JP4618046B2 - Diesel particulate filter - Google Patents

Description

  The present invention relates to a diesel particulate filter that is disposed in an exhaust passage of a diesel engine, collects particulates by circulating exhaust gas, and burns and purifies the particulates with a particulate oxidizing material.

  Since particulates discharged from diesel engines (hereinafter referred to as PM) have a large impact on the environment, the number of automobiles provided with diesel particulate filters (hereinafter referred to as DPF) for collecting PM has increased. ing. When the DPF is provided in this way, it is necessary to remove PM collected by the DPF in order to maintain engine output and fuel consumption.

For this purpose, for example, in a wall flow type cylindrical filter generally used as a DPF, platinum (Pt) -carrying alumina and a NOx trap material are disposed on the inner wall surface of the flow path on the exhaust gas outflow side. One that burns PM by NO ₂ absorbed in the trap material is known (see Patent Document 1).

In addition, the inner wall surface of the exhaust gas passage of the filter is coated with a cerium-zirconium double oxide having an oxygen storage capacity, and the double oxide is loaded with a catalytic noble metal having an oxidation catalytic action, and is switched instantaneously. A technique has also been proposed in which active oxygen is released from the double oxide in a rich air-fuel ratio atmosphere, and PM is combusted by the active oxygen (see Patent Document 2).
JP-A-9-94434 JP 2003-334443 A

  In the DPFs described in these patent documents, it is said that PM can be burned at a relatively low combustion temperature, but in order to further lower the PM combustion temperature, the PM is efficiently and quickly removed. There is a need to regenerate the DPF.

  By the way, in this type of DPF, an oxidation catalyst that oxidizes HC and the like is often provided on the upstream side, and fuel increased by rich purge control or the like in a diesel engine is introduced into the DPF by burning with this oxidation catalyst. Means for increasing the exhaust gas temperature and promoting PM combustion are taken. Therefore, it is required to efficiently regenerate the DPF that oxidizes and burns PM in order to shorten the increased fuel injection period or to reduce the fuel injection amount. Here, in order to efficiently oxidize and burn PM in a short period of time, it may be possible to support a catalyst noble metal such as platinum on a carrier and increase the amount of catalyst noble metal supported, but increase the amount of catalyst noble metal supported. If this is the case, not only will the cost be increased, but there is also a concern that the degree of dispersion of the catalyst noble metal will decrease and sintering will easily occur.

  In view of the above circumstances, an object of the present invention is to provide a diesel particulate filter capable of lowering the PM combustion temperature while suppressing the amount of catalyst noble metal used by efficiently burning PM. .

  As a result of diligent research, the present inventor has found that a zirconium-based double oxide containing a rare earth metal except zirconium and cerium and yttrium, and a rare earth metal or alkaline earth mainly containing cerium and excluding cerium. A double oxide containing at least one of a cerium-based double oxide containing a metal and the like has an oxygen ion (also referred to as oxide ion) conductivity. In addition, the particulate oxidation catalyst can contain the cerium-zirconium double oxide having the oxygen storage ability, thereby improving the continuity of the PM oxidation reaction. Can be burned efficiently and in a short time, and cerium with equivalent PM burning performance And we have completed the present invention found that it is possible to suppress the amount of the catalyst precious metal contained in the particulate oxidation catalyst compared to zirconium mixed oxide.

That is, a DPF (diesel particulate filter) according to the present invention is a diesel particulate filter that is provided in a diesel engine exhaust passage and provided with a particulate oxidation catalyst having a catalytic noble metal for burning particulates. The particulate oxidation catalyst comprises a zirconium-based double oxide containing zirconium as a main component and a rare earth metal excluding cerium and yttrium, and a rare earth metal or alkaline earth metal containing cerium as a main component and excluding cerium. Both of the cerium-based complex oxides contained, and the cerium-based complex oxides in a proportion of 10 mass% or more and 80 mass% or less with respect to the total mass of the zirconium complex oxide added. It is characterized that you have been mixed with the oxide It is intended.

  According to this invention, PM deposited on the filter can be burned efficiently and in a short time. This is presumed to be due to the following reason.

