JP2011000503A - Carrier for exhaust gas cleaning catalyst, exhaust gas cleaning catalyst and honeycomb structure of exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for an exhaust gas cleaning catalyst and an exhaust gas cleaning catalyst which show the low content of Tand Tand excellent light-off performance and high temperature durability as DOC for cleaning a diesel engine exhaust gas, as well as a honeycomb structure of the exhaust gas cleaning catalyst, and also, a carrier for an exhaust gas cleaning catalyst and an exhaust gas cleaning catalyst which can reduce the use quantity of a precious metal beyond the known level, and shows higher cleaning performance than ever known and excellent high temperature durability as a three-way catalyst for cleaning an exhaust gas from a gasoline engine, as well as a honeycomb structure of the exhaust gas cleaning catalyst.SOLUTION: The carrier for the exhaust gas cleaning catalyst and the exhaust gas cleaning catalyst using the carrier, are composed of composite oxide particles which contain alkali earth metals M, Fe and Ti and also, includes a plurality of crystal phases. In addition, Ti/(Fe+Ti) is 0.01 to 0.45. Also, the honeycomb structure of the exhaust gas cleaning catalyst is provided.

Description

  The present invention relates to an exhaust gas purification catalyst carrier for purifying exhaust gas generated from a combustion engine, an exhaust gas purification catalyst, and an exhaust gas purification catalyst honeycomb structure.

  Exhaust gas generated from combustion engines using fossil fuels, for example, internal combustion engines such as boilers, heating furnaces, thermal power plants, and automobile engines, contains various harmful substances that can be removed and purified. It has been broken. Such technology for exhaust gas purification is desired to be further improved in accordance with recent serious global environmental problems.

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, and particulate matter. , Also referred to as PM, etc.) and soluble organic fraction (SOF). Among these, as a method for removing CO, HC, and SOF, there is a method in which an oxidation catalyst is disposed in the exhaust gas passage to oxidize CO, HC, and SOF. Such an oxidation catalyst used in exhaust gas treatment of a diesel engine is called a diesel oxidation catalyst (DOC).

  The DOC is also used for the following purposes. In exhaust gas purification of a diesel engine, a diesel particulate filter (DPF) is disposed in the exhaust gas flow path in order to collect and remove the PM. PM is collected by the DPF, but as the PM accumulates in the DPF, the exhaust pressure rises and the engine output decreases, etc., so when the amount of collected PM exceeds a predetermined amount, PM collected by some method must be burned and removed. As a method of burning the PM collected by the DPF, for example, there is a method of causing the PM combustion by forcibly raising the exhaust gas temperature. Therefore, a DOC is disposed in the exhaust gas passage of the diesel engine upstream of the DPF in order to oxidize HC components and the like contained in the exhaust gas and raise the exhaust gas temperature. 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 increased to promote the combustion of PM collected in the DPF.

Major of the DOC is alumina _Al 2 _{O 3} as a catalyst is a noble metal such as platinum Pt, palladium Pd as a carrier. Among them, a Pt—Pd / Al ₂ O ₃ catalyst supporting Pt—Pd is generally used. In DOC, it is disclosed to use oxides such as silica SiO ₂ -alumina, zeolite, titania TiO ₂ other than the alumina carrier (Patent Documents 1 and 2).

In exhaust gas purification of a gasoline engine, a three-way catalyst that purifies all of CO, NO _x , and HC in gas discharged from the engine is used. As the catalyst, a catalyst in which noble metals of Pt, Pd, and rhodium Rh are combined is used and supported on alumina. With the recent tightening of exhaust gas regulations, catalytic metals and their support oxides have been studied in order to improve performance such as high activity and long life of the catalyst. Regarding the support oxide, not only the alumina but also other oxides have been studied as follows.

The three-way catalyst works effectively near the stoichiometric air-fuel ratio, but in order to expand the effective air-fuel ratio width (wind), oxygen storage materials such as cerium oxide are part of the support to improve the catalyst performance. Has also been done. For example, Patent Document 3 discloses a method of adding ceria CeO ₂ as a promoter to a noble metal / alumina oxide catalyst. Catalysts that have been able to exert catalytic performance in a wide range from lean to rich (fuel overmixing) with oxygen storage capacity by ceria have been developed (wide windows).

Further, as oxides other than ceria, composite oxides have been studied as carriers, and in particular, there are many perovskite structure composite oxides containing rare earth elements. For example, in Patent Document 4, LaAl _1-x M _x O ₃ containing La (M: 1 to 5 group, 12 to 14 group) for the purpose of improving the activity of the three-way catalyst, in particular, improving the durability of the activity. A catalyst in which Pd is supported on a perovskite complex oxide of (element) is disclosed. Further, Patent Document 5 contains a rare earth element such as (La, Sr) FeO ₃ or (La, Sr) MnO ₃ in order to obtain similarly high catalytic activity, and particularly to improve low-temperature activity. It is disclosed that a noble metal element is supported on a perovskite complex oxide. Furthermore, the composition and additive elements of (La, Sr) FeO ₃ and (La, Sr) MnO ₃ have been studied, and their durability and heat resistance have been improved (Patent Document 6). Furthermore, in order to improve the durability of the catalytic activity of the noble metal, composite oxides such as La (Fe, Rh) O _{3 in} which the noble metal Rh is incorporated into the perovskite lattice are disclosed (Patent Documents 7 and 8). As described above, the perovskite complex oxide can select many kinds of elements and has a wide design range as a support. However, in order to effectively improve the catalytic performance of the three-way catalyst, La or the like Rare earth elements are essential. In the case of using an oxide of a carrier supporting a metal catalyst, particularly a noble metal catalyst, an oxide used as a carrier is desired to have a low raw material cost. That is, it is desirable to use an oxide that does not use expensive raw materials such as rare earth elements as a carrier.

An example of a three-way catalyst using a perovskite oxide containing no rare earth element as a carrier is disclosed in Patent Document 9, for example. Specifically, A _α B _1-x B ′ _x O _3-δ not containing a rare earth element (where A is substantially one element selected from Ba and Sr or a combination of two elements) B represents one element or a combination of two elements substantially selected from Fe and Co, and B ′ represents one element selected from Nb, Ta, and Ti. Represents a combination of two or more elements, α is 0.95 or more and 1.0 or less, x is 0.05 or more and 0.3 or less, and δ is a value determined to satisfy the charge neutrality condition. .), And the purification performance of a three-way catalyst is shown with a noble metal supported on the composite oxide.

Regarding the three-way catalyst, in Patent Document 10, the perovskite structure is unstable at a high temperature of 900 ° C. or more, and the catalytic activity is reduced by reacting with other components. In a reducing atmosphere (rich atmosphere), the perovskite structure is As a fracture, tetragonal complex oxide A ₂ BO ₄ (wherein A represents at least one selected from the group consisting of Ca, Sr and Ba, and B consists of Mn, Fe, Ti, Sn and V) Represents at least one selected from the group) and is shown as a three-way catalyst in which a noble metal is dissolved or supported.

Although a nitrogen oxide decomposing catalyst of an exhaust gas such as a diesel engine, in Patent Document 11, the general formula _{AB 1-x M x O 3} ± z ( where, A is one selected from alkaline earth elements Metal, B is one kind of metal selected from titanium group elements, M is one kind of metal selected from iron group, platinum group or copper group elements, 0 <x <1, z is metal at room temperature and atmospheric pressure There is disclosed a nitrogen oxide decomposition catalyst of a composite oxide represented by the number of oxygen defects or the excess number of oxygen in the oxide, and as the composite oxide, SrTi _1-x Fe _x O ₃ (where x is 0 <x A nitrogen oxide (NO _x ) decomposition catalyst having a composition represented by <1) is disclosed. The catalyst is such that the composite oxide itself has a reduction catalytic action without using a precious metal, and NO is directly reduced and decomposed into N ₂ and O ₂ at a high decomposition rate without using a reducing agent. I can do it.

