JPH05184928A - Exhaust gas purifying material and method for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To effectively remove particulates and NOx contained in exhaust gas high in oxygen concn. discharged from a diesel engine and also remove CO and HC being as other harmful components in the exhaust gas. CONSTITUTION:A fine powder of a composite oxide catalyst represented by the formula Ln1-xRxO3+a (wherein Ln is one or more kinds of elements selected from a group consisting of La, Pr, Nd, Sm and Gd, R is one or more kinds of elements selected from a group consisting of Li, Na, K and Cs, M is one or more kinds of elements selected from a group consisting of V, Cr, Mn, Fe, Co, Ni and Cu, (x) is 0<X<1 and (a) is-1<a<0.2) and a ceramic carrier are supported on a heat-resistant filter.

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, nitrogen oxides (hereinafter referred to as NOx) in exhaust gas of diesel engines and the like are particulated. Exhaust gas purification material that can be reduced and removed by a carbon substance (hereinafter referred to as particulates) and can also reduce CO and hydrocarbons (hereinafter referred to as HC) in the exhaust gas, and exhaust gas using the exhaust gas purification material Regarding purification methods.

[0002]

2. Description of the Related Art In recent years,
Particulate carbonaceous substances, NO _X, etc. in exhaust gas emitted from diesel engines are becoming a problem as environmentally harmful substances.

As a method of removing particulates, the following two methods are roughly studied. One of them is a method to capture particulates by filtering the exhaust gas using a heat resistant filter, and burn the captured particulates with a burner, an electric heater, etc. to regenerate the filter if the pressure loss due to this is increased. Is. The other is the action of the catalyst carried on the filter,
This is a method of self-combusting with the filtration operation of particulates.

In the former case, it is considered that as the effect of removing particulates increases, the pressure loss increases, the frequency of regeneration increases, the reliability of regeneration is required to be high, and it is 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, exhaust gas contains a large amount of SO ₂ .
Further, the oxygen concentration in the exhaust gas changes in a wide range of 5 to 15% depending on the operating condition of the diesel engine. Under such exhaust gas conditions, a method for regenerating an exhaust gas purifying filter that satisfactorily ignites and burns the accumulated particulate matter and does not cause secondary pollution has not yet been established.

On the other hand, as a method for removing NOx, a method has been proposed in which HC is introduced into exhaust gas and NOx in the exhaust gas is reduced and removed by this hydrocarbon (Japanese Patent Publication No. 44-13002).
No.).

As another method of not introducing HC into exhaust gas, a method of reducing NOx by using a specific catalyst and particulates and residual HC existing in exhaust gas as a reducing agent has been tried. Various studies have been made on catalysts for removing hydrogen. For example, Japanese Patent Laid-Open No. 3-47539
The publication discloses an exhaust gas purifying material in which a catalyst composed of (a) an alkali element, (b) a specific transition metal element, and (c) a rare earth element is supported on a heat-resistant porous filter. This exhaust gas purification material can efficiently burn and remove the particulates contained in the exhaust gas and purify NOx and other harmful components. However, it has long-term heat resistance against exhaust gas at a temperature of 900 ° C or higher. Is inferior. Even with exhaust gas purification methods using other catalysts, it is difficult to efficiently remove NOx in exhaust gas with a high oxygen concentration without introducing HC,
An effective method for removing harmful components such as NOx has not yet been established.

Therefore, an object of the present invention is to effectively remove particulates and NOx contained in exhaust gas having a high oxygen concentration such as that emitted by a diesel engine, and to remove other harmful components such as CO and CO in the exhaust gas. An object of the present invention is to provide an exhaust gas purifying material that can also remove HC and an exhaust gas purifying method.

[0009]

As a result of earnest research in view of the above problems, the present inventors have found that if a fine powder of a composite oxide catalyst having a specific metal element as a catalyst and a ceramic carrier are both supported on a filter. It was discovered that good exhaust gas purification performance was obtained, and the present invention was completed.

