JPH11169669A - Exhaust gas cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the cleaning method by treating the exhaust gas containing hydrocarbon and carbon monoxide together with nitrogen oxides under an oxygen excessive atmosphere. SOLUTION: The treating atmosphere of the exhaust gas is swung alternately between the oxygen excessive atmosphere and a reductive atmosphere, and the exhaust gas is brought into contact with the first catalyst consisting of at least one kind platinum group element among Pt, Rh, Pd and Ir, at least one kind metal, its compd. or its ion among silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel and at least one kind oxide among titanium oxide, zirconia and tin oxide. Then the exhaust gas is brought into contact with the second catalyst (nitrogen oxides occluding catalyst) consisting of one or >=2 kinds metal oxides or composite oxides among alkali metal, alkaline earth metal, aluminum, silver, titanium and rare earth elements and at least one kind platinum group element among Pt, Rh, Pd and Ir.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for treating an exhaust gas containing hydrocarbons and carbon monoxide together with nitrogen oxides in an oxygen-excess atmosphere to remove hydrocarbons and carbon monoxide along with these nitrogen oxides. And a method for purification. Specifically, the present invention is a method for removing and purifying nitrogen oxides in exhaust gas discharged from factories, automobiles, and the like, and is a method for purifying nitrogen monoxide in exhaust gas on a catalyst under an oxygen-excess atmosphere. Nitrogen dioxide is then converted to nitrogen dioxide and then adsorbed onto the catalyst together with the nitrogen dioxide present in the exhaust gas from the beginning, where a reducing agent such as fuel is intermittently introduced into the exhaust gas for a short period of time, In addition, the present invention relates to a method for purifying exhaust gas in which the exhaust gas atmosphere is periodically changed to a reducing atmosphere to perform catalytic reduction and oxidize and remove harmful components such as hydrocarbons and carbon monoxide in an oxidizing atmosphere.

[0002]

2. Description of the Related Art Conventionally, as a method of removing nitrogen oxides from exhaust gas discharged from factories, automobiles, etc., there is a method of oxidizing the nitrogen oxides and then absorbing the same with an alkali, ammonia, hydrogen, carbon monoxide, or the like. And a method of converting to nitrogen by using a reducing agent such as hydrocarbon. However, according to the former method, it is necessary to take measures for treating the generated alkaline waste liquid to prevent the occurrence of pollution. On the other hand,
According to the latter method, when ammonia is used as the reducing agent, it reacts with the sulfur oxide in the exhaust gas to form salts, and as a result, there is a problem that the reducing activity of the catalyst is reduced. In addition, even when hydrogen, carbon monoxide, hydrocarbons, and the like are used as a reducing agent, since they react with oxygen present at a higher concentration than nitrogen oxide present at a lower concentration, it is necessary to reduce nitrogen oxides. Has the problem that a large amount of reducing agent is required.

[0003] For this reason, recently, a method of directly decomposing nitrogen oxides with a catalyst in the absence of a reducing agent has been proposed.
There is a problem that it is difficult to be put to practical use due to low nitrogen oxide decomposition activity.

As a new catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon or an oxygen-containing compound as a reducing agent, various zeolites have been proposed.
M-5 and H-type _{ZSM-5 (SiO 2 / Al} 2 O 3 molar ratio = 30 to 40) are to be optimal. However, even with such Cu-ZSM-5 or H-type ZSM-5, it is still difficult to say that they have a sufficient reducing activity. In particular, when moisture is contained in the exhaust gas, aluminum in the zeolite structure is removed. Since the performance of aluminum is sharply reduced, there is a demand for a catalyst for catalytic reduction of nitrogen oxides having higher reduction activity and having excellent durability even when the exhaust gas contains moisture. .

Therefore, various catalysts such as a catalyst comprising silver or silver oxide supported on an inorganic oxide have been proposed.
Among such catalysts, a catalyst having a high reaction rate has a high oxidizing activity and a low selectivity for nitrogen oxides, so that the removal rate of nitrogen oxides is low, and on the other hand, a reaction selectivity such as alumina is high. The catalyst has a serious problem in practical use, such as a low reaction rate and difficulty in use at a high SV (space velocity). Further, there is a problem that the catalyst activity is significantly deteriorated in the coexistence of sulfur oxide (JP-A-5-31764).
No. 7). Further, the conventional catalyst for catalytic reduction of nitrogen oxides does not have sufficient heat resistance, and depending on the application, further heat resistance is strongly demanded.

Therefore, as one method for solving such a problem, nitrogen monoxide (NO) is converted to nitrogen dioxide (NO ₂ ) on a catalyst under an excess of oxygen (lean conditions), and thus the produced product is produced. Nitrogen dioxide is adsorbed on the catalyst, and a reducing agent, for example, a hydrocarbon such as fuel or an oxygen-containing organic compound is intermittently injected for a short period of time, that is, in a pulsating manner (hereinafter, referred to as pulsating).
Injecting "pulse". ), A nitrogen oxide storage catalyst that reduces nitrogen oxides to nitrogen under a reducing atmosphere (rich conditions) has been proposed (Japanese Patent Application Laid-Open No. Hei 9-1).
No. 22486). However, since the exhaust gas usually contains sulfur oxides, according to this method, the sulfur oxides are adsorbed at the adsorption points of the nitrogen oxides, and therefore, the hydrocarbons such as fuel are pulsed. Even if the exhaust gas treatment atmosphere is reduced to a reducing atmosphere by injecting into the engine chamber or supplying hydrocarbons such as fuel to the engine chamber in a pulsed manner with a stoichiometric amount or more, this sulfur oxide does not desorb from the catalyst. Thus, there is a problem that the adsorption amount of nitrogen oxide on the catalyst gradually decreases, and the nitrogen oxide removal rate sharply decreases.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in a conventional exhaust gas purifying method using a nitrogen oxide storage type exhaust gas purifying catalyst. However, under an excess of oxygen, nitric oxide is converted to nitrogen dioxide on the catalyst with high efficiency, and thus the generated nitrogen dioxide is adsorbed on the catalyst, and a reducing agent is injected in a pulsed manner to this, In an exhaust gas purification method using a nitrogen oxide storage type catalyst, in which an exhaust gas atmosphere is set as a reducing atmosphere, nitrogen oxides are reduced to nitrogen, and hydrocarbons and carbon monoxide are also oxidized and removed under an excess of oxygen. Even when it contains sulfur oxides,
In a preferable case, even at a relatively low temperature, the nitrogen oxide storage function of the nitrogen oxide storage type catalyst does not decrease, and the heat resistance is excellent. An object of the present invention is to provide an exhaust gas purifying catalyst capable of stably and efficiently reducing and removing substances.

[0008]

The first aspect of the exhaust gas purifying method according to the present invention is to alternately oscillate the exhaust gas treatment atmosphere between an oxygen-excess atmosphere and a reducing atmosphere to thereby reduce nitrogen oxides and carbon dioxide in the exhaust gas. In the exhaust gas purifying method for purifying ternary components of hydrogen and carbon monoxide, the exhaust gas is subjected to (1)
(a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir and (b) silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel And (c) at least one metal selected from the group consisting of titanium oxide, zirconia, and tin oxide.
And then (2) (a) an alkali metal,
(B) at least one selected from the group consisting of oxides or composite oxides of one or more metals selected from the group consisting of alkaline earth metals, aluminum, silver, titanium and rare earth elements, and (b) Pt, Rh, Pd and Ir It is characterized in that it is brought into contact with a second catalyst comprising a kind of platinum group element.

Here, the second catalyst is a nitrogen oxide storage type catalyst, and among them, one kind selected from alkali metal, alkaline earth metal, aluminum, silver, titanium and rare earth element which are the component (a). Alternatively, an oxide or composite oxide of two or more metals is a nitrogen oxide storage.

A second aspect of the exhaust gas purifying method according to the present invention is to alternately oscillate the exhaust gas treatment atmosphere between an oxygen-excess atmosphere and a reducing atmosphere to thereby reduce nitrogen oxides, hydrocarbons and carbon monoxide in the exhaust gas. In the exhaust gas purifying method for purifying ternary components, exhaust gas is subjected to (1) (a) Pt, Rh,
At least one platinum group element selected from the group consisting of Pd and Ir and (b) at least one selected from the group consisting of silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel 1
Contacting a first catalyst comprising a metal or its compound or its ion with (c) at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide; (B) at least one platinum group element selected from the group consisting of Pt, Rh, Ir and Pd;
Contacting with an intermediate catalyst comprising at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide, and then (3) (a) an alkali metal, an alkaline earth metal, aluminum, silver, titanium and A second oxide comprising one or more metal oxides or composite oxides selected from rare earth elements and (b) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir It is characterized by being brought into contact with a catalyst.

