JP2010013975A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of satisfactorily restraining NO<SB>x</SB>from being produced from ammonia in a reversible fashion as well as sufficiently reducing an amount of discharged ammonia to the atmosphere, produced in an NO<SB>x</SB>occlusion reduction catalyst device by the passage of an exhaust gas with a rich air-fuel ratio. <P>SOLUTION: The exhaust emission control device is equipped with the NO<SB>x</SB>occlusion reduction catalyst device 2 arranged in an engine exhaust system and a downstream-side catalytic device 3 arranged on a downstream side of the NO<SB>x</SB>occlusion reduction catalyst device to carry an iron-based catalyst. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

In order to purify NO _x contained in the lean combustion exhaust gas in a relatively large amount, a NO _x storage reduction catalyst device is arranged in the engine exhaust system. This _the NO _X storage reduction catalyst device, when the air-fuel ratio of the exhaust gas is lean satisfactorily absorb NO _X in the exhaust gas, the air-fuel ratio in the exhaust gas to release NO _X occluding becomes rich, thus The released NO _x is reduced and purified by the reducing substance in the exhaust gas having a rich air-fuel ratio.

Further, the exhaust gas of lean combustion contains SO _x , and the NO _x storage reduction catalyst device also stores SO _x by the same mechanism as that of NO _x . In order to release the stored SO _X , it is necessary to raise the temperature of the NO _X storage reduction catalyst device so that the air-fuel ratio of the exhaust gas becomes rich.

Thus NO is the _X occluding and reducing catalyst device might be passed through the exhaust gas of a rich air-fuel ratio, at this time, a part of NO _X in the exhaust gas by the supported noble metal catalyst to the NO _X occluding and reducing catalyst device It is reduced and ammonia NH ₃ is produced.

In order to adsorb the ammonia thus generated, it has been proposed to dispose the NO _X selective reduction catalyst device downstream of the NO _X storage reduction catalyst device (see, for example, Patent Document 1). The ammonia thus adsorbed on the NO _x selective reduction catalyst device is used to reduce and purify NO _x in the exhaust gas.

Special table 2007-527314 JP 2000-265828 A JP2008-51009 JP2007-56682

In the background art described above, when a platinum-based catalyst is supported on the NO _x selective reduction catalyst device, NO _x is reversibly generated from a part of the inflowing ammonia and released into the atmosphere.

Accordingly, an object of the present invention is to sufficiently reduce the atmospheric emissions of ammonia produced in _the NO _X storage reduction catalyst device by passing the exhaust gas of a rich air-fuel ratio, is reversibly NO _X from the ammonia generated It is another object of the present invention to provide an exhaust emission control device for an internal combustion engine that can be sufficiently suppressed.

An exhaust purification system of an internal combustion engine according to claim 1 according to the present invention includes a _the NO _X storage reduction catalyst device disposed in the exhaust system, the _the NO _X storage reduction catalyst device is disposed on the downstream side iron catalyst And a downstream catalyst device to be supported.

According to a second aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, in which the SO _X is released from the NO _X storage reduction catalyst apparatus according to the stoichiometric air-fuel ratio. A slightly rich air-fuel ratio exhaust gas is caused to flow into the NO _x storage reduction catalyst device.

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the second aspect, wherein the exhaust gas having an air-fuel ratio slightly richer than the stoichiometric air-fuel ratio is the NO _x. It is formed by mixing a rich air-fuel ratio exhaust gas and a lean air-fuel ratio exhaust gas or air on the upstream side of the storage reduction catalyst device.

According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the second or third aspect of the present invention, wherein the NO _X storage reduction catalyst apparatus releases the SO _X in the exhaust gas purification apparatus for the internal combustion engine according to the second or third aspect. _{X On} the downstream side of the NOx storage reduction catalyst device, air is mixed into the exhaust gas having an air / fuel ratio slightly richer than the stoichiometric air / fuel ratio, and the exhaust gas having a slightly lean air / fuel ratio is allowed to flow into the downstream catalyst device. Features.