That is, the exhaust gas purifying material of the present invention has the general formula Ln _1-X R _X MO _{3 + a} (where Ln is La, Pr, Nd, Sm,
And one or more elements selected from the group consisting of Gd, R is one or more elements selected from the group consisting of Li, Na, K, and Cs, and M is V, Cr, Mn, F
1 or 2 selected from the group consisting of e, Co, Ni, and Cu
More than one element, and 0 <X <1, and -1 <a
<0.2. ), A fine powder of the composite oxide catalyst and a ceramic carrier are both supported on a heat resistant filter.

The exhaust gas purifying method of the present invention is a method for purifying exhaust gas using the above exhaust gas purifying material, wherein particulates in exhaust gas are burned by the composite oxide catalyst carried on the filter. At the same time as the removal, the particulates are caused to act as a reducing agent to reduce and remove the nitrogen oxides, and the residual CO and the residual HC are oxidized and removed.

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,
It is particularly preferable to use a material having high thermal shock resistance. Further, it is necessary that the pressure loss is within the allowable range and that the particulate collection performance is maintained. As such a filter forming material, ceramics or metal having good heat resistance can be used. Examples of ceramics as a filter forming material include cordierite and mullite.

As the shape of the filter, a known honeycomb type or foam type can be used. Further, the shape and size of the filter can be variously changed according to the purpose.

As the catalyst supported on the above filter,
General formula: Ln _1-X R _X MO _{3 + a} (1) (where Ln is one or more elements selected from La, Pr, Nd, Sm, and Gd, and Rn Is one or more elements selected from Li, Na, K and Cs, and M is V, Cr, Mn,
It is one or more elements selected from Fe, Co, Ni, and Cu, and 0 <X <1 and -1 <a <0.2. ) The fine powder of the complex oxide represented by As described above, two or more kinds of elements may be selected from the above group as Ln, but in that case, the total amount thereof should be the composition ratio (1-x). Similarly, regarding R and M, the total amount of each is defined within the range that conforms to the above composition formula.

The above-mentioned composite oxide is basically represented by the general formula: Ln _1-X R _X MO ₃ (2) (Ln, R, and M are the same as those in the above formula (1). ), The composition ratio of oxygen varies somewhat depending on the type of constituent metals and the use conditions (temperature conditions, etc.). That is, a so-called oxygen-deficient oxide whose oxygen composition ratio is slightly less than 3 (-1 <a <0 in the above formula (1))
Or in excess of oxygen (corresponding to 0 <a <0.2 in the above formula (1)) in some cases. In the present invention, such an oxygen-deficient oxide,
Oxygen-excessive oxide is also included as a catalyst.

Ln _1-X R _X M containing the above metal elements
The composite oxide catalyst represented by O _{3 + a} has a high NOx removal property by allowing particulates to act as a reducing agent even in an oxidizing atmosphere. In addition, it has excellent heat resistance, and even if it is exposed to exhaust gas at a high temperature of about 800 to 850 ° C for a long time, there is almost no deterioration in its catalytic activity. Incidentally, according to the present inventors' study, a mixture of simple oxides of the above metal element (i.e., without taking the form of a complex oxide in the form of _{Ln 1-X R X MO 3} , Ln 2 O 3 , R ₂ O, and a simple mixture of oxides of M), heat resistance is not good, and exhaust gas cannot be sufficiently purified.

The above-mentioned composite oxide catalyst is prepared by mixing oxides, hydroxides, carbonates, nitrates, sulfates, acetates, oxalates, chlorides, etc. of the respective metal elements in a desired ratio and finally mixing them. To
It can be prepared by firing at 850 ° C. or higher for 5 hours or longer. As the mixing method of the above-mentioned substances, a method of mixing each substance in a solid state, a method of evaporating a mixed aqueous solution of each metal salt to dryness, and a mixed aqueous solution of each metal salt with an alkaline aqueous solution such as ammonia water is used. A so-called coprecipitation method in which hydrolysis is performed can be used. The composite oxide catalyst thus prepared is used after being made into a fine powder.

The fine powder of the complex oxide catalyst described above is preferably loaded on the heat-resistant porous filter together with the ceramic carrier which is more porous and has a larger surface area than the filter.

Materials for forming the carrier include alumina, alumina-based composite oxides such as titania-alumina and alumina-silica, titania, zirconia, magnesia,
It is preferable to use porous ceramics (usually powder) having a large surface area such as titania-silica and silica-zirconia.