Therefore, the second method is different from the first method only in that the exhaust gas is brought into contact with the intermediate catalyst while the exhaust gas is brought into contact with the first catalyst and the second catalyst, respectively.

According to the present invention, in any of the first and second methods, the first catalyst may comprise silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, which is the component (b). The compound of at least one metal selected from the group consisting of manganese, iron, cobalt and nickel is usually an oxide. However, in the first catalyst, when the component (b) is silver or a compound thereof, such a component may be metallic silver or silver aluminate (or silver aluminate, AgAlO ₂ ). On the other hand, in any of the first and second methods, the second catalyst comprises (a) a composite oxide of barium and aluminum and (b)
It is preferably made of at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir.

[0013]

DETAILED DESCRIPTION OF THE INVENTION According to a first method of the present invention, nitrogen oxides, hydrocarbons and exhaust gas in an exhaust gas are treated by alternately oscillating an exhaust gas treatment atmosphere between an oxygen-excess atmosphere and a reducing atmosphere. In an exhaust gas purifying method for purifying ternary components of carbon monoxide, exhaust gas is subjected to (1) (a) Pt,
At least one platinum group element selected from the group consisting of Rh, Pd and Ir, and (b) silver, copper, zinc, aluminum,
Gallium, tin, zirconium, chromium, manganese,
At least one metal selected from the group consisting of iron, cobalt and nickel, or a compound or ion thereof, and (c)
Contacting with a first catalyst comprising at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide, and then (2) (a) an alkali metal, an alkaline earth metal, aluminum, silver, An oxide or composite oxide of one or more metals selected from titanium and rare earth elements and (b) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir 2. Contact catalyst No. 2.

In the present invention, in the first catalyst, at least one selected from the group consisting of component (b) copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel.
The compound of the species metal is usually an oxide. However, the first
In the above catalyst, when the component (b) is silver or a compound thereof, preferred examples thereof include metallic silver, silver oxide or silver aluminate (or silver aluminate, AgAlO ₂ ).
Can be mentioned.

The silver aluminate is prepared by immersing alumina, preferably hydrated alumina, in a mixed aqueous solution of a water-soluble aluminum salt such as aluminum nitrate and a water-soluble silver salt such as silver nitrate. After impregnating the pores of the alumina with the salt, the powder is dried by a suitable means such as a spray drier, and then dried at 600 to 900 ° C., preferably 700 ° C. in an oxidizing atmosphere in the presence of steam. By heating and firing at a temperature of about 800 ° C., that is, by firing under hydrothermal conditions, a γ-alumina powder carrying silver aluminate can be obtained. The amount of water vapor in the oxidizing atmosphere is usually 3
-20% by weight, preferably 5-15% by weight.

In the first method according to the present invention, the first catalyst preferably contains (a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd, and Ir in terms of metal. 0.1 to 10% by weight, preferably
In the range of 0.5 to 5% by weight, (c) the carrier is supported on a carrier comprising at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide;
Component (b) (except when the component (b) is contained in the catalyst as metallic silver or silver aluminate) in an amount of 0.1 to 20% by weight in terms of oxide, preferably , 0.
The carrier (c) is supported on the carrier (c) in the range of 5 to 10% by weight.

In the first catalyst, when the component (b) is metallic silver or silver aluminate, the amount supported on the carrier is calculated in terms of metallic silver. In the catalyst, metallic silver or silver aluminate is used in an amount of 0.1 to 20% by weight in terms of silver, preferably 0.5% by weight.
It is assumed that the carrier (c) is carried on the carrier (c) in the range of 10 to 10% by weight (the same applies hereinafter).

The second catalyst, which is a nitrogen oxide storage catalyst, comprises (a) at least one kind selected from an alkali metal, an alkaline earth metal, aluminum, titanium, silver and a rare earth element as a nitrogen oxide storage material. 25-75% by weight of a (mixed) metal oxide or a composite oxide of at least two metals selected from alkali metals, alkaline earth metals, aluminum, titanium, silver and rare earth elements; Group element is 0.1 to 10% by weight, preferably 0.5 to 5% by weight in any conventionally known carrier such as alumina, titania, zirconia, silica, silica-alumina and the like.
75 to 25% by weight. In the present invention, in the second catalyst,
(a) The silver composite oxide as a component shall contain silver aluminate.

However, according to the present invention, in the second catalyst, a composite oxide of barium and aluminum is preferably used as the component (a). As is already known, this composite oxide of barium and aluminum is a composite oxide composed of barium, aluminum and oxygen, and is usually BaO.Al ₂ O ₃ or Ba.
Represented by O · 6Al ₂ O ₃ (Hiromichi Arai, Masato Machida,
"Metal" June 1989 issue, heat-resistant ceramic fine particles).

The first catalyst used in the first method according to the present invention particularly oxidizes sulfur oxides (SOx) by a platinum group element in the catalyst, and when lean, sulfur oxides contained in exhaust gas (SOx). SOx) is easily adsorbed on the catalyst, and this sulfur oxide is mainly desorbed as sulfur dioxide (SO ₂ ) or hydrogen sulfide when rich, thus preventing the sulfur oxide from adsorbing on the second catalyst when lean. Then, the second catalyst has a role of preventing a decrease in the catalytic ability of the second catalyst to reduce nitrogen oxides by suppressing a decrease in the ability to adsorb nitrogen dioxide (NO ₂ ). Also,
The second catalyst oxidizes nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ) during lean operation, adsorbs NO ₂ on the catalyst, and reduces the adsorbed NO ₂ to nitrogen with a reducing agent during lean operation. Take a role.

Therefore, in the first catalyst, the carrier of the platinum group element as the component (a), that is, (c) at least one selected from the group consisting of titanium oxide, zirconia and tin oxide.
When the supported amount of the seed oxide is less than 0.1% by weight in terms of metal, the oxidation of sulfur oxides in the exhaust gas is insufficient. However, the loading does not need to exceed 10% by weight.

In the first catalyst, the component (b), that is, at least one selected from the group consisting of silver, copper, zinc, aluminum, gallium, tin, zirconia, chromium, manganese, iron, cobalt and nickel. The amount of the metal or its compound or its ion supported on the carrier, i.e., (c) the amount of the metal supported on at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide is calculated in terms of oxide. When the amount is less than 0.1% by weight, the sulfur oxides contained in the exhaust gas cannot be sufficiently adsorbed on the first catalyst at the time of leaning, and the sulfur oxides not adsorbed thereon are reduced to the second catalyst. Thus, sulfur oxides are not desorbed from the second catalyst at the time of richness and are gradually accumulated in the catalyst. As a result, the ability to adsorb nitrogen dioxide is reduced, and the ability to reduce nitrogen oxides is reduced. Power drops.

If titanium oxide is used as the carrier, the titanium oxide preferably releases sulfur oxides as hydrogen sulfide when rich. Therefore, according to the present invention, titanium oxide is particularly preferably used as the carrier in the first catalyst.

However, in the first catalyst, even if the amount of the component (b) supported on the carrier, that is, the component (c) exceeds 20% by weight in terms of oxide, the amount of the obtained first catalyst cannot be reduced. This is disadvantageous because the adsorption capacity of sulfur oxides is not improved correspondingly and the production cost of the catalyst is unnecessarily increased.

Next, in the first method according to the present invention,
Among the second catalysts, in particular, as described above, the catalyst component composed of a platinum group element oxidizes nitrogen oxides to nitrogen dioxide when lean, and produces alkali metals, alkaline earth metals, aluminum, silver, titanium and titanium. A catalyst component comprising an oxide or a composite oxide of one or more metals selected from rare earth elements adsorbs this nitrogen dioxide,
When rich, it is reduced to nitrogen by a catalyst component comprising a platinum group element in the presence of a reducing agent.

In the second catalyst, examples of the alkali metal include lithium, sodium and potassium, and examples of the alkaline earth metal include beryllium, magnesium, calcium, strontium and barium, and rare earth elements. Examples of the element include scandium, yttrium, a lanthanoid element, an actinoid element, and the like. Among these, yttrium, lanthanum, cerium, thorium and the like are particularly preferable. Among these, as mentioned above,
In particular, a composite oxide of barium and aluminum is preferably used.

