JP2009167844A - Exhaust emission control catalyst device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve exhaust emission control performance when starting an engine in a cold state, without causing malfunction such as the deterioration in fuel economy. <P>SOLUTION: An exhaust gas passage 1 is provided with an NOx adsorbent 4 for desorbing 50% or more of adsorbed NOx at the temperature of 200°C or more by adsorbing NOx in exhaust gas at the temperature of 100°C or less, and an NO oxidation catalyst 5 oxidizing NO to NO<SB>2</SB>among the NOx desorbed from the NOx adsorbent 4. These NOx adsorbent 4 and NO oxidation catalyst 5 are separately arranged on the upstream side of an exhaust gas flow from an HC adsorbing catalyst 3 so that most of the NOx desorbed from the NOx adsorbent 4 and contacted with the NO oxidation catalyst 5, flow in the HC adsorbing catalyst 3 at the exhaust gas temperature lower than the temperature of becoming the peak in an HC desorption quantity of the HC adsorbent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to an exhaust gas purification catalyst device.

    In recent years, regarding engine emissions, reduction of HC (hydrocarbon) emissions when the engine is cold is strongly desired. In contrast, a three-way catalyst in which a catalyst metal is supported on alumina or the like has a relatively high temperature at which it becomes active, so that it can sufficiently purify HC discharged from the engine when the engine is cold. Can not.

    Therefore, an HC adsorption type catalyst combining an HC adsorbent and a three-way catalyst has been developed. That is, HC is adsorbed by the HC adsorbent when the three-way catalyst is not activated and the HC adsorbed from the HC adsorbent is subsequently purified by the three-way catalyst. That's it. However, HC adsorbents typified by zeolite tend to start desorbing HC adsorbed (trapped) in the pores when the engine is cold before the three-way catalyst is activated (HC desorption temperature is not high). ). Therefore, even if it is an HC adsorption type catalyst, the HC purification rate is not necessarily high.

    On the other hand, regarding an exhaust gas purification catalyst device for a diesel engine, a catalyst component A in which an inorganic oxide supporting a platinum group metal, a NOx adsorbent, and an HC adsorbent are mixed, and a NOx purification catalyst component B. In addition, those arranged on the upstream side and the downstream side of the exhaust gas flow are known (see Patent Document 1). This is to reduce and purify NOx desorbed from the NOx adsorbent of the upstream catalyst component A at a high temperature by the downstream catalyst component B using HC desorbed from the HC adsorbent as a reducing agent at the same time. Therefore, HC desorbed from the HC adsorbent is purified together with NOx desorbed from the NOx adsorbent.

In addition, a NOx adsorption type three-way catalyst that adsorbs NOx under lean conditions and reduces NOx under stoichiometric conditions is arranged upstream of the exhaust gas flow, adsorbs HC on the downstream side, and reduces NOx under stoichiometric conditions. An exhaust gas purification catalyst device in which an HC adsorption type three-way catalyst is arranged is also known (see Patent Document 2). This is because when HC adsorbed on the downstream HC adsorbent is used as a reducing agent to purify NOx desorbed from the upstream NOx adsorbent, when switching from stoichiometric to lean, A / F is not required to be excessively rich and avoids deterioration of fuel consumption.
JP 2002-1124 A Japanese Patent Laid-Open No. 9-79026

    However, in the case of the catalyst configuration described in Patent Document 1, NOx and HC desorbed from the upstream catalyst component A at the high temperature of the exhaust gas simultaneously flow into the downstream catalyst component B. Therefore, in the catalyst component B, the active points are competing with each other for NOx and HC, and the amount of NOx and HC discharged without purification is increased. In particular, the catalyst temperature at the time of starting the gasoline engine is not a slow temperature increase speed (20 ° C./min) as described in paragraph 0076 of the document, but a temperature at which the catalyst is activated in several tens of seconds from the start. Since it rapidly rises to (for example, about 250 ° C. to 300 ° C.), a large amount of NOx and HC flow into the catalyst component B in a short time, and purification thereof becomes difficult. Therefore, a gasoline engine, particularly a gasoline engine that does not mainly use lean combustion, cannot be expected to greatly improve the exhaust gas purification performance.

