JP5358362B2 - Particulate combustion catalyst and diesel particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particulate matter (PM) combustion catalyst for combustion of particulate matter contained in exhaust gas produced by a diesel engine which can burn PM at low temperatures and has excellent durability and a diesel particulate filter which contains the PM combustion catalyst and can remove deposited PM easily at low temperatures. <P>SOLUTION: The particulate matter combustion catalyst consists of particles of a compound oxide comprising an alkaline earth metal M and (Fe<SB>1-x</SB>Ti<SB>x</SB>) in a molar ratio of (Fe<SB>1-x</SB>Ti<SB>x</SB>)/ä(Fe<SB>1-x</SB>Ti<SB>x</SB>)+M} of 0.33-0.93 and a molar ratio x of Ti/(Fe+Ti) of 0-0.24. A diesel particulate filter applied with the particulate matter combustion catalyst is also provided. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a particulate matter combustion catalyst and a diesel particulate filter (Diesel Particulate Filter, DPF) for burning particulate matter (Particulate Matter, PM) contained in exhaust gas generated from a diesel engine.

Diesel engine exhausts that use diesel oil as fuel include unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ), as well as soot (particulate matter, particulate matter) , Also referred to as PM, etc.), soluble organic fraction (SOF), and the like. Among these, a DPF is disposed in the exhaust gas flow path in order to collect and remove soot (hereinafter referred to as PM). PM is collected by the DPF, but as PM accumulates in the DPF, the back pressure increases and causes a reduction in engine output. Therefore, the DPF must be regenerated by removing the collected PM by burning it intermittently or continuously by some method.

As a method of burning and regenerating PM collected in the DPF, for example, a method of forcibly raising the exhaust gas temperature to cause PM combustion, or NO contained in the exhaust gas is converted to NO ₂ by an oxidation catalyst, and NO ₂ For example, there is a method of burning PM with the oxidizing power. In the latter method, the current NO oxidation catalyst cannot efficiently generate NO ₂ , and the operating conditions of the engine are limited in order to include NO required for PM combustion in the exhaust gas. There is a problem that becomes complicated.

  On the other hand, as one of the former methods, a diesel oxidation catalyst (DOC) is disposed upstream of the DPF to oxidize HC components contained in the exhaust gas and raise the exhaust gas temperature. To do. That is, during automatic regeneration control of the DPF, the amount of fuel injected into the engine is increased to increase the amount of HC components in the exhaust gas, and this surplus HC is oxidized and burned by the DOC on the exhaust gas flow path, and the exhaust heat is generated by the combustion heat at that time. The temperature is raised to promote the combustion of PM collected in the DPF. Since this method does not depend on the NO content in the exhaust gas, there is a merit that the engine management becomes easy (no restrictions). On the other hand, since the fuel is consumed to raise the exhaust gas temperature, the fuel consumption is deteriorated or the heat load on the DPF is deteriorated. In particular, since cordierite DPF, which is cheaper than SiC DPF, is inferior in heat resistance, it becomes a serious problem.

  Therefore, it has been studied to apply a catalyst for PM combustion to the DPF. If a catalyst that can reduce the PM combustion start temperature (PM combustion catalyst) is applied to the DPF, the PM accumulated in the DPF can be burnt and removed and regenerated at a low temperature, reducing the load on the DOC (improving fuel efficiency), The heat load on the DPF can also be reduced.

  As the PM combustion catalyst, generally, alumina having a high specific surface area on which platinum (Pt) is supported is used. However, since the exhaust gas temperature of the diesel engine is low and the catalytic action for burning PM of Pt at this temperature level is low, the burden of the DOC that raises the exhaust gas temperature is large. Ideally, if there is a catalyst that burns PM at about the exhaust gas temperature of a diesel engine, PM can be burned without heating the exhaust gas, and the DPF can be regenerated continuously. Therefore, a PM combustion catalyst capable of burning PM at a low temperature has been demanded, and several catalysts have been developed. In addition, since Pt used as a PM combustion catalyst is expensive, a reduction in the amount of Pt used and an inexpensive catalyst other than Pt are under development.

  For example, it is disclosed that a ceria-based oxide is effective as a PM combustion catalyst, and further, when a platinum group metal is supported on the oxide, it is disclosed that PM can be combusted at a lower temperature (Patent Document 1 and 2). PM combustion catalysts supporting silver (Ag) as a metal other than the platinum group have also been proposed (see Patent Documents 3 to 6).

Further, it is disclosed that the composite oxide acts as a PM combustion catalyst (see Patent Documents 7 to 11). Also described are modes in which a noble metal is supported on a composite oxide (see Patent Document 7), or a constituent element of the composite oxide contains a noble metal (see Patent Documents 9 and 11). In Patent Document 11, composite oxide AM _x O _y (A: alkali metal or alkaline earth metal, M: Fe, Co or Ni, O represents oxygen, and 0 <x ≦ 4 and 0 <y ≦ 8. ) Is effective in removing both PM and nitrogen oxides in the exhaust gas of a diesel engine.

JP 2007-216150 A JP 2008-136951 A JP 2007-196135 A JP 2009-45584 A JP 2007-296518 A JP 2009-78224 A JP 2007-14873 A JP 09-267040 A JP 09-271665 A JP-A-5-184929 JP 2005-66559 A

  Regarding the PM combustion catalyst, in Patent Document 1, a ceria-based oxide has been developed as a PM combustion catalyst that does not use a noble metal. However, since cerium is a rare and relatively expensive rare earth metal element, it is a sufficiently inexpensive catalyst. However, there is a problem that the supply of the cerium raw material is unstable. Further, regarding the low temperature activity of the PM combustion catalyst, there is a problem that the ceria oxide alone is still insufficient. Therefore, Pt is also supported on the ceria-based oxide to form a PM combustion catalyst (Patent Document 2).

  On the other hand, Patent Documents 3 to 6 disclose that a catalyst using Ag, which is an inexpensive noble metal other than a platinum group metal, is excellent in low-temperature activity as a PM combustion catalyst. The present inventors have also confirmed that Ag is superior to a PM combustion catalyst. However, as can be seen from the fact that Ag has a lower melting point (961.9 ° C.) than other precious metals (eg, Pt has a melting point of 1772 ° C.), Ag migrates and aggregates. Easy to do. Therefore, there is a problem that it is difficult to maintain the catalytic activity of Ag for a long time and the durability is poor. Further, a catalyst using Ag has poor heat resistance, that is, when the temperature rises, there is a problem that Ag particles are enlarged due to melting or aggregation and the catalytic activity is lowered.

  Further, among oxides other than ceria-based oxides, particularly composite oxides, composite oxides that act as PM combustion catalysts have been developed, but there is a problem that low-temperature activity is insufficient. Of course, if the constituent metal ions of the composite oxide contain noble metal ions or rare earth metal ions, an inexpensive PM combustion catalyst cannot be obtained.

  Furthermore, although many PM combustion catalysts proposed in the above-mentioned prior art documents are excellent in low-temperature activity, the catalytic action is caused by the contact condition between PM and catalyst (for example, tight contact and loose contact). Different. That is, the PM combustion catalyst, unlike a normal exhaust gas purification catalyst, must promote the oxidation reaction between solid PM and oxygen gas, that is, the reaction between solid and gas. Therefore, effective catalytic action cannot be obtained unless the PM solid is in contact with the catalyst. Since an ordinary exhaust gas purification catalyst is a gas (gas) and the catalyst accelerates the oxidation or reduction reaction of the gas, it is only necessary to consider the diffusion of the gas (increasing the porosity and increasing the specific surface area). . Therefore, basically, an excellent exhaust gas purification catalyst can be obtained as long as the catalytic activity is improved. However, in the design of a PM combustion catalyst, it has become clear that even if active oxygen is generated by Ag or a composite oxide, sufficient catalytic action cannot be obtained unless PM is in contact with the catalyst.

