JP2007301471A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for cleaning an exhaust gas which can sufficiently inhibit the generation of hydrogen sulfide when cleaning the exhaust gas and further maintain the catalyst activity even in the case of using for a long period of time. <P>SOLUTION: The catalyst for cleaning the exhaust gas includes a carrier powder (A) comprising a ceria containing composite oxide, a carrier powder (B) containing alumina and/or zirconia as a main component, a noble metal carried by the carrier powder (A) and/or the carrier powder (B) and an iron compound carried by the carrier powder (A) and/or the carrier powder (B). The quantity of the iron compound carried by the carrier powder (A) is 45 mass% or more in terms of the metal to the total quantity of the iron compound contained in the catalyst. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying catalyst.

Recently, in view of global environmental protection, hydrocarbons (HC) and NO _X, etc. discharged from the internal combustion engine such as an automobile is seen as a problem. In order to remove harmful components in the exhaust gas of such an internal combustion engine, various exhaust gas purification catalysts have been conventionally used. Such exhaust gas purifying catalyst is generally a three-way catalyst and _the NO _X storage reduction catalyst or the like is used. In addition, such an exhaust gas purifying catalyst occludes the sulfur component as a stable sulfate or sulfite when exposed to an exhaust gas containing a sulfur component. And if the sulfur component occluded in the exhaust gas purification catalyst accumulates, the catalytic activity decreases (sulfur poisoning). Further, the occluded sulfur component is desorbed in a high temperature rich state, and is discharged as hydrogen sulfide (H ₂ S) that reacts with hydrogen in the exhaust gas to generate a strong odor. Therefore, research on exhaust gas purifying catalysts capable of purifying exhaust gas while suppressing generation of H ₂ S has been conducted, and in order to suppress generation of H ₂ S, a component such as nickel or iron is supported on the catalyst. Is known to be effective.

As such an exhaust gas purifying catalyst on which iron is supported, for example, in JP 2005-138100 A (Patent Document 1), platinum (Pt), ceria (CeO ₂ ), and iron (Fe) are contained. An exhaust gas purifying catalyst having a platinum to iron molar ratio (iron / platinum) of 0.0035 to 1.0 is disclosed. In Example 1 described in Patent Document 1, 79.5% of CeO ₂ on which 1.1% by mass of Pt was supported, 9.9% by mass of alumina sol, and 10.6% by mass of γ-alumina were used. An exhaust gas purifying catalyst is disclosed in which a slurry obtained by mixing is supported on a monolith substrate, and Rh is supported at a rate of 0.35 g / L and Fe is supported at a rate of 0.53 g / L.

However, such an exhaust gas purifying catalyst described in Patent Document 1 does not have a sufficient effect of suppressing the generation of H ₂ S, and maintains the catalytic activity sufficiently when used for a long time. I couldn't.
JP 2005-138100 A

  The present invention has been made in view of the above-described problems of the prior art, and can sufficiently suppress the generation of hydrogen sulfide when purifying exhaust gas. Furthermore, even when used for a long period of time, the catalytic activity is improved. An object of the present invention is to provide a catalyst for exhaust gas purification that can be maintained.

As a result of intensive studies to achieve the above object, the present inventors have found that a carrier powder (A) composed of a ceria-containing composite oxide and a carrier powder (B) containing alumina and / or zirconia as a main component. An exhaust gas purifying catalyst comprising a noble metal supported on carrier powder (A) and / or carrier powder (B) and an iron compound supported on carrier powder (A) and / or carrier powder (B). The generation of H ₂ S is suppressed by an exhaust gas purifying catalyst obtained by selectively supporting 45 mass% or more (metal equivalent) of the iron compound contained in the catalyst on the carrier powder (A). The effect of synergistically improving, it is found that the generation of hydrogen sulfide can be sufficiently suppressed when purifying exhaust gas, and the catalytic activity can be maintained even when used for a long time. It was completed

That is, the exhaust gas purifying catalyst of the present invention comprises a carrier powder (A) comprising a ceria-containing composite oxide,
A carrier powder (B) containing alumina and / or zirconia as a main component;
A noble metal supported on the carrier powder (A) and / or the carrier powder (B);
An iron compound supported on carrier powder (A) and / or carrier powder (B);
An exhaust gas purifying catalyst containing
The amount of the iron compound supported on the carrier powder (A) is 45% by mass or more in terms of metal with respect to the total amount of the iron compound contained in the catalyst;
It is characterized by.