In the case of a ceramic filter, the loading amount of the ceramic carrier is preferably 2 to 20% by weight, particularly 5 to 15% by weight of the filter. The amount of the complex oxide catalyst supported on the filter is preferably 0.1 to 15% by weight, more preferably 2 to 1.2% by weight, and 5 to 20% by weight of the ceramic carrier.
It is preferably 0% by weight, especially 50 to 150% by weight. If the supported amount of the catalyst is less than 5% by weight based on the ceramic carrier, the effect of supporting the catalyst is not remarkable. On the other hand, 200% by weight
When the amount of catalyst supported exceeds, the particulate combustion characteristics are improved, but the reactivity between particulates and NOx is reduced. Generally, it is better to increase the amount of catalyst to improve the combustion characteristics of particulates, and to increase the reactivity of particulates and NOx, it is better to decrease the amount of catalysts. It is preferable to appropriately adjust the amount of the catalyst supported in the above range in consideration of (exhaust gas component) and the like.

By using the exhaust gas purifying material having the above-mentioned structure, it is possible to ignite and burn the particulates in the exhaust gas at a relatively low temperature and to effectively remove NOx. That is, when the particulates in the exhaust gas coexist in the filter with the catalyst and oxygen supported on the carrier, the ignition temperature is lowered, and the particulates are burned (oxidized) at about 400 ° C. or lower. At the same time, the particulates act as a reducing agent to reduce NOx, and the exhaust gas is effectively purified. Thus, the reduction of NOx occurs efficiently at a relatively low temperature because the presence of the particulates in the exhaust gas and the above-mentioned catalysts simultaneously increases the reaction activity of the particulates and oxygen and is activated by oxygen. This is probably because particulates react with NOx with high selectivity.

Furthermore, by using the above-mentioned catalyst, it becomes possible to oxidize and remove other harmful components CO and HC contained in the exhaust gas.

In the present invention, the above-mentioned catalyst is slurried together with the above-mentioned carrier and loaded on a filter or sol.
It can be simultaneously loaded on the filter by the gel method.

The loading by the sol-gel method is carried out as follows, taking titania as an example. First, an acid such as CH ₃ COOH, HNO ₃ , and HCl and an aqueous solution of catalyst fine powder are added to an alcohol solution of Ti alkoxide to form a coating solution. Then, after immersing the filter in the coating liquid, it is reacted with water vapor or water to form a sol, and further gelation. Then dry the filter,
Baking is performed to form a coating layer made of titania supporting a catalyst.

In the sol-gel method, the acid is added as a catalyst for the hydrolysis reaction during gelation. However, the addition of alkali instead of acid can accelerate the hydrolysis reaction.

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 the catalyst is supported on alumina, an alkoxide of aluminum is used, and the same method as in the case of the above-mentioned titania is performed. The same applies when other porous carriers are used.

According to the sol-gel method, it is possible to support the catalyst in the filter very uniformly, and
The catalytic activity is increased and the exhaust gas purification ability is improved.

[0028]

EXAMPLES The method of the present invention will be described in more detail with reference to the following specific examples, but the present invention is not limited thereto.

Examples 1 to 3 La (NO ₃ ) ₃ , KNO ₃ or NaNO ₃ , and Co (NO ₃ ).
₂ , and these were used as La _0.9 K _0.1 Co O ₃ (Example 1),
La _0.8 K _0.2 Co O ₃ (Example 2), or La _{0. 9} Na _0.1 Co
O ₃ (Example 3) was weighed and mixed so as to have the composition,
An aqueous solution was prepared. The resulting aqueous solution was evaporated to dryness, then calcined at 850 ° C. 10 hours to prepare a composite oxide having a composition of _{La 0.9 K 0. 1 Co O 3} .

On the other hand, Ti (O-isoC ₃ H ₇ ) ₄ was dissolved in ethanol and added with acetic acid to hydrolyze to form a titania sol.

Then, the obtained La _0.9 K _0.1 Co O ₃ , La
_0.8 K _0.2 Co O _3, or La _0.9 Na _{0. 1} respectively from each powder and titania sol Co O ₃ to prepare a slurry.

