JP4978581B2 - Particulate filter - Google Patents

Description

  The present invention relates to a particulate filter for suppressing release of particulates contained in exhaust gas such as a lean burnable diesel engine or lean burn gasoline engine.

  Particulate (PM) mainly composed of carbonaceous components is contained in exhaust gas discharged from diesel engines, lean burn gasoline engines, and the like. In order to reduce the environmental impact caused by the exhaust of PM to the outside air, PM is collected by arranging a particulate filter in the exhaust passage. The collected PM gradually accumulates on the particulate filter according to the operation time (engine operating time). Therefore, before the PM is accumulated more than a predetermined amount, the accumulated PM is burned to remove the particulate filter. Playback control is performed.

  As a method for burning PM, for example, a method for burning PM using a burner or a heater has been known. In recent years, hydrocarbon (HC) components contained in fuel and exhaust gas are combusted by an oxidation catalyst arranged upstream of the particulate filter, and the combustion heat increases the temperature of the exhaust gas to increase the combustion of PM. A method of promoting it is also used.

  In addition, PM usually ignites spontaneously at a little under 700 ° C. in an oxidizing atmosphere. It is known that this ignition temperature is lowered by the action of a catalytic noble metal such as platinum (Pt). Therefore, as a particulate filter, for example, PM can be burned at a relatively low temperature by wash-coating a catalyst layer containing alumina particles or the like carrying Pt on the surface of a flow path through which exhaust gas flows. May have a configuration. Further, in order to effectively promote the ignition and combustion of PM, the catalyst layer contains an oxygen storage / release material containing an oxide of cerium (Ce) and capable of releasing active oxygen. Utilizing the released oxygen, or containing oxygen (Zr) oxide and oxygen ion conductive material containing oxygen ion conductivity in the catalyst layer to use the oxygen conducted through the oxygen ion conductive material It has been proposed to do.

  As an example of such a wash-coated particulate filter, for example, the following Patent Document 1 discloses a CeZr-based composite oxide containing Ce, Zr, and a rare earth element R other than Ce, and R / (Ce + Zr + R). A diesel particulate filter having a catalyst layer containing one having a molar ratio of 2 to 11% is disclosed.

  Patent Document 2 below discloses a Zr-based double oxide containing Zr as a main component and containing a rare earth metal excluding Ce and yttrium (Y), and a rare earth metal containing Ce as a main component and excluding Ce. A diesel particulate filter having a particulate oxidation catalyst containing at least one of a Ce-based double oxide containing an alkaline earth metal is disclosed.

  Patent Document 3 below includes a Zr-based double oxide containing Zr as a main component and a rare earth metal excluding Ce and alumina, and each of the Zr-based double oxide and alumina carries a catalyst noble metal. A diesel particulate filter having a particulate oxidation catalyst is disclosed.

Further, as an example of an exhaust gas purifying catalyst provided with a catalyst layer containing a composite oxide containing Zr, for example, in Patent Document 4 below, a catalyst carrier base material is provided on the surface of the catalyst carrier base material. There is disclosed an exhaust gas purifying catalyst comprising a plurality of catalyst layers formed and containing stabilized zirconia containing Zr and CeZr composite oxide in the outermost layer forming the surfaces of the plurality of catalyst layers.
JP 2006-326573 A JP 2007-54713 A JP 2007-83224 A International Publication No. 06/46316 Pamphlet

  When the PM is burned, that is, when the filter is regenerated, the exhaust gas needs to be heated to a high temperature. For example, the fuel injected into the engine combustion chamber is increased and the fuel is supplied to the exhaust passage of the engine. Post injection control is often performed. This increased amount of fuel is burned with an oxidation catalyst, and the temperature of the exhaust gas is increased by the combustion heat to promote the combustion of PM. When the combustion speed of PM is low, it takes time to completely burn PM, so that the consumption of fuel for burning PM increases, resulting in deterioration of fuel consumption. In order to reduce the consumption of fuel for burning such PM, it is required to further increase the PM combustion rate as compared with the catalysts disclosed in Patent Documents 1 to 3.

  According to Patent Documents 1 to 3, it is disclosed that the burning rate of initial PM can be increased by increasing the content of rare earth metals excluding Ce. However, it has been considered that increasing the content of rare earth metals excluding Ce lowers the heat resistance, causes thermal damage to the catalyst, and lowers the catalyst efficiency.

  The catalyst described in Patent Document 4 is intended to increase the durability of the catalyst by containing stabilized zirconium and CeZr composite oxide in the outermost layer of the catalyst layer, Cannot be promoted, and cannot be directly applied to the particulate filter.

  An object of this invention is to provide the particulate filter which can burn PM in a short time.

The particulate filter of the present invention is a particulate filter disposed in the exhaust gas passage for collecting particulates in the exhaust gas discharged from the engine, and a plurality of the exhaust gas passes through the particulate filter. A filter body comprising a porous partition wall defining an exhaust gas flow path, and a Zr-based composite oxide formed on the surface of the porous partition wall and comprising zirconium (Zr), a rare earth metal other than cerium , and oxygen (O). The Zr-based composite oxide has a rare earth metal oxide content of more than 33 mol% and less than 40 mol% with respect to the total amount of ZrO ₂ and the rare earth metal oxide. It is characterized by being.

  Although the Zr-based composite oxide contained in the catalyst layer can increase the PM combustion rate when the rare earth metal oxide content is increased, the crystal structure of the Zr-based composite oxide is likely to change. It was thought that the heat resistance was lowered, the catalyst was thermally damaged, and the catalyst efficiency was lowered. However, if the content of the rare earth metal oxide is within the above range, even if the crystal structure of the Zr-based composite oxide may slightly change after exposure to high-temperature exhaust gas, Almost no further change. And what changed the crystal structure discovered that the burning rate of PM was high.

  Therefore, according to the said structure, the combustion speed of PM can be raised and PM can be burned in a shorter time. Further, since the PM combustion rate is increased, fuel efficiency can be improved when post injection control is performed.

  The Zr-based composite oxide is identified as a mixed phase of the phase composed of the Zr-based composite oxide and the phase composed of the rare-earth metal oxide in X-ray diffraction measurement after heat treatment at 1000 ° C. for 6 hours or more. It is preferable that

  Such a Zr-based composite oxide can increase the PM combustion rate as described above, and can burn PM in a shorter time. This is considered to be due to the following. First, it is considered that such a Zr-based composite oxide is obtained by dispersing a phase composed of the rare earth metal oxide in a phase composed of the Zr-based composite oxide. And, in such a dispersion of the rare earth metal oxide phase, the presence of the rare earth metal oxide phase facilitates the conduction of oxygen ions inside the Zr-based composite oxide, This is probably because the oxygen ion conductivity of the Zr-based composite oxide is increased. Further, the Zr-based composite oxide is identified as a mixed phase of the phase composed of the Zr-based composite oxide and the phase composed of the rare earth metal oxide even after heat treatment at 1000 ° C. for 6 hours or more. . That is, even when heat-treated for a long time, the mixed phase is stable as described above, so that the catalyst layer is prevented from being deteriorated due to thermal damage.

The catalyst layer contains the Zr-based composite oxide on the upstream side when the side closer to the exhaust gas inflow portion is the upstream side and the side closer to the outflow portion is the downstream side. Includes Zr and a rare earth metal other than cerium, and the content of the rare earth metal oxide with respect to the total amount of ZrO ₂ and the rare earth metal oxide is 8 mol% or more and 33 mol% or less. It is preferable to contain the Zr-based composite oxide.

