JPH05138025A - Exhaust gas purifying material and method - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purifying material capable of burning and removing the particulate contained in the exhaust gas discharged from a diesel engine. CONSTITUTION:In an exhaust gas purifying material constituted by supporting a catalyst on a heat-resistant porous filter, the catalyst consists of one or more kind of an element (a) selected from a group consisting of Cs, K and Na, a Cu element and an Mo element (b) and one or more kind of an element (c) selected from Ca and La.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material and an exhaust gas purifying method using the exhaust gas purifying material. More specifically, the particulate carbonized material (hereinafter referred to as particulates) in the exhaust gas of a diesel engine or the like is efficiently used. The present invention relates to an exhaust gas purification material that can be removed well, and an exhaust gas purification method using the exhaust gas purification material.

[0002]

2. Description of the Related Art In recent years,
Particulate carbonaceous substances (mainly composed of solid carbon fine particles, called particulates) in exhaust gas of diesel engines have become a problem in terms of environmental hygiene. This is because particulates have an average particle size of 0.1 to 1 μm and are easily suspended in the atmosphere, so they are easily incorporated into the human body by respiration, and recent clinical test results also contain carcinogens. This is because it was confirmed.

As a method of removing these particulates, the following two methods are roughly studied. One of them is a method of trapping particulates by filtering exhaust gas with a heat-resistant filter, and then burning the trapped particulates by a burner, an electric heater, etc. to regenerate the filter when the pressure loss due to this is increased. is there. Examples of heat-resistant filters used include honeycomb-type ceramic filters, foam-type ceramic filters having a three-dimensional mesh structure, steel wool, and wire mesh.

The other is a method of self-combusting the particulates together with the filtering operation of the particulates by the action of the catalyst carried on the filter as described above.

In the former case, the higher the effect of removing particulates, the faster the pressure loss rises, the more frequently the regeneration occurs, the higher the reliability required for regeneration, and the more economically disadvantageous. On the other hand, the latter method is considered to be a far superior method if there is a catalyst that can retain the catalytic activity under the exhaust gas emission conditions (gas composition and temperature) of the diesel engine. However, the exhaust gas temperature of a diesel engine is lower than that of a gasoline engine, and since light oil is used as the fuel, the amount of SO ₂ in the exhaust gas is large. A regeneration method that satisfactorily ignites and burns particulates accumulated under such exhaust gas conditions and does not cause secondary pollution has not yet been established.

[0006] For example, the combustion reaction of particulates in a heat resistant filter that generally supports only a base metal is usually about
Occurs at temperatures above 400 ° C. In most of the normal operations, the temperature of the exhaust gas is lower than that, and the combustion reaction does not occur, so that the particulates are once captured by the catalyst-carrying filter, and when the temperature rises, the particulates are burned out to regenerate the filter. In the case where only the conventional base metal catalyst is supported in this way, the pressure loss increases rapidly until the temperature reaches a predetermined value, that is, the combustion reaction does not easily occur, and the frequency of combustion regeneration by a burner, an electric heater, etc. becomes high, and it is practical. Lacks. Also, when using a catalyst to which a noble metal is added,
As an initial characteristic, the combustion reaction of particulates is likely to occur at a lower temperature, and the pressure loss rises slowly.
However, at the same time, SO _{2 in} the exhaust gas also oxidizes, which causes very harmful SO ₃ and sulfuric acid mist, which causes secondary pollution.

Under such circumstances, without causing secondary pollution,
Energetic research has been conducted on a method for efficiently burning and removing particulates. For example, Japanese Patent Laid-Open No. 3-118811 discloses an exhaust gas purifying material having a catalyst composed of (a) Cs, (b) Cu, and (c) any one or two of Ce and La. However, although Cu among the catalyst components has high particulate combustion characteristics, there is a problem in that the purification characteristics thereof deteriorate due to SO _{2 in} the exhaust gas.

Therefore, in order to prevent the activity of Cu from decreasing due to SO ₂ , the applicant of the present invention previously disclosed in Japanese Patent Application No. 2-270200 (a) an alkali metal element and (b) Cu and V. (c) An exhaust gas purifying material having a catalyst composed of a rare earth element is proposed. However, according to the study by the present inventors, V
It was found that when Cu is added, the decrease in Cu activity due to SO ₂ can be suppressed, but the combustion reaction of particulates is less likely to occur, and it is not always sufficient to remove particulates efficiently.

Therefore, an object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently burning and removing particulates contained in exhaust gas discharged from a diesel engine or the like.

[0010]

Means for Solving the Problems As a result of intensive studies on purification of particulates in exhaust gas, the present inventors have found that a catalyst composed of a specific alkali metal element, Cu and Mo, and a specific rare earth metal. The present invention was completed by discovering that it is possible to efficiently remove particulates in exhaust gas by burning by using a purifying agent carrying the above.

That is, an exhaust gas purifying material comprising a heat-resistant porous filter carrying a catalyst, wherein the catalyst is (a) Cs
One or two of the elements selected from the group consisting of, K and Na
It is characterized by comprising at least one kind, (b) Cu element and Mo element, and (c) one or two kinds of elements selected from Ce and La.

