JP2008296090A - Exhaust cleaning catalyst, exhaust cleaning system, and exhaust cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust cleaning catalyst, an exhaust cleaning system, and an exhaust cleaning method having a high activity with respect to low temperature exhaust discharged from an internal combustion engine being started up or run at a low load capable of exhibiting excellent cleaning capacity even if carbon monoxide (CO) and hydrocarbon (HC) are present therein. <P>SOLUTION: The exhaust cleaning catalyst 1A to 1D is characterized by comprising a first catalyst layer 12 supporting a mixture of an oxide capable of adsorbing oxygen and an oxide semiconductor disposed on the upstream side of an exhaust flow path 2 and a second catalyst layer 13 supporting a noble metal catalyst or a mixture of a hydrocarbon (HC) adsorbent and a noble metal catalyst disposed on the downstream side of the exhaust flow path 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst having low temperature activity, an exhaust gas purification system, and an exhaust gas purification method used for purifying exhaust gas of an internal combustion engine or the like.

  Various studies and proposals have been made on exhaust gas purifying devices for purifying exhaust gas from internal combustion engines such as diesel engines and gasoline engines. Among them, there is an exhaust gas purification device in which a DPF (diesel particulate filter) and a NOx purification catalyst for purifying NOx (nitrogen oxide) are arranged. Examples of the NOx purification catalyst include a three-way catalyst, a NOx occlusion reduction type catalyst, a urea-added SCR catalyst (selective contact catalyst), and a NOx direct reduction type catalyst.

  In an exhaust gas purification device for a diesel engine, an oxidation catalyst is arranged upstream of these DPF and NOx purification catalysts, and when the temperature of the exhaust gas is low, a reducing agent such as HC is applied by post injection or exhaust pipe injection. By supplying the exhaust gas into the exhaust gas and oxidizing the reducing agent with the oxidation catalyst, the temperature of the oxidation catalyst and the exhaust gas on the downstream side of the oxidation catalyst is raised to keep the oxidation catalyst at the activation temperature or more and The PM combustion of the DPF on the side is promoted, and the downstream NOx purification catalyst is kept at the activation temperature or higher.

In addition, in the exhaust gas purification apparatus in which an oxidation catalyst is arranged upstream of the SCR catalyst, this oxidation catalyst promotes the reaction from NO (nitrogen monoxide) to NO ₂ (nitrogen dioxide), and the NH on the SCR catalyst is increased. ₃ The reaction with (ammonia) is also promoted.

This oxidation catalyst exhibits effects such as oxidation of CO (carbon monoxide), HC (hydrocarbon) and NO in addition to the temperature rise of the exhaust gas, and the PM (particulate matter) of the downstream DPF. It also has a role for promoting combustion by NO ₂ and ensuring the performance of the NOx purification catalyst.

  As this oxidation catalyst, a catalyst in which a noble metal is supported on a noble metal oxide is mainly used, and appropriate configurations, components, and loadings are selected for each use, but in these oxidation catalysts, the internal combustion engine is started. There is a problem that the catalyst activity is not high when the exhaust gas temperature is low, such as when the load is low or when the load is low.

  Therefore, in order to improve the performance of this oxidation catalyst and to function as an oxidation catalyst having high low-temperature activity, a promoter that adsorbs HC and CO is used, or a material having an oxygen storage capacity (OSC) is supported. Or added as a catalyst.

One material having this oxygen storage capability is cerium dioxide (ceria: CeO ₂ ), which releases oxygen when the air-fuel ratio of the exhaust gas is rich, stores oxygen in a lean state, and stores oxygen in a self-heating manner. Using a substance containing Ce (cerium) element as a substance and utilizing the self-heating action of this oxygen storage substance during oxygen storage, the temperature raising method of the exhaust gas purification apparatus and the exhaust gas purification for raising the catalyst temperature An apparatus has been proposed (see, for example, Patent Documents 1 and 2).

  In addition, from the analysis and performance evaluation of experiments on catalysts up to now, active oxygen released from the oxygen storage capacity material greatly contributes to the low temperature activity of HC and CO even in exhaust gas of diesel engines with high oxygen concentration. It is known that it is effective to lower the release temperature of active oxygen as a measure for increasing the low temperature activity of the catalyst having an oxygen storage capacity material.

