JP2006255638A - Catalyst for exhaust-gas cleaning and exhaust-gas cleaning apparatus equipped with the catalyst for exhaust-gas cleaning - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for exhaust-gas cleaning which can prevent solid solution of Pt and Rh and maintain a high catalyst activity even in high temperature atmosphere. <P>SOLUTION: The catalyst for exhaust-gas cleaning has a base material 11, where a plurality of cells 12, in which the exhaust gas can pass, is formed, and at least (1) Rh and (2) Pt and/or Pd as catalytic metals. Cells 14 containing Rh in the inner part of cells of two or more do not have Pt and Pd, and also cells 16 containing Pt or Pd in the inner part do not have Rh. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas discharged from an automobile engine or other internal combustion engine, and an exhaust gas purifying apparatus provided with the exhaust gas purifying catalyst.

Carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO _x ), which are harmful components in exhaust gas discharged from internal combustion engines (engines) of automobiles, are respectively carbon dioxide (CO ₂ ), A so-called three-way catalyst is used as an exhaust gas purifying catalyst that is rendered harmless by changing to steam (H ₂ O) and nitrogen (N ₂ ). The three-way catalyst uses a platinum group metal as a catalyst component. Generally, a suitable porous carrier is coated on the cell wall of a heat-resistant monolith substrate, and a plurality of types of platinum group metals are coated on the carrier. It is used in a supported form.
Of the platinum group metals, platinum (Pt) and palladium (Pd) are particularly excellent in catalytic ability to oxidize CO and HC. On the other hand, rhodium (Rh) is excellent in catalytic ability, especially for reducing the NO _X. Due to such a difference in performance, generally, in a three-way catalyst, Pt and / or Pd and Rh are used in combination as catalyst components. Further, in order to secure more catalytic active sites, a catalyst metal (Pt, Pd, Rh, etc.) in the form of fine particles (for example, the particle size is 50 nm or less, typically 10 nm or less) is used.

As a conventional problem related to such a three-way catalyst, it is possible to suppress solid solution of catalyst metal fine particles or the fine particles and a carrier. The generation and progress of such a solid solution is not preferable because it causes a decrease in the catalytic activity point of the catalytic metal and causes a decrease in the catalytic activity. Particularly in recent years, the exhaust gas temperature has become higher than before due to the high performance of the engine, and accordingly the working temperature of the exhaust gas purifying catalyst has also increased. In such a high-temperature atmosphere (for example, 800 to 1000 ° C.), the catalyst metal fine particles are more easily dissolved.
In this regard, for example, Patent Document 1 discloses exhaust gas purification that employs θ-alumina excellent in high-temperature stability as a carrier for supporting Rh in order to suppress sintering and solid solution of Rh and the carrier in a high-temperature atmosphere. A catalyst for use (three-way catalyst) is described. Patent Document 2 discloses a two-layer structure of a surface layer containing Rh and an inner layer containing Pt and / or Pd in order to suppress solid solution (that is, alloying) between Rh and Pt or Pd in a high-temperature atmosphere. An exhaust gas purifying catalyst having a catalyst layer made of is described.

JP-A-10-277398 JP-A-5-293376

  The present invention is an exhaust gas purifying catalyst capable of preventing solid solution of catalyst metals by an approach different from the prior art as described in Patent Documents 1 and 2 and maintaining high catalytic activity even in a high temperature atmosphere. The purpose is to provide. Another object of the present invention is to provide an exhaust gas purification apparatus using such an exhaust gas purification catalyst.

  The exhaust gas-purifying catalyst provided by the present invention is at least (1) as a base material on which a plurality of cells through which exhaust gas can flow is formed and a catalytic metal (that is, a metal component that exhibits catalytic action; the same shall apply hereinafter). Rhodium and (2) platinum and / or palladium. Among the plurality of cells, a cell containing rhodium inside does not contain platinum and palladium, and a cell containing platinum or palladium inside does not contain rhodium.