    On the other hand, in the case of the catalyst configuration described in Patent Document 2, the details of the NOx adsorbent are not described in this document, but NOx is adsorbed under lean conditions and NOx is desorbed under stoichiometric conditions. Therefore, the NOx adsorbent absorbs NOx under lean conditions and becomes a nitrate compound, and releases alkaline oxides or alkali metals that release NOx under stoichiometric or rich conditions into carbonate compounds, such as Ba, Sr, K, It is inferred that Li is used. However, in NOx adsorbents using alkaline earth metals, etc., even if the exhaust gas is stoichiometric, NOx will not be desorbed unless a high temperature atmosphere of 300 ° C. or higher is reached. Since the HC desorption of the type three-way catalyst is usually proceeding considerably, it is not possible to expect effective purification of HC by the NOx.

    Moreover, in order to desorb NOx from the NOx adsorbent, it is necessary to control the air / fuel ratio of exhaust gas (engine fuel injection control), and this control is performed immediately after engine startup when the exhaust gas temperature rises rapidly. The detection accuracy of various sensors such as a temperature sensor and an air-fuel ratio sensor is not high, so even if NOx can be desorbed at a relatively low temperature, the fuel efficiency is not deteriorated by the air-fuel ratio control. It is difficult to desorb NOx.

    Therefore, an object of the present invention is to improve the exhaust gas purification performance at the time of engine cold start without causing problems such as deterioration in fuel consumption by combining the HC adsorbent and the NOx adsorbent.

In the present invention, in order to solve such problems, a NOx adsorbent that releases the temperature the NOx adsorbing NOx (nitrogen oxide) at low temperatures is high, the NO oxidation catalyst to oxidize NO to NO ₂ In addition, the HC adsorption catalyst, the NOx adsorbent, and the NO oxidation catalyst so that NO ₂ with high oxidizing power flows into the HC adsorption catalyst before the amount of HC desorption from the HC adsorption catalyst increases. Was arranged.

Hereinafter, specifically described, the present invention relates to an exhaust gas purification catalyst device provided with an HC adsorption catalyst having an HC adsorbent in an exhaust gas passage.
NOx in the exhaust gas is adsorbed in the exhaust gas passage upstream of the HC adsorption type catalyst at a temperature of 100 ° C. or less, and 50% or more of the adsorbed NOx is desorbed at a temperature of 200 ° C. or more. includes a NOx adsorbent that is released, and the NO oxidation catalyst that oxidizes NO of the NOx desorbed from the NOx adsorbent in NO _2,
The NOx adsorbent and the NO oxidation catalyst are provided separately from each other so that NOx desorbed from the NOx adsorbent flows into the HC adsorption catalyst after contacting the NO oxidation catalyst. And the HC adsorption so that most of the NOx that has passed through the NO oxidation catalyst flows into the HC adsorption catalyst until the HC desorption amount of the HC adsorbent reaches a peak catalyst temperature. It is characterized by being spaced apart from the type catalyst upstream of the exhaust gas flow.

    That is, the present inventor adopts a NOx adsorbent that adsorbs NOx at a low temperature and releases the NOx when the temperature rises, depending on the temperature as in the case of the HC adsorbent. It was noted that NOx desorbed from the NOx adsorbent can be allowed to flow into the HC adsorption catalyst when the temperature rises to some extent without performing control.

However, such NOx adsorbent desorbs as adsorbed NOx as NO when the temperature is relatively low (for example, 300 ° C. or lower), and gradually desorbs as NO ₂ when the temperature increases. However, NO desorbed when the temperature is low has lower oxidizing power than NO ₂ .

