CN101614147B - Exhaust purification apparatus of internal-combustion engine - Google Patents

Abstract

An exhaust purification device for an internal combustion engine, which is provided with an oxidation catalyst (10) on the upstream side of a NOx storage catalyst (11), and has the function of concentrating exhaust gas flowing into the NOx storage catalyst and reducing and removing NOx stored on the NOx storage catalyst The NOx removal device, the oxidation catalyst consists of an upstream side oxidation catalyst (10a) containing catalyst noble metals such as Pt, and a downstream side oxidation catalyst comprising zeolite of an adsorption additive and catalyst noble metals such as Pt, which is arranged on the downstream side of the upstream side oxidation catalyst (10b) Composition.

Description

Exhaust purification device for internal combustion engines

technical field

The present invention relates to an exhaust purification device of an internal combustion engine, and more particularly to a configuration of an oxidation catalyst provided on an upstream side of an exhaust purification unit. the

Background technique

As a device (exhaust gas purification means) for purifying diesel engine exhaust, there is a structure in which a NOx (nitrogen oxide) adsorption catalyst is provided in the exhaust passage. The NOx storage catalyst is capable of storing NOx and SOx (sulfur oxides) in exhaust gas. In addition, there is known a regeneration method in which an oxidation catalyst is provided upstream of the NOx storage catalyst, an additive is injected and supplied to the upstream side of the oxidation catalyst, and an oxidation reaction (combustion) occurs by the oxidation catalyst to generate high-temperature and oxygen-poor exhaust gas. The atmosphere (rich air-fuel ratio atmosphere) reduces and removes NOx and SOx stored on the NOx storage catalyst. In particular, when the additive supplied to the oxidation catalyst is fuel, the fuel added from the additive supply device is in the form of droplets, so it is necessary to promote the vaporization of the added fuel and oxidize the main component HC in the added fuel to raise the exhaust gas temperature. , and by the consumption of oxygen in the exhaust gas and the supply of HC by this oxidation reaction, the air-fuel ratio of the exhaust atmosphere is enriched, and a reducing atmosphere is realized on the NOx storage catalyst. the

However, in this regeneration method, when the temperature of the exhaust gas discharged from the engine is low, such as at the time of low-temperature startup, the fuel injected into the exhaust passage is added to the oxidation catalyst in the form of droplets, or undergoes an oxidation reaction through the inside of the oxidation catalyst. It cannot be done efficiently, so a large amount of HC may be emitted downstream. Or, when the temperature of the catalyst is low, such as when starting at a low temperature, and has not reached the activation temperature of the catalyst (the temperature necessary for fully oxidizing HC), even if droplet or vaporized fuel is supplied to the oxidation catalyst, the oxidation reaction will It cannot be fully carried out, so a large amount of HC may be discharged downstream. Furthermore, since the catalyst temperature of the NOx storing catalyst is low and regeneration cannot be performed sufficiently, unburned HC may flow out of the NOx storing catalyst downstream. In addition, if the oxidation reaction does not proceed sufficiently, only the easily oxidized fuel is oxidized by the oxidation catalyst arranged on the upstream side, and the difficultly oxidized fuel is discharged downstream as unburned HC, which may not be efficiently used. In order to control NOx Fuel added for regeneration of the adsorption catalyst. the

Therefore, a technique is being developed in which a zeolite capable of adsorbing HC is provided between the oxidation catalyst and the NOx storage catalyst to adsorb excess HC and prevent HC from flowing downstream (see JP-A-2006-329020). the

However, even if the exhaust purification system is configured as disclosed in the above publication, the oxidation function of the oxidation catalyst is lowered, oxygen is not fully consumed, or the exhaust gas temperature does not rise to a predetermined temperature, as in the case of low-temperature startup. In this case, the additive has to be supplied to the oxidation catalyst to achieve a reducing atmosphere, or the exhaust gas temperature has to be raised to a predetermined temperature, resulting in an increase in additive consumption. In addition, although a method of increasing the amount of catalytic noble metal contained in the oxidation catalyst is also considered to improve the oxidation performance, there is also a problem of a significant increase in cost. the

Contents of the invention

The present invention has been made in view of such problems, and an object of the present invention is to provide an exhaust gas purification device capable of suppressing an increase in product cost of an oxidation catalyst and unnecessary consumption of the catalyst while improving oxidation performance at low temperatures and ensuring necessary exhaust gas purification. performance. the

