JP4904458B2 - Composite oxide and filter for PM combustion catalyst - Google Patents

Description

  The present invention relates to a composite oxide suitable for a catalyst for burning PM (particulate matter) discharged from a diesel engine such as an automobile, and a catalyst and a diesel exhaust gas purification filter using the same.

Nitrogen oxides (NO _x ) and PM are particularly problematic with regard to exhaust gas from diesel engines. Among these, PM is fine particles mainly composed of carbon, and a method for trapping PM by installing a particulate filter (DPF) in an exhaust gas flow path is becoming common as a method for removing the particulate matter. The trapped PM is burned intermittently or continuously, and the DPF is regenerated.

In this DPF regeneration process, a method of burning PM by external heating using an electric heater, a burner or the like, an oxidation catalyst is installed on the engine side of the DPF, NO in the exhaust gas is changed to NO ₂ by the oxidation catalyst, and NO ₂ There is a method of burning PM by the oxidizing power of the. However, electric heaters and burners need to be externally applied, which complicates the system. In addition, regarding the oxidation catalyst, the exhaust gas temperature is not so high that the catalytic activity is sufficiently exhibited, and NO necessary for PM combustion is not contained in the exhaust gas unless under certain operating conditions. There's a problem. Under such circumstances, a catalyst system in which a catalyst is supported on a DPF, the PM combustion temperature is lowered by the catalytic action, and combustion is continuously performed at the exhaust gas temperature is desirable.

  Patent Document 1 discloses a material carrying Pt as a catalyst metal. However, since Pt has a low catalytic action for burning PM at the exhaust gas temperature level, it is considered difficult to continuously burn PM at the fuel exhaust gas temperature. Further, since noble metals are used, an increase in cost is inevitable.

Japanese Patent Laid-Open No. 11-253757

  The present applicant has proposed a PM combustion catalyst containing a composite oxide of Ce and a transition metal element in Japanese Patent Application No. 2005-336408 as a catalyst that does not use a noble metal element, thereby significantly reducing the PM combustion temperature. It has been realized. However, in this technology, no special consideration is given to the heat resistance of the PM combustion catalyst. Considering the case where the catalyst temperature suddenly rises due to the heat generated during PM combustion, Development of a catalytic material having heat resistance that can maintain high catalytic activity is awaited.

  The present invention develops and provides composite oxides that have catalytic activity that can burn PM of diesel engine exhaust gas at low temperatures without containing precious metal elements, and that have heat resistance that can withstand the heat generated during PM combustion. It is to try.

The above object is achieved, Ce, and a transition metal element T, and one or more elemental M, is achieved by oxygen composite oxide composed. More specifically, a composite oxide for PM combustion catalyst having a composition in which the molar ratio of Ce, transition metal element T and element M satisfies the following [a] is provided.
[A] When the molar ratio of Ce, transition metal element T and element M is Ce: T: M = (1-xy): x: y, 0 <x ≦ 0.6, 0 <y ≦ 0.4, x + y <1 holds .

As the transition metal element T, here we adopt Fe. That is, it is the Target those having a composition satisfying the following [a] '.
[A] When the molar ratio of Ce, Fe and element M is Ce: Fe: M = (1-xy): x: y, 0 <x ≦ 0.6, 0 <y ≦ 0. 4, x + y <1 holds.
However, in this case, the element M is an element selected from the element group consisting of La, Y, Co, and Ba .

This composite oxide is mainly composed of a cerium oxide (CeO ₂ ) structure, and is composed of Ce , Fe, one or more elements M, and oxygen. In the following composition formula (1), 0 <x It can also be regarded as a composite oxide having a composition satisfying ≦ 0.6, 0 <y ≦ 0.4, and x + y <1.
_{Ce (1-xy) Fe x} M y O δ ...... (1)
Here, δ> 0, and typically δ = 2 or a value close thereto, for example, 1 ≦ δ ≦ 3, or 1.3 ≦ δ ≦ 2.5. That is, what has a composition close | similar to following composition formula (1) 'can be illustrated.
_{Ce (1-xy) Fe x} M y O 2 ...... (1) '
According to X-ray diffraction, this composite oxide has a peak of a cerium oxide structure, and an iron oxide phase may be detected in addition to a cerium oxide phase from a microscopic analysis means.

