JP2007313443A - Exhaust gas cleaning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning apparatus capable of using oxygen in a gas phase as an oxidant, sufficiently oxidizing components like PM, HC, CO or NO in a further lower temperature region, and sufficiently regenerating the apparatus by regeneration processing at a relatively low temperature even if PM has accumulated. <P>SOLUTION: This exhaust gas cleaning apparatus is provided with a coagulant comprising silver particles serving as cores, and ceria fine particles with an average primary particle size of 1-100 nm, covering the periphery of the silver particles. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that can be suitably used to purify exhaust gas containing PM.

  As for gasoline engines, harmful components in the exhaust are steadily reduced due to strict regulations on exhaust and technological advances that can cope with it. However, since diesel engines contain PM (particulate matter: particulate matter), many technical problems for exhaust purification remain. Therefore, in recent years, an oxidation catalyst that can oxidize PM, particularly a soot component, from a low temperature has been developed.

For example, in JP-A-1-318715 (Patent Document 1), a honeycomb monolith having a catalyst for oxidizing NO in exhaust gas to NO ₂ , and passing the exhaust gas through the catalyst to pass NO into NO _2. Disclosed is an exhaust gas purification device comprising a device for converting to NO. ₂ and a filter disposed on the downstream side for receiving NO ₂ containing gas discharged from the device and for burning PM in the exhaust gas with NO ₂ containing gas. ing. However, in the exhaust gas purifying apparatus described in Patent Document 1, PM cannot be oxidized using only oxygen in the gas phase as an oxidizing agent.

In addition, in Japanese Patent Application Laid-Open No. 2004-42021 (Patent Document 2), a catalyst composition having ceria (CeO ₂ ) stabilized by silver (Ag) and / or cobalt (Co) is oxidized by soot oxidation during regeneration of DPF. The molar ratio of Ag to ceria is preferably 4: 1 to 1: 4 (the Ag content (mol%) relative to the total amount of Ce and Ag is equivalent to 20 mol% to 80 mol%), It is described that 3: 1 to 1: 3 (Ag content (mol%) with respect to the total amount of Ce and Ag corresponds to 33 mol% to 67 mol%) is more preferable. And it is said that activity was the maximum about the mixture whose content of Ag is 75 mol% and whose content of Ce is 25 mol%. In addition, a mixture having an Ag content of 25 mol% and a Ce content of 75 mol% is active with respect to soot oxidation even if oxygen is used as the only oxidant. In this case, active oxygen species are generated in the gas phase. It is shown that you can. In addition, the manufacturing method of the catalyst described in Patent Document 2 is obtained by impregnating a cellulose material (Whatman (registered trademark) filter paper 540) with a nitrate precursor and drying it overnight at room temperature. This is a method for obtaining a catalyst composition having a porosity concentrated to about 70 to 200 m ² and a high specific surface area of 14 to 150 m ² / g by burning cellulose under conditions.

There are mainly two evaluation methods in Patent Document 2, and one is a method in which the decomposition rate is measured by TGA in a 10% oxygen atmosphere or the like in which the diesel soot and the catalyst composition are loose-contacted with a spatula, The other is a method of performing a pressure loss balance test using a DPF. For example, in the TGA evaluation for the catalyst composition having an Ag content of 75 mol%, the oxidation rate at 323 ° C. is 0. 0 even under the best catalyst composition of NO ₂ : 1010 ppm and O ₂ : 10%. 117 hr ⁻¹ . That is, even under the condition that a strong oxidizer of NO ₂ is sufficiently present, the ratio of soot oxidized in one hour is only 11.7%. On the other hand, in the pressure loss balance test, CPF-15, which is an Ag-Ce system, can oxidize PM at around 325 ° C, but this test result is inconsistent with the previous test result. Therefore, the present inventors consider that the soot component slipped out in the actual pressure loss balance test, and the catalyst composition described in Patent Document 2, that is, simply Ag and CeO ₂ or Ce and CeO _2. Only in the presence of, components such as soot such as PM, HC, CO or NO could not be sufficiently oxidized at a low temperature.
Moreover, in such a catalyst as described in Patent Document 2, PM cannot be oxidized using only oxygen in the gas phase as an oxidizing agent.
JP-A-1-318715 JP 2004-42021 A

  The present invention has been made in view of the above-described problems of the prior art, and oxygen in the gas phase can be used as an oxidant, so that PM, HC, CO, NO or the like can be sufficiently obtained in a lower temperature range. An object of the present invention is to provide an exhaust gas purifying apparatus that can oxidize components and can be sufficiently regenerated by a relatively low temperature regeneration process even when PM is deposited.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have found that a core particle and a ceria fine particle having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particle. The exhaust gas purification device equipped with a collection can use oxygen in the gas phase as an oxidant, and can sufficiently oxidize components such as PM, HC, CO or NO in a lower temperature range, and PM is deposited. Even in such a case, it has been found that sufficient regeneration can be achieved by a relatively low temperature regeneration process, and the present invention has been completed.

  That is, the exhaust gas purifying apparatus of the present invention comprises an aggregate composed of silver particles serving as a nucleus and ceria fine particles having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particles. It is.

  The exhaust gas purification apparatus of the present invention preferably includes a base material and the aggregate.

  In the exhaust gas purification apparatus of the present invention, the base material has pores of 1 to 300 μm, and an average thickness of 0.5 to 50 times the average particle size of the aggregates is formed in the pores. It is preferable that the coat layer to be formed is formed of the aggregate.

  In the exhaust gas purifying apparatus of the present invention, the substrate preferably has a porosity of 30 to 70%.

In the exhaust gas purification apparatus of the present invention, the first standard (A) of the PM deposition amount that requires the forced regeneration process and the second standard of the PM deposition amount that is lower than the first standard (A). Based on criteria (B)
The second regeneration process that is lower than the first regeneration process temperature for the forced regeneration process when the obtained PM deposition amount is between the first standard (A) and the second standard (B). Apply low temperature regeneration treatment at temperature,
When the obtained PM deposition amount exceeds the first standard (A), a forced regeneration process is performed.
It is preferable to further comprise a control means for controlling the exhaust gas purification device.

  In the exhaust gas purification apparatus of the present invention further including the control means, a plurality of temperature conditions are set as the second regeneration processing temperature, and the obtained PM deposition amount is equal to the first reference (A). When the temperature is between the second standard (B) and the low temperature regeneration process is performed at the low temperature side second regeneration process temperature, and the subsequent PM deposition amount is less than the second standard (B) When the low temperature regeneration process is completed and the PM accumulation amount is still between the first standard (A) and the second standard (B), the temperature is sequentially changed to the second regeneration process temperature on the high temperature side. It is more preferable to control the exhaust gas purification device so as to repeat the low temperature regeneration process.