According to the present invention, in the second catalyst, when the components (a) and (b) are out of the above range, the reduction activity of nitrogen oxides is greatly reduced. When the amount of the supported platinum group element in component (b) is less than 0.1% by weight, the second catalyst does not have sufficient nitrogen oxide reduction activity, while the other catalyst has 10% by weight. If it exceeds, the catalytic reduction ability of the second catalyst for nitrogen oxides is not improved correspondingly, and the production cost of the catalyst is unnecessarily increased, which is disadvantageous.

The first method used in the method according to the present invention.
The second catalyst can be prepared, for example, as follows.

First, (a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir and (b)
At least one metal selected from the group consisting of silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel, or a compound or ion thereof, and (c) titanium oxide, zirconia and oxidation The first catalyst comprising at least one oxide selected from the group consisting of tin can be prepared as follows.

That is, a water-soluble salt such as nitrate of at least one element selected from the group consisting of silver, copper, zinc, aluminum, gallium, tin, zirconium, chromium, manganese, iron, cobalt and nickel, and the platinum By immersing the oxide carrier, which is the component (c), in an aqueous solution containing a water-soluble salt of a group III element, removing the excess aqueous solution attached thereto, drying, and baking in air to obtain the above oxide. A catalyst in which the above components (a) and (b) are supported on a carrier can be obtained.

Next, one example of the second catalyst, (a) a catalyst comprising a mixed oxide or a composite oxide of an alkali metal or an alkaline earth metal and aluminum and (b) a platinum group element, It can be prepared as follows.

As a first method, for example, a water-soluble salt of an alkali metal or an alkaline earth metal, for example, barium carbonate or barium acetate is dissolved or dispersed in water together with alumina, and sufficiently mixed with a ceramic grinding medium. After mixing and pulverizing, and thus drying the obtained slurry, 60
The powder is fired in air at a temperature of 0 to 1500 ° C. to obtain a powder of a composite oxide of barium and aluminum (powder A).

On the other hand, a water-soluble salt of a precursor of zirconium oxide, titanium oxide or aluminum oxide (eg, nitrate)
Is dissolved in ion-exchanged water, an alkali such as ammonia is gradually added thereto, and the pH of the slurry is increased until a hydroxide is formed from the water-soluble salt to form a precipitate. The precipitate thus obtained is separated by filtration, washed with water and dried, and then dried under an oxidizing atmosphere such as air at about 400 to 800 ° C., preferably 600 to 80 ° C.
By heating and firing at a temperature of about 0 ° C., powders of zirconium oxide, titanium oxide, and aluminum oxide can be obtained.

Next, the powder of zirconium oxide, titanium oxide or aluminum oxide is immersed in a separately prepared aqueous solution of a water-soluble salt of a platinum group element, dried, and fired in an oxidizing atmosphere. Further, by sintering in a reducing atmosphere, a powder (powder B) in which the above-mentioned zirconium oxide, titanium oxide or aluminum oxide carries a catalyst component comprising a platinum group element is obtained.

Then, by mixing the powder A and the powder B thus obtained, a mixed oxide or a composite oxide of aluminum and an alkali metal or alkaline earth metal such as barium and a platinum group element can be obtained. Can be obtained as a powder.

As a second method, for example, an aqueous solution of a water-soluble salt which is a precursor of alumina such as aluminum nitrate or a water-soluble salt which is a precursor of zirconium oxide such as zirconium nitrate is prepared, or These homogeneous mixed aqueous solutions are prepared, an alkali such as ammonia is gradually added to the aqueous solution, and the mixture is neutralized to form a precipitate. Then, the precipitate is filtered, washed with water, and repulpted repeatedly. , A wet cake was obtained, the wet cake was repulped in ion-exchanged water, and barium hydroxide was further added thereto.
Hydrothermal treatment is performed at a temperature of 0 ° C. After the hydrothermal treatment, the solid content is filtered, washed with water, dried, and calcined in air at a temperature of 800 to 1500 to obtain an alumina and / or zirconia powder supporting a composite oxide of barium and aluminum. .

Next, this powder is immersed in a separately prepared aqueous solution of a water-soluble salt of a platinum group element, dried, fired in an oxidizing atmosphere, and optionally fired in a reducing atmosphere. In addition, a catalyst in which a platinum group element is supported on a composite oxide of barium and aluminum and zirconium oxide and / or aluminum oxide can be obtained as a powder.

Further, as another method, as described above,
A powder in which silver aluminate is supported on γ-alumina is prepared, immersed in a separately prepared aqueous solution of a water-soluble salt of a platinum group element, dried, and then baked in an oxidizing atmosphere. Further, by firing in a reducing atmosphere, a catalyst comprising a platinum group element supported on γ-alumina together with silver aluminate can be obtained as a powder.

The second method according to the present invention is characterized in that, in the first method, while contacting the exhaust gas with the first catalyst and the second catalyst, respectively, (a) from the group consisting of Pt, Rh, Ir and Pd. The first method described above, except that it is brought into contact with an intermediate catalyst comprising at least one platinum group element selected and (b) at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide. Is the same.

The intermediate catalyst used in the second method preferably contains (a) a platinum group element in an amount of 0.1 to 0.1 in terms of metal.
The component (b) is supported on the oxide carrier in the range of 10% by weight, preferably in the range of 0.5 to 5% by weight. As the oxide, titanium oxide is particularly preferable.

According to the second method, the intermediate catalyst reduces the sulfur compound desorbed from the first catalyst to hydrogen sulfide, thereby converting the sulfur oxide into the second catalyst at the subsequent stage. Has a role to prevent adsorption.

Therefore, when the amount of the platinum group element supported on the oxide carrier in the intermediate catalyst is less than 0.1% by weight, the sulfur compound desorbed from the first catalyst is sufficiently reduced to hydrogen sulfide. Can not do it. However, the supported amount of the platinum group element on the oxide carrier does not need to exceed 5% by weight.

The intermediate catalyst used in the second method can be prepared, for example, as follows. That is, titanium oxide, zirconia or tin oxide is immersed in an aqueous solution of a water-soluble salt such as the nitrate of the platinum group element, and after removing an excessive amount of the attached aqueous solution, drying is performed.
By calcination in the air, a catalyst in which the platinum group element is supported on the oxide carrier can be obtained.

Purification of exhaust gas by the method of the present invention is performed by the following mechanism. However, the present invention is not at all limited by such a mechanism or theory. That is, first, in the first method, an exhaust gas containing hydrocarbons and carbon monoxide together with nitrogen oxides and sulfur oxides is brought into contact with a first catalyst under an oxygen-excess atmosphere (lean condition), Depending on the catalyst component consisting of elements,
Such sulfur oxides are effectively adsorbed on the first catalyst while oxidizing the sulfur oxides in the exhaust gas, and then, on the second catalyst, the nitrogen oxides, in particular, the nitric oxide are removed from the platinum group. Conversion to nitrogen dioxide with high efficiency over a catalyst component composed of elemental elements, and thus the generated nitrogen dioxide is an oxide of at least one metal selected from alkali metals, alkaline earth metals, aluminum, titanium, silver and rare earth elements Alternatively, the exhaust gas was adsorbed on the first catalyst under a reducing atmosphere (rich condition) by, for example, adsorbing on a catalyst component composed of a composite oxide and injecting a reducing agent such as fuel into the catalyst component. Desorbing sulfur oxides as sulfur dioxide or hydrogen sulfide, suppressing the adsorption and accumulation on the catalyst, preventing the deterioration of the second catalyst containing the catalyst component having the ability to adsorb nitrogen dioxide, this 2. In the catalyst of No. 2, the nitrogen oxides adsorbed on a catalyst component comprising an oxide or a composite oxide of at least one metal selected from alkali metals, alkaline earth metals, aluminum, silver, titanium and rare earth elements are enriched. Under the conditions, the above reducing agent is used to catalytically reduce nitrogen to remove nitrogen oxides from exhaust gas.

In the second method according to the present invention, an exhaust gas containing hydrocarbons and carbon monoxide together with nitrogen oxides and sulfur oxides is brought into contact with the first catalyst under an oxygen-excess atmosphere (lean condition), While oxidizing sulfur oxides in the exhaust gas by the catalyst component composed of a platinum group element, such sulfur oxides are effectively adsorbed on the first catalyst,
The exhaust gas is brought into contact with the intermediate catalyst to convert the sulfur compound desorbed from the first catalyst into hydrogen sulfide that is not adsorbed by the second catalyst at the subsequent stage. Thereafter, the exhaust gas is brought into contact with the second catalyst, As in the first method, the nitrogen oxides are catalytically reduced to nitrogen to remove the nitrogen oxides from the exhaust gas.

