JP2018001140A - Exhaust emission control catalyst body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control catalyst body using a catalyst material which enables exhaust emission to be controlled even in a state in which temperature of exhaust gas is low.SOLUTION: The exhaust emission control catalyst body comprises: an insulating substrate which causes the exhaust gas to flow through a plurality of pores formed inside the substrate; and a catalyst material provided on wall surfaces of the substrate pores. The catalyst material is composed of a conductive compound oxide having a perovskite structure represented by general formula ABOand is formed as a conductive coating layer which forms a conductive path on wall surfaces of the substrate pores and generates heat by energization.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a catalyst body for purifying exhaust gas of an automobile.

  2. Description of the Related Art Conventionally, exhaust gas purification apparatuses using a catalyst material that purifies exhaust gas from automobiles have been used. Since the normal catalyst material needs to be heated to 300 ° C. or higher in order to be activated, conventionally, the catalyst material is heated using the heat of the exhaust gas. However, immediately after the cold start of the engine, the temperature of the exhaust gas itself is low, so that the catalyst material cannot be heated sufficiently. In recent automobiles with high environmental performance, the temperature of the exhaust gas tends to decrease, and the catalyst material may not be heated to a sufficient activation temperature even if the heat of the exhaust gas is used.

  As a countermeasure against this, there has been proposed a method in which a so-called preheater is provided on the front side of the catalyst body and the catalyst material is electrically heated using the preheater (Patent Documents 1 and 2). For example, Patent Document 1 discloses a catalytic converter in which a corrugated plate made of a metal member such as stainless steel and a flat plate are wound to form a honeycomb preheater, and the preheater is disposed in close contact with a main catalyst body. It is disclosed. Further, in Patent Document 2, a preheater is produced by mixing a metal powder with an organic binder and water, then forming into a honeycomb shape and firing it, and this preheater is disposed close to the upstream of the main monolith catalyst body. A catalytic converter is disclosed.

Japanese Patent Laid-Open No. 11-179157 Japanese Patent Laid-Open No. 03-295184

  However, in the above-described prior art, it is necessary to prepare a preheater separately from the main catalyst body having an exhaust gas purification function. Alternatively, it is necessary to prepare a catalyst material for exhaust gas purification separately from a honeycomb body formed of a material having a function as a heating element (for example, a metal member or metal powder) and apply the catalyst material to the honeycomb body. there were. For this reason, an exhaust gas purifying catalyst body capable of purifying exhaust gas even when the temperature of the exhaust gas is low is desired by a configuration different from these conventional techniques.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, an insulating base that allows exhaust gas to flow through a plurality of holes formed therein, and a catalyst material provided on a wall surface of the hole of the base are provided. An exhaust gas purifying catalyst body is provided. The catalyst material is composed of a conductive complex oxide having a perovskite structure represented by the general formula ABO ₃ , and covers the wall surface of the hole of the base to form a conductive path and generate heat when energized. It is formed as follows.
According to this exhaust gas purifying catalyst body, since the catalyst material is composed of a complex oxide having a perovskite structure represented by ABO _3, it has high catalytic activity. Further, since the conductive catalyst material is formed as a conductive coating layer on the wall surface of the hole of the substrate, the temperature of the exhaust gas can be increased by energizing the conductive coating layer. It is possible to purify the exhaust gas even in a low state.

(2) In the exhaust gas purifying catalyst body, the catalyst material may include at least one of Pt, Pd, and Rh at the B site of the perovskite structure.
According to this configuration, since the catalyst material contains at least one of Pt, Pd, and Rh at the B site of the perovskite structure, higher exhaust gas purification performance can be obtained.

(3) The exhaust gas purifying catalyst body may further include a plurality of energization terminals connected to the conductive coating layer.
According to this configuration, the conductive coating layer of the catalyst material can be energized through a plurality of current-carrying terminals to generate heat, so that the temperature of the catalyst body can be easily raised.

