JPH10235199A - Exhaust gas purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify efficiently exhaust gas of an automobile engine driven at the air-fuel ratio in the wide range without lowering the function of a three way catalyst by specifying the volume ratio of pores of diameters of respectively different specified values to the specified % or more in a metal carrying porous crystalline aluminosilicate. SOLUTION: A honeycomb-shaped catalyst 1 containing a metal carrying porous crystalline aluminosilicate catalyst layer and a noble metal carrying alumina catalyst layer is disposed on the upstream side of exhaust gas flow, while a honeycomb-shaped catalyst 2 containing a three way catalyst is disposed on the downstream side of exhaust gas flow in an exhaust gas purifying catalyst. The total volume sum of pores of diameters of 4nm or less in the metal carrying porous crystalline aluminosilicate in the honeycomb-shaped catalyst 1 is set as 60% or more, preferably 75% or more of the total volume sum of pores of diameters of 1-100nm. Also it is preferable to constitute the catalyst formed of a metal carrying porous crystalline aluminosilicate as an upper layer and a noble metal carrying alumina silica catalyst as a lower layer.

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 more particularly, to an exhaust gas purifying catalyst excellent in exhaust gas purifying efficiency and durability from an internal combustion engine such as an automobile engine and various combustors.

[0002]

2. Description of the Related Art Conventionally, a three-way catalyst has been widely used as a catalyst for purifying exhaust gas from an automobile engine or the like. Conventional three-way catalysts are predominantly alumina-based catalysts containing various components such as noble metal components such as platinum, palladium and rhodium and cerium components, and when the engine is operated near the stoichiometric air-fuel ratio. It shows high purification efficiency with respect to exhaust gas.

[0003] On the other hand, in recent years, from the viewpoint of improving fuel efficiency and reducing carbon dioxide emission, a lean burn engine that operates even at an air-fuel ratio higher than the stoichiometric air-fuel ratio has attracted attention. The exhaust gas of such a lean burn engine (lean exhaust gas) has a higher oxygen content than the exhaust gas of a conventional engine (stoichiometric exhaust gas) that operates only near the stoichiometric air-fuel ratio, and the conventional three-way exhaust gas. The catalyst uses nitrogen oxides (N
Ox) purification is insufficient. Therefore, a new catalyst applicable to a lean burn engine operated at a wide air-fuel ratio has been desired.

A metal-supported zeolite catalyst (hereinafter, referred to as “zeolite catalyst”) obtained by supporting various metal components on a porous crystalline aluminosilicate (hereinafter, referred to as “zeolite”) has an oxygen content of It has been noted that even in an exhaust gas having a high concentration (lean exhaust gas), if hydrocarbons (HC) are present, it has a capability of purifying NOx relatively efficiently.

The metal components include copper (Cu), cobalt (Co), silver (Ag), nickel (Ni), and iron (Fe).
In addition to the transition metal components such as
t) has also been recognized for its effectiveness, but in particular copper (Cu)
Is high in NOx activity and has relatively excellent NOx purification performance even under high flow rate exhaust gas conditions. It is expected to be applied to purification of exhaust gas from engines for industrial use.

However, the zeolite-based catalyst alone cannot sufficiently purify the exhaust gas of an engine operated at a wide air-fuel ratio from stoichiometric air-fuel (stoichiometric) to oxygen-excess (lean). Combination was essential. This is because the zeolite-based catalyst has poor purification performance of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in stoichiometric exhaust gas, and on the other hand, even in lean exhaust gas having a high oxygen content. This is because although the NOx purification performance is excellent, the ability to purify HC and CO is inferior.

For this reason, a catalyst system in which a zeolite-based catalyst and a three-way catalyst are combined in series in the exhaust gas flow direction has been considered. For example, Japanese Patent Application Laid-Open No. 1-139145 discloses that a transition metal is provided upstream of the exhaust gas. It has been proposed to place a supported zeolite catalyst downstream of an oxidation catalyst or a three-way catalyst.

Such a combination of arranging a zeolite-based catalyst on the upstream side of the exhaust gas and a three-way catalyst on the downstream side of the exhaust gas purifies the exhaust gas of a lean burn engine operating at a wide air-fuel ratio from stoichiometric to lean. Is considered to be an effective catalyst system.