That is, since the zirconium-based complex oxide and the cerium-based complex oxide have oxygen ion conductivity, if PM adheres to the inside of the DPF and a portion having a locally low oxygen concentration is generated on the surface, Oxygen ions move from the high oxygen concentration through the complex oxide, and are sequentially released as active oxygen (O ₂ ⁻ ).

  This active oxygen reacts with PM containing carbon as a main component, that is, oxidizes PM to form a fire type. When this kind of fire is formed, the surrounding oxygen is deficient, but as described above, oxygen ions move sequentially through the zirconium-based oxide and cerium-based oxide, and active oxygen continues to the deficient site. Therefore, the combustion area is expanded around this fire type. In this way, since the fire kind generated at a certain site continuously burns and expands the combustion region, PM can be oxidized and burned efficiently even at a low temperature. For this reason, when the DPF is regenerated (PM combustion purification), even when fuel is supplied to the engine or the DPF, the fuel injection amount can be reduced, and the filter can be regenerated efficiently and in a short time. And fuel consumption can be improved.

  Moreover, as will be shown later in the experimental data, the amount of catalyst noble metal contained in the particulate oxidation catalyst used to achieve a combustion rate equivalent to that of the cerium-zirconium-based double oxide can be reduced. It becomes possible to manufacture a curate oxidation catalyst, and thus a diesel particulate filter, at a low cost.

Here, the reason why cerium is excluded from the rare earth metal of the zirconium-based double oxide is that the cerium-zirconium double oxide mainly functions as an oxygen storage material and has low oxygen ion conductivity. This is because the particulate oxidation catalyst containing zirconium-yttrium double oxide (ZrO ₂ —Y ₂ O ₃ ) is specified in the prior application (Japanese Patent Application No. 2004-83078) by the applicant of the present application. The present invention is based on the discovery of a zirconium-based double oxide that can obtain a better burning rate than the zirconium-yttrium double oxide as a result of further earnest studies.

  The rare earth metal contained in the zirconium-based double oxide is preferably at least one metal selected from scandium, neodymium and ytterbium. That is, these rare earth metals can improve the combustion rate of PM as will be shown later in experimental data, and thereby PM can be oxidized and burned efficiently.

  The rare earth metal contained in the cerium-based double oxide is preferably at least one metal selected from samarium and gadolinium. That is, these rare earth metals can improve the combustion rate of PM as will be shown later in experimental data, and thereby PM can be oxidized and burned efficiently.

  Furthermore, the alkaline earth metal contained in the cerium-based double oxide is preferably at least one metal selected from magnesium, calcium, strontium, and barium. That is, these alkaline earth metals can improve the combustion rate of PM, and can efficiently oxidize and burn PM, as will be shown later in experimental data.

Further, in the present invention, both the zirconium-based double oxide and the cerium-based double oxide are contained, and the cerium-based double oxide is zirconium-based at a ratio of 10% by mass to 80% by mass with respect to the total mass. that is mixed with the mixed oxide.

  If constituted in this way, as shown in experimental data later, it shows higher PM combustion performance than the case of single composition due to the interaction between zirconium-based double oxide and cerium-based double oxide, and more efficiently PM can be burned.

  The diesel particulate filter of the present invention can burn PM deposited on the filter efficiently and in a short period of time, thereby improving fuel efficiency and reducing the amount of catalyst noble metal used, There is an advantage that the manufacturing cost can be suppressed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the DPF 3 assembled in the exhaust passage 1 of the diesel engine. In this figure, an exhaust pipe constituting the exhaust passage 1 is connected to a diesel engine main body (not shown) via an exhaust manifold. And the exhaust gas discharged | emitted from a diesel engine main body flows into the exhaust passage 1 from the left side to the right side in FIG. 1, as shown by the white arrow.

  The exhaust passage 1 is provided with a DPF (Diesel Particulate Filter) 3 for collecting PM (Particulate Matter) in the exhaust gas. 2 and 3 are explanatory diagrams schematically showing the DPF 3. FIG.

