JP2000042370A - Catalyst device for purifying exhaust gas and its using method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst device for purifying exhaust gas capable of preventing the poisoning due to the sulfur in the exhaust gas, improving the NOx purifying performance in lean atmosphere and sufficiently manifesting the function as a ternary catalyst, and to provide the using method capable of effectively manifesting the NOx purifying function. SOLUTION: This catalyst device for purifying the exhaust gas is constituted by arranging the catalyst containing at least one element among Na, Mg, Ca, Sr, Ba, Y and La and alumina is arranged at the first half of exhaust gas stream, and arranging the catalyst containing the powder carrying at least one kind noble metal selected among platinum, palladium and rhodium on a porous body and a composite oxide powder expressed by formula (Ln1-αAα)1-βBOδ (In the formula, Ln is at least one kind element among La, Ce, Nd and Sm, A is Mg, Ca, Sr, Ba, Na, K and Cs, B is at least one kind element among Fe, Co, Ni and Mn, 0<=α<=1, 0<β<1, δ is the oxygen quantity satisfying the valency of each element) at the second half of the exhaust gas stream.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas discharged from internal combustion engines such as automobiles (gasoline and diesel) and boilers.
The present invention relates to an exhaust gas purifying catalyst device for purifying nitrogen oxides (NOx) and a method of using the same, and more particularly to an exhaust gas purifying catalyst device excellent in NOx purifying performance in an oxygen-excess atmosphere and a method of using the same.

[0002]

2. Description of the Related Art In recent years, in view of the problem of depletion of petroleum resources and the problem of global warming, the realization of fuel-efficient vehicles is expected. . In a lean-burn vehicle, the exhaust gas atmosphere during lean-burn operation is an oxygen-excess atmosphere (hereinafter, referred to as a "lean atmosphere") as compared to a stoichiometric air-fuel state (hereinafter, referred to as a "stoichiometric state"). When a conventional three-way catalyst is applied in a lean atmosphere, there has been a problem that the effect of excessive oxygen makes the NOx purification action insufficient. Therefore, even in a lean atmosphere, N
The development of a catalyst that can purify Ox has been desired.

Conventionally, NOx in a lean atmosphere has been
Various catalysts for improving the purification performance have been proposed. For example, JP-A-5-168860 discloses that lanthanum and platinum (Pt) are supported on a porous carrier to convert lanthanum into NOx.
Catalysts for use as absorbers have been proposed. This is to absorb NOx in a lean atmosphere and to release and purify NOx in a stoichiometric or fuel-rich (rich) atmosphere.

[0004] However, the conventional NOx-absorbing catalytic fuel and lubricating oil contain sulfur, and this sulfur is exhausted as an oxide into the exhaust gas, so that the NOx absorbent is poisoned by the sulfur. In addition, the reduction of NOx absorption capacity, so-called sulfur poisoning, occurs. In order to prevent this sulfur poisoning, a sulfur trap catalyst is arranged in front of the NOx absorption catalyst to absorb sulfur oxides in a lean region, and the subsequent NOx
A method for preventing sulfur oxides from flowing into the absorption catalyst has been proposed in JP-A-6-58138. However, in this method, the sulfur trap catalyst is saturated by the absorbed sulfur oxides, and more sulfur oxides flow into the NOx absorption catalyst, resulting in sulfur poisoning.

[0005] Therefore, a method has been proposed in which sulfur oxide is released from the sulfur trap catalyst during stoichiometry to absorb the next sulfur oxide. However, this method also has a problem that the sulfur trap catalyst does not have sufficient release performance at the time of stoichiometry, depending on the catalyst composition of the sulfur trap catalyst, and a problem that the released sulfur oxides poison the subsequent NOx absorption catalyst. May occur.

[0006]

SUMMARY OF THE INVENTION Accordingly, claims 1 to 6 are provided.
An object of the described invention is to prevent poisoning by sulfur in exhaust gas, improve NOx purification performance under a lean atmosphere, which did not show sufficient activity with a conventional catalyst, and achieve a three-way catalyst. An object of the present invention is to provide an exhaust gas purifying catalyst device capable of sufficiently exhibiting functions.

It is another object of the present invention to provide a method of using an exhaust gas purifying catalyst which can exhibit the NOx purifying action of the exhaust gas purifying catalyst device of the present invention particularly effectively.

[0008]

According to a first aspect of the present invention, there is provided a catalyst device for purifying exhaust gas, comprising at least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La; A catalyst comprising at least one element selected from the group consisting of Fe, Mn, Co and Ni is disposed upstream of the exhaust stream, and at least one noble metal selected from the group consisting of platinum, palladium and rhodium; And a powder having the following general formula

(Equation 2) (Where Ln is at least one element selected from the group consisting of La, Ce, Nd and Sm, and A is Mg, Ca, S
at least one element selected from the group consisting of r, Ba, Na, K and Cs; B is at least one element selected from the group consisting of iron, cobalt, nickel and manganese; 0 ≦ α ≦ 1, 0 <β <1, δ indicates the amount of oxygen that satisfies the valence of each element), and a catalyst containing a composite oxide powder represented by the following formula: And

The exhaust gas purifying catalyst device according to claim 2 is
2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage is at least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La;
A composite oxide with at least one element selected from the group consisting of Fe, Mn, Co and Ni is supported on alumina.

