JP2009255073A - Exhaust gas cleaning catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the durability of an exhaust gas cleaning catalyst containing rhodium. <P>SOLUTION: The exhaust gas cleaning catalyst 10 formed by laminating at least two layers of catalyst includes a catalyst layer 11 containing at least Rh, and a catalyst layer 12 containing at least one kind of oxides selected from Fe, Mn, Ni, Co. The catalyst layer 12 containing at least one kind of oxides selected from Fe, Mn, Ni, Co is disposed on the upper layer of the catalyst layer 11 containing at least Rh. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst suitable for being applied to a process for purifying exhaust gas discharged from an internal combustion engine.

In recent years, in order to remove harmful substances such as hydrocarbon compounds (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) contained in exhaust gas discharged from an internal combustion engine, alumina (Al ₂ Exhaust gas purification catalysts in which noble metal particles such as platinum (Pt) and rhodium (Rh) are supported on a metal oxide carrier such as O ₃ ) are widely used. In conventional exhaust gas purification catalysts, a large amount of noble metal particles is used in order to improve the durability of the noble metal particles against ambient fluctuations. However, using a large amount of noble metal particles is not desirable from the viewpoint of protecting earth resources.

  Against this background, recently, transition metals or transition metal compounds such as cerium (Ce) and manganese (Mn), which function as OSC (Oxygen Storage Component) materials, are disposed in the vicinity of noble metal particles by an impregnation method. Attempts have been made to improve the durability of noble metal particles by suppressing changes in the atmosphere around the noble metal particles with a transition metal or a transition metal compound (see Patent Documents 1 to 4). In addition, according to such a method, in addition to the improvement in durability of the noble metal particles, an improvement in the activity of the noble metal particles can be expected.

JP-A-8-131830 JP-A-2005-000829 Japanese Patent Laid-Open No. 2005-000830 JP 2003-117393 A

  Of the noble metal particles used in the exhaust gas purification catalyst, Rh (rhodium) is a noble metal effective for purification of exhaust gas, but rhodium has a small amount of noble metal resources and high cost. Therefore, in the exhaust gas purification catalyst containing rhodium, it is required to reduce the amount of rhodium used.

  One measure for reducing the amount of rhodium used while maintaining the performance of purifying exhaust gas above a certain level is to reduce the particle size of the rhodium noble metal particles. If the particle diameter of the rhodium noble metal particles is reduced, the specific surface area is increased, so that it is possible to reduce the amount of rhodium used while maintaining the performance of purifying exhaust gas at a certain level or more.

  However, a catalyst containing rhodium with a small particle size may cause a reduction in catalyst purification performance after exhaust gas purification at a high temperature or for a long time, and as a result, the amount of rhodium used is to compensate for this performance reduction. There was a need to increase. Accordingly, there is a need for an exhaust gas purification catalyst that improves the durability of an exhaust gas purification catalyst containing rhodium, and consequently reduces the amount of rhodium used.

  In order to solve the above-described problems, an exhaust gas purification catalyst according to the present invention is formed by laminating at least two catalyst layers, and the catalyst layer includes a catalyst layer containing at least Rh, {Fe, Mn, Ni, Co And a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} than a catalyst layer containing at least Rh. Is also on the upper layer side.

  According to the exhaust gas purification catalyst of the present invention, the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is on the upper layer side than the catalyst layer containing at least Rh. This catalyst layer containing Rh is prevented from coming into direct contact with the exhaust gas. Thereby, in the exhaust gas purification catalyst containing rhodium, it is possible to improve the durability, and thus it is possible to further reduce the amount of rhodium used.

It is a typical perspective view of the support | carrier with which the exhaust-gas purification catalyst used as one Embodiment of this invention was carry | supported. It is an expanded sectional view in a section perpendicular to the penetration direction about one pore in a career of Drawing 1. It is an expanded sectional view in a section perpendicular to the penetration direction about one pore in a career showing an exhaust gas purification catalyst which becomes another embodiment of the present invention. It is a schematic diagram of the laminated structure of the catalyst layer laminated | stacked on the catalyst support | carrier in an Example. 6 is a photomicrograph showing a laminated structure of an exhaust gas purification catalyst of Example 5. FIG. FIG. 6 is a schematic view of a laminated structure of the exhaust gas purification catalyst of FIG. 5. 3 is a graph showing the relationship between the noble metal particle diameter after durability and the HC50% conversion temperature in Examples. It is a graph which shows about the relationship between the thickness of the catalyst layer in Example, and HC50% conversion rate temperature. 3 is a graph showing the relationship between the average particle diameter of transition oxides in the catalyst layer and the HC50% conversion temperature in the examples.

  Hereinafter, embodiments of an exhaust gas purification catalyst of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view of a carrier carrying an exhaust gas purification catalyst according to an embodiment of the present invention. The carrier 1 shown in FIG. 1 is made of a heat-resistant material, has a substantially cylindrical shape, and has a large number of pores 1a penetrating from one end surface to the other end surface. In addition, in FIG. 1, the pore 1a is typically drawn so that an understanding of invention may be made easy. Therefore, the shape, size and number of the pores 1a are different from the actual carrier pores.

  FIG. 2 shows an enlarged cross-sectional view of one pore 1a in the carrier 1 of FIG. 1 in a cross section perpendicular to the penetrating direction. As shown in the enlarged sectional view of FIG. 2, an exhaust gas purification catalyst 10 according to an embodiment of the present invention is carried. The exhaust gas purification catalyst 10 shown in FIG. 2 is formed by laminating a total of two catalyst layers, a first catalyst layer 11 and a second catalyst layer 12, on the inner surface of the carrier 1. Of these two catalyst layers, the first catalyst layer 11 is a catalyst layer containing at least Rh, and the second catalyst layer 12 is at least one selected from {Fe, Mn, Ni, Co}. It is a catalyst layer containing the oxide of. Moreover, the second catalyst layer 12 is located on the upper layer side of the first catalyst layer 11, that is, on the upper side when viewed from the inner wall of the carrier.

  FIG. 3 is an enlarged cross-sectional view in a cross section perpendicular to the penetrating direction of one pore 1a in the carrier 1, showing an exhaust gas purification catalyst according to another embodiment of the present invention. An exhaust gas purification catalyst 20 shown in FIG. 2 is formed by laminating a total of three catalyst layers, a first catalyst layer 11, a second catalyst layer 12, and a third catalyst layer 13, on the inner surface of the carrier 1. . Of these three catalyst layers, any one layer is a catalyst layer containing at least Rh, and any one layer contains at least one oxide selected from {Fe, Mn, Ni, Co}. The catalyst layer is configured such that the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is on the upper layer side than the catalyst layer containing at least Rh. Yes. As an example, the first catalyst layer 11 is a catalyst layer containing at least Rh, and the second catalyst layer 12 is a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co}. Yes, the third catalyst layer can be a catalyst layer different from the first catalyst layer 11 and the second catalyst layer 12.

  The catalyst layer containing Rh is an effective catalyst layer for purifying exhaust gas. However, when the catalyst layer containing Rh directly touches exhaust gas having a high temperature or high concentration, the catalyst layer deteriorates. Therefore, the exhaust gas purification catalyst of the present invention is provided with a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} in addition to the catalyst layer containing Rh, and this {Fe, The catalyst layer containing at least one oxide selected from Mn, Ni, Co} is positioned above the catalyst layer containing Rh. Thus, the exhaust gas purifying catalyst of the present invention is a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} when supported on a carrier and used for purifying exhaust gas. However, it comes into contact with the exhaust gas preferentially over the catalyst layer containing Rh. This prevents high-concentration exhaust gas from directly hitting Rh, which can prevent Rh from deteriorating due to exhaust gas purification at high temperatures or for long periods of time, thus making Rh effective. Can be used. Further, the exhaust gas purification catalyst of the present invention has at least one HC selected from {Fe, Mn, Ni, Co} in which HC having a large molecular weight in the exhaust gas is provided on the upper layer side of the catalyst layer containing Rh. Partial oxidation is performed by the oxide-containing layer. This also suppresses the deterioration of Rh due to HC when the exhaust gas is purified at a high temperature or for a long time. Therefore, Rh can be used more effectively.