  In the exhaust gas purifying catalyst having such a configuration, rhodium (Rh) and platinum (Pt) and / or palladium (Pd) are supported in a state of being separated from each other, and the same cell in the base material. Do not coexist in. As a result, even when used in a high temperature atmosphere, solid solution of (1) Rh and (2) Pt and / or Pd can be physically and completely prevented. As a result, stabilization of the catalyst activity and longer life achieved by the exhaust gas purifying catalyst are realized.

As a preferred embodiment of the exhaust gas-purifying catalyst disclosed herein, a monolith having a structure in which a plurality of cells (typically long hole-shaped cells) having openings at both ends of the base material are aligned in the opening direction. An exhaust gas purifying catalyst which is a base material can be mentioned.
The monolith substrate is a substrate constituted by a large number of cells having the same shape. According to the exhaust gas purifying catalyst employing such a monolith substrate, it is possible to ensure a large total area (that is, a catalyst area) of the cell inner wall (for example, 20 cm ² / cm ^{3 to} 50 cm ² / cm ³ ). In addition, since the shape of the cell is the same, it is easy to make the amount of catalyst metal supported per cell almost constant.

In addition, the present invention provides an exhaust gas purification apparatus provided with the exhaust gas purification catalyst disclosed herein. In other words, the exhaust gas purification device disclosed herein is an exhaust gas purification device including an exhaust pipe through which exhaust gas flows and one or more exhaust gas purification catalysts disposed in the exhaust pipe. Here, the exhaust gas purifying catalyst includes a base material on which a plurality of cells through which exhaust gas can flow is formed, and at least (1) rhodium and (2) platinum and / or palladium as catalyst metals, Among them, a cell containing rhodium does not contain platinum and palladium, and a cell containing platinum or palladium inside does not contain rhodium, and has an exhaust gas purifying catalyst.
The exhaust gas purifying apparatus having such a configuration is equipped with an exhaust gas purifying catalyst disclosed here, that is, an exhaust gas purifying catalyst in which two types of catalyst metals that are easily solidified with each other are separated and supported for each cell. For this reason, under severe conditions (for example, in an atmosphere in which a solid solution of Pt and Rh is likely to be generated, in an atmosphere in which a high-temperature and rich air-fuel ratio (rich) state and a lean air-fuel ratio (lean) state fluctuate). Even if it exists, the solid solution of the catalyst metal components contained in the exhaust gas purifying catalyst can be physically and completely prevented. Thereby, in this apparatus, exhaust gas purification capability is maintained over a long period of time.
Therefore, the exhaust gas purifying apparatus disclosed herein can be mounted on various exhaust gas generation sources (for example, exhaust systems of automobile engines, boilers). In addition, the purifying apparatus has a harmful component (hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NO _x )) over a long period of time in such a use environment without reducing the exhaust gas purification capacity. The purification process can be performed.

In a preferred embodiment of the exhaust gas purifying apparatus disclosed herein, a three-way catalyst is provided downstream of the exhaust gas purifying catalyst in the exhaust pipe, and (1) rhodium and (2) platinum and / or in the same cell. Or the three way catalyst provided with the base material in which the several cell which contains palladium and in which exhaust gas can distribute | circulate was formed is arrange | positioned.
According to the exhaust gas purification apparatus having such a configuration, the exhaust gas purified on the upstream side is further supplementarily purified on the downstream side, so that the exhaust gas purification effect is further improved.
Further, the exhaust gas purification catalyst provided on the downstream side is introduced with a relatively low temperature exhaust gas that has passed through the exhaust gas purification catalyst provided on the upstream side. For this reason, in the exhaust gas purification catalyst provided on the downstream side, even when Rh and Pt and / or Pd coexist in the same cell, the catalyst metals as described above (Rh and Pt and / or Pd) hardly dissolves. Therefore, in the exhaust gas purification apparatus of the present embodiment, a catalyst (three-way catalyst) in a form in which Rh and Pt and / or Pd coexist in the same cell is employed as the exhaust gas purification catalyst disposed on the downstream side of the exhaust pipe. A higher exhaust gas purification effect can be obtained.

