JPH05245380A - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purifying material capable of effectively burning off the particulates contained in an exhaust gas from a diesel engine and having a large change in concn., further capable of purifying an exhaust gas contg. SO2 and capable of efficiently removing NOX at the same time. CONSTITUTION:A catalyst having active species consisting of (a) one or >=2 kinds of alkali metal elements, (b) Cu element and V element and (c) one or >=2 kinds of rare-earth elements is deposited on a heat-resistant porous filter to form a porous ceramic layer. In this case, 1-15 pts.wt. of the ceramic layer and 1-20 pts.wt of the active species are used per 100 pts.wt. of the filter, and the molar ratio of V to Cu elements is controlled to 1-6 to obtain this exhaust gas purifying material.

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, and more specifically, nitrogen oxides (hereinafter referred to as NOx) and particulate matter in exhaust gas of diesel engines and the like. (hereinafter particulates referred to as) and can simultaneously be removed, the exhaust gas purification material that can be SO ₂ to maintain a relatively large included also be good exhaust gas purifying characteristics in the exhaust gas, and the exhaust gas purification material The present invention relates to an exhaust gas purification method using.

[0002]

2. Description of the Related Art In recent years,
Particulate matter (mainly composed of solid carbon fine particles, called particulates), NO _X, etc. in exhaust gas discharged from diesel engines and the like have become problems as environmentally harmful. In particular, since particulates have an average particle size of 0.1 to 1 μm and are easily suspended in the air, they are easily incorporated into the human body by respiration, and recent clinical test results confirmed that they also contain carcinogens. Has been done.

As a method of removing particulates, the following two methods are roughly studied. One of them is to capture particulates by filtering exhaust gas using a heat resistant filter, and if the pressure loss due to this is increased, burner the particulates with a burner, electric heater, etc. to regenerate the filter. Is. The heat-resistant filters used include honeycomb-type ceramic filters, foam-type ceramic filters having a three-dimensional mesh structure, steel wool, wire mesh and the like.

The other one is a method of filtering particulates by the above-mentioned filter and causing the trapped particulates to self-combust by the action of the oxidation catalyst carried by the filter.

In the former case, the higher the effect of removing particulates, the faster the pressure loss rises, and the more frequently the filter is regenerated. Therefore, high reliability is required for regeneration, and it is considered to be 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, since the diesel engine uses light oil as a fuel, it contains a large amount of SO ₂ in the exhaust gas, which causes problems such as poisoning of the catalyst and secondary pollution.

[0007] For example, the oxidation catalysts for particulates in exhaust gas of diesel engines, etc., which have been proposed so far, are roughly classified into noble metal type and base metal type.
Precious metal-based catalysts have high durability and oxidation characteristics such as CO and unburned hydrocarbons (hereinafter referred to as HC), but on the other hand, they easily convert SO ₂ present in exhaust gas to SO ₃ , It is highly likely to cause pollution. There is also a drawback that the combustion characteristics of the soot in the particulates are deteriorated. On the other hand, a base metal catalyst is effective as a particulate purification catalyst, but has a problem in durability. That is, SO in exhaust gas
_{Due to 2} , the characteristics of the catalyst carried on the filter are easily deteriorated.

As described above, an effective method for trapping particulates in exhaust gas with a filter and igniting and burning this to regenerate an exhaust gas purification filter has not yet been established.

Most of the exhaust gas purifying catalysts and purifying agents proposed so far are focused on lowering the ignition temperature of particulates, and the oxygen concentration in the exhaust gas is generally high or the oxygen concentration is high. The removal of NOx contained in exhaust gas from diesel engines, which undergoes drastic changes, remains unsolved.

Therefore, an object of the present invention is to efficiently combust and remove particulates contained in exhaust gas having a large change in oxygen concentration such as that emitted from a diesel engine, and to be good for exhaust gas containing SO _2. It is an object of the present invention to provide an exhaust gas purification material that can maintain purification characteristics and at the same time effectively remove nitrogen oxides, and an exhaust gas purification method using the same.

[0011]

As a result of earnest research in view of the above problems, the present inventor has found that an alkali metal, a copper element, a vanadium element, and a rare earth element are formed on a heat-resistant porous filter. If you use a purification material that forms a ceramic layer that supports a catalyst and that defines the molar ratio of vanadium element and copper element in the catalyst to a specific range, you can efficiently remove particulates and NOx at the same time. The present invention has been completed by discovering that the removal ability can be maintained for a long time.