Therefore, in the present invention, in order to convert NO desorbed at a low temperature into NO ₂ , the NOx adsorbent and the NO oxidation catalyst are combined to oxidize NO to NO ₂ and flow into the HC adsorption catalyst. I did it. In this case, it is conceivable to mix the NOx adsorbent and the NO oxidation catalyst, but in this case, NO desorbed from the NOx adsorbent does not necessarily come into contact with the NO oxidation catalyst. Therefore, in the present invention, the NOx adsorbent and the NO oxidation catalyst are provided separately without mixing, and NOx desorbed from the NOx adsorbent flows into the HC adsorption catalyst after contacting the NO oxidation catalyst. . The NOx adsorbent and the NO oxidation catalyst are preferably divided so that the former is located on the upstream side of the exhaust gas flow and the latter is located on the downstream side of the exhaust gas flow. You may make it classify | categorize with the form laminated | stacked so that it may become an upper layer.

On the other hand, even if NO ₂ is caused to flow into the HC adsorption type catalyst as described above, if the HC is desorbed from the HC adsorbent, the NO ₂ cannot be effectively used for purification of HC.

    Therefore, in the present invention, the NOx adsorbent and the NO oxidation catalyst are set to a catalyst temperature at which the HC desorption amount of the HC adsorbent reaches a peak with respect to most of the NOx that has passed through the NO oxidation catalyst. The HC adsorption-type catalyst is disposed upstream of the exhaust gas flow so as to flow in (until the temperature of the HC adsorption-type catalyst reaches 200 ° C., for example).

    The HC adsorption catalyst preferably includes an HC adsorbent layer and a three-way catalyst layer for oxidizing and purifying HC desorbed from the HC adsorbent layer. The HC adsorbent layer and the three-way catalyst layer may be arranged on the carrier in layers such that the former is on the inside and the latter is on the outside, or the former is on the upstream side of the exhaust gas flow and the latter is on the downstream side. May be arranged in series so that

As a result, even if HC adsorbed on the HC adsorbent layer is desorbed without reacting with NO ₂ , the desorbed HC passes through the three-way catalyst layer, so that the three-way catalyst is used for purification of the HC. It works efficiently and is advantageous for improving the HC purification rate. In addition, when the HC adsorbent layer and the three-way catalyst layer are provided in layers, the three-way catalyst layer located outside is exposed to the exhaust gas whose temperature has been increased by the oxidation reaction heat in the NO oxidation catalyst. Therefore, the temperature of the three-way catalyst can be increased quickly, which is advantageous for improving the exhaust gas purification performance.

    As the NOx adsorbent, it is preferable to employ a composite oxide containing Zr and a rare earth metal, or a composite oxide containing Zr and an alkaline earth metal, particularly a composite containing Zr and a rare earth metal. Oxides are preferred.

Such a complex oxide has a high NOx adsorbing capacity, and the amount of desorption on the high temperature side of 300 ° C. or higher where the adsorbed NOx is desorbed as NO ₂ with high oxidizing power increases. This is advantageous for the purification of HC adsorbed on the catalyst.

    As the NO oxidation catalyst, it is preferable to employ Pt-supported alumina in which Pt is supported on alumina particles.

Such NO oxidation catalyst, a NO desorbed at a low temperature side from the NOx adsorbent can be efficiently oxidized to NO _2.

    As the HC adsorbent, β-type, mordenite-type, Y-type or pentasil-type zeolite is preferably employed.

According to the present invention, since a combination of a NOx adsorbent that releases the temperature the NOx adsorbs NOx at low temperatures is high, the NO oxidation catalyst to oxidize NO to NO _2, the oxidizing power higher NO ₂ HC adsorbing The NO adsorbent and the NO oxidation catalyst can be supplied to the HC so that most of the NOx that has passed through the NO oxidation catalyst flows into the HC adsorption catalyst before the HC desorption amount reaches its peak. Since the adsorbing catalyst is arranged away from the upstream side of the exhaust gas flow, NO ₂ with high oxidizing power can be supplied to the HC adsorbing catalyst before the HC desorption amount increases, By effectively using NOx, it is possible to improve the exhaust gas purification performance when the exhaust gas temperature is low, such as when the engine is cold started, without causing deterioration of fuel consumption.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

    In FIG. 1, reference numeral 1 denotes an exhaust gas passage of a gasoline engine. In this exhaust gas passage 1, a NOx adsorption oxidation catalyst 2 and an HC adsorption catalyst 3 are arranged in series so that the former is on the upstream side of the exhaust gas flow and the latter is on the downstream side.