  From the above, in the exhaust gas purification catalyst of the present invention, each of the layer containing an oxide of at least one transition element selected from {Fe, Mn, Ni, Co} and the layer containing Rh serves as a catalyst layer. It is necessary to be laminated. In addition, it is necessary that the layer containing an oxide of at least one transition element selected from {Fe, Mn, Ni, Co} be on the upper layer side than the layer containing Rh.

  The layer containing Rh will be described later in a preferred embodiment, but is a layer having at least Rh having a performance excellent in exhaust gas purification in the form of noble metal particles.

  The catalyst layer on the upper layer side of the layer containing Rh is a layer containing an oxide of at least one transition element selected from {Fe, Mn, Ni, Co}, {Fe, Mn, Ni, This is because any of the oxides of the transition element of Co} is a compound having an exhaust gas catalytic action, and in particular, a compound that can be rendered harmless by partially oxidizing HC in the exhaust gas. Specific examples are iron oxide, manganese oxide, nickel oxide, and cobalt oxide. This catalyst layer only needs to contain at least one oxide selected from {Fe, Mn, Ni, Co}, but may contain two or more oxides. A composite oxide containing a transition element may be included.

  The layer containing an oxide of at least one transition element selected from {Fe, Mn, Ni, Co} located on the upper layer side of the layer containing Rh is a catalyst layer containing Rh in the pores of the support. The entire surface may be covered, but even if it is formed so as to cover only a part of the catalyst layer, more specifically, the upstream side of the exhaust gas flow in the pores of the carrier, the effect is exhibited. In this case, it is preferable to cover at least one third of the length of the carrier in the penetration direction of the pores.

  From the viewpoint that the layer containing an oxide of at least one transition element selected from {Fe, Mn, Ni, Co} comes into contact with the exhaust gas preferentially over the catalyst layer containing Rh, according to the present invention. The structure of the exhaust gas purification catalyst is different from that in which a plurality of catalyst layers are stacked in the thickness direction of the catalyst layer, and {Fe, Mn, Ni on the upstream side of the exhaust gas flow in the penetration direction of the pores in the carrier , Co}, an exhaust gas purifying catalyst structure in which a layer containing an oxide of at least one transition element selected from the group consisting of oxides of Rh is formed on the downstream side is also conceivable. However, with such a structure, exhaust gas purification performance cannot be sufficiently exhibited. This is because when the catalyst layer containing Rh is formed on the downstream side of the exhaust gas flow in the direction of penetration of the pores in the carrier, the exhaust gas temperature becomes low, so the catalytic activity decreases, This is because sufficient purification performance cannot be exhibited. Therefore, in the exhaust gas purification catalyst of the present invention, a catalyst layer containing Rh in the thickness direction of the catalyst layer from the inner wall of the carrier, and an oxide of at least one transition element selected from {Fe, Mn, Ni, Co} A layer including a layer including

  When three or more catalyst layers are laminated, the positional relationship between the catalyst layer containing at least Rh and the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} Is not particularly limited as long as the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is on the upper layer side than the catalyst layer containing at least Rh.

  More preferably, the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is preferably located in the outermost layer. When considering the durability deterioration of Rh, according to the present invention, the catalyst layer containing oxides of these transition elements is positioned higher than the catalyst layer containing Rh, so that the catalyst layer containing Rh has a high concentration. Exhaust gas is not directly hit, thereby suppressing the deterioration of Rh. In the case of a catalyst composed of three layers as shown in FIG. 3 or a catalyst composed of a larger number of catalyst layers, the catalyst layer containing oxides of these transition elements is located on the outermost layer. As a result, performance can be improved. This is presumably because the deterioration of not only the catalyst layer containing Rh but also the other catalyst layers can be suppressed by positioning the catalyst layer containing the oxide of the transition element as the outermost layer. In the case of the two-layer catalyst shown in FIG. 2, the catalyst layer containing the transition element oxide is naturally located in the outermost layer.

The exhaust gas purifying catalyst of the present invention is formed by laminating three catalyst layers, a catalyst layer containing at least Rh, and a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} When the catalyst layer comprises other catalyst layers, the catalyst layer containing at least Rh is defined as layer A, and the catalyst layer including at least one oxide selected from {Fe, Mn, Ni, Co} is defined as layer B. Assuming that the catalyst layer other than them is a C layer, as a preferable example of the laminated structure of the catalyst layer from the surface layer side toward the inner wall of the carrier,
(1) B layer-A layer-C layer order
(2) B layer-C layer-A layer in this order,
(3) C layer-B layer-A layer order
There is. Among these three examples, the example of (1) is most preferable because the performance is improved, and then the example of (2) is preferable. The exhaust gas purification catalyst of the present invention is not limited to the examples (1) to (3) above.

  More preferably, the catalyst layer containing at least Rh and the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} are in contact with each other. When the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is located in the outermost layer, it is directly below the outermost catalyst layer, that is, in the outermost catalyst layer. In contact with the Rh-containing catalyst layer, exhaust gas diffusibility to the Rh-containing catalyst layer is sufficiently secured, so that the catalyst performance can be improved. Conversely, if there is one or more other catalyst layers between the outermost catalyst layer and the catalyst layer containing Rh, the diffusibility of the exhaust gas to the catalyst layer containing Rh is not sufficient. There is a possibility that exhaust gas purification performance cannot be sufficiently improved. When the exhaust gas purification catalyst is composed of two catalyst layers, a catalyst layer containing at least Rh and a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} are provided. Of course, they are in contact with each other.

The catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} has an effect of adhering at least one oxide selected from {Fe, Mn, Ni, Co} to each other It is preferable that it is further included. A transition element selected from {Fe, Mn, Ni, Co} is difficult to be formed as a catalyst layer as it is, and a material called a binder is required. Without the binder, the catalyst layer formed on the carrier is easy to peel off. Therefore, it is preferable that the binder contains a compound having an effect of adhering oxides of these transition elements. The binder generally includes Al ₂ O ₃ sol and ZrO ₂ sol, and both Al ₂ O ₃ sol and ZrO ₂ sol can be applied to the exhaust gas purification catalyst of the present invention. However, when Al ₂ O ₃ sol is used, the transition element is dissolved in Al ₂ O _3, and as a result, the effect of the transition element as a catalyst may not be sufficiently exhibited. Therefore, it is preferable to use a sol that hardly dissolves with the transition element as the binder. For this reason, a ZrO ₂ sol is more preferable.

  When the exhaust gas purifying catalyst of the present invention is composed of three or more catalyst layers, a catalyst layer other than a catalyst layer containing Rh and a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co}. The catalyst layer is preferably a catalyst layer containing at least one of Pt and Pd. Pt and Pd are both noble metals having exhaust gas purification performance, and the function as the exhaust gas purification catalyst of the present invention is enhanced by providing a catalyst layer having at least one of these noble metals. The catalyst layer containing at least Pt and Pd may be any of a catalyst layer containing Pt, a catalyst layer containing Pd, and a catalyst layer containing both Pt and Pd. Moreover, it can also be set as the structure which comprises the catalyst layer containing these noble metals in multiple layers. Furthermore, the position of the catalyst layer containing the noble metal in the exhaust gas purification catalyst of the present invention is not limited. However, the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is preferably the outermost layer, and the catalyst layer containing Rh contains the oxide of the transition element of the outermost layer. The catalyst layer containing at least one of Pt and Pd is preferably located on the lower layer side (side wall side of the carrier) than the catalyst layer containing Rh.

The catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} can further contain an oxide having an oxygen storage / release capability. The presence and absence of oxygen-absorbing / releasing materials such as CeO ₂ , Ce-Zr-Ox, Pr ₆ O _{11 and the} like in the same layer as the above-mentioned transition element enables more efficient oxygen transfer on the transition element. Thus, the effect of the present invention is enhanced.

The oxide having the ability to absorb and release oxygen is preferably composed of at least one oxide selected from {Ce, Pr, Nd, Y}. This is because these oxides have an excellent oxygen storage / release capability. Specific examples include CeO ₂ , Ce—Zr—Ox, Pr ₆ O ₁₁ , Ce—Zr—Nd—Ox, and Ce—Zr—Y—Ox.

  The exhaust gas purification catalyst of the present invention can further contain at least one compound selected from {Ba, Mg, Ca, Na, Cs}. Since compounds such as Ba can adsorb NOx under lean conditions, the exhaust gas purification catalyst contains at least one compound selected from {Ba, Mg, Ca, Na, Cs}. It can function as a catalyst that adsorbs NOx and purifies the adsorbed NOx under rich conditions. These NOx-adsorbing compounds are advantageous in the production process to be contained in all the laminated catalyst layers, but they can also be contained in a part of the catalyst layers of the plurality of catalyst layers.

  In the exhaust gas purification catalyst of the present invention, the average particle diameter of the noble metal is preferably 20 nm or less. For Rh in the catalyst layer containing Rh and Pt and / or Pd that may be contained in the other catalyst layers, the catalyst having an average particle diameter exceeding 20 nm, for example, a catalyst after deterioration, has little effect of the present invention. . In the region where the average particle size is 20 nm or less, particularly 10 nm or less, the effect of increasing the surface area with respect to the noble metal particle size is high, and Rh is exposed on the surface. Such fine noble metal particles having an average particle diameter of 20 nm or less are generally easily deteriorated by high temperature or long-term exhaust gas purification. On the other hand, according to the configuration of the exhaust gas purification catalyst of the present invention, durability can be improved even in the case of such fine noble metal particles having an average particle diameter of 20 nm or less. Therefore, the present invention is particularly effective when the average particle diameter is 20 nm or less after endurance or the initial one (average particle diameter is 1 nm or less). In addition, the minimum of the average particle diameter of a noble metal is not specifically limited. In the case of industrial production, there can be a lower limit of the average particle diameter of the noble metal that can be carried out by the manufacturing process, but it is not limited to such a lower limit.

  The catalyst powder constituting the catalyst layer containing the noble metal includes a noble metal, a compound that contacts the noble metal and has a function of suppressing the movement of the noble metal, covers the noble metal and the compound, suppresses the movement of the noble metal, and a compound. It is preferable to comprise an oxide that suppresses aggregation due to mutual contact. By supporting the precious metal particles having exhaust gas purifying ability on a compound that comes into contact with the precious metal particles and suppresses the movement of the precious metal, the compound acts as an anchor material for chemical bonding, and the movement of the precious metal particles is suppressed. Chemically suppressed. Then, by forming an oxide covering the compound carrying the noble metal particles, the oxide physically suppresses the movement of the noble metal. Further, since the oxide is interposed between the compounds supporting the noble metal particles, the compounds are separated from each other by the oxide. As a result, the compounds carrying the noble metal particles are prevented from contacting and aggregating with each other. The suppression of aggregation of the compound supporting the noble metal particles contributes to suppression of aggregation of the noble metal particles. From these facts, the catalyst powder having such a compound and an oxide can suppress the aggregation of the noble metal particles even after durability, and can suppress the average particle diameter of the noble metal particles to about 5 to 15 nm. The effect of the invention is particularly high.

  The thickness of the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is preferably 20 μm or less. If the catalyst layer containing the transition element oxide laminated on the Rh catalyst layer is too thick, the gas diffusibility is impaired. Therefore, it is necessary to control the thickness of the catalyst layer containing the transition element oxide. As a result of intensive studies by the inventors, it has been found that when a catalyst layer containing an oxide of a transition element is laminated, if the thickness is 20 μm or less, the effect is large and if it is more, the effect is small. Therefore, the thickness of the catalyst layer is preferably 20 μm or less. The lower limit value of the thickness of the catalyst layer is not particularly limited. However, if the thickness is too thin, there is a possibility that the catalyst layer may be peeled off when the catalyst layer is formed on the support. Therefore, there may be a lower limit from the viewpoint of industrial production that does not cause peeling. It is not restricted to such a lower limit.

  The particle diameter of at least one oxide selected from {Fe, Mn, Ni, Co} is preferably 2 μm or less. This is because the effect of the present invention is further promoted when the oxide particle diameter of the transition element is 2 μm or less. This is considered to be because the specific surface area is improved and the contact with the exhaust gas is improved by reducing the oxide particles.

  When producing the exhaust gas catalyst of the present invention, the catalyst slurry for the catalyst layer containing at least Rh and the catalyst for the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} A slurry and, if necessary, a slurry for another catalyst layer are prepared, and are sequentially attached to a carrier, dried and fired to form each catalyst layer. The method for preparing the slurry for each catalyst layer is not particularly limited, and can be carried out by a known method. In addition, when at least one compound selected from {Ba, Mg, Ca, Na, Cs} is included, after laminating each catalyst layer on the carrier, the carrier is placed in a slurry or solution of these compounds or their raw materials. After impregnation, these compounds can be included in the catalyst layer by drying and firing.

  Hereinafter, the present invention will be specifically described based on examples. In each example described below, as shown in FIG. 4, a schematic diagram of the laminated structure of the catalyst layers laminated on the catalyst carrier, the catalyst layer laminated structure has a total of two layers of catalyst on the inner surface of the carrier 1. An example in which the layers were laminated (FIG. 4A) and an example in which a total of three catalyst layers were laminated (FIGS. 4B and 4C) were used. The flow direction of the exhaust gas passing through the pores of the carrier 1 is indicated by an arrow G in the figure. 4A shows a laminated structure in which a total of two catalyst layers of catalyst layer 1 (reference numeral 11 in the figure) and catalyst layer 2 (reference numeral 12 in the figure) are laminated, and FIG. 4B shows the catalyst layer. 1 (reference numeral 11 in the figure), catalyst layer 2 (reference numeral 12 in the figure) and catalyst layer 3 (reference numeral 13 in the figure), a laminated structure in which a total of three catalyst layers are laminated, FIG. 4. A laminated structure in which a total of three catalyst layers are laminated, and the outermost catalyst layer 3A (reference numeral 13A in the figure) is formed so as to cover a part of the catalyst layer 2 immediately below, FIG. (D) is a comparative example, which has a structure in which one different catalyst layer 2 and one catalyst layer 1 are formed on the upstream side and the downstream side of the exhaust gas flow in the pores of the carrier.

  In all of the following Examples and Comparative Examples, an alumina layer 14 is formed on the base between the carrier 1 (reference numeral 1 in the figure) and the catalyst layer 1 (reference numeral 11 in the figure).

  First, as the exhaust gas purification catalyst corresponding to the catalyst layer in FIG. 4A, the exhausted gas purification catalysts of Examples 1 to 4 and Comparative Examples 1 and 2 are as follows. It was created by the process.

