JP2005021895A - Catalyst for cleaning exhaust gas for lean-burn engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a catalyst for removing nitrogen oxides for efficiently removing NOx and having superior high temperature heat resistance and poison resistance, and a production method therefor. <P>SOLUTION: This catalyst contains a refractory inorganic oxide carrying platinum in a part or the whole of it, a cerium-containing oxide carrying palladium in a part or the whole of it, and an alkali metal compound and/or an alkaline earth metal compound. The alkali metal and/or alkaline earth metal is carried on or mixed into the whole of a mixture of the refractory inorganic oxide carrying platinum in a part or the whole of it with the cerium-containing oxide carrying palladium in a part or the whole of it. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst for purifying exhaust gas of a lean combustion type gasoline engine mainly used as a driving engine of an automobile and a method for manufacturing the same.

  In recent years, the introduction of lean burn gasoline engines has been studied in order to improve fuel efficiency in driving engines such as automobiles. In this case, in order to improve fuel efficiency, the vehicle is operated in a state where the amount of air introduced is excessive with respect to the fuel during constant speed operation. A conventional gasoline engine is operated at an air-fuel ratio (weight ratio of fuel to air: hereinafter referred to as A / F) of around 14.6. This ratio is called the stoichiometric air-fuel ratio. Since oxygen in the fuel and the oxide are in a stoichiometric relationship, when complete combustion is performed, unburned matter and oxygen are in the exhaust gas. Does not remain.

  Conventionally, various catalysts have been studied for purifying engine exhaust gas. Of these, a so-called three-way catalyst that simultaneously removes hydrocarbons, carbon monoxide, and nitrogen oxides in the vicinity of the theoretical air-fuel ratio does not consider nitrogen oxide purification ability in an excessive oxidizing atmosphere. For this reason, it is difficult to purify nitrogen oxides in a lean combustion gasoline engine that has an oxygen-excess atmosphere during constant speed running.

  Of the internal combustion engines, diesel engines and boilers generally use a reducing agent such as ammonia, hydrogen or carbon monoxide when removing nitrogen oxides. However, this method has a problem that a special apparatus is required for collecting and treating the unreacted reducing agent.

Recently, as a method for removing nitrogen oxides, a method using a NOx decomposition catalyst composed of crystalline aluminosilicate containing copper ions has been proposed (Patent Document 1 and Patent Document 2). It has only been shown that (NO) can be decomposed into nitrogen (N ₂ ) and oxygen (O ₂ ), and it is difficult to effectively remove nitrogen oxides under actual exhaust gas conditions. is there.

  Patent Document 3 discloses that when exhaust gas is treated with a copper-containing catalyst in an oxidizing atmosphere in the presence of hydrocarbons, the reaction between NOx and hydrocarbons is promoted preferentially, and NOx can be removed efficiently. Are listed. The hydrocarbon used in this method may be a hydrocarbon contained in the exhaust gas or a hydrocarbon added from the outside as required. As a specific embodiment, the exhaust gas is first treated with a copper-containing catalyst. A method is also disclosed in which NOx is removed by contacting with NO and then hydrocarbons, carbon monoxide and the like are removed by contacting with an oxidation catalyst. However, this method has a high temperature at which nitrogen oxides can be removed, and is less effective at low temperatures.

  Furthermore, since the above-mentioned catalyst is inferior in heat resistance and the NOx decomposition performance decreases when exposed to high-temperature exhaust gas, the catalyst is arranged in parallel as a countermeasure against this, and when the exhaust gas becomes high temperature, the oxidation catalyst or A method of bypassing to the three-way catalyst side is disclosed (Patent Document 4).

  Patent Document 5 uses a catalyst composed of a catalytic active component composed of a noble metal such as platinum, palladium and rhodium, an alkali metal such as lithium, sodium and calcium, and an alkaline earth metal compound and a refractory inorganic oxide. Has been disclosed in which nitrogen oxides in exhaust gas are removed by intermittent introduction. This method only discloses a state in which the catalytically active component is uniformly mixed without being localized on the refractory inorganic oxide.

  Patent Document 6 includes an alumina carrier, a noble metal carrier comprising ceria on which a catalytic noble metal is supported, and a NOx absorber comprising an alkali metal, an alkaline earth metal, a rare earth element, and the like. An exhaust gas purifying catalyst in which the noble metal carrier and NOx absorbent are uniformly dispersed is disclosed. In this catalyst, all noble metals are supported on ceria.