However, the conventional exhaust gas purifying catalyst system cannot actually exhibit the function of the three-way catalyst installed on the downstream side of the exhaust gas sufficiently, and the exhaust gas purifying performance at the stoichiometric ratio is insufficient. Problem. This is because when the state of the exhaust gas switches from lean to stoichiometric and from stoichiometric to lean, the zeolite-based catalyst temporarily and selectively captures some of the gas components in the exhaust gas, It is generally considered that the balance between the oxidizing gas component (NOx) and the reducing gas component in the exhaust gas at the entrance is lost, and the function of the three-way catalyst is reduced. Therefore, in order not to lower the function of the three-way catalyst, it is necessary to weaken the ability of the zeolite-based catalyst to capture gas components.

Further, the operating temperature range (temperature window) of the conventional Cu-zeolite catalyst does not operate effectively in a low temperature range such as 250 to 300 ° C., the exhaust gas purification performance is low, and the temperature window is lowered. Need to expand to the side.

On the other hand, for example, Japanese Patent Laid-Open No.
No. 044 and JP-A-5-68888, Cu
-Exhaust gas that operates the upper Cu-zeolite catalyst from a low temperature and expands the temperature window by using the reaction heat in the noble metal catalyst layer to form a multilayer by using the zeolite-based catalyst as the upper layer and the noble metal catalyst layer as the lower layer. Purification catalysts have been proposed.

However, since the zeolite-based catalyst originally has a property of being easily degraded when exposed to a high temperature state in which moisture coexists, the above-mentioned conventional exhaust gas purifying catalyst has a reaction of a noble metal catalyst layer provided below. Heat degrades the catalyst, and furthermore, the hydrocarbons are oxidized and consumed in the lower noble metal layer, which causes a problem of lowering the NOx purification rate.

[0013]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to efficiently purify exhaust gas from an automobile engine operating at a wide air-fuel ratio from stoichiometric to lean without deteriorating the function of the three-way catalyst. An object of the present invention is to provide an exhaust gas purifying catalyst which can be used and has durability.

[0014]

Means for Solving the Problems The present inventors have studied to solve the above problems, and as a result, by specifying the pore distribution of the zeolite-based catalyst, the ability of the zeolite-based catalyst to capture a specific gas component. Changes, the function of the three-way catalyst can be sufficiently exhibited, and the bulky hydrocarbons contained in the exhaust gas are less likely to diffuse into the lower noble metal catalyst layer. The occurrence is suppressed,
Since oxidation consumption in the lower layer of hydrocarbons as a reducing agent required for NOx purification is also suppressed, it has been found that the NOx purification rate is improved, and the present invention has been reached.

According to the exhaust gas purifying catalyst of the present invention, a honeycomb-shaped catalyst [1] including a metal-supported porous crystalline aluminosilicate catalyst layer and a noble metal-supported alumina catalyst layer is disposed upstream of an exhaust gas flow. An exhaust gas purifying catalyst comprising a honeycomb catalyst [2] including a source catalyst disposed downstream of an exhaust gas flow, wherein the catalyst contained in the metal-supported porous crystalline aluminosilicate in the honeycomb catalyst [1] is The total volume of pores having a pore diameter of 4 nm or less is 60% or more of the total volume of pores having a pore diameter of 1 to 100 nm.

That is, the pores having a diameter of 4 to 100 nm are considered to have a temporary and selective trapping force for the specific gas component. By controlling the proportion of the pores, the function of the three-way catalyst is reduced. Can be suppressed. Particularly preferably, the volume sum of pores having a diameter of 4 nm or less is
75% of the total volume of pores having a diameter of 1 nm to 100 nm or less
Above. This is preferable because the function of the three-way catalyst can be more effectively prevented from lowering.