    The NOx adsorption oxidation catalyst 2 includes a NOx adsorbent 4 and a NO oxidation catalyst 5, and the NOx adsorbent 4 is disposed on the upstream side of the exhaust gas flow, and the NO oxidation catalyst 5 is disposed on the downstream side thereof. The NOx adsorbent 4 is made by supporting a NOx adsorbing material on a honeycomb carrier, and the NO oxidation catalyst 5 is made by carrying a NO oxidation catalyst material on a honeycomb carrier. The HC adsorption catalyst 3 includes an HC adsorbent layer and a three-way catalyst layer, and is provided on the honeycomb carrier in layers so that the HC adsorbent layer is on the inner side and the three-way catalyst layer is on the outer side.

The NOx adsorbent 4 adsorbs NOx in the exhaust gas at a temperature of 100 ° C. or less, and desorbs when 50% or more of the adsorbed NOx reaches a temperature of 200 ° C. or more. NO oxidizing catalyst 5 oxidizes NO of the NOx desorbed from the NOx adsorbent 4 to NO _2. The HC adsorbent adsorbs HC in the exhaust gas at a low temperature, and desorbs the adsorbed HC as the temperature rises. The temperature at which the HC desorption amount reaches a peak is often around 200 ° C., but there is a peak temperature around 180 ° C. and a peak temperature around 240 ° C., depending on the type of HC adsorbent. Different.

    Therefore, in the present invention, most of NOx desorbed from the NOx adsorbent 4 and passed through the NO oxidation catalyst 5 has a catalyst temperature at which the HC desorption amount of the HC adsorbent reaches a peak with respect to the HC adsorption catalyst 3. The NOx adsorption oxidation catalyst 2 is disposed away from the HC adsorption catalyst 3 on the upstream side of the exhaust gas flow so as to flow into the exhaust gas flow.

<NOx desorption characteristics of NOx adsorbent>
As NOx adsorbents, a Pd-supported ZrCeNd composite oxide in which Pd is supported on a ZrCeNd composite oxide, a Pd-supported ZrPr composite oxide in which Pd is supported on a ZrPr composite oxide, and a ZrSr composite oxide (Pd support) None). The composition of the ZrCeNd composite oxide is ZrO ₂ : CeO ₂ : Nd ₂ O ₃ = 45: 45: 10 (mass ratio), and the supported amount of Pd is 1.0% by mass. The composition of the ZrPr composite oxide is ZrO ₂ : PrO ₂ = 60: 40 (mass ratio), and the supported amount of Pd is 1.0% by mass. The SrO content of the ZrSr composite oxide is 9.31% by mass.

For these three types of NOx adsorbents, the desorption characteristics related to the temperature of the adsorbed NOx were examined by a NO-TPD (temperature-programmed desorption) test. That is, as shown in FIG. 2, the pretreatment is performed on the NOx adsorbent, then NO is adsorbed, and then the adsorbed NO is desorbed, and the temperature change of the NO desorption amount is measured. Examined. In the pretreatment of FIG. 2, while supplying a reducing gas (H ₂ ; 0.45%, residual He, flow rate; 100 mL / min), the gas temperature is changed from room temperature (25 ° C.) at a rate of 30 ° C./min. The temperature is raised and held at a temperature of 600 ° C. for 10 minutes, and then the gas temperature is returned to room temperature. The NO + O ₂ adsorption treatment is to supply NO-containing gas (NO; 4000 ppm, O ₂ ; 3.0%, remaining He, flow rate; 100 mL / min) at room temperature for 15 minutes. The NO desorption treatment is to increase the gas temperature to 600 ° C. at a rate of 20 ° C./min while supplying He gas (flow rate: 50 mL / min). Note that the NO desorption amount in this case includes not only NO but also NO ₂ .

    FIG. 3 shows NO desorption characteristics of the Pd-supported ZrCeNd composite oxide. In this NO adsorbent, desorption peaks appear in the vicinity of 100 ° C., 200 ° C., and 400 ° C., and from the graph in the figure, 50% or more of the adsorbed NOx is desorbed at a temperature of 200 ° C. or more. Recognize.