  In the particulate filter, when PM burns in the exhaust gas upstream portion, the combustion heat propagates to the exhaust gas downstream portion. According to the above configuration, since the upstream catalyst layer has a high content of rare earth metal oxides, the performance of promoting PM combustion is high, so even on the upstream side where the exhaust gas temperature is relatively low PM can be burned efficiently. Accordingly, the combustion of the upstream PM can increase the temperature of the exhaust gas flowing downstream, and the PM combustion performance of the particulate filter is improved as a whole.

  Further, since the downstream catalyst layer has a lower rare earth metal oxide content than the upstream catalyst layer, the PM combustion performance is lower than that of the upstream catalyst layer, but the heat resistance is higher. Therefore, on the downstream side where the temperature of the exhaust gas becomes higher due to the combustion of PM on the upstream side, the thermal damage of the catalyst layer can be further suppressed. Can be promoted.

  Therefore, the catalyst layer can be further prevented from being thermally damaged, and PM can be burned in a short time. Further, since the PM combustion rate is increased, fuel efficiency can be improved when post injection control is performed.

  Moreover, it is preferable that the upstream catalyst layer is 20 to 60% of the length from the inflow portion to the outflow portion of the filter main body. According to this configuration, the exhaust gas is sufficiently heated due to the combustion of PM in the upstream catalyst layer, and PM can be burned even in the downstream catalyst layer with low PM combustion performance. .

  The rare earth metal is preferably selected from the group consisting of neodymium (Nd), lanthanum (La), and praseodymium (Pr). Such a catalyst layer containing a rare earth metal can further increase the combustion rate of PM.

Further, the Zr-based composite oxide, it is preferable to support platinum (Pt) as a catalytic noble metal. By supporting Pt, the combustion rate of PM can be further increased.

  Moreover, it is preferable that the said catalyst layer further contains the alumina by which platinum (Pt) was carry | supported. When such alumina is contained, exhaust gas purification performance such as light-off performance for carbon monoxide (CO) and hydrocarbon (HC) components is improved.

  It is preferable that the catalyst layer further includes a CeZr-based composite oxide containing zirconium (Zr) and cerium (Ce). When the ZrCe-based composite oxide is contained, exhaust gas purification performance such as light-off performance for CO and HC components is improved.

  According to the present invention, a particulate filter capable of burning PM in a short time can be provided.

  A diesel particulate filter (DPF) according to an embodiment of the present invention will be described.

  FIG. 1 is a schematic view showing a state in which a DPF 3 is disposed in an exhaust passage 1 of a diesel engine. An exhaust pipe constituting the exhaust passage (exhaust gas passage) 1 is connected to a diesel engine body (not shown) via an exhaust manifold. As shown in FIG. 1, the exhaust gas discharged from the diesel engine main body circulates in the exhaust passage 1 in the direction indicated by the white arrow (from the left side to the right side in FIG. 1). The exhaust passage 1 is equipped with a DPF 3 that collects PM in the exhaust gas.

FIG. 2 is a schematic view showing the DPF 3 viewed from the upstream side in the exhaust gas flow direction. FIG. 3 is a schematic cross-sectional view of the DPF 3 shown in FIG. 2 as seen from the section line III-III ′. The DPF 3 is a so-called wall flow type filter whose outer shape is formed in a cylindrical shape. Specifically, a large number of flow paths (cells) 4 are defined by a porous partition wall 5 formed of heat-resistant ceramics such as cordierite, SiC, and Si ₃ N _{4 and} substantially parallel to each other along the exhaust path. The filter main body 6 formed in a honeycomb shape and the exhaust gas inflow portion (upstream end portion) of a part of the flow paths 4b and the exhaust gas outflow portion (downstream end part) of the other flow paths 4a are staggered. And a sealing portion 15 for plugging. FIG. 4 shows an enlarged cross-sectional view of the porous partition wall 5. The porous partition wall 5 has fine pores 5a that connect the exhaust gas inflow passage 4a and the exhaust gas outflow passage 4b.

  In the DPF 3, the exhaust gas flowing in from the exhaust gas inflow passage 4a whose downstream end is sealed and whose upstream end is open passes through the surrounding porous partition walls 5 as shown by arrows in FIG. The upstream end portion is sealed and the downstream end portion is opened and discharged to the exhaust gas outflow passage 4b. That is, the exhaust gas flows from the exhaust gas inflow passage 4 a to the exhaust gas outflow passage 4 b by passing through the pores 5 a of the porous partition wall 5. In the meantime, PM is trapped and deposited on the DPF 3, mainly on the inner wall surface of the exhaust gas inflow passage 4 a and the surface of the pore 5 a of the porous partition wall 5.

  Further, as shown in FIG. 4, a catalyst layer 8 containing a particulate oxidation catalyst for promoting PM combustion is formed on the surface of the porous partition wall 5 of the DPF 3. The catalyst layer 8 containing the particulate oxidation catalyst only needs to be formed on the inner wall surface of the exhaust gas inflow passage 4a on which PM is mainly deposited and the surfaces of the pores 5a of the porous partition wall 5, for example, It may be formed over the entire area of the flow path 4.

  The particulate oxidation catalyst may be a complex oxide alone, but preferably carries a catalytic noble metal that lowers the combustion start temperature of PM.

  The catalyst noble metal not only lowers the combustion start temperature of PM, but also oxidizes hydrocarbons (HC) and carbon monoxide (CO). Examples of the catalyst noble metal include at least one selected from platinum (Pt), palladium (Pd), rhodium (Rh), and the like, and Pt is particularly preferable. For example, as a method of supporting Pt on a composite oxide, a dinitrodiamine platinum nitric acid solution is added to the composite oxide and mixed, and the composite oxide is supported on this composite oxide by evaporation to dryness. The amount of the catalyst noble metal supported on the composite oxide can be adjusted, for example, by adjusting the concentration and amount of the dinitrodiamine platinum nitric acid solution with respect to Pt.

The composite oxide includes a Zr-based composite oxide containing zirconium (Zr) as a main component, but includes a ZrCe-based composite oxide containing Zr and cerium (Ce) and alumina (Al ₂ O ₃ ). You may go out. In addition, when using ZrCe system complex oxide and an alumina, it is preferable that the catalyst noble metal is carry | supported respectively.

  The Zr-based composite oxide has oxygen ion conductivity as described later, is adjusted so that Zr is a main component, and contains rare earth metal R excluding Ce. Examples of the rare earth metal R contained in the Zr-based composite oxide include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), promethium (Pm), and samarium (Sm). ), Europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like. . Among these, at least one metal selected from Nd, La, and Pr is preferable, and a Zr-based composite oxide containing Nd is particularly preferable from the viewpoint of heat resistance.

  The Zr-based composite oxide is preferably contained in the catalyst layer 8 in the range of 1 to 80 g / L. Furthermore, the range of 5-40 g / L is desirable. Here, the content range can be appropriately determined according to the partition wall average pore diameter, porosity, cell density, and the like of the filter carrier. For example, focusing on the average pore diameter of the partition walls, if this is in the range of about 10 to 30 μm, the range is 1 to 30 g / L. If the average pore diameter of the partition walls exceeds about 30 μm, it is sufficient to carry more in the above range. Further, fine adjustment may be made according to the porosity and cell density. If the amount of the Zr-based composite oxide is too small, there is a tendency that the PM combustion performance cannot be sufficiently exhibited. If the amount is too large, the back pressure of the DPF 3 tends to be too high.