The DPF 3 is a so-called wall flow type filter whose outer shape is formed in a cylindrical shape, and is a porous material in which a large number of flow holes 5a (see FIG. 4) are formed of cordierite or SiC, Si ₃ N ₄ ceramics. A filter body 6 formed in a honeycomb shape having a large number of cells 4 (passages) partitioned by walls 5 and extending in parallel with each other along the exhaust path, the upstream end side of some of the cells 4b in a staggered manner, and the other A plugging portion 15 that plugs the downstream end side of the cell 4a is provided. Therefore, as shown by the arrow in FIG. 3, the DPF 3 is exhausted by the exhaust gas flowing in from the upstream cell 4a having the upstream end opened through the porous wall 5 to the downstream cell 4b having the downstream end opened. In the meantime, PM is collected. Instead of the DPF 3, a conventionally known three-dimensional network structure carrier using a heat-resistant material such as ceramics or sintered alloy may be used.

  As shown in FIG. 4, an oxidation catalyst layer 8 is formed in the internal flow path of the DPF 3 through which the exhaust gas flows by coating the inner wall surface with a particulate oxidation catalyst that burns PM. The particulate oxidation catalyst includes a catalytic noble metal for burning PM and a double oxide as a carrier supporting the catalytic noble metal. The oxidation catalyst layer 8 composed of the particulate oxidation catalyst may be formed over the entire area of the internal flow path, or may be formed upstream of the internal flow path, particularly the upstream cell 4a and the flow hole. It may be formed on the inner wall surface of 5a.

  The catalyst noble metal is exemplified by at least one selected from platinum (Pt), palladium (Pd), rhodium (Rh), and the like. For example, with respect to platinum (Pt), a dinitrodiamine platinum nitric acid solution is added to the above double oxide and mixed. The double oxide is supported by the evaporation to dryness method. The amount of the catalyst noble metal supported on the double oxide can be adjusted, for example, by adjusting the concentration and amount of the dinitrodiamine platinum nitrate solution for platinum (Pt).

  The double oxide supporting the catalytic noble metal includes at least one of a zirconium-based double oxide mainly containing zirconium (Zr) and a cerium-based double oxide mainly containing cerium (Ce). .

  The zirconium-based double oxide is adjusted so that the content of zirconium in the content is maximized, and includes rare earth metals excluding cerium (Ce) and yttrium (Y). The rare earth metal contained in the zirconium-based complex oxide is preferably a trivalent and stable metal, and excludes the above cerium (Ce) and yttrium (Y), Sc, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among them, at least one metal selected from scandium (Sc), neodymium (Nd), and ytterbium (Yb) is preferable.

  Note that cerium (Ce) is excluded from the rare earth metals contained in the zirconium-based complex oxide because cerium is tetravalent and stable and exhibits oxygen ion conductivity as described later under predetermined conditions. In other words, since it may function as an electron transfer medium, it is difficult to effectively exhibit oxygen ion conductivity.

  The cerium-based double oxide is adjusted so that the content of cerium among the contents is maximized, and includes rare earth metals other than cerium (Ce), or alkaline earth metals. The rare earth metal contained in the cerium-based double oxide is preferably a trivalent and stable metal, and excluding the cerium (Ce) and yttrium (Y), Sc, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among these, at least one metal selected from samarium (Sm) and gadolinium (Gd) is preferable. Further, the alkaline earth metal contained in the cerium-based double oxide is preferably at least one metal selected from magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

  In order to form the oxidation catalyst layer 8, a catalyst noble metal is supported on the double oxide, and then the catalyst noble metal-supported double oxide is mixed with water and a binder to produce a slurry. After coating the inner wall surface of the inner flow path and removing excess slurry by air blowing, drying and firing are performed. The thickness and the like of the oxidation catalyst layer 8 can be adjusted by the viscosity and concentration of the slurry. When two or more kinds of double oxides are included in the particulate oxidation catalyst forming the oxidation catalyst layer 8, it is preferable to carry a catalyst noble metal on each double oxide.

