JP2009028593A - Refreshing method of exhaust gas cleaning catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To regenerate exhaust gas cleaning catalyst deteriorated by being exposed to high temperature exhaust gas. <P>SOLUTION: Oxygen-lack exhaust gas is passed through the catalyst 3 containing a CeZr-based composite oxide formed by carrying the catalyst metal for more than a predetermined time, in the case that the catalyst 3 is determined and the determined result is obtained when high temperature oxygen-surplus exhaust gas flows in for more than a predetermined time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to a method for refreshing an exhaust gas purifying catalyst.

    For purification of exhaust gas discharged from the engine, a catalyst is often used in which Pt, Pd, Rh, etc. as catalyst metals are supported on a support material such as activated alumina or a Ce-containing oxygen storage material. For example, a catalyst in which a catalytic metal is dispersedly supported on the surface of inorganic oxide particles, such as a Pt-supported oxygen storage material, an Rh-supported oxygen storage material, and a Pd-supported alumina.

    Alumina has a high heat resistance and a large specific surface area, and is therefore a support material suitable for highly dispersed support of catalyst metal. On the other hand, the oxygen storage material has a property of storing oxygen in the exhaust gas when the exhaust gas is in an oxygen excess state and releasing the stored oxygen when the exhaust gas is in an oxygen deficient state. Therefore, the oxygen storage material is useful for absorbing fluctuations in the oxygen concentration of the exhaust gas, and the released oxygen promotes purification of the exhaust gas by the catalytic metal.

    As such oxygen storage materials, Ce and Zr composite oxides, and Ce and other rare earth composite oxides are known in addition to Ce oxides. For example, Patent Document 1 describes a catalyst in which a catalytic metal is supported on a hollow CeZr composite oxide formed by agglomerating primary particles having an average particle size of less than 10 nm. However, even if such a catalyst is exposed to high-temperature exhaust gas, the catalytic activity decreases.

On the other hand, Patent Document 2 discloses, for example, an oxidation treatment and a reduction treatment in which a catalyst formed by supporting Pt on a CeZrY composite oxide or a ZrLa composite oxide is heated in an oxidizing atmosphere containing oxygen. A method of refreshing the catalyst by applying is disclosed. That is, the grain-grown Pt becomes an oxide by the above oxidation treatment, spreads and disperses on a support such as a CeZrY composite oxide, and the dispersed Pt oxide is converted into fine Pt metal by a subsequent reduction treatment. It becomes particles and the catalytic activity is restored. The catalyst is refreshed periodically according to the driving time and mileage of the vehicle equipped with the catalyst, or a NOx sensor or CO sensor is provided downstream of the catalyst to detect the catalyst performance, and the value is the reference. This is done when the value is exceeded.
JP 2007-136419 A JP 2007-29768 A

    However, in the refresh method described in Patent Document 2, it is necessary to subject the deteriorated catalyst to an oxidation treatment and subsequently to a reduction treatment on the catalyst, and the catalyst refresh treatment is complicated and troublesome.

    Therefore, an object of the present invention is to make it possible to easily refresh a deteriorated catalyst.

    The present inventor has found that the catalyst can be regenerated by a simple refresh process if it is determined that the catalyst has deteriorated when a predetermined load is applied to the catalyst. Was completed.

The present invention is a method for refreshing an exhaust gas purifying catalyst disposed in an exhaust gas passage of an engine,
The catalyst contains a CeZr-based composite oxide that supports a catalytic metal,
Exhaust gas having a temperature equal to or higher than the predetermined value Tt and containing excess oxygen (exhaust gas containing oxygen at a concentration exceeding the stoichiometric ratio necessary for complete combustion of the reducing components in the gas) flows into the catalyst. When the time exceeds the predetermined time Tm0, it is determined that the exhaust gas purification function of the catalyst has deteriorated,
When the deterioration of the catalyst is determined, oxygen-deficient exhaust gas (exhaust gas containing oxygen at a concentration lower than the stoichiometric ratio necessary for complete combustion of the reducing components in the gas) is supplied to the catalyst for a predetermined time. The exhaust gas purifying function of the catalyst is recovered by allowing the catalyst to flow in at least Tm1.

