WO2000027508A1

WO2000027508A1 - Method and system for purifying exhaust gases and exhaust gas purification catalyst for use therein and method for preparation thereof

Info

Publication number: WO2000027508A1
Application number: PCT/JP1999/006125
Authority: WO
Inventors: Takahiro Hayashi; Takaaki Kanazawa; Akemi Sato; Juji Suzuki
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 1998-11-05
Filing date: 1999-11-02
Publication date: 2000-05-18

Abstract

The emission of HC is greatly inhibited over a wide range from a low temperature to a high temperature by contacting an oxidation-reduction catalyst comprising an oxygen occluding and reducing agent and, carried thereon, at least one of Rh and Pd, with exhaust gases having been reduced with respect to HC. An oxidation-reduction catalyst comprising an oxygen occluding and reducing agent and, carried thereon, at least one of Rh and Pd exhibits a greatly improved activity for a gas having a low content of HC. And, a catalyst comprising ceria and Pd carried thereon produces a Pd in an oxidation state of more than two, which results in more improved oxidation activity of the catalyst. Further, the contact of an exhaust gas purification catalyst with exhaust gases which have been reduced in Nox content by means of an absorbent for Nox significantly improves the activity of the exhaust gas purification catalyst for purifying HC. In a low temperature region, the emission of Nox can be inhibited due to the adsorption of Nox, and in a low temperature region, HC and CO can be efficiently purified by the exhaust gas purification catalyst. The employment of a reduction catalyst of Nox occlusion type leads to more efficient purification of Nox.

Description

Specification

TECHNICAL FIELD The present invention relates to an exhaust gas purifying method, an exhaust gas purifying apparatus, an exhaust gas purifying catalyst used in the exhaust gas purifying method, and a method for producing the same.

The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus, an exhaust gas purifying catalyst used in the exhaust gas purifying method, and a method for producing the same. More specifically, the present invention relates to hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxidation from low to high temperatures. The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus capable of efficiently purifying a substance (II), an exhaust gas purifying catalyst used in these apparatuses, and a method for producing the same. Background art

Three-way catalysts are widely used as exhaust gas purifying catalysts for purifying HC, CO and nitrogen oxides (NOx) contained in exhaust gas from automobiles. The three-way catalyst, alumina (A1 ₂ 0 _3), silica (Si0 _2), Jirukonia (ZrO, a porous oxide support, such as titania (Ti0 _2), platinum (Pt), rhodium (Rh), palladium (Pd), etc. This three-way catalyst oxidizes HC and CO in exhaust gas and purifies it by reducing NOx. The highest effect is exhibited in the exhaust gas in the stoichiometric atmosphere burned in the stoichiometric atmosphere.

However, since the temperature of the exhaust gas is low at the time of startup or in a cold state, there is a problem that HC is not purified and discharged until the exhaust gas temperature exceeds the activation temperature of the catalyst. Also, when driving in a city area, sudden acceleration or deceleration, etc., the air-fuel ratio fluctuates around the stoichiometry, and the exhaust gas atmosphere varies widely from the HC rich atmosphere to the HC clean atmosphere. Purification by the primary catalyst may be insufficient.

Thus, as disclosed in, for example, JP-A-5-057148 and JP-A-6-154538, an exhaust gas purifying apparatus in which an HC adsorbent such as zeolite is disposed upstream of a three-way catalyst has been developed. ing. In this exhaust gas purification device, HC in the exhaust gas is adsorbed by the HC adsorbent at a low temperature, and the adsorbed HC is desorbed at a temperature rise and oxidized and purified by a three-way catalyst. It is. Therefore, according to this exhaust gas purification device, HC contained in the exhaust gas is adsorbed by the HC adsorbent at the time of cold or start-up, so the emission is suppressed, and HC released from the HC adsorbent at high temperature and HC contained in the exhaust gas is oxidized and purified by a three-way catalyst that is at or above the activation temperature, so that HC emissions can be suppressed from low to high temperatures. However, in an exhaust gas purification device in which an HC adsorbent is arranged upstream of the three-way catalyst, the exhaust gas passing through the three-way catalyst is reduced by HC desorbed by HC desorbed from the HC adsorbent at the time of temperature rise and high temperature. It becomes a reducing atmosphere. Therefore, the activity of the three-way catalyst designed to have the highest activity in the stoichiometric atmosphere was insufficient, and there was a limit to the improvement of the HC and NOx purification rates.

In recent years, a lean-burn engine for burning in an oxygen-rich atmosphere in order to reduce carbon dioxide (C0 ₂₎ is used. This lean-burn engine is driven by a system that constantly burns under lean conditions of excess oxygen and intermittently sets stoichiometric to rich conditions to reduce and purify NOx using exhaust gas as a reducing atmosphere. And as the best catalysts for this system, stores NOx in a lean atmosphere, NOx occlusion reduction type exhaust gas purifying catalyst using the NOx storage element that releases stored _NOx has been developed in Sutiki-rich atmosphere.

If this NOx storage reduction catalyst is used, the air-fuel ratio is controlled in a pulsed manner from the lean side to the stoichiometric to rich side, so that on the lean side, the NOx power is stored in the SN0 _X storage element, which is stored in the stoichiometric state. Alternatively, since it is released on the rich side and reacted with reducing components such as HC and CO and purified, NO can be efficiently purified even from exhaust gas from a lean burn engine.

And JP-A-7- one hundred and sixty-three thousand eight hundred seventy-one, discloses NOx adsorbent made of CeO _2, it has been described to increase the NOx purification activity by combining such a NOx reduction catalyst.

However, even with the NOx storage-reduction catalyst, the NOx storage capacity in the low temperature range where the exhaust gas temperature is less than 300 ° C is insufficient, and the NOx storage capacity decreases as the temperature decreases. Therefore, when the exhaust gas is in a low temperature range, such as during a start-up time, there is a problem that the NOx purification ability is lower than in a high temperature range.

Note that JP-A-7- one hundred sixty-three thousand eight hundred seventy-one, child improved N0 _X purification performance by the NOx adsorbent However, there is no description on HC and NOx purification in the low temperature range below 300 ° C.

Meanwhile, in actual exhaust gas purifying catalysts, a honeycomb catalyst in which a coat layer made of a carrier powder is formed on a honeycomb base material such as that manufactured by Codeilite and a noble metal is supported on the coat layer is used. When the coat layer is formed, a carrier powder and a binder for bonding the carrier powder and the honeycomb substrate are required. Conventionally, alumina sol or the like has been used as the binder. However, according to the study of the present inventors, in the case of a catalyst in which Pd is supported on an oxide having an oxygen storage / release capability, since the alumina sol or the like is used during the production, the activation temperature of the obtained exhaust gas purifying catalyst is reduced. It became clear that it was difficult to lower.

The present invention has been made in view of such circumstances, and a main object of the present invention is to sufficiently suppress the emission of HC, CO, and NOx from a low temperature range to a high temperature range.

Further, a second object of the present invention is to provide an exhaust gas purifying catalyst capable of efficiently purifying HC, CO and NO from a low activation temperature, that is, a low temperature range. Disclosure of the invention

The feature of the exhaust gas purifying method of the present invention that solves the above-mentioned problems is that an HC concentration in the exhaust gas is reduced to a low HC exhaust gas, and an oxidation / reduction catalyst supporting at least one of Pd and an oxygen storage / release material. Low contact with HC exhaust gas.

To form low HC exhaust gas, there are a method of contacting the exhaust gas with the HC adsorbent and a method of controlling the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine to a fuel-lean atmosphere of 13 or more.

Further, a feature of the exhaust gas purifying apparatus of the present invention that solves the above problems is that it comprises an HC adsorbent and an oxidation / reduction catalyst in which at least one of Rh and Pd is supported on an oxygen storage / release material.

The characteristics of the exhaust gas purification device that further embodies the above exhaust gas purification device are that the powder of the HC adsorbent and the powder of the oxidation / reduction catalyst in which at least one of Rh and Pd is supported on the oxygen storage / release material are mixed. Is to become. Another feature of the exhaust gas purifying apparatus of the present invention that embodies the above exhaust gas purifying apparatus is that an adsorbent layer composed of HC adsorbent powder and at least one of Rh and Pd are contained in the oxygen storage / release material. It comprises a reaction layer composed of powder of a supported oxidation / reduction catalyst, and is characterized in that an adsorption layer and a reaction layer are laminated.

In the exhaust gas purifying apparatus in which the adsorption layer and the reaction layer are laminated, it is desirable that the reaction layer constitutes a lower layer and the adsorption layer is laminated on the reaction layer.

Yet another characteristic of the exhaust gas purifying device that embodies the exhaust gas purifying device is that the HC adsorbent disposed upstream of the exhaust gas flow path, the oxygen storage / release material disposed downstream of the HC adsorbent, and Pd And an oxidation-reduction catalyst carrying at least one of the following.

In the exhaust gas purifying apparatus, the oxygen storage / release material is desirably ceria, and particularly desirably thermally stabilized ceria.

The HC adsorbent preferably supports a noble metal, and it is particularly preferable to use Pt and Rh together as the noble metal.

Another feature of the exhaust gas purifying method of the present invention that solves the above-mentioned problems is that the NOx concentration in the exhaust gas is reduced to a low NOx exhaust gas, and an oxidation-reduction catalyst and a low NOx catalyst in which a porous oxide carries a noble metal. Contacting exhaust gas.

The exhaust gas purifying apparatus of the present invention capable of implementing the above exhaust gas purifying method is characterized by an oxidation / reduction catalyst comprising a porous oxide carrying a noble metal and a NOx adsorber which is disposed near the exhaust gas purifying catalyst and adsorbs NOx. In the low temperature range, the NOx contained in the NOx adsorbent makes the exhaust gas adsorbed by the NOx adsorbent contact the oxidation / reduction catalyst, and in the high temperature range, the exhaust gas containing NOx released from the NOx adsorbent is oxidized / reduction catalyst It has been configured to contact with.

Further, the further practical feature of the exhaust gas purifying apparatus of the present invention is that a porous oxide carrier, a noble metal supported on the porous oxide carrier, a porous oxide selected from an alkali metal, an alkaline earth metal and a rare earth element are used. NOx storage element composed of a NOx storage element supported on an oxide carrier and a NOx storage reduction catalyst consisting of a NOx storage element selected from alkali metals, alkaline earth metals and rare earth elements on a porous oxide support. Is that the NOx adsorbent carrying the NOx is disposed upstream of the NOx storage reduction catalyst in the exhaust gas flow path. The feature of the exhaust gas purifying catalyst of the present invention that solves the above-mentioned problems is that the catalyst is composed of an oxide having an oxygen storage / release capability and Pd supported on the carrier in a peroxidized state having a valence of more than two. Is to become. This carrier is desirably composed only of ceria. Another feature of the exhaust gas purifying catalyst of the present invention is a carrier substrate, a coat layer formed on the carrier substrate and containing an oxide having an oxygen storage / release capability, and Pd carried on the coat layer. The coating layer is bonded by ultrafine ceria. In this exhaust gas purifying catalyst, the oxide having the ability to store and release oxygen is seria, the coat layer is composed of only ceria, and Pd is supported on the coat layer in a peroxidized state having a valence of more than 2 valences. It is desirable.

The method for producing the exhaust gas purifying catalyst of the present invention, which is most suitable for producing the above exhaust gas purifying catalyst, is characterized by a step of preparing a slurry from an oxide powder having oxygen storage / release capability, ceria sol and water, It consists of a step of forming a coat layer by applying a slurry to a material, drying and firing, and a step of supporting Pd on a coat layer. Note that Pd may be supported first.In this case, the production method includes a step of preparing a catalyst powder in which Pd is supported on an oxide powder having an oxygen storage / release capability, and a step of preparing the catalyst powder, ceria sol, and water. The method comprises the steps of preparing a slurry and forming a coat layer by applying the slurry to a carrier substrate, drying and firing. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a graph showing the C050% purification temperature catalyst supporting the noble metal on A1 ₂ 0 ₃ carrier. 2 CeO ₂ - is a Zr0 ₂ shows to graphs C050% purification temperature of the catalyst carrying various noble metal on a carrier. FIG. 3 is a front view of an exhaust gas purifying apparatus according to one embodiment of the present invention. FIG. 4 is a graph showing the 50% purification temperatures of the exhaust gas purification devices of the example and the comparative example. FIG. 5 is a sectional view of a main part of an exhaust gas purifying apparatus according to another embodiment of the present invention. Figure 6 is CeO ₂ - is a graph showing 50% purification temperature of Zr (catalyst supporting Pd on L carriers 7 CeO ₂ -. Showing the Zr 0 ² 50% purification temperature of the carrier in the catalyst carrying Rh is a graph 8 CeO ₂ -.. Zr 0 ₂ graph showing a 50% reduction temperature of the catalyst carrying Pt on a support 9 is a graph showing the relationship between the endurance temperature and specific surface area of the various carriers. Figure 10 is a graph showing the CO 50% purification temperature of the catalyst carrying various noble metal on a carrier doped with Zr to CeO _2. 11 5 is a graph showing the initial 50% purification temperature of the exhaust gas purification devices of the example and the comparative example. FIG. 12 is a graph showing the 50% purification temperature after the durability test of the exhaust gas purification devices of the example and the comparative example. FIG. 13 is a graph showing HC emissions of the exhaust gas purifying devices of the example and the comparative example. FIG. 14 is a graph showing the relationship between the air-fuel ratio (A / F) of the air-fuel mixture and the HC50% purification temperature. FIG. 15 is a graph showing a 50% purification temperature of the exhaust gas purification device of the example.

