JP4946658B2 - Exhaust gas purification catalyst device - Google Patents

Description

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

    Regarding engine exhaust gas purification catalyst devices, it is required to ensure low temperature purification performance when the exhaust gas temperature is low, such as when the engine is cold start, and when the exhaust gas temperature is high such as during engine acceleration operation. It is required to suppress deterioration of the catalyst. With regard to the low-temperature purification performance, the problem is how to suppress the emission of unpurified exhaust gas and how quickly the catalyst is activated at a low temperature of the exhaust gas where the catalyst is not sufficiently activated. On the other hand, regarding thermal degradation of the catalyst, it suppresses the sintering of the catalyst metal, and suppresses the decrease in the specific surface area due to the change in the crystal structure of the oxygen storage / release material supporting the catalyst metal and other metal oxide-based support materials. Is a problem.

    Due to the development and advancement of the high-dispersion support technology of catalyst metal and the composite technology of support materials, the problem of thermal degradation of the catalyst is being solved. However, with regard to the problem of emission of unpurified exhaust gas at low temperatures, the use of HC adsorbents has only been attempted, and for early activation of the catalyst, the catalyst is placed close to the engine, etc. The catalyst is only heated to an early temperature.

    For example, Patent Document 1 describes that a three-way catalyst, an HC trap catalyst, and a NOx trap catalyst are sequentially arranged from the upstream side in an engine exhaust passage. This is because the exhaust air-fuel ratio becomes rich when the engine is cold started, thereby reducing the NOx emission amount and raising the temperature of the catalyst at an early stage. It traps on the HC trap catalyst.

    Patent Document 2 discloses a temperature at which a secondary air pipe is connected between a three-way catalyst disposed upstream of an engine exhaust passage and an HC trap catalyst disposed downstream, and the HC trap catalyst desorbs HC. In this case, it is described that secondary air is supplied between the catalysts. This is to bring the HC trap catalyst into an oxygen-excess atmosphere by supplying the secondary air, thereby promoting the purification of the desorbed HC.

Patent Document 3 describes that an HC adsorbent, a NOx adsorbent and a NOx catalyst or a three-way catalyst are provided in the exhaust passage of the engine in order from the upstream side. This is because HC and NOx in the exhaust gas are adsorbed by the HC adsorbent and NOx adsorbent at a low temperature when the catalyst does not reach the activation temperature range, such as when the engine is cold started, and the catalyst reaches the activation temperature range. After that, HC and NOx desorbed from the HC adsorbent and the NOx adsorbent are purified by a catalyst.
JP 2004-285832 A JP 2004-169583 A JP 2000-345832 A

    By the way, the engine is required to obtain high output with low fuel consumption. In order to meet these conflicting demands, engine control technologies such as fuel injection control, air-fuel ratio control, ignition control, etc., technology for reducing friction of valve system components, and technology related to the structure of the engine body are being developed. For example, a direct injection engine that directly injects fuel into an in-cylinder combustion chamber is used, and a high compression ratio engine is used in terms of the structure of the engine body.

    However, in the case of a direct injection engine, when the engine is cold, fuel vaporization in the cylinder tends to be insufficient, and the amount of HC emission increases. Also, if the compression ratio is high, fuel vaporization tends to be insufficient, and the fuel is pushed into an unburned area in the cylinder (such as a clevis defined between the upper surface of the cylinder block and the lower surface of the cylinder head). This increases the amount of HC emission.

    The engine output is also related to the structure of the exhaust system. That is, the exhaust gas purification catalyst is a factor that increases the back pressure of the engine by hindering the flow of exhaust gas. In addition, there is a problem that exhaust interference occurs in the exhaust manifold where the pressure of the exhaust gas discharged for each cylinder interferes with the exhaust of other cylinders. Therefore, it is required to reduce the back pressure (exhaust resistance) in order to improve engine output.

    For that purpose, for example, in the case of a four-cylinder engine, exhaust interference is obtained by collecting the four branch pipes of the exhaust manifold into two, and then combining the two into one. It is effective to increase the back pressure by increasing the distance from the engine body to the exhaust manifold assembly (for example, 65 cm or more) and providing a catalyst downstream thereof.

    However, when the distance from the engine body to the catalyst is increased, it is advantageous for suppressing the sintering of the catalyst metal and the crystal structure of the support material, but the exhaust gas temperature decreases until reaching the catalyst. This is extremely disadvantageous from the viewpoint of improving the low-temperature purification performance (early catalyst activation and suppression of emission of unpurified exhaust gas).

    On the other hand, in the past, each problem has been individually addressed, such as suppression of unpurified HC emissions by the HC trap catalyst as described above, and early activation of the three-way catalyst by the CO oxidation catalyst. It is hard to say that has been made. Regarding the suppression of the emission of unpurified exhaust gas, no significant progress has been made from the viewpoint of catalyst material technology, and further technical progress is required for the early activation of the catalyst.

    Accordingly, an object of the present invention is to enable early activation of the catalyst while suppressing the emission of unpurified exhaust gas, that is, to solve the problem of the low-temperature purification performance of the catalyst in a unified manner. To do.

    In the present invention, the three-way catalyst is activated at an early stage by using an exhaust gas component adsorbent that suppresses the discharge of unpurified exhaust gas.

The invention according to claim 1 is an exhaust gas purification catalyst device in which a three-way catalyst is provided in an exhaust passage through which exhaust gas containing HC, CO and NOx discharged from an engine flows.
An HC adsorbent that preferentially adsorbs HC when the exhaust gas contacts the upstream side of the exhaust gas flow with respect to the three-way catalyst, and CO that preferentially adsorbs CO when the exhaust gas contacts. An adsorbent and a NOx adsorbent that preferentially adsorbs NOx when the exhaust gas comes into contact therewith are arranged ,
The HC adsorbent, the CO adsorbent and the NOx adsorbent are coated on the cell wall of one honeycomb carrier, and one of the three adsorbents remains in the upstream portion of the exhaust gas flow. One of the seeds is located in the downstream part of the exhaust gas flow and the other in the middle part,
The temperature difference at which the desorption amount of the exhaust gas component of each of the HC adsorbent, the CO adsorbent and the NOx adsorbent reaches a peak is 20 ° C. at the maximum .

    Therefore, at low temperatures where the three-way catalyst is not lighted off, such as when the engine is cold started, HC, CO, and NOx in the exhaust gas are adsorbed by the HC adsorbent, CO adsorbent, and NOx adsorbent. It is prevented that it is discharged without being purified. Moreover, according to the present invention, HC, CO, and NOx can be efficiently purified even when the activity before the three-way catalyst reaches its active peak is relatively low, and the three-way catalyst can be activated early. To be advantageous.