  The ZrCe-based composite oxide has an oxygen storage / release capability, and uses oxygen released from the ZrCe-based composite oxide to promote oxidation of HC and CO and improve light-off performance. .

The alumina improves the light-off performance for HC and CO by increasing the dispersibility of the catalyst noble metal. Alumina stabilized with a rare earth metal R such as La is preferable from the viewpoint of heat resistance, and an alumina having a specific surface area of 250 m ² / g or more is useful for preventing sintering of the catalyst noble metal. preferable.

  In order to form the catalyst layer 8, a catalyst noble metal is supported on the composite oxide, and then the catalyst noble metal-supported composite oxide is mixed with water and a binder to produce a slurry. After coating the inner wall surface of the internal channel and removing excess slurry by air blowing, drying and firing are performed. The layer thickness and the like of the catalyst layer 8 can be adjusted by the viscosity and concentration of the slurry. Further, when the particulate oxidation catalyst forming the catalyst layer 8 contains two or more composite oxides, it is preferable to support a catalyst noble metal on each composite oxide.

  The Zr-based composite oxide contained in the particulate oxidation catalyst has oxygen ion conductivity. The mechanism by which PM is oxidized by the particulate oxidation catalyst using the complex oxide having oxygen ion conductivity is estimated as follows. FIG. 5 is an explanatory view showing the oxidation mechanism of PM. 5A is an enlarged cross-sectional view showing the catalyst layer 8 on which the carbon 9 is deposited, and FIG. 5B is a schematic diagram showing the crystal lattice of the Zr-based composite oxide contained in the catalyst layer 8. FIG.

  When exhaust gas is discharged from the diesel engine main body and PM is collected in the DPF 3, carbon 9 as PM is deposited on the catalyst layer 8. Since the carbon 9 is porous and has a characteristic of being easily bonded to oxygen, release / desorption of oxygen occurs in the surface portion of the catalyst layer 8 on which the carbon 9 is deposited under oxygen-excess conditions. The oxygen concentration is lowered, and a microscopic difference in oxygen concentration is produced with respect to other portions.

Thus, when the oxygen concentration of a portion of the surface of the catalyst layer 8 is lowered, the Zr-based composite oxide included in the composite oxide constituting the catalyst layer 8 has oxygen ion conductivity. Oxygen ions O ²⁻ move from the inside of the oxide to the surface portion where the oxygen concentration is reduced. This oxygen ion O ²⁻ reaches the surface of the catalyst layer 8 to become active oxygen, and as a result, a place where the oxidation reaction of the carbon 9 is likely to occur locally occurs on the surface of the composite oxide.

  Then, the oxidation reaction of the carbon 9 starts at the site where the reaction conditions are the best. As shown in FIG. 5A, when this oxidation reaction is started, a fire type 10 is generated there, and oxygen around it is depleted by this fire type 10 to form an oxygen-deficient space 11. In an oxygen-deficient state, the oxidation reaction of carbon 9, that is, the fire is weakened and the fire type 10 disappears. However, in the DPF 3 according to this embodiment, the particulate oxidation catalyst constituting the catalyst layer 8 is oxygen ion conductive. Since the active oxygen is continuously supplied to the oxygen-deficient space 11 by the action of the Zr-based composite oxide, the oxidation reaction of the carbon 9 is accelerated. As a result, the combustion region expands with the fire type 10 as the center.

  In other words, under oxygen-excess conditions, an oxygen concentration difference occurs between the oxygen-deficient space 11 and its surroundings, and based on this concentration difference, charge imbalance occurs in a microscopic region inside the composite oxide of the catalyst layer 8. Along with this, oxygen ions are moved from the portion having a high oxygen concentration to the oxygen-deficient space 11 through the Zr-based composite oxide of the catalyst layer 8. The oxygen ions are released as active oxygen into the oxygen-deficient space 11, thereby promoting the combined combustion of carbon 9 and active oxygen, that is, oxidation. Therefore, the fire type 10 generated on a part of the surface of the catalyst layer 8 is not lost, and the combustion region is expanded, so that the PM that is the carbon 9 can be burned and purified efficiently and in a short time. The burning rate can be increased.

  Here, since the rare earth metal R which is a trivalent metal is included in the Zr-based composite oxide, inside the Zr-based composite oxide, as shown in FIG. (Represented by black circles in the figure). That is, the crystal lattice of tetravalent metal atoms is replaced with trivalent metal atoms. Thereby, as shown in FIG. 5B, oxygen deficient portions (oxygen ion vacancies) exist, and oxygen ions are transported through the vacancies. In FIG. 5B, alumina is omitted.

As can be seen from the above mechanism, the Zr-based composite oxide has a higher content of the rare earth metal R, that is, a higher content of the oxide RO of the rare earth metal R (RO / (ZrO ₂ + RO)). There will be many vacancies and the combustion rate of PM will increase. It is confirmed experimentally that the higher the content ratio of the oxide RO of the rare earth metal R (RO / (ZrO ₂ + RO)), the higher the PM burning rate is, as will be described later. .

  Further, in the Zr-based composite oxide, when the content ratio of the oxide RO of the rare earth metal R increases, as understood from the mechanism, the oxygen deficient portion increases. Therefore, the crystal lattice of the Zr-based composite oxide is destroyed, crystal phase separation tends to occur, and the crystal structure tends to change. That is, it has been considered that the heat resistance of the Zr-based composite oxide tends to decrease as the content of the rare earth metal oxide RO increases. However, when the content of the oxide RO of the rare earth metal R is more than 33 mol% and less than 40 mol%, the crystal structure of the Zr-based composite oxide may slightly change after exposure to high-temperature exhaust gas. However, once it changed, it hardly changed any more. And what changed the crystal structure discovered that the burning rate of PM was high. When the content of the oxide RO of the rare earth metal R is 33 mol% or less, the phase separation of the crystal of the Zr-based composite oxide hardly occurs and the heat resistance is further improved. The burning rate tends to decrease. Further, when the content of the oxide RO of the rare earth metal R is 40 mol% or more, there is a possibility that the crystal structure cannot be maintained when exposed to high-temperature exhaust gas.

  The reason for the high PM burning rate of the Zr-based composite oxide having a changed crystal structure is considered to be due to the following mechanism. FIG. 6 is a drawing for explaining the mechanism by which the PM combustion rate of the Zr-based composite oxide is increased.

  When the Zr-based composite oxide containing the rare earth metal R oxide RO content exceeding 33 mol% is exposed to a high-temperature exhaust gas, as shown in FIG. 6, the Zr-based composite oxide is formed. In the base phase 21, the separated phase 22 made of the oxide RO of the rare earth metal R is finely dispersed. In such a case where the separated phase 22 is dispersed in the base phase 21, the presence of the separated phase 22 facilitates the conduction of oxygen ions inside the Zr-based composite oxide, and the oxygen ion conduction of the Zr-based composite oxide. It is thought that the burning rate of PM of the Zr-based composite oxide having a changed crystal structure is increased due to the increase in properties.

  In addition, the Zr-based composite oxide is subjected to heat treatment at 1000 ° C. for 6 hours or more, and then as a mixed phase of the phase composed of the Zr-based composite oxide and the phase composed of the rare earth metal oxide in X-ray diffraction measurement. To be identified. From this, it is estimated that the separated phase 22 is dispersed in the base phase 21. Further, the Zr-based composite oxide is identified as a mixed phase of the phase composed of the Zr-based composite oxide and the phase composed of the rare earth metal oxide even after heat treatment at 1000 ° C. for 6 hours or more. . That is, even if it is heat-treated for a long time, it is stable as a mixed phase. Therefore, even if the crystal structure of the Zr-based composite oxide is changed, the catalyst layer 8 is thermally damaged, resulting in a decrease in catalyst efficiency. Is suppressed.