These composite oxides have excellent heat resistance that hardly causes thermal degradation even when subjected to a high-temperature thermal history. That is, the composite oxide was heat-treated at 800 ° C. for 2 hours in the atmosphere, and then mixed with carbon black and a mortar to obtain a powder having a mass ratio of (heat-treated composite oxide) :( carbon black) = 6: 1 The sample has excellent heat resistance such that the carbon black combustion temperature T ₉₀ defined by the following [b] is 520 ° C. or less.
[B] carbon black combustion temperature T ₉₀ is a powder sample in the weight change of the powder sample upon heating at 10 ° C. / min from room temperature by TG / DTA apparatus, weight loss from 50 ° C. to 700 ° C. On the other hand, it is defined as the temperature at which the weight loss from 50 ° C. becomes 90% (see FIG. 2 described later).

  Such a complex oxide is extremely suitable as a catalyst (PM combustion catalyst) for burning PM in exhaust gas from a diesel engine. By supporting an oxidation catalyst using this composite oxide as a catalyst material on a DPF made of a porous material such as SiC, cordierite, mullite, alumina, etc., the collected PM can be effectively used for the heat of exhaust gas. Thus, a diesel exhaust gas purification filter that can be burned and removed is constructed.

  Since the composite oxide of the present invention exhibits high catalytic activity from a relatively low temperature, when it is used as a catalyst substance, the PM combustion temperature can be lowered, and the exhaust gas temperature can be effectively used to burn and remove PM. It is possible to construct a diesel exhaust gas purification filter that can be used. Moreover, since the composite oxide of the present invention is excellent in heat resistance, high catalytic activity is maintained even when sudden heat generation due to PM combustion occurs. Furthermore, since no precious metal element is required, it can contribute to the reduction of the material cost of DPF.

The composite oxide of the present invention contains Ce, a transition metal element T ( specifically, Fe), and the element M as essential components. This composite oxide is mainly composed of an oxide phase having a form in which Fe or an element M is combined with a cerium oxide structure. A typical composition formula is represented as the above-mentioned formula (1).

A part of the cerium atom of this cerium oxide structure is substituted with an atom of the transition metal element T ( specifically, Fe). At this time, the apparent valence change of the cation of the complex oxide mainly composed of cerium atoms occurs, and the lattice distortion due to substitution of elements having different ionic radii causes oxygen in the lattice to move out of the lattice. It is considered that the active oxygen necessary for PM combustion is supplied to the PM from a relatively low temperature range, and the PM combustion temperature is lowered. In the case of the conventional mere cerium oxide (CeO ₂ ) that does not contain the transition metal element T, it is considered that it has a stable structure in which the release of oxygen in the lattice is unlikely to occur. It is difficult to obtain activity.

According to the study by the inventors, a complex oxide formed with a transition metal element T ( specifically, Fe) in a cerium oxide structure can obtain a high catalytic activity for PM, but 800 ° C. It was found that once a thermal history heated to a high temperature was received, the original high catalytic activity could not be sufficiently maintained (thermal degradation occurred). Therefore, as a result of detailed studies, it has been clarified that the problem of thermal degradation is greatly improved by using the complex oxide structure to which the element M is added. That is, by combining the element M, the heat resistance of the composite oxide having a cerium oxide structure partially substituted with the transition metal element T (for example, Fe) is improved, and the PM combustion temperature is excellent even when subjected to a high temperature thermal history. The reduction effect is maintained. The reason for this is not fully understood at the present time, but it is presumed that the addition of the element M has the effect of suppressing the coarsening of the composite oxide particles due to heat.

X representing the molar ratio of the transition metal element T ( specifically Fe) is preferably in the range of 0 <x ≦ 0.6, as indicated by [a] above. When x = 0, that is, when the transition metal element T is not present, high catalytic activity cannot be obtained as described above. When x is larger than 0.6, the transition metal element T ( specifically, Fe) exists in the form of replacing Ce in the cerium oxide structure, and the phase of the cerium oxide structure and the oxide phase of the transition metal element T It is considered that a mixed phase with ( specifically, iron oxide phase) is likely to be formed. Then, since the oxide phase of the transition metal element T ( specifically, the iron oxide phase) has a low catalytic activity for PM combustion, the presence of such a different phase reduces the catalytic activity point of the composite oxide, and the catalytic activity. Is expected to decrease. The range of x is more preferably 0.05 ≦ x ≦ 0.6, and more preferably 0.05 ≦ x ≦ 0.5.

