JP2009178673A - Exhaust gas cleaning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning apparatus capable of efficiently oxidizing a granular substance in an exhaust gas discharged from an internal combustion engine at a temperature area of low temperature and sufficiently regenerating an oxidation activity by applying regeneration treatment utilizing carbon monoxide (CO) contained in the exhaust gas even after poisoned with sulfur. <P>SOLUTION: The exhaust gas cleaning apparatus for oxidizing/eliminating the granular substance contained in the exhaust gas is provided with a catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia, a catalyst for a CO shift reaction having a noble metal carried on the catalyst carrier and a catalyst containing silver for removing the granular substance. The catalyst for the CO shift reaction is arranged in an upstream side of a gas flow passage circulated with the exhaust gas, and the catalyst for removing the granular substance is arranged in a downstream side of the gas flow passage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that oxidizes and removes particulate matter contained in exhaust gas.

  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, exhaust gas purification apparatuses capable of oxidizing and removing PM, particularly soot components, from low temperatures have been developed.

For example, JP-A-2004-42021 (Patent Document 1) has ceria (CeO ₂ ) stabilized with silver (Ag) and / or cobalt (Co) at an Ag equivalent in the range of 5 to 90 mol%. A platinum group metal-free catalyst is disclosed. In JP-A-2006-177346 (Patent Document 2), a base material capable of collecting particulate matter discharged from an internal combustion engine, and included in or present on the base material, An exhaust gas comprising an acidic compound adsorbing means for adsorbing an acidic compound and an acidic compound desorbing means for desorbing the acidic compound adsorbed on the acidic compound adsorbing means, wherein the acidic compound adsorbing means is a composition containing Ce and Ag. A purification device is disclosed.

However, in the conventional exhaust gas purification apparatuses as described in Patent Documents 1 and 2, regeneration processing using carbon monoxide (CO: reducing gas) contained in the exhaust gas when poisoned by sulfur components is performed. Even if applied, the oxidation activity of the particulate matter could not be sufficiently recovered.
JP 2004-42021 A JP 2006-177346 A

  The present invention has been made in view of the above-described problems of the prior art, and can efficiently oxidize particulate matter in exhaust gas discharged from an internal combustion engine in a low temperature range, and after sulfur poisoning. The purpose of the present invention is to provide an exhaust gas purifying apparatus capable of sufficiently regenerating the oxidation activity by applying a regeneration treatment using carbon monoxide (CO) contained in the exhaust gas.

  As a result of intensive studies to achieve the above object, the present inventors comprise a catalyst support containing at least one selected from the group consisting of ceria, titania and zirconia, and a noble metal supported on the catalyst support. A CO shift reaction catalyst and a particulate matter purification catalyst containing silver, and the CO shift reaction catalyst is disposed upstream of the gas flow path through which the exhaust gas flows, By the exhaust gas purification device in which the particulate matter purification catalyst is arranged on the downstream side, the particulate matter in the exhaust gas discharged from the internal combustion engine can be efficiently oxidized in a low temperature range, and after sulfur poisoning In addition, it has been found that the oxidation activity can be sufficiently regenerated by performing a regeneration treatment using carbon monoxide (CO: reducing gas) contained in the exhaust gas, and the present invention has been completed. It was.

That is, the exhaust gas purification apparatus of the present invention is an exhaust gas purification apparatus that oxidizes and removes particulate matter contained in exhaust gas,
A catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia, a CO shift reaction catalyst comprising a noble metal supported on the catalyst carrier, and a particulate matter purification catalyst containing silver Prepared, and
The CO shift reaction catalyst is disposed upstream of the gas flow path through which the exhaust gas flows, and the particulate matter purification catalyst is disposed downstream of the gas flow path;
It is characterized by.

In the exhaust gas purifying apparatus of the present invention, the particulate matter purification catalyst comprises agglomerates comprising silver particles as nuclei and ceria fine particles having an average primary particle diameter of 1 to 100 nm covering the periphery of the silver particles. It is preferable to provide a collection. Here, “ceria fine particles” refer to metal oxide fine particles made of a complex oxide containing CeO ₂ or Ce.

  Moreover, in the exhaust gas purification apparatus of the present invention, it is more preferable that the particulate matter purification catalyst includes a base material and the aggregate, and the base material has pores of 1 to 300 μm. More preferably, a coat layer having an average thickness of 0.5 to 50 times the average particle diameter of the aggregate is formed in the pores.

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

  Furthermore, in the exhaust gas purifying apparatus of the present invention, the catalyst carrier preferably contains ceria, and more preferably contains a mixture in which ceria and alumina are dispersed on the nm scale.

In addition, the particulate matter in the exhaust gas discharged from the internal combustion engine can be efficiently oxidized in the low temperature range by the exhaust gas purification apparatus of the present invention, and carbon monoxide contained in the exhaust gas even after sulfur poisoning The reason why the oxidation activity can be sufficiently regenerated by performing a regeneration process using (CO: reducing gas) is not necessarily clear, but the present inventors speculate as follows. That is, in the present invention, a particulate matter purification catalyst containing silver (Ag) is provided. It is assumed that the mechanism for oxidizing PM by such a particulate matter purification catalyst is as follows. That is, first, oxygen is released from the oxygen-containing substance by Ag even at a relatively low temperature. Next, the active oxygen species (O ^* : for example, oxygen ions) generated by liberation move to the surface of the PM, 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 thus formed is oxidized by gas phase oxygen or the like. In this way, it is presumed that the oxidized portion is removed and reduced from the periphery of the PM, and finally it can be completely oxidized and disappear. And, it is presumed that the particulate matter purification catalyst containing Ag can efficiently oxidize the particulate matter even in a relatively low temperature range.

