharged from each cylinder of the engine 1 is sent to a turbine 2b of the turbocharger 2 via an exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b is exhausted to the outside of the vehicle via an exhaust pipe 9. It is made to be discharged.
[0014]
A high-temperature active HC selective reduction catalyst composed of a base metal-based oxidation catalyst with enhanced reaction selectivity so that NOx can be selectively reacted with HC even in the presence of oxygen in the exhaust pipe 9 through which the exhaust gas 7 flows. A NOx catalyst 10 is mounted and held in a casing 11. A low-temperature NOx catalyst composed of a noble metal-based oxidation catalyst is used only in a required range from the front end face of the carrier carrying the HC selective reduction type NOx catalyst 10 to the rear. The active HC oxidation catalyst 12 is replaced with the HC selective reduction type NOx catalyst 10 and is carried.
[0015]
Here, the HC selective reduction type NOx catalyst 10 employs a conventionally known base metal-based oxidation catalyst such as copper / zeolite or iron / zeolite, and the HC oxidation catalyst 12 employs a conventional base metal such as platinum or palladium. A well-known noble metal-based oxidation catalyst may be employed, and the carrier supporting the HC selective reduction NOx catalyst 10 and the HC oxidation catalyst 12 is formed as a flow-through type honeycomb structure using alumina or the like. You just need to adopt something.
[0016]
In order to keep the NOx reduction effect of the main HC selective reduction type NOx catalyst 10 high, it is preferable to minimize the supporting range of the HC oxidation catalyst 12 in the vicinity of the front end of the carrier. If the supporting range is too small, the efficiency of the HC oxidation treatment described later deteriorates. Therefore, it is preferable that the supporting range is limited to the minimum necessary range within which good oxidation treatment of HC can be expected.
[0017]
Further, in the example shown here, the vicinity of the entrance of the casing 11 in the exhaust pipe 9 and a fuel tank 13 provided at a required location are connected by a fuel supply pipe 14. By driving the supply pump 15 provided on the way, fuel 16 (HC) such as light oil in the fuel tank 13 can be added to the vicinity of the inlet of the casing 11 through the injection nozzle 17.
[0018]
Thus, by configuring the exhaust gas purifying apparatus in this way, the HC selective reduction type NOx catalyst can be used when low-speed traveling with low exhaust gas temperature continues, HC is excessively added, or a large amount of soot is generated. Even if HC from the injection nozzle 17 adheres to the front end face of the carrier carrying the carrier 10, since the low-temperature activated HC oxidation catalyst 12 made of a noble metal-based oxidation catalyst is carried here, the HC adheres. As a result of the HC being oxidized satisfactorily, the front end face of the carrier is kept in a dry state, so that adhesion of soot is less likely to occur. No more problems such as waking up.
[0019]
Therefore, according to the above-described embodiment, clogging can be reliably prevented when the high-temperature activated HC selective reduction type NOx catalyst 10 is employed, so that NOx reduction by the HC selective reduction type NOx catalyst 10 can be prevented. The effect can be stably maintained over a long period of time.
[0020]
It should be noted that the exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.
[0021]
【The invention's effect】
According to the exhaust gas purifying apparatus of the present invention described above, clogging can be reliably prevented when a high-temperature activated HC selective reduction NOx catalyst is employed, and therefore, a high-temperature activated HC selective reduction NOx catalyst is used. An excellent effect that the NOx reduction effect of the catalyst can be stably maintained over a long period of time can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.
FIG. 2 is an enlarged view showing details of a high-temperature activation type HC selective reduction type NOx catalyst of FIG. 1;
FIG. 3 is a graph showing a relationship between a NOx reduction rate and a temperature.
FIG. 4 is a graph showing a relationship between HC combustion rate and temperature.
[Explanation of symbols]
7 Exhaust gas 9 Exhaust pipe 10 High temperature active type HC selective reduction type NOx catalyst 12 HC oxidation catalyst

Claims (1)

Equipped with a high-temperature activated HC selective reduction NOx catalyst consisting of a base metal-based oxidation catalyst with enhanced reaction selectivity so that NOx can be selectively reacted with HC even in the presence of oxygen in the exhaust pipe through which exhaust gas flows. The low-temperature activated HC oxidation catalyst composed of a noble metal-based oxidation catalyst is converted to the high-temperature activated HC selective reduction only in a required range from the front end face of the support carrying the HC selective reduction type NOx catalyst to the rear. An exhaust gas purifying apparatus characterized in that the exhaust gas purifying apparatus is carried by replacing a type NOx catalyst.

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