Patent Document 12 discloses that AM _x O _y (A: alkali metal or alkaline earth metal, M: Fe, Co, or Ni) composite oxide, in particular, spinel-type AM _x O _y composite oxide is combined with a noble metal. Te, are said to be effective in removing particulate carbonaceous material (PM) and NO _x in exhaust gas such as a diesel engine.

Further, in Patent Document 13, although it is not a direct exhaust gas purification catalyst, ATO ₃ (A: alkaline earth metal, T: transition) such as SrFeO ₃ or CaFeO _{3 is} used as an oxygen storage material such as a promoter of the exhaust gas purification catalyst. It is disclosed that a catalyst metal is supported using a composite oxide of (metal) as a support, and oxygen is absorbed and released by the support.

JP 2007-111625 A JP 2006-81988 A JP 54-159391 A JP-A-2005-205280 JP 2006-36558 A JP 2003-175337 A JP 2004-41866 A JP 2004-41867 A JP 2007-160149 A Republished WO2004-089538 Japanese Patent Laid-Open No. 11-151440 JP 2005-66559 A JP 2006-176346 A

  As described above, the catalyst mainly composed of Pt is used for the DOC of diesel engine exhaust gas, and alumina is mainly used for the carrier. Since Pt is excellent in oxidation activity and high in activity even at low temperatures, it is effective when the exhaust gas temperature is low, such as diesel engine exhaust gas. However, Pt has a problem that compared to Pd and Rh, sintering tends to proceed in a lean atmosphere (oxidizing atmosphere, oxygen concentration of 5 to 21%) such as diesel exhaust gas, and durability is inferior. Although it is possible to increase the amount of Pt in advance in anticipation of a decrease in activity due to deterioration, there arises a problem that the cost increases. Moreover, in order to improve the durability of Pt, Pd is also added, but sufficient durability is not obtained.

Although it is not DOC as a catalyst related to diesel engine exhaust gas, in Patent Document 11, a composite oxide itself such as SrTi _1-x Fe _x O ₃ (where x is 0 <x <1) reductively decomposes nitrogen oxides. It is said to have catalytic action. Further, in Patent Document 12, a catalytic action that purifies both PM and NO _{x by} combining AM _x O _y (A: alkali metal or alkaline earth metal, M: Fe, Co, or Ni) composite oxide with a noble metal. There is going to be.

The inventors of the present invention are composite oxide (M-Fe-O-based oxide) particles containing alkaline earth metals M and Fe, wherein the composite oxide particles contain a plurality of crystal phases. It has been found that it is excellent as a carrier. It has been found that a DOC catalyst obtained by supporting a noble metal on this carrier is excellent in light-off performance and durability. However, as shown in FIG. 1, even when the durability test is performed, the temperature (T ₅₀ ) of 50% conversion is low and the light-off performance is excellent. However, the temperature (T ₈₀ ) of 80% conversion is also lowered. Thus, if a DOC having better light-off performance can be obtained, the burden of the DPF regeneration process is reduced.

It relates the three-way catalyst for gasoline engine exhaust, a conventional three-way catalyst, CO in the exhaust gas, HC, and NO _x in order to efficiently purify the noble metal that mainly Pt (other than Pt is, Rh, Pd) Is used. Furthermore, as described above, oxides such as ceria having oxygen storage ability are used as a carrier so as to show catalytic activity in a wider range with respect to the mixture ratio (air-fuel ratio) of air and fuel supplied to the engine. Has been. That is, in a lean atmosphere (oxygen excess atmosphere) larger than the stoichiometric air-fuel ratio, the purification rate of HC and CO is high, and conversely, in a rich atmosphere (excess fuel atmosphere) smaller than the stoichiometric air-fuel ratio, the NO _x purification rate is high. high. Oxides such as ceria release oxygen in the gas phase in a rich atmosphere, occlude oxygen in the gas phase in a lean atmosphere, and suppress atmospheric fluctuations in the vicinity of noble metals, resulting in a wider catalyst active window. It is. However, even when an oxide such as ceria is used, its oxygen storage capacity is limited, and therefore, if the lean atmosphere continues continuously, excess oxygen cannot be absorbed and NO _x purification does not proceed. On the other hand, if the rich atmosphere continues, the stored oxygen is released, and oxygen cannot be released from a certain point in time, and the purification of HC and CO does not proceed. Therefore, when oxides such as ceria are used, there is a problem that effective exhaust gas purification cannot be performed unless lean and rich are repeated in an appropriate cycle. Actually, considering the improvement in fuel efficiency, the engine tends to operate under lean conditions, and therefore, a catalyst that exhibits high catalytic activity even in a lean atmosphere is required. Further, when the generation amount of CO, HC, and NO _x changes drastically due to acceleration or deceleration, the conventional catalyst has its processing capacity. Oxides other than ceria, particularly composite oxides, have been studied as carriers, but carriers that have high catalytic activity even in a lean atmosphere have not been developed. According to detailed studies by the inventors, it has been found that when the composite oxide is supported by a noble metal catalyst in a single phase to form a three-way catalyst, sufficient catalytic activity cannot be obtained in a lean atmosphere. Further, there may be a case where sufficient processing cannot be performed even when the exhaust gas component changes greatly with acceleration or deceleration.

Accordingly, the inventors of the present invention are composite oxide (M-Fe-O-based oxide) particles containing alkaline earth metals M and Fe, wherein the composite oxide particles include a plurality of crystal phases. It has been found that it is excellent as a support for the original catalyst. When the noble metal is supported on the carrier, the actual vehicle performance is excellent as a three-way catalyst, and the amount of expensive Pt and Rh used in the noble metal can be reduced or the catalytic activity can be obtained without using it. The carrier which can be made was found. The reason why the actual vehicle performance is excellent is considered to be that the catalytic activity can be maintained high under a wide range of exhaust gas conditions from lean to rich because the composite oxide particles contain a plurality of crystal phases. However, in order to further reduce the cost of the three-way catalyst, a support capable of obtaining higher catalytic activity is required. For example, a carrier comprising a three-way catalyst which is excellent in _the NO _x purification. Further, regarding the usage environment of the three-way catalyst, it is desired to have a smaller reduction in purification performance even in an endurance test at a temperature exceeding 1000 ° C.

In the present invention has been made in view of the above problems, a DOC of the exhaust gas purification of a diesel engine, excellent light-off performance low T _80, a catalyst carrier for excellent exhaust gas temperature durability, exhaust gas purification An object is to provide a catalyst and an exhaust gas purification catalyst honeycomb structure. In addition, as a three-way catalyst for exhaust gas purification of gasoline engines, exhaust gas purification catalyst carrier, exhaust gas purification catalyst, and exhaust gas purification having higher purification performance that can further reduce the amount of precious metals used, and excellent high-temperature durability An object is to provide a catalyst honeycomb structure.

The inventors of the present invention provide a composite oxide (M-Fe-O-based oxide) particle containing an alkaline earth metal M and Fe, wherein the composite oxide particle includes a plurality of crystal phases. It has been found that when a catalyst is supported by supporting a noble metal, the DOC has excellent light-off performance and durability, and the three-way catalyst has excellent purification performance and durability of an actual vehicle. For light-off performance is further improved (lowered T ₈₀₎ in the DOC, the found that a part of Fe of the mixed oxide is effective to replace at Ti; Furthermore, in order to obtain the effect The present inventors have found that there is a specific Ti content in composite oxide particles containing a plurality of crystal phases, and completed the present invention. Moreover, it discovered that high temperature durability improved as DOC by containing Ti.