The reason why the above object is achieved by the diesel exhaust gas purification structure of the present invention and the exhaust gas purification method using the same is not necessarily clear, but the present inventors speculate as follows. That is, in the present invention, first, aggregates composed of silver (Ag) particles serving as nuclei and second ceria (CeO ₂ ) fine particles having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particles. Although an agglomerate is provided, PM is sufficiently purified by such agglomerates even in a relatively low temperature range. The mechanism for oxidizing PM by such aggregates is presumed as follows. That is, first, oxygen is released from the oxygen-containing substance by the Ag particles even at a relatively low temperature. Next, active oxygen species (O ^* : oxygen ions, for example) generated by liberation are moved to the surface of PM by CeO ₂ fine particles, where a surface oxide is formed. In addition, it is known that the bond of C and O in such a surface oxide can be classified mainly into C═O, C═C, and C—O (Applied Catalysis B, 50, 185-194 (2004)). ). Next, the surface oxide formed in this way is oxidized by gas-phase oxygen or by oxygen-activated species moving through CeO ₂ fine particles. In this way, the oxidized portion is removed and reduced from the periphery of the PM, and finally it can be completely oxidized and disappear. In addition, it is speculated that such an aggregate can sufficiently oxidize components such as HC and NO in addition to PM at a relatively low temperature.

  Therefore, the exhaust gas purifying apparatus of the present invention can sufficiently oxidize components such as PM, HC, CO or NO in a lower temperature region using oxygen in the gas phase as an oxidant, Since PM can be sufficiently oxidized by this, PM deposited in the exhaust gas purification apparatus can also be removed at a low temperature, so that it can be sufficiently regenerated by a relatively low temperature regeneration process.

  According to the present invention, oxygen in the gas phase can be used as an oxidizing agent, and components such as PM, HC, CO, or NO can be sufficiently oxidized in a lower temperature range, and PM is deposited. In addition, it is possible to provide an exhaust gas purification device that can be sufficiently regenerated by a relatively low temperature regeneration process.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  The exhaust gas purifying apparatus of the present invention is characterized by comprising an agglomerate composed of silver particles serving as nuclei and ceria fine particles having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particles. .

The silver (Ag) particles and ceria (CeO ₂ ) fine particles themselves according to the present invention are primary particles, and the former is a secondary particle covered with the latter as an “aggregate (or primary aggregate)”, and further A tertiary particle formed by aggregation of such aggregates is referred to as an “aggregate (or secondary aggregate)”.

  The Ag particles may be one using Ag alone, but may be an alloy composed of two or more metals of Ag and another metal other than Ag. Furthermore, a part of the Ag particles may form an oxide or a compound with another element. When a part of the Ag particles forms an oxide or a compound, the Ag content is preferably 0.3% by mass or more.

  Such Ag particles can release at least oxygen of the oxygen-containing substance and generate oxygen active species. That is, such Ag particles function as an oxygen release material. Such Ag particles enable oxygen atoms to be taken into a reaction system that efficiently oxidizes PM or the like. In addition, such Ag particles (oxygen release material) may function as an oxygen-containing substance capturing material. Therefore, with such Ag particles, it is possible to supply a large amount of oxygen active species from a lower temperature to components such as PM, HC, CO, or NO through the oxygen active species transfer material to promote oxidation.

Further, the particle diameter of such Ag particles is not particularly limited, but the average particle diameter after baking for 5 hours at 500 ° C. in the air is preferably 10 to 100 nm (more preferably 10 to 50 nm), Moreover, it is preferable that the average particle diameter after baking at 800 degreeC for 5 hours in the atmosphere which consists of 10 volume% of oxygen and 90 volume% of nitrogen is 10-400 nm (more preferably 10-80 nm). When the average particle size of such Ag particles is less than the lower limit, delivery of oxygen-activated species generated by Ag particles (oxygen-releasing material) to CeO ₂ fine particles (oxygen-activated species transfer material) tends to be inhibited. On the other hand, when the upper limit is exceeded, the Ag particles tend to be difficult to be covered with the CeO ₂ fine particles.

Such ceria fine particles can move oxygen active species generated by the Ag particles (oxygen release material) and function as an oxygen active species transfer material. Such ceria fine particles are materials that can move oxygen active species (for example, oxygen ions) through valence change and the like. When the oxygen active species generated by the Ag particles (oxygen release material) is received by using such a material, the oxygen active species are adsorbed by moving CeO ₂ fine particles (oxygen active species transfer material). It becomes possible to reach PM. Routes such oxygen active species is moved need not pass through the bulk interior of the CeO ₂ fine particles, for example, it is sufficient movement of the surface of CeO ₂ fine particles. In addition, when oxidizing the PM, if the oxidizing power of the oxygen active species is too strong, the contact portion between the PM and the CeO ₂ fine particles is preferentially oxidized, and the contact state between the two is lost. Therefore, it becomes difficult to completely oxidize PM because of the generation of voids. Therefore, the oxygen active species have a moderate oxidizing power (the PM and oxygen active species do not react immediately and the oxygen active species can move on the PM). ).

In such an aggregate, La, Nd, Pr, Sm, Y, Ca, in order to increase the mobility of oxygen active species in the CeO ₂ fine particles and more reliably prevent the coarsening of the CeO ₂ particles. It is more preferable to further contain at least one selected from the group consisting of Ti, Fe, Zr and Al (particularly preferably La and / or Nd). In addition, when such an additive component is contained, the content of the additive component is preferably about 1 to 30 mol%, more preferably about 5 to 20 mol% with respect to the total amount of Ce and the additive component. . Such an additive component is preferably contained in the CeO ₂ fine particles.

The particle diameter of such CeO ₂ fine particles is not particularly limited, but the average particle diameter after baking at 500 ° C. for 5 hours in the atmosphere is 1 to 75 nm (more preferably 8 to 20 nm, still more preferably 8 to 15 nm). The average particle size after baking for 5 hours at 800 ° C. in an atmosphere consisting of 10 volume% oxygen and 90 volume% nitrogen is preferably 8 to 100 nm (more preferably 8 to 60 nm, still more preferably 8). ˜40 nm). If the average particle size of the CeO ₂ fine particles (oxygen-activated species transfer material particles) is less than the lower limit, contact with PM such as soot tends to be inhibited. On the other hand, if the upper limit is exceeded, Ag particles (oxygen free material particles) ) Tends to be difficult to cover.

