JPH11221466A - Catalyst for purifying exhaust gas and purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst for purifying exhaust gas which can improve an NOx purification capacity even in a low temperature area and in a low HC/NOx ratio and control deterioration even under high temperature hydrothermal conditions, and to provide a method for purifying exhaust gas. SOLUTION: A catalyst containing zeolite is arranged in a preceding stage to an exhaust gas flow, and a catalyst which consists of a first catalyst layer containing at least one component selected from the group consisting of platinum(Pt), palladium(Pd), and rhodium(Rh) and at least one component selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, a second catalyst layer containing alumina and/or silica, and a third catalyst layer containing a copper (Cu) component and/or a cobalt (Co) component and in which the first, second, and third catalyst layers are overlaid in turn, is arranged in a succeeding stage to the exhaust gas flow. Appropriately, a catalyst for purifying exhaust gas is used for an internal combustion engine in which the air/fuel ratio of exhaust gas is at the lowest 14.7, an oxygen concentration is at the lowest 5%, and an HC/NOx ratio is at the highest 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying method, and more particularly to an exhaust gas purifying catalyst for purifying nitrogen oxides (NO _x ) in exhaust gas containing excess oxygen with high efficiency. And a method for purifying exhaust gas.

[0002]

2. Description of the Related Art A three-way catalyst is generally widely used as a catalyst for purifying an exhaust gas containing an oxidation component and a reduction component substantially equal to each other, such as a conventional automobile engine exhaust gas. These are platinum (Pt), palladium (P
d), noble metal components such as rhodium (Rh) and ceria (C
e) a catalyst composed mainly of supported activated alumina various metal components of the components or the like, to purify a harmful components hydrocarbons (HC) such in the exhaust gas, carbon monoxide (CO) and NO _x Can be.

On the other hand, in recent years, from the viewpoint of improving fuel efficiency and reducing carbon dioxide emissions, a lean burn engine that can be operated even at an air-fuel ratio higher than the stoichiometric air-fuel ratio has attracted attention. The exhaust gas of such an engine (hereinafter, referred to as "lean exhaust gas") has a higher oxygen content than the exhaust gas of a conventional engine operating near the stoichiometric air-fuel ratio (hereinafter, referred to as "stoichiometric exhaust gas"). rate is high, the purification of the NO _x becomes insufficient in the conventional three-way catalyst. Therefore, new catalyst that can purify the NO _x in lean exhaust gas with high efficiency is desired.

[0004] Various metallic components Y type, L-type, mordenite, zeolite-supported zeolite-based catalyst such as MFI zeolite, the presence of HC classes in a lean exhaust gas, the ability to relatively efficiently purify NO _x have. Such metal components include copper (Cu), cobalt (Co), silver (Ag), nickel (Ni), and iron (Fe).
And noble metal components such as platinum (Pt) have also been found to be effective.
u- zeolitic catalysts, to indicate a relatively good _the NO _x purification performance even at a high flow rate gas conditions, for application to the exhaust gas purification of small mobile sources and stationary private power generation engine such as an automobile Expectations are over.

However, a zeolite-based metal component is supported.
The catalyst has the following problems. In other words, conventional zeorai
Catalyst is NO_xTemperature range that can relatively efficiently purify
The surrounding area is narrow, especially the relatively low temperature range of 150 ° C to 300 ° C.
NO in the area_xPurification capacity cannot be obtained, and exhaust gas
Under relatively low levels of HCs, especially under NO _xAnd H
C reacts and NO_xNecessary to convert nitrogen into nitrogen
Classification and NO_xRatio to the amount (HC / NO_xRatio) is 5-6 or less
Under the conditions below, NO_xPurification capacity has dropped sharply
I will. On the other hand, high temperature (600 ° C or higher)
Under conditions (hydrothermal conditions), catalyst degradation is extremely large
Because of a fundamental problem, lean burn
Has not yet been put into practical use as an exhaust gas purification catalyst
Is the current situation.

Accordingly, in order to improve the NO _x purification ability in the low temperature region, for example, by providing a noble metal catalyst layer below the Cu-zeolite catalyst layer, the reaction heat of the noble metal catalyst layer is utilized. It has been proposed to operate the upper Cu-zeolite catalyst from a low temperature (Japanese Patent Application Laid-Open Nos. 1-127044 and 5-68888).

However, in this case, the heat of the oxidation reaction in the lower noble metal catalyst layer causes a large deterioration of the catalyst, and the strong oxidation activity of the noble metal catalyst layer causes the preferential oxidation and consumption of HC by the noble metal catalyst layer. , A decrease in the NO _x purification rate is caused. This effect is caused by the coexistence of a noble metal component in the Cu-zeolite-based catalyst layer (JP-A-1-31074,
In Japanese Patent Application Laid-Open No. 5-168939, this is particularly large.

When a Pt-based catalyst is used, 20
Although NO _x can be converted even in a relatively low temperature range of ₀ to 250 ° C., not only conversion to N ₂ but also generation of N ₂ O cannot be ignored, and it is difficult to use because of adverse effects on the environment. It is in.