Example 1
Example 1 is an example of a catalyst layer in which the catalyst layer 1 contains Rh, and a catalyst layer in which the catalyst layer 2 contains an oxide of Fe.

La-containing ZrO ₂ having a specific surface area of 70 [m ² / g] was impregnated with an Rh nitrate solution and supported so that the supported concentration was 0.1 [wt%]. This was dried at 150 [° C.] for a whole day and night and then calcined at 400 [° C.] for 1 hour to obtain powder A. This powder A was charged with 225 [g], alumina sol 25 [g], water 240 [g] and nitric acid 10 [g] in a magnetic ball mill, and mixed and ground to obtain a catalyst slurry. The obtained slurry was attached to a cordierite monolith support (0.12 [L], 400 cells), and the excess slurry in the cells was removed by air flow and dried at 150 [° C.], and then 400 [° C.]. Was fired for 1 hour to obtain a catalyst layer 1 having a coat layer of 100 [g / L].

  Further, iron oxide 225 [g], zirconia sol 25 [g], water 240 [g] and nitric acid 10 [g] were charged into a magnetic ball mill, mixed and ground to obtain a catalyst slurry. The obtained slurry was deposited on the catalyst layer 1, the excess slurry in the cell was removed with an air stream, dried at 150 [° C.], and then fired at 400 [° C.] for 1 hour, and the coating layer [30 g / L] catalyst layer 2 was obtained.

(Example 2)
Example 2 is an example of a catalyst layer in which the catalyst layer 1 contains Rh, and a catalyst layer in which the catalyst layer 2 contains an oxide of Mn.

  The process is the same as that of Example 1 except that the iron oxide of Example 1 is changed to manganese oxide.

(Example 3)
Example 3 is an example of a catalyst layer in which the catalyst layer 1 includes Rh, and a catalyst layer in which the catalyst layer 2 includes an oxide of Ni.

  The process is the same as that of Example 1 except that the iron oxide of Example 1 is changed to nickel oxide.

Example 4
Example 4 is an example of a catalyst layer in which the catalyst layer 1 includes Rh, and a catalyst layer in which the catalyst layer 2 includes an oxide of Co.

  The process is the same as that of Example 1 except that the iron oxide of Example 1 is changed to cobalt oxide.

(Comparative Example 1)
Comparative Example 1 is an example in which a plurality of catalyst layers are not stacked and only the catalyst layer 1 is provided.

  The process is the same as that of Example 1 except that the catalyst obtained in the preparation process of the catalyst layer 1 in Example 1 is used as it is.

(Comparative Example 2)
Comparative Example 2 is an example in which one catalyst layer 2 and one catalyst layer 1 corresponding to the catalyst layer in FIG. 4D are formed on the upstream and downstream sides of the exhaust gas flow in the pores of the carrier. .

  Iron oxide 225 [g], zirconia sol 25 [g], water 240 [g], and nitric acid 10 [g] were charged into a magnetic ball mill, mixed and ground to obtain a catalyst slurry. The obtained slurry was attached to a cordierite monolith support (0.12 [L], 400 cells), and the excess slurry in the cells was removed by air flow and dried at 150 [° C.], and then 400 [° C.]. Was fired for 1 hour to obtain a catalyst layer 2 having a coat layer of 100 g / L.

  The catalyst thus obtained was cut so as to be 0.04 [L], and this was placed in front of the catalyst of Comparative Example 1.

  Exhaust gas purification performance was examined for the exhaust gas purification catalysts of Examples 1 to 4 and Comparative Examples 1 and 2 described above. This exhaust gas purification performance was evaluated by mounting a carrier carrying the exhaust gas purification catalyst of each Example or each Comparative Example on the exhaust system of a 3500 [cc] gasoline engine and setting the catalyst inlet temperature to 150 [° C. The temperature was raised at 500 [° C.] at a temperature raising rate of 10 [° C./min], and the conversion rate was measured over the temperature raising process. The conversion rate is calculated according to the following formula.

HC conversion rate (%) = [(Catalyst inlet HC concentration)-(Catalyst outlet HC concentration)] / (Catalyst inlet HC concentration) x 100
CO conversion rate (%) = [(catalyst inlet CO concentration)-(catalyst outlet CO concentration)] / (catalyst inlet CO concentration) x 100
NOx conversion rate (%) = [(NOx concentration at catalyst inlet)-(NOx concentration at catalyst outlet) / (NOx concentration at catalyst inlet) x 100
The temperature at which the conversion calculated by the above formula becomes 50% was defined as the 50% conversion temperature, and the exhaust gas purification performance was evaluated based on this 50% conversion temperature. It can be said that the lower the 50% conversion temperature, the better the low temperature activity and the better the catalyst.

The 50% conversion temperature of the exhaust gas purifying catalysts of Examples 1 to 4 and Comparative Examples 1 and 2 is defined as the noble metal species or oxide metal species of each catalyst layer in the exhaust gas purifying catalysts of the respective Examples and Comparative Examples. Together with Table 1. From Table 1, Examples 1-4 were excellent in low-temperature activity, and had the outstanding exhaust gas purification performance. In contrast, Comparative Example 1 had a 50% conversion temperature higher than that of each Example because the catalyst layer 2 was not laminated. Further, Comparative Example 2 in which the catalyst layer 2 was provided on the upstream side of the exhaust gas flow and the catalyst layer 1 was provided on the downstream side had a 50% conversion temperature similar to that of Comparative Example 1. From the comparison between Comparative Example 2 and Example 1, Example 1 in which a plurality of catalyst layers are laminated has a lower temperature than Comparative Example 2 in which a plurality of catalyst layers are provided upstream and downstream of the exhaust gas flow. It was an excellent catalyst with good activity.

  Next, as the exhaust gas purification catalyst corresponding to the catalyst layer of FIG. 4B or FIG. 4C, the stacked catalyst layers are composed of a total of three layers, Examples 5 to 9 and Comparative Examples 3 to 5 An exhaust gas purification catalyst was prepared by the following steps. Moreover, although it became the laminated structure of Fig.4 (a), the exhaust-gas purification catalyst of the comparative examples 6-7 which does not satisfy | fill the requirements of this invention was created with the following processes.

(Example 5)
Example 5 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, and a catalyst layer in which the catalyst layer 3 contains an oxide of Fe.

La-containing ZrO ₂ having a specific surface area of 70 [m ² / g] was impregnated with an Rh nitrate solution and supported so that the supported concentration was 0.4 [wt%]. This was dried at 150 [° C.] for a whole day and night and then calcined at 400 [° C.] for 1 hour to obtain powder B. The powder B was charged with 225 [g], alumina sol 25 [g], water 240 [g] and nitric acid 10 [g] in a magnetic ball mill, and mixed and ground to obtain catalyst slurry A.

Further, Ce and La-containing ZrO ₂ having a specific surface area of 80 [m ² / g] was impregnated with a Pd nitrate solution and supported so that the supported concentration was 1.6 [wt%]. This was dried at 150 [° C.] for a whole day and night, and calcined at 400 [° C.] for 1 hour to obtain powder C. This powder C was charged with 225 [g], alumina sol 25 [g], water 240 [g] and nitric acid 10 [g] in a magnetic ball mill, mixed and ground to obtain catalyst slurry B.

  Further, iron oxide 225 [g], zirconia sol 25 [g], water 240 [g] and nitric acid 10 [g] were charged into a magnetic ball mill, mixed and ground, and catalyst slurry C was obtained.

  Next, the slurry B was attached to a cordierite monolith support (0.12 [L], 400 cells), excess slurry in the cells was removed with an air flow and dried at 150 [° C.], and then 400 [ The catalyst layer 1 having a coat layer of 150 [g / L] was obtained.