However, these catalysts also have a problem that the catalytic activity is not sufficiently high when the exhaust gas temperature is low, such as when the internal combustion engine is started or when the load is low, and when HC, CO, NOx coexist, There was a problem that sufficient performance could not be obtained due to adsorption inhibition.
JP 2006-207524 A JP 2006-207549 A

  The present invention has been made to solve the above-described problems, and has an object of being highly active against low-temperature exhaust gas at the start of an internal combustion engine or at a low load, and carbon monoxide ( An object of the present invention is to provide an exhaust gas purification catalyst, an exhaust gas purification system, and an exhaust gas purification method capable of exhibiting a high purification capacity even when CO) and hydrocarbons (HC) coexist.

  An exhaust gas purifying catalyst for achieving the above object is an exhaust gas purifying catalyst for purifying exhaust gas, and an oxide and an oxide semiconductor having an oxygen storage capacity upstream of the exhaust gas flow path. The first catalyst layer supported in a mixed manner is disposed, and a noble metal catalyst or a hydrocarbon adsorbent (HC adsorbent) and a noble metal catalyst are supported in the downstream side of the exhaust gas flow path. Two catalyst layers are arranged.

  Further, in the exhaust gas purification catalyst, in the first catalyst layer, with respect to the diffusion direction of the exhaust gas in the first catalyst layer, on the side after the exhaust gas has passed through the first catalyst layer by diffusion, A noble metal catalyst or a third catalyst layer on which a hydrocarbon adsorbent and a noble metal catalyst are mixed and provided is provided.

  Alternatively, an exhaust gas purifying catalyst for achieving the above object is an exhaust gas purifying catalyst for purifying exhaust gas, wherein the exhaust gas purifying catalyst has an exhaust gas diffusion direction in the catalyst layer of the exhaust gas purifying catalyst. A first catalyst layer in which an oxide having an oxygen storage ability and an oxide semiconductor are mixed and supported is provided on the side through which gas first passes, and a noble metal catalyst, or on the side through which exhaust gas passes after diffusion, or In addition, a second catalyst layer in which a hydrocarbon adsorbent and a noble metal catalyst are mixed and supported is provided.

  In these configurations, a first catalyst layer that combines an oxide semiconductor and a material having an oxygen storage capacity that is excellent in purifying carbon monoxide (CO) is disposed upstream of the exhaust gas, and a hydrocarbon ( By disposing a second catalyst layer such as a platinum (Pt) catalyst that is excellent in the purification of HC), a catalyst having excellent low-temperature activity can be obtained.

In the first catalyst layer of these configurations, by combining a material having an oxygen storage capacity (OSC) such as cerium dioxide (ceria: CeO ₂ ) and an oxide semiconductor such as titanium dioxide (titania: TiO ₂ ), It exhibits oxygen storage capacity characteristics from low temperatures and functions as an oxidation catalyst with high low-temperature activity. The catalyst in which the oxide having the oxygen storage ability and the oxide semiconductor are mixed exhibits the oxygen storage ability from a low temperature because the coexistence of the oxygen storage ability and the oxide semiconductor causes the parallel movement of electron energy. This is considered to be due to the band offset effect that causes an unstable state.

  Since the first catalyst layer can purify carbon monoxide (CO) in the exhaust gas, the carbon monoxide has a very low concentration on the downstream side. Therefore, in the second catalyst layer on the downstream side, it is only necessary to purify hydrocarbons (HC) and NOx that could not be purified by the first catalyst layer. Therefore, the second catalyst layer formed of a platinum catalyst or a platinum-palladium catalyst can sufficiently exhibit hydrocarbon purification performance from a low temperature without being affected by inhibition or poisoning by carbon monoxide. Further, if the HC / NOx ratio is higher than 3, NOx purification can be achieved by hydrocarbon selective reduction.

Then, in the exhaust gas purification catalyst, the oxide having an oxidative storage capacity is formed of an oxide containing cerium (Ce), and the oxide semiconductor is formed of titanium dioxide (TiO ₂ ), zinc oxide (ZnO), oxidized It is formed of any one of yttrium (Y ₂ O ₃ ) or a combination thereof.