The catalyst device for purifying exhaust gas according to claim 3 is
2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed in the preceding stage is a composite oxide of alumina and at least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La. And at least one element selected from the group consisting of Fe, Mn, Co and Ni.

The catalyst device for purifying exhaust gas according to claim 4 is
2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed in the preceding stage is a composite oxide of alumina and at least one element selected from the group consisting of Fe, Mn, Co and Ni, and Na, Mg, It is characterized by carrying at least one element selected from the group consisting of Ca, Sr, Ba, Y and La.

The catalyst device for purifying exhaust gas according to claim 5 is
2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage is at least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La;
It is characterized by comprising a composite oxide of alumina and at least one element selected from the group consisting of Fe, Mn, Co and Ni.

[0013] The exhaust gas purifying catalyst device according to claim 6 is
The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein the catalyst disposed in the preceding stage further contains a noble metal.

According to a seventh aspect of the present invention, there is provided a method of using the exhaust gas purifying catalyst device according to any one of the first to sixth aspects, wherein the exhaust gas purifying catalytic device has an air-fuel ratio of 10 to 14.8,
It is characterized in that it is used for a lean burn engine vehicle which repeats a range of 5 to 50.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Na, Mg, Ca, S
at least one element selected from the group consisting of r, Ba, Y and La, alumina, Fe, Mn, Co and N
and at least one element selected from the group consisting of i, i.e., Na, Mg, Ca, S
When alumina carries a composite oxide of at least one element selected from the group consisting of r, Ba, Y and La and at least one element selected from the group consisting of Fe, Mn, Co and Ni , Na, Mg, Ca, Sr, B
When the composite oxide of alumina and at least one element selected from the group consisting of a, Y and La carries at least one element selected from the group consisting of Fe, Mn, Co and Ni, , Mn, Co and Ni at least one element selected from the group consisting of alumina and Na, Mg, Ca, Sr, Ba, Y and L
a carrying at least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y
And a composite oxide of at least one element selected from the group consisting of La and La, and at least one element selected from the group consisting of Fe, Mn, Co and Ni, and alumina.

As described above, the catalyst at the first stage used in the present invention includes:
By containing a composite oxide of an alkali metal or an alkaline earth metal, a transition metal, and alumina, the absorbed sulfur oxide is easily decomposed. This is presumably because the resulting sulfate is a complex sulfate, which weakens the bond between alkali metal, alkaline earth metal, transition metal and alumina and sulfuric acid as compared with a single sulfate.

It is preferable that all of the components of the former catalyst are complexed. However, even when a part of the components is complexed, the above effect can be obtained.

The catalyst in the first stage is composed of Na, Mg. Ca, Sr,
Even if at least one member selected from the group consisting of Ba, Y and La and alumina are not used as a composite oxide, Fe, M
By supporting on alumina together with at least one selected from the group consisting of n, Co and Ni, the release performance of sulfur oxides is improved. Na, Mg. Ca, Sr, B
If at least one selected from the group consisting of a, Y, and La is complexed with alumina, Fe, Mn,
By carrying or complexing at least one selected from the group consisting of Co and Ni, the release performance is further improved.

In order to effectively absorb and desorb the sulfur in the exhaust gas, the composite oxide is preferably contained in an amount of 0.1 to 200 g per liter of the catalyst for purifying exhaust gas at the preceding stage of the present invention. Na, Mg. Ca, Sr, Ba, Y and La
It is preferable that at least one element selected from the group consisting of 1 to 30% by weight is contained in the catalyst for purifying exhaust gas in order to absorb and desorb sulfur in exhaust gas,
Further, Fe, Mn. At least one element selected from the group consisting of Co and Ni is preferably contained in an amount of 0.1 to 10% by weight from the viewpoint of promoting the desorption of sulfur absorbed in the upstream exhaust gas purifying catalyst.

The exhaust gas purifying catalyst used in the present invention, which is disposed upstream of the exhaust stream, preferably contains at least one noble metal selected from the group consisting of platinum, palladium and rhodium. As such a noble metal, at least one selected from the group consisting of platinum, palladium and rhodium is used. For example, Pt, Rh, P
Various combinations such as only d, Rh, and Pd are possible, and by supporting such a catalytic noble metal, the absorption performance of sulfur oxides is improved.

The content of the noble metal is not particularly limited, but is preferably 0.1 to 10 g per liter of the preceding exhaust gas purifying catalyst from the viewpoint of improving the absorption performance of sulfur.

