JP5154890B2 - Complex oxide for exhaust gas purification and exhaust gas purification filter for diesel engine - Google Patents

Description

  The present invention relates to a composite oxidation for purifying exhaust gas for burning particulate matter (hereinafter sometimes referred to as “PM” (Particulate Matter)) discharged from a diesel engine or the like for use in automobiles. And a filter for purifying exhaust gas of a diesel engine using the same.

Regarding exhaust gas from diesel engines, nitrogen oxide (NO _x ) and PM are particularly problematic. Among these, PM is fine particles mainly composed of carbon. As a method for removing the PM, a method of installing a diesel particulate filter (hereinafter sometimes referred to as DPF) in an exhaust gas flow path and trapping the diesel particulate filter is being generalized. PM trapped in the DPF is burned intermittently or continuously. Then, the DPF is regenerated by burning and removing the PM. This is the DPF regeneration process.

In this DPF regeneration process, an electric heater, a burner or the like is installed and PM is burned by external heating, an oxidation catalyst is installed on the engine side from the DPF, and NO in the exhaust gas is converted to NO ₂ by the oxidation catalyst. and to a method for combusting PM by oxidizing power of the NO _2, and coexist _the NO _X storage catalyst DPF, the active oxygen produced during the absorption and desorption of the NO _X by the air-fuel ratio and a method for combusting PM, there is.

However, the method of installing an electric heater, a burner or the like has a problem that it is necessary to apply energy from the outside, and the regeneration of the system and the DPF becomes complicated. On the other hand, the method of installing the oxidation catalyst has a low activity of the oxidation catalyst because the exhaust gas temperature is low. For this reason, there is a problem that, unless the operating condition is constant, it is not possible to oxidize NO and secure the amount of NO ₂ required for PM combustion in the exhaust gas. Further, the reduction NO _X in the exhaust gas by the exhaust gas regulations enhancement to NO _X future, sufficient NO ₂ is also expected not be obtained. On the other hand, in the method in which the NO _X storage catalyst coexists, there is a problem that the NO _X storage and release ability is reduced by the sulfur contained in the exhaust gas, and the PM combustion activity is also reduced.

  As described above, each method has various problems. Under such circumstances, the catalyst is supported on the DPF, and the catalytic combustion lowers the combustion start temperature of PM, and the PM is continuously burned at the fuel exhaust gas temperature, and is durable against toxic substances such as sulfur. A certain catalyst system is considered.

As a method along this direction, Patent Document 1 discloses a DPF carrying Pt as a catalyst.
Patent Document 2 discloses a zirconium-based composite oxide or a cerium-based composite oxide that does not contain a platinum group metal element as a catalyst. Since these complex oxides release active oxygen (O ²⁻ ) due to oxygen ion conductivity, this active oxygen is supposed to burn PM at a low temperature.

Japanese Patent Laid-Open No. 11-253757 JP 2007-54713 A

According to the description of these patent documents, the PM combustion catalysts described in Patent Documents 1 and 2 are said to be able to burn PM at a relatively low temperature.
However, according to the study by the present inventors, in the method described in Patent Document 1, although the temperature level of the exhaust gas is low, Pt is supported but the supported Pt burns PM. The effect does not increase. Moreover, those carrying Pt has a high ability to oxidize NO to NO _2, but the combustion action of the PM using NO ₂ can be expected, as described above, the exhaust gas by the exhaust gas regulations enhancement to NO _X after since the nO _X in which is reduced, a sufficient nO ₂ is also expected not be obtained. Therefore, it was considered difficult to continuously burn PM at the fuel exhaust gas temperature. Moreover, since Pt is a noble metal, the cost increase resulting from the use of Pt has also been a problem to be solved.

  On the other hand, the PM combustion catalyst described in Patent Document 2 is supposed to be able to burn PM at a relatively low temperature. However, it has been found that the catalyst is liable to be poisoned and deteriorated by sulfur components generally contained in the fuel and also in the exhaust gas, and the PM combustion activity is lowered.

