JP2019173583A - Exhaust emission control device for vehicle - Google Patents

Abstract

An exhaust gas purifying apparatus for a vehicle is provided that improves both the heating efficiency and the exhaust gas purification rate at a high temperature. An exhaust gas purifying catalyst having a base material and a coating layer containing a microwave absorbing material and a noble metal-supported catalyst coated on the base material, and a microwave positioned in front of the exhaust gas purifying catalyst with respect to a flow direction of the exhaust gas. An exhaust gas purifying apparatus for a vehicle, comprising: a microwave generator for heating a microwave absorbing material, wherein the microwave absorbing material includes silicon carbide (SiC), and the noble metal-supported catalyst is platinum (Pt), palladium. The exhaust gas purifying apparatus for a vehicle, including at least one selected from the group consisting of (Pd) and rhodium (Rh), wherein the coat layer further includes nickel oxide (NiO) and / or chromium (III) oxide (Cr2O3). About. [Selection diagram] FIG.

Description

  The present invention relates to an exhaust gas purifying apparatus for a vehicle, and more particularly to an exhaust gas purifying apparatus for a vehicle including an exhaust gas purifying catalyst including a microwave absorber and a noble metal-supported catalyst and a microwave generator.

  Exhaust gas discharged from internal combustion engines such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). These harmful components are exhaust gas purification catalysts. It is discharged into the atmosphere after being purified by

  The temperature of the exhaust gas purification catalyst necessary for purifying harmful components is generally 200 ° C. or higher. Therefore, the heat of the exhaust gas is used for heating the exhaust gas purification catalyst.

  However, when the temperature of the exhaust gas purification catalyst does not reach the temperature required for purification, such as immediately after a cold start of the engine, the activity of the exhaust gas purification catalyst is insufficient, and unpurified harmful components (also called cold emission) ) May be discharged into the environment. In addition, automobiles that take environmental performance into account in recent years tend to lower the exhaust gas temperature as the engine becomes more thermal efficient and fuel-efficient, so even if the exhaust gas heat is used, the temperature of the exhaust gas purification catalyst May not be heated to the temperature required for purification.

  In order to solve such a problem, for example, Patent Document 1 is provided on the inner surface of a hole of a base material that is irradiated with microwaves and circulates exhaust gas through a plurality of holes formed inside. A catalyst material for purifying exhaust gas, comprising magnetic oxide particles that can generate heat by absorbing microwaves, and a catalyst-supporting coating material that covers the surface of the magnetic oxide particles, A catalyst material for microwave heating is disclosed, wherein the catalyst-supporting coating material includes a catalyst-supporting oxide and at least one of Pt, Pd, and Rh supported on the catalyst-supporting oxide. In addition, a three-way catalyst is exemplified as a catalyst material for microwave heating, and further, in the magnetic oxide particles, by prescribing a Curie temperature at which heating by microwaves stops autonomously, noble metal particles It is described to suppress the deterioration of catalyst performance due to sintering.

JP, 2006-187766, A

  However, the conventional techniques such as Patent Document 1 have room for improvement from the viewpoint of effectively absorbing microwaves and generating heat.

  Therefore, an object of the present invention is to provide a vehicle exhaust gas purification device that improves both the heating efficiency and the exhaust gas purification rate at a high temperature.

  In an engine equipped with a microwave generation (heating) device for improving warm-up performance, silicon carbide (SiC) has a high dielectric loss factor, excellent microwave absorption characteristics, and even in high-temperature exhaust gas. Since deterioration of microwave absorption is small, it is used as a microwave absorber for exhaust gas purification catalysts.

FIG. 1 shows the temperature rise (temperature rise) of each material when each material (25 g) is irradiated with microwaves (500 W, 10 seconds). From FIG. 1, for example, iron oxide (Fe ₃ O ₄ ) exhibits a large temperature rising effect by microwave irradiation, but when the temperature reaches 500 ° C., the temperature rising effect decreases. On the other hand, SiC maintains a good temperature rising effect even in high temperature exhaust gas.

  However, it has been found that SiC contained in the exhaust gas purification catalyst deteriorates the performance of the exhaust gas purification catalyst by poisoning and degrading noble metals when an actual machine durability test is performed at a high temperature of 900 ° C. or higher.