That is, the exhaust gas purifying material of the present invention comprises: (a) one or two kinds of alkali metal elements on a heat-resistant porous filter.
A ceramic layer carrying a catalyst having an active species comprising at least one species, (b) Cu element and V element, and (c) one or more rare earth elements, The ceramic layer is 1 to 15 per 100 parts by weight of the filter
The catalyst active species is 1 to 20 parts by weight, and the molar ratio of V element to Cu element in the catalyst (V / Cu)
Is 1 to 6.

Further, the exhaust gas purifying method of the present invention uses the exhaust gas purifying material to oxidize particulates in the exhaust gas by the catalytically active species carried on the filter, and at the same time reduce nitrogen oxides using the particulates as a reducing agent. It is characterized by doing.

The present invention will be described in detail below. Since the filter used in the present invention filters high-temperature exhaust gas, its forming material must be porous and have high heat resistance, particularly high thermal shock resistance. Moreover, it is necessary that the pressure loss be within an allowable range while maintaining the required particulate collection performance. Materials for forming such filters include ceramics such as alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, cordierite. Is mentioned.

The porosity of the filter may be 40-80%. The shape and size of the filter can be variously changed according to the purpose.

In the present invention, a ceramic layer carrying a catalyst, which will be described later, is provided on the filter made of the above-mentioned material. As a material for forming this ceramic layer, porous materials having a large surface area such as titania, alumina, silica, titania-alumina and titania-silica can be used. Of these, titania is particularly preferable.

As a catalyst to be carried on the above filter through the ceramic layer having a large surface area as described above,
Those having an active species consisting of (a) one or more alkali metal elements, (b) Cu and V, and (c) one or more rare earth elements are used.

Examples of the alkali metal element (a) include lithium, sodium, potassium and cesium. Among them, cesium and potassium are particularly preferable. Examples of the rare earth element (c) include cerium, lanthanum, neodymium and praseodymium. Among them, cerium and lanthanum are particularly preferable.

In the present specification, the components (a), (b) and (c) of each catalytically active species are represented by metal elements for simplification of the description, but in the case of ordinary purification materials Under the use temperature conditions, these components (catalytically active species) exist in the state of oxides.

By using the catalyst composed of the above components, the particulates in the exhaust gas can be ignited and burned at a relatively low temperature, and NOx can be effectively removed. That is, since the particulates in the exhaust gas coexist with oxygen on the surface of the catalyst in the filter, the ignition temperature of the particulates is lowered, and the particulates are burned (oxidized) near 400 ° C.

At the same time, the particulates act as a reducing agent to reduce NOx, and the exhaust gas is effectively purified. As described above, the efficient reduction of NOx at a relatively low temperature is due to the synergistic effect of the simultaneous presence of the particulates in the exhaust gas and the above catalytically active species (a), (b) and (c). It seems to be.

Simultaneous removal of NOx and particulates is
Alkali metal elements, transition metals, and catalysts consisting of rare earth elements, especially when Cu is used as the transition metal, its purification ability is excellent at the initial stage of use, but the above three elements (alkali metal As element, transition metal element
If only a combination of Cu and rare earth elements) is used, the purification characteristics of the catalyst will gradually deteriorate due to the presence of sulfur and its oxides contained in the exhaust gas. In particular, since exhaust gas has a high temperature, sulfur oxides such as SO ₂ cause a sharp deterioration in the purification characteristics of the catalyst. Therefore, in the present invention, Cu and V are used as the (b) transition metal element. Although the addition of V (that is, the combination of alkali metals, Cu and V, rare earth elements) is not expected to significantly improve the initial characteristics of the catalytically active species, it is possible to stably remove NOx and particulates for a long period of time. The characteristics are obtained.

Further, in the present invention, the molar ratio of V and Cu in the component (b) (V / Cu, which is the ratio of the metal content) is 1 to.
6 When the molar ratio of V and Cu is set within the above range, the exhaust gas purification characteristics do not deteriorate even if SO ₂ exists in the exhaust gas at a relatively high concentration. If this molar ratio (V / Cu) is less than 1, the ignition temperature of the particulates cannot be kept low for a long period of time. Further, the simultaneous removal characteristic also gradually deteriorates. On the other hand, if this ratio exceeds 6, the exhaust gas purification characteristics will deteriorate significantly.

The catalytic active species (a), (b) and (c) are blended in such amounts that the molar ratio of the respective metal components is (a) :( b) :( c).
However, it is preferable that the ratio is 0.5 to 1: 1.5 to 10: 0.1 to 1. More preferably, this ratio is 0.5 to 1: 1.5 to 8: 0.2 to 1.