The exhaust gas purifying apparatus disclosed herein is not limited to various air-fuel ratio states (theoretical air-fuel ratio (stoichiometric) state) even when the exhaust gas temperature is high (for example, 800 ° C. to 1000 ° C.). Even in such an atmosphere where the rich air-fuel ratio (rich) state and the lean air-fuel ratio (lean) state fluctuate), solid solution of the catalytic metal components is prevented and an excellent catalytic effect is maintained.
Therefore, a preferred embodiment of the exhaust gas purification apparatus disclosed herein is an automobile exhaust gas purification apparatus (for example, a catalytic converter) characterized in that the exhaust pipe is mounted on an exhaust system of an automobile engine.

  Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than the matters specifically mentioned in the present specification (for example, the type of the catalyst metal component, the method of separating and supporting the cell catalyst metal component of the catalyst base material) and matters necessary for the implementation of the present invention ( For example, a method of coating a cell wall of a catalyst substrate with a powdery porous support) can be understood as a design matter for those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

First, the base material constituting the exhaust gas purifying catalyst of the present invention will be described.
The substrate used for the exhaust gas purifying catalyst of the present invention has a plurality of cells (sections) through which exhaust gas can flow. Typically, adjacent cells are separated from each other by a partition wall. Various porous materials can be used as a base material. As a base material shape preferably applied to the exhaust gas purifying catalyst disclosed herein, cells having openings at both ends (typically long hole-shaped cells) are mutually connected. Examples include a so-called monolithic base material having a structure in which a plurality of openings are aligned in the opening direction.
When such a monolith substrate is applied, the material is not particularly limited as long as it has heat resistance. Typically, a ceramic monolith substrate composed of cordierite, mullite, α-alumina, silicon carbide, etc., and a metal monolith substrate composed of ferrite stainless steel (Fe—Cr—Al), etc. Broadly divided into materials. In particular, a monolith substrate made of a heat-resistant ceramic mainly composed of cordierite is excellent in strength due to temperature change and can be used stably in a high temperature (for example, 800 ° C. to 1200 ° C.) atmosphere. It is suitable as a base material for an exhaust gas purification catalyst disposed in the system.

The cells formed on the substrate are not particularly limited as long as the exhaust gas can flow and the cells are blocked by the partition walls. A preferable example of the cell structure is a honeycomb structure. Here, the honeycomb (honeycomb) structure means an integrated structure composed of a plurality of through-holes partitioned by partition walls and the partition walls, and the cross-sectional shape of the holes (that is, the cross-sectional shape of the cells) is not particularly limited. , Square, rectangle and hexagon. The substrate having such a honeycomb structure may have cells formed at a high density of, for example, 200 to 600 cells / in ² (about 30 to 92 cells / cm ² ). For example, for a cylindrical monolith substrate having a substrate diameter of approximately 100 mm (eg, 103 mm), the cell density can be about 400 cells / in ² (62 cells / cm ² ).
Such a honeycomb-structured substrate (typically a monolith substrate) can ensure a large cell wall surface area (for example, 20 cm ² / cm ^{3 to} 50 cm ² / cm ³ ), and has a wider catalyst area. Since it is obtained, it is preferable.

In the exhaust gas purifying catalyst disclosed herein, various carriers are used in order to efficiently carry a large amount of catalytic metal on the base material, as in the conventional exhaust gas purifying catalyst. Preferably, a high surface area porous carrier is used. Porous supports made of various materials used in conventional three-way catalysts can be used. Examples thereof include alumina, silica, silica-alumina composite oxide, titania, zirconia, zeolite, ceria, and ceria-zirconia composite oxide. One or two or more of these are used depending on the catalyst metal species to be supported.
For example, ceria-zirconia composite oxide (CZ) is preferably used as a porous carrier for supporting Pt, Pd, or Rh because of its excellent oxygen storage capacity and excellent high-temperature stability. In order to obtain a large catalyst area, the porous carrier preferably has a powder shape having a high specific surface area (for example, 10 to 1000 m ² / g, typically 100 to 500 m ² / g).

  The porous support (preferably in powder form) is coated in the cell (inner wall) of the base material to form a catalyst support layer. As a typical method for forming the catalyst support layer, for example, a powdered porous support, water, and a slurry containing appropriate secondary components (for example, an inorganic or organic binder) as required are applied to the cell walls in the substrate. (Preferably, a part of the substrate is immersed in the slurry), and the drying step is repeated a plurality of times, followed by heating and baking. Moreover, you may form the catalyst support layer which consists of said various oxide by the general sol-gel method.