Accordingly, in the conventional catalyst such as Cu- zeolite-based catalyst and Pt-based catalysts, in the low exhaust gas conditions HC / NO _x ratio, NO _x purifying performance becomes insufficient, and therefore, the reducing agent HC A purification method has also been proposed in which alcohols, alcohols, and the like are secondarily supplied to the catalyst inlet.

However, in this case, it is necessary to mount a reducing agent tank on the vehicle or to directly use fuel as the reducing agent. A problem arises in that the fuel efficiency of the engine is sacrificed.

[0011]

The purpose of the invention [0006] claims 1-11, wherein also NO _x in the low temperature range and the low HC / NO _x ratio in the conventional catalyst could not exhibit sufficient purification performance An object of the present invention is to provide an exhaust gas purifying catalyst capable of improving purification performance and suppressing catalyst deterioration even under high-temperature hydrothermal conditions.

The purpose of the description of claim 12 is to provide
NO of the catalyst for purification of exhaust gas of Ming _xEspecially effective
To provide a method for purifying an exhaust gas purifying catalyst that can be effectively used
In

[0013]

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising platinum (Pt), palladium (Pd), and rhodium (Rh) before a catalyst containing zeolite is disposed in front of an exhaust gas flow. A first catalyst layer containing one or more components selected from the group and one or more components selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals; and alumina and / or silica. A second catalyst layer,
A third catalyst layer containing a zeolite containing a copper (Cu) and / or cobalt (Co) component, a second catalyst layer on the first catalyst layer, and a third catalyst layer on the second catalyst layer. The catalyst provided with is provided at a stage subsequent to the exhaust gas flow.

According to a second aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first aspect, wherein the alkali metal, the alkaline earth metal and the rare earth metal contained in the first catalyst layer of the latter catalyst are magnesium. (Mg), calcium (Ca), potassium (K), barium (Ba), lanthanum (La), strontium (Sr), cesium (C
s) and cerium (Ce).

According to a third aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the first or second aspect, wherein the first, second, and third catalyst layers of the second-stage catalyst comprise an alkali metal, an alkaline earth metal, and a rare earth metal. The content of one or more components selected from the group consisting of:
It is characterized by a range of more than 0.1 mol per L and not more than 0.6 mol.

According to a fourth aspect of the present invention, there is provided the exhaust gas purifying catalyst according to any one of the first to third aspects, wherein the zeolite in the first stage catalyst is β zeolite, Y type zeolite, MFI type zeolite. And mordenite, wherein the zeolite has a silica / alumina ratio of 20-15.
0, the Y / zeolite has a silica / alumina ratio of 4 to 50,
MFI zeolite having a silica / alumina ratio of 20 to 10
The mordenite has a silica / alumina ratio of 9 to 25.

According to a fifth aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the fourth aspect, wherein the amount of zeolite in the first stage catalyst is 30 to 300 per liter of the first stage catalyst.
g.

According to a sixth aspect of the present invention, there is provided the exhaust gas purifying catalyst according to the fourth or fifth aspect, wherein the zeolite in the pre-catalyst comprises copper (Cu), cobalt (C
o), at least one selected from the group consisting of iron (Fe) and / or manganese (Mn) is supported at 1 to 20% by weight.

According to a seventh aspect of the present invention, there is provided the exhaust gas purifying catalyst according to any one of the first to sixth aspects, wherein a Cu and / or Co component in the third catalyst layer of the second stage catalyst is contained. Has a silica / alumina ratio of 20 to
80 MFI zeolite and / or β zeolite.

The exhaust gas purifying catalyst according to claim 8 is the exhaust gas purifying catalyst according to claim 7, wherein the amount of Cu and / or Co component in the third catalyst layer of the latter catalyst is less than 1 L of the latter catalyst. It is characterized by being in the range of 0.05 to 0.5 mol.

The exhaust gas purifying catalyst according to a ninth aspect is the exhaust gas purifying catalyst according to the eighth aspect, wherein the amount of the zeolite containing Cu and / or Co component in the third catalyst layer is 1 L of the latter catalyst. 120 g to 300 g per unit.

The exhaust gas purifying catalyst according to claim 10 is
The exhaust gas purifying catalyst according to any one of claims 1 to 9, wherein the amount of alumina and / or silica in the second catalyst layer is 20 g to 100 g per 1 L of the subsequent catalyst.

An exhaust gas purifying catalyst according to claim 11 is
The exhaust gas purifying catalyst according to any one of claims 1 to 10, wherein a volume ratio of the front catalyst and the rear catalyst is 1: 1.
１ ： 1: 7.

According to a twelfth aspect of the present invention, there is provided an exhaust gas purifying method according to any one of the first to eleventh aspects, wherein the exhaust gas purifying catalyst has an air-fuel ratio (A / F) of 14.7 or more, at a concentration of 5% or more, and the ratio of the amount of hydrocarbon and nitrogen oxide amount necessary to convert the nitrogen oxides and hydrocarbons react with nitrogen oxides into nitrogen (= HC / NO _x ratio) of 10 or less It is characterized in that it is used for an internal combustion engine.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
The catalyst arranged upstream of the exhaust stream is a catalyst containing zeolite. As the zeolite in the pre-stage catalyst, at least one selected from the group consisting of β zeolite, Y-type zeolite, MFI-type zeolite and mordenite can be used. In particular, when USY-type zeolite is used as Y-type zeolite, This is preferable because the heat property can be further improved.