  From the above, the exhaust gas purifying catalyst according to this embodiment has a rare earth metal R oxide RO content of more than 33 mol% and 40 mol% in the catalyst layer 8 formed on the surface of the porous partition wall 5. Since the Zr-based composite oxide that is less than the lower limit is contained, PM can be burned in a short time. In the exhaust gas purifying catalyst according to the present embodiment, the entire surface of the catalyst layer 8 formed on the surface of the porous partition wall 5 has a rare earth metal R oxide RO content of more than 33 mol% and less than 40 mol%. The Zr-based composite oxide may be included, or a part of the Zr-based composite oxide may be included.

Further, even when a Zr-based composite oxide whose content of the oxide RO of the rare earth metal R is out of the above range is used, the oxidation of the rare earth metal R with respect to the total amount of ZrO ₂ and the oxide RO of the rare earth metal R It is preferable that the content rate (RO / (ZrO ₂ + RO)) of the product RO does not exceed 40 mol% at the maximum. When this content rate exceeds 40 mol%, even in the catalyst layer in the region where the temperature of the surrounding exhaust gas is low, the crystal lattice tends to collapse and heat resistance tends not to be ensured.

  Further, when the catalyst layer 8 containing a Zr-based composite oxide having a rare earth metal R oxide RO content of more than 33 mol% and less than 40 mol% is formed on a part of the surface of the porous partition wall 5. As described later, it is preferable that the exhaust gas is formed on the upstream side where the temperature of the surrounding exhaust gas is relatively low. That is, when the catalyst layer 8 containing the Zr-based composite oxide is formed on a part of the surface of the porous partition wall 5, the catalyst layer 8 is from the upstream side where the temperature of the surrounding exhaust gas is relatively low. The downstream side where the temperature of the surrounding exhaust gas is relatively high is preferably configured so that the content of the oxide RO of the rare earth metal R is lower.

  Specifically, as shown in FIG. 3, the catalyst layer 8 includes a region closer to the exhaust gas inflow portion (upstream side) 6a on the side where the catalyst layer is coated and a side closer to the exhaust gas outflow portion ( (Downstream side) 6b is divided into the region covered with the catalyst layer, and the upstream 6a catalyst layer and the downstream 6b catalyst layer are connected to each other. Further, the rare earth metal R in the upstream 6a catalyst layer is formed. The content of the oxide RO of the rare earth metal R in the catalyst layer on the downstream side 6b is lower than the content of the oxide RO.

  Further, the ratio (6a / 6a + 6b) of the length (6a) of the region covered with the catalyst layer on the upstream side 6a to the length (6a + 6b) extending from the inflow portion to the outflow portion of the filter body 6 is 20-60. %, And more preferably 50% or less.

Further, the content in the catalyst layer on the upstream side 6a is preferably more than 33 mol% and less than 40 mol%, and more preferably 36 mol% or more. If this content is too low, the temperature of the exhaust gas around the catalyst layer on the upstream side 6a is relatively low, and it tends to be difficult to promote PM combustion. Examples of the Zr-based composite oxide in the catalyst layer on the upstream side 6a include, for example, Zr-12Nd-24Pr, Zr-18Nd-18Pr, Zr-12Nd-18Pr-3La, Zr-18Nd-18Pr- shown in FIG. 3La etc. are mentioned. Here, the Zr-based composite oxide (Zr-xR) indicates a Zr-based composite oxide containing x mol% of R ₂ O ₃ and the balance being ZrO ₂ , and such description is also given in the following description. do. Specifically, for example, Zr-12Nd-24Pr represents a Zr-based composite oxide containing 12 mol% Nd ₂ O ₃ and 24 mol% Pr ₂ O ₃ with the balance being ZrO ₂ .

  The content of the catalyst layer on the downstream side 6b is preferably 8 mol% or more and 33 mol% or less, and more preferably 30 mol% or less. If this content is too low, the temperature of the exhaust gas around the catalyst layer on the downstream side 6b is high, but even if the temperature of the exhaust gas is high, the combustion of PM tends to be difficult to promote. Moreover, when this content rate is too high, there exists a tendency for it to become difficult to exhibit the effect which arrange | positions the catalyst layer with higher heat resistance with respect to high temperature exhaust gas downstream.

  From the above, the catalyst layer on the upstream side 6a including the Zr-based composite oxide having a high content of the oxide RO of the rare earth metal R has a high performance of promoting PM combustion. Therefore, PM can be efficiently burned even on the upstream side 6a where the temperature of the exhaust gas is relatively low. Further, the combustion of PM raises the temperature of the exhaust gas, and raises the temperature of the exhaust gas flowing to the downstream side 6b. The catalyst layer on the downstream side 6b containing the Zr-based composite oxide having a low content of the rare earth metal R oxide RO has a lower content of the rare earth metal R oxide RO than the upstream layer 6a. Although the PM combustion performance is lower than that of the catalyst layer of 6a, the heat resistance is higher. Therefore, on the downstream side 6b where the temperature of the exhaust gas is increased by the combustion of PM on the upstream side 6a, thermal damage of the catalyst layer can be further suppressed, and further, the combustion heat of PM on the upstream side 6a is utilized, PM combustion can be promoted. Therefore, the catalyst layer 8 can be further prevented from being thermally damaged, and PM can be burned in a short time. Further, since the PM combustion rate is increased, fuel efficiency can be improved when post injection control is performed.

  In the above embodiment, the catalyst layer 8 is described by taking as an example a catalyst layer formed by connecting two catalyst layers of the upstream 6a catalyst layer and the downstream 6b catalyst layer. If the content ratio of the oxide RO of the metal R is lower in the catalyst layer on the downstream side 6b than on the catalyst layer on the upstream side 6a, it may be composed of three or more catalyst layers. Alternatively, a slight clearance may be provided between the catalyst layer on the upstream side 6a and the catalyst layer on the downstream side 6b. By doing so, PM is burned in the catalyst layer on the upstream side 6a, and the PM deposited in the slight clearance portion by the combustion heat can be burned sufficiently.

  Examples of the DPF 3 which is an embodiment of the present invention will be described below, but the present invention is not limited to the examples.

[Example A]
The influence of the composition and content ratio of the Zr-based composite oxide on the PM burning rate was examined.

  First, the several DPF3 which changed the component and content ratio of Zr type complex oxide was produced as follows.

  As a DPF carrier (filter body 6), the cell structure has a wall thickness of 12 mil of the porous partition wall 5 and a volume of 25 ml from a DPF carrier made of silicon carbide (SiC) having a cell number of 300 cpsi (cells per square inch). What was cut out was used.

  Next, each Zr-based composite oxide having the components and content ratios shown in Table 1 was prepared. These Zr-based composite oxides are prepared by dissolving a predetermined amount of each metal (Zr, Nd, Pr, La, etc.) nitrate mixed in ion-exchanged water, dropping a basic solution adjusted with ammonia, A Zr-based composite oxide is obtained by producing a precipitate containing a metal element, followed by filtration, washing with water, drying, and firing at 500 ° C. for 2 hours. In addition, about Zr-18Nd-18Pr, what produced | generated by baking for 6 hours at 1000 degreeC was also prepared.