  Moreover, in order to evaluate a PM combustion catalyst, PM and a catalyst are mixed. In many cases, in this evaluation method, since the mixing is performed in a mortar or in a ball mill for a long time (particularly, mixing in a mixer having a crushing action), the evaluation is performed in a tight contact (TC) state. However, when the same catalyst is evaluated in a loose contact (LC) state obtained by mixing without using a mixer such as a mortar or a ball mill, the temperature of PM combustion does not decrease (FIG. 1 (a)), PM May not burn completely (FIG. 1 (b)). For example, FIGS. 1A and 1B are schematic diagrams of PM in a loose contact state, but PMs that are in contact with the catalyst surface as shown in FIG. It can be burned at a low temperature by being catalyzed (combustion [3]), but PM not in contact with the catalyst is not catalyzed (combustion [4]). Is required. In addition, as shown in FIG. 1B, PM in the vicinity of the catalyst in the loose contact state is burned under the catalytic action (PM [5]), but PM not in contact with the catalyst remains without being burned ( PM [6]).

  The state of PM actually deposited on the DPF is close to the loose contact. Therefore, in view of practicality, a PM combustion catalyst that exhibits sufficient catalytic action even in a loose contact state is desired.

  From this point of view, a perovskite complex oxide obtained by using a metal or metal oxide as a nucleus has been proposed as a PM combustion catalyst that is high even in loose contact (see Japanese Patent Application Laid-Open No. 2006-110519). The metal or metal oxide cleaves the C—C bond of PM, and the oxygen released by the perovskite complex oxide binds to the cleaved carbon to cause an oxidation reaction. It is not shown how the PM in loose contact is efficiently burned. Further, the inventors have confirmed that even the catalyst of Patent Document 12 cannot obtain sufficient low-temperature PM combustion in an environment having a lower oxygen concentration than air (oxygen concentration 21%).

  Further, some of the present inventors have found that an oxide containing two or more kinds of crystal phases and containing an alkaline earth metal M and Fe or Co is effective as a carrier for an exhaust gas purification catalyst. (See JP2009-142789). However, the exhaust gas purification is based on an oxidation reaction or a reduction reaction between gases (gases) such as a three-way catalyst. PM combustion involving a solid reaction (PM oxidation reaction) is a completely different reaction from the reaction between gases. For this reason, it has not been predicted at all what kind of composition the oxide has on PM combustion.

  The present invention has been made in view of the above problems, and an object thereof is to provide a PM combustion catalyst that can combust PM contained in exhaust gas generated from a diesel engine at a low temperature and has excellent durability. That is. Another object of the present invention is to provide a diesel particulate filter including a PM combustion catalyst that can easily remove the deposited PM at a low temperature.

  In the development of conventional PM combustion catalysts, for example, (i) an action of oxidizing and burning PM with active oxygen generated by Ag or a specific composite oxide, and (ii) an action of cutting a C—C bond with alkali metal ions Attention has been focused on catalytic action utilizing the above. On the other hand, since the PM combustion catalyst promotes the reaction between the solid (PM) and the gas (oxygen), the PM adheres in addition to the conventional catalytic action. It was considered that an easy-to-use catalyst would exhibit better catalytic action even in realistic situations such as loose contact.

Based on this idea, the inventors examined in detail an oxide having a large adhesion work with PM (carbon) and having PM combustion catalytic action. As a result, it has been found that the oxide containing Fe has a large adhesion work with PM, and has an excellent PM combustion catalytic action by using a complex oxide containing an alkaline earth metal. It was also found that the composite oxide has an excellent PM combustion catalytic action even when a part of Fe is substituted with Ti, and heat resistance is further improved. That is, the composite oxide containing the alkaline earth metal M and (Fe _1-x Ti _x ) and containing a specific ratio of (Fe _1-x Ti _x ) is positively adhered to the PM. The present inventors have found that the combustion temperature can be lowered and completed the present invention.

（ここで、ｘは０．０３≦ｘ≦０．２４であり、δは電荷中性条件を満たすように決まる値である。）
［５］前記複合酸化物粒子が複数の結晶相を含むことを特徴とする上記［１］〜［４］のいずれかに記載の粒子状物質燃焼触媒。
［６］前記アルカリ土類金属Ｍが、Ｓｒ若しくはＣａ、又はＳｒとＣａの両方であることを特徴とする上記［１］〜［５］のいずれかに記載の粒子状物質燃焼触媒。
［７］上記［１］〜［６］のいずれかに記載の粒子状物質燃焼触媒を含有することを特徴とするディーゼル・パーティキュレート・フィルター。 That is, the present invention has the following gist.
[1] Composite oxide particles containing an alkaline earth metal M and (Fe1-xTix), and a (Fe1-xTix) / {(Fe1-xTix) + M} molar ratio is 0.33 or more and 0.93 The particulate material combustion catalyst, wherein x is a Ti / (Fe + Ti) molar ratio and is 0.03 ≦ x ≦ 0.24.
[2] The particulate matter combustion catalyst according to (1), further comprising Ag supported on the composite oxide particles.
[3] The particulate matter combustion catalyst according to (1) or (2), further comprising Pd supported on the composite oxide particles.
[4] The particulate oxide according to any one of [1] to [3], wherein the composite oxide particles have a crystal phase represented by any one of formulas (I) to (V). Material combustion catalyst.

(Here, x is 0.03 ≦ x ≦ 0.24, and δ is a value determined so as to satisfy the charge neutrality condition.)
[5] The particulate matter combustion catalyst according to any one of [1] to [4], wherein the composite oxide particles include a plurality of crystal phases.
[6] The particulate matter combustion catalyst according to any one of [1] to [5], wherein the alkaline earth metal M is Sr or Ca, or both Sr and Ca.
[7 ] A diesel particulate filter comprising the particulate combustion catalyst according to any one of [1] to [ 6 ].

  According to the present invention, since PM contained in exhaust gas generated from a diesel engine can be burned at a low temperature, the burden of raising the exhaust gas temperature in order to burn PM is reduced. That is, since the PM combustion start temperature can be lowered, PM accumulated in the DPF can be burned and removed at a low temperature to regenerate the DPF. In addition, the load on the DOC can be reduced, and fuel consumption can be improved. Since the DPF regeneration temperature can be lowered, the heat load on the DPF can also be reduced. Moreover, since the PM combustion catalyst of the present invention does not contain rare earth metals and is excellent in durability, an inexpensive catalyst system can be designed.