  Next, the slurry A is deposited on the catalyst layer 1, the excess slurry in the cell is removed with an air flow, dried at 150 [° C.], and then baked at 400 [° C.] for 1 hour. A catalyst layer 2 having a layer of 50 [g / L] was obtained.

  Next, the slurry C is deposited on the catalyst layer 2, the excess slurry in the cell is removed with an air flow, dried at 150 [° C.], and then fired at 400 [° C.] for 1 hour, and the coating layer 30 [g / L] catalyst layer 3 was obtained.

(Example 6)
Example 6 is an example of a catalyst layer in which the catalyst layer 1 contains Rh, a catalyst layer in which the catalyst layer 2 contains an oxide of Fe, and a catalyst layer in which the catalyst layer 3 contains Pd.

  The process is the same as that of Example 5 except that the method of laminating the catalyst layers in Example 5 is the order of slurry A, slurry C, and slurry B from the side closer to the carrier.

(Example 7)
Example 7 is an example of a catalyst layer in which the catalyst layer 1 includes Rh, a catalyst layer in which the catalyst layer 2 includes Pd, and a catalyst layer in which the catalyst layer 3 includes an oxide of Fe.

  The process is the same as that of Example 5 except that the way of stacking in Example 5 is the order of slurry A, slurry B, and slurry C from the side closer to the carrier.

(Example 8)
Example 8 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe contains an oxide of Fe, as shown in FIG. In this example, the outermost catalyst layer 3 is formed only on the upstream side of the exhaust gas flow in the pores of the carrier.

  In the process, the stacking in Example 5 was performed in the order of slurry B and slurry A from the side closer to the carrier, and then exhausted in the carrier in which the catalyst layer 1 and the catalyst layer 2 were formed in the slurry C accommodated in the container. Example except that slurry C was partially adhered on the catalyst layer by immersing only the portion corresponding to the upstream side of the gas flow (the range of the length of one half of the through-hole penetration direction). Same as 5.

Example 9
Example 9 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer in which the catalyst layer 2 contains Rh, and a catalyst layer in which the catalyst layer 3 contains an oxide of Fe.

La-containing ZrO ₂ having a specific surface area of 70 [m ² / g] was impregnated with a Rh nitrate solution and supported so that the supported concentration was 0.2 [wt%]. This was dried at 150 [° C.] for a whole day and night and then calcined at 400 [° C.] for 1 hour to obtain powder D. 225 g of this powder D, 25 g of alumina sol, 240 g of water, and 10 g of nitric acid were put into a magnetic ball mill, mixed and ground, and catalyst slurry D was obtained.

Further, La, Ce and Zr-containing Al ₂ O ₃ having a specific surface area of 160 [m ² / g] was impregnated with a dinitrodiamine Pt solution and supported so that the supported concentration was 0.2 [wt%]. This was dried at 150 [° C.] for a whole day and night, and calcined at 400 [° C.] for 1 hour to obtain powder E. This powder E was charged with 225 [g], alumina sol 25 [g], water 240 [g] and nitric acid 10 [g] in a magnetic ball mill, and mixed and ground to obtain catalyst slurry E.

  Further, iron oxide 225 [g], alumina sol 25 [g], water 240 [g] and nitric acid 10 [g] were put into a magnetic ball mill, mixed and ground, and catalyst slurry F was obtained.

  Next, the slurry E was attached to a cordierite monolith support (0.12 [L], 400 cells), excess slurry in the cells was removed by air flow, and the slurry E was dried at 150 [° C.], and then 400 [ The catalyst layer 1 having a coat layer of 150 [g / L] was obtained.

  Next, the slurry D is deposited on the catalyst layer 1, the excess slurry in the cell is removed by air flow, dried at 150 [° C.], and then fired at 400 [° C.] for 1 hour, A catalyst layer 2 having a layer of 50 [g / L] was obtained.

  Next, the slurry F is deposited on the catalyst layer 2, the excess slurry in the cell is removed with an air flow, dried at 150 [° C.], and then fired at 400 [° C.] for 1 hour, and the coating layer 30 [g / L] catalyst layer 3 was obtained.

(Comparative Example 3)
In Comparative Example 3, the iron oxide layer is the catalyst layer 2 in FIG. 4B and the Rh layer is the catalyst layer 3.

  The process is the same as that of Example 5 except that the stacking method of Example 5 is changed to the order of slurry B, slurry C, and slurry A from the side closer to the carrier.

(Comparative Example 4)
In Comparative Example 4, the iron oxide layer is the catalyst layer 1 in FIG. 4B and the Rh layer is the catalyst layer 3.

  The process is the same as that of Example 5 except that the stacking method of Example 5 is changed in the order of slurry C, slurry B, and slurry A from the side close to the carrier.

(Comparative Example 5)
In Comparative Example 5, the iron oxide layer is the catalyst layer 1 in FIG. 4B and the Rh layer is the catalyst layer 2.

  The process is the same as that of Example 5 except that the stacking of Example 5 is performed in the order of slurry C, slurry A, and slurry B from the side closer to the carrier.

(Comparative Example 6)
Comparative Example 6 is an example in which two layers are laminated without having an iron oxide layer, and the catalyst layer containing a noble metal is a catalyst layer containing Pd.

  The process is the same as that of Example 5 except that the way of stacking in Example 5 is changed to the order of slurry B and slurry A from the side closer to the carrier.

(Comparative Example 7)
Comparative Example 7 is an example in which two layers are laminated without having an iron oxide layer, and the catalyst layer containing a noble metal is an example of a catalyst layer containing Pt.

  The process is the same as that of Example 9 except that the stacking of Example 9 is performed in the order of slurry E and slurry D from the side closer to the carrier.

  Regarding the exhaust gas purification catalysts of Examples 5 to 9 and Comparative Examples 3 to 7 described above, the exhaust gas purification performance was examined before and after the durability test. In the endurance test, a carrier carrying the exhaust gas purification catalyst of each Example or each Comparative Example was mounted on the exhaust system of a gasoline engine having a displacement of 3500 [cc], and the catalyst inlet temperature was set to 700 ° C. and the system was operated for 50 hours. The exhaust gas purification performance was evaluated based on the 50% conversion temperature described above.

  The 50% conversion temperature before and after the endurance test of the exhaust gas purifying catalysts of Examples 5 to 9 and Comparative Examples 3 to 7 is the noble metal species or oxidation of each catalyst layer in the exhaust gas purifying catalysts of each Example and each Comparative Example. It shows in Table 2 with the metal kind of a thing. From Table 2, Examples 5 to 9 were more excellent in low-temperature activity than Examples 1 to 4 shown in Table 1, and had excellent exhaust gas purification performance. By comparison with Examples 5 to 7, Example 5 in which the catalyst layer containing an oxide of Fe as a transition element was in the outermost layer and was in contact with the Rh layer had the best exhaust gas purification performance. . In addition, the effect of the present invention was obtained even when the catalyst layer containing Fe oxide covered a part of the catalyst layer containing Rh as in Example 8. Furthermore, the effect of the present invention was obtained even when the catalyst layer containing a noble metal other than Rh was Pt as in Example 9. On the other hand, in Comparative Examples 3 to 5, the catalyst layer containing the oxide of Fe was positioned closer to the support than the catalyst layer containing Rh. The 50% conversion temperature was high. Moreover, since Comparative Examples 6 and 7 did not have a catalyst layer containing an oxide of Fe, the 50% conversion temperature after durability was particularly high, and the exhaust gas purification performance was inferior to Examples 5 to 7. It was.