Therefore, as a result of examining various means for solving the above problems, the inventor of the present invention uses a SiC as a microwave absorber in a vehicle exhaust gas purification apparatus including an exhaust gas purification catalyst that performs heating by microwaves. By using the transition metal oxides nickel oxide (NiO) and / or chromium (III) oxide (Cr ₂ O ₃ ) with SiC, noble metals, especially palladium (Pd) and / or rhodium (Rh) The inventors have found that poisoning deterioration can be suppressed and completed the present invention.

That is, the gist of the present invention is as follows.
(1) An exhaust gas purification catalyst having a base material and a coating layer containing a microwave absorbing material and a noble metal-supported catalyst coated on the base material;
A microwave generator for heating the microwave absorber located in front of the exhaust gas purification catalyst with respect to the flow direction of the exhaust gas;
An exhaust gas purification apparatus for a vehicle comprising:
The microwave absorber comprises silicon carbide (SiC);
The noble metal-supported catalyst includes at least one selected from the group consisting of platinum (Pt), palladium (Pd), and rhodium (Rh);
The vehicle exhaust gas purification apparatus, wherein the coating layer further includes nickel oxide (NiO) and / or chromium oxide (III) (Cr ₂ O ₃ ).

  According to the present invention, it is possible to provide a vehicle exhaust gas purification device that improves both the heating efficiency and the exhaust gas purification rate at a high temperature.

It is a figure which shows the raise temperature (temperature rise) of each material at the time of irradiating each material (25g) with a microwave (500W, 10 second). It is a figure which shows one Embodiment of the exhaust gas purification apparatus for vehicles of this invention. It is a figure which shows the temperature rising result of Examples 1 and 2 and Comparative Examples 1-5. It is a figure which shows CO adsorption amount of Examples 1 and 2 and Comparative Examples 1-5.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present specification, features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the size and shape of each part are exaggerated for clarity, and the actual size and shape are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the size and shape of each part shown in these drawings. The vehicle exhaust gas purification apparatus of the present invention is not limited to the following embodiments, and various modifications and improvements can be made by those skilled in the art without departing from the spirit of the present invention. Can be implemented.

The present invention relates to an exhaust gas purification catalyst having a base material and a coating layer containing a microwave absorber and a noble metal-supported catalyst coated on the base material, and a micro located in front of the exhaust gas purification catalyst with respect to the flow direction of the exhaust gas. An exhaust gas purifying device for a vehicle comprising a microwave generator for heating a wave absorber, wherein the microwave absorber includes silicon carbide (SiC), and the noble metal-supported catalyst is platinum (Pt), palladium The vehicle includes at least one selected from the group consisting of (Pd) and rhodium (Rh), and the coating layer further includes nickel oxide (NiO) and / or chromium (III) oxide (Cr ₂ O ₃ ). The present invention relates to an exhaust gas purification device.

  In the present invention, the base material is a material to which a coating layer is applied, for example, but not limited to, a base material having a known honeycomb shape, for example, a honeycomb-shaped monolith base material, and the cell shape is hexagonal, square, etc. It is. Examples of the material of the base material include ceramics such as cordierite, silica, alumina, mullite, and silicon carbide other than metals that reflect microwaves. The number of cells of the honeycomb-shaped monolith substrate is not limited, but is usually 300 to 900 per square inch, preferably 400 to 750 per square inch. In the present invention, it is preferable to use a honeycomb-shaped monolith substrate made of cordierite having 400 to 750 cells per square inch as the substrate.

  The length of the substrate in the flow direction of the exhaust gas is not limited, but is usually 40 mm to 120 mm, preferably 50 mm to 90 mm.

  The diameter of the exhaust gas inlet of the base material (when the shape of the exhaust gas inlet of the base material is not a circle, the equivalent circle diameter) can be appropriately changed according to the desired catalyst capacity and is not limited, but is usually 40 mm. ˜120 mm, preferably 50 mm to 110 mm.

  Although the capacity | capacitance of a base material is not limited, Usually, 0.3L-1.2L, Preferably it is 0.4L-0.8L.