It is a figure explaining PM combustion in a loose contact state in a PM combustion catalyst with low wettability to PM. (A) PM that contacts the catalyst undergoes catalytic action and burns at a low temperature. However, PM that does not contact the catalyst does not receive catalytic action, and therefore PM combustion requires a high temperature. (B) PM in the vicinity of the catalyst burns under catalytic action, but PM that is not in contact with the catalyst may not burn. It is a figure explaining PM combustion in a loose contact state in PM combustion catalyst (PM combustion catalyst of the present invention) with high wettability to PM. (A) PM in a loose contact state is positively attached to the catalyst surface and is in the same state as a tight contact, and therefore can be burned by receiving a catalytic action. (B) When PM [5] in contact with the catalyst surface burns, PM [6] not in contact with the catalyst surface sequentially moves to the catalyst surface (PM [8]) and burns under catalytic action. Therefore, PM burns efficiently at low temperature. It is a schematic diagram which shows PM combustion catalytic action at the time of carrying | supporting a noble metal on the complex oxide particle which concerns on this invention. (A) It is a general view which shows the complex oxide particle | grains which carry | supported the noble metal. (B) is a diagram illustrating a site to absorb dissociated oxygen (O _2). (C) It is a figure explaining the site which accelerates | stimulates PM combustion by active oxygen. When Ag is supported on a conventional carrier such as alumina, it is a schematic diagram showing a process in which the supported Ag easily moves, aggregates and coarsens. It is a schematic diagram which shows PM tracking effect | action of Ag carry | supported by the complex oxide particle which concerns on this invention. (A) When PM in contact with Ag supported on the composite oxide particles burns, the temperature of the portion rises and Ag easily moves. (B) The PM in contact with the supported Ag or the PM in the vicinity of Ag burns, and at the same time, Ag moves on the surface of the composite oxide particles toward the unburned PM. (C) Ag that has moved to unburned PM promotes PM combustion (exhibits catalytic action) together with the composite oxide particles. As a result, the PM deposited on the composite oxide particles burns sequentially. It is a schematic diagram of PM combustion (PM oxidation) reaction that occurs only in composite oxide particles including a plurality of crystal phases (phase I, phase II, phase III) according to the present invention. It is a PM combustion (PM oxidation) reaction schematic diagram which arises when the noble metal is carry | supported by the composite oxide particle containing several crystal phases (Phase I, Phase II, Phase III) based on this invention. (A) It is a figure showing the whole complex oxide particle | grains with which the noble metal was carry | supported. (B) It is a schematic diagram explaining the process in which the oxygen ion from an oxygen molecule is taken in the crystal lattice of complex oxide on the carry | supported noble metal. (C) It is a schematic diagram explaining the process which accelerates | stimulates PM combustion reaction by the oxygen ion in the grating | lattice of complex oxide on the carry | supported noble metal. It is a schematic diagram explaining PM combustion reaction in case a noble metal is carry | supported by the composite oxide particle containing two types of crystal phases (phase i, phase ii). It is a schematic diagram which shows the cross section of the porous honeycomb side wall of DPF. (A) When DPF is coated with a fine particle catalyst as in the prior art, the entire hole is blocked by the catalyst from the surface of the hole to the inside, and a large pressure loss occurs. (B) When the DPF is coated with a catalyst having a specific particle size with respect to the pores of the DPF, only the surface of the pores is blocked, and the gas permeability of the catalyst layer is not limited even when the pores are blocked. Since it is high, almost no pressure loss occurs. It is a graph which shows the combustion behavior of simulation PM (carbon black). (A) CO ₂ Concentration - temperature curve; (b) CO Concentration - temperature curve.

The PM combustion catalyst of the present invention is a composite oxide particle containing an alkaline earth metal M and Fe. A part of Fe may be substituted with Ti, and may contain (Fe _1-x Ti _x ).

The ratio of the alkaline earth metal M, Fe, and Ti in the composite oxide particles is such that the molar ratio “(Fe _1−x Ti _x ) / {(Fe _1−x Ti _x ) + M}” is 0.33 or more. By making it 0.93 or less, even in a loose contact state with PM, composite oxide particles exhibiting superior PM combustion catalytic activity in a lower oxygen concentration environment than air (21% oxygen concentration) Is obtained. Even if this is in a loose contact state (for example, a state where PM and catalyst are put in a sample bottle and shaken and mixed), as shown in FIG. 2A, the PM combustion catalyst [7] of the present invention [7] This is because PM [2] tends to adhere positively to the surface. On the other hand, the tight contact state (for example, the state mixed in a mortar or ball mill) usually refers to the state shown in FIG.

The reason why the PM is positively attached is presumed to be because the work of adhesion W _PM-CAT of the PM on the surface of the PM combustion catalyst of the present invention is large (high wettability). Unlike the state shown in FIG. 1A, since PM is in contact with the catalyst surface, it can be catalyzed in the PM combustion reaction. That is, PM combustion occurs efficiently at a low temperature. Further, even if the PM is not in contact with the catalyst surface, as shown in FIG. 2B, when PM [5] in contact with the surface of the catalyst [7] burns, the PM not in contact with the catalyst surface [6] sequentially moves to the catalyst surface, and the moved PM [8] undergoes catalytic action and burns, so that PM burns efficiently at a low temperature.

The reason why PM actively adheres to the surface of the composite oxide of the present invention, that is, the reason why the adhesion work W _PM-CAT is large, is that the π electrons of the benzene ring (carbon six-membered ring) constituting PM are: It is inferred that this is caused by coordination with Fe ions to form a stable bond. Furthermore, by using a composite oxide of Fe and alkaline earth metal M, oxygen ion conductivity is imparted, and active oxygen is formed to promote PM combustion (catalytic action is exhibited).

Thus, the PM combustion catalyst of the present invention exhibits an excellent PM combustion catalytic action due to a synergistic effect of the ability to positively adhere PM and the ability to promote combustion of PM. Therefore, in order to exhibit an excellent PM combustion catalytic action, it is preferable to use composite oxide particles having a specific composition range. Specifically, as described above, the molar ratio of (Fe _1-x Ti _x ) / {(Fe _1-x Ti _x ) + M} is set to a range of 0.33 or more and 0.93 or less, and more preferably 0. The range is from 40 to 0.80.

When the (Fe _1-x Ti _x ) / {(Fe _1-x Ti _x ) + M} molar ratio is less than 0.33, PM combustion is promoted, but PM hardly adheres to the catalyst surface (adhesion work is As a PM combustion catalyst, the combustion temperature does not become low, or PM cannot be burned efficiently. On the other hand, when the molar ratio of (Fe _1-x Ti _x ) / {(Fe _1-x Ti _x ) + M} exceeds 0.93, PM tends to adhere, but combustion of the adhered PM is not promoted (combustion temperature). Does not drop).

  Further, in the composite oxide serving as the PM combustion catalyst of the present invention, part of Fe may be replaced with Ti. When substituted with Ti, the heat resistance is improved. That is, it is stable even at temperatures exceeding 900 ° C., and the catalytic activity as a PM combustion catalyst can be maintained. For example, when the DPF containing the PM combustion catalyst of the present invention is exposed to a high temperature for a long time, if the alkaline earth metal ion of the composite oxide constituting the catalyst is a DPF made of silicon carbide (SiC), its components In the case of DPF made of cordierite, it may gradually react with aluminum (Al) which is a component thereof. However, when Ti is contained in the composite oxide, these reactions are suppressed.

  The reason for such improvement in heat resistance is considered as follows. The composite oxide according to the present invention can be considered as a compound formed by an acid-base combination of an oxide that is an acidic oxide and an alkaline earth metal oxide that is a basic oxide. Based on the concept of an acid-base combination, when an oxide that is more acidic than iron oxide is brought into contact with the composite oxide, the alkaline earth metal ion is more acidic than iron oxide. The reaction may proceed particularly under high temperature conditions. Silica and alumina constituting the DPF are more acidic oxides than iron oxide. Therefore, as described above, when the DPF containing the PM combustion catalyst of the present invention is exposed to conditions such as high temperature, there is a possibility that the composite oxide and the constituent components of the DPF react. On the other hand, titanium oxide is an oxide having higher acidity than iron oxide. Therefore, if a compound of an alkaline earth metal ion and an iron oxide-titanium oxide solid solution is used, the reaction of the alkaline earth metal ion with another oxide is suppressed. That is, if a part of Fe of the composite oxide according to the present invention is substituted with Ti, alkaline earth metal ions are difficult to react with other oxides.

The radius of iron ions (Fe ³⁺ ) is 65 pm (6-coordinate), and the radius of iron ions (Fe ²⁺ ) is 78 pm (6-coordinate). On the other hand, since the radius of titanium ions (Ti ⁴⁺ ) is 61 pm (6-coordinate) and is smaller than iron ions, Fe in the composite oxide can be replaced with Ti. Furthermore, from the viewpoint of the ionic radius, when iron ions are replaced with titanium ions having a small ionic radius, the Madelung energy of the composite oxide crystal is lowered and stabilized. Therefore, it becomes difficult for alkaline earth metals to escape. Therefore, it can be considered that it becomes difficult to react with other coexisting oxides. In particular, when the alkaline earth metal has a large ionic radius (Ca or more), the Madelung energy increases, so that the stabilization effect by Ti substitution is considered to be large.