    That is, when the activity of the three-way catalyst is still low, the exhaust gas component is adsorbed on the catalyst active point, and the catalytic reaction (adsorption → surface reaction → desorption of product) does not proceed smoothly. Therefore, when the amount of the exhaust gas component flowing into the three-way catalyst is large, the number of active points decreases due to the adsorption of the exhaust gas component, and the amount discharged without purification is increased. In particular, if a large amount of three components of HC, CO, and NOx flows at the same time, the active points of the catalyst compete with each other among these three components, and purification of them cannot be expected.

    On the other hand, in the case of the present invention, most of the exhaust gas components of HC, CO and NOx in the exhaust gas are adsorbed by the three adsorbents, and the activity of the three-way catalyst is low (accordingly, the exhaust gas). When the gas temperature is low and the adsorbent temperature is low), the amount of HC, CO and NOx flowing into the three-way catalyst is small. For this reason, the exhaust gas components are not competing for catalyst active points, and these exhaust gas components can be purified relatively efficiently in the three-way catalyst, and the amount that is exhausted without purification is reduced.

    Thus, when the purification of HC, CO, and NOx proceeds efficiently in the three-way catalyst, the temperature of the three-way catalyst rises due to the heat of catalytic reaction, and its activity increases. Therefore, even if a relatively large amount of HC is subsequently desorbed from the three adsorbents, they are purified by the three-way catalyst, and this purification further increases the temperature of the three-way catalyst and increases its activity. It will become.

    Here, the honeycomb carrier provided in the exhaust passage of the engine gradually increases in temperature from the upstream side toward the downstream side with the passage of time due to the heat of the exhaust gas. Therefore, HC, CO, and NOx adsorbed on the three types of adsorbents of the honeycomb carrier are separated from the exhaust gas components adsorbed on the upstream portion of the honeycomb carrier first, and then are adsorbed on the midstream portion. The components are desorbed, and finally the exhaust gas components adsorbed in the downstream portion are desorbed. In other words, HC, CO, and NOx are desorbed in the order of the upstream portion, the midstream portion, and the downstream portion, and flow into the three-way catalyst when the amount of each desorption amount reaches a peak.

    Therefore, it is avoided that HC, CO, and NOx are simultaneously desorbed from the three kinds of adsorbents and flow into the three-way catalyst, that is, the active point of the catalyst is not competed between these three components.

    For example, when desorption proceeds in the order of HC → CO → NOx, when HC desorbs, the amount of HC flowing into the three-way catalyst increases, but CO and NOx are adsorbed by the adsorbent. The amount flowing into the original catalyst is less than the amount discharged from the engine. For this reason, it is avoided that the purification of HC by the three-way catalyst is hindered by CO and NOx. Subsequently, when CO is desorbed, and when NOx is desorbed, it is also possible to prevent the respective purification from being hindered by other exhaust gas components. The same applies when HC, CO and NOx desorption proceeds in other orders.

    Therefore, exhaust gas components desorbed from each adsorbent can be efficiently purified by the three-way catalyst, and the three-way catalyst becomes highly active due to its own catalytic reaction heat.

    The difference in desorption peak temperature between the three adsorbents is 20 ° C. at the maximum, which means that they have approximately the same desorption peak temperature characteristics. Therefore, the exhaust gas components are desorbed in order from the adsorbent at the upstream portion of the honeycomb carrier to the adsorbent at the downstream side, and the time when the desorption amount peaks is surely shifted. The exhaust gas component desorbed from the material can be efficiently purified by the three-way catalyst.

As the HC adsorbent, zeolite is preferable, and β zeolite is particularly preferable. Examples of the CO adsorbent include a Pb supported on a perovskite oxide such as SrTiO ₃ , a Cu supported material in which Cu is supported on alumina, ceria, or the like, or Fe, CO, Ni, W and Mo on alumina. Those carrying at least one of them are preferred. Examples of the NOx adsorbent include ceria, zeolite, alkali metal, alkaline earth metal, or Mn-based composite oxide (particularly Mn-Ce composite oxide), Mn / SiO ₂ in which Mn is supported on silica, and Mn in zirconia. the _Mn / ZrO 2 which was supported, BaCuO ₂ Pd / BaCuO ₂ or the like by supporting Pd on are preferable.

    A preferable combination of the three adsorbents having a maximum desorption peak temperature difference of 20 ° C. is as follows.

    When β zeolite with a desorption peak temperature of 180 ° C. to 220 ° C. is used as the HC adsorbent, CeO is used as the CO adsorbent. ₂ Cu / CeO with Cu supported on ₂ (Desorption peak temperature around 200 ° C.) or alumina carrying at least one of Fe, CO, Ni, W, and Mo (desorption peak temperature around 180 ° C.) is employed, and NOx adsorbent is Mn− Ce composite oxide (desorption peak temperature around 200 ° C.) is employed.

    When β zeolite having a desorption peak temperature of 200 ° C. to 220 ° C. is used as the HC adsorbent, the Cu / CeO is used as the CO adsorbent. ₂ (Desorption peak temperature around 200 ° C.) and Mn / SiO with Mn supported on silica as NOx adsorbent ₂ (Desorption peak temperature around 220 ° C.), Mn / ZrO with Mn supported on zirconia ₂ (Desorption peak temperature around 220 ° C.) is employed.

    In short, it is known that β zeolite has different HC desorption temperatures depending on its composition (see JP 2007-76989 A), and the desorption peak temperature difference depends on the desorption peak temperature of the HC adsorbent used. The CO adsorbent and the NOx adsorbent may be selected so that the maximum is 20 ° C.

    In the present specification, claims, etc., the exhaust gas component is chemically or physically adsorbed or captured when the temperature is low, and the adsorbed or captured exhaust gas component is removed when the temperature rises. The material to be detached is referred to as “adsorbent”, but may be referred to as “occlusion material” or “trap material” by those skilled in the art.

The invention according to claim 2 is the invention according to claim 1,
The three-way catalyst, the HC adsorbent, the CO adsorbent, and the NOx adsorbent are housed in one converter.

Therefore, HC desorbed from the adsorbent, CO and NOx will be flowing into the three-way catalyst without causing a large drop in temperature, advantageously ing to purify their exhaust gas components by the three-way catalyst.

The invention according to claim 3 is the invention according to claim 1 or claim 2 ,
The three-way catalyst comprises Rh / ZrLaO obtained by carrying Rh on a composite material in which Pd / alumina obtained by carrying Pd on alumina particles and a composite oxide containing Zr and La on the alumina particle surface. -Alumina and Rh / OSC formed by supporting Rh on oxygen storage / release material particles.

    That is, Pd / alumina has a high activity for HC oxidation purification, Rh / ZrLaO-alumina has a high activity for CO oxidation purification, and Rh / OSC has a high activity for NOx reduction purification. Therefore, according to the present invention, when HC, CO, and NOx are desorbed from the three kinds of adsorbents, they can be purified efficiently.