  The particulate oxidation catalyst may contain any one of the plural types of zirconium-based double oxides or cerium-based double oxides exemplified above, but at least one of the zirconium-based double oxides In addition, it is preferable to select at least one of cerium-based double oxides and include these multiple types of double oxides. That is, as will become clear from the experimental data described later, it has been experimentally found that the PM combustion rate is improved by including each system of double oxides in the particulate oxidation catalyst. This mechanism is not necessarily clear, but by mixing double oxides with different physical properties, oxygen ion conductivity and oxygen storage / release ability are matched to achieve a synergistic effect on improving PM combustion rate. It is thought that there is.

  These zirconium-based complex oxides and cerium-based complex oxides have oxygen ion conductivity. The mechanism by which PM is oxidized by the particulate oxidation catalyst using the double oxide having oxygen ion conductivity is assumed as follows. FIG. 4 is an enlarged cross-sectional view showing the porous wall 5, and FIG. 5 is an explanatory view showing the oxidation mechanism of PM.

  When exhaust gas is discharged from the diesel engine body and PM is collected in the DPF 3, carbon 9 is deposited on the oxidation catalyst layer 8. Since the carbon 9 is porous and has a characteristic of adsorbing oxygen, oxygen adsorption / desorption occurs on the surface portion of the oxidation catalyst layer 8 on which the carbon 9 is deposited in an oxygen-excess atmosphere. It reduces and produces a microscopic difference in oxygen concentration with respect to other parts.

Thus, when the oxygen concentration in a certain portion of the surface of the oxidation catalyst layer 8 decreases, the double oxide constituting the oxidation catalyst layer 8 has oxygen ion conductivity. O ²⁻ moves to the surface portion where the oxygen concentration is lowered. This oxygen ion O ²⁻ reaches the surface of the oxidation catalyst layer 8 to become active oxygen, and as a result, a place where a carbon oxidation reaction is likely to occur on the surface of the double oxide locally occurs.

  Then, the oxidation reaction of the carbon 9 starts at the site where the reaction conditions are the best. When this oxidation reaction starts, 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 of this embodiment, the particulate oxidation catalyst constituting the PM oxidation catalyst layer 8 has oxygen ion conductivity. Since it is configured to contain the complex oxide, the active oxygen is continuously supplied to the oxygen-deficient space 11 by the function of the complex oxide, whereby the oxidation reaction of the carbon 9 is promoted, and the fire type 10 is the center. As the combustion area expands.

  That is, in an oxygen-excess atmosphere, an oxygen concentration difference is generated between the oxygen-deficient space 11 and its surroundings, and charge imbalance is caused in a microscopic region inside the double oxide of the oxidation catalyst layer 8 based on the concentration difference. As a result, oxygen ions are moved from the portion having a high oxygen concentration to the oxygen-deficient space 11 through the double oxide of the PM oxidation 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, since the fire type 10 generated on a part of the surface of the oxidation catalyst layer 8 is not lost, the combustion region is expanded, so that the PM that is the carbon 9 can be burned and purified efficiently and in a short period of time. For this reason, the combustion temperature of PM can be substantially reduced.

  Here, when the double oxide contains a trivalent metal such as a rare earth metal or a divalent metal such as an alkaline earth metal, zirconium or cerium is used inside the double oxide as shown in FIG. Since a part of the metal is replaced with a trivalent or divalent metal (indicated by black circles in the figure), oxygen ion vacancies exist, and oxygen ions are transported through the vacancies.

  In order to confirm such an effect, an experiment conducted for evaluating PM combustion performance in the DPF 3 and the result thereof will be described below.

(Sample and experimental method)
(Evaluation experiment of PM burning rate)
For the evaluation experiment, a plurality of samples in which the components and content ratios of the double oxide contained in the particulate oxidation catalyst were changed were prepared. That is, as a sample of DPF3, carbon black, which is simulated PM, is formed on the surface of the catalyst layer of nine types of examples of zirconium-based double oxides, ten types of examples of cerium-based double oxides, and four types of comparative examples. An experiment was conducted in which the carbon burning rate was measured at an atmospheric temperature of 590 ° C.

  As the DPF carrier (filter body 6) of this experiment, a cell carbide structure of 12 mil / 300 cspi silicon carbide DPF carrier hollowed out into a cylindrical shape with an apparent volume of 25 cc was used.