Various catalysts have been proposed, but the present situation is that a nitrogen oxide decomposition catalyst that efficiently decomposes and removes NOx in the exhaust gas of a lean combustion engine and has excellent high-temperature heat resistance has not been developed.
JP-A-60-125250 US Pat. No. 4,297,328 JP-A 63-1000091 JP-A-1-171625 International Publication WO 94/25143 JP-A-8-117600

  An object of the present invention is to provide a nitrogen oxide removing catalyst that efficiently removes NOx, has excellent high temperature heat resistance and poisoning resistance, and a method for producing the same.

  As a result of diligent research to solve the above problems, the present inventors have found that a) a refractory inorganic oxide partially or entirely supporting platinum, and b) a cerium-containing oxide partially or entirely supporting palladium. And c) an alkali metal compound and / or an alkaline earth metal compound, provided that the c) alkali metal and / or alkaline earth metal carries a) platinum partially or entirely. A catalyst for purifying exhaust gas for a lean combustion engine, characterized in that it is supported or mixed in the whole of a mixture of an inorganic oxide and b) a cerium-containing oxide partially or entirely supported by palladium. .

  Another object of the present invention is to provide: a) a refractory inorganic oxide partially or entirely supported by platinum; b) a cerium-containing oxide partially or entirely supported by palladium; c) an alkali metal compound and / or Further, exhaust gas purification for a lean combustion engine characterized by 1) forming a three-dimensional structure or 2) or coating a fire-resistant three-dimensional structure with a ground and mixed alkaline earth metal compound This is achieved by a method for producing a catalyst for use.

  Further, the object of the present invention is to pulverize and mix a) a refractory inorganic oxide carrying platinum partially or entirely, and b) a cerium-containing oxide carrying palladium partially or entirely. C) forming into a three-dimensional structure, or 2) or coating with a refractory three-dimensional structure, and c) carrying an alkali metal compound and / or a salt of an alkaline earth metal compound on the resulting coating. This is achieved by the manufacturing method of the exhaust gas purifying catalyst for the lean combustion engine.

  According to the catalyst of the present invention, nitrogen oxides, hydrocarbons, and carbon monoxide in the exhaust gas of a lean combustion engine can be purified simultaneously or repeatedly through accumulation / decomposition.

  According to the method for producing a catalyst of the present invention, it is possible to provide a method for producing a catalyst that is very easily suitable for purifying exhaust gas from a lean combustion engine.

In purifying exhaust gas of a lean combustion engine, the catalyst of the present invention oxidizes NOx such as HC, CO, NO, and N ₂ O under oxidizing conditions, adsorbs NO ₂ , and exhausts under reducing conditions. The exhaust gas can be purified by reducing or decomposing NO ₂ adsorbed using HC in the gas as a reducing agent and oxidizing CO using the adsorbed oxygen. Here, in order to improve fuel efficiency, the engine is usually operated in an oxidized state in which the amount of air introduced is excessive with respect to the fuel, but a reducing atmosphere is repeated for a short time to reduce NOx. On the other hand, the reduced state is preferably about 2 to 5 seconds.

  The exhaust gas of the lean combustion engine is preferably an exhaust gas that is used at least at an air / fuel (A / F) ratio of 15 or more when traveling at a low speed, and is further exhausted in a state where the vicinity of stoichiometry and lean are repeatedly fluctuated. More preferred is an exhaust gas.

  a) As the refractory inorganic oxide used for the refractory inorganic oxide partially or wholly supported by platinum, any refractory inorganic oxide may be used as long as it is usually used as a catalyst support, except for cerium oxide. Use α-alumina or activated alumina such as γ, δ, η, θ, etc., titania, zirconia, titania, silicon oxide or a composite oxide thereof such as alumina-titania, alumina-zirconia, titania-zirconia, etc. Preferably, it is an oxide of aluminum, zirconium, titanium or silicon, a composite oxide or a mixture thereof, particularly preferably activated alumina. When platinum is supported in part, it may contain a refractory inorganic oxide not containing platinum up to 20% by weight with respect to the weight of the refractory inorganic oxide containing platinum.