FIG. 5 shows a photomicrograph showing the laminated structure of the exhaust gas purifying catalyst of Example 5. 5 (a) and 5 (b) are micrographs of the same part, and FIG. 5 (a) is a photograph using a scanning microscope (FE-SEM) S-4000 manufactured by Hitachi High-Tech, FIG. 5 (b). ) Is a photograph at the same magnification of the same part of the same sample as FIG. 5 (a), which was subjected to component analysis using an electron beam microanalyzer (EPMA) EPMA-1600 manufactured by Shimadzu Corporation. In FIG. 5B, the portion of the catalyst layer 3 appears white due to Fe contained in the catalyst layer 3. That is, the portion that looks white in FIG. 5B is the portion of the catalyst layer 3. FIG. 6 is a schematic depiction of the stack structure of the exhaust gas purification catalyst shown in FIG. In FIG. 6, the catalyst layer 1 (reference numeral 11 in the figure), the catalyst layer 2 (reference numeral 12), and the catalyst layer 3 (reference numeral 13) are formed on the inner surface of the carrier 1 in this order. An alumina layer 14 is formed on the base of the catalyst layer 1.

  Next, exhaust gas purification catalysts of Examples 10 and 11 were prepared by the following steps as exhaust gas purification catalysts having a total of three stacked catalyst layers corresponding to the catalyst layer of FIG.

(Example 10)
Example 10 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe is contained. The binder is alumina.

  The process is the same as that of Example 5 except that the zirconia sol in the slurry C of Example 5 is changed to alumina sol.

(Example 11)
Example 11 is an example where the catalyst layer 1 includes a catalyst layer containing Pd, the catalyst layer 2 includes a catalyst layer including Rh, and the catalyst layer 3 includes an oxide of Fe. It is not included.

  The process is the same as that of Example 5 except that the zirconia sol in the slurry C of Example 5 is eliminated.

  Regarding the exhaust gas purification catalysts of Examples 10 and 11 described above, the exhaust gas purification performance was examined before and after the durability test, respectively. The durability test and the evaluation of the exhaust gas purification performance are the same as described above.

The above-mentioned Example 5 and Comparative Example 6 showing the 50% conversion temperature before and after the endurance test of the exhaust gas purification catalysts of Examples 10 and 11 above for comparison with these Examples, each Example and Comparison Table 3 shows the noble metal species or oxide metal species of each catalyst layer in the exhaust gas purifying catalyst of the example and the binder type of the catalyst layer 3 of each example. From Table 3, Example 11, which does not contain a binder in the catalyst layer containing Fe oxide, is superior to Comparative Example 6 that does not have a catalyst layer containing Fe oxide, but is not much different from Comparative Example 6. Met. This is a low conversion rate because it peels off after the endurance without a binder. Further, in Example 10 in which the binder was alumina, performance superior to that of Comparative Example 6 was obtained. In contrast to Example 10 and Example 5, Example 5 in which the binder was ZrO ₂ was more effective than Example 10 in which the binder was Al ₂ O ₃ . This is because Example 10 in which the binder was Al ₂ O ₃ was less effective than Example 5 because the transition element was dissolved in Al ₂ O ₃ .

  Next, the exhaust gas purification catalysts of Examples 12 to 16 were prepared by the following steps as exhaust gas purification catalysts corresponding to the catalyst layer of FIG.

(Example 12)
Example 12 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe is contained. This is an example in which CeO ₂ is contained as an oxygen storage / release material.

  In the process, for catalyst slurry C of Example 5, iron oxide 175 [g], ceria 50 [g], zirconia sol 25 [g], water 240 [g], and nitric acid 10 [g] were charged into a magnetic ball mill, Example 5 is the same as Example 5 except that the catalyst slurry C is obtained by mixing and grinding.

(Example 13)
Example 13 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, and a catalyst layer in which the catalyst layer 3 contains an oxide of Fe. This is an example in which Ce—Zr—Ox is included as an oxygen storage / release material.

The process is the same as that of Example 12 except that CeO ₂ of Example 12 is changed to Ce—Zr—Ox.

(Example 14)
Example 14 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, a catalyst layer in which the catalyst layer 3 contains an oxide of Fe, and the catalyst layer 3 includes In this example, Ce—Pr—Ox is included as the oxygen storage / release material.

The process is the same as that of Example 12 except that CeO ₂ of Example 12 is changed to Ce—Pr—Ox.

(Example 15)
Example 15 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe is contained. This is an example in which Ce—Zr—Nd—Ox is contained as an oxygen storage / release material.

The process is the same as that of Example 12 except that CeO ₂ of Example 12 is changed to Ce—Zr—Nd—Ox.

(Example 16)
Example 16 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe is contained. This is an example in which Ce—Zr—Y—Ox is contained as an oxygen storage / release material.

The process is the same as that of Example 12 except that CeO ₂ of Example 12 is changed to Ce—Zr—Y—Ox.

  Regarding the exhaust gas purification catalysts of Examples 10 and 11 described above, the exhaust gas purification performance was examined before and after the durability test, respectively. The durability test and the evaluation of the exhaust gas purification performance are the same as described above.

In the exhaust gas purification catalyst of each of the above-mentioned Examples 5 and 10 showing the 50% conversion temperatures before and after the endurance test of the exhaust gas purification catalysts of Examples 12 to 16 above for comparison with these Examples. Table 4 shows the noble metal species or oxide metal species of each catalyst layer and the types of oxygen storage / release materials in the catalyst layer 3 of each example. From Table 4, Examples 12-16 which contain an oxygen absorption-release material in the catalyst layer containing the oxide of Fe showed the conversion rate superior to Example 5 which does not contain an oxygen absorption-release material.

  Next, an exhaust gas purification catalyst of Example 17 was prepared by the following steps as an exhaust gas purification catalyst corresponding to the catalyst layer of FIG.

(Example 17)
Example 17 is an example of a catalyst layer in which the catalyst layer 1 includes Pd, a catalyst layer in which the catalyst layer 2 includes Rh, and a catalyst layer in which the catalyst layer 3 includes an oxide of Fe. The powder used in the above is a precious metal, a compound that comes into contact with the precious metal and has a function of suppressing the movement of the precious metal, covers the precious metal and the compound, suppresses the movement of the precious metal, and aggregates due to contact between the compounds. It is an example which consists of the oxide to suppress.

A Ce and La-containing ZrO ₂ powder having a specific surface area of 80 [m ² / g] was loaded with a Pd nitrate solution so that the loading concentration was 3.2 wt% as Pd. This was dried at 150 [° C.] for a whole day and night and then calcined at 400 [° C.] for 1 hour to obtain Pd (3.2 [wt%]) / Ce, Zr-containing ZrO ₂ powder G. This powder G was pulverized to obtain a Pd / Ce, La-ZrO ₂ powder having an average particle diameter (D ₅₀ ) of 200 nm. On the other hand, boehmite, nitric acid and water were mixed and stirred for 1 [hr]. The Pd / Ce and La-ZrO ₂ powders were slowly put into this and further stirred for 2 [hr]. Next, after drying for 3 [hr] at 80 [° C.] under reduced pressure, the powder was baked in air at 550 [° C.] for 3 [hr] to obtain powder H. The ratio of powder G to Al ₂ O _{3 in} this powder H is 50:50.

  This powder H was charged with 225 [g], alumina sol 25 [g], water 240 [g], and nitric acid 10 [g] into a magnetic ball mill, and mixed and ground to obtain a catalyst slurry. The obtained slurry was attached to a cordierite monolith support (0.12 [L], 400 cells), and the excess slurry in the cells was removed by air flow and dried at 130 [° C.], and then 400 [° C.]. Was fired for 1 hour to obtain a catalyst layer 1 having a coat layer of 150 [g / L].