Further, in such an aggregate, after firing at 500 ° C. for 5 hours in the atmosphere and after firing for 5 hours at 800 ° C. in an atmosphere composed of 10% by volume of oxygen and 90% by volume of nitrogen, The average particle diameter of Ag particles (oxygen free material particles) is preferably 1.3 times or more, more preferably 2.0 times or more of the average particle diameter of CeO ₂ fine particles (oxygen active species transfer material particles). More preferred. If the average particle size of Ag particles and CeO ₂ fine particles does not satisfy the above conditions, the periphery of the Ag particles will not be sufficiently covered with CeO ₂ fine particles, and the ability to oxidize components such as PM, HC, CO or NO will be reduced. Tend to.

In addition, such an aggregate is formed by covering the periphery of the Ag particles with CeO ₂ fine particles. While such Ag ratio of the particles and the CeO ₂ fine particles is not particularly limited, the ratio of the Ag particles and the CeO ₂ fine particles (molar ratio) is 4: 1 to 1: is preferably 9, 35: 65-60: 40 Is more preferable, and 40:60 to 60:40 is particularly preferable. If the amount of Ag particles is less than the above lower limit, the amount of active oxygen species liberated from the gas phase tends to decrease and the ability to oxidize components such as PM, HC, CO or NO tends to decrease, If the amount of CeO ₂ fine particles is less than the above lower limit, the amount of active oxygen species that can move to components such as PM, HC, CO, or NO tends to decrease, and the ability to oxidize PM tends to decrease. Then, the above ratio is 40: 60 to 60: If it is 40, it is easy to cover the CeO ₂ fine particles around the Ag particles and the proportion of the two components that do not form aggregates thereof are particularly preferred for reduction.

The average particle diameter of such an aggregate, that is, the average particle diameter of the aggregate formed by covering the Ag particles with the CeO ₂ fine particles is not particularly limited, but is preferably 0.05 to 0.5 μm, More preferably, the thickness is from 07 to 0.2 μm. If the average particle size is less than the lower limit, the contact between the oxygen-containing substance and the Ag particles tends to be inhibited. On the other hand, if the average particle size exceeds the upper limit, the contact between the CeO ₂ fine particles and PM or the like tends to be inhibited.

  Such aggregates preferably have high dispersibility, and 60% by volume or more of all aggregates may have a particle size in the range of the average particle size ± 50%. preferable. When the dispersibility of the agglomerates is thus high, the ability to oxidize PM is further improved, and it tends to be uniformly supported by a carrier such as DPF.

  Further, the aggregate may further include third metal ultrafine particles supported on the surface of the ceria fine particles. When such third metal ultrafine particles are present, the ceria fine particles (oxygen active species transfer material particles) tend to easily supply the oxygen active species to components such as PM, HC, CO, or NO.

  As the third metal constituting the third ultrafine metal particles, those having an ionization tendency smaller than that of H (for example, Au, Pt, Pd, Rh, Ru, Ag, Hg, Cu, Bi). , Sb, Ir, Os), and those having an ionization tendency equal to or lower than the ionization tendency of Ag (noble metals: for example, Au, Ag, Cu, Pt, Pd, Rh, Ru, Ir, Os) Is more preferable, and Ag is particularly preferable. Moreover, it is preferable that a 3rd metal ultrafine particle consists of 1-1000 atoms.

  The aggregate may be aggregated in a state where the ceria fine particles covering the periphery of the silver particles are cracked on the surface thereof. Furthermore, the shape of the aggregate is not particularly limited, but the aggregate is preferably spherical.

Next, a method for producing such an aggregate will be described. As a method for producing such an aggregate, an aggregate in which Ag particles derived from Ag salt are covered with Ce compound fine particles derived from Ce salt from a solution containing Ag salt and Ce salt. A step of generating a precursor, and by firing the obtained aggregate precursor, Ag particles serving as nuclei, and fine particles of ceria having an average primary particle size of 1 to 100 nm covering the periphery of the Ag particles Examples of such Ag and Ce salts include water-soluble compounds such as nitrates, acetates, chlorides, sulfates, sulfites, and inorganic complex salts of Ag and Ce. Among them, nitrates (for example, silver nitrate and cerium nitrate) are preferably used. Further, the solvent for preparing the solution containing the Ag salt and the Ce salt is not particularly limited, and may be water, alcohol (for example, methanol, ethanol, ethylene glycol alone or a mixed solvent), and the like. Although various solvents are mentioned, water is particularly preferable.

Note that the blending amount (preparation amount) of the Ag salt and the Ce salt does not need to completely match the ratio of the obtained Ag particles to the CeO ₂ fine particles, and the Ag particles in the aggregate to be obtained The combination of the Ag salt and the Ce salt and the condition of the blending amount are appropriately set according to the suitable conditions of the combination and ratio of the CeO ₂ fine particles. Further, if the Ag salt is excessively present with respect to the Ce salt, the CeO ₂ fine particles generated in the solution tend to be easily made part of the aggregate, and components other than the aggregate are in the solution. It is preferable because it does not form inside.

  Further, in such an aggregate production method, in the step of producing the aggregate precursor, Ce compound fine particles are produced in the presence of a pH adjusting agent, and the Ag particles are reduced by the reducing action of the Ce compound fine particles. It is preferable to produce the aggregate precursor by precipitation.

The requirement for the oxidation-reduction reaction can be explained by the potential between Ag and Ce, but the potential is pH-dependent. In general, the potential decreases as the pH increases. Therefore, in such an aggregate production method, it is preferable to control the oxidation-reduction reaction by adding a pH adjuster as appropriate. Further, since the activation energy is changed by adding the pH adjuster, the oxidation-reduction reaction can be made the optimum condition. Examples of such a pH adjuster include NaOH, KOH, NH ₃ , HNO ₃ , and H ₂ SO _4, but it is sufficient to use a general acid or alkali.

  In addition, since Ag has a high potential on the acidic side and the reaction proceeds too quickly, there is a tendency that coarse Ag is likely to precipitate, so that it is preferable to make it alkaline in the presence of a base. At that time, if NaOH is used as a pH adjuster, precipitation occurs, and therefore it is preferable to make it alkaline with ammonia. In this case, ammonia also functions as a complexing agent. Further, the concentration of such a base is not particularly limited, but when ammonia is used as the base, it is generally preferable to use a solution having an ammonia concentration of about 1 to 50%. Furthermore, the Ce compound fine particles in this case are considered to be a hydroxide of Ce.

  Further, in such a method for producing an aggregate, in the step of producing the aggregate precursor, a first metal compound derived from the Ag salt is produced in the presence of a complexing agent, and the Ce compound is produced. More preferably, the silver particles are precipitated by reducing the first metal compound by the reducing action of the fine particles.