  In the exhaust gas purifying catalyst of the present invention, the amount of the noble metal supported on the carrier powder (B) is 65% by mass or more (more preferably 80%) in terms of metal with respect to the total amount of the noble metal contained in the catalyst. (Mass% or more) is preferable.

  In the exhaust gas purifying catalyst of the present invention, the amount of the iron compound supported on the carrier powder (A) is 80% by mass or more in terms of metal with respect to the total amount of the iron compound contained in the catalyst. More preferably, it is more preferably 95% by mass or more. Further, in the exhaust gas purifying catalyst of the present invention, the mass ratio of the carrier powder (A) and the carrier powder (B) is preferably in the range of 20:80 to 75:25.

Although the reason why the above object is achieved by the exhaust gas purifying catalyst of the present invention is not necessarily clear, the present inventors speculate as follows. That is, in the present invention, the carrier powder (A) containing ceria that is particularly susceptible to sulfur poisoning is 45% by mass or more of the total amount of Fe compounds contained in the catalyst, more preferably 80% by mass or more, and still more preferably. it becomes possible to easily desorbed since the selectively allowed to support more than 90 wt% (metal basis) of sulfur stored in the ceria as sO _x. Therefore, since the proportion of SO _x desorbed from the entire catalyst (particularly the carrier powder (A)) can be increased, the generation of H ₂ S is suppressed. Further, when the Fe compound and alumina coexist, the heat resistance of the support decreases, and this tends to cause a decrease in the surface area of the support and a decrease in the activity of the noble metal. In the present invention, however, alumina and / or zirconia is mainly used. It is assumed that the catalyst activity can be easily maintained because the amount of the Fe compound contained in the carrier powder (B) as a component is small.

  In the case where the amount of the noble metal supported on the carrier powder (B) is 65% by mass or more (more preferably 80% by mass or more) in terms of metal with respect to the total amount of the noble metal contained in the catalyst. The catalytic activity tends to be maintained at a higher level. That is, when the noble metal is selectively supported at a high concentration on the carrier powder (B), the probability that the Fe compound and the noble metal come into contact with each other decreases, so that the Fe compound covers the surface of the noble metal when using the catalyst. There is a tendency that the resulting decrease in catalytic activity is more prevented.

  According to the present invention, it is possible to provide an exhaust gas purifying catalyst that can suppress the generation of hydrogen sulfide when purifying exhaust gas, and can maintain the catalytic activity even when used for a long period of time. It becomes possible.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

The exhaust gas purifying catalyst of the present invention comprises a carrier powder (A) comprising a ceria-containing composite oxide,
A carrier powder (B) containing alumina and / or zirconia as a main component;
A noble metal supported on the carrier powder (A) and / or the carrier powder (B);
An iron compound supported on carrier powder (A) and / or carrier powder (B);
An exhaust gas purifying catalyst containing
The amount of the iron compound supported on the carrier powder (A) is 45% by mass or more in terms of metal with respect to the total amount of the iron compound contained in the catalyst;
It is characterized by.

  The carrier powder (A) according to the present invention is not particularly limited as long as it is composed of a complex oxide containing ceria, and is a known complex oxide obtained by complexing ceria and another metal oxide. A carrier powder made of can be used as appropriate. Examples of such other metal oxides include alumina, titania, zirconia, silica, silica-alumina, alkaline earth metal elements, rare earth elements, group 3A elements, and the like that can be used as a carrier for exhaust gas purification catalysts. The oxide of this is mentioned. Further, such other metal oxides may be combined with one kind of ceria, or plural kinds may be combined with ceria.

  As such carrier powder (A), specifically, ceria-zirconia composite oxide, alumina-ceria composite oxide, alumina-ceria-zirconia composite oxide, silica-ceria-zirconia composite oxide, Examples include silica-ceria composite oxides, and ceria-zirconia composite oxides and silica-ceria-zirconia composite oxides are used from the viewpoint that high oxygen storage capacity can be obtained based on the structural stabilization of ceria by zirconia. Is preferred, and ceria-zirconia composite oxide is particularly preferred.

  In the carrier powder (A), the content of ceria contained in the carrier is not particularly limited, and the amount can be appropriately adjusted according to the design of the target catalyst. In the case of using a catalyst, it is preferably 50 to 5 g per liter of the catalyst from the viewpoint of sufficiently preventing sulfur poisoning.