    That is, simply detecting that the driving time or mileage of a vehicle exceeds a predetermined value, or detecting a decrease in catalyst performance by a NOx sensor or the like, does not necessarily mean that the catalyst is deteriorated at that time. Whether the catalyst has been exposed to high-temperature exhaust gas in a stoichiometric atmosphere for a long time or whether it has been exposed to high-temperature exhaust gas in an oxidizing atmosphere for a long time, the deterioration state of the catalyst differs depending on the state of the exhaust gas to which the catalyst has been exposed. For this reason, it is difficult to reliably regenerate the catalyst when triggered by such an operation time or a decrease in catalyst performance.

    On the other hand, in the present invention, a catalyst containing a CeZr-based composite oxide supporting a catalytic metal is used, and oxygen-exhaust exhaust gas having a temperature higher than a predetermined value Tt flows into the catalyst for a predetermined time Tm0 or more. Therefore, it is determined that the catalyst has deteriorated. Therefore, without performing oxidation treatment in advance, only the reduction treatment is performed, that is, the oxygen-deficient exhaust gas is allowed to flow into the catalyst for a predetermined time Tm1 or more. The exhaust gas purification function can be recovered.

    When it is determined that the catalyst has deteriorated, it is preferable that the temperature of the exhaust gas flowing into the catalyst is lowered to a predetermined range lower than the predetermined value Tt. Thereby, the grain growth of catalyst metal particles can be suppressed.

    If the CeZr-based composite oxide is produced by spray pyrolysis, the primary particle size is small even when exposed to high-temperature exhaust gas (15 nm or less in the case of hollow fine particles). Its specific surface area and pore volume are relatively large, and the agglomeration of the strength of the catalytic metal supported on the composite oxide hardly occurs. Therefore, it is considered that the deterioration of the catalyst in this case is mainly due to the oxidation of the catalyst metal. Therefore, in the case of the catalyst employing the CeZr-based composite oxide by the spray pyrolysis method, in the regeneration, the conventional oxidation treatment for dispersing the catalyst metal is not necessary. The exhaust gas purification function can be recovered by changing the oxidation state of the metal.

    According to the present invention, when a catalyst containing a CeZr-based composite oxide carrying a catalytic metal is targeted, and oxygen-exhaust exhaust gas having a temperature higher than a predetermined value Tt flows into the catalyst for a predetermined time Tm0 or more. Since it is determined that the catalyst has deteriorated and the determination is obtained, the oxygen-deficient exhaust gas is allowed to flow into the catalyst for a predetermined time Tm1 or more. The exhaust gas purification function can be restored.

    Further, if it is determined that the catalyst has deteriorated, the temperature of the exhaust gas flowing into the catalyst is lowered, so that the growth of catalyst metal particles can be avoided.

    Further, in the case of a catalyst that employs a CeZr-based composite oxide by spray pyrolysis, the exhaust gas purification function can be easily recovered by the above treatment.

    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.

<Overview of catalyst refresh method>
FIG. 1 shows the configuration of an exhaust gas purifying apparatus for an engine for executing the catalyst refreshing method according to the present invention. In the figure, reference numeral 1 denotes an engine, and 2 denotes an exhaust gas passage thereof. The exhaust gas passage 2 is provided with an exhaust gas purification catalyst 3 containing a CeZr-based composite oxide carrying a catalytic metal. . In the exhaust gas passage 2 upstream of the catalyst 3, temperature detecting means 4 for detecting the temperature of the exhaust gas flowing into the catalyst 3 and upstream oxygen concentration for detecting the oxygen concentration (A / F) of the exhaust gas. Detection means 5 is provided. In the exhaust gas passage 2 downstream of the catalyst 3, downstream oxygen concentration detection means 6 for detecting the oxygen concentration of the exhaust gas that has passed through the catalyst 3 is provided.

    Detection signals from the temperature detection means 4 and the oxygen concentration detection means 5 and 6 are given to an engine control means 7 using a microcomputer. That is, the control means 7 determines whether or not the catalyst 3 has deteriorated based on the temperature of the exhaust gas flowing into the catalyst 3, the oxygen concentration, and the inflow time to the catalyst 3. The engine 3 controls the regeneration of the catalyst 3 by changing the oxygen concentration of the exhaust gas flowing into the catalyst.

    In this case, the exhaust gas purification function of the catalyst 3 deteriorated when the time during which the exhaust gas whose temperature is equal to or higher than the predetermined value Tt and oxygen is excessive flows into the catalyst 3 becomes equal to or longer than the predetermined time Tm0. The exhaust gas in an oxygen-deficient state is allowed to flow into the catalyst 3 for a predetermined time Tm1 or more, and if necessary, the exhaust gas temperature is lowered to a predetermined range lower than the predetermined value Tt, The exhaust gas purification function of the catalyst 3 is restored.