  Further, a noble metal such as platinum (Pt), gold (Au), silver (Ag), rhodium (Rh), iridium (Ir) is supported on an oxide having an oxygen storage capacity, or similar to an oxide semiconductor. By supporting a noble metal, the oxidation reaction on the surface of the oxide semiconductor can be adjusted. The amount of the noble metal supported is adjusted according to the composition of the exhaust gas because various HC and moisture are contained in the exhaust gas.

When a noble metal is supported on an oxide having an oxygen storage capacity, CO and HC are adsorbed on a highly active noble metal, and oxygen in the material having an oxygen storage capacity such as cerium dioxide (ceria: CeO ₂ ) is released, and CO, HC is oxidized. That is, precious metals help release oxygen. On the other hand, when a noble metal is supported on the oxide semiconductor, CO and HC are adsorbed on the noble metal, and CO and HC are oxidized there.

  And the exhaust gas purification system for achieving said objective is comprised so that the said exhaust gas purification catalyst may be used in the exhaust gas purification system which purifies | cleans the exhaust gas of the internal combustion engine mounted in a motor vehicle. An exhaust gas purification method for achieving the above object is characterized in that the exhaust gas purification catalyst is used in the exhaust gas purification method for purifying exhaust gas of an internal combustion engine mounted on an automobile.

  According to the exhaust gas purification catalyst, the exhaust gas purification system, and the exhaust gas purification method of the present invention, in the first catalyst layer on the upstream side of the exhaust gas, the coexistence of the oxygen storage capacity material and the oxide semiconductor allows the energy of electrons to be absorbed. Since the band offset effect that results in parallel movement and becomes unstable occurs, the low temperature activity of the catalyst can be increased by using this band offset effect.

  Since this first catalyst layer is excellent in purifying carbon monoxide and can also purify high-concentration carbon monoxide at a low temperature, carbon monoxide has an extremely low concentration in the second catalyst layer or the third catalyst layer on the downstream side thereof. Therefore, hydrocarbons and NOx that could not be purified by the first catalyst layer need only be purified, and platinum catalysts and platinum-palladium catalysts are not affected by inhibition and poisoning by carbon monoxide. The hydrocarbon purification performance can be fully exhibited. Further, if the HC / NOx ratio is higher than 3, NOx purification can be achieved by hydrocarbon selective reduction.

  Therefore, even when the internal combustion engine is started or in a low temperature exhaust gas at a low load, the catalyst activity can be kept high and the exhaust gas can be purified efficiently. Moreover, since this phenomenon of low temperature activity is based on the band offset effect, the amount of noble metal supported on the exhaust gas purification catalyst can be reduced as compared with the exhaust gas purification catalyst of the prior art.

  Hereinafter, an exhaust gas purification catalyst, an exhaust gas purification system, and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings.

  As shown in FIGS. 1 to 6, exhaust gas purification catalysts 1 </ b> A to 1 </ b> F according to an embodiment of the present invention are a large number of polygons formed of structural materials such as cordierite, silicon carbide (SiC), and stainless steel. It is formed of a monolith honeycomb having cells. The catalyst is supported on the honeycomb which is the support 11 constituting the inner wall of the cell. In the embodiment shown in FIGS. 1 to 6, the carrier 11 is formed of cordierite.

In the present invention, the following first catalyst layer 12, second catalyst layer 13, third catalyst layer 14, and fourth catalyst layer 15 are used. The first catalyst layer 12 is formed by supporting an oxide having an oxygen storage capacity (OSC), that is, an oxygen storage material (OSC material) and a catalyst in which an oxide semiconductor is mixed. This oxygen storage material is made of cerium dioxide (ceria: CeO ₂ ) or the like carrying platinum (Pt), and the oxide semiconductor is made of titanium dioxide (titania: TiO ₂ ) or the like carrying platinum (Pt). . The first catalyst layer 12 is a catalyst layer excellent in HC purification characteristics in which an oxygen storage material and an oxide semiconductor are mixed and supported.

The oxygen storage material, oxides or zirconium oxide, such as cerium dioxide _{(CeO 2) (ZrO 2)} - is formed of an oxide containing cerium dioxide, cerium, such composite oxide (CeO ₂₎ (Ce). The oxide semiconductor is formed of any one of titanium dioxide (TiO ₂ ), zinc oxide (ZnO), yttrium oxide (Y ₂ O ₃ ), or a combination thereof.