In general, in a catalyst containing Ag, when the catalyst is exposed to an exhaust gas containing a sulfur component and a large amount of the sulfur component adheres, silver sulfate is generated by the silver in the catalyst and the sulfur component. . And when such silver sulfate is produced | generated, the oxygen active species production | generation performance of silver will fall and the oxidation activity of a catalyst will fall. Therefore, a catalyst containing silver is generally subjected to a sulfur regeneration process for supplying a reducing gas to the catalyst when the supply of the sulfur component reaches a certain amount. Such reducing gas mainly uses CO. However, when CO is used as the reducing gas, the silver sulfate produced in the catalyst is not sufficiently decomposed and the sulfur component is hardly desorbed. Therefore, in the conventional catalyst containing Ag, the oxidation activity could not be sufficiently recovered after sulfur poisoning. Accordingly, in the present invention, a catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia and a noble metal supported on the catalyst carrier are provided upstream of the particulate matter purification catalyst. A CO shift reaction catalyst is provided. When the CO shift reaction catalyst is thus arranged on the upstream side of the gas flow path, H ₂ can be added to the exhaust gas on the upstream side of the gas flow path. That is, by such a CO shift reaction catalyst, H ₂ is generated from CO and H ₂ O (water vapor) in the exhaust gas by a CO shift reaction (CO + H ₂ O → CO ₂ + H ₂ ), and upstream of the gas flow path. In this case, H ₂ can be added to the exhaust gas. Therefore, the exhaust gas to which H ₂ is added comes into contact with the particulate matter purification catalyst arranged on the downstream side of the gas flow path. Since H ₂ is a reducing gas capable of efficiently decomposing silver sulfate produced in the particulate matter purification catalyst, in the present invention, the sulfur component deposited on the catalyst is sufficiently removed. Can be separated. Therefore, in the exhaust gas purifying apparatus of the present invention, even when it comes into contact with the exhaust gas containing the sulfur component, H ₂ is generated on the upstream side of the gas flow path using CO in the exhaust gas, and the H ₂ Thus, the present inventors speculate that the oxidation activity of the particulate matter purification catalyst on the downstream side can be efficiently recovered and the oxidation activity of the particulate matter can be kept sufficiently high.

  According to the present invention, particulate matter in exhaust gas discharged from an internal combustion engine can be efficiently oxidized in a low temperature range, and carbon monoxide (CO :) contained in exhaust gas even after sulfur poisoning. It is possible to provide an exhaust gas purifying apparatus capable of sufficiently regenerating the oxidation activity by performing a regeneration process using a reducing gas.

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

The exhaust gas purification apparatus of the present invention is an exhaust gas purification apparatus that oxidizes and removes particulate matter contained in exhaust gas,
A catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia, a CO shift reaction catalyst comprising a noble metal supported on the catalyst carrier, and a particulate matter purification catalyst containing silver Prepared, and
The CO shift reaction catalyst is disposed upstream of the gas flow path through which the exhaust gas flows, and the particulate matter purification catalyst is disposed downstream of the gas flow path;
It is characterized by.

First, the CO shift reaction catalyst according to the present invention will be described. Such a catalyst for CO shift reaction includes a catalyst support containing at least one selected from the group consisting of ceria, titania and zirconia, and a noble metal supported on the catalyst support. Such a catalyst for CO shift reaction has a sufficiently high activity for the CO shift reaction. The reason why a sufficiently high CO shift reaction activity can be obtained by such a catalyst for CO shift reaction is not necessarily clear, but the present inventors speculate as follows. That is, first, a catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia has high hydrophilicity and high water vapor (H ₂ O) adsorption. Further, the noble metal supported on the catalyst carrier easily adsorbs CO. Therefore, according to the CO shift reaction catalyst comprising these, it is possible to adsorb a large amount of CO and H ₂ O on the catalyst surface, and improve the probability that CO and H ₂ O react on the catalyst surface. be able to. Therefore, the present inventors speculate that the CO shift reaction catalyst according to the present invention has a sufficiently high CO shift reaction activity. In the present invention, by arranging such a CO shift reaction catalyst on the upstream side of the gas flow path, it is possible to efficiently add H ₂ to the exhaust gas flowing downstream, It is possible to sufficiently maintain the oxidation activity of the particulate matter purification catalyst disposed in the column.

  Further, as such a catalyst carrier, any catalyst carrier may be used as long as it contains at least one selected from the group consisting of ceria, titania and zirconia. For example, ceria alone, titania alone, zirconia alone, these Examples include composite oxides (for example, ceria-zirconia composite oxide). Among them, ceria is contained from the viewpoint of improving the thermal stability of the metal oxide in the support and the effect of suppressing the grain growth of the supported noble metal. It is preferable to use one.

  In addition to ceria, titania and zirconia, such a catalyst carrier preferably contains a metal oxide which does not dissolve in ceria, titania and zirconia. By further containing such a metal oxide, in the catalyst support, at least one selected from the group consisting of ceria, titania and zirconia, and the metal oxide serve as a diffusion barrier between each other, There is a tendency that not only the aggregation of the same kind of oxides is suppressed but also the grain growth of the supported noble metal can be suppressed. Such metal oxides that do not form a solid solution with ceria, titania and zirconia are not particularly limited, and examples thereof include alumina, silica, etc., among others, from the viewpoint of improving the thermal stability of the metal oxide in the carrier. Alumina is preferred.

  Among such catalyst supports, a mixture in which ceria and alumina are dispersed in nm scale from the viewpoint that higher CO shift reaction activity can be expressed even after being exposed to high temperature ( A catalyst carrier containing a composite oxide) is preferred. Moreover, in such a mixture, it is preferable that ceria and alumina are dispersed on the nm scale. By using the composite oxide in which each particle is dispersed on the nm scale in this way, the catalytic activity tends to be more sufficiently maintained. Examples of the catalyst carrier in which ceria and alumina are dispersed in nm scale include, for example, composite oxides in which ceria and alumina are dispersed in nm scale as described in JP-A No. 2002-21908. It is done. Note that nm-scale dispersion refers to a dispersion state at a level that is not observed as independent particles even when measured using a microanalyzer having a high resolution of about 1 nm. As such a microanalyzer, for example, an FE-STEM scanning transmission electron microscope such as “HD-2000” manufactured by Hitachi, Ltd. may be used.

  Furthermore, the form of such a catalyst carrier is not particularly limited, but is preferably in the form of a powder. When such a catalyst carrier is in a powder form, the average particle diameter of the primary particles of each metal oxide contained is preferably 2 to 50 nm, and more preferably 5 to 20 nm. If the average particle size is less than the lower limit, the thermal stability of the metal oxide in the support tends to be reduced and the grains tend to grow.On the other hand, if the upper limit is exceeded, the dispersibility of the noble metal to be supported is reduced. It tends to decrease.

  Further, the method for producing such a catalyst carrier is not particularly limited, and a known method can be appropriately employed. As an example of a method for producing such a catalyst carrier, a method for producing a catalyst carrier containing a mixture (composite oxide) in which ceria and alumina are dispersed on the nm scale will be described below.