FIG. 16 is an explanatory diagram showing the configuration of an exhaust gas purifying apparatus according to one embodiment of the present invention. FIG. 17 is a graph showing the NOx storage amounts of the exhaust gas purifying devices of the example of the present invention and the comparative example. FIG. 18 is a graph showing the difference in HC50% purification temperature depending on the difference between the noble metal supported on the three-way catalyst and the presence or absence of NO. FIG. 19 is a graph showing the difference in the C050% purification temperature depending on the difference between the noble metal supported on the three-way catalyst and the presence or absence of NO. FIG. 20 is a schematic explanatory view of the evaluation device in the embodiment of the present invention. Figure 21 is a graph showing 50% purification temperatures for HC, CO and N0 _X in the exhaust gas purifying device of Examples and Comparative Examples. FIG. 22 is a diagram showing a model gas temperature evaluation pattern used in the example. Fig. 23 is a graph showing the difference in NOx purification rate due to the difference in NOx adsorbent. Figure 24 is a graph showing the difference in the NOx purification rate due to the difference in the NOx adsorbent type and 0 ₂ presence. FIG. 25 shows the NOx purification amounts of the exhaust gas purification devices of the example and the comparative example. Figure 26 shows the relationship between the exhaust gas temperature of various NOx adsorbents and the amount of NOx adsorbed. FIG. 27 is a diagram showing an evaluation pattern of the model gas temperature used in the example. FIG. 28 is a graph showing the NOx purification rate of the exhaust gas purification device of the example. Figure 29 is a graph showing the amount of ML adsorbed by various NOx adsorbents. Figure 30 is a graph showing the amount of NOx adsorbed by various NOx adsorbents. FIG. 31 is a diagram showing a model gas temperature evaluation pattern used in the example. FIG. 32 is a graph showing the NOx purification rates of the exhaust gas purification devices of the example and the comparative example.

FIG. 33 is a graph showing 50% purification temperatures of the exhaust gas purification devices of the example and the comparative example. FIG. 34 is an XPS chart of Pd supported on various carriers. FIG. 35 is a front view of the exhaust gas purifying apparatus used in the example. FIG. 36 is a graph showing a 50% purification temperature of the exhaust gas purification device of the example. FIGS. 37 to 40 are graphs showing the relationship between the hydrocarbon concentration in the model gas and the C050% purification temperature of the Pd / Ce0 catalyst. Fig. 41 is a graph showing the amount of C ₃ H ₆ adsorbed on various zeolites, and Fig. 42 is an adsorption of HC with ZSM-5 carrying various metals on ion exchange. 4 is a graph showing C ₃ H ₆ adsorption amounts of materials. BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors have conducted intensive studies on a catalyst in which a noble metal is supported on an oxygen storage / release material, and have found that the activity of the catalyst is extremely improved when the HC concentration in the exhaust gas is low. That is, in the exhaust gas purification method of the present invention, the HC concentration in the exhaust gas is reduced to low HC exhaust gas, and the oxidation / reduction catalyst supporting at least one of Rh and Pd on the oxygen storage / release material is brought into contact with the low HC exhaust gas. I have. When the HC concentration of the low HC exhaust gas decreases, the catalytic activity of the oxidation / reduction catalyst significantly increases, and the purification performance of HC, CO and NOx improves. At low temperatures, such as during start-up, emissions are low because the HC concentration in the exhaust gas is low. When the temperature of the exhaust gas rises, the catalyst supporting the noble metal in the oxygen storage / release material exhibits high catalytic activity, and HC, CO and NOx are efficiently purified. Therefore, the emission of harmful substances from low to high temperatures can be suppressed.

In order to reduce HC concentration in exhaust gas to lower HC exhaust gas, a method using HC adsorbent and an air-fuel ratio (A / F) of air-fuel mixture supplied to an automobile engine in a fuel-lean atmosphere of 13 or more There is a way to control. The former method will be described in detail in an exhaust gas purifying apparatus described later.

If the latter method is adopted, the air-fuel ratio (A / F) should be controlled to a fuel-lean atmosphere of 13 or more from the start of the engine until the activation of the precious metal carried on the oxygen storage / release material. Is desirable. This is because if the atmosphere is fuel-lean even after the precious metal has been activated, the NOx purification performance will be adversely affected. Also, even when controlling to a fuel-lean atmosphere immediately after starting, the engine performance deteriorates if the air-fuel ratio (A / F) becomes too large. Therefore, the air-fuel ratio (A / F) is set to a maximum value. It is desirable. In the exhaust gas purifying apparatus of the present invention employing the former method, an HC adsorbent and an oxidation / reduction catalyst in which at least one of Rh and Pd is supported on an oxygen storage / release material are used. As a result of HC in the exhaust gas being adsorbed by the HC adsorbent, the low HC exhaust gas in which the HC concentration in the exhaust gas has decreased contacts the oxidation / reduction catalyst. Therefore, the catalytic activity of the oxidation / reduction catalyst is significantly improved, and the purification performance is improved. And in the low temperature range such as when starting, Since HC in the exhaust gas is adsorbed by the HC adsorbent, the emission of HC is suppressed. 'When the exhaust gas becomes lean or at high temperature and the HC adsorbed on the HC adsorbent is released, the released HC is efficiently purified by the activated oxidation-reduction catalyst. Therefore, high purification performance is exhibited from a low temperature range to a high temperature range. The HC adsorbent adsorbs and releases HC, and the oxygen storage and release material stores and releases oxygen. Therefore, when the atmosphere of the exhaust gas fluctuates, the effect of adjusting the atmosphere by adsorption (occlusion) and release of HC and oxygen is also exerted. Due to these interactions, the exhaust gas purification device of the present invention exhibits extremely high purification performance.

The HC adsorbent and the oxidation-reduction catalyst can be used in various forms. For example, a mixture of the HC adsorbent powder and the oxidation / reduction catalyst powder can be used. The operation of this exhaust gas purifying device is considered to be as follows.

When the exhaust gas in the clean atmosphere burned at the air-fuel ratio of the fuel lean comes into contact, HC is released from the HC adsorbent, and oxygen is stored in the oxygen storage / release material. As a result, the exhaust gas quickly becomes near stoichiometric, and HC, CO and NOx are purified by the oxidation / reduction catalyst powder near the HC adsorbent powder.

On the other hand, when exhaust gas in a rich atmosphere comes into contact, HC is adsorbed by the HC adsorbent, and oxygen is released from the oxygen storage / release material. As a result, the exhaust gas quickly becomes close to the stoichiometric state, and the activity of the oxidation / reduction catalyst is improved because HC is reduced. This results in high purification performance.

Further, the exhaust gas purifying apparatus of the present invention comprises an adsorption layer composed of HC adsorbent powder and a reaction layer composed of oxidation-reduction catalyst powder, wherein the adsorption layer and the reaction layer are stacked. It can be. It is considered that the operation of this exhaust gas purifying device is as follows.

When the exhaust gas in the lean atmosphere comes into contact, HC is released from the HC adsorbent in the adsorption layer, and oxygen is stored in the oxygen storage / release material in the reaction layer. As a result, the exhaust gas quickly becomes close to the stoichiometric state, and HC, CO and NOx are purified by the oxidation / reduction catalyst in the reaction layer.

On the other hand, when exhaust gas in a rich atmosphere comes into contact, HC is adsorbed to the HC adsorbent in the adsorbent layer, and oxygen is released from the oxygen storage / release material in the reverse layer. As a result, exhaust gas Quickly becomes close to the stoichiometric ratio, and the activity of the oxidation / reduction catalyst is improved because HC is reduced. Thereby, high purification performance is obtained.

Either the adsorption layer or the reaction layer may be located on the surface side.However, considering that the oxidation-reduction catalyst has a particularly high activity in exhaust gas with a low HC concentration, the adsorption layer and the reaction layer are located on the surface of the reaction layer. It is preferred to make the adsorption layer the outermost surface by laminating. As a result, the concentration of HC in the exhaust gas reaching the reaction layer is reduced, so that the purification activity is improved.

Further, the exhaust gas purifying apparatus of the present invention can be configured such that the HC adsorbent is disposed on the upstream side of the exhaust gas flow path and the oxidation / reduction catalyst is disposed on the downstream side thereof. It is considered that the operation of this exhaust gas purifying device is as follows.

When the exhaust gas in the lean atmosphere passes, HC is released from the HC adsorbent, so that the exhaust gas flows near the stoichiometry and flows into the oxidation / reduction catalyst. Oxygen is stored and released in the oxidation and reduction catalyst according to the exhaust gas atmosphere, so the exhaust gas on the oxidation and reduction catalyst is very close to stoichiometric, and HC, CO and NOx are oxidized and reduced by at least one of Rh and Pd. Is done.

Also, when exhaust gas in a rich atmosphere passes, HC is adsorbed by the HC adsorbent, whereby the exhaust gas becomes close to stoichiometric and flows into the oxidation / reduction catalyst. Oxygen is stored and released from the oxidation / reduction catalyst in accordance with the atmosphere of the exhaust gas, so that the exhaust gas on the oxidation / reduction catalyst is very close to stoichiometric, and HC is almost completely contained in the exhaust gas flowing into the oxidation / reduction catalyst. Can be absent. Thereby, high purification performance can be obtained.

Zeolites such as Huelierite, ZSM-5, mordenite, and Y-type zeolite can be used as the HC adsorbent. It is also preferable to use a zeolite carrying a noble metal as the HC adsorbent. By supporting the noble metal in this way, the adsorption of low molecular weight HC is further improved. As this noble metal, it is particularly preferable to support both Pt and Rh.

To support the noble metal on the HC adsorbent, the noble metal may be directly supported, or a ternary powder of the noble metal supported on alumina or the like may be mixed with the zeolite powder to form the HC adsorbent, It is also possible to form a coat layer made of a three-way catalyst on the surface of the material. The carrier of the oxidation 'reduction catalyst may be include at least oxygen storage material may be constituted of only the oxygen absorbing and desorbing material, alumina oxygen storage material (A1 ₂ 0 _3), silica (Si0 ₂ ), A porous carrier such as zirconia (ZrO ₂ ), or a composite oxide with an oxygen storage / release material.

The oxygen storage material, ceria (CeO ₂₎ is but one representative, rare earth metal oxides such as _{_{Pr0 4, NiO, Fe 2 0}} 3, CuO, transition metal oxides such as Mn ₂ 0 _5, etc. Can also be used.

This oxygen storage / release material is desirably thermally stabilized. This makes it possible to purify at low temperatures even after long-term durability at high temperatures. For example, in the case of CeO ₂ is thermally stabilized by a solid solution or a composite oxide of Zr0 _2. The method for supporting the CeO ₂ on Al ₂ 0 _3, a method of de one-flop zirconium (Zr) in CeO _2, a method of highly dispersed the Zr0 ₂ in _{_{_{Ce0 2, Ce0 2, A1 2}}} 0 3 and Zr0 ₂ The mixture can be thermally stabilized by a method of producing the mixture by a coprecipitation method.

By using the heat-stabilized oxygen storage / release material as a carrier for the oxidation / reduction catalyst, the heat resistance can be further improved and a high purification activity can be maintained even after long-term exposure to a high temperature.

In the oxidation catalyst, at least one of Rh and Pd is supported on the carrier. Other noble metals such as Pt have low catalytic activity and are not practical compared to at least one of Rh and Pd. The loading amount of at least one of Rh and Pd is preferably in the range of 0.1 to 10% by weight based on the above-mentioned carrier. If the supported amount is less than this, sufficient purification activity cannot be obtained, and if the amount is more than this, the purification activity is saturated and excess noble metal is wasted. Note Rh is Zr0 when used with _2, a high hydrogen generation activity by the steam reforming reaction and water gas Sushifu preparative reactions in a reducing atmosphere. Thus oxidation and reduction catalyst, CeO ₂ - a ZrO ² as a carrier, it is most preferable that carrying Rh. By doing so, the generated hydrogen can be used for the reduction of ΝΟχ, and 浄化 the purification performance is further improved.