The silica / alumina of these zeolites as the HC trap material has a β zeolite content of 20 to 15%.
0, the Y-type zeolite is preferably 4 to 50, the MFI-type zeolite is preferably 20 to 1000, and the mordenite is preferably 9 to 25. When the silica / alumina ratio is smaller than this range, the framework of the zeolite becomes unstable, while the silica / alumina ratio becomes unstable. If the / alumina ratio is greater than this range, the ability to retain HCs will be weak, and it will not be possible to store HCs until the temperature at which the NO _x reducing material in the third catalyst layer starts operating.

The amount is 30 to 30 per liter of the pre-stage catalyst.
0 g is preferred because the heat capacity is not too large and the activity of the latter catalyst is not hindered.

The zeolite in the pre-catalyst is C
It is preferable to carry at least one selected from the group consisting of u, Co, Fe and Mn because NO _x purification performance at the time of desorbing HC from zeolite in the pre-stage catalyst can be improved. 20% by weight is preferred. This is because the above effect can be effectively exhibited within this range.

The pre-catalyst for purifying exhaust gases in the catalyst of the present invention, the exhaust gas is the HC classes efficiently trapped when in the low temperature region, the temperature range where _the NO _x reduction material is activated H
By supplying C compound promotes the reduction of NO _x. In particular, HCs are efficiently adsorbed by being disposed upstream of the exhaust gas flow, and H adsorbed as the exhaust gas temperature rises.
C is desorbed at once at the temperature required for NO _x reduction, and NO
_x It can be used for purification.

The second-stage catalyst in the exhaust gas purifying catalyst of the present invention has a three-layer structure.
It contains one or more components selected from the group consisting of t, Pd and Rh, and one or more components selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals.

The at least one noble metal component selected from the group consisting of Pt, Pd and Rh is, for example, Pt, Rh, P
Various combinations such as only d, Rh, and Pd are possible. By containing the precious metal component according to the first catalyst layer, giving oxidizing power, by removing the excess reducing gas component in a lean atmosphere, it is possible to promote the absorption of NO _x activity.

The content of the noble metal, but of absorption of NO _x performance and three-way catalyst performance is not particularly limited as long enough to obtain,
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
The amount is preferably 0.1 to 10 g per 1 L of the latter-stage catalyst, since no significant improvement in properties is observed even when the amount is more than g.

The first catalyst layer contains an alkali metal, an alkaline earth metal and a rare earth metal component in the latter catalyst 1.
It is preferable to contain the compound in a range of more than 0.1 mol and not more than 0.6 mol per L. Potassium, lithium, and sodium, particularly sodium, are alkaline metals; barium strontium, calcium, and magnesium are alkaline earth metals; and Y and L are rare earth metals.
a, Cs, Ce, Pr, Nd, Pm, Sm
It is preferable to use s, Ce.

If the amount is less than 0.1 mol per 1 L of the latter catalyst, the NO _x absorption becomes insufficient, and if it exceeds 0.6 mol, the effect of the above-mentioned noble metal is negated. It is preferably at most 0.6 mol.

The first catalyst used in the present invention is preferably used in a honeycomb form. As this honeycomb material,
Generally, cordierite is widely used, but is not limited thereto. A honeycomb carrier made of a metal material is also effective, and the catalyst powder itself can be formed in a honeycomb shape. In a car, by making the shape of the catalyst into a honeycomb shape, the contact area between the catalyst and the exhaust gas is increased and the pressure loss is suppressed, so that there is vibration and a large amount of exhaust gas is limited in a limited space. This is extremely advantageous when used as a catalyst for automobiles requiring processing.

The first catalyst layer oxidizes NO _x by coexisting a noble metal component and at least one component selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals. It has the function of converting to highly reactive NO _x species, and promotes the low-temperature activity of the NO _x reducing material of the third catalyst layer described later.

In the second stage catalyst in the exhaust gas purifying catalyst of the present invention, a second catalyst layer containing alumina and / or silica as an isolation layer is provided on the first catalyst layer. Such alumina and / or silica do not contain any precious metal components. By including such alumina and / or silica in the catalyst, the thermal stability of the active component in the first and third catalyst layers can be improved, and high durability can be realized.

That is, when the noble metal-containing catalyst layer as the first catalyst layer and the NO _x reducing material layer as the third catalyst layer come into direct contact, a reaction between the active components occurs, which is not always preferable in terms of catalyst deterioration. Therefore, the second catalyst layer has a function as an isolation layer.

The amount is 20 to 10 per liter of the latter-stage catalyst.
0 g is not too small and is preferred as the separating layer. If it exceeds 100 g, diffusion of the gas into the first catalyst layer becomes difficult.