In the present invention, the oxygen-excess atmosphere (lean condition) refers to a hydrocarbon, carbon monoxide,
Atmosphere conditions that contain more oxygen than combustible components such as hydrogen are completely burned by oxygen contained in exhaust gas. That is, it refers to an atmosphere condition in which the exhaust gas contains more oxygen than the stoichiometric air-fuel ratio condition (stoichiometric condition). On the other hand, the reducing atmosphere (rich condition) is the opposite of the above-mentioned lean condition, which means that the hydrocarbon contained in the exhaust gas,
Atmosphere conditions in which combustible components such as carbon monoxide and hydrogen do not contain oxygen in an amount sufficient for complete combustion by oxygen contained in exhaust gas.

According to the first exhaust gas purifying method of the present invention, in the process of detoxifying the nitrogen oxides in the exhaust gas containing sulfur oxides together with nitrogen oxides by reducing the nitrogen oxides to nitrogen as described above, The sulfur oxide therein is adsorbed to the component (b) in the first catalyst under lean conditions while being oxidized by the platinum group component, which is the component (a) in the first catalyst. The first catalyst easily desorbs the sulfur oxides partially as hydrogen sulfide in the exhaust gas under rich conditions, and further, under rich conditions, the latter catalyst does not adsorb the sulfur oxides. Thus, according to the method of the present invention,
In addition to detoxifying hydrocarbons and carbon monoxide, which are harmful components in exhaust gas, even if the exhaust gas contains sulfur oxides along with nitrogen oxides, the exhaust gas purification ability of the catalyst does not decrease, and therefore, it is stable for a long period of time. Nitrogen oxides can be removed from exhaust gas by catalytic reduction.

According to the second method of the present invention,
By bringing the exhaust gas into contact with the intermediate catalyst between the first catalyst and the second catalyst, almost all of the sulfur compounds in the exhaust gas become hydrogen sulfide, and thus the nitrogen oxidation in the subsequent second catalyst. It is possible to completely prevent the deterioration of the substance occlusion component.

Therefore, the method for purifying exhaust gas according to the present invention
For example, it can be suitably used as a catalyst exclusively for lean burn gasoline or GDI (Gasoline Direct Injection, gasoline direct injection) vehicles operated in an oxygen-excess atmosphere. Furthermore, the catalyst used in the process according to the invention has excellent heat resistance.

The first, second and intermediate catalysts used in the first and second methods of the present invention can be usually obtained as powders or granules as described above. Conventionally, it can be easily formed into various structures and shapes such as a honeycomb shape, a spherical shape, and an annular shape by a conventionally known ordinary molding method. When forming each catalyst into a required structure or shape, if necessary, various conventionally known forming auxiliaries, formed body reinforcing materials, inorganic fibers, organic binders and the like may be appropriately compounded. .

A structure such as a honeycomb or a sphere, which itself is made of the above-described catalyst, can be obtained, for example, as follows. That is, as described above, each catalyst was prepared as a powder, kneaded with an organic binder using an appropriate solvent, and formed into a honeycomb structure,
After drying, firing may be performed.

Further, according to the present invention, an inert base material is formed into a required shape in advance, and each of the powdery catalysts is coated and supported by an appropriate method such as a wash coat method. It can also be a catalyst structure. Examples of the molded body made of the inert substrate include, for example, a corrugated honeycomb made of stainless steel foil, a honeycomb made of a mineral substance such as cordierite, a sphere, and a structure such as a ring. A three-dimensional catalyst structure can be obtained by carrying a catalyst on these.

According to the present invention, as described above, a catalyst layer is formed on the surface of a structure such as a honeycomb, a sphere or a ring made of an inert base material by a wash coat method or the like. When the catalyst is supported, the catalyst layer has a thickness of 30 μm or more from the surface thereof (hereinafter, for simplicity,
It is called the catalyst layer thickness. ) Is preferably carried on the surface of the structure. By thus forming the catalyst layer supported on the structure over a thickness of 30 μm or more from the surface, a catalyst structure having high reactivity to nitrogen oxides, that is, high selective reduction of nitrogen oxides is obtained. be able to. However, according to the present invention, the thickness of the catalyst layer may be usually 300 μm or less. Even if the thickness of the catalyst layer exceeds 300 μm, it is not possible to obtain a corresponding improvement in the selective reduction property, which is not preferable from the viewpoint of the cost of the catalyst structure.

In the solid-type honeycomb catalyst structure itself composed of the catalyst component as described above, the thickness of the catalyst layer is substantially uniform in the thickness direction of the cell walls of the honeycomb catalyst structure. Therefore, the cell wall of the honeycomb structure is 6
If it is 0 μm or more, the catalyst is 30 μm from the surface of the cell wall.
m or more. This is because the cell wall is brought into contact with exhaust gas on both surfaces thereof.

However, when purifying exhaust gas by the first method of the present invention, a single honeycomb structure is divided into two in the direction of its through hole, that is, in the direction of flow of exhaust gas.
Along the flow of the exhaust gas, the first and second catalysts are sequentially applied by a wash coat method or the like, and are supported to form a catalyst layer composed of the first and second catalysts, respectively, adjacent to each other. be able to. According to the present invention, for example, a second catalyst layer is sequentially formed as a lower layer and a first catalyst layer is formed as an upper layer on a single honeycomb structure by a wash coat method or the like. Thus, the catalyst layer may be formed in two layers on a single honeycomb structure.

Similarly, when purifying exhaust gas by the second method of the present invention, a single honeycomb structure is divided into three in the direction of the through hole, that is, in the flow direction of the exhaust gas, and is divided along the flow of the exhaust gas. The first, middle, and second catalysts are sequentially applied by a wash coat method or the like, and supported, thereby forming catalyst layers composed of the first, middle, and second catalysts, respectively, adjacent to each other. Can be. Further, for example, a second catalyst layer is sequentially formed as a lowermost layer on a single honeycomb structure by a wash coat method or the like, an intermediate catalyst layer is formed thereon, and a first catalyst layer is formed as an uppermost layer. A catalyst layer may be formed, and thus a single honeycomb structure may be formed with three catalyst layers.

In the present invention, as a reducing agent for keeping the exhaust gas under rich conditions, preferably, hydrogen, hydrocarbon or an oxygen-containing organic compound is used. Among them, hydrocarbons include, for example, methane,
Hydrocarbon gases such as ethane, propane, ethylene, propylene, 1-butene, and 2-butene; and liquid components such as pentane, hexane, octane, heptane, benzene, toluene, xylene and other single component hydrocarbons; Mineral oil-based hydrocarbons such as gasoline, kerosene, light oil, and heavy oil can be used. In particular, according to the present invention, among the above, lower alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, lower alkanes such as propane and butane, and light oil are preferably used. These hydrocarbons may be used alone or, if necessary,
More than one kind may be used in combination.

In particular, according to the present invention, when purifying automobile engine exhaust gas, the fuel can be suitably used as a reducing agent. Further, it is possible to control the combustion of the engine (A / F control) to satisfy the rich condition.

Examples of the oxygen-containing organic compound include alcohols such as methanol, ethanol, propanol, butanol and octanol; ethers such as dimethyl ether, diethyl ether and dipropyl ether; methyl acetate, ethyl acetate, oils and fats and the like. And the like, for example, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and aldehydes such as acetaldehyde and propionaldehyde. These oxygen-containing organic compounds may be used alone or in combination of two or more as necessary.

Further, in the present invention, a mixture of the above hydrocarbon and an oxygen-containing organic compound may be used as a reducing agent.

In the present invention, the reducing agent varies depending on the specific hydrocarbon or oxygen-containing organic compound used, but usually, the oxygen in the exhaust gas reacts with the reducing agent to reduce the oxygen concentration to 0%. Is used in a molar ratio of about 0.9 to about 10 with respect to the minimum amount of the reducing agent required (i.e., stoichiometric amount). The minimum amount of reducing agent used is the above minimum amount (stoichiometric amount)
When the molar ratio is less than 0.9, the nitrogen oxides are not sufficiently reduced. On the other hand, when the molar ratio exceeds 10, the amount of the unreacted reducing agent is increased.
After the purification treatment of the nitrogen oxides in the exhaust gas, a post-treatment for removing the nitrogen oxides is required.