  The present invention has been made under the above-described circumstances, and the problem to be solved is that PM combustion activity for poisoning by sulfur contained in exhaust gas of a diesel engine can be solved without using a noble metal such as Pt. It is an object of the present invention to provide a catalyst capable of suppressing the decrease and burning PM at a low temperature, and a filter for purifying exhaust gas from a diesel engine using the catalyst.

The present inventors have found that the results of intensive studies in order to solve the above problems, and at least one element of A alkaline earth, composite oxide for exhaust gas purification comprising an acidic element or amphoteric element, diesel The present invention was completed by discovering that the decrease in PM combustion activity due to poisoning by sulfur contained in engine exhaust gas is suppressed, and that the conditions for a catalyst capable of burning PM at a low temperature are satisfied.
In addition, an acidic element is an element in which the oxide of the said element shows acidity, and an amphoteric element is an element in which the oxide of the said element shows both acidity and alkalinity.

That is, the first invention for solving the above-described problem is
A complex oxide for purifying exhaust gas that burns and removes particulate matter discharged from a diesel engine,
At least one element A selected from the alkaline earth metals barium and strontium;
Bismuth being an acidic element, or at least one element selected from bismuth being an acidic element and an amphoteric element, and an element B being
The element A and the element B are represented by the general formula:
A _(1-x) B _x O _δ (where, x and δ in the formula indicate 0 <x ≦ 0.9 and 0 <δ <10).
It is a complex oxide for exhaust gas purification characterized by satisfying the above.

The second invention is
The amphoteric element is at least one selected from the group consisting of titanium, zirconium, aluminum, gallium, indium and tin. The exhaust gas purifying composite oxide according to the first aspect of the invention is there.

The third invention is
The amphoteric element is zirconium and / or aluminum. The composite oxide for purifying exhaust gas according to the first aspect of the invention .

The fourth invention is:
The composite oxide for purifying exhaust gas according to any one of the first to third inventions, wherein the combustion activity is high with respect to the particulate matter and the oxidation activity with respect to sulfurous acid gas is low.

The fifth invention is:
An exhaust gas purifying filter for a diesel engine, characterized in that the composite oxide for purifying exhaust gas according to any one of the first to fourth inventions is used.

The sixth invention is:
The diesel engine exhaust gas purifying filter according to the fifth aspect of the present invention further contains at least one element selected from the group consisting of Pt, Rh and Pd.

  The composite oxide for purifying exhaust gas according to the present invention can combust PM at a low temperature without containing a noble metal such as Pt, and exhibits PM combustion activity due to sulfur poisoning contained in diesel engine exhaust gas. The decrease is suppressed.

  The composite oxide for purifying exhaust gas according to the present invention can be composed of a composite oxide containing at least one of an alkali metal and an alkaline earth metal and at least one of an acidic element and an amphoteric element.

Here, it is preferable to use one or both of potassium and cesium as the alkali metal. As the alkaline earth metal element, it is preferable to use barium, strontium, calcium or magnesium, and any combination thereof, and more preferably one of strontium and barium, or a mixture thereof.
On the other hand, bismuth is preferably used as the acidic element. Further, as the amphoteric element, it is preferable to use titanium, zirconium, aluminum, gallium, indium or tin, and those related to any combination thereof, and more preferably one of zirconium and aluminum or a mixture thereof. .

In the exhaust gas purifying composite oxide, at least one element A selected from alkali metals and alkaline earth metals, and at least one element B selected from acidic elements and amphoteric elements; Is a composite oxide satisfying the following general formula: A _(1-x) B _x O _δ (where x and δ represent 0 <x ≦ 0.9 and 0 <δ <10) More preferably.

  According to the study by the present inventors, the coexistence of A and B in the range of 0 <x ≦ 0.9 allows the coverage by sulfur contained in the exhaust gas of diesel engine without using noble metals such as Pt. It has been found that it is difficult to be poisoned and that PM can be burned at a low temperature. It was also found that the range of 0 <x ≦ 0.8 is more preferable.