  The platinum is not particularly limited as long as it exhibits catalytic activity, but platinum metal, platinum oxide, platinum black and the like can be exemplified.

In addition, these refractory inorganic oxides usually have a BET surface area of 5 to 500 m ² / g, preferably 50 to ²⁰⁰ m ² / g.

  Usually, platinum may be supported uniformly on a part or the whole of the refractory inorganic oxide, but uniform support is preferable from the viewpoint of dispersibility.

  The amount of platinum used is usually 0.1 to 20 g, preferably 0.5 to 10 g, most preferably 1 to 5 g per liter of the finished catalyst. If the amount used is less than 0.1 g, sufficient oxidation activity after the initial stage and after durability cannot be obtained. On the other hand, if it exceeds 20 g, sufficient oxidation activity cannot be obtained in proportion to the amount used, such being undesirable. The amount of the refractory inorganic oxide used is usually 10 to 500 g, preferably 50 to 400 g, most preferably 100 to 300 g, per liter of the finished catalyst. If the amount used is less than 10 g, platinum may not be sufficiently dispersed and the platinum may agglomerate. On the other hand, if it exceeds 500 g, the density of platinum will be low and sufficient oxidation activity will not be obtained, and the exhaust pressure loss will increase. This is not preferable because of such inconveniences. Here, the amount of the constituent component used per liter of the finished catalyst means that when the catalyst component itself is molded, the volume of the molded body itself is used as a reference, and the constituent component is supported on the fire-resistant three-dimensional structure. In the case, the volume of the three-dimensional structure is displayed as a reference.

The component having oxidation activity used in the present invention mainly comes in contact with exhaust gas containing NOx in an oxidizing atmosphere, so that NO, N ₂ O, etc. present in the exhaust gas at a high ratio as NOx components It plays the role of oxidizing or activating to NO ₂ .

  b) The cerium-containing oxide used for the cerium-containing oxide partially or entirely supported by palladium was selected from the group consisting of cerium oxide alone and cerium and zirconium, yttrium, and rare earth elements (excluding cerium). An oxide composed of one or more elements, a mixture thereof, a composite oxide, or a mixture of an oxide and a composite oxide can be given. Among these, a cerium-zirconium composite oxide is preferable from the viewpoint of heat resistance. When palladium is partially supported, the cerium-containing oxide containing no palladium may be contained up to 50% by weight based on the weight of the cerium-containing oxide containing palladium. When combining cerium and other materials, the oxide is preferably in the range of 20 to 400 g per 100 g of cerium. This is because the ability to adsorb and release oxygen from cerium oxide cannot be fully exerted if it is out of this range. Here, examples of rare earth elements include scandium, lanthanum, praseodymium, and neodymium.

  The palladium is not particularly limited as long as it exhibits catalytic activity, and examples thereof include palladium metal, palladium oxide, and palladium black.

Also, zirconium, oxides of yttrium and rare earth elements (excluding cerium) are, BET surface area, respectively, usually, 1~300m ² / g, is preferably in the range of preferably 10 to 150 m ² / g.

  Palladium is usually only required to be uniformly supported on a part or the whole of the cerium-containing oxide, but uniform support is preferable from the viewpoint of dispersibility.

  The amount of palladium used is usually 0.1 to 50 g, preferably 0.5 to 30 g, most preferably 1 to 20 g per liter of the finished catalyst. If the amount used is less than 0.1 g, sufficient redox activity after the initial stage and after durability cannot be obtained. On the other hand, if it exceeds 50 g, sufficient redox activity cannot be obtained in proportion to the amount used, such being undesirable. The amount of cerium-containing oxide used is usually 0.5 to 500 g, preferably 1 to 200 g, and most preferably 5 to 100 g per liter of the finished catalyst. If the amount used is less than 0.5 g, palladium cannot be sufficiently dispersed and oxygen cannot be adsorbed sufficiently. On the other hand, if it exceeds 500 g, the density of palladium is lowered and sufficient reduction activity is obtained. This is not preferable because there is a disadvantage that the pressure loss of the exhaust gas is increased.