Furthermore, in the case where such a carrier powder (A) is a ceria-zirconia composite oxide, the content ratio of ceria (CeO ₂ ) and zirconia (ZrO ₂ ) is not particularly limited, but the molar ratio ( Ce: Zr) is preferably 0.8: 0.2 to 0.1: 0.9 (more preferably 0.6: 0.4 to 0.15: 0.85). If the molar ratio is less than the lower limit, the carrier powder (A) tends to be unable to exhibit sufficient oxygen storage capacity. On the other hand, if the upper limit is exceeded, the structural stability is lowered and sulfur resistance is reduced. Toxicity tends to decrease. For example, when the molar ratio is about 0.5: 0.5, the carrier powder (A) has sufficient structural stability and sufficient oxygen storage ability. When the molar ratio is about 0.2: 0.8, the carrier powder (A) has high structural stability and is more excellent in sulfur poisoning resistance.

  The solid solubility of ceria and other metal oxides in the carrier powder (A) is not particularly limited, but is preferably 70% or more (more preferably 90% or more). When the solid solution degree is less than the lower limit, sufficient oxygen storage ability tends to be not obtained. In addition, regarding such a solid solution degree, the oxide solid solution particle | grains and method which are illustrated by Unexamined-Japanese-Patent No. 9-221304 are employable. Furthermore, the average particle size of the carrier powder (A) is not particularly limited, but is more preferably 0.1 to 10 μm.

There are no particular limitations on the specific surface area of the support powder (A), is preferably in the be 0.1 to 100 m ² / g, more preferably 0.5 to 30 m ² / g. When the specific surface area is less than the lower limit, it becomes difficult to exhibit an appropriate amount of oxygen storage capacity to exert sufficient catalytic activity, while when the upper limit is exceeded, the sulfur-poisoned portion increases, Even if the Fe compound is supported, it is difficult to obtain an effective H ₂ S reduction. Such a specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using a BET isotherm adsorption equation. Further, the carrier powder (A) is a catalyst that the specific surface area does not change in a high temperature atmosphere. Since this is one of the important factors for maintaining the activity, a material having a specific surface area reduced by adding a heat history (for example, firing at a high temperature of about 1100 ° C.) in advance may be used. From such a viewpoint, as the carrier powder (A), a carrier having a specific surface area of 20 m ² / g or less by adding a heat history in advance may be used. Furthermore, as the support powder (A), from the viewpoint of more fully suppress the sulfur poisoning with maintenance of catalytic activity, in addition to previously heat history, the specific surface area of 10 m 2 / ^g or less, more preferably 5 m ² / g or less, more preferably 3 m ² / g or less, particularly preferably 1 m ² / g or less may be used.

  In the carrier powder (A), various additives that can be contained in the carrier of the exhaust gas purifying catalyst (for example, La, Nd, Y, Pr, added to achieve higher thermal stabilization) (A heat stabilizer such as Sc or Ba) may be appropriately contained.

  Furthermore, it does not restrict | limit especially as a manufacturing method of carrier powder (A), A well-known method can be employ | adopted suitably, for example, the following methods can be employ | adopted. That is, from an aqueous solution containing a salt of each metal (for example, nitrate) as a raw material of the carrier powder (A) and, if necessary, a surfactant (for example, a nonionic surfactant), A method in which a coprecipitate is produced in the presence, the obtained coprecipitate is filtered, washed, dried, and further calcined can be employed. In the case of producing a ceria-zirconia composite oxide suitable as the carrier powder (A), for example, the production method described in JP-A-9-221304 can be referred to.

  Further, the carrier powder (B) according to the present invention is not particularly limited as long as it contains alumina and / or zirconia as a main component, and is known alumina and / or can be used as an exhaust gas purifying catalyst. Alternatively, a carrier powder containing zirconia as a main component can be used as appropriate. In the carrier powder (B), it is preferable that alumina and / or zirconia as the main component is contained in the carrier powder (B) in an amount of 60% by mass or more (more preferably 70% by mass or more). If the content ratio of such a main component is less than the lower limit, the durability tends to be insufficient.