The combination of the honeycomb catalyst [1] containing the zeolite catalyst and the noble metal-supported alumina catalyst and the honeycomb catalyst [2] containing the three-way catalyst of the present invention includes the zeolite catalyst and the noble metal-supported alumina catalyst. It is preferable to dispose the honeycomb catalyst [1] on the upstream side of the exhaust gas and arrange the honeycomb catalyst [2] including the three-way catalyst on the downstream side. When this arrangement is reversed, the reducing gas component necessary for the NOx purification reaction of the lean exhaust gas is consumed before reaching the honeycomb-shaped catalyst [1], and the NOx purification action is hindered. For the same reason, it is preferable that the honeycomb catalyst [1] including the zeolite catalyst and the noble metal-supported alumina catalyst has a zeolite catalyst as an upper layer and a noble metal-supported alumina catalyst as a lower layer.

Zeolite catalyst and noble metal supported alumina
Used in the upper layer of the honeycomb catalyst containing the catalyst [1]
Of zeolite in zeolite-based catalysts_Two/
Al _TwoO_ThreeIs preferably in the range of 25 to 60. S
iO_Two/ Al_TwoO_ThreeWhen the molar ratio of
Insufficient thermal stability of light, heat resistance and durability of catalyst
Is reduced. Conversely, if the molar ratio exceeds 60, the active metal
The amount of the component carried is reduced, and the catalytic activity is reduced.

The zeolite used in the present invention can be appropriately selected from known zeolites, and in particular, a group called a pentacidium type zeolite is effective. Examples of such zeolites include ferrierite, ZSM5, ZSM11,
Examples thereof include β zeolite and Y zeolite, and MFI zeolite is particularly preferable in terms of heat resistance and durability.

Zeolite is preferred because it is stabilized by increasing the crystallinity by hydrothermal treatment, resynthesis, etc., and a catalyst having high heat resistance and durability can be obtained.

As the metal component supported on the zeolite used in the present invention, various transition metal species are effective.
In particular, Cu, Co, Ag, Ni, and Pt are preferable.
Is most preferred. The supported amount is 1.0 to 7.0% by weight in terms of metal based on zeolite excluding adsorbed water.
It is preferable in terms of Ox purification performance and durability.

Further, the Cu / Si atomic ratio [indicated as = B (Cu / Si)] of the entire catalyst particles constituting the zeolite-based catalyst layer of the honeycomb-shaped catalyst [1] arranged on the upstream side and X-ray photoelectron spectroscopy analysis Ratio [S (Cu to S)] with the Cu / Si atomic ratio [= S (Cu / Si)] in the portion from the catalyst particle surface to a depth of 5 nm determined by the XPS method.
i) / B (Cu / Si)] of more than 0 to 5.0 or less, a high-performance catalyst having high activity and excellent durability can be obtained.

An extremely active metal species is easily generated near the surface of the zeolite particles, and the presence of the active species enhances the effect of trapping gas components in the exhaust gas during the conversion of the exhaust gas from lean to stoichiometric. Therefore, the function of the three-way catalyst is greatly reduced. Therefore, in order to exhibit the function of the three-way catalyst, it is necessary to suppress the generation of active species on the surface of the zeolite particles, and it is important not to segregate the active species on the particle surface. Whole C
u / Si atomic ratio [= B (Cu / Si)] and 5n from the catalyst particle surface determined by X-ray photoelectron spectroscopy
m Cu / Si atomic ratio [= S
(Cu / Si)] [S (Cu / Si) / B (Cu
/ Si)] to more than 0 and not more than 5.0,
The effect of trapping gas components is suppressed without lowering the NOx purification activity, and the three-way catalyst can exhibit its function sufficiently.

In the honeycomb catalyst [1] including the zeolite-based catalyst and the noble metal-supported alumina catalyst, the noble metal supported on the noble metal-supported alumina catalyst used in the lower layer is:
Pt and / or Pd, and the supported amount of NO is 0.1 to 1.4 g / L in terms of metal per unit honeycomb volume.
x It is preferable from the viewpoint of purification performance and durability performance. In addition, as a carrier for supporting a noble metal, a general catalyst carrier such as alumina, silica, silica-alumina, magnesia, zirconia, and titania can be used, but alumina has a large specific surface area and excellent heat resistance. This is preferable because noble metals can be highly dispersed and supported, and less noble metals can be effectively used.