In order to achieve the above object, the exhaust purification device of the present invention includes: an exhaust purification unit provided on the exhaust passage of the internal combustion engine to purify exhaust gas; A catalyst; an additive supply device for supplying a liquid additive to the oxidation catalyst provided on the exhaust passage on the upstream side of the oxidation catalyst, characterized in that the oxidation catalyst is oxidized by the upstream side containing the catalyst precious metal; the oxidation catalyst is oxidized on the upstream side The downstream side of the catalyst is divided into an additive-adsorbing material containing the additive in a liquid state that has passed through the upstream-side oxidation catalyst, and a downstream-side oxidation catalyst that oxidizes the catalyst precious metal released from the additive-adsorbing material. the

Accordingly, when the oxidation reaction does not sufficiently proceed due to the low temperature of the upstream oxidation catalyst, even if the additive passes through, it is adsorbed by the additive adsorbent included in the downstream oxidation catalyst. Therefore, additives other than necessary do not flow into the exhaust gas purification unit, and outflow of additives downstream is suppressed. the

When the exhaust gas temperature and the oxygen concentration of the exhaust gas, or the catalyst temperature and the oxygen concentration near the catalyst reach predetermined conditions, the additive adsorbed on the additive adsorbing material is released to the outside of the additive adsorbing material. In particular, in the present invention, since the additive adsorbing material is contained in the downstream side oxidation catalyst, the additive is released from the additive adsorbing material, and the released additive is oxidized by the catalytic noble metal contained in the downstream side oxidation catalyst, and the emission can be improved efficiently. air temperature and the air-fuel ratio of the enriched exhaust atmosphere. Therefore, additives added to the oxidation catalyst can be used without waste, and an increase in additive consumption can be suppressed. In particular, by improving the oxidation performance at low temperature, the exhaust purification unit can be efficiently regenerated and the exhaust purification performance can be ensured. In addition, by using the additive adsorbent, it is possible to suppress the amount of catalytic noble metal used in the downstream side oxidation catalyst, and it is possible to suppress an increase in the product cost of the oxidation catalyst. the

Preferably, the upstream side oxidation catalyst is composed of at least one noble metal containing at least rhodium as the catalytic noble metal, and the downstream side oxidation catalyst is composed of at least one or more noble metals not containing rhodium as the catalytic noble metal. the

As a result, the expensive catalytic noble metal rhodium is not used in the downstream side oxidation catalyst, and an increase in the cost of the oxidation catalyst can be suppressed. the

In this case, it is desirable that the upstream side oxidation catalyst contains platinum, palladium and rhodium as the catalyst noble metal, and the downstream side oxidation catalyst contain platinum and palladium as the catalyst noble metal and zeolite as the additive adsorbent. the

As a result, the oxidation performance can be improved without using the expensive catalytic noble metal rhodium in the downstream side oxidation catalyst, and thus the increase in the cost of the oxidation catalyst can be significantly suppressed while sufficiently securing the oxidation performance. In addition, by using platinum and palladium as catalyst noble metals, sufficient oxidation performance for droplet-shaped additives can be ensured even at low temperatures. the

Description of drawings

The present invention can be better understood from the following detailed description and the accompanying drawings, which are provided for illustration only, but do not limit the present invention. the

Fig. 1 is a structural schematic diagram of the exhaust system of the engine of the present invention. the

FIG. 2 is a graph showing the relationship between the configuration of the oxidation catalyst and the exhaust gas purification performance. the

Fig. 3 is a graph comparing HC purification efficiency at each catalyst temperature. the

Detailed ways

Next, embodiments of the present invention will be described with reference to the drawings. the

FIG. 1 is a schematic structural view of an exhaust system of a turbocharged diesel engine (hereinafter referred to as engine 1 ) to which the exhaust purification device of the present invention is applied. the

Two catalyst units, an upstream side catalyst unit 3 and a downstream side catalyst unit 4 , are attached to the exhaust pipe 2 of the engine 1 . the

The upstream oxidation catalyst unit 3 is disposed close to the downstream side of the turbine 5 of the turbocharger, and houses an oxidation catalyst 10 therein. The oxidation catalyst 10 is formed by supporting a catalytic noble metal such as platinum (Pt) on the porous wall forming the channel, and can oxidize CO and HC in the exhaust gas to convert them into CO ₂ and H 2 O, and convert the NO in the exhaust gas into CO 2 and H ₂ O. Oxidation produces NO ₂ .