The reducing component used in the present invention mainly reduces or decomposes the adsorbed NO ₂ using HC contained in the exhaust gas as a reducing agent in a reducing atmosphere, and adsorbs CO contained in the exhaust gas to the ceria. It plays a role to oxidize using oxygen. In addition, noble metals such as rhodium easily oxidize in an oxygen atmosphere to form oxides, which may easily deactivate the catalytic activity. Especially when used with ceria that has an action of adsorbing and releasing oxygen, it will come into contact with oxygen. The probability increases and the tendency is strong. However, in the catalyst of the present invention, only palladium having a high temperature resistance against oxygen is used as the noble metal, so there is little risk of catalyst deactivation.

c) The alkali metal compound and / or alkaline earth metal compound is not particularly limited as long as it has an ability to adsorb oxidized and activated NOx, particularly NO ₂ , but sodium, potassium, rubidium, cesium , At least one oxide selected from the group consisting of beryllium, magnesium, strontium, and barium, or a mixture thereof is preferable.

The amount of alkali metal compound and / or alkaline earth metal compound used is usually 0.1 to 200 g, preferably 0.5 to 150 g, most preferably 1 to 100 g per liter of the finished catalyst. If the amount used is less than 0.1 g, NO ₂ cannot be sufficiently adsorbed under oxidizing conditions, and the oxidizing activity of palladium cannot be sufficiently suppressed under reducing conditions. On the other hand, if it exceeds 200 g, the suppression of the oxidation activity by palladium becomes large, the oxidation activity of CO and HC decreases, the NOx purification activity also decreases, and the pressure loss of the exhaust gas also increases. Is not preferable.

The component that adsorbs NO ₂ used in the present invention mainly serves to adsorb oxidized or activated NO ₂ in an oxidizing atmosphere.

The measurement of the adsorbed amount of adsorbed NO ₂ can be confirmed by, for example, the following preliminary experiment. The amount of adsorption can be measured directly in an internal combustion engine or on a desktop device that mimics the temperature, composition, flow rate, etc. of exhaust gas from the internal combustion engine under the conditions of treatment using the catalyst of the present invention (International Publication). And the like described in WO 94/25143).

  First, a predetermined amount of the catalyst according to the present invention is filled in a catalyst packed bed in which nitrogen oxide analyzers are installed in front and rear. Next, let the mixed gas of oxygen and nitrogen set to the exhaust gas temperature and flow rate under the catalyst usage conditions flow and stabilize sufficiently, then switch the nitrogen oxide under the catalyst usage conditions to a gas containing concentration It introduce | transduces into a catalyst packed bed. A nitrogen oxide analyzer installed at the back of the catalyst packed bed is continuously measured until the change in nitrogen oxide concentration does not occur. The amount of nitrogen oxide adsorbed by the catalyst can be determined by an amount.

  Some catalysts decompose nitrogen oxides when measuring the amount of nitrogen oxide adsorbed, and the amount of adsorption for such a catalyst is based on the concentration of nitrogen oxides in front of the catalyst packed bed. Instead, the adsorption amount is calculated in the same manner as described above using a value at which the nitrogen oxide behind the catalyst packed bed shows a steady value when measuring the adsorption amount.

The relationship between the catalyst components a), b) and c) is as follows: a) a refractory inorganic oxide supporting platinum partially or entirely and b) a cerium-containing oxide supporting palladium partially or entirely. It is preferable that c) an alkali metal compound and / or an alkaline earth metal compound be supported on a part or all of a) and b), and in particular, from the viewpoint of NO ₂ adsorption rate. Is preferred.

  The amount of catalyst components used a), b) and c) is usually 50 to 500 g, preferably 100 to 300 g, most preferably 150 to 250 g per liter of the finished catalyst. If the amount used is less than 50 g, sufficient catalyst performance after the initial stage and after durability cannot be obtained. On the other hand, if it exceeds 300 g, sufficient catalyst activity cannot be obtained in proportion to the amount used, resulting in problems such as exhaust pressure loss. Therefore, it is not preferable.

  In general, specific embodiments of the catalyst used in the present invention are as follows: (1) a method in which the catalyst itself is formed into a predetermined shape, for example, a spherical shape or a cylindrical shape, and (2) a carrier referred to as a refractory three-dimensional structure, for example, A honeycomb monolith carrier, a foam carrier, a corrugated carrier and the like are preferably made of ceramic or metal, and examples thereof include a method in which a constituent component is coated thereon.

  Hereinafter, a method for preparing the catalyst will be described.