  By using the material described above as the base material, a sufficient exhaust gas flow path for purifying the exhaust gas is secured, and the reaction with the catalyst component applied to the base material is secured. Moreover, the component which absorbs a microwave is hold | maintained similarly to a catalyst component, and temperature rising is ensured.

  In the present invention, the coating layer coated on the substrate includes a microwave absorber and a noble metal-supported catalyst.

  A microwave absorber is a material that absorbs microwaves, converts them into heat, and generates heat. In the present invention, the microwave absorber includes silicon carbide (SiC), for example, β-SiC. The microwave absorber is preferably SiC.

  The microwave absorber may include other microwave absorbers. Examples of other microwave absorbers include, but are not limited to, perovskite complex oxides such as lanthanum (La) and cobalt (Co). There are composite oxides, strontium (Sr) / cobalt composite oxides, lanthanum / strontium / cobalt composite oxides, ferrite (including iron oxide), manganese oxide, cobalt oxide, zirconium boride and the like.

  The amount of the microwave absorbing material is not limited, but is usually 5% to 50% by weight, preferably 10% to 20% by weight, based on the total weight of the exhaust gas purification catalyst.

  Although the particle size of a microwave absorber is not limited, Usually, 0.1 micrometer-10 micrometers, Preferably they are 0.5 micrometer-5 micrometers.

The specific surface area by BET of microwave absorbing material is not limited, usually ^{2m 2} / ^g~100m 2 / g, preferably from ^{5m 2} / ^g~30m 2 / g.

  When the microwave absorbing material contains SiC, the microwave absorbing material can efficiently absorb the microwave irradiated from the microwave generator and convert it into heat.

  The noble metal supported catalyst is a catalyst in which a noble metal is supported on a carrier.

Here, the carrier is a material supporting a noble metal that functions as a main catalyst, and is not limited to, for example, a metal oxide such as aluminum oxide (Al ₂ O ₃ , alumina), cerium oxide (CeO ₂ , ceria). ), Zirconium oxide (ZrO ₂ , zirconia), silicon oxide (SiO ₂ , silica), yttrium oxide (Y ₂ O ₃ , yttria), neodymium oxide (Nd ₂ O ₃ ), and composite oxides thereof. . In the present invention, it is preferable to use a composite oxide of CeO ₂ and ZrO ₂ and Al ₂ O ₃ as the support.

  A noble metal is a material that functions as a main catalyst capable of purifying harmful components in exhaust gas. In the present invention, the noble metal includes at least one selected from the group consisting of platinum (Pt), palladium (Pd), and rhodium (Rh). Other precious metals may include, for example, but are not limited to, gold (Au), silver (Ag), iridium (Ir), ruthenium (Ru), and mixtures thereof.

  The amount of the noble metal supported on the carrier is not limited, but is usually 0.2% to 2.0% by weight, preferably 0.4% to 1.0% by weight based on the total weight of the carrier in terms of noble metal. %.

  The amount of the noble metal-supported catalyst is not limited, but is usually 35% to 60% by weight, preferably 45% to 56% by weight, based on the total weight of the exhaust gas purification catalyst.

  The noble metal supported catalyst can be produced by a conventional production method. For example, the noble metal-supported catalyst is dispersed uniformly in water at 5 ° C. to 30 ° C. while adding a support and a noble metal precursor such as a noble metal hydrochloride or nitrate, and stirring with a stirrer. It is produced by drying such as evaporation to dryness, optionally pulverization, and further firing in the atmosphere at, for example, 450 ° C. to 550 ° C. for 0.5 to 1.5 hours. Conventional pulverization techniques such as a mortar, a hammer mill, a ball mill, a bead mill, a jet mill, and a roller mill can be used for pulverization regardless of whether they are dry or wet.

  By using the material described above as the noble metal-supported catalyst, harmful components in the exhaust gas can be efficiently purified.

The coating layer further includes nickel oxide (NiO) and / or chromium oxide (III) (Cr ₂ O ₃ ) in addition to the microwave absorber and the noble metal-supported catalyst. In addition to the microwave absorber and the noble metal-supported catalyst, the coating layer preferably further includes NiO that itself absorbs microwaves, converts them into heat, and generates heat.