(4) In the exhaust gas purifying catalyst body, the composite oxide has a composition formula (RE _1−x Sr _x ) (M1 _1−y M2 _y ) O ₃ (RE is one or more rare earth elements, and M1 is Cr. , Mn, Fe, Co, Ni, Cu, M2 may be one or more of Pt, Pd, Rh, 0 ≦ x ≦ 0.5, 0 <y ≦ 0.2) .
According to this configuration, higher exhaust gas purification performance can be obtained.

  Note that the present invention can be realized in various modes. For example, the present invention can be realized in the form of a catalyst body for exhaust gas purification provided with a substrate and a catalyst material for energization heating, a method for raising the temperature of the catalyst body, a method for purifying exhaust gas using the catalyst body, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the exhaust gas purification catalyst body as one Embodiment of this invention. Explanatory drawing which shows the example of attachment of the terminal for electricity supply of the catalyst body for exhaust gas purification. Explanatory drawing which shows the other example of attachment of the electricity supply terminals of the catalyst body for exhaust gas purification. The flowchart which shows the manufacturing method of a catalyst material. Explanatory drawing which shows the exhaust gas purification rate of a catalyst material sample. Explanatory drawing which shows the specific resistance of a catalyst material sample.

  FIG. 1 (A) is a front view of an exhaust gas purifying catalyst body 100 as one embodiment of the present invention, and FIG. 1 (B) is a longitudinal sectional view thereof. 1C and 1D are enlarged views of parts of FIGS. 1A and 1B. In these drawings, for convenience of illustration, individual members are drawn with dimensions different from the actual dimensions.

  The catalyst body 100 includes a substrate 120 as a carrier for supporting a catalyst material. The substrate 120 has a honeycomb shape and includes a wall portion 122 and a plurality of holes 124 partitioned by the wall portion 122. These holes 124 function as exhaust gas passages. The base 120 can be formed using, for example, an electrically insulating ceramic material such as cordierite. The plurality of holes 124 linearly penetrates from the entrance to the exit of the base 120. A conductive coating layer 126 is formed on the wall surface of the hole 124 to cover the wall surface of the hole 124 to form a conductive path and generate heat when energized. The conductive coating layer 126 is formed using a conductive catalyst material described later.

  As shown in FIG. 1D, the conductive coating layer 126 is formed so as to cover the end surface 122e of the wall 122 at both ends (inlet side and outlet side) of the catalyst body 100. In FIG. 1C, for convenience of illustration, the end surface 122e of the wall portion 122 is not shown, and a structure in a cross section of the inner wall portion 122 is depicted. Since the conductive coating layer 126 is formed so as to cover the end surface 122 e of the wall portion 122, the entire conductive coating layer 126 is continuous over the inside of the catalyst body 100. However, the conductive coating layer 126 may be formed so that the conductive coating layer 126 does not cover the end surface 122e of the wall portion 122 in a part or all of both ends of the catalyst body 100. The conductive coating layer 126 can be formed, for example, by applying a catalyst material to the wall surface of the hole 124 of the substrate 120 using a known wash coat method or dip coating method. Note that it is not necessary to form the conductive coating layer 126 on the cylindrical surface on the outer peripheral side of the base 120.

  FIGS. 2A to 2D are explanatory views showing an example of attachment of the energization terminal to the catalyst body. In the catalyst body 100a shown in FIG. 2 (A), electrodes 211 and 212 are provided on the outer sides of the outer periphery of the base 120, and the electrodes 211 and 212 are provided with energizing terminals 221 and 222, respectively. Each is connected. The electrodes 211 and 212 are electrically connected to the conductive coating layer 126 (FIG. 1) at both ends (inlet and outlet ends) of the catalyst body 100a. In the catalyst body 100a shown in FIG. 2B, the electrodes 211 and 212 and the current-carrying terminals 221 and 222 are provided at positions facing each other along the diagonal direction of the base 120 in FIG. Different from the medium 100a. In FIG. 2B, the first electrode 211 and the energizing terminal 221 are electrically connected to the conductive coating layer 126 at the end of the base body 120 on the inlet side, and the second electrode 221 and the energizing terminal 222 are connected. Is electrically connected to the conductive coating layer 126 at the end of the substrate 120 on the outlet side. The catalyst body 100c shown in FIG. 2 (C) has a larger range in which the electrodes 211 and 212 spread along the outer peripheral edges of both ends of the base body 120 than the catalyst body 100b in FIG. 2 (B). . The catalyst body 100d shown in FIG. 2D is provided with the first electrode 211 over the entire outer peripheral edge on the inlet side, and with the first electrode 211 over the entire peripheral edge on the outlet side. Is.