Further, the latter catalyst in the exhaust gas purifying catalyst of the present invention has a third catalyst layer containing zeolite containing a Cu and / or Co component on the second catalyst layer.

Examples of zeolites containing Cu and / or Co components include MFI-type zeolites, Y-type zeolites,
Mordenite, ferrierite, β-zeolite and the like can be used, but MFI-zeolite and β-zeolite are particularly preferred in that they have high NO _x purification performance.

Further, the silica / alumina ratio of the zeolite containing the Cu and / or Co component is preferably 20 to 80. If the silica / alumina ratio is smaller than this range, the zeolite skeleton becomes unstable and is supported by ion exchange. In addition, the amount of the components (Cu and / or Co) becomes excessive, the dispersibility is reduced, the activity per active point is rapidly reduced, and aggregation between the active sites is likely to occur. On the other hand, if the silica / alumina ratio is larger than this range, the number of active sites is too small to obtain sufficient activity.

[0043] Cu and / or Co component to be supported has _the NO _x purification function in a lean exhaust gas. The amount is
It is preferable to contain it in the range of 0.05 to 0.5 mol per 1 L of the latter catalyst. This is because sintering due to heat is less likely to occur within this range.

The total coating amount of the third catalyst layer is preferably 120 to 300 g per 1 L of the latter catalyst. If the coating amount of the third catalyst layer is less than this range, the activity under high SV becomes insufficient, and if it is more than this range, the first layer,
Adverse effects such as hindering diffusion of reactive molecules into the second layer and increasing pressure loss occur.

The third layer uses HCs desorbed from the pre-catalyst to form H 3 when the exhaust gas is in a low temperature range.
The C class efficiently trap, and supplies the HC classes when _the NO _x reduction material is a temperature range to operate to promote the reduction of NO _x. In particular, the way to push mixing uniformly and trap material and _the NO _x reduction material HC classes, the HC classes in _the NO _x reduction, it is possible to more efficiently use.

The latter-stage catalyst in the exhaust gas purifying catalyst of the present invention comprises the above three layers, and the combination thereof is such that the third catalyst layer containing NO _x reduction is provided on the outermost surface and the first catalyst containing noble metal components
A catalyst layer disposed on the bottom layer, arranged between them a second layer that isolates the _the NO _x reduction material layer and the precious metal catalyst layer. With this arrangement of the catalyst layer, as a reducing agent HC in the first layer, and activated to work convenient form, an activated HC and NO _x efficiently react in the third layer.

[0047] The first catalyst layer of the front catalyst and in the rear catalyst, since the NO _x oxidation ability and HC such adsorption of the third catalyst layer deteriorates under high temperature hydrothermal conditions and compensate for the reforming action, the total catalyst As a result, catalyst deterioration due to high-temperature hydrothermal conditions can be suppressed.

In the exhaust gas purifying catalyst of the present invention, the above-mentioned first-stage catalyst and second-stage catalyst are used in combination with respect to the exhaust gas flow. By arranging the pre-catalyst on the pre-stage side with respect to the exhaust gas flow, HCs are efficiently adsorbed, and the adsorbed HCs are desorbed at once at a temperature required for NO _x reduction with an increase in the exhaust gas temperature. it is possible to use the _x purification, by positioning the rear of the front catalyst and the rear catalyst against the exhaust flow, efficiently reducing of the NO _x using the HC classes that came out desorbed from the pre-catalyst Can be implemented.

The volume ratio of the former catalyst and the latter catalyst is:
The ratio is preferably from 1: 1 to 1: 7, and when combined within this range, the NO _x purification performance is particularly improved. That is, if the ratio is smaller than 1: 1, the HC trapping effect is not effectively exhibited, and if the ratio is larger than 1: 7, the heat capacity of the front-stage catalyst is too large, and the NO.
Inhibits the low temperature activity in _x reduction.

The various zeolites used in the present invention are stabilized by increasing the crystallinity by hydrothermal treatment, resynthesis, etc., and a catalyst having high heat resistance and durability can be obtained. Is preferred.

As the metal raw material compound for catalyst preparation used in the present invention, inorganic acid salts, carbonates, ammonium salts, organic acid salts, halides, oxides, sodium salts, ammine complex compounds and the like can be used in combination. Although it is possible, it is particularly preferable to use a water-soluble salt from the viewpoint of improving the catalyst performance. The method of supporting the noble metal is not limited to a special method, and various methods such as a known evaporation and drying method, a precipitation method, an impregnation method, and an ion exchange method can be used as long as no significant uneven distribution of components is involved. In particular, the ion-exchange method is preferably used for loading on zeolite from the viewpoint of ensuring metal dispersibility.

In the case of the ion exchange method or the impregnation method, since the metal raw material is often used in a solution, the pH can be adjusted by adding an acid or a base to the solution. pH
By adjusting the value, the state of supporting the metal can be further controlled, and the heat resistance can be ensured.

The thus obtained catalyst used in the present invention is pulverized into a slurry, coated on a catalyst carrier, and calcined at a temperature of 400 to 900 ° C. to obtain the exhaust gas purifying catalyst of the present invention. Obtainable.