When the noble metal-supported alumina catalyst layer in the honeycomb catalyst [1] contains barium and / or potassium and / or lanthanum, the strong oxidizing ability of the noble metal component is suppressed, and the NOx reduction and purification are required under lean conditions. H
This is advantageous in securing the C component and suppressing the heat of oxidation reaction in the noble metal catalyst layer to prevent the deterioration of the metal-supported zeolite catalyst layer.

Further, when cerium is contained in the noble metal-carrying alumina catalyst layer, a function as a three-way catalyst is added, and the purification performance of exhaust gas is improved.

In preparing the exhaust gas purifying catalyst of the present invention, the raw materials of the metal-supporting component include inorganic acid salts, oxides, organic acid salts, chlorides, carbonates, sodium salts, ammonium salts, and ammine complex compounds. And various other compounds can be used, and the metal component can be supported on each carrier, for example, zeolite or alumina by a commonly used method such as an ion exchange method or an impregnation method. Further, a method in which a metal raw material is evaporated at a high temperature and supported in a gas phase, or a method in which the metal material is supported by a physical mixing method is also effective. In the case of the usual ion exchange method or impregnation method, the metal raw material is often used in a solution, and a preferable result may be obtained by adding an acid or a base to the solution and appropriately adjusting the pH. There is
The present invention is not limited by the loading method.

The method for controlling the pore size distribution of the zeolite catalyst includes (1) a method in which zeolite particles are pulverized under wet or dry conditions to control the particle size, and (2) a method in which the zeolite particles are calcined at a high temperature of at least 600 ° C. or higher. (3) a method of mixing various oxide fine powders, (4)
There is a method of coating the catalyst surface with various oxides and controlling the particle size. As the various oxides in the methods (3) and (4), those which are as inert as possible and do not adversely affect the catalytic performance are preferable.
₂ O ₃ ), silica (SiO ₂ ), titania (Ti
O ₂ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ )
And the like are preferably used. Although the above method is effective alone, an even greater effect can be obtained by appropriately combining the above methods (1) to (4).

In the production of the honeycomb catalyst [1] including the zeolite catalyst and the noble metal-supported alumina catalyst, a method according to a conventional method for producing a honeycomb three-way catalyst can be applied. That is, this is a method in which various kinds of silica, alumina, silica-alumina and the like are added as a binder to the powder of the zeolite-based catalyst and the noble metal-supported alumina catalyst, and water is further added to form a slurry to coat the honeycomb carrier. As a specific example, when the zeolite-based catalyst layer and the noble metal-supported alumina catalyst layer are separately applied to an upper layer and a lower layer, respectively, first, a slurry of a noble metal-supported alumina catalyst is coated on a honeycomb carrier, dried at 120 ° C., and then dried.
By firing at 0 ° C., the catalyst layer is fixed on the honeycomb carrier. Next, a slurry of a zeolite-based catalyst is coated thereon, and dried and fired similarly.

The catalyst disposed downstream of the exhaust gas flow is a honeycomb catalyst [2] including a three-way catalyst. The three-way catalyst is generally obtained by supporting a refractory inorganic substance with a noble metal component. Noble metals contained in such catalysts include P
At least one element selected from the group consisting of t, Pd, and Rh is included. Further, as the refractory inorganic material, alumina, silica, silica-alumina, magnesia, zirconia, can be used a general catalyst carrier such as titania,
It is not limited by this. Alumina is a preferable catalyst carrier because it has a large specific surface area and is excellent in heat resistance, so that noble metals can be highly dispersed and supported, and less noble metals can be effectively used.

The three-way catalyst of the honeycomb catalyst [2] on the downstream side of the exhaust gas usually contains cerium. Cerium has a function (oxygen storage capacity) that expands the air-fuel ratio range that can simultaneously purify three components of HC, CO, and NOx in the stoichiometric region where the air-fuel ratio (air / fuel ratio) is around 14.6. Is well known. Barium is NOx
It has the ability to adsorb, from stoichiometric to lean,
This is effective in efficiently purifying NOx under the transient operation condition from lean to stoichiometric.