The composition ratio between the HC adsorbent and the oxidation / reduction catalyst is not particularly limited, but the HC adsorbent / oxidation / reduction catalyst is preferably in a volume ratio in the range of 1/10 to 1/1.

That is, according to the exhaust gas purifying method and the exhaust gas purifying apparatus of the present invention, it is possible to suppress the emission of HC even in the case of exhaust gas in a low temperature range such as at the time of starting, and can be used in a wide temperature range. Thus, HC, CO and NOx can be purified at a high purification rate.

The present inventors have conducted intensive studies on the purification behavior of exhaust gas purifying catalysts such as three-way catalysts.As a result, the NOx concentration in the exhaust gas was reduced to make it a low NOx exhaust gas. By contacting the purification catalyst with low NOx exhaust gas, we have found that HC and CO are efficiently purified from low temperature range.

That is, in the exhaust gas purifying method of the present invention, the exhaust gas having a low NOx concentration is brought into contact with the exhaust gas purifying catalyst. As a result, HC and CO can be purified from a low temperature range, and the purification temperature window is expanded. While such cause is not clear becomes, the reactivity with HC and CO and 0 ₂ in the NOx does not exist was improved, poison noble metal surface by NOx can be considered like to hardly occur.

For example, if exhaust gas does not originally contain NOx, it can be purified by oxidizing HC and CO from a low temperature range by contacting it with an exhaust gas purification catalyst. However, since exhaust gas from automobile engines inevitably contains NO., In order to carry out the purification method of the present invention for exhaust gas from automobile engines, NOx must be removed from exhaust gas in advance. There is a need.

Therefore, the exhaust gas purifying apparatus of the present invention has a configuration in which the NOx adsorbent is disposed near the exhaust gas purifying catalyst. As a result, in the low temperature region, NOx contained in the exhaust gas is adsorbed and removed by the NOx adsorbent, so that the exhaust gas with a reduced NOx concentration can be brought into contact with the exhaust gas purification catalyst, and HC and CO are efficiently used. It is well purified and can control NOx emissions. When the temperature of the exhaust gas rises to a high temperature range, NOx adsorbed by the NOx adsorbent is released, and the NOx is reduced and purified by coming into contact with an oxidation-reduction catalyst having a catalyst activation temperature or higher.

The NOx adsorbent, oxides of alkali metals, oxides of alkaline earth metals, oxides of rare earth _{_{_{elements, Co 3 0 4, Ni0 2}}} , Mn0 2, Fe 2 0 3, a transition metal such as Zr0 ₂ Oxides, zeolites and the like are exemplified. These can be used alone or in combination of two or more to form a NO adsorbent. A metal oxide selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements supported on a porous oxide carrier such as alumina, silica, silica-alumina, zirconia, titania, and zeolite is referred to as a NOx adsorbent. You can also.

In the case of the former NOx adsorbent, for example, an oxide of an alkali metal or an oxide of an alkaline earth metal has a high ability to adsorb NOx, but, on the other hand, does not easily release the adsorbed NOx. As a result, the temperature at which NOx is released rises, and when used in low to medium temperature ranges, the amount of NOx adsorbed is saturated, making it more difficult to adsorb NOx. However, if the latter NOx adsorbent is made of a porous oxide carrier such as zeolite, which carries an alkali metal alkali metal or a rare earth element by ion exchange, the temperature at which the adsorbed NOx is released will be low. Therefore, NOx adsorption / release can be repeated even at low to medium temperature exhaust gas temperatures.

Further, Zr0 ₂ obtained by adding an alkali metal or alkaline earth metal exhibit particularly excellent NOx adsorption capability as compared to other NOx absorption Chakuzai. Such addition of alkali metal and Al force Li earth metal is not effective cause clearly, but force Li by Al force Li metal and Al force Li earth metals forms a solid solution with Zr0 ₂ lattice metal and Al force Li earth metal and Zr0 ₂ are complexed, it is due connexion Zr0 ₂ surface is considered to probably because newly N (L adsorption sites is modified is generated.

Then, Zr0 ₂ with the addition of an alkali metal or an alkaline earth metal, to carry Pt, Rh, a noble metal such as Pd, or _{_{_{Co 3 0 4, Ni0 2,}}} Mn0 transition metal oxides, such as _2, Fe ₂ 0 ₃ and Then, the NOx adsorption capacity is further improved. This is thought to be because Pt and _{_{_{Co 3 0 4, Ni0 2,}}} Mn0 oxidation activity is expressed, such as by _{₂ j} Fe ₂ 0 _3, NOx adsorption amount is increased by the NO in the exhaust gas is oxidized into N0 ₂ Have been.

In order to further increase the oxidation activity, it is also preferable to provide an exhaust gas purification device in which an oxygen supply device for supplying oxygen is arranged upstream of the NOx adsorbent. Accordingly likely to be oxidized to NO gar layer N0 ₂ in the exhaust gas, which further improves the NOx adsorption capability. It is sufficient to supply gas containing oxygen, and it is easy to supply air. The same operation and effect can also be obtained as an exhaust gas purifier equipped with an oxidation catalyst upstream of the NOx adsorbent.

As described above, the temperature at which NOx is adsorbed differs depending on the type of NOx adsorbent. Therefore, it is also preferable to use a plurality of types of NOx adsorbents having different temperatures at which the maximum amount of NOx is adsorbed. For example, low-temperature NOx adsorption that efficiently adsorbs NOx at low temperature on the uppermost stream side If a medium-temperature NOx adsorbent that efficiently adsorbs NOx at medium to high temperatures is placed downstream of it, NOx is gradually adsorbed from the upstream side where the adsorption temperature is low. NOx can be adsorbed in a wide temperature range up to a high temperature range. In addition, since the exhaust gas is heated by the heat generated by the adsorption of NOx, there is also an effect that the activity of the NOx adsorbent on the downstream side or the catalyst for purifying the exhaust gas is expressed early.

For example, NOx adsorbents that exhibit maximum adsorption at room temperature to 100 ° C include those in which zeolite supports a rare earth element such as Ce, and those in which zeolite supports an alkali metal, alkaline earth metal, or transition metal. There are exemplified, as the NOx adsorbent indicating the maximum adsorption amount at 100 to 200 ° C, obtained by loading a noble metal on Zr0 _2, such as those carrying the transition metals such as Co ₃ 0 ₄ is illustrated, 300 ° as a NOx adsorbent that indicates the maximum amount of adsorption in C or more, such as Zr0 _{_2,} A1 ₂ 0 ₃ obtained by loading a noble metal and Al force Li metal and Al force re-earth metals and the like are exemplified.

In the case of a NOx adsorbent in which a porous oxide carrier carries a metal element selected from the group consisting of alkali metal, alkaline earth metal and rare earth element, the total amount of metal elements supported per liter of porous oxide carrier It is desirable to be in the range of 0.01 to 1 mol. If the supported amount is less than this range, the NOx adsorption capacity in the low temperature range will be reduced, and the NOx purification capacity will be reduced.If the supported amount is larger than this range, it will be difficult for NOx to be desorbed, which will make regeneration difficult. .

In this NOx adsorbent, zeolite is used as a porous oxide carrier, and zeolite is ion-exchanged with at least one metal element selected from alkali metal, alkaline earth metal and rare earth element. Is particularly desirable.

Zeolite, which is also called a molecular sieve, has pores comparable to the size of a molecule, and is used as an adsorbent and as a catalyst in many reactions. Also includes a cation to neutralize the negative charge of which is a main component A1 ₂ 0 _3, utilizing Therefore cations are readily exchanged with other cations in aqueous solution, also as a cation exchanger Have been. Therefore, at least one type of -metal element selected from an alkali metal, an alkaline earth metal and a rare earth element can be supported by ion exchange, and can be supported in a very highly dispersed state.

The metal element supported by ion exchange is extremely highly dispersed on zeolite. Therefore, the activity is extremely high, and the oxidation activity of NO at low temperature is thought to be improved. Therefore the NO in the exhaust gas is oxidized on the N0 _X adsorbent NOx, and the 'thought it is adsorbed by the NOx adsorbent, it is the NOx is sufficiently adsorbed even at the low temperature range.

In addition, since HC in exhaust gas is also adsorbed to zeolite, a reaction between the adsorbed HC and NOx is also expected. Therefore, the NOx purification ability is further improved.

As zeolite, zeolites such as huelierite, ZSM-5, mordenite, and Y-type zeolite can be used. Among them, ZSM-5 and mordenite are excellent in ion exchange ability, and it is desirable to use them by selecting them. By the way, the NOx purification reaction in the NOx storage reduction catalyst is performed in the following manner: a first step of oxidizing NO in exhaust gas to NOx in a lean atmosphere, a second step of storing NOx in the NOx storage element, and a stoichiometric to rich step. It is known that the process consists of a third step of reducing NOx released from NOx storage elements on the catalyst in the atmosphere. Therefore, in order for the NOx purification reaction to proceed smoothly, each of these steps must proceed smoothly.

However, in a low-temperature region of, for example, less than 300 ° C., it is considered that the first oxidation does not easily proceed, and the first step does not proceed smoothly. Therefore, it is considered that the amount of generated NOx decreases in the low temperature range, the second and third steps do not proceed smoothly, and the NOx purification ability in the low temperature range decreases.

Therefore, the exhaust gas purifying apparatus of the present invention using the NOx storage reduction type catalyst as the exhaust gas purification catalyst has a configuration in which a NOx adsorbent is disposed on the exhaust gas upstream side of the NOx storage reduction type catalyst. The NOx adsorbent easily adsorbs NOx, and even at low temperatures. Therefore, in the low temperature range, exhaust gas containing almost no NOx is supplied to the NOx storage reduction catalyst, so that NOx is hardly emitted. When the temperature of the exhaust gas rises, the adsorbed NOx desorbs from the NOx adsorbent and flows into the NOx storage reduction catalyst, but since the NOx storage reduction catalyst has already reached the activation temperature, The reaction proceeds smoothly, and NOx is efficiently reduced and purified. With such a mechanism, according to the exhaust gas purifying apparatus of the present invention, a high NOx purification rate can be secured from low to high temperatures. a.

The NOx storage reduction catalyst is a porous oxide carrier, a noble metal supported on the porous oxide carrier, and an NOx supported on the porous oxide carrier selected from an alkali metal, an alkaline earth metal and a rare earth element. The same elements as those of the related art, which are made up of the storage element and, can be used.

Alumina, silica, silica-alumina, zirconia, titania, zeolite, and the like can be used as the porous oxide carrier used in the NOx storage reduction catalyst. One of these may be used, or a plurality of them may be mixed or combined for use. Among them, it is preferable to use alumina having high activity. The porous oxide carrier used for the NOx storage reduction catalyst may be of the same type as the porous oxide carrier of the NOx adsorbent, or may be different.

Examples of the noble metal used in the NOx storage reduction catalyst include Pt, Rh, Pd, and Ir. Among them, Pt having high activity is particularly preferable. The amount of the noble metal supported is preferably 0.1 to 10 g per liter of the porous oxide carrier. If the amount is less than this, the purification activity is insufficient, and if the amount is more than this, the effect is saturated and the cost increases. The amount of the NOx storage element carried by the NOx storage reduction catalyst is preferably in the range of 0.01 to 1 mol per liter of the porous oxide carrier. If the supported amount is less than this range, the NOx adsorption capacity will decrease and the NOx purification ability will decrease, and if it exceeds this range, the noble metal will be covered with the NOx storage element and the activity will decrease.

N0 _X occluding element and a metal element used in the NOx storage reduction catalyst and the NOx adsorbent may be the same type, may use different ones. The NOx storage element used in the NOx storage reduction catalyst is at least one selected from alkali metals, alkaline earth metals, and rare earth elements.

Examples of the alkali metal include lithium, sodium, potassium, and cesium. The alkaline earth metal refers to Group 2A element of the periodic table, and examples include norium, beryllium, magnesium, calcium, strontium, and the like. Examples of rare earth elements include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, dysprosium, and ytterbium.