The downstream side catalyst unit 4 is arranged on the downstream side of the upstream side oxidation catalyst unit 3 as an underfloor catalyst (D: under-bed catalyst), and houses a NOx storage catalyst 11 therein. The NOx storage catalyst 11 is loaded with NOx storage agents such as barium (Ba) and potassium (K) on a carrier containing catalytic noble metals such as platinum (Pt) and palladium (Pd), and can be used in a lean air-fuel ratio atmosphere (oxidizing atmosphere) ) to capture NOx, on the other hand, in a high-temperature rich air-fuel ratio atmosphere (reducing atmosphere), the captured NOx is released to react with HC and CO in the exhaust gas to be reduced. the

In order to realize the high temperature and reducing atmosphere necessary for releasing NOx on the NOx storing catalyst 11, a NOx storing catalyst regenerating device (NOx removing device) is equipped. The NOx removal device is composed of an in-exhaust fuel injection valve 12 as an additive supply device and an ECU 13 that controls it. The exhaust pipe fuel injection valve 12 is disposed upstream of the oxidation catalyst 10, and can supply fuel as an additive from a fuel tank (not shown) by a fuel pump, and inject the fuel into the exhaust pipe 2 upstream of the oxidation catalyst 10. ECU13 includes input and output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), central processing unit (CPU), etc. The detected information, that is, the operating state of the engine 1 controls the exhaust pipe fuel injection valve 12 to inject fuel into the exhaust pipe 2 . Accordingly, HC, the main component of the fuel injected into the exhaust pipe 2, undergoes an oxidation reaction on the oxidation catalyst 10, raises the temperature of the passing exhaust gas, consumes the oxygen in the exhaust gas, and makes the exhaust gas flowing into the NOx storage catalyst 11 The air-fuel ratio is enriched. When removing NOx, the fuel injection from the fuel injection valve 12 in the exhaust pipe is performed intermittently, so that the air-fuel ratio of the exhaust gas changes periodically between lean and rich. the

In the present embodiment, the oxidation catalyst 10 of the upstream oxidation catalyst unit 3 is particularly divided into two parts, the upstream oxidation catalyst 10a and the downstream oxidation catalyst 10b. The catalyst noble metal of the upstream side oxidation catalyst 10 a is composed of Pt, Pd, and rhodium (Rh). The downstream side oxidation catalyst 10b uses Pt and Pd as catalyst noble metals, and adds zeolite as an additive adsorption material. Zeolite is capable of adsorbing HC, the main component of the fuel, and is added in a state of being in contact with the periphery of the catalyst noble metal, or near the extreme vicinity of the catalyst noble metal. the

With the above structure, in this embodiment, fuel is injected from the exhaust pipe fuel injection valve 12 into the oxidation catalyst 10 in order to remove NOx. First, HC undergoes an oxidation reaction on the upstream side oxidation catalyst 10a to raise the temperature of the exhaust gas and deplete the air. The fuel ratio is reduced. However, when the oxidation catalyst 10 is in a low-temperature state, such as immediately after starting the engine, the fuel flowing into the oxidation catalyst 10 is not sufficiently oxidized, and a large amount of HC may pass through the oxidation catalyst 10 . In this embodiment, zeolite is added to the downstream side oxidation catalyst 10b, and HC passing through the upstream side oxidation catalyst 10a is adsorbed on the zeolite, so that a large amount of HC can be prevented from being discharged downstream of the catalyst unit 3 . In addition, HC once adsorbed on the zeolite in the downstream oxidation catalyst is released from the zeolite contained in the downstream oxidation catalyst 10b due to operating conditions, and is immediately oxidized sequentially by catalytic noble metals such as Pt contained in the downstream oxidation catalyst 10b. In particular, the zeolite added to the downstream side oxidation catalyst 10b is placed in contact with the surroundings of the catalyst noble metal contained in the downstream side oxidation catalyst 10b, or is arranged near the extreme vicinity of the catalyst noble metal, so that the downstream side oxidation catalyst 10b Above all, the HC released from the zeolite can be oxidized immediately and efficiently by the catalyst noble metal, and as a result, the overall oxidation function of the oxidation catalyst 10 is improved. In this way, the fuel injected from the fuel injection valve 12 in the exhaust pipe can be efficiently used to raise the temperature of the exhaust gas to a predetermined temperature and reduce the air-fuel ratio to achieve a reducing atmosphere, so that the amount of fuel added can be suppressed to the necessary minimum amount, The fuel utilization efficiency can be further improved. the

FIG. 2 is a graph showing the relationship between the configuration of the oxidation catalyst and the exhaust gas purification performance. In this figure, the present embodiment (A in the figure) and the conventional technology (B, C in the figure) are compared based on the HC throughput and the NOx throughput which have an antinomy relationship as the exhaust gas purification performance. The figure indicates that the closer the position is to the lower left, the smaller the HC passing amount and the NOx passing amount become, and the better the exhaust purification performance becomes. In the present embodiment (A), Pt, Pd, and Rh are used as catalyst noble metals in the upstream oxidation catalyst 10a, Pt, Pd are used as catalyst noble metals in the downstream oxidation catalyst 10b, and zeolite is used as an additive adsorbent. In the prior art (B), Pt, Pd, and Rh are used as catalyst noble metals in the upstream side oxidation catalyst 10a, and Pt, Pd are used as catalyst noble metals in the downstream side oxidation catalyst 10b. Furthermore, in the prior art (C), Pt, Pd, and Rh are used as catalyst noble metals in the upstream side oxidation catalyst 10a, and Pt, Pd, and Rh are used as catalyst noble metals in the downstream side oxidation catalyst 10b. the