As such a carrier powder (B), for example, an alumina carrier, a carrier containing a composite oxide of alumina and zirconia, a zirconia carrier and the like can be used as appropriate. Examples of such an alumina carrier include carriers made of various types of alumina such as α-alumina, γ-alumina, θ-alumina, η-alumina, and δ-alumina. Moreover, as said alumina, you may use a commercially available alumina, Furthermore, you may use what is precipitated from water-soluble aluminum solutions, such as aluminum nitrate, aluminum halide, and aluminum sulfate. Further, such an alumina carrier includes a composite oxide of alumina as described above and an oxide of another metal such as an alkali metal, an alkaline earth metal, a rare earth element, a group 3A element, or a transition metal. It may be. For example, as such an alumina carrier, a composite oxide of alumina and titania may be used from the viewpoint of sulfur poisoning, or a composite oxide of alumina and lantana may be used from the viewpoint of heat resistance. Examples of the carrier composed of a composite oxide of alumina and lantana suitable as such a carrier powder (B) include, for example, a carrier composed of a composite oxide of alumina and lantana described in Japanese Patent Publication No. 5-21030 ( Alumina having a purity of 99.95% and lanthanum impregnated at a ratio of 1.5 to 6% by mass with respect to the alumina, and having a specific surface area of 60 m ² / g after heating at 1200 ° C. for 5 hours (Alumina carrier).

  Further, the carrier containing the composite oxide of alumina and zirconia is not particularly limited, and a known carrier containing a composite oxide of alumina and zirconia that can be used for an exhaust gas purification catalyst can be appropriately used. For example, a support containing a composite oxide of zirconia and alumina and an oxide of another metal such as a transition metal, an alkaline earth metal element, a rare earth element, and a group 3A element can be given. Further, the zirconia support is not particularly limited, and a known zirconia support that can be used as a catalyst for exhaust gas purification can be used as appropriate. For example, zirconia, transition metals, alkaline earth metal elements, rare earth elements and Examples thereof include a support containing a complex oxide with an oxide of another metal such as a group 3A element.

  In addition, as the other metals that can be contained in such a composite oxide, there is a strong interaction with the noble metal supported on the carrier powder (B) and the oxide, and the affinity tends to be large. From the viewpoint, magnesium (Mg), calcium (Ca), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd) preferable.

  The average particle size of the carrier powder (B) is not particularly limited, but is preferably 0.01 to 10 μm, and more preferably 0.1 to 5 μm. When the average particle diameter of the carrier powder (B) exceeds the above range, the catalyst layer may be easily peeled off.

There are no particular limitations on the specific surface area of the support powder (B), it is preferably 1~150m ² / g, and more preferably 20 to 100 m ² / g. When the specific surface area is less than the lower limit, the degree of dispersion of the noble metal tends to be low and it is difficult to obtain sufficient catalytic activity. On the other hand, when the upper limit is exceeded, the sulfur poisoning amount tends to increase. .

Furthermore, the carrier powder (B) preferably has a specific surface area of 10 m ² / g or more, more preferably 15 m ² / g or more after heating for 5 hours under a temperature condition of 1000 ° C.

  Furthermore, it does not restrict | limit especially as a manufacturing method of carrier powder (B), A well-known method can be employ | adopted suitably, For example, it can obtain by the following methods. That is, from the aqueous solution containing each metal salt (for example, nitrate) used as the raw material of the composite oxide and, if necessary, a surfactant (for example, a nonionic surfactant) in the presence of ammonia. The carrier powder (B) made of the composite oxide can be obtained by forming a coprecipitate of the composite oxide and filtering, washing and drying the resulting coprecipitate, followed by firing. Moreover, as a manufacturing method of carrier powder (B), you may refer the manufacturing method as described in Japanese Patent Publication No. 5-21030 etc., for example.

  In the exhaust gas purifying catalyst of the present invention, the mass ratio of the carrier powder (A) and the carrier powder (B) contained in the catalyst is 20:80 to 75:25 (more preferably 30:70 to 65: 35) is preferable. If the mass ratio of the carrier powder (A) is less than the lower limit, the oxygen storage capacity tends to be insufficient. On the other hand, if the upper limit is exceeded, the sulfur poisoning amount increases and the catalyst layer is peeled off. Or the durability of the precious metal tends to be insufficient.

Furthermore, in the exhaust gas purifying catalyst of the present invention, an iron (Fe) compound supported on the carrier powder (A) and / or the carrier powder (B) is supported. The Fe compound according to the present invention refers to a compound containing Fe supported on a carrier, for example, Fe oxide. Such an Fe compound converts and releases H ₂ S into SO ₂ with less odor near the stoichiometric state. Therefore, in the present invention, it is possible to suppress the generation of H 2 _S.