Furthermore, in order to make the redox reaction optimal, it is preferable to add a pH adjuster as described above. In this case, however, a precipitate may be generated depending on the pH. Therefore, even when the precipitate is generated when the complexing agent is not used, the metal salt can be obtained by adding the complexing agent. By doing so, the potential and the activation energy also change, so that the conditions can be appropriately adjusted. For example, Ag is preferably [Ag (NH ₃ ) ₂ ] ⁺ . Examples of such a complexing agent include ammonia, alkali salts of organic acids (such as glycolic acid, citric acid, and tartaric acid), thioglycolic acid, hydrazine, triethanolamine, ethylenediamine, glycine, pyridine, and cyanide.

  In such a method for producing an aggregate, it is preferable to adjust the temperature in the step of producing the aggregate precursor. The temperature condition of the reaction solution is an important factor governing the redox reaction. It is preferable to appropriately adjust the temperature of the solution within a range in which the solvent functions as a liquid. For example, it is preferable to set it as 30 degreeC or more, and it is more preferable to set it as 60 degreeC or more. And if it is the conditions of about 1-3 atmospheres and about 100-150 degreeC, it exists in the tendency which can raise | generate reaction reliably, and since reaction time can be shortened, it is preferable also on the application to industry.

  Even in the so-called “precipitation method” in which a pH adjusting agent-containing solution (for example, a basic solution) is added to and mixed with the salt solution of Ag and Ce in the step of forming the aggregate precursor, the pH adjusting agent is included. A so-called “reverse precipitation method” in which a salt solution of Ag and Ce is added to and mixed with a solution (for example, a basic solution) may be used. In this case, you may add and mix sequentially in the order of the salt of Ag, the salt of Ce, or the reverse order. The reaction time is not particularly limited, but it is preferably about 0.1 to 24 hours, more preferably about 0.1 to 3 hours for aggregation. Moreover, when using a complexing agent, you may perform the said operation, after previously making a metal salt with a complexing agent.

  Further, the solid content concentration in the reaction solution in the step of producing such an aggregate precursor is not particularly limited, but is preferably 1% by mass to 50% by mass, and is preferably 10% by mass to 40% by mass. It is more preferable, and it is still more preferable that it is 15-30 mass%. If the solid content concentration is less than the lower limit, the accelerating effect of the agglomeration treatment tends to decrease. By performing the aggregation treatment in this way, an aggregate precursor in which silver particles are covered with Ce compound fine particles as described above can be obtained efficiently and reliably.

  Furthermore, the average particle diameter of such an aggregate precursor is not particularly limited, but is preferably 0.05 to 0.5 μm, and more preferably 0.07 to 0.2 μm. Moreover, it is preferable that the dispersibility of the aggregate precursor is high, and 60% by volume or more of all aggregate precursors have a particle size in the range of the average particle size ± 50%. Is preferred. When the dispersibility of the aggregate precursor is high as described above, the dispersibility of the obtained aggregate is high, and it tends to be supported uniformly by a carrier such as DPF.

  And the above-mentioned aggregate can be obtained by baking, after wash | cleaning the aggregate precursor obtained by such an aggregation process as needed. The conditions for such firing are not particularly limited, but in general, firing in an oxidizing atmosphere (for example, air) at 300 to 600 ° C. for about 1 to 5 hours is preferable.

Further, the method for producing an aggregate may further include a step of supporting third metal ultrafine particles on the surface of the Ce compound fine particles or the CeO ₂ fine particles. As described above, the method for supporting the third metal ultrafine particles includes (i) a method of supporting the third metal ultrafine particles on the surface of the ceria fine particles after firing the aggregate precursor obtained by the aggregation treatment. And (ii) a method of precipitating the third metal ultrafine particles on the surface of the Ce compound fine particles simultaneously with the aggregation treatment.

  In the method (i), a method of impregnating and supporting the third metal nitrate, sulfate, acetate, ammonium salt or the like described above, or a method of utilizing a redox reaction on the surface of the metal oxide Can be adopted. The former impregnation supporting method is a general supporting method of ultrafine metal particles used for obtaining a catalyst or the like.

On the other hand, the latter method is a method in which, for example, Ag ⁺ is reduced by a defect site (for example, a portion where CeO ₂ is partially Ce ³⁺ ) in the fine particles of ceria to precipitate ultrafine metal particles. At that time, it is preferable to add a complexing agent as necessary in order to control the precipitation reaction rate to control the particle size of the ultrafine metal particles. For example, when [Ag (NH ₃ ) ₂ ] ⁺ is produced by dropping ammonia water into AgNO ₃ , the oxidation-reduction potential changes and the deposition rate decreases, so that finer metal ultrafine particles tend to be obtained. It is in.

  The method (ii) uses the oxidation-reduction reaction at the time of the above-described aggregation treatment, and is a particularly preferable method when the third metal is Ag. In this method, the first metal is precipitated by the Ce compound fine particles and the third metal ultrafine particles are also precipitated on the surface of the Ce compound fine particles in the step of generating the above-mentioned aggregate precursor. It is.

  Moreover, the exhaust gas purifying apparatus of the present invention is not particularly limited as long as it includes the agglomerates, but more preferably includes a base material and the agglomerates.

  Such a substrate is not particularly limited, and a DPF substrate, a monolith substrate, a honeycomb substrate, a pellet substrate, a plate substrate, a foamed ceramic substrate, and the like are suitably employed. Further, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chromium and aluminum is suitably employed. .

  Further, in the exhaust gas purifying apparatus of the present invention, the amount of the aggregate to be applied to the base material is not particularly limited, and the amount can be appropriately adjusted according to the target internal combustion engine or the like. The amount that the amount of aggregate is about 10 to 300 g per liter is preferable. The exhaust gas purifying apparatus of the present invention can be used by pelletizing the aggregate itself.

  Moreover, in such an exhaust gas purification apparatus of the present invention, the substrate has pores of 1 to 300 μm, and 0.5 to 50 times the average particle size of the aggregates in the pores. It is preferable that the coat layer having an average thickness is formed of the aggregate. In addition, in the exhaust gas purification apparatus of this invention, as long as the effect of this invention is not impaired, another component may be further provided with the said aggregate. Examples of such other components include first metal particles such as Pt, Rh, Pd, Ru, Ir, Os, and Au serving as nuclei and an average primary particle diameter covering the periphery of the first metal particles. May be an aggregate comprising 1 to 100 nm of second metal oxide fine particles such as La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd.

  Moreover, as such a base material, it is preferable that the porosity is 30 to 70% (more preferably 50 to 65%). Here, the “porosity” refers to the volume ratio of the hollow portion inside the substrate. Further, if the porosity is less than the lower limit, it tends to be clogged with particulate matter in the exhaust gas and tends to make it difficult to form the coat layer of the aggregate. On the other hand, if the upper limit is exceeded, It is difficult to collect the particulate matter, and the strength of the base material tends to decrease.