In the present invention, each of the lean conditions for oxidizing nitrogen oxides in the exhaust gas to be adsorbed on the catalyst and the rich conditions for reducing and removing the adsorbed nitrogen oxides with a reducing agent is determined by the time required for the exhaust gas treatment. Although it can be appropriately determined depending on the conditions, usually, the lean condition is 30 seconds to 1 second.
The minute and rich conditions are from 1 second to 1 minute.

The optimum temperature at which the catalyst according to the present invention exhibits a reducing activity on nitrogen oxides varies depending on the reducing agent and the type of catalyst used, but is usually from 100 to 800 ° C. In this temperature range, the space velocity (SV) 5000 to 1000
It is preferable that the exhaust gas is circulated at about 00 hr ^-1 .
A particularly preferred reaction temperature range in the present invention is 200 to 5
It is in the range of 00 ° C.

[0064]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

(1) Preparation of Catalyst Example 1 (Preparation of First Catalyst for First Method) Aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) 2.57
g, silver nitrate (AgNO ₃ ) 2.05 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g) 38.74 g were dispersed in ion-exchanged water 100 mL. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide carrying 1% by weight of platinum and 2% by weight of silver.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) are mixed with an appropriate amount of water, and the mixture is wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
It was applied to a square inch cordierite honeycomb substrate, and platinum-silver / titanium oxide was supported at a rate of about 150 g / L (layer thickness 77 μm).

(Preparation of Second Catalyst for First Method)
75.00 g of barium carbonate (BaCO ₃ ) and hydrated alumina (Al ₂ O ₃ .nH ₂ O, GB- manufactured by Mizusawa Chemical Industry Co., Ltd.)
45) 41.65 g (38.74 g as alumina) was dispersed in 200 mL of ion-exchanged water. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The slurry thus obtained was separated by filtration, dried, and then dried in air at 1100 ° C.
For 3 hours to obtain a composite oxide of barium and aluminum (BaO.Al ₂ O ₃ ).

30 g of this barium / aluminum composite oxide powder and γ-alumina powder (Sumitomo Chemical Co., Ltd.)
30 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) and 6 g of silica sol were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A slurry for coating was prepared. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / in 2, and BaO.AlO ₃ / γ-alumina was added at about 150 g /
L (layer thickness 79 μm).

Next, 6.25 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above BaO.Al ₂ O
After immersing the honeycomb substrate supporting ₃ / γ-alumina, the excess aqueous solution attached is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours. BaO.Al ₂ O ₃ / supporting 2% by weight of platinum /
A γ-alumina catalyst was obtained. The component ratio (weight ratio) of this catalyst is BaO.Al ₂ O ₃ / Pt / γ-alumina = 9
6.2 / 3.8 / 96.2.

Example 2 (Preparation of First Catalyst for First Method) Aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) 2.57
g of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) 2.32 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g)
38.74 g was dispersed in 100 mL of ion-exchanged water. This slurry is dried with a spray drier,
For 3 hours to obtain a powder comprising titanium oxide carrying 1% by weight of platinum and 2% by weight of cupric oxide (CuO).

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
A platinum-cupric oxide / titanium oxide of about 150 g / applied to a square inch cordierite honeycomb substrate.
L (layer thickness: 77 μm).

(Preparation of Second Catalyst) Barium carbonate (Ba)
75.00 g of CO ₃ ) and 49.98 g of hydrated alumina (GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd.)
48 g) was dispersed in 200 mL of ion-exchanged water. 100 ml of zirconia balls as a grinding medium in this slurry
And wet-milled for 30 minutes in a planetary mill. The slurry thus obtained was separated by filtration, dried, and calcined in air at 1200 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO.Al ₂ O ₃ and BaO.6A).
mixed crystal with l ₂ O ₃ ).

30 g of this barium / aluminum composite oxide powder and γ-alumina powder (Sumitomo Chemical Co., Ltd.)
30 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) and 6 g of silica sol were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A slurry for coating was prepared. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and a composite oxide of barium and aluminum / γ-alumina was supported at a ratio of about 150 g / L (layer thickness: 81 μm).

Next, 6.25 g of an aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) was added to ion-exchanged water for 3 times.
0 mL, and a honeycomb substrate supporting the barium / aluminum composite oxide and γ-alumina was immersed in this aqueous solution to remove the excess aqueous solution attached thereto.
The resultant was dried at 00 ° C. for 12 hours and further calcined in air at 600 ° C. for 3 hours to obtain a barium / aluminum composite oxide / γ-alumina catalyst supporting 2% by weight of platinum.
The component ratio (weight ratio) of this catalyst is BaO.Al ₂ O ₃
And it was mixed / Pt / .gamma.-alumina = 96.2 / 3.8 / 96.2 and BaO · 6Al ₂ O _3.

[0075] Example 3 (8.45 wt% as Rh) rhodium nitrate aqueous solution (first preparation of the catalyst for the second method) 2.80 g and ferric nitrate (Fe (NO _{3) 3} · 9H ₂ O) 2.70 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g) 38.74
g was dispersed in 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide carrying 1% by weight of rhodium and 2% by weight of ferric oxide (Fe ₂ O ₃ ). Was.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
The ferric oxide / titanium oxide was applied at a ratio of about 150 g / L (layer thickness: 77 μm) on a honeycomb substrate made of cordierite having a square inch.

(Preparation of Intermediate Catalyst) 5.13 g of dinitrodiammine platinum aqueous solution (15.09% by weight as platinum) and activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g) 38.
74 g was added to 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide and 2% by weight of platinum.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industry Co., Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
A platinum / titanium oxide coating of about 150 g / L (layer thickness 7
5 μm).

(Preparation of Second Catalyst) Barium carbonate (Ba)
75.00 g of CO ₃ ) and alumina sol (A-20 manufactured by Nissan Chemical Industries, Ltd., alumina content 20% by weight) 193.7
0 g (38.74 g as alumina) of deionized water 20
Dispersed in 0 mL. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The thus obtained slurry was evaporated to dryness, and then calcined in air at 600 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO.Al ₂ O).
₃ ) Got it.

On the other hand, aluminum nitrate (Al (NO ₃ )
₃ · 9H ₂ O) _275.96g and titanium tetrachloride (TiCl
₄ ) 125.01 g of an aqueous solution (containing 10% by weight of titanium as titanium oxide) was dissolved in 2 L of ion-exchanged water. To this, 1/10 normal ammonia water was added under stirring with p
The solution was added dropwise while adjusting the pH with a pH controller set to H8. After completion of the dropwise addition, the mixture was aged for 1 hour to obtain a slurry of a mixture of aluminum hydroxide and titanium hydroxide. This slurry was filtered, washed with water, and calcined at 700 ° C. for 3 hours in air to obtain a weight ratio of alumina to titania of 75 /
A mixture of 25 was obtained.

Next, 30 g of the barium / aluminum composite oxide powder, 30 g of γ-alumina-titania mixture powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, This was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium to prepare a wash coat slurry. The slurry is applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and a composite oxide of barium and aluminum and γ-alumina-titania are supported at a rate of about 150 g / L (layer thickness 79 μm). Was.

Next, 6.25 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the composite oxide of barium and aluminum and γ-alumina-titania were supported in the aqueous solution. After dipping the honeycomb substrate, the excess aqueous solution attached is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours to carry 2% by weight of platinum. A composite oxide of barium and aluminum / γ-alumina-titania catalyst was obtained. The component ratio (weight ratio) of this catalyst was BaO.Al ₂ O ₃ /Pt/γ-alumina/titania=96.2/3.8/72.1/24.0.

Example 4 (Preparation of First Catalyst for Second Method) 2.80 g of an aqueous solution of rhodium nitrate (8.45% by weight as Rh) and zinc nitrate (Zn (NO ₃ ) ₂ .6H ₂ O) ) 2.83 g and 38.74 g of activated titanium oxide (TiO ₂ , specific surface area 109 m ^{2 /} g)
Was dispersed in 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising 1% by weight of rhodium and 2% by weight of zinc oxide (ZnO) supported on titanium oxide.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
About 150 g of rhodium-zinc oxide / titanium oxide applied to a square inch cordierite honeycomb substrate
/ L (layer thickness 77 μm).