In the exhaust gas purifying catalyst of the present invention, the amount of the iron compound supported on the carrier powder (A) is 45% by mass or more (more preferably) in terms of metal with respect to the total amount of the iron compound contained in the catalyst. Is 80% by mass or more, more preferably 90% by mass or more. When the amount of the iron compound supported on the carrier powder (A) is less than the lower limit, the carrier powder (A) can not sufficiently prevent sulfur poisoning, the sulfur poisoning resistance of the entire catalyst is reduced, and hydrogen sulfide Generation cannot be suppressed sufficiently. That is, in the present invention, the carrier powder (A) is selectively loaded with 45 mass% or more (in metal conversion) of the total amount of Fe compounds contained in the catalyst, so that the accumulated sulfur is 500 to 600 ° C. In the following, SO _x can be easily desorbed, and the amount of sulfur component stored and accumulated in the entire catalyst can be reduced. Therefore, when the air-fuel ratio of the exhaust gas is in a rich state at a high temperature, the amount of H ₂ S desorbed from the entire catalyst (particularly the carrier powder (A)) can be reduced.

  In the exhaust gas purifying catalyst of the present invention, the total amount of the Fe compound contained in the catalyst is not particularly limited, and the amount can be appropriately adjusted according to the design of the target catalyst. For example, the catalyst is a honeycomb catalyst. In this case, from the viewpoint of more sufficiently preventing sulfur poisoning, the amount may be 0.01 to 0.3 mol (more preferably 0.03 to 0.2 mol) per liter of the catalyst in terms of metal. preferable.

  Furthermore, in the exhaust gas purifying catalyst of the present invention, the Fe compound is preferably in a highly dispersed state on the carrier powder (A) and / or the carrier powder (B). By making the Fe compound dispersed by the carrier, the effect of the Fe compound tends to increase.

  The method for supporting the Fe compound on each carrier powder is not particularly limited, and a known method such as a coprecipitation method, a spray pyrolysis method, a gas phase method, and an impregnation method can be appropriately employed. A method may be employed in which an aqueous solution containing an iron salt (for example, carbonate, nitrate, citrate, acetate, sulfate) or a complex is contacted with the carrier, dried, and further calcined. In order to adjust the amount of the iron compound supported on the carrier powder (A) to 45% by mass or more in terms of metal with respect to the total amount of iron compound contained in the catalyst, for example, an Fe compound is supported. After the operations are separately performed for the carrier powder (A) and the carrier powder (B), the carrier powder (A) and the carrier powder (B) having different Fe compound loadings may be mixed.

  In the exhaust gas purifying catalyst of the present invention, a noble metal is supported on the carrier powder (A) and / or the carrier powder (B). Examples of such noble metals include platinum, rhodium, palladium, osmium, iridium, gold, and the like, and platinum, rhodium, and palladium are preferable from the viewpoint that the obtained exhaust gas purifying catalyst exhibits higher catalytic activity.

  In the exhaust gas purifying catalyst of the present invention, the amount of the noble metal supported on the carrier powder (A) and / or the carrier powder (B) is not particularly limited, and the amount is appropriately determined according to the design of the target catalyst. For example, when the catalyst is a honeycomb catalyst, it is preferable that the amount be in the range of 0.1 to 5% by mass (more preferably 0.5 to 3% by mass) with respect to the total mass of the catalyst. Is preferably 0.1 to 5 g (more preferably 0.5 to 3 g) per liter of the catalyst from the viewpoint of sufficiently preventing sulfur poisoning. If the amount of the noble metal supported is less than the lower limit, the catalytic activity obtained from the noble metal tends to be insufficient. On the other hand, if the amount exceeds the upper limit, the cost increases and grain growth tends to occur.

  Furthermore, the amount of the noble metal supported on the carrier powder (B) is preferably 65% by mass or more in terms of metal with respect to the total amount of the noble metal contained in the catalyst, and is 80 to 99% by mass. Is more preferable. When the amount of the noble metal supported on the carrier powder (B) is less than the lower limit, the Fe compound is supported at a high concentration of the carrier powder (A), so that the Fe compound and the noble metal are supported closer. The probability increases, and the surface of the noble metal may be covered with the Fe compound when the catalyst is used, and the catalytic activity tends to decrease due to this. On the other hand, when the amount of the noble metal supported on the carrier powder (B) exceeds the upper limit, sufficient oxygen storage ability tends to be not obtained.