  In a method for producing a catalyst carrier containing such a composite oxide, a cerium oxide precursor and an aluminum oxide precursor are prepared from an aqueous solution or a solution containing water in which a cerium compound and an aluminum compound are dissolved. Alternatively, precipitates of the precursor compounds are deposited. The cerium compound or aluminum compound is not particularly limited, and a cerium or aluminum salt is used. As such salts, sulfates, nitrates, hydrochlorides, acetates and the like can be used. Moreover, the method in particular of depositing precipitation is not restrict | limited, A well-known method can be employ | adopted, For example, you may employ | adopt the method of depositing precipitation, etc., adjusting pH by addition, such as aqueous ammonia.

  Examples of the noble metal supported on the catalyst carrier include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru). From the viewpoint of high CO adsorption capability, at least Pt is preferably used. The amount of such noble metal supported is not particularly limited, but is preferably 0.05 to 30 parts by mass, and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the catalyst carrier. When the amount of the noble metal supported is less than the lower limit, sufficient catalytic activity tends to be not obtained. On the other hand, when the amount exceeds the upper limit, the catalytic activity is saturated and economy tends to be lowered. In addition, you may use such a noble metal individually by 1 type or in combination of 2 or more types. Further, the method for supporting the noble metal is not particularly limited. For example, the aqueous solution containing a noble metal salt (for example, a dinitrodiamine salt) or a complex (for example, a tetraammine complex) is contacted with the catalyst support and then dried. A method of firing can be employed.

  Further, the form of the catalyst for CO shift reaction is not particularly limited, and it can be in the form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The catalyst substrate for CO shift reaction that can be used here is not particularly limited, and a particulate filter substrate (DPF substrate), a monolith substrate, a pellet substrate, a plate substrate, and the like are preferable. Can be adopted. The material of such a catalyst substrate is not particularly limited, but a substrate made of a ceramic such as cordierite, silicon carbide, mullite, or a substrate made of a metal such as stainless steel including chromium and aluminum is preferably used. Can be adopted. In addition, the manufacturing method of the catalyst for CO shift reaction in such a form is not particularly limited, and a known method can be appropriately employed. For example, after the catalyst carrier is wash-coated on the substrate, the catalyst carrier For example, a method of supporting a noble metal can be employed.

  When a catalyst for CO shift reaction is supported on such a catalyst base, it is preferable to support 10 to 400 g, preferably 50 to 200 g, of the catalyst carrier per 1 L of the catalyst base. When the supported amount of the catalyst carrier is less than the lower limit, it tends to be difficult to perform the CO shift reaction efficiently. On the other hand, when the upper limit is exceeded, the cell (vent hole) of a substrate such as a monolith substrate Is blocked and the pressure loss of the exhaust gas tends to increase. Further, when a catalyst for CO shift reaction is supported on such a catalyst base, it is preferable to support 0.05 to 30 g of the noble metal per liter of the catalyst base from the viewpoint of catalyst activity and economy. It is more preferable to carry 1 to 10 g.

  Next, the particulate matter purification catalyst according to the present invention will be described. The particulate matter purifying catalyst according to the present invention is a catalyst containing silver (Ag). By containing such Ag, it is possible to liberate oxygen from the oxygen-containing substance and efficiently generate oxygen active species. In addition, as such a particulate matter purification catalyst, metal oxide fine particles containing Ag in a metal carrier and having an average primary particle size of 1 to 400 nm made of an oxide of a first metal are formed on the metal carrier. Are preferably further provided.

  Further, such a metal carrier containing Ag is not particularly limited as long as it contains Ag, but the metal carrier may further contain a metal other than Ag. For example, Ag and Ag Alloys with other metals may be used. Examples of metals other than Ag that can be used for such metal carriers include Pt, Rh, Pd, Ru, Ir, Os, from the viewpoint of efficiently generating oxygen active species by releasing oxygen from oxygen-containing substances. At least one selected from the group consisting of Au and Cu is preferable. Moreover, when such a metal support | carrier contains components other than Ag, it is preferable that the content rate of Ag is 0.3 mass% or more. Further, the size of the metal in such a metal carrier is preferably large to some extent so that the electronic state can maintain the properties as a metal (for example, it is not an oxide). A metal having a smaller ionization tendency tends to maintain its properties as a metal even if the metal is smaller. Thus, it is in the tendency which can produce | generate adsorption | suction oxygen seed | species more efficiently, when metals other than Ag and Ag maintain the property as a metal.

  Further, the shape of such a metal carrier is not particularly limited, and may be a film shape or a particle shape. When such a metal carrier is in the form of a film, the thickness is preferably 3 nm or more, and more preferably 3 to 1000 nm from the viewpoint of cost reduction. Moreover, when such a metal support is a particulate form, the average primary particle size is preferably 7 nm or more, and more preferably 7 to 1000 nm from the viewpoint of cost reduction. Such a metal carrier may be formed by the presence of a plurality of particles in contact with each other.

In addition, as the first metal, a metal capable of changing its valence is suitably used from the viewpoint of being an oxygen active species transfer material capable of transferring and / or storing oxygen active species. Such first metal oxides include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Zr, Fe, Ti, At least one selected from the group consisting of oxides of Al, Mg, Co, Ni, Mn, Cr, Mo, W and V, solid solutions thereof, and composite oxides thereof is preferable. CeO ₂ , Fe ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , MgO, Co ₃ O ₄ , Pr ₂ O ₃ , Nd ₂ O ₃ , a solid solution thereof, and a composite oxide thereof In particular, a composite oxide containing CeO ₂ and Ce is particularly preferable. Further, the oxide of the first metal preferably has a certain amount of defects in order to move the oxygen active species.

It should be noted that such metal oxide fine particles (hereinafter simply referred to as “ceria fine particles”) composed of a complex oxide containing CeO ₂ or Ce move oxygen active species generated by the metal carrier (oxygen release material). It is speculated that it functions as an oxygen active species transfer material in the catalyst. Such an oxide of Ce in the ceria fine particles can move oxygen active species (for example, oxygen ions) through its valence change or the like. Therefore, when the ceria fine particles receive the oxygen active species generated by the Ag particles (oxygen release material), the oxygen active species move to the ceria fine particles (oxygen active species transfer material) and reach the contacting PM. Such a route for the oxygen active species to move does not need to pass through the inside of the bulk of the ceria fine particles. For example, the oxygen active species may move on the surface of the fine particles.

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

  The average primary particle size of the metal oxide fine particles made of such an oxide of the first metal needs to be 1 to 400 nm, and more preferably 1 to 100 nm. When the average primary particle size of the metal oxide fine particles is less than 1 nm, it becomes difficult for oxygen-containing substances to pass through the voids of the fine particles, and the generation of active oxygen species in the metal carrier is inhibited. On the other hand, when the average primary particle size of the metal oxide fine particles exceeds 400 nm, the particulate matter easily passes through the voids of the fine particles, the contact property between the metal oxide fine particles and the particulate matter decreases, and the active oxygen species Supply to particulate matter is hindered.