The NOx adsorbent and the NOx storage-reduction catalyst can be used as pellets or honeycombs, respectively. For honeycomb shape, use Cordiera A porous oxide carrier is applied to a honeycomb carrier substrate made of

A NOx storage element or the above-mentioned metal element is supported on the coat layer. Alternatively, the porous oxide carrier powder may be produced by previously supporting the NOx storage element or the above-mentioned metal element and forming a coat layer from the powder. In the exhaust gas purifying apparatus of the present invention, the arrangement of the NOx adsorbent and the exhaust gas purifying catalyst may be, for example, a mixture of a powdery NOx adsorbent and a powdery exhaust gas purifying catalyst to form a mixed powder, and then into a pellet form. It can be used as an exhaust gas purifying device by molding or forming a coat layer on a honeycomb carrier substrate. Further, as described above, an evening exhaust gas purifying apparatus in which the NOx adsorbent is arranged upstream of the exhaust gas flow and an exhaust gas purifying catalyst is arranged downstream of the NOx adsorbent may be used. Alternatively, an exhaust gas purifying apparatus having a two-layer structure in which an exhaust gas purifying catalyst layer is formed as a lower layer and a NOx adsorbent layer is formed as an upper layer.

That is, according to the exhaust gas purifying method and the exhaust gas purifying apparatus of the present invention, the emission of NOx can be suppressed even in the exhaust gas in a low temperature range, and HC, CO and NO can be purified in a wide temperature range. .

Further, alkali metal Zeorai bets, by arranging the N0 _X storage reduction catalyst downstream of the NOx adsorbent at least one metal element were supported by ion exchange selected from alkaline earth metals and rare earth elements, even in a low temperature range Since NO has already been converted to NOx, even if there is NOx that could not be adsorbed by the NOx adsorbent, it can be stored in the downstream NOx storage reduction catalyst. Therefore, NOx storage capacity in the low temperature range is improved, and NOx purification capacity is further improved.

According to the study of the present inventors, in the case of a catalyst in which Pd is supported on an oxide capable of absorbing and releasing oxygen, such as the above-mentioned oxidation-reduction type catalyst, alumina sol or the like was used at the time of production, so that it was used in a low-temperature region. It was revealed that the activity was inhibited. As a result of intensive studies, they found that the use of ultrafine ceria as the binder significantly improved the activity in the low temperature range.

That is, this exhaust gas purifying catalyst comprises a carrier substrate, a coat layer formed on the carrier substrate and containing an oxide capable of occluding and releasing oxygen, and Pd carried on the coat layer. In addition, the coat layer is bonded by ultrafine ceria. As a result, the low-temperature activity is remarkably improved, and the purification rate of HC, CO and N0.x at the time of starting and during cold is improved.

As the carrier substrate, a conventionally used pellet-like substrate or honeycomb-like substrate can be used. In addition, the material can be selected from cordierite, metal foil and the like as in the prior art.

Coating layer may be included oxides having at least oxygen storage capacity may be constituted only by an oxygen occlusion-release material, alumina oxygen storage material (A1 ₂ 0 _3), silica force (Si0 ₂ ), it can be used as Jirukonia (Zr0 ₂₎ as a mixture of a porous carrier such as, or oxygen occlusion and release material and C complex oxide. The oxygen storage material, ceria (CeO ₂₎ is but one representative, rare earth metal oxides such as _{_{Pr0 4, NiO, Fe 2 0}} 3, CuO, transition metal oxides such as Mn ₂ 0 _5, etc. Can also be used.

This oxygen storage / release material is desirably thermally stabilized. This suppresses a decrease in low-temperature activity even after long-term durability at high temperatures. For example, in the case of CeO ₂ is thermally stabilized by a solid solution or a composite oxide of Zr0 _2. The method for supporting the CeO ₂ on the k 1 ₂ 0 _3, a method of de one-flop zirconium (Zr) in CeO _2, a method of highly dispersed the Zr0 ₂ to Ce 0 in _{_{_{2, Ce0 2, A1 2 0}}} 3 and Thermal stabilization can also be performed by, for example, a method of producing a mixture of ZrO _{2 by} a coprecipitation method.

Pd is carried on the coat layer. Other noble metals, such as Pt and Rh, have lower activity than Pd and are not practical. The amount of Pd carried is preferably in the range of 0.1 to 20% by weight based on the above-mentioned coat layer. If the supported amount is less than this, sufficient purification activity cannot be obtained. If the supported amount is more than this, the activity is saturated and excess noble metal is wasted.

The amount of the particulate ceria is not particularly limited, but is preferably the minimum amount necessary for binding the carrier powders in the coating layer and binding the coat layer and the carrier substrate. Usually, the range is 0.1 to 20 parts by weight with respect to 100 parts by weight of the carrier powder.

It is also preferable to use the exhaust gas purifying catalyst as the above-mentioned oxidation and reduction catalyst together with the HC adsorbent. Thereby, the activity in the low temperature range is further improved. Further, in this exhaust gas purifying catalyst, the coat layer is formed by using ceria as an oxide having an oxygen storage capacity and ceria sol as a binder. It is preferable that the coating layer is composed of only Pd and that Pd is supported on the coat layer in a peroxide state having a valence of more than 2 as described later. This greatly improves low-temperature activity, as described below.

That is, according to the exhaust gas purifying catalyst of the present invention, HC, CO and NOx can be efficiently purified even in the exhaust gas in a low temperature range, and HC, CO and NOx can be purified in a wide temperature range.

The present inventors have studied the various purification methods and catalytic devices described above, and have found that a catalyst in which Pd is supported on an oxide powder having an oxygen storage / release capability, such as seria, has a remarkably improved low-temperature activity. discovered. As a result of pursuing the cause, they found that Pd is supported in a peroxide state having a valence of more than two, and completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention is composed of a support made of an oxide having an oxygen storage / release ability and Pd supported on the support in a peroxidized state having a valence of more than two.

According to the exhaust gas-purifying catalyst of the present invention, Pd is supported in a peroxidized state having a valence of more than 2, and therefore has extremely high oxidizing activity, and exhibits high oxidizing activity even in a low temperature range. The higher the oxidizing activity, the higher the reducing activity. Therefore, the exhaust gas purifying catalyst of the present invention can efficiently oxidize and reduce HC, CO and NOx from a low temperature range and purify it. Although the reason why Pd enters a peroxidized state with a valence of more than 2 is not clear, it is considered that the oxygen storage / release capacity of ceria and the properties of Pd have a large effect.

The oxide having an oxygen storage and release capacity, ceria (CeO _2), rare earth metal oxides such as Pr0 _4, NiO, and Fe ₂ 0 _3, CuO, transition metal oxides such as Mn ₂ 0 ₅ and Mochiiruko Can be. Ceria is most preferred.

Studies to date have shown that if the carrier contains an oxide other than an oxide capable of storing and releasing oxygen, Pd will be in a normal divalent oxidation state. Therefore, it is desirable that the carrier is composed only of an oxide capable of storing and releasing oxygen. Therefore, when the coat layer is formed from the carrier powder as in the exhaust gas purifying catalyst described above, seria powder is used as the carrier powder, and serisol is used as the binder. Is most desirable.

The supported amount of Pd in the exhaust gas purifying catalyst of the present invention is preferably as large as possible, but even if it is supported too much, the catalytic activity is saturated and the cost increases. Therefore, the amount of Pd carried is preferably in the range of 0.1 to 20% by weight. If the amount is less than 0.1% by weight, it becomes difficult to exhibit the catalytic activity.

That is, according to the exhaust gas purifying catalyst of the present invention, HC, CO and NOx can be efficiently purified even in the exhaust gas in a low temperature range, and HC, CO and NOx can be purified in a wide temperature range. Further, the exhaust gas purifying catalyst of the present invention can be used alone, and is also preferably used as an oxidation / reduction catalyst used together with the HC adsorbent described above.

(Example)

Hereinafter, the present invention will be described specifically with reference to Test Examples, Examples, and Comparative Examples.

(Test Example 1)

Pt as the precious metal, chosen from the three types of Rh and Pd, A1 ₂ 0 ₃ and CeO ₂ - and it it carried on two carriers of Zr0 ₂ composite oxide was prepared six kinds of catalyst. The loading amount of each noble metal is 0.6% by weight of Pt, 0.6% by weight of Rh, and 0.6% by weight of Pd.

Using the two types of stoichiometric gases (1) and (2) shown in Table 1, the 50% CO purification temperature was measured for each catalyst. The results are shown in FIGS. The difference of the gas (1) and gas (2) is the presence of HC, and the results of catalyst the A1 ₂ 0 ₃ with the carrier in FIG. 1, in FIG. 2 CeO ₂ - of Zr0 ₂ was used as a supported catalyst The results are shown.

TABLE 1 Gas (1) HC, CO, 0 2, N 2 gas (2) CO, O2, N 2 gas (3) HC, CO, NO , C0 2, O2, N 2 From FIG. 1 and FIG. _{_2,} Ce0 2 _ Zr0 2 was carrying a carrier Toshikatsu Pd or Rh catalyst differs greatly good in purification activity of the presence of HC, is high very clean activity 'properties when HC is not present You can see that. However, it can also be seen that when Pt is supported, the purification activity is reduced in the absence of HC. And this phenomenon is not seen in the case of ALOs carriers.

(Example 1)

Ce0 _₂ - Zr0 ₂ prepared composite oxide powder (molar ratio Ce / Zr = 0.25 / 0.05) , carrying Pd by impregnation evaporated to dryness predetermined amount of an aqueous palladium nitrate solution having a predetermined concentration. The amount of Pd carried is 0.6% by weight.

Pd / CeOz- Zr0 ₂ powder was slurried in water, it was coated ceramic monolithic carrier substrate capacitance 1. 3 L. The coating amount is 200 g per liter of the monolithic carrier substrate. This was dried at 250 ° C for 15 minutes and calcined at 500 ° C for 1 hour to obtain an oxidation-reduction catalyst.

On the other hand, ZSM 5 (molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 40) was slurried to obtain a HC adsorbing material coated on a different monolithic carrier substrates in the same manner as described above. The coating amount is 150 g per liter of the monolithic carrier substrate.

Then, as shown in FIG. 3, an HC adsorbent 1 was disposed on the upstream side of the exhaust gas flow path, and an oxidation / reduction catalyst 2 was disposed on the downstream side of the HC adsorbent 1, thereby obtaining an exhaust gas purifying apparatus of the present embodiment.

Using the gas in the stoichiometric atmosphere (3) shown in Table 1, the 50% purification temperatures of HC, CO and NO were measured. Fig. 4 shows the results.

(Example 2)

An exhaust gas purifying apparatus of Example 2 was prepared in the same manner as in Example 1 except that an aqueous solution of nitric acid was used in place of the aqueous solution of palladium nitrate. The supported amount of Rh is 0.6% by weight.

Using the stoichiometric gas (3) shown in Table 1, the 50% purification temperatures of HC, CO and NO were measured. Fig. 4 shows the results.

(Comparative Example 1) ―

Example 3 is the same as Example 1 except that the oxidation-reduction catalyst prepared in Example 1 was arranged on both the upstream side and the downstream side in FIG. Then, as in Example 1, HC, CO and NO The 50% purification temperature was measured, and the results are shown in Figure 4.

(Comparative Example 2)

Example 3 is the same as Example 1 except that the oxidation-reduction catalyst prepared in Example 2 was arranged on both the upstream side and the downstream side in FIG. Then, the 50% purification temperature of HCO and NO was measured in the same manner as in Example 1, and the results are shown in FIG.

Evaluation>

As is evident from Fig. 4, by arranging the HC adsorbent on the upstream side, the 50% purification temperature is extremely low, and the purification activity is significantly improved. This is considered to be mainly due to the HC in the gas (3) being adsorbed and removed by the HC adsorbent on the upstream side.

(Example 3)

It prepared a composite oxide Ce0 _₂ -Zr0 ₂ powder (molar ratio Ce / Zr = 0.25 / 0.05) , carrying Pd by impregnating a predetermined amount of an aqueous palladium nitrate solution of Jo Tokoro concentration evaporation to dryness. The supported amount of Pd is 0.6% by weight.

The resulting Pd / Ce0 _₂ - Zr0 ₂ powder was slurried in water, it was coated ceramic monolithic carrier substrate capacity 1.3 L. The coating amount is g per liter of the monolithic carrier substrate, and 3 g of Pd is supported per liter of the monolithic carrier substrate. This was dried at 250 ° C for 15 minutes and calcined at 500 ° C for 1 hour to obtain an oxidation-reduction catalyst.

Meanwhile, in Y-type Zeorai preparative (molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 400) and ZSM 5 (a molar ratio _{_{Si0 2 / Al 2 0s = 40}} ) the weight ratio of 25: 75 to those混粉at a ratio of It was slurried, and was coated on another monolithic carrier substrate in the same manner as above to obtain an HC adsorbent. The coating amount is 150 g per liter of the monolith substrate.