  In the exhaust gas purifying catalyst of the present invention, the noble metal is preferably supported on a carrier in the form of finer particles. The particle diameter of such noble metal is preferably 5 nm or less, more preferably 3 nm or less, and even more preferably 2 nm or less. When the particle diameter of the noble metal exceeds the upper limit, it tends to be difficult to obtain high catalytic activity.

  The method for supporting the noble metal on the carrier is not particularly limited. For example, after bringing an aqueous solution containing a salt of a noble metal (eg, dinitrodiamine salt) or a complex (eg, tetraammine complex) into contact with the carrier. A method of drying and further firing can be employed.

  The form of the exhaust gas purifying catalyst of the present invention is not particularly limited, and may be a form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The substrate used here is not particularly limited, and is appropriately selected depending on the use of the obtained catalyst, etc., but a DPF substrate, a monolith substrate, a pellet substrate, a plate substrate, etc. are suitably employed. Is done. Also, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chromium and aluminum is suitably employed. Is done. Further, the method for producing such a catalyst is not particularly limited. For example, in the case of producing a monolithic catalyst, the amount of Fe compound supported on the honeycomb-shaped base material formed from cordierite or metal foil, respectively. A method in which a coat layer is formed using different carrier powder (A) and carrier powder (B) and a noble metal is supported thereon is preferably employed. Alternatively, the above-described carrier powder (A) and carrier powder (B) may be preliminarily supported with a noble metal, and then the coating layer may be formed on the substrate using the noble metal-supported powder.

In addition, such an exhaust gas purifying catalyst of the present invention can purify the exhaust gas while sufficiently suppressing the generation of H ₂ S by bringing the catalyst into contact with the exhaust gas. When the exhaust gas purification catalyst of the present invention is used, it is possible to sufficiently purify HC and NO _x , and even when exposed to exhaust gas containing a sulfur component, generation of H ₂ S is suppressed. In addition, the catalytic activity can be maintained. Therefore, the exhaust gas purifying catalyst of the present invention can be suitably used for purifying exhaust gas discharged from, for example, an internal combustion engine of an automobile.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Production Example 1: Carrier powder (A))
Carrier powder (A) was prepared as follows. That is, first, an aqueous solution in which cerium (III) nitrate and zirconyl nitrate were mixed so that the molar ratio of Ce to Zr (Ce / Zr) in terms of metal was 5/5 was prepared. A hydrogen peroxide solution containing hydrogen peroxide having a mole number ½ of the cerium ion contained in the aqueous solution was added, mixed and stirred, and then dropped into ammonia water while stirring to neutralize to form a precipitate.

Next, the obtained slurry is washed with water, filtered, sprayed in an atmosphere having an introduced air temperature of 800 ° C. and a discharged air temperature of 650 ° C., dried and fired, and the coexisting ammonium nitrate is evaporated or decomposed to form oxide solid solution particles. A carrier powder (A) containing was prepared. When the solid solubility of such oxide solid solution particles was calculated from the lattice constant by X-ray diffraction and the blending ratio of the starting materials, the solid solubility was 100%. Moreover, when the average diameter of the crystallites was calculated from the 311 peak of the X-ray diffraction pattern using the Schuler equation, the average diameter was 10 nm. Furthermore, the specific surface area of the carrier powder (A) measured by the BET method was 45 m ² / g.

(Production Example 2: Carrier powder (B))
Carrier powder (B) was prepared as follows. That is, first, to a purity of 99.99% or more commercially available alumina (.delta.-alumina), lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O) as the impregnation ratio is 3.0 mol% impregnated with an aqueous solution did. Such impregnation was performed by immersing the alumina in an aqueous lanthanum nitrate solution and stirring sufficiently. And after impregnating the alumina lanthanum nitrate aqueous solution in this way, it was made to dry, and after that, it calcined in air | atmosphere for 10 hours at the temperature conditions of 600 degreeC, and prepared the carrier powder (B).

Example 1
Using the carrier powder (A) obtained in Production Example 1 and the carrier powder (B) obtained in Production Example 2, an exhaust gas purification catalyst was obtained. That is, first, a carrier powder (A) is immersed in an aqueous solution in which iron nitrate (III) nonahydrate is dissolved, and a powder impregnated and supported by an iron compound is prepared by evaporation to dryness. The Fe-supported carrier powder (A) was obtained by firing for 3 hours under the temperature condition of ° C.