The above-mentioned catalysts disposed on the upstream side and the downstream side of the exhaust gas stream of the present invention are preferably used in a honeycomb shape. In this case, the catalyst used in the present invention is usually applied to a honeycomb-shaped carrier and used. As the honeycomb material, cordierite-based materials are generally widely used, but are not limited thereto, and a honeycomb carrier made of a metal material is also effective, and the catalyst powder itself is formed into a honeycomb shape. You can also. Furthermore, by making the shape of the catalyst a honeycomb shape, the contact area between the catalyst and the exhaust gas is increased and the pressure loss is suppressed, so that a large amount of exhaust gas is processed in a limited space with vibration. This is extremely advantageous when used as an automotive catalyst which is required to be used.

[0033]

The present invention will be described below with reference to the following examples and comparative examples.
The present invention will be described in more detail with reference to
Not.Example 1 (1) Zeolite-based catalyst and noble metal-supported alumina catalyst
Honeycomb-like catalyst containing [1] (a) zeolite-based catalyst slurry_Two/ Al_TwoO_Three
NH with a molar ratio of about 37 _FourGood by adding type ZSM5 powder
The solid and liquid were separated by vigorous stirring and filtration.
By repeating the stirring / filtration operation five times, Cu
Obtaining ZSM5 zeolite catalyst cake carrying ion exchange
Was. This cake is dried at 120 ° C. for 24 hours using a dryer.
After drying, 670 under air atmosphere using an electric furnace.
5.8% by weight of Cu
The obtained Cu-ZSM5 catalyst powder was obtained. The obtained Cu-
[S (Cu / Si) / ZSM5 zeolite catalyst
BCu / Si)] was measured by the XPS method.
Met.

The thus obtained Cu-ZSM5 catalyst powder, aluminum sol, silica sol, titania sol and water were placed in a magnetic ball mill pot and mixed and pulverized for 1 hour to form a slurry. The added amounts of the alumina sol, silica sol and titania sol are Al ₂ O ₃ and Si
Cu-ZSM5 excluding adsorbed water as O ₂ and TiO ₂
It was 2% by weight, 6% by weight, and 2% by weight based on the catalyst powder.

(B) Noble metal-supported alumina catalyst slurry 10% by weight of cerium oxide (CeO ₂ ) was added to activated alumina containing γ-alumina as a main component, and the Pd component was supported by impregnation using an aqueous dinitrodiammine palladium solution. , Dried in a dryer at 120 ° C for 8 hours, and dried in an air stream for 45 hours.
Baking at 0 ° C. for 2 hours, Pd carrying 0.5% by weight of Pd
to give the _{d-CeO 2 -Al 2 O 3} . This Pd-CeO ₂
-Al ₂ O ₃ was mixed with an acidic alumina sol and water, and pulverized in a magnetic ball mill pot for 2 hours to obtain a slurry.

(C) Preparation of honeycomb catalyst [1] containing zeolite-based catalyst and noble metal-supported alumina catalyst The noble metal-supported alumina catalyst slurry obtained in the above (b) was subjected to a flow rate of about 400 per square inch cross section. To 1.0 L of cordierite honeycomb carrier with
After drying with hot air at 0 ° C., firing was performed at 500 ° C. for 1 hour to bake the Pd—CeO ₂ —Al ₂ O ₃ catalyst on the honeycomb support. The coating amount of the Pd catalyst layer was about 80 g / L. Further, the honeycomb catalyst is added to the C obtained in the above (a).
The slurry of u-ZSM5 was applied, dried with hot air at 150 ° C., and then baked at 500 ° C. for 1 hour, so that about 150 g / L of Cu-ZSM5 catalyst was baked on the honeycomb support. The honeycomb-shaped catalyst is immersed in a colloidal silica solution for 2 seconds, and then the excess solution is blown off with compressed air, dried at 100 ° C. in a drier, and calcined at 600 ° C. for 1 hour in an electric furnace, and used in the present invention. A honeycomb-like catalyst [1] containing a zeolite-based catalyst and a noble metal-supported alumina catalyst was obtained. The amount of the impregnated carrier of colloidal silica was 4 g / L as SiO ₂ .