  Furthermore, platinum (Pt), gold (Au), silver (Ag), rhodium (Rh), iridium (Ir), or any other combination of noble metal catalysts may be supported on the oxygen storage material, By supporting the same noble metal catalyst on the oxide semiconductor, the oxidation reaction on the surface of the oxygen storage material or the oxide semiconductor is adjusted. The amount of these noble metal catalysts supported is adjusted according to the composition of the exhaust gas to be purified because various types of HC and moisture are contained in the exhaust gas.

The second catalyst layer 13 and the third catalyst layer 14 are formed by supporting a catalyst that is composed of a hydrocarbon adsorbent (HC adsorbent) and a platinum catalyst (Pt catalyst) and has excellent HC purification characteristics. . The HC adsorbent is formed of zeolite or the like, and the Pt catalyst is formed of aluminum oxide (alumina: Al ₂ O ₃ ) or the like carrying platinum (Pt). Note that the second catalyst layer 13 and the third catalyst layer 14 can be formed by supporting only the noble metal catalyst without providing the HC adsorbent. This noble metal catalyst is formed of a Pt catalyst such as aluminum oxide carrying platinum (Pt). That is, the second catalyst layer 13 and the third catalyst layer 14 are catalyst layers in which a noble metal catalyst or a hydrocarbon adsorbent (HC adsorbent) and a noble metal catalyst are mixed and supported.

  The fourth catalyst layer 15 is formed by supporting a Pt catalyst. The fourth catalyst layer 15 is a catalyst layer having the same configuration as the second catalyst layer 13 and the third catalyst layer 14 formed by supporting only the noble metal catalyst without providing the HC adsorbent.

  As shown in FIG. 1, the catalyst 1A according to the first embodiment of the present invention includes a catalyst 1Aa in which a first catalyst layer 12 is stacked on a support 11 on the upstream side (front stage) of an exhaust passage 2, The catalyst 1Ab in which the second catalyst layer 13 is laminated on the carrier 11 is arranged on the downstream side (rear stage).

  Further, as shown in FIG. 2, the catalyst 1B of the second embodiment has a third catalyst layer 14 laminated on the support 11 of the catalytic converter on the upstream side (front stage) of the exhaust passage 2 and the surface side thereof. The catalyst 1Ba having the first catalyst layer 12 laminated thereon is arranged, and the catalyst 1Bb having the second catalyst layer 13 laminated on the carrier 11 is arranged on the downstream side (rear stage).

  As shown in FIG. 3, the catalyst 1 </ b> C of the third embodiment has a fourth catalyst layer 15 stacked on the carrier 11 on the upstream side (front stage) of the exhaust passage 2, and the first catalyst is formed on the surface side thereof. The catalyst 1Ca in which the catalyst layer 12 is stacked is disposed, and the catalyst 1Cb in which the second catalyst layer 13 is stacked on the carrier 11 is disposed on the downstream side (rear stage).

  As shown in FIG. 4, the catalyst 1 </ b> D of the fourth embodiment has a fourth catalyst layer 15 laminated on the carrier 11 on the upstream side of the exhaust passage 2, and the first catalyst layer 12 on the surface side thereof. The catalyst 1Da in which (A) is laminated is arranged, the fourth catalyst layer 15 is laminated on the carrier 11 on the downstream side, and the catalyst 1Db in which the second catalyst layer 13 is laminated on the surface side is arranged. In other words, instead of the catalyst 1Cb of the third embodiment, the catalyst 1Db to which the fourth catalyst layer 15 is added is used.

  The exhaust gas purification catalysts 1A to 1D for purifying the exhaust gas according to the first to fourth embodiments are provided with an oxide (oxygen storage material) having an oxygen storage capacity upstream of the exhaust gas flow path 2. ) And an oxide semiconductor and the first catalyst layer 12 is disposed, and a noble metal catalyst or a hydrocarbon adsorbent (HC adsorbent) and a noble metal catalyst are mixed on the downstream side of the exhaust gas flow path 2. The second catalyst layer 13 supported in this manner is arranged. With this configuration, the catalysts 1Aa to 1Da excellent in HC purification characteristics are arranged on the upstream side, and the catalysts 1Ab to 1Db excellent in HC purification characteristics are arranged on the downstream side.