The exhaust gas purifying catalyst of the present invention is preferably used in a honeycomb shape. In this case, the catalyst carrier can be appropriately selected from known catalyst carriers and used, for example, from a refractory material. A honeycomb carrier or a metal carrier having a monolith structure is used, and a zeolite-based catalyst is applied to the carrier and used.

Although the shape of the catalyst carrier is not particularly limited, it is usually preferable to use a honeycomb shape. As the honeycomb material, cordierite materials such as ceramics are generally used, but ferrite-based materials are generally used. It is also possible to use a honeycomb made of a metal material such as stainless steel, and further, the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst a honeycomb shape, the contact area between the catalyst and the exhaust gas increases,
Since the pressure loss is also suppressed, it is suitable for use as a catalyst for automobiles or the like which requires vibration and is required to process a large amount of exhaust gas in a limited space.

The use conditions of the exhaust gas purifying catalyst of the present invention are not particularly limited. However, in order to exhibit high-efficiency purifying performance, the exhaust gas purifying catalyst is preferably used under an air-fuel ratio (A / F) of 14.7 or more. The exhaust gas purifying catalyst of the present invention is installed in an exhaust system of an internal combustion engine operated at a temperature of 5% or more, and nitrogen oxides and hydrocarbons react to convert nitrogen oxides to nitrogen. It is preferable that an exhaust gas having a ratio of the amount of hydrocarbon and the amount of nitrogen oxide (= HC / NO _x ratio) of 10 or less be passed and contacted. This is because if the oxygen concentration is low and the amount of hydrocarbons is too large, coking on the catalyst surface is likely to occur, and catalyst deterioration is promoted. Can withstand long-term use and maintain high purification performance.

[0057]

[Example 1]

(A) Formation of Pre-Catalyst H-type zeolite having an SiO ₂ / Al ₂ O ₃ molar ratio of about 25 was mixed with alumina sol and water, and ground in a magnetic ball mill pot for 20 minutes to form a slurry. The slurry thus obtained is applied to 1.0 L of cordierite-based honeycomb carrier having about 400 channels per square inch cross section, dried with hot air at 150 ° C., and fired at 500 ° C. for 1 hour. And a pre-stage catalyst having a coating amount of about 150 g / L.

(B) Formation of Second-Stage Catalyst (1) Formation of First Catalyst Layer After adding activated alumina powder to an aqueous solution of dinitrodiammineplatinum and stirring well, the mixture was dried in a dryer at 120 ° C. for 8 hours and then air Bake at 500 ° C for 2 hours in air stream, Pt
Was obtained, whereby about 1.0% by weight of Pt-activated alumina powder was obtained. A nitric acid-alumina sol and water were added to the catalyst powder in a magnetic ball mill pot, mixed and pulverized for about 20 minutes to obtain a slurry of Pt-activated alumina. The addition amount of alumina sol was 5% by weight. The thus obtained slurry was applied to 1.0 L of cordierite-based honeycomb carrier having about 400 channels per square inch cross section, dried with hot air at 150 ° C., and fired at 500 ° C. for 1 hour. Thus, a honeycomb catalyst having a coating amount of about 35 g / L was obtained.

The honeycomb catalyst was immersed in a mixed aqueous solution containing calcium acetate, barium acetate and lanthanum nitrate, dried at 120 ° C., and calcined at 500 ° C. for 1 hour to obtain Ca, Ba and La. Thus, a honeycomb catalyst A1 coated with the first catalyst layer containing 0.1 mol, 0.15 mol and 0.1 mol of the above-mentioned honeycomb catalyst, respectively, was obtained.

(2) Formation of the second catalyst layer Alumina sol and water were added to activated alumina powder containing γ-alumina as a main component in a magnetic ball mill pot, and the mixture was added for about 20 minutes.
The mixture was mixed and crushed for minutes to obtain a slurry. At this time, the addition amount of the alumina sol was 5% by weight as Al ₂ O ₃ . The slurry obtained in this manner is applied to the honeycomb catalyst A1 obtained in the above (1), dried at 150 ° C. with hot air, baked at 500 ° C. for 1 hour, and coated at about 55 g / L.
The honeycomb catalyst A2 having the second catalyst layer was obtained.

(3) Formation of Third Catalyst Layer SiO ₂ / Al ₂ O _{3 was} added to a 0.17 M / L copper nitrate / cobalt nitrate mixed aqueous solution (Cu: Co = 8.2).
A powder of NH ₄ type MFI zeolite having a molar ratio of about 35 was added, stirred well, and then filtered to separate a solid and a liquid. By repeating the above-mentioned stirring / filtration operation three times, an MFI zeolite catalyst cake carrying Cu and Co on ion exchange was obtained. This catalyst cake is placed in a dryer for 12 hours.
By drying at 0 ° C. for 24 hours or more, and then baking at 600 ° C. for 4 hours in an air atmosphere using an electric furnace, Cu-Co carrying 3.9% by weight of Cu and 0.8% by weight of Co
-An MFI zeolite catalyst powder was obtained.