On the other hand, in the exhaust gas purifying catalyst used in the present invention and disposed downstream of the exhaust gas flow, platinum, platinum,
The powder includes at least one noble metal selected from the group consisting of palladium and rhodium supported on a porous body. As such a noble metal, at least one selected from the group consisting of platinum, palladium and rhodium is used. For example, various combinations such as Pt and Rh, Pd and Rh, and Pd alone are possible. The use of a noble metal of only Pd is preferable because the interaction with the complex oxide represented by the above formula (2) is further enhanced, and the NOx absorption action is further improved.

The content of the noble metal is not particularly limited as long as the NOx absorption capacity and the three-way catalyst performance are sufficiently obtained.
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
From the point that no significant improvement in characteristics is observed even when the amount is larger than 0.1 g, the amount is preferably 0.1 to 10 g per liter of the latter-stage exhaust gas purifying catalyst used in the present invention.

Since the latter catalyst used in the present invention also needs to function as a three-way catalyst at the time of stoichiometry, at least one selected from the group consisting of Pt, Pd and Rh is at least partially formed into a porous material. It is preferably supported, and particularly preferably supported on alumina. The alumina used here is preferably one having high heat resistance, and among them, activated alumina having a specific surface area of 50 to 300 m ² / g is preferred. In order to improve the heat resistance of alumina, a rare earth compound such as cerium or lanthanum or an additive such as zirconium may be further added as conventionally used in a three-way catalyst.

Further, since the latter catalyst used in the present invention also needs to function as a three-way catalyst during stoichiometry, additives conventionally used in three-way catalysts may be further added.
For example, there are ceria having an oxygen storage function, barium which reduces HC adsorption poisoning to noble metals, and zirconia which contributes to improvement in heat resistance of Rh.

The composite oxide contained in the catalyst for purifying the second stage exhaust gas used in the present invention is represented by the following general formula:

(Equation 3) It is represented by

Rare earth metals include lanthanum, cerium, neodymium and samarium, potassium, sodium and cesium as alkali metals, magnesium, calcium, strontium and barium as alkaline earth metals, and iron as a transition metal. , Cobalt, nickel and manganese can be suitably used.

A complex oxide such as the above-described perovskite oxide has a property that oxygen deficiency is generated, NOx is easily adsorbed through the generated oxygen deficiency, and NOx is absorbed in a lean atmosphere. Utilization makes it possible to improve NOx purification performance.

In general, the perovskite-type oxide may cause a solid phase reaction with the alumina-based oxide in the catalyst composition and deactivate the activity. And a method using a material having low reactivity with perovskite such as zirconia.

On the other hand, by slightly losing the A site of the perovskite oxide from the stoichiometric ratio as in the present invention, the A site of the perovskite oxide can be exchanged with another oxide (alumina or the like) in contact with the perovskite oxide. It has become possible to suppress the solid-phase reaction, improve the thermal stability, and maintain high purification performance after heat endurance.

The substitution amount of the A site is 0.ltoreq..alpha..ltoreq.1, and is not particularly limited. However, in order to obtain a sufficient NOx absorbing ability, it is particularly preferably 0.2.ltoreq..alpha..ltoreq.1.

If the value of β is 1 or more, a single-phase perovskite structure is not formed, so that 0 <β <1 is preferable. The value of δ is the amount of oxygen that satisfies the valence of each atom, and is approximately 0 <δ <4.

The composite oxide used in the present invention, particularly the partially substituted perovskite oxide, exhibits the ability to absorb NOx in a lean atmosphere together with the partially substituted amount thereof. Oxidized to NO ₂ on the composite oxide, and Mg, Ca, S on the surface of the composite oxide
It is considered that nitric acid is absorbed in the vicinity of at least one element selected from the group consisting of r, Ba, Na, K, and Cs in the state of or close to nitric acid groups. Therefore, the composition of the composite oxide for effectively absorbing NOx under a lean atmosphere is made of Mg, Ca, Sr, B which can easily produce nitrate.
a, containing at least one element selected from the group consisting of Na, K and Cs, further, it is important to contain a transition metal element capable of oxidizing NOx to NO _2.

Each of the constituent elements of the composite oxide exerts the above effects to the maximum when all of these contained in the catalyst are complexed, but at least a part of the complex oxide forms a complex. Even if it is possible, the above effect can be sufficiently obtained.

Each constituent element of the composite oxide can exist as a composite oxide without being separated as a separate oxide even after thermal endurance, and this can be confirmed by, for example, X-ray diffraction measurement.

Each constituent element in the composite oxide may contain a trace amount of impurities as long as it does not interfere with the above-mentioned action. For example, strontium contained in barium,
Cerium, neodymium, samarium contained in lanthanum and hafnium and sulfur contained in zirconium.

The content of the composite oxide is not particularly limited as long as the effect of the composite oxide is obtained in the catalyst, and is 20 to 100 g per liter of the second-stage exhaust gas purifying catalyst of the present invention.
It is preferable to be contained.