  On the other hand, when x = 0, that is, an oxide of an alkali or alkaline earth metal element, the affinity of the oxide to an acidic gas is strong. Therefore, when the oxide is exposed to the exhaust gas of a diesel engine for a long time, the poisoning deterioration is likely to proceed, and the PM combustion activity may be lowered. Therefore, it is preferable that x ≠ 0.

  It has been found that the complex oxide for purifying exhaust gas according to the present invention has excellent PM oxidation activity due to the action of the complex oxide composed of the above elements, and can reduce the PM combustion temperature. Although the mechanism of this excellent oxidation activity for PM is not necessarily clear, it is considered that this is because the oxygen storage / release ability on the surface of the composite oxide is excellent.

On the other hand, it has been found that the complex oxide for purifying exhaust gas according to the present invention has low oxidation activity with respect to sulfurous acid gas. As will be apparent from the experimental data described later, sulfur adsorption is very difficult to occur on the surface of the composite oxide. Therefore, it can be seen that the exhaust gas purifying composite oxide according to the present invention has low oxidation activity with respect to sulfurous acid gas.
This is because the mechanism of the adsorption of sulfurous acid gas (SO ₂ ) is that, in an oxygen-containing atmosphere, SO ₂ is oxidized to SO ₃ , and the SO ₃ is unstable. It is because it is considered that it is what adsorbs by taking.

A method of applying the exhaust gas purifying composite oxide according to the present invention to a DPF will be described.
First, the particle size of the composite oxide is adjusted to a particle size suitable for the pore diameter of the DPF base material and the roughness of the inner wall surface of the DPF, such as cordierite and SiC. Next, the composite oxide with adjusted particle size is dispersed in a solvent such as pure water to produce a slurry. The slurry is brought into contact with the DPF inner wall using a general method such as impregnation. After the contact, water as a solvent is removed by blowing with gas or the like, and then the slurry is dried and fired. However, the firing is not necessarily performed.

It is also preferable that the DPF according to the present invention further contains a platinum group element.
The platinum group element is preferably at least one of platinum, rhodium, and palladium.
This is because when DPF regeneration or NO _X storage catalyst regeneration, fuel is injected into the exhaust gas and the fuel is combusted. Compared to normal operation, carbon monoxide, carbonization in the exhaust gas is performed. The ratio of hydrogen increases. Further, when PM is burned by the purification catalyst component, carbon monoxide may be generated due to incomplete combustion. Therefore, it is considered that a structure including a platinum group element for purifying these carbon monoxide and hydrocarbon is considered preferable.

The platinum group element used may be present at any position on the engine side, in the DPF from the DPF, or on the atmosphere release side from the DPF, but preferably in the DPF or on the atmosphere release side from the DPF. Since the platinum group element is required to purify carbon monoxide or hydrocarbon gas, it is preferably supported in a highly dispersed state. The supporting method in the highly dispersed state may be a general method such as evaporation to dryness or impregnation, and the supporting method is not particularly limited.

  The composite oxide for purifying exhaust gas according to the present invention can be produced by, for example, a usual coprecipitation method, an organic complex method, an amorphous precursor, a production method using a solid phase method, or the like. Hereinafter, each manufacturing method will be described.

[Co-precipitation method]
In the coprecipitation method, first, a raw salt aqueous solution containing each element suitable for producing a desired composite oxide in a stoichiometric ratio is prepared, and this aqueous solution and a neutralizing agent are mixed to produce a coprecipitate. . And the obtained coprecipitate is heat-processed after drying.
At this time, the form of the salt of each element used as a raw material is not particularly limited. For example, inorganic salts such as sulfates, nitrates, phosphates and chlorides, and organic acid salts such as acetates and oxalates are used. it can. Of these, acetates and nitrates can be preferably used. The raw salt aqueous solution can be prepared by adding and stirring the above-mentioned salt of each element that has been weighed and mixed so that the desired stoichiometric ratio is obtained.

  Next, this raw material 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. The amount of the neutralizing agent to be added and mixed is adjusted so that the pH of the slurry produced after adding the neutralizing agent is 6 to 14. A coprecipitate can be obtained by mixing in this way.