  Then, Pt was supported on these Zr-based composite oxides as a catalyst noble metal. As for the method of supporting Pt, a dinitrodiamine platinum nitric acid solution is added to each Zr-based composite oxide and mixed, and Pt is supported on the Zr-based composite oxide by evaporation to dryness. The amount of Pt supported is set to 1% by mass with respect to the Zr-based composite oxide.

  After drying this, it was pulverized in a mortar and baked in an electric furnace in an air atmosphere at 500 ° C. for 2 hours to obtain a catalyst powder (Pt-supported composite oxide powder) containing a Zr-based composite oxide. Thereafter, an aging treatment was performed in which the Pt-supported composite oxide powder was allowed to stand for 24 hours at 800 ° C. under atmospheric pressure.

  The Pt-supported composite oxide powder subjected to the aging treatment was mixed with water and a binder to form a slurry, and the slurry was coated on the filter body 6 plugged with the sealing portion 15 and dried. The coating amount at this time was adjusted to 20 g / L. Then, DPF3 in which the catalyst layer 8 was formed in substantially the entire area of the internal flow path of the filter main body 6 was obtained by heating in an air furnace at 500 ° C. for 2 hours and baking.

  About the obtained DPF, the carbon burning rate was measured by the following method.

(Carbon burning rate)
A carbon combustion rate evaluation experiment was conducted to examine the carbon combustion performance in a state where each of the DPFs 3 was set in a model gas flow catalyst evaluation device for flowing simulated exhaust gas.

In this experiment, carbon black powder (manufactured by Sigma-Aldrich) was deposited on DPF3 instead of PM as an index for determining PM combustion performance, and when the temperature was raised while flowing simulated exhaust gas, Evaluation was performed using the concentration of CO ₂ and CO discharged by combustion. The carbon black powder is deposited by adding 10 cc of ion exchange water to a carbon black powder equivalent to 10 g / L and stirring and mixing for 5 minutes using a stirrer to sufficiently disperse the carbon black powder. The upstream end side of the DPF 3 was immersed in this, and at the same time, suction was performed by an aspirator from the opposite side of the immersed end surface. Moisture that could not be removed by this suction was removed by air blow from the soaked end face side, and dried at 150 ° C. for 2 hours in a dryer.

In the model gas flow catalyst evaluation apparatus, the oxygen gas and water vapor are each contained in an amount of 10% by volume with respect to the total gas flow rate while the temperature is raised to 600 ° C. at a rate of 15 ° C./min, and the remainder is nitrogen gas or the like. The simulated exhaust gas was circulated so that the space velocity was 50000 / h, and the CO and CO ₂ concentrations immediately after the outlet of the DPF 3 were measured. Then, the CO, was based on the CO ₂ concentration determined a carbon burning rate defined by the following equation. This carbon burning rate indicates the amount of carbon burned per liter of the carrier (DPF3).

The obtained results are shown in Table 1, FIG. 7 and FIG. FIG. 7 is a graph showing the burning rate of carbon in various DPFs 3, and FIG. 8 shows changes in the content of Nd ₂ O _{3 in} the Zr—Nd composite oxide and the Zr—Nd—Pr composite oxide. It is a graph which shows the change of the carbon burning rate accompanying.

  As can be seen from Table 1, FIG. 7 and FIG. 8, the higher the content of the oxide RO of the rare earth metal R, the higher the PM burning rate. In addition, the PM burning rate was highest when the content ratio of the rare earth metal R oxide RO exceeded 33% and the Zr-based composite oxide fired at 1000 ° C. for 6 hours was used. From this, even if the DPF including the catalyst layer containing the Zr-based composite oxide whose rare earth metal R oxide RO content is more than 33 mol% and less than 40 mol% is exposed to high-temperature exhaust gas, It was found that the combustion rate of PM was improved without deterioration. In FIG. 7, for example, when using Zr-6Nd-12Pr, Zr-6Nd-6La, Zr-6Nd-12La, Zr-12Nd-6La, compared with the case using Zr-20La, rare earth metal Despite the low content of R oxide RO, the PM burning rate was equal or higher. From this, it is understood that the rare earth metal R preferably contains Nd. This is considered to be because the heat resistance of the Zr-based composite oxide is further improved by containing Nd.

  Next, the difference between the Pt-supported composite oxide powder containing Zr-18Nd-18Pr and the Pt-supported composite oxide powder containing Zr-12Nd-18Pr was examined.

  First, these catalyst powders were subjected to aging treatment at 1000 ° C. for 24 hours in the atmosphere. Thereafter, X-ray diffraction measurement (XRD) was performed on each of the catalyst powders subjected to the aging treatment. FIG. 9 is a chart showing measurement results of X-ray diffraction measurement of a Pt-supported composite oxide powder containing Zr-18Nd-18Pr and a Pt-supported composite oxide powder containing Zr-12Nd-18Pr. 9A shows the result of the Pt-supported composite oxide powder containing Zr-12Nd-18Pr, and FIG. 9B shows the result of the Pt-supported composite oxide powder containing Zr-18Nd-18Pr.

  From FIG. 9, the catalyst powder containing the Zr-based composite oxide having a rare earth metal R content of 33 mol% or less has a sharp peak, and even at high temperatures (1000 ° C.), It can be seen that the crystal lattice is retained.

On the other hand, the catalyst powder containing the Zr-based composite oxide having a rare earth metal R content of more than 33% shows a sharp peak, but a little peak based on Pr ₆ O ₁₁ appears, and the temperature is high (1000 ° C.). It can be seen that phase separation of the crystal of the Zr-based composite oxide occurs.

_Further, the crystallite diameter of Pr _{6 O 11,} on the basis of the peak based on the Pr _{6 O 11} position (2θ = 28.3 ° and 32.7 °), as calculated from the equation of Scherrer was 20 nm. On the other hand, when the crystallite diameter of Pr ₆ O ₁₁ obtained by firing Pr ₂ O ₃ at 1000 ° C. was calculated by the same method, it was 150 nm. From this, the catalyst powder containing the Zr-based composite oxide in which the content of the rare earth metal R exceeds 33% is calcined at a high temperature, so that the base phase composed of the Zr-based composite oxide is transformed from the Zr-based composite oxide. The separated phase composed of separated Pr ₆ O ₁₁ is finely dispersed.

  From the above, it is considered that the combustion performance of PM is improved because the oxygen ion conductivity of the Zr-based composite oxide is increased as described above by the phase separation in which such a separated phase is finely dispersed in the base phase.

[Example B]
Furthermore, PM combustion performance and the like were evaluated using Zr-18Nd-18Pr and Zr-12Nd-18Pr.

Example 1
A DPF 3 provided with a catalyst layer containing Zr-18Nd-18Pr on the entire surface of the filter body was produced as follows.

  As the DPF carrier (filter body 6), the cell structure is 25 ml (diameter 25 .mu.m) from a silicon carbide (SiC) DPF carrier having a wall thickness of 16 mil of the porous partition wall 5 and a cell number of 178 cpsi (cells per square inch). What was cut out to have a volume of 4 mm) was used.

Next, La-containing alumina adjusted so that Zr-18Nd-18Pr, Zr-23Ce-4Nd, La ₂ O ₃ is contained by 5% by mass, and Al ₂ O ₃ is contained by 95% by mass is 2: 2. It mixed so that it might become 1: 6, and the catalyst material was obtained.

  Then, Pt was supported on the catalyst material as a catalyst noble metal. In the Pt loading method, a dinitrodiamine platinum nitric acid solution is added to and mixed with the catalyst material, and Pt is supported on the catalyst material by evaporation to dryness. The supported amount of Pt is set to 1.5 g / L with respect to the catalyst material.