  Y representing the molar ratio of the element M is preferably in the range of 0 <y ≦ 0.4, as indicated by the above [a]. When y = 0, that is, when the element M does not exist, the effect of suppressing thermal degradation does not occur. When y exceeds 0.4 and the content of element M increases, the coarsening of the composite oxide particles is suppressed, but the particles tend to be excessively necked, and the catalytic activity is reduced by reducing the active point of PM combustion. It is thought that the reduction tends to occur. The range of y is more preferably 0 <y ≦ 0.3, and more preferably 0.01 ≦ y ≦ 0.15.

The composite oxide of the present invention can be produced, for example, by a usual coprecipitation method, an organic complex method, a production method using an amorphous precursor, or the like. Hereinafter, each manufacturing method will be described.
[Co-precipitation method]
In the coprecipitation method, a salt of each element constituting the composite oxide is formed to produce a composite oxide in which the molar ratio of Ce, transition metal element T ( specifically, Fe), and element M is as described above. A raw salt aqueous solution containing an appropriate stoichiometric ratio is prepared, this aqueous solution and a neutralizing agent are mixed and coprecipitated, and the obtained coprecipitate is dried and then heat-treated. Although it does not specifically limit as a salt of each element, For example, organic acid salts, such as inorganic salts, such as a sulfate, nitrate, phosphate, and chloride, acetate, oxalate, etc. can be used. Of these, acetates and nitrates can be preferably used. The raw salt aqueous solution can be prepared by adding the salt of each of the above elements to water so as to achieve the desired stoichiometric ratio and stirring.

  Then, this raw salt aqueous solution and a neutralizing agent are mixed and coprecipitated. The neutralizing agent is not particularly limited, and for example, inorganic bases such as ammonia, caustic soda and caustic potash, and organic bases such as triethylamine and pyridine can be used. Moreover, a neutralizing agent is mixed so that the pH of the slurry produced | generated after adding the neutralizing agent may be 6-14. By mixing in this way, it is possible to obtain a coprecipitate of a hydroxide of each element having good crystallinity.

  The obtained coprecipitate is washed with water as necessary. For example, the coprecipitate is dried by, for example, vacuum drying or ventilation drying, and then heat-treated at, for example, 500 to 1200 ° C., preferably 550 to 1000 ° C. The composite oxide can be obtained. At this time, the atmosphere during the heat treatment is not particularly limited as long as the above complex oxide is generated. For example, in air, nitrogen, argon, hydrogen, and an atmosphere in which water vapor is combined with them, preferably in air. In addition, an atmosphere in nitrogen and a combination thereof with water vapor can be used.

[Organic complex method]
In the organic complex method, for example, a salt that forms an organic complex such as citric acid, malic acid, sodium ethylenediaminetetraacetate, and the salt of each of the aforementioned elements is added to water so as to achieve the desired stoichiometric ratio, and stirred. Can be prepared.
After this raw material aqueous solution is dried to form an organic complex of each of the aforementioned elements, a composite oxide having a desired composition can be obtained by pre-baking and heat treatment.

As the salt of each element, the same salt as in the coprecipitation method can be used. The raw salt aqueous solution is prepared by mixing the raw salt of each element in the desired stoichiometric ratio and dissolving it in water. It can be prepared by mixing with an aqueous solution of the salt that forms. In addition, it is preferable that the mixture ratio of the salt which forms an organic complex is about 1.2-3 mol with respect to 1 mol of complex oxides obtained.
Thereafter, this raw material solution is dried to obtain the aforementioned organic complex. Drying is not particularly limited as long as it is a temperature at which the organic complex does not decompose. Thereby, the above-mentioned organic complex is obtained.

  The obtained organic complex is heat-treated after calcination. Pre-baking may be performed at 250 ° C. or higher, for example, in a vacuum or an inert gas atmosphere. Thereafter, for example, a heat treatment is performed at 500 to 1000 ° C., preferably 550 to 950 ° C., to obtain a composite oxide having a target composition. At this time, the atmosphere during the heat treatment is not particularly limited as long as the above complex oxide is generated. For example, in air, nitrogen, argon, hydrogen, and an atmosphere in which water vapor is combined with them, preferably in air. In addition, an atmosphere in nitrogen and a combination thereof with water vapor can be used.

[Production method using amorphous precursor]
In the production method using an amorphous precursor, a powdery amorphous precursor material containing the above-described elements at a stoichiometric ratio suitable for forming a composite oxide having a target composition is formed at a low temperature. Can be obtained by heat treatment.