The amount of NiO and / or Cr ₂ O ₃ is not limited, but the weight ratio of SiC to NiO and / or Cr ₂ O ₃ (SiC: NiO and / or Cr ₂ O ₃ ) is usually 9: 1-7: 3, preferably 17: 3 to 4: 1.

In other words, the amount of NiO and / or Cr ₂ O ₃ is usually 1% to 9% by weight, preferably 2% to 6% by weight, based on the total weight of the exhaust gas purification catalyst.

When the microwave absorbing material further contains NiO and / or Cr ₂ O ₃ in addition to the microwave absorbing material and the noble metal-supported catalyst, the poisoning deterioration of the noble metal can be suppressed. Although this effect is guessed as follows, this invention is not limited by the following guess.

S as a microwave absorber in the coating layer of the exhaust gas purification catalyst heated by microwaves
When iC is included, the SiC surface is oxidized at a high temperature of 700 ° C. or higher to generate SiO ₂ . The generated SiO ₂ film protects the internal SiC, thereby improving the oxidation resistance of SiC. However, when the temperature further rises to 1600 ° C. or higher, SiO ₂ cannot exist stably and decomposes and evaporates into gaseous SiO (SiO vapor). When SiC and the noble metal are close to each other, even if the contact point between the SiC and the noble metal does not reach 1600 ° C. or higher, a part of SiO ₂ is decomposed and becomes SiO vapor, which can poison the noble metal. Since this phenomenon occurs only in the surface layer of SiC, there is no change in the crystal structure of the entire SiC.

In such a situation where SiC and noble metal are close to each other and SiO vapor is generated from SiC, if a transition metal oxide such as NiO and / or Cr ₂ O ₃ is present near the contact point of SiC and noble metal, the generated SiO The vapor reacts with NiO and / or Cr ₂ O ₃ in proximity to the noble metal to form a composite oxide. That is, NiO and / or Cr ₂ O ₃ can suppress poisoning deterioration of noble metals by trapping SiO vapor. Here, when NiO is added, Ni ₂ SiO ₄ is generated, and when Cr ₂ O ₃ is added, Cr ₂ SiO ₄ is generated. Since the produced complex oxide cannot be identified by XRD or the like, it is considered to be in a very minute amorphous state.

The coating layer is at least one layer, for example, one layer, two layers, or three layers or more. For example, the coat layer is composed of a microwave absorber, a noble metal-supported catalyst, and one layer containing NiO and / or Cr ₂ O ₃ . Alternatively, coating layer includes a microwave absorbing material and NiO and / or Cr ₂ O _3, a two-layer comprising a noble metal supported catalyst to each separate layers. Alternatively, coating layer consists of two layers including a microwave absorbing material, the noble metal loaded catalyst and NiO and / or Cr ₂ O ₃ and to each separate layers. Alternatively, coating layer comprises a microwave absorbing material and a noble metal supported catalyst, NiO and / or Cr ₂ O ₃ and the two layers respectively comprising in separate layers. Alternatively, coating layer, a microwave-absorbing material, the noble metal loaded catalyst, as well as a three-layer comprising NiO and / or Cr ₂ O ₃ to each separate layers. In the present invention, as the coating layer, it is preferable to use a coating layer composed of a microwave absorber, a noble metal-supported catalyst, and a single layer containing NiO and / or Cr ₂ O ₃ .

  The total thickness of the coating layers coated on the substrate is not limited, but is usually 50 μm to 150 μm, preferably 80 μm to 120 μm.

  By using the thickness described above as the thickness of the coat layer, the microwave absorber contained in the coat layer can efficiently contact with the microwave, and as a result, efficient absorption of the microwave, It leads to conversion to heat, and the noble metal-supported catalyst contained in the coat layer can efficiently contact with the exhaust gas, resulting in efficient purification of the exhaust gas.

The relative positional relationship in the microwave absorber, the noble metal-supported catalyst, and the coating layer of NiO and / or Cr ₂ O ₃ is not limited. For example, the microwave absorber, the noble metal-supported catalyst, and NiO and / or Cr ₂ O ₃ can be present separately in the coat layer, for example, the microwave absorber in the single coat layer. The coating layer including the noble metal-supported catalyst and the coating layer including NiO and / or Cr ₂ O ₃ may be present side by side.