As described above, the composite oxide according to the present invention has improved heat resistance when part of Fe is replaced with Ti. On the other hand, if the ratio of Ti to be substituted is too large, catalytic action as a PM combustion catalyst cannot be obtained. Accordingly, when the Ti / (Fe + Ti) molar ratio, that is, x of (Fe1-xTix) is 0.03 ≦ x ≦ 0.24, excellent PM combustion catalytic activity is obtained.

In addition, when Ti is contained in the composite oxide according to the present invention, the reactivity of alkaline earth metal ions is suppressed as described above, so that it is difficult to form a compound with sulfur (S). However, it becomes a more stable PM combustion catalyst. Diesel engine fuel (light oil) has been desulfurized and low-sulfur fuel has been used. However, fuel containing sulfur is still used depending on the region and application. Therefore, it is preferable that the PM combustion catalyst is stable with respect to sulfur. In the composite oxide according to the present invention, if it is x is 0.03 ≦ x ≦ 0.24 range of (Fe1-xTix), stability and that Do to sulfur. When x is less than 0.03, it may form a compound with sulfur (sulfur oxide or the like) contained in the exhaust gas, and when it exceeds 0.24, it is sufficient as a PM combustion catalyst as described above. No catalytic action can be obtained.

  The PM combustion catalyst of the present invention may further have a noble metal supported on the composite oxide particles according to the present invention. Although it does not specifically limit as a noble metal to carry | support, For example, Pt, Pd, Rh, Ir, Ag, Au etc. are mentioned.

As shown in FIG. 3, in the composite oxide particle [10] in which a noble metal (for example, Ag) [9] is supported, the supported noble metal portion serves as an oxygen (O ₂ ) intake port, It becomes a catalyst combustion part, and combustion of PM [11] is made efficient. As a result, complete combustibility of PM is promoted. That is, CO generation due to PM combustion is reduced.

  The precious metal loading rate (percentage of the precious metal mass relative to the total mass of the precious metal and the composite oxide) is not particularly limited because it is designed according to the purpose as described above, but is in the range of 0.1% by mass to 18% by mass. Is preferable, the range of 0.1% by mass to 15% by mass is more preferable, and the range of 0.3% by mass to 11.0% by mass is still more preferable.

  In the PM combustion catalyst, among the noble metals to be supported, Ag is inexpensive and excellent in low-temperature activity. However, as described above, Ag is more likely to migrate and aggregate than other noble metals. Therefore, in general, it is difficult to maintain the catalytic activity for a long period of time, or when the temperature rises, Ag particles are enlarged due to melting or aggregation, and the catalytic activity is reduced. That is, as shown in FIG. 4, even if Ag [13] is finely supported on a conventional oxide support [12] such as alumina or between the support particles, the particles are easily moved and aggregated on the support surface [ 14], and coarser Ag particles [15]. Further, the melting point of Ag (961.9 ° C.) is low, and the exhaust gas temperature may rise to the melting point or higher, or the temperature may locally rise to the melting point or higher due to PM combustion. Therefore, Ag may melt and become coarse easily. Therefore, the composite oxide particles supporting Ag have been poor in durability and heat resistance.

However, it has been found that when Ag is supported on the composite oxide according to the present invention, the PM combustion catalyst is excellent in durability and heat resistance and can further lower the PM combustion temperature. To regenerate the DPF, PM is burned (oxidized with oxygen) and removed as a gas such as carbon monoxide CO or carbon dioxide CO ₂ . The PM combustion catalyst including the composite oxide particles according to the present invention supporting Ag is likely to cause complete combustion of PM and hardly generate carbon monoxide.

  The inventors have conducted various investigations based on the idea that it is effective to use an oxide having high wettability with Ag in order for Ag supported on the carrier to exist stably. As a result, it became clear that copper oxide, cobalt oxide, and iron oxide have high wettability with respect to Ag. Based on this knowledge, Ag was supported on the composite oxide particles according to the present invention to obtain an excellent PM combustion catalyst.

  Further, when the composite oxide particles carrying Ag are used as a PM combustion catalyst, the reason why the low-temperature activity, complete combustibility, durability / heat resistance and the like are improved is investigated, and the following knowledge is obtained. In the case of a carrier that is difficult to wet with Ag such as alumina, the supported Ag aggregates and becomes coarse as described above. Since the wettability is low around the coarsened Ag, movement is less likely to occur. However, on the surface of a carrier having high wettability with Ag, Ag can freely move on the surface. Ag is easier to move than other precious metals. That is, Ag selectively moves only on the surface of the composite oxide according to the present invention, and the moving range is limited to the surface of the composite oxide particles having high wettability. Thus, it can be considered that the composite oxide particles have an action of confining Ag on the particle surface (Ag confinement action).

  Further, PM combustion occurs due to catalytic action at a portion where Ag and PM are in contact with each other on the surface of the composite oxide particle, and the temperature rises. As the temperature rises, Ag becomes easy to move (in some cases, it melts or moves in a semi-molten state), and moves to unburned PM. Thus, Ag [19] supported on the surface of the composite oxide particle [16] may be considered to have an action of tracking and burning PM [17] (PM tracking action [20]). Yes (Figure 5). The “Ag confinement effect” improves the durability and heat resistance of the PM combustion catalyst, and the “PM tracking effect” improves the low temperature activity and complete combustibility of the PM combustion catalyst.

  In order to obtain the above effect as a PM combustion catalyst by the composite oxide particles supporting Ag, the support ratio of Ag (100 × Ag mass / (Ag mass + composite oxide mass)) is 0.15% by mass to 11%. It is preferable to set it as the range of 0.5 mass%, and it is more preferable to set it as the range of 0.25 mass%-6.5 mass%. If it is less than 0.15% by mass, the above synergistic effect may not be obtained sufficiently. On the other hand, even if the content exceeds 11.5% by mass, the obtained effect may be constant and no further improvement may be observed.

Further, even if Pd is supported on the composite oxide particles according to the present invention, a more excellent PM combustion catalyst is obtained. That is, PM combustion occurs at a lower temperature, and PM is easily burned completely. Pd has a higher melting point (1554 ° C.) than Ag and is unlikely to migrate like Ag. In other words, the “PM tracking action” is hardly present. On the other hand, the present composite oxide particles supporting Pd have a PM combustion temperature lower than that of alumina supporting Pt, and are excellent in durability and heat resistance. The mechanism for promoting PM combustion is thought to be as shown in FIG. 3, but Pd on the surface of the composite oxide particles has a high effect of reducing the activation energy related to the dissociation of oxygen (O ₂ ). Infer.

  In order to obtain the effect of loading Pd, the loading ratio of Pd is preferably in the range of 0.1% by mass to 11.0% by mass, and in the range of 0.1% by mass to 7.0% by mass. It is more preferable. If it is less than 0.1% by mass, the effect of Pd may not be sufficiently obtained. On the other hand, even if the content is higher than 11.0% by mass, the obtained effect may be constant and no further improvement may be observed.

  The composite oxide particles according to the present invention supporting both Pd and Ag can further lower the PM combustion temperature. This is because both noble metals share roles of oxygen molecule dissociation and PM combustion promotion. For example, the supported Pd part promotes the dissociation of oxygen and acts as an oxygen ion absorption port into the composite oxide, and oxygen ions (active oxygen) are supplied to the supported Ag part, and the oxygen ions By this, PM combustion is promoted. It is considered that PM combustion is promoted efficiently (synergistically) by such role sharing. When both Pd and Ag are supported, the ratio of Pd support / Ag support is preferably 0.01 to 2.0, and more preferably 0.02 to 1.0.