(Example 4)

Example 3 with similarly prepared Pd / Ce0 _₂ - Zr0 ₂ powder was slurried and Seramidzukusu monolithic carrier base Oniko one preparative capacity 1.3 L. The coating amount is 200 g per 1 L of the monolith carrier substrate, and 3 g of Pd is carried per 1 L of the monolith carrier substrate. This was dried at 250 ° C for 15 minutes, and then baked at 500 ° C for 1 hour to obtain the reaction layer 3 shown in Fig. 5. -Formed.

Then, Y-type zeolite preparative (molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 400) and ZSM 5 (a molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 40) in a weight ratio of 25: and混粉75 ratio of The slurry was formed into a slurry, the surface of the reaction layer 3 was further coated, dried at 250 ° C. for 15 minutes, and then baked at 500 ° C. for 1 hour to form an adsorption layer 4 shown in FIG. The adsorption layer 4 was formed in an amount of 150 g per liter of the monolithic carrier substrate.

(Comparative Example 3)

The exhaust gas purifying apparatus of Comparative Example 3 was obtained in the same manner as in Example 4 except that the adsorption layer 4 was not formed.

(Example 5)

An exhaust gas purifying apparatus of Example 5 was prepared in the same manner as in Example 3 except that an aqueous solution of rhodium nitrate was used instead of the aqueous solution of palladium nitrate. The loading amount of Rh is 3 g per liter of the monolithic carrier substrate.

(Example 6)

An exhaust gas purifying apparatus of Example 6 was prepared in the same manner as in Example 4, except that an aqueous solution of rhodium nitrate was used instead of the aqueous solution of palladium nitrate. The loading amount of Rh is 3 g per liter of the monolithic carrier substrate.

(Comparative Example 4)

An exhaust gas purifying apparatus of Comparative Example 4 was obtained in the same manner as in Example 4, except that an aqueous solution of rhodium nitrate was used instead of the aqueous solution of palladium nitrate, and that no adsorption layer was formed.

(Comparative Example 5)

An exhaust gas purifying apparatus of Comparative Example 5 was prepared in the same manner as in Example 3 except that a dinitrodiammineplatinum nitric acid aqueous solution was used instead of the palladium nitrate aqueous solution. The supported amount of Pt was 3 g per liter of the monolithic carrier substrate.

(Comparative Example 6)

An exhaust gas purifying apparatus of Comparative Example 6 was prepared in the same manner as in Example 4, except that an aqueous solution of dinitrodiammineplatinic nitric acid was used in place of the aqueous solution of nordium nitrate. The supported amount of Pt is 3 g per liter of the monolithic carrier substrate. ί

(Comparative Example 7)

An exhaust gas purifying apparatus of Comparative Example 7 was obtained in the same manner as in Example 4, except that an aqueous solution of dinitrodiammineplatinic nitric acid was used instead of the aqueous solution of palladium nitrate, and that the adsorption layer 4 was not formed.

Each exhaust gas purification device was installed in the exhaust system of a 3.0-liter gasoline engine, and the temperature was raised at a rate of 10 ° C / min under the gas space velocity of 100,000h- ^1. The NOx and NOx purification rates were measured, and the respective 50% purification temperatures were determined. The results are shown in Figs.

From FIG. 8, it can be seen that when Pt is supported, almost the same purification performance is exhibited regardless of the presence or absence of the HC adsorbent, and it is hard to say that the purification performance is excellent. However, in the case of supporting Pd or Rh, it is clear that the purification activity is remarkably improved by combining HC adsorbents in series or in layers, which is the effect of the configuration of the present invention. It is clear that

(Test Example 2)

CeO and ₂ carrier, and the carrier carrying the 0.25 mole of CeO ₂ on A1 ₂ 0 ₃ with cerium nitrate, CeO _2, Zr0 ₂ and A1 ₂ 0 ₃ mixed carrier produced by a coprecipitation method (molar ratio Ce: Zr: Al = l: 1: 1) Three types of carriers were selected and subjected to an endurance test in which they were heated in air at each temperature for 5 hours. The specific surface of each carrier after the durability test was measured, and the relationship between the temperature and the specific surface area is shown in FIG.

From FIG. 9, A1 ₂ 0 ₃ on the CeO ₂ supported by the carrier and co-precipitation by the produced mixed responsible bodies, both showed a high specific surface area even after the durability as compared with CeO ₂ carrier, it is thermally stabilized You can see that

(Test Example 3)

The CeO ² powder and water were stirred, and zirconium nitrate was added thereto and evaporated to dryness. This was dried and calcined to dope 0.05 mol% of Zr. Next, three kinds of noble metals were selected from Pt, Rh and Pd, and supported on the Zr / CeO ₂ support to prepare three kinds of catalysts. The loading amount of each noble metal is 0.6% by weight of Pt, 0.6% by weight of Rh, and 0.6% by weight of Pd. Using the gases (3) shown in Table 1, the catalysts were measured for their 50% CO purification temperature. The results are shown in FIG.

From FIG. 10, it can be seen that the purification activity of the catalyst in which Pd or Rh is supported on the Zr / CeO ₂ carrier varies greatly depending on the presence or absence of HC, and is extremely high in the absence of HC. However, it can also be seen that when Pt is supported, the purification activity is reduced when HC is not present.

(Example 7)

Cerium nitrate, a mixed aqueous solution of zirconium nitrate and aluminum nitrate, to precipitate a precipitate by coprecipitation, it dried 'and then fired to prepare mixed powder of CeO _2, Zr0 ₂ and A1 ₂ 0 _3. The composition of this mixed powder is Ce: Zr: Al = 1: 1: 1: 1 in molar ratio.

Pd was supported on this mixed powder using an aqueous solution of palladium nitrate having a predetermined concentration. The supported amount of Pd is 1.6% by weight. The resulting catalyst powder was slurried and coated on a ceramic monolith carrier base material having a capacity of 1.3 L. The coating amount is 200 g per liter of the monolithic carrier substrate. This was dried at 250 ° C. for 15 minutes, and then baked at 500 ° C. for 1 hour to form a reaction layer 3 shown in FIG.

Then, Y-type Zeorai preparative (molar ratio ^{^{_{Si0 2 / Al 2 0 3 =}}} 400) and ZSM 5 (molar ratio SiOs / AL 0 ₃ = 40) in a weight ratio of 25: 75 to those混粉at a ratio of The slurry was slurried, further coated on the surface of the above reaction layer, dried at 250 ° C. for 15 minutes, and then baked at 500 ° C. for 1 hour to form an adsorption layer 4 shown in FIG. The adsorption layer 4 was formed in an amount of 150 g per liter of the monolithic carrier substrate.

(Example 8)

Using an aqueous palladium nitrate solution having a predetermined concentration, it was supported Pd to CeO ₂ powder. Except that this catalyst powder was used, a reaction layer 3 was formed in the same manner as in Example 7, and an adsorption layer 4 was formed in the same manner. The reaction layer 3 carries 3 g of Pd per liter of the monolithic carrier substrate.

(Comparative Example 8) "

An exhaust gas purifying apparatus of Comparative Example 8 was produced in the same manner as in Example 7, except that the adsorption layer 4 was not formed. <Test / Evaluation>

Mounting the exhaust gas purifying apparatus of Example 7, 8 and Comparative Example 8 in exhaust system 3. 0 L gasoline engine, gas space velocity Iotaomikuron'omikuron, under the conditions of Omikuron'omikuron'omikuron'iota ^1, raising the temperature at a 10 ° C / min rate The purification rates of HC, CO and NOx were measured, and the 50% purification temperature for each was determined. Figure 11 shows the results.

The exhaust gas purifiers of Examples 7 and 8 and the comparative example were mounted on the exhaust system of a 3.0 L gasoline engine, and a durability test was conducted in which the gas flow rate was 800 ° C for 100 hours. Then, for each catalyst device after the durability test, the 50% purification temperature was determined in the same manner as above, and the results are shown in FIG.

From FIG. 11, it is clear that the exhaust gas purifying devices of Examples 7 and 8 are much more active than Comparative Example 8, and it is clear that this is the effect of the configuration of the present invention. Also, there is no difference between Example 7 and Example 8.

However, looking at FIG. 12, it is clear that the catalyst device of Example 7 has higher purification performance than that of Example 8, and that the catalyst device of Example 7 is excellent in heat resistance. This is apparently due to the effect of using a mixed powder of CeO ₂ , ZrO _2, and A ₁₂ O ₃ prepared on the support by the coprecipitation method.

(Example 9)

Using the same oxidation / reduction catalyst as used in Example 1, it was installed in the exhaust system of a 2.2 L gasoline engine, and was driven in a lean atmosphere of A / F = about 15.0 for about 30 seconds from the start, After that, it was driven in the stoichiometric atmosphere of A / F = 14.5. The HC emissions were measured for 50 seconds from the start, and the results are shown in Figure 13.

(Example 10)

Using the same exhaust gas purifying apparatus as in Example 1, mounted on the exhaust system of a 2.2 L gasoline engine, it was driven in a lean atmosphere with an A / F of about 15.0 for about 30 seconds from the start, and then Was driven in a stoichiometric atmosphere with A / F = 14.5. The HC emissions were measured for 50 seconds from the start, and the results are shown in Figure 13.

(Comparative Example 9) ―

Using the same oxidation / reduction catalyst as that used in Example 1, mounted on a 2.2 L gasoline engine exhaust system, A / F = about 13.5 litz atmosphere for about 30 seconds from the start After that, it was driven in a stoichiometric atmosphere with A / F = 14.5. The HC emission was measured for 50 seconds from the start, and the results are shown in Figure 13.

From a comparison of Example 9 and Comparative Example 9 in FIG. 13, it is clear that the HC emission is reduced when the atmosphere is lean for about 30 seconds from the start, compared to when the atmosphere is rich. It is also clear from a comparison between Example 9 and Example 10 that it is particularly preferable to use the exhaust gas purifying apparatus of Example 1 and further provide a lean atmosphere for about 30 seconds from the start.

The same oxidation / reduction catalyst as that used in Example 1 was used, and the A / F of the air-fuel mixture was adopted at five levels from 12.0 to 16.0, and the HC50% purification temperature in each exhaust gas was adjusted. It was measured. The results are shown in FIG.

From FIG. 14, it can be seen that the higher the A / F of the mixture, that is, the leaner, the lower the HC50% purification temperature and the higher the purification activity. When the A / F is less than 13, the HC50% purification temperature sharply rises, and it is clear that it is desirable to set the A / F to 13 or more.

(Example 11)

Pt and Rh were supported on the HC adsorbent prepared in Example 1 using an aqueous dinitrodiammineplatinum solution and an aqueous rhodium nitrate solution. Per 100 g of HC adsorbent, 3 g of Pt was loaded and 1 g of Rh was loaded.

Using this Pt—Rh-loaded HC adsorbent and the same oxidation / reduction catalyst as used in Example 1, an exhaust gas purification device was constructed in the same manner as in Example 1. Using the gas (3) in the stoichiometric atmosphere shown in Table 1, the 50% purification temperatures of HC, CO and NO were measured. Figure 15 shows the results.

(Example 12)

Powder 50 parts by weight of the three-way catalyst Pt on alumina powder 100 g is formed by 3 g supported, ZS M- 5 (molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 40) were mixed with 100 parts by weight of the slurry one Then, the HC adsorbent prepared in Example 1 was subjected to a wet coating to form a three-way catalyst coat layer. The coat weight is 100 g per 100 g of HC adsorbent.

An HC adsorbent having this coat layer was oxidized and reduced in the same manner as that used in Example 1. An exhaust gas purifying apparatus was configured in the same manner as in Example 1 using the medium. Using the gas in the stoichiometric atmosphere (3) shown in Table 1, the 50% purification temperatures of HC, CO and NO were measured. The results are shown in FIG.

Fig. 15 also shows the results of the exhaust gas purification device of Example 1 (same as those shown in Fig. 4). As can be seen from Fig. 15, the exhaust gas purifying apparatus of Example 11 in which Pt-Rh is supported on the HC adsorbent and the exhaust gas purifying apparatus of Example 12 in which a three-way catalyst coat layer is formed on the HC adsorbent have further purification performance compared to Example 1. It is clear that it has improved.

(Test Example 4)

A predetermined amount of alumina powder was mixed with a predetermined amount of an aqueous solution of potassium acetate having a predetermined concentration, and evaporated to dryness to support K. The pellets were then pelletized to prepare the NOx adsorbent of Test Example 1. The loading amount of K is 0.1 mol per liter of alumina powder.