Next, the catalytic metal component used in the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purifying catalyst disclosed herein comprises Rh having a high reduction activity of nitrogen oxide (NO _x ) and Pt and / or Pd having a high oxidation activity of carbon monoxide (CO) and hydrocarbon (HC). At least as catalyst metal. The catalyst metal loading method may be carried out by appropriately selecting conventional techniques. For example, after impregnating the catalyst support layer with a compound solution containing a metal element constituting the catalyst, the compound is decomposed by firing, and the metal (catalyst metal) is supported on the catalyst support layer. According to such a supporting method, the catalyst metal can be supported in a very fine particle shape (for example, a particle size of 50 nm or less, typically a particle size of 10 nm or less). For this reason, even if it is a small amount of loading, the specific surface area becomes large and a wide catalyst area is realized. Further, in the exhaust gas purifying catalyst disclosed herein, the cell containing Rh in the inner (inner wall) does not contain Pt and / or Pd, and the cell containing Pt and / or Pd in the inner (inner wall) The catalyst metal is supported on each cell so that Rh is not contained. For example, a part of the cell opening surface of the monolith substrate is closed and Rh is supported inside the open cell. Next, while closing the opening surface of the Rh carrying cell, the covered cell opening surface may be opened during the Rh carrying treatment, and Pt or Pd may be carried inside the cell.

The amount of the catalyst metal supported is not particularly limited as long as it is appropriately determined according to the conditions of exhaust gas discharged from the exhaust gas generation source (for example, temperature and the composition ratio of harmful components). For example, in an exhaust gas purifying catalyst used in an automobile engine, the ratio of Pt and Pd excellent in oxidation catalytic ability of carbon monoxide (CO) and hydrocarbon (HC) (for example, Pt and Pd in the total supported amount of catalyst metal) The ratio (mass ratio) of 3/5 to 9/10) is excellent in the reduction catalytic ability of nitrogen oxides (NO _x ) (for example, the ratio (mass ratio) of Rh occupying the total supported amount of catalyst metal is 1). The content ratio of the catalytic metal can be determined to exceed / 10 to 2/5).
When mounted on the exhaust system of an automobile engine, when mounted on a sports car type equipped with an engine with good acceleration performance, it is effective for the oxidation catalytic ability of carbon monoxide (CO) and hydrocarbon (HC). The amount of Pt and / or Pd supported can be increased, and the proportion of Pt and / or Pd supported cells in the catalyst base can be increased accordingly. In addition, when mounted on an eco-car or the like equipped with an engine having a moderate acceleration performance, the ratio of the supporting cells is changed to increase the effective amount of Rh supported for the reduction catalytic ability of nitrogen oxides (NO _x ). be able to.
There is no particular limitation on the distribution (positional relationship) of the catalyst metal (Rh, Pt and / or Pd) supporting cells on the substrate. For example, in the cross section of the substrate, the Rh-supporting cells and the Pt and / or Pd-supporting cells may be arranged in a lattice pattern, or the Rh-supporting cells and the Pt and / or Pd-supporting cells are alternately arranged. You may make it distribute in concentric form. Further, the Rh carrying cell and the Pt and / or Pd carrying cell may be arranged so as to spread radially with respect to the center of the cross section.

The separation and loading of the catalyst metal for each cell can be performed, for example, by performing the following steps. That is:
(First step) Cover both end faces corresponding to the cell openings of a monolith substrate having a structure in which a plurality of cells, to which a catalyst carrier layer has been applied in advance, are aligned in the opening direction, with an appropriate mask material. The inner space of the cell is sealed. Examples of the mask material include a liquid agent mainly composed of a thermosetting resin such as an epoxy resin, but may be a sheet made of a thermoplastic resin (for example, polyethylene or polypropylene). Such a sheet-like mask material can easily block the end face of the substrate by heat welding.
(2nd process) By irradiating a laser to the both end surfaces of the said base material, the mask material which covers the cell opening part which is going to carry | support Pt and / or Pd is selectively removed, and the said cell is exposed.
(Third step) The cell exposed in the second step is impregnated with a Pt compound solution and / or a Pd compound solution, and then fired to selectively carry Pt and / or Pd on the cell. The mask material is decomposed during firing.
(Fourth step) As in the first step, both end faces of the base material are again covered with a mask material.
(Fifth step) By irradiating the both end faces of the base material with laser, the mask material covering the cell opening to be loaded with Rh is selectively removed to expose the cell.
(Sixth Step) The cell exposed in the fifth step is impregnated with the Rh compound solution, and then fired to selectively carry Rh on the cell.