Alkaline earth present invention and the metal M, the composite oxide particles containing the _{(Fe 1-x} Ti x), for example, the general formula _{M s (Fe 1-X Ti} x) expressed as m _{O n.} Specific examples of the general formula _{M (Fe 1-x Ti x} ) O n, M (Fe 1-x Ti x) 2 O n, M 7 (Fe 1-x Ti x) 10 O n, M 2 _{(Fe 1-X Ti x)} O n, M 3 (Fe 1-x Ti x) 2 O n, M 5 (Fe 1-x Ti x) 14 O n, M (Fe 1-X Ti x) 4 O _{n, M 2 (Fe 1-} x Ti x) 14 O n, M 3 (Fe 1-x Ti x) 32 O n, M 4 (Fe 1-x Ti x) 9 O n, M 4 (Fe 1- _{x Ti x) 6 O n,} M (Fe 1-x Ti x) 3 O n, M 3 (Fe 1-x Ti x) 15 O n, M 3 (Fe 1-x Ti x) 4 O n, and _{M (Fe 1-x Ti x} ) expressed as ₁₂ O _n. Particularly preferred are composite oxide particles having a crystal phase represented by general formulas (I) to (V).

（ここで、ｘは０．０３≦ｘ≦０．２４であり、δは電荷中性条件を満たすように決まる値である。）

(Here, x is 0.03 ≦ x ≦ 0.24, and δ is a value determined so as to satisfy the charge neutrality condition.)

  The composite oxide particles having these crystal phases have a larger PM combustion catalytic action, and if a noble metal (particularly Ag or Pd) is supported to form a PM combustion catalyst, a more excellent catalytic effect can be obtained.

  The crystal phase of these composite oxides can be analyzed by the oxide crystal analysis method. For example, the crystal phase can be determined and quantified using X-ray diffraction, electron beam diffraction, neutron diffraction, or the like.

The composite oxide according to the present invention is a mixed conductor of oxygen ions and electrons. As shown in FIG. 3, oxygen ions (O ²⁻ ) in the crystal lattice of the complex oxide move easily (electrons move in the opposite direction as compensation, but in FIG. 3, the description of electron transfer is omitted. The oxygen ions are involved in PM combustion (PM oxidation reaction). Therefore, the composite oxide according to the present invention is considered to have high catalytic activity as a PM combustion catalyst. It is known that oxygen ions have a higher activity (active oxygen) than the oxygen molecule O ₂ and are effective in oxidation reactions (see, for example, JP-A-6-57470).

Conventionally, in order to contribute to the oxidation reaction using oxygen ions O ²⁻ as active oxygen, a method of applying a voltage to the oxygen ion conductor, or an oxygen supply source (high oxygen partial pressure) and a reaction chamber are separated. A method of moving and supplying oxygen ions with a concentration gradient (see JP 2009-142789 A) is known. In these methods, if there is no voltage application or oxygen concentration gradient, oxygen ions are not generated and the oxidation reaction is not promoted even if there is an oxide in which oxygen ions easily move.

  However, the composite oxide particles according to the present invention include a plurality of crystal phases (at least two crystal phases), and phases having different chemical potentials are in contact with each other. In this way, when there are parts having different chemical potentials in one particle, oxygen ions can move from the higher chemical potential to the lower one (the difference in chemical potential becomes the driving force). . Accordingly, a reaction cycle is formed in which the deposited PM is oxidized with oxygen ions while oxygen molecules are taken in as oxygen ions without intentionally creating a voltage application or oxygen concentration gradient, and PM combustion is further promoted. As described above, the composite oxide particle according to the present invention having a plurality of crystal phases has an oxygen ion intake port (phase II [25] in FIG. 6) from oxygen molecules and a site (FIG. 6) that releases oxygen ions. 6 has a phase I [24]).

  In order to incorporate oxygen ions from oxygen molecules into the crystal lattice of the complex oxide, it is necessary to dissociate the oxygen molecules into oxygen ions as represented by the following formula (1). When noble metal [27] is supported on the composite oxide particles in which a plurality of crystal phases (phase I [24], phase II [25], phase III [26]) are present (FIG. 7B) The noble metal promotes the dissociation of oxygen molecules as shown in the following formula (2).

  Furthermore, as another role of the supported noble metal, PM [23] is adsorbed and activated (especially effective for PM whose surface is covered with HC such as SOF), and a complex oxide lattice. The oxidation reaction (combustion of PM [23]) with oxygen ions therein is promoted (FIG. 7 (c)).

The inclusion of a plurality of crystal phases in the composite oxide particles means that there are a plurality of phases having different chemical potentials from the technical idea as described above. For example, it means that a plurality of compounds or phases having different types and compositions of cations constituting the composite oxide exist in one particle. The different compound or phase may be an oxide crystal having a different composition ratio between the alkaline earth metal M and (Fe _1-x Ti _x ) as illustrated above. Moreover, even if it is the same compound, it can be said that it is a different phase also when crystal structures differ.

  In the present invention, including a plurality of (two or more) crystal phases includes, for example, two types of crystal phases, a first crystal phase and a second crystal phase, and the content of the second crystal phase. Is 0.5 mol% or more of the entire crystal phase. When the content of the second crystal phase is less than 0.5 mol%, the above-described effect of forming a plurality of crystal phases may not be obtained. More preferably, the composite oxide particle including a plurality of crystal phases includes one crystal phase and one or more other crystal phases, and the content of the other one or more crystal phases is such that the entire crystal phase 3 mol% or more, 5 mol% or more, or 9 mol% or more, and further 12 mol% or more. It may be 20 mol% or more.

  Based on the above mechanism, the above effect can be obtained if a plurality of crystal phases exist in one particle. Accordingly, the number of crystal phases present in one particle may be any number as long as it is plural. However, producing particles containing 6 or more crystal phases in one particle may be difficult to obtain efficiently due to complicated manufacturing conditions.

  Moreover, the size of the plurality of crystal phases present in one particle is less than the particle size and may be 2 to 5 nm. However, it is shown schematically schematically in FIG.

Examples of the alkaline earth metal M include Be, Mg, Ca, Sr, Ba, and Ra. The alkaline earth metal can be used alone or in combination of two or more. Mg, Ca, Sr, and Ba are preferable because of the ease of forming a composite oxide with (Fe _1-x Ti _x ).

  When Sr is contained in the alkaline earth metal M, excellent PM combustion catalytic activity is exhibited even in a region where the oxygen partial pressure is low (for example, less than 10%) in the oxygen partial pressure range in the exhaust gas of the diesel engine. Moreover, when Ca is contained in the alkaline earth metal M, a PM combustion catalyst that is superior in durability (heat resistance) can be obtained. In particular, when the PM combustion catalyst of the present invention is coated on a honeycomb substrate using activated alumina as an adhesive, the above-described effect is remarkably exhibited. The molar ratio Ca / M of Ca to the total amount of the alkaline earth metal M is preferably 0.1 to 1.0, and more preferably 0.2 to 0.95.

  The particle size of the composite oxide particles according to the present invention is preferably in the range of 0.5 μm to 100.0 μm in terms of volume accumulation standard D50 (center particle size) measured by a laser diffraction / scattering particle size distribution measurement method. In a normal oxide carrier or oxide catalyst, a smaller particle size (for example, 100 nm or less) is preferable because the noble metal can be finely dispersed and the catalyst area is increased. On the other hand, since the catalyst of the present invention exhibits the PM combustion catalytic action as described above, sufficient PM combustion catalytic activity can be obtained without using such small particles.

  When the center particle size D50 is less than 0.5 μm, the PM combustion catalyst activity is sufficient, but it takes time to prepare the particle size by pulverization or the like in the production process, which may not be economical. On the other hand, when the center particle diameter D50 exceeds 100.0 μm, it may be difficult to disperse uniformly in the slurry to be coated on DPF or the like (sedimentation is likely to occur).