The second-stage exhaust gas purifying catalyst used in the present invention is capable of obtaining a NOx purifying action which cannot be obtained independently by coexistence of the noble metal and the composite oxide. That is, when the exhaust gas atmosphere becomes lean, high NOx purification performance can be obtained by the NOx absorbing action of the composite oxide in the exhaust gas purification catalyst of the present invention. When the composite oxide absorbs NOx and the exhaust gas atmosphere changes from lean to stoichiometric, NOx is released from the composite oxide and high NOx purification performance is obtained. It is intended to obtain excellent NOx purification performance which cannot be obtained by simply mixing individual components of the composite oxide.

The post-catalyst used in the present invention has a high NOx absorbing effect even after heat endurance. This is because the composite oxide has a perovskite type structure having a small proportion of A site, and other components (for example, alumina) This is because the solid-phase reaction with is avoided.

In the catalyst device of the present invention, the first-stage catalyst is disposed upstream with respect to the exhaust gas flow, and the second-stage catalyst is disposed downstream with respect to the exhaust gas flow. With this arrangement, in the lean region, the catalyst at the preceding stage absorbs the sulfur oxides in the exhaust gas, and the exhaust gas without sulfur oxides flows into the NOx absorption catalyst at the subsequent stage. for that reason,
The subsequent NOx absorbing butterfly can efficiently absorb only NOx without absorbing sulfur oxides, that is, without being poisoned by sulfur. Then, at the time of stoichiometric to rich, sulfur oxides are released from the preceding catalyst, and at the same time,
NOx of the subsequent catalyst is also released. By repeating such a cycle, NOx can be eliminated without being poisoned by sulfur oxides.
Can be absorbed / purified. Further, since the absorption of sulfur oxides released from the pre-stage catalyst during stoichiometric to rich conditions is suppressed, the released sulfur oxides are
It does not require a special engine that does not flow into the x-absorption catalyst.

The composite oxide used in the present invention is prepared by mixing nitrate, acetate, carbonate, citric acid, hydrochloride and the like of each constituent element of the composite oxide in a desired composition ratio of the composite oxide, and calcining the mixture. And then pulverized and heat treated and calcined, and the nitrate, acetate, carbonate, hydrochloride,
Citrate and the like are mixed in a desired composite oxide composition ratio and dissolved in water, and then, if necessary, NH ₄ OH or NH ₃
A precipitate is formed by dropping an alkaline solution such as CO _{3 and the} like, and the precipitate can be prepared by a coprecipitation method in which the precipitate is dried, filtered, dried and calcined, but is not limited to these methods. Any other method may be used as long as the composite oxide is formed.

According to such a method, at least a part of each component constituting the composite oxide can be composited.

As described above, the raw material for preparing the catalyst of the composite oxide used in the present invention may contain a trace amount of impurities as long as the amount does not interfere with the above-mentioned effects. For example, strontium contained in barium, Cerium, neodymium, and samarium contained in lanthanum, and hafnium and sulfur contained in zirconium.

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

In the case of the ion exchange method or the impregnation method, since the metal raw material is often used in a solution, the pH can be adjusted by adding an acid or a base to the solution. pH
By adjusting the value, it is possible that the particles can be further highly dispersed and supported.

The catalyst of the present invention is preferably used by being supported on a monolithic carrier. The noble metal-supported porous body and the composite oxide are pulverized to form a slurry, which is coated on the catalyst carrier.
By firing at a temperature of 400 to 900 ° C., the exhaust gas purifying catalyst of the present invention can be obtained.

The pulverization method for pulverizing the noble metal-supported porous body and the composite oxide is not particularly limited, and preferably, a method of adjusting the aqueous slurry containing the noble metal-supported porous body and the composite oxide by wet pulverization. Can be used.

The apparatus that can be used for the pulverization is not particularly limited, and a commercially available ball-type vibrating mill can be used, and a desired particle size is obtained by adjusting the ball diameter, the pulverizing time, the amplitude, and the vibration frequency.

The catalyst carrier can be appropriately selected from known catalyst carriers and used, for example, a honeycomb carrier or a metal carrier having a monolith structure made of a refractory material.

Although the shape of the catalyst carrier is not particularly limited, it is usually preferable to use a honeycomb shape. As the honeycomb material, for example, cordierite materials such as ceramics are generally used. It is also possible to use a honeycomb made of a metal material such as stainless steel, and further, the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst into a honeycomb shape, the area of the catalyst and the exhaust gas becomes large, and the pressure loss is suppressed, which is extremely advantageous when the catalyst is used for an automobile or the like.

More preferably, the obtained exhaust gas purifying catalyst is impregnated and supported with an alkali metal and / or an alkaline earth metal. The usable alkali metal and alkaline earth metal are at least one element selected from the group consisting of lithium, sodium, potassium, cesium, magnesium, calcium, strontium and barium.

The alkali metal and alkaline earth metal compounds that can be used include oxides, acetates, hydroxides, nitrates,
It is water-soluble such as carbonate. This makes it possible to carry the alkali metal and / or alkaline earth metal as a basic element in the vicinity of palladium with good dispersibility.
At this time, the starting compounds of the alkali metal and the alkaline earth metal may be contained simultaneously or separately.