In addition, the metal compound (Rh compound, Pt compound, Pd compound, etc.) used here is a catalyst carrier layer composed of a porous carrier formed on the substrate surface or the cell inner wall of the substrate in advance by a wash coat method or the like. For the purpose of supporting the catalyst metal, a metal compound that has been conventionally used may be used and is not particularly limited. For example, as the Rh (rhodium) compound, rhodium nitrate, rhodium chloride or the like is preferably used. Further, as the Pt (platinum) compound, dinitrodiammine platinum, hexachloroplatinic acid hexahydrate, tetraamminedichloroplatinum, an organic platinum aqueous solution, or the like is preferably used. As the Pd (palladium) compound, palladium nitrate, palladium chloride, dinitrodiammine palladium, tetraammine palladium dichloride, or the like is preferably used.
Moreover, what is necessary is just to set the baking conditions after metal solution immersion according to the decomposition temperature of each metal solution (catalyst metal compound). In general, when carried out under firing conditions in the temperature range of 500 to 1000 ° C., most of the catalyst metal component compounds are decomposed, and the fixability of the catalyst metal to the porous carrier constituting the catalyst carrier layer is good. . Note that, under such heating conditions, the polymer mask material is also preferable because it can be decomposed and disappeared well.

In the above-described method, the separation method using the mask material and the laser irradiation is given in the separation and support for each catalyst metal component, but the method is not limited to this method.
For example, a mask material made of a photosensitive polymer (for example, a material mainly composed of phenol resin, polyvinyl alcohol resin, or polyvinyl pyrrolidone resin) is used, and the photosensitive polymer is selectively solidified by irradiation with light such as ultraviolet rays or excimer laser. (Photoresist method) can be used.

Next, an exhaust gas purification apparatus using the exhaust gas purification catalyst disclosed herein will be described.
The exhaust gas purifying apparatus disclosed herein is an apparatus provided for purifying exhaust gas discharged from various exhaust gas generation sources (internal combustion engines such as automobile engines and boilers). The exhaust gas purification apparatus includes an exhaust pipe through which exhaust gas flows and an exhaust gas purification catalyst that purifies gas flowing through the exhaust pipe. Here, the exhaust gas purifying catalyst of the present invention is provided as an exhaust gas purifying catalyst in the exhaust pipe. Further, in the exhaust gas purifying catalyst disclosed here, the Rh carrying cell and the Pt and / or Pd carrying cell are physically completely separated. For this reason, even when used at a high temperature, solid solution of Rh and Pt or solid solution of Rh and Pd does not occur. Therefore, in the exhaust gas purification apparatus disclosed here, it is preferable to dispose the exhaust gas purification catalyst of the present invention upstream of the exhaust pipe into which high-temperature exhaust gas is introduced.