  (1) When the catalyst composition itself is used as a catalyst, (b) a method in which the catalyst composition is sufficiently mixed and then formed into a cylinder, a sphere, or the like to form a catalyst, and (b) a refractory inorganic substance having a predetermined shape ( For example, there is a method of coating a catalyst substance after forming into a spherical or cylindrical shape.

  (2) When using a monolithic structure or an inert inorganic carrier (hereinafter referred to as “monolithic structure or the like”), (a) putting the catalyst composition in a ball mill or the like in a lump, wet pulverizing it into an aqueous slurry, A method of immersing a structure or the like, drying and firing, (b) wet-grinding a refractory inorganic oxide with a ball mill or the like to form an aqueous slurry, immersing the integral structure or the like, drying and firing. Next, there is a method in which the monolithic structure coated with a refractory inorganic oxide is immersed in an aqueous solution containing an alkali metal and / or alkaline earth metal, dried and fired. Of these, a method of coating an integrated structure or the like is desirable.

  Examples of the integral structure and the like include pellets and honeycomb carriers, but an integrally formed honeycomb structure is preferable. Examples thereof include a monolith honeycomb carrier, a metal honeycomb carrier, and a plug honeycomb carrier.

  As the monolith carrier, what is usually called a ceramic honeycomb carrier may be used, particularly cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, aluminum titanate, betalite, spodumene, aluminosilicate, A honeycomb carrier made of magnesium silicate or the like is preferable, and cordierite is particularly preferable. In addition, an integrated structure using an oxidation-resistant heat-resistant metal such as stainless steel or Fe—Cr—Al alloy is used.

  These monolith carriers are manufactured by an extrusion molding method or a method of winding and hardening a sheet-like element. The shape of the gas passage port (cell shape) may be any of a hexagon, a quadrangle, a triangle, and a corrugation. A cell density (number of cells / unit cross-sectional area) of 100 to 600 cells / square inch can be sufficiently used, and preferably 200 to 500 cells / square inch.

  In the present invention, the method for coating the constituent components is not particularly limited, but a normal impregnation method is suitably used.

  First, after impregnating a predetermined amount of refractory inorganic oxide powder such as alumina into an aqueous solution containing a salt such as a nitrate of platinum, it is usually dried at 80 to 250 ° C. Calcination at a temperature of 300 to 850 ° C. for 0.5 to 5 hours to obtain a refractory inorganic oxide carrying platinum.

  Separately, a predetermined amount of a cerium-containing oxide powder such as a complex oxide of ceria and zirconium is impregnated into an aqueous solution containing a salt such as nitrate of palladium, and then dried usually at 80 to 250 ° C. Then, usually, calcination is carried out at a temperature of 300 to 850 ° C. for 0.5 to 5 hours to obtain a cerium-containing oxide carrying palladium.

  Furthermore, as the alkali metal compound and / or alkaline earth metal compound, oxides such as barium, hydroxides, carbonates, nitrates, nitrites or acetates can be used.

  The obtained refractory inorganic oxide supporting platinum, cerium-containing oxide supporting palladium partially or wholly, and powder of alkali metal compound and / or alkaline earth metal compound are added with water at a predetermined ratio. And then wet-pulverized into a slurry, and after immersing a fire-resistant three-dimensional structure such as a honeycomb carrier in the slurry and removing excess slurry, the slurry is usually dried at a temperature of 80 to 250 ° C. Calcination is performed at 800 ° C. for 0.5 to 3 hours to obtain a finished catalyst.

  Further, a slurry of the refractory inorganic oxide supporting platinum and the cerium-containing oxide supporting palladium is prepared, applied to the honeycomb structure, dried, fired as necessary, and then refractory supporting platinum. An aqueous solution of an alkali metal compound and / or an alkaline earth metal compound, for example, carbonate such as barium, nitrate, nitrite or acetate, with a monolithic structure in which an inorganic oxide and a cerium-containing oxide supporting palladium are coated After immersing in and supporting a predetermined amount, it may be dried and fired if necessary.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.