  Next, a catalyst slurry was prepared by mixing Fe-supported carrier powder (A), carrier powder (B), and acetic acid-stabilized alumina sol. Next, the cordierite honeycomb substrate having a cell density of 400 cells / in and a cell thickness of 4 mil was wash-coated, and further fired in the atmosphere at 500 ° C. for 1 hour to obtain a catalyst precursor. . Thereafter, the catalyst precursor was immersed in an aqueous platinum nitrate solution to adsorb and carry platinum, and calcined in the atmosphere at a temperature of 300 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of the present invention. In the preparation of such an exhaust gas purification catalyst, the amounts of the carrier powder (A) and the carrier powder (B) used were adjusted so that the respective coating amounts were 60 g and 40 g per liter of the catalyst. did. Further, the amount of iron used was adjusted so that 0.05 mol was supported in terms of metal per liter of catalyst. Further, the amount of platinum used was adjusted so that 1% by mass of platinum was supported with respect to the total mass of the catalyst. Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

(Example 2)
Instead of the carrier powder (B), an Fe-supported carrier powder (B) in which iron is supported on the carrier powder (B) using the same method as the method in which the carrier powder (A) is impregnated with Fe is used. Exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that. In the obtained exhaust gas purifying catalyst, the amounts of the carrier powder (A) and the carrier powder (B) used and the amounts of supported iron and platinum were the same as in Example 1. Further, the ratio of iron supported on the carrier powder (A) and the carrier powder (B) was set to 90:10 by mass ratio (carrier powder (A): carrier powder (B)). Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

(Example 3)
The same as Example 2 except that the ratio of the iron supported on the carrier powder (A) and the carrier powder (B) was 70:30 in the mass ratio (carrier powder (A): carrier powder (B)). Thus, an exhaust gas purification catalyst was obtained. Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

Example 4
Similar to Example 2 except that the ratio of the iron supported on the carrier powder (A) and the carrier powder (B) was 50:50 in mass ratio (carrier powder (A): carrier powder (B)). Thus, an exhaust gas purification catalyst was obtained. Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

(Comparative Example 1)
Same as Example 2 except that the ratio of the iron supported on the carrier powder (A) and the carrier powder (B) is 40:60 by mass ratio (carrier powder (A): carrier powder (B)). Thus, an exhaust gas purification catalyst for comparison was obtained. Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

(Comparative Example 2)
Example 2 except that the ratio of the iron supported on the carrier powder (A) and the carrier powder (B) was 30:70 by mass ratio (carrier powder (A): carrier powder (B)). Thus, an exhaust gas purification catalyst for comparison was obtained. Table 1 shows the loading ratio of iron compounds and platinum in the obtained exhaust gas purification catalyst.

<Evaluation of Characteristics of Exhaust Gas Purification Catalysts Obtained in Examples 1-4 and Comparative Examples 1-2>
Examples 1-4 and Comparative Example 1 in a rich / lean fluctuation atmosphere in which lean gas and rich gas (engine exhaust model gas) shown in Table 2 are alternately flowed at intervals of 1.5 minutes so that the flow rate is 40 L / min. After placing the exhaust gas purifying catalyst obtained in ~ 2 for 10 minutes under the temperature condition of 800 ° C, the exhaust gas in the rich / lean fluctuation atmosphere shown in Table 2 under the temperature condition of 650 ° C The production ratio (H ₂ S / total S) of hydrogen sulfide with respect to the total sulfur component was examined. The results are shown in Table 3 and FIG.

As is apparent from the results shown in Table 3 and FIG. 1, the iron loading ratio on the carrier powder (A) is 45% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. , The generation ratio of H ₂ S is reduced, and the generation of H ₂ S is suppressed.

(Examples 5 to 9)
Using the carrier powder (A) obtained in Production Example 1 and the carrier powder (B) obtained in Production Example 2, an exhaust gas purification catalyst was obtained. That is, first, a carrier powder (A) is immersed in an aqueous solution in which iron nitrate (III) nonahydrate is dissolved, and a powder impregnated and supported by an iron compound is prepared by evaporation to dryness. The Fe-supported carrier powder (A) was obtained by firing for 3 hours under the temperature condition of ° C. Next, after the Fe-supported carrier powder (A) is dispersed in ion-exchanged water, platinum nitrate is added thereto, adsorbed and supported for 30 minutes, filtered and dried, and then at 500 ° C. in the atmosphere. Firing was carried out for 1 hour to obtain a Pt-supported / Fe-supported carrier powder (A).