  The obtained coprecipitate is washed with water as necessary, dried using vacuum drying, ventilation drying or the like, and then heat-treated at, for example, 600 to 1200 ° C., preferably 800 to 1000 ° C. for 2 to 10 hours. Thus, the exhaust gas purifying composite oxide according to the present invention can be obtained. At this time, the atmosphere during the heat treatment is not particularly limited as long as it is within the range of generating the composite oxide of the coexisting substances and the purification catalyst component. For example, the atmosphere in air, nitrogen, argon, hydrogen, and a combination thereof Preferably, an atmosphere in air, nitrogen, and a combination thereof with water vapor can be used.

[Organic complex method]
In the organic complex method, first, a salt that forms an organic complex such as citric acid, malic acid, sodium ethylenediaminetetraacetate, and the salt of each of the above elements is added to water so as to have a desired stoichiometric ratio, A raw material aqueous solution is prepared by stirring.
The aqueous raw material solution is heated to dryness to form an organic complex of each element described above, and then calcined and heat-treated to obtain the exhaust gas purifying composite oxide according to the present invention.

In addition, as a salt of each element, the same salt as in the case of the coprecipitation method can be used.
The raw salt aqueous solution can be prepared by mixing the raw salt of each element in the desired stoichiometric ratio and dissolving it in water, and then mixing with an aqueous salt solution that forms an organic complex. In addition, it is preferable that the compounding ratio of the salt which forms an organic complex is about 1.2-3 mol with respect to 1 mol of complex oxides obtained.
Then, this raw material solution is heated and dried to obtain the aforementioned organic complex. Heating is not particularly limited as long as the organic complex is not decomposed. For example, the water is rapidly removed at room temperature to about 150 ° C., preferably at room temperature to 110 ° C. Thereby, the above-mentioned organic complex is obtained.

The obtained organic complex is heat-treated after pre-baking.
Specifically, the preliminary baking is performed by heating at 250 ° C. or higher in a vacuum or an inert gas atmosphere. After the preliminary calcination, the exhaust gas purifying composite oxide according to the present invention can be obtained by heat treatment at 600 to 1000 ° C., preferably 600 to 950 ° C. for 2 to 10 hours. The atmosphere at the time of heat treatment is not particularly limited as long as it is within a range that can produce a composite oxide. For example, an atmosphere in which air, nitrogen, argon, hydrogen, and water vapor are combined with these is preferably air, nitrogen. , And a combination of them with water vapor can be used.

[Production method using amorphous precursor]
In the production method using an amorphous precursor, each of the aforementioned elements is contained in a stoichiometric ratio suitable for forming a desired composite oxide, and the precursor that is an amorphous powder is subjected to low-temperature heat treatment. Can be obtained.

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

  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 desired composition molar ratio is prepared. The upper limit of the ion concentration of each constituent element in the liquid for generating the precipitate is determined by the solubility of the salt used, but a concentration at which the crystalline compound of the constituent element does not precipitate is desirable. Furthermore, it is usually desirable that the total ion concentration of each of the above-mentioned elements be in the range of about 0.01 to 0.60 mol / L, but in some cases it may exceed 0.60 mol / L.

  In order to obtain an amorphous precursor from the above solution, it is preferable to use a precipitating agent made of carbonate containing alkali carbonate or ammonium ion. As a specific precipitant, 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.

When obtaining an amorphous precursor, the pH of the liquid is preferably controlled in the range of 6-11. In the region where the pH is 6 or more, rare earth elements also form a precipitate, which is preferable. On the other hand, in the region where the pH is 11 or less, even when the precipitating agent is used alone, the resulting precipitate is preferably amorphized sufficiently and is preferable.
Here, when a precipitate is formed using a base such as sodium hydroxide or ammonia, the pH of the liquid may be controlled in the range of 6 to 11 by blowing carbon dioxide gas.
On the other hand, the reaction temperature is preferably 60 ° C. or lower. If it is 60 degrees C or less, the crystalline compound particle | grains of a constituent element may not be produced | generated, and amorphousization of a precursor substance is not prevented, and it is preferable.