Further, the exhaust gas purifying method of the present invention is characterized in that the exhaust gas purifying material is used, and particulates in the exhaust gas are oxidized by the catalyst carried on the filter.

The present invention will be described in detail below. As a filter that is the base material of the exhaust gas purification material, it is porous and heat resistant,
Especially those with high thermal shock resistance are used. Further, it is necessary that the pressure loss is within the allowable range and that the particulate collection performance is maintained. Such filter forming materials include alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, ceramic fibers such as cordierite, Examples thereof include, but are not limited to, ceramic foam, ceramic monolith, and metal wire mesh.

As the catalyst supported on the above filter,
(a) one or two of Cs, K and Na, and (b) Cu
And Mo and (c) any one or two of La and Ce are used.

In the present specification, the catalyst components (a) to
Although (c) is shown as a metal element, the catalyst components (a) to (c) exist in the state of oxides under the normal use temperature condition of the purification material.

The above-mentioned catalyst components (a), (b) and (c) are blended in amounts of 10 to 50 parts by weight of (a) and 20 to 400 parts of (b) in terms of their respective metal components. It is preferable to use 10 to 50 parts by weight of (c). The ratio of Cu and Mo in (b) is 1 by weight.
It is preferable to set it to about / 10 to 2/1.

By using the exhaust gas purifying material having the catalyst having the above-mentioned structure, the particulates in the exhaust gas can be effectively burned and removed. That is, the particulate matter in the exhaust gas in the filter is the above-mentioned catalyst component.
By coexisting with the catalyst consisting of (a), (b) and (c) and oxygen, the ignition temperature is lowered, and combustion (oxidation) is efficiently carried out near 400 ° C. In this way, the exhaust gas can be purified at around 400 ° C at all times, and the pressure loss of the filter becomes gentle.

By the way, if the catalyst component (a), Cu and the catalyst component (c) are used in combination, the purification characteristics of the catalyst gradually deteriorate due to the presence of the sulfur oxides contained in the exhaust gas. I will end up. Therefore, in the present invention, by adding Mo, that is, the catalyst component (a), Cu and Mo
By combining with the catalyst component (c), stable combustion characteristics of particulates can be obtained.

Even if V is used instead of Mo, the deterioration of the purification characteristics of the catalyst due to the presence of sulfur oxide can be suppressed, but V
If the addition of is added, the combustion reaction of particulates becomes considerably difficult to occur. On the other hand, when Mo is added, such deterioration of the combustion characteristics of particulates is hardly observed.

Further, the rate of oxidation of particulates increases due to the presence of NOx in the exhaust gas. The above catalyst components
If a catalyst consisting of (a), (b) and (c) is used, at around 400 ° C, the particulates will efficiently react with oxygen in the exhaust gas and be oxidized, while at the same time, some of the particulates will be exhausted. It is oxidized by reacting with NOx in it. That is, part of the particulates acts as a reducing agent to remove NOx from N ₂
It can also be reduced to.

As described above, the catalyst may be supported directly on the filter. However, in order to increase the catalyst supporting area, the catalyst is supported through a carrier layer made of ceramics which is more porous and has a larger surface area than the filter. It is preferably carried indirectly on the filter.

As the material for forming the carrier layer, porous and large surface area ceramics such as titania, alumina, silica, titania-alumina, titania-silica, etc. are used. -20% by weight, particularly 2-15% by weight is preferred. As the catalytically active species, the total is 5 to 20% of that of the carrier.
It is preferably 0% by weight, especially 10 to 150% by weight.

The carrier layer made of ceramics can be formed by a wash coat method or a sol-gel method.

The wash coating method is a method of forming a carrier layer on the filter by immersing the filter in the slurry of the above-mentioned porous ceramic and drying it.

The carrier layer is formed by the sol-gel method as follows. After hydrolyzing an organic salt of a metal (for example, an alkoxide) forming the ceramics for the carrier layer, the obtained sol is coated on a filter, and a film of colloidal particles is formed by contact with steam or the like, followed by drying and firing. To form a catalyst carrier layer on the filter. For example, when titania (TiO ₂ is used as the ceramics for the carrier layer, first, an alkoxide of Ti (for example, Ti (O-iso C ₃ H
₇ ) In an alcohol solution of ₄ , CH ₃ COOH, HNO ₃ , HCl
To produce a coating solution to which an acid such as is added. The filter is dipped in this coating solution, pulled up, and then reacted with water vapor or water to cause gelation. Next, when the filter is dried and fired, a titania film is formed on the pore surface of the filter. In the sol-gel method, an acid is added as a catalyst for the hydrolysis reaction at the time of gelation, but the hydrolysis reaction can be promoted by adding an alkali instead of the acid.

Although titania is used as an example of the ceramics for the carrier layer in the above, other ceramics can be similarly loaded by the sol-gel method. For example, when forming a carrier layer of alumina, aluminum alkoxide is used, and the same method as in the case of titania described above is performed. The same applies when other porous carriers are used.