(2) Honeycomb catalyst containing a three-way catalyst [2] 20% by weight of cerium oxide was added to activated alumina mainly composed of γ-alumina, and Pd was supported by impregnation using an aqueous solution of dinitrodiammine palladium. Thereafter, the resultant was dried at 120 ° C. for 8 hours using a dryer, and calcined at 450 ° C. for 2 hours in an air stream to obtain Pd-activated alumina carrying 1.4% by weight of Pd. 3% by weight of cerium oxide was further added to the Pd-CeO2-activated alumina, and ₂ % by weight of activated alumina and 1% by weight of nitric acid boehmite sol were added.
2% by weight was added and mixed, and the mixture was pulverized in a magnetic ball mill pot for 8 hours to obtain a slurry. The slurry was coated on 0.9 L of a honeycomb carrier in the same manner as in the above zeolite-based catalyst, dried at 120 ° C, and calcined at 400 ° C. The coating amount of the catalyst was about 150 g / L.

Next, an aqueous rhodium nitrate solution was added to activated alumina containing 35% by weight of cerium oxide, and Ph was carried by an impregnation method. Then, it was dried at 120 ° C. for 8 hours using a drier, and dried at 450 ° C. in an air stream. After firing for an hour, Rh is reduced to 0.
9% by weight of supported Rh-CeO ₂ -activated alumina was obtained. A nitric acid boehmite sol was added to the Rh-CeO ₂ -activated alumina, mixed and pulverized in a magnetic ball mill pot for 3 hours to obtain a slurry. This slurry was mixed with the above Pd-
It was coated on a honeycomb coated with CeO ₂ -activated alumina, dried at 120 ° C., and fired at 400 ° C. The obtained honeycomb catalyst was impregnated with an aqueous barium acetate solution, followed by drying at 120 ° C. and firing at 400 ° C. to obtain a honeycomb catalyst [2] containing a three-way catalyst. The coating amount of the Ph-activated alumina was 42 g / L.
And the supported amount of barium is barium oxide (BaO)
Was 13 g / L per honeycomb capacity.

The honeycomb catalyst [1] containing the above-mentioned Cu-ZSM5 is arranged in series on the upstream side of the exhaust gas flow, and the honeycomb catalyst [2] containing the three-way catalyst is arranged in series on the downstream side, and incorporated in the catalytic converter. 1.0 L + 0.9 L] = 1.9 L of tandem catalyst (1) was obtained.

Example 2 A tandem catalyst (2) was obtained in the same manner as in Example 1, except that CeO ₂ was not added when preparing the noble metal-supported alumina catalyst in the honeycomb catalyst [1].

Example 3 In Example 1, the calcination of the Cu-ZSM5 catalyst powder was performed for 70 minutes.
A tandem catalyst (3) was obtained in the same manner except that the temperature was set at 0 ° C. for 4 hours and the impregnation with colloidal silica was not performed. [S (Cu / Si) /
B (Cu / Si)] ratio was 1.5.

Example 4 In Example 1, the calcination of the Cu-ZSM5 catalyst powder was performed for 70 minutes.
At 0 ° C. for 4 hours, the amount of colloidal silica impregnated
A tandem catalyst (4) was obtained in the same manner except that g / L was used.

Example 5 In Example 1, the calcination of the Cu-ZSM5 catalyst powder was performed for 70 minutes.
At 0 ° C. for 4 hours, the amount of colloidal silica impregnated
A tandem catalyst (5) was obtained in the same manner except that the amount was changed to g / L.

Example 6 In the method for producing the honeycomb catalyst [1] of Example 1, a Pd-CeO ₂ -Al ₂ O ₃ catalyst layer was baked on a honeycomb carrier, and then this was replaced with barium acetate and lanthanum nitrate.
a: La = 2: 1 (atomic ratio), impregnated in an aqueous solution, then dried and fired to obtain BaO and La ₂ O.
_A honeycomb-shaped catalyst [1] was obtained in the same manner except that 3g was contained at 8 g / L and 2 g / L per honeycomb capacity, respectively. This honeycomb catalyst [1] and the honeycomb catalyst [2] including the three-way catalyst of Example 1 were incorporated in a catalytic converter in the same manner as in Example 1 to obtain a tandem catalyst (6).