  FIG. 3 is an explanatory view showing another example of attachment of the energization terminal to the catalyst body. In the catalyst body 100e, metal porous plates 231 and 232 are joined to the inlet side and the outlet side of the base 120, respectively, and are electrically connected to the conductive coating layer 126 (FIG. 1) of the base 120. This joining can be performed using, for example, a conductive adhesive. These metal porous plates 231 and 232 can be formed, for example, as punching metal. The metal porous plates 231 and 232 are provided with energizing terminals 221 and 222, respectively. Note that the positions of the holes in the metal porous plates 231 and 232 are preferably aligned with the positions of the holes in the base 120, but the numbers of the holes do not necessarily have to match.

  The above-described structures shown in FIGS. 2A to 2D and FIG. 3 are merely examples of the electrical connection structure with the outside of the catalyst body 100, and various electrical connection structures other than these can be adopted. is there. For example, the electrodes 211 and 212 may be omitted, and the energization terminals 221 and 222 may be directly connected to the conductive coating layer 126 of the base 120. In addition, the number of energization terminals 221 and 222 is not limited to two, and generally a plurality of energization terminals can be provided. In these configurations, the conductive path can be designed by arranging the energization terminals 221 and 222, and the entire catalyst body 100 can be efficiently heated.

Each component shown in FIGS. 1 to 3 is preferably manufactured using a member having the following electrical properties.
(1) Base 120: Insulating member (especially ceramics)
(2) Conductive coating layer 126 of catalyst material: conductive member (especially perovskite oxide)
(3) Electrodes 211 and 212, current-carrying terminals 221 and 222, and metal porous plates 231 and 232: conductive members having a specific resistance smaller than that of the conductive coating layer 126 (particularly good metal conductors)
In this specification, “insulating” means that the specific resistance is 1 × 10 ⁶ Ωm or more, and “conductive” means that the specific resistance is 1 × 10 ⁻¹ Ωm or less. The “good conductor” means that the specific resistance is 1 × 10 ⁻⁶ Ωm or less.

  In the above-described various catalyst bodies 100, 100a to 100e, the conductive coating layer 126 generates heat when the conductive coating layer 126 is energized. Therefore, even when the temperature of the exhaust gas is low, the temperature can be raised to the activation temperature by the heat generation of the conductive catalyst material itself, and the exhaust gas can be purified. In addition, since the conductive coating layer 126 has a combined function of heating and catalytic properties, there is an advantage that it is not necessary to prepare a heating element and a catalyst material separately.

<Preferred composition of catalyst material>
As the catalyst material, a conductive complex oxide having a perovskite structure represented by the general formula ABO ₃ and having a function as an exhaust gas purification catalyst can be used. Since such a catalyst material is composed of a complex oxide having a perovskite structure represented by ABO ₃ , high catalytic activity can be realized. The B site having a perovskite structure preferably contains a metal element that exhibits a catalytic function (for example, a noble metal element such as Pt, Pd, or Rh, Mn, Co, Ni, or the like).