After weighing 2 g of this pellet-shaped NOx adsorbent, placing it in the evaluation device, performing a pretreatment of heating at 400 ° C for 30 minutes in a nitrogen gas stream, and cooling it to 40 ° C or less, Table 2 The model gas shown in Fig. 3 was allowed to flow for 30 minutes while flowing at a gas temperature of 100 ° C and a space velocity (S / V) of 100,000 / h. Then, the supply of model gas was stopped, and the amount of desorbed NOx when the temperature was raised to 100 to 500 ° C at a rate of 18 minutes was measured and determined as the NOx adsorption amount. Table 3 shows the results.

[Table 2]

(Test Example 5)

NOx B and a binder in Test Example 5 were prepared in the same manner as in Test Example 4 except that an aqueous solution of barium acetate was used in place of the aqueous solution of acetic acid-based realm. The supported amount of Ba is 0.1 mol per liter of alumina powder. The amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3. (Test Example 6)

The NOx adsorbent of Test Example 6 was prepared in the same manner as in Test Example 4, except that an aqueous lanthanum nitrate solution was used instead of the aqueous acetic acid solution. The amount of La carried is 0.1 mol per liter of alumina powder. The amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 7)

The NOx adsorbent of Test Example 7 was prepared in the same manner as in Test Example 4, except that zirconia powder was used instead of alumina powder. The loading of K is 0.1 mol per liter of zirconia powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 8)

The NO adsorbent of Test Example 8 was prepared in the same manner as in Test Example 4, except that zirconia powder was used instead of alumina powder, and an aqueous solution of barium acetate was used instead of the aqueous solution of acetic acid. The supported amount of Ba is 0.1 mol per liter of zirconia powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 9)

The N0 adsorbent of Test Example 9 was prepared in the same manner as in Test Example 4, except that zirconia powder was used in place of the alumina powder, and a racnic acid nitrate aqueous solution was used in place of the aqueous acetic acid aqueous solution. The supported amount of La was 0.1 mol per liter of zirconia powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 10)

A predetermined amount of Morudenai Doo (Si0 ₂ / A1 ₂ 0 ₃ molar ratio = 30) was Hitatsubushi powder in acetic acid potassium © anhydrous solution of a predetermined concentration, the K after drying and baking to filtered supported by ion exchange. Next, the NOx adsorbent of Test Example 10 was prepared by pelletizing. The supported amount of K is 0.1 mol per liter of mordenite powder. And in the same manner as in Test Example 4 were measured N0 _X amount desorbed and the results are shown in Table 3.

(Test Example 11) "

The NOx adsorbent of Test Example 11 was prepared in the same manner as in Test Example 10, except that an aqueous solution of barium acetate was used instead of the aqueous solution of acetic acid. Ba loading is mordenite 0.1 mol per liter of powder. The amount of desorbed NO was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 12)

The NOx adsorbent of Test Example 12 was prepared in the same manner as in Test Example 10, except that a lanthanum nitrate aqueous solution was used instead of the acetic acid aqueous solution solution. The amount of La supported is 0.1 mol per liter of mordenite powder. The amount of desorbed NO was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 13)

The NOx adsorbent of Test Example 13 was prepared in the same manner as in Test Example 10, except that an aqueous solution of cerium nitrate was used instead of the aqueous solution of acetic acid. The supported amount of Ce is 0.1 mol per liter of mordenite powder. The amount of desorbed NO was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 14)

Instead of Morudenai bets powder _{_{ZSM- 5 (Si0 2 / Al 2}} 0 3 molar ratio = 40) than with this with powder in the same manner as in Test Example 10, was prepared NOx adsorbent in Test Example 14. The loading amount of K is 0.1 mol per liter of ZSM-5 powder. The amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 15)

Morudenai bets instead of powder _{_{ZSM- 5 (Si0 2 / Al 2}} 0 3 molar ratio = 40) using a powder, except for using acetic acid Bariumu aqueous solution in place of acetic acid strength potassium aqueous solution in the same manner as in Test Example 10 The NOx adsorbent of Test Example 15 was prepared. The supported amount of Ba is 0.1 mol per liter of ZSM-5 powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

(Test Example 16)

Morudenai bets instead of powder _{_{ZSM- 5 (Si0 2 / Al 2}} 0 3 molar ratio = 40) using powder, except for using lanthanum nitrate solution in place of acetic acid force potassium solution in the same manner as in Test Example 10 The NOx adsorbent of Test Example 16 was prepared. The supported amount of La is 0.1 mol per liter of ZSM-5 powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Clothing 3. (Test Example 17)

Morudenai bets instead of powder _{_{ZSM- 5 (Si0 2 / Al 2}} 0 3 molar ratio = 40) using powder, except that nitric acid was used Seriumu aqueous solution in place of acetic acid force potassium solution in the same manner as in Test Example 10 The NOx adsorbent of Test Example 17 was prepared. The supported amount of Ce is 0.1 mol per liter of ZSM-5 powder. Then, the amount of desorbed NOx was measured in the same manner as in Test Example 4, and the results are shown in Table 3.

[Table 3]

Comparing the materials carrying the same type of metal, the amount of NOx adsorbed by the NOx adsorbent using zeolite as a carrier is remarkably large. In other words, since the metal supported on zeolite by ion exchange is in a highly dispersed state, the surface area of the metal is extremely large, the NOx adsorption site is increasing, and N0 on the metal is high. it has been pro-oxidant to the adsorption easily Nth or NO ³ is considered to be the reason.

(Example 13)

FIG. 16 shows the configuration of the exhaust gas purifying apparatus of the present embodiment. The exhaust gas purifying apparatus includes a NOx storage reduction catalyst 5 disposed in an exhaust gas passage, and a NOx storage reduction catalyst 5 upstream of the storage reduction catalyst 5. And a NOx adsorbent 6 arranged in the exhaust gas passage.

The NOx storage-reduction catalyst 5 is supported on a honeycomb carrier substrate (volume 1.7 liters) made of code daylight, a coat layer of alumina formed on the carrier substrate surface, and a coat layer. It consists of Pt and Ba. The coat layer is formed in an amount of 120 g per liter of the carrier substrate, 2 g of Pt is supported per liter of the carrier substrate, and 0.3 mol of Ba is supported per liter of the carrier substrate.

The NOx adsorbent 6, and Morudenai Doo (Si0 _₂ / Al ₂ 0 ₃ molar ratio = 30), consists of a La carried on Morudenai Bok, are formed in a pellet shape. The supported amount of La is 0.1 mol per liter of moldenite.

(Comparative Example 10)

Only the NOx storage-reduction catalyst 6 used in Example 13 was disposed in the exhaust gas flow path, and an exhaust gas purification device of this comparative example was obtained.

The exhaust gas purifying apparatus of Comparative Example 10 and Example 13 above, the lean model gas shown in Table 4 under the conditions of a space velocity 100,000 h ^1, enters gas temperature 40 ° C, 100 ° 200 ° 300. Flow at each of the four levels of C for 5 minutes, and then raise the temperature to 450 ° C at a heating rate of 18 ° CZ under the flow of the Litchi model gas shown in Table 4, and reduce the NOx purification amount during that time. It was measured. The results are shown in FIG. The NOx purification amount was calculated by the following equation.

NOx purification amount = total NOx amount in gas containing catalyst-total NOx amount after catalyst circulation

[Table 4]

As shown in FIG. 17, when the incoming gas temperature is 300 ° C., there is no difference between Example 13 and Comparative Example 10. However, when the incoming gas temperature is lower than 300 ° C., the exhaust gas purifying apparatus of Comparative Example 10 has a smaller NOx purification amount than that of Example 13, and the difference becomes larger as the incoming gas temperature is lower. In the exhaust gas purifying apparatus of the thirteenth embodiment, the incoming gas temperature is low. At the very least, the amount of NOx purification is large and the purification performance is stable from low to high temperatures. This is clearly the effect of the NOx adsorbent disposed upstream of the NOx storage reduction catalyst.

(Test Example 18)

Three types of catalysts were prepared in which 1 g of alumina supported 2 g of Pd and Rh, respectively, and as shown in Table 5, HC and HC in the flow of two types of model gas with or without NO as shown in Table 5 The purification rates of CO were measured respectively. The space velocity (S / V) of the model gas is 100,000 / h, and the purification rate at each temperature is measured while increasing the temperature from 28 ° C to 450 ° C at a rate of 18 ° CZ. The temperatures at which HC and CO were purified by 50% (50% purification temperature) were calculated. The results are shown in FIGS.

[Table 5]

From FIGS. 18 and 19, it can be seen that the absence of N0 lowers the 50% purification temperature of HC and C0 and improves the purification performance at low temperatures.

(Example 14)

A pellet-shaped NOx adsorbent with 0.06 mol% of Ce ion-exchanged on mordenite and a pelletized three-way catalyst with 1 g of alumina impregnated with 2 g of Pt were prepared, as shown in Fig. 20; As a result, 2 g of each of the evaluation devices was arranged in series. Then, under the flow of the model gas (stoichiometric) with N0 shown in Table 5, the 50% purification temperature of HC, CO and NOx was determined in the same manner as in Test Example 18. The results are shown in FIG.

(Example 15)

A powdery NOx adsorbent with 0.06 mol% of ion-exchanged Ce supported on mordenite and a powdered three-way catalyst with 2 g of Pt impregnated and supported on 1 L of alumina at a volume ratio of 1: The mixture was mixed into 1 and further pelletized. Then, the 50% purification temperature of HC, CO, and NOx was determined in the same manner as in Example 14, and the results are shown in FIG.

(Comparative Example 11) The 50% purification temperature of HC, CO and NOx was determined in the same manner as in Example 14 except that only the three-way catalyst was used without using the NOx adsorbent. The results are shown in FIG.

From Fig. 21, it is clear that in the purification devices of Examples 14 and 15, the 50% purification temperature of HC, CO and NOx is lower than that of Comparative Example 11, and the purification performance at low temperatures is improved. It is. Further, since the value of Example 14 is lower than that of Example 15, it is understood that it is preferable to arrange the NOx adsorbent and the three-way catalyst in series rather than mixing them.

(Test Example 19)

Next, the adsorption and release characteristics of various NOx adsorbents were investigated. As NOx adsorbents, one in which 0.06 mol% of Ce was ion-exchanged and supported on moldenite, one in which 0.06 mol% of ion-exchanged Cu was supported on ZSM-5, and one in which 0.06 mol% of Ba was ion-exchanged and supported on mordenite _{_{_{, Co 3 0 4, Mn0 2}}} , Zr0 2, Zr0 2 those LOG / L impregnated support Pt in, Mg0, with nine but was 0.3 mol / L impregnation with 2 g / L and Ba to Pt on alumina .

The adsorption characteristics were as follows: 2 g of NOx adsorbent in the form of pellets were placed in the evaluation device, and the model gas in the lean atmosphere shown in Table 6 was applied at 100 ° C at space velocity (S / V) = 100,000 / h. The amount of NOx adsorbed after flowing for 30 minutes was measured. Table 7 shows the results.

The release characteristics were measured by measuring the amount of NOx released while raising the temperature at a rate of 17.5 ° 〇 min under a stream of N ₂ , and the temperature at which it reached its maximum value (NOx desorption beak temperature). The temperature at the end of NOx emission (end temperature) was determined. Table 7 shows the results.

[Table 6]

[Table 7]

As a NOx adsorbent, a regenerative performance that repeats NOx adsorption and NOx release is necessary, and a material with a too high NOx desorption temperature is not preferable. Thus, in Table 7, MgO and Pt · Ba / Al ₂ 0 ₃ is less preferred. Since addition N0 _X adsorption amount is, the more virtuous preferable, in the NOx-absorbing material described above, such as _{_{Ce / Mor30, Co 3 0 4}} , Mn0 2, Pt / Zr 0 2, MgO is particularly preferred material.

(Example 16)

Therefore, pelletized NOx adsorbent composed of Ce / Mor30 with 0.06 mol% Ce ion-exchange supported on mordenite and pelletized three-way catalyst with 2 g of Pt supported on 1 L alumina were prepared. As shown in Table 2, 2 g were placed in series on the evaluation device. Then, under the flow of the model gas in the lean atmosphere shown in Table 6, the NOx was adsorbed by holding at 100 ° C for 5 minutes as shown in Fig. 22, and then 400 ° C at a heating rate of 17.5 ° C / min. The NOx purification amount when the temperature was raised to C was measured. The same test was performed again, and the first and second results are shown in Figure 23.

The NOx purification amount was shown as the difference between the total NOx amount in the incoming gas and the total NOx amount in the outgoing gas during the evaluation pattern in Fig. 22.

(Example 17)

Prepared Peretsuto shaped N0 _X adsorbent consisting of MgO in place of Ce / Mor30, was measured NOx purification amount in the same manner as in Example 16. The results are shown in FIG.