That is, an aqueous solution of a powder comprising an alkali metal compound and / or an alkaline earth metal compound is impregnated with the above-mentioned catalyst supporting a washcoat component, dried, and then dried in air and / or under a stream of air. ° C to 600
It is baked at ℃. This is because, once the alkali metal and alkaline earth metal raw material compounds are heat-treated at a low temperature and contained in the coat layer in the form of an oxide, it becomes difficult to form a composite oxide even when exposed to a high temperature later. If the calcination temperature is lower than 200 ° C., the alkali metal compound and the alkaline earth metal compound cannot be sufficiently converted into an oxide form. If the calcination temperature exceeds 600 ° C., the raw material salt is rapidly decomposed, and However, it is not preferable because it may crack.

The use conditions of the exhaust gas purifying catalyst of the present invention are not particularly limited.
0 to 50, more preferably an air-fuel ratio of 10 to 14.8 and 1
It can be used for lean burn engine vehicles that repeat the range of 5 to 50. With such a method of use, the cycle of NOx absorption / release is extremely effectively established, and particularly efficient NOx purification becomes possible. That is,
High NOx purification performance is achieved by absorbing NOx in a large air-fuel ratio region (lean region) within an air-fuel ratio range of 10 to 50 and purifying NOx in a small air-fuel ratio region (rich and / or stoichiometric). More preferable ranges are 10 to 14.8 for a region having a small air-fuel ratio and 15 to 50 for a region having a large air-fuel ratio.

[0055]

The present invention will be described below with reference to the following examples and comparative examples. Example 1 Activated alumina was impregnated with an aqueous solution of magnesium acetate, dried, and calcined in air at 900 ° C. for 4 hours to obtain a composite oxide powder of magnesium and alumina (powder A). The magnesium concentration of this powder was 10.0% by weight. The powder A was prepared by mixing an aqueous solution of magnesium acetate and aluminum nitrate with the magnesium concentration of the powder A being 10.0% by weight.
And dried and calcined in air at 400 ° C. for 4 hours, or by adding an aqueous solution of magnesium acetate to activated alumina so that the magnesium concentration of powder A becomes 10.0% by weight. And coprecipitated with aqueous ammonia. The precipitate is dried and then calcined at 400 ° C. for 4 hours in air.

900 g of the powder A and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1, 3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g /
An L-support pre-catalyst was obtained.

The activated alumina powder was impregnated with an aqueous palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain Pd-supported alumina powder (powder B). The Pd concentration of this powder B was 5.0% by weight.

The activated alumina powder was impregnated with an aqueous rhodium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain a Rh-supported alumina powder (powder C). The Rh concentration of the powder C was 3.0% by weight.

Citric acid was added to a mixture of lanthanum carbonate, barium carbonate and cobalt carbonate, dried and calcined at 700 ° C. to obtain a powder D. This powder D had a metal atom ratio of lanthanum / barium / cobalt = 2/7/10.

347 g of the powder B and 58 of the powder C were used.
g, the powder D was 360 g, and the activated alumina powder was 136.
g of water and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. A post-stage catalyst having a coat layer weight of 200 g / L-carrier was obtained.

The exhaust gas purification catalyst device of the present invention was obtained by installing the above-mentioned first-stage catalyst and the above-mentioned second-stage catalyst in combination with respect to the exhaust gas flow.

Example 2 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 1 except that magnesium acetate of the powder A was changed to sodium acetate.

Example 3 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 1 except that magnesium acetate of the powder A was changed to calcium acetate.

Example 4 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 1 except that strontium acetate was used as the magnesium acetate of the powder A.

Example 5 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 1 except that barium acetate was used as the magnesium acetate of the powder A.

Example 6 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 1 except that magnesium acetate of the powder A was changed to yttrium nitrate.

Example 7 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 1 except that lanthanum nitrate was used as the magnesium acetate of the powder A.

Example 8 An aqueous solution of magnesium acetate and an aqueous solution of iron nitrate were mixed and calcined at 900 ° C. for 4 hours in dry air to obtain a composite oxide of magnesium acetate and iron nitrate. This was impregnated with activated alumina, dried and calcined in air at 400 ° C. for 2 hours to obtain a powder of alumina supporting magnesium and iron composite oxide (powder E). The powder E had a magnesium concentration of 10.0% by weight and an iron concentration of 5% by weight.

The above powder E (900 g) and water (900 g) were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g /
An L-carrier pre-catalyst was obtained. A catalyst device for purifying exhaust gas of the present invention was obtained in the latter stage using the catalyst arranged in the latter stage of Example 1.

Example 9 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 8, except that sodium acetate was used as the magnesium acetate of the powder E.

Example 10 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 8 except that magnesium acetate in the powder E was changed to calcium acetate.

Example 11 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 8, except that strontium acetate was used as the magnesium acetate for the powder E.