  As the catalyst material, it is more preferable to use a catalyst material containing at least one of Pt, Pd, and Rh at the B site of the perovskite structure. Since such a conductive catalyst material contains at least one of Pt, Pd, and Rh, which are noble metal elements, at the B site, extremely high exhaust gas purification performance can be obtained. In this specification, the phrase “catalyst material” means a catalytic substance (catalyst agent) having a catalytic action by itself, and does not include a substrate (support) that does not have a catalytic action. I mean.

One or more rare earth elements (Sc, Y, and lanthanoid) can be used as the metal element at the A site of the perovskite complex oxide. In addition to the rare earth element, Sr may be included as a metal element at the A site. Such a perovskite complex oxide is represented by the following composition formula.
(RE _1-x Sr _x ) (M1 _1-y M2 _y ) O ₃ (1)
Here, RE is one or more of rare earth elements, M1 is one or more of Cr, Mn, Fe, Co, Ni, and Cu, M2 is one or more of Pt, Pd, and Rh, 0 ≦ x ≦ 0.5, 0 <Y ≦ 0.2.

  As the perovskite complex oxide represented by the composition formula (1), it is particularly preferable to use a La-based perovskite complex oxide in which the rare earth element RE at the A site is lanthanum. Further, among the La-based perovskite complex oxides, those containing at least one of Pt, Pd, and Rh and at least one of Fe and Co at the B site are preferable.

  Since the perovskite complex oxide represented by the composition formula (1) can contain Sr in addition to the rare earth element RE at the A site, it can have high exhaust gas purification performance. In particular, when x satisfies 0 <x ≦ 0.5, both the rare earth elements RE and Sr are included at the A site, so that it is possible to have higher exhaust gas purification performance. Further, in the composition formula (1), it is particularly preferable that the rare earth element RE is La. Considering these points and the test results of Examples described later, the range of x in the composition formula (1) may be 0 ≦ x ≦ 0.5, but 0 <x ≦ 0.5 is preferable, and 0 <X ≦ 0.2 is more preferable, and 0.01 ≦ x ≦ 0.2 is most preferable. On the other hand, the range of y may be 0 <y ≦ 0.2, preferably 0 <y ≦ 0.1, more preferably 0 <y ≦ 0.05, and most preferably 0 <y ≦ 0.03. .

  The perovskite complex oxide given by the above composition formula (1) is a complex oxide in which the noble metal element M2 (one or more of Pt, Pd, and Rh) is solid-solved at the B site of the perovskite structure, This is different from a mixture in which noble metal particles are mixed separately from a perovskite complex oxide not containing a noble metal element. Which of these is applicable can be determined by observation using a transmission electron microscope (TEM). That is, by observing a mixture of noble metal particles in a perovskite complex oxide not containing a noble metal element with a TEM and obtaining a mapping diagram of the noble metal element, the noble metal element has an island shape with a diameter of several nm to several tens of nm. Appears to be distributed. This indicates that the noble metal is not dissolved in the perovskite complex oxide but is precipitated as a simple substance. On the other hand, even if the perovskite type complex oxide in which the noble metal element is dissolved in the B site is observed by TEM and the element mapping diagram is obtained in the same manner, the distribution is uniform and the noble metal is uniformly dissolved. It shows that.

  FIG. 4 is a flowchart showing a method for producing a conductive catalyst material according to an embodiment of the present invention. In step T110, the raw materials for the conductive catalyst material are weighed, and then a mixed solution is prepared in addition to the solvent and stirred. As a raw material for the conductive catalyst material, nitrates of A-site metal (such as lanthanum nitrate) and nitrates of B-site metal (such as cobalt nitrate and palladium nitrate) can be used. Moreover, distilled water can be used as a solvent. If necessary, citric acid and ethylene glycol are added. In step T120, this aqueous solution is evaporated to dryness, and then the obtained solid is transferred to a crucible, dried in the atmosphere at 200 to 250 ° C. for 12 hours, and the dried powder is pulverized in a mortar. In Step T130, the pulverized powder is fired at 600 to 900 ° C. for 2 hours in the air atmosphere. As a result, a conductive catalyst material powder is obtained.