(Sample preparation method)
First, preparation methods of each example and comparative example will be described.

  In the preparation of the zirconium-based examples, a total of nine types of zirconium-based double oxides are prepared by changing the content of rare earth metal oxides different from the zirconium oxide in three stages. These zirconium complex oxides dissolve nitrates of each metal mixed in ion-exchanged water, drop an alkaline solution adjusted with ammonia to form a precipitate containing each metal element, and filter, wash, dry, and calcine. Generated to go. Then, platinum (Pt) as a catalyst noble metal is supported on these zirconium-based double oxides. The amount of platinum supported is set to 0.5 g / L with respect to 50 g / L (50 g per 1 L of DPF3) zirconium-based double oxide. As shown in FIG. 6, some samples are prepared with the platinum loadings set to 1.0 g / L and 2.0 g / L with respect to 50 g / L of the zirconium-based double oxide. The burning rate is measured.

_{That, ZrO 2 -Yb 2 O 3 (} Yb 2 O 3: 3mol%), ZrO 2 -Nd 2 O 3 (Nd 2 O 3: 3mol%), ZrO 2 -Sc 2 O 3 (Sc 2 O 3: 3mol _{%), ZrO 2 -Yb 2 O} 3 (Yb 2 O 3: 8mol%), ZrO 2 -Nd 2 O 3 (Nd 2 O 3: 8mol%), ZrO 2 -Sc 2 O 3 (Sc 2 O 3: _{8mol%), ZrO 2 -Yb 2} O 3 (Yb 2 O 3: 12mol%), ZrO 2 -Nd 2 O 3 (Nd 2 O 3: 12mol%), ZrO 2 -Sc 2 O 3 (Sc 2 O 3 : 12 mol%) each of the double oxide powders was mixed with a dinitrodiamine platinum nitric acid solution, and Pt was supported on the zirconium-based double oxide by evaporation to dryness.

  After drying this, it was pulverized in a mortar, and was heated and fired in an air furnace at 500 ° C. for 2 hours to obtain a zirconium-based catalyst powder (Pt-supported double oxide powder) composed of a zirconium-based double oxide. . The obtained Pt-supported double oxide is mixed with water and a binder to form a slurry. The slurry is sucked into the filter body 6 plugged by the plugging portion 15 and excess slurry is removed by air blowing. The zirconium-based catalyst in which the oxidation catalyst layer 8 is formed in substantially the entire area of the internal flow path of the filter main body 6 after being coated with a dry coat, dried and heated in an electric furnace at 500 ° C. in an air atmosphere for 2 hours. A sample was obtained.

  In preparing the cerium-based examples, a total of 10 kinds of cerium-based double oxides are prepared by changing the contents of different alkaline earth metal oxides with respect to the cerium oxide. These cerium-based double oxides were mixed with an aqueous solution of cerous nitrate and an aqueous nitrate solution of each alkaline earth metal and co-precipitated with ammonia in the same manner as the formation of zirconium-based double oxides to obtain hydroxides. Thereafter, it is filtered, washed with water, dried and fired to produce a powder. Then, platinum (Pt) as a catalyst noble metal is supported on these cerium-based double oxides. The supported amount of platinum is set to 0.5 g / L with respect to a cerium-based double oxide of 50 g / L (50 g per 1 L of DPF3). As shown in FIG. 6, some samples are prepared in which the platinum loading is set to 1.0 g / L and 2.0 g / L for 50 g / L cerium-based double oxide. The burning rate is measured.

_{That, CeO 2 -MgO (MgO: 8mol} %), CeO 2 -CaO (CaO: 8mol%), CeO 2 -SrO (SrO: 8mol%), CeO 2 -BaO (BaO: 8mol%), CeO 2 -CaO _{(CaO: 20mol%), CeO} 2 -BaO (BaO: 20mol%), CeO 2 -Sm 2 O 3 (Sm 2 O 3: 4mol%), CeO 2 -Sm 2 O 3 (Sm 2 O 3: 10mol% ), CeO ₂ —Gd ₂ O ₃ (Sm ₂ O ₃ : 4 mol%), CeO ₂ —Gd ₂ O ₃ (Sm ₂ O ₃ : 10 mol%) Were added and mixed, and Pt was supported on the cerium-based double oxide by the evaporation to dryness method.