In order to improve the purification performance (particularly NO _x purification performance) in the three-way catalyst, it has been found that it is effective to substitute a part of Fe of the composite oxide with Ti; Found that there is a specific Ti content in the composite oxide particles contained in a plurality of crystal phases, and completed the present invention. In addition, it has also been found that the deterioration of the purification performance can be reduced in a durability test exceeding 1000 ° C. as a three-way catalyst by containing Ti.

That is, the present invention has the following gist.
(1) Composite oxide particles containing alkaline earth metals M, Fe, and Ti, wherein the composite oxide particles contain a plurality of crystal phases, and the Ti / (Fe + Ti) molar ratio is 0.01 to 0. A catalyst carrier for purifying exhaust gas, which is .45.
(2) The exhaust gas purifying catalyst carrier according to (1), wherein the alkaline earth metal M is Sr or Ca, or both Sr and Ca.
(3) The composite oxide is M (Fe _1-z Ti _z ) O _{2.5 ± δ} , M ₇ (Fe _1-z Ti _z ) ₁₀ O _{22 ± δ} , M (Fe _1-z Ti _z ) ₂ O _{4 ± δ} and M (Fe _1−z Ti _z ) ₁₂ O _{19 ± δ} (where z is 0.01 ≦ z ≦ 0.45, and δ is determined to satisfy the charge neutrality condition) The catalyst carrier for purifying exhaust gas according to the above (1) or (2), comprising at least one crystal phase selected from
(4) An exhaust gas purifying catalyst comprising a noble metal supported on the exhaust gas purifying catalyst carrier according to any one of (1) to (3).
(5) The exhaust gas according to (4), wherein the noble metal is Pd, or both Pd and Pt, and the loading ratio of the noble metal is 0.2 mass% to 15 mass%. Purification catalyst.
(6) An exhaust gas purifying catalyst honeycomb structure, wherein the exhaust gas purifying catalyst according to the above (4) or (5) is coated on a metal or ceramic honeycomb inner wall.
(7) The exhaust gas purification catalyst honeycomb structure according to the above (6), wherein the total amount of noble metals is 0.2 g / L to 22.0 g / L of noble metals.

  As described above, according to the present invention, regarding the exhaust gas purification of a diesel engine, the DOC light-off performance is excellent, so that the oxidation treatment for exhaust gas purification of the diesel engine can be performed at a low temperature. That is, for example, even in the case of low-temperature exhaust gas, an oxidation reaction can be caused to raise the exhaust gas temperature, and combustion of PM collected in the DPF can be promoted. Furthermore, since it is excellent in durability at a high temperature as a DOC, the oxidation treatment related to exhaust gas purification of a diesel engine can be efficiently performed over a long period of time. In addition, the oxidation treatment can be performed at a low cost because it has excellent durability (long life) and can reduce the amount of Pt used.

  Further, according to the present invention, a three-way catalyst that is excellent in actual vehicle purification performance and excellent in durability can be provided with respect to the three-way catalyst for exhaust gas purification of a gasoline engine. In addition, since the carrier does not contain an expensive rare earth element and excellent purification performance can be obtained without using platinum as a three-way catalyst, the cost can be reduced.

Conversion in DOC - shows the temperature _{curve, T 50} and _an example of a _{T 80} Schematic diagram explaining the oxidation reaction by a conventional DOC catalyst Schematic for explaining oxidation reaction by DOC catalyst according to the present invention (a) Two or more crystal phases according to the present invention (phase I (reference numeral 11), phase II (reference numeral 12), phase III (reference numeral 13)) Schematic explaining the oxidation reaction that occurs only in complex oxide particles containing (B) DOC of the present invention (two or more kinds of crystal phases (phase I (reference numeral 11), phase II (reference numeral 12), phase III (reference numeral 13)) (C) Explaining the process of incorporating oxygen molecules from oxygen molecules into the crystal lattice of the composite oxide in the DOC of the present invention. (D) Schematic diagram illustrating the process of adsorbing and activating HC and CO in the DOC of the present invention and promoting the reaction with oxygen ions in the lattice of the complex oxide. Schematic explaining the oxidation reaction by the DOC catalyst according to the present invention (e) The composite oxide particles containing the DOC of the present invention (two or more crystal phases (phase I (symbol 11), phase II (symbol 12)) Schematic diagram explaining the oxidation reaction that occurs when noble metal is supported) Schematic diagram showing the form of Pd and Pt precious metal support in the DOC Schematic diagram showing the process of reaction proceeding when reactive species diffuse on the surface of the carrier and move to the reaction point (noble metal) when the reactive species are easily adsorbed on the surface of the carrier Adsorption isotherm 1 of reactive species of composite oxide not containing Ti (M-Fe-O-based oxide), and adsorption isotherm 2 of reactive species of composite oxide containing Ti Schematic explaining the electronic state of the surface of M-Fe-O-based composite oxide (a-1) Electrons on the surface of M-Fe-O-based composite oxide containing Ti in a high oxygen concentration atmosphere (diesel engine exhaust gas) The figure explaining a state (a-2) The figure explaining the electronic state of the surface of the M-Fe-O type complex oxide which does not contain Ti in high oxygen concentration atmosphere (diesel engine exhaust gas) Schematic diagram for explaining the electronic state of the surface of the M-Fe-O composite oxide (b-1) Electrons on the surface of the M-Fe-O composite oxide containing Ti in a low oxygen concentration atmosphere (gasoline engine exhaust gas) The figure explaining a state (b-2) The figure explaining the electronic state of the surface of the M-Fe-O type complex oxide which does not contain Ti in a low oxygen concentration atmosphere (gasoline engine exhaust gas)

The exhaust gas purifying catalyst carrier of the present invention is a composite oxide particle containing alkaline earth metals M, Fe, and Ti, that is, a composite oxide containing alkaline earth metals M and Fe (M-Fe-O-based oxide). ) Composite oxide particles in which Fe of particles is replaced with Ti. Furthermore, the composite oxide particles include a plurality of crystal phases. Further, the Ti content is in the range of 0.01 to 0.45 in terms of a Ti / (Fe + Ti) molar ratio. With this configuration, when used in DOC used in the oxygen partial pressure conditions of the diesel engine exhaust gas (oxygen concentration from 5 to 21%), excellent light-off performance, in particular, T ₈₀ is more low-temperature side . Further, even in an endurance test at a temperature exceeding 900 ° C., a decrease in DOC activity is not observed, or the decrease is extremely small. Further, when used as a three-way catalyst of gasoline engine exhaust gas (exhaust gas environment where oxygen concentration is 3% or less and repeats lean and rich), purification performance in an actual vehicle is improved, particularly NO _x purification performance is improved. Moreover, even if an endurance test exceeding 1000 ° C. is performed, the decrease in the purification performance of the three-way catalyst is reduced, and the durability is excellent.