  In addition, the metal oxide fine particles made of the oxide of the first metal preferably have an average particle diameter of 2 to 100 nm (more preferably 10 to 50 nm) after being fired at 500 ° C. in the air for 5 hours. It is preferable that 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 2 to 400 nm (more preferably 10 to 80 nm). If the average particle size of the metal oxide fine particles is less than the lower limit, contact with particulate matter such as soot tends to be inhibited. On the other hand, if the upper limit is exceeded, the particulate matter easily passes through the voids of the fine particles. Therefore, the contact property between the metal oxide fine particles and the particulate matter is lowered, and the supply of the active oxygen species to the particulate matter tends to be hindered.

In addition, the layer made of oxide fine particles of the first metal disposed on the metal support must have a structure that allows oxygen-containing substances such as O ₂ to pass through the voids of the fine particles and reach the metal support. It is. Whether or not it has such a structure can be confirmed by an electron microscope, or by measuring the amount of exposed metal with respect to the metal in the metal support (oxidation-reduction titration with O ₂ and H ₂ ).

The thickness of the layer made of the fine particles of the first metal oxide is not particularly limited. From the viewpoint of efficient supply of active oxygen species to the particulate matter, and the amount of electrons generated during oxidation of the particulate matter. From the viewpoint of efficient transfer to the metal support, it is preferably 10 μm or less, more preferably 400 nm or less, even more preferably 100 nm or less, particularly preferably 30 nm or less, and 10 nm or less. More particularly preferably. On the other hand, when the thickness of the first metal oxide fine particle layer is less than 1 nm, the particles grow to inhibit contact between the metal carrier and O ₂ and reduce the amount of active oxygen species stored. Therefore, it is not preferable.

  Further, as the particulate matter purifying catalyst according to the present invention, when the metal support is in the form of particles, the first silver particle (metal support) serving as a nucleus and the periphery of the metal support are covered. An aggregate composed of metal oxide fine particles having an average primary particle diameter of 1 to 100 nm made of a metal oxide is preferable. In such an aggregate, silver (Ag) particles and metal oxide fine particles themselves are primary particles, and secondary particles formed by the former being covered by the latter are referred to as “aggregates (or primary aggregates)”. Called. Further, the “silver particles (Ag particles)” referred to here indicate particles in which the above-described metal carrier is formed, and may contain other metals in addition to Ag.

  Further, as the metal oxide fine particles in the aggregate, the above-mentioned ceria fine particles are more preferable. The particle size of the ceria fine particles in such an aggregate is not particularly limited, but the average particle size after baking for 5 hours at 500 ° C. in the air is preferably 2 to 75 nm (more preferably 8 to 20 nm, still more preferably 8 to 15 nm), and the average particle size after baking for 5 hours at 800 ° C. in an atmosphere of 10% oxygen and 90% nitrogen by volume is more preferably 8 to 100 nm (more preferably 8 to 60 nm, still more preferably 8 to 40 nm). If the average particle size of the ceria fine 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, it is difficult to cover the Ag particles (oxygen free material particles). There is a tendency.

  Further, when the metal oxide fine particles in the aggregate are the ceria particles, after baking for 5 hours at 500 ° C. in the atmosphere, and in an atmosphere composed of 10 vol% oxygen and 90 vol% nitrogen. In any case after calcination at 5 ° C. for 5 hours, the average particle diameter of the Ag particles is preferably 1.3 times or more, more preferably 2.0 times or more of the average particle diameter of the metal oxide fine particles. More preferred. If the average particle size of Ag particles and ceria fine particles does not satisfy the above conditions, the periphery of the Ag particles is not sufficiently covered with ceria fine particles, and the ability to oxidize components such as PM, HC, CO, or NO tends to decrease. It is in.

Further, the ratio of Ag particles to the ceria fine particles in such an aggregate is not particularly limited, but the ratio (molar ratio) of Ag particles to ceria fine particles is preferably 4: 1 to 1: 9. It is more preferable that it is 35: 65-60: 40, and it is especially preferable that it is 40: 60-60: 40. 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. And it is especially preferable that said ratio is 40: 60-60: 40, since ceria microparticles | fine-particles are easy to cover the circumference | surroundings of Ag particle | grains, and the ratio of both components which do not form those aggregates falls.

  In addition, such a particulate matter purification catalyst may further include second metal ultrafine particles supported on the surface of the metal oxide fine particles made of the first metal. When such second metal ultrafine particles are present, adsorbed oxygen species are further generated by exchange of charges between the metal whose valence is variable, the adsorbed oxygen species, and the metal ultrafine particles, and further the adsorbed oxygen species to the oxide. It tends to be easier to supply.

  The second metal constituting such second metal ultrafine particles has 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 less than the ionization tendency of Ag (noble metals: for example, Au, Ag, Cu, Pt, Pd, Rh, Ru, Ir, Os) are more preferable. It is particularly preferable that the metal is the same as the metal in the metal carrier. Moreover, it is preferable that a 2nd metal ultrafine particle consists of 1-1000 atoms.

As such second metal ultrafine particles, those that cannot be observed as particles even by FE-TEM observation are preferable. In the case of Ag, charges are exchanged with a metal that exists in isolation and has a variable valence. What is detected as Ag ²⁺ is exemplified.

  Further, in such a particulate matter purification catalyst, a noble metal such as Pt, Rh, Pd may be further supported by a normal impregnation method or the like for the purpose of coexistence with oxidation of HC, CO and NO. .

  Further, the form of such a particulate matter purification catalyst is not particularly limited, and may be in the form of, for example, a catalyst formed into a honeycomb shape, a pellet-shaped pellet catalyst, or the like. It is more preferable to include 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 such a particulate matter purification catalyst, the amount of aggregate to be applied to the substrate is not particularly limited, and the amount can be appropriately adjusted according to the target internal combustion engine or the like. The amount of the aggregate is preferably about 10 to 300 g per 1 liter of material volume.

  In such a particulate matter purification catalyst, the base material 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, such a particulate matter purification catalyst may further include other components together with the aggregate as long as the effect is not impaired. Such other components include core metal particles such as Pt, Rh, Pd, Ru, Ir, Os, Au, and La having an average primary particle size of 1 to 100 nm covering the periphery of the metal particles. , Ce, Pr, Nd, Pm, Sm, Eu, Gd and other aggregates made of metal oxide fine particles may be used.