  Such an amorphous precursor is prepared by preparing a raw salt aqueous solution containing a salt of each element described above in a stoichiometric ratio suitable for forming a composite oxide having a desired composition, and an alkali carbonate or ammonium ion. It can be obtained by reacting with a precipitating agent such as carbonate containing at a reaction temperature of 60 ° C. or lower and a pH of 6 or higher to produce a precipitated product, and drying the filtrate.

  More specifically, first, an aqueous solution in which water-soluble mineral salts such as nitrates, sulfates, and chlorides of each element are dissolved so as to have a molar ratio of a target composition is prepared. The upper limit of the ion concentration of the constituent element in the liquid for generating the precipitate is determined by the solubility of the salt used, but it is desirable that the crystalline compound of the constituent element does not precipitate. Usually, the total ion concentration of each of the above elements is 0. The range of about 0.01 to 0.60 mol / L is desirable, but in some cases, it may exceed 0.60 mol / L.

  In order to obtain an amorphous precipitate from this liquid, it is preferable to use a precipitating agent composed of a carbonate containing an alkali carbonate or ammonium ion. Examples of such a precipitating agent include sodium carbonate, sodium hydrogen carbonate, ammonium carbonate, Ammonium hydrogen carbonate or the like can be used, and a base such as sodium hydroxide or ammonia can be added as necessary. Further, after forming a precipitate using sodium hydroxide, ammonia or the like, an amorphous suitable for the precursor material for obtaining the composite oxide of the present invention can be obtained by blowing carbon dioxide gas. When obtaining an amorphous precipitate, the pH of the liquid should be controlled in the range of 6-11. In the region where the pH is less than 6, rare earth elements may not form a precipitate, which is inappropriate. On the other hand, in the region where the pH exceeds 11, in the case of the precipitating agent alone, the generated precipitate may not be sufficiently amorphized and a crystalline precipitate such as a hydroxide may be formed. The reaction temperature is preferably 60 ° C. or lower. When the reaction is started at a temperature exceeding 60 ° C., crystalline compound particles of the constituent elements may be formed, which is not preferable because it prevents the precursor material from becoming amorphous.

  The obtained amorphous precursor is washed with water as necessary, dried by vacuum drying or ventilation drying, and then heat treated at, for example, 500 to 1000 ° C., preferably 500 to 800 ° C. An oxide can be obtained. At this time, the atmosphere during the heat treatment is not particularly limited as long as the above complex oxide is generated. For example, in air, nitrogen, argon, hydrogen, and an atmosphere in which water vapor is combined, preferably air. Medium, nitrogen, and an atmosphere that combines them with water vapor can be used.

<Production of catalyst material>
The catalyst materials of each Example and Comparative Example were prepared as follows.
[Examples 1-7]
Cerium nitrate, iron nitrate, and lanthanum nitrate were mixed so that the molar ratio of Ce: Fe: La was as shown in Table 1. Water was added to this mixture so that the total molar concentration of Ce, Fe, and element M (here, La) in the liquid was 0.2 mol / L to obtain a raw material solution. While stirring this solution, the temperature of the solution was adjusted to 15 ° C., and when the temperature reached 15 ° C., the pH was adjusted to 8 while adding ammonium carbonate as a precipitant. The resulting precipitate was collected by filtration, washed with water, and dried at 125 ° C. The obtained powder is called precursor powder.

Next, the precursor powder was heat-treated at 600 ° C. for 2 hours in an air atmosphere and fired. In order to evaluate the heat resistance, the powder after firing was heat-treated at 800 ° C. for 2 hours in an air atmosphere to obtain a catalyst material composed of powder that received a high-temperature heat history. Hereinafter, this heat treatment is referred to as “heat-resistant treatment”.
In the heat-resistant treatment, 3 g of powder was put in an alumina crucible (capacity 50 cc, outer diameter 54 mm, height 43 mm), the crucible was put in a muffle furnace having a furnace temperature of 800 ° C. and held for 2 hours, and then in the atmosphere outside the furnace It was done by the method of rapid cooling.

[Examples 8 and 9]
It was produced under the same conditions as in Examples 1 to 7, except that cerium nitrate, iron nitrate and yttrium sulfate were mixed so that the molar ratio of Ce: Fe: Y would be the value shown in Table 1. Here, Y is the element M.