  Next, after dispersing the carrier powder (B) in ion-exchanged water, platinum nitrate is added thereto, adsorbed and supported for 30 minutes, filtered and dried, and then in the atmosphere at a temperature of 500 ° C. for 1 hour. Firing was performed to obtain a Pt-supported carrier powder (B).

  Next, Pt-supported / Fe-supported carrier powder (A), Pt-supported carrier powder (B), and acetic acid-stabilized alumina sol (binder) were mixed to prepare a slurry. Then, the obtained slurry is wash-coated on a cordierite honeycomb substrate having a cell density of 400 cells / in and a cell thickness of 4 mils, and further fired in the atmosphere at 500 ° C. for 1 hour for exhaust gas purification. Catalysts were obtained (Examples 5-9). In the preparation of such an exhaust gas purification catalyst, the amount of each component used was adjusted so that each component in the obtained exhaust gas purification catalyst was supported at a ratio shown in Table 4 below. . Further, the amount of carrier powder (A) supported in the obtained exhaust gas purification catalyst, the ratio of carrier powder (A) and carrier powder (B), the amount of iron supported, the amount of platinum supported, the carrier powder (A) and Table 4 shows the loading ratio of platinum with respect to the carrier powder (B).

<Evaluation of Characteristics of Exhaust Gas Purification Catalysts Obtained in Examples 5-9>
Exhaust gas purification obtained in Examples 5 to 9 in a rich / lean fluctuation atmosphere in which lean gas and rich gas (engine exhaust model gas) shown in Table 2 are alternately flowed so as to have a flow rate of 40 L / min at intervals of 1 minute The catalyst for catalyst was placed and treated at 850 ° C. for 5 hours (endurance test). Then, such catalysts the NO (0.1% by volume) for each exhaust gas purification after the durability test and _SO 2 was heated to 250 ° C. to 400 ° C. under a model gas atmosphere containing (0.002% by volume) It was measured 50% purification temperature of the NO _X Te. The obtained results are shown in Table 5 and FIG.

As is clear from the results shown in Table 5 and FIG. 2, in the exhaust gas purifying catalysts obtained in Examples 5 to 6 in which the support powder (B) contains 65% by mass or more of the noble metal contained in the catalyst. , than the exhaust gas purifying catalyst obtained in example 7-9, from the fact that exhibits higher NO _X purification activity, over 65% of the noble metal contained in the catalyst to the support powder (B) It was confirmed that the catalyst activity can be maintained at a higher level by supporting the catalyst.

  As described above, according to the present invention, the exhaust gas that can sufficiently suppress the production of hydrogen sulfide when purifying the exhaust gas, and can maintain the catalytic activity even when used for a long period of time. It is possible to provide a purification catalyst.

  Therefore, the exhaust gas purifying catalyst of the present invention is particularly useful in that it can suppress the production of hydrogen sulfide, and is therefore particularly useful as a catalyst for purifying automobile exhaust gas.

Is a graph showing the rate of production of hydrogen sulfide to total sulfur component emitted in the gas of the catalyst for purification of exhaust gas obtained in Examples 1 to 4 and Comparative Examples 1~2 (H 2 _{S /} total S). 50% and purification temperature of the NO _X in the exhaust gas purifying catalyst obtained in Example 5-9 is a graph showing the relationship between the bearing ratio of the noble metal to the alumina.

Claims (2)

A carrier powder (A) comprising a ceria-containing composite oxide;
A carrier powder (B) containing alumina and / or zirconia as a main component;
A noble metal supported on the carrier powder (A) and / or the carrier powder (B);
An iron compound supported on carrier powder (A) and / or carrier powder (B);
An exhaust gas purifying catalyst containing
The amount of the iron compound supported on the carrier powder (A) is 45% by mass or more in terms of metal with respect to the total amount of the iron compound contained in the catalyst;
An exhaust gas purifying catalyst characterized by.   2. The exhaust gas purifying apparatus according to claim 1, wherein the amount of the noble metal supported on the carrier powder (B) is 65% by mass or more in terms of metal with respect to the total amount of the noble metal contained in the catalyst. catalyst.

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