  Moreover, in such a particulate matter purification catalyst, the base material preferably has a porosity of 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.

  A method for producing such a particulate matter purification catalyst is not particularly limited, and a known method can be appropriately employed. For example, as a method of forming the metal carrier, a method of forming by using a metal plate, plating, paste, a vapor deposition method (for example, chemical vapor deposition method, physical vapor deposition method, sputter vapor deposition method) or the like may be employed. . Further, the method for forming a layer of metal oxide fine particles on the surface of the metal carrier is not particularly limited, and coating is performed using a dispersion or sol of metal oxide fine particles or a precursor thereof (after that, firing is performed if necessary). You may employ | adopt the method of forming by using a method, a vapor deposition method (For example, a chemical vapor deposition method, a physical vapor deposition method, a sputter vapor deposition method) etc. Hereinafter, as an example of a method for producing the particulate matter purification catalyst of the present invention, a method for producing the agglomerates suitably used in the present invention will be described.

As a suitable method for producing such an aggregate, Ag particles derived from the Ag salt are derived from the solution containing the Ag salt and the first metal salt. A step of generating an aggregate precursor covered with monometallic compound fine particles, and an average particle covering the periphery of the Ag particles by firing the obtained aggregate precursor And a step of obtaining an aggregate comprising primary metal oxide fine particles having a primary particle diameter of 1 to 100 nm. Examples of such Ag and first metal salts include Ag and first metal nitrates. , Acetates, chlorides, sulfates, sulfites, inorganic complex salts, and the like, and nitrates (for example, silver nitrate and cerium nitrate) are preferably used. Further, the solvent for preparing the solution containing the salt of Ag and the salt of the first metal is not particularly limited, and water, alcohol (for example, methanol, ethanol, ethylene glycol alone or a mixed solvent) Among them, water is particularly preferable.

It should be noted that the blending amount (preparation amount) of the Ag salt and the first metal salt needs to completely match the ratio of the obtained Ag particles to the first metal oxide fine particles (for example, CeO ₂ fine particles). The combination of the Ag salt and the first metal salt and the condition of the blending amount are appropriately set according to the suitable conditions of the combination and ratio of the Ag particles and the first metal oxide fine particles in the aggregate to be obtained. Is done. Further, if an excessive amount of Ag salt is present with respect to the salt of the first metal, the oxide fine particles of the first metal generated in the solution tend to be easily made part of the aggregate, and the agglomeration tends to occur. It is preferable because components other than the aggregate are not formed in the solution.

  Further, in such an aggregate production method, in the step of producing the aggregate precursor, first metal compound fine particles are produced in the presence of a pH adjuster, and the first metal compound fine particles are reduced. It is preferable to produce the aggregate precursor by precipitating the Ag particles by action.

The requirement for the oxidation-reduction reaction can be explained by the potential between Ag and the first metal, 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 and coarse Ag tends to precipitate, 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%. Further, the fine particles of the first metal in this case are considered to be hydroxides of the first metal.

  Further, in such a method for producing an aggregate, in the step of generating the aggregate precursor, the first metal compound derived from the salt of Ag is generated in the presence of a complexing agent, and the first More preferably, the first metal compound is reduced by the reducing action of the metal compound fine particles to precipitate the silver 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 the first metal in the step of forming the aggregate precursor, the pH is adjusted. A so-called “reverse precipitation method” in which Ag and a salt solution of the first metal are added to and mixed with an agent-containing 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 a 1st metal, 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. On the other hand, if the solid content concentration exceeds the upper limit, it tends to be difficult to obtain an aggregate having silver particles as nuclei. By performing the aggregation treatment in this manner, an aggregate precursor in which the silver particles are covered with the fine particles of the first metal 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 homogeneity of the aggregate precursor is high, and 60% by volume or more of all the aggregate precursors have a particle size in the range of the average particle size ± 50%. Is preferred. When the homogeneity of the aggregate precursor is high as described above, the homogeneity of the obtained aggregate becomes high, and it tends to be supported uniformly by a substrate 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.

  Furthermore, the method for producing an aggregate may further include a step of supporting the second metal ultrafine particles on the surface of the first metal compound fine particles or the first metal oxide fine particles. The method for supporting the second metal ultrafine particles in this way is as follows: (i) the second metal ultrafine particles are supported on the surface of the oxide fine particles of the first metal after firing the aggregate precursor obtained by the aggregation treatment. And (ii) a method of precipitating the second metal ultrafine particles on the surface of the first metal compound fine particles simultaneously with the aggregation treatment.

  In the method (i), a method of impregnating and supporting the above-mentioned second metal nitrate, sulfate, acetate, ammonium salt or the like, 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, in the latter method, for example, Ag ⁺ is reduced by a defect site in the oxide fine particles of the first metal (for example, when the first metal is Ce, CeO ₂ is partially Ce ³⁺ ). This is a method for precipitating 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, in the step of generating the above-mentioned aggregate precursor, Ag particles are precipitated by the first metal compound fine particles, and at the same time, third metal ultrafine particles are also formed on the surface of the first metal compound fine particles. It is what is deposited.

  In addition, a method for arranging such an aggregate on the substrate is not particularly limited. For example, after the first aggregate dispersion or the second aggregate dispersion described below is brought into contact with the substrate. The method of baking is mentioned suitably.

  The first aggregate dispersion liquid 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 method using the second aggregate dispersion liquid, the component capable of oxidizing the particulate matter is the aggregate itself. Therefore, the component itself serves as a binder, and more effective for particulate matter purification. There is a tendency to provide a catalyst.

As described above, the CO shift reaction catalyst and the particulate matter purification catalyst used in the exhaust gas purification apparatus of the present invention have been described. In the present invention, the CO shift reaction catalyst has a gas flow path through which exhaust gas flows. Arranged on the upstream side, the particulate matter purification catalyst is arranged on the downstream side of the gas flow path. In this way, the CO shift reaction catalyst is disposed on the upstream side of the gas flow path, and the particulate matter purification catalyst is disposed on the downstream side of the gas flow path, so that the exhaust gas contacts the CO shift reaction catalyst. After that, it is possible to contact the particulate matter purification catalyst, and H ₂ generated by the CO shift reaction can be added to the exhaust gas in contact with the particulate matter purification catalyst. Therefore, in the present invention, the particulate matter purification catalyst can be efficiently regenerated from sulfur poisoning, and sufficiently high particulate matter oxidation activity can be maintained.