  After drying this, it was pulverized in a mortar and baked in an electric furnace in an air atmosphere at 500 ° C. for 2 hours to obtain a catalyst powder (Pt-supported composite oxide powder) containing a Zr-based composite oxide.

  The Pt-supported composite oxide powder was mixed with water and a binder to form a slurry, and the slurry was coated on the filter body 6 plugged by the sealing portion 15 and dried. The coating amount at this time was adjusted to 20 g / L. Then, DPF3 in which the catalyst layer 8 was formed in substantially the entire area of the internal flow path of the filter main body 6 was obtained by heating in an air furnace at 500 ° C. for 2 hours and baking.

(Example 2)
A DPF 3 having a catalyst layer containing Zr-18Nd-18Pr on the upstream side of the filter body was produced as follows. DPF3 using was prepared as follows.

  As a DPF carrier (filter body 6), the cell structure has a wall thickness of 16 mil of the porous partition wall 5 and a volume of 25 ml from a DPF carrier made of silicon carbide (SiC) having a cell number of 178 cpsi (cells per square inch). What was cut out was used.

Next, La-containing alumina adjusted so that Zr-18Nd-18Pr, Zr-23Ce-4Nd, La ₂ O ₃ is contained by 5% by mass, and Al ₂ O ₃ is contained by 95% by mass is 2: 2. It mixed so that it might become 1: 6, and the catalyst material was obtained.

  Then, Pt was supported on the catalyst material as a catalyst noble metal. In the Pt loading method, a dinitrodiamine platinum nitric acid solution is added to and mixed with the catalyst material, and Pt is supported on the catalyst material by evaporation to dryness. The supported amount of Pt is set to 1.8 g / L with respect to the catalyst material.

  After drying this, it was pulverized in a mortar and baked in an electric furnace in an air atmosphere at 500 ° C. for 2 hours to obtain a catalyst powder (Pt-supported composite oxide powder) containing a Zr-based composite oxide.

  The Pt-supported composite oxide powder was mixed with water and a binder to form a slurry, and the slurry was coated in a region of 50% from the upstream end portion of the filter body 6 plugged by the sealing portion 15 and dried. The coating amount at this time was adjusted to 20 g / L. Then, DPF3 by which the catalyst layer 8 was formed in the upstream of the internal flow path of the filter main body 6 was obtained by heating and baking with an electric furnace at 500 degreeC air atmosphere for 2 hours.

(Comparative Example 1)
A DPF 3 provided with a catalyst layer containing Zr-12Nd-18Pr on the entire surface of the filter body was produced as follows.

  As a DPF carrier (filter body 6), the cell structure has a wall thickness of 16 mil of the porous partition wall 5 and a volume of 25 ml from a DPF carrier made of silicon carbide (SiC) having a cell number of 178 cpsi (cells per square inch). What was cut out was used.

Next, La-containing alumina adjusted so that Zr-12Nd-18Pr, Zr-23Ce-4Nd, La ₂ O ₃ is contained in an amount of 5% by mass, and Al ₂ O ₃ is contained in an amount of 95% by mass is represented by 2: It mixed so that it might become 1: 6, and the catalyst material was obtained.

  Then, Pt was supported on the catalyst material as a catalyst noble metal. In the Pt loading method, a dinitrodiamine platinum nitric acid solution is added to and mixed with the catalyst material, and Pt is supported on the catalyst material by evaporation to dryness. The supported amount of Pt is set to 1.8 g / L with respect to the catalyst material.

  After drying this, it was pulverized in a mortar and baked in an electric furnace in an air atmosphere at 500 ° C. for 2 hours to obtain a catalyst powder (Pt-supported composite oxide powder) containing a Zr-based composite oxide.

  The Pt-supported composite oxide powder was mixed with water and a binder to form a slurry, and the slurry was coated on the filter body 6 plugged by the sealing portion 15 and dried. The coating amount at this time was adjusted to 20 g / L. Then, DPF3 in which the catalyst layer 8 was formed in substantially the entire area of the internal flow path of the filter main body 6 was obtained by heating in an air furnace at 500 ° C. for 2 hours and baking.

  About the obtained DPF, carbon combustion performance and gas purification performance (light-off temperature, high temperature purification rate) were evaluated by the following methods.

(Carbon combustion performance)
A carbon combustion time evaluation experiment was conducted in which each DPF 3 was set in a model gas flow catalyst evaluation device for flowing simulated exhaust gas to examine the carbon combustion performance.

In this experiment, carbon black powder (manufactured by Sigma-Aldrich) was deposited on DPF3 instead of PM as an index for determining PM combustion performance, and when the temperature was raised while flowing simulated exhaust gas, Evaluation was performed using the concentration of CO ₂ and CO discharged by combustion. The carbon black powder is deposited by adding 10 cc of ion-exchanged water to a carbon black powder equivalent to 5 g / L, and stirring and mixing for 5 minutes using a stirrer to sufficiently disperse the carbon black powder. The upstream end side of the DPF 3 was immersed in this, and at the same time, suction was performed by an aspirator from the opposite side of the immersed end surface. Moisture that could not be removed by this suction was removed by air blow from the soaked end face side, and dried at 150 ° C. for 2 hours in a dryer.

In the model gas flow catalyst evaluation apparatus, the temperature of the inlet of the DPF 3 was increased to 580 ° C. or 640 ° C. while flowing nitrogen gas. Thereafter, simulated exhaust gas containing 10% by volume and 300 ppm of oxygen and NOx with respect to the total gas flow rate and the remainder being nitrogen gas was circulated so that the space velocity was 40,000 / hour, and DPF3 The CO and CO ₂ concentrations immediately after the outlet of the were measured over time. Then, the CO, based on CO ₂ concentration, determine the carbon burning rate defined by the above equation was calculated integrated value of carbon combustion amount per second. From the integrated value, the time when carbon burned 90% was measured, and the time was defined as the carbon combustion time.

  The results are shown in FIGS. FIG. 10 is a graph showing the measurement result of the carbon combustion time when the temperature of the DPF 3 inlet is 580 ° C. FIG. 11 is a graph showing the measurement result of the carbon combustion time when the temperature of the inlet of the DPF 3 is 640 ° C. In each figure, the measurement results using the DPF 3 subjected to heat treatment for 24 hours under an atmospheric pressure condition of 800 ° C. for 24 hours and those not subjected to the heat treatment are displayed side by side.

  10 and 11, Example 1 and Example 2 using the Zr-based composite oxide in which the content of the oxide RO of the rare earth metal R is more than 33 mol% and less than 40 mol% are It can be seen that the carbon combustion rate is higher than that of Comparative Example 1 using the Zr-based composite oxide having an oxide RO content of 33 mol% or less.

(Gas purification performance)
As gas purification performance, light-off temperature and high temperature purification rate were measured. In the evaluation, each DPF 3 is set in a model gas flow catalyst evaluation apparatus, and the simulated exhaust gas is circulated so that the space velocity is 50,000 / h, and the temperature is raised at a rate of 15 ° C./min. It was. The simulated exhaust gas at this time is oxygen gas (O ₂ ), water vapor (H ₂ O), nitrogen monoxide gas (NO), hydrocarbon (propylene) (C ₃ H ₆ ), carbon monoxide gas (CO), It is constituted by a balance of nitrogen _{(N 2),} except the balance nitrogen, respectively, 10%, 10%, 100 ppm, 200 ppmC (carbon equivalent), contains 400 ppm.