In the present invention, the microwave absorbing material, the noble metal-supported catalyst, and NiO and / or Cr ₂ O ₃ are used for the microwave absorber heated by the microwave to efficiently heat the noble metal-supported catalyst and the activity of the noble metal at a low temperature. In the coating layer consisting of one layer, the SiO vapor generated from the microwave absorber can be efficiently trapped by the transition metal oxides NiO and / or Cr ₂ O ₃ . A uniformly mixed state is preferable. Therefore, it is preferable that SiC, which is a microwave absorber, a noble metal, and NiO and / or Cr ₂ O ₃ are close to each other.

In the present invention, the exhaust gas purifying catalyst is formed by forming a coating layer containing a microwave absorber, a noble metal-supported catalyst, and NiO and / or Cr ₂ O ₃ on a base material using the materials described above. The coating layer can be formed by a conventional coating technique. For example, the exhaust gas purification catalyst is coated with a coating layer slurry containing a microwave absorbing material, a noble metal-supported catalyst, and NiO and / or Cr ₂ O ₃ on a substrate masked except for the portion to be coated, After the excess slurry is blown off, for example, the solvent is removed by drying at 120 ° C. to 150 ° C. in the air for 0.5 hour to 1.5 hours, and in the air at 450 ° C. to 550 ° C. for 1 hour. It can be produced by firing for ˜2 hours to form a coat layer. In the exhaust gas purification catalyst, when two or more coat layers are formed on a substrate, the formation of the coat layer may be repeated. For example, when forming a microwave absorbing material and a coat layer comprising NiO and / or Cr ₂ O ₃ in the lower layer and a noble metal supported catalyst in the upper layer, first, the microwave absorbing material and the NiO and / or NiO and / or Alternatively, the coat layer may be formed using a coat layer slurry containing Cr ₂ O ₃ , and then the coat layer may be formed again using a coat layer slurry containing a noble metal supported catalyst.

  In the present invention, the microwave generator refers to an apparatus that generates a microwave that can be absorbed by the microwave absorber, and is positioned in front of the exhaust gas purification catalyst with respect to the flow direction of the exhaust gas.

  Here, the microwave generator is located in front of the exhaust gas purification catalyst with respect to the flow direction of the exhaust gas, where microwaves can be irradiated toward the exhaust gas purification catalyst having a base material coated with a microwave absorber, that is, the exhaust gas. (An angle formed by a line connecting the exhaust gas inlet and the center of the exhaust gas purification catalyst and a line connecting the microwave irradiation port of the microwave generator and the center of the exhaust gas purification catalyst ( In the present specification and the like, there is no limitation as long as it is located between the microwave irradiation angle (0 °) = 0 °) and the direction perpendicular to the exhaust gas flow direction (microwave irradiation angle = 90 °). The microwave irradiation angle is usually 30 ° to 90 °, preferably 45 ° to 90 °.

  By setting the position of the microwave generator to the position described above, the exhaust gas purification catalyst can be efficiently irradiated with microwaves.

  The frequency of the microwave generated from the microwave generator can be appropriately changed and is not limited, but is usually 1.5 GHz to 3 GHz, preferably 2 GHz to 2.5 GHz. In the present invention, it is more preferable to use 2.45 GHz which is the frequency of an industrial microwave power source as the frequency of the microwave.

  The output of the microwave generator can be appropriately changed depending on the scale of the vehicle exhaust gas purification device to be used, the desired warm-up performance, and the like. The microwave generator can be used in both single mode and multimode. The present invention is preferably implemented in a single mode.

  In FIG. 2, one Embodiment of the exhaust gas purification apparatus for vehicles of this invention is shown. In FIG. 2, an exhaust gas purification catalyst (2) and a microwave generator (1) for heating a microwave absorber located in front of the exhaust gas purification catalyst (2) with respect to the flow direction of the exhaust gas are provided. An exhaust gas purification apparatus for a vehicle is shown, and another catalyst is installed behind the exhaust gas flow direction of the exhaust gas purification apparatus for a vehicle. By installing another catalyst, the purification performance can be further improved. The exhaust gas enters the exhaust gas purification apparatus for vehicles from the exhaust gas inflow pipe, passes through the exhaust gas purification catalyst (2), and is discharged from the exhaust gas outflow pipe. In FIG. 2, the microwave irradiation angle is about 45 °.