According to a fourth aspect of the present invention, in any one of the first to third aspects,
The exhaust gas flowing into the three-way catalyst when the engine is cold started is in an oxygen-excess state exceeding the stoichiometric ratio necessary for oxidizing the reducing component in the exhaust gas.

    This is advantageous for HC and CO oxidation purification by the three-way catalyst at the time of engine cold start. Here, the exhaust gas supplies secondary air to the exhaust passage upstream of the three-way catalyst when the engine is started at a lean air-fuel ratio or when the engine is started at a stoichiometric or rich air-fuel ratio. By doing so, the oxygen-excess state can be obtained. In the latter case where secondary air is supplied, when the temperature of the three-way catalyst rises above a predetermined value, particularly when the temperature rises above the light-off temperature, the supply of the secondary air may be exhausted. It is preferable from the viewpoint of suppressing a decrease in gas temperature. Secondary air may be supplied when the temperature is lower than the light-off temperature, but in this case, it is preferable to take measures such as increasing the temperature of exhaust gas emitted from the engine by retarding the ignition timing of the engine, for example. .

    In addition, when the secondary air is supplied to the upstream side of the exhaust gas flow from the position where the adsorbent is disposed, it is preferable to supply the secondary air after exhaust gas components are desorbed from all the adsorbent. This is because if the secondary air is supplied before desorption, the adsorbent is thereby cooled, making it difficult for the exhaust gas component to desorb.

As described above, according to the invention according to claim 1, on the upstream side of the exhaust gas flow than the three-way catalyst, it is arranged a HC adsorbent and the CO adsorbent and the NOx adsorbent, the HC adsorbent, CO The adsorbent and the NOx adsorbent are coated on the cell wall of one honeycomb carrier, and the three kinds of adsorbents are arranged at the upstream, middle and downstream of the exhaust gas flow. Since the difference in temperature at which the desorption amount of the exhaust gas component of each material reaches a peak is 20 ° C. at the maximum, while preventing HC, CO and NOx in the exhaust gas from being discharged without being purified, By utilizing the exhaust gas components desorbed from these adsorbents, the activity of the three-way catalyst can be enhanced early , and HC, CO and NOx are simultaneously desorbed from these three adsorbents to form the three-way catalyst. Inflow is avoided, that is, The exhaust gas components are desorbed in the order of the upstream portion of the Niccam carrier, the midstream portion, and the downstream portion, and the desorption of each exhaust gas component proceeds, and the active point of the catalyst competes between these exhaust gas components. Thus, the exhaust gas component desorbed from each adsorbent can be efficiently purified by the three-way catalyst, and it is advantageous for further activation of the three-way catalyst.

    According to the invention according to claim 2, since the three-way catalyst, the HC adsorbent, the CO adsorbent and the NOx adsorbent are accommodated in one converter, HC, CO and NOx desorbed from each adsorbent are It will flow into the three-way catalyst without causing a large decrease in temperature, which is advantageous for purification of these exhaust gas components.

According to the invention of claim 3, upper Symbol three-way catalyst, Pd / alumina, from containing Rh / ZrLaO- alumina and Rh / OSC, HC from the three adsorbents, CO and NOx, respectively de When they are separated, these can be purified efficiently.

According to the invention of claim 4 , since the exhaust gas flowing into the three-way catalyst at the time of cold start of the engine is in an oxygen excess state, it is advantageous for HC and CO oxidation purification by the three-way catalyst.

    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.

    FIG. 1 shows an automobile engine and an exhaust system. In the figure, 1 is a dash panel (cabinet front plate) that partitions the engine room 2 and the passenger compartment, 3 is a hood of the engine compartment 2, and 4 is a floor tunnel portion that extends in the vehicle longitudinal direction in the center of the floor panel of the passenger compartment. is there. In the engine room 2, 5 is a horizontal multi-cylinder engine body, 6 is a radiator, 7 is an intake manifold, and 8 is an exhaust manifold.

    In the engine main body 5, 11 is a cylinder, 12 is a piston, and 13 is a spark plug. The engine is a high-compression-ratio direct-injection gasoline engine having a side injector 14 to obtain high output with low fuel consumption. The exhaust manifold 8 extends rearward from the engine body 5, and a catalytic converter 16 is coupled to a collecting portion 15 thereof. An exhaust pipe 17 extends rearward from the catalytic converter 16.

<Exhaust manifold structure>
In the present embodiment, the collecting portion 15 of the exhaust manifold 8 is far from the engine body 5 (for example, 60 cm or more and 100 cm or less at the shortest pipe length portion) and is disposed at a position below the dash panel 1. Therefore, although the catalytic converter 16 is directly connected to the exhaust manifold 8, the catalytic converter 16 is disposed far from the engine body 5 and below the dash panel 1 or behind the dash panel 1. The catalytic converter 16 and the exhaust pipe 17 are disposed in the floor tunnel portion 4, and the exhaust pipe 17 extends rearward through the floor tunnel portion 4.

    As described above, the reason why the distance from the engine body 5 to the manifold assembly portion 15 is long is to suppress exhaust interference between cylinders of the engine. That is, as shown in FIG. 2 as an example of a four-cylinder engine, the exhaust manifold 8 includes two branch pipes 21 at both ends of four branch pipes 21 to 24 extending from each cylinder (not shown in FIG. 2). 24 is assembled in one collecting pipe 25 on the way, while the central two branch pipes 22 and 23 are gathered on one collecting pipe 26 and the two collecting pipes 25 and 26 are assembled. The collecting unit 15 is used.

    With such an exhaust manifold structure, the ignition order of the four cylinders is determined so that exhaust is performed in the order of the branch pipe 21 → the branch pipe 23 → the branch pipe 24 → the branch pipe 22. Exhaust interference generated between the cylinders can be reduced.

    Further, by adopting the exhaust manifold structure, the exhaust passage from the engine body 5 to the catalytic converter 16 becomes long (for example, 65 cm or more), so that a catalyst described later contained in the converter 16 flows into the exhaust. This reduces the resistance of the engine, which is advantageous for increasing the fuel efficiency and output of the engine. In the present embodiment, the catalytic converter 16 is disposed below a pedal such as an accelerator or a brake that is operated by the driver for driving the automobile.

<Catalyst and adsorbent>
The catalytic converter 16 accommodates an exhaust gas component adsorbing member 31 and a three-way catalyst 32 such that the former is located upstream of the exhaust gas flow and the latter is located downstream thereof. A secondary air supply pipe 34 is connected to the collecting portion 15 of the exhaust manifold 8.