The Ti content is in a range of 0.01 to 0.45 in terms of a Ti / (Fe + Ti) molar ratio. When the Ti / (Fe + Ti) molar ratio is less than 0.01, the effect of Ti cannot be sufficiently obtained. In other words, with respect to the _{DOC, T 80} is not low enough. Further, sufficient durability cannot be obtained in a durability test at a temperature exceeding 900 ° C. With regard to the three-way catalyst, there is no improvement in the purification performance in the actual vehicle. In particular, not seen improvement of the NO _x purification performance. On the other hand, if the Ti / (Fe + Ti) molar ratio exceeds 0.45, a catalyst capable of obtaining sufficient catalytic activity cannot be produced. That is, with respect to the DOC, but durability is obtained in durability test temperatures above 900 ° C., not lower T ₈₀ is obtained. For a three-way catalyst, high purification performance in an actual vehicle cannot be obtained. In particular, high NO _x purification performance cannot be obtained. A more preferable range of the Ti / (Fe + Ti) molar ratio is 0.02 to 0.34.

  In the conventional alumina support 100, when a noble metal 200 such as Pt is supported and used as a catalyst, HC and CO are adsorbed and activated on the surface of the noble metal 200 as shown in FIG. Complex), and the activated chemical species readily oxidizes with oxygen molecules. In such a case, high catalytic activity is exhibited when the noble metal particles are small and the specific surface area is large. Therefore, from the viewpoint of the durability of the catalyst, the precious metal particles that can maintain the above-described precious metal particles, that is, the precious metal particles that do not coarsen the grain or reduce the specific surface area due to the sintering of the precious metal, have excellent durability. Show. On the contrary, when the precious metal particles are slightly sintered and the specific surface area is reduced, the catalytic activity is greatly reduced. In particular, diesel exhaust gas has a large oxygen partial pressure (oxygen concentration), so that the catalytic activity is significantly reduced. This is because, when the oxygen partial pressure is large, oxygen is stably adsorbed on the surface of the noble metal and hinders the reaction as shown in FIG. Among precious metals, Pt has a high oxidation catalytic activity, but is easily incinerated in an oxidizing atmosphere, and therefore has poor durability as a DOC.

  A carrier developed by the present inventors for the above conventional catalytic activity, that is, a composite oxide (M-Fe-O-based oxide) particle containing an alkaline earth metal M and Fe, wherein the composite oxidation In the carrier in which the product particles include a plurality of crystal phases, when a noble metal is supported and used as a catalyst, the catalytic activity (acceleration of oxidation reaction) in DOC is different, so that it has excellent durability.

In the composite oxide, oxygen ions (O ²⁻ ) in the crystal lattice easily move, and the oxygen ions are involved in the oxidation of HC and CO. Therefore, when the DOC is used, the catalytic activity is high. I think. It is known that oxygen ions have higher activity (active oxygen) than the oxygen molecule O ₂ and are effective in oxidation reactions. However, if there is no oxygen concentration gradient, even if there is an oxide in which oxygen ions easily move, oxygen ions are not generated and the oxidation reaction is not promoted. In the present invention, the composite oxide particle includes a plurality of crystal phases (at least two types of crystal phases), and has a structure in which phases having different chemical potentials are in contact with each other. (The difference in chemical potential becomes the driving force) and oxygen ions can move. Therefore, without intentionally creating an oxygen concentration gradient, a reaction cycle is formed in which HC and CO are oxidized with oxygen ions while oxygen molecules are taken in as oxygen ions, as shown in FIG. Such a phenomenon does not occur when the composite oxide particles are composed of one kind of crystal phase. In other words, in the composite oxide particle 10 according to the present invention, the oxygen ions are taken in as oxygen ions (phase II (reference numeral 12) in FIG. 3A and FIG. 3E), and the site for releasing oxygen ions ( It is characterized by having a phase I (reference numeral 11) in FIGS. 3A and 3E and an arbitrary phase (phase III (reference numeral 13) in FIG. 3A).

In order to incorporate oxygen molecules from the oxygen molecules into the crystal lattice of the composite oxide, it is necessary to dissociate the oxygen molecules as in the following formula (1) into oxygen ions, but at low temperatures (for example, 400 to 500 ° C. or lower) Oxygen molecule dissociation hardly occurs. Therefore, in the present invention, the noble metal 20 of Pd or Pt is supported (FIG. 3B), and as one of its roles, the dissociation of oxygen molecules at a low temperature is promoted as shown in the following formula (2). (FIG. 3C).
O ₂ + 2e ⁻ → 2O ²⁻ (1)
O ₂ → O ₂ −noble metal → O ²⁻ −noble metal → [O ²⁻ ] _lattice (2)

  Incidentally, at a high temperature (for example, a temperature exceeding 400 to 500 ° C. depending on the type of composite oxide), dissociation of oxygen molecules occurs on the surface of the composite oxide particle 10 even without the noble metal 20, and composite oxidation occurs. Oxygen ions are taken into the crystal lattice of the object 10.

  Further, as another role of the noble metal 20 supported, HC and CO are adsorbed and activated to promote reaction with oxygen ions in the lattice of the composite oxide 10 (FIG. 3D).

Since the catalyst activity is shown in the above reaction process, the reaction related to the reaction formula (1) or (2) becomes rate-limiting, and the oxygen partial pressure P (O ₂ ) becomes higher. Formation of oxygen ions O ²⁻ , which is oxygen, easily proceeds and the amount of generation thereof increases. Therefore, an advantageous effect as DOC activity appears when the oxygen partial pressure (oxygen concentration) is 5% or more. That is, in the catalyst of the present invention, the catalytic action as DOC appears remarkably when the oxygen partial pressure as in the exhaust gas of a diesel engine is high.

  Further, in the present composite oxide, the electron density of oxygen ions in the crystal lattice is increased (being greatly polarized) due to its cation structure, so that it is supported on the composite oxide 10 of the present invention as shown in FIG. The noble metal 20 easily forms a Pt—O bond (see FIG. 4A) and a Pd—O bond (see FIG. 4B) with the composite oxide 10 (strong interaction with the noble metal), Even at high temperatures, surface diffusion of noble metals tends to be suppressed. As a result, the aggregation (sintering) of noble metals is suppressed and the durability is excellent. Further, in the above reaction process (see FIG. 3), even if there is some agglomeration of noble metal, unlike the catalytic action as shown in FIG. 2, the catalytic activity hardly changes and is another factor showing excellent durability. It has become. Even when the oxygen partial pressure is large, oxygen molecules and oxygen ions adsorbed on the surface of the noble metal are always moving by the mechanism as described above. It doesn't happen to decline.

When the composite oxide particles as described above are used, a DOC having high durability and excellent light-off performance, that is, the conversion rate-temperature curve of FIG. 1 is shifted to a low temperature side can be formed. - high conversion zone at temperatures curves _{(T 80)} to be shifted to the low temperature side, as described above, it is contained Ti, the content thereof, at a Ti / (Fe + Ti) molar ratio, from 0.01 to 0 It was found that it is possible to make it in the range of .45. The reason is considered as follows.

Since the reaction rate depends on the concentration (partial pressure) of the reaction species (reaction gas), when the reaction proceeds and the conversion rate increases, the reaction species (here, HC and CO. O ₂ is also O _2. is a reactive species, since the excess present in the exhaust gas conditions of a diesel engine may be considered to be constant concentration.) is reduced (e.g., in T _80), further reaction is unlikely to proceed. However, if the reactive species are easily adsorbed on the surface of the composite oxide particle 10 as the carrier, the reactive species are adsorbed on the surface of the composite oxide particle 10 even if the concentration of the reactive species is decreased. The reaction proceeds by diffusing the surface up to 20) (FIG. 5). As shown in FIG. 6, the adsorption isotherm 1 of the reactive species of the complex oxide (M-Fe-O-based oxide) not containing Ti adsorbs when the relative pressure is small (the partial pressure of the reactive species is small). Although the amount is small, the adsorption isotherm 2 of the reactive species of the complex oxide containing Ti has a large amount of adsorption even if the relative pressure is small. That is, when Ti is contained, the surface state (electron density and its distribution state) of the composite oxide particles changes (FIGS. 7A-1 and 7A-2), and it is easy to adsorb reactive species. It has become. Therefore, a reaction occurs as shown in FIG. 5, as a result, T ₈₀ is shifted to the low temperature side.