(Preparation of Intermediate Catalyst) Dinitrodiammine White
5.13g of gold aqueous solution (15.09% by weight as platinum) and active
Zirconia (calcinate zirconium hydroxide at 500 ° C for 3 hours
And ZrO _Two, Specific surface area 46m^Two/ G) 3
8.74 g was added to 100 mL of ion-exchanged water. This sla
And dried at 500 ° C for 3 hours.
After firing for 2 hours, 2% by weight of platinum is supported on zirconia
Powder was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-pulverized with a planetary mill for 5 minutes using 100 g of zirconia balls as a pulverizing medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
It is applied to a honeycomb substrate of square inch cordierite, and about 150 g / L of platinum / zirconia (layer thickness 7
5 μm).

(Preparation of Second Catalyst) The second catalyst was prepared in the same manner as in Example 3.

Example 5 (Preparation of First Catalyst for Second Method) 2.80 g of an aqueous solution of rhodium nitrate (8.45% by weight as Rh) and aluminum nitrate (Al (NO ₃ ) ₃ .9H ₂ O) ) 2.85 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g) 3
8.74 g was dispersed in 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide carrying 1% by weight of rhodium and 2% by weight of aluminum oxide (Al ₂ O ₃ ).

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
About 150 g / aluminum oxide / titanium oxide applied to a honeycomb substrate of square inch cordierite
L (layer thickness: 77 μm).

(Preparation of Intermediate and Second Catalysts) The catalysts were prepared in the same manner as in Example 3.

Example 6 (Preparation of First Catalyst for Second Method) 7.75 g of an aqueous iridium chloride solution (5.00% by weight as iridium) and manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) ) 2.56g
And tin oxide (obtained by firing tin hydroxide at 500 ° C. for 3 hours, SnO ₂ , specific surface area 31 m ^{2 /} g) 38.74 g
Was dispersed in 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising 1% by weight of iridium and 2% by weight of manganese dioxide (MnO ₂ ) on tin oxide.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
An iridium-manganese dioxide / tin oxide coating was applied to a honeycomb substrate consisting of square inches of cordierite and applied to a honeycomb substrate of about 1 inch.
It was carried at a rate of 50 g / L (layer thickness 77 μm).

(Preparation of Intermediate Catalyst) The intermediate catalyst was prepared in the same manner as in Example 3.

(Preparation of Second Catalyst) In the preparation of the second catalyst in Example 3, 5.00 g of an aqueous solution of chloroplatinic acid (15.09 wt% as platinum) and rhodium nitrate were used instead of the aqueous solution of dinitrodiammine platinum. Aqueous solution (8.4 as Rh)
5% by weight) 30 mL of 2.24 g of the mixture with ion-exchanged water
Except that an aqueous solution was used as in Example 3.
A composite oxide of barium and aluminum / γ-alumina catalyst supporting 1.6% by weight of platinum and 0.4% by weight of rhodium was obtained. The component ratio (weight ratio) of this catalyst is BaO · A
l ₂ O ₃ /Pt/Rh/γ-alumina=96.1/3.1/
0.8 / 96.2.

Example 7 (Preparation of Intermediate Catalyst for Second Method) In the preparation of the intermediate catalyst in Example 3, an iridium chloride aqueous solution (5.00% by weight as iridium) was used instead of the dinitrodiammineplatinum aqueous solution. Example 3 except that .48 g was used.
In the same manner as in the above, a powder comprising 2% by weight of iridium supported on titanium oxide was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
The coating was applied to a square inch cordierite honeycomb substrate, and iridium / titanium oxide was supported at a rate of about 150 g / L (layer thickness 75 μm).

(Preparation of First and Second Catalysts) The catalysts were prepared in the same manner as in Example 3.

Example 8 (Preparation of Second Catalyst for Second Method) Silver nitrate (Ag
NO ₃ ) 4.75 g and hydrated alumina (Al ₂ O ₃ .nH ₂₎
O, 41.65 g (38.74 g as alumina) of GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd. was dispersed in 100 mL of ion-exchanged water, and this slurry was dried with a spray dryer and calcined at 500 ° C. for 3 hours. , And then add 10
% In air atmosphere at 800 ° C. for 18 hours to obtain a powder in which silver aluminate (AgAlO ₂ ) was supported on γ-alumina at 2% by weight in terms of silver.

FIG. 1 shows an X-ray diffraction pattern of γ-alumina loaded with silver aluminate, and FIG. 2 shows an X-ray diffraction pattern of γ-alumina alone. In FIG.
Indicates a peak due to silver aluminate, X indicates a peak due to alumina, and Δ indicates a peak due to silver.

Next, 30 g of the thus obtained silver aluminate supported on γ-alumina, 30 g of γ-alumina powder (AC11K, manufactured by Sumitomo Chemical Co., Ltd.) and silica sol (manufactured by Nissan Chemical Industries, Ltd.) Snowtex N) 6
g of water and an appropriate amount of water.
The slurry for wet coating was prepared by wet grinding with a planetary mill for 5 minutes using 00 g as a grinding medium. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / in 2, and silver aluminate / γ-
Alumina was supported at a rate of about 150 g / L (layer thickness 77 μm).

Separately, a chloroplatinic acid aqueous solution (15.
09% by weight) and 2.24 g of an aqueous rhodium nitrate solution (8.45% by weight as Rh) were mixed with ion-exchanged water.
0 mL, and the silver aluminate / γ-
A honeycomb base material supporting alumina and γ-alumina is immersed to remove an excessive amount of the attached aqueous solution.
For 12 hours, and further calcined in air at 600 ° C. for 3 hours to obtain a silver aluminate / γ-alumina / γ-alumina supporting 1.6% by weight of platinum and 0.4% by weight of rhodium. A catalyst was obtained. The component ratio (weight ratio) of this catalyst is silver aluminate / γ-alumina / Pt / Rh / γ-alumina =
It was 96.1 / 3.1 / 0.8 / 96.2.

(Preparation of First and Intermediate Catalysts) The catalysts were prepared in the same manner as in Example 3.

Example 9 (Preparation of First Catalyst for Second Method) 2.80 g of an aqueous solution of rhodium nitrate (8.45% by weight as Rh) and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) ) 3.01 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ^{2 /} g) 38.7
4 g was dispersed in 100 mL of ion-exchanged water. The slurry is dried with a spray drier and then dried at 500 ° C. for 3 hours.
After calcination for a period of time, a powder comprising 1% by weight of rhodium and 2% by weight of cobalt oxide (Co ₃ O ₄ ) supported on titanium oxide was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N, manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-pulverized for 5 minutes with a planetary mill using 100 g of zirconia balls as a pulverizing medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
Rhodium-cobalt oxide / titanium oxide was applied to a honeycomb substrate of square inches of cordierite to form a coating of about 15
It was carried at a rate of 0 g / L (layer thickness 77 μm).

(Preparation of Intermediate and Second Catalysts) The catalysts were prepared in the same manner as in Example 3.

Example 10 (Preparation of First Catalyst for Second Method) Aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) 2.57
g and ferric nitrate _{(Fe (NO 3) 3 ·} 9H 2 O) 2.70
g and activated titanium oxide (TiO ₂ , specific surface area 109 m ² /
g) 38.74 g was dispersed in 100 mL of ion-exchanged water. This slurry is dried with a spray drier and
Baking at 00 ° C for 3 hours, 1% by weight of platinum in titanium oxide
And 2% by weight of ferric oxide (Fe ₂ O ₃ ).

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
A platinum-ferric oxide / titanium oxide of about 150 g / applied to a honeycomb substrate of square inch cordierite.
L (layer thickness: 77 μm).

(Preparation of Intermediate Catalyst) 5.13 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) and 38.000 g of activated titanium oxide (TiO ₂ , specific surface area 109 m ² / g)
74 g was added to 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide and 2% by weight of platinum.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industry Co., Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
A platinum / titanium oxide coating of about 150 g / L (layer thickness 7
5 μm).

(Preparation of Second Catalyst) Barium carbonate (Ba)
75.00 g of CO ₃ ) and alumina sol (A-20 manufactured by Nissan Chemical Industries, Ltd., alumina content 20% by weight) 193.7
0 g (38.74 g as alumina) of deionized water 20
Dispersed in 0 mL. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The thus obtained slurry was evaporated to dryness, and then calcined in air at 600 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO.Al ₂ O).
₃ ) Got it.