<Preferable engine control for catalyst refresh>
FIG. 2 shows an engine control flow for determining deterioration and regeneration of the catalyst 3. After the start, the detection values of the temperature detection means 4 and the oxygen concentration detection means 5 are read, and it is determined in step S1 whether or not the exhaust gas temperature Ts flowing into the catalyst 3 is equal to or higher than a predetermined temperature Tt. When the exhaust gas temperature Ts is equal to or higher than the predetermined value Tt, the routine proceeds to step S2, and it is determined whether or not the A / F of the exhaust gas flowing into the catalyst 3 is lean (oxygen excess exhaust gas) above the predetermined value. When A / F lean is determined, the process proceeds to step S3, the time when Ts ≧ Tt and the exhaust gas of A / F lean flows into the catalyst 3 is counted by a timer, and the integrated value TM up to the present time of that time is predetermined. It is determined whether or not the value Tm0 has been exceeded. This is a determination as to whether or not the catalyst 3 has deteriorated.

    When the deterioration of the catalyst 3 is determined based on the integrated value TM> Tm0, the process proceeds to step S4 to set the exhaust gas A / F to a predetermined rich state (exhaust gas lacking oxygen), and if necessary, the exhaust gas temperature. Reduce Ts. This is a regeneration process (reduction process) of the catalyst 3. In the next step 5, the timer is started to determine whether or not the regeneration processing time TN has exceeded the predetermined value Tm1, that is, whether or not the regeneration process has been completed, and A / F enrichment and exhaust are performed until the regeneration process is completed. Continue regeneration by reducing gas temperature.

    The predetermined value Tt of the exhaust gas temperature Ts for determining the deterioration is preferably about 650 ° C. This is because if such a high-temperature exhaust gas continues to flow into the catalyst 3, the catalyst 3 deteriorates in a relatively short time. In this case, the predetermined value Tm0 of the integrated value TM may be set to 5 seconds, for example. However, the deterioration of the catalyst 3 is related to temperature and time. Even if the exhaust gas has a temperature lower than 650 ° C. (for example, about 500 ° C.), if the time for flowing into the catalyst 3 becomes long, the deterioration of the catalyst 3 is reduced. Invite. Therefore, when the predetermined value Tt of the exhaust gas temperature Ts is set low, the predetermined value Tm0 of the integrated value TM may be lengthened accordingly.

    The A / F value of the exhaust gas for determining the deterioration is preferably set to 17, for example. This is because if the state where such exhaust gas of A / F lean flows into the catalyst 3 continues, the catalyst 3 deteriorates in a relatively short time. However, even with respect to this A / F, even when the lean degree is low (for example, A / F = 16 or A / F = 15.5), the time during which such exhaust gas flows into the catalyst 3 becomes long, Alternatively, in the case where the exhaust gas temperature Ts is high, the catalyst 3 is deteriorated. Therefore, when the A / F lean degree is set low, the predetermined value Tt of the exhaust gas temperature Ts may be set higher or the predetermined value Tm0 of the integrated value TM may be increased accordingly.

    Regarding the regeneration treatment conditions for the catalyst, the A / F is preferably 13.6 or more and 14.6 or less. A / F ≧ 13.6 is for avoiding deterioration of engine fuel consumption or abnormal combustion of the engine, and A / F ≦ 14.6 is for regeneration of the catalyst 3 by making the exhaust gas a reducing atmosphere. It is for aiming at. More preferably, A / F is 14.3 or more and 14.6 or less. The predetermined value Tm1 of the reproduction processing time TN may be, for example, 1 second or more and 600 seconds or less. The regeneration of the catalyst 3 becomes difficult in a short time, and the fuel consumption is deteriorated in a long time. It is preferable that the predetermined value Tm1 is 2 seconds or more and 30 seconds or less.

    The reduction of the exhaust gas temperature Ts in the regeneration process is not essential, and when the predetermined value Tt of the exhaust gas temperature Ts in the deterioration determination is set higher, the exhaust gas temperature Ts is lowered to prevent catalyst metal grain growth. . For example, when the predetermined value Tt of the exhaust gas temperature Ts in the deterioration determination is set to 650 ° C. or higher, the exhaust gas temperature Ts during the regeneration process may be lowered to 450 ° C. or higher and lower than 650 ° C. It is preferable to set the exhaust gas temperature Ts to 500 ° C. or more and 600 ° C. or less, and further 530 ° C. or more and 580 ° C. or less. As is clear from the above, when the predetermined value Tt of the exhaust gas temperature Ts in the deterioration determination is set to a low value of 600 ° C. or less, the exhaust gas temperature Ts is not necessarily lowered during the regeneration process.