  Next, the suitable manufacturing method of an exhaust gas purification apparatus provided with a base material and an aggregate is demonstrated. A preferred first production method of such an exhaust gas purification device is a method characterized in that an exhaust gas purification device is obtained by firing after contacting the first aggregate dispersion with a substrate, and The second production method is a method characterized in that an exhaust gas purification device is obtained by firing after bringing the second aggregate dispersion into contact with the substrate.

  Such a first aggregate dispersion contains the aggregate and a dispersion medium. Such a first aggregate dispersion preferably further contains a binder. The binder used here is not particularly limited, and for example, ceria sol is preferably used. Further, the mixing ratio of the aggregate and the binder is not particularly limited, and the mixing ratio of the aggregate and the binder is preferably about 99: 1 to 80:20 by weight ratio. For example, even when a binder is used, a highly dispersible dispersion (slurry) can be easily obtained by ultrasonic treatment.

  The second aggregate dispersion liquid contains an aggregate precursor obtained in the course of the aggregate manufacturing method and a dispersion medium. Such a second aggregate dispersion is obtained by separating 50 to 99.9% of residual ions in the system from a solution containing the aggregate precursor obtained in the above-described aggregate production process. It is preferable to contain the obtained aggregate precursor. Although there is a certain degree of dispersibility even at the stage of agglomeration, a dispersion with very high dispersibility can be obtained by removing residual ions caused by salts and complexing agents.

  Here, the method for bringing the first and second aggregate dispersions into contact with the base material is not particularly limited. For example, when entering the pores of the filter base material such as DPF, contact is made while applying ultrasonic waves. It is preferable to make it. In addition, the firing conditions in this case are preferably the same conditions as the aforementioned firing conditions.

  In addition, according to the second production method, since the component capable of oxidizing PM, HC, CO, NO, or the like is an aggregate itself, it plays the role of a binder itself and is more effective in the present invention. An exhaust gas purification apparatus can be provided.

Furthermore, in the exhaust gas purification apparatus of the present invention, the first standard (A) of the PM deposition amount that requires the forced regeneration process and the second PM deposition amount that is a lower standard than the first standard (A). Based on the criteria (B)
The second regeneration process that is lower than the first regeneration process temperature for the forced regeneration process when the obtained PM deposition amount is between the first standard (A) and the second standard (B). Apply low temperature regeneration treatment at temperature,
When the obtained PM deposition amount exceeds the first standard (A), a forced regeneration process is performed.
It is preferable to further comprise a control means for controlling the exhaust gas purification device. By providing such a control means, it is possible to efficiently remove PM accumulated in the exhaust gas purification device, and it is possible to regenerate the exhaust gas purification device and use it continuously.

  Examples of such control means include an engine control unit (ECU). Such an ECU is configured as a computer combining a microprocessor and peripheral devices such as ROM and RAM necessary for its operation.

  The first regeneration treatment temperature is preferably 600 ° C. or higher (more preferably 600 to 650 ° C.). The second regeneration treatment temperature is lower than the first regeneration treatment temperature, preferably 200 to 500 ° C, and preferably about 250 to 400 ° C. Furthermore, “forced regeneration treatment” refers to heat treatment at the first regeneration treatment temperature, and “low temperature regeneration treatment” refers to heat treatment at the second regeneration treatment temperature. It should be noted that such heat treatment time is not preferably unnecessarily long from the viewpoint of suppressing fuel consumption deterioration that occurs when the exhaust gas temperature is raised for the purpose of regeneration treatment, and should be about 1 to 10 minutes. Is preferred.

  The first standard (A) and the second standard (B) can be appropriately set according to the size, form, type of base, etc. of the exhaust gas purification device. In the present invention, the first standard (A) is larger than the second standard (B). Further, the suitable value of the second standard (B) is not particularly limited because it varies depending on the type of the base material. For example, a base material having a porosity of 65% is used. When used, the second standard (B) is preferably 1.5 g / L or less, more preferably 1.0 g / L or less, and 0.5 g / L or less per liter of the base material. More preferably it is.

  The method for measuring the amount of PM deposited is not particularly limited, and for example, the following method can be employed. That is, as a method for measuring the amount of accumulated PM, a map relating to the operating state of the internal combustion engine, the use history of the exhaust gas purification device, etc., and the amount of accumulated PM is prepared in advance, and PM In the case where the aggregate is arranged in an exhaust gas pipe or the like, a map relating to the pressure difference between the exhaust gas before and after the position where the aggregate is arranged and the PM deposition amount is prepared in advance. In addition, a method of calculating the PM accumulation amount by measuring the pressure difference based on the map, a method of calculating the PM accumulation amount by correcting the pressure difference by the intake air amount, and all of these methods are adopted. Methods and the like can be adopted as appropriate. In measuring the amount of PM deposited, various sensors necessary for the measurement may be used as appropriate.

  Hereinafter, the case where such a control means is used will be described with reference to a flowchart. FIG. 1 is a flowchart showing a preferred embodiment of such control. In step 1 shown in FIG. 1, the control unit calculates a PM deposition amount, and in step 2, it is determined whether or not the PM deposition amount is equal to or greater than the second reference (B). If the PM accumulation amount is equal to or greater than the second reference (B), the process proceeds to step 3, and if the PM accumulation amount is less than the second reference (B), the process is terminated without performing the regeneration process. In step 3, it is determined whether or not the PM accumulation amount exceeds the first reference (A). When the amount of PM deposition is equal to or less than the first reference (A), that is, when the amount of PM deposition is between the first reference (A) and the second reference (B), Proceeding to step 4, low temperature regeneration processing is performed. On the other hand, if it is determined in step 3 that the amount of accumulated PM exceeds the first reference (A), the process proceeds to step 5 where forced regeneration processing is performed.

  In the case of performing such low temperature regeneration processing or the like, a plurality of temperature conditions are set as the second regeneration processing temperature, and the obtained PM deposition amount is determined based on the first reference (A) and the second reference ( B), the low-temperature regeneration process is performed at the second regeneration temperature on the low temperature side, and the low-temperature regeneration process is terminated when the PM deposition amount thereafter is less than the second reference (B). If the PM accumulation amount is still between the first standard (A) and the second standard (B), the low temperature regeneration process is repeated by sequentially changing to the second regeneration process temperature on the high temperature side. It is more preferable to control the exhaust gas purification device.