The catalyst powder and H-type β zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 25 were mixed with alumina sol and water at a ratio of 2: 1 and pulverized in a magnetic ball mill pot for 20 minutes to obtain a slurry. And This slurry was coated on the above-mentioned honeycomb catalyst body A2 and dried in a dryer.
C. for 8 hours and then calcined at 450.degree. C. for 1 hour in an air stream to obtain a second-stage catalyst. The coating amount of the third catalyst layer was about 300 g / L.

(C) Combination of Pre-Catalyst and Post-Catalyst The pre-catalyst and the post-catalyst are changed and combined so that the obtained volume ratio of the pre-catalyst and the post-catalyst is 1: 3. Was obtained.

Example 2 N in the third catalyst layer of the latter catalyst
H_FourType MFI zeolite powder is converted to SiO_Two/ Al _TwoO_Three
NH with a molar ratio of about 42_FourExcept that it was replaced with β-zeolite
In the same manner as in Example 1, the exhaust gas purifying catalyst of the present invention
Obtained.

Example 3 The H-type β zeolite powder of the pre-catalyst was mixed with NH ₄ having a SiO ₂ / Al ₂ O ₃ molar ratio of about 30.
An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the type Y zeolite was used instead.

Example 4 P in the first catalyst layer of the latter catalyst
t (1.0% by weight) was converted to Pd-Rh (1.2% by weight-0.1%).
2% by weight) to obtain an exhaust gas purifying catalyst of the present invention in the same manner as in Example 1.

Example 5 C in the first catalyst layer of the latter catalyst
a for the purification of exhaust gas of the present invention in the same manner as in Example 1 except that a1.0 mol, 0.15 mol of Ba and 0.1 mol of La were changed to 0.01 mol of Mg, 0.1 mol of Ba and 0.01 mol of K. A catalyst was obtained.

Example 6 C in the first catalyst layer of the latter catalyst
a1.0 mol, 0.15 mol of Ba and 0.1 mol of La were converted to 0.2 mol of Ba, 0.05 mol of Sr, and 0.04 mol of Cs0.04 mol.
In the same manner as in Example 1 except that the mol and Ce were changed to 0.29 mol, an exhaust gas purifying catalyst of the present invention was obtained.

Example 7 NH in the third catalyst of the latter catalyst
An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the _4- type MFI zeolite powder was changed to an H-type MFI zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 24.

Example 8 N in the third catalyst layer of the latter catalyst
H_FourType MFI zeolite powder is converted to SiO_Two/ Al _TwoO_Three
Except that the molar ratio was changed to H-form MFI zeolite of about 76
In the same manner as in Example 1, the exhaust gas purifying catalyst of the present invention
Obtained.

Example 9 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the activated alumina powder in the second catalyst layer of the latter catalyst was changed to silica powder.

[0072] Example 10 a H type β-zeolite powder in the pre-catalyst, SiO ₂ / Al ₂ O ₃ molar ratio of about 35 H
An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the type MFI zeolite was used.

[Example 11] The H-type β zeolite powder in the pre-catalyst was converted to a H ₂ powder having a SiO ₂ / Al ₂ O ₃ molar ratio of about 15
Except having replaced with the mordenite type, it carried out similarly to Example 1, and
An exhaust gas purifying catalyst of the present invention was obtained.

[Example 12] The H-type β zeolite powder in the pre-stage catalyst was mixed with H ₂ having a SiO ₂ / Al ₂ O ₃ molar ratio of about 25.
Β-zeolite and SiO ₂ / Al ₂ O ₃ molar ratio of about 70
Exhaust gas purification catalyst of the present invention was obtained in the same manner as in Example 1 except that zeolite powder in which H-type MFI zeolite 0 was mixed at a ratio of 1: 1 was used.

[Example 13] The H-type β zeolite powder in the pre-stage catalyst was mixed with H ₂ having a SiO ₂ / Al ₂ O ₃ molar ratio of about 25.
Type β zeolite and a SiO ₂ / Al ₂ O ₃ molar ratio of about 7
00 H-type MFI zeolite and SiO ₂ / Al ₂ O ₃
Exhaust gas purification catalyst of the present invention was obtained in the same manner as in Example 1 except that zeolite powder in which H-type zeolite having a molar ratio of about 30 was mixed at a ratio of 2: 1: 1 was used. Was.

Example 14 The coating amount of the first-stage catalyst was set to 15
An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the amount was changed from 0 g / L to 40 g / L.

Example 15 The coating amount of the first-stage catalyst was set to 15
An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the amount was changed from 0 g / L to 300 g / L.

Example 16 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the volume ratio of the former catalyst to the latter catalyst was 1: 1.

Example 17 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the volume ratio between the former catalyst and the latter catalyst was 1: 5.

Example 18 Exhaust gas purification of the present invention was carried out in the same manner as in Example 1 except that 5% by weight of copper was supported on the H-type zeolite powder of the first-stage catalyst using an aqueous copper phosphate solution. A catalyst was obtained.

Example 19 Exhaust gas purification of the present invention was carried out in the same manner as in Example 1 except that 5% by weight of iron was supported on the H-type β zeolite powder of the pre-catalyst using an aqueous solution of iron phosphate. A catalyst was obtained.