    FIG. 4 shows NO desorption characteristics of the Pd-supported ZrPr composite oxide. In this NO adsorbent, desorption peaks appear at around 250 ° C. and around 430 ° C., and it can be seen from the graph in the figure that 50% or more of the adsorbed NOx is desorbed at a temperature of 200 ° C. or more.

    FIG. 5 shows the NO desorption characteristics of the ZrSr composite oxide. In this NO adsorbent, desorption peaks appear at around 100 ° C. and around 500 ° C., and it can be seen from the graph in the figure that 50% or more of the adsorbed NOx is desorbed at a temperature of 200 ° C. or more.

    3 to 5, the Pd-supported ZrCeNd composite oxide containing rare earth metal and supporting Pd and the Pd-supported ZrPr composite oxide are more suitable for the ZrSr composite containing an alkaline earth metal. It can be seen that the amount of adsorption / desorption of NO is larger than that of the oxide (no Pd supported). The NO adsorption / desorption amount of the Pd-supported ZrPr composite oxide is particularly large.

<Cool exhaust gas purification performance>
-Experimental equipment-
FIG. 6 shows an experimental device for examining the cold exhaust gas purification performance. In the figure, reference numeral 6 denotes a quartz tube forming an exhaust gas passage, and the NOx adsorbent 4, the NO oxidation catalyst 5 and the HC adsorption catalyst 3 are placed in the exhaust gas passage of the quartz tube 6 from the upstream side of the exhaust gas flow. Arranged in order. The carrier capacity is 25 mL for the NOx adsorbent, 12.5 mL for the NO oxidation catalyst, and 32.5 mL for the HC adsorption catalyst. A quartz tube 6 was provided with a heater 7 for heating the NOx adsorbent 4 and the NO oxidation catalyst 5 and a heat insulating material 8 for keeping the HC adsorption catalyst 3 warm.

    Further, when temperature sensors (thermocouples) 9 and 10 are provided in the intermediate part of the NOx adsorbent 4 and the upstream part of the HC adsorption type catalyst 3, the heating temperature of the NOx adsorbent 4 by the heater 7 becomes 300 ° C. The position of the HC adsorption type catalyst 3 can be adjusted so that the temperature of the upstream portion of the HC adsorbent (HC adsorption type catalyst 3) is 180 ° C. or 200 ° C. or higher.

-Test catalyst device-
With the above experimental apparatus, the cold HC purification rate and the cold NO purification rate were measured in the following six cases.

First case: Pd-supported ZrPr composite oxide is used as NOx adsorbent
(HC adsorbent upstream temperature 180 ° C when NOx adsorbent temperature is 300 ° C)
Second case: Pd-supported ZrCeNd composite oxide is used as NOx adsorbent
(HC adsorbent upstream temperature 180 ° C when NOx adsorbent temperature is 300 ° C)
Third case: ZrSr composite oxide (no Pd supported) is used as NOx adsorbent
(HC adsorbent upstream temperature 180 ° C when NOx adsorbent temperature is 300 ° C)
4th case: NOx adsorbent and NO oxidation catalyst 5th case: NO oxidation catalyst in the 1st case
(HC adsorbent upstream temperature 180 ° C when NOx adsorbent temperature is 300 ° C)
Sixth case: HC adsorbent upstream temperature at the time of NOx adsorbent temperature of 300 ° C in the first case is 200 ° C

    For the HC adsorption type catalyst 3, the HC adsorbent and the three-way catalyst are provided on the honeycomb carrier in layers so that the former is on the inside and the latter is on the outside, and the three-way catalyst layer is the outer three-way catalyst layer. And an inner three-way catalyst layer.

    The specific configuration of the test catalyst device is as follows. The unit (g / L) is the mass per 1 L of honeycomb carrier.