    In the regeneration process, by performing post-injection in which a small amount of fuel is supplied to the engine in the expansion stroke or exhaust stroke after fuel intake stroke injection (main injection), or by increasing the main injection amount, The A / F of the exhaust gas can be made rich. Further, if the A / F of the air-fuel mixture of the engine is overrich (richer than the theoretical air-fuel ratio) by such fuel injection control, the exhaust gas temperature can be lowered due to the latent heat of the fuel. The exhaust gas temperature Ts may be lowered by supplying the secondary air to such an extent that the exhaust gas A / F does not become leaner than the stoichiometric air-fuel ratio together with the post-injection.

<Specific Example of Exhaust Gas Purification Catalyst 3>
As the exhaust gas purification catalyst 3, Pt / hollow fine particles, Pt / fine particles, and Pt / normal particles were prepared. In any of these, Ce _0.19 Zr _0.81 O ₂ (CeO ₂ : ZrO ₂ = 25: 75 (mass ratio)) as CeZr-based composite oxide particles was supported by 1 mass% of Pt as a catalyst metal. However, the preparation method of each composite oxide particle is different from each other. Hereinafter, the preparation method will be described.

-Preparation method-
For the Pt / hollow fine particles, a spray pyrolysis method was adopted for the preparation of the composite oxide particles, and these were made into hollow fine particles. That is, a raw material solution prepared by dissolving predetermined amounts of zirconium oxynitrate, cerium nitrate and magnesium sulfate in water was sprayed as air as a carrier gas to form droplets and supplied to the heating furnace. The furnace chamber temperature of the heating furnace was set to 800 ° C. or higher and 1000 ° C. or lower. Particles exiting the heating furnace were collected by a bag filter, washed with water and dried to obtain hollow fine particles of the CeZr composite oxide.

    The hollow fine particles are impregnated with a Pt solution, dried at a temperature of 200 ° C. for 2 hours, and subjected to a firing treatment (atmosphere) at a temperature of 600 ° C. for 2 hours, whereby the catalyst (Pt / hollow) Fine particles) were obtained.

    In addition, the said magnesium sulfate is added to the said raw material solution in order to make the said composite oxide particle into a hollow structure, and does not remain | survive in the obtained hollow fine particle.

    For the Pt / fine particles, the spray pyrolysis method was similarly used for the preparation of the CeZr composite oxide particles, but the composite oxide particles were made solid solid particles without adding magnesium sulfate to the raw material solution. did. Other than that, the catalyst (Pt / fine particles) was obtained in the same manner as the Pt / hollow fine particles.

    For Pt / normal particles, a coprecipitation method was used for preparing the composite oxide particles. That is, zirconium oxynitrate and cerium nitrate were mixed, water was added, and the mixture was stirred at room temperature for about 1 hour. Next, this nitrate mixed solution and aqueous ammonia were mixed at room temperature to 80 ° C. for neutralization, and the cloudy solution was allowed to stand for a whole day and night. The cake washed with water was dried at a temperature of about 150 ° C. and then fired under the condition that it was held at a temperature of 400 ° C. for 5 hours, and then pulverized to obtain solid particles of the CeZr composite oxide. Thus, the catalyst (Pt / normal particles) was obtained by the same method as the above Pt / hollow fine particles.

-Primary particle size of catalyst-
The above three kinds of catalysts were subjected to heat treatment (oxidation) held at a temperature of 800 ° C. for 24 hours in an air atmosphere, and then a TEM (transmission electron microscope) photograph was taken. 3 is a TEM photograph of Pt / hollow fine particles, FIG. 4 is a TEM photograph of Pt / fine particles, and FIG. 5 is a TEM photograph of Pt / normal particles. As a result of TEM observation, the average primary particle diameter of each of the Pt / hollow fine particles adopting the spray pyrolysis method is in the range of 10 nm to 15 nm, and the Pt / fine particles is in the range of 10 nm to 20 nm. Pt / normal particles adopting the precipitation method were in the range of 15 nm to 30 nm. Incidentally, the average primary particle size of the initial product (before the above heat treatment) is, according to TEM observation, that both Pt / hollow fine particles and Pt / fine particles are in the range of 5 nm to 10 nm, and Pt / normal particles are 10 nm. It was in the range of 20 nm or less.