Example 12 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 8, except that magnesium acetate of the powder E was changed to barium acetate.

Example 13 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 8 except that magnesium acetate of the powder E was changed to yttrium nitrate.

Example 14 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 8, except that lanthanum nitrate was used as the magnesium acetate of the powder E.

Example 15 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 8 except that the iron nitrate of the powder E was changed to manganese nitrate.

Example 16 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 8, except that iron nitrate of the powder E was changed to cobalt nitrate.

Example 17 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 8, except that nickel nitrate was used instead of iron nitrate of the powder E.

Example 18 Powder A obtained in Example 1 was impregnated with an aqueous solution of iron nitrate, dried, and calcined in air at 400 ° C. for 2 hours to obtain Powder F.
900 g of the powder F and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was applied to a cordierite monolithic carrier (1.3 L,
After drying at 130 ° C. and calcining at 400 ° C. for 1 hour, a pre-stage catalyst having a coat layer weight of 200 g / L-carrier was obtained. In the subsequent stage, the same catalyst as that arranged in the latter stage of Example 1 was arranged to obtain an exhaust gas purifying catalyst device of the present invention.

Example 19 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 18 except that magnesium acetate of the powder A was changed to sodium acetate.

Example 20 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 18 except that the magnesium acetate of the powder A was changed to calcium acetate.

Example 21 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 18 except that strontium acetate was used as the magnesium acetate for the powder A.

Example 22 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 18 except that barium acetate was used as the magnesium acetate of the powder A.

Example 23 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 18 except that the magnesium A of the powder A was changed to yttrium nitrate.

Example 24 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 18, except that magnesium acetate of the powder A was changed to lanthanum nitrate.

Example 25 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 18 except that manganese nitrate was used as the iron nitrate of the powder F.

Example 26 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 18 except that the iron nitrate of the powder F was changed to cobalt nitrate.

Example 27 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 18 except that the iron nitrate of the powder F was changed to nickel nitrate.

Example 28 Activated alumina was impregnated with an aqueous solution of iron nitrate, dried and calcined in air at 900 ° C. for 4 hours to obtain a powder of a composite oxide of iron nitrate and alumina. This powder was impregnated with an aqueous solution of magnesium acetate, dried, and calcined at 400 ° C. for 2 hours in the air to obtain a powder. This powder had a magnesium concentration of 10.0% by weight and an iron concentration of 5% by weight.

900 g of the above powder and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g /
An L-carrier pre-catalyst was obtained. A catalyst device for purifying exhaust gas of the present invention was obtained in the latter stage using the catalyst arranged in the latter stage of Example 1.

Example 29 Activated alumina was impregnated with an aqueous solution of magnesium acetate and an aqueous solution of iron nitrate, dried, and calcined in air at 900 ° C. for 4 hours to obtain a powder of a composite oxide of magnesium and alumina (powder G). Was. The magnesium concentration of this powder G was 10.0
% By weight, and the iron concentration was 5% by weight.

The powder G was mixed with an aqueous solution of magnesium acetate, iron nitrate, and aluminum nitrate at a ratio such that the magnesium concentration of the powder G was 10.0% by weight and the iron concentration was 5% by weight. By calcination in air at 400 ° C. for 4 hours, or by adding an aqueous solution of magnesium acetate and iron nitrate to activated alumina so that the magnesium concentration of powder G is 1
0.0% by weight, impregnated at a ratio such that the iron concentration becomes 5% by weight, coprecipitated with aqueous ammonia, and after drying the precipitate,
It can also be obtained by baking in air at 400 ° C. for 4 hours.

900 g of the powder G and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g /
An L-carrier pre-catalyst was obtained. A catalyst device for purifying exhaust gas of the present invention was obtained in the latter stage using the catalyst arranged in the latter stage of Example 1.

Example 30 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 29 except that magnesium acetate of the powder G was changed to sodium acetate.

Example 31 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 29 except that magnesium acetate of the powder G was changed to calcium acetate.

Example 32 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 29 except that strontium acetate was used as the magnesium acetate of the powder G.

Example 33 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 29 except that barium acetate was used as the magnesium acetate for the powder G.

Example 34 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 29 except that the powder G was changed from magnesium acetate to yttrium nitrate.

Example 35 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 29, except that lanthanum nitrate was used as the magnesium acetate for the powder G.

Example 36 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 29 except that manganese nitrate was used as the iron nitrate of the powder G.

Example 37 A catalyst device for purifying exhaust gas was obtained in the same manner as in Example 29 except that the iron nitrate of the powder G was changed to cobalt nitrate.

Example 38 An exhaust gas purifying catalyst device was obtained in the same manner as in Example 29 except that nickel nitrate was used as the iron nitrate of the powder G.

Example 39 Powder H obtained by impregnating the powder G obtained in Example 29 with an aqueous solution of palladium nitrate. The Pd concentration of this powder H was 5% by weight. 900 g of the powder H and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite type monolith carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air flow, and the cells were dried at 130 ° C.
It was calcined at 400 ° C. for 1 hour to obtain a pre-stage catalyst having a coat layer weight of 200 g / L and one carrier. A catalyst device for purifying exhaust gas of the present invention was obtained in the latter stage using the catalyst arranged in the latter stage of Example 1.