  Then, similarly to the above-mentioned zirconium double oxidation catalyst, drying, pulverization, and thermal firing were performed to obtain a cerium-based catalyst powder (Pt-supported double oxide powder) composed of a cerium-based double oxide. The obtained Pt-supported double oxide was mixed with water and a binder to form a slurry, which was removed by suction and air blow, dried and fired, as in the case of the zirconium double oxidation catalyst, A cerium-based sample in which the oxidation catalyst layer 8 was formed over substantially the entire flow path was obtained.

As comparative examples, zirconium oxide (ZrO ₂ ) (manufactured by Daiichi Rare Element Chemical Co., Ltd.), cerium oxide (CeO ₂ ) (manufactured by JGC Universal), zirconium-cerium double oxide (Zr _0.63 Ce _{0) .37} O ₂ ) (manufactured by Anan Kasei Co., Ltd.), zirconium-yttrium double oxide (ZrO ₂ —Y ₂ O ₃ (Y ₂ O ₃ : 3 mol%)) (manufactured by Daiichi Rare Element Chemical Industries, Ltd.) Similar to the oxide, platinum (Pt) is supported, this Pt-supported oxide is made into a slurry, and suction, removal, drying, and firing are performed, and an oxide catalyst layer is formed over substantially the entire internal flow path of the filter body 6. A formed sample was obtained. In addition, the platinum carrying amount of this comparative example is set to be larger than the carrying amount of each of the double oxides, and is set to 2.0 g / L for 50 g / L of oxide (per 1 L of DPF3). Yes.

(Carbon burning rate evaluation experiment)
Each sample thus obtained is subjected to an aging treatment that is allowed to stand for 24 hours under an atmospheric pressure condition of 800 ° C., and carbon combustion is examined for evaluation of carbon combustion performance in a state in which it is set in a model gas flow catalyst evaluation apparatus for circulating simulated exhaust gas. A speed evaluation experiment was conducted.

In this experiment, carbon black powder (manufactured by Katayama Chemical Industry) 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. In the deposition of the carbon black powder, 10 cc of ion exchange water is added to the carbon black powder equivalent to 10 g / L, and the mixture is stirred and mixed for 5 minutes using a stirrer to sufficiently disperse the carbon black powder. The upstream end side of the filter body 6 as a sample was immersed in this, and at the same time, suction was performed by an aspirator from the opposite side of the immersed end surface. Water that could not be removed by this suction was removed by air blowing from the soaked end face side, and dried at 150 ° C. for 2 hours in a dryer.

The DPF 3 in which the carbon black powder is collected is set in the model gas flow catalyst evaluation apparatus, and the oxygen gas and the water vapor are respectively supplied to the total gas flow rate while the temperature is raised to 600 ° C. at a rate of 15 ° C./min. A simulated exhaust gas containing 10% by volume and the remainder being nitrogen gas or the like was circulated so that the space velocity was 80000 / h, and the CO and CO ₂ concentrations immediately after the outlet portion 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 result is shown in FIG. FIG. 6 is a graph showing the carbon combustion rate measurement results for each comparative example and each example.

  According to FIG. 6, the oxidation catalyst layer 8 was formed of the zirconium-based example (in FIG. 6, the Zr-based example) in which the oxidation catalyst layer 8 was formed from the zirconium-based double oxide, and the cerium-based double oxide. In the cerium-based examples (Ce-based examples in FIG. 6), a better carbon combustion rate was measured than in each comparative example. That is, all the comparative examples resulted in a carbon burning rate lower than 0.5 g / h, but both the zirconium-based example and the cerium-based example resulted in a carbon burning rate exceeding 0.5 g / h. It became.

  In particular, even when the example in which the amount of Pt supported was 0.5 g / L and the comparative example in which the amount of Pt supported was 2.0 g / L were compared, the example showed that although the amount of Pt supported was smaller, the carbon combustion You can see that the speed is high. That is, it can be seen that a good carbon combustion rate can be obtained with a small amount of supported Pt by including a zirconium-based or cerium-based double oxide in the particulate oxidation catalyst.