    The adsorbing member 31 is a honeycomb adsorbent formed by forming an adsorbent layer on the cell wall of the honeycomb carrier. The adsorbing member 31 adsorbs exhaust gas components when the three-way catalyst 32 is inactive or low in activity, and the three-way catalyst 32. When the activity of is increased, three types of adsorbents that begin to desorb the exhaust gas components that have been adsorbed are provided. That is, HC in the exhaust gas is preferentially adsorbed when the adsorbent temperature is low, and begins to desorb the adsorbed HC when the adsorbent temperature is high. In the exhaust gas when the adsorbent temperature is low CO adsorbs preferentially and begins to desorb CO adsorbed when the adsorbent temperature rises, and adsorbs NOx in the exhaust gas preferentially when the adsorbent temperature is low, There are three types of NOx adsorbents that begin to desorb adsorbed NOx as the temperature rises.

    When the temperatures at which the exhaust gas component desorption amounts of the three adsorbents peak are substantially the same (when there is a difference in peak temperature of only 20 ° C. at the maximum), the three adsorbents are As shown in FIG. 3, it is preferable that the exhaust gas flow is divided into an upstream portion 41, a midstream portion 42, and a downstream portion 43. The adsorbing member 31 receives the heat of the exhaust gas, and the temperature becomes higher in the order of the upstream portion 41 → the midstream portion 42 → the downstream portion 43. Therefore, the exhaust gas component of each adsorbent is desorbed in that order. Thus, it can be avoided that HC, CO and NOx are simultaneously desorbed from the respective adsorbents and a large amount of exhaust gas components flow into the three-way catalyst 32.

Each adsorbent can be supported on the upstream portion 41, the midstream portion 42, and the downstream portion 43 of the honeycomb carrier, for example, as follows. That is, the upstream portion 41 is immersed in the first adsorbent slurry, and the first adsorbent is adhered to the upstream portion 41. Next, the midstream portion 42 and the downstream portion 43 are immersed in the slurry of the second adsorbent, and the second adsorbent is attached to the midstream portion 42 and the downstream portion 43. Next, the second adsorbent adhering to the downstream portion 43 is removed by ultrasonic cleaning or the like. Then, the downstream portion 43 is immersed in a slurry of the third adsorbent depositing a third adsorbent downstream portion 43, thereafter, dried and calcined row.

The three- way catalyst 32 is a catalyst having a high purification rate near the theoretical air-fuel ratio for simultaneously purifying HC, CO and NOx in the exhaust gas, and a catalyst layer is formed on the cell wall of the honeycomb carrier, and the catalyst layer is Pd. , Rh, and the like, and alumina and oxygen storage / release material (OSC) supporting the catalyst metal. Pd / alumina (catalyst powder in which Pd is supported on alumina particles) having high activity regarding HC oxidation purification, and Rh / ZrLaO-alumina (Zr on the alumina particle surface) having high activity regarding CO oxidation purification are preferable. A catalyst powder in which Rh is supported on a composite material in which a composite oxide containing La is supported, and Rh / OSC (oxygen occlusion / release material particles having Rh supported on NOx reduction and purification activity). The catalyst layer of the three-way catalyst 32 contains the catalyst powder. More preferably, the catalyst layer contains Pt / alumina (catalyst powder in which Pt is supported on alumina particles) having high activity relating to the oxidation and purification of alkanes.

    The three-way catalyst 32 is a mixed type in which the catalyst powders of Pd / alumina, Rh / ZrLaO-alumina, and Rh / OSC are mixed and supported so as to form a single catalyst layer on the cell wall of the honeycomb carrier. Alternatively, a two-layer stacked type in which a catalyst layer containing two types of the three types of catalyst powder and a catalyst layer containing the remaining one type of catalyst powder are stacked on the cell wall of the honeycomb carrier may be used. Of course, a three-layer laminate type in which each of the three kinds of catalyst powders forms a separate catalyst layer and is laminated on the cell wall of the honeycomb carrier may be employed.

    In the case of the two-layer stacked type, an upper layer of catalyst powder having high activity for purifying exhaust gas components desorbed from the upstream portion 41 and catalyst powder having high activity for purifying exhaust gas components desorbed from the midstream portion 42 are used. It is preferable to arrange catalyst powder having high activity for purifying exhaust gas components desorbed from the downstream portion 43 in the lower layer.

    That is, the adsorbing member 31 is warmed in the order of the upstream portion 41 → the midstream portion 42 → the downstream portion 43 as the exhaust gas temperature rises, and the exhaust gas components are desorbed from the adsorbents in this order. Therefore, when desorption occurs from the upstream portion 41 and the midstream portion 42, the exhaust gas temperature is lower than when desorption occurs from the downstream portion 43, which is disadvantageous for exhaust gas purification by the three-way catalyst 32. Therefore, the catalyst powder for each exhaust gas component desorbed from the upstream portion 41 and the midstream portion 42 is disposed in the upper layer, which is easily heated by the exhaust gas, in the upper and lower two layers to increase its purification efficiency, and from the downstream portion 43. The catalyst powder for the exhaust gas component to be desorbed is placed in the lower layer because it is in a condition that is more advantageous for purification than the previous two components.

    The catalyst powder for the exhaust gas component desorbed from the midstream portion 42 can also be disposed in the lower layer.

    In the case of a three-layer stacked type, the catalyst powder for each exhaust gas component desorbed from the upstream portion 41 is in the upper layer, the catalyst powder for the exhaust gas component desorbed from the midstream portion 42 is in the intermediate layer, and the downstream The catalyst powder for the exhaust gas component desorbed from the portion 43 may be disposed in the lower layer.

    In addition, in the case of a two-layer stacked type or a three-layer stacked type, it is preferable that an OSC component (OSC alone or one in which a noble metal is supported on OSC) is disposed in each layer.

    The secondary air is supplied from the secondary air supply pipe 34 to the exhaust manifold collecting portion 15 after the exhaust gas component is desorbed from the adsorbent in the downstream portion 43. This is because if the secondary air is supplied before desorption, the adsorbent is thereby cooled, making it difficult for the exhaust gas component to desorb. Thus, the supply of the secondary air causes the exhaust gas flowing into the three-way catalyst 32 to be in an oxygen excess state, which is advantageous for the HC and CO oxidation purification in the three-way catalyst 32. Further, the supply of the secondary air is executed when the temperature of the three-way catalyst 32 rises to a predetermined value or more, particularly when it rises to the light-off temperature or more. When secondary air is supplied when the temperature is lower than the light-off temperature, the temperature of the exhaust gas emitted from the engine is increased by retarding the engine ignition timing.

<Preliminary experiment for temperature rise simulation>
A preliminary experiment was conducted to investigate how the light-off temperature of the three-way catalyst differs depending on the composition of the simulated exhaust gas for the temperature rise simulation described later.