Example 40 Example 29 was repeated except that the aqueous solution of powder H in palladium nitrate was a mixed aqueous solution of palladium nitrate and rhodium nitrate, and the concentration of the noble metal was 5% by weight (Pd: Rh = 17: 1).
An exhaust gas purifying catalyst device was obtained in the same manner as described above.

Example 41 The same procedure as in Example 29 was carried out except that the aqueous solution of powder H in palladium nitrate was a mixed aqueous solution of dinitrodiamine platinum and rhodium nitrate, and the concentration of the noble metal was 5% by weight (Pt: Rh = 17: 1). A catalyst was obtained in a similar manner.

Comparative Example 1 An exhaust gas purifying catalyst device was obtained by arranging nothing in the former stage of the exhaust gas flow and arranging only the latter stage catalyst in Example 1.

Comparative Example 2 Activated alumina was impregnated with an aqueous dinitrodiamine platinum solution.
After drying, the powder was calcined at 400 ° C. for 1 hour in the air to obtain a platinum-supported activated alumina powder. The platinum concentration of this powder was 5.0% by weight. 900 g of this powder and 900 g of water were charged into a magnetic ball mill and mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g /
A post-stage catalyst of L-carrier was obtained. Thereafter, the carrier was post-impregnated in an aqueous solution of barium acetate. Barium was 30 g / L as barium oxide. This catalyst is placed in the latter stage,
In the former stage, the catalyst obtained in Example 1 was installed to obtain a catalyst device for purifying exhaust gas.

COMPARATIVE EXAMPLE 3 Activated alumina was impregnated with an aqueous solution of magnesium acetate, dried, and calcined at 400 ° C. for 1 hour in air to obtain a magnesium-supported activated alumina powder. The magnesium concentration of this powder was 10.0% by weight. 900 g of this powder and 9 parts of water
And the mixture was mixed and pulverized for 1 hour to obtain a slurry liquid. This slurry liquid was adhered to a cordierite monolithic carrier (1.3 L, 400 cells),
The excess slurry in the cell is removed by air flow to remove 130
After drying at ℃, it was baked at 400 ℃ for 1 hour to obtain a pre-stage catalyst having a coat layer weight of 200 g / L per carrier. An exhaust gas purifying catalyst device was obtained in the latter stage using the catalyst arranged in the latter stage of Example 1.

From a comparison between Example 1 and Comparative Example 1, it is understood that the NOx conversion rate of Comparative Example 1 is worse than that of Example 1.
This is because, unless the catalyst of the present invention is arranged in front of the NOx absorption catalyst, the sulfur oxides in the exhaust gas directly flow into the NOx absorption catalyst, combine with the NOx absorbent in the lean region, do not desorb, and the NOx It is considered that the absorption capacity is reduced.

Also, from the comparison between Example 1 and Comparative Example 2,
It can be seen that the NOx conversion rate deteriorates unless the catalyst placed in the latter stage is the NOx absorption catalyst used in the present invention. This is because the sulfur oxide discharged from the preceding catalyst at the time of stoichiometry flows into the latter catalyst, and in the catalyst as in Comparative Example 2, the sulfur oxide becomes sulfate and combines with the NOx absorbent, so that it is not desorbed. Therefore, it is considered that the NOx absorption capacity is reduced. From this, it can be seen that the combination of the catalyst placed in the first stage and the NOx absorption catalyst placed in the second stage of the present invention has durability against sulfur poisoning.

Also, from the comparison between Example 1 and Comparative Example 3,
It can be seen that good results cannot be obtained unless at least one of the catalysts placed in the former stage is selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La, even if it is partly combined with alumina. This is considered to be due to the fact that the ability to desorb the generated sulfur salt is improved by complexing with alumina.

Test Examples The catalyst activities for exhaust gas purification obtained in Examples 1 to 41 and Comparative Examples 1 to 3 were evaluated under the following conditions for initial and endurance catalytic activities. For the activity evaluation, an automatic evaluation device using a model gas simulating the exhaust gas of an automobile was used.

Endurance conditions A catalyst was mounted on the exhaust system of a 4400 cc engine, and the system was operated at a pre-stage catalyst inlet temperature of 650 ° C. for 50 hours. Thereafter, the pre-stage catalyst inlet temperature was set at 350 ° C. and operated for 5 hours. At this time,
Gasoline containing 300 ppm sulfur was used.