  FIG. 5 is an explanatory diagram showing experimental results of the composition of the catalyst material sample and the exhaust gas purification rate. Samples # 01 to # 10 were respectively produced according to the procedure of FIG. 4 described above so that the composition shown in FIG. 5 was obtained. Samples # 01 and # 02 with “*” attached to the sample number are comparative examples, and the other samples # 03 to # 10 are examples.

The activity of samples # 01 to # 10 shown in FIG. 5 as a three-way catalyst material was evaluated. Specifically, 0.1 g of the catalyst powder of each sample was filled in a reaction tube made of quartz glass, and C ₃ H ₆ : 0.04%, NO: 0.10%, CO: 0.0. A room temperature gas consisting of 30%, H ₂ : 0.10%, H ₂ O: 2.00%, O ₂ : 0.33%, N ₂ : bal. (Remainder) at a flow rate of 500 ml / min. Distributed. Moreover, the catalyst powder installed in the reaction tube was heated to about 350 ° C., and the gas emitted from the reaction tube was analyzed with a gas analyzer. FIG. 5 shows the purification rates (C ₃ H ₆ purification rate, CO purification rate, NO purification rate) thus measured. In addition, the purification rate said here was computed by the following formula.
Purification rate = {(analyzed value before heating−analyzed value during heating) / analyzed value before heating} × 100 [%]

  In samples # 01 and # 02 of the comparative example, the purification rates were both low and less than 10%. On the other hand, Samples # 03 to # 10 of Examples all obtained a sufficiently high purification rate as compared with the Comparative Example. Further, samples # 03 to # 10 of the example are compared with each other as follows.

  In sample # 03, the value of y in the composition formula (1) is y = 0.15, which has sufficient purification performance. However, it has been found that when the value of y is decreased from 0.15, the purification performance tends to be improved. Considering this point, the value of y may be 0 <y ≦ 0.2, preferably 0 <y ≦ 0.1, more preferably 0 <y ≦ 0.05, and 0 <y ≦ 0. 03 is most preferred.

  Sample # 04 has a y value of y = 0.02, and has excellent purification performance compared to sample # 03. In addition, the metal element M1 at the B site of sample # 04 is Co, but as the metal element M1, the purification performance of Co is better than that of metal elements other than Co (Cr, Mn, Fe, Ni, Cu). It turns out that there is a tendency to. Therefore, it is preferable that the B-site metal element M1 contains Co, and it is particularly preferable that the B-site metal element M1 contains only Co.

Samples # 04, # 05, and # 06 have the same B site composition (Co _0.98 Pd _0.02 ), and the x value in the A site composition (La _1-x Sr _x ) is x = 0 in sample # 04. The difference is that in sample # 05, x = 0.1, and in sample # 06, x = 0.3. When the purification rates of these samples # 04 to # 06 are compared, sample # 05 with x = 0.1 is the most excellent. Considering this point, the value of x may be 0 ≦ x ≦ 0.5, preferably 0 <x ≦ 0.5, more preferably 0 <x ≦ 0.2, and 0.01 ≦ x ≦ 0.5. 0.2 is most preferred.

Samples # 04, # 07, and # 08 have the same A-site element (La), and the noble metal element M2 of the B-site composition (Co _0.98 M2 _0.02 ) is Pd in sample # 04, and in sample # 07 Pt is different from Sample # 08 in that it is Rh. Comparing the purification rates of these samples # 04, # 07, and # 08, with respect to the C ₃ H ₆ purification rate and the CO purification rate, samples # 04 and # 07 are equivalent, and sample # 08 is slightly inferior to these. ing. Regarding the NO purification rate, sample # 08 is the best, sample # 04 follows this, and sample # 07 is slightly inferior to these. Further, when the three purification rates are combined, Pd is preferable. Accordingly, the noble metal element M2 at the B site preferably contains Pd, and particularly preferably contains only Pd as the noble metal element M2 at the B site.