Example 1
100 g of activated alumina having a BET surface area of 100 m ² / g is mixed with a dinitrodiaminoplatinum nitric acid aqueous solution containing 1 g of platinum, then dried at 120 ° C. for 2 hours, pulverized, and calcined at 500 ° C. for 2 hours. Powder a was obtained. On the other hand, an aqueous solution of cerium nitrate containing 10 g of cerium in terms of cerium oxide is added to 40 g of zirconium oxide having a BET surface area of 80 m ² / g, mixed, then dried at 120 ° C. for 2 hours, pulverized, and 2 at 500 ° C. The raw material powder b ′ was obtained by firing for a period of time. An aqueous palladium nitrate solution containing 3 g of palladium was added to the raw material powder b ′, mixed, then dried at 120 ° C. for 2 hours, pulverized, and calcined at 500 ° C. for 2 hours to obtain a raw material powder b. Powder a and b are wet-ground by a ball mill to obtain an aqueous slurry, and a commercially available cordierite honeycomb carrier (manufactured by Nippon Choshi, having a cross section of 400 gas distribution cells per square inch, After dipping a diameter of 33 mm, a length of 76 mmL, and a volume of 65 mL, excess slurry was blown away with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked for 2 hours at 500 degreeC, and obtained the intermediate catalyst (A '). This intermediate catalyst (A ′) was immersed in an aqueous potassium acetate solution containing 10 g of potassium as potassium oxide, and then the excess solution was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and the completed catalyst (A) was obtained. This catalyst (A) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 2
In Example 1, when preparing the powder a, instead of 100 g of activated alumina having a BET surface area of 100 m ² / g, 100 g of activated alumina having a BET surface area of 150 m ² / g and containing 5% of zirconia oxide is used. Except for this, the same procedure as in Example 1 was carried out to obtain a finished catalyst (B). This catalyst (B) supported 1 g of platinum, 2 g of palladium, 95 g of activated alumina, 45 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 3
In Example 1, in the preparation of the powder a, instead of the active alumina 100g having a BET surface area l00m ² / g, having a BET surface area of 150 meters ² / g, using active alumina 100g containing 5% of titanium oxide Except for this, the same procedure as in Example 1 was carried out to obtain a finished catalyst (C). This catalyst (C) was characterized by 1 g of platinum, 2 g of palladium, 95 g of activated alumina, 5 g of titanium oxide, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 4
In Example 1, when preparing the powder a, 100 g of activated alumina containing 5% silicon oxide having a BET surface area of 150 m ² / g is used instead of 100 g of activated alumina having a BET surface area of 100 m ² / g. Except for this, the same procedure as in Example 1 was carried out to obtain a finished catalyst (D). This catalyst (D) supported 1 g of platinum, 2 g of palladium, 95 g of activated alumina, 5 g of silicon oxide, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per 1 liter of honeycomb catalyst volume.

Example 5
In Example 1, in the preparation of the powder a, instead of the active alumina 100g having a BET surface area of 100 m ² / g, similarly except for using zirconium oxide 100g having a BET surface area of 100 m ² / g as in Example 1 And finished catalyst (E) was obtained. This catalyst (E) supported 1 g of platinum, 2 g of palladium, 140 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 6
In Example 1, in the preparation of the powder a, except using in place of the active alumina 100g having a BET surface area of 100 m ² / g, with a BET surface area of 100 m ² / g, titanium oxide 100g with anatase type crystal structure Was carried out in the same manner as in Example 1 to obtain a finished catalyst (F). This catalyst (F) supported 1 g of platinum, 2 g of palladium, 100 g of titanium oxide, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 7
In Example 1, in preparing the powder a, instead of the active alumina 100g having a BET surface area of 100 m ² / g, similarly except for using a silicon oxide 100g having a BET surface area of 100 m ² / g as in Example 1 The finished catalyst (G) was obtained. This catalyst (G) was loaded with platinum lg, palladium 2 g, silicon oxide 100 g, zirconium oxide 40 g, cerium oxide 10 g, and potassium oxide 10 g per liter of honeycomb catalyst volume.

Example 8
In Example 1, the powder b was prepared in the same manner as in Example 1 except that a lanthanum nitrate aqueous solution containing 5 g of lanthanum as lanthanum oxide was added simultaneously with the cerium nitrate solution to obtain a finished catalyst (H). . This catalyst (H) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, 5 g of lanthanum oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Example 9
Example 1 was carried out in the same manner as in Example 1 except that a potassium acetate aqueous solution containing 20 g of potassium as potassium oxide was used instead of the potassium acetate aqueous solution containing 10 g of potassium as potassium oxide, to obtain a finished catalyst (I). It was. This catalyst (I) was loaded with 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 20 g of potassium oxide per liter of the honeycomb catalyst volume.