<Evaluation> As shown in FIG. 23, in Example 17, the difference between the first time and the second time was large, and the NOx purification amount decreased due to repetition. This is considered to be because the amount of NOx released from the NOx adsorbent was smaller than that in Example 16, and the amount of NOx adsorbed during the second test was smaller. Therefore, under the above test conditions, it can be said that Ce / Mor30 is more preferable than MgO as the adsorbent.

(Test Example 20)

As the NOx adsorbent, Ce / Mo r30 was 0.06 mol% ion exchange carries a Ce to Morudenai DOO, CeO ₂ Select and Fe ₂ 0 ₃ of 3 types, different presence of 0 ₂ As shown in Table 8 2 The amount of NOx adsorbed under the flow of various model gases was measured. The space velocity (S / V) of the model gas was 100,000 / h, and the amount of NOx adsorbed when flowing at an incoming gas temperature of 100 ° C for 30 minutes was measured. The results are shown in FIG.

[Table 8]

As apparent from FIG. 24, it can be seen that the NOx adsorption amount is increased to rated stage by using a model gas containing 0 _2. This is the following reaction occurs in the NOx adsorbent surface, N0 is considered to be due to the improved absorptive by being converted to N0 _2.

N0 + 1/20 ₂ → N0 ₂

(Example 18)

Therefore, a pellet-shaped NOx adsorbent composed of Ce / Mor30 with 0.06 mol% of ion-exchanged Ce supported on mordenite and a pellet-shaped three-way catalyst with 2 g of Pt supported on 1 L of alumina were prepared. As shown in FIG. 20, 2 g was arranged in series in the evaluation device. Then, under the flow of the lean model gas with O2 shown in Table 8, the NOx was absorbed at 100 ° C for 5 minutes as in Fig. 22, and then 450 ° C at a rate of 17.5 ° C / min. The NOx purification amount when the temperature was raised to ° C was measured. The results are shown in FIG.

(Example 19) Except that the 0 ₂ Yes model gas shown in Table 8 was used a model gas having a composition excluding the 0 ₂ in the same manner as in Example 18 was measured NOx purification amount. The results are shown in FIG.

(Comparative Example 12)

The amount of purified NOx was measured in the same manner as in Example 18 except that only the three-way catalyst was used without using the NOx adsorbent. The results are shown in FIG.

From FIG. 25, Example NOx purification amount is greatly reduced as compared to 19 In Example 18, this is by using a model gas containing no 0 _2. Further, as in Comparative Example 12, the amount of N0 _X purified by the three-way catalyst alone is small even in the presence of O ₂ .

Therefore, the effect due to the presence of 0 ₂ is found to be obtained only by the coexistence of the NOx adsorbent and a three-way catalyst. When the light of the results of the above test example, show a high NO conversion weight Example 18, it is apparent that the NOx adsorption amount is resulted from the increased by 0 ₂ is present.

(Test Example 21)

As the NOx adsorbent, and Perez bets like Ce / Mor30 was 0.06 mol% ion exchange carries a Ce to Morudenai Bok, Pt and is 2 g impregnated supported pelletized Pt / Zr0 ₂ in Zr0 ₂ volume 1 L, select three to that using the above Ce / Mor30 and Pt / Zr0 ₂ in series, the NOx adsorption amount in the distribution of a 0 2 Yes lean model gas shown in Table 8 was it that measurements. The space velocity (S / V) of Delgas was 100,000 / h, and the NOx adsorption amount was measured when the incoming gas temperature was flown at three levels of room temperature, 100 ° C and 200 ° C for 30 minutes. . The results are shown in FIG.

From FIG. 26, Ce / Mor30 have many N0 _X adsorption at room temperature ~ 100 ° C, Pt / Zr0 2 has many NOx adsorption amount at 100 to 200 ° C. It can be seen that the combination of the two can secure a stable NOx adsorption amount in a wide temperature range from room temperature to 100 ° C.

(Example 20)

Therefore, a pellet-shaped NOx adsorbent consisting of Ce / Mor30 with 0.06 mol% of ion-exchanged Ce supported on mordenite and a pellet-shaped three-way catalyst with 2 g of Pt supported on a 1 L alumina volume were prepared. As shown in FIG. 20, 2 g each was placed in series on the evaluation device. The 0 ₂ Yes gas (lean shown in N0 Yes strike I key model gas and table 8 shown in Table 5 As shown in Fig. 27, the temperature is maintained at room temperature for 10 minutes under the flow of lean model gas, and the temperature is increased up to 100 ° C at a rate of 17.5 ° C / min under the flow of stoichiometric model gas. At a temperature of 100 ° C for 10 minutes under the flow of lean model gas, and then at a heating rate of 17.5 ° C / min to 200 ° C under the flow of stoichiometric gas to increase the lean model gas. The temperature was kept at 200 ° C for 10 minutes under the flow of, and the NOx purification rate was measured when the temperature was raised to 450 ° C at a rate of 17.5 ° C / min under the flow of stoichiometric gas. Space velocity (S / V) is 100,000 / h. The results are shown in FIG.

The NOx purification rate is indicated by the ratio of the total NOx in all outgoing gases to the total NOx in all incoming gases under evaluation.

(Example 21)

Instead of Ce / Mor30, except that the Zr0 ₂ volume 1 L Pt was used 2 g supported pelletized Pt / Zr0 ₂ in the same manner as in Example 20 was measured NOx purifying ratio. Figure 28 shows the results.

(Example 22)

Instead of Ce / Mor30, except to the arrangement of the Pt / Zr 0 ₂ used in Ce / Mor30 Example 21 used in Example 20 in series one by 1 g in the same manner as in Example 20, NOx purification rate Was measured. The results are shown in FIG. Incidentally, Ce / Mor30 is upstream, Pt / Zr0 ₂ is disposed on the downstream side.

From FIG. 28, purifier of two N0 Example 22 that combines _X adsorbent shows a high extremely NOx purification rate. This is due to the fact that the use of two types of NOx adsorbents with different temperature ranges showing the maximum amount of NOx adsorbed resulted in stable and high NOx adsorbability from room temperature to 200 ° C.

(Test Example 21)

The adsorption characteristics of various NOx adsorbents based on ZrO ² were investigated. The NOx adsorbent, 1 0 _2, Li ₂ 0 is 0.1 mol% the added Zr0 _{_2,} Zr0 Na ₂ 0 was added 0.1 mol% _2, K ₂ 0 is 0.1 mol% the added Zr0 _{_2,} Cs ₂ 0 is Zr0 _2, MgO was added 0.1 mol% was used 0.1 mol% the added Zr0 ₂ of six.

The adsorption characteristics were determined by placing 2 g of a belt-shaped NOx adsorbent on the evaluation device The NOx adsorption amount was measured when flowing nitrogen gas containing 600 ppm at a space velocity (S / V) of 100,000 / h at 40 ° C for 30 minutes. The results are shown in FIG.

From FIG. 29, ZrO ² or Ranaru NOx adsorbent oxides of various Al force Li metal and Al force Li earth metal is added, many N0 _X adsorption than only Zr0 _2, of 40 ° C It can be seen that good NOx adsorption characteristics are exhibited even at low temperatures.

(Test Example 22)

The adsorption properties of Zr0 ₂ based various NOx adsorbent was further investigated. The NOx adsorbent, Zr0 ₂ Zr0 ₂ those 2 g / L impregnated support Pt in, that Li ₂ 0 is 2 g / L impregnated support Pt in ₂ Zr0 which is added 0.1 mol%, Na ₂ 0 is which ZrO 2 Na ₂ 0 was added 0.1 mol% was 2 g / L impregnated support Pt in ₂ Zr0 which is added 0.1 mol%, K ₂ 0 is 0.1% by mole the added Zr0 ₂ 2 a Pt in g / L obtained by impregnation, Cs ₂ 0 were used seven but was 2 g / L impregnated support Pt in ₂ Zr0 which is added 0.1 mol%.

The adsorption characteristics were as follows: 2 g of NOx adsorbent in the form of pellets were placed in the evaluation device, and the gas shown in Table 8 was replaced with a gas-free gas (stoichiometric model gas) at space velocity (S / V) Then, the NOx adsorption amount when flowing at 100 ° C for 30 minutes was measured. The results are shown in FIG. From FIG. 30, various alkali metal NOx adsorbent further loading Pt on Zr0 ₂ was added, the ones only Zr0 _2, obtained by supporting Pt on Zr0 _2, and Zr0 ₂ material obtained by adding alkali metal oxides It is clear that the amount of NOx adsorbed is further increased compared to

(Example 23)

So prepared and Perez preparative shape of the NOx adsorbent consisting of Zr0 _2, the Peretsuto shaped three-way catalyst Pt was 2 g supported on alumina volume 1 L, series one by 2 g in the evaluation device as shown in FIG. 20 Was placed. Then, using the stoichiometric model gas with NO shown in Table 5 and the gas (lean model gas) shown in Table 8, the heating rate was 5 ° C / min under the flow of the lean model gas as shown in Figure 31. The temperature was then raised to 100 ° C, and then the NOx purification rate was measured when the temperature was raised to 450 ° C at a rate of 18 ° C / min under the flow of stoichiometric gas. The results are shown in FIG.

(Example 24) ―

Zr0 ₂ in place, except for the use of pellet-like NOx adsorbent K ₂ 0 is formed of Zr0 ₂ which are added 0.1 mol% in the same manner as in Example 23 was measured NOx purifying ratio. result Is shown in FIG.

(Example 25)

Zr0 ₂ in place, except for using K ₂ 0 is 0.1 mol% the added Zr0 ₂ more Pt is 2 g / L supported pellets of the NOx adsorbent in the same manner as in Example 23 The NOx purification rate was measured. The results are shown in FIG.

(Comparative Example 13)

The NOx purification rate was measured in the same manner as in Example 23 except that only the two-way catalyst was used without using the NOx adsorbent. The results are shown in FIG.

From FIG. 32, improves Example 23, 24, 25 and turn NOx purification rate, which, Zr0 ₂ only by a material obtained by adding remote K ₂ 0, NOx adsorbent that further loading Pt on it than This is due to the excellent NO adsorption capacity.

(Example 26)

Ceria powder, ceria sol and distilled water were placed in a container and milled for 2 hours with a ball mill to prepare a slurry. Next, a cordierite honeycomb base material was prepared, dipped in a slurry, pulled up, blown off excess slurry, dried at 120 ° C, and fired at 250 ° C. This process was repeated to form a coat layer of 240 g per liter of the honeycomb substrate, and finally fired at 500 ° C. The coat layer contains 30% by weight of ceria sol.

Next, a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration was absorbed into a honeycomb substrate having a coat layer, and dried and calcined to support Pd. 2 g of Pd was supported as metallic Pd per liter of the honeycomb substrate.

Mounting the exhaust gas purifying catalyst of Example 26 2.5 to the exhaust system of a gasoline engine of L, the gas space velocity Iotaomikuron'omikuron, under the conditions of ΟΟΟΙΓ ^1, while raising the temperature at a 10 ° C / min rate, HC, CO及Beauty The NOx purification rates were measured and the 50% purification temperature for each was determined. The results are shown in FIG.

(Comparative Example 14)

Exhaust gas purification catalysts were prepared in the same manner as in Example 26 except that alumina sol was used instead of serisol, and the 50% purification temperature was determined in the same manner. The results are shown in FIG.

(Comparative Example 15) An exhaust gas purifying catalyst was prepared in the same manner as in Example 26 except that zirconazole was used instead of celisol, and the 50% purification temperature was determined in the same manner. The results are shown in FIG. '(Comparative Example 16)

Exhaust gas purification catalyst was prepared in the same manner as in Example 26 except that silica sol was used instead of ceria sol, and the 50% purification temperature was determined in the same manner. The results are shown in FIG.

(Comparative Example 17)

An exhaust gas purifying catalyst was prepared in the same manner as in Example 26, except that titania sol was used instead of ceria sol, and the 50% purification temperature was similarly set. The results are shown in FIG.

(Evaluation)

As can be seen from Fig. 33, the exhaust gas purifying catalyst of Example 26 has a remarkably lower 50% purification temperature than each of the comparative examples, and the difference from the catalyst of Comparative Example 14 is approximately 200 ° C, and the activity in the low temperature region is significantly improved. It is clear that you are.

(Test Example 23)

In order to investigate the cause of the high performance of the catalyst of Example 26, four types of carriers, alumina, ceria, ceria-zirconia composite oxide, and a mixture of alumina and ceria-zirconia composite oxide were used as carriers, and Pd Each catalyst was prepared by evaporating to dryness. Then, XPS analysis was performed for each of the catalysts, and the state of the supported Pd was investigated.