-Configuration of three-way catalyst-
A honeycomb carrier having a cell wall thickness of 3.5 mil (88.9 × 10 ⁻³ mm) and 600 cells per square inch (635.16 mm ² ) was employed. A two-layered catalyst layer was formed on the cell wall. The upper layer is composed of Pt / alumina (alumina amount; 25 g / L), Rh / OSC (OSC amount; 56 g / L) and Zr binder (9 g / L), and the lower layer is Pd / alumina (alumina amount; 60 g). / L), OSC (6 g / L), and Zr binder (7 g / L). The ratio of the catalyst noble metal was Pd: Pt: Rh = 30: 1: 2 (mass ratio), and the total amount was 7.0 g / L.

-Composition of simulated exhaust gas-
The light-off temperature was measured for seven types of simulated exhaust gases whose base gas composition (gas composition during stoichiometry) is shown in Table 1. “Normal gas” in the table includes all gas components of HC, CO and NOx (NO).

For each simulated exhaust gas, the A / F was varied between lean (A / F = 15.6) and rich (A / F = 13.8) at a frequency of 1.0 Hz. When leaning, O ₂ was introduced into the base gas, and when rich, CO and H ₂ were introduced into the base gas. For example, in the case of the normal gas in Table 1, the gas composition at the time of lean and rich is as shown in Table 2.

-Measurement of light-off temperature-
In measuring the light-off temperature with each simulated exhaust gas, the above three-way catalyst was subjected to thermal aging that was held at a temperature of 540 ° C. for 1 hour in an air atmosphere. Then, the three-way catalyst was attached to a fixed bed flow type reaction evaluation apparatus, the amount of simulated exhaust gas flowing into the catalyst was 25 L / min, and the gas temperature was gradually increased at a rate of 30 ° C./min. The light-off temperature is the time when the concentration of each component (HC, CO, and NOx) detected in the downstream of the catalyst becomes half the concentration of each component (HC, CO, and NOx) in the gas flowing into the catalyst (that is, It is the catalyst inlet gas temperature when the purification rate reaches 50%.

-Result-
The light-off temperature for each simulated exhaust gas is shown in FIG.

    That is, the light-off temperature for HC purification decreases by 25 ° C. when CO is removed from normal gas, decreases by 12 ° C. when NO is excluded, and decreases by 43 ° C. when CO and NO are excluded. The light-off temperature for CO purification usually decreases by 2 ° C. when HC is removed from the gas, decreases by 8 ° C. when NO is excluded, and decreases by 20 ° C. when NO and HC are excluded. The light-off temperature for NOx purification is usually high when CO is removed from the gas and when HC is removed, but it is reduced by 10 ° C. when HC and CO are excluded.

    This result shows that in the case of normal gas, HC purification is prevented by CO and NO, CO purification is inhibited by HC and NO, respectively, and NOx purification is also prevented by HC and CO. means. In other words, HC, CO, and NOx rob each other of the active points of the catalyst, so that the purification efficiency of each is lowered.

    Therefore, from the above, it is understood that the three components of HC, CO, and NOx are not simultaneously purified, but the purification efficiency is higher when each of them is flown into the three-way catalyst alone (with few other components). .

<Temperature increase simulation>
A temperature rise simulation was performed for Embodiments 1 to 6 and Comparative Examples described later, which differ in the arrangement of the three kinds of adsorbents on the upstream portion 41, the midstream portion 42, and the downstream portion 43 of the adsorption member 31. That is, when the temperature of the exhaust gas flowing into the catalytic converter 16 (temperature A before the adsorbing member 31 shown in FIG. 2, hereinafter referred to as “pre-catalyst temperature A”) gradually increases, the outlet temperature of the catalytic converter 16 It was simulated how the temperature B after the three-way catalyst 32 shown in FIG. 2 (hereinafter referred to as “post-catalyst temperature B”) increases.

In any embodiment, the HC adsorbent, the CO adsorbent, and the NOx adsorbent are used in combination with a maximum temperature difference of 20 ° C. at which the desorption amount of each exhaust gas component reaches a peak. It was. That is, β zeolite (desorption peak temperature of 180 ° C) is used as the HC adsorbent, and Cu / CeO ₂ (Cu with CeO ₂ supported, desorption peak temperature of 200 ° C) is used as the CO adsorbent. As the NOx adsorbent, a Mn—Ce composite oxide (desorption peak temperature 200 ° C.) was employed.

    In the simulation, it is assumed that the HC concentration and the NOx concentration in the exhaust gas discharged from the engine are the same, and the CO concentration is 10 times the HC concentration and the NOx concentration. In Embodiments 1 to 6, the desorption interval of HC, CO, and NOx was 20 ° C. That is, when the pre-catalyst temperature A rises by 20 ° C. from when the adsorbent in the upstream portion 41 reaches the desorption peak, the adsorbent in the midstream portion 42 becomes the desorption peak, and when the temperature further rises by 20 ° C., the downstream It was assumed that the adsorbent of the portion 43 has a desorption peak. In addition, a purification reaction of the gas desorbed from the adsorbent also occurs, and the heat of reaction is obtained by adding the desorbed amount to the normal gas concentration.

Then, the amount of heat generated with the passage of time was calculated by the following thermochemical equation, and the temperature rise characteristics described later were obtained. As the reaction heat, the reaction formula relating to the component that flows into the three-way catalyst and is purified is used. For formulas (1) and (6), the heat of reaction was converted based on the assumption regarding the CO concentration (CO concentration is 10 times the HC concentration or NOx concentration). That is, the simulation was performed by applying the converted reaction heat of “−2835 kJ / mol” to the equation (1) and the converted reaction heat of “−397 kJ / mol” to the equation (6).
227 ° C.-t = (ΔH _{227 ° C.-} ΔH _t ) / C
t; temperature, ΔH _{227 °} C .; heat of reaction, C; heat capacity CO + 1 / 2O ₂ = CO ₂ ΔH _{227 ° C.} = − 283.5 kJ / mol (1)
C ₃ H ₆ + 9 / 2O ₂ = 3CO ₂ + 3H ₂ O ΔH _{227 ° C.} = − 1924 kJ / mol (2)
NO + CO = CO ₂ + 1 / 2N ₂ ΔH _{227 ° C.} = − 1924 kJ / mol (3)
C ₃ H ₆ + 6NO = 3CO + 3H ₂ O + 3N ₂ ΔH _{227 ° C.} = − 1615 kJ / mol (4)
NO + H ₂ = 1 / 2N ₂ + H ₂ O ΔH _{227 ° C.} = − 334.1 kJ / mol (5)
CO + H ₂ O = CO ₂ + H ₂ ΔH _{227 ° C.} = − 39.7 kJ / mol (6)
C ₃ H ₆ + 6H ₂ O = 3CO ₂ + 9H ₂ ΔH _{227 ° C.} = + 270 kJ / mol (7)
H ₂ + 1 / 2O ₂ = H ₂ O ΔH _{227 ° C.} = − 243.8 kJ / mol (8)

[Embodiment 1]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of CO → NOx → HC.