  According to a fifth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the fourth aspect, wherein the downstream side catalyst device also carries a platinum-based oxidation catalyst. Features.

According to the exhaust purification device for an internal combustion engine according to claim 1 of the present invention, the NO _x storage reduction catalyst device disposed in the engine exhaust system, and the iron catalyst disposed downstream of the NO _x storage reduction catalyst device Thus, the ammonia produced in the NO _x storage reduction catalyst device when the air-fuel ratio of the exhaust gas is made rich is reduced to the iron supported on the downstream catalyst device. The system catalyst can be satisfactorily decomposed into nitrogen and water with almost no NO _x reversibly generated, and the amount of ammonia released into the atmosphere can be sufficiently reduced.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 2 of the present invention, in the exhaust gas purification apparatus for the internal combustion engine according to claim 1, when the SO _x is released from the NO _x storage reduction catalyst apparatus, the stoichiometric air-fuel ratio. It has become a more slightly richer air-fuel ratio of the exhaust gas so as to flow into _the NO _X storage reduction catalyst device, whereby the _the NO _X storage reduction catalyst device sO _X released from is reduced to almost hydrogen sulfide There is no.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 3 of the present invention, in the exhaust gas purification apparatus for the internal combustion engine according to claim 2, the exhaust gas having an air-fuel ratio slightly richer than the stoichiometric air-fuel ratio is NO _x. It is formed by mixing the rich air-fuel ratio exhaust gas and the lean air-fuel ratio exhaust gas or air on the upstream side of the storage reduction catalyst device. Since the unburned fuel burns in the NO _x storage reduction catalyst device using oxygen in the exhaust gas having a lean air-fuel ratio or in the air, the temperature of the NO _x storage reduction catalyst device can be raised satisfactorily.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 4 of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3, when SO _x is released from the NO _x storage reduction catalyst device, _On the downstream side of the _X storage reduction catalyst device, air is mixed into the exhaust gas having an air-fuel ratio slightly richer than the stoichiometric air-fuel ratio, and the exhaust gas having a slightly lean air-fuel ratio flows into the downstream catalyst device. Thus, HC and CO contained in the rich air-fuel ratio exhaust gas for releasing SO _X from the NO _X storage reduction catalyst device can be oxidized and purified in the downstream catalyst device.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 5 of the present invention, in the exhaust gas purification apparatus for the internal combustion engine according to claim 4, the downstream catalyst device also carries a platinum-based oxidation catalyst, Thus, HC and CO contained in the rich air-fuel ratio exhaust gas for releasing SO _X from the NO _X storage reduction catalyst device can be favorably oxidized and purified in the downstream side catalyst device.

FIG. 1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. The exhaust emission control device is for an internal combustion engine that performs lean combustion, such as a diesel engine or a direct injection spark ignition internal combustion engine. In FIG. 1, reference numeral 1 denotes an upstream side catalyst device that is disposed in the vicinity of the engine body and is activated early when the engine is started to purify exhaust gas, for example, a three-way catalyst device. Reference numeral 2 denotes a NO _X storage reduction catalyst device, and reference numeral 3 denotes a downstream side catalyst device, for example, a NO _X selective reduction catalyst device in which an iron-based catalyst as a catalyst is supported using zeolite as a carrier.

The NO _x storage reduction catalyst device 2 uses, for example, alumina as a carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth metal such as barium Ba and calcium Ca, and lanthanum La. In addition, at least one selected from rare earths such as yttrium Y is supported as a NO _x storage catalyst, and also supports a noble metal oxidation catalyst (for example, platinum).