Preferably, a general three-way catalyst that has been conventionally used is disposed downstream of the exhaust pipe (that is, downstream of the exhaust gas purifying catalyst of the present invention). Here, the general three-way catalyst refers to a catalyst in which Rh and Pt and / or Pd are contained together in the same cell of the catalyst base. In the purification apparatus of this aspect, in the three-way catalyst provided on the downstream side, the exhaust gas temperature decreases until it reaches the catalyst from the exhaust gas generation source. As a result, the exhaust gas at a relatively low temperature (for example, 400 to 500 ° C.) Will be processed. Under such a low temperature condition, even if Rh and Pt and / or Pd coexist in the same cell, solid solution hardly occurs and the catalytic effect is hardly reduced. Therefore, the exhaust gas can be effectively purified by disposing the exhaust gas purifying catalyst of the present invention upstream and disposing a general three-way catalyst downstream.
In addition, in the exhaust gas purifying catalyst (that is, the exhaust gas purifying catalyst according to the present invention) arranged on the upstream side, the porous carrier and the catalyst metal that constitute the catalyst carrier layer under a relatively high temperature condition (for example, 800 ° C. or higher). From the viewpoint of preventing sintering, it is preferable to use a ceramic that is stable at high temperatures (that is, difficult to cause sintering), such as ceria-zirconia composite oxide, as a porous carrier, and exhaust gas purification disposed downstream From the viewpoint of preventing sintering of the porous support and the catalyst metal constituting the catalyst support layer under relatively low temperature conditions (for example, less than 800 ° C.), the catalyst for use (for example, the above-described three-way catalyst) is alumina or the like. It is preferable to use a ceramic that is stable in a low temperature range as a porous carrier.

  Hereinafter, an embodiment of the exhaust gas purifying catalyst and the exhaust gas purifying apparatus of the present invention will be described with reference to the drawings. It should be noted that the present invention is not intended to be limited to the forms shown in the following description and related drawings.

<Example 1: Preparation of exhaust gas purification catalyst>
FIG. 1 schematically shows an exhaust gas purifying catalyst 10 according to this embodiment. The exhaust gas-purifying catalyst 10 includes a cylindrical monolith substrate 11 having a structure in which a plurality of long hole-shaped cells 12 having openings at both ends are aligned in the opening direction. As shown in the figure, the substrate 11 has a honeycomb structure in which cells 12 having a substantially square cross-sectional shape are densely arranged. In the exhaust gas purifying catalyst 10 having such a structure, the exhaust gas is introduced into each cell 12 from one opening end face of the exhaust gas purifying catalyst, the component to be treated in the exhaust gas is purified when passing through the cell 12, and the other The purified gas flows out from the opening end face.
Specifically, the exhaust gas-purifying catalyst 10 according to the present embodiment is a porous carrier (hereinafter abbreviated as “CZ carrier”) made of ceria-zirconia (CeO—ZrO ₂ ) composite oxide on the inner wall of the cell 12. Is an exhaust gas-purifying catalyst 10 in which Pt and Rh are supported on a cordierite monolith substrate of 400 cells / in ² (about 62 cells / cm ² ) coated with. As shown in FIG. 2, the exhaust gas purifying catalyst 10 according to this embodiment includes a cell 14 containing Rh but not containing Pt, and a cell 16 containing Pt inside but not containing Rh. 2 schematically shows a Pt and rhodium support pattern. In FIG. 2, the cell 14 containing Rh is shown by shading, and the cell 16 containing Pt is shown by a solid color (outlined).

The exhaust gas-purifying catalyst 10 was produced by the following procedure. That is, a cordierite monolith substrate (400 cells / square inch, 1 liter capacity) is immersed in a slurry containing a powdered CeO—ZrO ₂ composite oxide based on a general washcoat method, and then dried. And by carrying out calcination (about 400 ° C.), a catalyst carrier layer composed of a CZ carrier was formed inside the cell (inner wall) of the substrate.
Next, an epoxy resin as a mask material was applied to both end faces of the monolith substrate 11 and dried to coat the cell openings. Next, a predetermined laser was applied to the opening surface (that is, the surface covered with the mask material) of the cell 16 (FIG. 2) that is to carry Pt, and the mask material was selectively removed. As a result, only the Pt carrying cell 16 was exposed. Then, the base material 11 is immersed in a dinitroammine platinum solution whose concentration is adjusted so that 2 g of Pt is supported on the exposed Pt supporting cell 16 as a whole, and the catalyst carrier layer is impregnated with the solution. It was. Thereafter, a baking process was performed at 550 ° C. for 2 hours, and Pt was selectively supported on the Pt supporting cell 16. Note that the mask material was completely decomposed and disappeared by the firing.