Example 1
As for the adsorbing member 31, a CO adsorbent is disposed in the upstream portion 41, a NOx adsorbent is disposed in the midstream portion 42, and an HC adsorbent is disposed in the downstream portion 43. The capacity of the adsorbing member 31 was 0.3 L, and the carrying amounts of the CO adsorbent, NOx adsorbent and HC adsorbent on the honeycomb carrier were the same. The component which becomes a catalyst metal is not supported. The honeycomb carrier of the adsorbing member 31 has a cell wall thickness of 3.5 mil and a cell number of 600 / square inch.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Rh / ZrLaO-alumina and Rh / OSC in the upper layer, and arrange | positioned Pd / alumina and OSC in the lower layer. That is, it has the same configuration as the three-way catalyst in the preliminary experiment, the honeycomb carrier has a cell wall thickness of 3.5 mil, the number of cells is 600 / square inch, and the upper layer is Rh / ZrLaO-alumina (alumina amount; 25 g / L), Rh / OSC (OSC amount; 56 g / L) and Zr binder (9 g / L), and the lower layer is Pd / alumina (alumina amount; 60 g / L), OSC (6 g / L) and The composition is composed of a Zr binder (7 g / L), and the total amount of the catalyst noble metal is 7.0 g / L (Pd: Pt: Rh = 30: 1: 2). The capacity of the three-way catalyst 32 is 0.7L.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

-Comparative Example 1-
The adsorbing member was removed and only a three-way catalyst having a capacity of 1.0 L was used. The three-way catalyst is a mixed type having the same structure as the three-way catalyst of Example 2 except for the capacity.

-Comparative Example 2-
As the adsorbing member, the same configuration as in Example 2 was adopted except that the entire honeycomb carrier having a capacity of 0.3 L was coated with only the HC adsorbing material.

-Comparative Example 3-
As the adsorbing member, the same configuration as in Example 2 was adopted except that the entire honeycomb carrier having a capacity of 0.3 L was coated with only the CO adsorbing material.

-Comparative Example 4-
As the adsorbing member, the same configuration as in Example 2 was adopted except that the entire honeycomb carrier having a capacity of 0.3 L was coated with only the NOx adsorbent.

(Temperature increase simulation result)
FIG. 5 shows the simulation results. Looking at Comparative Example 1 (only the three-way catalyst), the post-catalyst temperature B is initially lower than the pre-catalyst temperature A because the heat of the exhaust gas is taken away by the three-way catalyst and the converter vessel. Then, purification of the exhaust gas starts with the three-way catalyst, and the exhaust gas is heated by the reaction heat, so that the temperature B gradually rises above the pre-catalyst temperature A.

    In the case of Comparative Example 2 (only HC adsorbed), since HC is reduced from the exhaust gas, CO purification start is accelerated (the purification start temperature is lowered), and the reaction heat causes Comparative Example 1 (three-way catalyst). ), The post-catalyst temperature B rises earlier and the temperature rising gradient becomes larger. In Comparative Example 3 (CO only adsorption) and Comparative Example 4 (NOx only adsorption), similar to Comparative Example 2 (HC only adsorption), the post-catalyst temperature B is earlier than Comparative Example 1 (three-way catalyst only). The rise and temperature rise gradient are large.

    The rise of the post-catalyst temperature B is faster in Comparative Example 4 (NOx only adsorption) than in Comparative Example 2 (HC only adsorption). The CO light-off temperature in the absence of NOx is the same as that in the absence of HC. This is because the reaction starts earlier than the light-off temperature. That is, the rise of the post-catalyst temperature B is accelerated by the CO purification reaction heat. Moreover, the rise of Comparative Example 3 (CO only adsorption) is faster than Comparative Example 4 because the light-off temperatures of HC and NOx in the absence of CO are even lower.

    In contrast to Comparative Examples 1 to 4, in Example 1 (adsorbent + stacked three-way catalyst), the exhaust gas component is adsorbed on the adsorbent when the pre-catalyst temperature A is relatively low, and three of HC and NOx. Since there is almost no inflow to the original catalyst 32, the light-off temperature of the CO is lowered, and the desorbed CO and the CO in the exhaust gas react by the equations (1) and (6), so that the post-catalyst temperature B rises more quickly than Comparative Examples 1 to 4. That is, there is little competition between the active points of the three-way catalyst 32 between the CO and other exhaust gas components, and Rh / ZrLaO-alumina, which is highly active in oxidizing CO, is disposed in the upper layer of the three-way catalyst 32. Therefore, even when the temperature of the three-way catalyst 32 is low, CO purification proceeds efficiently.

    Next, when NOx is desorbed from the midstream portion 42, desorption NOx and the heat of purification reaction of NOx in the exhaust gas (formulas (3) and (5)) are generated, and the post-catalyst temperature B further increases.

    The temperature increase gradient of the post-catalyst temperature B during NOx desorption is smaller than that during CO desorption. The exhaust gas temperature and the three-way catalyst temperature are higher during NOx desorption than when CO desorption. However, this is due to the difference in gas concentration between NOx and CO and the difference in reaction heat between the gases.

    Next, when HC is desorbed from the downstream portion 43, desorption HC and the heat of purification reaction of HC in the exhaust gas (formulas (2) and (4)) are generated, and the post-catalyst temperature B further increases. Although Pd / alumina, which is highly active in oxidizing HC, is arranged in the lower layer of the three-way catalyst 32, the exhaust gas temperature at the time of HC desorption is higher than that at the time of desorption of CO and NOx. Since the temperature of the source catalyst 32 is increased by the purification reaction of the desorbed CO and desorbed NOx, the purification efficiency of the desorbed HC is high.

    The temperature gradient of the post-catalyst temperature B during HC desorption is greater than that during CO desorption and NOx desorption. The desorbed HC and the HC in the exhaust gas are efficiently purified and a large amount of reaction heat is generated. Because.

    Next, in Example 2 (adsorbent + mixed three-way catalyst), CO, NOx, and HC that are sequentially desorbed are purified by the three-way catalyst 32 in the same manner as in Example 1, so that the post-catalyst temperature B is reduced. It rises earlier than Comparative Examples 1 to 4, and becomes a higher temperature than Comparative Examples 1 to 4. However, at the time of CO desorption at which the exhaust gas temperature is not yet high, the three-way catalyst 32 is a mixed type, and Rh / ZrLaO-alumina having high activity for CO oxidation is dispersed throughout the mixed catalyst layer. Therefore, the temperature rising gradient is smaller than that of Example 1 in which Rh / ZrLaO-alumina is disposed in the upper layer. This is the same when NOx is desorbed. That is, since Rh / OSC having high activity for NOx reduction is dispersed throughout the mixed catalyst layer, the temperature rising gradient is smaller than that in Example 1 in which the Rh / OSC is disposed in the upper layer.