Example 20 5% by weight of manganese pyrophosphate aqueous solution was added to H-type β zeolite powder of the pre-stage catalyst.
Except that manganese was supported, an exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1.

Example 21 The exhaust gas purifying method of the present invention was carried out in the same manner as in Example 1 except that 5% by weight of cobalt was supported on the H-type zeolite powder of the first-stage catalyst using an aqueous solution of cobalt phosphate. A catalyst was obtained.

Comparative Example 1 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that only the latter-stage catalyst was used without providing the former-stage catalyst.

Comparative Example 2 Mg of 0.01 mol, BaO.
1 mol, 0.01 mol of K, 0.03 mol of Mg, Ba
Example 5 except for changing to 0.04 mol and K0.01 mol
In the same manner as in the above, an exhaust gas purifying catalyst was obtained.

[Comparative Example 3] Ba 0.2 mol, Sr 0.0
5 mol, Cs 0.04 mol, Ce 0.29 mol
0.3 mol, Sr 0.02 mol, Cs 0.3 mol, Ce
An exhaust gas purifying catalyst was obtained in the same manner as in Example 6, except that the amount was changed to 0.01 mol.

Comparative Example 4 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that the coating amount of the third catalyst layer of the latter catalyst was changed to 100 g / L.

Comparative Example 5 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the coating amount of the third catalyst layer of the latter catalyst was changed to 350 g / L.

[Comparative Example 6] The coating amount of the former catalyst was 20 g.
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that / L was changed.

[Comparative Example 7] The coating amount of the former catalyst was 350
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that g / L was used.

Comparative Example 8 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the H-type zeolite in the pre-stage catalyst was changed to about 10.

Comparative Example 9 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the H-type β zeolite as the pre-stage catalyst was changed to about 200. .

Comparative Example 10 Exhaust gas purification catalyst was prepared in the same manner as in Example 3 except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the NH ₄ type Y zeolite of the pre-stage catalyst was changed to about 1.5. I got

Comparative Example 11 An exhaust gas purifying catalyst was obtained in the same manner as in Example 10 except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the H-type MFI zeolite as the pre-stage catalyst was changed to about 10. .

Comparative Example 12 An exhaust gas purifying catalyst was obtained in the same manner as in Example 11 except that the molar ratio of SiO ₂ / Al ₂ O _{3 in} the H-type mordenite of the pre-stage catalyst was changed to about 7.

Comparative Example 13 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the volume ratio between the former catalyst and the latter catalyst was changed to 2: 1.

[Comparative Example 14] An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the capacity ratio between the former catalyst and the latter catalyst was 1: 7.

Comparative Example 15 Exhaust gas purification was carried out in the same manner as in Example 1 except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the NH ₄ type MFI zeolite in the third catalyst layer of the latter catalyst was changed to about 17. A catalyst was obtained.

Comparative Example 16 Exhaust gas purification was carried out in the same manner as in Example 1 except that the molar ratio of SiO ₂ / Al ₂ O ₃ of the NH ₄ type MFI zeolite of the third catalyst layer of the latter catalyst was changed to about 82. A catalyst was obtained.

The compositions of the exhaust gas purifying catalysts obtained in Examples 1 to 21 and Comparative Examples 1 to 16 are shown in Tables 1 to 4.

[0101]

[Table 1]

[0102]

[Table 2]

[0103]

[Table 3]

[0104]

[Table 4]

Test Example The catalytic performance of the exhaust gas purifying catalysts obtained in Examples 1 to 21 and Comparative Examples 1 to 16 was evaluated by the following method.

Catalyst Performance Test Example 1 Each exhaust gas purifying catalyst was incorporated into the exhaust system of an engine dynamo apparatus equipped with a 4-cylinder 2.5-liter diesel engine, and subjected to a rapid endurance treatment at 630 ° C. × 30 hours.
Next, the exhaust gas purifying catalyst after the endurance treatment is incorporated into an exhaust system of an engine dynamo device equipped with a 4-cylinder 2.5L diesel engine, and the catalyst inlet temperature is raised to 100 ° C to 500 ° C. The NO _x conversion performance at the time was measured. The rate of temperature rise from 100 ° C. to 500 ° C. was about 30 ° C./min, the average HC / NO _x ratio in the exhaust gas was 2.8, and the gas space velocity was 45000 h with respect to the subsequent catalyst.
^{It was set to -1} .

The above engine dynamo device can change the HC / NO _x ratio in the exhaust gas by injecting light oil from a nozzle provided between the engine manifold and the catalyst.

The NO _x conversion performance was determined by _{measuring the} concentration of NO _{x at the} inlet and the concentration of NO _{x at the} outlet of the catalyst, MEXA-6 manufactured by HORIBA, Ltd.
000SH and were determined by the following equation.

[0109]

(Equation 1)

Table 5 shows the obtained catalyst activity evaluations.