  Further, M-Fe-O-based composite oxide particles containing a plurality of phases are excellent in durability under normal diesel exhaust gas temperature conditions (900 ° C. or lower), but when Ti is contained under the above-described conditions, durability at higher temperatures is also achieved. Even in the test, the decrease in DOC activity is suppressed. In particular, the effect that durability is improved by containing Ti appears remarkably when the composite oxide particles of the present invention and other oxide particles (oxides more acidic than iron oxide) coexist. .

As described above, when a noble metal is supported on M-Fe-O-based composite oxide particles containing a plurality of phases to form a three-way catalyst for exhaust gas purification of a gasoline engine, the exhaust gas components, temperature, air-fuel ratio The exhaust gas purification performance is comprehensively excellent under a wide range of conditions such as (A / F). In the case where each crystal phase of the composite oxide is supported alone (single phase) as a catalyst carrier and a three-way catalyst is supported, CO oxidation reaction, HC oxidation reaction, HC partial oxidation reaction, NO _x reduction reaction, The catalytic effect of the three-way catalyst acting on the NO _x reduction reaction using partially oxidized HC as a reducing agent varies depending on the crystal phase, the catalytic action temperature range varies depending on each phase, and the A / F window region varies depending on each phase. It ’s different. This is not only because the catalyst carrier simply disperses the metal particles to prevent agglomeration and maintains the effective surface area of the metal catalyst, but also changes the electronic state and characteristics of the supported catalyst metal particles, and catalysis and This is because the catalyst effect is also affected. Therefore, when the composite oxide is viewed in a single phase, the catalytic effect is excellent under specific conditions, but the range in which the catalytic effect is exhibited is limited. However, by making the composite oxide into a plurality of phases, the maximum value of the catalytic effect does not become as large as in the case of a single phase, but the range in which the catalytic effect is exerted is widened, and the exhaust gas purification of the engine whose actual load fluctuates is reduced. Show excellent exhaust gas purification performance. That is, in exhaust gas (mode test, etc.) of an engine whose load fluctuates, the components, temperature, A / F, etc. of the exhaust gas are constantly fluctuating. The better the exhaust gas purification below, the better the exhaust gas purification performance.

Furthermore, when Ti is contained in M-Fe-O-based composite oxide particles containing a plurality of phases and a noble metal is supported to form a three-way catalyst, as described above, the purification performance in an actual vehicle is further improved. _the NO _x purification performance is significantly improved. In an environment with low oxygen concentration (usually 3% or less) such as exhaust gas from gasoline engines, the effect of being able to respond widely to fluctuations in exhaust gas conditions such as actual vehicle operation by combining multiple phases as described above appears remarkably However, when the particles composed of a plurality of phases containing Ti are the carrier, it seems that the reactive species are easily adsorbed on the surface of the carrier, thereby promoting the catalytic action of the supported noble metal. In particular, in an environment where the oxygen concentration is low, it is easy to adsorb NO _x , and as a result, the NO _x purification performance is considered to be significantly improved. This is because even if Ti is contained, there is no remarkable effect in the single phase, so the interface between the two phases containing Ti promotes the surface diffusion of NO _x , or Ti contains It can be inferred that the vicinity of the interface between the two phases is in an electronic state in which NO _x is easily adsorbed (FIGS. 7B-1 and 7B-2).

  Furthermore, even if an endurance test exceeding 1000 ° C. is performed, the effect of reducing the reduction in the purification performance of the three-way catalyst can be obtained. In particular, the effect of improving durability by containing Ti is particularly remarkable when the composite oxide particles of the present invention and other oxide particles (oxides more acidic than iron oxide) coexist. Appear in

Alkaline earth metal M, Fe, and as the crystalline phase contained in the composite oxide particles containing Ti, e.g., _M s (Fe, _Ti) in the general formula are those represented as m _{O n.} As a specific example, for _{example, M (Fe 1-z Ti} z) O 2.5 ± δ, M (Fe 1-z Ti z) 2 O 4 ± δ, M 7 (Fe 1-z Ti z) ₁₀ O _{22 ± δ} , M ₅ (Fe _1-z T i _z ) ₂ O _{8 ± δ} , M ₂ (Fe _1-z T i _z ) O _{3.5 ± δ} , M ₃ (Fe _1-z T i _z ) _{2 O 6 ± δ, M 5 (} Fe 1-z Ti z) 14 O 26 ± δ, M 2 (Fe 1-z Ti z) 6 O 11 ± δ, M (Fe 1-z Ti z) 4 O 7 ± _δ , M ₂ (Fe _1−z T i _z ) ₁₄ O _{23 ± δ} , M ₃ (Fe _1−z T i _z ) ₃₂ O _{51 ± δ} , M ₄ (Fe _1−z T i _z ) ₉ O _{17.5 ± δ} , M ₄ (Fe _1−z T i _z ) ₆ O _{13 ± δ} , M (Fe _1−z T i _z ) ₃ O _{5.5 ± δ} , M ₃ (Fe _1−z T i _z ) ₁₅ O _{25.5 ± δ, M 3 (Fe 1} -z _{i z) 4 O 9 ± δ} , and _{M (Fe 1-z Ti z} ) 12 O 19 ± δ ( wherein, z is 0.01 to 0.45, [delta] is determined in the charge neutrality condition is satisfied Value). A more preferable range of z is 0.02 to 0.34. Among the crystal phases, M (Fe _1-z Ti _z ) O _{2.5 ± δ} , M ₇ (Fe _1-z Ti _z ) ₁₀ O _{22 ± δ} , M (Fe _1-z Ti _z ) ₂ O _{4 ± δ} and M (Fe _1−z Ti _z ) ₁₂ O _{19 ± δ} (where z is 0.01 ≦ z ≦ 0.45, and δ is a value determined so as to satisfy the charge neutrality condition) The composite oxide particles containing one or more crystal phases selected from the above are more preferable because they have excellent purification performance. The crystal phase of the composite oxide can be analyzed by an 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.

  Examples of the alkaline earth metal M contained in the composite oxide include Be, Mg, Ca, Sr, Ba, and Ra. The alkaline earth metal can be used alone or in combination of two or more. M is preferably Mg, Ca, Sr, or Ba because it is easy to form a complex oxide with Fe. Furthermore, since it is Sr or Ca, or both Sr and Ca, the catalyst performance excellent in the case of using DOC and a three-way catalyst is obtained.

  In the present invention, “a plurality of (two or more) crystal phases are included” means that, for example, when there are two types of the first crystal phase and the second crystal phase, the second crystal phase is the entire crystal phase. It means that 0.5 mol% or more is contained. When the second crystal phase is less than 0.5 mol%, the performance is almost the same as that of the single phase of the first crystal phase, and the above-described effect of using a plurality of crystal phases may not be obtained. One particle has a first crystal phase and one or more other crystal phases; and the content of the other one or more other crystal phases is 3 mol. % Or more or 5 mol% or more, or 9 mol% or more, and further preferably 12 mol% or more. It can also be 20 mol% or more. Further, considering the above-described mechanism for obtaining the effect of the present invention, the effect can be obtained if there are a plurality of crystal phases present in one particle. May be present. However, producing particles containing six or more crystal phases in one particle may be difficult because the manufacturing conditions are complicated. In addition, the effect of the present invention can be obtained even if the size of the plurality of crystal phases present in one particle is less than the particle size and is 2 to 5 nm.