The supported amount of the catalyst is 1 to 20 parts by weight (converted to metal (active species)) per 100 parts by weight of the filter. If the amount of catalyst is less than 1 part by weight, it becomes difficult to simultaneously remove particulates and NOx. On the other hand, even if the catalyst is loaded in an amount exceeding the upper limit, the purification performance of exhaust gas is not significantly improved, so the upper limit is set to 20 parts by weight. The preferred amount of catalyst is 5 to 15 parts by weight.

The amount of the ceramic layer serving as a catalyst carrier is 1 to 15 parts by weight per 100 parts by weight of the filter. If the amount of the ceramic layer is less than the above lower limit value, a sufficient amount of catalyst cannot be supported. On the other hand, if the amount of the ceramic layer exceeds the above upper limit value, the pressure loss in the purification material becomes too large. The preferred amount of ceramic layer is 2
~ 10 parts by weight.

The above-mentioned catalytically active species can be supported on the filter through the ceramic carrier layer by a wash coating method or the like. In the preparation of an exhaust gas purifying material by the washcoat method, a metal salt that becomes a catalytically active species is used as a starting material to impregnate the above-mentioned ceramic powder such as titania with the active species in advance, and then a metal salt that becomes an active species After immersing the filter in a slurry of the supported ceramic powder and then dried and fired, or after forming a catalyst supporting ceramic layer by coating the filter with a ceramic powder slurry forming a carrier layer, This layer can be impregnated with a solution of a salt of a catalytically active species, dried and calcined. In both of the above two methods, the firing temperature is preferably about 700 ° C.

As the metal salt or compound serving as the catalytically active species, any kind such as carbonate, nitrate, acetate, hydroxide and the like can be used as long as it is soluble in water. For loading V, a solution of NH ₄ VO ₃ and oxalic acid can be used. Also, alkali vanadate (for example, potassium vanadate, sodium vanadate,
It is also possible to simultaneously support the alkali metal and V by using cesium vanadate or the like).

If a catalyst-supporting layer is formed by using a porous ceramic powder in which catalytically active species are uniformly supported in advance, a relatively large amount of catalytic activity can be obtained even if the amount of ceramics serving as a catalyst carrier is small. The seed can be supported on the filter, and thus the pressure loss of the filter can be reduced. That is, a sufficient amount of catalytically active species can be supported even with a small amount of ceramics that does not cause a large pressure loss.

[0030]

The present invention will be described in more detail by the following specific examples. Examples 1 and 2 A predetermined amount of Ti sol was added to a predetermined concentration of CuCl ₂ , La (NO ₃ ) ₃ ,
A coating solution was prepared by adding an aqueous solution of CsNO ₃ and a mixed aqueous solution of NH ₄ VO ₃ and oxalic acid.

A cordierite ceramic foam (apparent volume 20 ml, density 0.65 g / ml) was used and immersed in the above coating solution.

This ceramic foam was taken out, dried, and then calcined at 700 ° C. for 3 hours to obtain a foam type filter having a ceramic layer (TiO ₂ layer) having a catalyst formed thereon. The amount of TiO ₂ supported on the filter is 10 for the filter.
% (% By weight, the same applies hereinafter). In addition, the total amount of Cu, La, Cs and V (the amount of metal content) is 10% with respect to the filter.
And Furthermore, the molar ratio of each component in the catalyst Cs: Cu: V:
La was 1: 1: 5: 1. (TiO ₂ : Cs / Cu / V / La = 1: 1: 5: 1, Example 1)

Molar ratio of each component in the catalytically active species Cs: Cu:
An exhaust gas purification material was prepared in the same manner as in Example 1 except that V: La was set to 1: 1: 1: 0.5. (TiO ₂ : Cs / Cu / V / La = 1: 1: 1: 0.5, Example 2)

The exhaust gas purifying materials of Example 1 and Example 2 were set in a flow-type reaction system, respectively, and under this temperature condition of 500 ° C., NO 800 ppm, H ₂ O 10%,
A first simulated exhaust gas consisting of 10% of O _2, 1000 ppm of SO ₂ and the balance of nitrogen was flowed, and the exhaust gas purification material was contacted with the first simulated exhaust gas for a predetermined time (20 to 100 hours).