These of the NO _X storage catalyst, the air-fuel ratio of the exhaust gas is satisfactorily absorb NO _X in the exhaust gas when the lean state, release the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich state occluded NO _X To do. _The NO _X storage reduction catalyst device 2 is not able to absorb unlimited NO _X, periodically, or when a set amount of the NO _X is occluded, _the NO _X storage reduction air-fuel ratio of the exhaust gas as a rich state A regeneration process is performed in which NO _x stored in the catalyst device 2 is released and reduced and purified by a reducing substance in the exhaust gas.

Further, the NO _X storage reduction catalyst device 2 also stores SO _X in the exhaust gas by the same mechanism as NO _X. Thus the SO _X is occluded, SO _X can not be released in the regeneration process of releasing in order to be stably absorbing than nitrate as the sulphate, the NO _X by decomposing nitrates, NO _X storable Reduce the amount (S poisoning). As a result, when the set amount of SO _x is occluded regularly or when the NO _x occlusion reduction catalyst device 2 is heated to about 700 ° C., the S-poisoning recovery is performed so that the air-fuel ratio of the exhaust gas becomes rich. Processing is performed.

Thus, in the regeneration process and the S poison recovery process, the air-fuel ratio of the exhaust gas is made rich, and at this time, the exhaust gas is exhausted by the noble metal catalyst supported on the upstream side catalyst device 1 and the NO _x storage reduction catalyst device 2. NO _x in the gas is reduced to produce ammonia NH ₃ . However, the ammonia produced in this way is used to reduce and purify NO _x when the NO _x selective reduction catalytic device 3 as the downstream side catalytic device 3 adsorbs part of the ammonia and the air-fuel ratio of the exhaust gas is lean. At the same time, the iron-based catalyst supported by the NO _x selective reduction catalyst device 3 is decomposed into nitrogen and water, so that it is hardly released into the atmosphere.

In the regeneration process, the air-fuel ratio of the exhaust gas is made rich for several seconds, but in the S poison recovery process, the air-fuel ratio of the exhaust gas is made rich for several tens of minutes. Thus, almost no ammonia is released into the atmosphere. FIG. 3 shows a case where ammonia-containing gas is introduced into a first catalyst device (marked by a circle) supporting iron using zeolite as a carrier and a second catalyst device (cross mark) supporting platinum using ceria as a support. the experimental results showing the variation of the NO _X generation rate for incoming gas temperature. As shown in the figure, whereas the NO _X from the ammonia in the second catalyst device is produced, in the first catalyst device is hardly NO _X is produced, that the ammonia is decomposed into nitrogen and water I understand.

In the present embodiment, the downstream catalyst device 3 is the NO _x selective reduction catalyst device 3 carrying the iron-based catalyst, but ammonia can be satisfactorily decomposed into nitrogen and water as a simple oxidation catalyst device carrying the iron-based catalyst. Thus, the amount of ammonia released into the atmosphere can be sufficiently reduced.

By the way, in the S poisoning recovery process, the NO _x storage reduction catalyst device 2 must be heated to about 700 ° C. Therefore, in the present embodiment, the engine body is operated at a rich air-fuel ratio (12 to 13.5), or fuel is injected into the cylinder in the expansion stroke or the exhaust stroke and discharged from the engine body. The air-fuel ratio of the exhaust gas is made rich (12 to 13.5), and air is mixed into the exhaust gas from the first air supply device 4 on the upstream side of the NO _x storage reduction catalyst device 2 to The air-fuel ratio is made slightly rich (14.0 to less than 14.6).

As a result, in the NO _x storage reduction catalyst device 2, the unburned fuel in the exhaust gas is burned using the oxygen in the supplied air by the supported oxidation catalyst such as platinum, and this combustion heat causes NO to be burned. _The temperature of the _X storage reduction catalyst device 2 can be easily raised to about 700 ° C. SO _x is released from the NO _x storage reduction catalyst device 2 that has been heated to a slight rich state in this way, but SO _x is not reduced to hydrogen sulfide, and hydrogen sulfide is released into the atmosphere. There is hardly anything.