The particle size of the composite oxide particles according to the present invention is a volume cumulative standard D50 (center particle size) measured by a laser diffraction scattering type particle size distribution measuring device because of the production efficiency and the ability to effectively support noble metals. A range of 0.5 μm to 10.0 μm is preferable. The range of 1.0 μm to 5.0 μm is more preferable. In a normal oxide support, a smaller particle size of 100 nm or less is preferable because the noble metal can be finely dispersed. However, in the present invention, the catalytic activity is exhibited in the above-described reaction process. Sufficient catalytic activity is obtained. Therefore, when the center particle diameter D50 is less than 0.5 μm, there is no problem as catalyst activity, but it takes time to prepare the particle diameter 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 10.0 μm, it becomes difficult to uniformly disperse and carry the catalyst metal, and a large amount of the catalyst metal may be required. In addition, the specific surface area of the composite oxide particles is preferably in the range of 1 to ²⁰ m ² / g from the reason that production efficiency and noble metal can be effectively supported, as described above. If the specific surface area is less than 1 m ² / g, the noble metal may not be highly dispersed or the noble metal may be aggregated during the loading process. On the other hand, when the specific surface area exceeds 20 m ² / g, the composite oxide particles may not be economically prepared or may be difficult to disperse during slurry preparation.

  The exhaust gas purifying catalyst carrier of the present invention can provide an exhaust gas purifying catalyst (DOC, three-way catalyst) by supporting a noble metal. Examples of the noble metal to be supported include platinum Pt, rhodium Rh, palladium Pd, and the like. Among these, it is preferable that Pd or both Pd and Pt are supported. In order to activate the DOC at a low temperature (improve the light-off performance), it is necessary to increase the loading ratio of Pd, but the PD is inexpensive. On the other hand, although Pt is expensive, it is excellent in low temperature activity (light-off performance) of DOC. Pd and Pt may be selected according to the purpose and cost of diesel engine engine management, post-processing design, etc., and the usage amount may be determined. In particular, it is preferable to support both noble metals of Pd and Pt because it is easy to achieve both performance and cost. Regarding the three-way catalyst, when supported on the exhaust gas purification catalyst carrier of the present invention, Pt and Pd exhibit the same level of catalyst performance, and therefore, it is preferable to use only Pd from the viewpoint of cost. The precious metal loading ratio (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 0.2% by mass to 15% by mass. Is more preferable. If it is less than 0.2% by mass, when the honeycomb substrate is coated, if the amount of noble metal (g / L) is to be increased, the catalyst layer will be coated thickly, and the cell (through hole) opening of the honeycomb substrate will be There is a case where the pressure loss becomes large as it becomes smaller. If it exceeds 15% by mass, the noble metal becomes difficult to finely disperse on the surface of the exhaust gas purification catalyst carrier, and sufficient catalytic activity may not be obtained. The more preferable noble metal loading in the exhaust gas purifying catalyst carrier of the present invention is 0.3 mass% to 4.3 mass%.

  The exhaust gas purification catalyst of the present invention may be used by mixing with a catalyst in which a noble metal is supported on another oxide carrier such as activated alumina or ceria (ceria-zirconia).

  The composite oxide particles containing alkaline earth metals M, Fe, and Ti according to the present invention are prepared by a solid phase reaction method, a liquid phase method such as a coprecipitation method or a sol-gel method, a chemical vapor deposition method, a laser ablation method. It may be manufactured by any method such as law. 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, oxides, hydroxides, carbonates, nitrates, organic acid salts, sulfates, etc. of alkaline earth metals M are used as starting materials; Fe oxides, hydroxides, nitrates, sulfuric acid, etc. Salts and the like; Ti oxides and 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 any existing method such as mortar mixing, ball mill, planetary ball mill, drum mixer, pin mill, etc. may be used. 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 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 solution pH 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 a plurality (two or more) of crystal phases in the composite oxide particles according to the present invention, in each of the above production methods, as a raw material composition different from the stoichiometric ratio of the composite oxide single phase, It is formed as a plurality of phases after calcination. That is, composite oxide particles including a plurality of crystal phases can be produced by using a raw material having a composition in which a plurality of metals do not form a single composite oxide. For example, previous _M s (Fe, _Ti) For m _{O n,} and M in the starting material (Fe, Ti) a composition ratio of, do not form stoichiometric single crystalline phase (single compound) composition And The composition ratio (molar ratio) between M and (Fe, Ti) in the raw material is at least 0.005, at least 0.03, at least 0.05, or even at least 0.09 from the composition forming a single crystal phase. Preferably at least 0.20 different.

  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, for example, nitrate, nitrite, chloride, acetate, sulfate, ammine complex, or the like, or a noble metal colloid is added to water, and the composite oxide particles are further added to the solution and stirred. Disperse by ultrasonic dispersion or the like. After removing the water from the suspended solution and drying, the exhaust gas purifying catalyst of the present invention carrying the noble metal can be produced 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 exhaust gas purification catalyst of the present invention can be made into an exhaust gas purification catalyst honeycomb structure (DOC honeycomb structure, three-way catalyst honeycomb structure) by wash-coating a ceramic or metal honeycomb. The ceramic honeycomb that can be used in the present invention is not particularly limited, and examples thereof include a cordierite honeycomb and a silicon carbide honeycomb. The metal honeycomb that can be used in the present invention is not particularly limited, and examples thereof include a stainless steel honeycomb and an Al-enriched stainless steel honeycomb.

  When the diesel exhaust gas oxidation catalyst of the present invention is wash-coated on a honeycomb, first, a slurry in which the catalyst, the binder, and the like are dispersed is prepared, and the honeycomb is immersed therein or the slurry is allowed to flow into the honeycomb. . Examples of the binder include aluminum nitrate, colloidal silica, organic binder, and ρ-alumina. Next, excess slurry on the honeycomb surface is removed by a method such as blowing off, and after drying, heat treatment is performed at a temperature of 500 to 900 ° C. When the slurry is allowed to flow into the honeycomb, the slurry is applied only to the inner wall of the honeycomb. As one of the methods, a method of sucking up the slurry by devising a jig for mounting the honeycomb. There is.

  In the diesel exhaust catalyst honeycomb structure of the present invention, the content of the noble metal is preferably in the range of 0.2 g / L to 22.0 g / L. If it is less than 0.2 g / L, sufficient catalytic performance as a diesel exhaust catalyst honeycomb structure may not be exhibited. If it exceeds 22.0 g / L, the catalyst performance of the exhaust gas oxidation catalyst honeycomb structure is saturated, and even if the amount of noble metal is increased, the catalyst performance may not be improved further. The content of the noble metal is more preferably 0.4 g / L to 11.0 g / L, still more preferably 0.8 g / L to 8 g / L.

Example 1
A composite oxide particle of alkaline earth metals M, Fe, and Ti is used to prepare composite oxide particles containing a plurality of crystal phases as a support, and a precious metal is supported on the support to prepare a diesel exhaust gas oxidation catalyst (DOC). And evaluated.

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, “M / (Fe + Ti) molar ratio” column, and “Ti / (Fe + Ti) molar ratio (z value)” in Table 1 (Tables 1-1 to 1-4) As shown in the column, the raw materials were weighed and mixed by a ball mill in relation to the molar ratio of M, Fe, and Ti. The mixed powder was calcined at 900 to 1100 ° C. shown in the “calcination temperature (° C.)” column of Table 1 for 5 hours, and the calcined powder was pulverized with a ball mill. The pulverized powder was further calcined at the same temperature for 5 hours, and the calcined powder was pulverized with a ball mill to prepare composite oxide particles according to the present invention and a composite oxide particle as a comparative example, and used as a carrier. Center particle diameter D50 of the composite oxide particles these produced is between 1.3Myuemu～5.5Myuemu, the specific surface area was between 2.1m ² /g~3.2m ² / g .