  According to the second to fourth configurations, in addition to the configuration of the first embodiment, the exhaust gas G diffuses through the first catalyst layer 12 with respect to the diffusion direction of the exhaust gas G in the first catalyst layer 12. The third catalyst layer 14 carrying the HC adsorbent and the noble metal catalyst mixedly or the fourth catalyst 15 carrying the noble metal catalyst is provided on the side after passing through (the lower layer side in FIGS. 2 to 4). Can do.

    Next, fifth and sixth embodiments according to the present invention will be described. As shown in FIG. 5, the catalyst 1E of the fifth embodiment has a first catalyst layer on the surface side of the carrier 11 from the upstream side to the downstream side of the exhaust passage 2, in other words, from the inlet side to the outlet side. 12 and the second catalyst layer 13 are laminated with a gradient composition. That is, the thickness of the first catalyst layer 12 is gradually decreased along the surface side from the upstream side toward the downstream side, and the thickness of the second catalyst layer 13 is gradually increased along the carrier 11 side.

  Further, as shown in FIG. 6, the catalyst 1F of the sixth embodiment has a fourth catalyst layer 14 laminated on a carrier 11, and on the surface side, from the upstream side to the downstream side of the exhaust passage 2, in other words, The first catalyst layer 12 and the second catalyst layer 13 are laminated with a gradient composition from the inlet side to the outlet side.

  That is, the exhaust gas purification catalysts 1E and 1F for purifying the exhaust gas of the fifth and sixth embodiments are related to the diffusion direction of the exhaust gas G in the catalyst layers of the exhaust gas purification catalysts 1E and 1F. The first catalyst layer 12 is provided on the side through which the exhaust gas G first passes, and the oxide catalyst having the oxygen storage ability and the oxide semiconductor are supported on the side where the exhaust gas G passes through. In addition, the second catalyst layer 13 that supports the noble metal catalyst or the HC adsorbent and the noble metal catalyst is provided.

  An exhaust gas purification system that purifies the exhaust gas of the internal combustion engine is configured by disposing an exhaust gas purification device using the exhaust gas purification catalysts 1A to 1F in the exhaust passage of the internal combustion engine mounted on the automobile. In addition, an exhaust gas purification method for purifying exhaust gas of an internal combustion engine can be implemented.

  According to the exhaust gas purification catalyst 1, the exhaust gas purification system, and the exhaust gas purification method having the above-described configuration, in the first catalyst layer 12 on the upstream side of the exhaust gas, due to the coexistence of the oxygen storage capacity material and the oxide semiconductor, Since a band offset effect that causes parallel movement of energy and an unstable state occurs, the low temperature activity of the catalyst can be increased by using this band offset effect.

  The first catalyst layer 12 is excellent in purifying carbon monoxide and can also purify high-concentration carbon monoxide at a low temperature. Therefore, in the second catalyst layer 13 on the downstream side, the carbon monoxide has an extremely low concentration. As a result, hydrocarbons and NOx that could not be purified by the first catalyst layer 12 need only be purified, and the platinum catalyst and the platinum-palladium catalyst are not affected by inhibition or poisoning by carbon monoxide from a low temperature. The hydrocarbon purification performance can be fully exhibited. Further, if the HC / NOx ratio is higher than 3, NOx purification can be achieved by hydrocarbon selective reduction.

  Therefore, even when the internal combustion engine is started or in a low temperature exhaust gas at a low load, the catalyst activity can be kept high and the exhaust gas can be purified efficiently. Moreover, since this phenomenon of low temperature activity is based on the band offset effect, the amount of noble metal supported on the exhaust gas purification catalyst can be reduced as compared with the exhaust gas purification catalyst of the prior art.

  In order to confirm the performance of the catalysts 1A to 1F, the CO and HC purification performances of the first catalyst formed by the first catalyst layer 12 and the second catalyst formed by the second catalyst layer 14 were tested, and Purification of CO and HC in Examples C to F of the catalysts 1C to 1F of the third to sixth embodiments and Comparative Examples X and Y of the following comparative catalysts 1X and 1Y A performance test was performed. In Examples C and D, the catalyst 1C and the catalyst 1D are respectively provided in the exhaust gas passage 3 as shown in FIG. 7, and in Examples E and F, the catalyst 1E and the catalyst 1F are shown in FIG. Are provided in the exhaust gas passage 3.