Further, since the slightly rich exhaust gas flowing out from the NO _x storage reduction catalyst device 2 contains slightly HC and CO, it is preferable to purify them. For this purpose, air is mixed into the exhaust gas from the second intake air supply device 5 on the downstream side of the NO _x storage reduction catalyst device 2 to slightly reduce the air-fuel ratio of the exhaust gas (greater than 14.6 to 17 or less). ) And HC and CO are oxidized using oxygen in the air that is introduced into the downstream side catalyst device 3 and mixed by the iron-based catalyst of the downstream side catalyst device 3.

Further, if the air is mixed into the exhaust gas from the second intake air supply device 5 and the air-fuel ratio of the exhaust gas is made lean in the downstream side of the NO _X storage reduction catalyst device 2 in this way, the NO _X storage reduction catalyst. also SO _X when the air-fuel ratio of the exhaust gas was released too rich flowing into the apparatus 2 is reduced to hydrogen sulfide, it can be re-oxidized back to the SO _X.

  FIG. 4 shows that a gas containing oxygen and CO is allowed to flow into a first catalyst device (marked by a circle) supporting iron using zeolite as a carrier and a second catalyst device (cross mark) supporting platinum using ceria as a support. It is an experimental result which shows the change of the CO purification | cleaning rate with respect to the inlet gas temperature in the case of. As shown in the figure, the first catalyst device has a low CO purification rate, whereas the second catalyst device can purify CO well. Thereby, the downstream catalyst device 3 supports not only the iron-based catalyst but also the platinum-based oxidation catalyst, so that HC and CO can be further oxidized and purified in the S poison recovery process.

In this case, it is preferable to support the iron-based catalyst on the upstream side of the downstream side catalyst device 3 and to support the platinum-based oxidation catalyst on the downstream side. Thus, ammonia in the exhaust gas flowing into the downstream side catalyst device 3 can be decomposed into nitrogen and water by the iron-based catalyst before being converted to NO _x by the platinum-based oxidation catalyst. Of course, the downstream side catalyst device 3 may be divided into an upstream side carrying an iron-based catalyst and a downstream side carrying a platinum-based oxidation catalyst.

  As the lean state of the air-fuel ratio of the exhaust gas flowing into the downstream side catalyst device 3 is closer to the stoichiometric air-fuel ratio, the oxidation of HC and CO in the downstream side catalyst device 3 tends to become insufficient. As the control air-fuel ratio of the exhaust gas controlled by mixing air into the exhaust gas from 5 is closer to the theoretical air-fuel ratio, the platinum-based oxidation with respect to the total supported amount of the iron-based catalyst and the platinum-based oxidation catalyst of the downstream side catalyst device 3 It is preferable to increase the ratio of the amount of catalyst supported.

FIG. 2 is a schematic view showing another exhaust gas purification apparatus for an internal combustion engine according to the present invention. Only the difference from the exhaust emission control device of FIG. 1 will be described below. This exhaust purification device controls the air-fuel ratio of exhaust gas discharged from the engine body and controls the amount of air supplied from the first air supply device 4 and the second air supply device 5 in the S poison recovery process. As a result, when the air-fuel ratio of the exhaust gas on the downstream side of the NO _x storage reduction catalyst device 2 changes, the switching valve 6 is switched to send the exhaust gas to the first downstream catalyst device 3a and the second downstream catalyst device. 3b is selected to be passed.

  For example, in the first downstream catalyst device 3a, the ratio of the supported amount of platinum-based oxidation catalyst to the supported amount of iron-based catalyst is 6: 4, and in the second downstream-side catalyst device 3b, the support of the platinum-based oxidation catalyst is performed. The ratio of the amount and the amount of iron-based catalyst supported is 4: 6. Preferably, in each of the first downstream catalyst device 3a and the second downstream catalyst device 3b, an iron-based catalyst is supported on the upstream side and a platinum-based oxidation catalyst is supported on the downstream side. The air-fuel ratio of the exhaust gas after the air is mixed by the second air supply device 5 is detected by an air-fuel ratio sensor (not shown), and when it is richer than 15.5, the exhaust gas is in the first downstream The switching valve 6 is switched so as to pass through the side catalytic device 3a, and when the detected air-fuel ratio is leaner than 15.5, switching is performed so that the exhaust gas passes through the second downstream side catalytic device 3b. Valve 6 is switched.