Comparative Example 1 In Example 1, the calcination of the Cu-ZSM5 catalyst powder was
At 0 ° C. for 4 hours, when producing the slurry, only alumina sol was added without adding silica sol. The amount of addition was Cu-ZSM5 excluding adsorbed water as Al ₂ O _3.
Honeycomb-shaped C disposed upstream of the exhaust gas flow in the same manner as in Example 1 except that the amount was 12% by weight with respect to the catalyst powder.
A u-ZSM5 catalyst was obtained. The [S (Cu / Si) / B (Cu / Si)] ratio in this Cu-ZSM5 catalyst is:
3.2. The honeycomb catalyst [1] containing the above-mentioned Cu-ZSM5 and the honeycomb catalyst [2] containing the three-way catalyst obtained in Example 1 were incorporated into a catalytic converter in the same manner as in Example 1, and 1.9 L [= 1.0 L + 0.9 L] of the tandem catalyst (7).

Comparative Example 2 In the preparation process of the Cu-ZSM5 catalyst powder in Example 1,
The concentration of the aqueous solution of copper nitrate was adjusted to 0.23 M, and the pH of the solution was adjusted to 8.5 by adding an aqueous solution of ammonia. Using this solution, a tandem catalyst (8) was obtained in the same manner as in Example 1 except for the above. C in the Cu-ZSM5 catalyst obtained in this comparative example
The supported amount of u was 10.2% by weight with respect to the Cu-ZSM5 catalyst powder excluding the adsorbed water, and was measured by XPS [S (C
u / Si) / B (Cu / Si)] ratio was 5.2.

Test Example The pore volume and catalytic performance of the exhaust gas purifying catalysts obtained in Examples 1 to 5 and Comparative Example 1 were examined by the following methods.

The details of the zeolite catalyst supporting the metal component
Pore volume measurement device; Asap 2400 type manufactured by Shimadzu (Micromeritex) Measuring method; Constant volume method by N ₂ gas adsorption Pore distribution data analysis; BJH method Sample pretreatment method; Degas at 250 ° C. for about 15 hours Treatment (10 ⁻³ mmHg or less) Analysis data; From the data on the adsorption side, the integrated adsorption pore volume is plotted against the pore diameter, and the volume sum V ₄ of the pores having a diameter of 4 nm or less and the diameter of 1 to 100 nm are obtained. obtains the following pore volume total V _100, [V ₄ / V _100] × 1
00 (%) was calculated. Table 1 shows the results.

An apparatus for XPS measurement and analysis of Cu-ZSM5 catalyst : ESCA5600 manufactured by Parkin Elmer
X-ray photoelectron spectroscopy analyzer Analysis conditions: Mg-Kα ray (1253.6e) as X-ray source
V) and operated at 15 KV x 26.7 mA. Charging correction: binding energy of SiO ₂ is 103.2 eV
To correct the charge. Test sample: molded into a disk at a pressure of 230 kg / cm ^{2 by} a pressure molding machine. From the results of quantitative analysis of Si and Cu components at a depth of about 5 nm from the catalyst surface for each of the zeolite catalysts of Examples and Comparative Examples by the above method, the results show that Cu on the surface of the catalyst particles including up to the above depth was obtained. / Si atomic ratio =
S (Cu / Si) was calculated. On the other hand, the contents of Si and Cu in the entire catalyst were determined by the IPC method,
u / Si atomic ratio = BCu / Si) was calculated. From the above, [S (Cu / Si) / B (Cu /
Si)] ratio is calculated and is shown in Table 1 together with the evaluation results of the catalyst performance.

Catalyst Initial Performance Test Example The tandem-type catalysts of the above embodiment and comparative example were mounted on the exhaust system of a vehicle equipped with an inline 6-cylinder 2L engine, and the air-fuel ratio (A / F) was 14.6 (stoichiometric). After running for 40 seconds, the A / F switching operation mode in which A / F = 21 (lean) for 20 seconds was repeated 20 times. The average purification rate of HC, CO, and NOx in the exhaust gas in the switching motion mode was calculated by the following equation, and the result is shown in Table 1.
The average catalyst inlet temperature during this mode switching operation is 380
° C.