  The particle size (particle diameter Dp) of the composite oxide particles according to the present invention is preferably further in a relationship of Dh / 20 ≦ Dp ≦ Dh with respect to the average pore diameter Dh of the DPF porous honeycomb side wall. In most cases, the PM combustion catalyst is coated on a DPF. It is important for the DPF to collect PM and to reduce the pressure loss of the exhaust gas. Therefore, it is desirable that the pressure loss of the exhaust gas does not increase when the DPF is coated with the PM combustion catalyst. Therefore, it is preferable that the PM combustion catalyst of the present invention also has little influence on the pressure loss of the DPF when the DPF is coated (the pressure loss does not increase). That is, as shown in FIG. 8A, it is not desirable that the PM combustion catalyst is deposited in the hole of the DPF and closes the hole, like PM.

  From the above viewpoints, the present inventors believe that if the particle size of the particles serving as the PM combustion catalyst is a particle size that enters the pores of the DPF and closes the pores, a large pressure loss of the exhaust gas is caused. , Examined in detail. As a result, as described above, it was found that the pressure loss of the exhaust gas hardly occurs when the particle size is 1/20 or more of the average pore diameter Dh of the DPF (FIG. 8B). That is, as shown in FIG. 8A, the fine particles [31] close the entire pore including the inside of the DPF porous component [30] densely, making it difficult for gas to pass through and causing high pressure loss. Become. On the other hand, as shown in FIG. 8 (b), the somewhat large particles [32] remain in the vicinity of the hole entrance even if they block the hole of the DPF porous component [30], and there is a large gap through which gas can pass. Therefore, almost no pressure loss occurs. However, when Dp is larger than Dh, the pressure loss of DPF does not occur, but the catalytic action may not be sufficiently exhibited as a PM combustion catalyst.

  Here, the particle diameter Dp means a volume accumulation standard D50 (center particle diameter) measured by a laser diffraction / scattering particle size distribution measurement method. The average pore diameter Dh means an average pore diameter calculated from a pore distribution measured by a mercury intrusion method.

  Furthermore, from the viewpoint of suppressing the pressure loss of the DPF, in the particle size distribution obtained by the measurement method of the oxide particles, it is more preferable that the particle size is 0.1 μm or less and less than 10%.

The composite oxide particles containing the alkaline earth metal M and (Fe _1-x Ti _x ) according to the present invention are prepared by a liquid phase method such as a solid phase reaction method, a coprecipitation method or a sol-gel method, It can be produced by any method such as a phase precipitation method or a laser ablation method. For example, a production method using a solid phase reaction method and a coprecipitation method will be described below.

  In the production by the solid phase reaction method, as starting materials, oxides, hydroxides, carbonates, nitrates, organic acid salts, sulfates, etc. of alkaline earth metals M; Fe oxides, hydroxides, nitrates, sulfuric acid, etc. Salt; Ti oxide or the like can be used. The starting materials of M, Fe, and Ti are weighed so as to have a desired composition, mixed, and then calcined within a range of 800 to 1250 ° C. Mixing of the starting materials may be either wet or dry, and may be performed by any existing method such as mortar mixing, ball mill, planetary ball mill, drum mixer, pin mill and the like. The composite oxide obtained by calcination is used after being pulverized and classified in some cases.

  In the production by the coprecipitation method, as starting materials, nitrates, sulfates, organic acid salts, etc. of alkaline earth metals M; Fe and Ti nitrates, sulfates, hydroxides, chlorides, chelate complexes, organic acid salts, etc. Can be used. The starting materials of M, Fe and Ti are weighed so as to have a desired composition and dissolved in water. Add pH adjuster to make the pH of the solution neutral to basic, or add coprecipitate (oxalate, citrate, etc.) to dissolve dissolved M, Ti, Fe ions Co-precipitate. The coprecipitate is separated and washed by filtration or centrifugation, dried, and calcined in the range of 800 to 1250 ° C. The composite oxide obtained by calcination is used after being pulverized and classified as necessary.

In order to include multiple (two or more) crystal phases in the composite oxide particles according to the present invention, the raw material composition in each production method is different from the stoichiometric ratio of the composite oxide single phase. And it is sufficient. Thereby, a plurality of phases are formed by calcination. That is, composite oxide particles including a plurality of crystal phases can be produced by using a raw material composition in which a plurality of metals cannot form a single composite oxide. For example, the above-mentioned _M s (Fe, _Ti) when forming a crystal phase represented by m _{O n,} M and (Fe, Ti) composition ratio of the stoichiometric single crystal phase (single Compound) is not formed. The composition ratio (molar ratio) of M and (Fe, Ti) is at least 0.005, at least 0.03, at least 0.05, or even at least 0.09 from the composition ratio forming a single phase. It is preferable that the difference is 0.20.

  The method for supporting the noble metal on the composite oxide particles according to the present invention is not particularly limited, and for example, it can be supported by the following method. A water-soluble noble metal salt (eg, nitrate, nitrite, chloride, acetate, sulfate, ammine complex, etc.) or a noble metal colloid is added to water. Further, the composite oxide particles are added to the solution and dispersed by stirring, ultrasonic dispersion or the like. The PM combustion catalyst of the present invention carrying a noble metal can be produced by removing the water from the suspension and drying it, followed by heat treatment in the range of 400 to 900 ° C. A more preferable range of the heat treatment temperature is 450 to 700 ° C.

  The PM combustion catalyst of the present invention is wash-coated on DPF as a slurry, and can be a diesel particulate filter (Catalyzed DPF). The slurry is prepared by dispersing a PM combustion catalyst and a binder. Examples of the binder include aluminum nitrate, colloidal silica, ρ-alumina, and an organic binder. The DPF that can be used in the present invention is not particularly limited, and examples thereof include cordierite DPF and silicon carbide DPF. The average pore size of the porous wall surface serving as the wall-through of the DPF is preferably in the range of 5 μm to 80 μm.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
Composite oxide particles containing alkaline earth metal M and (Fe _1-x Ti _x ) were prepared and evaluated as PM combustion catalysts.

Carbonate (MCO ₃ ) was used as a raw material for alkaline earth metal M, and oxides (Fe ₂ O ₃ , TiO ₂ ) were used as raw materials for Fe and Ti. “Molar ratio of alkaline earth metal M” column in Table 1-1 to 1-17, “(Fe _1−x Ti _x ) / {(Fe _1−x Ti _x ) + M} molar ratio” column, “Ti / The raw materials are weighed in the relationship of the molar ratio of M, Fe, and Ti as shown in the column of (Fe + Ti) molar ratio (x value) and the phase of composite oxide particles and their ratio (%). And mixed with a ball mill.

  The mixed powder was calcined for 5 hours at 900 to 1100 ° C. shown in the “calcining temperature (° C.)” column of Tables 1-1 to 1-17, and the calcined powder was pulverized with a ball mill. The pulverized powder is further calcined at the same temperature for 5 hours, and the calcined powder is pulverized with a ball mill to produce composite oxide particles according to the present invention and a composite oxide particle as a comparative example, supporting a noble metal. The PM combustion catalyst was not used.

  The crystal phase of the powder composed of the obtained particles was identified by a powder X-ray diffraction method. When a plurality of phases were contained, the respective contents were calculated from the area of the X-ray diffraction peak. The calibration curve was created using the diffraction peak area of the single crystal phase. Further, the presence of a plurality of crystal phases in one particle was confirmed by observing the particle with a transmission electron microscope (TEM) and utilizing electron diffraction.

  The noble metals shown in Tables 1-1 to 1-17 were supported on the composite oxide prepared by the above procedure at the indicated loading rates, and PM combustion catalysts supporting the noble metals were manufactured. Specifically, Ag, Pd, Pt, and Ir were respectively supported using silver nitrate, palladium nitrate, platinum colloid, and chloroiridic acid. An aqueous solution containing silver nitrate, palladium nitrate, platinum colloid or iridium chloride and 100 g of the oxide carrier powder were put in a rotary evaporator, and defoamed first while rotating and stirring at room temperature and under reduced pressure. After returning to normal pressure and heating between 60-70 ° C., the pressure was reduced, followed by dehydration and drying. After cooling to room temperature, the pressure was returned to normal pressure, the solid was taken out, and dried at 180 ° C. for 2 hours. The dried solid (powder) was heat-treated in the atmosphere at 650 ° C. for 2 hours. Through the above operation, a PM combustion catalyst powder carrying a noble metal was produced.