    That is, even when a catalyst prepared by spray pyrolysis of CeZr-based composite oxide is exposed to high-temperature exhaust gas, its primary particle size is smaller than that of a catalyst prepared by co-precipitation of CeZr-based composite oxide. It can be seen that it is less likely to be larger than 20 nm or 15 nm.

-Specific surface area of the catalyst-
The BET specific surface area of each of the three types of catalysts in the initial product and the heat-treated (oxidized) product was measured. The results are shown in FIG. The specific surface area of the initial product is not significantly different among the above three types of catalysts, but in the heat-treated (oxidized) product, Pt / hollow fine particles employing the spray pyrolysis method are the largest, about 60 m ² / g, Pt / fine particles However, Pt / ordinary particles employing the coprecipitation method were as small as about 50 m ² / g, and were slightly smaller than 20 m ² / g. The% value added to the “heat treated (oxidized) product” in the figure is the rate of decrease of the specific surface area due to the heat treatment. The reduction rate of the specific surface area increases in the order of Pt / hollow fine particles → Pt / fine particles → Pt / normal particles.

That is, the catalyst prepared by spray pyrolysis of CeZr-based composite oxide has a small decrease in specific surface area when exposed to high-temperature exhaust gas, and has a specific surface area of 40 m ² / g or more or 50 m ² / g or more. It can be seen that the heat resistance is high. This point coincides with the small primary particle size.

-Pore characteristics of catalyst-
The pore distribution in the heat-treated (oxidized) product of each of the three types of catalysts was examined using a pore distribution measuring device manufactured by Shimadzu Corporation. The results are shown in FIG. In Pt / normal particles adopting the coprecipitation method, the pore distribution has a sharp peak in the vicinity of the pore diameter of 50 nm, but in Pt / fine particles adopting the spray pyrolysis method, the pore diameter is around 30 nm. The pore distribution is wide, and the Pt / hollow fine particles have a wider pore distribution. As shown in Table 1, the pore volume obtained from the pore distribution of each catalyst decreases in the order of Pt / hollow fine particles → Pt / fine particles → Pt / normal particles. It can be seen that the catalyst prepared by the spray pyrolysis method has a high heat resistance because a pore volume of 0.3 cm ³ / g or more is secured even after being exposed to high-temperature exhaust gas. This point signifies that the primary particle size is small and that the reduction rate of the specific surface area is small. In addition, the vertical axis | shaft of FIG. 7 represents the log differential pore volume, and the pore volume of Table 1 is represented by the integrated pore volume.

    From the above measurement results of the primary particle diameter, specific surface area and pore volume, Pt / hollow fine particles and Pt / fine particles adopting the spray pyrolysis method have high heat resistance and can be exposed to high-temperature exhaust gas. It can be seen that there is no aggregation of Pt strength.

<Effect of catalyst refresh>
-Changes in exhaust gas purification performance due to catalyst regeneration-
The light-off performance related to the purification of CO was examined for the heat treatment (oxidation) product of each of the three types of catalysts and the regeneration treatment product subjected to regeneration treatment (reduction) after the heat treatment. In this case, the atmosphere of the heat treatment (oxidation) corresponds to an exhaust gas containing excess oxygen, and it can be considered that the catalyst has deteriorated due to the heat treatment. The regeneration treatment is to hold the heat treatment (oxidation) product in a 2.2% CO gas (residue; He) atmosphere at a temperature of 600 ° C. for 10 minutes. This CO gas atmosphere corresponds to an oxygen-deficient exhaust gas.

In the measurement of the light-off performance, a simulated exhaust gas having a CO concentration of 1% and an O ₂ concentration of 0.5% (remaining: He) was supplied to 0.05 g of each catalyst at a space velocity of 96000 h ⁻¹ while maintaining 20 ° C. The simulated exhaust gas temperature was increased at a rate of / min. The temperature at which the CO purification rate reaches 50% (light-off temperature) was determined. The results are shown in FIG.

    In any of the above three types of catalysts, the temperature at which the CO purification rate reaches 50% is lowered by the regeneration treatment. That is, the exhaust gas purification function is restored. In particular, in the case of Pt / hollow fine particles and Pt / fine particles that employ the spray pyrolysis method for the preparation of CeZr double oxide, the ultimate temperature is reduced to around 100 ° C.