Example of Performance Test after Catalyst Endurance The tandem catalysts of the above embodiment and the comparative example were mounted on the exhaust system of a vehicle equipped with a V-type 6-cylinder 3 engine, and A / F = 1
After operating for 20 seconds at 4.6, and operating for 40 seconds at A / F = about 21, 1 in the stoichiometric / lean A / F switching operation mode
After operating for 00 hours, NC, CO, NOx in exhaust gas
Was calculated by the following equation, and the results are shown in Table 1. The catalyst inlet temperature under these operating conditions is 650 ° C.
Met.

(Equation 1)

[0052]

[Table 1]

[0053]

The automobile exhaust gas purifying catalyst of the present invention is
By specifying the pore distribution of the zeolite-based catalyst, the ability of the zeolite-based catalyst to capture a specific gas component can be suppressed, so that it operates with a wide air-fuel ratio from stoichiometric to lean without reducing the function of the three-way catalyst. Engine exhaust gas can be purified with high efficiency and at 600 ° C
Since there is little deterioration even when used for a long time at the above-mentioned high temperature, it is possible to provide an automobile with little environmental pollution and excellent economy (fuel efficiency).

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI F01N 3/10 F01N 3/28 301P 3/28 301 B01D 53/36 ZAB 102B 102H 104A

Claims (9)

[Claims] 1. A honeycomb-shaped catalyst [1] including a metal-supported porous crystalline aluminosilicate catalyst layer and a noble metal-supported alumina catalyst layer is disposed upstream of an exhaust gas flow, and a honeycomb-shaped catalyst including a three-way catalyst [1]. 2] is disposed on the downstream side of the exhaust gas flow, and has a pore diameter of 4 nm or less in the metal-supported porous crystalline aluminosilicate in the honeycomb catalyst [1]. An exhaust gas purifying catalyst, wherein the total volume of pores is 60% or more of the total volume of pores having a pore diameter of 1 to 100 nm. 2. The exhaust gas purifying catalyst according to claim 1, wherein the total volume of pores having a pore diameter of 4 nm or less in the metal-supported porous crystalline aluminosilicate in the honeycomb catalyst [1]. Is 75% or more of the total volume of pores having a pore diameter of 1 to 100 nm. 3. The exhaust gas purifying catalyst according to claim 1, wherein the honeycomb catalyst [1] arranged on the upstream side of the exhaust gas flow has a metal-supported porous crystalline aluminosilicate as an upper layer, An exhaust gas purifying catalyst comprising a noble metal-supported alumina catalyst layer as a lower layer. 4. The exhaust gas purifying catalyst according to claim 1, wherein the metal component carried on the porous crystalline aluminosilicate in the honeycomb catalyst [1] is copper, and Noble metal component supported on Pt
And / or Pd. 5. The exhaust gas purifying catalyst according to claim 4, wherein a Cu / Si atomic ratio [B (Cu / Cu / Si) of the entire catalyst particles constituting the metal-supported porous crystalline aluminosilicate catalyst layer.
Si)] and the ratio [S (Cu / Si)] of the Cu / Si atomic ratio [S (Cu / Si)] in the portion from the catalyst particle surface to a depth of 5 nm determined by X-ray photoelectron spectroscopy (XPS).
(Cu / Si) / B (Cu / Si)] exceeds 0,5.
An exhaust gas purifying catalyst characterized by being 0 or less. 6. The exhaust gas according to claim 1, wherein:
Catalysts for purification of porous, crystalline aluminosilicate
Silica (SiO_Two) / Alumina (Al_TwoO _Three) Ratio is 2
Characterized in that it is an MFI-type zeolite of 5-60.
Exhaust gas purification catalyst. 7. The exhaust gas purifying catalyst according to claim 1, wherein the noble metal-supported alumina catalyst layer in the honeycomb catalyst [1] further comprises at least one selected from the group consisting of barium, potassium and lanthanum. An exhaust gas purifying catalyst characterized by containing one kind. 8. The exhaust gas purifying catalyst according to claim 1, wherein cerium is further contained in the noble metal-supported alumina catalyst layer in the honeycomb catalyst [1]. catalyst. 9. The exhaust gas purifying catalyst according to claim 1, wherein the three-way catalyst comprises at least one noble metal selected from the group consisting of platinum, palladium and rhodium and cerium and barium. An exhaust gas purifying catalyst, which is a supported alumina.