  Thereby, HC and CO can be favorably oxidized and purified by the platinum-based oxidation catalyst in the S poisoning recovery treatment, and ammonia can be favorably decomposed into nitrogen and water by the iron-based catalyst. In the present embodiment, at the time of regeneration treatment, it is preferable that the exhaust gas is switched so as to pass through the second downstream side catalyst device 3b, and ammonia is favorably decomposed into nitrogen and water by a large amount of iron-based catalyst.

During the S poisoning recovery process, the exhaust gas containing a relatively large amount of unburned fuel is supplied with air by the first air supply device 4 to make the air-fuel ratio slightly rich, and the exhaust gas is supplied to the NO _x storage reduction catalyst device 2. In the case of a V-type engine, the exhaust gas discharged from one bank contains a relatively large amount of unburned fuel, and the exhaust gas discharged from the other bank Is mixed with the rich air-fuel ratio exhaust gas and the lean air-fuel ratio exhaust gas (preferably with a slightly rich air-fuel ratio and hydrogen sulfide It may be allowed to flow into the NO _x storage reduction catalyst device 2 (without being generated).

Of course, not only in the V-type engine but also in the in-line engine, the exhaust gas discharged from some cylinders contains a relatively large amount of unburned fuel and the exhaust gas discharged from the other bank. Is mixed with the rich air-fuel ratio exhaust gas and the lean air-fuel ratio exhaust gas (preferably with a slightly rich air-fuel ratio and hydrogen sulfide It may be allowed to flow into the NO _x storage reduction catalyst device 2 (without being generated).

It is the schematic which shows the exhaust gas purification apparatus of the internal combustion engine by this invention. It is the schematic which shows the exhaust gas purification apparatus of another internal combustion engine by this invention. A first catalyst device carrying an iron, in the second catalyst device carrying the platinum, the experimental results showing the variation of the NO _X generation rate for incoming gas temperature when allowed to flow into the ammonia-containing gas. It is an experimental result which shows the change of CO purification | cleaning rate with respect to inlet gas temperature at the time of flowing the gas containing oxygen and CO into the 1st catalyst apparatus which carry | supports iron, and the 2nd catalyst apparatus which carries platinum.

Explanation of symbols

1 upstream catalyst device 2 NO _X occluding and reducing catalyst device 3, 3a, 3b downstream catalyst unit

Claims (5)

An internal combustion engine comprising: a NO _x storage reduction catalyst device disposed in an engine exhaust system; and a downstream catalyst device disposed downstream of the NO _x storage reduction catalyst device and carrying an iron catalyst. Exhaust purification equipment. The NO from _X occluding and reducing catalyst device when releasing the SO _X is according to the exhaust gas slightly richer than the stoichiometric air-fuel ratio to claim 1, characterized in that to flow into the NO _X occluding and reducing catalyst device An exhaust purification device for an internal combustion engine. The exhaust gas slightly richer than the stoichiometric air-fuel ratio on the upstream side of the _the NO _X storage reduction catalyst device and an exhaust gas of a rich air-fuel ratio, by mixing the exhaust gas or air lean The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is formed. The NO from _X occluding and reducing catalyst device when releasing the SO _X, the NO _X occluding and reducing downstream of the catalytic converter, slightly lean by mixing air to the exhaust gas slightly richer than the stoichiometric air-fuel ratio The exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3, wherein an exhaust gas having a low air-fuel ratio is caused to flow into the downstream side catalyst device.   The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein a platinum-based oxidation catalyst is also carried on the downstream side catalyst device.

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