[Examples 10 to 12]
It was produced under the same conditions as in Example 1 except that cerium nitrate, iron nitrate and cobalt nitrate were mixed so that the molar ratio of Ce: Fe: Co would be the value shown in Table 1. Here, Co becomes the element M.

Example 13
It was produced under the same conditions as in Examples 1 to 7, except that cerium nitrate, iron nitrate, and barium nitrate were mixed so that the molar ratio of Ce: Fe: Ba was a value shown in Table 1. Here, Ba is the element M.

Example 14
It was produced under the same conditions as in Examples 1 to 7, except that cerium nitrate, iron nitrate, lanthanum nitrate, and cobalt nitrate were mixed so that the molar ratio of Ce: Fe: La: Co was the value shown in Table 1. . Here, La and Co become the element M.

Example 15
Prepared under the same conditions as in Examples 1 to 7 except that cerium nitrate, iron nitrate, lanthanum nitrate and barium nitrate were mixed so that the molar ratio of Ce: Fe: La: Ba was the value shown in Table 1. . Here, La and Ba are the elements M.

[Comparative Example 1]
Commercially available γ-alumina (specific surface area 250 m ² / g) was impregnated with Pt using a dinitrodiamine platinum aqueous solution, and then air-dried at 90 ° C. for 12 hours. The obtained impregnated product was heat-treated at 500 ° C. for 1 hour in an air atmosphere to obtain Pt-supported alumina. This was subjected to the same heat treatment as in Examples 1 to 7 to obtain a test catalyst material. The catalyst material after the heat resistance treatment had a Pt content in alumina of 3.42% by mass.

[Comparative Examples 2 and 3]
It was produced under the same conditions as in Examples 1 to 7 except that cerium nitrate and iron nitrate were mixed so that the molar ratio of Ce: Fe was the value shown in Table 1. Here, an element to be the element M is not added.

The following experiment was conducted using the catalyst material obtained as described above.
<< X-ray diffraction measurement >>
X-ray diffraction measurement was performed on the catalyst materials (except for Comparative Example 1) obtained in each Example and Comparative Example. The measurement conditions are as follows.
X-ray diffractometer: RINT-2100 manufactured by Rigaku Corporation
・ Measurement range: 2θ = 10-90 °
-Tube: Co tube-Tube voltage: 40 kV
・ Tube current: 30mA
As a result of the measurement, it was confirmed that all of the catalyst materials (after heat-resistant treatment) obtained in each example except Comparative Example 1 were complex oxides having a CeO ₂ structure.
FIG. 1 illustrates an X-ray diffraction pattern for the catalyst material of Example 1.

《PM combustion temperature evaluation using powder sample》
Each embodiment, for the catalyst material obtained in Comparative Example, create a mixed powder of carbon black were evaluated PM combustion temperature by determining the carbon black combustion temperature T _90. Specifically, it was as follows.
Commercially available carbon black (Mitsubishi Chemical) was used as a simulated PM, weighed so that the mass ratio of the catalyst material powder to carbon black would be 6: 1, and 20 minutes with an automatic mortar machine (AGA type manufactured by Ishikawa Factory). Mixing was performed to obtain a mixed powder of carbon black and each powder. The mixed powder was subjected to thermogravimetry (TG), and the combustion temperature of carbon black was determined from the weight loss associated with the combustion of carbon black. The evaluation method uses a TG / DTA device (TG / DTA 6300 type, manufactured by Seiko Instruments Inc.), and after 20 mg of the mixed powder is brought to a constant temperature of 50 ° C., the temperature is increased from 50 ° C. to 700 ° C. at a temperature rising rate of 10 ° C./min. The temperature was raised and the weight was measured. FIG. 2 schematically shows a weight change curve (TG curve). Carbon black combustion temperature T ₉₀ is defined as the temperature at which the weight change occurs 90% change in weight from 50 ° C. of the TG curve up to 700 ° C.. By setting the combustion temperature at the time when a weight change of 90% occurs, it is possible to evaluate the temperature at which almost the entire amount of carbon black burns.
The results are shown in Table 1.

From the test results shown in Table 1, the composite oxide of Ce and a transition metal element Fe (Comparative Examples 2 and 3) is significantly reduced the carbon black combustion temperature T ₉₀ as compared to a Pt catalyst (Comparative Example 1) Yes. That is, according to the composite oxide of Ce and the transition metal element Fe, the PM combustion temperature can be significantly reduced. However, in the case of using a composite oxide of each example having the subject of the present invention is seen more reduction in significant T _90.