[0111]

[Table 5]

[0112] Catalyst examples are clearly higher _the NO _x purification rate than the catalyst of Comparative Example, those of the embodiment, the HC such a low temperature range to efficiently trap and high and HC in temperature rising process It is considered that since it is used for efficiency, it exhibits excellent NO _x purification efficiency.

If the supported amount of alkali metal, alkaline earth metal and rare earth metal and the silica / alumina ratio of the zeolite are out of the range of the present invention, the first catalyst of the second-stage catalyst may be used.
It can be seen that the above functions of the layer and the third layer are reduced, and the silica / alumina ratio of the third layer zeolite of the former catalyst and the latter catalyst has a great influence on the catalytic performance. Further, it is clear that the coating amount of the third layer of the first catalyst and the second catalyst has a large effect on the catalyst performance. In order to improve the catalyst performance,
It is particularly effective to carry at least one selected from the group consisting of Cu, Co, Fe and Mn on the pre-catalyst.

[0114]

The exhaust gas purifying catalyst according to any one of claims 1 to 11 includes a low temperature region of 150 ° C. or less,
And also the exhaust gas purification at low HC / NO _x ratio conditions, because in particular can be carried out in the purification of the NO _x is high efficiency, can be environmental pollution less provides excellent automobile economy (fuel consumption).

[0115] Furthermore, exhaust gas purification method according to claim 12, wherein the exhaust gas purifying catalyst of the present invention, the _the NO _x purification action even in a low temperature region and a low HC / NO _x ratio conditions may particularly efficient Can be expressed.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/28 301 B01D 53/36 102B

Claims (12)

[Claims] 1. A catalyst containing zeolite, which is provided in advance of an exhaust stream with one or more components selected from the group consisting of platinum (Pt), palladium (Pd) and rhodium (Rh), an alkali metal and an alkali. A first catalyst layer containing at least one component selected from the group consisting of earth metals and rare earth metals, a second catalyst layer containing alumina and / or silica,
A third catalyst layer containing a zeolite containing a copper (Cu) and / or cobalt (Co) component, a second catalyst layer on the first catalyst layer, and a third catalyst layer on the second catalyst layer. An exhaust gas purifying catalyst comprising: a catalyst provided with a gas turbine disposed downstream of an exhaust gas flow. 2. The alkali metal, alkaline earth metal and rare earth metal contained in the first catalyst layer of the latter catalyst are magnesium (Mg), calcium (Ca), potassium (K),
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is barium (Ba), lanthanum (La), strontium (Sr), cesium (Cs), or cerium (Ce). 3. The content of at least one component selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals contained in the first catalyst layer of the latter catalyst is 0.1 mol per 1 L of the latter catalyst. 3. The exhaust gas purifying catalyst according to claim 1, wherein the range is more than 0.6 mol and less. 4. The zeolite in the pre-stage catalyst is at least one zeolite selected from the group consisting of β zeolite, Y zeolite, MFI zeolite and mordenite, and the β zeolite has a silica / alumina ratio of 20.
~ 150, silica / alumina ratio of Y type zeolite is 4 ~
50, silica / alumina ratio of MFI type zeolite is 20
~ 1000, mordenite silica / alumina ratio is 9 ~
The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the catalyst is 25. 5. The exhaust gas purifying catalyst according to claim 4, wherein the amount of zeolite in the pre-catalyst is 30 to 300 g per liter of the pre-catalyst. 6. The zeolite in the pre-catalyst is copper (C
u), cobalt (Co), iron (Fe) and / or manganese (Mn), at least one selected from the group consisting of:
6. The exhaust gas purifying catalyst according to claim 4, wherein the catalyst is loaded at 1 to 20% by weight. 7. The zeolite containing Cu and / or Co component in the third catalyst layer of the latter catalyst is an MFI zeolite and / or β zeolite having a silica / alumina ratio of 20 to 80. Item 7. An exhaust gas purifying catalyst according to any one of Items 1 to 6. 8. The amount of the Cu and / or Co component in the third catalyst layer of the second catalyst is 0.05 to 0.1 / L per 1 L of the second catalyst.
The exhaust gas purifying catalyst according to claim 7, wherein the amount is within a range of 5 mol. 9. The amount of zeolite containing a Cu and / or Co component in the third catalyst layer is 12 per 1 L of the latter catalyst.
The exhaust gas purifying catalyst according to claim 8, wherein the weight is 0 g to 300 g. 10. The exhaust gas purifying catalyst according to claim 1, wherein the amount of alumina and / or silica in the second catalyst layer is 20 g to 100 g per liter of the second-stage catalyst. 11. The volume ratio between the first-stage catalyst and the second-stage catalyst is as follows:
11. 1 to 1: 7.
An exhaust gas purifying catalyst according to any one of the preceding claims. 12. An exhaust gas purifying catalyst according to claim 1, wherein the exhaust gas has an air-fuel ratio (A / F) of 14.7 or more, an oxygen concentration of 5% or more, and nitrogen. The ratio of the amount of hydrocarbons and the amount of nitrogen oxides necessary for the oxides and hydrocarbons to react and convert nitrogen oxides to nitrogen (= HC / NO
_(x ratio) of 10 or less for an internal combustion engine.