NOx adsorbent; Pd / ZrCeNd composite oxide, Pd / ZrPr composite oxide,
Or ZrSr composite oxide (no Pd supported) 80 g / L
NO oxidation catalyst: Pt / La-containing alumina 100 g / L (Pt loading 2.0 g / L)
HC adsorbent layer; β-zeolite 160g / L
Outer three-way catalyst layer; CeO ₂ 5.5 g / L
ZrCeNd composite oxide 5.7 g / L
Pd / La containing alumina 45.45 g / L
(Pd 0.45 g / L)
Pd / CeZrLaY alumina composite oxide 22.85 g / L
(Pd 0.25 g / L)
Inner three-way catalyst layer; Rh / ZrCeNd composite oxide 70.1 g / L
(Rh 0.1g / L)
Rh / ZrLa composite oxide supported alumina 30.05 g / L
(Rh 0.05g / L)
La-containing alumina 13g / L

    “Pd /”, “Pt /” and “Rh /” mean that Pd, Pt or Rh is supported on the base material described next to “/”.

The composition of the ZrCeNd composite oxide of the outer three-way catalyst layer is ZrO ₂ : CeO ₂ : Nd ₂ O ₃ = 55: 35: 10 (mass ratio), and the composition of the ZrCeNd composite oxide of the inner three-way catalyst layer is ZrO ₂ : CeO ₂ : Nd ₂ O ₃ = 80: 10: 10 (mass ratio). The composition of the CeZrLaY alumina composite oxide was Al ₂ O ₃ : CeO ₂ : ZrO ₂ : La ₂ O ₃ : Y ₂ O ₃ = 80.1: 10.4: 7.4: 1.7: 0.4 (mass Ratio). The La ₂ O ₃ content of the La-containing alumina is 4% by mass. The composition of the ZrLa composite oxide-supported alumina is ZrO ₂ : La ₂ O ₃ : Al ₂ O ₃ = 38: 2: 60 (mass ratio).

    Alumina sol was used as a binder for supporting the HC adsorbent on the honeycomb carrier, and zirconyl nitrate was used as a binder for supporting each material such as NO adsorbent and three-way catalyst on the honeycomb carrier.

-Experimental procedure-
In each of the above six cases, first, only the HC adsorption catalyst is attached to a gas flow device different from the experimental device, and a toluene-containing gas (toluene concentration 2500 ppmC, remaining N ₂ ) is allowed to flow at a temperature of 50 ° C. for 900 seconds. Then, toluene was adsorbed. The amount of toluene supplied in 900 seconds at that time is A, and the amount of adsorbed toluene is B. The toluene adsorption amount B was determined from the amount of toluene passed through the HC adsorption catalyst.

    The HC adsorption type catalyst that has been subjected to the toluene adsorption treatment is set in the heat insulating material disposition site of the experimental apparatus, and in the first to third cases and the sixth case, the NO adsorbent and the NO oxidation catalyst are used in the experimental apparatus. It set to the heater arrangement | positioning site | part. In the fifth case, only NOx adsorbent (no NO oxidation catalyst) was set. The fourth case has no NOx adsorbent and NO oxidation catalyst.

Next, in the above experimental apparatus, simulated exhaust gas with A / F = 14.7 (CO ₂ : 13.9%, O ₂ : 0.6%, CO: 0.6%, H ₂ : 0.2% NO: 1000 ppm, H ₂ O: 10%, balance: N ₂ (without HC) was allowed to flow at a constant temperature of 50 ° C. for 600 seconds. The NO supply amount in 600 seconds at that time is D1, and the adsorbed NO amount is E. The NO adsorption amount E was determined from the passed NO amount.

    Subsequently, while the simulated exhaust gas is flowing, the heater 7 raises the temperature of the heater arrangement site (NOx adsorbent, NO oxidation catalyst) to 600 ° C. at a rate of 30 ° C./min. The amount of HC and NOx flowing out downstream were measured. The HC outflow amount is C, and the NOx outflow amount is F. The amount of NO supply by the simulated exhaust gas until the temperature of the HC adsorption catalyst reaches 250 ° C. (corresponding to the light-off temperature of the three-way catalyst) is D2.