  Further, the CO shift reaction catalyst and the particulate matter purification catalyst respectively disposed on the upstream side and the downstream side of the gas flow path may be disposed adjacent to each other or separated from each other. Also good. In addition, the upstream side portion of one catalyst base is used as a base material for a catalyst for CO shift reaction, and the downstream side portion is used as a base material for a catalyst for purifying particulate matter. The CO shift reaction catalyst and the particulate matter purification catalyst may be arranged on the upstream side and the downstream side, respectively.

Further, in the exhaust gas purification apparatus of the present invention, the first standard (A) of the PM deposition amount on the particulate matter purification catalyst that requires forced regeneration treatment, and the standard lower than the first standard (A) Based on the second standard (B) of PM deposition amount which is
The first regeneration processing temperature for forced regeneration processing when the amount of PM deposited on the obtained particulate matter purification catalyst is between the first criterion (A) and the second criterion (B) Lower temperature regeneration treatment at a lower second regeneration treatment temperature,
When the PM deposition amount on the obtained particulate matter purification catalyst exceeds the first standard (A), a forced regeneration process is performed on the particulate matter purification catalyst.
It is preferable to further comprise a control means for controlling the exhaust gas purification device. By providing such a control means, PM deposited on the particulate matter purification catalyst can be efficiently removed, and the exhaust gas purification apparatus can be regenerated and continuously used.

  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.

  Further, the values of the first standard (A) and the second standard (B) can be appropriately set according to the size, form, type of base material, and the like of the catalyst used. 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 on the particulate matter purification catalyst is not particularly limited, and for example, the following method can be employed. That is, as a method for measuring the amount of PM deposited on the particulate matter purification catalyst, the operating status of the internal combustion engine, the use history of the exhaust gas purification device, etc., and the amount of PM deposited on the particulate matter purification catalyst And a map for calculating the amount of PM deposited on the particulate matter purification catalyst based on the map, and when the particulate matter purification catalyst is disposed in an exhaust pipe or the like, A map relating to the pressure difference between the exhaust gas before and after the position where the particulate matter purification catalyst is disposed and the amount of PM deposited on the particulate matter purification catalyst is created in advance, and the pressure difference is calculated based on the map. A method of calculating the PM deposition amount by measurement, a method of calculating the PM deposition amount by correcting the pressure difference with the intake air amount, a method of adopting all of these methods, and the like can be appropriately employed. In the measurement of the amount of PM deposited on the particulate matter purification catalyst, 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 the amount of PM deposited on the particulate matter purification catalyst, and in step 2, it is determined whether the amount of PM deposited is equal to or greater than the second reference (B). to decide. 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 controlling 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. In performing such control, first, the control unit calculates the amount of PM deposited on the particulate matter purification catalyst, and the amount of PM deposition on the particulate matter purification catalyst is the first reference (A ) And the second reference (B), 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 amount Xi of PM deposited on the particulate matter purification catalyst (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 increased to Ti _{+ 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, the NOx purification is performed at a position after the particulate matter purification catalyst is arranged (a position on the downstream side of the gas flow path from the position where the particulate matter purification catalyst is arranged). A catalyst may be further arranged. By arranging the NOx purification catalyst in this way, the exhaust gas from which particulate matter (PM) has been sufficiently removed comes into contact with the NOx purification catalyst during exhaust gas purification. Poisoning deterioration can be 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 remove PM using oxygen in the gas phase as an oxidizing agent, and can sufficiently oxidize PM in a lower temperature range. Further, even when PM is deposited, the exhaust gas purification device can be sufficiently regenerated by a relatively low temperature regeneration process. 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
After preparing the CO shift reaction catalyst and the particulate matter purification catalyst as follows, on the upstream side of the gas flow path of the exhaust gas pipe (diameter 30 mm) (site upstream when the gas is circulated) An exhaust gas purification apparatus of the present invention in which a CO shift reaction catalyst is disposed, a particulate matter purification catalyst is disposed downstream thereof, and the CO shift reaction catalyst and the particulate matter purification catalyst are connected in series. Manufactured.

<Method for Preparing CO Shift Reaction Catalyst>
First, to a mixed solution obtained by mixing 0.37 mol (139 g) of aluminum nitrate nonahydrate with 2000 ml of ion-exchanged water, 202 g of an aqueous cerium nitrate solution having a concentration of 28% by mass (0.33 mol in terms of CeO ₂ ). The mixture was further mixed and stirred for 5 minutes to obtain a mixed aqueous solution. Next, 177 g of ammonia water having a concentration of 25% by mass was added to the obtained mixed aqueous solution and stirred for 10 minutes to obtain an aqueous solution containing a precipitate. Thereafter, the aqueous solution containing the precipitate was heat-treated at a temperature of 120 ° C. for 2 hours under a pressure of 2 atm (aging step) to age the precipitate. Next, the aqueous solution containing the precipitate thus aged is heated at a heating rate of 100 ° C./hour, then calcined at 400 ° C. for 5 hours, and further calcined at 600 ° C. for 5 hours to obtain CeO ₂ —Al. _A composite oxide powder made of ₂ O ₃ was obtained. The composite oxide powder thus obtained was composed of about 75% by mass of CeO ₂ and about 25% by mass of Al ₂ O ₃ and had a specific surface area of 125 m ² / g. The composite oxide powder was subjected to EDS analysis (composition analysis) in a very small range with a beam diameter of 0.5 nm by a FE-STEM scanning transmission electron microscope (“HD-2000” manufactured by Hitachi, Ltd.). CeO ₂ and Al ₂ O ₃ were detected at a composition ratio within ± 20% of the charged composition at 90% or more of each analysis point, and were not observed as independent particles. From these results, it was found that CeO ₂ and Al ₂ O ₃ were dispersed on the nm scale in the composite oxide powder.

Next, 180 g of the composite oxide powder obtained as described above, 133 g of ceria sol binder (solid content: 15% by mass) and 70 g of ion-exchanged water are mixed and pulverized using a ball mill until the particle size becomes 3 μm. Thus, a slurry was obtained. Next, the obtained slurry was coated on a cordierite honeycomb monolith substrate having a diameter of 30 mm, a length of 15 mm, and a volume of 10.5 ml at a rate of 100 g per liter of the substrate volume, and then fired at 500 ° C. for 3 hours. A catalyst carrier-supporting substrate was obtained. Thereafter, the catalyst carrier-supporting substrate is impregnated with a Pt (NO ₂ ) ₂ (NH ₃ ) ₂ aqueous solution so that the amount of Pt supported is 2 g per liter of the substrate volume, and is fired at 300 ° C. for 3 hours. Thus, Pt was supported and a catalyst for CO shift reaction was obtained.