Then, as shown in FIG. 34, Pd supported on alumina has a peak at a position where the binding energy is low, and Pd exists as PdO in a divalent oxidation state. However, it supported Pd on a carrier containing Seria, binding energy-saving one compared to Pd supported on alumina is shifted to the higher energy side and on the valence of the peroxide state more than divalent Pd0 ₂ levels It became clear. In particular, it can be said that most of Pd supported only on ceria is in a peroxide state. And Pd in such a peroxidized state is considered to act as a strong oxidizing agent.

Therefore, it is considered that the catalyst of Example 26 had extremely high oxidation activity because Pd was supported in a peroxidized state having a valence of more than two.

(Example 27)

Next, as shown in FIG. 35, a catalyst 8 supporting Pd on ceria was provided downstream of the HC adsorbent 7. The 50% purification temperature of C, CO and NOx was measured.

The honeycomb substrate surface of 300 cc, the coating layer made of a molar ratio Si0 _₂ / Al ₂ 0 ₃ = 2000 ZSM 5 and 40 g and the molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 400 Y -type Zeorai DOO 20 g The material on which was formed was designated as the HC adsorbent 7 in the preceding stage. The honeycomb substrate LOOOcc (a ceria sol as a binder) CeO ₂ was 360 g coated, it those carrying Pd of 5 g was later stage of the catalyst 8.

The catalytic device 2.5 is mounted in the exhaust system of a gasoline engine of L, the gas space velocity 10 Omicron, under the conditions of Omikuron'omikuron'omikuron'iotaganma ^1, while raising the temperature at a 10 ° C / min rate, measuring the purification rate of H C0 and NOx Then the 50% purification temperature was determined. The results are shown in FIG.

As a result, this catalyst device did not exhibit the expected performance.

(Test Example 24)

Therefore using a Pd / CeO ₂ catalyst used in Example 27, C050% purification using a model gas containing CH _4, C ₂ H _4, each HC of C ₃ H ₆ and C ₃ H ₆ in which it various concentrations The temperature was measured for each. The results are shown in FIGS.

From FIG. 37~40, Pd / Ce0 ₂ catalyst activity decreases greatly, especially by the presence of C ₃ H _6, revealed that poisoning is caused by the C ₃ H _6.

(Test Example 25)

Therefore, if adsorb C ₃ H ₆ upstream of the HC adsorbent, it is expected to improve the low-temperature activity of Pd / CeO ₂ catalyst.

Therefore, the C ₃ H ₆ adsorption characteristics of various zeolite at room temperature were investigated. The results are shown in FIG. As can be seen from FIG. 41, ZSM-5 is particularly excellent in adsorbing C ₃ H ₆ . This is thought to be because the molecular diameter of (4.89Α) and the pore size of ZSM-5 (5.5Α) are similar.

However, even with 5, the adsorption amount of C ₃ H ₆ is less than 2 X 10- ⁴ mole, it can not be said sufficient.

Therefore, the use of ZSM-5 carrying various metals by ion exchange was recalled, and the supported metal species were examined. That is, 2 g of each of the metals shown in No. 42 was carried on 100 g of ZSM-5, and the adsorption amount of C ₃ H ₆ at 200 ° C. was measured. The results are shown in FIG. As shown in Fig. 42, the adsorption capacity of C ₃ H ₆ can be significantly improved by carrying A on ZSM-5 by ion exchange. It is clear that

The larger the amount of Ag ion-exchange supported, the better the HC adsorption ability. Therefore ZSM- the Si0 _₂ / Al ₂ 0 ₃ molar ratio of 5 is more than 200, since the amount of supported Ag too small ion exchange sites may be insufficient, Si0 _₂ / Al ₂ 0 ₃ molar ratio of 200 It is desirable to use the following ZSM-5. However Si0 _₂ / Al ₂ 0 ₃ molar ratio than drops is extremely small becomes, the heat resistance, Si0 _₂ / Al ₂ 0 ₃ molar ratio is preferably used over 20 ZSM 5. Those having Si0 ₂ / Al ₂ O ₃ = about 40 are particularly preferred.

(Example 28)

Therefore, coating the molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 40 of ZSM 5 powder 60 g were 100% I O-exchange loading Ag on ion-exchange sites Bok of the honeycomb substrate surface 300 cc, this HC Except for using as an adsorbent, the 50% purification temperature of HC, CO and NOx was determined in the same manner as in Example 27. Ag loading is about 12% by weight. The results are shown in FIG.

(Example 29)

The coated molar ratio _{_{_{Si0 2 / Al 2 0 3 =}}} 70 powder 60 g of ZSM- the ion exchange sites of the 5 and lifting 100% ion-exchange換担A in the honeycomb substrate surface of 300 cc, which HC adsorbent A 50% purification temperature of HC, CO, and NOx was determined in the same manner as in Example 27 except that the temperature was reduced. Ag loading is about 7% by weight. The results are shown in FIG.

(Evaluation)

According to Fig. 36, the catalytic devices of Examples 28 and 29 have significantly improved low-temperature activity compared to the catalytic devices of Example 27. This is due to the effect of arranging the HC adsorbent made of ZSM-5 carrying Ag ion exchange. It is clear that

Claims

The scope of the claims .

1. The hydrocarbon concentration in the exhaust gas is reduced to low HC exhaust gas, and the oxygen storage / release material is brought into contact with an oxidation / reduction catalyst supporting at least one of rhodium and palladium and the low HC exhaust gas. Exhaust gas purification method.

2. The low HC exhaust gas according to claim 1, wherein the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is controlled to a fuel-lean atmosphere of 13 or more. 2. The exhaust gas purification method according to item 1.

3. Exhaust gas purification characterized by comprising a hydrocarbon adsorbent and an oxidation / reduction catalyst in which at least one of rhodium and palladium is supported on an oxygen storage / release material.

4. The powder according to claim 3, wherein a powder of the hydrocarbon adsorbent and a powder of an oxidation / reduction catalyst in which at least one of rhodium and palladium is supported on the oxygen storage / release material are mixed. Exhaust gas purifying apparatus according to Item. '

5. An adsorption layer composed of a powder of a hydrocarbon adsorbent, and a reaction layer composed of a powder of an oxidation-reduction catalyst in which at least one of rhodium and palladium is supported on an oxygen storage / release material, 4. The exhaust gas purifying apparatus according to claim 3, wherein the adsorption layer and the reaction layer are laminated.

6. The exhaust gas purifying apparatus according to claim 5, wherein the reaction layer constitutes a lower layer, and the adsorption layer is stacked on the reaction layer.

7. A hydrocarbon adsorbent disposed on the upstream side of the exhaust gas channel, and an oxidation / reduction catalyst disposed downstream of the hydrocarbon adsorbent and supporting at least one of rhodium and palladium on the oxygen storage / release material, 4. The exhaust gas purifying apparatus according to claim 3, comprising:

8. The exhaust gas purifying apparatus according to claim 3, wherein the oxygen storage / release material is cerium oxide (ceria).

9. The exhaust gas purifying apparatus according to claim 3, wherein the oxygen storage / release material is thermally stabilized. '

10. The exhaust gas purifying apparatus according to claim 9, wherein the cerium oxide is thermally stabilized by being supported on alumina.

11. The exhaust gas purifying apparatus according to claim 9, wherein the cerium oxide is thermally stabilized by doping zirconium.

12. The exhaust gas purifying apparatus according to claim 9, wherein the cerium oxide is thermally stabilized by dissolving zirconium in cerium oxide or forming a composite oxide.

13. The exhaust gas purifying apparatus according to claim 9, wherein zirconium is highly stabilized by being highly dispersed in cerium oxide.

14. The exhaust gas purifying apparatus according to claim 9, wherein the oxide is manufactured by a coprecipitation method, and is stabilized by heat.

15. The exhaust gas purifying apparatus according to claim 3, wherein the hydrocarbon adsorbent carries a noble metal.

16. The exhaust gas purifying apparatus according to claim 15, wherein the noble metals are platinum and rhodium.

17. The oxidation / reduction catalyst comprises a carrier made of ceria and palladium supported on the carrier in a peroxidized state having a valence of more than two, and the hydrocarbon adsorbent ion-exchanges silver for silver. 4. The exhaust gas purifying apparatus according to claim 3, wherein the exhaust gas purifying apparatus is ZSM-5.

1 8. The Si0 _₂ / Al ₂ 0 ₃ molar ratio exhaust gas purifying apparatus according to the first item 7 claims, characterized in that 200 or less.

1 9. An exhaust gas purification method characterized by lowering the concentration of nitrogen oxides in exhaust gas to obtain low NOx exhaust gas, and contacting the exhaust gas purification catalyst comprising a porous oxide with a noble metal and the low NOx exhaust gas. .

2 0. And the porous oxide in an exhaust gas purifying catalyst obtained by loading a noble metal, it is more and N0 _X adsorbent is disposed in the vicinity of the catalyst for exhaust gas purification to adsorb nitrogen oxides, Oite low temperature zone The exhaust gas in which the nitrogen oxides contained are adsorbed by the NOx adsorbent is brought into contact with the exhaust gas purifying catalyst, and in a high temperature region, the exhaust gas containing the nitrogen oxides released from the NOx adsorbent is discharged into the exhaust gas purifying catalyst. An exhaust gas purifying apparatus characterized by being configured to be brought into contact with the exhaust gas. '

21. The NOx adsorbent is at least one selected from the group consisting of oxides and zeolites of elements selected from alkali metals, alkaline earth metals, rare earth elements and transition metals. The exhaust gas purifying apparatus according to claim 20, characterized in that:

22. The exhaust gas purifying apparatus according to claim 20, wherein the NOx adsorbent is zirconia to which at least one selected from an alkali metal and an alkaline earth metal is added.

23. The exhaust gas purification apparatus according to claim 20, wherein the NOx adsorbent carries at least one selected from a transition metal oxide and a noble metal.

24. The exhaust gas purifying apparatus according to claim 20, further comprising an oxygen supply device that supplies oxygen upstream of said NOx adsorbent when said exhaust gas purifying catalyst is at or below an activation temperature.

25. The exhaust gas purifying apparatus according to claim 20, wherein the NOx adsorbent is composed of a plurality of types of NOx adsorbents having a maximum amount of nitrogen oxide adsorbed depending on a temperature. apparatus.

26. A porous oxide carrier, a noble metal supported on the porous oxide carrier, and an alkaline metal, an alkaline earth metal, and a rare earth element, which are supported on the porous oxide carrier A nitrogen oxide storage element and a NOx storage reduction catalyst consisting of

A NOx adsorbent comprising a metal element selected from an alkaline metal, an alkaline earth metal and a rare earth element supported on a porous oxide carrier is disposed upstream of the NOx storage reduction catalyst in the exhaust gas channel. An exhaust gas purifying device characterized by the following.

27. The NOx adsorbent, wherein at least one metal element selected from an alkali metal, an alkaline earth metal, and a rare earth element is ion-exchanged and supported on zeolite, wherein the NOx adsorbent is ion-exchanged and supported on zeolite. An exhaust gas purifying apparatus according to claim 1.

28. The exhaust gas purifying apparatus according to claim 27, wherein the porous oxide carrier of the NOx adsorbent is zeolite.

29. An exhaust gas purifying catalyst comprising: a carrier made of an oxide having an oxygen storage / release capability; and a paradium supported on the carrier in a peroxidized state having a valence of more than two.

30. The discharge according to claim 29, wherein the carrier is ceria. Gas purification catalyst. '

31. A carrier substrate, a coat layer formed on the carrier substrate and containing an oxide having oxygen storage / release capability, and palladium carried on the coat layer, wherein the coat layer is in the form of ultrafine particles. An exhaust gas purifying catalyst, wherein the catalyst is combined with ceria.

32. The oxide is ceria, the coat layer is composed only of ceria, and palladium is supported on the coat layer in a peroxidized state having a valence of more than two. An exhaust gas purifying catalyst according to item 31.

33. a step of preparing a slurry from an oxide powder having an oxygen storage / release capability, ceria sol, and water;

A method for producing an exhaust gas purifying catalyst, comprising: attaching a slurry to a carrier substrate; drying and baking to form a coat layer; and supporting palladium on the coat layer.

34. a step of preparing a catalyst powder in which palladium is supported on an oxide powder having an oxygen storage / release capability;

Preparing a slurry from the catalyst powder, ceria sol and water,

A step of attaching the slurry to a carrier substrate, drying and firing to form a coat layer.

34. An exhaust gas purification method comprising contacting an exhaust gas with a reduced hydrocarbon concentration with the exhaust gas purification catalyst according to any one of claims 29 to 32.