Example 10
In Example 1, a finished catalyst (J) was obtained in the same manner as in Example 1 except that an aqueous barium acetate solution containing 10 g of barium as barium oxide was used instead of an aqueous potassium acetate solution containing 10 g of potassium as potassium oxide. It was. This catalyst (J) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of barium oxide per 1 liter of honeycomb catalyst volume.

Example 11
In Example 1, instead of the potassium acetate aqueous solution containing 10 g of potassium as potassium oxide, a mixed aqueous solution of 10 g of potassium acetate containing potassium as potassium oxide and barium acetate containing 10 g of barium as barium oxide was used. To give a finished catalyst (K). This catalyst (K) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, 10 g of potassium oxide, and 10 g of barium oxide per liter of honeycomb catalyst volume.

Comparative Example l
A platinum nitrate aqueous solution containing 1 g of platinum and a rhodium nitrate solution containing rhodium 0 and 2 g were added to 100 g of activated alumina used in Example 1, mixed, dried at 120 ° C. for 2 hours, calcined at 500 ° C. for 2 hours, and powdered Body s was obtained. The powder s was wet pulverized with a ball mill to obtain an aqueous slurry. A cordierite honeycomb carrier similar to that in Example 1 was dipped in this, and then excess slurry was blown off with compressed air. Next, after drying at 120 ° C. for 2 hours, it was calcined at 500 ° C. for 2 hours to obtain a finished catalyst (S). The catalyst (S) contained 1 g of platinum, 0.2 g of rhodium and 100 g of activated alumina per liter of honeycomb catalyst volume.

Comparative Example 2
In Comparative Example 1, a slurry was prepared in the same manner as Comparative Example 1 except that the powder b ′ prepared in Example 1 was added to obtain a finished catalyst (T). The catalyst (T) contained 1 g of platinum, 0.2 g of rhodium, 100 g of activated alumina, 40 g of zirconium oxide and 10 g of cerium oxide per liter of honeycomb catalyst volume.

Comparative Example 3
After immersing the catalyst (T) of Comparative Example 2 in a potassium acetate aqueous solution containing 10 g of potassium as potassium oxide, the excess solution was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and the completed catalyst (U) was obtained. The catalyst (U) contained 1 g of platinum, 0.2 g of rhodium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Comparative Example 4
In Example 1, when preparing an aqueous slurry, it carried out similarly to Example 1 except having used powder b 'instead of powder b, and obtained the complete catalyst (V). Catalyst (V) contained 1 g of platinum, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Comparative Example 5
In Example 1, when preparing an aqueous slurry, it carried out similarly to Example 1 except using 100 g of activated alumina instead of the powder a, and obtained the finished catalyst <W>. The catalyst (W) contained 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Comparative Example 6
A dinitrodiaminoplatinum nitric acid aqueous solution containing 1 g of platinum and an aqueous palladium nitrate solution containing 3 g of palladium are added to 100 g of activated alumina having a BET surface area of 100 m ² / g, mixed, dried at 120 ° C. for 2 hours, pulverized, and 2 at 500 ° C. The raw material powder w was obtained by firing for a period of time. The powder w and the powder b ′ prepared in Example (1) were wet pulverized with a ball mill to obtain an aqueous slurry. A cordierite honeycomb carrier similar to that in Example 1 was dipped in this, and then excess slurry was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and obtained the intermediate catalyst (X '). This intermediate catalyst (X ′) was immersed in an aqueous potassium acetate solution containing 10 g of potassium as potassium oxide, and then the excess solution was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and completed catalyst (X) was obtained. This catalyst (X) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide and 10 g of potassium oxide per 1 liter of honeycomb catalyst.