  As the light-off temperature, the simulated exhaust gas temperature on the inlet side of the DPF 3 when the HC and CO concentrations immediately after the outlet portion of the DPF 3 reached 50% was measured.

  The measurement results are shown in FIG. In FIG. 12, the measurement results using the DPF 3 subjected to heat treatment for 24 hours under the atmospheric pressure condition of 800 ° C. for 24 hours and those not subjected to the heat treatment are displayed side by side. From FIG. 12, Example 1 and Example 2 using the Zr-based composite oxide in which the content of the oxide RO of the rare earth metal R is more than 33 mol% and less than 40 mol% are the oxides of the rare earth metal R. It can be seen that the light-off temperature is lower than that of Comparative Example 1 using the Zr-based composite oxide having a RO content of 33 mol% or less, and the exhaust gas purification performance is improved.

  As the high temperature purification rate, the purification rate of HC and CO immediately after the outlet portion of the DPF 3 when the simulated exhaust gas temperature on the inlet side of the DPF 3 reached 400 ° C. was measured.

  The measurement results are shown in FIG. In FIG. 13, the measurement results using the DPF 3 subjected to heat treatment for 24 hours under an atmospheric pressure condition of 800 ° C. for 24 hours and those not subjected to the heat treatment are displayed side by side. From FIG. 13, it can be seen that there is no significant difference between the DPFs 3.

[Example C]
Next, a case where Zr-based composite oxides in which the content of the oxide RO of the rare earth metal R is different between the upstream side and the downstream side was examined.

Example 3
The DPF carrier (filter body 6) of the present example has a cell structure of 25 ml from a DPF carrier made of silicon carbide (SiC) having a wall thickness of 12 mil of the porous partition wall 5 and a cell number of 300 cpsi (cells per square inch). What was cut out to have a volume of 25.4 mm in diameter was used.

  Next, Zr-based composite oxides (Zr-18Nd-18Pr, Zr-12Nd-18Pr) were prepared. These Zr-based composite oxides are prepared by dissolving a predetermined amount of a nitrate of each metal (Zr, Nd, Pr) mixed in ion-exchanged water, dropping a basic solution adjusted with ammonia, and adding each metal element. A Zr-based composite oxide is obtained by producing a precipitate containing it, followed by filtration, washing with water, drying, and firing at 500 ° C. for 2 hours.

  Then, Pt was supported on these Zr-based composite oxides as a catalyst noble metal. As for the method of supporting Pt, a dinitrodiamine platinum nitric acid solution is added to each Zr-based composite oxide and mixed, and Pt is supported on the Zr-based composite oxide by evaporation to dryness. The amount of Pt supported is set to 1% by mass with respect to the Zr-based composite oxide.

  After drying this, it is pulverized in a mortar and heated and fired in an electric furnace at 500 ° C. in an air atmosphere for 2 hours to obtain a Zr-based catalyst powder (Pt-supported composite oxide powder) containing a Zr-based composite oxide. It was. The Pt-supported composite oxide powder containing Zr-18Nd-18Pr was used as the upstream catalyst powder, and the Pt-supported composite oxide powder containing Zr-12Nd-18Pr was used as the downstream catalyst powder.

  In order to simulate the difference in heat between the upstream catalyst layer and the downstream catalyst layer, the upstream catalyst powder is subjected to an aging treatment in which the upstream catalyst powder is allowed to stand for 24 hours under an atmospheric pressure condition of 800 ° C., and the downstream catalyst powder is heated to 1000 ° C. An aging treatment was performed for 24 hours under atmospheric pressure.

  The Pt-supported composite oxide powder subjected to the aging treatment is mixed with water and a binder to form a slurry, and the upstream catalyst is placed in a region 20% from the upstream end of the filter body 6 plugged by the sealing portion 15. The slurry containing the powder is coated and dried, and then the remaining region is coated with the slurry containing the downstream catalyst powder and dried. At this time, the coating amount of each of the upstream catalyst layer and the downstream catalyst layer is distributed according to the ratio of the area to be coated with a total coating amount of 20 g / L. In the case of this example, the upstream 20% and the downstream 80%, so that 4 g / L is coated on the upstream catalyst layer and 16 g / L is coated on the downstream catalyst layer. Thereafter, the DPF 3 (upstream 20) according to Example 1 in which the catalyst layer 8 was formed in substantially the entire area of the internal flow path of the filter body 6 by heating and firing in an air atmosphere at 500 ° C. for 2 hours with an electric furnace. % Zr-18Nd-18Pr and 80% downstream Zr-12Nd-18Pr).

Example 4
The same as Example 3 except that the slurry containing the upstream catalyst powder is coated in a region 40% from the upstream end (Zr-18Nd-18Pr in the upstream 40% and Zr-12Nd-18Pr in the downstream 60%). ).

(Example 5)
Same as Example 3 except that 50% from the upstream end is coated with slurry containing upstream catalyst powder (Zr-18Nd-18Pr at 50% upstream, Zr-12Nd-18Pr at 50% downstream) ).

(Example 6)
Same as Example 3 except that 60% from the upstream end is coated with slurry containing upstream catalyst powder (upstream 60% Zr-18Nd-18Pr, downstream 40% Zr-12Nd-18Pr). ).

(Example 7)
It is the same as Example 4 except using Zr-12Nd-24Pr instead of Zr-18Nd-18Pr (Zr-12Nd-24Pr upstream 40%, Zr-12Nd-18Pr downstream 60%).

(Example 8)
It is the same as Example 4 except using Zr-18Nd-18Pr-3La instead of Zr-18Nd-18Pr (Zr-18Nd-18Pr-3La upstream 40%, Zr-12Nd-18Pr downstream 60%) ).

Example 9
The same as Example 4 except that Zr-12Nd is used instead of Zr-12Nd-18Pr (Zr-18Nd-18Pr in the upstream 40% and Zr-12Nd in the downstream 60%).

(Example 10)
It is the same as that of Example 4 except using Zr-12Nd-12Pr instead of Zr-12Nd-18Pr (Zr-18Nd-18Pr in upstream 40%, Zr-12Nd-12Pr in downstream 60%).

(Example 11)
Ce _0.25 Zr _0.75 O ₂ carrying Pt on the upstream catalyst powder and downstream catalyst powder (Pt loading: 1% by mass with respect to Ce _0.25 Zr _0.75 O ₂ ) And Pt-supported alumina (Pt-supported amount: 1% by mass with respect to alumina).

(Comparative Example 2)
The same as Example 3 except that the entire surface of the filter body 6 was coated with the slurry containing the downstream catalyst powder in Example 3 (uniform coating of Zr-12Nd-18Pr).

(Comparative Example 3)
In the downstream catalyst powder in Example 3 , Ce _0.25 Zr _0.75 O ₂ carrying Pt (Pt loading: 1 mass% with respect to Ce _0.25 Zr _0.75 O ₂ ) and Pt The same as in Example 3 except that a mixture of supported alumina (Pt supported amount: 1% by mass with respect to alumina) was mixed, and the slurry containing the obtained powder was coated on the entire surface of the filter body 6. It is.

(Carbon combustion performance)
A carbon combustion rate evaluation experiment was conducted to examine the carbon combustion performance in a state where the DPF 3 according to the above Examples 3 to 10 and Comparative Example 2 was set in a model gas flow catalyst evaluation device for flowing simulated exhaust gas.