A foam type filter made of cordierite (apparent volume 0.02 liter, density 0.40 g / ml, porosity 50%) was coated with the slurry obtained by the sol-gel method, and the filter was coated with La. _0.9 K _0.1 Co O ₃ , La _0.8
Each of K _0.2 Co O ₃ or La _0.9 Na _0.1 Co O ₃ fine powder and titania powder is supported by 10% (weight%, the same applies below), dried and baked at 700 ℃ to purify 3 types. I got the wood.

Diesel engine exhaust gas was passed through these purification materials to trap 0.3 g of particulates. A purification material that trapped particulates was installed in a fixed-bed flow reactor, and a simulated gas (oxygen concentration: 10%, NOx: 800 ppm, similar to the exhaust gas from a diesel engine,
SO ₂ : 100 ppm, H ₂ O concentration: 10%, N ₂ : balance) 1.2
The purifying material was heated at a rate of 5 ° C./min by passing liter / min, the ignition temperature of the particulates was determined based on the amount of CO ₂ produced, and the NOx purification rate at the ignition temperature was determined.
The results are shown in Table 1.

Comparative Example 1 TiO 2 was applied to the same filter as in Example 1 by the sol-gel method.
_The filter was coated with 10% of ₂ to obtain a purification material. Regarding the obtained purifying material, the ignition temperature of the particulates and the NOx purification rate were determined in the same manner as in Example 1. The results are shown in Table 1.

Table 1 Example No. Ignition temperature (° C) NOx purification rate ⁽¹⁾ Example 1 350 44 Example 2 360 35 Example 3 350 35 Comparative Example 1 600 10 Table 1 Note (1): Before filter passage , NO in exhaust gas after passing
NOx purification rate calculated from x amount (%)

As is clear from Table 1, the exhaust gas purifying materials of the respective examples have a higher NOx purification rate than that of the comparative example 1. Moreover, the ignition temperature of the filter at that time was also low, and it can be seen that the exhaust gas was satisfactorily purified.

[0037]

As described above in detail, when the exhaust gas purifying material of the present invention is used, the particulates in the exhaust gas are burned and removed at a relatively low temperature, and at the same time the particulates act as a reducing agent to effectively reduce NOx. It can be reduced and removed. Further, CO and HC in the exhaust gas can also be removed by oxidation.

Further, since the composite oxide catalyst in the exhaust gas purifying material of the present invention has good heat resistance, it maintains a good exhaust gas purifying ability for a long period of time.

The exhaust gas purifying method of the present invention is particularly suitable for purifying exhaust gas in an oxidizing atmosphere such as that found in exhaust gas of diesel engines.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location B01J 23/72 A 8017-4G (72) Inventor Yasushi Teraoka 384-1 Tanakacho, Nagasaki, Nagasaki Prefecture Higashi Nagasaki Housing 4-33 (72) Inventor Shuichi Kagawa 6-10 Yawatacho, Nagasaki City, Nagasaki Prefecture

Claims (3)

[Claims] 1. The general formula Ln _1-X R _X MO _{3 + a} (where Ln
Is one or more elements selected from the group consisting of La, Pr, Nd, Sm, and Gd, and R is one or two elements selected from the group consisting of Li, Na, K, and Cs. Is more than a seed element,
M is one or more elements selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, and Cu, and 0 <X <
1 and -1 <a <0.2. ) An exhaust gas purifying material, characterized in that a fine powder of a composite oxide catalyst represented by (4) and a ceramic carrier are both supported on a heat resistant filter. 2. The exhaust gas purifying material according to claim 1, wherein the ceramic carrier is any one of Al ₂ O ₃ , Al ₂ O ₃ -based composite oxide, TiO ₂ , ZrO ₂ , and TiO ₂ —ZrO _2. Exhaust gas purification material characterized by the above. 3. A method for purifying exhaust gas using the exhaust gas purifying material according to claim 1 or 2, wherein particulates in the exhaust gas are mainly formed by fine powder of the complex oxide catalyst carried on the filter. A method for purifying exhaust gas, characterized in that, at the same time as burning and removing, the particulates are made to act as a reducing agent to reduce and remove nitrogen oxides, and residual CO and residual hydrocarbons are oxidized and removed.