The obtained amorphous precursor is washed with water as necessary, dried by vacuum drying or ventilation drying, and then heat-treated at 500 to 1000 ° C., preferably 600 to 900 ° C. for 2 to 10 hours, The composite oxide for purifying exhaust gas according to the present invention can be obtained.
The atmosphere at the time of heat treatment is not particularly limited as long as it is within a range that can produce a composite oxide. For example, an atmosphere in which air, nitrogen, argon, hydrogen, and water vapor are combined with these is preferably air, nitrogen. , And a combination of them with water vapor can be used.

[Solid phase method]
In the solid phase method, first, a raw material salt containing an element suitable for generating a desired composite oxide in a stoichiometric ratio is prepared.
There are various raw material salts such as nitrates, carbonates, oxides, and acetates, but there is no particular limitation as long as the heat treatment causes crystallization of the target coexisting complex oxide or purification catalyst component. . Mixing is performed using a mixer such as a mortar.

By heat-treating the obtained raw material salt at 500 to 1000 ° C., preferably 700 to 900 ° C. for 2 to 30 hours, the composite oxide for exhaust gas purification according to the present invention can be obtained.
The atmosphere at the time of heat treatment is not particularly limited as long as it is within a range that can produce a composite oxide. For example, an atmosphere in which air, nitrogen, argon, hydrogen, and water vapor are combined with these is preferably air, nitrogen. , And a combination of them with water vapor can be used.

[Measurement and evaluation method]
A measurement / evaluation method that can be carried out on the physical properties, crystal structure, durability against sulfur, and PM combustion performance of the above-described composite oxide for exhaust gas purification according to the present invention will be described.

<X-ray diffraction measurement>
X-ray diffractometer (measured using Rigaku Corporation, X-ray diffractometer RINT-2100.
The measurement conditions are: measurement range: 2θ = range of 20 to 70 degrees, tube: Co tube, tube voltage: 40 kV, tube current: 30 mA.

<Sulfur poisoning treatment material>
Using a mold press, the composite oxide is compression molded at 100 kg / cm ² and then pulverized to produce a granular sample having a particle size of 1.0 to 2.0 mm.
3 g of the granular sample was placed in a vertical tubular furnace, and under a processing condition of 300 ° C. × 10 hours, SO ₂ 200 ppm, O ₂ 10%, H ₂ O 10%, and the balance N ₂ gas at a flow rate of 500 cc / min. The sulfur poisoning treatment was carried out to obtain a sulfur poisoning treatment material. The sulfur poisoning treatment material is pulverized in a mortar.

<PM combustion temperature evaluation with composite oxide sample and sulfur poisoning treatment material>
As a simulated PM, commercially available carbon black (CB) (manufactured by Mitsubishi Chemical Corporation) is used, so that the mass ratio of each sample of composite oxide and sulfur poisoning treatment to carbon black is 6: 1. And mixed with an automatic mortar machine (AGA type manufactured by Ishikawa Factory) for 20 minutes to obtain a mixed powder of carbon black and each sample.
Next, the combustion start temperature of the carbon black is determined from the mass reduction associated with the combustion of the carbon black in each mixed powder by thermal mass measurement (TG). For the TG measurement, a TG / DTA apparatus (manufactured by Seiko Instruments Inc., TG / DTA6300 type) was used. Warm and measure mass. The combustion temperature of carbon black is the point at which the peak intensity of DTA is maximized.

<Analysis of adsorbed sulfur amount by sulfur poisoning treatment material>
Quantitative analysis of the amount of adsorbed sulfur of the sulfur-poisoned treatment material prepared in the above-described “PM oxide temperature evaluation by composite oxide sample, sulfur-poisoned treatment material” is performed.
A carbon / sulfur analyzer (EMIA-220V manufactured by HORIBA) can be used for the quantitative analysis.