  In the powder composed of the obtained particles, the contained crystal phase was identified by the powder X-ray diffraction method. The content of each was calculated from the area of the X-ray diffraction peak. The calibration curve was created using the single-phase diffraction peak area. 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.

Further, as a conventional catalyst, γ-alumina was tested as a support. The center particle diameter D50 of the γ-alumina used here was 0.06 μm, and the specific surface area was 90.4 m ² / g.

  Here, the specific surface area was measured by a BET method using nitrogen gas adsorption using a specific surface area measuring device manufactured by Nippon Bell Co., Ltd. The particle size was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation.

  Next, the noble metals shown in Table 1 were supported on the above-described carriers at various loading rates as follows. Specifically, platinum colloid, palladium nitrate, and rhodium nitrate were used to carry Pt, Pd, and Rh, respectively. An aqueous solution containing platinum colloid, palladium nitrate and rhodium nitrate and 100 g of the carrier powder were placed 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 at 600 ° C. for 3 hours in the atmosphere. Through the above operation, a catalyst powder having a noble metal supported on a carrier was produced.

  Next, a slurry was prepared using the catalyst powder, and was washed on the honeycomb.

  19 parts by mass of catalyst powder shown in Table 1, 5 parts by mass of ρ-alumina, 7 parts by mass of pure water, and 10 parts by mass of a commercial methylcellulose solution (solid content of 2.5% by mass) as a binder were added with stirring. Further, an antifoaming agent was added and mixed to obtain a slurry.

  A cylindrical stainless steel honeycomb having a diameter of 25.4 mm, a length of 25.4 mm, and a honeycomb cell density of 300 cells per inch (25.4 mm) square is used as the honeycomb to coat the catalyst powder. It was. The slurry was applied to the honeycomb inner wall and dried. Thereafter, a heat treatment was performed in the atmosphere at 650 ° C. for 1 hour to obtain a stainless steel honeycomb catalyst structure obtained by wash-coating the catalyst powders of the present invention and the comparative example. The total amount of precious metal fixed to the honeycomb is 2.6 g / L as shown in Table 2 (Tables 2-1 to 2-2).

Regarding the produced honeycomb catalyst structure, the DOC catalyst performance was evaluated as follows. As a simulation gas of diesel exhaust gas, THC (propane, C ₃ H ₆ ): 550 ppm (1650 ppm C), NO: 500 ppm, CO: 1200 ppm, O ₂ : 9%, H ₂ O: 10%, N ₂ : balance was used. . Here, HC is represented by THC as total HC (total hydrocarbons). SV (space velocity): 120,000 h ⁻¹ , the simulated gas was passed through the honeycomb catalyst structure, the temperature of the catalyst was heated from normal temperature to 600 ° C. in an electric furnace, and the gas composition after passing through the catalyst at each temperature was gas chromatographed and it was measured by NO _x meter. THC conversion (%) is 100 × {1- [THC] _out / [THC] _in } and CO conversion (%) is 100 × {1- [CO] _out / [CO] _in } The DOC catalyst activity was determined from the concentration changes of THC and CO before and after. The conversion rate at each temperature was measured, and the temperature T _{80 at} which the conversion rate was 80% was determined from the conversion rate-temperature curve as shown in FIG. 1 and shown in Table 3 (Tables 3-1 to 3-2). As described above, the DOC catalytic activity of each catalyst was compared.

The durability of the catalyst, 950 ° C. The honeycomb catalyst structure in the air, after 72h heat treatment in the same manner as described above performs a DOC catalyst performance evaluation was compared before and after the heat treatment the T _80.

Table 3 summarizes the results of Table 2. Not heat-treated THC conversion of T ₈₀ and the CO conversion of the T ₈₀ in the (initial catalyst prior to the durability test), the results in the case of each of γ- alumina used in conventional catalyst was used as a carrier (No. 1-68) as compared to the case of more than _{T 80} of No.1-68 as "×", in the case of difference drop of less than 5 ° C. with the _{T 80} of No.1-68 "△", If differences are reduced below 10 ° C. and T ₈₀ of the No.1-68 are expressed as "○", when the reduction of more than 10 ° C. was observed "◎", "○" and "◎" is present It was judged that the effect of the invention was seen. Moreover, compared with T ₈₀ of the THC conversion rate and T ₈₀ of the CO conversion rate of the initial catalyst before performing the durability test, each T ₈₀ after performing the durability test at 950 ° C. decreased by more than 15 ° C. ( “X” when there was a temperature rise), “△” when it exceeded 10 ° C. and 15 ° C. or less, “◯” when it exceeded 5 ° C. and 10 ° C. or less, and 0 ° C. (T ₅₀ When there was no change) and the temperature was 5 ° C. or less, it was expressed as “◎”, and “◯” and “◎” were judged to show the effect of the present invention.

As shown in Tables 1 to 3, Example Nos. 1-2 to 1-4, Nos. 1-7 to 1-9, Nos. 1-13 to 1-17, Nos. 1-19 to 1- No. 26, No. 1-29 to 1-33, No. 1-35 to 1-40, No. 1-43 to 1-47, No. 1-49 to 1-67 include a plurality of crystal phases, Since the alkaline earth metal M-Fe-O-based composite oxide particles contain Ti and the content thereof is within a range of 0.01 to 0.45 in terms of Ti / (Fe + Ti) molar ratio, T ₈₀ Excellent results and excellent durability. Comparative Examples No. 1-1, No. 1-6, No. 1-11, No. 1-27, No. 1-41 are alkaline earth metal M-Fe-O systems containing a plurality of crystal phases. Since Ti is not contained in the composite oxide particles, T ₈₀ as excellent as that in Examples is not obtained. Comparative Examples No. 1-12, No. 1-28, and No. 1-42 contain Ti in alkaline earth metal M-Fe-O-based composite oxide particles containing a plurality of crystal phases. However, since the content is too small, the effect of the present invention is not obtained. Conversely, Comparative Examples No.1-5, No.1-10, No.1-18, No.1-34, the No.1-48, _{T 80} and the content of Ti is too large, the low temperature side Rather than shifting, DOC activity is decreasing.

(Example 2)
A composite oxide particle containing a plurality of crystal phases with a composite oxide of alkaline earth metals M, Fe, and Ti was prepared as a support, a noble metal was supported on the support, and a three-way catalyst was prepared and evaluated.

Carbonate (MCO ₃ ) was used as the raw material for the alkaline earth metal M, and oxides (Fe ₂ O ₃ , TiO ₂ ) were used as the raw material for Fe and Ti. “Molar ratio of alkaline earth metal M” column, “M / (Fe + Ti) molar ratio” column, and “Ti / (Fe + Ti) molar ratio (z value)” in Table 4 (Tables 4-1 to 4-4) As shown in the column, the raw materials were weighed and mixed by a ball mill in relation to the molar ratio of M, Fe, and Ti. The mixed powder was calcined at 900 to 1100 ° C. shown in the “calcination temperature (° C.)” column of Table 5 for 5 hours, and the calcined powder was pulverized with a ball mill. The pulverized powder was further calcined at the same temperature for 5 hours, and the calcined powder was pulverized with a ball mill to prepare composite oxide particles according to the present invention and a composite oxide particle as a comparative example, and used as a carrier. Center particle diameter D50 of the composite oxide particles these produced is between 1.3Myuemu～5.5Myuemu, the specific surface area was between 2.1m ² /g~3.2m ² / g .