    On the other hand, at the time of HC desorption, Example 2 in which Pd / alumina having high activity for oxidizing HC is dispersed throughout the mixed catalyst layer is more HC than Example 1 in which Pd / alumina is disposed in the lower layer. However, the temperature rising gradient is slightly larger in Example 1. In the case of Example 1, the temperature of the three-way catalyst 32 is higher than that of Example 2 at the time of HC desorption, and even if Pd / alumina is in the lower layer, the catalyst temperature is high. This is because it works efficiently for the purification of HC.

    As a result, the post-catalyst temperature B of Example 2 at the end of HC desorption is lower than that of Example 1.

[Embodiment 2]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of CO → HC → NOx.

Example 1
Regarding the adsorbing member 31, a CO adsorbent was disposed in the upstream portion 41, an HC adsorbent was disposed in the midstream portion 42, and a NOx adsorbent was disposed in the downstream portion 43. Other configurations of the adsorbing member 31 are the same as those of Example 1 of the first embodiment.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Rh / ZrLaO-alumina, Pd / alumina, and OSC in the upper layer, and arrange | positioned Rh / OSC in the lower layer. Other configurations of the three-way catalyst 32 are the same as those of Example 1 of the first embodiment.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

(Temperature increase simulation result)
FIG. 6 shows the simulation results of Examples 1 and 2 together with Comparative Examples 1 to 4 described above. Regarding Example 1 (adsorbent + stacked three-way catalyst) and Example 2 (adsorbent + mixed three-way catalyst), when HC is desorbed from the midstream portion 42, the NOx case of the first embodiment is used. Also, the temperature increase gradient of the post-catalyst temperature B is small. This is because the reaction related to HC in the second embodiment (Equations (2) and (7)) and the reaction related to NOx in the first embodiment (Equations (3) and (5)) are compared. This is because the amount of heat generated by the reaction relating to NOx is higher.

    Similarly, at the time of desorption of NOx from the downstream portion 43, since the reaction heat of NOx is higher than that of HC, the temperature increase gradient of the post-catalyst temperature B is larger than that of the HC case of the first embodiment.

    In the second embodiment, when NOx is desorbed from the downstream portion 43, reaction heat is generated by the reaction between the desorbed NOx and NOx in the exhaust gas. This is because HC is desorbed at the end of the case of the first embodiment. Since the reaction heat is higher than in the case where the catalyst is removed, the post-catalyst temperature B at the end of the desorption becomes higher.

[Embodiment 3]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of HC → CO → NOx.

Example 1
As for the adsorbing member 31, an HC adsorbing material is disposed in the upstream portion 41, a CO adsorbing material is disposed in the midstream portion 42, and a NOx adsorbing material is disposed in the downstream portion 43. Other configurations of the adsorbing member 31 are the same as those of Example 1 of the first embodiment.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Rh / ZrLaO-alumina, Pd / alumina, and OSC in the upper layer, and arrange | positioned Rh / OSC in the lower layer. Other configurations of the three-way catalyst 32 are the same as those of Example 1 of the first embodiment.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

(Temperature increase simulation result)
FIG. 7 shows the simulation results of Examples 1 and 2 together with Comparative Examples 1 to 4 described above. Regarding Example 1 (adsorbent + stacked three-way catalyst) and Example 2 (adsorbent + mixed three-way catalyst), when HC is desorbed from the upstream portion 41, the case of CO in Embodiment 1 Also, the temperature increase gradient of the post-catalyst temperature B is small. This is because the reaction related to HC in the third embodiment (Equations (2) and (7)) and the reaction related to CO in the first embodiment (Equations (1) and (6)) are compared. This is because the amount of heat generated by the reaction relating to CO is higher.

    However, at the time of desorption of CO from the midstream portion 42, the CO concentration is high, and therefore, the temperature increase gradient of the post-catalyst temperature B is larger than that of the NOx case of the first embodiment. Thus, when NOx desorption from the downstream portion 43 starts, the concentration of NOx increases, and high reaction heat is obtained by reactions related to NOx (Equations (3), (4), and (5)). The temperature increase gradient of the post-catalyst temperature B is increased, and finally the post-catalyst temperature B is higher than that of the HC case of the first embodiment.

[Embodiment 4]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of HC → NOx → CO.

Example 1
As for the adsorbing member 31, an HC adsorbing material is disposed in the upstream portion 41, a NOx adsorbing material is disposed in the midstream portion 42, and a CO adsorbing material is disposed in the downstream portion 43. Other configurations of the adsorbing member 31 are the same as those of Example 1 of the first embodiment.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Pd / alumina and OSC in the upper layer, and arrange | positioned Rh / ZrLaO-alumina and Rh / OSC in the lower layer. Other configurations of the three-way catalyst 32 are the same as those of Example 1 of the first embodiment.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

(Temperature increase simulation result)
FIG. 8 shows the simulation results of Examples 1 and 2 together with Comparative Examples 1 to 4 described above. Regarding Example 1 (adsorbent + stacked three-way catalyst) and Example 2 (adsorbent + mixed three-way catalyst), at the time of desorption of HC from the upstream portion 41, the embodiment is the same as in the third embodiment. The temperature increase gradient of the post-catalyst temperature B is smaller than that of the case of 1 CO.

    When the amount of NOx desorbed from the midstream portion 42 increases, not only the reaction of the equation (5) but also the reaction of the equation (4) occurs with the HC present in the exhaust gas. The temperature increase gradient of the post-catalyst temperature B is larger than that at the time of HC desorption from 41.

    When the desorption of CO from the downstream portion 43 starts, the reactions of the formulas (1), (3) and (6) occur, and the temperature increase gradient of the post-catalyst temperature B is further increased. Since the post-catalyst temperature B reached until the start of is not high, the post-catalyst temperature B finally reached is not so high.

[Embodiment 5]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of NOx → CO → HC.

Example 1
As for the adsorbing member 31, a NOx adsorbing material is disposed in the upstream portion 41, a CO adsorbing material is disposed in the midstream portion 42, and an HC adsorbing material is disposed in the downstream portion 43. Other configurations of the adsorbing member 31 are the same as those of Example 1 of the first embodiment.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Rh / OSC and Rh / ZrLaO-alumina in the upper layer, and arrange | positioned Pd / alumina and OSC in the lower layer. Other configurations of the three-way catalyst 32 are the same as those of Example 1 of the first embodiment.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

(Temperature increase simulation result)
FIG. 9 shows the simulation results of Examples 1 and 2 together with Comparative Examples 1 to 4 described above. Regarding Example 1 (adsorbent + stacked three-way catalyst) and Example 2 (adsorbent + mixed three-way catalyst), when NOx is desorbed from the upstream portion 41, the catalyst is more effective than the case of CO in the first embodiment. The temperature increase gradient of the post temperature B is small. This is because the reaction relating to NOx in the case of Embodiment 4 (equation (5)) and the reaction relating to CO in the case of Embodiment 1 (equations (1) and (6)) are compared. This is because the amount of heat generated by is higher.