Example 1
Barium nitrate and bismuth nitrate are mixed so that the molar ratio of barium element and bismuth element is 0.5: 0.5, and a raw material aqueous solution in which the total molar concentration in the liquid is 0.2 mol / L is prepared. did.
While stirring this aqueous solution, the temperature of the aqueous solution was adjusted to 25 ° C., and when the temperature reached 25 ° C., ammonium carbonate was added as a precipitating agent to adjust the pH to 8 to produce a precipitate. The obtained precipitate was collected by filtration, washed with water, and dried at 125 ° C. to obtain a precursor powder. Next, the precursor powder was baked by heat treatment at 800 ° C. for 5 hours in an air atmosphere to obtain an exhaust gas purifying composite oxide according to Example 1. The X-ray diffraction pattern of the composite oxide according to Example 1 is shown in FIG.

(Example 2)
The composite oxide according to Example 2 was obtained by performing the same operation as in Example 1 except that barium nitrate was replaced with strontium nitrate and the molar ratio of the strontium element to the bismuth element was 0.2: 0.8. Obtained. FIG. 2 shows an X-ray diffraction pattern of the complex oxide for exhaust gas purification according to Example 2.

(Example 3)
Exhaust gas purification according to Example 3, except that barium nitrate was replaced with strontium nitrate and the molar ratio of strontium and bismuth elements was 0.3: 0.7 A composite oxide was obtained.

Example 4
Barium nitrate, zirconium oxynitrate, and bismuth nitrate are mixed so that the molar ratio of barium element, zirconium element, and bismuth element is 1.0: 0.8: 0.2. A raw material aqueous solution having a total molar concentration of 0.2 mol / L was prepared.
In the subsequent steps, the same operation as in Example 1 was performed to obtain a composite oxide for exhaust gas purification according to Example 4.

(Comparative Example 1)
A 0.2 mol / L feed solution of cerium nitrate was prepared.
While stirring this aqueous solution, the temperature of the aqueous solution was adjusted to 25 ° C., and when the temperature reached 25 ° C., ammonium carbonate was added as a precipitating agent to adjust the pH to 8 to produce a precipitate. The obtained precipitate was collected by filtration, washed with water, and dried at 125 ° C. to obtain a precursor powder. Next, the precursor powder was heat-treated at 800 ° C. for 2 hours in an air atmosphere and fired to obtain cerium oxide according to Comparative Example 1.

(Comparative Example 2)
30 g of commercially available γ-alumina (specific surface area 250 m ² / g) (PURALOX SCFa140 manufactured by SASOL), 3.6 g of dinitrodiammine platinum aqueous solution (produced by Tanaka Kikinzoku Kogyo Co., Ltd.) and 285 g of pure water Was immersed in an aqueous solution of dinitrodiammine platinum mixed at 25 ° C. for 15 hours to impregnate γ-alumina with Pt. After collecting the γ-alumina, it was dried by ventilation at 90 ° C. for 12 hours, and further heat-treated at 500 ° C. for 1 hour in an air atmosphere to obtain a Pt-supported alumina having a Pt content of 1.0 mass% according to Comparative Example 2. Obtained.

(Evaluation)
For the composite oxide samples according to Examples 1 to 4 and the oxide sample according to Comparative Example 1, the above-described “PM combustion temperature evaluation using a composite oxide and a sulfur poisoning treatment material” was performed, and subsequently “sulfur” Analysis of the amount of adsorbed sulfur by poisoning materials ”was performed. On the other hand, for the Pt-supported alumina sample according to Comparative Example 2, the above-described “PM combustion temperature evaluation using a composite oxide and sulfur poisoning treatment material” was performed.
Among the evaluation results, the PM combustion temperature evaluation results and the adsorbed sulfur amount analysis results of the composite oxide and sulfur poisoning treatment material are shown in Table 1 and FIG.
However, FIG. 3 is a bar graph in which the horizontal axis represents the sample name and the vertical axis represents the carbon black (CB) combustion temperature, with the diagonal line before the sulfur poisoning treatment and the solid color after the sulfur poisoning treatment.