  Further, in Comparative Example X, as shown in FIG. 9, a catalyst 1X in which a fourth catalyst layer 15 is laminated on a support 11 and a first catalyst layer 12 is laminated on the surface side is used to illustrate this catalyst 1X. 11, the exhaust gas passage 2 was provided. Further, in the second comparative example Y, as shown in FIG. 10, a catalyst 1Y in which a fourth catalyst layer 15 is laminated on a carrier 11 and a second catalyst layer 13 is laminated on the surface side is used. Is provided in the exhaust gas passage 2 as shown in FIG.

12 to 13 show the test results regarding the CO and HC purification performance of the first catalyst formed by the first catalyst layer 12 and the second catalyst formed by the second catalyst layer 14. FIG. 12 shows that the catalyst formed in the first catalyst layer 12 has a CO concentration of 1000 ppm, an HC (propylene) concentration of 500 ppm, and other gas compositions having an O ₂ concentration of 4%, an NO concentration of 100 ppm, and a CO ₂ concentration of The purification performance of CO and HC in a mixed gas simulating an exhaust gas of 8% and H ₂ O of 8% is shown. FIG. 13 shows the CO and HC purification performance in a mixed gas that simulates exhaust gas having the same composition in the second catalyst. FIG. 14 shows the purification performance of CO and HC in a mixed gas simulating exhaust gas with the CO concentration lowered to 500 ppm (others have the same composition) in the second catalyst.

  For the simulated gas with a CO concentration of 1000 ppm, the CO and HC purification rate of the second catalyst is lower than that of the first catalyst, but for the simulated gas with the CO concentration lowered to 500 ppm, It can be seen that the second catalyst has higher CO and HC purification performance than the first catalyst.

  15 and 16 show the results of measuring the purification performance when the HC concentration is 500 ppm constant and the CO concentration is changed. 15 indicates the 80% purification temperature of CO, and HC-T50 in FIG. 16 indicates the 50% purification temperature of HC. From these results, it can be seen that the second catalyst is more sensitive to the CO concentration than the first catalyst, and that the CO and HC purification performance is significantly reduced as the CO concentration increases. It can also be seen that the HC-T50 of the first catalyst is lower than the HC-T50 of the second catalyst when the CO concentration is lowered.

  17 and 18, CO and HC purification performance was measured using Examples C to F and Comparative Examples X and Y under the conditions of a CO concentration of 1500 ppm and an HC concentration of 1000 ppm. As a result, as shown in FIG. 17, Example C showed higher purification performance for both CO and HC than Comparative Examples X and Y. This is because the upstream side (front stage) catalyst including the first catalyst layer excellent in CO purification performance is sufficiently purified of CO, and the HC is also purified, and the downstream side (rear stage) is arranged. This is the result that the catalyst including the two catalyst layers effectively purifies HC by effectively utilizing the active points of the reaction without being influenced by CO.

  Further, as shown in FIG. 18, in Examples C to F in which the configuration of the catalyst is changed, the CO and HC purification performance is slightly different, but the first catalyst layer is disposed upstream and the second catalyst is disposed downstream. It was found that excellent purification performance can be obtained by arranging the layers. Furthermore, since the same effect was obtained even when the first catalyst layer was arranged in the upper layer and the second catalyst layer was arranged in the lower layer as in Example E, the catalyst was made to be layered with respect to the gas flow. Even when the gas is disposed, the gas comes into contact with the lower catalyst layer by diffusion, and it has been found that good CO and HC purification performance can be obtained even when the catalyst is disposed along the gas flow.