  After the loading of Pt was completed, both end surfaces of the base material 11 were again covered with a mask material. Then, in the same manner as the above Pt carrying process, a predetermined laser is irradiated to the opening surface (that is, the surface covered with the mask material) of the cell 14 (FIG. 2) where Rh is to be carried to select the mask material. Removed. As a result, only the Rh carrying cell 14 was exposed. Then, the base material 11 is immersed in a rhodium nitrate solution whose concentration is adjusted so that 0.5 g of Rh is supported on the entire base material 11 in the exposed Rh-supporting cell 14, and the catalyst carrier layer is impregnated with the solution. I let you. Thereafter, firing was performed at 550 ° C. for 2 hours, and Rh was selectively supported on the Rh-supporting cell 14. Note that the mask material was completely decomposed and disappeared by the firing. The exhaust gas purifying catalyst 10 according to this example was obtained by the above procedure.

<Comparative example: Production of exhaust gas purification catalyst (general three-way catalyst)>
Next, using the same monolith substrate as in the above example, a three-way catalyst in a form (for comparison) in which Rh and Pt coexist in the same cell was produced. The production procedure is as follows.
A base material in which a catalyst carrier layer composed of a CZ carrier was formed in the cell in the same manner as in Example was prepared. Next, the substrate is immersed in a mixed solution containing dinitroammineplatinum and rhodium nitrate, the concentration of which is adjusted so that Pt (equivalent to 2 g) and Rh (equivalent to 0.5 g) are supported in the cell of the monolith substrate. The catalyst support layer was impregnated with the solution. Thereafter, baking treatment was performed at 550 ° C. for 2 hours, and Pt and Rh were supported on all the cells.

  Next, an exhaust gas purification apparatus for an automobile engine equipped with the exhaust gas purification catalyst according to the above example and the three-way catalyst according to the comparative example was constructed, and the exhaust gas purification performance (catalyst performance) was evaluated.

<Example 2: Construction of exhaust gas purification device>
FIG. 3 schematically shows the configuration of the exhaust gas purification apparatus 20 according to the present embodiment. As shown in the figure, an exhaust gas purification apparatus 20 according to the present embodiment includes an exhaust pipe 24 that is a part of an exhaust system of an automobile engine 22 and two catalyst housing portions 24A formed in a part of the exhaust pipe 24. The exhaust gas purifying catalysts 10 and 30 are respectively housed in 24B. The exhaust gas purifying catalyst 10 according to the present embodiment is provided in the catalyst accommodating portion 24A on the upstream side of the exhaust pipe 24, and the three-way catalyst 30 according to the comparative example is provided in the downstream catalyst accommodating portion 24B. is doing.

<Comparative example 2: Construction of exhaust gas purification device>
An exhaust gas purification apparatus having the same configuration as that of Example 2 was constructed, except that the catalyst accommodating portion 24A on the upstream side of the exhaust gas purification apparatus according to the above example was also equipped with the three-way catalyst 30 according to the above comparative example.

<Catalyst durability test>
The above two exhaust gas purification apparatuses were mounted on an actual exhaust system of an automobile engine, and the durability test of the exhaust gas purification catalyst according to this example was performed. That is, the automobile in which the exhaust gas purification device is mounted in the engine exhaust system was repeatedly stopped, accelerated and decelerated in the cycle mode shown in FIG. Thereby, the fluctuation | variation of a rich state and a lean state is implement | achieved. This was continued for 100 hours. After such continuous operation, the exhaust gas purification catalyst (that is, the exhaust gas purification catalyst according to Example 1 and the three-way catalyst according to Comparative Example 1) mounted in the upstream side catalyst housing unit is taken out from each exhaust gas purification device, Catalyst metal was collected from the inner cell wall of the substrate. In addition, about the exhaust gas purifying catalyst which concerns on Example 1, the catalyst metal was extract | collected separately from both Pt carrying | support cell and Rh carrying | support cell.
The lattice constant of each catalytic metal component collected after the durability test was determined from the position (angle) of the diffraction peak obtained by XRD (X-ray diffraction method), and a standard sample of Pt and Rh (JCPDS (Joint Committee of Powder Diffraction Standards) The presence or absence and progress of solid solution (alloying) were evaluated from the change in the lattice constant compared to the lattice constant on the card basis.