On the other hand, aluminum nitrate (Al (NO ₃ )
₃ · 9H ₂ O) _275.96g and titanium tetrachloride (TiCl
₄ ) 125.01 g of an aqueous solution (containing 10% by weight of titanium as titanium oxide) was dissolved in 2 L of ion-exchanged water. To this, 1/10 normal ammonia water was added under stirring with p
The solution was added dropwise while adjusting the pH with a pH controller set to H8. After completion of the dropwise addition, the mixture was aged for 1 hour to obtain a slurry of a mixture of aluminum hydroxide and titanium hydroxide. This slurry was filtered, washed with water, and calcined at 700 ° C. for 3 hours in air to obtain a weight ratio of alumina to titania of 75 /
A mixture of 25 was obtained.

Next, 30 g of the barium / aluminum composite oxide powder, 30 g of γ-alumina-titania mixture powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, This was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium to prepare a wash coat slurry. The slurry is applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and a composite oxide of barium and aluminum and γ-alumina-titania are supported at a rate of about 150 g / L (layer thickness 79 μm). Was.

Next, an aqueous solution of chloroplatinic acid (1% as platinum)
A mixture of 5.00 g of 5.09% by weight) and 2.24 g of an aqueous rhodium nitrate solution (8.45% by weight as Rh) was made up to 30 mL with ion-exchanged water. After dipping the honeycomb substrate supporting alumina-titania, the excess aqueous solution adhering is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours to obtain platinum. A composite oxide of barium and aluminum / γ-alumina-titania catalyst supporting 1.6% by weight and 0.4% by weight of rhodium was obtained. The component ratio (weight ratio) of this catalyst is BaO.Al ₂ O ₃ /
Pt / Rh / γ-alumina-titania = 96.1 / 3.3 /
0.8 / 96.2.

Example 11 (Preparation of First Catalyst for Second Method) 4.58 g of an aqueous rhodium nitrate solution (8.45% by weight as Rh) and gallium nitrate (Ga (NO ₃ ) ₃ .nH ₂ O) ) 7.12 g and activated titanium oxide (TiO ₂ , specific surface area 109 m ^{2 /} g) 38.7
4 g was dispersed in 100 mL of ion-exchanged water. The slurry is dried with a spray drier and then dried at 500 ° C. for 3 hours.
After calcination for a period of time, a powder obtained by supporting 1% by weight of rhodium and 2% by weight of gallium on titanium oxide was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
About 150 g of rhodium-gallium / titanium oxide applied to a honeycomb substrate of square inches of cordierite
/ L (layer thickness 73 μm).

(Preparation of Intermediate and Second Catalyst) Example 10
It was prepared in the same manner as described above.

Example 12 (Preparation of First Catalyst for First Method) Aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) 2.57
g and palladium nitrate aqueous solution (4.37% by weight as Pd)
8.84g and chromium nitrate _{(Cr (NO 3) 2 ·} 9H 2 O)
10.02 g and activated titanium oxide (TiO ₂ , specific surface area 10
38.74 g of 9 m ² / g) was dispersed in 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to form platinum 1 on titanium oxide.
Wt%, palladium 0.5 wt% and chromium oxide (Cr
2% by weight of O ₃ was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
It was applied to a honeycomb substrate of square inches of cordierite, and was loaded with platinum-palladium / chromium oxide / titanium oxide at a ratio of about 150 g / L (layer thickness 73 μm).

(Preparation of Intermediate and Second Catalyst) Example 10
It was prepared in the same manner as described above.

Example 13 (Preparation of Intermediate Catalyst) 2.57 g of an aqueous solution of platinum dinitrodiammine (15.09% by weight as platinum), 4.58 g of an aqueous solution of rhodium nitrate (8.45% by weight as Rh) and an aqueous solution of palladium nitrate (Pd 8.37 g) and activated titanium oxide (TiO ₂ , specific surface area 109 m ^{2 /} g) 38.7
4 g was added to 100 mL of ion-exchanged water. The slurry was dried with a spray drier and calcined at 500 ° C. for 3 hours to obtain a powder comprising titanium oxide carrying 1% by weight of platinum, 1% by weight of rhodium and 1% by weight of palladium.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industry Co., Ltd.) were mixed with an appropriate amount of water, and this was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
The coating was applied to a square inch cordierite honeycomb substrate, and platinum-rhodium-palladium / titanium oxide was supported at a ratio of about 150 g / L (layer thickness 75 μm).

(Preparation of First and Second Catalysts) Example 10
It was prepared in the same manner as described above.

[0123] Example 14 (a first preparation of the catalyst for the first method) iridium chloride solution (5.00 wt% as iridium) 7.75 g and ferric nitrate _{(Fe (NO 3) 2 ·} 9H ₂ O) 9.42 g
And activated titanium oxide (TiO ₂ , specific surface area 109 m ² /
g) 38.74 g was dispersed in 100 mL of ion-exchanged water. This slurry is dried with a spray drier and
Baking at 00 ° C. for 3 hours, iridium 1
Thus, a powder carrying 2% by weight of ferric oxide and 2% by weight of ferric oxide was obtained.

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
Iridium-ferric oxide / titanium oxide is applied to a honeycomb substrate consisting of square inches of cordierite to form about 15
It was carried at a rate of 0 g / L (layer thickness 73 μm).

(Preparation of Second Catalyst) Barium carbonate (Ba)
75.00 g of CO ₃ and hydrated alumina (Al ₂ O ₃ .nH)
₂ O, GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd.) 41.65 g
(38.74 g as alumina) was ion-exchanged to 200 m
L. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The slurry thus obtained was separated by filtration, dried, and calcined in air at 1100 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO · A).
l ₂ O ₃ ) was obtained.

30 g of the barium / aluminum composite oxide powder and γ-alumina powder (Sumitomo Chemical Co., Ltd.)
30 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) and 6 g of silica sol were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A slurry for coating was prepared. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / in 2, and BaO.AlO ₃ / γ-alumina was added at about 150 g /
L (layer thickness 79 μm).

Next, 6.25 g of a dinitrodiammine platinum aqueous solution (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above-mentioned BaO.Al ₂ O
After immersing the honeycomb substrate supporting ₃ / γ-alumina, the excess aqueous solution attached is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours. BaO.Al ₂ O ₃ / supporting 2% by weight of platinum /
A γ-alumina catalyst was obtained. The component ratio (weight ratio) of this catalyst is BaO.Al ₂ O ₃ / Pt / γ-alumina = 9
6.2 / 3.8 / 96.2.

Example 15 Preparation of Second Catalyst for Second Method Potassium Acetate
A solution was prepared by dissolving 9.8 g, 61.2 g of aluminum triisopropoxide, and 14.2 g of titanium tetraisopropoxide in 345 mL of 2-propanol. The solution was stirred at 80 ° C. for 2 hours, mixed with 18.0 g of 2,4-pentanedione, further stirred for 3 hours, and then mixed with 39.6 mL of ion-exchanged water and 40 mL of 2-propanol. The solution was added dropwise while maintaining the temperature at 80 ° C., and the mixture was stirred at 80 ° C. for 5 hours. Thereafter, the obtained reaction mixture was dried under reduced pressure,
This is further fired in an air atmosphere at 800 ° C. for 5 hours,
Complex oxide of potassium, titanium and aluminum (K ₂ O
_{· 3Al 2 O 3 · TiO 2} ) was obtained in powder.

30 g of the composite oxide powder, 30 g of γ-alumina powder (AC11K manufactured by Sumitomo Chemical Co., Ltd.) and silica sol (Snowtex N manufactured by Nissan Chemical Industry Co., Ltd.) 6
g of water and an appropriate amount of water.
The slurry for wet coating was prepared by wet grinding with a planetary mill for 5 minutes using 00 g as a grinding medium. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and the composite oxide of potassium, titanium and aluminum / γ-alumina was added to about 150 μm.
g / L (layer thickness 79 μm).

Next, 6.25 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above-mentioned complex oxide of potassium, titanium and aluminum / γ-alumina was carried in this aqueous solution. After dipping the honeycomb substrate, the excess aqueous solution is removed, dried at 100 ° C. for 12 hours, and baked in air at 600 ° C. for 3 hours to carry 2% by weight of platinum. The obtained K ₂ O.3Al ₂ O ₃ .TiO ₂ / γ-alumina catalyst was obtained. The component ratio (weight ratio) of this catalyst is K ₂ O
_{· 3Al 2 O 3 · TiO 2} / Pt / γ- alumina = 96.
2 / 3.8 / 96.2.

(Preparation of First and Intermediate Catalysts) The catalysts were prepared in the same manner as in Example 13.