After the porous carrier layer made of ceramics is formed on the filter by the above-mentioned washcoat method or sol-gel method, the catalytically active species carbonate, nitrate, acetate, hydroxide, etc. are then formed. The catalyst solution is supported by impregnating the carrier layer with the aqueous solution of, and drying and firing again. As the salt of the catalytically active metal species, if it is soluble in water,
As described above, any kind of carbonate, nitrate, acetate, hydroxide and the like can be used. Also, Mo
A solution of molybdate can be used for the loading.

[0028]

The present invention will be described in more detail by the following specific examples. Examples 1 to 4 Commercial diesel exhaust cordierite (ceramics containing magnesia, alumina and silica as main components)
Made foam filter (bulk density 0.65g / cm ³ , porosity 86.0
%, Volume 35 cm ³ ) and TiO 2 by the washcoat method.
₂ was coated on the filter by 10% (% by weight, and so on).

The obtained filter was impregnated with 2.5% of Cs with respect to TiO ₂ using an aqueous solution of CsNO ₃ . Then CuCl
₂ , Ce (NO ₃ ) ₃ and ammonium molybdate ((N
With an aqueous solution of _{H 4) 6 Mo 7 O 24} ), C with respect to TiO ₂
It was impregnated with 10% u, 2.5% Ce and 50% Mo. Prior to use, this catalyst-supporting ceramic filter was dried at 150 ° C. or lower and calcined at 700 ° C. for 3 hours (Example 1). (Hereafter, such an exhaust gas purifying material is expressed as Cs / Cu / Mo / Ce.)

In the same manner as in Example 1, Cs was added to TiO ₂ .
2.5%, Cu 10%, Mo 50% and La (using LaCl ₃ )
A Cs / Cu / Mo / La exhaust gas purification material supporting 2.5% of C was produced (Example 2).

Similarly, K / Cu / Mo / Ce exhaust gas purifying material (Example 3) in which K was supported in place of Cs in Example 1 and K was supported in place of Cs in Example 2 A K / Cu / Mo / La exhaust gas purification material (Example 4) was produced.

The exhaust gas of the diesel engine was passed through each of the exhaust gas purifying materials of Examples 1 to 4 to capture 100 g of particulates. Each of the purification materials that captured particulates was installed in a fixed-bed flow reactor, and a simulated gas (oxygen concentration: 10%, NOx: 800 ppm, SO ₂ : 100 ppm, H ₂ O
Concentration: 10%, N _2: balance) 1.2 l / min was circulated, each purification material heated at a 5 ° C. / minute rate, evaluate the particulate combustion characteristics of the purification material from the amount of CO ₂ did.
The results are shown in Figure 1. The results of Example 1 were almost the same as the results of Example 2, and the results of Example 3 were almost the same as the results of Example 4. That is, the peak showing the amount of CO ₂ produced in Example 1 is almost the same as that in Example 2, and the peak showing the amount of CO ₂ produced in Example 3 is almost the same as that in Example 4. Therefore, in FIG. 1, the results of Example 2 and Example 4 are omitted.

Comparative Example 1 Using the same foam filter as in Example 1, 10% of the TiO ₂ filter was coated by the wash coat method. An aqueous solution of CuCl ₂ and ammonium vanadate was used for the obtained filter, and 10% Cu and V were added to TiO _2.
Supported 40%. The method of supporting each metal was the same as in Example 1.

With respect to the obtained filter, the particulate combustion characteristics of the purifying material were determined in the same manner as in Example 1. The results are shown together with FIG.

As is apparent from FIG. 1, the exhaust gas purifying materials of Examples 1 to 4 have higher particulate combustion characteristics than the exhaust gas purifying material of Comparative Example 1.
Further, in the exhaust gas purifying materials of Examples 1 to 4, it is found that the particulates burn at a temperature near 400 ° C., which is far lower than that of the exhaust gas purifying material of Comparative Example 1.

[0036]

As described above, when the exhaust gas purifying material of the present invention is used, the particulates in the exhaust gas are effectively removed, and the purification is efficiently performed.

Further, since the purifying material of the present invention contains Cu and Mo as transition metals in the catalyst, even if the exhaust gas with a high SO ₂ concentration does not deteriorate its purifying characteristics, it is possible to remove the particulates satisfactorily. It can be performed.

The purifying material of the present invention is suitable for purifying exhaust gas from diesel engines and the like.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the temperature of a purifying material and the amount of CO ₂ produced in Examples 1 to 4 and Comparative Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaichi Takahashi 4-14-1, Suehiro, Kumagaya, Saitama Prefecture Riken Kumagaya Business Office (72) Inventor Kiyohide Yoshida 4--14, Suehiro, Kumagaya, Saitama No. 1 Stock Company Riken Kumagaya Works

Claims (2)

[Claims] 1. An exhaust gas purifying material comprising a catalyst supported on a heat resistant porous filter, wherein the catalyst comprises (a) Cs, K and
One or more elements selected from the group consisting of Na,
An exhaust gas purification material comprising (b) Cu element and Mo element and (c) one or two elements selected from Ce and La. 2. A method for purifying exhaust gas using the exhaust gas purifying material according to claim 1, wherein the catalyst carried on the filter oxidizes particulates in the exhaust gas. ..