Comparative Example 7
A dinitrodiaminoplatinum nitric acid aqueous solution containing 1 g of platinum and a palladium nitrate aqueous solution containing 3 g of palladium were added to the raw material powder b ′ obtained in Example l, mixed, dried at 120 ° C. for 2 hours, pulverized, The raw material powder y was obtained by baking at 2 ° C. for 2 hours. Powder y and 100 g of activated alumina having a BET surface area of 100 m ² / g are wet pulverized by a ball mill to obtain an aqueous slurry. After immersing a cordierite honeycomb carrier similar to that in Example 1, the excess slurry is compressed. Blowed away with air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and obtained the medium catalyst (Y '). This intermediate catalyst (Y ′) was immersed in an aqueous potassium acetate solution containing 10 g of potassium as potassium oxide, and then the excess solution was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and the finished catalyst (Y) was obtained. This catalyst (Y) supported 1 g of platinum, 2 g of palladium, 100 g of activated alumina, 40 g of zirconium oxide, 10 g of cerium oxide, and 10 g of potassium oxide per liter of honeycomb catalyst volume.

Comparative Example 8
400 g of pure water was added to 100 g of commercially available ZSM type 15 zeolite (SiO ₂ / Al ₂ O ₃ ratio 80), stirred at 98 ° C. for 2 hours, and then 0.2 mol / liter copper ammine complex aqueous solution at 80 ° C. Was slowly added dropwise. The dropped zeolite was filtered, washed thoroughly, and dried at 120 ° C. for 24 hours. The obtained powder was wet pulverized by a ball mill to obtain an aqueous slurry. A cordierite honeycomb carrier similar to that in Example 1 was dipped in this, and then excess slurry was blown off with compressed air. Subsequently, after drying at 120 degreeC for 2 hours, it baked at 500 degreeC for 2 hours, and the completed catalyst (Z) was obtained. This catalyst supported 5.6% by weight of copper with respect to ZSM-5 type zeolite.

  The catalysts (A) to (X) and (S) to (Z) prepared in Examples 1 to 8 and Comparative Examples 1 and 2 were subjected to the following initial performance test and time performance test.

[Initial performance]
Each catalyst was evaluated by the following performance evaluation methods 1 and 2. The obtained results are shown in Tables 2 and 3.

[Performance evaluation method 1]
After filling a catalyst into a stainless steel reaction tube having a diameter of 34.5 mm and a length of 300 mm, the reaction gas having the above composition was subjected to a space velocity of 40000 Hr ⁻ so that the gas composition 1 was repeated for 60 seconds and the gas composition 2 was repeated for 10 seconds. ¹ was introduced. The catalyst performance was evaluated by measuring the average HC, CO, and NOx purification rates for three cycles at a catalyst bed inlet temperature of 350 ° C. The obtained initial performance results are shown in Table 2.

[Durability test 2]
Each catalyst is packed into a multi-converter, and exhaust gas (A / F = 20) during cruising of a commercially available lean burn engine is charged into the packed catalyst bed with a space velocity (SV) of 160000Hr ⁻¹ and a catalyst bed temperature of 700. It was passed for 20 hours under the condition of ° C. Thereafter, the catalyst performance was evaluated by measuring the NOx purification rate in the same manner as the initial performance test. The results of the time performance obtained are shown in Table 3.

Claims (4)

  a) a refractory inorganic oxide partially or entirely supporting platinum; b) a cerium-containing oxide partially or entirely supporting palladium; and c) an alkali metal compound and / or an alkaline earth metal compound. C) an alkali metal and / or an alkaline earth metal, a) a refractory inorganic oxide partially or entirely supported by platinum, and b) cerium partially or entirely supported by palladium. A catalyst for exhaust gas purification for a lean combustion engine, characterized in that it is supported or mixed in the entire mixture with the contained oxide.   The catalyst according to claim 1, wherein the constituent components a), b) and c) are coated with a refractory three-dimensional structure.   a) a refractory inorganic oxide partially or entirely supporting platinum; b) a cerium-containing oxide partially or entirely supporting palladium; and c) an alkali metal compound and / or an alkaline earth metal compound. A method for producing a catalyst for exhaust gas purification for a lean combustion engine, characterized in that the pulverized and mixed material is 1) molded into a three-dimensional structure or 2) or coated with a refractory three-dimensional structure.   1) Three-dimensional structure is formed by crushing and mixing a) a refractory inorganic oxide partially or entirely supporting platinum, and b) a cerium-containing oxide partially or entirely supporting palladium. Or 2) or an exhaust for a lean combustion engine, wherein c) an alkali metal compound and / or a salt of an alkaline earth metal compound is supported on the obtained coating after being coated on a refractory three-dimensional structure. A method for producing a gas purification catalyst.