Next, a Rh nitrate solution was supported on La-containing ZrO ₂ powder having a specific surface area of 70 [m ² / g] so that the supported concentration was 0.8 wt% as Rh. This was dried at 150 [° C.] for a whole day and night and then calcined at 400 [° C.] for 1 hour to obtain Rh (0.8 wt%) / La—ZrO ₂ x powder I. This powder I was pulverized into Rh / La-ZrO ₂ powder having an average particle diameter (D ₅₀ ) of 160 nm. On the other hand, boehmite and water were mixed and stirred for 1 [hr]. The powder I was slowly put into this and further stirred for 2 [hr]. Subsequently, after drying for 3 [hr] at 80 [° C.] under reduced pressure, the powder was fired at 550 [° C.] for 3 [hr] in air to obtain powder J. The ratio of the powder I in this powder J to Al ₂ O ₃ is 50:50.

  This powder J was charged with 225 [g], alumina sol 25 [g], water 240 [g], and nitric acid 10 [g] in a magnetic ball mill, and mixed and ground to obtain a catalyst slurry. This catalyst slurry was deposited on the catalyst layer 1, the excess slurry in the cell was removed by air flow, dried at 130 [° C.], and then calcined at 400 [° C.] for 1 hour, and the coating layer 50 [g / L] catalyst layer 2 was obtained.

  Next, iron oxide 225 [g], zirconia sol 25 [g], water 240 [g], and nitric acid 10 [g] were charged into a magnetic ball mill, mixed and ground to obtain a catalyst slurry. This catalyst slurry was deposited on the catalyst layer 2, the excess slurry in the cell was removed by air flow, dried at 130 [° C.], and then calcined at 400 [° C.] for 1 hour, and the coating layer 30 [g / L] catalyst layer was obtained.

  The endurance temperature of Example 5 is shown in order to compare the 50% conversion temperature before and after the endurance test of the exhaust gas purification catalyst of Example 17 and the noble metal particle diameter before and after the endurance test. Various examples of endurance tests were performed, the noble metal particle diameter was changed, the noble metal species or oxide metal species of each catalyst layer in the exhaust gas purification catalyst of each example, the durability temperature of each example, It shows in Table 5 with the noble metal particle diameter after durability of each Example. FIG. 7 is a graph showing the relationship between the noble metal particle diameter after durability and the HC50% conversion temperature based on the results in Table 5. The noble metal particle diameter was an average value of the particle diameter measured by TEM.

From Table 5, the powder used for the catalyst layer 1 and the catalyst layer 2 is a noble metal, a compound that comes into contact with the noble metal and has a function of suppressing the movement of the noble metal, and the movement of the noble metal covering the noble metal and the compound. In Example 17, consisting of an oxide that suppresses and suppresses aggregation due to contact between compounds, the noble metal particle diameter after the durability test is kept small compared to Example 5, and even after the endurance example A conversion better than 5 was shown. Further, from the graph of FIG. 7, it was revealed that particularly excellent exhaust gas purification performance is exhibited when the average particle diameter of the noble metal is 20 [nm] or less.

  Next, exhaust gas purification catalysts of Examples 18 to 20 were prepared by the following steps as exhaust gas purification catalysts corresponding to the catalyst layer of FIG.

(Example 18)
Example 18 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, a catalyst layer in which the catalyst layer 3 contains an oxide of Fe, and In this example, the thickness is 15 [μm].

  The process is the same as that of Example 5 except that the adhesion amount of slurry C in Example 5 was changed and a catalyst layer of coat layer 25 [g / L] was obtained.

(Example 19)
Example 19 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, and a catalyst layer in which the catalyst layer 3 contains an oxide of Fe. In this example, the thickness is 25 [μm].

  The process is the same as that of Example 5 except that the amount of the slurry C of Example 5 is changed and a catalyst layer of the coat layer 40 [g / L] is obtained.

(Example 20)
Example 20 is an example of a catalyst layer in which the catalyst layer 1 includes Pd, a catalyst layer in which the catalyst layer 2 includes Rh, a catalyst layer in which the catalyst layer 3 includes an oxide of Fe, and In this example, the thickness is 30 [μm].

  The process is the same as that of Example 5 except that the amount of the slurry C deposited in Example 5 was changed and a catalyst layer of a coat layer 50 [g / L] was obtained.

  The 50% conversion rate temperature before the endurance test of the exhaust gas purifying catalysts of the above Examples 18 to 20 is shown for comparison with these examples, and the 50% conversion rate before the endurance test for Example 5 described above, Table 6 shows the noble metal species or oxide metal species of each catalyst layer in the exhaust gas purifying catalyst of each example and the thickness of the catalyst layer 3 of each example. Further, the relationship between the thickness of the catalyst layer 3 and the HC50% conversion temperature based on the results of Table 6 is shown in a graph in FIG.

From Table 6, Example 5 and Example 18 in which the thickness of the catalyst layer 3 is 20 [μm] or less are more than Examples 19 and 20 in which the thickness of the catalyst layer 3 exceeds 20 [μm]. 50% conversion temperature was low. Further, from the graph of FIG. 8, it became clear that particularly excellent exhaust gas purification performance is exhibited when the thickness of the catalyst layer 3 is 20 [μm] or less.

  Next, exhaust gas purification catalysts of Examples 21 to 23 were prepared by the following steps as exhaust gas purification catalysts corresponding to the catalyst layer of FIG.

(Example 21)
Example 21 is an example in which the catalyst layer 1 contains Pd, the catalyst layer 2 contains Rh, the catalyst layer 3 contains Fe oxide, and the catalyst layer 3 includes This is an example in which the average particle size of the contained Fe oxide is 1.5 [μm].

  The process is the same as that of Example 5 except that the slurry average particle size of the slurry C of Example 5 was changed from 0.7 [μm] to 1.5 [μm] by changing the mixing and grinding conditions.

(Example 22)
Example 22 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer in which the catalyst layer 2 contains Rh, and a catalyst layer in which the catalyst layer 3 contains an oxide of Fe. This is an example in which the average particle size of the contained oxide of Fe is 2 [μm].

  The process is the same as that of Example 5 except that the slurry average particle size of the slurry C of Example 5 was changed from 0.7 [μm] to 2 [μm] by changing the mixing and grinding conditions.

(Example 23)
Example 23 is an example of a catalyst layer in which the catalyst layer 1 contains Pd, a catalyst layer 2 in which the catalyst layer 2 contains Rh, and a catalyst layer 3 in which the oxide of Fe is contained. This is an example in which the average particle diameter of the oxide of Fe contained is 2.8 [μm].

The process is the same as Example 5 except that the average particle size of slurry C of Example 5 was changed from 0.7 [μm] to 2.8 [μm] by changing the mixing and grinding conditions. The 50% conversion temperature before the endurance test of the exhaust gas purification catalyst is shown for comparison with these examples, and the 50% conversion before the endurance test for the above-mentioned Example 5 and the exhaust gas purification of each example Table 7 shows the noble metal species or oxide metal species of each catalyst layer in the catalyst and the average particle diameter of the oxide in the catalyst layer 3 of each Example. FIG. 9 is a graph showing the relationship between the average particle diameter of the transition oxide in the catalyst layer 3 and the HC50% conversion temperature based on the results in Table 7.

From Table 7, Example 5, Example 21 and Example 22 in which the average particle diameter of the oxide of the transition element in the catalyst layer 3 is 2 [μm] or less are 2 [μm]. More than Example 23, the 50% conversion temperature was lower. Further, from the graph of FIG. 9, it became clear that particularly excellent exhaust gas purification performance is exhibited when the thickness of the catalyst layer 3 is 20 μm or less.