  As described above, the examples showed that the carbon burning rate better than that of the comparative example was obtained because the zirconium-based oxide and the cerium-based oxide included in the particulate oxidation catalyst were oxygen ion conductive. It is estimated that having the following is the largest factor. This oxygen ion conductivity is considered to occur for the following reason. That is, among the zirconium-based complex oxides and cerium-based complex oxides, a part of which is substituted with a trivalent or divalent metal has a trivalent or 2 valence in the crystal lattice of tetravalent metal atoms such as zirconium or cerium. Since it is replaced by a valent metal atom, it is considered that an oxygen deficient portion (oxygen ion vacancy portion) is formed as shown in FIG. 5, and oxygen ions are conducted through this oxygen deficient portion.

  Therefore, as shown in FIG. 6, when the content of rare earth metal or alkaline earth metal mixed in each oxide increases in any of the zirconium-based oxide and cerium-based oxide, the oxygen ion conductivity is increased. It is considered that the carbon burning rate is improved by improving the.

(Carbon burning rate evaluation experiment in composite double oxide)
Next, a DPF3 particulate oxidation catalyst was mixed with a complex double oxide obtained by mixing a zirconium-based complex oxide and a cerium-based complex oxide, and an experiment for measuring the carbon combustion rate at that time was performed.

First, as an example, the mixing ratio of ZrO ₂ —Nd ₂ O ₃ double oxide (Nd ₂ O ₃ : 12 mol%) and CeO ₂ —Sm ₂ O ₃ double oxide (Sm ₂ O ₃ : 4 mol%) is set. A plurality of composite double oxides that were changed, that is, the content of CeO ₂ —Sm ₂ O ₃ contained in the total mass at a rate of 0, 33, 66, 100 mass% were prepared as samples. For each of the double oxides, a Pt loading amount of 0.5 g per liter of DPF3 is used as in the above experiment. Then, each Pt-supported double oxide is mixed with water and a binder to form a slurry, and this slurry is sucked into the filter body 6 plugged by the plugging portion 15 and excess slurry is removed by air blowing. Zirconium-based, in which the oxidation catalyst layer 8 is formed in substantially the entire area of the internal flow path of the filter body 6 after being coated by washing, dried and then heated by an electric furnace in an air atmosphere at 500 ° C. for 2 hours. A sample of was obtained.

  Each sample obtained in this manner was subjected to aging treatment in the same manner as the carbon burning rate evaluation experiment described above, and a model gas flow catalyst evaluation device for depositing carbon black powder as simulated PM on each sample and flowing simulated exhaust gas. A carbon burning rate evaluation experiment was conducted to examine the carbon burning performance evaluation in the set state. The conditions for the carbon black powder deposition method and the carbon burning rate evaluation experiment are the same as in the above experiment.

The result is shown in FIG. According to FIG. 7, a composite complex of zirconium complex oxide (here ZrO ₂ —Nd ₂ O ₃ complex oxide) and cerium complex oxide (here CeO ₂ —Sm ₂ O ₃ complex oxide). It has been found that changing the mass ratio of the cerium-based double oxide in the oxide increases the carbon combustion rate when both oxides are mixed and used as a particulate oxidation catalyst. It was.

  The mechanism by which the carbon combustion rate is increased by mixing zirconium-based and cerium-based mixed oxides as a particulate oxidation catalyst is not clear, but the physical properties of each mixed oxide are mutually different. It shows high carbon combustion rate by acting effectively, that is, oxygen ion conductivity due to zirconium-based double oxide and oxygen ion conductivity due to cerium-based double oxide and oxygen storage / release ability interact mutually. PM can be burned efficiently.