FIG. 5 shows a catalyst metal sampled from the Pt-supporting cell of the exhaust gas purifying catalyst according to Example 1 (Example Pt in the drawing), a catalyst metal sampled from the Rh-supporting cell (Example Rh in the drawing), and a comparative example. 1 shows lattice constants of catalytic metals (comparative examples in the figure) collected from the cell of the exhaust gas purifying catalyst according to No. 1; The lattice constants of Pt and Rh in the JCPDS card standard are Pt: 3.9231Å and Rh: 3.8031Å, respectively.
In the exhaust gas purifying catalyst according to Example 1 mounted on the upstream side of the exhaust gas purifying device, each catalytic metal component (Pt and Rh) is supported in a separate cell, so the solid solution of Pt and Rh is None of the lattice constants of Pt and Rh changed. On the other hand, in the three-way catalyst according to Comparative Example 1 mounted on the upstream side of the exhaust gas purification apparatus, it can be seen that the lattice constant is changed from the standard one, indicating an intermediate value between Pt and Rh. It is thought that solid solution (alloying) occurred because each catalytic metal component (Pt and Rh) coexisted in the same cell under high temperature conditions (high exhaust gas temperature) on the upstream side.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, in the above embodiment, the exhaust gas purifying catalyst carrying Pt and Rh has been described. However, an exhaust gas purifying catalyst containing another catalytic metal component may be used. For example, an exhaust gas purifying catalyst containing Pd instead of Pt may be used.
Further, the properties of the base material are not limited to cordierite monolith base materials, but can be applied to other ceramic or metal monolith base materials such as stainless steel alloys and pipe-type base materials.
In addition to the main catalytic metals such as Rh, Pt, and Pd, it is possible to add secondary elements that improve catalytic performance to the exhaust gas purification catalyst. For example, in the exhaust gas purification catalyst, it is possible to add a secondary component selected from alkali metals, alkaline earth metals, and rare earth elements that improve the storage effect of NO _x , HC, CO, and the like.

In the above embodiment, a catalyst carrier layer composed of a porous carrier is formed in advance in the cell of the base material, and then the catalyst metal is introduced and supported in the cell. However, the present invention is not limited to this method. For example, the catalyst metal may be supported in the cell by introducing a slurry containing a powdery porous carrier on which the catalyst metal is previously supported into the cell of the base material and performing firing or the like.
It should be noted that the technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

It is the perspective view which showed typically one Example of the catalyst for exhaust gas purification. It is the II-II sectional view taken on the line of FIG. It is the block diagram which showed typically one Example of the exhaust gas purification apparatus. It is a graph which shows the motor vehicle operation mode (engine operation mode) in a durability test. It is a graph which shows the change of the lattice constant of a catalyst metal component after a durability test.

Explanation of symbols

10 Exhaust gas purification catalyst 12 cell 20 Exhaust gas purification device 24 Exhaust pipe 30 Three-way catalyst

Claims (3)

A base material on which a plurality of cells through which exhaust gas can flow is formed;
An exhaust gas purifying catalyst comprising at least (1) rhodium and (2) platinum and / or palladium as catalytic metals,
The exhaust gas-purifying catalyst, wherein a cell containing rhodium inside does not contain platinum and palladium, and a cell containing platinum or palladium inside does not contain rhodium. An exhaust gas purification apparatus comprising an exhaust pipe through which exhaust gas circulates and one or more exhaust gas purification catalysts disposed in the exhaust pipe, wherein the exhaust gas purification catalyst,
A base material on which a plurality of cells through which exhaust gas can flow is formed;
Comprising at least (1) rhodium and (2) platinum and / or palladium as catalytic metals,
The exhaust gas purifying apparatus, wherein a cell containing rhodium inside does not contain platinum and palladium, and a cell containing platinum or palladium inside does not contain rhodium.   A plurality of cells which are three-way catalysts downstream of the exhaust gas purifying catalyst in the exhaust pipe and contain (1) rhodium and (2) platinum and / or palladium in the same cell and which can flow exhaust gas The exhaust gas purifying apparatus according to claim 2, further comprising a three-way catalyst including a base material on which is formed.

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