From Table 1 and FIG. 3, the complex oxides according to Examples 1 to 4 have different PM combustion temperatures before the sulfur poisoning treatment. However, the temperature difference between the PM combustion temperatures before and after the sulfur poisoning treatment is 15 ° C. or less. That is, it was found that the PM combustion temperature was hardly increased by the sulfur poisoning treatment.
On the other hand, in Comparative Example 1, the increase in PM combustion temperature due to sulfur poisoning treatment exceeded 160 ° C. That is, it was found that the increase in PM combustion temperature due to the sulfur poisoning treatment was remarkable. Furthermore, in Comparative Example 2, the PM combustion temperature was high both before and after the sulfur poisoning treatment, and the increase in the PM combustion temperature due to the sulfur poisoning treatment was 65 ° C.

The PM combustion temperature evaluation result explained above will be examined from the result of the adsorption sulfur amount analysis.
Then, in the composite oxides according to Examples 1 to 4, the maximum adsorption amount of sulfur was 0.27% by mass, whereas in the oxide according to Comparative Example 1, 0.69% by mass of sulfur was adsorbed. It has been found.

As described above, the adsorption of sulfurous acid gas (SO ₂ ) is considered to proceed when SO ₂ is oxidized by the catalyst to become SO _{3 and} adsorbed as the sulfate. Here, since the composite oxides according to Examples 1 to 4 have low oxidation activity with respect to SO ₂ , the amount of adsorbed sulfur after the sulfur poisoning treatment is low, and as a result, it is considered strong against sulfur poisoning. . On the other hand, since the oxide according to Comparative Example 1 has high oxidizing power against SO ₂ , it is considered that sulfur is easily adsorbed.
This data is also considered to support that the composite oxides according to Examples 1 to 4 are more resistant to sulfur poisoning than the composite oxide according to Comparative Example 1.

From the above, the exhaust gas purifying material according to the present invention which is a composite oxide containing at least one of alkali and alkaline earth and an acidic element or an amphoteric element exhibits high PM combustion activity, and sulfur in the exhaust gas. It has been found that since the oxidizing power for the components is low and sulfur is hardly adsorbed, the PM combustion activity is hardly reduced due to sulfur poisoning.
Furthermore, the exhaust gas purification material according to the present invention has a lower PM combustion temperature before and after the sulfur poisoning treatment and a smaller increase in PM combustion temperature due to the sulfur poisoning treatment than the Pt-supported alumina type exhaust gas purification material. There was found.

2 is an X-ray diffraction pattern of a complex oxide according to Example 1. FIG. 3 is an X-ray diffraction pattern of a composite oxide according to Example 2. FIG. It is a graph which shows the combustion temperature of carbon black before and behind sulfur treatment of the complex oxide which concerns on an Example and a comparative example.

Claims (6)

A complex oxide for purifying exhaust gas that burns and removes particulate matter discharged from a diesel engine,
At least one element A selected from the alkaline earth metals barium and strontium;
Bismuth being an acidic element, or at least one element selected from bismuth being an acidic element and an amphoteric element, and an element B being
The element A and the element B are represented by the general formula:
A _(1-x) B _x O _δ (where, x and δ in the formula indicate 0 <x ≦ 0.9 and 0 <δ <10).
A composite oxide for exhaust gas purification characterized by satisfying The exhaust gas purifying composite oxide according to claim 1, wherein the amphoteric element is at least one selected from the group consisting of titanium, zirconium, aluminum, gallium, indium and tin. 2. The composite oxide for exhaust gas purification according to claim 1, wherein the amphoteric element is zirconium and / or aluminum. The composite oxide for exhaust gas purification according to any one of claims 1 to 3, wherein the particulate matter has high combustion activity and low oxidation activity to sulfurous acid gas. An exhaust gas purification filter for a diesel engine, wherein the composite oxide for exhaust gas purification according to any one of claims 1 to 4 is used. The exhaust gas purification filter for a diesel engine according to claim 5, further comprising at least one element selected from the group consisting of Pt, Rh and Pd.

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