The composite oxide of each example contains the element M in addition to Ce and the transition metal element Fe. It is considered that the inclusion of this element M improved the heat resistance of the composite oxide, and as a result, the carbon black combustion temperature was greatly reduced.
FIG. 3 shows a TEM photograph of the composite oxide obtained in Example 1. FIG. 4 shows a TEM photograph of the composite oxide obtained in Comparative Example 2. These composite oxides are subjected to a heat-resistant treatment in which the fired powder is heated at 800 ° C. for 2 hours. It can be seen that the particles in FIG. 3 to which the element M is added are suppressed from coarsening as compared to those in FIG. 4 to which the element M is not added. From this, when element M is added, coarsening due to high-temperature thermal history is prevented, and the reduction of active sites for combustion of carbon black is suppressed, so that excellent catalytic activity is maintained even after heat treatment. it is conceivable that.

As described above, in the composite oxide of Ce and the transition metal element Fe, by replacing a part of the cerium atom of the cerium oxide structure with an iron atom, the appearance of the cation of the composite oxide mainly containing cerium is apparent. As a result, the oxygen in the lattice is easily released out of the lattice, and the catalytic activity for PM combustion is improved by the oxidizing power of the oxygen. It is considered a thing. It is thought that the element M is further added to the complex oxide which is the object of the present invention, and the element M also substitutes a part of the cerium atom and contributes to the above apparent valence change and lattice distortion. this is also considered can be a factor that led to further reduction of the carbon black combustion temperature T _90.

<< Evaluation of PM combustion temperature by granular sample >>
The powder of each catalyst material obtained in Example 4, Example 11 and Comparative Example 2 (after heat-resistant treatment) was compression molded at 100 kg / cm ² by a mold press and then pulverized to produce particles. A granular sample having a diameter of 0.5 to 1.0 mm was produced. Carbon black was added to this granular sample so that it might become 5 mass%, and these were mixed by rotating in a glass bottle.

The granular sample mixed with carbon black is filled in a flow-type fixed bed, and a simulated diesel engine exhaust gas of “500 ppm NO + 10% O ₂ + remaining N ₂ ” is circulated at a space velocity of SV75000 / h, and the temperature rising rate is 10 ° C. / The CO ₂ concentration discharged from the flow-through fixed bed was continuously measured while the temperature was raised from room temperature to 800 ° C. in min. The measurement of the CO ₂ concentration was performed using Nicolet 4700FT-IR manufactured by NICOLET.
FIG. 5 schematically shows a curve representing changes in the CO ₂ concentration discharged. The temperature at the time when the total emission amount of CO ₂ becomes 90% (the hatched area in FIG. 5) with respect to the total generation amount of CO ₂ emitted from the flow-through fixed bed was obtained as the carbon black combustion temperature here. .
The results are shown in Table 2.

As shown in Table 2, when the catalyst material of the example made of the composite oxide to which the element M was added was used, the catalyst material of the comparative example to which the element M was not added even in the granulated state. compared with the case of using carbon black combustion temperature as seen from the emission of CO ₂ is decreased. From this, it can be said that the catalyst material of the example has high practical performance compared to the catalyst material to which the element M is not added.

The X-ray-diffraction pattern about complex oxide (after heat-resistant process) obtained in Example 1. FIG. The figure which showed the TG curve typically. 4 is a TEM photograph of the complex oxide (after heat treatment) obtained in Example 1. 4 is a TEM photograph of the composite oxide (after heat treatment) obtained in Comparative Example 2. Graph schematically showing the change in emission CO ₂ concentration at the time of the carbon black combustion in a simulated diesel exhaust gas.

Claims (3)

Ce, a transition metal element T, and one or more elemental M, is composed of oxygen, Ce, the molar ratio of the transition metal elements T and the element M satisfies the following [a] PM combustion catalyst composite oxide.
[A] When the molar ratio of Ce, transition metal element T and element M is Ce: T: M = (1-xy): x: y, 0 <x ≦ 0.6, 0 <y ≦ 0.4, x + y <1 holds.
However , the transition metal element T is Fe, and the element M is an element selected from an element group consisting of La, Y, Co, and Ba . A PM combustion catalyst using the composite oxide according to claim 1 as a catalyst material. A diesel exhaust gas purification filter using the catalyst according to claim 2 .