Evaluation Conditions The catalyst activity was evaluated by mounting each catalyst in an exhaust system of an engine with a displacement of 2,000 cc, A / F = 10 (stoichiometric state) for 20 seconds, and then A / F = 22 (lean atmosphere).
For one second, then one cycle of A / F = 50 (lean atmosphere) for 30 seconds, measuring the average conversion,
The average conversion rate when A / F = 14.6 (stoichiometric state), the average conversion rate when A / F = 22 (lean atmosphere), and the average conversion rate when A / F = 50 (lean atmosphere) Were averaged to obtain a total conversion. This evaluation was performed at the initial stage and after the endurance test, and the catalytic activity evaluation value was determined by the following equation. However, gasoline contained 300 ppm of sulfur.

[0115]

(Equation 4)

Table 1 shows the catalytic activity evaluation results obtained as the total conversion. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention described later could be confirmed.

[0117]

[Table 1]

[0118]

The exhaust gas purifying catalyst device according to any one of claims 1 to 6 prevents poisoning by sulfur in exhaust gas, and purifies NOx in a lean atmosphere, which does not show sufficient activity with a conventional catalyst. And a function as a three-way catalyst can be sufficiently exhibited, and excellent NOx purification performance can be exhibited even after heat durability. The method of using the exhaust gas purifying catalyst device according to claim 7 enables the effective NOx absorption / release cycle of the exhaust gas purifying catalyst of the present invention to be exhibited particularly efficiently.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 23/76 B01J 23/89 A 23/89 33/00 B 33/00 F01N 3/28 301E F01N 3 / 28 301 B01J 23/56 A F-term (reference) 3G091 AA02 AA12 AA13 AB01 AB03 AB06 BA07 BA11 BA14 BA15 BA19 BA39 FB10 FB11 FB12 GA06 GA20 GB01W GB01X GB02W GB03W GB04W GB05W GB06W GB07W GB10W GB11W GB16A03 GB17 BA01X BA02X BA03X BA09X BA13X BA14X BA15X BA18X BA19Y BA28X BA30X BA31X BA33X BA36X BA37X BA38X BA41X BA42X BB02 BB17 BC01 CA01 CC32 CC46 CC51 DA01 DA06 DA11 EA04 4G069 AA01 AA03 AA08 AA12 BA01A BA01B BA06A BA06B BA13B BB02A BB02B BB04A BB04B BB06A BB06B BC02A BC02B BC03A BC06A BC09A BC09B BC12A BC12B BC13A BC13B BC40A BC40B BC42A BC42B BC43A BC44A BC62A BC62B BC66A B C66B BC67A BC67B BC68A BC68B BC69A BC71A BC71B BC72A BC72B BC75A BC75B CA03 CA09 DA05 EA01Y EA19 EB12Y EC02Y EC03Y EC28 ED06 ED07 EE09 FA02 FA06 FB09 FB14 FB15 FB30

Claims (7)

[Claims] 1. At least one element selected from the group consisting of Na, Mg, Ca, Sr, Ba, Y and La;
A catalyst comprising alumina and at least one element selected from the group consisting of Fe, Mn, Co and Ni is disposed upstream of the exhaust stream, and comprises at least one catalyst selected from the group consisting of platinum, palladium and rhodium. A powder in which a kind of noble metal is supported on a porous body, and the following general formula: (Where Ln is at least one element selected from the group consisting of La, Ce, Nd and Sm, and A is Mg, Ca, S
at least one element selected from the group consisting of r, Ba, Na, K and Cs, B is at least one element selected from the group consisting of iron, cobalt, nickel and manganese; 0 ≦ α ≦ 1, 0 <β <1, δ indicates the amount of oxygen that satisfies the valence of each element), and a catalyst containing a composite oxide powder represented by the following formula: Exhaust gas purification catalyst device. 2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage comprises Na, Mg, Ca, S
a composite oxide of at least one element selected from the group consisting of r, Ba, Y and La and at least one element selected from the group consisting of Fe, Mn, Co and Ni;
A catalyst device for purifying exhaust gas, which is supported on alumina. 3. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage comprises Na, Mg, Ca, S
A composite oxide of alumina and at least one element selected from the group consisting of r, Ba, Y, and La, Fe, M
at least one selected from the group consisting of n, Co and Ni
A catalyst device for purifying exhaust gas, wherein the catalyst device carries a kind of element. 4. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage comprises Fe, Mn, Co and N.
i, a composite oxide of at least one element selected from the group consisting of i and alumina, Na, Mg, Ca, Sr, B
A catalyst device for purifying exhaust gas, comprising at least one element selected from the group consisting of a, Y and La. 5. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst disposed at the preceding stage comprises Na, Mg, Ca, S
It is characterized by comprising a composite oxide of alumina with at least one element selected from the group consisting of r, Ba, Y and La, and at least one element selected from the group consisting of Fe, Mn, Co and Ni, and alumina. Exhaust gas purification catalyst device. 6. The exhaust gas purifying catalyst device according to claim 1, wherein the catalyst disposed in the preceding stage further contains a noble metal. 7. The exhaust gas purifying apparatus according to claim 1, wherein the air-fuel ratio is in the range of 10 to 14.8,
A method for using an exhaust gas purifying catalyst device, which is used for a lean burn engine vehicle that repeats a range of 5 to 50.