After the exhaust gas purifying material was brought into contact with the first simulated exhaust gas for a predetermined time, 100 mg of diesel exhaust gas particulate was trapped in the exhaust gas purifying material. Next, to this exhaust gas purification material, NO 800 ppm, H ₂ O 10%,
The temperature at which the particulates trapped in the exhaust gas purifying material ignite was determined by gradually passing through the second simulated exhaust gas consisting of 10% O _2, 100 ppm SO ₂ , and the balance nitrogen. The ignition temperature was determined by changing the concentration of carbon dioxide in the exhaust gas downstream of the exhaust gas purification material (checking the production of carbon dioxide). The results are shown in Figure 1.

Comparative Examples 1 and 2 Using the same filter as in Example 1, 10% of TiO ₂ was coated on the filter by the same method as in Example 1, and further,
An exhaust gas purifying material was produced by supporting Cu, La, Cs and V.
The total amount of Cu, La, Cs and V (the amount of metal content) was set to 10% with respect to the filter. At this time, the molar ratio Cs: Cu: V: La of each component in the catalyst was set to 1: 7: 1: 1 (Comparative Example 1).

Using the same filter as in Example 1, an exhaust gas purifying material having a TiO ₂ layer carrying copper was prepared in the same manner as in Example 1. At this time, the amount of the TiO ₂ layer was 10% by weight of the filter, and the amount of copper was 10% with respect to the filter.
The weight percentage was set (Comparative Example 2).

With respect to the obtained purifying materials of Comparative Examples 1 and 2, the ignition temperature of the trapped particulates was determined by the same method as in Example 1. The results are shown in Figure 1.

As is apparent from FIG. 1, Examples 1 and 2
The exhaust gas purifying agent ignites particulates at a low temperature even after being in contact with a gas containing a high concentration of SO ₂ for a long time. Further, as can be seen from FIG. 1, the longer the time of contact with the (exhaust) gas containing SO ₂ , the lower the ignition temperature of the particulates.

On the other hand, in the exhaust gas purifying material of the comparative example, the initial characteristics (the characteristics at the time of first contact with the exhaust gas containing SO ₂ ) are relatively good, and the particulates are ignited and burned at around 400 ° C. , The longer the time of contact with the exhaust gas containing SO ₂ , the higher the ignition temperature of the particulates.

[0041]

As described above, when the exhaust gas purifying material of the present invention is used, even if the exhaust gas contains a relatively large amount of SO ₂ , the purifying characteristics thereof are not deteriorated, and the particulate matter is maintained at a low temperature of about 400 ° C. Can be ignited and burned.

Further, the purifying material of the present invention can simultaneously perform excellent NOx and particulate removal simultaneously.

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 ignition temperatures of particulates in Examples 1 and 2 and Comparative Examples 1 and 2.

[Procedure amendment]

[Submission date] April 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

[0030]

The present invention will be described in more detail by the following specific examples. In Examples 1 and 2 given amount of titania sol, a predetermined concentration CuCl _2, La
(NO ₃ ) ₃ , aqueous solution of CsNO ₃ , and NH ₄ VO ₃
A coating solution was prepared by adding a mixed aqueous solution of oxalic acid.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kozo Ogasawara 4-14-1, Suehiro, Kumagaya-shi, Saitama Stock company Riken Kumagaya Works (72) Inventor Kiyohide Yoshida 4--14, Suehiro, Kumagaya, Saitama No. 1 Stock company Riken Kumagaya Works (72) Inventor Tomoaki Honma 1-26 Takitanihonmachi, Niitsu City, Niigata JGC Chemical Co., Ltd. Niitsu Works

Claims (4)

[Claims] 1. A heat-resistant porous filter comprising (a) one or more kinds of alkali metal elements, (b) Cu elements and V elements, and (c) one or more kinds of rare earth elements. An exhaust gas purifying material in which a porous ceramic layer supporting a catalyst having an active species is formed, wherein the ceramic layer is 1 to 15 parts by weight per 100 parts by weight of the filter, and the catalytic active species is Is 1 to 20 parts by weight, and the molar ratio (V / Cu) of V element and Cu element in the catalyst is 1 to 6, which is an exhaust gas purifying material. 2. The exhaust gas purifying material according to claim 1, wherein the mixing ratio of the component (a), the component (b) and the component (c) in the catalyst is 0.5 to 1: in terms of the molar ratio of each metal component. 1.5 ~ 1
An exhaust gas purifying material, characterized in that it is 0: 0.1 to 1. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the ceramic layer is made of TiO ₂ . 4. 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, and at the same time An exhaust gas purification method characterized by reducing nitrogen oxides using particulates as a reducing agent.