    However, at the time of desorption of CO from the midstream portion 42, the CO concentration is high, and therefore, the temperature increase gradient of the post-catalyst temperature B is larger than that of the NOx case of the first embodiment. Thus, when HC desorption from the downstream portion 43 starts, the concentration of HC increases, and the reaction related to HC (formulas (2) and (4)) yields a high reaction heat. The post-catalyst temperature B at that time is high.

[Embodiment 6]
In this embodiment, these exhaust gas components are desorbed from the adsorbing member 31 in the order of NOx → HC → CO.

Example 1
For the adsorbing member 31, a NOx adsorbent was disposed in the upstream portion 41, an HC adsorbent was disposed in the midstream portion 42, and a CO adsorbent was disposed in the downstream portion 43. Other configurations of the adsorbing member 31 are the same as those of Example 1 of the first embodiment.

    About the three-way catalyst 32, it was set as the two-layer lamination type which arrange | positioned Rh / OSC and Pd / alumina in the upper layer, and arrange | positioned Rh / ZrLaO-alumina and OSC in the lower layer. Other configurations of the three-way catalyst 32 are the same as those of Example 1 of the first embodiment.

-Example 2-
The configuration of the suction member 31 is the same as that of the first embodiment. The three-way catalyst 32 was a mixed type in which a single catalyst layer was formed by mixing Rh / ZrLaO-alumina, Rh / OSC, Pd / alumina and OSC. Other configurations are the same as those of the first embodiment.

(Temperature increase simulation result)
FIG. 10 shows the simulation results of Examples 1 and 2 together with Comparative Examples 1 to 4 described above. Regarding Example 1 (adsorbent + stacked three-way catalyst) and Example 2 (adsorbent + mixed three-way catalyst), when desorbing NOx from the upstream portion 41, the post-catalyst temperature is the same as in the fifth embodiment. The gradient of B is small.

    Next, when HC desorption from the midstream portion 42 begins, the reactions of equations (2), (4), and (7) occur, but the case where CO desorbs from the midstream portion 42 of Embodiment 5 (formula (1 ), (3) and (6)), since the latter generates more heat, the temperature increase gradient of the post-catalyst temperature B is smaller than that of the fifth embodiment. However, after that, the post-catalyst temperature B at the end of the desorption increases due to a large amount of CO desorbed from the downstream portion 43.

[Summary of temperature rise simulation]
From the above, when the NOx adsorbent is disposed in the downstream portion 43 as in the second and third embodiments, all exhaust gas components are desorbed regardless of whether the HC adsorbent or the CO adsorbent is disposed in the upstream portion 41. It can be seen that the post-catalyst temperature B becomes the highest, that is, the activity of the three-way catalyst 32 becomes higher by the time when is finished. In addition, regarding the early activation of the three-way catalyst 32, the cases of Embodiments 4 and 6 in which the CO adsorbent is disposed in the downstream portion 43 are preferable next.

<Others>
The three adsorbents are not completely separated into the upstream portion 41, the midstream portion 42, and the downstream portion 43 of the adsorbing member 31, but the adsorbents adjacent to each other partially overlap each other. May be supported .

    Each adsorbent may carry a catalyst metal.

It is a side view which shows the layout of the exhaust gas purification catalyst apparatus of the engine in a motor vehicle front part. It is a perspective view which shows the exhaust-gas purification catalyst apparatus of an engine. It is a side view which shows the adsorption member of the catalyst apparatus. It is a graph which shows that the light-off temperature of a three way catalyst changes with kinds of simulated exhaust gas. 3 is a graph showing the relationship between exhaust gas component desorption characteristics of each adsorbent of Embodiment 1 and temperature rise characteristics of pre-catalyst temperature A and post-catalyst temperature B. FIG. FIG. 6 is a graph similar to FIG. 5 in the second embodiment. It is a graph similar to FIG. 5 in Embodiment 3. It is a graph similar to FIG. 5 in Embodiment 4. FIG. 10 is a graph similar to FIG. 5 in the fifth embodiment. It is a graph similar to FIG. 5 in Embodiment 6.

DESCRIPTION OF SYMBOLS 1 Dash panel 4 Floor tunnel part 5 Engine main body 8 Exhaust manifold 15 Collecting part 16 Catalytic converter 17 Exhaust pipe 31 Adsorption member 32 Three way catalyst 34 Secondary air supply pipe 41 Upstream part 42 Middle stream part 43 Downstream part

Claims (4)

In an exhaust gas purification catalyst device in which a three-way catalyst is provided in an exhaust passage through which exhaust gas containing HC, CO and NOx discharged from an engine flows,
An HC adsorbent that preferentially adsorbs HC when the exhaust gas contacts the upstream side of the exhaust gas flow with respect to the three-way catalyst, and CO that preferentially adsorbs CO when the exhaust gas contacts. An adsorbent and a NOx adsorbent that preferentially adsorbs NOx when the exhaust gas comes into contact therewith are arranged ,
The HC adsorbent, the CO adsorbent and the NOx adsorbent are coated on the cell wall of one honeycomb carrier, and one of the three adsorbents remains in the upstream portion of the exhaust gas flow. One of the seeds is located in the downstream part of the exhaust gas flow and the other in the middle part,
An exhaust gas purification catalyst apparatus, wherein the difference in temperature at which the desorption amount of the exhaust gas component of each of the HC adsorbent, the CO adsorbent and the NOx adsorbent reaches a peak is 20 ° C. at the maximum . In claim 1,
An exhaust gas purification catalyst device, wherein the three-way catalyst, the HC adsorbent, the CO adsorbent and the NOx adsorbent are accommodated in one converter. In claim 1 or claim 2 ,
The three-way catalyst comprises Rh / ZrLaO obtained by carrying Rh on a composite material in which Pd / alumina obtained by carrying Pd on alumina particles and a composite oxide containing Zr and La on the alumina particle surface. An exhaust gas purifying catalyst device comprising alumina and Rh / OSC in which Rh is supported on oxygen storage / release material particles. In any one of Claim 1 thru | or 3 ,
Exhaust gas characterized in that the exhaust gas flowing into the three-way catalyst at the time of cold start of the engine is in an oxygen excess state exceeding the stoichiometric ratio necessary for oxidizing the reducing component in the exhaust gas Gas purification catalyst device.

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