  By repeatedly performing the low temperature regeneration process in this manner, the exhaust gas purification device can be regenerated at a lower temperature without performing the forced regeneration process, and the number of times of performing the forced regeneration process can be greatly reduced. Further, it is possible to reduce the reduction in fuel consumption of the internal combustion engine at the time of regeneration, and further, when further including a base material, it is possible to sufficiently suppress melting damage, cracking and the like of the base material. When the low temperature regeneration process is repeated, the second regeneration process temperature is sequentially changed to the high temperature side when it is between the first standard (A) and the second standard (B). However, it is preferable to terminate the regeneration process at a lower temperature among the plurality of second regeneration process temperatures that are set. Note that the conditions of the plurality of temperatures set as the second regeneration processing temperature are not particularly limited, and are preferably in the temperature range of 200 to 500 ° C. as described above. The temperature can be appropriately set to an optimum temperature for purifying PM depending on the property of PM.

Hereinafter, a preferred example in the case of performing control so as to repeatedly perform the low temperature regeneration process will be described with reference to a flowchart. FIG. 2 is a flowchart showing a preferred embodiment of such control. When performing such control, first, the control unit calculates the PM accumulation amount, and the PM accumulation amount is between the first reference (A) and the second reference (B). Then, the process proceeds to step 1 shown in FIG. In such a step 1, it is recognized that the number i of the low-temperature regeneration process is 1. Next, the process proceeds to step 2 where the second regeneration processing temperature is set to T _i (i represents the number of times of the low temperature regeneration processing, and for example, the second regeneration processing temperature is divided into four stages: T ₁ , T ₂ , T ₃ , T _4. In this case, T ₁ is adopted when i = 1, and the temperature is set to T ₁ <T ₂ <T ₃ <T ₄ . Warm and apply low temperature regeneration treatment. Then, the process proceeds to step 3 after the low temperature regeneration process, and the PM accumulation amount Xi (i indicates the number of low temperature regeneration processes) is calculated. Thereafter, in step 4, it is determined whether or not the PM accumulation amount Xi calculated in this way is less than the second reference (B), and when Xi is less than the second reference (B). Ends the low temperature regeneration process. When the PM accumulation amount Xi is still greater than or equal to the second reference (B), that is, when Xi is still between the first reference (A) and the second reference (B), Proceeding to step 5, the number i of the low-temperature regeneration processes performed so far and the set number e of temperatures set as the second regeneration process temperature (for example, the second regeneration process temperature is T ₁ , T ₂ , T ₃ , T ₄ and e = 4 when four stages are set), and if i = e, the low temperature regeneration process is terminated. . If the value of the number of times i of the low-temperature regeneration processing performed so far is less than the second regeneration processing temperature setting number e (if e> i), the process proceeds to step 6 to perform the low-temperature regeneration processing. The number of times i is recognized as i + 1, and the process proceeds to step 2 again to perform the i + 1th low-temperature regeneration process. Note that such i + 1-th low temperature regeneration process is a regeneration process in which the temperature is raised to T _{i + 1,} which is higher than the i-th process. Under such control, steps 2 to 6 are sequentially repeated until the end condition is determined to be satisfied in step 4 or step 5, and the low temperature regeneration process is repeatedly performed.

  In the exhaust gas purification apparatus of the present invention, a NOx purification catalyst may be further disposed at a position after the aggregate is disposed. By arranging the NOx purification catalyst in this way, the exhaust gas from which PM has been sufficiently removed by the aggregates contacts the NOx purification catalyst during exhaust gas purification, so that the NOx purification catalyst is poisoned and deteriorated by PM. Is sufficiently suppressed.

  In addition, such an exhaust gas purifying apparatus of the present invention can sufficiently purify exhaust gas containing PM by contacting exhaust gas discharged from an internal combustion engine. Such an exhaust gas purification apparatus can use oxygen in the gas phase as an oxidant, and can sufficiently oxidize components such as PM, HC, CO, or NO in a lower temperature range. Even when PM is deposited, the exhaust gas purification device can be sufficiently regenerated by a regenerating process at a relatively low temperature. Furthermore, when the exhaust gas purification apparatus of the present invention further includes the control means, it can be used for a longer period of time while preventing deterioration of the catalyst activity.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
First, Preparation and _{Ce (NO 3) 3 · 6H} 2 O of 50.46G, and La _{(NO 3)} 3 of 5.59 g, a solution of the AgNO ₃ of 29.62g was is dissolved in water 120 mL, Next, ammonia water was prepared by diluting 38.21 g of 25% aqueous ammonia into 100 g of water. And the solution prepared as mentioned above was thrown into the place which stirred the said ammonia water, and the aggregate was prepared.

  Next, the obtained agglomerate was coated on a test piece size (35 ml) DPF (manufactured by cordierite, porosity: 65%, average pore diameter: 30 μm) by the following coating method to obtain an exhaust gas purification apparatus of the present invention. It was. That is, the precipitate (aggregate) after reverse precipitation and aggregation treatment was collected by centrifugation, and water was added to obtain a slurry having a concentration of 15% by mass. Next, the slurry was contacted so as to enter the pores of the DPF. After being sucked in this state, while carrying out baking at 500 ° C. for 1 hour in the atmosphere, it was repeated until the carrying amount (covering amount) reached 150 g / L. The merit of this method is that the precipitate itself sinters at the time of firing and acts as a binder, so that it is possible to form a coating consisting only of components effective for soot oxidation. Further, when the particle size distribution of the slurry was measured, it was confirmed that about 0.1 μm aggregates were stably dispersed, so that the coating on the DPF was easy. In the above coating method, the contact is made without applying ultrasonic waves, but it may be performed while applying ultrasonic waves.

(Example 2)
Against exhaust gas purification devices obtained in the same manner as in Example 1, O 2 _10%, subjected to durability test firing for 5 hours at 800 ° C. in an atmosphere consisting of N 2 _90%, after the durability test of the present invention An exhaust gas purification device was obtained.

(Example 3)
Exhaust gas purification apparatus of the present invention was obtained in the same manner as in Example 1 except that the carrying amount (coating amount) was 50 g / L when coating the aggregate.

Example 4
Exhaust gas purification apparatus of the present invention was obtained in the same manner as in Example 1 except that 2L size DPF (manufactured by cordierite, porosity: 65%, average pore diameter: 30 μm) was used (coating amount: 150 g / L).

(Example 5)
A method similar to the method for producing an aggregate employed in Example 1 was adopted except that La (NO ₃ ) ₃ was not used when obtaining the aggregate, and the Ag concentration in the aggregate was 60 mol%. Thus, an aggregate was prepared.

(Comparative Example 1)
First, DPF (manufactured by cordierite, porosity: 65%, average pore diameter: 30 μm, diameter: 14.38 cm × length: 15.24 cm) was added to 325 ml of distilled water with 125 g of Ce (NO ₃ ) ₃ x6H ₂ O, 18 g Of ZrO (NO ₃ ) ₂ , 6.4 g Sm (NO ₃ ) ₃ x6H ₂ O, 2.1 g Y (NO ₃ ) ₃ x6H ₂ O, and 38.4 g citric acid And dried at 105 ° C. and then calcined at 600 ° C. for 4 hours.