  Next, in order to evaluate the performance of the exhaust gas purification catalyst of the present invention under the condition where the air-fuel ratio is changed, the exhaust gas purification catalysts of Examples 24-29 and Comparative Example 8 are prepared by the following steps. did.

(Example 24)
Example 24 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer 2 in which the catalyst layer 2 contains Rh, a catalyst layer 3 in which the catalyst layer 3 contains Fe oxide, and a compound that adsorbs NOx. In this example, Ca is contained in the catalyst layer.

  In the step, the catalyst obtained in Example 9 and having a total of three catalyst layers on the support was impregnated with Ba acetate as BaO to 25 [g / L]. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 24.

(Example 25)
Example 25 is an example in which the catalyst layer 1 is a catalyst layer containing Pt, the catalyst layer 2 is a catalyst layer containing Rh, the catalyst layer 3 is a catalyst layer containing Fe oxide, and a compound that adsorbs NOx. In this example, Mg is contained in the catalyst layer.

  In the step, the catalyst obtained in Example 9 and having a total of three catalyst layers on the support was impregnated with Mg acetate as MgO so as to be 5 [g / L]. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 25.

(Example 26)
Example 26 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer 2 in which the catalyst layer 2 contains Rh, a catalyst layer 3 in which the catalyst layer 3 contains Fe oxide, and a compound that adsorbs NOx. In this example, Ca is contained in the catalyst layer.

  In the process, the catalyst obtained in Example 9 and having a total of three catalyst layers on the support was impregnated with Ca acetate as CaO so as to be 25 [g / L]. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 26.

(Example 27)
Example 27 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer 2 in which the catalyst layer 2 contains Rh, a catalyst layer 3 in which the catalyst layer 3 contains Fe oxide, and a compound that adsorbs NOx. In this example, Na is contained in the catalyst layer.

In the step, the catalyst having a total of three catalyst layers on the support obtained in Example 9 was impregnated with Na acetate as Na ₂ O so as to be 5 [g / L]. This was dried at 130 [° C.] and calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 27.

(Example 28)
Example 28 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer 2 in which the catalyst layer 2 contains Rh, a catalyst layer 3 in which the catalyst layer 3 contains Fe oxide, and a compound that adsorbs NOx. In this example, Cs is contained in the catalyst layer.

In the process, the catalyst obtained in Example 9 and having a total of three catalyst layers on the support was impregnated with Cs acetate as Cs ₂ O to 20 [g / L]. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 28.

(Example 29)
Example 29 is an example of a catalyst layer in which the catalyst layer 1 contains Pt, a catalyst layer 2 in which the catalyst layer 2 contains Rh, a catalyst layer 3 in which the oxide of Fe is present, and a compound that adsorbs NOx. In this example, Ba and Mg are included in the catalyst layer.

  In the process, the catalyst having a total of three catalyst layers on the support obtained in Example 9, a mixed solution of Ba acetate and Mg acetate as BaO was 20 [g / L], and MgO was 5 [g / L]. Impregnation was performed. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Example 29.

(Comparative Example 8)
In Comparative Example 8, the catalyst layer 1 is a catalyst layer containing Pt, the catalyst layer 2 is a catalyst layer containing Rh, and Ba and Mg are contained in the catalyst layer as compounds that adsorb NOx. However, this is an example that does not have a catalyst layer containing an oxide of Fe.

  In the process, the catalyst obtained in Comparative Example 7 having a total of two catalyst layers on the support was impregnated with Ba acetate as BaO to 25 [g / L]. This was dried at 130 [° C.] and then calcined at 400 [° C.] for 1 hour to obtain a catalyst of Comparative Example 8.

  With respect to the exhaust gas purification catalysts of Examples 24 to 29 and Comparative Example 8, the exhaust gas purification performance was examined. The exhaust gas purification performance was evaluated by attaching a carrier carrying a catalyst to the exhaust system of a gasoline engine with a displacement of 3500 [cc], setting the catalyst inlet temperature to 700 ° C., and conducting a durability test for 50 hours. A carrier carrying the catalyst is mounted on the exhaust system of a 2000 cc gasoline engine, and the temperature is 300 [° C] to 350 [° C] and the lean condition (A / F = 25) is 40 [sec. After that, operation was performed for 2 seconds under rich conditions (A / F = 11), and the NOx exhaust purification rate in this section was obtained.

The exhaust gas purification rates of NOx in Examples 24 to 29 and Comparative Example 8 are the same as the noble metal species or oxide metal species of each catalyst layer in the exhaust gas purification catalysts of each Example and Comparative Example, and each Example and Comparative Example. Table 8 shows the average particle diameter of the oxide in the catalyst layer 3 and the NOx absorbent material types contained in the exhaust gas purifying catalysts of the examples and comparative examples. From Table 8, Examples 24-29 containing the compound which is a NOx adsorbent had excellent exhaust gas purification performance even under lean conditions. On the other hand, although the compound which is a NOx adsorbent was included, the comparative example 8 which did not have the catalyst layer containing the oxide of the transition element was inferior in the NOx purification rate than Examples 24-29.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Support | carrier 1a Pore 10 Exhaust-gas purification catalyst 11 1st catalyst layer 12 2nd catalyst layer 13 3rd catalyst layer

Claims (13)

  At least two catalyst layers are stacked, and the catalyst layer includes a catalyst layer containing at least Rh, and a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co}. An exhaust gas purification catalyst comprising: a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} on an upper layer side than the catalyst layer containing at least Rh.   2. The exhaust gas purification catalyst according to claim 1, wherein a catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is in an outermost layer.   The exhaust gas according to claim 2, wherein the catalyst layer containing at least Rh and the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} are in contact with each other. Purification catalyst.   The catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is at least one oxide selected from {Fe, Mn, Ni, Co} included in the catalyst layer. The exhaust gas purification catalyst according to any one of claims 1 to 3, further comprising a compound having an effect of adhering to the catalyst. The exhaust gas purification catalyst according to claim 4, wherein the compound having an effect of adhering at least one oxide selected from {Fe, Mn, Ni, Co} is ZrO ₂ .   The catalyst layer other than the catalyst layer containing at least Rh and the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is a catalyst layer containing at least one of Pt and Pd. The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein   The catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} further contains an oxide having an oxygen absorption / release capability. The exhaust gas purification catalyst according to 1.   The exhaust gas purifying catalyst according to claim 7, wherein the oxide having oxygen absorbing / releasing ability comprises at least one oxide selected from {Ce, Pr, Nd, Y}.   The exhaust gas purification catalyst according to any one of claims 1 to 8, further comprising at least one compound selected from {Ba, Mg, Ca, Na, Cs}.   The exhaust gas purification catalyst according to any one of claims 1 to 9, wherein an average particle diameter of the noble metal is 20 nm or less in the exhaust gas purification catalyst.   The noble metal-containing powder is in contact with the noble metal and the compound having a function of suppressing the movement of the noble metal, the noble metal and the compound are covered, the movement of the noble metal is suppressed, and aggregation due to contact between the compounds is performed. The exhaust gas purification catalyst according to claim 10, comprising an oxide to be suppressed.   The exhaust gas purification catalyst according to claim 3, wherein a thickness of the catalyst layer containing at least one oxide selected from {Fe, Mn, Ni, Co} is 20 µm or less.   The exhaust gas purification catalyst according to any one of claims 1 to 12, wherein a particle diameter of at least one oxide selected from {Fe, Mn, Ni, Co} is 2 µm or less.