The particle diameter Dp (D ₅₀ ) of the PM combustion catalyst in Tables 1-1 to 1-17 satisfies the relationship of Dh / 20 ≦ Dp ≦ Dh with respect to the average pore diameter Dh (20 μm) of the DPF porous honeycomb side wall. . The particle size was measured using a laser diffraction particle size distribution analyzer manufactured by Shimadzu Corporation.

The first to ninth phases in the column of “Phase of Composite Oxide Particles and Their Ratio (%)” in Tables 1-1 to 1-17 respectively indicate the following.
First phase: M ₅ (Fe _1-x Ti _x ) ₂ O _{8 ± δ}
Second phase: M ₂ (Fe _1-x Ti _x ) O _{3.5 ± δ}
Third phase: M ₃ (Fe _1-x Ti _x ) ₂ O _{7 ± δ}
Fourth phase: M (Fe _1-x Ti _x ) O _{2.5 ± δ}
Fifth phase: M ₄ (Fe _1-x Ti _x ) ₆ O _{13 ± δ}
Sixth phase: M (Fe _1-x Ti _x ) ₂ O _{4 ± δ}
Seventh phase: M ₂ (Fe _1-x Ti _x ) ₆ O _{11 ± δ}
Eighth phase: M (Fe _1-x Ti _x ) ₁₂ O _{19 ± δ}
Ninth phase: M (Fe _1-x Ti _x ) ₁₈ O _{28 ± δ}

The PM combustion catalysts shown in Table 1-1 to Table 1-17 were evaluated by the following methods, respectively. Carbon black CB (# 7350F) manufactured by Tokai Carbon Co., Ltd. was used as a PM simulation material. 30 mg of the sample in Table 1 and 1.6 mg of the CB (# 7350F) were placed in a sample bottle and shaken to mix to obtain a mixed sample in a loose contact state. 20 mg of the mixed sample was taken out, filled in a U-shaped tube, and heated while circulating a reaction gas. The reaction gas was a 10% O ₂ -He balance gas and allowed to flow at 100 ml / min. While raising the temperature of the U-shaped tube from room temperature to 750 ° C. at 10 ° C./min, CO ₂ and CO as outlet gases were analyzed with a gas chromatograph. As a reference (Comparative Example No. 1-344), a similar experiment was performed using a sample of only CB (# 7350F). FIG. 9 shows the result.

As shown in FIG. 9, the temperature at which the peak point of CO ₂ generation is measured, and how much is the temperature at the peak point of CO ₂ (699 ° C.) generated from the sample of only CB (# 7350F). Based on the decrease, the catalyst performance as a PM combustion catalyst was judged. Further, the degree of complete combustion was judged by comparing the CO concentration, which is the peak point of CO generation, with the CO concentration (1425 ppm) generated from the sample containing only CB (# 7350F). The results are shown in the “Unheated” column of Tables 2-1 to 2-10. In Tables 2-1 to 2-10, the CO concentration of ≦ 2 ppm means that it was 2 ppm or less, and was below the detection limit (0.5 ppm) of the gas chromatograph. Including cases.

  Furthermore, regarding heat resistance evaluation, the samples of Tables 1-1 to 1-17 were heat-treated at 980 ° C. for 48 hours, and then the same evaluation as above was performed. The results are shown in the “After heat treatment” column of Tables 2-1 to 2-8.

Example No. which falls within the scope of the present invention. 1- 9 ~1-11, No. 1-1 5 to 1-17, No. 1-5. 1- 25 ~1-3 0, No. 1-33 to 1-35, no . 1- 43 ~1- 48, No. 1-51 to 1-53, no . 1-5 7 to 1-59, no. 1-6 3 to 1-65, no. 1-6 9 to 1-71, no. 1-7 5 to 1-77, no. 1-79 to 1-8 4 , no . 1-87 to 1-89, no . 1-9 3 to 1-95, no. 1- 103 ~1-1 08, No. 1-111-1-113, No. 1-1 21 ~No. 1-1 26, No. 1-129 to 1-131, no . 1-13 5 -No. 1-137, no. 1-1 41 ~1-143, No. 1-14 7 to 1-149, No. 1-15 3 to 1-155, No. 1 1-157~1-1 70, No. 1-178-184, No.1. 1-187-1-189, no . 1-19 8 ~20 4, No. 1-207-209, no . 1-211~1-2 36, No. No. 1-246 to 1-248, No. 1-25 7 ~1-26 3, No. 1-266 to 1-268, no . 1-270-28 4 , No. 1-287-1-289, no . 1-291-29 < 3 >, No. 1- 301 ~3 07, No. 1-310-312, no . 1-314~1-3 25, No. 1-3 34 to 1-341 had a low PM combustion temperature and exhibited excellent PM combustion catalyst performance.

On the other hand, No. which is a comparative example. 1-1 to 1-4 have a (Fe _1−x Ti _x ) / {(Fe _1−x Ti _x ) + M} molar ratio of less than 0.33 and out of the scope of the present invention. Compared with the case of, PM combustion temperature hardly decreased and PM combustion catalytic ability was not seen. Moreover, No. which is a comparative example. 1-342～1-343 is, to be outside the range of _{(Fe 1-x Ti x)} / {(Fe 1-X Ti x) + M} molar ratio, the present invention beyond 0.93, PM Compared with the case of only the PM combustion temperature, the PM combustion temperature was hardly lowered, and the PM combustion catalytic ability was not seen.

  Furthermore, No. as a comparative example. 1-12, No. 1 1-18, No. 1 1-36, no. 1-54, no. 1-66, no. 1-72, no. 1-78, no. 1-90, no. 1-96, no. 1-114, no. 1-132. 1-138, no. 1-144, no. 1-150, no. 1-156, no. 1-190, no. 1-210, no. 1-249, no. 1-269, no. 1-290, no. 1-313 has too much Ti content, that is, the Ti / (Fe + Ti) molar ratio (x value) exceeds 0.24 and is outside the scope of the present invention. Thus, the PM combustion temperature was not so low, and sufficient PM combustion catalyst performance was not observed.

Among the above examples, Example N o supporting the noble metal. 1- 25 ~ 1-30, No. 1-33 to 1-35, no. 1- 43 ~1- 48, No. 1-51 to 1-53 , no. 1-5 7 to 1-59, no. 1-6 3 to 1-65, no. 1-6 9 to 1-71, no. 1-7 5 to 1-77, no. 1-79 to 1-84, no. 1- 103 ~1- 108, No. 1-111-1-113, No. 1-1 21 ~1-1 26, No. 1-129 to 1-131, no . 1-13 5 to 1-137, No. 1-1 41 ~1-143, No. 1-14 7 to 1-149, No. 1-15 3 to 1-155, No. 1 1-157~1-170, N o. 1-179 to 1-18 4 , no . 1-187-1-189, No. 1-199 to 1-20 4 , no . 1-207-1-209 , no. 1-211-1-229, no. 1-231-236, No. 1-2 46 ~1-248, N o. 1-258~1-26 3, No. 1-266 to 1-268, no . 1-270-28 4 , No. 1-287-1-289, no . 1-291~1-293, N o. 1-302~1-3 07, No. 1-310-1312, No.1. 1-314~1-325, N o. In 1-334 to 1-341, PM combustion occurred at a low temperature and almost no CO was generated, and PM could be completely burned to CO2.