Then 68.5 g AgNO ₃ , 155 g Ce (NO ₃ ) ₃ x6H ₂ O, 8.5 g ZrO (NO ₃ ) ₂ , 12.8 g Sm (NO ₃ ) ₃ × 6H in 325 ml distilled water. After impregnating the substrate with a solution in which ₂ O and 3.0 g of Y (NO ₃ ) ₃ x6H ₂ O were mixed, the substrate was dried overnight at room temperature, further dried at 105 ° C. for 10 hours, and then 600 ° C. For 4 hours.

And 69.6 g Ce (NO ₃ ) ₃ x6H ₂ O, 5.4 g Cu (NO ₃ ) ₂ x3H ₂ O, 0.51 g AgNO _3, and 9 g urea in 100 ml distilled water. The DPF mixed at 105 ° C. was impregnated with the solution, dried at 80 ° C., and further calcined at 650 ° C. for 4 hours to produce an exhaust gas purification device for comparison. The composition of the catalyst layer on the substrate surface in the exhaust gas purifying apparatus was Ag _0.5 Ce _0.5 having ceria stabilized by the addition of Sm, Zr and Y.

[Evaluation of characteristics of exhaust gas purifying apparatus obtained in Example 1 and Comparative Example 1]
<PM oxidation performance evaluation test 1>
Using the exhaust gas purifying apparatus obtained in Example 1 and Comparative Example 1, about 2 g / L of PM is deposited at 200 ° C. in the exhaust gas of the diesel engine, and then maintained at 500 ° C. and N ₂ atmosphere for 15 minutes. Then, the unburned hydrocarbon component was removed, and the temperature was increased at a rate of temperature increase of 20 ° C./min in a flow rate of 30 L / min and an O ₂ 10% atmosphere. Then, to compare the PM oxidation performance by CO ₂ peak at this time. The obtained results are shown in FIG. In order to match the properties of the deposited PM, the process of depositing PM was performed at the same time.

As is clear from the graph shown in FIG. 3, the CO ₂ peak of the exhaust gas purification apparatus of the present invention is around 440 ° C., and the CO ₂ peak of the exhaust gas purification apparatus for comparison is around 600 ° C. In the exhaust gas purification apparatus of the invention, it was confirmed that PM can be sufficiently oxidized and removed at a relatively low temperature.

<PM oxidation performance evaluation test 2>
Except for using each of the exhaust gas purification apparatuses of the present invention obtained in Examples 1 and 2, PM was deposited using the same method as in the oxidation performance evaluation test 1, and the PM oxidation performance was measured by the CO ₂ peak. . The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 4, first, it was confirmed that in the exhaust gas purification apparatus of the present invention obtained in Example 1, three peaks were observed. Such peaks are thought to be caused by dry soot collected inside the wall, non-flammable soot collected inside the wall, and soot accumulated outside the wall, respectively. . Moreover, since the same peak was shown by the thing of the initial stage (Example 1) and the thing after an endurance test (Example 2), it turned out that the exhaust gas purification apparatus of this invention has high durability.

Thus, in the exhaust gas purifying apparatus of the present invention obtained in Example 1, there are three CO ₂ peaks when PM is oxidized, so each peak temperature (T2 to T4) and soot oxidation described later are obtained. By setting the temperature TG (T1) at which the oxidation performance is confirmed by the speed measurement test (see FIG. 12) as the above-mentioned second regeneration processing temperature, and performing the low-temperature regeneration processing as described above, it is efficient. It was confirmed that it can be played.

<HC oxidation performance evaluation test>
Using the exhaust gas purification apparatus of the present invention obtained in Example 3, the HC oxidation performance was evaluated. That is, when evaluating the oxidation performance of HC, CO, CO2, THC was heated at a rate of temperature increase of 20 ° C./min in a flow rate of 30 L / min, C ₃ H ₆ (THC) 500 ppm, and O ₂ 10% atmosphere. The concentration (vol%) of was measured. The results are shown in FIG.

  As is clear from the results shown in FIG. 5, it was confirmed that the exhaust gas purifying apparatus of the present invention exhibited sufficient activity in a temperature range of 200 ° C. or higher, and that no CO was generated even when HC was oxidized.

<NO oxidation performance evaluation test>
Using the exhaust gas purification apparatus of the present invention obtained in Example 3, the oxidation performance of NO was evaluated. That is, when evaluating the oxidation performance of NO, the NO concentration (vol%) was measured by raising the temperature at a rate of temperature increase of 20 ° C./min in a flow rate of 30 L / min, NO 600 ppm, and O ₂ 10% atmosphere. The results are shown in FIG.

  As is clear from the results shown in FIG. 6, it was confirmed that NO can be sufficiently oxidized in the exhaust gas purifying apparatus of the present invention. Note that the NO concentration started to increase in the region of 350 ° C. or higher because it was governed by chemical equilibrium.

<PM oxidation performance evaluation test 3>
Using the exhaust gas purifying apparatus obtained in Example 4 and a 2 L size DPF for comparison (made by cordierite, porosity of 60%, average pore diameter of 30 μm), each was provided in the piping from the engine, PM oxidation performance was evaluated by measuring fluctuations. In addition, the engine used the 2L diesel engine, and measured the pressure of the base-material entrance on the operating conditions of 3000 rpm and 11.0 kgm. The exhaust temperature at the substrate inlet was about 360 ° C. And when it became a stable driving | running condition, the time change of the pressure difference from a certain time was measured. The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 7, the pressure does not oxidize when only the DPF substrate is used, so that the pressure increases monotonously with time, whereas the composite material substrate of the present invention has a slight pressure fluctuation. Although it was observed, it remained at almost constant pressure. From this result, it was confirmed that PM could be continuously oxidized according to the composite material base material of this invention. From these results, it is considered that the amount of PM deposited and the pressure are proportional. Therefore, when adopting the control means as described above, it has been found that a method of measuring a change in pressure and measuring a PM deposition amount can be suitably employed as a method for measuring a PM deposition amount.

<PM oxidation performance evaluation test 4>
Using the three exhaust gas purifying devices obtained in Example 1, PM was deposited at 200 ° C. in the exhaust of each diesel engine, and then kept at 500 ° C. for 15 minutes in an N ₂ atmosphere for unburned hydrocarbons. The components were removed, and the temperature was further increased at a rate of temperature increase of 20 ° C./min in a flow rate of 30 L / min and an O ₂ 10% atmosphere. In addition, the accumulation amount of PM of each exhaust gas purification apparatus was 1 g / L, 2 g / L, and 5 g / L, respectively. Then, to compare the PM oxidation performance by CO ₂ peak at this time. The obtained results are shown in FIG. 8 (PM deposition amount 1 g / L), FIG. 9 (PM deposition amount 2 g / L), and FIG. 10 (PM deposition amount 5 g / L). In order to match the properties of the deposited PM, the process of depositing PM was performed at the same time.