  The exhaust gas purifying apparatus for vehicles provided with the exhaust gas purifying catalyst and the microwave generator of the present invention can be used for a vehicle exhaust gas purifying apparatus conventionally known in the technical field, and is not limited to an engine of a gasoline vehicle. It can be used as a three-way catalyst in a hybrid vehicle engine and a plug-in hybrid vehicle engine, and as an oxidation catalyst in a diesel vehicle engine.

  By using the exhaust gas purification apparatus for vehicles provided with the exhaust gas purification catalyst and the microwave generator of the present invention, the heating efficiency can be improved and the power consumption can be reduced.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

1. Sample Preparation Example 1. Preparation of an exhaust gas purification apparatus for a vehicle comprising an exhaust gas purification catalyst and a microwave generator, wherein the coating layer includes SiC, a noble metal-supported catalyst, and NiO.

(1) Preparation of composite powder β-SiC powder and NiO powder as a microwave absorber are wet-mixed in a beaker at a weight ratio of 4: 1, dried, and then heat-treated at 950 ° C. for 2 hours in the air. A composite powder was prepared. After the heat treatment, a composite oxide of SiC and NiO was not detected by XRD.
(2) powder _CeO 2 -ZrO ₂ composite oxide _CeO 2 -ZrO ₂ Pd supported catalyst and Rh which is supported on the composite oxide powder and _Al 2 _{O 3} and Pd as prepared noble metal loaded catalyst of the exhaust gas purifying catalyst and Al _The Rh-supported catalyst supported on ₂ O ₃ and the composite powder prepared in (1) were added to water and mixed uniformly to obtain a slurry. The slurry was coated on a cordierite honeycomb monolith substrate having a diameter of 103 mm, a length of 84 mm, and 600 cells / in ² by a method of charging and suctioning. Then, after drying and baking at 500 ° C. for 20 minutes, a three-way catalyst coat layer was formed to prepare an exhaust gas purification catalyst.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Pd: 2.87 g, Rh: 0.17 g, β-SiC and NiO: 71 g)
Coat layer thickness: 120 μm

(3) Preparation of vehicle exhaust gas purification device A vehicle exhaust gas purification device was prepared by combining the exhaust gas purification catalyst prepared in (2) and a microwave generator. The microwave irradiation angle was set to 45 °.

Example 2 Preparation of an exhaust gas purification apparatus for a vehicle comprising an exhaust gas purification catalyst and a microwave generator, wherein the coating layer includes SiC, a noble metal-supported catalyst, and Cr ₂ O ₃

  A vehicle exhaust gas purification apparatus was prepared in the same manner as in Example 1 except that (1) in Example 1 was changed as follows.

(1) a beta-SiC powder and the _Cr 2 _{O 3} powder as prepared microwave absorbing material of the composite powder, 4: 1 weight ratio, and wet-mixed in a beaker and dried in air, 2 at 950 ° C. A composite powder was prepared by heat treatment for a period of time. After the heat treatment, a composite oxide of SiC and Cr ₂ O ₃ was not detected by XRD.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Pd: 2.87 g, Rh: 0.17 g, β-SiC and Cr ₂ O ₃ : 71 g)
Coat layer thickness: 120 μm

  Comparative Example 1 Preparation of an exhaust gas purification apparatus for a vehicle including an exhaust gas purification catalyst and a microwave generator that does not include a microwave absorber

  Exhaust gas purification apparatus for vehicle was prepared in the same manner as in Example 1 except that Example 1 (1) was not carried out and Example 1 (2) was not used with composite powder.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Including Pd: 2.87 g, Rh: 0.17 g)
Coat layer thickness: 120 μm

  Comparative Example 2 Preparation of an exhaust gas purification apparatus for a vehicle comprising an exhaust gas purification catalyst and a microwave generator, wherein the coat layer includes SiC and a noble metal supported catalyst.