Among noble metal, examples contains a Ag N o. 1- 25 ~1-3 0, No. 1-33 to 1-35, no . 1- 43 ~1- 48, No. 1-51 to 1-53, no . 1-6 9 to 1-71, no. 1-7 5 to 1-77, no. 1-79 to 1-84, no. 1- 103 ~1-1 08, No. 1-111-1-113, No. 1-1 21 ~1-1 26, No. 1-129 to 1-131, no . 1-14 7 to 1-149, No. 1-15 3 to 1-155, No. 1 1-157~1-170, N o. 1-179 to 1-18 4 , no . 1-187-1-189, No. 1-199 to 1-20 4 , no . 1-207-1-209, No. 1-211-1-216, no. 1-221-1-229, no. 1-231-236, No. 1-2 46 ~1-248, N o. 1-258~1-26 3, No. 1-266 to 1-268, no . 1-270-28 4 , No. 1-287-1-289, no . 1-291-1-293, no. 1-302~1-3 07, No. 1-310-312, No.1 . 1-314~1-325, N o. In 1-334 to 341, the PM combustion temperature became lower, and the Ag carrying rate became remarkable when the amount was 0.15% by mass or more. In addition, the PM combustion temperature was lower when Ag and Pd were supported.

  Among the examples, the content of Ti, that is, the Ti / (Fe + Ti) molar ratio (x value) is 0.03 or more. 1-10 to 1-11, no. 1-16 to 1-17, no. 1-25 to 1-30, No. 1-34 to 1-35, no. 1-43 to 1-48, no. 1-52 to 1-53, no. 1-58 to 1-59, no. 1-64 to 1-65, no. 1-70-1-71, no. 1-76 to 1-77, no. 1-88 to 1-89, no. 1-94 to 1-95, no. 1-103 to 1-108, No.1. 1-112 to 1-113, no. 1-12-11-126, No. 1-130-1 to 131, No. 1-136 to 1-137, no. 1-142 to 1-143, No. 1-148-1-149, No. 1-154 to 1-155, no. 1-157 to 1-170, No. 1-178-184, No.1. 1-188-1-189, no. 1-198-1-204, no. 1-208-1-209, No. 1-211-1-236, no. 1-247 to 1-248, No. 1-257 to 1-263, No. No. 1-267 to 1-268, No. 1-270-284, No. 1 1-288-1 to 289, No.1. 1-291-1-293, no. 1-301 to 1-307, no. 1-311 to 2-312, No. 1-314 to 1-325, no. In 1-334 to 1-341, the PM combustion temperature hardly changed even after heat treatment at 980 ° C. for 48 hours.

(Example 2)
Regarding the PM combustion catalyst produced in Example 1, the performance evaluation of the PM combustion catalyst was further conducted in the same manner as in Example 1 with the reaction gas composition of 5% and 7% O ₂ -He balance. Table 3 shows typical examples of the results. In Table 3, catalyst No. 1 containing Sr in alkaline earth metal M was used. 1-111, no. 1-142, no. 1-332 showed excellent PM combustion catalyst performance even in an atmosphere of less than 10% O ₂ .

(Example 3)
Example No. in Table 1 The calcination temperature (800 ° C. to 1200 ° C.) and the calcination time (2 hours to 48 hours) are changed in the same sample preparation conditions as in 1-247, 1-257, and 1-305, and further pulverization and classification Thus, various composite oxide particles having different particle size distributions were prepared, and PM combustion catalysts having particle diameters Dp as shown in Tables 4-1 to 4-2 were prepared.

On the other hand, diameter 75 mm, length 60 mm, cordierite DPF cell density 200 cpsi (31 cells / cm ^2), and a diameter of 75 mm, length 60 mm, a silicon carbide DPF cell density 200 cpsi (31 cells / cm ²⁾ The PM combustion catalysts in Tables 4-1 to 4-2 were coated. In addition, the average pore diameter Dh of the DPF shown in Table 4 was obtained by measurement using a mercury intrusion method. The coating of the PM combustion catalyst onto the DPF was performed by baking at 650 ° C. for 1 hour after applying and drying the slurry. The slurry was stirred with 20 parts by mass of each PM combustion catalyst powder, 2 parts by mass of ρ-alumina, 40 parts by mass of pure water, and 10 parts by mass of a commercially available methylcellulose solution (solid content 2.5% by mass) as a binder. Added, and further antifoam was added and mixed. The amount of catalyst coated on the DPF is all 50 g / L.

Compressed air was allowed to flow from the inlet side of the DPF prepared as described above, the differential pressure between the inlet side and the outlet side was measured, and each DPF was compared using the differential pressure when the air flow rate was 5 m / s as the pressure loss. Also, for each catalyst powder of Table 4 performs PM combustion catalyst evaluated in the same manner as in Example 1, the peak temperature of the CO ₂ evolution, the same as the same sample of Table 1 ◎, high 5 ° C. to 10 ° C. The result is shown as “◯” in the column of “PM combustion catalytic action” in Table 4.

  As shown in Tables 4-1 to 4-2, Example No. in which the particle diameter Dp of the catalyst has a relationship of Dh / 20 ≦ Dp ≦ Dh with respect to the average pore diameter Dh of the DPF. 3-2 to 3-7, no. 3-11 to 3-15, no. 3-18 to 3-23, no. 3-27 to 3-31, no. 3-34 to 3-39, no. 3-43 to 3-47 had low pressure loss and excellent PM combustion catalyst performance.

1 Catalyst (PM combustion catalyst)
2 PM
3 PM combustion with catalysis 4 PM combustion without catalysis 5 Combustion PM
6 PM not burning
7 PM combustion catalyst of the present invention (composite oxide particles)
8 PM stuck to the catalyst surface following the burned PM [5]
9 Ag supported on the composite oxide according to the present invention
10 Composite oxide particles according to the present invention 11 PM adhered to the PM combustion catalyst of the present invention
DESCRIPTION OF SYMBOLS 12 Conventional support | carrier 13 Ag particle | grains 14 currently supported by the support | carrier Agglomerated Ag particle 15 Ag particle | grains 16 which the aggregated Ag particle enlarged The composite oxide particle (composite oxide particle | grains which carry | supported Ag) which concerns on this invention
17 PM
PM burned by the action of 18 Ag (19)
19 Ag supported on composite oxide particles according to the present invention
20 Arrow indicating movement of Ag (PM tracking action) 21 Moved Ag
22 Ag before moving
23 PM deposited on composite oxide particles containing a plurality of phases according to the present invention
24 Phase I
25 Phase II
26 Phase III
27 Noble Metal 28 Supported on Composite Oxide Particles Containing Multiple Phases According to the Present Invention Phase 28 (i)
29 phase (ii)
30 DPF porous side component 31 Fine catalyst particles 32 Large catalyst particles

Claims (7)

A composite oxide particle containing an alkaline earth metal M and (Fe1-xTix), wherein a (Fe1-xTix) / {(Fe1-xTix) + M} molar ratio is 0.33 or more and 0.93 or less And x, which is Ti / (Fe + Ti) molar ratio, is 0.03 ≦ x ≦ 0.24.   The particulate matter combustion catalyst according to claim 1, further comprising Ag supported on the composite oxide particles.   The particulate matter combustion catalyst according to claim 1, further comprising Pd supported on the composite oxide particles. The particulate oxide combustion catalyst according to any one of claims 1 to 3, wherein the composite oxide particles have a crystal phase represented by any one of the following formulas (I) to (V). .

(Here, x is 0.03 ≦ x ≦ 0.24, and δ is a value determined so as to satisfy the charge neutrality condition.)   The particulate matter combustion catalyst according to any one of claims 1 to 4, wherein the composite oxide particles include a plurality of crystal phases.   The particulate earth combustion catalyst according to any one of claims 1 to 5, wherein the alkaline earth metal M is Sr or Ca, or both Sr and Ca. A diesel particulate filter comprising the particulate matter combustion catalyst according to any one of claims 1 to 6 .

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