  In the powder composed of the obtained particles, the contained crystal phase was identified by the powder X-ray diffraction method. The content of each was calculated from the area of the X-ray diffraction peak. The calibration curve was created using the single-phase diffraction peak area. 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.

Further, as a conventional catalyst, γ-alumina was tested as a support. The center particle diameter D50 of the γ-alumina used here was 0.06 μm, and the specific surface area was 90.4 m ² / g.

  Here, the specific surface area was measured by a BET method using nitrogen gas adsorption using a specific surface area measuring device manufactured by Nippon Bell Co., Ltd. The particle size was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation.

  Next, the noble metals shown in Table 4 were supported on the above-described carriers at various loading rates as follows. Specifically, platinum colloid, palladium nitrate, and rhodium nitrate were used to carry Pt, Pd, and Rh, respectively. An aqueous solution containing platinum colloid, palladium nitrate and rhodium nitrate and 100 g of the carrier powder were placed 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 at 600 ° C. for 3 hours in the atmosphere. Through the above operation, a catalyst powder having a noble metal supported on a carrier was produced.

  Next, a slurry was prepared using the catalyst powder, and was washed on the honeycomb.

  19 parts by weight of catalyst powder shown in Table 4, 4 parts by weight of aluminum hydroxide, 7 parts by weight of pure water, and 10 parts by weight of a commercially available methylcellulose solution (solid content of 2.5% by weight) as a binder were added with stirring. Further, an antifoaming agent was added and mixed to obtain a slurry.

  A cylindrical stainless steel honeycomb having a diameter of 40 mm, a length of 45 mm, and a honeycomb cell density of 300 cells per inch (25.4 mm) square was used as a honeycomb to wash coat the catalyst powder. The slurry was applied to the honeycomb inner wall and dried. Thereafter, a heat treatment was performed in the atmosphere at 650 ° C. for 2 hours to obtain a stainless steel honeycomb catalyst structure obtained by wash-coating the catalyst powders of the present invention and the comparative example. The total amount of precious metal fixed to the honeycomb is 1.4 g / L as shown in Table 5 (Tables 5-1 to 5-2).

  Catalyst performance evaluation was performed on the manufactured honeycomb catalyst structure as follows.

  In order to evaluate the catalyst performance, a test using a practical vehicle (engine with a displacement of 125 mL) was performed. First, the manufactured honeycomb catalyst structure was attached to a muffler by welding. After everything was installed, it was confirmed that there was no gas leak from the exhaust gas system. In addition, warm-up operation was performed before the evaluation, and after that, it was confirmed that there was no gas leakage from the exhaust gas system. The test method was performed according to the test method (TRIAS) defined by the Ministry of Land, Infrastructure, Transport and Tourism. The driving mode was an EU motorcycle motorcycle test cycle.

For the durability test, the honeycomb catalyst structure was repeatedly heat treated at 1050 ° C. for 48 hours for 1 hour with 1% CO reducing atmosphere (N ₂ balance) for 1 hour and 2% O ₂ oxidizing atmosphere (N ₂ balance) for 1 hour. The catalyst performance was evaluated in the same manner as described above.

CO, THC, the evaluation results of the purification rate of the NO _x shown in Table 5. In Table 5, each purification rate is calculated based on the amount of exhaust gas component in the same condition without a catalyst as 100, and the reduction rate of each exhaust gas component amount when the catalyst is installed is calculated in mass%. Is
CO purification rate ×: less than 65%, Δ: 65% or more, ○: 68% or more, ◎: 75% or more THC purification rate ×: less than 65%, Δ: 65% or more, ○: 68% or more, ◎: 75 % Or more NO _x purification rate ×: less than 18%, Δ: 18% or more, ○: 22% or more, ◎: 26% or more, ◎: ◎: 30% or more

As shown in Tables 4 to 5, Example Nos. 2-2 to 2-4, Nos. 2-7 to 2-9, Nos. 2-13 to 2-17, Nos. 2-19 to 2- No. 26, Nos. 2-29 to 2-33, Nos. 2-35 to 2-39, Nos. 2-42 to 2-46, Nos. 2-49 to 2-67 include a plurality of crystal phases. Since the alkaline earth metal M-Fe-O-based composite oxide particles contain Ti and the content thereof is within a range of 0.01 to 0.45 in terms of a Ti / (Fe + Ti) molar ratio, the purification rate is improved. The result is excellent, and the overall NO _x purification rate is excellent, and the durability is also excellent. Comparative Examples No. 2-1, No. 2-6, No. 2-11, No. 2-27, No. 2-40 are alkaline earth metal M-Fe-O systems containing a plurality of crystal phases. Since the composite oxide particles do not contain Ti, a purification rate as excellent as that in Examples is not obtained. In Comparative Examples No. 2-12, No. 2-28, and No. 2-41, Ti is contained in alkaline earth metal M-Fe-O-based composite oxide particles including a plurality of crystal phases. However, since the content is too small, the effect of the present invention is not obtained. On the other hand, in Comparative Examples No. 2-5, No. 2-10, No. 2-18, No. 2-34, No. 2-47, the content of Ti is too much and the purification rate is deteriorated. Yes.

  According to the exhaust gas purifying catalyst carrier, the exhaust gas purifying catalyst or the exhaust gas purifying catalyst honeycomb structure of the present invention, the catalyst performance is high and the durability is excellent, so the amount of noble metal can be reduced. In particular, the amount of Pt used can be reduced, or it is not necessary to use Pt, so the cost is reduced.

1 Adsorption isotherm of reactive species of composite oxide not containing Ti (M-Fe-O composite oxide) 2 Reaction of composite oxide containing Ti (M-Fe, Ti-O composite oxide) Species adsorption isotherm

Claims (7)

  Composite oxide particles containing alkaline earth metals M, Fe, and Ti, wherein the composite oxide particles contain a plurality of crystal phases, and the Ti / (Fe + Ti) molar ratio is 0.01 to 0.45. A catalyst carrier for purifying exhaust gas, characterized in that it exists.   2. The exhaust gas purifying catalyst carrier according to claim 1, wherein the alkaline earth metal M is Sr or Ca, or both Sr and Ca. The composite _{oxide, M (Fe 1-z Ti} z) O 2.5 ± δ, M 7 (Fe 1-z Ti z) 10 O 22 ± δ, M (Fe 1-z Ti z) 2 O 4 _{± δ} and M (Fe _1−z T i _z ) ₁₂ O _{19 ± δ} (where z is 0.01 ≦ z ≦ 0.45, and δ is a value determined so as to satisfy the charge neutrality condition) The catalyst carrier for exhaust gas purification according to claim 1 or 2, comprising at least one crystal phase selected from   An exhaust gas purification catalyst comprising a noble metal supported on the exhaust gas purification catalyst carrier according to any one of claims 1 to 3.   The exhaust gas purifying catalyst according to claim 4, wherein the noble metal is Pd, or both Pd and Pt, and the loading ratio of the noble metal is 0.2 mass% to 15 mass%.   An exhaust gas purification catalyst honeycomb structure, wherein the exhaust gas purification catalyst according to claim 4 or 5 is coated on an inner wall of a metal or ceramic honeycomb. The exhaust gas purifying catalyst honeycomb structure according to claim 6, wherein the total amount of noble metals is 0.2 g / L to 22.0 g / L of noble metals.

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