  Example 1 (1) was not carried out, and the same procedure as in Example 1 was performed except that “composite powder prepared in (1)” was changed to “β-SiC” in Example 1 (2). A vehicle exhaust gas purification device was prepared.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Pd: 2.87 g, Rh: 0.17 g, β-SiC: 71 g)
Coat layer thickness: 120 μm

Comparative Example 3 Preparation of a vehicle exhaust gas purification device comprising an exhaust gas purification catalyst and a microwave generator, wherein the coating layer includes SiC, a noble metal-supported catalyst, and zirconium boride (ZrB ₂ ).

  A vehicle exhaust gas purification apparatus was prepared in the same manner as in Example 1 except that (1) in Example 1 was changed as follows.

(1) Preparation of composite powder β-SiC powder and ZrB ₂ powder as a microwave absorber were wet-mixed in a beaker at a weight ratio of 4: 1, dried, and then heat treated at 950 ° C. for 2 hours in the air. Thus, a composite powder was prepared. After the heat treatment, no complex oxide of SiC and ZrB ₂ was detected by XRD.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Pd: 2.87 g, Rh: 0.17 g, β-SiC and ZrB ₂ : 71 g)
Coat layer thickness: 120 μm

  Comparative Example 4 Preparation of an exhaust gas purification apparatus for a vehicle comprising an exhaust gas purification catalyst and a microwave generator, wherein the coat layer contains SiC and NiO and does not contain a noble metal.

In Example 2 (2), “Pd as a noble metal-supported catalyst was supported on CeO ₂ —ZrO ₂ composite oxide powder and Al ₂ O ₃ and Rh was supported on CeO ₂ —ZrO ₂ composite oxide powder. And an Rh-supported catalyst supported on Al ₂ O ₃ “CeO ₂ —ZrO ₂ composite oxide powder and Al ₂ O ₃ ”, except that the exhaust gas purifying apparatus for vehicles was changed in the same manner as in Example 1. Prepared.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Including β-SiC and NiO: 71 g)
Coat layer thickness: 120 μm

Comparative Example 5 Preparation of a vehicle exhaust gas purification device including an exhaust gas purification catalyst and a microwave generator, wherein the coat layer contains SiC and Cr ₂ O ₃ and does not contain a noble metal

In Example 2 (2), “Pd as a noble metal supported catalyst was supported on CeO ₂ —ZrO ₂ composite oxide powder and Al ₂ O ₃ and Rh was supported on CeO ₂ —ZrO ₂ composite oxide powder. And an Rh-supported catalyst supported on Al ₂ O ₃ “CeO ₂ —ZrO ₂ composite oxide powder and Al ₂ O ₃ ”, except that the exhaust gas purifying apparatus for vehicles was changed in the same manner as in Example 2. Prepared.

Characteristics of exhaust gas purification catalyst Exhaust gas purification catalyst: 357 g
Coat layer: 168g
(Of which, β-SiC and Cr ₂ O ₃ : 71 g)
Coat layer thickness: 120 μm

2. Sample measurement 2-1. Temperature rise test by microwave For each of the vehicle exhaust gas purification apparatuses prepared in Examples 1 and 2 and Comparative Examples 1 to 5 in sample preparation, the temperature of the exhaust gas purification catalyst immediately after microwave irradiation was measured using the following microwave conditions, and the microwave The heating efficiency by was evaluated. The temperature measurement was performed by measuring the temperature of the upstream end face of the exhaust gas purification catalyst with an infrared thermometer using an optical fiber. The optical fiber was installed from a temperature measuring hole provided upstream of the exhaust gas purification catalyst container.

Microwave condition output: 500W
Frequency: 2.45 GHz (wavelength 0.122 m)
Irradiation time: 10 seconds

  FIG. 3 shows the temperature rise results of Examples 1 and 2 and Comparative Examples 1-5. From FIG. 3, in the exhaust gas purification apparatus for vehicles of Examples 1 and 2 and Comparative Examples 2 to 5, the temperature rise by the microwave was good at 15 ° C. to 20 ° C. That is, in these vehicle exhaust gas purifying apparatuses, the irradiated microwave energy is efficiently converted into heat. However, the vehicle exhaust gas purification apparatus of Comparative Example 1 does not contain SiC as a microwave absorber, so that the temperature rise by the microwave hardly occurred. That is, the vehicle exhaust gas purification apparatus of Comparative Example 1 indicates that the irradiated microwave energy could not be efficiently converted into heat.