In this experiment, carbon black powder (manufactured by Sigma-Aldrich) was deposited on DPF3 instead of PM as an index for determining PM combustion performance, and when the temperature was raised while flowing simulated exhaust gas, Evaluation was performed using the concentration of CO ₂ and CO discharged by combustion. The carbon black powder is deposited by adding 10 cc of ion exchange water to a carbon black powder equivalent to 10 g / L and stirring and mixing for 5 minutes using a stirrer to sufficiently disperse the carbon black powder. The upstream end side of the DPF 3 was immersed in this, and at the same time, suction was performed by an aspirator from the opposite side of the immersed end surface. Moisture that could not be removed by this suction was removed by air blow from the soaked end face side, and dried at 150 ° C. for 2 hours in a dryer.

In the model gas flow catalyst evaluation device, the oxygen gas and water vapor are each contained in an amount of 10% by volume with respect to the total gas flow rate while the temperature is raised to 600 ° C. at a rate of 15 ° C./min, and the remainder is nitrogen gas or the like. The simulated exhaust gas was circulated so that the space velocity was 50000 / h, and the CO and CO ₂ concentrations immediately after the outlet of the DPF 3 were measured. Based on the CO and CO ₂ concentrations, the carbon burning rate determined by the above equation was obtained. This carbon burning rate indicates the amount of carbon burned per liter of the carrier (DPF3).

  The results are shown in FIGS. FIG. 14 is a graph showing the measurement result of the carbon combustion rate when the ratio of the length of the upstream catalyst layer to the length of the filter body 6 in the flow direction is changed. FIG. 15 is a graph showing the measurement results of the carbon combustion rate when the composition of the upstream catalyst layer and the downstream catalyst layer is changed.

  14 and 15, Examples 3 to 6 in which the content of the oxide RO of the rare earth metal R is lower on the downstream side than on the upstream side are comparative examples in which a catalyst layer having the same composition is formed on the entire surface of the filter body 6. It can be seen that the carbon burning rate is higher than 2.

(Light-off temperature)
The DPF 3 according to Example 11 and Comparative Example 3 is set in the model gas flow catalyst evaluation apparatus, and the simulated exhaust gas is circulated so that the space velocity is 50,000 / h, and the rate of 15 ° C./min. The simulated exhaust gas temperature on the inlet side of the DPF 3 was measured when the HC and CO concentrations immediately after the outlet portion of the DPF 3 reached 50%. The simulated exhaust gas at this time is oxygen gas (O ₂ ), water vapor (H ₂ O), nitrogen monoxide gas (NO), hydrocarbon (propylene) (C ₃ H ₆ ), carbon monoxide gas (CO), Consists of nitrogen (N ₂ ), where each gas is included in this order in the order of 10% by volume, 10% by volume, 300ppm, 200ppmC (carbon conversion), 400ppm, and the remainder with respect to the total gas flow rate. ing.

The measurement result of this light-off temperature is shown in FIG . From FIG. 16 , the content ratio of the oxide RO of the rare earth metal R with respect to the Zr-based composite oxide in the catalyst containing the alumina supporting the Pt and the CeZr-based composite oxide on each of the upstream side and the downstream side. In Example 11, which is lower on the downstream side than on the upstream side, the light-off temperature is lower than that in Comparative Example 3 in which the entire surface of the filter body 6 contains the Zr-based composite oxide on the downstream side in Example 11. It can be seen that the exhaust gas purification performance is improved.

  From the above, the Zr-based composite oxide having a high content of the oxide RO of the rare earth metal R is suitable on the upstream side where the temperature of the exhaust gas is relatively low, and the content of the oxide RO of the rare earth metal R is It can be seen that a low Zr-based composite oxide is suitable on the downstream side where the temperature of the exhaust gas is relatively high.

It is the schematic which shows the state which assembled | attached DPF3 in the exhaust passage 1 of a diesel engine. It is the schematic which shows DPF3 seen from the upstream of the flow direction of exhaust gas. It is the schematic sectional drawing which looked at DPF3 shown in Drawing 2 from cut surface line III-III '. The expanded sectional view of the porous partition wall 5 is shown. It is explanatory drawing which shows the oxidation mechanism of PM. It is drawing for demonstrating the mechanism in which the combustion rate of PM of Zr system complex oxide becomes high. It is the graph which showed the burning rate of carbon in various DPF3. Is a graph showing changes in carbon burning rate with changes in the content of _Nd 2 _{O 3} in the Zr-Nd composite oxide and Zr-Nd-Pr composite oxide. It is a chart figure which shows the measurement result of the X-ray-diffraction measurement of Pt carrying | support complex oxide powder containing Zr-18Nd-18Pr, and Pt carrying | support complex oxide powder containing Zr-12Nd-18Pr. It is a graph which shows the measurement result of carbon combustion time when the temperature of the inlet_port | entrance of DPF3 shall be 580 degreeC. It is a graph which shows the measurement result of carbon combustion time when the temperature of the inlet_port | entrance of DPF3 shall be 640 degreeC. It is a graph which shows the measurement result of light-off temperature. It is a graph which shows the measurement result of a high temperature purification rate. It is a graph which shows the measurement result of the carbon combustion rate when changing the ratio of the length of the upstream catalyst layer to the length of the flow direction of the filter body 6. It is a graph which shows the measurement result of the carbon combustion rate when changing the composition of an upstream catalyst layer and a downstream catalyst layer. It is a graph which shows the measurement result of light-off temperature.

Explanation of symbols

1 Exhaust passage 3 DPF
4 Flow path 6 Filter body 8 Catalyst layer 9 Carbon 15 Sealing part

Claims (8)

A particulate filter disposed in the exhaust gas passage for collecting particulates in the exhaust gas discharged from the engine,
A filter body comprising a porous partition wall defining a plurality of exhaust gas passages through which the exhaust gas passes, formed on the surface of the porous partition wall, zirconium (Zr), a rare earth metal other than cerium, and oxygen (O) And a catalyst layer containing a Zr-based composite oxide consisting of
The Zr-based composite oxide is characterized in that the rare earth metal oxide content is more than 33 mol% and less than 40 mol% with respect to the total amount of ZrO ₂ and the rare earth metal oxide. filter.   The Zr-based composite oxide is identified as a mixed phase of the phase composed of the Zr-based composite oxide and the phase composed of the rare earth metal oxide in X-ray diffraction measurement after heat treatment at 1000 ° C. for 6 hours or more. The particulate filter according to claim 1, which is a filter. When the catalyst layer has a side closer to the exhaust gas inflow portion as an upstream side and a side closer to the outflow portion as a downstream side,
The upstream side contains the Zr-based composite oxide,
The downstream side contains Zr and a rare earth metal other than cerium, and the content of the rare earth metal oxide with respect to the total amount of ZrO ₂ and the rare earth metal oxide is 8 mol% or more and 33 mol% or less. The particulate filter according to claim 1 or 2, which contains a certain second Zr-based composite oxide.   The particulate filter according to claim 3, wherein the upstream catalyst layer is 20 to 60% of a length from the inflow portion to the inflow portion of the filter main body to the discharge portion.   The particulate filter according to any one of claims 1 to 4, wherein the rare earth metal is at least one selected from the group consisting of neodymium, lanthanum, and praseodymium. The Zr-based composite oxide, the particulate filter according to any one of 請 Motomeko 1-5 of supporting platinum as the catalyst noble metal.   The particulate filter according to any one of claims 1 to 6, wherein the catalyst layer further includes alumina on which platinum is supported. The particulate filter according to any one of claims 1 to 7, wherein the catalyst layer further includes a ZrCe-based composite oxide containing zirconium (Zr) and cerium (Ce) and supporting platinum.

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