    Then, the HC purification rate obtained by the formula [(BC) × 100 / A] is used as the cold HC purification rate of each case, and the NOx purification amount (NO adsorption) with respect to the total amount of the NO supply amounts D1 and D2. The ratio of the amount E−NOx outflow amount F) was obtained by [(E−F) × 100 / (D1 + D2)] and used as the cold NOx purification rate. The results are shown in Table 1.

According to Table 1, the first case to the third case (examples) having the NOx adsorbent and the NO oxidation catalyst and the HC adsorbent upstream temperature at the time of the NOx adsorbent temperature of 300 ° C are 180 ° C. The cold HC purification rate and the cold NO purification rate are higher than those in the fourth to sixth cases (comparative example). The cold HC purification rate and cold NO purification rate of the first case (with NO oxidation catalyst) are higher than those of the fifth case (without NO oxidation catalyst) because of NO → NO ₂ oxidation by the NO oxidation catalyst. It is an effect. Further, in the sixth case where the temperature of the upstream portion of the HC adsorbent at the time of the NOx adsorbent temperature of 300 ° C. is 200 ° C. or more, the cold HC purification rate and the temperature of the first case (HC upstream portion temperature of 180 ° C.) Although the cold NO purification rate is considerably low, most of the NOx that has passed through the NO oxidation catalyst after the HC desorption amount of the HC adsorbent reaches its peak flows into the HC adsorption catalyst, and the NOx is reduced. This is probably because it was not effectively used to purify the previously adsorbed HC.

    In the first to third cases, the purification rate decreases in the order of Pd-supported ZrPr composite oxide, Pd-supported ZrCeNd composite oxide, and ZrSr composite oxide (no Pd support). This can be considered as a result of the amount of NOx adsorption / desorption of each NOx adsorbent affecting the cold HC purification rate and the cold NO purification rate of each sample catalyst device.

1 is a configuration diagram of an exhaust gas purification catalyst device according to an embodiment of the present invention. It is a graph which shows the aspect of a NO-TPD test. It is a graph which shows the NO desorption characteristic of Pd carrying | support ZrCeNd complex oxide. It is a graph which shows the NO desorption characteristic of Pd carrying | support ZrPr complex oxide. It is a graph which shows the NO desorption characteristic of ZrSr complex oxide. It is a figure which shows the experimental apparatus which evaluates cold exhaust gas purification performance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas passage 2 NOx adsorption oxidation catalyst 3 HC adsorption type catalyst 4 NOx adsorption material 5 NO oxidation catalyst

Claims (4)

In an exhaust gas purification catalyst device provided with an HC adsorption type catalyst having an HC adsorbent in an exhaust gas passage,
NOx in the exhaust gas is adsorbed in the exhaust gas passage upstream of the HC adsorption type catalyst at a temperature of 100 ° C. or less, and 50% or more of the adsorbed NOx is desorbed at a temperature of 200 ° C. or more. includes a NOx adsorbent that is released, and the NO oxidation catalyst that oxidizes NO of the NOx desorbed from the NOx adsorbent in NO _2,
The NOx adsorbent and the NO oxidation catalyst are provided separately from each other so that NOx desorbed from the NOx adsorbent flows into the HC adsorption catalyst after contacting the NO oxidation catalyst. And the HC adsorption so that most of the NOx that has passed through the NO oxidation catalyst flows into the HC adsorption catalyst until the HC desorption amount of the HC adsorbent reaches a peak catalyst temperature. An exhaust gas purifying catalyst device, wherein the exhaust gas purifying catalyst device is spaced apart from the mold catalyst upstream of the exhaust gas flow. In claim 1,
The HC adsorption catalyst comprises an HC adsorbent layer and a three-way catalyst layer for oxidizing and purifying HC desorbed from the HC adsorbent layer. In claim 1 or claim 2,
The exhaust gas purifying catalyst device, wherein the NOx adsorbent is a composite oxide containing Zr and a rare earth metal. In any one of Claim 1 thru | or 3,
The exhaust gas purifying catalyst device, wherein the NO oxidation catalyst contains Pt-supported alumina in which Pt is supported on alumina particles.

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