2-2. Purification performance measurement Each of the exhaust gas purification catalysts prepared in Examples 1 and 2 and (1) of Comparative Examples 1 to 5 in sample preparation was wound with an alumina mat and press-fitted into a stainless steel container to produce a catalytic converter. Each catalytic converter was attached to the exhaust pipe of a gasoline engine bench with a heat exchanger.

  Subsequently, each catalytic converter was endured at 950 ° C. for 50 hours in the actual gas (actual gas composition). After the endurance, the coat layer of each catalyst was scraped off, and the CO adsorption amount was measured by a CO pulse adsorption method.

  FIG. 4 shows the CO adsorption amounts of Examples 1 and 2 and Comparative Examples 1-5. It will be described below that Comparative Example 1 was found from FIG. 4 as a standard product without poisoning deterioration due to SiO vapor.

  Example 1 shows the same amount of CO adsorption (102%) as that of Comparative Example 1 that does not contain SiC, and even if the amount of CO adsorption of Comparative Example 4 showing CO adsorption on NiO is taken into consideration, Comparative Example 1 The same amount of CO adsorption (101%) as that containing no SiC was shown, and it was confirmed that noble metals were not poisoned and deteriorated.

Example 2 showed a CO adsorption amount of 55% as compared with that of Comparative Example 1 containing no SiC, and an effect of suppressing noble metal poisoning was observed. Considering the amount of CO adsorption of Comparative Example 5 showing CO adsorption to Cr ₂ O ₃ , the amount of CO adsorption of 47% is shown compared to that of Comparative Example 1 not containing SiC, and the poisoning deterioration of the noble metal is one. The part was suppressed.

The difference between Example 1 (including SiC and NiO) and Example 2 (including SiC and Cr ₂ O ₃ ) is considered to be a difference in reactivity between each transition metal oxide and SiO vapor. Ni ₂ SiO ₄ and Cr ₂ SiO ₄ were not actually detected, but the production temperatures of Ni ₂ SiO ₄ and Cr ₂ SiO ₄ were 1200 ° C. and 1723 ° C., respectively, and Ni ₂ SiO ₄ was produced. Easy to react and highly reactive with SiO vapor. For this reason, the ability to trap SiO vapor that poisons noble metals is NiO> Cr ₂ O ₃ .

The comparative example 2 showed 1/5 CO adsorption amount compared with the comparative example 1 which does not contain SiC. When the coating layer did not contain NiO or Cr ₂ O ₃ other than the noble metal-supported catalyst and SiC, no effect of suppressing noble metal poisoning was confirmed as compared with Comparative Example 1.

Comparative Example 3 showed a CO adsorption amount of 11% as compared with Comparative Example 1 not containing SiC. In the case where the coating layer contains ZrB ₂ in addition to the noble metal-supported catalyst and SiC, no noble metal poisoning suppression effect was confirmed as compared with Comparative Example 1.

  The comparative example 4 showed 1% CO adsorption amount compared with the thing of the comparative example 1 which does not contain SiC, and there was almost no CO adsorption.

  Comparative Example 5 showed a CO adsorption amount of 9% as compared with Comparative Example 1 not containing SiC.

1. 1. microwave generator, Exhaust gas purification catalyst

Claims (1)

An exhaust gas purification catalyst having a base material and a coating layer containing a microwave absorbent and a noble metal-supported catalyst coated on the base material;
A microwave generator for heating the microwave absorber located in front of the exhaust gas purification catalyst with respect to the flow direction of the exhaust gas;
An exhaust gas purification apparatus for a vehicle comprising:
The microwave absorber comprises silicon carbide (SiC);
The noble metal-supported catalyst includes at least one selected from the group consisting of platinum (Pt), palladium (Pd), and rhodium (Rh);
The vehicle exhaust gas purification apparatus, wherein the coating layer further includes nickel oxide (NiO) and / or chromium oxide (III) (Cr ₂ O ₃ ).

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