<Method for preparing catalyst for purification of particulate matter>
The content of Ce and the additive component to the total amount of additive component (La) (mol%) is prepared nitrate solution containing Ce, Ag and the additive component such that La10mol%, as follows, CeO ₂ A particulate matter purifying catalyst having a DPF substrate coated with -Ag-La aggregates was obtained. That is, first, a solution in which 50.46 g of Ce (NO ₃ ) ₃ .6H ₂ O, 5.59 g of La (NO ₃ ) ₃ and 29.62 g of AgNO ₃ were dissolved in 120 mL of water was prepared. did. Next, ammonia water was prepared by diluting 38.21 g of 25% aqueous ammonia into 100 g of water. Then, the solution prepared as described above is put into the place where the aqueous ammonia is being stirred (reverse precipitation), and the stirring is continued for 10 minutes, and then under the condition of 2 atm in the closed system in the presence of water. Then, the mixture was heated to 120 ° C. and subjected to an aggregation treatment for 2 hours to prepare an aggregate.

  Next, the agglomerates obtained as described above were applied to a DPF (made by cordierite, porosity: 65%, average pore diameter: 30 μm) having a test piece size (diameter: 30 mm, length: 50 mm, 35 ml) as follows: It was coated by the method to obtain a particulate matter purification catalyst. 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 is brought into contact with the pores of the DPF, sucked in that state, and then baked at 500 ° C. for 1 hour in the air. The aggregate loading amount (coating amount) is 75 g / L. Repeat until The merit of this method is that the precipitate itself sinters at the time of firing and acts as a binder, so that a coating composed only of components effective for soot oxidation can be sufficiently formed. Further, when the particle size distribution of the above slurry was measured, it was confirmed that about 0.1 μm aggregates were stably dispersed, so that coating on DPF was easy.

(Comparative Example 1)
A particulate matter purification catalyst is manufactured by adopting the same method as the method for preparing the particulate matter purification catalyst employed in Example 1, and the particulate matter purification catalyst is disposed in the gas flow path of the exhaust gas pipe. An exhaust gas purification device for comparison was obtained.

(Comparative Example 2)
A CO shift for comparison was performed in the same manner as in Example 1 except that a comparative CO shift reaction catalyst obtained by employing the following preparation method was used instead of the CO shift reaction catalyst. An exhaust gas purification apparatus for comparison was obtained in which the reaction catalyst was arranged on the upstream side and the particulate matter purification catalyst was arranged on the downstream side.

<Method for preparing catalyst for CO shift reaction for comparison>
First, 150 g of γ-alumina powder (trade name “TN-4” manufactured by JGC Universal Co., Ltd., specific surface area 150 m ² / g), 60 g concentration 40% by weight aluminum nitrate aqueous solution, 3.0 g boehmite and 50 g ion-exchanged water were mixed. The slurry was pulverized using a ball mill until the particle size became 3 μm. Next, the obtained slurry was coated on a cordierite honeycomb monolith substrate having a diameter of 30 mm, a length of 15 mm, and a volume of 10.5 ml at a rate of 120 g per liter of the substrate volume, and then fired at 500 ° C. for 3 hours. Thus, an alumina-supporting base material was obtained. Thereafter, the alumina-supported base material is impregnated with a Pt (NO ₂ ) ₂ (NH ₃ ) ₂ aqueous solution so that the Pt support amount is 2 g per liter of the base material volume, and is fired at 300 ° C. for 3 hours. Thus, a catalyst for CO shift reaction for comparison was obtained.

[Evaluation of characteristics of exhaust gas purification apparatus obtained in Example 1 and Comparative Examples 1 and 2]
<Sulfur regeneration test>
Using the exhaust gas purification devices obtained in Example 1 and Comparative Examples 1 and 2, first, each device was subjected to a treatment (heat treatment) that was maintained for 5 hours at a temperature of 750 ° C. while circulating air in the exhaust gas pipe. It was. Next, from the SO ₂ (32 ppm), O ₂ (10%), CO ₂ (10%), H ₂ O (3%) and N ₂ (remainder) into the exhaust gas pipe of each exhaust gas purifier after the heat treatment. The gas mixture (entered gas) was supplied at 350 ° C. (entered gas temperature) for 20 hours under a gas flow rate of 1.3 L / min (sulfur poisoning treatment). In addition, the total supply amount of the sulfur component supplied in such a sulfur poisoning process is 2.0 g / L.

Next, a mixed gas composed of O ₂ (10%), CO ₂ (10%), H ₂ O (10%) and N ₂ (remainder) is gas-filled into the exhaust gas pipe of the exhaust gas purification apparatus after sulfur poisoning treatment. After supplying at a flow rate of 30 L / min and raising the temperature until the catalyst bed temperature of the particulate matter purification catalyst reaches 550 ° C., the gas species to be supplied are CO (1.4%), O ₂ (0.4 %), CO ₂ (8%), H ₂ O (10%) and N ₂ (remainder), and the rich atmosphere mixed gas is maintained while maintaining the catalyst bed temperature at 550 ° C. A process of supplying for 10 minutes was performed (sulfur poisoning regeneration process). And the density | concentration of all the sulfur components contained in the outgas discharged | emitted from the exhaust gas pipe | tube of each exhaust gas purification apparatus was measured for 10 minutes from the supply start of rich atmosphere mixed gas. A graph showing the relationship between the supply time of such a rich atmosphere mixed gas and the concentration of the sulfur component in the outgas (shown as “S concentration” in the figure) is shown in FIG. Moreover, in the exhaust gas purifying apparatus obtained in Example 1 and Comparative Example 2, the average concentrations of H ₂ and CO contained in the outgas for 10 minutes from the start of supply of the rich atmosphere mixed gas were measured. FIG. 4 shows a graph of the average concentrations of H ₂ and CO contained in the output gas from the exhaust gas purification apparatus obtained in Example 1 and Comparative Example 2.