Example 16 (Preparation of a second catalyst for the second method) 75.00 g of barium carbonate (BaCO ₃ ) and hydrated alumina (Al ₂ O ₃₎
・ NH ₂ O, GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd. 41.6
5 g (38.74 g of alumina as ion-exchanged water 200
Dispersed in mL. 100 mL of zirconia balls are added to this slurry as a grinding medium,
Wet pulverized. The slurry thus obtained was separated by filtration, dried, and calcined in air at 1100 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO · A).
l ₂ O ₃ ) was obtained.

25 g of the barium / aluminum composite oxide powder, 5 g of zirconia stabilized ceria (zirconia content: 20%), 30 g of γ-alumina powder (AC11K manufactured by Sumitomo Chemical Co., Ltd.) and silica sol (Nissan Chemical Industries, Ltd.) 6 g of Snowtex N) manufactured by Co., Ltd.) was mixed with an appropriate amount of water, and wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium to prepare a slurry for wash coating. This slurry was prepared using 200 /
It was applied to a square inch cordierite honeycomb substrate, and was loaded with BaO.Al ₂ O ₃ -zirconia stabilized ceria / γ-alumina at a ratio of about 150 g / L (layer thickness 79 μm).

Next, 6.25 g of an aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above-mentioned BaO.Al ₂ O
After immersing the honeycomb substrate supporting ₃ / γ-alumina, the excess aqueous solution attached is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours. BaO.Al ₂ O ₃ / supporting 2% by weight of platinum /
A zirconia stabilized ceria / γ-alumina catalyst was obtained. The component ratio (weight ratio) of this catalyst is BaO.Al ₂ O ₃ /
Zirconia stabilized ceria / Pt / γ-alumina = 86.6
/9.6/3.8/96.2.

(Preparation of First and Intermediate Catalysts) The catalysts were prepared in the same manner as in Example 13.

Comparative Example 1 20 g of barium carbonate (BaCO ₃ ), 40 g of γ-alumina powder (AC11K manufactured by Sumitomo Chemical Co., Ltd.) and 6 g of silica sol were mixed with an appropriate amount of water, and 100 g of zirconia balls were mixed with a grinding medium. Was wet-ground with a planetary mill for 5 minutes to prepare a wash coat slurry. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and barium carbonate and γ were coated.
Alumina was supported at a rate of about 150 g / L (layer thickness 79 μm).

6.25 g of an aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) was added to 30 mL of ion-exchanged water.
The honeycomb substrate supporting barium carbonate and γ-alumina was immersed in the aqueous solution to remove the excess aqueous solution attached thereto, dried at 100 ° C. for 12 hours, and further dried in air at 600 ° C. Calcination was performed at 3 ° C. for 3 hours to obtain a barium oxide / γ-alumina catalyst supporting 2% by weight of platinum. The component ratio (weight ratio) of this catalyst is BaO / Pt /
γ-alumina = 96.2 / 3.8 / 96.2.

(2) Evaluation Test Purification of exhaust gas containing nitrogen oxides (catalytic reduction of nitrogen oxides) was carried out using the catalysts of the above Examples and Comparative Examples under the following test conditions. The removal rate of the substance was determined by a chemical luminescence method. At this time, the nitrogen oxide removal rate was determined from an integrated value of the nitrogen oxide concentration time under a rich condition and a lean condition as a function.

(Test conditions) (1) Gas composition Rich conditions NO 500 ppm O ₂ 0 vol% Propylene 5000 ppm H ₂ 2 vol% SO ₂ 40 ppm Water 6 vol% Nitrogen balance

Lean conditions NO 500 ppm O ₂ 10% by volume Propylene 500 ppm SO ₂ 40 ppm Water 6% by volume Nitrogen balance The above rich conditions and lean conditions were alternately vibrated at one minute intervals.

(2) Space velocity Exhaust gas was supplied at 100,000 hr ^-1 to each of the reactors filled with the first and second catalysts or the first, intermediate, and second catalysts.

(3) Reaction temperature 200 ° C., 250 ° C.
300 ° C., 350 ° C., 400 ° C. The results are shown in Table 1.

[0143]

[Table 1]

Next, Examples 1, 3, 8, 10, 13, 1
Using the catalysts prepared in 5, 16 and Comparative Example 1, the reaction was carried out for 24 hours under the above reaction conditions except that the reaction temperature was 600 ° C., and then the exhaust gas was purified under the above reaction conditions. The heat resistance and sulfur oxide resistance of the catalyst were evaluated.
Table 2 shows the results.

[0145]

[Table 2]

[0146]

As is clear from the results shown in Tables 1 and 2, according to the method of the present invention, even if the exhaust gas contains sulfur oxides, and if the catalyst is placed in a high temperature environment, Even in this case, the nitrogen oxides can be stably and efficiently removed.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of γ-alumina supporting silver aluminate.

FIG. 2 is an X-ray diffraction diagram of γ-alumina.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 8, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

In the first method according to the present invention, the first catalyst preferably contains (a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd, and Ir in terms of metal. 0.1 to 10% by weight, preferably
In the range of 0.5 to 5% by weight, (c) the carrier is supported on a carrier comprising at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide;
The component (b) (except when the component (b) is contained in the catalyst as metallic silver or silver aluminate) in the range of 0.1 to 20% by weight in terms of oxide, preferably 0.5-1
It is supported on the carrier (c) in a range of 0% by weight.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0076

[Correction method] Change

[Correction contents]

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
A rhodium- ferric oxide / titanium oxide coating of about 150 square inches of cordierite was applied to a honeycomb substrate.
g / L (layer thickness 77 μm).

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0088

[Correction method] Change

[Correction contents]

60 g of this powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water, and the mixture was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium. A wash coat slurry was prepared. This slurry was prepared using 200 /
The coating was applied to a honeycomb substrate of square inches of cordierite, and rhodium- aluminum oxide / titanium oxide was supported at a rate of about 150 g / L (layer thickness 77 μm).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiichi Tabata 5-1-1 Ebisshima-cho, Sakai-shi, Osaka Sakai Chemical Industry Co., Ltd. (72) Inventor Kazuyuki Ueda 5-1-1 Ebisshima-cho, Sakai-shi, Osaka Sakai Chemical Industry Central Research Laboratory

Claims (3)

[Claims] An exhaust gas purification catalyst for purifying ternary components of nitrogen oxides, hydrocarbons and carbon monoxide in exhaust gas by alternately oscillating an exhaust gas treatment atmosphere between an oxygen excess atmosphere and a reducing atmosphere. The method comprises: (1) (a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir, and (b) silver, copper, zinc, aluminum, gallium, tin, zirconium, At least one metal selected from the group consisting of chromium, manganese, iron, cobalt and nickel or a compound or ion thereof and (c) at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide; And (2) (a) one selected from alkali metals, alkaline earth metals, aluminum, silver, titanium and rare earth elements Or (b) Pt, R
at least one selected from the group consisting of h, Pd and Ir
An exhaust gas purification method comprising contacting a second catalyst comprising a kind of platinum group element with a second catalyst. 2. An exhaust gas purifying catalyst for purifying ternary components of nitrogen oxides, hydrocarbons, and carbon monoxide in exhaust gas by alternately oscillating an exhaust gas treatment atmosphere between an oxygen-excess atmosphere and a reducing atmosphere. The method comprises: (1) (a) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir, and (b) silver, copper, zinc, aluminum, gallium, tin, zirconium, At least one metal selected from the group consisting of chromium, manganese, iron, cobalt and nickel or a compound or ion thereof and (c) at least one oxide selected from the group consisting of titanium oxide, zirconia and tin oxide; (2) (a) at least one platinum group element selected from the group consisting of Pt, Rh, Ir, and Pd; and (b) titanium oxide ,
Contacting with an intermediate catalyst comprising at least one oxide selected from the group consisting of zirconia and tin oxide, and then (3) (a) from an alkali metal, an alkaline earth metal, aluminum, silver, titanium and a rare earth element Oxides or composite oxides of one or more selected metals and (b) Pt, R
at least one selected from the group consisting of h, Pd and Ir
An exhaust gas purification method comprising contacting a second catalyst comprising a kind of platinum group element with a second catalyst. 3. The second catalyst comprises (a) a composite oxide of barium and aluminum and (b) at least one platinum group element selected from the group consisting of Pt, Rh, Pd and Ir. The exhaust gas purifying method according to claim 1 or 2.