It is a figure which shows the structure of the exhaust gas purification catalyst of 1st Embodiment which concerns on this invention. It is a figure which shows the structure of the catalyst for exhaust gas purification of 2nd Embodiment which concerns on this invention. It is a figure which shows the structure of the catalyst for exhaust gas purification of 3rd Embodiment which concerns on this invention. It is a figure which shows the structure of the exhaust gas purification catalyst of 4th Embodiment which concerns on this invention. It is a figure which shows the structure of the exhaust gas purification catalyst of 5th Embodiment which concerns on this invention. It is a figure which shows the structure of the catalyst for exhaust gas purification of 6th Embodiment which concerns on this invention. It is a figure which shows arrangement | positioning of the exhaust gas purification catalyst of the 1st-4th embodiment which concerns on this invention. It is a figure which shows arrangement | positioning of the exhaust gas purification catalyst of 5th and 6th embodiment which concerns on this invention. It is a figure which shows the structure of the catalyst for exhaust gas purification of a comparative example. It is a figure which shows the structure of the exhaust gas purification catalyst of another comparative example. It is a figure which shows arrangement | positioning of the exhaust gas purification catalyst of a comparative example. It is a figure which shows the CO and HC purification performance of the 1st catalyst which concerns on this invention. It is a figure which shows the CO and HC purification performance of the 2nd catalyst which concerns on this invention. It is a figure which shows CO and HC purification | cleaning performance of the 2nd catalyst based on this invention when CO concentration is lower than the simulation gas of FIG. It is a figure which shows the CO purification performance of the 1st catalyst and 2nd catalyst which concern on this invention. It is a figure which shows the HC purification performance of the 1st catalyst and 2nd catalyst which concern on this invention. It is a figure which shows CO and HC purification performance of Example C and Comparative Examples X and Y. It is a figure which shows CO and HC purification performance of Examples C-F.

Explanation of symbols

1A to 1F Exhaust gas purification catalyst 2 Exhaust passage 11 Cordierite (support)
12 1st catalyst layer 13 2nd catalyst layer 14 3rd catalyst layer 15 4th catalyst layer 1Aa, 1Ba, 1Ca, 1Da Catalyst which laminated | stacked 1st catalyst layer 1Ab, 1Bb, 1Cb, 1Db Catalyst which laminated | stacked 2nd catalyst layer

Claims (8)

  In the exhaust gas purifying catalyst for purifying the exhaust gas, the first catalyst layer supporting the mixed oxide and oxide semiconductor having an oxygen storage capacity is disposed on the upstream side of the exhaust gas flow path. An exhaust gas purification catalyst, wherein a second catalyst layer on which a noble metal catalyst or a hydrocarbon adsorbent and a noble metal catalyst are mixed is disposed downstream of an exhaust gas flow path.   In the first catalyst layer, with respect to the diffusion direction of the exhaust gas in the first catalyst layer, a noble metal catalyst or a hydrocarbon adsorbent is disposed on the side after the exhaust gas has passed through the first catalyst layer by diffusion. The exhaust gas purification catalyst according to claim 1, further comprising a third catalyst layer on which a noble metal catalyst is mixed and supported.   In an exhaust gas purification catalyst for purifying exhaust gas, an oxide having an oxygen storage capacity and an oxidation are formed on the side where the exhaust gas first passes with respect to the diffusion direction of the exhaust gas in the catalyst layer of the exhaust gas purification catalyst. A first catalyst layer supported by mixing a semiconductor and a second catalyst layer supported by mixing a noble metal catalyst or a hydrocarbon adsorbent and a noble metal catalyst on a side where exhaust gas passes after diffusion. An exhaust gas purification catalyst characterized by comprising: The oxide having oxygen storage capacity is formed of an oxide containing cerium (Ce), and the oxide semiconductor is any one of titanium dioxide (TiO ₂ ), zinc oxide (ZnO), and yttrium oxide (Y ₂ O ₃ ). The exhaust gas purification catalyst according to claim 1, 2 or 3, wherein the exhaust gas purification catalyst is formed of one or a combination thereof.   The exhaust gas purification catalyst according to claim 1, 2, 3, or 4, wherein a noble metal is supported on the oxide having oxygen storage capacity.   6. The exhaust gas purifying catalyst according to claim 1, wherein a noble metal is supported on the oxide semiconductor.   An exhaust gas purification system for purifying exhaust gas of an internal combustion engine mounted on an automobile, wherein the exhaust gas purification catalyst according to claim 1, 2, 3, 4, 5, or 6 is used.   An exhaust gas purification method for purifying exhaust gas of an internal combustion engine mounted on an automobile, wherein the exhaust gas purification catalyst according to claim 1, 2, 3, 4, 5, or 6 is used.

Images