As is apparent from the results shown in FIG. 3, in the exhaust gas purification apparatus (Example 1) of the present invention, it is understood that a large amount of sulfur components can be desorbed by supplying the rich atmosphere mixed gas. On the other hand, in the exhaust gas purification apparatus for comparison (Comparative Examples 1 and 2), the sulfur component was hardly desorbed even when the rich atmosphere mixed gas was supplied. Further, as is apparent from the results shown in FIG. 4, in the exhaust gas purifying apparatus (Example 1) of the present invention, the H ₂ concentration in the outgas is sufficiently high, whereas the exhaust gas for comparison is used. In the purification device (Comparative Example 2), it was confirmed that the concentration of H ₂ was not sufficient. From these results, in the exhaust gas purification apparatus (Example 1) of the present invention, H ₂ can be efficiently generated by the upstream side CO shift reaction catalyst, and the sulfur component from the downstream particulate matter purification catalyst is sufficiently obtained. It is assumed that it can be removed.

<PM oxidation performance evaluation test>
Obtained in the exhaust gas purifying apparatus obtained in Example 1 and Comparative Examples 1 and 2 before the above-mentioned sulfur poisoning treatment in which only the above heat treatment was performed, and in Example 1 and Comparative Examples 1 and 2 after the above-described sulfur regeneration test. The following PM oxidation performance evaluation test was performed on each of the obtained exhaust gas purification apparatuses. That is, first, 0.10 g of carbon powder (trade name “Printex-U” manufactured by Degussa) as model PM was mixed with 50 ml of special grade ethanol, and sufficiently dispersed using an ultrasonic washer to obtain a dispersion. . Next, with the upstream side of each exhaust gas purifying apparatus facing upward, the process of collecting the dispersion liquid after pouring the dispersion liquid and pouring the passed dispersion liquid again from above is performed until the dispersion liquid becomes almost transparent. Repeatedly, after that, the carbon powder was allowed to adhere to the catalyst in the exhaust gas purification device (PM adhesion treatment). By the PM adhesion treatment, almost the entire amount of carbon powder in the dispersion was filtered to DPF, and the carbon adhesion amount in each exhaust gas purification device was 2.8 g / L.

Then, _{N 2} (incoming gas) 500 ° C. for each exhaust gas purification apparatus after PM deposition process (incoming gas temperature), 15 minutes after heating was supplied at a gas flow rate 30L / min of conditions, _{N 2} While supplying the gas, the inside of the exhaust pipe was naturally cooled to 200 ° C. Next, for each exhaust gas purifying device, a mixed gas (entering gas) composed of O ₂ (10%), H ₂ O (10%) and N ₂ (remainder) is heated to 20 ° C./min. While the temperature was increased from 200 ° C. to 740 ° C. at a rate, the gas was supplied under conditions of a gas flow rate of 30 L / min. Then, until completion supply starting supply of the mixed gas to determine the concentration of CO ₂ contained in the output gas discharged from the exhaust gas supply pipe of each exhaust gas purifying apparatus. Then, based on the CO ₂ concentration in the output gas and the temperature of the incoming gas, the temperature of the mixed gas (80%) required to oxidize 80% of the carbon adhering to each exhaust gas purification device. (PM oxidation temperature) was calculated and used as an index of PM oxidation activity (it can be said that the lower the 80% PM oxidation temperature, the higher the PM oxidation activity). FIG. 5 shows a graph of the 80% PM oxidation temperature of each exhaust gas purification device before the sulfur poisoning treatment and after the sulfur regeneration test.

  As is clear from the results shown in FIG. 5, the PM oxidation activity of the exhaust gas purifying apparatus of the present invention (Example 1) after the sulfur regeneration test is higher than that of the exhaust gas purifying apparatus for comparison (Comparative Examples 1 and 2). It was confirmed to be much higher. As shown in FIG. 3, in the exhaust gas purification apparatus (Example 1) of the present invention, such a result is obtained by sufficiently removing the sulfur component adhering to the particulate matter purification catalyst by the sulfur regeneration test and oxidizing activity. Can be sufficiently produced, but in the exhaust gas purification apparatus for comparison (Comparative Examples 1 and 2), the sulfur component adhering thereto cannot be sufficiently removed even in the sulfur regeneration test, and the oxidation activity This can be attributed to the inability to fully reproduce Moreover, from such a result, the exhaust gas purification apparatus (Example 1) of the present invention can efficiently oxidize particulate matter in a low temperature range, and is contained in the gas even after sulfur poisoning. It was found that the oxidation activity of PM can be sufficiently regenerated by performing sulfur poisoning regeneration treatment using CO.

  As described above, according to the present invention, the particulate matter in the exhaust gas discharged from the internal combustion engine can be efficiently oxidized in a low temperature range, and is contained in the exhaust gas even after sulfur poisoning. It is possible to provide an exhaust gas purification apparatus capable of sufficiently regenerating the oxidation activity by performing a regeneration process using carbon monoxide (CO).

  Therefore, the exhaust gas purifying apparatus of the present invention is particularly useful as an exhaust gas purifying apparatus for purifying exhaust gas from a diesel engine.

It is a flowchart which shows suitable one Embodiment of the control performed by a control means. It is a flowchart which shows other suitable embodiment of the control performed by a control means. It is a graph which shows the relationship between the supply time of rich atmosphere mixed gas with respect to each exhaust gas purification apparatus (Example 1 and Comparative Examples 1-2) after sulfur poisoning, and the density | concentration of the sulfur component in an outgas. . It is a graph of the average concentration of H ₂ and CO contained in the output gas from the exhaust gas purifying device obtained in Example 1 and Comparative Example 2. Graph of 80% PM oxidation temperature of each exhaust gas purification device (Example 1 and Comparative Examples 1-2) before sulfur poisoning treatment and each exhaust gas purification device (Example 1 and Comparative Examples 1-2) after the sulfur regeneration test It is.

Claims (7)

An exhaust gas purification apparatus that oxidizes and removes particulate matter contained in exhaust gas,
A catalyst carrier containing at least one selected from the group consisting of ceria, titania and zirconia, a CO shift reaction catalyst comprising a noble metal supported on the catalyst carrier, and a particulate matter purification catalyst containing silver Prepared, and
The CO shift reaction catalyst is disposed upstream of the gas flow path through which the exhaust gas flows, and the particulate matter purification catalyst is disposed downstream of the gas flow path;
An exhaust gas purification device characterized by the above.   The particulate matter purifying catalyst comprises 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 1.   The exhaust gas purifying apparatus according to claim 2, wherein the particulate matter purification catalyst includes 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 purification apparatus according to claim 3, wherein   The exhaust gas purifying apparatus according to claim 3 or 4, wherein the porosity of the base material is 30 to 70%.   The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein the catalyst carrier contains ceria.   The exhaust gas purifying device according to any one of claims 1 to 6, wherein the catalyst carrier contains a mixture in which ceria and alumina are dispersed on a nanometer scale.