  In this case, the mixing ratio of the zirconium-based complex oxide and the cerium-based complex oxide is not particularly limited, but when the carbon burning rate is measured individually, the content rate of the higher burning rate is increased. It is good. For example, the cerium-based double oxide is preferably 10% by mass or more with respect to the total mass, and more preferably 20% by mass. The cerium-based double oxide is preferably 80% by mass or less, more preferably 70% by mass or less, based on the total weight. By mixing the cerium-based complex oxide with the zirconium-based complex oxide in such a ratio, PM can be more efficiently compared to the case where each of the zirconium-based complex oxide or the cerium-based complex oxide is used alone. And it can be burned in a short time.

As mentioned above, according to DPF3 of this embodiment, PM deposited on this DPF3 can be burned efficiently and in a short time. That is, since the zirconium-based oxide and cerium-based oxide included in the particulate oxidation catalyst have oxygen ion conductivity, PM adheres to the inside of the DPF 3 and the region where the oxygen concentration is locally low on the surface As a result, oxygen ions move from the place where the oxygen concentration is high to the site through the double oxide, and oxygen is supplied to the oxygen-deficient site as active oxygen (O ₂ ⁻ ), and PM is continuously and efficiently produced. In the regeneration of DPF3 (PM combustion purification), even when fuel is supplied to the engine or the DPF, the fuel injection amount or the injection period can be reduced, thereby efficiently regenerating the filter. Can be carried out in a short period of time and fuel efficiency can be improved.

  Moreover, the amount of catalyst precious metals such as Pt contained in the particulate oxidation catalyst can be reduced to achieve the same burning rate as that of the cerium-zirconium-based double oxide, saving the amount of catalyst precious metals used. Thus, the particulate oxidation catalyst, and hence the diesel particulate filter can be manufactured at low cost.

  The DPF 3 described above is an embodiment of the DPF according to the present invention, and the specific configuration and the like can be changed as appropriate without departing from the spirit of the present invention, and modifications will be described below. To do.

  (1) In the above example, a zirconium complex oxide and a cerium complex oxide were mixed one by one to create a complex complex oxide. These may be selected and mixed.

(2) An oxidation catalyst that oxidizes HC, CO, and NO may be provided on the upstream side (upstream side in the exhaust gas flow direction) of the DPF 3 in the above embodiment. In this case, NO ₂ discharged from this oxidation catalyst. This makes it easier to burn PM.

It is explanatory drawing which shows the state which assembled | attached DPF and the oxidation catalyst in the exhaust passage of the diesel engine. It is a front view which shows typically DPF of this embodiment. It is a longitudinal cross-sectional view which shows the same DPF typically. It is sectional drawing which expands and shows the porous wall of DPF. It is explanatory drawing which shows the combustion mechanism of PM. It is a graph which shows the carbon combustion rate by the particulate oxidation catalyst formed from each Pt carrying | support powder. It is a graph which shows a carbon combustion rate change at the time of changing the mixing ratio of a zirconium system double oxide and a cerium system double oxide.

Explanation of symbols

1 Exhaust passage 3 DPF
6 Filter body 7 Oxidation catalyst layer 9 Carbon 10 Fire type 11 Oxygen deficient space 15 Plugged portion

Claims (4)

In a diesel particulate filter provided with a particulate oxidation catalyst disposed in an exhaust passage of a diesel engine and having a catalytic noble metal for burning particulates,
The particulate oxidation catalyst comprises a zirconium-based double oxide containing zirconium as a main component and containing a rare earth metal excluding cerium and yttrium, and a rare earth metal or an alkaline earth metal containing cerium as a main component and excluding cerium. Contains both the included cerium-based double oxide ,
Diesel which the cerium-based mixed oxide is characterized that you have been mixed with the zirconium-based composite oxide in a proportion of less than 80 wt% with 10 wt% or more based on the total weight obtained by adding the zirconium-based composite oxide Curate filter.   2. The diesel particulate filter according to claim 1, wherein the rare earth metal contained in the zirconium-based double oxide is at least one metal selected from scandium, neodymium and ytterbium.   3. The diesel particulate filter according to claim 1, wherein the rare earth metal contained in the cerium-based double oxide is at least one metal selected from samarium and gadolinium.   The alkaline earth metal contained in the cerium-based double oxide is at least one metal selected from magnesium, calcium, strontium, and barium, according to any one of claims 1 to 3. Diesel particulate filter.

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