  As is clear from the results shown in FIGS. 8 to 10, in the exhaust gas purification apparatus (Example 1) of the present invention, in order to perform the regeneration process at a lower temperature, the low temperature regeneration process is performed with a smaller amount of PM deposition. It has been confirmed that it is preferable to apply, for example, when the amount of PM deposited is 1 g / L or less, it has been found that it is preferable to perform a low temperature regeneration treatment.

<Oxidation rate measurement test>
Using the exhaust gas purifying apparatus of the present invention obtained in Example 1, PM was deposited at 200 ° C. in an exhaust gas of a diesel engine at 200 ° C., and then kept at 500 ° C. for 15 minutes in an N ₂ atmosphere for unburned. The hydrocarbon component was removed, and the temperature was maintained at each temperature for 10 minutes in a flow rate of 30 L / min and an O ₂ atmosphere of 10%, and the oxidation rate of PM was determined from the measured CO ₂ concentration. The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 11, it was confirmed that PM could be sufficiently oxidized at about 300.degree.

<Measurement test of soot oxidation rate>
First, the agglomerates before coating and the agglomerates obtained in Example 5 were mixed with the soot (carbon composition 99.9% or more) by the following mixing method using the DPF produced in Examples 1-2. A sample for measurement was prepared. In addition, the mixing ratio of each aggregate and soot was set to 2: 0.1 by weight ratio (g). The agglomerates produced in Example 2 were subjected to a durability test by adopting the same method as that employed in Example 2.

  [Mixing method] Using a stirrer (manufactured by ASONE, MMPS-M1) and a magnetic mortar (manufactured by ASONE, MP-02), the mixture was mixed for 3 minutes by electric mixing with a speed scale of "3" (sample for measurement) )

Next, the obtained measurement samples (Examples 1 to 2 and 5) were measured using a thermogravimetric analyzer “GC-MS5972A” (manufactured by Hewlett Packard) in an O ₂ 10% / He balance atmosphere. The soot oxidation rate was calculated from the weight M ₁ and the total soot weight M _{2 at} that time. The calculation method calculates the soot weight M ₂ based on the weight when the temperature is finally raised to 800 ° C. after the measurement of the first weight M ₁ , and starts from the measurement time t (here, 1/6 hour). formula:
Soot oxidation rate = (M ₁ −M ₂ ) / {(M ₁ + M ₂ ) × t / 2}
Calculated by The obtained result is shown in FIG.

  As is clear from the results shown in FIG. 12, soot oxidation activity was observed from around 240 ° C. in any aggregate. Moreover, it was confirmed that both the initial aggregate (Example 1) and the aggregate after the durability test (Example 2) have very high soot oxidation activity.

  As described above, according to the present invention, oxygen in the gas phase can be used as an oxidizing agent, and components such as PM, HC, CO, or NO can be sufficiently oxidized in a lower temperature range. It is possible to provide an exhaust gas purifying apparatus that can be sufficiently regenerated by a relatively low temperature regeneration process even when PM is deposited.

  Therefore, since the exhaust gas purification apparatus of the present invention is excellent in PM purification performance, it is particularly useful as an exhaust gas purification apparatus for purifying exhaust gas discharged from a heavy truck diesel engine.

It is a flowchart which shows suitable one Embodiment of the control performed by the control means of this invention. It is a flowchart which shows other suitable embodiment of the control performed by the control means of this invention. It is a graph which shows the result of the PM oxidation performance test of the exhaust gas purification apparatus obtained in Example 1 and Comparative Example 1. It is a graph which shows the result of the PM oxidation performance test of the exhaust gas purification apparatus of this invention of Examples 1-2. 4 is a graph showing the results of an HC oxidation performance test of the exhaust gas purification apparatus of the present invention obtained in Example 3. 6 is a graph showing the results of a NO oxidation performance test of the exhaust gas purification apparatus of the present invention obtained in Example 3. It is a graph which shows the result of the PM oxidation performance test of 2L size DPF for comparison with the exhaust gas purification apparatus obtained in Example 4. It is a graph which shows the result of the PM oxidation performance test of the exhaust gas purification apparatus obtained in Example 1 with a PM deposition amount of 1 g / L. It is a graph which shows the result of the PM oxidation performance test of the exhaust gas purification apparatus obtained in Example 1 with a PM deposition amount of 2 g / L. It is a graph which shows the result of the PM oxidation performance test of the exhaust gas purification apparatus obtained in Example 1 with a PM deposition amount of 5 g / L. It is a graph which shows the result of the oxidation rate measurement test of the exhaust gas purification apparatus of this invention obtained in Example 1 made PM deposition amount 2g / L. It is a graph which shows the result of having measured the soot oxidation rate of the exhaust gas purification apparatus obtained in Examples 1-2 and 5. FIG.

Claims (6)

  An exhaust gas purification apparatus comprising an aggregate composed of silver particles serving as nuclei and ceria fine particles having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particles.   The exhaust gas purification apparatus according to claim 1, comprising a base material and the aggregate.   The substrate has pores of 1 to 300 μm, and a coat layer having an average thickness of 0.5 to 50 times the average particle size of the aggregate is formed by the aggregate in the pores. The exhaust gas purifying device according to claim 1 or 2, wherein the exhaust gas purifying device according to claim 1 or 2 is provided.   The exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the porosity of the base material is 30 to 70%. Based on the first standard (A) of the PM deposition amount that requires the forced regeneration process and the second standard (B) of the PM deposition amount that is lower than the first standard (A),
The second regeneration process that is lower than the first regeneration process temperature for the forced regeneration process when the obtained PM deposition amount is between the first standard (A) and the second standard (B). Apply low temperature regeneration treatment at temperature,
When the obtained PM deposition amount exceeds the first standard (A), a forced regeneration process is performed.
The exhaust gas purification apparatus according to any one of claims 1 to 4, further comprising control means for controlling the exhaust gas purification apparatus.   When a plurality of temperature conditions are set as the second regeneration processing temperature and the obtained PM deposition amount is between the first reference (A) and the second reference (B), When low temperature regeneration processing is performed at the second regeneration processing temperature and the subsequent PM deposition amount becomes less than the second reference (B), the low temperature regeneration processing is terminated, and the PM deposition amount is still the first reference ( If it is between A) and the second reference (B), the exhaust gas purification apparatus is controlled so as to repeat the low temperature regeneration process by sequentially changing to the second regeneration process temperature on the high temperature side. The exhaust gas purification apparatus according to claim 5.