Samples # 04, # 09, and # 10 have the same B site composition (Co _0.98 Pd _0.02 ), and the A site metal is La in sample # 04, Nd in sample # 09, and sample # 10. The difference is that Sm. When the purification rates of these samples # 04, # 09, and # 10 are compared, sample # 04 is most excellent in any of the C ₃ H ₆ purification rate, the CO purification rate, and the NO purification rate. However, samples # 09 and # 10 also show a sufficiently high purification rate as compared with samples # 01 and # 02 of the comparative example. Therefore, the rare earth element at the A site preferably contains La.

  FIG. 6 is an explanatory view showing the specific resistance of the catalyst material sample. Here, the specific resistance was measured at room temperature using a DC four-terminal method. The compositions of Samples # 04 to # 06 are the same as Samples # 04 to # 06 shown in FIG. In addition, although specific resistance is not shown about sample # 03 of the Example shown in FIG. 5, # 07- # 10, since these are compositions close to sample # 04- # 06, they have a substantially equivalent specific resistance. It is estimated to be. Samples # 11 to # 14 added in FIG. 6 do not contain a noble metal element at the B site, but contain a metal element having a catalytic function such as Mn, Co, or Ni. Mn, Co, and Ni are known to change in valence at a high temperature of about 350 ° C., and perform exchange of elements and electrons in the exhaust gas when the valence changes. Therefore, these samples # 11 to # 14 can also be used as catalyst materials having an exhaust gas purification function.

Samples # 03 to # 14 of the embodiment shown in FIGS. 5 and 6 are all conductive complex oxides having a perovskite structure represented by the general formula ABO ₃ and functioning as an exhaust gas purification catalyst. It is. Moreover, these samples # 03 to # 14 all have a specific resistance of 1 × 10 ⁻¹ or less, and have sufficient conductivity to form the conductive coating layer 126 that generates heat when energized. In order for the conductive coating layer 126 to generate sufficient heat upon energization, the specific resistance is preferably not excessively small. For example, the conductive coating layer 126 preferably has a specific resistance of 1 × 10 ⁻⁶ or more and 1 × 10 ⁻¹ or less.

  In addition, this invention is not restricted to said Example and embodiment, In the range which does not deviate from the summary, it is possible to implement in various aspects.

DESCRIPTION OF SYMBOLS 100,100a-100e ... Exhaust gas purification catalyst body 120 ... Base | substrate 122 ... Wall part 122e ... End surface of wall part 124 ... Hole (exhaust gas flow path)
126 ... Conductive coating layer of catalyst material 211, 212 ... Electrodes 221, 222 ... Current-carrying terminals 231, 232 ... Metal porous plate

Claims (4)

An exhaust gas purifying catalyst body comprising an insulating base through which exhaust gas flows through a plurality of holes formed therein, and a catalyst material provided on a wall surface of the hole of the base,
The catalyst material is composed of a conductive complex oxide having a perovskite structure represented by the general formula ABO ₃ , and covers the wall surface of the hole of the base to form a conductive path and generate heat when energized. An exhaust gas purifying catalyst body characterized by being formed as follows. The exhaust gas purifying catalyst body according to claim 1,
The exhaust gas purifying catalyst body, wherein the catalyst material contains at least one of Pt, Pd, and Rh at the B site of the perovskite structure. The exhaust gas purifying catalyst body according to claim 1, further comprising:
An exhaust gas purifying catalyst body comprising a plurality of energizing terminals connected to the conductive coating layer. The exhaust gas purifying catalyst body according to any one of claims 1 to 3,
The composite oxide has a composition formula (RE _1-x Sr _x ) (M1 _1-y M2 _y ) O ₃ (RE is one or more of rare earth elements, M1 is Cr, Mn, Fe, Co, Ni, Cu) One or more types, M2 is represented by one or more of Pt, Pd, and Rh, 0 ≦ x ≦ 0.5, 0 <y ≦ 0.2).

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