As shown in FIG. 2 , it can be seen that the present embodiment shown in (A) in the figure has improved exhaust gas purification performance compared to (B) in which zeolite is not used. Furthermore, the present embodiment (A) also has improved exhaust purification performance compared to the prior art (C) in which Rh is also used in the downstream side oxidation catalyst 10b. the

Rhodium (Rh), one of the noble metals of the catalyst, has an increased oxidation effect from a low-temperature region and exhibits a high oxidation effect in an atmosphere with a rich air-fuel ratio. Therefore, it is known that rhodium is used to improve exhaust gas purification performance. Problems with expensive precious metals for other catalysts. In the present embodiment, rhodium is used as one of the catalytic noble metals in the upstream oxidation catalyst 10a, but by adding zeolite as an additive adsorbent to the downstream oxidation catalyst 10b, it is possible to provide oxidation with predetermined oxidation performance without using rhodium. Catalyst, can save product cost. In addition, as described above, by adding zeolite as an additive adsorbent to the downstream side oxidation catalyst 10b, the oxidation performance can be conversely improved compared to the prior art oxidation catalyst using rhodium. the

Fig. 3 is a graph showing HC purification efficiency (oxidation efficiency), which is one of exhaust gas purification performance indicators, at each catalyst temperature, comparing the present embodiment having the above-mentioned configuration (A) with the conventional technology having the configuration (B) . the

As shown in FIG. 3 , it can be seen that the present embodiment (A) improves the HC purification efficiency in the low-temperature region especially compared with the prior art (B) without zeolite. Therefore, in this embodiment, the NOx storage catalyst 11 can be regenerated even at a low temperature, and sufficient exhaust gas purification performance can be ensured. the

In this embodiment, zeolite is used for the downstream side oxidation catalyst 10b, but it is not limited thereto, and any material may be used as long as it has the function of adsorbing additives. In particular, a material added in a state of being in contact with the catalyst noble metal is preferable. the

Furthermore, in the present embodiment, by improving the oxidation function of the oxidation catalyst 10, the NOx storage catalyst can be efficiently regenerated on the NOx storage catalyst 11 while maintaining the exhaust gas purification performance, but the present invention is not limited thereto. S (sulfur) release control (S regeneration control, S purge control) is efficiently performed on the NOx storage catalyst 11 . Furthermore, when a DPF (Diesel Particulate Filter) is provided downstream of the oxidation catalyst 10, it can also contribute to improving the regeneration efficiency of the DPF. the

Claims (3)

1. the Exhaust gas purifying device of an internal-combustion engine comprises:

Be located at exhaust gas purification unit (11) on the exhaust passageway (2) of internal-combustion engine (1), purifying exhaust gas gas;

Be located at the oxidation catalyst (10) on the exhaust passageway of upstream side of said exhaust gas purification unit;

Be located on the exhaust passageway of upstream side of said oxidation catalyst, supply with the additive supplier (12) of liquid additive to this oxidation catalyst, it is characterized in that,

Said oxidation catalyst (10) comprising: the upstream side oxidation catalyst (10a) that comprises the catalyzer precious metal; The additive sorbing material of the said additive of the liquid state of being divided in the downstream side of this upstream side oxidation catalyst, comprise this upstream side oxidation catalyst of absorption process and oxidation are from the downstream side oxidation catalyst (10b) of the catalyzer precious metal of this additive of this additive sorbing material release.

2. the Exhaust gas purifying device of internal-combustion engine as claimed in claim 1 is characterized in that,

Said upstream side oxidation catalyst (10a) is made up of more than one the precious metal that comprises rhodium at least as said catalyzer precious metal;

Said downstream side oxidation catalyst (10b) is made up of more than one the precious metal that does not comprise rhodium as said catalyzer precious metal.

3. the Exhaust gas purifying device of internal-combustion engine as claimed in claim 2 is characterized in that,

Said upstream side oxidation catalyst (10a) comprises platinum, palladium and rhodium as said catalyzer precious metal;

Said downstream side oxidation catalyst (10b) comprises platinum, palladium as said catalyzer precious metal, and comprises zeolite as said additive sorbing material.

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