-Changes in the Pt electronic state of the catalyst-
The peak of 3d absorption of Pt was measured by XPS (X-ray photoelectron spectroscopy) analysis of the heat-treated (oxidized) product of each of the three types of catalysts and the regenerated product obtained by performing the regeneration treatment after the heat treatment.

    FIG. 9 shows the result of the heat-treated (oxidized) product, and FIG. 10 shows the result of the regenerated product. It can be seen that in any of the three types of catalysts, the oxidation state of Pt is changed to the reduction side as compared with the heat-treated (oxidized) product by the regeneration treatment. It is considered that this change in the oxidation state of Pt leads to the recovery of the exhaust gas purification function of the catalyst.

-Changes in catalyst oxygen release characteristics-
The oxygen release characteristics (CO-TPR) of the heat-treated (oxidized) product of each of the three types of catalysts and the regenerated product subjected to the regeneration treatment after the heat treatment were examined. That is, while supplying a mixed gas of O ₂ and He (O ₂ ; 20%) to 0.05 g of each catalyst, the temperature was raised and held at 600 ° C. for 10 minutes, and then cooled to room temperature (oxygen) Occlusion treatment). Thereafter, while supplying 2.2% CO gas (residue; He), the temperature was increased at a rate of 20 K / min, and the amount of CO _{2 at} each temperature was measured. The amount of CO ₂ corresponds to the amount of oxygen released from the catalyst.

    FIG. 11 shows the result of the heat-treated (oxidized) product, and FIG. 12 shows the result of the regenerated product. In the case of the heat-treated (oxidized) product, the oxygen release start temperature is around 420 K for Pt / normal particles, but is as low as 340 K to 350 K for Pt / hollow fine particles and Pt / fine particles. As a result, the oxygen release characteristics of all of the three types of catalysts are changed so that oxygen is released at a lower temperature by the regeneration process than the heat-treated (oxidized) product. In particular, Pt / hollow fine particles have a strong tendency, and the amount of released oxygen increases at 420K to 560K (150 ° C to 290 ° C). Such an increase in the amount of released oxygen on the low temperature side is considered to lead to the recovery of the exhaust gas purification function of the catalyst.

It is a block diagram of the exhaust-gas purification apparatus of the engine which concerns on this invention. It is a flowchart of engine control for catalyst deterioration determination and regeneration according to the present invention. It is a TEM photograph of Pt / hollow fine particle catalyst. It is a TEM photograph figure of Pt / fine particle catalyst. It is a TEM photograph figure of Pt / normal particle catalyst. It is a graph which shows the BET specific surface area of the initial goods and heat-treated goods of three types of catalysts. It is a graph which shows the pore distribution of the heat processing goods of three types of catalysts. It is a graph which shows the CO purification rate 50% attainment temperature before and behind the regeneration process of three types of catalysts. It is a graph which shows the Pt electronic state by the XPS analysis of the heat processing goods of three types of catalysts. It is a graph which shows the Pt electronic state by the XPS analysis of the regeneration process goods of three types of catalysts. It is a graph which shows the oxygen release characteristic of the heat processing goods of three types of catalysts. It is a graph which shows the oxygen release characteristic of the reproduction | regeneration processing goods of three types of catalysts.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust gas passage 3 Exhaust gas purification catalyst 4 Temperature detection means 5, 6 Oxygen concentration detection means 7 Control means

Claims (3)

A method for refreshing an exhaust gas purifying catalyst disposed in an exhaust gas passage of an engine,
The catalyst contains a CeZr-based composite oxide that supports a catalytic metal,
It is determined that the exhaust gas purification function of the catalyst has deteriorated when the temperature is equal to or higher than a predetermined value Tt and the time during which oxygen-exhaust exhaust gas flows into the catalyst reaches a predetermined time Tm0;
When the deterioration of the catalyst is judged, the exhaust gas purifying catalyst is refreshed by allowing the exhaust gas having an oxygen shortage to flow into the catalyst for a predetermined time Tm1 or more to restore the exhaust gas purifying function of the catalyst. Method. In claim 1,
A method for refreshing an exhaust gas purifying catalyst, wherein when the deterioration of the catalyst is determined, the temperature of the exhaust gas flowing into the catalyst is lowered to a predetermined range lower than the predetermined value Tt. In claim 1 or claim 2,
A method for refreshing an exhaust gas purifying catalyst, characterized in that the CeZr-based composite oxide is produced by spray pyrolysis.